MUSCLE-TARGETING COMPLEXES AND USES THEREOF

RELATED APPLICATIONS

[0001] This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional

Application Serial No. 63/181450, entitled “MUSCLE-TARGETING COMPLEXES AND USES THEREOF”, filed on April 29, 2021, to U.S. Provisional Application Serial No. 63/143831, entitled “MUSCLE-TARGETING COMPLEXES AND USES THEREOF”, filed on January 30, 2021, to U.S. Provisional Application Serial No. 63/069078, entitled “MUSCLE-TARGETING COMPLEXES AND USES THEREOF”, filed on August 23, 2020, to U.S. Provisional Application Serial No. 63/061842, entitled “MUSCLE-TARGETING COMPLEXES AND USES THEREOF”, filed on August 6, 2020, and to U.S. Provisional Application Serial No. 63/055785, entitled “MUSCLE-TARGETING COMPLEXES AND USES THEREOF”, filed on July 23, 2020; the contents of each of which are incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

[0002] The present application relates to targeting complexes for delivering molecular payloads (e.g., oligonucleotides) to cells and uses thereof, particularly uses relating to treatment of disease.

REFERENCE TO SEQUENCE LISTING SUBMITTED AS A TEXT FILE VIA EFS-WEB

[0003] The instant application contains a sequence listing which has been submitted in

ASCII format via EFS-Web and is hereby incorporated by reference in its entirety. Said ASCII copy, created on July 8, 2021, is named D082470041WO00-SEQ-DWY and is 152,275 bytes in size.

BACKGROUND OF INVENTION

[0004] Muscle diseases are often associated with muscle weakness and/or (e.g., and) muscle dysfunction that lead to life-threatening complications. Many examples of such diseases have been characterized, including various forms of muscular dystrophy (e.g., Duchenne, facioscapulohumeral, myotonic, and oculopharyngeal), Pompe disease, centronuclear myopathy, familial hypertrophic cardiomyopathy, Laing distal myopathy, Fibrodysplasia Ossificans Progressiva, Friedreich’s ataxia, myofibrillar myopathy, and others. These conditions are generally hereditary, but can arise spontaneously. These conditions are often congenital but can arise later in life. Many rare muscle diseases are single gene disorders associated with gain-of-function or loss-of-function mutations, which may have dominant or recessive phenotypes. For example, activating mutations have been identified in genes encoding ion channels, structural proteins, metabolic proteins, and signaling proteins that contribute to muscle disease. Despite advances in understanding the genetic etiology of muscle disease, effective treatment options remain limited.

SUMMARY OF INVENTION

[0005] According to some aspects, the disclosure provides complexes that target muscle cells for purposes of delivering molecular payloads to those cells. In some embodiments, the complexes of the present disclosure facilitate muscle-specific delivery of molecular payloads that target muscle disease alleles. For example, in some embodiments, complexes provided herein are particularly useful for delivering molecular payloads that modulate the expression or activity of a gene in a subject having or suspected of having a muscle disease associated with the gene ( e.g ., a gene/disease of Table 1). In some embodiments, complexes provided herein comprise muscle-targeting agents (e.g., muscle targeting antibodies) that specifically bind to receptors on the surface of muscle cells for purposes of delivering molecular payloads to the muscle cells. In some embodiments, the complexes are taken up into the cells via a receptor (e.g., transferrin receptor) mediated internalization, following which the molecular payload may be released to perform a function inside the cells. For example, complexes engineered to deliver oligonucleotides may release the oligonucleotides such that the oligonucleotides can modulate expression or activity of a muscle disease allele. In some embodiments, the oligonucleotides are released by endosomal cleavage of covalent linkers connecting oligonucleotides and muscle-targeting agents of the complexes.

[0006] One aspect of the present disclosure relates to a complex comprising an anti transferrin receptor (TfR) antibody covalently linked to a molecular payload configured to modulate expression or activity of a muscle disease gene, wherein the antibody comprises:

(i) a heavy chain variable region (VH) comprising an amino acid sequence at least 95% identical to SEQ ID NO: 76; and/or a light chain variable region (VL) comprising an amino acid sequence at least 95% identical to SEQ ID NO: 75;

(ii) a heavy chain variable region (VH) comprising an amino acid sequence at least 95% identical to SEQ ID NO: 69; and/or a light chain variable region (VL) comprising an amino acid sequence at least 95% identical to SEQ ID NO: 70;

(iii) a heavy chain variable region (VH) comprising an amino acid sequence at least 95% identical to SEQ ID NO: 71; and/or a light chain variable region (VL) comprising an amino acid sequence at least 95% identical to SEQ ID NO: 70;

(iv) a heavy chain variable region (VH) comprising an amino acid sequence at least 95% identical to SEQ ID NO: 72; and/or a light chain variable region (VL) comprising an amino acid sequence at least 95% identical to SEQ ID NO: 70;

(v) a heavy chain variable region (VH) comprising an amino acid sequence at least 95% identical to SEQ ID NO: 73; and/or a light chain variable region (VL) comprising an amino acid sequence at least 95% identical to SEQ ID NO: 74;

(vi) a heavy chain variable region (VH) comprising an amino acid sequence at least 95% identical to SEQ ID NO: 73; and/or a light chain variable region (VL) comprising an amino acid sequence at least 95% identical to SEQ ID NO: 75;

(vii) a heavy chain variable region (VH) comprising an amino acid sequence at least 95% identical to SEQ ID NO: 76; and/or a light chain variable region (VL) comprising an amino acid sequence at least 95% identical to SEQ ID NO: 74;

(viii) a heavy chain variable region (VH) comprising an amino acid sequence at least 95% identical to SEQ ID NO: 77; and/or a light chain variable region (VL) comprising an amino acid sequence at least 95% identical to SEQ ID NO: 78;

(ix) a heavy chain variable region (VH) comprising an amino acid sequence at least 95% identical to SEQ ID NO: 79; and/or a light chain variable region (VL) comprising an amino acid sequence at least 95% identical to SEQ ID NO: 80; or

(x) a heavy chain variable region (VH) comprising an amino acid sequence at least 95% identical to SEQ ID NO: 77; and/or a light chain variable region (VL) comprising an amino acid sequence at least 95% identical to SEQ ID NO: 80.

[0007] In some embodiments, the antibody comprises:

(i) a VH comprising the amino acid sequence of SEQ ID NO: 76 and a VL comprising the amino acid sequence of SEQ ID NO: 75;

(ii) a VH comprising the amino acid sequence of SEQ ID NO: 69 and a VL comprising the amino acid sequence of SEQ ID NO: 70;

(hi) a VH comprising the amino acid sequence of SEQ ID NO: 7 land a VL comprising the amino acid sequence of SEQ ID NO: 70;

(iv) a VH comprising the amino acid sequence of SEQ ID NO: 72 and a VL comprising the amino acid sequence of SEQ ID NO: 70;

(v) a VH comprising the amino acid sequence of SEQ ID NO: 73 and a VL comprising the amino acid sequence of SEQ ID NO: 74; (vi) a VH comprising the amino acid sequence of SEQ ID NO: 73 and a VL comprising the amino acid sequence of SEQ ID NO: 75;

(vii) a VH comprising the amino acid sequence of SEQ ID NO: 76 and a VL comprising the amino acid sequence of SEQ ID NO: 74;

(viii) a VH comprising the amino acid sequence of SEQ ID NO: 77 and a VL comprising the amino acid sequence of SEQ ID NO: 78;

(ix) a VH comprising the amino acid sequence of SEQ ID NO: 79 and a VL comprising the amino acid sequence of SEQ ID NO: 80; or

(x) a VH comprising the amino acid sequence of SEQ ID NO: 77 and a VL comprising the amino acid sequence of SEQ ID NO: 80.

[0008] In some embodiments, the antibody is selected from the group consisting of a

Fab fragment, a Fab' fragment, a F(ab’)2 fragment, a scFv, a Fv, and a full-length IgG. In some embodiments, the antibody is a Fab fragment.

[0009] In some embodiments, the antibody comprises:

(i) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 101; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 90;

(ii) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 97; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 85;

(iii) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 98; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 85;

(iv) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 99; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 85;

(v) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 100; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 89;

(vi) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 100; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 90;

(vii) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 101; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 89;

(viii) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 102; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 93;

(ix) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 103; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 95; or

(x) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 102; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 95.

[00010] In some embodiments, the antibody comprises:

(i) a heavy chain comprising the amino acid sequence of SEQ ID NO: 101; and a light chain comprising the amino acid sequence of SEQ ID NO: 90;

(ii) a heavy chain comprising the amino acid sequence of SEQ ID NO: 97; and a light chain comprising the amino acid sequence of SEQ ID NO: 85;

(iii) a heavy chain comprising the amino acid sequence of SEQ ID NO: 98; and a light chain comprising the amino acid sequence of SEQ ID NO: 85;

(iv) a heavy chain comprising the amino acid sequence of SEQ ID NO: 99; and a light chain comprising the amino acid sequence of SEQ ID NO: 85;

(v) a heavy chain comprising the amino acid sequence of SEQ ID NO: 100; and a light chain comprising the amino acid sequence of SEQ ID NO: 89;

(vi) a heavy chain comprising the amino acid sequence of SEQ ID NO: 100; and a light chain comprising the amino acid sequence of SEQ ID NO: 90;

(vii) a heavy chain comprising the amino acid sequence of SEQ ID NO: 101; and a light chain comprising the amino acid sequence of SEQ ID NO: 89;

(viii) a heavy chain comprising the amino acid sequence of SEQ ID NO: 102; and a light chain comprising the amino acid sequence of SEQ ID NO: 93;

(ix) a heavy chain comprising the amino acid sequence of SEQ ID NO: 103; and a light chain comprising the amino acid sequence of SEQ ID NO: 95; or

(x) a heavy chain comprising the amino acid sequence of SEQ ID NO: 102; and a light chain comprising the amino acid sequence of SEQ ID NO: 95.

[00011] In some embodiments, the antibody does not specifically bind to the transferrin binding site of the transferrin receptor and/or the antibody does not inhibit binding of transferrin to the transferrin receptor. [00012] In some embodiments, the antibody is cross -reactive with extracellular epitopes of two or more of a human, non-human primate and rodent transferrin receptor.

[00013] In some embodiments, the complex is configured to promote transferrin receptor mediated internalization of the molecular payload into a muscle cell.

[00014] In some embodiments, the molecular payload is an oligonucleotide. In some embodiments, oligonucleotide comprises a region of complementarity to a muscle disease gene having a gain-of-function disease allele.

[00015] In some embodiments, the oligonucleotide comprises at least one modified intemucleoside linkage. In some embodiments, the at least one modified internucleoside linkage is a phosphorothioate linkage.

[00016] In some embodiments, the oligonucleotide comprises one or more modified nucleosides. In some embodiments, the one or more modified nucleosides are 2’-modified nucleosides.

[00017] In some embodiments, the oligonucleotide is a gapmer oligonucleotide that directs RNAse H-mediated cleavage of an mRNA transcript encoded by the muscle disease gene in a cell.

[00018] In some embodiments, the oligonucleotide is a mixmer oligonucleotide.

[00019] In some embodiments, the oligonucleotide is an RNAi oligonucleotide that promotes RNAi-mediated cleavage of a mRNA transcript encoded by the muscle disease gene. [00020] In some embodiments, the 2’-modified nucleoside is selected from the group consisting of: 2'-0-methyl, 2'-fluoro (2'-F), 2'-0-methoxyethyl (2'-MOE), and 2', 4'-bridged nucleosides.

[00021] In some embodiments, the one or more modified nucleosides are 2', 4 '-bridged nucleosides.

[00022] In some embodiments, the oligonucleotide is phosphorodiamidate morpholino oligomer.

[00023] In some embodiments, the antibody is covalently linked to the molecular payload via a cleavable linker. In some embodiments, the cleavable linker comprises a valine- citmlline sequence.

[00024] In some embodiments, the antibody is covalently linked to the molecular payload via conjugation to a lysine residue or a cysteine residue of the antibody.

[00025] In some embodiments, modulating expression or activity of a muscle disease gene comprises reducing expression of RNA and/or protein. [00026] Another aspect of the present disclosure relates to a method of modulating expression or activity of a muscle disease gene in a cell, the method comprising contacting the cell with a complex disclosed herein in an amount effective for promoting internalization of a molecular payload to the cell, optionally wherein the cell is a muscle cell.

[00027] In some embodiments, the muscle disease is a disease selected from the group consisting of: Adult Pompe Disease, Centronuclear myopathy (CNM), Duchenne Muscular Dystrophy, Facioscapulohumeral Muscular Dystrophy (FSHD), Familial Hypertrophic Cardiomyopathy, Fibrodysplasia Ossificans Progressiva (FOP), Friedreich's Ataxia (FRDA), Inclusion Body Myopathy 2, Laing Distal Myopathy, Myofibrillar Myopathy, Myotonia Congenita (autosomal dominant form, Thomsen Disease), Myotonic Dystrophy Type I, Myotonic Dystrophy Type II, Myotubular Myopathy, Oculopharyngeal Muscular Dystrophy, and Paramyotonia Congenita.

[00028] Another aspect of the present disclosure relates to a method of treating a subject having a muscle disease, the method comprising administering to the subject an effective amount of a complex disclosed herein, optionally wherein the muscle disease is a disease selected from the group consisting of: Adult Pompe Disease, Centronuclear myopathy (CNM), Duchenne Muscular Dystrophy, Facioscapulohumeral Muscular Dystrophy (FSHD), Familial Hypertrophic Cardiomyopathy, Fibrodysplasia Ossificans Progressiva (FOP), Friedreich's Ataxia (FRDA), Inclusion Body Myopathy 2, Laing Distal Myopathy, Myofibrillar Myopathy, Myotonia Congenita (autosomal dominant form, Thomsen Disease), Myotonic Dystrophy Type I, Myotonic Dystrophy Type II, Myotubular Myopathy, Oculopharyngeal Muscular Dystrophy, and Paramyotonia Congenita.

BRIEF DESCRIPTION OF THE DRAWINGS [00029] FIG. 1 depicts a non-limiting schematic showing the effect of transfecting

Hepa 1-6 cells with an antisense oligonucleotide that targets DMPK (ASO300) on expression levels of DMPK relative to a vehicle transfection;

[00030] FIG. 2A depicts a non-limiting schematic showing an HIL-HPLC trace obtained during purification of a muscle targeting complex comprising an anti-transferrin receptor antibody covalently linked to a DMPK antisense oligonucleotide.

[00031] FIG. 2B depicts a non-limiting image of an SDS-PAGE analysis of a muscle targeting complex. [00032] FIG. 3 depicts a non-limiting schematic showing the ability of a muscle targeting RI7 217 Fab antibody-oligonucleotide complex (DTX-C-008) comprising ASO300 to reduce expression levels of DMPK.

[00033] FIGs. 4A-4E depict non-limiting schematics showing the ability of a muscle targeting RI7 217 Fab antibody-oligonucleotide complex (DTX-C-008) comprising ASO300 to reduce expression levels of DMPK in mouse muscle tissues in vivo , relative to a vehicle treatment, treatment with naked ASO300, or treatment with a control non-targeting complex (DTX-C-007). (N=3 C57B1/6 WT mice)

[00034] FIGs. 5A-5B depict non-limiting schematics showing the tissue selectivity of a muscle targeting RI7217 Fab antibody-oligonucleotide complex (DTX-C-008) comprising ASO300. The muscle targeting complex (DTX-C-008) comprising ASO300 does not reduce expression levels of DMPK in mouse brain or spleen tissues in vivo, relative to a vehicle treatment, treatment with naked ASO300, or treatment with a control non-targeting complex (DTX-C-007). (N=3 C57B1/6 WT mice)

[00035] FIGs. 6A-6F depict non-limiting schematics showing the ability of a muscle targeting RI7 217 Fab antibody-oligonucleotide complex (DTX-C-008) comprising ASO300 to reduce expression levels of DMPK in mouse muscle tissues in vivo, relative to a vehicle treatment, treatment with naked ASO300, or treatment with a control non-targeting complex (DTX-C-007). (N=5 C57B1/6 WT mice)

[00036] FIGs. 7A-7L depict non-limiting schematics showing the ability of a muscle targeting antibody-oligonucleotide complex (DTX-C-012) comprising ASO300 covalently linked to an anti-hTfR antibody to reduce expression levels of DMPK in cynomolgus monkey muscle tissues in vivo, relative to a vehicle treatment (saline) and compared to naked DMPK ASO (ASO300). (N=3 male cynomolgus monkeys)

[00037] FIGs. 8A-8B depict non-limiting schematics showing the ability of a muscle targeting antibody-oligonucleotide complex (DTX-C-012) comprising ASO300 covalently linked to an anti-hTfR antibody to reduce expression levels of DMPK in cynomolgus monkey smooth muscle tissues in vivo, relative to a vehicle treatment (saline) and compared to naked DMPK ASO (ASO300). (N=3 male cynomolgus monkeys)

[00038] FIGs. 9A-9D depict non-limiting schematics showing the tissue selectivity of a muscle targeting antibody-oligonucleotide complex (DTX-C-012) comprising ASO300 covalently linked to an anti-hTfR antibody. The muscle targeting complex comprising DMPK- ASO does not reduce expression levels of DMPK in cynomolgus monkey kidney, brain, or spleen tissues in vivo, relative to a vehicle treatment. (N=3 male cynomolgus monkeys) [00039] FIG. 10 shows normalized DMPK mRNA tissue expression levels across several tissue types in cynomolgus monkeys. (N=3 male cynomolgus monkeys)

[00040] FIGs. 11A-11B depict non-limiting schematics showing the ability of a muscle targeting RI7 217 Fab antibody-oligonucleotide complex (DTX-C-008) comprising ASO300 to reduce expression levels of DMPK in mouse muscle tissues in vivo for up to 28 days after dosing with DTX-C-008, relative to a vehicle treatment (saline) and compared to naked DMPK ASO (ASO300).

[00041] FIG. 12 shows that a single dose of a muscle targeting complex (DTX-C-012) comprising ASO300 covalently linked to an anti-hTfR antibody is safe and tolerated in cynomolgus monkeys. (N=3 male cynomolgus monkeys)

[00042] FIGs. 13A-13B depict non-limiting schematics showing the ability of a muscle targeting RI7 217 Fab antibody-oligonucleotide complex (DTX-C-008) comprising ASO300 to reduce expression levels of DMPK in mouse muscle tissues in vivo for up to twelve weeks after dosing with DTX-C-008, relative to a vehicle treatment (PBS); and compared to a control IgG2a Fab antibody-oligonucleotide complex (DTX-C-007) and naked DMPK ASO (ASO300). (N=5 C57B1/6 WT mice)

[00043] FIGs. 14A-14B depict non-limiting schematics showing the ability of a muscle targeting RI7 217 Fab antibody-oligonucleotide complex (DTX-C-008) comprising ASO300 to target nuclear mutant DMPK RNA in a mouse model. (N=6 mice)

[00044] FIGs. 15A-15B depict non-limiting schematics showing the ability of a muscle targeting RI7 217 Fab antibody- ASO complex (DTX-Actin) comprising an oligonucleotide that targets actin to dose-dependently reduce expression levels of actin and functional grades of myotonia in muscle tissues. (N=2 HSA ^LR mice)

[00045] FIGs. 16A-16C depict non-limiting schematics showing that a muscle-targeting RI7 217 Fab antibody-oligonucleotide complex (DTX-C-008) comprising ASO300 is capable of significantly reducing the prolonged QTc interval in a mouse model for validation of the functional correction of arrhythmia in a DM1 cardiac model. (N=10 mice)

[00046] FIGs. 17A-17B depict non-limiting schematics showing that a muscle-targeting antibody-oligonucleotide complex (DTX-C-012) comprising ASO300 antisense oligonucleotide covalently linked to an anti-hTfR antibody is capable of reducing expression levels of DMPK and correcting splicing of a DMPK-specific target gene (Binl) in human cells from a DM1 patient. (N=3)

[00047] FIG. 18 depicts a non-limiting schematic showing the ability of a muscle targeting complex (anti-TfR antibody-FMlO) comprising an anti-TfRl Fab (RI7 217) conjugated to FM10 antisense oligonucleotide to reduce expression levels of downstream DUX4 genes (ZSCAN4, MBD3L2, TRIM43) in human U-2 OS cells, relative to naked FM10 antisense oligonucleotide.

[00048] FIG. 19 depicts a non-limiting schematic showing the ability of an anti transferrin receptor muscle targeting complex comprising an exon-23 skipping phosphorodiamidate morpholino oligomer (PMO) to dose-dependently enhance exon skipping in muscle tissues of a mdx mouse model.

[00049] FIGs. 20A-20B depict non-limiting schematics showing the ability of an anti-transferrin receptor muscle targeting complex comprising an exon-23 skipping PMO to dose-dependently increase dystrophin in skeletal muscle (quadriceps) of a mdx mouse model. [00050] FIGs. 21A-21E depict non-limiting schematics showing the ability of an anti-transferrin receptor muscle targeting complex comprising an exon-23 skipping PMO to improve functional performance (FIGs. 21A, 21B, 21C, and 21D) and reduce creatine kinase levels (FIG. 21E) in an mdx mouse model. (** p < 0.01; *** p < 0.001; **** p < 0.0001) [00051] FIGs. 22A-22C depict non-limiting schematics showing the dose response of selected antisense oligonucleotides (DMPK-ASO-1, DMPK-ASO-2, and DMPK-ASO-3) in DMPK knockdown in human DM1 myotubes. ASO300 was used as control. All tested oligonucleotides showed activity in DMPK knockdown. Statistical analysis: One-way ANOVA with Tukey’s HSD post-hoc test vs. naked ASO300 treatment; *p<0.05, **p<0.01,

***p<0.001, ****p<0.0001.

[00052] FIGs. 23A-23B depict non-limiting schematics showing the dose response of selected antisense oligonucleotides (DMPK-ASO-1, DMPK-ASO-2, and DMPK-ASO-3) in DMPK knockdown in non-human primate (NHP) DM1 myotubes. ASO300 was used as control. All tested oligonucleotides showed activity in DMPK knockdown.

[00053] FIG. 24 shows the serum stability of the linker used for linking an anti-TfR antibody and a molecular payload (e.g., an oligonucleotide) in various species over time after intravenous administration.

[00054] FIGs. 25A-25F show binding of humanized anti-TfR Fabs to human TfRl (hTfRl) or cynomolgus monkey TfRl (cTfRl), as measured by ELISA. FIG. 25A shows binding of humanized 3M12 variants to hTfRl. FIG. 25B shows binding of humanized 3M12 variants to cTfRl. FIG. 25C shows binding of humanized 3A4 variants to hTfRl. FIG. 25D shows binding of humanized 3A4 variants to cTfRl. FIG. 25E shows binding of humanized 5H12 variants to hTfRl. FIG. 25F shows binding of humanized 5H12 variants to hTfRl. [00055] FIG. 26 shows the quantified cellular uptake of anti-TfR Fab conjugates into rhabdomyosarcoma (RD) cells. The molecular payload in the tested conjugates are DMPK- targeting oligonucleotides and the uptake of the conjugates were facilitated by indicated anti- TfR Fabs. Conjugates having a negative control Fab (anti-mouse TfR) or a positive control Fab (anti-human TfRl) are also included this assay. Cells were incubated with indicated conjugate at a concentration of 100 nM for 4 hours. Cellular uptake was measured by mean Cypher5e fluorescence.

[00056] FIGs. 27A-27F show binding of oligonucleotide-conjugated or unconjugated humanized anti-TfR Fabs to human TfRl (hTfRl) and cynomolgus monkey TfRl (cTfRl), as measured by ELISA. FIG. 27A shows the binding of humanized 3M12 variants alone or in conjugates with a DMPK targeting oligo to hTfRl. FIG. 27B shows the binding of humanized 3M12 variants alone or in conjugates with a DMPK targeting oligo to cTfRl. FIG. 27C shows the binding of humanized 3 A4 variants alone or in conjugates with a DMPK targeting oligo to hTfRl. FIG. 27D shows the binding of humanized 3A4 variants alone or in conjugates with a DMPK targeting oligo to cTfRl. FIG. 27E shows the binding of humanized 5H12 variants alone or in conjugates with a DMPK targeting oligo to hTfRl. FIG. 27F shows the binding of humanized 5H12 variants alone or in conjugates with a DMPK targeting oligo to cTfRl. The respective EC50 values are also shown.

[00057] FIG. 28 shows DMPK expression in RD cells treated with DMPK-targeting oligonucleotides relative to cells treated with PBS. The duration of treatment was 3 days. DMPK-targeting oligonucleotides were delivered to the cells as free oligonucleotides (gymnotic uptake, “free”) or with transfection reagent (“trans”).

[00058] FIG. 29 shows DMPK expression in RD cells treated with various concentrations of conjugates containing the indicated humanized anti-TfR antibodies conjugated to a DMPK-targeting oligonucleotide (ASO300). The duration of treatment was 3 days. ASO300 delivered using transfection agents (labeled “Trans”) was used as control. [00059] FIG. 30 shows results of splicing correction in Atp2al by an anti-TfRl antibody-oligonucleotide conjugate (Ab-ASO) in the HSA-LR mouse model of DM1, measured in the gastrocnemius muscle. The anti-TfR antibody used is RI7 217 and the oligonucleotide is targeting human skeletal actin.

[00060] FIG. 31 shows splicing correction in more than 30 different RNAs related to DM1, measured in the gastrocnemius muscle of HSA-LR mice treated anti-TfRl antibody- oligonucleotide (Ab-ASO) conjugate or saline. The anti-TfR antibody used is RI7217 and the oligonucleotide is targeting human skeletal actin. [00061] FIG. 32 shows splicing derangement in quadriceps, gastrocnemius, or tibialis anterior muscles of HSA-LR mice treated with anti-TfRl antibody-oligonucleotide conjugate (Ab-ASO) or saline. The data represent composite splicing derangement measured in the more than 30 RNAs shown in FIG. 31.

[00062] FIG. 33 shows myotonia grade measured in quadriceps, gastrocnemius, and tibialis anterior muscles of HSA-LR mice treated with saline, unconjugated oligonucleotide (ASO), or anti-TfRl antibody-oligonucleotide conjugate (Ab-ASO). Myotonia was measured by electromyography (EMG), and graded 0, 1, 2, or 3 based on the frequency of myotonic discharge.

[00063] FIG. 34 shows skipping of exon 51 in human DMD myotubes, facilitated by a DMD exon 51 skipping oligonucleotide (a PMO). Cells were treated with the naked PMO or with PMO conjugated to an anti-TfRl Fab (Ab-PMO).

[00064] FIG. 35 shows dose-dependent increase of dystrophin expression in quadriceps muscles of mdx mice after treatment with anti-mouse TfRl (RI7217) conjugated to an oligonucleotide (a PMO) targeted to exon 23, as measured by western blotting for dystrophin, with alpha-actin as a loading control. The standards were generated using pooled wild-type protein and pooled mdx protein. The percent indicates the amount of WT protein spiked into the sample.

[00065] FIG. 36 shows quantification of dystrophin protein levels within quadriceps muscles of mdx mice after treatment with various doses of anti-mouse TfR (RI7217) conjugated to an oligonucleotide (a PMO) targeting exon 23.

[00066] FIG. 37 shows immunofluorescent staining images of quadriceps muscles from wild-type (WT) mice treated with saline, or mdx mice treated with saline, naked oligonucleotide or oligonucleotide conjugated to anti-mouse TfRl (RI7217).

[00067] FIGs. 38A-38B show expression of MBD3L2, TRIM43, and ZSCAN4 transcripts in FSHD patient-derived myotubes treated with naked FM10 (FIG. 38A) or FM10 conjugated to anti-TfRl (FIG. 38B) over a range concentrations.

[00068] FIG. 39 shows data illustrating that conjugates containing designated anti-TfR Fabs (3M12 VH3/VK2, 3M12 VH4/VK3, and 3A4 VH3 N54S/VK4) conjugated to a DMD exon- skipping oligonucleotide resulted in enhanced exon skipping compared to the naked DMD exon skipping oligo in DMD patient myotubes.

[00069] FIGs. 40A-40E show in vivo activity of conjugates containing designated anti- TfR Fabs (control, 3M12 VH3/VK2, 3M12 VH4/VK3, and 3A4 VH3 N54S/VK4) conjugated to DMPK-targeting oligonucleotide in reducing DMPK mRNA expression in mice expressing human TfRl (hTfRl knock-in mice). FIG. 40A shows the experimental design (e.g., IV dosage, dosing frequency). DMPK mRNA levels were measured 14 days post first dose in the tibialis anterior (FIG. 40B), gastrocnemius (FIG. 40C), heart (FIG. 40D), and diaphragm (FIG. 40E), of the mice.

[00070] FIGs. 41A-41C show that conjugates containing anti-TfR antibody conjugated to DMPK-targeting oligonucleotide corrected splicing and reduced foci in CM-DM1-32F primary cells expressing a DMPK mutant mRNA containing 380 CUG repeats. FIG. 41A shows that the conjugates reduced mutant DMPK mRNA expression. FIG. 4 IB shows that the conjugates corrected BIN1 Exon 11 splicing. FIG. 41C shows images of a fluorescence in situ hybridization (FISH) analysis and quantification of the images, demonstrating that the conjugate reduced nuclear foci formed by the mutant DMPK mRNA. In the microscopy images shown in the top panels of FIG. 41C, the light rounded shapes show cell nuclei, and the bright puncta within the nuclei of the DM1 cells (right three microscopy panels) show CUG foci.

[00071] FIG. 42 shows ELISA measurements of binding of anti-TfR Fab 3M12 VH4/Vk3 to recombinant human (circles), cynomolgus monkey (squares), mouse (upward triangles), or rat (downward triangles) TfRl protein, at a range of concentrations from 230 pM to 500 nM of the Fab. Measurement results show that the anti-TfR Fab is reactive with human and cynomolgus monkey TfRl. Binding was not observed to mouse or rat recombinant TfRl. Data is shown as relative fluorescent units normalized to baseline.

[00072] FIG. 43 shows results of an ELISA testing the affinity of anti-TfR Fab 3M12 VH4/Vk3 to recombinant human TfRl or TfR2 over a range of concentrations from 230 pM to 500 nM of Fab. The data are presented as relative fluorescence units normalized to baseline. The results demonstrate that the Fab does not bind recombinant human TfR2.

[00073] FIG. 44 shows the serum stability of the linker used for linking anti-TfR Fab 3M12 VH4/Vk3 to a control antisense oligonucleotide over 72 hours incubation in PBS or in rat, mouse, cynomolgus monkey or human serum.

[00074] FIG. 45 shows that conjugates containing an anti-TfR Fab 3M12 VH4/Vk3 conjugated to a DUX4-targeting oligonucleotide (SEQ ID NO: 147) inhibited DUX4 transcriptome in C6 (AB1080) immortalized FSHD1 cells, as indicated by decreased mRNA expression of MDB3L2, TRIM43, and ZSCAN4. The conjugates showed superior activities relative to the unconjugated DUX4-targeting oligonucleotide in inhibiting DUX4 transcriptome. [00075] FIGs. 46A-46B show dose response curves for gene knockdown. FIG. 46A shows MBD3L2 knockdown in C6 (AB1080) immortalized FSHD1 cells treated with conjugates containing an anti-TfR Fab 3M12 VH4/Vk3 conjugated to a DUX4-targeting oligonucleotide (SEQ ID NO: 147). FIG. 46B shows MBD3L2, TRIM43, and ZSCAN4 knockdown in FSHD patient myotubes treated with conjugates containing an anti-TfR Fab 3M12 VH4/Vk3 conjugated to a DUX4-targeting oligonucleotide (SEQ ID NO: 147). FIG. 46B includes the MBD3L2 data shown in FIG. 46A.

[00076] FIGs. 47A-47C show EMG myotonia grade in quadriceps (FIG. 47 A), gastrocnemius (FIG. 47B), and tibialis anterior (FIG. 47C) of HSA-LR mice treated with vehicle, a single dose of unconjugated ASO, or a single dose of anti-TfRl antibody- ASO conjugate (Ab-ASO). The anti-TfRl antibody used is RI7217 Fab and the oligonucleotide targets human skeletal actin (ACTA1).

[00077] FIG. 48 shows human ACTA1 expression measured by qPCR in HSA ^LR DM1 mice after a single dose of naked ASO or dose equivalent of anti-TFRl antibody-ASO conjugate (Ab-ASO), relative to vehicle-treated mice. The anti-TfRl antibody used is RI7217 Fab and the oligonucleotide targets human skeletal actin (ACTA1).

[00078] FIGs. 49A-49C show ACTA1 expression in quadriceps (FIG. 49A), gastrocnemius (FIG. 49B), and tibialis anterior (FIG. 49C) in HSA ^LR DM1 mice after a single dose of 10 mg/kg naked ASO, 20 mg/kg naked ASO, or dose equivalents of anti-TFR antibody-ASO conjugate (Ab-ASO), relative to vehicle-treated mice. The anti-TfRl antibody used is RI7 217 Fab and the oligonucleotide targets human skeletal actin (ACTA1). (* p < 0.05; *** p < 0.001)

[00079] FIGs. 50A-50C show quantification of exon 23 skipping in quadriceps (FIG. 50A), heart (FIG. 50B), and diaphragm (FIG. 50C) of wild-type (WT) and mdx mice two- or four-weeks following administration of a single dose of saline, unconjugated oligonucleotide (ASO) that induces exon 23 skipping in DMD, or conjugates containing an anti-TfRl RI7217 Fab conjugated to the ASO (Ab-ASO). Little or no exon 23 skipping was observed in tissues from WT mice or from mdx mice administered saline or unconjugated ASO, whereas significant levels of exon 23 skipping was observed in tissues of mdx mice treated with Ab- ASO. (* p < 0.05, ** p < 0.01, **** p < 0.0001)

[00080] FIGs. 51A-51D show measurement of dystrophin protein in quadriceps of mdx mice following administration of a single dose of unconjugated oligonucleotide (ASO) that induces exon 23 skipping in DMD, or conjugates containing an anti-TfRl RI7217 Fab conjugated to the ASO (Ab-ASO). FIG. 51A shows western blots of dystrophin and alpha- actinin protein in muscle tissue two weeks following injection of ASO or Ab-ASO. FIG. 51B shows quantification of the dystrophin in the western blot of FIG. 51 A relative to dystrophin protein in wild-type muscle. FIG. 51C shows western blots of dystrophin and alpha-actinin protein in muscle tissue four weeks following injection of ASO or Ab-ASO. FIG. 51D shows quantification of the dystrophin in the western blot of FIG. 51C relative to dystrophin protein in wild-type muscle. The standard curves in FIGs. 51A and 51C were generated by pooling tissue from wild-type (WT) and mdx mouse samples, and the percent WT indicates the amount of WT protein spiked into each sample. (* p < 0.05; ns, not significant)

[00081] FIGs. 52A-52D show measurement of dystrophin protein in heart muscle of mdx mice following administration of a single dose of unconjugated oligonucleotide (ASO) that induces exon 23 skipping in DMD, or conjugates containing an anti-TfRl RI7217 Fab conjugated to the ASO (Ab-ASO). FIG. 52A shows western blots of dystrophin and alpha- actinin protein in muscle tissue two weeks following injection of ASO or Ab-ASO. FIG. 52B shows quantification of the dystrophin in the western blot of FIG. 52A relative to dystrophin protein in wild-type muscle. FIG. 52C shows western blots of dystrophin and alpha-actinin protein in muscle tissue four weeks following injection of ASO or Ab-ASO. FIG. 52D shows quantification of the dystrophin in the western blot of FIG. 52C relative to dystrophin protein in wild-type muscle. The standard curves in FIGs. 52A and 52C were generated by pooling tissue from wild-type (WT) and mdx mouse samples, and the percent WT indicates the amount of WT protein spiked into each sample. (* p < 0.05, **** p < 0.0001)

[00082] FIGs. 53A-53D show measurement of dystrophin protein in diaphragm muscle of mdx mice following administration of a single dose of unconjugated oligonucleotide (ASO) that induces exon 23 skipping in DMD, or conjugates containing an anti-TfRl RI7217 Fab conjugated to the ASO (Ab-ASO). FIG. 53A shows western blots of dystrophin and alpha- actinin protein in muscle tissue two weeks following injection of ASO or Ab-ASO. FIG. 53B shows quantification of the dystrophin in the western blot of FIG. 53A relative to dystrophin protein in wild-type muscle. FIG. 53C shows western blots of dystrophin and alpha-actinin protein in muscle tissue four weeks following injection of ASO or Ab-ASO. FIG. 53D shows quantification of the dystrophin in the western blot of FIG. 53C relative to dystrophin protein in wild-type muscle. The standard curves in FIGs. 53A and 53C were generated by pooling tissue from wild-type (WT) and mdx mouse samples, and the percent WT indicates the amount of WT protein spiked into each sample. (** /? < 0.01, *** p < 0.001)

[00083] FIGs. 54A-54C show quantification of the amount of administered oligonucleotide (ASO) in quadriceps (FIG. 54A), diaphragm (FIG. 54B), and heart (FIG. 54C) of wild-type (WT) or mdx mice two- or four- weeks following administration of a single dose of saline, unconjugated exon 23 skipping oligonucleotide (ASO), or conjugates containing an anti-TfRl RI7217 Fab conjugated to the ASO (Ab-ASO).

[00084] FIG. 55 shows non-human primate plasma levels of DUX4-targeting oligonucleotide (SEQ ID NO: 147) over time following administration of 30 mg/kg unconjugated (‘naked’) oligonucleotide or 3, 10, or 30 mg/kg oligonucleotide equivalent of conjugates comprising anti-TfRl Fab 3M12 VH4/Vk3 covalently linked to the DUX4- targeting oligonucleotide (‘Fab-oligonucleotide conjugate’).

[00085] FIG. 56 shows tissue levels of DUX4-targeting oligonucleotide (SEQ ID NO: 147) measured in non-human primate muscle tissue samples two-weeks following administration of 30 mg/kg unconjugated (‘naked’) oligonucleotide or 3, 10, or 30 mg/kg oligonucleotide equivalent of conjugates comprising anti-TfRl Fab 3M12 VH4/Vk3 covalently linked to the DUX4-targeting oligonucleotide (‘Fab-Oligonucleotide conjugate’).

[00086] FIG. 57 shows tissue levels of DUX4-targeting oligonucleotide (SEQ ID NO: 147) measured in non-human primate muscle tissue samples collected by biopsy one-week following administration (left 5 bars) or by necropsy two- weeks following administration (right 5 bars) of 30 mg/kg unconjugated oligonucleotide (‘Oligo’) or 3, 10, or 30 mg/kg oligonucleotide equivalent of conjugates comprising anti-TfRl Fab 3M12 VH4/Vk3 covalently linked to the DUX4-targeting oligonucleotide (‘Conjugate’).

[00087] FIGs. 58A-58B show splicing correction in more than 30 different RNAs known to be mis-spliced in DM1 patients, measured in the tibialis anterior (FIG. 58 A) or the quadriceps (FIG. 58B) of HSA-LR mice treated with a single dose of anti-TfRl antibody- oligonucleotide (Ab-ASO) conjugate or saline. The anti-TfRl antibody used is RI7217 Fab and the oligonucleotide targets skeletal actin (ACTA1).

[00088] FIG. 59 shows % exon 53 skipping in DMD patient cells harboring a deletion of DMD exon 52, following gymnotic uptake of exon 53-skipping oligonucleotides over a range of concentrations.

[00089] FIG. 60 shows % exon 53 skipping in DMD patient cells harboring a deletion of DMD exon 52, following treatment with exon 53-skipping PMO either not linked to an antibody (“Naked ASO”) or covalently linked to an anti-TfRl Fab (“Anti-TfRl Fab-ASO complex”) at a variety of concentrations.

[00090] DETAILED DESCRIPTION OF INVENTION [00091] Aspects of the disclosure relate to a recognition that while certain molecular payloads (e.g., oligonucleotides, peptides, small molecules) can have beneficial effects in muscle cells, it has proven challenging to effectively target such cells. As described herein, the present disclosure provides complexes comprising muscle-targeting agents covalently linked to molecular payloads in order to overcome such challenges. In some embodiments, the complexes are particularly useful for delivering molecular payloads that modulate expression or activity of target genes in muscle cells, e.g., in a subject having or suspected of having a muscle disease. For example, in some embodiments, complexes are useful for treating subjects having rare muscle diseases, including Pompe disease, Centronuclear myopathy,

Fibrodysplasia Ossificans Progressiva, Friedreich’s ataxia, or Duchenne muscular dystrophy.

In some embodiments, depending on the condition to be treated, different molecular payloads may be used in such complexes. For example, if the underlying mutation gives rise to a splicing defect, then an oligonucleotide or other payload may be used to correct the splicing defect (e.g., an oligonucleotide that inhibits exon skipping or promotes alternative splicing). If the underlying mutation results in a gain-of-function allele, then an oligonucleotide (e.g.,

RNAi, PMO, ASO-gapmer) may be used to inhibit the expression or activity of the allele. In some embodiments, e.g., when the mutation results in a loss-of-function allele, the payload may comprise an expression construct, e.g., for expressing a wild-type version of the allele. In some embodiments, the payload may comprise machinery (e.g., a guide nucleic acid, expression construct encoding a gene editing enzyme) for correcting the underlying defect, e.g., by gene editing.

[00092] Further aspects of the disclosure, including a description of defined terms, are provided below.

I. Definitions

[00093] Administering: As used herein, the terms “administering” or “administration” means to provide a complex to a subject in a manner that is physiologically and/or (e.g., and) pharmacologically useful (e.g., to treat a condition in the subject).

[00094] Approximately: As used herein, the term “approximately” or “about,” as applied to one or more values of interest, refers to a value that is similar to a stated reference value. In certain embodiments, the term “approximately” or “about” refers to a range of values that fall within 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, or less in either direction (greater than or less than) of the stated reference value unless otherwise stated or otherwise evident from the context (except where such number would exceed 100% of a possible value).

[00095] Antibody: As used herein, the term “antibody” refers to a polypeptide that includes at least one immunoglobulin variable domain or at least one antigenic determinant, e.g., paratope that specifically binds to an antigen. In some embodiments, an antibody is a full- length antibody. In some embodiments, an antibody is a chimeric antibody. In some embodiments, an antibody is a humanized antibody. However, in some embodiments, an antibody is a Fab fragment, a Fab’ fragment, a F(ab')2 fragment, a Fv fragment or a scFv fragment. In some embodiments, an antibody is a nanobody derived from a camelid antibody or a nanobody derived from shark antibody. In some embodiments, an antibody is a diabody. In some embodiments, an antibody comprises a framework having a human germline sequence. In another embodiment, an antibody comprises a heavy chain constant domain selected from the group consisting of IgG, IgGl, IgG2, IgG2A, IgG2B, IgG2C, IgG3, IgG4, IgAl, IgA2, IgD, IgM, and IgE constant domains. In some embodiments, an antibody comprises a heavy (H) chain variable region (abbreviated herein as VH), and/or (e.g., and) a light (L) chain variable region (abbreviated herein as VL). In some embodiments, an antibody comprises a constant domain, e.g., an Fc region. An immunoglobulin constant domain refers to a heavy or light chain constant domain. Human IgG heavy chain and light chain constant domain amino acid sequences and their functional variations are known. With respect to the heavy chain, in some embodiments, the heavy chain of an antibody described herein can be an alpha (a), delta (D), epsilon (e), gamma (g) or mu (m) heavy chain. In some embodiments, the heavy chain of an antibody described herein can comprise a human alpha (a), delta (D), epsilon (e), gamma (g) or mu (m) heavy chain. In a particular embodiment, an antibody described herein comprises a human gamma 1 CHI, CH2, and/or (e.g., and) CH3 domain. In some embodiments, the amino acid sequence of the VH domain comprises the amino acid sequence of a human gamma (g) heavy chain constant region, such as any known in the art. Non-limiting examples of human constant region sequences have been described in the art, e.g., see U.S. Pat. No. 5,693,780 and Kabat E A et ah, (1991) supra. In some embodiments, the VH domain comprises an amino acid sequence that is at least 70%, 75%, 80%, 85%, 90%, 95%, 98%, or at least 99% identical to any of the variable chain constant regions provided herein. In some embodiments, an antibody is modified, e.g., modified via glycosylation, phosphorylation, sumoylation, and/or (e.g., and) methylation. In some embodiments, an antibody is a glycosylated antibody, which is conjugated to one or more sugar or carbohydrate molecules.

In some embodiments, the one or more sugar or carbohydrate molecule are conjugated to the antibody via N-glycosylation, O-glycosylation, C-glycosylation, glypiation (GPI anchor attachment), and/or (e.g., and) phosphoglycosylation. In some embodiments, the one or more sugar or carbohydrate molecule are monosaccharides, disaccharides, oligosaccharides, or glycans. In some embodiments, the one or more sugar or carbohydrate molecule is a branched oligosaccharide or a branched glycan. In some embodiments, the one or more sugar or carbohydrate molecule includes a mannose unit, a glucose unit, an N-acetylglucosamine unit, an N-acetylgalactosamine unit, a galactose unit, a fucose unit, or a phospholipid unit. In some embodiments, an antibody is a construct that comprises a polypeptide comprising one or more antigen binding fragments of the disclosure linked to a linker polypeptide or an immunoglobulin constant domain. Linker polypeptides comprise two or more amino acid residues joined by peptide bonds and are used to link one or more antigen binding portions. Examples of linker polypeptides have been reported (see e.g., Holliger, R, et al. (1993) Proc. Natl. Acad. Sci. USA 90:6444-6448; Poljak, R. J., et al. (1994) Structure 2:1121-1123). Still further, an antibody may be part of a larger immunoadhesion molecule, formed by covalent or noncovalent association of the antibody or antibody portion with one or more other proteins or peptides. Examples of such immunoadhesion molecules include use of the streptavidin core region to make a tetrameric scFv molecule (Kipriyanov, S. M., et al. (1995) Human Antibodies and Hybridomas 6:93-101) and use of a cysteine residue, a marker peptide and a C-terminal polyhistidine tag to make bivalent and biotinylated scFv molecules (Kipriyanov, S. M., et al. (1994) Mol. Immunol. 31:1047-1058).

[00096] CDR: As used herein, the term "CDR" refers to the complementarity determining region within antibody variable sequences. A typical antibody molecule comprises a heavy chain variable region (VH) and a light chain variable region (VL), which are usually involved in antigen binding. The VH and VL regions can be further subdivided into regions of hypervariability, also known as “complementarity determining regions” (“CDR”), interspersed with regions that are more conserved, which are known as “framework regions” (“FR”). Each VH and VL is typically composed of three CDRs and four FRs, arranged from amino-terminus to carboxy-terminus in the following order: FR1, CDR1, FR2, CDR2, FR3, CDR3, FR4. The extent of the framework region and CDRs can be precisely identified using methodology known in the art, for example, by the Rabat definition, the IMGT definition, the Chothia definition, the AbM definition, and/or (e.g., and) the contact definition, all of which are well known in the art. See, e.g., Rabat, E.A., et al. (1991) Sequences of Proteins of Immunological Interest, Fifth Edition, U.S. Department of Health and Human Services, NIH Publication No. 91-3242; IMGT®, the international ImMunoGeneTics information system® http://www.imgt.org, Lefranc, M.-P. et al., Nucleic Acids Res., 27:209-212 (1999); Ruiz, M. et al., Nucleic Acids Res., 28:219-221 (2000); Lefranc, M.-P, Nucleic Acids Res., 29:207-209 (2001); Lefranc, M.-P, Nucleic Acids Res., 31:307-310 (2003); Lefranc, M.-P. et al., In Silico Biol., 5, 0006 (2004) [Epub], 5:45-60 (2005); Lefranc, M.-P. et al., Nucleic Acids Res., 33:D593-597 (2005); Lefranc, M.-P. et al., Nucleic Acids Res., 37:D1006-1012 (2009); Lefranc, M.-P. et al., Nucleic Acids Res., 43:D413-422 (2015); Chothia et al., (1989) Nature 342:877; Chothia, C. et al. (1987) J. Mol. Biol. 196:901-917, Al-lazikani et al (1997) J. Molec. Biol. 273:927-948; and Almagro, J. Mol. Recognit. 17:132-143 (2004). See also hgmp.mrc.ac.uk and bioinf.org.uk/abs. As used herein, a CDR may refer to the CDR defined by any method known in the art. Two antibodies having the same CDR means that the two antibodies have the same amino acid sequence of that CDR as determined by the same method, for example, the IMGT definition.

[00097] There are three CDRs in each of the variable regions of the heavy chain and the light chain, which are designated CDR1, CDR2 and CDR3, for each of the variable regions. The term "CDR set" as used herein refers to a group of three CDRs that occur in a single variable region capable of binding the antigen. The exact boundaries of these CDRs have been defined differently according to different systems. The system described by Rabat (Rabat et al, Sequences of Proteins of Immunological Interest (National Institutes of Health, Bethesda, Md. (1987) and (1991)) not only provides an unambiguous residue numbering system applicable to any variable region of an antibody, but also provides precise residue boundaries defining the three CDRs. These CDRs may be referred to as Rabat CDRs. Sub-portions of CDRs may be designated as LI, L2 and L3 or HI, H2 and H3 where the "L" and the "H" designates the light chain and the heavy chains regions, respectively. These regions may be referred to as Chothia CDRs, which have boundaries that overlap with Rabat CDRs. Other boundaries defining CDRs overlapping with the Rabat CDRs have been described by Padlan (FASEB J. 9:133-139 (1995)) and MacCallum (J Mol Biol 262(5):732-45 (1996)). Still other CDR boundary definitions may not strictly follow one of the above systems, but will nonetheless overlap with the Rabat CDRs, although they may be shortened or lengthened in light of prediction or experimental findings that particular residues or groups of residues or even entire CDRs do not significantly impact antigen binding. The methods used herein may utilize CDRs defined according to any of these systems. Examples of CDR definition systems are provided in Table 6.

Table 6. CDR Definitions

¹ IMGT ^® , the international ImMunoGeneTics information system ^® , imgt.org, Lefranc, M.-P. et al., Nucleic Acids Res., 27:209-212 (1999)

² Rabat et al. (1991) Sequences of Proteins of Immunological Interest, Fifth Edition, U.S. Department of Health and Human Services, NIH Publication No. 91-3242

³ Chothia et al., J. Mol. Biol. 196:901-917 (1987))

[00098] CDR-grafted antibody: The term "CDR-grafted antibody" refers to antibodies which comprise heavy and light chain variable region sequences from one species but in which the sequences of one or more of the CDR regions of VH and/or (e.g., and) VL are replaced with CDR sequences of another species, such as antibodies having murine heavy and light chain variable regions in which one or more of the murine CDRs (e.g., CDR3) has been replaced with human CDR sequences.

[00099] Chimeric antibody: The term "chimeric antibody" refers to antibodies which comprise heavy and light chain variable region sequences from one species and constant region sequences from another species, such as antibodies having murine heavy and light chain variable regions linked to human constant regions.

[000100] Complementary: As used herein, the term “complementary” refers to the capacity for precise pairing between two nucleotides or two sets of nucleotides. In particular, complementary is a term that characterizes an extent of hydrogen bond pairing that brings about binding between two nucleotides or two sets of nucleotides. For example, if a base at one position of an oligonucleotide is capable of hydrogen bonding with a base at the corresponding position of a target nucleic acid (e.g., an mRNA), then the bases are considered to be complementary to each other at that position. Base pairings may include both canonical Watson-Crick base pairing and non-Watson-Crick base pairing (e.g., Wobble base pairing and Hoogsteen base pairing). For example, in some embodiments, for complementary base pairings, adenosine-type bases (A) are complementary to thymidine-type bases (T) or uracil- type bases (U), that cytosine-type bases (C) are complementary to guanosine-type bases (G), and that universal bases such as 3-nitropyrrole or 5-nitroindole can hybridize to and are considered complementary to any A, C, U, or T. Inosine (I) has also been considered in the art to be a universal base and is considered complementary to any A, C, U or T.

[000101] Conservative amino acid substitution: As used herein, a “conservative amino acid substitution” refers to an amino acid substitution that does not alter the relative charge or size characteristics of the protein in which the amino acid substitution is made. Variants can be prepared according to methods for altering polypeptide sequence known to one of ordinary skill in the art such as are found in references which compile such methods, e.g. Molecular Cloning: A Laboratory Manual, J. Sambrook, et ah, eds., Fourth Edition, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, New York, 2012, or Current Protocols in Molecular Biology, F.M. Ausubel, et ah, eds., John Wiley & Sons, Inc., New York. Conservative substitutions of amino acids include substitutions made amongst amino acids within the following groups: (a) M, I, L, V; (b) F, Y, W; (c) K, R, H; (d) A, G; (e) S, T; (f) Q, N; and (g) E, D.

[000102] Covalently linked: As used herein, the term “covalently linked” refers to a characteristic of two or more molecules being linked together via at least one covalent bond.

In some embodiments, two molecules can be covalently linked together by a single bond, e.g., a disulfide bond or disulfide bridge, that serves as a linker between the molecules. However, in some embodiments, two or more molecules can be covalently linked together via a molecule that serves as a linker that joins the two or more molecules together through multiple covalent bonds. In some embodiments, a linker may be a cleavable linker. However, in some embodiments, a linker may be a non-cleavable linker.

[000103] Cross-reactive: As used herein and in the context of a targeting agent (e.g., antibody), the term “cross-reactive,” refers to a property of the agent being capable of specifically binding to more than one antigen of a similar type or class (e.g., antigens of multiple homologs, paralogs, or orthologs) with similar affinity or avidity. For example, in some embodiments, an antibody that is cross-reactive against human and non-human primate antigens of a similar type or class (e.g., a human transferrin receptor and non-human primate transferrin receptor) is capable of binding to the human antigen and non-human primate antigens with a similar affinity or avidity. In some embodiments, an antibody is cross -reactive against a human antigen and a rodent antigen of a similar type or class. In some embodiments, an antibody is cross-reactive against a rodent antigen and a non-human primate antigen of a similar type or class. In some embodiments, an antibody is cross-reactive against a human antigen, a non-human primate antigen, and a rodent antigen of a similar type or class.

[000104] Disease allele: As used herein, the term “disease allele” refers to any one of alternative forms (e.g., mutant forms) of a gene for which the allele is correlated with and/or (e.g., and) directly or indirectly contributes to, or causes, disease. A disease allele may comprise gene alterations including, but not limited to, insertions (e.g., disease-associated repeats described below), deletions, missense mutations, nonsense mutations and splice-site mutations relative to a wild-type (non-disease) allele. In some embodiments, a disease allele has a loss-of-function mutation. In some embodiments, a disease allele has a gain-of-function mutation. In some embodiments, a disease allele encodes an activating mutation ( e.g encodes a protein that is constitutively active). In some embodiments, a disease allele is a recessive allele having a recessive phenotype. In some embodiments, a disease allele is a dominant allele having a dominant phenotype.

[000105] Disease-associated-repeat: As used herein, the term “disease-associated- repeat” refers to a repeated nucleotide sequence at a genomic location for which the number of units of the repeated nucleotide sequence is correlated with and/or (e.g., and) directly or indirectly contributes to, or causes, genetic disease. Each repeating unit of a disease associated repeat may be 2, 3, 4, 5 or more nucleotides in length. For example, in some embodiments, a disease associated repeat is a dinucleotide repeat. In some embodiments, a disease associated repeat is a trinucleotide repeat. In some embodiments, a disease associated repeat is a tetranucleotide repeat. In some embodiments, a disease associated repeat is a pentanucleotide repeat. In some embodiments, embodiments, the disease-associated-repeat comprises CAG repeats, CTG repeats, CUG repeats, CGG repeats, CCTG repeats, or a nucleotide complement of any thereof. In some embodiments, a disease-associated-repeat is in a non-coding portion of a gene. However, in some embodiments, a disease-associated-repeat is in a coding region of a gene. In some embodiments, a disease-associated-repeat is expanded from a normal state to a length that directly or indirectly contributes to, or causes, genetic disease. In some embodiments, a disease-associated-repeat is in RNA (e.g., an RNA transcript). In some embodiments, a disease-associated-repeat is in DNA (e.g., a chromosome, a plasmid). In some embodiments, a disease-associated-repeat is expanded in a chromosome of a germline cell. In some embodiments, a disease-associated-repeat is expanded in a chromosome of a somatic cell. In some embodiments, a disease-associated-repeat is expanded to a number of repeating units that is associated with congenital onset of disease. In some embodiments, a disease- associated-repeat is expanded to a number of repeating units that is associated with childhood onset of disease. In some embodiments, a disease-associated-repeat is expanded to a number of repeating units that is associated with adult onset of disease.

[000106] Framework: As used herein, the term "framework" or "framework sequence" refers to the remaining sequences of a variable region minus the CDRs. Because the exact definition of a CDR sequence can be determined by different systems, the meaning of a framework sequence is subject to correspondingly different interpretations. The six CDRs (CDR-L1, CDR-L2, and CDR-L3 of light chain and CDR-H1, CDR-H2, and CDR-H3 of heavy chain) also divide the framework regions on the light chain and the heavy chain into four sub-regions (FR1, FR2, FR3 and FR4) on each chain, in which CDR1 is positioned between FR1 and FR2, CDR2 between FR2 and FR3, and CDR3 between FR3 and FR4. Without specifying the particular sub-regions as FR1, FR2, FR3 or FR4, a framework region, as referred by others, represents the combined FRs within the variable region of a single, naturally occurring immunoglobulin chain. As used herein, a FR represents one of the four sub-regions, and FRs represents two or more of the four sub-regions constituting a framework region. Human heavy chain and light chain acceptor sequences are known in the art. In one embodiment, the acceptor sequences known in the art may be used in the antibodies disclosed herein.

[000107] Human antibody: The term "human antibody", as used herein, is intended to include antibodies having variable and constant regions derived from human germline immunoglobulin sequences. The human antibodies of the disclosure may include amino acid residues not encoded by human germline immunoglobulin sequences ( e.g ., mutations introduced by random or site-specific mutagenesis in vitro or by somatic mutation in vivo), for example in the CDRs and in particular CDR3. However, the term "human antibody", as used herein, is not intended to include antibodies in which CDR sequences derived from the germline of another mammalian species, such as a mouse, have been grafted onto human framework sequences.

[000108] Humanized antibody: The term "humanized antibody" refers to antibodies which comprise heavy and light chain variable region sequences from a non-human species (e.g., a mouse) but in which at least a portion of the VH and/or (e.g., and) VL sequence has been altered to be more "human-like", i.e., more similar to human germline variable sequences. One type of humanized antibody is a CDR-grafted antibody, in which human CDR sequences are introduced into non-human VH and VL sequences to replace the corresponding nonhuman CDR sequences. In one embodiment, humanized anti-transferrin receptor antibodies and antigen binding portions are provided. Such antibodies may be generated by obtaining murine anti-transferrin receptor monoclonal antibodies using traditional hybridoma technology followed by humanization using in vitro genetic engineering, such as those disclosed in Kasaian et al PCT publication No. WO 2005/123126 A2.

[000109] Internalizing cell surface receptor: As used herein, the term, “internalizing cell surface receptor” refers to a cell surface receptor that is internalized by cells, e.g., upon external stimulation, e.g., ligand binding to the receptor. In some embodiments, an internalizing cell surface receptor is internalized by endocytosis. In some embodiments, an internalizing cell surface receptor is internalized by clathrin-mediated endocytosis. However, in some embodiments, an internalizing cell surface receptor is internalized by a clathrin- independent pathway, such as, for example, phagocytosis, macropinocytosis, caveolae- and raft-mediated uptake or constitutive clathrin-independent endocytosis. In some embodiments, the internalizing cell surface receptor comprises an intracellular domain, a transmembrane domain, and/or (e.g., and) an extracellular domain, which may optionally further comprise a ligand-binding domain. In some embodiments, a cell surface receptor becomes internalized by a cell after ligand binding. In some embodiments, a ligand may be a muscle-targeting agent or a muscle-targeting antibody. In some embodiments, an internalizing cell surface receptor is a transferrin receptor.

[000110] Isolated antibody: An "isolated antibody", as used herein, is intended to refer to an antibody that is substantially free of other antibodies having different antigenic specificities (e.g., an isolated antibody that specifically binds transferrin receptor is substantially free of antibodies that specifically bind antigens other than transferrin receptor). An isolated antibody that specifically binds transferrin receptor complex may, however, have cross-reactivity to other antigens, such as transferrin receptor molecules from other species. Moreover, an isolated antibody may be substantially free of other cellular material and/or (e.g., and) chemicals.

[000111] Kabat numbering: The terms "Kabat numbering", "Kabat definitions and "Kabat labeling" are used interchangeably herein. These terms, which are recognized in the art, refer to a system of numbering amino acid residues which are more variable (i.e. hypervariable) than other amino acid residues in the heavy and light chain variable regions of an antibody, or an antigen binding portion thereof (Kabat et al. (1971) Ann. NY Acad, Sci. 190:382-391 and, Kabat, E. A., et al. (1991) Sequences of Proteins of Immunological Interest, Fifth Edition, U.S. Department of Health and Human Services, NIH Publication No. 91-3242). For the heavy chain variable region, the hypervariable region ranges from amino acid positions 31 to 35 for CDR1, amino acid positions 50 to 65 for CDR2, and amino acid positions 95 to 102 for CDR3. For the light chain variable region, the hypervariable region ranges from amino acid positions 24 to 34 for CDR1, amino acid positions 50 to 56 for CDR2, and amino acid positions 89 to 97 for CDR3.

[000112] Molecular payload: As used herein, the term “molecular payload” refers to a molecule or species that functions to modulate a biological outcome. In some embodiments, a molecular payload is linked to, or otherwise associated with a muscle-targeting agent. In some embodiments, the molecular payload is a small molecule, a protein, a peptide, a nucleic acid, or an oligonucleotide. In some embodiments, the molecular payload functions to modulate the transcription of a DNA sequence, to modulate the expression of a protein, or to modulate the activity of a protein. In some embodiments, the molecular payload is an oligonucleotide that comprises a strand having a region of complementarity to a target gene.

[000113] Muscle Disease Gene: As used herein, the term “muscle disease gene” refers to a gene having a least one disease allele correlated with and/or (e.g., and) directly or indirectly contributing to, or causing, a muscle disease. In some embodiments, the muscle disease is a rare disease, e.g., as defined by the Genetic and Rare Diseases Information Center (GARD), which is a program of the National Center for Advancing Translational Sciences (NCATS). In some embodiments, the muscle disease is a rare disease that is characterized as affecting fewer than 200,000 people. In some embodiments, the muscle disease is a single-gene disease. In some embodiments, a muscle disease gene is a gene listed in Table 1.

[000114] Muscle-targeting agent: As used herein, the term, “muscle-targeting agent,” refers to a molecule that specifically binds to an antigen expressed on muscle cells. The antigen in or on muscle cells may be a membrane protein, for example an integral membrane protein or a peripheral membrane protein. Typically, a muscle-targeting agent specifically binds to an antigen on muscle cells that facilitates internalization of the muscle-targeting agent (and any associated molecular payload) into the muscle cells. In some embodiments, a muscle-targeting agent specifically binds to an internalizing, cell surface receptor on muscles and is capable of being internalized into muscle cells through receptor mediated internalization. In some embodiments, the muscle-targeting agent is a small molecule, a protein, a peptide, a nucleic acid (e.g., an aptamer), or an antibody. In some embodiments, the muscle-targeting agent is linked to a molecular payload.

[000115] Muscle-targeting antibody: As used herein, the term, “muscle-targeting antibody,” refers to a muscle-targeting agent that is an antibody that specifically binds to an antigen found in or on muscle cells. In some embodiments, a muscle-targeting antibody specifically binds to an antigen on muscle cells that facilitates internalization of the muscle targeting antibody (and any associated molecular payment) into the muscle cells. In some embodiments, the muscle-targeting antibody specifically binds to an internalizing, cell surface receptor present on muscle cells. In some embodiments, the muscle-targeting antibody is an antibody that specifically binds to a transferrin receptor.

[000116] Oligonucleotide: As used herein, the term “oligonucleotide” refers to an oligomeric nucleic acid compound of up to 200 nucleotides in length. Examples of oligonucleotides include, but are not limited to, RNAi oligonucleotides (e.g., siRNAs, shRNAs), microRNAs, gapmers, mixmers, phosphorodiamidate morpholinos, peptide nucleic acids, aptamers, guide nucleic acids (e.g., Cas9 guide RNAs), etc. Oligonucleotides may be single-stranded or double-stranded. In some embodiments, an oligonucleotide may comprise one or more modified nucleotides (e.g. 2'-0-methyl sugar modifications, purine or pyrimidine modifications). In some embodiments, an oligonucleotide may comprise one or more modified intemucleotide linkage. In some embodiments, an oligonucleotide may comprise one or more phosphorothioate linkages, which may be in the Rp or Sp stereochemical conformation. [000117] Recombinant antibody: The term "recombinant human antibody", as used herein, is intended to include all human antibodies that are prepared, expressed, created or isolated by recombinant means, such as antibodies expressed using a recombinant expression vector transfected into a host cell (described in more details in this disclosure), antibodies isolated from a recombinant, combinatorial human antibody library (Hoogenboom H. R.,

(1997) TIB Tech. 15:62-70; Azzazy H., and Highsmith W. E., (2002) Clin. Biochem. 35:425- 445; Gavilondo J. Y, and Larrick J. W. (2002) BioTechniques 29:128-145; Hoogenboom H., and Chames R (2000) Immunology Today 21:371-378), antibodies isolated from an animal (e.g., a mouse) that is transgenic for human immunoglobulin genes (see e.g., Taylor, L. D., et al. (1992) Nucl. Acids Res. 20:6287-6295; Kellermann S-A., and Green L. L. (2002) Current Opinion in Biotechnology 13:593-597; Little M. et al (2000) Immunology Today 21:364-370) or antibodies prepared, expressed, created or isolated by any other means that involves splicing of human immunoglobulin gene sequences to other DNA sequences. Such recombinant human antibodies have variable and constant regions derived from human germline immunoglobulin sequences. In certain embodiments, however, such recombinant human antibodies are subjected to in vitro mutagenesis (or, when an animal transgenic for human Ig sequences is used, in vivo somatic mutagenesis) and thus the amino acid sequences of the VH and VL regions of the recombinant antibodies are sequences that, while derived from and related to human germline VH and VL sequences, may not naturally exist within the human antibody germline repertoire in vivo. One embodiment of the disclosure provides fully human antibodies capable of binding human transferrin receptor which can be generated using techniques well known in the art, such as, but not limited to, using human Ig phage libraries such as those disclosed in Jermutus et al., PCT publication No. WO 2005/007699 A2.

[000118] Region of complementarity: As used herein, the term “region of complementarity” refers to a nucleotide sequence, e.g., of a oligonucleotide, that is sufficiently complementary to a cognate nucleotide sequence, e.g., of a target nucleic acid, such that the two nucleotide sequences are capable of annealing to one another under physiological conditions (e.g., in a cell). In some embodiments, a region of complementarity is fully complementary to a cognate nucleotide sequence of target nucleic acid. However, in some embodiments, a region of complementarity is partially complementary to a cognate nucleotide sequence of target nucleic acid (e.g., at least 80%, 90%, 95% or 99% complementarity). In some embodiments, a region of complementarity contains 1, 2, 3, or 4 mismatches compared with a cognate nucleotide sequence of a target nucleic acid.

[000119] Specifically binds: As used herein, the term “specifically binds” refers to the ability of a molecule to bind to a binding partner with a degree of affinity or avidity that enables the molecule to be used to distinguish the binding partner from an appropriate control in a binding assay or other binding context. With respect to an antibody, the term,

“specifically binds”, refers to the ability of the antibody to bind to a specific antigen with a degree of affinity or avidity, compared with an appropriate reference antigen or antigens, that enables the antibody to be used to distinguish the specific antigen from others, e.g., to an extent that permits preferential targeting to certain cells, e.g., muscle cells, through binding to the antigen, as described herein. In some embodiments, an antibody specifically binds to a target if the antibody has a K _D for binding the target of at least about 10 ⁴ M, 10 ⁵ M, 10 ⁶ M, 10 ⁷ M, 10 ⁸ M, 10 ⁹ M, 10 ¹⁰ M, 10 ¹¹ M, 10 ¹² M, 10 ¹³ M, or less. In some embodiments, an antibody specifically binds to the transferrin receptor, e.g., an epitope of the apical domain of transferrin receptor.

[000120] Subject: As used herein, the term “subject” refers to a mammal. In some embodiments, a subject is non-human primate, or rodent. In some embodiments, a subject is a human. In some embodiments, a subject is a patient, e.g., a human patient that has or is suspected of having a disease. In some embodiments, the subject is a human patient who has or is suspected of having a muscle disease (e.g., any of the diseases provided in Table 1). [000121] Transferrin receptor: As used herein, the term, “transferrin receptor” (also known as TFRC, CD71, p90, TFR or TFR1) refers to an internalizing cell surface receptor that binds transferrin to facilitate iron uptake by endocytosis. In some embodiments, a transferrin receptor may be of human (NCBI Gene ID 7037), non-human primate (e.g., NCBI Gene ID 711568 or NCBI Gene ID 102136007), or rodent (e.g., NCBI Gene ID 22042) origin. In addition, multiple human transcript variants have been characterized that encoded different isoforms of the receptor (e.g., as annotated under GenBank RefSeq Accession Numbers:

NP 001121620.1, NPJ303225.2, NP 001300894.1, and NP_001300895.1).

[000122] 2’-modified nucleoside: As used herein, the terms “2’-modified nucleoside” and “2’ -modified ribonucleoside” are used interchangeably and refer to a nucleoside having a sugar moiety modified at the 2’ position. In some embodiments, the 2’ -modified nucleoside is a 2’-4’ bicyclic nucleoside, where the 2’ and 4’ positions of the sugar are bridged (e.g., via a methylene, an ethylene, or a (S)-constrained ethyl bridge). In some embodiments, the 2’- modified nucleoside is a non-bicyclic 2’-modified nucleoside, e.g., where the 2’ position of the sugar moiety is substituted. Non-limiting examples of 2’-modified nucleosides include: 2’- deoxy, 2’-fluoro (2’-F), 2’-0-methyl (2’-0-Me), 2’-0-methoxyethyl (2’-MOE), 2’-0- aminopropyl (2’-0-AP), 2’-0-dimethylaminoethyl (2’-0-DMA0E), 2’-0- dimethylaminopropyl (2’-0-DMAP), 2’-0-dimethylaminoethyloxyethyl (2’-0-DMAE0E), 2’- O-N-methylacetamido (2’-0-NMA), locked nucleic acid (LNA, methylene -bridged nucleic acid), ethylene-bridged nucleic acid (ENA), and (S)-constrained ethyl-bridged nucleic acid (cEt). In some embodiments, the 2’ -modified nucleosides described herein are high-affinity modified nucleotides and oligonucleotides comprising the 2’ -modified nucleotides have increased affinity to a target sequences, relative to an unmodified oligonucleotide. Examples of structures of 2’-modified nucleosides are provided below:

2'-0-methoxyethyl ' 2'-fluoro locked nucleic acid ethylene-bridged (S)-constrained (LNA) nucleic acid (ENA) ethyl (cEt)

II. Complexes

[000123] Provided herein are complexes that comprise a targeting agent, e.g. an antibody, covalently linked to a molecular payload. In some embodiments, a complex comprises a muscle-targeting antibody covalently linked to an oligonucleotide. A complex may comprise an antibody that specifically binds a single antigenic site or that binds to at least two antigenic sites that may exist on the same or different antigens. A complex may be used to modulate the activity or function of at least one gene, protein, and/or (e.g., and) nucleic acid. In some embodiments, the molecular payload present with a complex is responsible for the modulation of a gene, protein, and/or (e.g., and) nucleic acids. A molecular payload may be a small molecule, protein, nucleic acid, oligonucleotide, or any molecular entity capable of modulating the activity or function of a gene, protein, and/or (e.g., and) nucleic acid in a cell. In some embodiments, a molecular payload is an oligonucleotide that targets a muscle disease allele in muscle cells.

[000124] In some embodiments, a complex comprises a muscle-targeting agent, e.g. an anti-transferrin receptor antibody, covalently linked to a molecular payload, e.g. an antisense oligonucleotide that targets a muscle disease allele.

[000125] In some embodiments, a complex is useful for treating a muscle disease, in which a molecular payload affects the activity of the corresponding gene provided in Table 1. For example, depending on the condition, a molecular payload may modulate (e.g., decrease, increase) transcription or expression of the gene, modulate the expression of a protein encoded by the gene, or to modulate the activity of the encoded protein. In some embodiments, the molecular payload is an oligonucleotide that comprises a strand having a region of complementarity to a target gene provided in Table 1.

[000126] Table 1 - List of muscle diseases and corresponding genes.

A. Muscle- Targeting Agents

[000127] Some aspects of the disclosure provide muscle-targeting agents, e.g., for delivering a molecular payload to a muscle cell. In some embodiments, such muscle-targeting agents are capable of binding to a muscle cell, e.g., via specifically binding to an antigen on the muscle cell, and delivering an associated molecular payload to the muscle cell. In some embodiments, the molecular payload is bound (e.g., covalently bound) to the muscle targeting agent and is internalized into the muscle cell upon binding of the muscle targeting agent to an antigen on the muscle cell, e.g., via endocytosis. It should be appreciated that various types of muscle-targeting agents may be used in accordance with the disclosure. For example, the muscle-targeting agent may comprise, or consist of, a nucleic acid (e.g., DNA or RNA), a peptide (e.g., an antibody), a lipid (e.g., a micro vesicle), or a sugar moiety (e.g., a polysaccharide). Exemplary muscle-targeting agents are described in further detail herein, however, it should be appreciated that the exemplary muscle-targeting agents provided herein are not meant to be limiting.

[000128] Some aspects of the disclosure provide muscle-targeting agents that specifically bind to an antigen on muscle, such as skeletal muscle, smooth muscle, or cardiac muscle. In some embodiments, any of the muscle-targeting agents provided herein bind to (e.g., specifically bind to) an antigen on a skeletal muscle cell, a smooth muscle cell, and/or (e.g., and) a cardiac muscle cell.

[000129] By interacting with muscle-specific cell surface recognition elements (e.g., cell membrane proteins), both tissue localization and selective uptake into muscle cells can be achieved. In some embodiments, molecules that are substrates for muscle uptake transporters are useful for delivering a molecular payload into muscle tissue. Binding to muscle surface recognition elements followed by endocytosis can allow even large molecules such as antibodies to enter muscle cells. As another example molecular payloads conjugated to transferrin or anti-transferrin receptor antibodies can be taken up by muscle cells via binding to transferrin receptor, which may then be endocytosed, e.g., via clathrin-mediated endocytosis. [000130] The use of muscle-targeting agents may be useful for concentrating a molecular payload ( e.g ., oligonucleotide) in muscle while reducing toxicity associated with effects in other tissues. In some embodiments, the muscle-targeting agent concentrates a bound molecular payload in muscle cells as compared to another cell type within a subject. In some embodiments, the muscle-targeting agent concentrates a bound molecular payload in muscle cells (e.g., skeletal, smooth, or cardiac muscle cells) in an amount that is at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, or 100 times greater than an amount in non muscle cells (e.g., liver, neuronal, blood, or fat cells). In some embodiments, a toxicity of the molecular payload in a subject is reduced by at least 1%, 2%, 3%, 4%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 90%, or 95% when it is delivered to the subject when bound to the muscle-targeting agent.

[000131] In some embodiments, to achieve muscle selectivity, a muscle recognition element (e.g., a muscle cell antigen) may be required. As one example, a muscle-targeting agent may be a small molecule that is a substrate for a muscle-specific uptake transporter. As another example, a muscle-targeting agent may be an antibody that enters a muscle cell via transporter-mediated endocytosis. As another example, a muscle targeting agent may be a ligand that binds to cell surface receptor on a muscle cell. It should be appreciated that while transporter-based approaches provide a direct path for cellular entry, receptor-based targeting may involve stimulated endocytosis to reach the desired site of action.

[000132] Muscle cells encompassed by the present disclosure include, but are not limited to, skeletal muscle cells, smooth muscle cells, cardiac muscle cells, myoblasts and myocytes. i. Muscle- Targeting Antibodies

[000133] In some embodiments, the muscle-targeting agent is an antibody. Generally, the high specificity of antibodies for their target antigen provides the potential for selectively targeting muscle cells (e.g., skeletal, smooth, and/or (e.g., and) cardiac muscle cells). This specificity may also limit off-target toxicity. Examples of antibodies that are capable of targeting a surface antigen of muscle cells have been reported and are within the scope of the disclosure. For example, antibodies that target the surface of muscle cells are described in Arahata K., et al. “Immunostaining of skeletal and cardiac muscle surface membrane with antibody against Duchenne muscular dystrophy peptide” Nature 1988; 333: 861-3; Song K.S., et al. “Expression of caveolin-3 in skeletal, cardiac, and smooth muscle cells. Caveolin-3 is a component of the sarcolemma and co-fractionates with dystrophin and dystrophin-associated glycoproteins” J Biol Chem 1996; 271: 15160-5; and Weisbart R.H. et al., “Cell type specific targeted intracellular delivery into muscle of a monoclonal antibody that binds myosin lib”

Mol Immunol. 2003 Mar, 39(13):78309; the entire contents of each of which are incorporated herein by reference. a. Anti- Transferrin Receptor Antibodies [000134] Some aspects of the disclosure are based on the recognition that agents binding to transferrin receptor, e.g., anti-transferrin-receptor antibodies, are capable of targeting muscle cell. Transferrin receptors are internalizing cell surface receptors that transport transferrin across the cellular membrane and participate in the regulation and homeostasis of intracellular iron levels. Some aspects of the disclosure provide transferrin receptor binding proteins, which are capable of binding to transferrin receptor. Accordingly, aspects of the disclosure provide binding proteins (e.g., antibodies) that bind to transferrin receptor. In some embodiments, binding proteins that bind to transferrin receptor are internalized, along with any bound molecular payload, into a muscle cell. As used herein, an antibody that binds to a transferrin receptor may be referred to interchangeably as an, transferrin receptor antibody, an anti-transferrin receptor antibody, or an anti-TfR antibody. Antibodies that bind, e.g. specifically bind, to a transferrin receptor may be internalized into the cell, e.g. through receptor-mediated endocytosis, upon binding to a transferrin receptor.

[000135] It should be appreciated that anti-transferrin receptor antibodies may be produced, synthesized, and/or (e.g., and) derivatized using several known methodologies, e.g. library design using phage display. Exemplary methodologies have been characterized in the art and are incorporated by reference (Diez, P. et al. “High-throughput phage-display screening in array format”, Enzyme and microbial technology, 2015, 79, 34-41.; Christoph M. H. and Stanley, J.R. “Antibody Phage Display: Technique and Applications” J Invest Dermatol. 2014, 134:2.; Engleman, Edgar (Ed.) “Human Hybridomas and Monoclonal Antibodies.” 1985, Springer.). In other embodiments, an anti-transferrin antibody has been previously characterized or disclosed. Antibodies that specifically bind to transferrin receptor are known in the art (see, e.g. US Patent. No. 4,364,934, filed 12/4/1979, “Monoclonal antibody to a human early thymocyte antigen and methods for preparing same”; US Patent No. 8,409,573, filed 6/14/2006, “Anti-CD71 monoclonal antibodies and uses thereof for treating malignant tumor cells”; US Patent No. 9,708,406, filed 5/20/2014, “Anti-transferrin receptor antibodies and methods of use”; US 9,611,323, filed 12/19/2014, “Low affinity blood brain barrier receptor antibodies and uses therefor”; WO 2015/098989, filed 12/24/2014, “Novel anti- Transferrin receptor antibody that passes through blood-brain barrier”; Schneider C. et al. “Structural features of the cell surface receptor for transferrin that is recognized by the monoclonal antibody OKT9.” J Biol Chem. 1982, 257:14, 8516-8522.; Lee et al. “Targeting Rat Anti-Mouse Transferrin Receptor Monoclonal Antibodies through Blood-Brain Barrier in Mouse” 2000, J Pharmacol. Exp. Ther., 292: 1048-1052.).

[000136] Provided herein, in some aspects, are new anti-TfR antibodies for use as the muscle targeting agents (e.g., in muscle targeting complexes). In some embodiments, the anti- TfR antibody described herein binds to transferrin receptor with high specificity and affinity.

In some embodiments, the anti-TfR antibody described herein specifically binds to any extracellular epitope of a transferrin receptor or an epitope that becomes exposed to an antibody. In some embodiments, anti-TfR antibodies provided herein bind specifically to transferrin receptor from human, non-human primates, mouse, rat, etc. In some embodiments, anti-TfR antibodies provided herein bind to human transferrin receptor. In some embodiments, the anti-TfR antibody described herein binds to an amino acid segment of a human or non human primate transferrin receptor, as provided in SEQ ID NOs: 105-108. In some embodiments, the anti-TfR antibody described herein binds to an amino acid segment corresponding to amino acids 90-96 of a human transferrin receptor as set forth in SEQ ID NO: 105, which is not in the apical domain of the transferrin receptor.

[000137] An example human transferrin receptor amino acid sequence, corresponding to NCBI sequence NP_003225.2 (transferrin receptor protein 1 isoform 1, homo sapiens) is as follows:

MMDQ ARS AF S NLF GGEPLS YTRFS LARQ VDGDN S H VEMKLA VDEEEN ADNNT KANVTKPKRCSGSICYGTIAVIVFFLIGFMIGYLGYCKGVEPKTECERLAGTESPVREEP GEDFP A ARRLYWDDLKRKLS EKLDS TDFT GTIKLLNEN S Y VPRE AGS QKDENLALY V EN QFREFKLS KVWRDQHFVKIQVKDS AQN S VIIVDKN GRLVYLVENPGGYV AY S KAA T VT GKLVH ANF GTKKDFEDLYTP VN GS IVIVR AGKITF AEKV AN AES LN AIG VLIYMD QTKFPIVNAELSFFGHAHLGTGDPYTPGFPSFNHTQFPPSRSSGLPNIPVQTISRAAAEK LF GNMEGDCPS D WKTDS T CRM VT S ES KN VKLT V S N VLKEIKILNIF G VIKGFVEPDH Y

V V V G AQRD A W GPG A AKS G V GT ALLLKLAQMF S DM VLKDGF QPS RS IIF AS W S AGDF GS V G ATE WLEG YLS S LHLK AFT YINLD KA VLGT S NFKV S AS PLLYTLIEKTMQN VKHP VTGQFLYQDSNWASKVEKLTLDNAAFPFLAYSGIPAVSFCFCEDTDYPYLGTTMDTY KELIERIPELNKV ARA A AE V AGQFVIKLTHD VELNLD YERYN S QLLS FVRDLN Q YR AD IKEMGLS LQWLY S ARGDFFR AT S RLTTDF GN AEKTDRF VMKKLNDR VMR VE YHFLS P

Y V S PKES PFRH VFW GS GS HTLP ALLENLKLRKQNN G AFNETLFRN QLALAT WTIQG A AN ALS GD VWDIDNEF (SEQ ID NO: 105). [000138] An example non-human primate transferrin receptor amino acid sequence, corresponding to NCBI sequence NP_001244232.1(transferrin receptor protein 1, Macaca mulatta) is as follows:

MMDQ ARS AF S NLF GGEPLS YTRFS LARQ VDGDN S H VEMKLG VDEEENTDNNTKPN G TKPKRCGGNIC Y GTIA VIIFFLIGFMIGYLGY CKGVEPKTECERLAGTESPAREEPEEDFP A APRLYWDDLKRKLS EKLDTTDFT S TIKLLNENLY VPRE AGS QKDENLALYIEN QFRE FKLSKVWRDQHFVKIQVKDSAQNSVIIVDKNGGLVYLVENPGGYVAYSKAATVTGK LVHANFGTKKDFEDLDSPVNGSIVIVRAGKITFAEKVANAESLNAIGVLIYMDQTKFPI VKADLS FF GH AHLGTGDP YTPGFPS FNHTQFPPS QS S GLPNIP V QTIS RA A AEKLF GNM EGDCPSDWKTDSTCKMVTSENKSVKLTVSNVLKETKILNIFGVIKGFVEPDHYVVVGA QRDAWGPGAAKSSVGTALLLKLAQMFSDMVLKDGFQPSRSIIFASWSAGDFGSVGAT EWLEG YLS S LHLKAFT YINLDKA VLGT S NFKV S AS PLLYTLIEKTMQD VKHPVT GRS L YQDSNWASKVEKLTLDNAAFPFLAYSGIPAVSFCFCEDTDYPYLGTTMDTYKELVERI PELNKV ARAAAE VAGQFVIKLTHDTELNLD YERYN S QLLLFLRDLN QYRAD VKEMGL S LQWLY S ARGDFFRAT S RLTTDFRN AEKRD KFVMKKLNDRVMRVE Y YFLS P YV S PKE S PFRH VFW GS GS HTLS ALLES LKLRRQNN S AFNETLFRN QLALAT WTIQG A AN ALS GD VWDIDNEF (SEQ ID NO: 106)

[000139] An example non-human primate transferrin receptor amino acid sequence, corresponding to NCBI sequence XP_005545315.1 (transferrin receptor protein 1, Macaca fascicularis) is as follows:

MMDQ ARS AF S NLF GGEPLS YTRFS LARQ VDGDN S H VEMKLG VDEEENTDNNTKAN G TKPKRCGGNIC Y GTIA VIIFFLIGFMIGYLGY CKGVEPKTECERLAGTESPAREEPEEDFP A APRLYWDDLKRKLS EKLDTTDFT S TIKLLNENLY VPRE AGS QKDENLALYIEN QFRE FKLSKVWRDQHFVKIQVKDSAQNSVIIVDKNGGLVYLVENPGGYVAYSKAATVTGK LVHANFGTKKDFEDLDSPVNGSIVIVRAGKITFAEKVANAESLNAIGVLIYMDQTKFPI VKADLS FF GH AHLGTGDP YTPGFPS FNHTQFPPS QS S GLPNIP V QTIS RA A AEKLF GNM EGDCPSDWKTDSTCKMVTSENKSVKLTVSNVLKETKILNIFGVIKGFVEPDHYVVVGA QRDAWGPGAAKSSVGTALLLKLAQMFSDMVLKDGFQPSRSIIFASWSAGDFGSVGAT EWLEG YLS S LHLKAFT YINLDKA VLGT S NFKV S AS PLLYTLIEKTMQD VKHPVT GRS L YQDSNWASKVEKLTLDNAAFPFLAYSGIPAVSFCFCEDTDYPYLGTTMDTYKELVERI PELNKV ARAAAE VAGQFVIKLTHDTELNLD YERYN S QLLLFLRDLN QYRAD VKEMGL S LQWLY S ARGDFFRAT S RLTTDFRN AEKRD KFVMKKLNDRVMRVE Y YFLS P YV S PKE S PFRH VFW GS GS HTLS ALLES LKLRRQNN S AFNETLFRN QLALAT WTIQG A AN ALS GD VWDIDNEF (SEQ ID NO: 107).

[000140] An example mouse transferrin receptor amino acid sequence, corresponding to

NCBI sequence NP_001344227.1 (transferrin receptor protein 1, mus musculus) is as follows: MMDQARSAFSNLFGGEPLSYTRFSLARQVDGDNSHVEMKLAADEEENADNNMKASV RKPKRFNGRFCFAAIAFVIFFFIGFMSGYFGYCKRVEQKEECVKFAETEETDKSETMET ED VPTS S RLYW ADLKTLLS EKLN S IEF ADTIKQLS QNT YTPRE AGS QKDES LA Y YIEN Q FHEFKFS KVWRDEH Y VKIQ VKS S IGQNM VTI V QS N GNLDP VES PEG Y V AFS KPTE V S G KLVHANFGTKKDFEELSYSVNGSLVIVRAGEITFAEKVANAQSFNAIGVLIYMDKNKF P V VE ADLALF GH AHLGTGDP YTPGFPS FNHTQFPPS QS S GLPNIP V QTIS R A A AEKLF G KMEGSCPARWNIDSSCKLELSQNQNVKLIVKNVLKERRILNIFGVIKGYEEPDRYVVV GAQRDALGAGVAAKSSVGTGLLLKLAQVFSDMISKDGFRPSRSIIFASWTAGDFGAVG ATEWLEGYLSSLHLKAFTYINLDKVVLGTSNFKVSASPLLYTLMGKIMQDVKHPVDG KSLYRDSNWISKVEKLSFDNAAYPFLAYSGIPAVSFCFCEDADYPYLGTRLDTYEALT QKVPQLN QM VRT A AE V AGQLIIKLTHD VELNLD YEM YN S KLLS FMKDLN QFKTDIRD MGLS LQWLY S ARGD YFR AT S RLTTDFHN AEKTNRF VMREINDRIMKVE YHFLS P Y V S PRES PFRHIFW GS GS HTLS ALVENLKLRQKNIT AFNETLFRN QLALAT WTIQG V AN ALS GDIWNIDNEF (SEQ ID NO: 108)

[000141] In some embodiments, an anti-transferrin receptor antibody binds to an amino acid segment of the receptor as follows:

FVKIQ VKDS AQN S VIIVDKN GRLV YLVENPGG Y V AY S KA AT VT GKLVH ANF GTKKDF EDLYTPVNGSIVIVRAGKITFAEKVANAESLNAIGVLIYMDQTKFPIVNAELSFFGHAH LGT GDP YTPGFPS FNHT QFPPS RS S GLPNIP V QTIS RA A AEKLF GNMEGDCPS D WKTDS TCRMVTSESKNVKLTVSNVLKE (SEQ ID NO: 109) and does not inhibit the binding interactions between transferrin receptors and transferrin and/or (e.g., and) human hemochromatosis protein (also known as HFE). In some embodiments, the anti-transferrin receptor antibody described herein does not bind an epitope in SEQ ID NO: 109.

[000142] Appropriate methodologies may be used to obtain and/or (e.g., and) produce antibodies, antibody fragments, or antigen-binding agents, e.g., through the use of recombinant DNA protocols. In some embodiments, an antibody may also be produced through the generation of hybridomas (see, e.g., Kohler, G and Milstein, C. “Continuous cultures of fused cells secreting antibody of predefined specificity” Nature, 1975, 256: 495-497). The antigen- of-interest may be used as the immunogen in any form or entity, e.g., recombinant or a naturally occurring form or entity. Hybridomas are screened using standard methods, e.g. ELISA screening, to find at least one hybridoma that produces an antibody that targets a particular antigen. Antibodies may also be produced through screening of protein expression libraries that express antibodies, e.g., phage display libraries. Phage display library design may also be used, in some embodiments, (see, e.g. U.S. Patent No 5,223,409, filed 3/1/1991, “Directed evolution of novel binding proteins”; WO 1992/18619, filed 4/10/1992, “Heterodimeric receptor libraries using phagemids”; WO 1991/17271, filed 5/1/1991, “Recombinant library screening methods”; WO 1992/20791, filed 5/15/1992, “Methods for producing members of specific binding pairs”; WO 1992/15679, filed 2/28/1992, and “Improved epitope displaying phage”). In some embodiments, an antigen-of-interest may be used to immunize a non-human animal, e.g., a rodent or a goat. In some embodiments, an antibody is then obtained from the non-human animal, and may be optionally modified using a number of methodologies, e.g., using recombinant DNA techniques. Additional examples of antibody production and methodologies are known in the art (see, e.g. Harlow et al. “Antibodies: A Laboratory Manual”, Cold Spring Harbor Laboratory, 1988.).

[000143] In some embodiments, an antibody is modified, e.g., modified via glycosylation, phosphorylation, sumoylation, and/or (e.g., and) methylation. In some embodiments, an antibody is a glycosylated antibody, which is conjugated to one or more sugar or carbohydrate molecules. In some embodiments, the one or more sugar or carbohydrate molecule are conjugated to the antibody via N-glycosylation, O-glycosylation, C-glycosylation, glypiation (GPI anchor attachment), and/or (e.g., and) phosphoglycosylation. In some embodiments, the one or more sugar or carbohydrate molecules are monosaccharides, disaccharides, oligosaccharides, or glycans. In some embodiments, the one or more sugar or carbohydrate molecule is a branched oligosaccharide or a branched glycan. In some embodiments, the one or more sugar or carbohydrate molecule includes a mannose unit, a glucose unit, an N- acetylglucosamine unit, an N-acetylgalactosamine unit, a galactose unit, a fucose unit, or a phospholipid unit. In some embodiments, there are about 1-10, about 1-5, about 5-10, about 1- 4, about 1-3, or about 2 sugar molecules. In some embodiments, a glycosylated antibody is fully or partially glycosylated. In some embodiments, an antibody is glycosylated by chemical reactions or by enzymatic means. In some embodiments, an antibody is glycosylated in vitro or inside a cell, which may optionally be deficient in an enzyme in the N- or O- glycosylation pathway, e.g. a glycosyltransferase. In some embodiments, an antibody is functionalized with sugar or carbohydrate molecules as described in International Patent Application Publication WO2014065661, published on May 1, 2014, entitled, “ Modified antibody, antibody -conjugate and process for the preparation thereof

[000144] In some embodiments, the anti-TfR antibody of the present disclosure comprises a VL domain and/or (e.g., and) VH domain of any one of the anti-TfR antibodies selected from Table 2, and comprises a constant region comprising the amino acid sequences of the constant regions of an IgG, IgE, IgM, IgD, IgA or IgY immunoglobulin molecule, any class (e.g., IgGl, IgG2, IgG3, IgG4, IgAl and IgA2), or any subclass (e.g., IgG2a and IgG2b) of immunoglobulin molecule. Non-limiting examples of human constant regions are described in the art, e.g., see Kabat E A et al., (1991) supra.

[000145] In some embodiments, agents binding to transferrin receptor, e.g., anti-TfR antibodies, are capable of targeting muscle cell and/or (e.g., and) mediate the transportation of an agent across the blood brain barrier. Transferrin receptors are internalizing cell surface receptors that transport transferrin across the cellular membrane and participate in the regulation and homeostasis of intracellular iron levels. Some aspects of the disclosure provide transferrin receptor binding proteins, which are capable of binding to transferrin receptor. Antibodies that bind, e.g. specifically bind, to a transferrin receptor may be internalized into the cell, e.g. through receptor-mediated endocytosis, upon binding to a transferrin receptor. [000146] Provided herein, in some aspects, are humanized antibodies that bind to transferrin receptor with high specificity and affinity. In some embodiments, the humanized anti-TfR antibody described herein specifically binds to any extracellular epitope of a transferrin receptor or an epitope that becomes exposed to an antibody. In some embodiments, the humanized anti-TfR antibodies provided herein bind specifically to transferrin receptor from human, non-human primates, mouse, rat, etc. In some embodiments, the humanized anti- TfR antibodies provided herein bind to human transferrin receptor. In some embodiments, the humanized anti-TfR antibody described herein binds to an amino acid segment of a human or non-human primate transferrin receptor, as provided in SEQ ID NOs: 105-108. In some embodiments, the humanized anti-TfR antibody described herein binds to an amino acid segment corresponding to amino acids 90-96 of a human transferrin receptor as set forth in SEQ ID NO: 105, which is not in the apical domain of the transferrin receptor. In some embodiments, the humanized anti-TfR antibodies described herein binds to TfRl but does not bind to TfR2.

[000147] In some embodiments, an anti-TFR antibody specifically binds a TfRl (e.g., a human or non-human primate TfRl) with binding affinity (e.g., as indicated by Kd) of at least about 10 ⁴ M, 10 ⁵ M, 10 ⁶ M, 10 ⁷ M, 10 ⁸ M, 10 ⁹ M, 10 ¹⁰ M, 10 ¹¹ M, 10 ¹² M, 10 ¹³ M, or less. In some embodiments, the anti-TfR antibodies described herein binds to TfRl with a KD of sub-nanomolar range. In some embodiments, the anti-TfR antibodies described herein selectively binds to transferrin receptor 1 (TfRl) but do not bind to transferrin receptor 2 (TfR2). In some embodiments, the anti-TfR antibodies described herein binds to human TfRl and cyno TfRl (e.g., with a Kd of 10 ⁷ M, 10 ⁸ M, 10 ⁹ M, 10 ¹⁰ M, 10 ¹¹ M, 10 ¹² M, lO ¹³ M, or less), but does not bind to a mouse TfRl. The affinity and binding kinetics of the anti-TfR antibody can be tested using any suitable method including but not limited to biosensor technology (e.g., OCTET or BIACORE). In some embodiments, binding of any one of the anti-TfR antibody described herein does not complete with or inhibit transferrin binding to the TfRl. In some embodiments, binding of any one of the anti-TfR antibody described herein does not complete with or inhibit HFE-beta-2-microglobulin binding to the TfRl.

[000148] The anti-TfR antibodies described herein are humanized antibodies. The CDR and variable region amino acid sequences of the mouse monoclonal anti-TfR antibody from which the humanized anti-TfR antibodies described herein are derived are provided in Table 2.

Table 2. Mouse Monoclonal Anti-TfR Antibodies

* mutation positions are according to Kabat numbering of the respective VH sequences containing the mutations

[000149] In some embodiments, the anti-TfR antibody of the present disclosure is a humanized variant of any one of the anti-TfR antibodies provided in Table 2. In some embodiments, the anti-TfR antibody of the present disclosure comprises a CDR-H1, a CDR- H2, a CDR-H3, a CDR-L1, a CDR-L2, and a CDR-L3 that are the same as the CDR-H1, CDR- H2, and CDR-H3 in any one of the anti-TfR antibodies provided in Table 2, and comprises a humanized heavy chain variable region and/or (e.g., and) a humanized light chain variable region.

[000150] Humanized antibodies are human immunoglobulins (recipient antibody) in which residues from a complementarity determining region (CDR) of the recipient are replaced by residues from a CDR of a non-human species (donor antibody) such as mouse, rat, or rabbit having the desired specificity, affinity, and capacity. In some embodiments, Fv framework region (FR) residues of the human immunoglobulin are replaced by corresponding non-human residues. Furthermore, the humanized antibody may comprise residues that are found neither in the recipient antibody nor in the imported CDR or framework sequences, but are included to further refine and optimize antibody performance. In general, the humanized antibody will comprise substantially all of at least one, and typically two, variable domains, in which all or substantially all of the CDR regions correspond to those of a non-human immunoglobulin and all or substantially all of the FR regions are those of a human immunoglobulin consensus sequence. The humanized antibody optimally also will comprise at least a portion of an immunoglobulin constant region or domain (Fc), typically that of a human immunoglobulin. Antibodies may have Fc regions modified as described in WO 99/58572. Other forms of humanized antibodies have one or more CDRs (one, two, three, four, five, six) which are altered with respect to the original antibody, which are also termed one or more CDRs derived from one or more CDRs from the original antibody. Humanized antibodies may also involve affinity maturation.

[000151] Humanized antibodies and methods of making them are known, e.g., as described in Almagro et ah, Front. Biosci. 13:1619-1633 (2008); Riechmann et ah, Nature 332:323-329 (1988); Queen et ah, Proc. Nat'l Acad. Sci. USA 86:10029-10033 (1989); U.S. Pat. Nos. 5,821,337, 7,527,791, 6,982,321, and 7,087,409; Kashmiri et ah, Methods 36:25-34 (2005); Padlan et ah, Mol. Immunol. 28:489-498 (1991); Dall'Acqua et ah, Methods 36:43-60 (2005); Osbourn et ah, Methods 36:61-68 (2005); and Klimka et ah, Br. J. Cancer, 83:252-260 (2000), the contents of all of which are incorporated herein by reference. Human framework regions that may be used for humanization are described in e.g., Sims et al. J. Immunol. 151:2296 (1993); Carter et al., Proc. Natl. Acad. Sci. USA, 89:4285 (1992); Presta et al., J. Immunol., 151:2623 (1993); Almagro et al., Front. Biosci. 13:1619-1633 (2008)); Baca et al.,

J. Biol. Chem. 272:10678-10684 (1997); and Rosok et al., J Biol. Chem. 271:22611-22618 (1996), the contents of all of which are incorporated herein by reference.

[000152] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising one or more amino acid variations (e.g., in the VH framework region) as compared with any one of the VHs listed in Table 2, and/or (e.g., and) a humanized VL comprising one or more amino acid variations (e.g., in the VL framework region) as compared with any one of the VLs listed in Table 2.

[000153] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH containing no more than 25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) in the framework regions as compared with the VH of any of the anti-TfR antibodies listed in Table 2 (e.g., any one of SEQ ID NOs: 17, 22, 26, 43, 61, 65, and 68). Alternatively or in addition (e.g., in addition), the humanized anti-TfR antibody of the present disclosure comprises a humanized VL containing no more than 25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) in the framework regions as compared with the VL of any one of the anti-TfR antibodies listed in Table 2 (e.g., any one of SEQ ID NOs: 18, 44, and 62).

[000154] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising an amino acid sequence that is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%, 98%, or 99%) identical in the framework regions to the VH of any of the anti-TfR antibodies listed in Table 2 (e.g., any one of SEQ ID NOs: 17, 22, 26,

43, 61, 65, and 68). Alternatively or in addition (e.g., in addition), In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VL comprising an amino acid sequence that is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%, 98%, or 99%) identical in the framework regions to the VL of any of the anti-TfR antibodies listed in Table 2 (e.g., any one of SEQ ID NOs: 18, 44, and 62).

[000155] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising a CDR-H1 having the amino acid sequence of SEQ ID NO: 1 (according to the IMGT definition system), a CDR-H2 having the amino acid sequence of SEQ ID NO: 2, SEQ ID NO: 19, or SEQ ID NO: 23 (according to the IMGT definition system), a CDR-H3 having the amino acid sequence of SEQ ID NO: 3 (according to the IMGT definition system), and containing no more than 25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) in the framework regions as compared with the VH as set forth in SEQ ID NO: 17, SEQ ID NO: 22, or SEQ ID NO: 26. Alternatively or in addition (e.g., in addition), the anti-TfR antibody of the present disclosure comprises a humanized VL comprising a CDR-L1 having the amino acid sequence of SEQ ID NO: 4 (according to the IMGT definition system), a CDR-L2 having the amino acid sequence of SEQ ID NO: 5 (according to the IMGT definition system), and a CDR-L3 having the amino acid sequence of SEQ ID NO: 6 (according to the IMGT definition system), and containing no more than 25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) in the framework regions as compared with the VL as set forth in SEQ ID NO: 18. [000156] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising a CDR-H1 having the amino acid sequence of SEQ ID NO: 1 (according to the IMGT definition system), a CDR-H2 having the amino acid sequence of SEQ ID NO: 2, SEQ ID NO: 19, or SEQ ID NO: 23 (according to the IMGT definition system), a CDR-H3 having the amino acid sequence of SEQ ID NO: 3 (according to the IMGT definition system), and is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%, 98%, or 99%) identical in the framework regions to the VH as set forth in SEQ ID NO: 17, SEQ ID NO: 22, or SEQ ID NO: 26. Alternatively or in addition (e.g., in addition), the humanized anti-TfR antibody of the present disclosure comprises a humanized VL comprising a CDR-L1 having the amino acid sequence of SEQ ID NO: 4 (according to the IMGT definition system), a CDR-L2 having the amino acid sequence of SEQ ID NO: 5 (according to the IMGT definition system), and a CDR-L3 having the amino acid sequence of SEQ ID NO: 6 (according to the IMGT definition system), and is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%, 98%, or 99%) identical in the framework regions to the VL as set forth in any one of SEQ ID NO: 18.

[000157] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising a CDR-H1 having the amino acid sequence of SEQ ID NO: 7 (according to the Rabat definition system), a CDR-H2 having the amino acid sequence of SEQ ID NO: 8, SEQ ID NO: 20, or SEQ ID NO: 24 (according to the Rabat definition system), a CDR-H3 having the amino acid sequence of SEQ ID NO: 9 (according to the Rabat definition system), and containing no more than 25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) in the framework regions as compared with the VH as set forth in SEQ ID NO: 17, SEQ ID NO: 22, or SEQ ID NO: 26. Alternatively or in addition (e.g., in addition), the humanized anti-TfR antibody of the present disclosure comprises a humanized VL comprising a CDR-L1 having the amino acid sequence of SEQ ID NO: 10 (according to the Rabat definition system), a CDR-L2 having the amino acid sequence of SEQ ID NO: 11 (according to the Rabat definition system), and a CDR-L3 having the amino acid sequence of SEQ ID NO: 6 (according to the Rabat definition system), and containing no more than 25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) in the framework regions as compared with the VL as set forth in SEQ ID NO: 18.

[000158] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising a CDR-H1 having the amino acid sequence of SEQ ID NO: 7 (according to the Kabat definition system), a CDR-H2 having the amino acid sequence of SEQ ID NO: 8, SEQ ID NO: 20, or SEQ ID NO: 24 (according to the Kabat definition system), a CDR-H3 having the amino acid sequence of SEQ ID NO: 9 (according to the Kabat definition system), and is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%, 98%, or 99%) identical in the framework regions to the VH as set forth in SEQ ID NO: 17, SEQ ID NO: 22, or SEQ ID NO: 26. Alternatively or in addition (e.g., in addition), the humanized anti-TfR antibody of the present disclosure comprises a humanized VL comprising a CDR-L1 having the amino acid sequence of SEQ ID NO: 10 (according to the Kabat definition system), a CDR-L2 having the amino acid sequence of SEQ ID NO: 11 (according to the Kabat definition system), and a CDR-L3 having the amino acid sequence of SEQ ID NO: 6 (according to the Kabat definition system), and is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%, 98%, or 99%) identical in the framework regions to the VL as set forth in any one of SEQ ID NO: 18.

[000159] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising a CDR-H1 having the amino acid sequence of SEQ ID NO: 12 (according to the Chothia definition system), a CDR-H2 having the amino acid sequence of SEQ ID NO: 13, SEQ ID NO: 21, or SEQ ID NO: 25 (according to the Chothia definition system), a CDR-H3 having the amino acid sequence of SEQ ID NO: 14 (according to the Chothia definition system), and containing no more than 25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) in the framework regions as compared with the VH as set forth in SEQ ID NO: 17, SEQ ID NO: 22 or SEQ ID NO: 26. Alternatively or in addition (e.g., in addition), the humanized anti-TfR antibody of the present disclosure comprises a humanized VL comprising a CDR-L1 having the amino acid sequence of SEQ ID NO: 15 (according to the Chothia definition system), a CDR-L2 having the amino acid sequence of SEQ ID NO: 5 (according to the Chothia definition system), and a CDR-L3 having the amino acid sequence of SEQ ID NO: 16 (according to the Chothia definition system), and containing no more than 25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) in the framework regions as compared with the VL as set forth in SEQ ID NO: 18.

[000160] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising a CDR-H1 having the amino acid sequence of SEQ ID NO: 12 (according to the Chothia definition system), a CDR-H2 having the amino acid sequence of SEQ ID NO: 13, SEQ ID NO: 21, or SEQ ID NO: 25 (according to the Chothia definition system), a CDR-H3 having the amino acid sequence of SEQ ID NO: 14 (according to the Chothia definition system), and is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%, 98%, or 99%) identical in the framework regions to the VH as set forth in SEQ ID NO: SEQ ID NO: 17, SEQ ID NO: 22 or SEQ ID NO: 26. Alternatively or in addition (e.g., in addition), the anti-TfR antibody of the present disclosure comprises a humanized VL comprising a CDR-L1 having the amino acid sequence of SEQ ID NO: 15 (according to the Chothia definition system), a CDR-L2 having the amino acid sequence of SEQ ID NO: 5 (according to the Chothia definition system), and a CDR-L3 having the amino acid sequence of SEQ ID NO: 16 (according to the Chothia definition system), and is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%, 98%, or 99%) identical in the framework regions to the VL as set forth in any one of SEQ ID NO: 18.

[000161] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising a CDR-H1 having the amino acid sequence of SEQ ID NO: 27 (according to the IMGT definition system), a CDR-H2 having the amino acid sequence of SEQ ID NO: 28 (according to the IMGT definition system), a CDR-H3 having the amino acid sequence of SEQ ID NO: 29 (according to the IMGT definition system), and containing no more than 25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21,

20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) in the framework regions as compared with the VH as set forth in SEQ ID NO: 43. Alternatively or in addition (e.g., in addition), the humanized anti-TfR antibody of the present disclosure comprises a humanized VL comprising a CDR-L1 having the amino acid sequence of SEQ ID NO: 30 (according to the IMGT definition system), a CDR-L2 having the amino acid sequence of SEQ ID NO: 31 (according to the IMGT definition system), and a CDR-L3 having the amino acid sequence of SEQ ID NO: 32 (according to the IMGT definition system), and containing no more than 25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) in the framework regions as compared with the VL as set forth in SEQ ID NO: 44.

[000162] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising a CDR-H1 having the amino acid sequence of SEQ ID NO: 27 (according to the IMGT definition system), a CDR-H2 having the amino acid sequence of SEQ ID NO: 28 (according to the IMGT definition system), a CDR-H3 having the amino acid sequence of SEQ ID NO: 29 (according to the IMGT definition system), and is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%, 98%, or 99%) identical in the framework regions to the VH as set forth in SEQ ID NO: 43. Alternatively or in addition (e.g., in addition), the humanized anti-TfR antibody of the present disclosure comprises a humanized VL comprising a CDR-L1 having the amino acid sequence of SEQ ID NO: 30 (according to the IMGT definition system), a CDR-L2 having the amino acid sequence of SEQ ID NO: 31 (according to the IMGT definition system), and a CDR-L3 having the amino acid sequence of SEQ ID NO: 32 (according to the IMGT definition system), and is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%, 98%, or 99%) identical in the framework regions to the VL as set forth in SEQ ID NO: 44.

[000163] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising a CDR-H1 having the amino acid sequence of SEQ ID NO: 33 (according to the Rabat definition system), a CDR-H2 having the amino acid sequence of SEQ ID NO: 34 (according to the Rabat definition system), a CDR-H3 having the amino acid sequence of SEQ ID NO: 35 (according to the Rabat definition system), and containing no more than 25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21,

20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) in the framework regions as compared with the VH as set forth in SEQ ID NO: 43. Alternatively or in addition (e.g., in addition), the humanized anti-TfR antibody of the present disclosure comprises a humanized VL comprising a CDR-L1 having the amino acid sequence of SEQ ID NO: 36 (according to the Rabat definition system), a CDR-L2 having the amino acid sequence of SEQ ID NO: 37 (according to the Rabat definition system), and a CDR-L3 having the amino acid sequence of SEQ ID NO: 32 (according to the Rabat definition system), and containing no more than 25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) in the framework regions as compared with the VL as set forth in SEQ ID NO: 44.

[000164] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising a CDR-H1 having the amino acid sequence of SEQ ID NO: 33 (according to the Rabat definition system), a CDR-H2 having the amino acid sequence of SEQ ID NO: 34 (according to the Rabat definition system), a CDR-H3 having the amino acid sequence of SEQ ID NO: 35 (according to the Rabat definition system), and is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%, 98%, or 99%) identical in the framework regions to the VH as set forth in SEQ ID NO: 43. Alternatively or in addition (e.g., in addition), the humanized anti-TfR antibody of the present disclosure comprises a humanized VL comprising a CDR-L1 having the amino acid sequence of SEQ ID NO: 36 (according to the Rabat definition system), a CDR-L2 having the amino acid sequence of SEQ ID NO: 37 (according to the Rabat definition system), and a CDR-L3 having the amino acid sequence of SEQ ID NO: 32 (according to the Kabat definition system), and is at least 75% (e.g., 75%,

80%, 85%, 90%, 95%, 98%, or 99%) identical in the framework regions to the VL as set forth in SEQ ID NO: 44.

[000165] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising a CDR-H1 having the amino acid sequence of SEQ ID NO: 38 (according to the Chothia definition system), a CDR-H2 having the amino acid sequence of SEQ ID NO: 39 (according to the Chothia definition system), a CDR-H3 having the amino acid sequence of SEQ ID NO: 40 (according to the Chothia definition system), and containing no more than 25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) in the framework regions as compared with the VH as set forth in SEQ ID NO: 43. Alternatively or in addition (e.g., in addition), the humanized anti-TfR antibody of the present disclosure comprises a humanized VL comprising a CDR-L1 having the amino acid sequence of SEQ ID NO: 41 (according to the Chothia definition system), a CDR-L2 having the amino acid sequence of SEQ ID NO: 31 (according to the Chothia definition system), and a CDR-L3 having the amino acid sequence of SEQ ID NO: 42 (according to the Chothia definition system), and containing no more than 25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) in the framework regions as compared with the VL as set forth in SEQ ID NO: 44.

[000166] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising a CDR-H1 having the amino acid sequence of SEQ ID NO: 38 (according to the Chothia definition system), a CDR-H2 having the amino acid sequence of SEQ ID NO: 39 (according to the Chothia definition system), a CDR-H3 having the amino acid sequence of SEQ ID NO: 40 (according to the Chothia definition system), and is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%, 98%, or 99%) identical in the framework regions to the VH as set forth in SEQ ID NO: 43. Alternatively or in addition (e.g., in addition), the humanized anti-TfR antibody of the present disclosure comprises a humanized VL comprising a CDR-L1 having the amino acid sequence of SEQ ID NO: 41 (according to the Chothia definition system), a CDR-L2 having the amino acid sequence of SEQ ID NO: 31 (according to the Chothia definition system), and a CDR-L3 having the amino acid sequence of SEQ ID NO: 42 (according to the Chothia definition system), and is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%, 98%, or 99%) identical in the framework regions to the VL as set forth in SEQ ID NO: 44. [000167] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising a CDR-H1 having the amino acid sequence of SEQ ID NO: 45, SEQ ID NO: 63, or SEQ ID NO: 66 (according to the IMGT definition system), a CDR-H2 having the amino acid sequence of SEQ ID NO: 46 (according to the IMGT definition system), a CDR-H3 having the amino acid sequence of SEQ ID NO: 47 (according to the IMGT definition system), and containing no more than 25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) in the framework regions as compared with the VH as set forth in SEQ ID NO: 61, SEQ ID NO: 65, or SEQ ID NO: 68. Alternatively or in addition (e.g., in addition), the humanized anti-TfR antibody of the present disclosure comprises a humanized VL comprising a CDR-L1 having the amino acid sequence of SEQ ID NO: 48 (according to the IMGT definition system), a CDR-L2 having the amino acid sequence of SEQ ID NO: 49 (according to the IMGT definition system), and a CDR-L3 having the amino acid sequence of SEQ ID NO: 50 (according to the IMGT definition system), and containing no more than 25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) in the framework regions as compared with the VL as set forth in SEQ ID NO: 62.

[000168] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising a CDR-H1 having the amino acid sequence of SEQ ID NO: 45, SEQ ID NO: 63, or SEQ ID NO: 66 (according to the IMGT definition system), a CDR-H2 having the amino acid sequence of SEQ ID NO: 46 (according to the IMGT definition system), a CDR-H3 having the amino acid sequence of SEQ ID NO: 47 (according to the IMGT definition system), and is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%, 98%, or 99%) identical in the framework regions to the VH as set forth in SEQ ID NO: 61, SEQ ID NO: 65, SEQ ID NO: 68. Alternatively or in addition (e.g., in addition), the humanized anti-TfR antibody of the present disclosure comprises a humanized VL comprising a CDR-L1 having the amino acid sequence of SEQ ID NO: 48 (according to the IMGT definition system), a CDR-L2 having the amino acid sequence of SEQ ID NO: 49 (according to the IMGT definition system), and a CDR-L3 having the amino acid sequence of SEQ ID NO: 50 (according to the IMGT definition system), and is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%, 98%, or 99%) identical in the framework regions to the VL as set forth in SEQ ID NO: 62.

[000169] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising a CDR-H1 having the amino acid sequence of SEQ ID NO: 51, SEQ ID NO: 64, or SEQ ID NO: 67 (according to the Kabat definition system), a CDR-H2 having the amino acid sequence of SEQ ID NO: 52 (according to the Kabat definition system), a CDR-H3 having the amino acid sequence of SEQ ID NO: 53 (according to the Kabat definition system), and containing no more than 25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) in the framework regions as compared with the VH as set forth in SEQ ID NO: 61, SEQ ID NO: 65, SEQ ID NO: 68. Alternatively or in addition (e.g., in addition), the humanized anti-TfR antibody of the present disclosure comprises a humanized VL comprising a CDR-L1 having the amino acid sequence of SEQ ID NO: 54 (according to the Kabat definition system), a CDR-L2 having the amino acid sequence of SEQ ID NO: 55 (according to the Kabat definition system), and a CDR-L3 having the amino acid sequence of SEQ ID NO: 50 (according to the Kabat definition system), and containing no more than 25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) in the framework regions as compared with the VL as set forth in SEQ ID NO: 62.

[000170] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising a CDR-H1 having the amino acid sequence of SEQ ID NO: 51, SEQ ID NO: 64, or SEQ ID NO: 67 (according to the Kabat definition system), a CDR-H2 having the amino acid sequence of SEQ ID NO: 52 (according to the Kabat definition system), a CDR-H3 having the amino acid sequence of SEQ ID NO: 53 (according to the Kabat definition system), and is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%, 98%, or 99%) identical in the framework regions to the VH as set forth in SEQ ID NO: 61, SEQ ID NO: 65, SEQ ID NO: 68. Alternatively or in addition (e.g., in addition), the humanized anti-TfR antibody of the present disclosure comprises a humanized VL comprising a CDR-L1 having the amino acid sequence of SEQ ID NO: 54 (according to the Kabat definition system), a CDR-L2 having the amino acid sequence of SEQ ID NO: 55 (according to the Kabat definition system), and a CDR-L3 having the amino acid sequence of SEQ ID NO: 50 (according to the Kabat definition system), and is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%, 98%, or 99%) identical in the framework regions to the VL as set forth in SEQ ID NO: 62.

[000171] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising a CDR-H1 having the amino acid sequence of SEQ ID NO: 56 (according to the Chothia definition system), a CDR-H2 having the amino acid sequence of SEQ ID NO: 57 (according to the Chothia definition system), a CDR-H3 having the amino acid sequence of SEQ ID NO: 58 (according to the Chothia definition system), and containing no more than 25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) in the framework regions as compared with the VH as set forth in SEQ ID NO: 61, SEQ ID NO: 65, SEQ ID NO: 68. Alternatively or in addition (e.g., in addition), the humanized anti- TfR antibody of the present disclosure comprises a humanized VL comprising a CDR-L1 having the amino acid sequence of SEQ ID NO: 59 (according to the Chothia definition system), a CDR-L2 having the amino acid sequence of SEQ ID NO: 49 (according to the Chothia definition system), and a CDR-L3 having the amino acid sequence of SEQ ID NO: 60 (according to the Chothia definition system), and containing no more than 25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) in the framework regions as compared with the VL as set forth in SEQ ID NO: 62.

[000172] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising a CDR-H1 having the amino acid sequence of SEQ ID NO: 56 (according to the Chothia definition system), a CDR-H2 having the amino acid sequence of SEQ ID NO: 57 (according to the Chothia definition system), a CDR-H3 having the amino acid sequence of SEQ ID NO: 58 (according to the Chothia definition system), and is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%, 98%, or 99%) identical in the framework regions to the VH as set forth in SEQ ID NO: 61, SEQ ID NO: 65, SEQ ID NO: 68. Alternatively or in addition (e.g., in addition), the humanized anti-TfR antibody of the present disclosure comprises a humanized VL comprising a CDR-L1 having the amino acid sequence of SEQ ID NO: 59 (according to the Chothia definition system), a CDR-L2 having the amino acid sequence of SEQ ID NO: 49 (according to the Chothia definition system), and a CDR-L3 having the amino acid sequence of SEQ ID NO: 60 (according to the Chothia definition system), and is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%, 98%, or 99%) identical in the framework regions to the VL as set forth in SEQ ID NO: 62.

[000173] Examples of amino acid sequences of the humanized anti-TfR antibodies described herein are provided in Table 3.

Table 3. Variable Regions of Humanized Anti-TfR Antibodies mutation positions are according to Kabat numbering of the respective VH sequences containing the mutations CDRs according to the Kabat numbering system are bolded

[000174] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising the CDR-H1, CDR-H2, and CDR-H3 of any one of the anti-TfR antibodies provided in Table 2 and comprises one or more (e.g., 1, 2, 3, 4,

5, 6, 7, 8, 9, 10 or more) amino acid variations in the framework regions as compared with the respective humanized VH provided in Table 3. Alternatively or in addition (e.g., in addition), the humanized anti-TfR antibody of the present disclosure comprises a humanized VL comprising the CDR-L1, CDR-L2, and CDR-L3 of any one of the anti-TfR antibodies provided in Table 2 and comprises one or more (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more) amino acid variations in the framework regions as compared with the respective humanized VL provided in Table 3.

[000175] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identical to SEQ ID NO: 69, and/or (e.g., and) a humanized VL comprising an amino acid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) to SEQ ID NO: 70. In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising the amino acid sequence of SEQ ID NO: 69 and a humanized VL comprising the amino acid sequence of SEQ ID NO: 70.

[000176] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identical to SEQ ID NO: 71, and/or (e.g., and) a humanized VL comprising an amino acid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) to SEQ ID NO: 70. In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising the amino acid sequence of SEQ ID NO: 71 and a humanized VL comprising the amino acid sequence of SEQ ID NO: 70.

[000177] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identical to SEQ ID NO: 72, and/or (e.g., and) a humanized VL comprising an amino acid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) to SEQ ID NO: 70. In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising the amino acid sequence of SEQ ID NO: 72 and a humanized VL comprising the amino acid sequence of SEQ ID NO: 70.

[000178] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identical to SEQ ID NO: 73, and/or (e.g., and) a humanized VL comprising an amino acid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) to SEQ ID NO: 74. In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising the amino acid sequence of SEQ ID NO: 73 and a humanized VL comprising the amino acid sequence of SEQ ID NO: 74.

[000179] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identical to SEQ ID NO: 73, and/or (e.g., and) a humanized VL comprising an amino acid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) to SEQ ID NO: 75. In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising the amino acid sequence of SEQ ID NO: 73 and a humanized VL comprising the amino acid sequence of SEQ ID NO: 75.

[000180] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identical to SEQ ID NO: 76, and/or (e.g., and) a humanized VL comprising an amino acid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) to SEQ ID NO: 74. In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising the amino acid sequence of SEQ ID NO: 76 and a humanized VL comprising the amino acid sequence of SEQ ID NO: 74.

[000181] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identical to SEQ ID NO: 76, and/or (e.g., and) a humanized VL comprising an amino acid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) to SEQ ID NO: 75. In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising the amino acid sequence of SEQ ID NO: 76 and a humanized VL comprising the amino acid sequence of SEQ ID NO: 75.

[000182] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identical to SEQ ID NO: 77, and/or (e.g., and) a humanized VL comprising an amino acid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) to SEQ ID NO: 78. In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising the amino acid sequence of SEQ ID NO: 77 and a humanized VL comprising the amino acid sequence of SEQ ID NO: 78.

[000183] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identical to SEQ ID NO: 79, and/or (e.g., and) a humanized VL comprising an amino acid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) to SEQ ID NO: 80. In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising the amino acid sequence of SEQ ID NO: 79 and a humanized VL comprising the amino acid sequence of SEQ ID NO: 80.

[000184] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identical to SEQ ID NO: 77, and/or (e.g., and) a humanized VL comprising an amino acid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) to SEQ ID NO: 80. In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a humanized VH comprising the amino acid sequence of SEQ ID NO: 77 and a humanized VL comprising the amino acid sequence of SEQ ID NO: 80. [000185] In some embodiments, the humanized anti-TfR antibody described herein is a full-length IgG, which can include a heavy constant region and a light constant region from a human antibody. In some embodiments, the heavy chain of any of the anti-TfR antibodies as described herein may comprises a heavy chain constant region (CH) or a portion thereof (e.g., CHI, CH2, CH3, or a combination thereof). The heavy chain constant region can of any suitable origin, e.g., human, mouse, rat, or rabbit. In one specific example, the heavy chain constant region is from a human IgG (a gamma heavy chain), e.g., IgGl, IgG2, or IgG4. An example of a human IgGl constant region is given below:

AS TKGPS VFPLAPS S KS TS GGT A ALGCLVKD YFPEP VT VS WN S GALT S G VHTFP A VLQ SSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPEL LGGPS VFLFPPKPKDTLMIS RTPE VT C V V VD VS HEDPE VKFNW Y VDG VE VHN AKTKP REEQ YN S T YRV V S VET VFHQD WEN GKE YKCKV S NKAFP APIEKTIS KAKGQPREPQ V YTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLY S KLT VD KS RW QQGN VFS C S VMHE ALHNH YTQKS LS LS PGK (SEQ ID NO: 81)

[000186] In some embodiments, the heavy chain of any of the anti-TfR antibodies described herein comprises a mutant human IgGl constant region. For example, the introduction of LALA mutations (a mutant derived from mAb bl2 that has been mutated to replace the lower hinge residues Leu234 Leu235 with Ala234 and Ala235) in the CH2 domain of human IgGl is known to reduce Fcg receptor binding (Bruhns, P., et al . (2009) and Xu, D. et al. (2000)). The mutant human IgGl constant region is provided below (mutations bonded and underlined):

AS TKGPS VFPLAPS S KS TS GGT A ALGCLVKD YFPEP VT VS WN S GALT S G VHTFP A VLQ SSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPEA AGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHN AKTKP REEQ YN S T YRV V S VLT VLHQD WLN GKE YKCKV S NKALP APIEKTIS KAKGQPREPQ V YTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLY S KLT VD KS RW QQGN VFS C S VMHE ALHNH YTQKS LS LS PGK (SEQ ID NO: 82)

[000187] In some embodiments, the light chain of any of the anti-TfR antibodies described herein may further comprise a light chain constant region (CL), which can be any CL known in the art. In some examples, the CL is a kappa light chain. In other examples, the CL is a lambda light chain. In some embodiments, the CL is a kappa light chain, the sequence of which is provided below: RT V A APS VFIFPPS DEQLKS GT AS V VCLLNNF YPRE AKV QWKVDN ALQS GN S QES VTE QDS KDS T Y S LS S TLTLS KAD YEKHKV Y ACE VTHQGLS S P VTKS FNRGEC (SEQ ID NO: 83)

[000188] Other antibody heavy and light chain constant regions are well known in the art, e.g., those provided in the IMGT database (www.imgt.org) or at www.vbase2.org/vbstat.php., both of which are incorporated by reference herein.

[000189] In some embodiments, the humanized anti-TfR antibody described herein comprises a heavy chain comprising any one of the VH as listed in Table 3 or any variants thereof and a heavy chain constant region that is at least 80%, at least 85%, at least 90%, at least 95%, or at least 99% identical to SEQ ID NO: 81 or SEQ ID NO: 82. In some embodiments, the humanized anti-TfR antibody described herein comprises a heavy chain comprising any one of the VH as listed in Table 3 or any variants thereof and a heavy chain constant region that contains no more than 25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) as compared with SEQ ID NO: 81 or SEQ ID NO: 82. In some embodiments, the humanized anti-TfR antibody described herein comprises a heavy chain comprising any one of the VH as listed in Table 3 or any variants thereof and a heavy chain constant region as set forth in SEQ ID NO: 81. In some embodiments, the humanized anti-TfR antibody described herein comprises heavy chain comprising any one of the VH as listed in Table 3 or any variants thereof and a heavy chain constant region as set forth in SEQ ID NO: 82.

[000190] In some embodiments, the humanized anti-TfR antibody described herein comprises a light chain comprising any one of the VL as listed in Table 3 or any variants thereof and a light chain constant region that is at least 80%, at least 85%, at least 90%, at least 95%, or at least 99% identical to SEQ ID NO: 83. In some embodiments, the humanized anti- TfR antibody described herein comprises a light chain comprising any one of the VL as listed in Table 3 or any variants thereof and a light chain constant region contains no more than 25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) as compared with SEQ ID NO: 83. In some embodiments, the humanized anti-TfR antibody described herein comprises a light chain comprising any one of the VL as listed in Table 3 or any variants thereof and a light chain constant region set forth in SEQ ID NO: 83.

[000191] Examples of IgG heavy chain and light chain amino acid sequences of the anti- TfR antibodies described are provided in Table 4 below. Table 4. Heavy chain and light chain sequences of examples of humanized anti-TfR IgGs mutation positions are according to Kabat numbering of the respective VH sequences containing the mutations CDRs according to the Kabat numbering system are bolded; VI I/VL sequences underlined

[000192] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain containing no more than 25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) as compared with the heavy chain as set forth in any one of SEQ ID NOs: 84, 86, 87, 88, 91, 92, and 94. Alternatively or in addition (e.g., in addition), the humanized anti-TfR antibody of the present disclosure comprises a light chain containing no more than 25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16,

15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) as compared with the light chain as set forth in any one of SEQ ID NOs: 85, 89, 90, 93, and 95.

[000193] In some embodiments, the humanized anti-TfR antibody described herein comprises a heavy chain comprising an amino acid sequence that is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%, 98%, or 99%) identical to any one of SEQ ID NOs: 84, 86, 87, 88, 91, 92, and 94. Alternatively or in addition (e.g., in addition), the humanized anti-TfR antibody described herein comprises a light chain comprising an amino acid sequence that is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%, 98%, or 99%) identical to any one of SEQ ID NOs: 85, 89, 90, 93, and 95. In some embodiments, the anti-TfR antibody described herein comprises a heavy chain comprising the amino acid sequence of any one of SEQ ID NOs: 84, 86, 87, 88,

91, 92, and 94. Alternatively or in addition (e.g., in addition), the anti-TfR antibody described herein comprises a light chain comprising the amino acid sequence of any one of SEQ ID NOs: 85, 89, 90, 93, and 95.

[000194] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identical to SEQ ID NO: 84, and/or (e.g., and) a light chain comprising an amino acid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) to SEQ ID NO: 85. In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 84 and a light chain comprising the amino acid sequence of SEQ ID NO: 85.

[000195] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identical to SEQ ID NO: 86, and/or (e.g., and) a light chain comprising an amino acid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) to SEQ ID NO: 85. In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 86 and a light chain comprising the amino acid sequence of SEQ ID NO: 85.

[000196] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identical to SEQ ID NO: 87, and/or (e.g., and) a light chain comprising an amino acid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) to SEQ ID NO: 85. In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 87 and a light chain comprising the amino acid sequence of SEQ ID NO: 85.

[000197] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identical to SEQ ID NO: 88, and/or (e.g., and) a light chain comprising an amino acid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) to SEQ ID NO: 89. In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 88 and a light chain comprising the amino acid sequence of SEQ ID NO: 89.

[000198] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identical to SEQ ID NO: 88, and/or (e.g., and) a light chain comprising an amino acid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) to SEQ ID NO: 90. In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 88 and a light chain comprising the amino acid sequence of SEQ ID NO: 90.

[000199] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identical to SEQ ID NO: 91, and/or (e.g., and) a light chain comprising an amino acid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) to SEQ ID NO: 89. In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 91 and a light chain comprising the amino acid sequence of SEQ ID NO: 89.

[000200] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identical to SEQ ID NO: 91, and/or (e.g., and) a light chain comprising an amino acid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) to SEQ ID NO: 90. In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 91 and a light chain comprising the amino acid sequence of SEQ ID NO: 90.

[000201] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identical to SEQ ID NO: 92, and/or (e.g., and) a light chain comprising an amino acid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) to SEQ ID NO: 93. In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 92 and a light chain comprising the amino acid sequence of SEQ ID NO: 93.

[000202] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identical to SEQ ID NO: 94, and/or (e.g., and) a light chain comprising an amino acid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) to SEQ ID NO: 95. In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 94 and a light chain comprising the amino acid sequence of SEQ ID NO: 95.

[000203] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identical to SEQ ID NO: 92, and/or (e.g., and) a light chain comprising an amino acid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) to SEQ ID NO: 95. In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 92 and a light chain comprising the amino acid sequence of SEQ ID NO: 95.

[000204] In some embodiments, the anti-TfR antibody is a Fab fragment, Fab' fragment, or F(ab')2 fragment of an intact antibody (full-length antibody). Antigen binding fragment of an intact antibody (full-length antibody) can be prepared via routine methods (e.g., recombinantly or by digesting the heavy chain constant region of a full length IgG using an enzyme such as papain). For example, F(ab')2 fragments can be produced by pepsin or papain digestion of an antibody molecule, and Fab' fragments that can be generated by reducing the disulfide bridges of F(ab')2 fragments. In some embodiments, a heavy chain constant region in a Fab fragment of the anti-TfRl antibody described herein comprises the amino acid sequence of:

ASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVL QSSGLYSLSSVVT VPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHT (SEQ ID NO: 96)

[000205] In some embodiments, the humanized anti-TfR antibody described herein comprises a heavy chain comprising any one of the VH as listed in Table 3 or any variants thereof and a heavy chain constant region that is at least 80%, at least 85%, at least 90%, at least 95%, or at least 99% identical to SEQ ID NO: 96. In some embodiments, the humanized anti-TfR antibody described herein comprises a heavy chain comprising any one of the VH as listed in Table 3 or any variants thereof and a heavy chain constant region that contains no more than 25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16,

15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) as compared with SEQ ID NO: 96. In some embodiments, the humanized anti-TfR antibody described herein comprises a heavy chain comprising any one of the VH as listed in Table 3 or any variants thereof and a heavy chain constant region as set forth in SEQ ID NO: 96.

[000206] In some embodiments, the humanized anti-TfR antibody described herein comprises a light chain comprising any one of the VL as listed in Table 3 or any variants thereof and a light chain constant region that is at least 80%, at least 85%, at least 90%, at least 95%, or at least 99% identical to SEQ ID NO: 83. In some embodiments, the humanized anti- TfR antibody described herein comprises a light chain comprising any one of the VL as listed in Table 3 or any variants thereof and a light chain constant region contains no more than 25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) as compared with SEQ ID NO: 83. In some embodiments, the humanized anti-TfR antibody described herein comprises a light chain comprising any one of the VL as listed in Table 3 or any variants thereof and a light chain constant region set forth in SEQ ID NO: 83.

[000207] Examples of Fab heavy chain and light chain amino acid sequences of the anti- TfR antibodies described are provided in Table 5 below.

Table 5. Heavy chain and light chain sequences of examples of humanized anti-TfR Fabs mutation positions are according to Kabat numbering of the respective VH sequences containing the mutations CDRs according to the Kabat numbering system are bolded; VI I/VL sequences underlined

[000208] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain containing no more than 25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) as compared with the heavy chain as set forth in any one of SEQ ID NOs: 97-103. Alternatively or in addition (e.g., in addition), the humanized anti-TfR antibody of the present disclosure comprises a light chain containing no more than 25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) as compared with the light chain as set forth in any one of SEQ ID NOs: 85, 89, 90, 93, and 95.

[000209] In some embodiments, the humanized anti-TfR antibody described herein comprises a heavy chain comprising an amino acid sequence that is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%, 98%, or 99%) identical to any one of SEQ ID NOs: 97-103. Alternatively or in addition (e.g., in addition), the humanized anti-TfR antibody described herein comprises a light chain comprising an amino acid sequence that is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%, 98%, or 99%) identical to any one of SEQ ID NOs: 85, 89, 90,

93, and 95. In some embodiments, the anti-TfR antibody described herein comprises a heavy chain comprising the amino acid sequence of any one of SEQ ID NOs: 97-103. Alternatively or in addition (e.g., in addition), the anti-TfR antibody described herein comprises a light chain comprising the amino acid sequence of any one of SEQ ID NOs: 85, 89, 90, 93, and 95. [000210] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identical to SEQ ID NO: 97, and/or (e.g., and) a light chain comprising an amino acid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) to SEQ ID NO: 85. In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 97 and a light chain comprising the amino acid sequence of SEQ ID NO: 85. [000211] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identical to SEQ ID NO: 98, and/or (e.g., and) a light chain comprising an amino acid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) to SEQ ID NO: 85. In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 98 and a light chain comprising the amino acid sequence of SEQ ID NO: 85.

[000212] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identical to SEQ ID NO: 99, and/or (e.g., and) a light chain comprising an amino acid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) to SEQ ID NO: 85. In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 99 and a light chain comprising the amino acid sequence of SEQ ID NO: 85.

[000213] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identical to SEQ ID NO: 100, and/or (e.g., and) a light chain comprising an amino acid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) to SEQ ID NO: 89. In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 100 and a light chain comprising the amino acid sequence of SEQ ID NO: 89.

[000214] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identical to SEQ ID NO: 100, and/or (e.g., and) a light chain comprising an amino acid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) to SEQ ID NO: 90. In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 100 and a light chain comprising the amino acid sequence of SEQ ID NO: 90.

[000215] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identical to SEQ ID NO: 101, and/or (e.g., and) a light chain comprising an amino acid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) to SEQ ID NO: 89. In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 101 and a light chain comprising the amino acid sequence of SEQ ID NO: 89.

[000216] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identical to SEQ ID NO: 101, and/or (e.g., and) a light chain comprising an amino acid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) to SEQ ID NO: 90. In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 101 and a light chain comprising the amino acid sequence of SEQ ID NO: 90.

[000217] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identical to SEQ ID NO: 102, and/or (e.g., and) a light chain comprising an amino acid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) to SEQ ID NO: 93. In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 102 and a light chain comprising the amino acid sequence of SEQ ID NO: 93.

[000218] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identical to SEQ ID NO: 103, and/or (e.g., and) a light chain comprising an amino acid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) to SEQ ID NO: 95. In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 103 and a light chain comprising the amino acid sequence of SEQ ID NO: 95.

[000219] In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identical to SEQ ID NO: 102, and/or (e.g., and) a light chain comprising an amino acid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) to SEQ ID NO: 95. In some embodiments, the humanized anti-TfR antibody of the present disclosure comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 102 and a light chain comprising the amino acid sequence of SEQ ID NO: 95.

[000220] In some embodiments, the humanized anti-TfR receptor antibodies described herein can be in any antibody form, including, but not limited to, intact (i.e., full-length) antibodies, antigen-binding fragments thereof (such as Fab, Fab', F(ab')2, Fv), single chain antibodies, bi-specific antibodies, or nanobodies. In some embodiments, humanized the anti- TfR antibody described herein is a scFv. In some embodiments, the humanized anti-TfR antibody described herein is a scFv-Fab (e.g., scFv fused to a portion of a constant region). In some embodiments, the anti-TfR receptor antibody described herein is a scFv fused to a constant region (e.g., human IgGl constant region as set forth in SEQ ID NO: 81 or SEQ ID NO: 82, or a portion thereof such as the Fc portion) at either the N-terminus of C-terminus. [000221] In some embodiments, conservative mutations can be introduced into antibody sequences (e.g., CDRs or framework sequences) at positions where the residues are not likely to be involved in interacting with a target antigen (e.g., transferrin receptor), for example, as determined based on a crystal structure. In some embodiments, one, two or more mutations (e.g., amino acid substitutions) are introduced into the Fc region of an anti-TfR antibody described herein (e.g., in a CH2 domain (residues 231-340 of human IgGl) and/or (e.g., and) CH3 domain (residues 341-447 of human IgGl) and/or (e.g., and) the hinge region, with numbering according to the Kabat numbering system (e.g., the EU index in Kabat)) to alter one or more functional properties of the antibody, such as serum half-life, complement fixation, Fc receptor binding and/or (e.g., and) antigen-dependent cellular cytotoxicity.

[000222] In some embodiments, one, two or more mutations (e.g., amino acid substitutions) are introduced into the hinge region of the Fc region (CHI domain) such that the number of cysteine residues in the hinge region are altered (e.g., increased or decreased) as described in, e.g., U.S. Pat. No. 5,677,425. The number of cysteine residues in the hinge region of the CHI domain can be altered to, e.g., facilitate assembly of the light and heavy chains, or to alter (e.g., increase or decrease) the stability of the antibody or to facilitate linker conjugation.

[000223] In some embodiments, one, two or more mutations (e.g., amino acid substitutions) are introduced into the Fc region of a muscle-targeting antibody described herein (e.g., in a CH2 domain (residues 231-340 of human IgGl) and/or (e.g., and) CH3 domain (residues 341-447 of human IgGl) and/or (e.g., and) the hinge region, with numbering according to the Kabat numbering system (e.g., the EU index in Kabat)) to increase or decrease the affinity of the antibody for an Fc receptor (e.g., an activated Fc receptor) on the surface of an effector cell. Mutations in the Fc region of an antibody that decrease or increase the affinity of an antibody for an Fc receptor and techniques for introducing such mutations into the Fc receptor or fragment thereof are known to one of skill in the art. Examples of mutations in the Fc receptor of an antibody that can be made to alter the affinity of the antibody for an Fc receptor are described in, e.g., Smith P et ah, (2012) PNAS 109: 6181-6186, U.S. Pat. No. 6,737,056, and International Publication Nos. WO 02/060919; WO 98/23289; and WO 97/34631, which are incorporated herein by reference.

[000224] In some embodiments, one, two or more amino acid mutations (i.e., substitutions, insertions or deletions) are introduced into an IgG constant domain, or FcRn- binding fragment thereof (preferably an Fc or hinge-Fc domain fragment) to alter (e.g., decrease or increase) half-life of the antibody in vivo. See, e.g., International Publication Nos. WO 02/060919; WO 98/23289; and WO 97/34631; and U.S. Pat. Nos. 5,869,046, 6,121,022, 6,277,375 and 6,165,745 for examples of mutations that will alter (e.g., decrease or increase) the half-life of an antibody in vivo.

[000225] In some embodiments, one, two or more amino acid mutations (i.e., substitutions, insertions or deletions) are introduced into an IgG constant domain, or FcRn- binding fragment thereof (preferably an Fc or hinge-Fc domain fragment) to decrease the half- life of the anti-anti-TfR antibody in vivo. In some embodiments, one, two or more amino acid mutations (i.e., substitutions, insertions or deletions) are introduced into an IgG constant domain, or FcRn-binding fragment thereof (preferably an Fc or hinge-Fc domain fragment) to increase the half-life of the antibody in vivo. In some embodiments, the antibodies can have one or more amino acid mutations (e.g., substitutions) in the second constant (CH2) domain (residues 231-340 of human IgGl) and/or (e.g., and) the third constant (CH3) domain (residues 341-447 of human IgGl), with numbering according to the EU index in Kabat (Kabat E A et ah, (1991) supra). In some embodiments, the constant region of the IgGl of an antibody described herein comprises a methionine (M) to tyrosine (Y) substitution in position 252, a serine (S) to threonine (T) substitution in position 254, and a threonine (T) to glutamic acid (E) substitution in position 256, numbered according to the EU index as in Kabat. See U.S. Pat.

No. 7,658,921, which is incorporated herein by reference. This type of mutant IgG, referred to as "YTE mutant" has been shown to display fourfold increased half-life as compared to wild- type versions of the same antibody (see Dall'Acqua W F et ah, (2006) J Biol Chem 281: 23514-24). In some embodiments, an antibody comprises an IgG constant domain comprising one, two, three or more amino acid substitutions of amino acid residues at positions 251-257, 285-290, 308-314, 385-389, and 428-436, numbered according to the EU index as in Kabat. [000226] In some embodiments, one, two or more amino acid substitutions are introduced into an IgG constant domain Fc region to alter the effector function(s) of the anti-anti-TfR antibody. The effector ligand to which affinity is altered can be, for example, an Fc receptor or the Cl component of complement. This approach is described in further detail in U.S. Pat. Nos. 5,624,821 and 5,648,260. In some embodiments, the deletion or inactivation (through point mutations or other means) of a constant region domain can reduce Fc receptor binding of the circulating antibody thereby increasing tumor localization. See, e.g., U.S. Pat. Nos. 5,585,097 and 8,591,886 for a description of mutations that delete or inactivate the constant domain and thereby increase tumor localization. In some embodiments, one or more amino acid substitutions may be introduced into the Fc region of an antibody described herein to remove potential glycosylation sites on Fc region, which may reduce Fc receptor binding (see, e.g., Shields R F et al., (2001) J Biol Chem 276: 6591-604).

[000227] In some embodiments, one or more amino in the constant region of an anti-TfR antibody described herein can be replaced with a different amino acid residue such that the antibody has altered Clq binding and/or (e.g., and) reduced or abolished complement dependent cytotoxicity (CDC). This approach is described in further detail in U.S. Pat. No. 6,194,551 (Idusogie et al). In some embodiments, one or more amino acid residues in the N- terminal region of the CH2 domain of an antibody described herein are altered to thereby alter the ability of the antibody to fix complement. This approach is described further in International Publication No. WO 94/29351. In some embodiments, the Fc region of an antibody described herein is modified to increase the ability of the antibody to mediate antibody dependent cellular cytotoxicity (ADCC) and/or (e.g., and) to increase the affinity of the antibody for an Fey receptor. This approach is described further in International Publication No. WO 00/42072.

[000228] In some embodiments, the heavy and/or (e.g., and) light chain variable domain(s) sequence(s) of the antibodies provided herein can be used to generate, for example, CDR-grafted, chimeric, humanized, or composite human antibodies or antigen-binding fragments, as described elsewhere herein. As understood by one of ordinary skill in the art, any variant, CDR-grafted, chimeric, humanized, or composite antibodies derived from any of the antibodies provided herein may be useful in the compositions and methods described herein and will maintain the ability to specifically bind transferrin receptor, such that the variant, CDR-grafted, chimeric, humanized, or composite antibody has at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95% or more binding to transferrin receptor relative to the original antibody from which it is derived.

[000229] In some embodiments, the antibodies provided herein comprise mutations that confer desirable properties to the antibodies. For example, to avoid potential complications due to Fab-arm exchange, which is known to occur with native IgG4 mAbs, the antibodies provided herein may comprise a stabilizing ‘Adair’ mutation (Angal S., et al., “A single amino acid substitution abolishes the heterogeneity of chimeric mouse/human (IgG4) antibody,” Mol Immunol 30, 105-108; 1993), where serine 228 (EU numbering; residue 241 Kabat numbering) is converted to proline resulting in an IgGl-like hinge sequence. Accordingly, any of the antibodies may include a stabilizing ‘Adair’ mutation.

[000230] In some embodiments, an antibody is modified, e.g., modified via glycosylation, phosphorylation, sumoylation, and/or (e.g., and) methylation. In some embodiments, an antibody is a glycosylated antibody, which is conjugated to one or more sugar or carbohydrate molecules. In some embodiments, the one or more sugar or carbohydrate molecule are conjugated to the antibody via N-glycosylation, O-glycosylation, C-glycosylation, glypiation (GPI anchor attachment), and/or (e.g., and) phosphoglycosylation. In some embodiments, the one or more sugar or carbohydrate molecules are monosaccharides, disaccharides, oligosaccharides, or glycans. In some embodiments, the one or more sugar or carbohydrate molecule is a branched oligosaccharide or a branched glycan. In some embodiments, the one or more sugar or carbohydrate molecule includes a mannose unit, a glucose unit, an N- acetylglucosamine unit, an N-acetylgalactosamine unit, a galactose unit, a fucose unit, or a phospholipid unit. In some embodiments, there are about 1-10, about 1-5, about 5-10, about 1- 4, about 1-3, or about 2 sugar molecules. In some embodiments, a glycosylated antibody is fully or partially glycosylated. In some embodiments, an antibody is glycosylated by chemical reactions or by enzymatic means. In some embodiments, an antibody is glycosylated in vitro or inside a cell, which may optionally be deficient in an enzyme in the N- or O- glycosylation pathway, e.g. a glycosyltransferase. In some embodiments, an antibody is functionalized with sugar or carbohydrate molecules as described in International Patent Application Publication WO2014065661, published on May 1, 2014, entitled, “ Modified antibody, antibody-conjugate and process for the preparation thereof ’.

[000231] In some embodiments, any one of the anti-TfRl antibodies described herein may comprise a signal peptide in the heavy and/or (e.g., and) light chain sequence (e.g., a N- terminal signal peptide). In some embodiments, the anti-TfRl antibody described herein comprises any one of the VH and VL sequences, any one of the IgG heavy chain and light chain sequences, or any one of the Fab heavy chain and light chain sequences described herein, and further comprises a signal peptide (e.g., a N-terminal signal peptide). In some embodiments, the signal peptide comprises the amino acid sequence of MGW S CIILFLV AT AT G VHS (SEQ ID NO: 104).

Other known anti-transferrin receptor antibodies

[000232] Any other appropriate anti-transferrin receptor antibodies known in the art may be used as the muscle-targeting agent in the complexes disclosed herein. Examples of known anti-transferrin receptor antibodies, including associated references and binding epitopes, are listed in Table 8. In some embodiments, the anti-transferrin receptor antibody comprises the complementarity determining regions (CDR-H1, CDR-H2, CDR-H3, CDR-L1, CDR-L2, and CDR-L3) of any of the anti-transferrin receptor antibodies provided herein, e.g., anti transferrin receptor antibodies listed in Table 8.

[000233] Table 8 - List of anti-transferrin receptor antibody clones, including associated references and binding epitope information.

[000234] In some embodiments, transferrin receptor antibodies of the present disclosure include one or more of the CDR-H ( e.g ., CDR-H1, CDR-H2, and CDR-H3) amino acid sequences from any one of the anti-transferrin receptor antibodies selected from Table 8. In some embodiments, transferrin receptor antibodies include the CDR-H 1, CDR-H2, and CDR- H3 as provided for any one of the anti-transferrin receptor antibodies selected from Table 8. In some embodiments, anti-transferrin receptor antibodies include the CDR-L1, CDR-L2, and CDR-L3 as provided for any one of the anti-transferrin receptor antibodies selected from Table 8. In some embodiments, anti-transferrin antibodies include the CDR-H1, CDR-H2, CDR-H3, CDR-L1, CDR-L2, and CDR-L3 as provided for any one of the anti-transferrin receptor antibodies selected from Table 8. The disclosure also includes any nucleic acid sequence that encodes a molecule comprising a CDR-H1, CDR-H2, CDR-H3, CDR-L1, CDR-L2, or CDR- L3 as provided for any one of the anti-transferrin receptor antibodies selected from Table 8. In some embodiments, antibody heavy and light chain CDR3 domains may play a particularly important role in the binding specificity/affinity of an antibody for an antigen. Accordingly, anti-transferrin receptor antibodies of the disclosure may include at least the heavy and/or (e.g., and) light chain CDR3s of any one of the anti-transferrin receptor antibodies selected from Table 8.

[000235] In some examples, any of the anti- transferrin receptor antibodies of the disclosure have one or more CDR (e.g., CDR-H or CDR-L) sequences substantially similar to any of the CDR-H1, CDR-H2, CDR-H3, CDR-L1, CDR-L2, and/or (e.g., and) CDR-L3 sequences from one of the anti-transferrin receptor antibodies selected from Table 8. In some embodiments, the position of one or more CDRs along the VH (e.g., CDR-H 1, CDR-H2, or CDR-H3) and/or (e.g., and) VL (e.g., CDR-L1, CDR-L2, or CDR-L3) region of an antibody described herein can vary by one, two, three, four, five, or six amino acid positions so long as immuno specific binding to transferrin receptor (e.g., human transferrin receptor) is maintained ( e.g ., substantially maintained, for example, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95% of the binding of the original antibody from which it is derived). For example, in some embodiments, the position defining a CDR of any antibody described herein can vary by shifting the N-terminal and/or (e.g., and) C-terminal boundary of the CDR by one, two, three, four, five, or six amino acids, relative to the CDR position of any one of the antibodies described herein, so long as immuno specific binding to transferrin receptor (e.g., human transferrin receptor) is maintained (e.g., substantially maintained, for example, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95% of the binding of the original antibody from which it is derived). In another embodiment, the length of one or more CDRs along the VH (e.g., CDR-H1, CDR-H2, or CDR-H3) and/or (e.g., and) VL (e.g., CDR-L1, CDR-L2, or CDR-L3) region of an antibody described herein can vary (e.g., be shorter or longer) by one, two, three, four, five, or more amino acids, so long as immuno specific binding to transferrin receptor (e.g., human transferrin receptor) is maintained (e.g., substantially maintained, for example, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95% of the binding of the original antibody from which it is derived).

[000236] Accordingly, in some embodiments, a CDR-L1, CDR-L2, CDR-L3, CDR-H1, CDR-H2, and/or (e.g., and) CDR-H3 described herein may be one, two, three, four, five or more amino acids shorter than one or more of the CDRs described herein (e.g., CDRS from any of the anti-transferrin receptor antibodies selected from Table 8) so long as immuno specific binding to transferrin receptor (e.g., human transferrin receptor) is maintained (e.g., substantially maintained, for example, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95% relative to the binding of the original antibody from which it is derived). In some embodiments, a CDR-L1, CDR-L2, CDR-L3, CDR-H1, CDR-H2, and/or (e.g., and) CDR-H3 described herein may be one, two, three, four, five or more amino acids longer than one or more of the CDRs described herein (e.g., CDRS from any of the anti transferrin receptor antibodies selected from Table 8) so long as immuno specific binding to transferrin receptor (e.g., human transferrin receptor) is maintained (e.g., substantially maintained, for example, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95% relative to the binding of the original antibody from which it is derived). In some embodiments, the amino portion of a CDR-L1, CDR-L2, CDR-L3, CDR-H1, CDR-H2, and/or (e.g., and) CDR-H3 described herein can be extended by one, two, three, four, five or more amino acids compared to one or more of the CDRs described herein (e.g., CDRS from any of the anti-transferrin receptor antibodies selected from Table 8) so long as immuno specific binding to transferrin receptor ( e.g ., human transferrin receptor is maintained (e.g., substantially maintained, for example, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95% relative to the binding of the original antibody from which it is derived). In some embodiments, the carboxy portion of a CDR-L1, CDR-L2, CDR-L3, CDR- Hl, CDR-H2, and/or (e.g., and) CDR-H3 described herein can be extended by one, two, three, four, five or more amino acids compared to one or more of the CDRs described herein (e.g., CDRS from any of the anti-transferrin receptor antibodies selected from Table 8) so long as immuno specific binding to transferrin receptor (e.g., human transferrin receptor) is maintained (e.g., substantially maintained, for example, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95% relative to the binding of the original antibody from which it is derived). In some embodiments, the amino portion of a CDR-L1, CDR-L2, CDR-L3, CDR-H1, CDR-H2, and/or (e.g., and) CDR-H3 described herein can be shortened by one, two, three, four, five or more amino acids compared to one or more of the CDRs described herein (e.g., CDRS from any of the anti-transferrin receptor antibodies selected from Table 8) so long as immuno specific binding to transferrin receptor (e.g., human transferrin receptor) is maintained (e.g., substantially maintained, for example, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95% relative to the binding of the original antibody from which it is derived). In some embodiments, the carboxy portion of a CDR-L1, CDR-L2, CDR-L3, CDR- Hl, CDR-H2, and/or (e.g., and) CDR-H3 described herein can be shortened by one, two, three, four, five or more amino acids compared to one or more of the CDRs described herein (e.g., CDRS from any of the anti-transferrin receptor antibodies selected from Table 8) so long as immuno specific binding to transferrin receptor (e.g., human transferrin receptor) is maintained (e.g., substantially maintained, for example, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95% relative to the binding of the original antibody from which it is derived). Any method can be used to ascertain whether immuno specific binding to transferrin receptor (e.g., human transferrin receptor) is maintained, for example, using binding assays and conditions described in the art.

[000237] In some examples, any of the anti-transferrin receptor antibodies of the disclosure have one or more CDR (e.g., CDR-H or CDR-L) sequences substantially similar to any one of the anti-transferrin receptor antibodies selected from Table 8. For example, the antibodies may include one or more CDR sequence(s) from any of the anti-transferrin receptor antibodies selected from Table 8 containing up to 5, 4, 3, 2, or 1 amino acid residue variations as compared to the corresponding CDR region in any one of the CDRs provided herein (e.g., CDRs from any of the anti-transferrin receptor antibodies selected from Table 8) so long as immuno specific binding to transferrin receptor (e.g., human transferrin receptor) is maintained ( e.g ., substantially maintained, for example, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95% relative to the binding of the original antibody from which it is derived). In some embodiments, any of the amino acid variations in any of the CDRs provided herein may be conservative variations. Conservative variations can be introduced into the CDRs at positions where the residues are not likely to be involved in interacting with a transferrin receptor protein (e.g., a human transferrin receptor protein), for example, as determined based on a crystal structure. Some aspects of the disclosure provide transferrin receptor antibodies that comprise one or more of the heavy chain variable (VH) and/or (e.g., and) light chain variable (VL) domains provided herein. In some embodiments, any of the VH domains provided herein include one or more of the CDR-H sequences (e.g., CDR-H1, CDR- H2, and CDR-H3) provided herein, for example, any of the CDR-H sequences provided in any one of the anti-transferrin receptor antibodies selected from Table 8. In some embodiments, any of the VL domains provided herein include one or more of the CDR-L sequences (e.g., CDR-L1, CDR-L2, and CDR-L3) provided herein, for example, any of the CDR-L sequences provided in any one of the anti-transferrin receptor antibodies selected from Table 8.

[000238] In some embodiments, anti-transferrin receptor antibodies of the disclosure include any antibody that includes a heavy chain variable domain and/or (e.g., and) a light chain variable domain of any anti-transferrin receptor antibody, such as any one of the anti transferrin receptor antibodies selected from Table 8. In some embodiments, anti-transferrin receptor antibodies of the disclosure include any antibody that includes the heavy chain variable and light chain variable pairs of any anti-transferrin receptor antibody, such as any one of the anti-transferrin receptor antibodies selected from Table 8.

[000239] Aspects of the disclosure provide anti-transferrin receptor antibodies having a heavy chain variable (VH) and/or (e.g., and) a light chain variable (VL) domain amino acid sequence homologous to any of those described herein. In some embodiments, the anti transferrin receptor antibody comprises a heavy chain variable sequence or a light chain variable sequence that is at least 75% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identical to the heavy chain variable sequence and / or any light chain variable sequence of any anti transferrin receptor antibody, such as any one of the anti-transferrin receptor antibodies selected from Table 8. In some embodiments, the homologous heavy chain variable and/or (e.g., and) a light chain variable amino acid sequences do not vary within any of the CDR sequences provided herein. For example, in some embodiments, the degree of sequence variation ( e.g ., 75%, 80%, 85%, 90%, 95%, 98%, or 99%) may occur within a heavy chain variable and/or (e.g., and) a light chain variable sequence excluding any of the CDR sequences provided herein. In some embodiments, any of the anti-transferrin receptor antibodies provided herein comprise a heavy chain variable sequence and a light chain variable sequence that comprises a framework sequence that is at least 75%, 80%, 85%, 90%, 95%, 98%, or 99% identical to the framework sequence of any anti-transferrin receptor antibody, such as any one of the anti-transferrin receptor antibodies selected from Table 8.

[000240] In some embodiments, an anti-transferrin receptor antibody, which specifically binds to transferrin receptor (e.g., human transferrin receptor), comprises a light chain variable VL domain comprising any of the CDR-L domains (CDR-L1, CDR-L2, and CDR-L3), or CDR-L domain variants provided herein, of any of the anti-transferrin receptor antibodies selected from Table 8. In some embodiments, an anti-transferrin receptor antibody, which specifically binds to transferrin receptor (e.g., human transferrin receptor), comprises a light chain variable VL domain comprising the CDR-L 1, the CDR-L2, and the CDR-L3 of any anti transferrin receptor antibody, such as any one of the anti-transferrin receptor antibodies selected from Table 8. In some embodiments, the anti-transferrin receptor antibody comprises a light chain variable (VL) region sequence comprising one, two, three or four of the framework regions of the light chain variable region sequence of any anti-transferrin receptor antibody, such as any one of the anti-transferrin receptor antibodies selected from Table 8. In some embodiments, the anti-transferrin receptor antibody comprises one, two, three or four of the framework regions of a light chain variable region sequence which is at least 75%, 80%, 85%, 90%, 95%, or 100% identical to one, two, three or four of the framework regions of the light chain variable region sequence of any anti-transferrin receptor antibody, such as any one of the anti-transferrin receptor antibodies selected from Table 8. In some embodiments, the light chain variable framework region that is derived from said amino acid sequence consists of said amino acid sequence but for the presence of up to 10 amino acid substitutions, deletions, and/or (e.g., and) insertions, preferably up to 10 amino acid substitutions. In some embodiments, the light chain variable framework region that is derived from said amino acid sequence consists of said amino acid sequence with 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 amino acid residues being substituted for an amino acid found in an analogous position in a corresponding non-human, primate, or human light chain variable framework region.

[000241] In some embodiments, an anti-transferrin receptor antibody that specifically binds to transferrin receptor comprises the CDR-L 1, the CDR-L2, and the CDR-L3 of any anti transferrin receptor antibody, such as any one of the anti-transferrin receptor antibodies selected from Table 8. In some embodiments, the antibody further comprises one, two, three or all four VL framework regions derived from the VL of a human or primate antibody. The primate or human light chain framework region of the antibody selected for use with the light chain CDR sequences described herein, can have, for example, at least 70% ( e.g ., at least 75%, 80%, 85%, 90%, 95%, 98%, or at least 99%) identity with a light chain framework region of a non-human parent antibody. The primate or human antibody selected can have the same or substantially the same number of amino acids in its light chain complementarity determining regions to that of the light chain complementarity determining regions of any of the antibodies provided herein, e.g., any of the anti-transferrin receptor antibodies selected from Table 8. In some embodiments, the primate or human light chain framework region amino acid residues are from a natural primate or human antibody light chain framework region having at least 75% identity, at least 80% identity, at least 85% identity, at least 90% identity, at least 95% identity, at least 98% identity, at least 99% (or more) identity with the light chain framework regions of any anti-transferrin receptor antibody, such as any one of the anti-transferrin receptor antibodies selected from Table 8. In some embodiments, an anti-transferrin receptor antibody further comprises one, two, three or all four VL framework regions derived from a human light chain variable kappa subfamily. In some embodiments, an anti-transferrin receptor antibody further comprises one, two, three or all four VL framework regions derived from a human light chain variable lambda subfamily.

[000242] In some embodiments, any of the anti-transferrin receptor antibodies provided herein comprise a light chain variable domain that further comprises a light chain constant region. In some embodiments, the light chain constant region is a kappa, or a lambda light chain constant region. In some embodiments, the kappa or lambda light chain constant region is from a mammal, e.g., from a human, monkey, rat, or mouse. In some embodiments, the light chain constant region is a human kappa light chain constant region. In some embodiments, the light chain constant region is a human lambda light chain constant region. It should be appreciated that any of the light chain constant regions provided herein may be variants of any of the light chain constant regions provided herein. In some embodiments, the light chain constant region comprises an amino acid sequence that is at least 75%, 80%, 85%, 90%, 95%, 98%, or 99% identical to any of the light chain constant regions of any anti-transferrin receptor antibody, such as any one of the anti-transferrin receptor antibodies selected from Table 8. [000243] In some embodiments, the anti-transferrin receptor antibody is any anti transferrin receptor antibody, such as any one of the anti-transferrin receptor antibodies selected from Table 8. [000244] In some embodiments, an anti-transferrin receptor antibody comprises a VL domain comprising the amino acid sequence of any anti-transferrin receptor antibody, such as any one of the anti-transferrin receptor antibodies selected from Table 8, and wherein the constant regions comprise the amino acid sequences of the constant regions of an IgG, IgE, IgM, IgD, IgA or IgY immunoglobulin molecule, or a human IgG, IgE, IgM, IgD, IgA or IgY immunoglobulin molecule. In some embodiments, an anti-transferrin receptor antibody comprises any of the VL domains, or VL domain variants, and any of the VH domains, or VH domain variants, wherein the VL and VH domains, or variants thereof, are from the same antibody clone, and wherein the constant regions comprise the amino acid sequences of the constant regions of an IgG, IgE, IgM, IgD, IgA or IgY immunoglobulin molecule, any class (e.g., IgGl, IgG2, IgG3, IgG4, IgAl and IgA2), or any subclass (e.g., IgG2a and IgG2b) of immunoglobulin molecule. Non-limiting examples of human constant regions are described in the art, e.g., see Kabat E A et al., (1991) supra.

[000245] In some embodiments, the muscle-targeting agent is a transferrin receptor antibody (e.g., the antibody and variants thereof as described in International Application Publication WO 2016/081643, incorporated herein by reference).

[000246] The heavy chain and light chain CDRs of the antibody according to different definition systems are provided in Table 9. The different definition systems, e.g., the Kabat definition, the Chothia definition, and/or (e.g., and) the contact definition have been described. See, e.g., (e.g., Kabat, E.A., et al. (1991) Sequences of Proteins of Immunological Interest, Fifth Edition, U.S. Department of Health and Human Services, NIH Publication No. 91-3242, Chothia et al., (1989) Nature 342:877; Chothia, C. et al. (1987) J. Mol. Biol. 196:901-917, Al- lazikani et al (1997) J. Molec. Biol. 273:927-948; and Almagro, J. Mol. Recognit. 17:132-143 (2004). See also hgmp.mrc.ac.uk and bioinf.org.uk/abs).

Table 9. Heavy chain and light chain CDRs of a mouse transferrin receptor antibody [000247] The heavy chain variable domain (VH) and light chain variable domain sequences are also provided:

[000248] VH

QVQLQQPGAELVKPGASVKLSCKASGYTFTSYWMHWVKQRPGQGLEWIGEINPTNG RTNYIEKFKSKATLTVDKSSSTAYMQLSSLTSEDSAVYYCARGTRAYHYWGQGTSVT VSS (SEQ ID NO: 124)

[000249] VL

DIQMTQS P AS LS VS V GET VTITCRAS DNLY S NLA W Y QQKQGKS PQLLV YD ATNLADG VPS RFS GS GS GTQ Y S LKIN S LQS EDF GT Y Y C QHFW GTPLTF G AGTKLELK (SEQ ID NO: 125)

[000250] In some embodiments, the transferrin receptor antibody of the present disclosure comprises a CDR-H1, a CDR-H2, and a CDR-H3 that are the same as the CDR-H1, CDR-H2, and CDR-H3 shown in Table 9. Alternatively or in addition (e.g., in addition), the transferrin receptor antibody of the present disclosure comprises a CDR-L1, a CDR-L2, and a CDR-L3 that are the same as the CDR-L1, CDR-L2, and CDR-L3 shown in Table 9.

[000251] In some embodiments, the transferrin receptor antibody of the present disclosure comprises a CDR-H1, a CDR-H2, and a CDR-H3, which collectively contains no more than 5 amino acid variations (e.g., no more than 5, 4, 3, 2, or 1 amino acid variation) as compared with the CDR-H1, CDR-H2, and CDR-H3 as shown in Table 9. “Collectively” means that the total number of amino acid variations in all of the three heavy chain CDRs is within the defined range. Alternatively or in addition (e.g., in addition), the transferrin receptor antibody of the present disclosure may comprise a CDR-L1, a CDR-L2, and a CDR- L3, which collectively contains no more than 5 amino acid variations (e.g., no more than 5, 4, 3, 2 or 1 amino acid variation) as compared with the CDR-L1, CDR-L2, and CDR-L3 as shown in Table 9.

[000252] In some embodiments, the transferrin receptor antibody of the present disclosure comprises a CDR-H1, a CDR-H2, and a CDR-H3, at least one of which contains no more than 3 amino acid variations (e.g., no more than 3, 2, or 1 amino acid variation) as compared with the counterpart heavy chain CDR as shown in Table 9. Alternatively or in addition (e.g., in addition), the transferrin receptor antibody of the present disclosure may comprise CDR-L1, a CDR-L2, and a CDR-L3, at least one of which contains no more than 3 amino acid variations (e.g., no more than 3, 2, or 1 amino acid variation) as compared with the counterpart light chain CDR as shown in Table 9. [000253] In some embodiments, the transferrin receptor antibody of the present disclosure comprises a CDR-L3, which contains no more than 3 amino acid variations (e.g., no more than 3, 2, or 1 amino acid variation) as compared with the CDR-L3 as shown in Table 9. In some embodiments, the transferrin receptor antibody of the present disclosure comprises a CDR-L3 containing one amino acid variation as compared with the CDR-L3 as shown in Table 9. In some embodiments, the transferrin receptor antibody of the present disclosure comprises a CDR-L3 of QHFAGTPLT (SEQ ID NO: 126) according to the Rabat and Chothia definition system) or QHFAGTPL (SEQ ID NO: 127) according to the Contact definition system). In some embodiments, the transferrin receptor antibody of the present disclosure comprises a CDR-H1, a CDR-H2, a CDR-H3, a CDR-L1 and a CDR-L2 that are the same as the CDR-H1, CDR-H2, and CDR-H3 shown in Table 9, and comprises a CDR-L3 of QHFAGTPLT (SEQ ID NO: 126) according to the Rabat and Chothia definition system) or QHFAGTPL (SEQ ID NO: 127) according to the Contact definition system).

[000254] In some embodiments, the transferrin receptor antibody of the present disclosure comprises heavy chain CDRs that collectively are at least 80% (e.g., 80%, 85%, 90%, 95%, or 98%) identical to the heavy chain CDRs as shown in Table 9. Alternatively or in addition (e.g., in addition), the transferrin receptor antibody of the present disclosure comprises light chain CDRs that collectively are at least 80% (e.g., 80%, 85%, 90%, 95%, or 98%) identical to the light chain CDRs as shown in Table 9.

[000255] In some embodiments, the transferrin receptor antibody of the present disclosure comprises a VH comprising the amino acid sequence of SEQ ID NO: 124. Alternatively or in addition (e.g., in addition), the transferrin receptor antibody of the present disclosure comprises a VL comprising the amino acid sequence of SEQ ID NO: 125.

[000256] In some embodiments, the transferrin receptor antibody of the present disclosure comprises a VH containing no more than 25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) as compared with the VH as set forth in SEQ ID NO: 124. Alternatively or in addition (e.g., in addition), the transferrin receptor antibody of the present disclosure comprises a VL containing no more than 15 amino acid variations (e.g., no more than 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) as compared with the VL as set forth in SEQ ID NO: 125.

[000257] In some embodiments, the transferrin receptor antibody of the present disclosure comprises a VH comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, or 98%) identical to the VH as set forth in SEQ ID NO: 124. Alternatively or in addition (e.g., in addition), the transferrin receptor antibody of the present disclosure comprises a VL comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, or 98%) identical to the VL as set forth in SEQ ID NO: 125.

[000258] In some embodiments, the transferrin receptor antibody of the present disclosure is a humanized antibody (e.g., a humanized variant of an antibody). In some embodiments, the transferrin receptor antibody of the present disclosure comprises a CDR-H1, a CDR-H2, a CDR-H3, a CDR-L1, a CDR-L2, and a CDR-L3 that are the same as the CDR- Hl, CDR-H2, and CDR-H3 shown in Table 9, and comprises a humanized heavy chain variable region and/or (e.g., and) a humanized light chain variable region.

[000259] Humanized antibodies are human immunoglobulins (recipient antibody) in which residues from a complementary determining region (CDR) of the recipient are replaced by residues from a CDR of a non-human species (donor antibody) such as mouse, rat, or rabbit having the desired specificity, affinity, and capacity. In some embodiments, Fv framework region (FR) residues of the human immunoglobulin are replaced by corresponding non-human residues. Furthermore, the humanized antibody may comprise residues that are found neither in the recipient antibody nor in the imported CDR or framework sequences, but are included to further refine and optimize antibody performance. In general, the humanized antibody will comprise substantially all of at least one, and typically two, variable domains, in which all or substantially all of the CDR regions correspond to those of a non-human immunoglobulin and all or substantially all of the FR regions are those of a human immunoglobulin consensus sequence. The humanized antibody optimally also will comprise at least a portion of an immunoglobulin constant region or domain (Fc), typically that of a human immunoglobulin. Antibodies may have Fc regions modified as described in WO 99/58572. Other forms of humanized antibodies have one or more CDRs (one, two, three, four, five, six) which are altered with respect to the original antibody, which are also termed one or more CDRs derived from one or more CDRs from the original antibody. Humanized antibodies may also involve affinity maturation.

[000260] In some embodiments, humanization is achieved by grafting the CDRs (e.g., as shown in Table 9) into the IGKV1-NL1*01 and IGHV1-3*01 human variable domains. In some embodiments, the transferrin receptor antibody of the present disclosure is a humanized variant comprising one or more amino acid substitutions at positions 9, 13, 17, 18, 40, 45, and 70 as compared with the VL as set forth in SEQ ID NO: 125, and/or (e.g., and) one or more amino acid substitutions at positions 1, 5, 7, 11, 12, 20, 38, 40, 44, 66, 75, 81, 83, 87, and 108 as compared with the VH as set forth in SEQ ID NO: 124. In some embodiments, the transferrin receptor antibody of the present disclosure is a humanized variant comprising amino acid substitutions at all of positions 9, 13, 17, 18, 40, 45, and 70 as compared with the VL as set forth in SEQ ID NO: 125, and/or (e.g., and) amino acid substitutions at all of positions 1, 5, 7, 11, 12, 20, 38, 40, 44, 66, 75, 81, 83, 87, and 108 as compared with the VH as set forth in SEQ ID NO: 124.

[000261] In some embodiments, the transferrin receptor antibody of the present disclosure is a humanized antibody and contains the residues at positions 43 and 48 of the VL as set forth in SEQ ID NO: 125. Alternatively or in addition (e.g., in addition), the transferrin receptor antibody of the present disclosure is a humanized antibody and contains the residues at positions 48, 67, 69, 71, and 73 of the VH as set forth in SEQ ID NO: 124.

[000262] The VH and VL amino acid sequences of an example humanized antibody that may be used in accordance with the present disclosure are provided:

[000263] Humanized VH

E V QLV QS G AE VKKPG AS VKV S C KAS G YTFTS YWMHW VRQ APGQRLEWIGEINPTN G RTN YIEKFKS RATLT VDKS AST A YMELS S LRS EDT A V Y Y C ARGTRA YH YWGQGTM V TVSS (SEQ ID NO: 128)

[000264] Humanized VL

DIQMTQS PS S LS AS V GDR VTITCRAS DNLY S NLA W Y QQKPGKS PKLLV YD ATNLADG VPS RFS GS GS GTD YTLTIS S LQPEDF AT Y Y C QHFW GTPLTFGQGTKVEIK (SEQ ID NO: 129)

[000265] In some embodiments, the transferrin receptor antibody of the present disclosure comprises a VH comprising the amino acid sequence of SEQ ID NO: 128. Alternatively or in addition (e.g., in addition), the transferrin receptor antibody of the present disclosure comprises a VL comprising the amino acid sequence of SEQ ID NO: 129.

[000266] In some embodiments, the transferrin receptor antibody of the present disclosure comprises a VH containing no more than 25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) as compared with the VH as set forth in SEQ ID NO: 128. Alternatively or in addition (e.g., in addition), the transferrin receptor antibody of the present disclosure comprises a VL containing no more than 15 amino acid variations (e.g., no more than 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) as compared with the VL as set forth in SEQ ID NO: 129.

[000267] In some embodiments, the transferrin receptor antibody of the present disclosure comprises a VH comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, or 98%) identical to the VH as set forth in SEQ ID NO: 128. Alternatively or in addition (e.g., in addition), the transferrin receptor antibody of the present disclosure comprises a VL comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, or 98%) identical to the VL as set forth in SEQ ID NO: 129.

[000268] In some embodiments, the transferrin receptor antibody of the present disclosure is a humanized variant comprising amino acid substitutions at one or more of positions 43 and 48 as compared with the VL as set forth in SEQ ID NO: 125, and/or (e.g., and) amino acid substitutions at one or more of positions 48, 67, 69, 71, and 73 as compared with the VH as set forth in SEQ ID NO: 124. In some embodiments, the transferrin receptor antibody of the present disclosure is a humanized variant comprising a S43A and/or (e.g., and) a V48L mutation as compared with the VL as set forth in SEQ ID NO: 125, and/or (e.g., and) one or more of A67V, L69I, V71R, and K73T mutations as compared with the VH as set forth in SEQ ID NO: 124.

[000269] In some embodiments, the transferrin receptor antibody of the present disclosure is a humanized variant comprising amino acid substitutions at one or more of positions 9, 13, 17, 18, 40, 43, 48, 45, and 70 as compared with the VL as set forth in SEQ ID NO: 125, and/or (e.g., and) amino acid substitutions at one or more of positions 1, 5, 7, 11, 12, 20, 38, 40, 44, 48, 66, 67, 69, 71, 73, 75, 81, 83, 87, and 108 as compared with the VH as set forth in SEQ ID NO: 124.

[000270] In some embodiments, the transferrin receptor antibody of the present disclosure is a chimeric antibody, which can include a heavy constant region and a light constant region from a human antibody. Chimeric antibodies refer to antibodies having a variable region or part of variable region from a first species and a constant region from a second species. Typically, in these chimeric antibodies, the variable region of both light and heavy chains mimics the variable regions of antibodies derived from one species of mammals (e.g., a non-human mammal such as mouse, rabbit, and rat), while the constant portions are homologous to the sequences in antibodies derived from another mammal such as human. In some embodiments, amino acid modifications can be made in the variable region and/or (e.g., and) the constant region.

[000271] In some embodiments, the transferrin receptor antibody described herein is a chimeric antibody, which can include a heavy constant region and a light constant region from a human antibody. Chimeric antibodies refer to antibodies having a variable region or part of variable region from a first species and a constant region from a second species. Typically, in these chimeric antibodies, the variable region of both light and heavy chains mimics the variable regions of antibodies derived from one species of mammals ( e.g ., a non-human mammal such as mouse, rabbit, and rat), while the constant portions are homologous to the sequences in antibodies derived from another mammal such as human. In some embodiments, amino acid modifications can be made in the variable region and/or (e.g., and) the constant region.

[000272] In some embodiments, the heavy chain of any of the transferrin receptor antibodies as described herein may comprises a heavy chain constant region (CH) or a portion thereof (e.g., CHI, CH2, CH3, or a combination thereof). The heavy chain constant region can of any suitable origin, e.g., human, mouse, rat, or rabbit. In one specific example, the heavy chain constant region is from a human IgG (a gamma heavy chain), e.g., IgGl, IgG2, or IgG4. An example of a human IgGl constant region is given below:

AS TKGPS VFPLAPS S KS TS GGT A ALGCLVKD YFPEP VT VS WN S GALT S G VHTFP A VLQ SSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPEL LGGPS VFLFPPKPKDTLMIS RTPE VT C V V VD VS HEDPE VKFNW Y VDG VE VHN AKTKP REEQ YN S T YRV V S VET VFHQD WEN GKE YKCKV S NKAFP APIEKTIS KAKGQPREPQ V YTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLY S KLT VD KS RW QQGN VFS C S VMHE ALHNH YTQKS LS LS PGK (SEQ ID NO: 130) [000273] In some embodiments, the light chain of any of the transferrin receptor antibodies described herein may further comprise a light chain constant region (CL), which can be any CL known in the art. In some examples, the CL is a kappa light chain. In other examples, the CL is a lambda light chain. In some embodiments, the CL is a kappa light chain, the sequence of which is provided below:

RT V A APS VFIFPPS DEQLKS GT AS V VCLLNNF YPRE AKV QWKVDN ALQS GN S QES VTE QDS KDS T Y S LS S TLTLS KAD YEKHKV Y ACE VTHQGLS S P VTKS FNRGEC (SEQ ID NO: 83)

[000274] Other antibody heavy and light chain constant regions are well known in the art, e.g., those provided in the IMGT database (www.imgt.org) or at www.vbase2.org/vbstat.php., both of which are incorporated by reference herein.

[000275] Examples of heavy chain and light chain amino acid sequences of the transferrin receptor antibodies described are provided below:

[000276] Heavy Chain (VH + human IgGl constant region)

QVQLQQPGAELVKPGASVKLSCKASGYTFTSYWMHWVKQRPGQGLEWIGEINPTNG RTNYIEKFKSKATLTVDKSSSTAYMQLSSLTSEDSAVYYCARGTRAYHYWGQGTSVT VS S AS TKGPS VFPLAPS S KS TS GGT A ALGCLVKD YFPEP VT VS WN S GALT S GVHTFP A VLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPA PELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKT KPREEQ YN S T YRV V S VLT VLHQD WLN GKE YKC KV S NKALP APIEKTIS K AKGQPREP QVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSF FLY S KLT VDKS RW QQGN VF S CS VMHE ALHNH YTQKS LS LS PGK (SEQ ID NO: 132) [000277] Light Chain (VL + kappa light chain)

DIQMTQS P AS LS VS V GET VTITCRAS DNLY S NLA W Y QQKQGKS PQLLV YD ATNLADG VPS RFS GS GS GTQ Y S LKIN S LQS EDF GT Y Y C QHFW GTPLTF G AGTKLELKRT V A APS VF IFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYS LS S TLTLS KAD YEKHKV Y ACE VTHQGLS S P VTKS FNRGEC (SEQ ID NO: 133)

[000278] Heavy Chain (humanized VH + human IgGl constant region)

E V QLV QS G AE VKKPG AS VKV S C KAS G YTFTS YWMHW VRQ APGQRLEWIGEINPTN G RTN YIEKFKS RATLT VDKS AST A YMELS S LRS EDT A V Y Y C ARGTRA YH YWGQGTM V TV S S AS TKGPS VFPLAPS S KS TS GGT A ALGCLVKD YFPEP VT VS WN S GALT S G VHTFP A VLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPA PELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKT KPREEQ YN S T YRV V S VLT VLHQD WLN GKE YKC KV S NKALP APIEKTIS K AKGQPREP QVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSF FLY S KLT VDKS RW QQGN VF S CS VMHE ALHNH YTQKS LS LS PGK (SEQ ID NO: 134) [000279] Light Chain (humanized VL + kappa light chain)

DIQMTQS PS S LS AS V GDR VTITCRAS DNLY S NLA W Y QQKPGKS PKLLV YD ATNLADG VPS RFS GS GS GTD YTLTIS S LQPEDF AT Y Y C QHFW GTPLTFGQGTKVEIKRT V A APS VFI FPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYS LS S TLTLS KAD YEKHKV Y ACE VTHQGLS S P VTKS FNRGEC (SEQ ID NO: 135)

[000280] In some embodiments, the transferrin receptor antibody described herein comprises a heavy chain comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, or 98%) identical to SEQ ID NO: 132. Alternatively or in addition (e.g., in addition), the transferrin receptor antibody described herein comprises a light chain comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, or 98%) identical to SEQ ID NO: 133. In some embodiments, the transferrin receptor antibody described herein comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 132. Alternatively or in addition (e.g., in addition), the transferrin receptor antibody described herein comprises a light chain comprising the amino acid sequence of SEQ ID NO: 133. [000281] In some embodiments, the transferrin receptor antibody of the present disclosure comprises a heavy chain containing no more than 25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) as compared with the heavy chain as set forth in SEQ ID NO: 132. Alternatively or in addition (e.g., in addition), the transferrin receptor antibody of the present disclosure comprises a light chain containing no more than 15 amino acid variations (e.g., no more than 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) as compared with the light chain as set forth in SEQ ID NO: 133.

[000282] In some embodiments, the transferrin receptor antibody described herein comprises a heavy chain comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, or 98%) identical to SEQ ID NO: 134. Alternatively or in addition (e.g., in addition), the transferrin receptor antibody described herein comprises a light chain comprising an amino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, or 98%) identical to SEQ ID NO: 135. In some embodiments, the transferrin receptor antibody described herein comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 134. Alternatively or in addition (e.g., in addition), the transferrin receptor antibody described herein comprises a light chain comprising the amino acid sequence of SEQ ID NO: 135. [000283] In some embodiments, the transferrin receptor antibody of the present disclosure comprises a heavy chain containing no more than 25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) as compared with the heavy chain of humanized antibody as set forth in SEQ ID NO: 134. Alternatively or in addition (e.g., in addition), the transferrin receptor antibody of the present disclosure comprises a light chain containing no more than 15 amino acid variations (e.g., no more than 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) as compared with the light chain of humanized antibody as set forth in SEQ ID NO: 135.

[000284] In some embodiments, the transferrin receptor antibody is an antigen binding fragment (Fab) of an intact antibody (full-length antibody). Antigen binding fragment of an intact antibody (full-length antibody) can be prepared via routine methods. For example, F(ab')2 fragments can be produced by pepsin digestion of an antibody molecule, and Fab' fragments that can be generated by reducing the disulfide bridges of F(ab')2 fragments. Examples of Fab amino acid sequences of the transferrin receptor antibodies described herein are provided below:

[000285] Heavy Chain Fab (VH + a portion of human IgGl constant region) QVQLQQPGAELVKPGASVKLSCKASGYTFTSYWMHWVKQRPGQGLEWIGEINPTNG RTNYIEKFKSKATLTVDKSSSTAYMQLSSLTSEDSAVYYCARGTRAYHYWGQGTSVT VS S AS TKGPS VFPLAPS S KS TS GGT A ALGCLVKD YFPEP VT VS WN S GALT S GVHTFP A VLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCP (SEQ ID NO: 136)

[000286] Heavy Chain Fab (humanized VH + a portion of human IgGl constant region)

E V QLV QS G AE VKKPG AS VKV S C KAS G YTFTS YWMHW VRQ APGQRLEWIGEINPTN G RTN YIEKFKS RATLT VDKS AST A YMELS S LRS EDT A V Y Y C ARGTRA YH YWGQGTM V TV S S AS TKGPS VFPLAPS S KS TS GGT A ALGCLVKD YFPEP VT VS WN S GALT S GVHTFP A VLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCP (SEQ ID NO: 137)

[000287] In some embodiments, the transferrin receptor antibody described herein comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 136. Alternatively or in addition (e.g., in addition), the transferrin receptor antibody described herein comprises a light chain comprising the amino acid sequence of SEQ ID NO: 133. [000288] In some embodiments, the transferrin receptor antibody described herein comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 137. Alternatively or in addition (e.g., in addition), the transferrin receptor antibody described herein comprises a light chain comprising the amino acid sequence of SEQ ID NO: 135. [000289] The transferrin receptor antibodies described herein can be in any antibody form, including, but not limited to, intact (i.e., full-length) antibodies, antigen-binding fragments thereof (such as Fab, Fab', F(ab')2, Fv), single chain antibodies, bi-specific antibodies, or nanobodies. In some embodiments, the transferrin receptor antibody described herein is a scFv. In some embodiments, the transferrin receptor antibody described herein is a scFv-Fab (e.g., scFv fused to a portion of a constant region). In some embodiments, the transferrin receptor antibody described herein is a scFv fused to a constant region (e.g., human IgGl constant region as set forth in SEQ ID NO: 130).

[000290] In some embodiments, any one of the anti-TfR antibodies described herein is produced by recombinant DNA technology in Chinese hamster ovary (CHO) cell suspension culture, optionally in CHO-K1 cell (e.g., CHO-K1 cells derived from European Collection of Animal Cell Culture, Cat. No. 85051005) suspension culture.

[000291] In some embodiments, an antibody provided herein may have one or more post- translational modifications. In some embodiments, N-terminal cyclization, also called pyroglutamate formation (pyro-Glu), may occur in the antibody at N-terminal Glutamate (Glu) and/or Glutamine (Gin) residues during production. As such, it should be appreciated that an antibody specified as having a sequence comprising an N-terminal glutamate or glutamine residue encompasses antibodies that have undergone pyroglutamate formation resulting from a post-translational modification. In some embodiments, pyroglutamate formation occurs in a heavy chain sequence. In some embodiments, pyroglutamate formation occurs in a light chain sequence. b. Other Muscle- Targeting Antibodies

[000292] In some embodiments, the muscle-targeting antibody is an antibody that specifically binds hemojuvelin, caveolin-3, Duchenne muscular dystrophy peptide, myosin lib or CD63. In some embodiments, the muscle-targeting antibody is an antibody that specifically binds a myogenic precursor protein. Exemplary myogenic precursor proteins include, without limitation, ABCG2, M-Cadherin/Cadherin-15, Caveolin-1, CD34, FoxKl, Integrin alpha 7, Integrin alpha 7 beta 1, MYF-5, MyoD, Myogenin, NCAM-1/CD56, Pax3, Pax7, and Pax9. In some embodiments, the muscle-targeting antibody is an antibody that specifically binds a skeletal muscle protein. Exemplary skeletal muscle proteins include, without limitation, alpha- Sarcoglycan, beta-Sarcoglycan, Calpain Inhibitors, Creatine Kinase MM/CKMM, eIF5A, Enolase 2/Neuron- specific Enolase, epsilon-Sarcoglycan, FABP3/H-FABP, GDF-8/Myostatin, GDF-ll/GDF-8, Integrin alpha 7, Integrin alpha 7 beta 1, Integrin beta 1/CD29, MCAM/CD146, MyoD, Myogenin, Myosin Fight Chain Kinase Inhibitors, NCAM-1/CD56, and Troponin I. In some embodiments, the muscle-targeting antibody is an antibody that specifically binds a smooth muscle protein. Exemplary smooth muscle proteins include, without limitation, alpha-Smooth Muscle Actin, VE-Cadherin, Caldesmon/CALDl, Calponin 1, Desmin, Histamine H2 R, Motilin R/GPR38, Transgelin/TAGLN, and Vimentin. However, it should be appreciated that antibodies to additional targets are within the scope of this disclosure and the exemplary lists of targets provided herein are not meant to be limiting. c. Antibody Features/Alterations

[000293] In some embodiments, conservative mutations can be introduced into antibody sequences (e.g., CDRs or framework sequences) at positions where the residues are not likely to be involved in interacting with a target antigen (e.g., transferrin receptor), for example, as determined based on a crystal structure. In some embodiments, one, two or more mutations (e.g., amino acid substitutions) are introduced into the Fc region of a muscle-targeting antibody described herein (e.g., in a CH2 domain (residues 231-340 of human IgGl) and/or (e.g., and) CH3 domain (residues 341-447 of human IgGl) and/or (e.g., and) the hinge region, with numbering according to the Kabat numbering system (e.g., the EU index in Kabat)) to alter one or more functional properties of the antibody, such as serum half-life, complement fixation, Fc receptor binding and/or (e.g., and) antigen-dependent cellular cytotoxicity.

[000294] In some embodiments, one, two or more mutations (e.g., amino acid substitutions) are introduced into the hinge region of the Fc region (CHI domain) such that the number of cysteine residues in the hinge region are altered (e.g., increased or decreased) as described in, e.g., U.S. Pat. No. 5,677,425. The number of cysteine residues in the hinge region of the CHI domain can be altered to, e.g., facilitate assembly of the light and heavy chains, or to alter (e.g., increase or decrease) the stability of the antibody or to facilitate linker conjugation.

[000295] In some embodiments, one, two or more mutations (e.g., amino acid substitutions) are introduced into the Fc region of a muscle-targeting antibody described herein (e.g., in a CH2 domain (residues 231-340 of human IgGl) and/or (e.g., and) CH3 domain (residues 341-447 of human IgGl) and/or (e.g., and) the hinge region, with numbering according to the Kabat numbering system (e.g., the EU index in Kabat)) to increase or decrease the affinity of the antibody for an Fc receptor (e.g., an activated Fc receptor) on the surface of an effector cell. Mutations in the Fc region of an antibody that decrease or increase the affinity of an antibody for an Fc receptor and techniques for introducing such mutations into the Fc receptor or fragment thereof are known to one of skill in the art. Examples of mutations in the Fc receptor of an antibody that can be made to alter the affinity of the antibody for an Fc receptor are described in, e.g., Smith P et ah, (2012) PNAS 109: 6181-6186, U.S. Pat. No. 6,737,056, and International Publication Nos. WO 02/060919; WO 98/23289; and WO 97/34631, which are incorporated herein by reference.

[000296] In some embodiments, one, two or more amino acid mutations (i.e., substitutions, insertions or deletions) are introduced into an IgG constant domain, or FcRn- binding fragment thereof (preferably an Fc or hinge-Fc domain fragment) to alter (e.g., decrease or increase) half-life of the antibody in vivo. See, e.g., International Publication Nos. WO 02/060919; WO 98/23289; and WO 97/34631; and U.S. Pat. Nos. 5,869,046, 6,121,022, 6,277,375 and 6,165,745 for examples of mutations that will alter (e.g., decrease or increase) the half-life of an antibody in vivo.

[000297] In some embodiments, one, two or more amino acid mutations (i.e., substitutions, insertions or deletions) are introduced into an IgG constant domain, or FcRn- binding fragment thereof (preferably an Fc or hinge-Fc domain fragment) to decrease the half- life of the anti-transferrin receptor antibody in vivo. In some embodiments, one, two or more amino acid mutations (i.e., substitutions, insertions or deletions) are introduced into an IgG constant domain, or FcRn-binding fragment thereof (preferably an Fc or hinge-Fc domain fragment) to increase the half-life of the antibody in vivo. In some embodiments, the antibodies can have one or more amino acid mutations ( e.g ., substitutions) in the second constant (CH2) domain (residues 231-340 of human IgGl) and/or (e.g., and) the third constant (CH3) domain (residues 341-447 of human IgGl), with numbering according to the EU index in Kabat (Kabat E A et al., (1991) supra). In some embodiments, the constant region of the IgGl of an antibody described herein comprises a methionine (M) to tyrosine (Y) substitution in position 252, a serine (S) to threonine (T) substitution in position 254, and a threonine (T) to glutamic acid (E) substitution in position 256, numbered according to the EU index as in Kabat. See U.S. Pat.

No. 7,658,921, which is incorporated herein by reference. This type of mutant IgG, referred to as "YTE mutant" has been shown to display fourfold increased half-life as compared to wild- type versions of the same antibody (see Dall'Acqua W F et al., (2006) J Biol Chem 281: 23514-24). In some embodiments, an antibody comprises an IgG constant domain comprising one, two, three or more amino acid substitutions of amino acid residues at positions 251-257, 285-290, 308-314, 385-389, and 428-436, numbered according to the EU index as in Kabat. [000298] In some embodiments, one, two or more amino acid substitutions are introduced into an IgG constant domain Fc region to alter the effector function(s) of the anti-transferrin receptor antibody. The effector ligand to which affinity is altered can be, for example, an Fc receptor or the C 1 component of complement. This approach is described in further detail in U.S. Pat. Nos. 5,624,821 and 5,648,260. In some embodiments, the deletion or inactivation (through point mutations or other means) of a constant region domain can reduce Fc receptor binding of the circulating antibody thereby increasing tumor localization. See, e.g., U.S. Pat. Nos. 5,585,097 and 8,591,886 for a description of mutations that delete or inactivate the constant domain and thereby increase tumor localization. In some embodiments, one or more amino acid substitutions may be introduced into the Fc region of an antibody described herein to remove potential glycosylation sites on Fc region, which may reduce Fc receptor binding (see, e.g., Shields R L et al., (2001) J Biol Chem 276: 6591-604).

[000299] In some embodiments, one or more amino in the constant region of a muscle targeting antibody described herein can be replaced with a different amino acid residue such that the antibody has altered Clq binding and/or (e.g., and) reduced or abolished complement dependent cytotoxicity (CDC). This approach is described in further detail in U.S. Pat. No. 6,194,551 (Idusogie et al). In some embodiments, one or more amino acid residues in the N- terminal region of the CH2 domain of an antibody described herein are altered to thereby alter the ability of the antibody to fix complement. This approach is described further in International Publication No. WO 94/29351. In some embodiments, the Fc region of an antibody described herein is modified to increase the ability of the antibody to mediate antibody dependent cellular cytotoxicity (ADCC) and/or (e.g., and) to increase the affinity of the antibody for an Fey receptor. This approach is described further in International Publication No. WO 00/42072.

[000300] In some embodiments, the heavy and/or (e.g., and) light chain variable domain(s) sequence(s) of the antibodies provided herein can be used to generate, for example, CDR-grafted, chimeric, humanized, or composite human antibodies or antigen-binding fragments, as described elsewhere herein. As understood by one of ordinary skill in the art, any variant, CDR-grafted, chimeric, humanized, or composite antibodies derived from any of the antibodies provided herein may be useful in the compositions and methods described herein and will maintain the ability to specifically bind transferrin receptor, such that the variant, CDR-grafted, chimeric, humanized, or composite antibody has at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95% or more binding to transferrin receptor relative to the original antibody from which it is derived.

[000301] In some embodiments, the antibodies provided herein comprise mutations that confer desirable properties to the antibodies. For example, to avoid potential complications due to Fab-arm exchange, which is known to occur with native IgG4 mAbs, the antibodies provided herein may comprise a stabilizing ‘Adair’ mutation (Angal S., et ah, “A single amino acid substitution abolishes the heterogeneity of chimeric mouse/human (IgG4) antibody,” Mol Immunol 30, 105-108; 1993), where serine 228 (EU numbering; residue 241 Rabat numbering) is converted to proline resulting in an IgGl-like hinge sequence. Accordingly, any of the antibodies may include a stabilizing ‘Adair’ mutation.

[000302] As provided herein, antibodies of this disclosure may optionally comprise constant regions or parts thereof. For example, a VL domain may be attached at its C-terminal end to a light chain constant domain like CK or C . Similarly, a VH domain or portion thereof may be attached to all or part of a heavy chain like IgA, IgD, IgE, IgG, and IgM, and any isotype subclass. Antibodies may include suitable constant regions (see, for example, Rabat et ah, Sequences of Proteins of Immunological Interest, No. 91-3242, National Institutes of Health Publications, Bethesda, Md. (1991)). Therefore, antibodies within the scope of this may disclosure include VH and VL domains, or an antigen binding portion thereof, combined with any suitable constant regions. ii. Muscle- Targeting Peptides

[000303] Some aspects of the disclosure provide muscle-targeting peptides as muscle targeting agents. Short peptide sequences (e.g., peptide sequences of 5-20 amino acids in length) that bind to specific cell types have been described. For example, cell-targeting peptides have been described in Vines e., et al., A. “Cell-penetrating and cell-targeting peptides in drug delivery” Biochim Biophys Acta 2008, 1786: 126-38; Jarver P., et al., “In vivo biodistribution and efficacy of peptide mediated delivery” Trends Pharmacol Sci 2010; 31: 528-35; Samoylova T.I., et al., “Elucidation of muscle-binding peptides by phage display screening” Muscle Nerve 1999; 22: 460-6; U.S. Patent No. 6,329,501, issued on December 11, 2001, entitled “METHODS AND COMPOSITIONS FOR TARGETING COMPOUNDS TO

MUSCLE”; and Samoylov A.M., et al., “Recognition of cell-specific binding of phage display derived peptides using an acoustic wave sensor.” Biomol Eng 2002; 18: 269-72; the entire contents of each of which are incorporated herein by reference. By designing peptides to interact with specific cell surface antigens ( e.g ., receptors), selectivity for a desired tissue, e.g., muscle, can be achieved. Skeletal muscle-targeting has been investigated and a range of molecular payloads are able to be delivered. These approaches may have high selectivity for muscle tissue without many of the practical disadvantages of a large antibody or viral particle. Accordingly, in some embodiments, the muscle-targeting agent is a muscle-targeting peptide that is from 4 to 50 amino acids in length. In some embodiments, the muscle-targeting peptide is 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30,

31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50 amino acids in length. Muscle-targeting peptides can be generated using any of several methods, such as phage display.

[000304] In some embodiments, a muscle-targeting peptide may bind to an internalizing cell surface receptor that is overexpressed or relatively highly expressed in muscle cells, e.g. a transferrin receptor, compared with certain other cells. In some embodiments, a muscle targeting peptide may target, e.g., bind to, a transferrin receptor. In some embodiments, a peptide that targets a transferrin receptor may comprise a segment of a naturally occurring ligand, e.g., transferrin. In some embodiments, a peptide that targets a transferrin receptor is as described in US Patent No. 6,743,893, filed 11/30/2000, “RECEPTOR-MEDIATED UPTAKE OF PEPTIDES THAT BIND THE HUMAN TRANSFERRIN RECEPTOR”. In some embodiments, a peptide that targets a transferrin receptor is as described in Kawamoto, M. et al, “A novel transferrin receptor-targeted hybrid peptide disintegrates cancer cell membrane to induce rapid killing of cancer cells.” BMC Cancer. 2011 Aug 18; 11:359. In some embodiments, a peptide that targets a transferrin receptor is as described in US Patent No. 8,399,653, filed 5/20/2011, “TRANSFERRIN/TRANSFERRIN RECEPTOR-MEDIATED SIRNA DELIVERY”.

[000305] As discussed above, examples of muscle targeting peptides have been reported. For example, muscle-specific peptides were identified using phage display library presenting surface heptapeptides. As one example a peptide having the amino acid sequence ASSLNIA (SEQ ID NO: 138) bound to C2C12 murine myotubes in vitro , and bound to mouse muscle tissue in vivo. Accordingly, in some embodiments, the muscle-targeting agent comprises the amino acid sequence ASSLNIA (SEQ ID NO: 138). This peptide displayed improved specificity for binding to heart and skeletal muscle tissue after intravenous injection in mice with reduced binding to liver, kidney, and brain. Additional muscle- specific peptides have been identified using phage display. For example, a 12 amino acid peptide was identified by phage display library for muscle targeting in the context of treatment for DMD. See, Yoshida D., et ah, “Targeting of salicylate to skin and muscle following topical injections in rats.” Int J Pharm 2002; 231: 177-84; the entire contents of which are hereby incorporated by reference. Here, a 12 amino acid peptide having the sequence SKTFNTHPQSTP (SEQ ID NO: 139) was identified and this muscle-targeting peptide showed improved binding to C2C12 cells relative to the ASSLNIA (SEQ ID NO: 138) peptide.

[000306] An additional method for identifying peptides selective for muscle ( e.g ., skeletal muscle) over other cell types includes in vitro selection, which has been described in Ghosh D., et ah, “Selection of muscle-binding peptides from context- specific peptide-presenting phage libraries for adenoviral vector targeting” J Virol 2005; 79: 13667-72; the entire contents of which are incorporated herein by reference. By pre-incubating a random 12-mer peptide phage display library with a mixture of non-muscle cell types, non-specific cell binders were selected out. Following rounds of selection the 12 amino acid peptide TARGEHKEEELI (SEQ ID NO: 140) appeared most frequently. Accordingly, in some embodiments, the muscle-targeting agent comprises the amino acid sequence TARGEHKEEELI (SEQ ID NO: 140).

[000307] A muscle-targeting agent may an amino acid-containing molecule or peptide. A muscle-targeting peptide may correspond to a sequence of a protein that preferentially binds to a protein receptor found in muscle cells. In some embodiments, a muscle-targeting peptide contains a high propensity of hydrophobic amino acids, e.g. valine, such that the peptide preferentially targets muscle cells. In some embodiments, a muscle-targeting peptide has not been previously characterized or disclosed. These peptides may be conceived of, produced, synthesized, and/or (e.g., and) derivatized using any of several methodologies, e.g. phage displayed peptide libraries, one-bead one-compound peptide libraries, or positional scanning synthetic peptide combinatorial libraries. Exemplary methodologies have been characterized in the art and are incorporated by reference (Gray, B.P. and Brown, K.C. “Combinatorial Peptide Libraries: Mining for Cell-Binding Peptides” Chem Rev. 2014, 114:2, 1020-1081.; Samoylova, T.I. and Smith, B.F. “Elucidation of muscle-binding peptides by phage display screening.” Muscle Nerve, 1999, 22:4. 460-6.). In some embodiments, a muscle-targeting peptide has been previously disclosed (see, e.g. Writer M.J. et al. “Targeted gene delivery to human airway epithelial cells with synthetic vectors incorporating novel targeting peptides selected by phage display.” J. Drug Targeting. 2004; 12: 185; Cai, D. “BDNF-mediated enhancement of inflammation and injury in the aging heart.” Physiol Genomics. 2006, 24:3, 191-7.; Zhang, L. “Molecular profiling of heart endothelial cells.” Circulation, 2005, 112:11, 1601-11.; McGuire, M.J. et al. “In vitro selection of a peptide with high selectivity for cardiomyocytes in vivo.” J Mol Biol. 2004, 342:1, 171-82.). Exemplary muscle-targeting peptides comprise an amino acid sequence of the following group: CQAQGQLVC (SEQ ID NO: 141), CSERSMNFC (SEQ ID NO: 142), CPKTRRVPC (SEQ ID NO: 143), WLSEAGPVVTVRALRGTGSW (SEQ ID NO: 144), ASSLNIA (SEQ ID NO: 138), CMQHSMRVC (SEQ ID NO: 145), and DDTRHWG (SEQ ID NO: 146). In some embodiments, a muscle-targeting peptide may comprise about 2-25 amino acids, about 2-20 amino acids, about 2-15 amino acids, about 2-10 amino acids, or about 2-5 amino acids. Muscle-targeting peptides may comprise naturally-occurring amino acids, e.g. cysteine, alanine, or non-naturally-occurring or modified amino acids. Non-naturally occurring amino acids include b-amino acids, homo-amino acids, proline derivatives, 3-substituted alanine derivatives, linear core amino acids, N-methyl amino acids, and others known in the art. In some embodiments, a muscle-targeting peptide may be linear; in other embodiments, a muscle targeting peptide may be cyclic, e.g. bicyclic (see, e.g. Silvana, M.G. et al. Mol. Therapy, 2018, 26:1, 132-147.). iii. Muscle- Targeting Receptor Ligands

[000308] A muscle-targeting agent may be a ligand, e.g. a ligand that binds to a receptor protein. A muscle-targeting ligand may be a protein, e.g. transferrin, which binds to an internalizing cell surface receptor expressed by a muscle cell. Accordingly, in some embodiments, the muscle-targeting agent is transferrin, or a derivative thereof that binds to a transferrin receptor. A muscle-targeting ligand may alternatively be a small molecule, e.g. a lipophilic small molecule that preferentially targets muscle cells relative to other cell types. Exemplary lipophilic small molecules that may target muscle cells include compounds comprising cholesterol, cholesteryl, stearic acid, palmitic acid, oleic acid, oleyl, linolene, linoleic acid, myristic acid, sterols, dihydrotestosterone, testosterone derivatives, glycerine, alkyl chains, trityl groups, and alkoxy acids. iv. Muscle- Targeting Aptamers

[000309] A muscle-targeting agent may be an aptamer, e.g. an RNA aptamer, which preferentially targets muscle cells relative to other cell types. In some embodiments, a muscle targeting aptamer has not been previously characterized or disclosed. These aptamers may be conceived of, produced, synthesized, and/or (e.g., and) derivatized using any of several methodologies, e.g. Systematic Evolution of Ligands by Exponential Enrichment. Exemplary methodologies have been characterized in the art and are incorporated by reference (Yan, A.C. and Levy, M. “Aptamers and aptamer targeted delivery” RNA biology, 2009, 6:3, 316-20.; Germer, K. et al. “RNA aptamers and their therapeutic and diagnostic applications.” Int. J. Biochem. Mol. Biol. 2013; 4: 27-40.). In some embodiments, a muscle-targeting aptamer has been previously disclosed (see, e.g. Phillippou, S. et al. “Selection and Identification of Skeletal-Muscle-Targeted RNA Aptamers.” Mol Ther Nucleic Acids. 2018, 10:199-214.;

Thiel, W.H. et al. “Smooth Muscle Cell-targeted RNA Aptamer Inhibits Neointimal Formation.” Mol Ther. 2016, 24:4, 779-87.). Exemplary muscle-targeting aptamers include the A01B RNA aptamer and RNA Apt 14. In some embodiments, an aptamer is a nucleic acid-based aptamer, an oligonucleotide aptamer or a peptide aptamer. In some embodiments, an aptamer may be about 5-15 kDa, about 5-10 kDa, about 10-15 kDa, about 1-5 Da, about 1-3 kDa, or smaller. v. Other Muscle- Targeting Agents

[000310] One strategy for targeting a muscle cell (e.g., a skeletal muscle cell) is to use a substrate of a muscle transporter protein, such as a transporter protein expressed on the sarcolemma. In some embodiments, the muscle-targeting agent is a substrate of an influx transporter that is specific to muscle tissue. In some embodiments, the influx transporter is specific to skeletal muscle tissue. Two main classes of transporters are expressed on the skeletal muscle sarcolemma, (1) the adenosine triphosphate (ATP) binding cassette (ABC) superfamily, which facilitate efflux from skeletal muscle tissue and (2) the solute carrier (SLC) superfamily, which can facilitate the influx of substrates into skeletal muscle. In some embodiments, the muscle-targeting agent is a substrate that binds to an ABC superfamily or an SLC superfamily of transporters. In some embodiments, the substrate that binds to the ABC or SLC superfamily of transporters is a naturally-occurring substrate. In some embodiments, the substrate that binds to the ABC or SLC superfamily of transporters is a non-naturally occurring substrate, for example, a synthetic derivative thereof that binds to the ABC or SLC superfamily of transporters.

[000311] In some embodiments, the muscle-targeting agent is a substrate of an SLC superfamily of transporters. SLC transporters are either equilibrative or use proton or sodium ion gradients created across the membrane to drive transport of substrates. Exemplary SLC transporters that have high skeletal muscle expression include, without limitation, the SATT transporter (ASCT1; SLC1A4), GLUT4 transporter (SLC2A4), GLUT7 transporter (GLUT7; SLC2A7), ATRC2 transporter (CAT-2; SLC7A2), LAT3 transporter (KIAA0245; SLC7A6), PHT1 transporter (PTR4; SLC15A4), OATP-J transporter (OATP5A1; SLC21A15), OCT3 transporter (EMT; SLC22A3), OCTN2 transporter (FLJ46769; SLC22A5), ENT transporters (ENT1; SLC29A1 and ENT2; SLC29A2), PAT2 transporter (SLC36A2), and SAT2 transporter (KIAA1382; SLC38A2). These transporters can facilitate the influx of substrates into skeletal muscle, providing opportunities for muscle targeting.

[000312] In some embodiments, the muscle-targeting agent is a substrate of an equilibrative nucleoside transporter 2 (ENT2) transporter. Relative to other transporters, ENT2 has one of the highest mRNA expressions in skeletal muscle. While human ENT2 (hENT2) is expressed in most body organs such as brain, heart, placenta, thymus, pancreas, prostate, and kidney, it is especially abundant in skeletal muscle. Human ENT2 facilitates the uptake of its substrates depending on their concentration gradient. ENT2 plays a role in maintaining nucleoside homeostasis by transporting a wide range of purine and pyrimidine nucleobases.

The hENT2 transporter has a low affinity for all nucleosides (adenosine, guanosine, uridine, thymidine, and cytidine) except for inosine. Accordingly, in some embodiments, the muscle targeting agent is an ENT2 substrate. Exemplary ENT2 substrates include, without limitation, inosine, 2',3'-dideoxyinosine, and calofarabine. In some embodiments, any of the muscle targeting agents provided herein are associated with a molecular payload (e.g., oligonucleotide payload). In some embodiments, the muscle-targeting agent is covalently linked to the molecular payload. In some embodiments, the muscle-targeting agent is non-covalently linked to the molecular payload.

[000313] In some embodiments, the muscle-targeting agent is a substrate of an organic cation/camitine transporter (OCTN2), which is a sodium ion-dependent, high affinity carnitine transporter. In some embodiments, the muscle-targeting agent is carnitine, mildronate, acetylcarnitine, or any derivative thereof that binds to OCTN2. In some embodiments, the carnitine, mildronate, acetylcarnitine, or derivative thereof is covalently linked to the molecular payload (e.g., oligonucleotide payload). [000314] A muscle-targeting agent may be a protein that is protein that exists in at least one soluble form that targets muscle cells. In some embodiments, a muscle-targeting protein may be hemojuvelin (also known as repulsive guidance molecule C or hemochromatosis type 2 protein), a protein involved in iron overload and homeostasis. In some embodiments, hemojuvelin may be full length or a fragment, or a mutant with at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, at least 98% or at least 99% sequence identity to a functional hemojuvelin protein. In some embodiments, a hemojuvelin mutant may be a soluble fragment, may lack a N-terminal signaling, and/or (e.g., and) lack a C-terminal anchoring domain. In some embodiments, hemojuvelin may be annotated under GenBank RefSeq Accession Numbers NM 001316767.1, NM_145277.4, NM_202004.3, NM_213652.3, or NM_213653.3. It should be appreciated that a hemojuvelin may be of human, non-human primate, or rodent origin.

B. Molecular Payloads

[000315] Some aspects of the disclosure provide molecular payloads, e.g., for modulating a biological outcome, e.g., the transcription of a DNA sequence, the expression of a protein, or the activity of a protein. In some embodiments, a molecular payload is linked to, or otherwise associated with a muscle-targeting agent. In some embodiments, such molecular payloads are capable of targeting to a muscle cell, e.g., via specifically binding to a nucleic acid or protein in the muscle cell following delivery to the muscle cell by an associated muscle-targeting agent. It should be appreciated that various types of muscle-targeting agents may be used in accordance with the disclosure. For example, the molecular payload may comprise, or consist of, an oligonucleotide (e.g., antisense oligonucleotide), a peptide (e.g., a peptide that binds a nucleic acid or protein associated with disease in a muscle cell), a protein (e.g., a protein that binds a nucleic acid or protein associated with disease in a muscle cell), or a small molecule (e.g., a small molecule that modulates the function of a nucleic acid or protein associated with disease in a muscle cell). In some embodiments, the molecular payload is an oligonucleotide that comprises a strand having a region of complementarity to a gene provided in Table 1. Exemplary molecular payloads are described in further detail herein, however, it should be appreciated that the exemplary molecular payloads provided herein are not meant to be limiting.

[000316] In some embodiments at least one (e.g., at least 2, at least 3, at least 4, at least 5, at least 10) molecular payload (e.g. oligonucleotides) is linked to a muscle-targeting agent. In some embodiments, all molecular payloads attached to a muscle-targeting agent are the same, e.g. target the same gene. In some embodiments, all molecular payloads attached to a muscle- targeting agent are different, for example the molecular payloads may target different portions of the same target gene, or the molecular payloads may target at least two different target genes. In some embodiments, a muscle-targeting agent may be attached to some molecular payloads that are the same and some molecular payloads that are different.

[000317] The present disclosure also provides a composition comprising a plurality of complexes, for which at least 80% ( e.g ., at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99%) of the complexes comprise a muscle-targeting agent linked to the same number of molecular payloads (e.g., oligonucleotides). i. Oligonucleotides

[000318] Any suitable oligonucleotide may be used as a molecular payload, as described herein. In some embodiments, the oligonucleotide may be designed to cause degradation of an mRNA (e.g., the oligonucleotide may be a gapmer, an siRNA, a ribozyme or an aptamer that causes degradation). In some embodiments, the oligonucleotide may be designed to block translation of an mRNA (e.g., the oligonucleotide may be a mixmer, an siRNA or an aptamer that blocks translation). In some embodiments, an oligonucleotide may be designed to caused degradation and block translation of an mRNA. In some embodiments, an oligonucleotide may be a guide nucleic acid (e.g., guide RNA) for directing activity of an enzyme (e.g., a gene editing enzyme). Other examples of oligonucleotides are provided herein. It should be appreciated that, in some embodiments, oligonucleotides in one format (e.g., antisense oligonucleotides) may be suitably adapted to another format (e.g., siRNA oligonucleotides) by incorporating functional sequences (e.g., antisense strand sequences) from one format to the other format.

[000319] In some embodiments, an oligonucleotide may comprise a region of complementarity to a target gene provided in Table 1. Further non-limiting examples are provided below for selected genes of Table 1.

DMPK/DM1

[000320] In some embodiments, examples of oligonucleotides useful for targeting DMPK, e.g., for the treatment of DM1, are provided in US Patent Application Publication 20100016215A1, published on January 1, 2010, entitled Compound And Method For Treating Myotonic Dystrophy; US Patent Application Publication 20130237585A1, published July 19, 2010, Modulation Of Dystrophia Myotonica-Protein Kinase (DMPK) Expression; US Patent Application Publication 20150064181A1, published on March 5, 2015, entitled “ Antisense Conjugates For Decreasing Expression Of Dmpk”; US Patent Application Publication 20150238627A1, published on August 27, 2015, entitled “ Peptide-Linked Morpholino Antisense Oligonucleotides For Treatment Of Myotonic Dystrophy Pandey, S.K. et al.

“ Identification and Characterization of Modified Antisense Oligonucleotides Targeting DMPK in Mice and Nonhuman Primates for the Treatment of Myotonic Dystrophy Type 1 ” J. of Pharmacol Exp Ther, 2015, 355:329-340.; Langlois, M. et al. “ Cytoplasmic and Nuclear Retained DMPK mRNAs Are Targets for RNA Interference in Myotonic Dystrophy Cells ” J. Biological Chemistry, 2005, 280:17, 16949-16954.; Jauvin, D. et al. “ Targeting DMPK with Antisense Oligonucleotide Improves Muscle Strength in Myotonic Dystrophy Type 1 Mice”, Mol. Ther: Nucleic Acids, 2017, 7:465-474.; Mulders, S.A. et al. “ Triplet-repeat oligonucleotide-mediated reversal of RNA toxicity in myotonic dystrophy” PNAS, 2009, 106:33, 13915-13920.; Wheeler, T.M. et al., “ Targeting nuclear RNA for in vivo correction of myotonic dystrophy” Nature, 2012, 488(7409): 111-115.; and US Patent Application Publication 20160304877A1, published on October 20, 2016, entitled “Compounds And Methods For Modulation Of Dystrophia Myotonica-Protein Kinase (Dmpk) Expression,” the contents of each of which are incorporated herein by reference in their entireties.

[000321] Examples of oligonucleotides for promoting DMPK gene editing include US Patent Application Publication 20170088819A1, published on March 3, 2017, entitled “ Genetic Correction Of Myotonic Dystrophy Type 1”; and International Patent Application Publication W018002812A1, published on April 1, 2018, entitled “Materials And Methods For Treatment Of Myotonic Dystrophy Type 1 (DM1 ) And Other Related Disorders,” the contents of each of which are incorporated herein by reference in their entireties.

[000322] In some embodiments, the oligonucleotide may have region of complementarity to a mutant form of DMPK, for example, a mutant form as reported in Botta A. et al. “The CTG repeat expansion size correlates with the splicing defects observed in muscles from myotonic dystrophy type 1 patients.” J Med Genet. 2008 Oct;45(10):639-46.; and Machuca- Tzili L. et al. “Clinical and molecular aspects of the myotonic dystrophies: a review.” Muscle Nerve. 2005 Jul;32(l): 1-18.; the contents of each of which are incorporated herein by reference in their entireties.

[000323] In some embodiments, an oligonucleotide provided herein is an antisense oligonucleotide targeting DMPK. In some embodiments, the oligonucleotide targeting is any one of the antisense oligonucleotides (e.g., a Gapmer) targeting DMPK as described in US Patent Application Publication US20160304877A1, published on October 20, 2016, entitled “ Compounds And Methods For Modulation Of Dystrophia Myotonica-Protein Kinase (DMPK) Expression ,” incorporated herein by reference. In some embodiments, the DMPK targeting oligonucleotide targets a region of the DMPK gene sequence as set forth in Genbank accession No. NM_001081560.2 or as set forth in Genbank accession No. NG_009784.1.

[000324] In some embodiments, the DMPK targeting oligonucleotide comprises a nucleotide sequence comprising a region complementary to a target region that is at least 10 continuous nucleotides (e.g., at least 10, at least 12, at least 14, at least 16, or more continuous nucleotides) in Genbank accession No. NM_001081560.2.

[000325] In some embodiments, the DMPK targeting oligonucleotide comprise a gapmer motif. “Gapmer” means a chimeric antisense compound in which an internal region having a plurality of nucleotides that support RNase H cleavage is positioned between external regions having one or more nucleotides, wherein the nucleotides comprising the internal region are chemically distinct from the nucleotide or nucleotides comprising the external regions. The internal region can be referred to as a “gap segment” and the external regions can be referred to as “wing segments.” In some embodiments, the DMPK targeting oligonucleotide comprises one or more modified nucleotides, and/or (e.g., and) one or more modified internucleotide linkages. In some embodiments, the internucleotide linkage is a phosphorothioate linkage. In some embodiments, the oligonucleotide comprises a full phosphorothioate backbone. In some embodiments, the oligonucleotide is a DNA gapmer with cET ends (e.g., 3-10-3; cET-DNA- cET). In some embodiments, the DMPK targeting oligonucleotide comprises one or more 6'- (S)-CH3 biocyclic nucleotides, one or more P-D-2'-deoxyribonucleotides, and/or (e.g., and) one or more 5-methylcytosine nucleotides.

DUX4/FSHD

[000326] In some embodiments, examples of oligonucleotides useful for targeting DUX4, e.g., for the treatment of FSHD, are provided in US Patent Number 9,988,628, published on February 2, 2017, entitled “AGENTS USEFUL IN TREATING

FACIOSCAPULOHUMERAL MUSCULAR DYSTROPHY”; US Patent Number 9,469,851, published October 30, 2014, entitled “RECOMBINANT VIRUS PRODUCTS AND METHODS FOR INHIBITING EXPRESSION OF DUX4”; US Patent Application Publication 20120225034, published on September 6, 2012, entitled “AGENTS USEFUL IN TREATING FACIOSCAPULOHUMERAL MUSCULAR DYSTROPHY”; PCT Patent Application Publication Number WO 2013/120038, published on August 15, 2013, entitled “MORPHOLINO TARGETING DUX4 FOR TREATING FSHD”; Chen et ah, “Morpholino- mediated Knockdown of DUX4 Toward Facioscapulohumeral Muscular Dystrophy Therapeutics,” Molecular Therapy, 2016, 24:8, 1405-1411.; and Ansseau et ah, “Antisense Oligonucleotides Used to Target the DUX4 mRNA as Therapeutic Approaches in Facioscapulohumeral Muscular Dystrophy (FSHD),” Genes, 2017, 8, 93.; the contents of each of which are incorporated herein in their entireties. In some embodiments, the oligonucleotide is an antisense oligonucleotide, a morpholino, a siRNA, a shRNA, or another nucleotide which hybridizes with the target DUX4 gene or mRNA.

[000327] In some embodiments, e.g., for the treatment of FSHD, oligonucleotides may have a region of complementarity to a hypomethylated, contracted D4Z4 repeat, as in Daxinger, et al., “Genetic and Epigenetic Contributors to FSHD,” published in Curr Opin Genet Dev in 2015, Lim J-W, et al., DICER/AGO-dependent epigenetic silencing of D4Z4 repeats enhanced by exogenous siRNA suggests mechanisms and therapies for FSHD Hum Mol Genet. 2015 Sep 1; 24(17): 4817-4828, the contents of each of which are incorporated in their entireties.

DNM2 /CNM

[000328] In some embodiments, examples of oligonucleotides useful for targeting DNM2, e.g., for the treatment of CNM, are provided in US Patent Application Publication Number 20180142008, published on May 24, 2018, entitled “DYNAMIN 2 INHIBITOR FOR THE TREATMENT OF DUCHENNE’S MUSCULAR DYSTROPHY”, and in PCT Application Publication Number WO 2018/100010A1, published on June 7, 2018, entitled “ALLELE-SPECIFIC SILENCING THERAPY FOR DYNAMIN 2-RELATED DISEASES”. For example, in some embodiments, the oligonucleotide is a RNAi, an antisense nucleic acid, a siRNA, or a ribozyme that interferes specifically with DNM2 expression. Other examples of oligonucleotides useful for targeting DNM2 are provided in Tasfaout, et al., “Single Intramuscular Injection of AAV-shRNA Reduces DNM2 and Prevents Myotubular Myopathy in Mice,” published in Mol. Ther. on April 4, 2018, and in Tasfaout, et al., “Antisense oligonucleotide-mediated Dnm2 knockdown prevents and reverts myotubular myopathy in mice,” Nature Communications volume 8, Article number: 15661 (2017). In some embodiments, the oligonucleotide is a shRNA or a morpholino that efficiently targets DNM2 mRNA. In some embodiments, the oligonucleotide encodes wild-type DNM2 which is resistant to miR-133 activity, as in Todaka, et al. “Overexpression of NF90-NF45 Represses Myogenic MicroRNA Biogenesis, Resulting in Development of Skeletal Muscle Atrophy and Centronuclear Muscle Fibers,” published in Mol. Cell Biol in July 2015 Further examples of oligonucleotides useful for targeting DNM2 are provided in Gibbs, et al., “Two Dynamin-2 Genes are Required for Normal Zebrafish Development” published in PLoS One in 2013, the contents of each of which are incorporated herein in their entirety.

[000329] In some embodiments, e.g., for the treatment of CNM, the oligonucleotide may have a region of complementarity to a mutant in DNM2 associated with CNM, as in Bohm et al, “Mutation Spectrum in the Large GTPase Dynamin 2, and Genotype-Phenotype Correlation in Autosomal Dominant Centronuclear Myopathy,” as published in Hum. Mutat. in 2012, the contents of which are incorporated herein in its entirety.

Pompe Disease

[000330] In some embodiments, e.g., for the treatment of Pompe disease, an oligonucleotide mediates exon 2 inclusion in a GAA disease allele as in van der Wal, et al., “GAA Deficiency in Pompe Disease is Alleviated by Exon Inclusion in iPSC-Derived Skeletal Muscle Cells,” Mol Ther Nucleic Acids. 2017 Jun 16; 7: 101-115, the contents of which are incorporated herein by reference. Accordingly, in some embodiments, the oligonucleotide may have a region of complementarity to a GAA disease allele.

[000331] In some embodiments, e.g., for the treatment of Pompe disease, an oligonucleotide, such as an RNAi or antisense oligonucleotide, is utilized to suppress expression of wild-type GYS1 in muscle cells, as reported, for example, in Clayton, et al., “Antisense Oligonucleotide-mediated Suppression of Muscle Glycogen Synthase 1 Synthesis as an Approach for Substrate Reduction Therapy of Pompe Disease,” published in Mol Ther Nucleic Acids in 2017, or US Patent Application Publication Number 2017182189, published on June 29, 2017, entitled “INHIBITING OR DOWNREGULATING GLYCOGEN SYNTHASE BY CREATING PREMATURE STOP CODONS USING ANTISENSE OLIGONUCLEOTIDES”, the contents of which are incorporated herein by reference. Accordingly, in some embodiments, oligonucleotides may have an antisense strand having a region of complementarity to a sequence a human GYS1 sequence, corresponding to RefSeq number NM_002103.4 and/or (e.g., and) a mouse GYS1 sequence, corresponding to RefSeq number NM_030678.3.

ACVR1 /FOP

[000332] In some embodiments, examples of oligonucleotides useful for targeting ACVR1, e.g., for the treatment of FOP, are provided in US Patent Application 2009/0253132, published 10/8/2009, “Mutated ACVR1 for diagnosis and treatment of fibrodyplasia ossificans progressiva (FOP)”; WO 2015/152183, published 10/8/2015, “Prophylactic agent and therapeutic agent for fibrodysplasia ossificans progressive”; Lowery, J.W. et al, "Allele- specific RNA Interference in FOP -Silencing the FOP gene", GENE THERAPY, vol. 19, 2012, pages 701 - 702; Takahashi, M. et al. “Disease-causing allele-specific silencing against the ALK2 mutants, R206H and G356D, in fibrodysplasia ossificans progressiva” Gene Therapy (2012) 19, 781-785; Shi, S. et al. “Antisense-Oligonucleotide Mediated Exon Skipping in Activin-Receptor-Like Kinase 2: Inhibiting the Receptor That Is Overactive in Fibrodysplasia Ossificans Progressiva” Plos One, July 2013, Vol 8:7, e69096.; US Patent Application 2017/0159056, published 6/8/2017, “Antisense oligonucleotides and methods of use thereof’; US Patent No. 8,859,752, issued 10/4/2014, “SIRNA-based therapy of Fibrodyplasia Ossificans Progressiva (FOP)”; WO 2004/094636, published 11/4/2004, “Effective sirna knock-down constructs”, the contents of each of which are incorporated herein in their entireties.

FXN / Friedreich 's Ataxia

[000333] In some embodiments, examples of oligonucleotides useful for targeting FXN and/or (e.g., and) otherwise compensating for frataxin deficiency, e.g., for the treatment of Friedreich Ataxia, are provided in Li, L. et al “Activating frataxin expression by repeat- targeted nucleic acids” Nat. Comm. 2016, 7:10606.; WO 2016/094374, published 6/16/2016, “Compositions and methods for treatment of Friedreich's ataxia.”; WO 2015/020993, published 2/12/2015, “RNAi COMPOSITIONS AND METHODS FOR TREATMENT OF FRIEDREICH'S ATAXIA”; WO 2017/186815, published 11/2/2017, “Antisense oligonucleotides for enhanced expression of frataxin”; WO 2008/018795, published 2/14/2008, “Methods and means for treating dna repeat instability associated genetic disorders”; US Patent Application 2018/0028557, published 2/1/2018, “Hybrid oligonucleotides and uses thereof’; WO 2015/023975, published 2/19/2015, “Compositions and methods for modulating RNA”; WO 2015/023939, published 2/19/2015, “Compositions and methods for modulating expression of frataxin”; US Patent Application 2017/0281643, published 10/5/2017, “Compounds and methods for modulating frataxin expression”; Li L. et al., “Activating frataxin expression by repeat-targeted nucleic acids” Nature Communications, Published 4 Feb 2016; and Li L. et al. “Activation of Frataxin Protein Expression by Antisense Oligonucleotides Targeting the Mutant Expanded Repeat” Nucleic Acid Ther. 2018 Feb;28(l):23-33., the contents of each of which are incorporated herein in their entireties. [000334] In some embodiments, an oligonucleotide payload is configured (e.g., as a gapmer or RNAi oligonucleotide) for inhibiting expression of a natural antisense transcript that inhibits FXN expression, e.g., as disclosed in US Patent No. 9,593,330, filed 6/9/2011, “Treatment of frataxin (FXN) related diseases by inhibition of natural antisense transcript to FXN”, the contents of which are incorporated herein by reference in its entirety.

[000335] Examples of oligonucleotides for promoting FXN gene editing include WO 2016/094845, published 6/16/2016, “Compositions and methods for editing nucleic acids in cells utilizing oligonucleotides”; WO 2015/089354, published 6/18/2015, “Compositions and methods of use of CRISPR-Cas systems in nucleotide repeat disorders”; WO 2015/139139, published 9/24/2015, “CRISPR-based methods and products for increasing frataxin levels and uses thereof’; and WO 2018/002783, published 1/4/2018, “Materials and methods for treatment of Friedreich ataxia and other related disorders”, the contents of each of which are incorporated herein in their entireties.

[000336] Examples of oligonucleotides for promoting FXN gene expression through targeting of non-FXN genes, e.g. epigenetic regulators of FXN, include WO 2015/023938, published 2/19/2015, “Epigenetic regulators of frataxin”, the contents of which are incorporated herein in its entirety.

[000337] In some embodiments, oligonucleotides may have a region of complementarity to a sequence set forth as: a FXN gene from humans (Gene ID 2395; NC_000009.12) and/or (e.g., and) a FXN gene from mice (Gene ID 14297; NC_000085.6). In some embodiments, the oligonucleotide may have region of complementarity to a mutant form of FXN, for example as reported in e.g., Montermini, L. et al. “The Friedreich ataxia GAA triplet repeat: premutation and normal alleles.” Hum. Molec. Genet., 1997, 6: 1261-1266.; Filla, A. et al.

“The relationship between trinucleotide (GAA) repeat length and clinical features in Friedreich ataxia.” Am. J. Hum. Genet. 1996, 59: 554-560.; Pandolfo, M. Friedreich ataxia: the clinical picture. J. Neurol. 2009, 256, 3-8.; the contents of each of which are incorporated herein by reference in their entireties.

DMD / Dystrophinopathies

[000338] Examples of oligonucleotides useful for targeting DMD are provided in U.S. Patent Application Publication US20100130591A1, published on May 27, 2010, entitled “MULTIPLE EXON SKIPPING COMPOSITIONS FOR DMD”; U.S. Patent No. 8,361,979, issued January 29, 2013, entitled “MEANS AND METHOD FOR INDUCING EXON SKIPPING”; U.S. Patent Application Publication 20120059042, published March 8, 2012, entitled “METHOD FOR EFFICIENT EXON (44) SKIPPING IN DUCHENNE MUSCULAR DYSTROPHY AND ASSOCIATED MEANS; U.S. Patent Application Publication 20140329881, published November 6, 2014, entitled “EXON SKIPPING COMPOSITIONS FOR TREATING MUSCULAR DYSTROPHY”; U.S. Patent No. 8,232,384, issued July 31, 2012, entitled “ANTISENSE OLIGONUCLEOTIDES FOR INDUCING EXON SKIPPING AND METHODS OF USE THEREOF”; U.S. Patent Application Publication 20120022134A1, published January 26, 2012, entitled “METHODS AND MEANS FOR EFFICIENT SKIPPING OF EXON 45 IN DUCHENNE MUSCULAR DYSTROPHY PRE-MRNA; U.S. Patent Application Publication 20120077860, published March 29, 2012, entitled “ADENO- ASSOCIATED VIRAL VECTOR FOR EXON SKIPPING IN A GENE ENCODING A DISPENSABLE DOMAN PROTEIN”; U.S. Patent No. 8,324,371, issued December 4, 2012, entitled “OLIGOMERS”; U.S. Patent No. 9,078,911, issued July 14, 2015, entitled “ANTISENSE OLIGONUCLEOTIDES”; U.S. Patent No. 9,079,934, issued July 14, 2015, entitled “ANTISENSE NUCLEIC ACIDS”; U.S. Patent No. 9,034,838, issued May 19, 2015, entitled “MIR-31 IN DUCHENNE MUSCULAR DYSTROPHY THERAPY”; and International Patent Publication WO2017062862A3, published April 13, 2017, entitled “OLIGONUCLEOTIDE COMPOSITIONS AND METHODS THEREOF”; the contents of each of which are incorporated herein in their entireties.

[000339] Examples of oligonucleotides for promoting DMD gene editing include International Patent Publication WO2018053632A1, published March 29, 2018, entitled “METHODS OF MODIFYING THE DYSTROPHIN GENE AND RESTORING DYSTROPHIN EXPRESSION AND USES THEREOF”; International Patent Publication W 02017049407 A 1 , published March 30, 2017, entitled “MODIFICATION OF THE DYSTROPHIN GENE AND USES THEREOF”; International Patent Publication W02016161380A1, published October 6, 2016, entitled “CRISPR/CAS-RELATED METHODS AND COMPOSITIONS FOR TREATING DUCHENNE MUSCULAR DYSTROPHY AND BECKER MUSCULAR DYSTROPHY”; International Patent Publication WO2017095967, published June 8, 2017, entitled “THERAPEUTIC TARGETS FOR THE CORRECTION OF THE HUMAN DYSTROPHIN GENE BY GENE EDITING AND METHODS OF USE”; International Patent Publication W02017072590A1, published May 4, 2017, entitled “MATERIALS AND METHODS FOR TREATMENT OF DUCHENNE MUSCULAR DYSTROPHY”; International Patent Publication W02018098480A1, published May 31, 2018, entitled “PREVENTION OF MUSCULAR DYSTROPHY BY CRISPR/CPFl-MEDIATED GENE EDITING”; US Patent Application Publication US20170266320A1, published September 21, 2017, entitled “RNA-Guided Systems for In Vivo Gene Editing”; International Patent Publication WO2016025469A1, published February 18, 2016, entitled “PREVENTION OF MUSCULAR DYSTROPHY BY CRISPR/CAS9-MEDIATED GENE EDITING”; U.S. Patent Application Publication 2016/0201089, published July 14, 2016, entitled “RNA-GUIDED GENE EDITING AND GENE REGULATION”; and U.S. Patent Application Publication 2013/0145487, published June 6, 2013, entitled “MEGANUCLEASE VARIANTS CLEAVING A DNA TARGET SEQUENCE FROM THE DYSTROPHN GENE AND USES THEREOF”, the contents of each of which are incorporated herein in their entireties. In some embodiments, an oligonucleotide may have a region of complementarity to DMD gene sequences of multiple species, e.g., selected from human, mouse and non-human species.

[000340] In some embodiments, the oligonucleotide may have region of complementarity to a mutant DMD allele, for example, a DMD allele with at least one mutation in any of exons 1-79 of DMD in humans that leads to a frameshift and improper RNA splicing/processing.

MYH7 / Hypertrophic Cardiomyopathy

[000341] Examples of oligonucleotides useful as payloads, e.g., for targeting MYH7, are provided in US Patent Application Publication 20180094262, published on April 5, 2018, entitled Inhibitors ofMYH7B and Uses Thereof ; US Patent Application Publication 20160348103, published on December 1, 2016, entitled Oligonucleotides and Methods for Treatment of Cardiomyopathy Using RNA Interference, US Patent Application Publication 20160237430, published on August 18, 2016, entitled "Allele-specific RNA Silencing for the Treatment of Hypertrophic Cardiomyopathy”, US Patent Application Publication 20160032286, published on February 4, 2016, entitled “ Inhibitors ofMYH7B and Uses Thereof ’; US Patent Application Publication 20140187603, published on July 3, 2014, entitled “ MicroRNA Inhibitors Comprising Locked Nucleotides”, US Patent Application Publication 20140179764, published on June 26, 2014, entitled “ Dual Targeting of miR-208 and miR-499 in the Treatment of Cardiac Disorders” ; US Patent Application Publication 20120114744, published on May 10, 2012, entitled “ Compositions and Methods to Treat Muscular and Cardiovascular Disorders the contents of each of which are incorporated herein in their entireties.

[000342] In some embodiments, the oligonucleotide may target lncRNA or mRNA, e.g., for degradation. In some embodiments, the oligonucleotide may target, e.g., for degradation, a nucleic acid encoding a protein involved in a mismatch repair pathway, e.g., MSH2, MutLalpha, MutSbeta, MutLalpha. Non-limiting examples of proteins involved in mismatch repair pathways, for which mRNAs encoding such proteins may be targeted by oligonucleotides described herein, are described in Iyer, R.R. et ah, “ DNA triplet repeat expansion and mismatch repair” Annu Rev Biochem. 2015;84:199-226.; and Schmidt M.H. and Pearson C.E., “Disease-associated repeat instability and mismatch repair” DNA Repair (Amst). 2016 Feb;38: 117-26.

[000343] In some embodiments, any one of the oligonucleotides can be in salt form, e.g., as sodium, potassium, or magnesium salts.

[000344] In some embodiments, the 5’ or 3’ nucleoside (e.g., terminal nucleoside) of any one of the oligonucleotides described herein is conjugated to an amine group, optionally via a spacer. In some embodiments, the spacer comprises an aliphatic moiety. In some embodiments, the spacer comprises a polyethylene glycol moiety. In some embodiments, a phosphodiester linkage is present between the spacer and the 5’ or 3’ nucleoside of the oligonucleotide. In some embodiments, the 5’ or 3’ nucleoside (e.g., terminal nucleoside) of any of the oligonucleotides described herein is conjugated to a spacer that is a substituted or unsubstituted aliphatic, substituted or unsubstituted heteroaliphatic, substituted or unsubstituted carbocyclylene, substituted or unsubstituted heterocyclylene, substituted or unsubstituted arylene, substituted or unsubstituted heteroarylene, -0-, -N(R ^A )-, -S-, -C(=0)-, -C(=0)0-, - C(=0)NR ^a -, -NR ^A C(=0)-, -NR ^A C(=0)R ^a -, -C(=0)R ^a -, -NR ^A C(=0)0-, -NR ^A C(=0)N(R ^a )-, - OC(=0)-, -0C(=0)0-, -OC(=0)N(R ^a )-, -S(0) ₂ NR ^a -, -NR ^A S(0) ₂ -, or a combination thereof; each R ^A is independently hydrogen or substituted or unsubstituted alkyl. In certain embodiments, the spacer is a substituted or unsubstituted alkylene, substituted or unsubstituted heterocyclylene, substituted or unsubstituted heteroarylene, -0-, -N(R ^A )-, or -C(=0)N(R ^A ) ₂ , or a combination thereof.

[000345] In some embodiments, the 5’ or 3’ nucleoside of any one of the oligonucleotides described herein is conjugated to a compound of the formula -NH ₂ -(CH ₂ ) _n -, wherein n is an integer from 1 to 12. In some embodiments, n is 6, 7, 8, 9, 10, 11, or 12. In some embodiments, a phosphodiester linkage is present between the compound of the formula NH ₂ - (CH ₂ ) _n - and the 5’ or 3’ nucleoside of the oligonucleotide. In some embodiments, a compound of the formula NH ₂ -(CH ₂ ) ₆ - is conjugated to the oligonucleotide via a reaction between 6- amino-l-hexanol (NH ₂ -(CH ₂ ) ₆ -OH) and the 5’ phosphate of the oligonucleotide.

[000346] In some embodiments, the oligonucleotide is conjugated to a targeting agent, e.g., a muscle targeting agent such as an anti-TfR antibody, e.g., via the amine group. a. Oligonucleotide Size/Sequence [000347] Oligonucleotides may be of a variety of different lengths, e.g., depending on the format. In some embodiments, an oligonucleotide is 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 35, 40, 45, 50, 75, or more nucleotides in length. In a some embodiments, the oligonucleotide is 8 to 50 nucleotides in length, 8 to 40 nucleotides in length, 8 to 30 nucleotides in length, 10 to 15 nucleotides in length, 10 to 20 nucleotides in length, 15 to 25 nucleotides in length, 21 to 23 nucleotides in lengths, etc. [000348] In some embodiments, a complementary nucleic acid sequence of an oligonucleotide for purposes of the present disclosure is specifically hybridizable or specific for the target nucleic acid when binding of the sequence to the target molecule (e.g., mRNA) interferes with the normal function of the target (e.g., mRNA) to cause a loss of activity (e.g., inhibiting translation) or expression (e.g., degrading a target mRNA) and there is a sufficient degree of complementarity to avoid non-specific binding of the sequence to non-target sequences under conditions in which avoidance of non-specific binding is desired, e.g., under physiological conditions in the case of in vivo assays or therapeutic treatment, and in the case of in vitro assays, under conditions in which the assays are performed under suitable conditions of stringency. Thus, in some embodiments, an oligonucleotide may be at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99% or 100% complementary to the consecutive nucleotides of an target nucleic acid. In some embodiments a complementary nucleotide sequence need not be 100% complementary to that of its target to be specifically hybridizable or specific for a target nucleic acid.

[000349] In some embodiments, an oligonucleotide comprises region of complementarity to a target nucleic acid that is in the range of 8 to 15, 8 to 30, 8 to 40, or 10 to 50, or 5 to 50, or 5 to 40 nucleotides in length. In some embodiments, a region of complementarity of an oligonucleotide to a target nucleic acid is 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45,

46, 47, 48, 49, or 50 nucleotides in length. In some embodiments, the region of complementarity is complementary with at least 8 consecutive nucleotides of a target nucleic acid. In some embodiments, an oligonucleotide may contain 1, 2 or 3 base mismatches compared to the portion of the consecutive nucleotides of target nucleic acid. In some embodiments the oligonucleotide may have up to 3 mismatches over 15 bases, or up to 2 mismatches over 10 bases.

[000350] In some embodiments, the oligonucleotide is complementary (e.g., at least 85% at least 90%, at least 95%, or 100%) to a target sequence of any one of the oligonucleotides provided herein. In some embodiments, such target sequence is 100% complementary to the oligonucleotide described herein.

[000351] In some embodiments, any one or more of the thymine bases (T’s) in any one of the oligonucleotides provided herein may optionally be uracil bases (U’s), and/or any one or more of the U’s may optionally be T’s. b. Oligonucleotide Modifications:

[000352] The oligonucleotides described herein may be modified, e.g., comprise a modified sugar moiety, a modified internucleoside linkage, a modified nucleotide and/or (e.g., and) combinations thereof. In addition, in some embodiments, oligonucleotides may exhibit one or more of the following properties: do not mediate alternative splicing; are not immune stimulatory; are nuclease resistant; have improved cell uptake compared to unmodified oligonucleotides; are not toxic to cells or mammals; have improved endosomal exit internally in a cell; minimizes TLR stimulation; or avoid pattern recognition receptors. Any of the modified chemistries or formats of oligonucleotides described herein can be combined with each other. For example, one, two, three, four, five, or more different types of modifications can be included within the same oligonucleotide.

[000353] In some embodiments, certain nucleotide modifications may be used that make an oligonucleotide into which they are incorporated more resistant to nuclease digestion than the native oligodeoxynucleotide or oligoribonucleotide molecules; these modified oligonucleotides survive intact for a longer time than unmodified oligonucleotides. Specific examples of modified oligonucleotides include those comprising modified backbones, for example, modified internucleoside linkages such as phosphorothioates, phosphotriesters, methyl phosphonates, short chain alkyl or cycloalkyl intersugar linkages or short chain heteroatomic or heterocyclic intersugar linkages. Accordingly, oligonucleotides of the disclosure can be stabilized against nucleolytic degradation such as by the incorporation of a modification, e.g., a nucleotide modification.

[000354] In some embodiments, an oligonucleotide may be of up to 50 or up to 100 nucleotides in length in which 2 to 10, 2 to 15, 2 to 16, 2 to 17, 2 to 18, 2 to 19, 2 to 20, 2 to 25, 2 to 30, 2 to 40, 2 to 45, or more nucleotides of the oligonucleotide are modified nucleotides. The oligonucleotide may be of 8 to 30 nucleotides in length in which 2 to 10, 2 to 15, 2 to 16, 2 to 17, 2 to 18, 2 to 19, 2 to 20, 2 to 25, 2 to 30 nucleotides of the oligonucleotide are modified nucleotides. The oligonucleotide may be of 8 to 15 nucleotides in length in which 2 to 4, 2 to 5, 2 to 6, 2 to 7, 2 to 8, 2 to 9, 2 to 10, 2 to 11, 2 to 12, 2 to 13, 2 to 14 nucleotides of the oligonucleotide are modified nucleotides. Optionally, the oligonucleotides may have every nucleotide except 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 nucleotides modified. Oligonucleotide modifications are described further herein. c. Modified Nucleosides

[000355] In some embodiments, the oligonucleotide described herein comprises at least one nucleoside modified at the 2' position of the sugar. In some embodiments, an oligonucleotide comprises at least one 2'-modified nucleoside. In some embodiments, all of the nucleosides in the oligonucleotide are 2’-modified nucleosides.

[000356] In some embodiments, the oligonucleotide described herein comprises one or more non-bicyclic 2’-modified nucleosides, e.g., 2’-deoxy, 2’-fluoro (2’-F), 2’-0-methyl (2’- O-Me), 2’-0-methoxyethyl (2’-MOE), 2’-0-aminopropyl (2’-0-AP), 2’-0- dimethylaminoethyl (2’-0-DMAOE), 2’-0-dimethylaminopropyl (2’-0-DMAP), 2’-0- dimethylaminoethyloxyethyl (2’-0-DMAEOE), or 2’-0-N-methylacetamido (2’-0-NMA) modified nucleoside.

[000357] In some embodiments, the oligonucleotide described herein comprises one or more 2’-4’ bicyclic nucleosides in which the ribose ring comprises a bridge moiety connecting two atoms in the ring, e.g., connecting the 2’-0 atom to the 4’-C atom via a methylene (LNA) bridge, an ethylene (ENA) bridge, or a (S)-constrained ethyl (cEt) bridge. Examples of LNAs are described in International Patent Application Publication WO/2008/043753, published on April 17, 2008, and entitled “RNA Antagonist Compounds For The Modulation Of PCSK9” , the contents of which are incorporated herein by reference in its entirety. Examples of ENAs are provided in International Patent Publication No. WO 2005/042777, published on May 12, 2005, and entitled ‘APP/ENA Antisense”·, Morita et al., Nucleic Acid Res., Suppl 1:241-242, 2001; Surono et al., Hum. Gene Ther., 15:749-757, 2004; Koizumi, Curr. Opin. Mol. Ther., 8:144-149, 2006 and Horie et al., Nucleic Acids Symp. Ser (Oxf), 49:171-172, 2005; the disclosures of which are incorporated herein by reference in their entireties. Examples of cEt are provided in US Patents 7,101,993; 7,399,845 and 7,569,686, each of which is herein incorporated by reference in its entirety.

[000358] In some embodiments, the oligonucleotide comprises a modified nucleoside disclosed in one of the following United States Patent or Patent Application Publications: US Patent 7,399,845, issued on July 15, 2008, and entitled “6 -Modified Bicyclic Nucleic Acid Analogs”; US Patent 7,741,457, issued on June 22, 2010, and entitled “ 6-Modified Bicyclic Nucleic Acid Analogs”; US Patent 8,022,193, issued on September 20, 2011, and entitled “<5- Modified Bicyclic Nucleic Acid Analogs”; US Patent 7,569,686, issued on August 4, 2009, and entitled “ Compounds And Methods For Synthesis Of Bicyclic Nucleic Acid Analogs”; US Patent 7,335,765, issued on February 26, 2008, and entitled “ Novel Nucleoside And Oligonucleotide Analogues”, US Patent 7,314,923, issued on January 1, 2008, and entitled ‘Wove/ Nucleoside And Oligonucleotide Analogues”, US Patent 7,816,333, issued on October 19, 2010, and entitled “Oligonucleotide Analogues And Methods Utilizing The Same” and US Publication Number 2011/0009471 now US Patent 8,957,201, issued on February 17, 2015, and entitled “ Oligonucleotide Analogues And Methods Utilizing The Same”, the entire contents of each of which are incorporated herein by reference for all purposes.

[000359] In some embodiments, the oligonucleotide comprises at least one modified nucleoside that results in an increase in Tm of the oligonucleotide in a range of 1°C, 2 °C, 3°C, 4 °C, or 5°C compared with an oligonucleotide that does not have the at least one modified nucleoside . The oligonucleotide may have a plurality of modified nucleosides that result in a total increase in Tm of the oligonucleotide in a range of 2 °C, 3 °C, 4 °C, 5 °C, 6 °C, 7 °C, 8 °C, 9 °C, 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, 40 °C, 45 °C or more compared with an oligonucleotide that does not have the modified nucleoside.

[000360] The oligonucleotide may comprise a mix of nucleosides of different kinds. For example, an oligonucleotide may comprise a mix of 2’-deoxyribonucleosides or ribonucleosides and 2’-fluoro modified nucleosides. An oligonucleotide may comprise a mix of deoxyribonucleosides or ribonucleosides and 2’-0-Me modified nucleosides. An oligonucleotide may comprise a mix of 2’-fluoro modified nucleosides and 2’-0-Me modified nucleosides. An oligonucleotide may comprise a mix of 2’-4’ bicyclic nucleosides and 2’- MOE, 2’-fluoro, or 2’-0-Me modified nucleosides. An oligonucleotide may comprise a mix of non-bicyclic 2’-modified nucleosides (e.g., 2’-MOE, 2’-fluoro, or 2’-0-Me) and 2’-4’ bicyclic nucleosides (e.g., LNA, ENA, cEt).

[000361] The oligonucleotide may comprise alternating nucleosides of different kinds.

For example, an oligonucleotide may comprise alternating 2’-deoxyribonucleosides or ribonucleosides and 2’-fluoro modified nucleosides. An oligonucleotide may comprise alternating deoxyribonucleosides or ribonucleosides and 2’-0-Me modified nucleosides. An oligonucleotide may comprise alternating 2’-fluoro modified nucleosides and 2’-0-Me modified nucleosides. An oligonucleotide may comprise alternating 2’-4’ bicyclic nucleosides and 2’-MOE, 2’-fluoro, or 2’-0-Me modified nucleosides. An oligonucleotide may comprise alternating non-bicyclic 2’-modified nucleosides (e.g., 2’-MOE, 2’-fluoro, or 2’-0-Me) and 2’- 4’ bicyclic nucleosides (e.g., LNA, ENA, cEt). [000362] In some embodiments, an oligonucleotide described herein comprises a 5 - vinylphosphonate modification, one or more abasic residues, and/or one or more inverted abasic residues. d. Internucleoside Linkages / Backbones [000363] In some embodiments, oligonucleotide may contain a phosphorothioate or other modified intemucleoside linkage. In some embodiments, the oligonucleotide comprises phosphorothioate intemucleoside linkages. In some embodiments, the oligonucleotide comprises phosphorothioate intemucleoside linkages between at least two nucleotides. In some embodiments, the oligonucleotide comprises phosphorothioate intemucleoside linkages between all nucleotides. For example, in some embodiments, oligonucleotides comprise modified intemucleoside linkages at the first, second, and/or (e.g., and) third intemucleoside linkage at the 5' or 3' end of the nucleotide sequence.

[000364] Phosphorus-containing linkages that may be used include, but are not limited to, phosphorothioates, chiral phosphorothioates, phosphorodithioates, phosphotriesters, aminoalkylphosphotriesters, methyl and other alkyl phosphonates comprising 3'alkylene phosphonates and chiral phosphonates, phosphinates, phosphoramidates comprising 3'-amino phosphoramidate and aminoalkylphosphoramidates, thionophosphoramidates, thionoalkylphosphonates, thionoalkylphosphotriesters, and boranophosphates having normal 3'-5' linkages, 2'-5' linked analogs of these, and those having inverted polarity wherein the adjacent pairs of nucleoside units are linked 3'-5' to 5'-3' or 2'-5' to 5'-2'; see US patent nos. 3,687,808; 4,469,863; 4,476,301; 5,023,243; 5, 177,196; 5,188,897; 5,264,423; 5,276,019; 5,278,302; 5,286,717; 5,321,131; 5,399,676; 5,405,939; 5,453,496; 5,455, 233; 5,466,677; 5,476,925; 5,519,126; 5,536,821; 5,541,306; 5,550,111; 5,563, 253; 5,571,799; 5,587,361; and

5,625,050.

[000365] In some embodiments, oligonucleotides may have heteroatom backbones, such as methylene(methylimino) or MMI backbones; amide backbones (see De Mesmaeker et al. Ace. Chem. Res. 1995, 28:366-374); morpholino backbones (see Summerton and Weller, U.S. Pat. No. 5,034,506); or peptide nucleic acid (PNA) backbones (wherein the phosphodiester backbone of the oligonucleotide is replaced with a polyamide backbone, the nucleotides being bound directly or indirectly to the aza nitrogen atoms of the polyamide backbone, see Nielsen et al., Science 1991, 254, 1497). e. Stereospecific Oligonucleotides [000366] In some embodiments, internucleotidic phosphorus atoms of oligonucleotides are chiral, and the properties of the oligonucleotides are adjusted based on the configuration of the chiral phosphorus atoms. In some embodiments, appropriate methods may be used to synthesize P-chiral oligonucleotide analogs in a stereocontrolled manner (e.g., as described in Oka N, Wada T, Stereocontrolled synthesis of oligonucleotide analogs containing chiral internucleotidic phosphorus atoms. Chem Soc Rev. 2011 Dec;40(12):5829-43.) In some embodiments, phosphorothioate containing oligonucleotides are provided that comprise nucleoside units that are joined together by either substantially all Sp or substantially all Rp phosphorothioate intersugar linkages. In some embodiments, such phosphorothioate oligonucleotides having substantially chirally pure intersugar linkages are prepared by enzymatic or chemical synthesis, as described, for example, in US Patent 5,587,261, issued on December 12, 1996, the contents of which are incorporated herein by reference in their entirety. In some embodiments, chirally controlled oligonucleotides provide selective cleavage patterns of a target nucleic acid. For example, in some embodiments, a chirally controlled oligonucleotide provides single site cleavage within a complementary sequence of a nucleic acid, as described, for example, in US Patent Application Publication 20170037399 Al, published on February 2, 2017, entitled “CHIRAL DESIGN”, the contents of which are incorporated herein by reference in their entirety. f. Morpholinos

[000367] In some embodiments, the oligonucleotide may be a morpholino-based compounds. Morpholino-based oligomeric compounds are described in Dwaine A. Braasch and David R. Corey, Biochemistry, 2002, 41(14), 4503-4510); Genesis, volume 30, issue 3, 2001; Heasman, J., Dev. Biol., 2002, 243, 209-214; Nasevicius et al., Nat. Genet., 2000, 26, 216-220; Lacerra et al., Proc. Natl. Acad. Sci., 2000, 97, 9591-9596; and U.S. Pat. No. 5,034,506, issued Jul. 23, 1991. In some embodiments, the morpholino-based oligomeric compound is a phosphorodiamidate morpholino oligomer (PMO) (e.g., as described in Iverson, Curr. Opin. Mol. Ther., 3:235-238, 2001; and Wang et al., J. Gene Med., 12:354-364, 2010; the disclosures of which are incorporated herein by reference in their entireties). g. Peptide Nucleic Acids (PNAs)

[000368] In some embodiments, both a sugar and an internucleoside linkage (the backbone) of the nucleotide units of an oligonucleotide are replaced with novel groups. In some embodiments, the base units are maintained for hybridization with an appropriate nucleic acid target compound. One such oligomeric compound, an oligonucleotide mimetic that has been shown to have excellent hybridization properties, is referred to as a peptide nucleic acid (PNA). In PNA compounds, the sugar-backbone of an oligonucleotide is replaced with an amide containing backbone, for example, an aminoethylglycine backbone. The nucleobases are retained and are bound directly or indirectly to aza nitrogen atoms of the amide portion of the backbone. Representative publication that report the preparation of PNA compounds include, but are not limited to, US patent nos. 5,539,082; 5,714,331; and 5,719,262, each of which is herein incorporated by reference. Further teaching of PNA compounds can be found in Nielsen etal., Science, 1991, 254, 1497-1500. h. Gapmers

[000369] In some embodiments, an oligonucleotide described herein is a gapmer. A gapmer oligonucleotide generally has the formula 5'-X-Y-Z-3', with X and Z as flanking regions around a gap region Y. In some embodiments, flanking region X of formula 5'-X-Y-Z- 3' is also referred to as X region, flanking sequence X, 5’ wing region X, or 5’ wing segment.

In some embodiments, flanking region Z of formula 5'-X-Y-Z-3' is also referred to as Z region, flanking sequence Z, 3’ wing region Z, or 3’ wing segment. In some embodiments, gap region

Y of formula 5'-X-Y-Z-3' is also referred to as Y region, Y segment, or gap-segment Y. In some embodiments, each nucleoside in the gap region Y is a 2’-deoxyribonucleoside, and neither the 5’ wing region X or the 3’ wing region Z contains any 2’-deoxyribonucleosides. [000370] In some embodiments, the Y region is a contiguous stretch of nucleotides, e.g., a region of 6 or more DNA nucleotides, which are capable of recruiting an RNAse, such as RNAse H. In some embodiments, the gapmer binds to the target nucleic acid, at which point an RNAse is recruited and can then cleave the target nucleic acid. In some embodiments, the

Y region is flanked both 5' and 3' by regions X and Z comprising high-affinity modified nucleosides, e.g., one to six high-affinity modified nucleosides. Examples of high affinity modified nucleosides include, but are not limited to, 2'-modified nucleosides (e.g., 2’-MOE, 2'O-Me, 2’-F) or 2’-4’ bicyclic nucleosides (e.g., LNA, cEt, ENA). In some embodiments, the flanking sequences X and Z may be of 1-20 nucleotides, 1-8 nucleotides, or 1-5 nucleotides in length. The flanking sequences X and Z may be of similar length or of dissimilar lengths. In some embodiments, the gap-segment Y may be a nucleotide sequence of 5-20 nucleotides, 5- 15 twelve nucleotides, or 6-10 nucleotides in length.

[000371] In some embodiments, the gap region of the gapmer oligonucleotides may contain modified nucleotides known to be acceptable for efficient RNase H action in addition to DNA nucleotides, such as C4'-substituted nucleotides, acyclic nucleotides, and arabino- configured nucleotides. In some embodiments, the gap region comprises one or more unmodified intemucleosides. In some embodiments, one or both flanking regions each independently comprise one or more phosphorothioate intemucleoside linkages (e.g., phosphorothioate intemucleoside linkages or other linkages) between at least two, at least three, at least four, at least five or more nucleotides. In some embodiments, the gap region and two flanking regions each independently comprise modified intemucleoside linkages (e.g., phosphorothioate intemucleoside linkages or other linkages) between at least two, at least three, at least four, at least five or more nucleotides.

[000372] A gapmer may be produced using appropriate methods. Representative U.S. patents, U.S. patent publications, and PCT publications that teach the preparation of gapmers include, but are not limited to, U.S. Pat. Nos. 5,013,830; 5,149,797; 5,220,007; 5,256,775; 5,366,878; 5,403,711; 5,491,133; 5,565,350; 5,623,065; 5,652,355; 5,652,356; 5,700,922; 5,898,031; 7,015,315; 7,101,993; 7,399,845; 7,432,250; 7,569,686; 7,683,036; 7,750,131; 8,580,756; 9,045,754; 9,428,534; 9,695,418; 10,017,764; 10,260,069; 9,428,534; 8,580,756;

U.S. patent publication Nos. US20050074801, US20090221685; US20090286969, US20100197762, and US20110112170; PCT publication Nos. W02004069991;

W 02005023825; W02008049085 and W02009090182; and EP Patent No. EP2, 149,605, each of which is herein incorporated by reference in its entirety.

[000373] In some embodiments, a gapmer is 10-40 nucleosides in length. For example, a gapmer may be 10-40, 10-35, 10-30, 10-25, 10-20, 10-15, 15-40, 15-35, 15-30, 15-25, 15-20, 20-40, 20-35, 20-30, 20-25, 25-40, 25-35, 25-30, 30-40, 30-35, or 35-40 nucleosides in length. In some embodiments, a gapmer is 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40 nucleosides in length.

[000374] In some embodiments, the gap region Y in a gapmer is 5-20 nucleosides in length. For example, the gap region Y may be 5-20, 5-15, 5-10, 10-20, 10-15, or 15-20 nucleosides in length. In some embodiments, the gap region Y is 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 nucleosides in length. In some embodiments, each nucleoside in the gap region Y is a 2’-deoxyribonucleoside. In some embodiments, all nucleosides in the gap region Y are 2’-deoxyribonucleosides. In some embodiments, one or more of the nucleosides in the gap region Y is a modified nucleoside (e.g., a 2’ modified nucleoside such as those described herein). In some embodiments, one or more cytosines in the gap region Y are optionally 5-methyl-cytosines. In some embodiments, each cytosine in the gap region Y is a 5-methyl-cytosines.

[000375] In some embodiments, the 5’wing region of a gapmer (X in the 5'-X-Y-Z-3' formula) and the 3 ’wing region of a gapmer (Z in the 5'-X-Y-Z-3' formula) are independently 1-20 nucleosides long. For example, the 5’wing region of a gapmer (X in the 5'-X-Y-Z-3' formula) and the 3 ’wing region of the gapmer (Z in the 5'-X-Y-Z-3' formula) may be independently 1-20, 1-15, 1-10, 1-7, 1-5, 1-3, 1-2, 2-5, 2-7, 3-5, 3-7, 5-20, 5-15, 5-10, 10-20,

10-15, or 15-20 nucleosides long. In some embodiments, the 5’wing region of the gapmer (X in the 5'-X-Y-Z-3' formula) and the 3 ’wing region of the gapmer (Z in the 5'-X-Y-Z-3' formula) are independently 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 nucleosides long. In some embodiments, the 5’wing region of the gapmer (X in the 5'-X-Y-Z- 3' formula) and the 3 ’wing region of the gapmer (Z in the 5'-X-Y-Z-3' formula) are of the same length. In some embodiments, the 5’wing region of the gapmer (X in the 5'-X-Y-Z-3' formula) and the 3’wing region of the gapmer (Z in the 5'-X-Y-Z-3' formula) are of different lengths. In some embodiments, the 5’wing region of the gapmer (X in the 5'-X-Y-Z-3' formula) is longer than the 3’wing region of the gapmer (Z in the 5'-X-Y-Z-3' formula). In some embodiments, the 5’wing region of the gapmer (X in the 5'-X-Y-Z-3' formula) is shorter than the 3’wing region of the gapmer (Z in the 5'-X-Y-Z-3' formula).

[000376] In some embodiments, a gapmer comprises a 5'-X-Y-Z-3' of 5-10-5, 4-12-4, 3- 14-3, 2-16-2, 1-18-1, 3-10-3, 2-10-2, 1-10-1, 2-8-2, 4-6-4, 3-6-3, 2-6-2, 4-7-4, 3-7-3, 2-7-2, 4- 8-4, 3-8-3, 2-8-2, 1-8-1, 2-9-2, 1-9-1, 2-10-2, 1-10-1, 1-12-1, 1-16-1, 2-15-1, 1-15-2, 1-14-3, 3- 14-1, 2-14-2, 1-13-4, 4-13-1, 2-13-3, 3-13-2, 1-12-5, 5-12-1, 2-12-4, 4-12-2, 3-12-3, 1-11-6, 6-

11-1, 2-11-5, 5-11-2, 3-11-4, 4-11-3, 1-17-1, 2-16-1, 1-16-2, 1-15-3, 3-15-1, 2-15-2, 1-14-4, 4-

14-1, 2-14-3, 3-14-2, 1-13-5, 5-13-1, 2-13-4, 4-13-2, 3-13-3, 1-12-6, 6-12-1, 2-12-5, 5-12-2, 3-

12-4, 4-12-3, 1-11-7, 7-11-1, 2-11-6, 6-11-2, 3-11-5, 5-11-3, 4-11-4, 1-18-1, 1-17-2, 2-17-1, 1-

16-3, 1-16-3, 2-16-2, 1-15-4, 4-15-1, 2-15-3, 3-15-2, 1-14-5, 5-14-1, 2-14-4, 4-14-2, 3-14-3, 1-

13-6, 6-13-1, 2-13-5, 5-13-2, 3-13-4, 4-13-3, 1-12-7, 7-12-1, 2-12-6, 6-12-2, 3-12-5, 5-12-3, 1-

11-8, 8-11-1, 2-11-7, 7-11-2, 3-11-6, 6-11-3, 4-11-5, 5-11-4, 1-18-1, 1-17-2, 2-17-1, 1-16-3, 3-

16-1, 2-16-2, 1-15-4, 4-15-1, 2-15-3, 3-15-2, 1-14-5, 2-14-4, 4-14-2, 3-14-3, 1-13-6, 6-13-1, 2-

13-5, 5-13-2, 3-13-4, 4-13-3, 1-12-7, 7-12-1, 2-12-6, 6-12-2, 3-12-5, 5-12-3, 1-11-8, 8-11-1, 2-

11-7, 7-11-2, 3-11-6, 6-11-3, 4-11-5, 5-11-4, 1-19-1, 1-18-2, 2-18-1, 1-17-3, 3-17-1, 2-17-2, 1-

16-4, 4-16-1, 2-16-3, 3-16-2, 1-15-5, 2-15-4, 4-15-2, 3-15-3, 1-14-6, 6-14-1, 2-14-5, 5-14-2, 3-

14-4, 4-14-3, 1-13-7, 7-13-1, 2-13-6, 6-13-2, 3-13-5, 5-13-3, 4-13-4, 1-12-8, 8-12-1, 2-12-7, 7-

12-2, 3-12-6, 6-12-3, 4-12-5, 5-12-4, 2-11-8, 8-11-2, 3-11-7, 7-11-3, 4-11-6, 6-11-4, 5-11-5, 1-

20-1, 1-19-2, 2-19-1, 1-18-3, 3-18-1, 2-18-2, 1-17-4, 4-17-1, 2-17-3, 3-17-2, 1-16-5, 2-16-4, 4-

16-2, 3-16-3, 1-15-6, 6-15-1, 2-15-5, 5-15-2, 3-15-4, 4-15-3, 1-14-7, 7-14-1, 2-14-6, 6-14-2, 3-

14-5, 5-14-3, 4-14-4, 1-13-8, 8-13-1, 2-13-7, 7-13-2, 3-13-6, 6-13-3, 4-13-5, 5-13-4, 2-12-8, 8-

12-2, 3-12-7, 7-12-3, 4-12-6, 6-12-4, 5-12-5, 3-11-8, 8-11-3, 4-11-7, 7-11-4, 5-11-6, 6-11-5, 1-

21-1, 1-20-2, 2-20-1, 1-20-3, 3-19-1, 2-19-2, 1-18-4, 4-18-1, 2-18-3, 3-18-2, 1-17-5, 2-17-4, 4- 17-2, 3-17-3, 1-16-6, 6-16-1, 2-16-5, 5-16-2, 3-16-4, 4-16-3, 1-15-7, 7-15-1, 2-15-6, 6-15-2, 3- 15-5, 5-15-3, 4-15-4, 1-14-8, 8-14-1, 2-14-7, 7-14-2, 3-14-6, 6-14-3, 4-14-5, 5-14-4, 2-13-8, 8- 13-2, 3-13-7, 7-13-3, 4-13-6, 6-13-4, 5-13-5, 1-12-10, 10-12-1, 2-12-9, 9-12-2, 3-12-8, 8-12-3, 4-12-7, 7-12-4, 5-12-6, 6-12-5, 4-11-8, 8-11-4, 5-11-7, 7-11-5, 6-11-6, 1-22-1, 1-21-2, 2-21-1,

1-21-3, 3-20-1, 2-20-2, 1-19-4, 4-19-1, 2-19-3, 3-19-2, 1-18-5, 2-18-4, 4-18-2, 3-18-3, 1-17-6,

6-17-1, 2-17-5, 5-17-2, 3-17-4, 4-17-3, 1-16-7, 7-16-1, 2-16-6, 6-16-2, 3-16-5, 5-16-3, 4-16-4,

1-15-8, 8-15-1, 2-15-7, 7-15-2, 3-15-6, 6-15-3, 4-15-5, 5-15-4, 2-14-8, 8-14-2, 3-14-7, 7-14-3,

4-14-6, 6-14-4, 5-14-5, 3-13-8, 8-13-3, 4-13-7, 7-13-4, 5-13-6, 6-13-5, 4-12-8, 8-12-4, 5-12-7,

7-12-5, 6-12-6, 5-11-8, 8-11-5, 6-11-7, or 7-11-6. The numbers indicate the number of nucleosides in X, Y, and Z regions in the 5'-X-Y-Z-3' gapmer.

[000377] In some embodiments, one or more nucleosides in the 5 ’wing region of a gapmer (X in the 5'-X-Y-Z-3' formula) or the 3 ’wing region of a gapmer (Z in the 5'-X-Y-Z-3' formula) are modified nucleotides (e.g., high-affinity modified nucleosides). In some embodiments, the modified nuclsoside (e.g., high-affinity modified nucleosides) is a 2’- modifeid nucleoside. In some embodiments, the 2’ -modified nucleoside is a 2’ -4’ bicyclic nucleoside or a non-bicyclic 2’ -modified nucleoside. In some embodiments, the high-affinity modified nucleoside is a 2’-4’ bicyclic nucleoside (e.g., LNA, cEt, or ENA) or a non-bicyclic 2’-modified nucleoside (e.g., 2’-fluoro (2’-F), 2’-0-methyl (2’-0-Me), 2’-0-methoxyethyl (2’- MOE), 2’-0-aminopropyl (2’-0-AP), 2’-0-dimethylaminoethyl (2’-0-DMAOE), 2’-0- dimethylaminopropyl (2’-0-DMAP), 2’-0-dimethylaminoethyloxyethyl (2’-0-DMAEOE), or 2 ’ -O-N -methylacetamido (2 ’ -O-NMA)) .

[000378] In some embodiments, one or more nucleosides in the 5 ’wing region of a gapmer (X in the 5'-X-Y-Z-3' formula) are high-affinity modified nucleosides. In some embodiments, each nucleoside in the 5’wing region of the gapmer (X in the 5'-X-Y-Z-3' formula) is a high-affinity modified nucleoside. In some embodiments, one or more nucleosides in the 3 ’wing region of a gapmer (Z in the 5'-X-Y-Z-3' formula) are high-affinity modified nucleosides. In some embodiments, each nucleoside in the 3 ’wing region of the gapmer (Z in the 5'-X-Y-Z-3' formula) is a high-affinity modified nucleoside. In some embodiments, one or more nucleosides in the 5’wing region of the gapmer (X in the 5'-X-Y-Z- 3' formula) are high-affinity modified nucleosides and one or more nucleosides in the 3 ’wing region of the gapmer (Z in the 5'-X-Y-Z-3' formula) are high-affinity modified nucleosides. In some embodiments, each nucleoside in the 5’wing region of the gapmer (X in the 5'-X-Y-Z-3' formula) is a high-affinity modified nucleoside and each nucleoside in the 3 ’wing region of the gapmer (Z in the 5'-X-Y-Z-3' formula) is high-affinity modified nucleoside. [000379] In some embodiments, the 5’wing region of a gapmer (X in the 5'-X-Y-Z-3' formula) comprises the same high affinity nucleosides as the 3 ’wing region of the gapmer (Z in the 5'-X-Y-Z-3' formula). For example, the 5’wing region of the gapmer (X in the 5'-X-Y-Z-3' formula) and the 3 ’wing region of the gapmer (Z in the 5'-X-Y-Z-3' formula) may comprise one or more non-bicyclic 2’-modified nucleosides (e.g., 2’-MOE or 2’-0-Me). In another example, the 5’wing region of the gapmer (X in the 5'-X-Y-Z-3' formula) and the 3’wing region of the gapmer (Z in the 5'-X-Y-Z-3' formula) may comprise one or more 2’ -4’ bicyclic nucleosides (e.g., LNA or cEt). In some embodiments, each nucleoside in the 5’wing region of the gapmer (X in the 5'-X-Y-Z-3' formula) and the 3’wing region of the gapmer (Z in the 5'-X- Y-Z-3' formula) is a non-bicyclic 2’-modified nucleosides (e.g., 2’-MOE or 2’-0-Me). In some embodiments, each nucleoside in the 5’wing region of the gapmer (X in the 5'-X-Y-Z-3' formula) and the 3’wing region of the gapmer (Z in the 5'-X-Y-Z-3' formula) is a 2’-4’ bicyclic nucleosides (e.g., LNA or cEt).

[000380] In some embodiments, a gapmer comprises a 5'-X-Y-Z-3' configuration, wherein X and Z is independently 1-7 (e.g., 1, 2, 3, 4, 5, 6, or 7) nucleosides in length and Y is 6-10 (e.g., 6, 7, 8, 9, or 10) nucleosides in length, wherein each nucleoside in X and Z is a non- bicyclic 2’-modified nucleosides (e.g., 2’-MOE or 2’-0-Me) and each nucleoside in Y is a 2’- deoxyribonucleoside. In some embodiments, the gapmer comprises a 5'-X-Y-Z-3' configuration, wherein X and Z is independently 1-7 (e.g., 1, 2, 3, 4, 5, 6, or 7) nucleosides in length and Y is 6-10 (e.g., 6, 7, 8, 9, or 10) nucleosides in length, wherein each nucleoside in X and Z is a 2’-4’ bicyclic nucleosides (e.g., LNA or cEt) and each nucleoside in Y is a 2’- deoxyribonucleoside. In some embodiments, the 5’wing region of the gapmer (X in the 5'-X- Y-Z-3' formula) comprises different high affinity nucleosides as the 3’wing region of the gapmer (Z in the 5'-X-Y-Z-3' formula). For example, the 5’wing region of the gapmer (X in the 5'-X-Y-Z-3' formula) may comprise one or more non-bicyclic 2’ -modified nucleosides (e.g., 2’-MOE or 2’-0-Me) and the 3’wing region of the gapmer (Z in the 5'-X-Y-Z-3' formula) may comprise one or more 2’-4’ bicyclic nucleosides (e.g., LNA or cEt). In another example, the 3’wing region of the gapmer (Z in the 5'-X-Y-Z-3' formula) may comprise one or more non-bicyclic 2’-modified nucleosides (e.g., 2’-MOE or 2’-0-Me) and the 5’wing region of the gapmer (X in the 5'-X-Y-Z-3' formula) may comprise one or more 2’ -4’ bicyclic nucleosides (e.g., LNA or cEt).

[000381] In some embodiments, a gapmer comprises a 5'-X-Y-Z-3' configuration, wherein X and Z is independently 1-7 (e.g., 1, 2, 3, 4, 5, 6, or 7) nucleosides in length and Y is 6-10 (e.g., 6, 7, 8, 9, or 10) nucleosides in length, wherein each nucleoside in X is a non- bicyclic 2’-modified nucleosides (e.g., 2’-MOE or 2’-0-Me), each nucleoside in Z is a 2’-4’ bicyclic nucleosides (e.g., LNA or cEt), and each nucleoside in Y is a 2’-deoxyribonucleoside. In some embodiments, the gapmer comprises a 5'-X-Y-Z-3' configuration, wherein X and Z is independently 1-7 (e.g., 1, 2, 3, 4, 5, 6, or 7) nucleosides in length and Y is 6-10 (e.g., 6, 7, 8,

9, or 10) nucleosides in length, wherein each nucleoside in X is a 2’-4’ bicyclic nucleosides (e.g., LNA or cEt), each nucleoside in Z is a non-bicyclic 2’-modified nucleosides (e.g., 2’- MOE or 2’-0-Me) and each nucleoside in Y is a 2’-deoxyribonucleoside.

[000382] In some embodiments, the 5’wing region of a gapmer (X in the 5'-X-Y-Z-3' formula) comprises one or more non-bicyclic 2’-modified nucleosides (e.g., 2’-MOE or 2’-0- Me) and one or more 2’-4’ bicyclic nucleosides (e.g., LNA or cEt). In some embodiments, the 3 ’wing region of the gapmer (Z in the 5'-X-Y-Z-3' formula) comprises one or more non- bicyclic 2’-modified nucleosides (e.g., 2’-MOE or 2’-0-Me) and one or more 2’-4’ bicyclic nucleosides (e.g., LNA or cEt). In some embodiments, both the 5’wing region of the gapmer (X in the 5'-X-Y-Z-3' formula) and the 3 ’wing region of the gapmer (Z in the 5'-X-Y-Z-3' formula) comprise one or more non-bicyclic 2’-modified nucleosides (e.g., 2’-MOE or 2’-0- Me) and one or more 2’-4’ bicyclic nucleosides (e.g., LNA or cEt).

[000383] In some embodiments, a gapmer comprises a 5'-X-Y-Z-3' configuration, wherein X and Z is independently 2-7 (e.g., 2, 3, 4, 5, 6, or 7) nucleosides in length and Y is 6- 10 (e.g., 6, 7, 8, 9, or 10) nucleosides in length, wherein at least one but not all (e.g., 1, 2, 3, 4,

5, or 6) of positions 1, 2, 3, 4, 5, 6, or 7 in X (the 5’ most position is position 1) is a non- bicyclic 2’-modified nucleoside (e.g., 2’-MOE or 2’-0-Me), wherein the rest of the nucleosides in both X and Z are 2’ -4’ bicyclic nucleosides (e.g., LNA or cEt), and wherein each nucleoside in Y is a 2’deoxyribonucleoside. In some embodiments, the gapmer comprises a 5'-X-Y-Z-3' configuration, wherein X and Z is independently 2-7 (e.g., 2, 3, 4, 5, 6, or 7) nucleosides in length and Y is 6-10 (e.g., 6, 7, 8, 9, or 10) nucleosides in length, wherein at least one but not all (e.g., 1, 2, 3, 4, 5, or 6) of positions 1, 2, 3, 4, 5, 6, or 7 in Z (the 5’ most position is position 1) is a non-bicyclic 2’-modified nucleoside (e.g., 2’-MOE or 2’-0-Me), wherein the rest of the nucleosides in both X and Z are 2’-4’ bicyclic nucleosides (e.g., LNA or cEt), and wherein each nucleoside in Y is a 2’deoxyribonucleoside. In some embodiments, the gapmer comprises a 5'-X-Y-Z-3' configuration, wherein X and Z is independently 2-7 (e.g., 2, 3, 4, 5,

6, or 7) nucleosides in length and Y is 6-10 (e.g., 6, 7, 8, 9, or 10) nucleosides in length, wherein at least one but not all (e.g., 1, 2, 3, 4, 5, or 6) of positions 1, 2, 3, 4, 5, 6, or 7 in X and at least one of positions but not all (e.g., 1, 2, 3, 4, 5, or 6) 1, 2, 3, 4, 5, 6, or 7 in Z (the 5’ most position is position 1) is a non-bicyclic 2’-modified nucleoside (e.g., 2’-MOE or 2’-0-Me), wherein the rest of the nucleosides in both X and Z are 2’ -4’ bicyclic nucleosides (e.g., LNA or cEt), and wherein each nucleoside in Y is a 2’deoxyribonucleoside.

[000384] Non-limiting examples of gapmers configurations with a mix of non-bicyclic 2’-modified nucleoside (e.g., 2’-MOE or 2’-0-Me) and 2’-4’ bicyclic nucleosides (e.g., LNA or cEt) in the 5 ’wing region of the gapmer (X in the 5'-X-Y-Z-3' formula) and/or the 3 ’wing region of the gapmer (Z in the 5'-X-Y-Z-3' formula) include: BBB-(D)n-BBBAA; KKK-(D)n- KKKAA; LLL-(D)n-LLLAA; BBB-(D)n-BBBEE; KKK-(D)n-KKKEE ; LLL-(D)n-LLLEE; BBB-(D)n-BBBAA; KKK-(D)n-KKKAA; LLL-(D)n-LLLAA; BBB-(D)n-BBBEE; KKK- (D)n-KKKEE; LLL-(D)n-LLLEE; BBB-(D)n-BBBAAA; KKK- (D)n- KKKA A A ; LLL-(D)n- LLLAAA; BBB-(D)n-BBBEEE; KKK-(D)n-KKKEEE; LLL-(D)n-LLLEEE; BBB-(D)n- BBBAAA; KKK-(D)n-KKKAAA; LLL-(D)n-LLLAAA; BBB-(D)n-BBBEEE; KKK-(D)n- KKKEEE; LLL- (D)n- LLLEEE ; B AB A-(D)n- AB AB ; KAKA-(D)n-AKAK; LALA-(D)n- ALAL; BEBE-(D)n-EBEB ; KEKE-(D)n-EKEK; LELE-(D)n-ELEL; BABA-(D)n-ABAB; KAKA-(D)n-AKAK; LALA-(D)n-ALAL; BEBE-(D)n-EBEB ; KEKE-(D)n-EKEK; LELE- (D)n-ELEL; ABAB-(D)n-ABAB; AKAK-(D)n-AKAK; ALAL-(D)n-ALAL; EBEB-(D)n- EBEB; EKEK-(D)n-EKEK; ELEL-(D)n-ELEL; ABAB-(D)n-ABAB; AKAK-(D)n-AKAK; ALAL-(D)n-ALAL; EBEB-(D)n-EBEB ; EKEK-(D)n-EKEK; ELEL-(D)n-ELEL; AABB- (D)n-BBAA; BB AA-(D)n- AABB ; AAKK-(D)n-KKAA; AALL-(D)n-LLAA; EEBB-(D)n- BBEE; EEKK-(D)n-KKEE; EELL-(D)n-LLEE; AABB-(D)n-BBAA; AAKK-(D)n-KKAA; AALL-(D)n-LLAA; EEBB-(D)n-BBEE; EEKK-(D)n-KKEE; EELL-(D)n-LLEE; BBB-(D)n- BBA; KKK-(D)n-KKA; LLL-(D)n-LLA; BBB-(D)n-BBE; KKK-(D)n-KKE; LLL-(D)n-LLE; BBB-(D)n-BBA; KKK-(D)n-KKA; LLL-(D)n-LLA; BBB-(D)n-BBE; KKK-(D)n-KKE; LLL- (D)n-LLE; BBB-(D)n-BBA; KKK-(D)n-KKA; LLL-(D)n-LLA; BBB-(D)n-BBE; KKK-(D)n- KKE; LLL-(D)n-LLE; ABBB-(D)n-BBBA; AKKK-(D)n-KKKA; ALLL-(D)n-LLLA; EBBB- (D)n-BBBE; EKKK-(D)n-KKKE; ELLL-(D)n-LLLE; ABBB-(D)n-BBBA; AKKK-(D)n- KKKA; ALLL-(D)n-LLLA; EBBB-(D)n-BBBE; EKKK-(D)n-KKKE; ELLL-(D)n-LLLE; ABBB-(D)n-BBBAA; AKKK- (D )n- KKKA A ; ALLL-(D)n-LLLAA; EBBB-(D)n-BBBEE; EKKK- (D)n- KKKEE ; ELLL-(D)n-LLLEE; ABBB-(D)n-BBBAA; AKKK-(D)n-KKKAA; ALLL- (D )n-LLLA A ; EBBB-(D)n-BBBEE; EKKK-(D)n-KKKEE ; ELLL- (D)n-LLLEE ; AABBB-(D)n-BBB; AAKKK-(D)n-KKK; AALLL-(D)n-LLL; EEBBB-(D)n-BBB; EEKKK- (D)n-KKK; EELLL-(D)n-LLL; AABBB-(D)n-BBB; AAKKK-(D)n-KKK; AALLL-(D)n-LLL; EEBBB-(D)n-BBB; EEKKK-(D)n-KKK; EELLL-(D)n-LLL; AABBB-(D)n-BBBA; AAKKK- (D)n-KKKA; AALLL-(D)n-LLLA; EEBBB-(D)n-BBBE; EEKKK-(D)n-KKKE; EELLL- (D)n-LLLE; AABBB-(D)n-BBBA; AAKKK-(D)n-KKKA; AALLL-(D)n-LLLA; EEBBB- (D)n-BBBE; EEKKK- (D )n- KKKE ; EELLL-(D)n-LLLE; ABBAABB-(D)n-BB; AKKAAKK- (D)n-KK; ALLAALLL-(D)n-LL; EBBEEBB-(D)n-BB; EKKEEKK-(D)n-KK; ELLEELL- (D)n-LL; AB B AAB B -(D)n-B B ; AKKAAKK-(D)n-KK; ALLAALL-(D)n-LL; EBBEEBB- (D)n-BB; EKKEEKK-(D)n-KK; ELLEELL-(D)n-LL; ABBABB-(D)n-BBB; AKKAKK-(D)n- KKK; ALLALLL-(D)n-LLL; EBBEBB-(D)n-BBB; EKKEKK- (D )n- KKK ; ELLELL-(D)n- LLL; ABBABB-(D)n-BBB; AKKAKK-(D)n-KKK; ALLALL-(D)n-LLL; EBBEBB-(D)n- BBB; EKKEKK-(D)n-KKK; ELLELL-(D)n-LLL; EEEK-(D)n-EEEEEEEE; EEK-(D)n- EEEEEEEEE; EK-(D)n-EEEEEEEEEE; EK-(D)n-EEEKK; K-(D)n-EEEKEKE; K-(D)n- EEEKEKEE; K-(D)n-EEKEK; EK-(D)n-EEEEKEKE; EK-(D)n-EEEKEK; EEK-(D)n- KEEKE; EK-(D)n-EEKEK; EK-(D)n-KEEK; EEK-(D)n-EEEKEK; EK-(D)n-KEEEKEE; EK- (D)n-EEKEKE; EK-(D)n-EEEKEKE; and EK-(D)n-EEEEKEK; . “A” nucleosides comprise a 2'-modified nucleoside; “B” represents a 2’-4’ bicyclic nucleoside; “K” represents a constrained ethyl nucleoside (cEt); “L” represents an LNA nucleoside; and “E” represents a 2'- MOE modified ribonucleoside; “D” represents a 2’-deoxyribonucleoside; “n” represents the length of the gap segment (Y in the 5'-X-Y-Z-3' configuration) and is an integer between 1-20. [000385] In some embodiments, any one of the gapmers described herein comprises one or more modified nucleoside linkages (e.g., a phosphorothioate linkage) in each of the X, Y, and Z regions. In some embodiments, each intemucleoside linkage in the any one of the gapmers described herein is a phosphorothioate linkage. In some embodiments, each of the X, Y, and Z regions independently comprises a mix of phosphorothioate linkages and phosphodiester linkages. In some embodiments, each intemucleoside linkage in the gap region Y is a phosphorothioate linkage, the 5’wing region X comprises a mix of phosphorothioate linkages and phosphodiester linkages, and the 3 ’wing region Z comprises a mix of phosphorothioate linkages and phosphodiester linkages. i. Mixmers

[000386] In some embodiments, an oligonucleotide described herein may be a mixmer or comprise a mixmer sequence pattern. In general, mixmers are oligonucleotides that comprise both naturally and non-naturally occurring nucleosides or comprise two different types of non- naturally occurring nucleosides typically in an alternating pattern. Mixmers generally have higher binding affinity than unmodified oligonucleotides and may be used to specifically bind a target molecule, e.g., to block a binding site on the target molecule. Generally, mixmers do not recruit an RNase to the target molecule and thus do not promote cleavage of the target molecule. Such oligonucleotides that are incapable of recruiting RNase H have been described, for example, see W02007/112754 or W02007/112753.

[000387] In some embodiments, the mixmer comprises or consists of a repeating pattern of nucleoside analogues and naturally occurring nucleosides, or one type of nucleoside analogue and a second type of nucleoside analogue. However, a mixmer need not comprise a repeating pattern and may instead comprise any arrangement of modified nucleoside s and naturally occurring nucleoside s or any arrangement of one type of modified nucleoside and a second type of modified nucleoside. The repeating pattern, may, for instance be every second or every third nucleoside is a modified nucleoside, such as LNA, and the remaining nucleoside s are naturally occurring nucleosides, such as DNA, or are a 2' substituted nucleoside analogue such as 2'-MOE or 2' fluoro analogues, or any other modified nucleoside described herein. It is recognized that the repeating pattern of modified nucleoside, such as LNA units, may be combined with modified nucleoside at fixed positions — e.g. at the 5' or 3' termini.

[000388] In some embodiments, a mixmer does not comprise a region of more than 5, more than 4, more than 3, or more than 2 consecutive naturally occurring nucleosides, such as DNA nucleosides. In some embodiments, the mixmer comprises at least a region consisting of at least two consecutive modified nucleoside, such as at least two consecutive LNAs. In some embodiments, the mixmer comprises at least a region consisting of at least three consecutive modified nucleoside units, such as at least three consecutive LNAs.

[000389] In some embodiments, the mixmer does not comprise a region of more than 7, more than 6, more than 5, more than 4, more than 3, or more than 2 consecutive nucleoside analogues, such as LNAs. In some embodiments, LNA units may be replaced with other nucleoside analogues, such as those referred to herein.

[000390] Mixmers may be designed to comprise a mixture of affinity enhancing modified nucleosides, such as in non-limiting example LNA nucleosides and 2’-0-Me nucleosides. In some embodiments, a mixmer comprises modified internucleoside linkages (e.g., phosphorothioate internucleoside linkages or other linkages) between at least two, at least three, at least four, at least five or more nucleosides.

[000391] A mixmer may be produced using any suitable method. Representative U.S. patents, U.S. patent publications, and PCT publications that teach the preparation of mixmers include U.S. patent publication Nos. US20060128646, US20090209748, US20090298916, US20110077288, and US20120322851, and U.S. patent No. 7687617.

[000392] In some embodiments, a mixmer comprises one or more morpholino nucleosides. Lor example, in some embodiments, a mixmer may comprise morpholino nucleosides mixed (e.g., in an alternating manner) with one or more other nucleosides (e.g., DNA, RNA nucleosides) or modified nucleosides (e.g., LNA, 2’-0-Me nucleosides).

[000393] In some embodiments, mixmers are useful for splice correcting or exon skipping, for example, as reported in Touznik A., et ah, LNA/DNA mixmer-based antisense oligonucleotides correct alternative splicing of the SMN2 gene and restore SMN protein expression in type 1 SMA fibroblasts Scientific Reports, volume 7, Article number: 3672 (2017), Chen S. et ah, Synthesis of a Morpholino Nucleic Acid (MNA)-Uridine Phosphoramidite, and Exon Skipping U sing MN A/2' -O-Methyl Mixmer Antisense Oligonucleotide, Molecules 2016, 21, 1582, the contents of each which are incorporated herein by reference. j. RNA Interference (RNAi)

[000394] In some embodiments, oligonucleotides provided herein may be in the form of small interfering RNAs (siRNA), also known as short interfering RNA or silencing RNA. SiRNA, is a class of double- stranded RNA molecules, typically about 20-25 base pairs in length that target nucleic acids (e.g., mRNAs) for degradation via the RNA interference (RNAi) pathway in cells. Specificity of siRNA molecules may be determined by the binding of the antisense strand of the molecule to its target RNA. Effective siRNA molecules are generally less than 30 to 35 base pairs in length to prevent the triggering of non-specific RNA interference pathways in the cell via the interferon response, although longer siRNA can also be effective. In some embodiments, the siRNA molecules are 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 35, 40, 45, 50, or more base pairs in length. In some embodiments, the siRNA molecules are 8 to 30 base pairs in length, 10 to 15 base pairs in length, 10 to 20 base pairs in length, 15 to 25 base pairs in length, 19 to 21 base pairs in length, 21 to 23 base pairs in length.

[000395] Following selection of an appropriate target RNA sequence, siRNA molecules that comprise a nucleotide sequence complementary to all or a portion of the target sequence, i.e. an antisense sequence, can be designed and prepared using appropriate methods (see, e.g., PCT Publication Number WO 2004/016735; and U.S. Patent Publication Nos. 2004/0077574 and 2008/0081791). The siRNA molecule can be double stranded (i.e. a dsRNA molecule comprising an antisense strand and a complementary sense strand strand that hybridizes to form the dsRNA) or single-stranded (i.e. a ssRNA molecule comprising just an antisense strand). The siRNA molecules can comprise a duplex, asymmetric duplex, hairpin or asymmetric hairpin secondary structure, having self-complementary sense and antisense strands.

[000396] In some embodiments, the antisense strand of the siRNA molecule is 7, 8, 9, 10,

11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 35, 40, 45, 50, or more nucleotides in length. In some embodiments, the antisense strand is 8 to 50 nucleotides in length, 8 to 40 nucleotides in length, 8 to 30 nucleotides in length, 10 to 15 nucleotides in length, 10 to 20 nucleotides in length, 15 to 25 nucleotides in length, 19 to 21 nucleotides in length, 21 to 23 nucleotides in lengths.

[000397] In some embodiments, the sense strand of the siRNA molecule is 7, 8, 9, 10, 11,

12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 35, 40, 45, 50, or more nucleotides in length. In some embodiments, the sense strand is 8 to 50 nucleotides in length,

8 to 40 nucleotides in length, 8 to 30 nucleotides in length, 10 to 15 nucleotides in length, 10 to 20 nucleotides in length, 15 to 25 nucleotides in length, 19 to 21 nucleotides in length, 21 to 23 nucleotides in lengths.

[000398] In some embodiments, siRNA molecules comprise an antisense strand comprising a region of complementarity to a target region in a target mRNA. In some embodiments, the region of complementarity is at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99% or 100% complementary to a target region in a target mRNA. In some embodiments, the target region is a region of consecutive nucleotides in the target mRNA. In some embodiments, a complementary nucleotide sequence need not be 100% complementary to that of its target to be specifically hybridizable or specific for a target RNA sequence. [000399] In some embodiments, siRNA molecules comprise an antisense strand that comprises a region of complementarity to a target RNA sequence and the region of complementarity is in the range of 8 to 15, 8 to 30, 8 to 40, or 10 to 50, or 5 to 50, or 5 to 40 nucleotides in length. In some embodiments, a region of complementarity is 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35,

36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50 nucleotides in length. In some embodiments, the region of complementarity is complementary with at least 6, at least 7, at least 8, at least 9, at least 10, at least 11, at least 12, at least 13, at least 14, at least 15, at least 16, at least 17, at least 18, at least 19, at least 20, at least 21, at least 22, at least 23, at least 24, at least 25 or more consecutive nucleotides of a target RNA sequence. In some embodiments, siRNA molecules comprise a nucleotide sequence that contains no more than 1, 2, 3, 4, or 5 base mismatches compared to the portion of the consecutive nucleotides of target RNA sequence. In some embodiments, siRNA molecules comprise a nucleotide sequence that has up to 3 mismatches over 15 bases, or up to 2 mismatches over 10 bases.

[000400] In some embodiments, siRNA molecules comprise an antisense strand comprising a nucleotide sequence that is complementary (e.g., at least 85%, at least 90%, at least 95%, or 100%) to the target RNA sequence of the oligonucleotides provided herein. In some embodiments, siRNA molecules comprise an antisense strand comprising a nucleotide sequence that is at least 85%, at least 90%, at least 95%, or 100% identical to the oligonucleotides provided herein. In some embodiments, siRNA molecules comprise an antisense strand comprising at least 6, at least 7, at least 8, at least 9, at least 10, at least 11, at least 12, at least 13, at least 14, at least 15, at least 16, at least 17, at least 18, at least 19, at least 20, at least 21, at least 22, at least 23, at least 24, at least 25 or more consecutive nucleotides of the oligonucleotides provided herein.

[000401] Double-stranded siRNA may comprise sense and anti-sense RNA strands that are the same length or different lengths. Double- stranded siRNA molecules can also be assembled from a single oligonucleotide in a stem-loop structure, wherein self-complementary sense and antisense regions of the siRNA molecule are linked by means of a nucleic acid based or non-nucleic acid-based linker(s), as well as circular single- stranded RNA having two or more loop structures and a stem comprising self-complementary sense and antisense strands, wherein the circular RNA can be processed either in vivo or in vitro to generate an active siRNA molecule capable of mediating RNAi. Small hairpin RNA (shRNA) molecules thus are also contemplated herein. These molecules comprise a specific antisense sequence in addition to the reverse complement (sense) sequence, typically separated by a spacer or loop sequence. Cleavage of the spacer or loop provides a single- stranded RNA molecule and its reverse complement, such that they may anneal to form a dsRNA molecule (optionally with additional processing steps that may result in addition or removal of one, two, three or more nucleotides from the 3' end and/or (e.g., and) the 5' end of either or both strands). A spacer can be of a sufficient length to permit the antisense and sense sequences to anneal and form a double- stranded structure (or stem) prior to cleavage of the spacer (and, optionally, subsequent processing steps that may result in addition or removal of one, two, three, four, or more nucleotides from the 3' end and/or (e.g., and) the 5' end of either or both strands). A spacer sequence is may be an unrelated nucleotide sequence that is situated between two complementary nucleotide sequence regions which, when annealed into a double-stranded nucleic acid, comprise a shRNA. [000402] The overall length of the siRNA molecules can vary from about 14 to about 100 nucleotides depending on the type of siRNA molecule being designed. Generally between about 14 and about 50 of these nucleotides are complementary to the RNA target sequence, i.e. constitute the specific antisense sequence of the siRNA molecule. For example, when the siRNA is a double- or single-stranded siRNA, the length can vary from about 14 to about 50 nucleotides, whereas when the siRNA is a shRNA or circular molecule, the length can vary from about 40 nucleotides to about 100 nucleotides.

[000403] An siRNA molecule may comprise a 3' overhang at one end of the molecule, The other end may be blunt-ended or have also an overhang (5' or 3')· When the siRNA molecule comprises an overhang at both ends of the molecule, the length of the overhangs may be the same or different. In one embodiment, the siRNA molecule of the present disclosure comprises 3' overhangs of about 1 to about 3 nucleotides on both ends of the molecule. In some embodiments, the siRNA molecule comprises 3’ overhangs of about 1 to about 3 nucleotides on the sense strand. In some embodiments, the siRNA molecule comprises 3’ overhangs of about 1 to about 3 nucleotides on the antisense strand. In some embodiments, the siRNA molecule comprises 3’ overhangs of about 1 to about 3 nucleotides on both the sense strand and the antisense strand.

[000404] In some embodiments, the siRNA molecule comprises one or more modified nucleotides (e.g. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more). In some embodiments, the siRNA molecule comprises one or more modified nucleotides and/or (e.g., and) one or more modified intemucleotide linkages. In some embodiments, the modified nucleotide is a modified sugar moiety (e.g. a 2’ modified nucleotide). In some embodiments, the siRNA molecule comprises one or more 2’ modified nucleotides, e.g., a 2'-deoxy, 2'-fluoro (2’-F), 2'-0-methyl (2’-0-Me), 2'-0-methoxyethyl (2'-MOE), 2'-0-aminopropyl (2'-0-AP), 2'-0-dimethylaminoethyl (2'-0- DMAOE), 2'-0-dimethylaminopropyl (2'-0-DMAP), 2'-0-dimethylaminoethyloxyethyl (2'-0- DMAEOE), or 2'-0— N-methylacetamido (2'-0— NMA). In some embodiments, each nucleotide of the siRNA molecule is a modified nucleotide (e.g., a 2’ -modified nucleotide). In some embodiments, the siRNA molecule comprises one or more phosphorodiamidate morpholinos. In some embodiments, each nucleotide of the siRNA molecule is a phosphorodiamidate morpholino.

[000405] In some embodiments, the siRNA molecule contains a phosphorothioate or other modified intemucleotide linkage. In some embodiments, the siRNA molecule comprises phosphorothioate internucleoside linkages. In some embodiments, the siRNA molecule comprises phosphorothioate internucleoside linkages between at least two nucleotides. In some embodiments, the siRNA molecule comprises phosphorothioate intemucleoside linkages between all nucleotides. For example, in some embodiments, the siRNA molecule comprises modified intemucleotide linkages at the first, second, and/or (e.g., and) third intemucleoside linkage at the 5' or 3' end of the siRNA molecule.

[000406] In some embodiments, the modified intemucleotide linkages are phosphorus- containing linkages. In some embodiments, phosphorus-containing linkages that may be used include, but are not limited to, phosphorothioates, chiral phosphorothioates, phosphorodithioates, phosphotriesters, aminoalkylphosphotriesters, methyl and other alkyl phosphonates comprising 3'alkylene phosphonates and chiral phosphonates, phosphinates, phosphoramidates comprising 3 '-amino phosphoramidate and aminoalkylphosphoramidates, thionophosphoramidates, thionoalkylphosphonates, thionoalkylphosphotriesters, and boranophosphates having normal 3'-5' linkages, 2'-5' linked analogs of these, and those having inverted polarity wherein the adjacent pairs of nucleoside units are linked 3'-5' to 5'-3' or 2'-5' to 5'-2'; see US patent nos. 3,687,808; 4,469,863; 4,476,301; 5,023,243; 5, 177,196; 5,188,897; 5,264,423; 5,276,019; 5,278,302; 5,286,717; 5,321,131; 5,399,676; 5,405,939; 5,453,496; 5,455, 233; 5,466,677; 5,476,925; 5,519,126; 5,536,821; 5,541,306; 5,550,111; 5,563, 253; 5,571,799; 5,587,361; and 5,625,050.

[000407] Any of the modified chemistries or formats of siRNA molecules described herein can be combined with each other. For example, one, two, three, four, five, or more different types of modifications can be included within the same siRNA molecule.

[000408] In some embodiments, the antisense strand comprises one or more modified nucleotides (e.g. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more). In some embodiments, the antisense strand comprises one or more modified nucleotides and/or (e.g., and) one or more modified intemucleotide linkages. In some embodiments, the modified nucleotide comprises a modified sugar moiety (e.g. a 2’ modified nucleotide). In some embodiments, the antisense strand comprises one or more 2’ modified nucleotides, e.g., a 2'-deoxy, 2'-fluoro (2’-F), 2'-0-methyl (2’-0-Me), 2'-0-methoxyethyl (2'-MOE), 2'-0-aminopropyl (2'-0-AP), 2'-0- dimethylaminoethyl (2'-0-DMAOE), 2'-0-dimethylaminopropyl (2'-0-DMAP), 2'-0- dimethylaminoethyloxyethyl (2'-0-DMAEOE), or 2'-0— N-methylacetamido (2'-0— NMA). In some embodiments, each nucleotide of the antisense strand is a modified nucleotide (e.g., a 2’- modified nucleotide). In some embodiments, the antisense strand comprises one or more phosphorodiamidate morpholinos. In some embodiments, the antisense strand is a phosphorodiamidate morpholino oligomer (PMO). [000409] In some embodiments, antisense strand contains a phosphorothioate or other modified intemucleotide linkage. In some embodiments, the antisense strand comprises phosphorothioate internucleoside linkages. In some embodiments, the antisense strand comprises phosphorothioate internucleoside linkages between at least two nucleotides. In some embodiments, the antisense strand comprises phosphorothioate internucleoside linkages between all nucleotides. For example, in some embodiments, the antisense strand comprises modified intemucleotide linkages at the first, second, and/or (e.g., and) third intemucleoside linkage at the 5' or 3' end of the siRNA molecule. In some embodiments, the modified intemucleotide linkages are phosphoms-containing linkages. In some embodiments, phosphorus-containing linkages that may be used include, but are not limited to, phosphorothioates, chiral phosphorothioates, phosphorodithioates, phosphotriesters, aminoalkylphosphotriesters, methyl and other alkyl phosphonates comprising 3'alkylene phosphonates and chiral phosphonates, phosphinates, phosphoramidates comprising 3'-amino phosphoramidate and aminoalkylphosphoramidates, thionophosphoramidates, thionoalkylphosphonates, thionoalkylphosphotriesters, and boranophosphates having normal 3'-5' linkages, 2'-5' linked analogs of these, and those having inverted polarity wherein the adjacent pairs of nucleoside units are linked 3'-5' to 5'-3' or 2'-5' to 5'-2'; see US patent nos. 3,687,808; 4,469,863; 4,476,301; 5,023,243; 5, 177,196; 5,188,897; 5,264,423; 5,276,019; 5,278,302; 5,286,717; 5,321,131; 5,399,676; 5,405,939; 5,453,496; 5,455, 233; 5,466,677; 5,476,925; 5,519,126; 5,536,821; 5,541,306; 5,550,111; 5,563, 253; 5,571,799; 5,587,361; and

5,625,050.

[000410] Any of the modified chemistries or formats of the antisense strand described herein can be combined with each other. For example, one, two, three, four, five, or more different types of modifications can be included within the same antisense strand.

[000411] In some embodiments, the sense strand comprises one or more modified nucleotides (e.g. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more). In some embodiments, the sense strand comprises one or more modified nucleotides and/or (e.g., and) one or more modified intemucleotide linkages. In some embodiments, the modified nucleotide is a modified sugar moiety (e.g. a 2’ modified nucleotide). In some embodiments, the sense strand comprises one or more 2’ modified nucleotides, e.g., a 2'-deoxy, 2'-fluoro (2’-F), 2'-0-methyl (2’-0-Me), 2'- O-methoxyethyl (2'-MOE), 2'-0-aminopropyl (2'-0-AP), 2'-0-dimethylaminoethyl (2'-0- DMAOE), 2'-0-dimethylaminopropyl (2'-0-DMAP), 2'-0-dimethylaminoethyloxyethyl (2'-0- DMAEOE), or 2'-0— N-methylacetamido (2'-0— NMA). In some embodiments, each nucleotide of the sense strand is a modified nucleotide (e.g., a 2’ -modified nucleotide). In some embodiments, the sense strand comprises one or more phosphorodiamidate morpholinos. In some embodiments, the antisense strand is a phosphorodiamidate morpholino oligomer (PMO). In some embodiments, the sense strand contains a phosphorothioate or other modified intemucleotide linkage. In some embodiments, the sense strand comprises phosphorothioate intemucleoside linkages. In some embodiments, the sense strand comprises phosphorothioate intemucleoside linkages between at least two nucleotides. In some embodiments, the sense strand comprises phosphorothioate intemucleoside linkages between all nucleotides. For example, in some embodiments, the sense strand comprises modified intemucleotide linkages at the first, second, and/or (e.g., and) third intemucleoside linkage at the 5' or 3' end of the sense strand.

[000412] In some embodiments, the modified intemucleotide linkages are phosphorus- containing linkages. In some embodiments, phosphorus-containing linkages that may be used include, but are not limited to, phosphorothioates, chiral phosphorothioates, phosphorodithioates, phosphotriesters, aminoalkylphosphotriesters, methyl and other alkyl phosphonates comprising 3'alkylene phosphonates and chiral phosphonates, phosphinates, phosphoramidates comprising 3 '-amino phosphoramidate and aminoalkylphosphoramidates, thionophosphoramidates, thionoalkylphosphonates, thionoalkylphosphotriesters, and boranophosphates having normal 3'-5' linkages, 2'-5' linked analogs of these, and those having inverted polarity wherein the adjacent pairs of nucleoside units are linked 3'-5' to 5'-3' or 2'-5' to 5'-2'; see US patent nos. 3,687,808; 4,469,863; 4,476,301; 5,023,243; 5, 177,196; 5,188,897; 5,264,423; 5,276,019; 5,278,302; 5,286,717; 5,321,131; 5,399,676; 5,405,939; 5,453,496; 5,455, 233; 5,466,677; 5,476,925; 5,519,126; 5,536,821; 5,541,306; 5,550,111; 5,563, 253; 5,571,799; 5,587,361; and 5,625,050.

[000413] Any of the modified chemistries or formats of the sense strand described herein can be combined with each other. For example, one, two, three, four, five, or more different types of modifications can be included within the same sense strand.

[000414] In some embodiments, the antisense or sense strand of the siRNA molecule comprises modifications that enhance or reduce RNA-induced silencing complex (RISC) loading. In some embodiments, the antisense strand of the siRNA molecule comprises modifications that enhance RISC loading. In some embodiments, the sense strand of the siRNA molecule comprises modifications that reduce RISC loading and reduce off-target effects. In some embodiments, the antisense strand of the siRNA molecule comprises a 2'-0- methoxyethyl (2’-MOE) modification. The addition of the 2'-0-methoxyethyl (2’-MOE) group at the cleavage site improves both the specificity and silencing activity of siRNAs by facilitating the oriented RNA-induced silencing complex (RISC) loading of the modified strand, as described in Song et ah, (2017) Mol Ther Nucleic Acids 9:242-250, incorporated herein by reference in its entirety. In some embodiments, the antisense strand of the siRNA molecule comprises a 2'-OMe-phosphorodithioate modification, which increases RISC loading as described in Wu et ah, (2014) Nat Commun 5:3459, incorporated herein by reference in its entirety.

[000415] In some embodiments, the sense strand of the siRNA molecule comprises a 5’- morpholino, which reduces RISC loading of the sense strand and improves antisense strand selection and RNAi activity, as described in Kumar et al., (2019) Chem Commun (Camb) 55(35):5139-5142, incorporated herein by reference in its entirety. In some embodiments, the sense strand of the siRNA molecule is modified with a synthetic RNA-like high affinity nucleotide analogue, Locked Nucleic Acid (LNA), which reduces RISC loading of the sense strand and further enhances antisense strand incorporation into RISC, as described in Elman et al., (2005) Nucleic Acids Res. 33(1): 439-447, incorporated herein by reference in its entirety. In some embodiments, the sense strand of the siRNA molecule comprises a 5' unlocked nucleic acic (UNA) modification, which reduce RISC loading of the sense strand and improve silencing potentcy of the antisense strand, as described in Snead et al., (2013) Mol Ther Nucleic Acids 2(7):el03, incorporated herein by reference in its entirety. In some embodiments, the sense strand of the siRNA molecule comprises a 5-nitroindole modification, which descresed the RNAi potency of the sense strand and reduces off-targent effects as described in Zhang et al., (2012) Chembiochem 13(13): 1940-1945, incorporated herein by reference in its entirety. In some embodiments, the sense strand comprises a 2’-0’methyl (2’- O-Me) modification, which reduces RISC loading and the off-target effects of the sense strand, as described in Zheng et al., FASEB (2013) 27(10): 4017-4026, incorporated herein by reference in its entirety. In some embodiments, the sense strand of the siRNA molecule is fully substituted with morpholino, 2’-MOE or 2’-0-Me residues, and are not recognized by RISC as described in Kole et al., (2012) Nature reviews. Drug Discovery 11(2): 125- 140, incorporated herein by reference in its entirety. In some embodiments the antisense strand of the siRNA molecule comprises a 2’-MOE modification and the sense strand comprises an 2’-0-Me modification (see e.g., Song et al., (2017) Mol Ther Nucleic Acids 9:242-250). In some embodiments at least one (e.g., at least 2, at least 3, at least 4, at least 5, at least 10) siRNA molecule is linked (e.g., covalently) to a muscle-targeting agent. In some embodiments, the muscle-targeting agent may comprise, or consist of, a nucleic acid (e.g., DNA or RNA), a peptide (e.g., an antibody), a lipid (e.g., a micro vesicle), or a sugar moiety (e.g., a polysaccharide). In some embodiments, the muscle-targeting agent is an antibody. In some embodiments, the muscle-targeting agent is an anti-transferrin receptor antibody (e.g., any one of the anti-TfR antibodies provided herein). In some embodiments, the muscle-targeting agent may be linked to the 5’ end of the sense strand of the siRNA molecule. In some embodiments, the muscle-targeting agent may be linked to the 3’ end of the sense strand of the siRNA molecule. In some embodiments, the muscle-targeting agent may be linked internally to the sense strand of the siRNA molecule. In some embodiments, the muscle-targeting agent may be linked to the 5’ end of the antisense strand of the siRNA molecule. In some embodiments, the muscle-targeting agent may be linked to the 3’ end of the antisense strand of the siRNA molecule. In some embodiments, the muscle-targeting agent may be linked internally to the antisense strand of the siRNA molecule. k. microRNA (miRNAs)

[000416] In some embodiments, an oligonucleotide may be a microRNA (miRNA). MicroRNAs (referred to as “miRNAs”) are small non-coding RNAs, belonging to a class of regulatory molecules that control gene expression by binding to complementary sites on a target RNA transcript. Typically, miRNAs are generated from large RNA precursors (termed pri-miRNAs) that are processed in the nucleus into approximately 70 nucleotide pre-miRNAs, which fold into imperfect stem-loop structures. These pre-miRNAs typically undergo an additional processing step within the cytoplasm where mature miRNAs of 18-25 nucleotides in length are excised from one side of the pre-miRNA hairpin by an RNase III enzyme, Dicer. [000417] As used herein, miRNAs including pri-miRNA, pre-miRNA, mature miRNA or fragments of variants thereof that retain the biological activity of mature miRNA. In one embodiment, the size range of the miRNA can be from 21 nucleotides to 170 nucleotides. In one embodiment the size range of the miRNA is from 70 to 170 nucleotides in length. In another embodiment, mature miRNAs of from 21 to 25 nucleotides in length can be used. l. Aptamers

[000418] In some embodiments, oligonucleotides provided herein may be in the form of aptamers. Generally, in the context of molecular payloads, aptamer is any nucleic acid that binds specifically to a target, such as a small molecule, protein, nucleic acid in a cell. In some embodiments, the aptamer is a DNA aptamer or an RNA aptamer. In some embodiments, a nucleic acid aptamer is a single- stranded DNA or RNA (ssDNA or ssRNA). It is to be understood that a single- stranded nucleic acid aptamer may form helices and/or (e.g., and) loop structures. The nucleic acid that forms the nucleic acid aptamer may comprise naturally occurring nucleotides, modified nucleotides, naturally occurring nucleotides with hydrocarbon linkers (e.g., an alkylene) or a polyether linker (e.g., a PEG linker) inserted between one or more nucleotides, modified nucleotides with hydrocarbon or PEG linkers inserted between one or more nucleotides, or a combination of thereof. Exemplary publications and patents describing aptamers and method of producing aptamers include, e.g., Lorsch and Szostak,

1996; Jayasena, 1999; U.S. Pat. Nos. 5,270,163; 5,567,588; 5,650,275; 5,670,637; 5,683,867; 5,696,249; 5,789,157; 5,843,653; 5,864,026; 5,989,823; 6,569,630; 8,318,438 and PCT application WO 99/31275, each incorporated herein by reference m. Ribozymes

[000419] In some embodiments, oligonucleotides provided herein may be in the form of a ribozyme. A ribozyme (ribonucleic acid enzyme) is a molecule, typically an RNA molecule, that is capable of performing specific biochemical reactions, similar to the action of protein enzymes. Ribozymes are molecules with catalytic activities including the ability to cleave at specific phosphodiester linkages in RNA molecules to which they have hybridized, such as mRNAs, RNA-containing substrates, IncRNAs, and ribozymes, themselves.

[000420] Ribozymes may assume one of several physical structures, one of which is called a "hammerhead." A hammerhead ribozyme is composed of a catalytic core containing nine conserved bases, a double-stranded stem and loop structure (stem-loop II), and two regions complementary to the target RNA flanking regions the catalytic core. The flanking regions enable the ribozyme to bind to the target RNA specifically by forming double-stranded stems I and III. Cleavage occurs in cis (i.e., cleavage of the same RNA molecule that contains the hammerhead motif) or in trans (cleavage of an RNA substrate other than that containing the ribozyme) next to a specific ribonucleotide triplet by a transesterification reaction from a 3', 5'- phosphate diester to a 2', 3'-cyclic phosphate diester. Without wishing to be bound by theory, it is believed that this catalytic activity requires the presence of specific, highly conserved sequences in the catalytic region of the ribozyme.

[000421] Modifications in ribozyme structure have also included the substitution or replacement of various non-core portions of the molecule with non-nucleotidic molecules. For example, Benseler et al. (J. Am. Chem. Soc. (1993) 115:8483-8484) disclosed hammerhead like molecules in which two of the base pairs of stem II, and all four of the nucleotides of loop II were replaced with non-nucleoside linkers based on hexaethylene glycol, propanediol, bis(triethylene glycol) phosphate, tris(propanediol)bisphosphate, or bis(propanediol) phosphate. Ma et al. (Biochem. (1993) 32:1751-1758; Nucleic Acids Res. (1993) 21:2585- 2589) replaced the six nucleotide loop of the TAR ribozyme hairpin with non-nucleotidic, ethylene glycol-related linkers. Thomson et al. (Nucleic Acids Res. (1993) 21:5600-5603) replaced loop II with linear, non-nucleotidic linkers of 13, 17, and 19 atoms in length.

[000422] Ribozyme oligonucleotides can be prepared using well known methods (see, e.g., PCT Publications W09118624; W09413688; W09201806; and WO 92/07065; and U.S. Patents 5436143 and 5650502) or can be purchased from commercial sources (e.g., US Biochemicals) and, if desired, can incorporate nucleotide analogs to increase the resistance of the oligonucleotide to degradation by nucleases in a cell. The ribozyme may be synthesized in any known manner, e.g., by use of a commercially available synthesizer produced, e.g., by Applied Biosystems, Inc. or Milligen. The ribozyme may also be produced in recombinant vectors by conventional means. See, Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory (Current edition). The ribozyme RNA sequences maybe synthesized conventionally, for example, by using RNA polymerases such as T7 or SP6. n. Guide Nucleic Acids

[000423] In some embodiments, oligonucleotides are guide nucleic acid, e.g., guide RNA (gRNA) molecules. Generally, a guide RNA is a short synthetic RNA composed of (1) a scaffold sequence that binds to a nucleic acid programmable DNA binding protein (napDNAbp), such as Cas9, and (2) a nucleotide spacer portion that defines the DNA target sequence (e.g., genomic DNA target) to which the gRNA binds in order to bring the nucleic acid programmable DNA binding protein in proximity to the DNA target sequence. In some embodiments, the napDNAbp is a nucleic acid-programmable protein that forms a complex with (e.g., binds or associates with) one or more RNA(s) that targets the nucleic acid- programmable protein to a target DNA sequence (e.g., a target genomic DNA sequence). In some embodiments, a nucleic acid -programmable nuclease, when in a complex with an RNA, may be referred to as a nuclease:RNA complex. Guide RNAs can exist as a complex of two or more RNAs, or as a single RNA molecule.

[000424] Guide RNAs (gRNAs) that exist as a single RNA molecule may be referred to as single-guide RNAs (sgRNAs), though gRNA is also used to refer to guide RNAs that exist as either single molecules or as a complex of two or more molecules. Typically, gRNAs that exist as a single RNA species comprise two domains: (1) a domain that shares homology to a target nucleic acid (i.e., directs binding of a Cas9 complex to the target); and (2) a domain that binds a Cas9 protein. In some embodiments, domain (2) corresponds to a sequence known as a tracrRNA and comprises a stem-loop structure. In some embodiments, domain (2) is identical or homologous to a tracrRNA as provided in Jinek et al., Science 337:816-821 (2012), the entire contents of which is incorporated herein by reference. [000425] In some embodiments, a gRNA comprises two or more of domains (1) and (2), and may be referred to as an extended gRNA. For example, an extended gRNA will bind two or more Cas9 proteins and bind a target nucleic acid at two or more distinct regions, as described herein. The gRNA comprises a nucleotide sequence that complements a target site, which mediates binding of the nuclease/RNA complex to said target site, providing the sequence specificity of the nuclease:RNA complex. In some embodiments, the RNA- programmable nuclease is the (CRISPR-associated system) Cas9 endonuclease, for example, Cas9 (Csnl) from Streptococcus pyogenes (see, e.g., “Complete genome sequence of an Ml strain of Streptococcus pyogenes.” Ferretti J.J., McShan W.M., Ajdic D.J., Savic D.J., Savic

G., Lyon K., Primeaux C., Sezate S., Suvorov A.N., Kenton S., Lai H.S., Lin S.P., Qian Y., Jia

H.G., Najar F.Z., Ren Q., Zhu H., Song L., White L, Yuan X., Clifton S.W., Roe B.A., McLaughlin R.E., Proc. Natl. Acad. Sci. U.S.A. 98:4658-4663 (2001); “CRISPR RNA maturation by trans-encoded small RNA and host factor RNase III.” Deltcheva E., Chylinski K., Sharma C.M., Gonzales K., Chao Y., Pirzada Z.A., Eckert M.R., Vogel L, Charpentier E., Nature 471:602-607 (2011); and “A programmable dual-RNA-guided DNA endonuclease in adaptive bacterial immunity.” Jinek M., Chylinski K., Fonfara I., Hauer M., Doudna J.A., Charpentier E. Science 337:816-821 (2012), the entire contents of each of which are incorporated herein by reference. o. Splice Altering Oligonucleotides

[000426] In some embodiments, a oligonucleotide (e.g., an antisense oligonucleotide including a morpholino) of the present disclosure target splicing. In some embodiments, the oligonucleotide targets splicing by inducing exon skipping and restoring the reading frame within a gene. As a non-limiting example, the oligonucleotide may induce skipping of an exon encoding a frameshift mutation and/or (e.g., and) an exon that encodes a premature stop codon. In some embodiments, an oligonucleotide may induce exon skipping by blocking spliceosome recognition of a splice site. In some embodiments, exon skipping results in a truncated but functional protein compared to the reference protein (e.g., truncated but functional DMD protein as described below). In some embodiments, the oligonucleotide promotes inclusion of a particular exon (e.g., exon 7 of the SMN2 gene described below). In some embodiments, an oligonucleotide may induce inclusion of an exon by targeting a splice site inhibitory sequence. RNA splicing has been implicated in muscle diseases, including Duchenne muscular dystrophy (DMD) and spinal muscular atrophy (SMA).

[000427] Alterations (e.g., deletions, point mutations, and duplications) in the gene encoding dystrophin (DMD) cause DMD. These alterations can lead to frameshift mutations and/or (e.g., and) nonsense mutations. In some embodiments, an oligonucleotide of the present disclosure promotes skipping of one or more DMD exons (e.g., exon 8, exon 43, exon 44, exon 45, exon 50, exon 51, exon 52, exon 53, and/or (e.g., and) exon 55) and results in a functional truncated protein. See, e.g., U.S. Patent No. 8,486,907 published on July 16, 2013 and U.S. 20140275212 published on September 18, 2014.

[000428] In SMA, there is loss of functional SMN1. Although the SMN2 gene is a paralog to SMN1, alternative splicing of the SMN2 gene predominantly leads to skipping of exon 7 and subsequent production of a truncated SMN protein that cannot compensate for SMN1 loss. In some embodiments, an oligonucleotide of the present disclosure promotes inclusion of SMN2 exon 7. In some embodiments, an oligonucleotide is an antisense oligonucleotide that targets SMN2 splice site inhibitory sequences (see, e.g., US Patent Number 7,838,657, which was published on November 23, 2010). p. Multimers

[000429] In some embodiments, molecular payloads may comprise multimers (e.g., concatemers) of 2 or more oligonucleotides connected by a linker. In this way, in some embodiments, the oligonucleotide loading of a complex/conjugate can be increased beyond the available linking sites on a targeting agent (e.g., available thiol sites on an antibody) or otherwise tuned to achieve a particular payload loading content. Oligonucleotides in a multimer can be the same or different (e.g., targeting different genes or different sites on the same gene or products thereof).

[000430] In some embodiments, multimers comprise 2 or more oligonucleotides linked together by a cleavable linker. However, in some embodiments, multimers comprise 2 or more oligonucleotides linked together by a non-cleavable linker. In some embodiments, a multimer comprises 2, 3, 4, 5, 6, 7, 8, 9, 10 or more oligonucleotides linked together. In some embodiments, a multimer comprises 2 to 5, 2 to 10 or 4 to 20 oligonucleotides linked together. [000431] In some embodiments, a multimer comprises 2 or more oligonucleotides linked end-to-end (in a linear arrangement). In some embodiments, a multimer comprises 2 or more oligonucleotides linked end-to-end via a oligonucleotide based linker (e.g., poly-dT linker, an abasic linker). In some embodiments, a multimer comprises a 5’ end of one oligonucleotide linked to a 3’ end of another oligonucleotide. In some embodiments, a multimer comprises a 3’ end of one oligonucleotide linked to a 3’ end of another oligonucleotide. In some embodiments, a multimer comprises a 5’ end of one oligonucleotide linked to a 5’ end of another oligonucleotide. Still, in some embodiments, multimers can comprise a branched structure comprising multiple oligonucleotides linked together by a branching linker. [000432] Further examples of multimers that may be used in the complexes provided herein are disclosed, for example, in US Patent Application Number 2015/0315588 Al, entitled Methods of delivering multiple targeting oligonucleotides to a cell using cleavable linkers, which was published on November 5, 2015; US Patent Application Number 2015/0247141 Al, entitled Multimeric Oligonucleotide Compounds, which was published on September 3, 2015, US Patent Application Number US 2011/0158937 Al, entitled Immuno stimulatory Oligonucleotide Multimers, which was published on June 30, 2011; and US Patent Number 5,693,773, entitled Triplex-Forming Antisense Oligonucleotides Having Abasic Linkers Targeting Nucleic Acids Comprising Mixed Sequences Of Purines And Pyrimidines, which issued on December 2, 1997, the contents of each of which are incorporated herein by reference in their entireties. ii. Small Molecules:

[000433] Any suitable small molecule may be used as a molecular payload, as described herein. Non-limiting examples are provided below for selected genes of Table 1.

DMPK/DM1

[000434] In some embodiments, e.g., for the treatment of DM, the small molecule is as described in US Patent Application Publication 2016052914A1, published on February 25, 2016, entitled “ Compounds And Methods For Myotonic Dystrophy Therapy”. Further examples of small molecule payloads are provided in Lopez-Morato M, et al., Small Molecules Which Improve Pathogenesis of Myotonic Dystrophy Type 1, (Review) Front. Neurol., 18 May 2018. For example, in some embodiments, the small molecule is an MBNL1 upregulator such as phenylbuthazone, ketoprofen, ISOX, or vorinostat. In some embodiments, the small molecule is an H-Ras pathway inhibitor such as manumycin A. In some embodiments, the small molecule is a protein kinase modulator such as Ro-318220, C16, C51, Metformin, AICAR, lithium chloride, TDZD-8 or Bio. In some embodiments, the small molecule is a plant alkaloid such as harmine. In some embodiments, the small molecule is a transcription inhibitor such as pentamidine, propamidine, heptamidiine or actinomycin D. In some embodiments, the small molecule is an inhibitor of Glycogen synthase kinase 3 beta (GSK3B), for example, as disclosed in Jones K, et al., GSK3P mediates muscle pathology in myotonic dystrophy. J Clin Invest. 2012 Dec;122(12):4461-72; and Wei C, et al., GSK3P is a new therapeutic target for myotonic dystrophy type 1. Rare Dis. 2013; 1: e26555; and Palomo V, et al., Subtly Modulating Glycogen Synthase Kinase 3 b: Allosteric Inhibitor Development and Their Potential for the Treatment of Chronic Diseases. J Med Chem. 2017 Jun 22;60(12):4983- 5001, the contents of each of which are incorporated herein by reference in their entireties. In some embodiments, the small molecule is a substituted pyrido[2,3-d]pyrimidines and pentamidine-like compound, as disclosed in Gonzalez AL, et ah, In silico discovery of substituted pyrido[2,3-d]pyrimidines and pentamidine-like compounds with biological activity in myotonic dystrophy models. PLoS One. 2017 Jun 5;12(6):e0178931, the contents of which are incorporated herein by reference in its entirety. In some embodiments, the small molecule is an MBNL1 modulator, for example, as disclosed in: Zhange F, et ah, A flow cytometry- based screen identifies MBNL1 modulators that rescue splicing defects in myotonic dystrophy type I. Hum Mol Genet. 2017 Aug 15;26(16):3056-3068, the contents of which are incorporated herein by reference in its entirety.

DUX4/FSHD

[000435] In some embodiments, e.g., for the treatment of FSHD, the small molecule payload is as described in US Patent Application Publication 20170340606, published on November 30, 2017, entitled “METHODS OF TREATING MUSCULAR DYSTROPHY” or as described in US Patent Application Publication 20180050043, published on February 22, 2018, entitled “INHIBITION OF DUX4 EXPRESSION USING BROMODOMAIN AND EXTRA-TERMINAL DOMAIN PROTEIN INHIBITORS (BETi). Further examples of small molecule payloads are provided in Bosnakovski, D., et ah, High-throughput screening identifies inhibitors of DUX4-induced myoblast toxicity, Skelet Muscle, Feb 2014, and Choi. S., et ah, “Transcriptional Inhibitors Identified in a 160,000-Compound Small-Molecule DUX4 Viability Screen,” Journal of Biomolecular Screening, 2016. For example, in some embodiments, the small molecule is a transcriptional inhibitor, such as SHC351, SHC540, SHC572. In some embodiments, the small molecule is STR00316 increases production or activity of another protein, such as integrin. In some embodiments, the small molecule is a bromodomain inhibitor (BETi), such as JQ1, PFl-1, 1-BET-762, 1-BET-151, RVX-208, or CPI-0610.

DNM/CNM

[000436] In some embodiments, e.g., for the treatment of CNM, the small molecule, for the treatment of CNM, is as described in US Patent Application Publication Number 20160264976, published on September 15, 2016, entitled “DYNAMIN 2 INHIBITOR FOR TREATMENT OF CENTRONUCLEAR MYOPATHIES”. For example, in some embodiments, the small molecule is selected from a group consisting of 3- Hydroxynaphthalene-2-carboxylic acid (3,4-dihydroxybenzylidene) hydrazide, 3-Hydroxy-N'- [(2,4,5-trihydroxyphenyl)methylidene]naphthalene-2-carbohydr -azide. In some embodiments, the small molecule is as described in US Patent Application Publication Number 20180000762, published January 4, 2018, entitled “COMPOSITION AND METHOD FOR MUSCLE REPAIR AND REGENERATION”. In some embodiments, the small molecule is a retinoic receptor agonist, such as 4-[(E)-2-[5,6,7,8-Tetrahydro-5,5,8,8-tetramethyl-3-(lH- pyrazol-l-ylmethyl- )-2-naphthalenyl]-ethenyl] -benzoic acid. In some embodiments, the small molecule is as described in US Patent Application Publication Number 20170119748, published May 4, 2017, entitled “METHODS, COMPOUNDS, AND COMPOSITIONS FOR THE TREATMENT OF MUSCULOSKELETAL DISEASES.” The contents of each of these publications listed above are incorporated herein in their entirety.

Pompe Disease

[000437] In some embodiments, e.g., for the treatment of Pompe disease, the small molecule is a 1-deoxynojirimycin (DNJ) derivative, such as N-butyl-DNJ, N-methyl-DNJ, or N-cyclopropylmethyl-DNJ as described in US Patent Application Publication Number 20160051528, published on February 25, 2016, entitled “METHOD FOR TREATMENT OF POMPE DISEASE USING 1-DEOXYNOJIRIMYCIN DERIVATIVES”. In some embodiments, the small molecule DNJ derivative is used as a molecular chaperone to increase the activity of a GAA. In some embodiments, the non-inhibitory acid alpha glucosidase chaperone ML247 small molecule is utilized as in Marugan, et al., “Discovery, SAR, and Biological Evaluation of a Non-inhibitory Chaperone for Acid Alpha Glucosidase,” published in Probe Reports from NIH Molecular Libraries in December 2011. For example, the small molecule chaperone ML247 is utilized to increase the activity of a PD-associated GAA allele or a wild-type GAA allele. The contents of each of these publications listed above are incorporated herein in their entirety.

FXN / Friedreich ’s Ataxia

[000438] In some embodiments, e.g., for the treatment of Friedreich’s Ataxia, the small molecule is as described in Herman D. et al. “Histone deacetylase inhibitors reverse gene silencing in Friedreich’s ataxia.” Nat Chem Biol. 2006;2:551-558. In some embodiments, the small molecule is as described in Rai, M. et al. “HD AC inhibitors correct frataxin deficiency in a Friedreich ataxia mouse model.” PLoS One. 2008 Apr 9; 3(4):el958. Further examples of small molecule payloads are provided in Richardson, T.E. et al, “Therapeutic strategies in Friedreich’s Ataxia”, Brain Res. 2013 Jun 13; 1514: 91-97; Zeier Z et al. “Bromodomain inhibitors regulate the C90RF72 locus in ALS” Exp Neurol. 2015 Sep;271:241-50.; and Gottesfeld J.M. “Small molecules affecting transcription in Friedreich ataxia.” Pharmacol Ther. 2007 Nov;116(2):236-48. For example, in some embodiments, the small molecule is an inhibitor of a histone deacetylase, e.g., BML-210 and compound 106. In some embodiments, the small molecule is 17P-Estradiol or methylene blue. In some embodiments, the small molecule targets, e.g., binds to, a disease-associated-repeat and/or (e.g., and) R-loop. In some embodiments, the small molecule is as described in WO 2004/003565, published 1/8/2004, “A screening method and compounds for treating friedreich ataxia”. In some embodiments, the small molecule is a Glutathione peroxidase mimetic.

DMD / Dystrophinopathies

[000439] In some embodiments, the small molecule enhances exon skipping of an mRNA expression from a mutant DMD allele. In some embodiments, the small molecule is as described in US Patent Application Publication US20140080896A1, published March 20,

2014, entitled “IDENTIFICATION OF SMALL MOLECULES THAT FACILITATE THERAPEUTIC EXON SKIPPING”. Further examples of small molecule payloads are provided in U.S. Patent No. 9,982,260, issued May 29, 2018, entitled “Identification of structurally similar small molecules that enhance therapeutic exon skipping”. For example, in some embodiments, the small molecule is an enhancer of exon skipping such as perphenazine, flupentixol, zuclopenthixol or corynanthine. In some embodiments, a small molecule enhancer of exon skipping inhibits the ryanodine receptor or calmodulin. In some embodiments, the small molecule is an H-Ras pathway inhibitor such as manumycin A. In some embodiments, the small molecule is a suppressor of stop codons and desensitizes ribosomes to premature stop codons. In some embodiments, the small molecule is ataluren, as described in McElroy S.P. et al. “A Lack of Premature Termination Codon Read Through Efficacy of PTC 124 (Ataluren) in a Diverse Array of Reporter Assays.” PLOS Biology, published June 25, 2013. In some embodiments, the small molecule is a corticosteroid, e.g., as described in Manzur, A.Y. et al. “Glucocorticoid corticosteroids for Duchenne muscular dystrophy”. Cochrane Database Syst Rev. 2004;(2):CD003725. In some embodiments, the small molecule upregulates the expression and/or (e.g., and) activity of genes that can replace the function of dystrophin, such as utrophin. In some embodiments, a utrophin modulator is as described in International Publication No. W02007091106, published August 16, 2007, entitled “TREATMENT OF DUCHENNE MUSCULAR DYSTROPHY” and/or (e.g., and) International Publication No. WO/2017/168151, published October 5, 2017, entitled “COMPOSITION FOR THE TREATMENT OF DUCHENNE MUSCULAR DYSTROPHY”.

MYH7 / Hypertrophic Cardiomyopathy

[000440] In some embodiments, the small molecule is a hypomethylating agent, such as 5-Azacytidine or 5-Aza-2’-Deoxycytidine, which modulates the expression of the MYH7 gene, such as in US Patent Application Publication 20160106771, published on April 21, 2016, entitled Therapies for Cardiomyopathy ; in some embodiments, the small molecule is a JAK- STAT inhibitor such as nifuroxazide, ketoprofen, sulfasalazine, 5,15-diphenylporphyrin, or AG490, such as in US Patent Application Publication 20180185478, published on July 5,

2018, entitled Treatment for Myopathy; in some embodiments the small molecule is para- Nitroblebbistatin, which reduces the force of myosin contraction while not changing the dissociation of ADP, as in Tang, W., et al. “Modulating Beta-Cardiac Myosin Function at the Molecular and Tissue Levels,” Front. Physiol. 2016 (7): 659, the contents of any of which are incorporated herein by reference in their entirety. iii. Peptides/Proteins

[000441] Any suitable peptide or protein may be used as a molecular payload, as described herein. In some embodiments, a protein is an enzyme ( e.g ., an acid alpha- glucosidase, e.g., as encoded by the GAA gene). These peptides or proteins may be produced, synthesized, and/or (e.g., and) derivatized using several methodologies, e.g. phage displayed peptide libraries, one-bead one-compound peptide libraries, or positional scanning synthetic peptide combinatorial libraries. Exemplary methodologies have been characterized in the art and are incorporated by reference (Gray, B.P. and Brown, K.C. “Combinatorial Peptide Libraries: Mining for Cell-Binding Peptides” Chem Rev. 2014, 114:2, 1020-1081.;

Samoylova, T.I. and Smith, B.F. “Elucidation of muscle-binding peptides by phage display screening.” Muscle Nerve, 1999, 22:4. 460-6.).

[000442] Non-limiting examples are provided below for selected genes of Table 1.

DMPK/DM1

[000443] A peptide or protein payload, e.g., for the treatment of DM1, may correspond to a sequence of a protein that preferentially binds to a nucleic acid, e.g. a disease-associated repeat, or a protein, e.g. MBNL1, found in muscle cells. In some embodiments, the peptide is as described in US Patent Application 2018/0021449, published on 1/25/2018, “Antisense conjugates for decreasing expression of DMPK”. In some embodiments, the peptide is as described in Garcia-Lopez et al., “/n vivo discovery of a peptide that prevents CUG-RNA hairpin formation and reverses RNA toxicity in myotonic dystrophy models”, PNAS July 19, 2011. 108 (29) 11866-11871. In some embodiments, the peptide or protein may target, e.g., bind to, a disease-associated repeat, e.g. a RNA CUG repeat expansion.

[000444] In some embodiments, e.g., for the treatment of DM1, the peptide or protein comprises a fragment of an MBNL protein, e.g., MBNL1. In some embodiments, the peptide or protein comprises at least one zinc finger. In some embodiments, the peptide or protein may comprise about 2-25 amino acids, about 2-20 amino acids, about 2-15 amino acids, about 2-10 amino acids, or about 2-5 amino acids. The peptide or protein may comprise naturally- occurring amino acids, e.g. cysteine, alanine, or non-naturally-occurring or modified amino acids. Non-naturally occurring amino acids include b-amino acids, homo-amino acids, proline derivatives, 3-substituted alanine derivatives, linear core amino acids, N-methyl amino acids, and others known in the art. In some embodiments, the peptide may be linear; in other embodiments, the peptide may be cyclic, e.g. bicyclic.

DUX4/FSHD

[000445] In some embodiments, e.g., for the treatment of FSHD, the peptide or protein may bind a DME1 or DME2 enhancer to inhibit DUX4 expression, e.g., by blocking binding of an activator.

DNM2/CNM

[000446] In some embodiments, e.g., for the treatment of CNM, the peptide is a dynamin inhibitor peptide with amino acid sequence QVPSRPNRAP (SEQ ID NO: 152), as described in US Patent Application Publication Number 20160264976, published on September 15, 2016, entitled “DYNAMIN 2 INHIBITOR FOR TREATMENT OF CENTRONUCLEAR MYOPATHIES”.

Pompe Disease

[000447] In some embodiments, e.g., for the treatment of Pompe disease, the molecular payload is a protein or enzyme such as an acid alpha-glucosidase or wild-type GAA protein or an active fragment thereof as in US Patent Application Publication Number 20160346363, published on December 1, 2016, entitled “METHODS AND ORAL FORMULATIONS FOR ENZYME REPLACEMENT THERAPY OF HUMAN LYSOSOMAL AND METABOLIC DISEASES,” US Patent Application Publication Number 20160279254, published September 29, 2016, entitled “METHODS AND MATERIALS FOR TREATMENT OF POMPE’S DISEASE”, or US Patent Application Publication Number 20130243746, published on September 19, 2013, entitled “METHODS AND MATERIALS FOR TREATMENT OF POMPE’S DISEASE”. In some embodiments, the acid alpha-glucosidase or wild-type GAA protein increases the GAA activity of a subject. In some embodiments, the acid alpha- glucosidase or wild-type GAA protein is encoded by the GAA gene.

ACVR1 /FOP

[000448] In some embodiments, e.g., for the treatment of FOP, the peptide or protein is a BMP inhibitor such as regulatory SMAD 6 and 7 or fragment thereof. Additional examples of peptides or proteins are included in Cappato, S. et al. “The Horizon of a Therapy for Rare Genetic Diseases: A “Druggable” Future for Fibrodysplasia Ossificans Progressiva” Int. J.

Mol. Sci. 2018, 19(4), 989. The contents of each of the foregoing are incorporated herein by reference in their entireties.

FXN / Friedreich Ataxia

[000449] In some embodiments, e.g., for the treatment of Friedreich’s Ataxia, the peptide is as described in US Patent No. 8,815,230, filed 8/30/2010, “Methods for treating Friedreich's ataxia with interferon gamma”. In some embodiments, the peptide is as described in Britti, E. et al. “Frataxin-deficient neurons and mice models of Friedreich ataxia are improved by TAT- MTScs-FXN treatment.” J Cell Mol Med. 2018 Feb;22(2):834-848. In some embodiments, the peptide is as described in Zhao, H. et al., “Peptide SS-31 upregulates frataxin expression and improves the quality of mitochondria: implications in the treatment of Friedreich ataxia”, Sci Rep. 2017 Aug 29;7(1):9840. In some embodiments, the peptide is as described in Vyas, P.M. et al. “A TAT-frataxin fusion protein increases lifespan and cardiac function in a conditional Friedreich's ataxia mouse model”, Hum Mol Genet. 2012 Mar 15;21(6): 1230-47. In some embodiments, the peptide or protein may target, e.g., bind to, a disease-associated repeat, e.g. a GAA repeat expansion.

DMD / Dystrophinopathies

[000450] In some embodiments, e.g., for the treatment of dystrophinopathies, such as Duchenne muscular dystrophy, a peptide may facilitate exon skipping in an mRNA expressed from a mutant DMD allele. In some embodiments, a peptide may promote the expression of functional dystrophin and/or (e.g., and) the expression of a protein capable of functioning in place of dystrophin. In some embodiments, payload is a protein that is a functional fragment of dystrophin, e.g. an amino acid segment of a functional dystrophin protein. iv. Nucleic Acid Constructs

[000451] Any suitable gene expression construct may be used as a molecular payload, as described herein. In some embodiments, a gene expression construct may be a vector or a cDNA fragment. In some embodiments, a gene expression construct may be messenger RNA (mRNA). In some embodiments, a mRNA used herein may be a modified mRNA, e.g., as described in US Patent 8,710,200, issued on April 24, 2014, entitled “ Engineered nucleic acids encoding a modified erythropoietin and their expression” . In some embodiments, a mRNA may comprise a 5' methyl cap. In some embodiments, a mRNA may comprise a polyA tail, optionally of up to 160 nucleotides in length. A gene expression construct may encode a sequence of a protein that is deficient in a muscle disease. In some embodiments, the gene expression construct may be expressed, e.g., overexpressed, within the nucleus of a muscle cell. In some embodiments, the gene expression construct encodes a gene that is deficient in a muscle disease. In some embodiments, the gene expression constructs encodes a protein that comprises at least one zinc finger. In some embodiments, the gene expression construct encodes a protein that binds to a gene in Table 1. In some embodiments, the gene expression construct encodes a protein that leads to a reduction in the expression of a protein (e.g., mutant protein) encoded by a gene in Table 1. In some embodiments, the gene expression construct encodes a gene editing enzyme. Additional examples of nucleic acid constructs that may be used as molecular payloads are provided in International Patent Application Publication WO2017152149A1, published on September 19, 2017, entitled, “CLOSED-ENDED LINEAR DUPLEX DNA FOR NON- VIRAL GENE TRANSFER”; US Patent 8,853,377B2, issued on October 7, 2014, entitled, “MRNA FOR USE IN TREATMENT OF HUMAN GENETIC DISEASES”; and US Patent US8822663B2, issued on September 2, 2014, ENGINEERED NUCLEIC ACIDS AND METHODS OF USE THEREOF,” the contents of each of which are incorporated herein by reference in their entireties.

[000452] Further non-limiting examples are provided below for selected genes/disease of Table 1.

DMPK/DM1 [000453] In some embodiments, e.g., for the treatment of DM, the gene expression construct encodes a MBNL protein, e.g., MBNL1.

DUX4/FSHD

In some embodiments, e.g., for the treatment of FSHD, the gene expression construct encodes an oligonucleotide (e.g., an shRNA targeting DUX4) or a protein that downregulates the expression of DUX4 (e.g., a peptide or protein that binds to DME1 or DME2 enhancer to inhibit DUX4 expression, e.g., by blocking binding of an activator).

DNM2 /CNM

In some embodiments, e.g., for the treatment of CNM1, a gene expression construct may encode a sequence of a protein that downregulates the expression of a mutant DNM2 protein, or which expresses wild-type DNM2. In some embodiments, a gene expression construct encodes an oligonucleotide (e.g., an shRNA) that inhibits expression of DNM2. However, in some embodiments, an expression construct encodes Spliceosome-Mediated RNA Trans splicing components that may be used to reprogram mutated DNM2-mRNA, as disclosed in Trochet D., et al., Reprogramming the Dynamin 2 mRNA by Spliceosome-mediated RNA Trans- splicing Mol Ther Nucleic Acids. 2016 Sep; 5(9): e362, the contents of which are incorporated herein by reference.

Pompe Disease

[000454] In some embodiments, e.g., for the treatment of Pompe disease, the gene expression construct encodes a wild-type GAA protein. A gene expression construct may encode a sequence of a protein that leads to decreased activity of GYS1 protein. In some embodiments, e.g., for the treatment of Pompe disease, the gene expression construct encodes and oligonucleotide (e.g., shRNA) that inhibits expression of GYS1.

ACVR1 /FOP

[000455] A gene expression construct may encode a sequence of a protein that leads to decreased expression of ACVR1 gene or decreased activity of ACVR1 protein. In some embodiments, the gene expression construct encodes a protein that leads to a reduction in the expression of a epigenetic regulators that negatively regulate the expression of ACVR1, e.g. histone deactylases. In some embodiments, the gene expression construct encodes an oligonucleotide (e.g., shRNA) that inhibits expression of ACVR1. FXN / Friedreich ’s ataxia

[000456] A gene expression construct may encode a sequence of a protein that leads to increased expression of frataxin. In some embodiments, the gene expression construct may be expressed, e.g., overexpressed, within the nucleus of a muscle cell. In some embodiments, the gene expression construct encodes frataxin. In some embodiments, the gene expression constructs encodes a protein that inhibit the function of epigenetic regulators that negatively regulate the expression of FXN, e.g. histone deactylases. In some embodiments, the gene expression construct encodes a protein that binds to a disease-associated-repeat expansion of a GAA trinucleotide. In some embodiments, the gene expression construct encodes a protein that leads to a reduction in the expression of a epigenetic regulators that negatively regulate the expression of FXN, e.g. histone deactylases. In some embodiments, the gene expression construct encodes a gene editing enzyme. In some embodiments, the gene expression construct encodes erythropoietin (see, e.g. Miller, J.L. et al, “Erythropoietin and small molecule agonists of the tissue-protective erythropoietin receptor increase FXN expression in neuronal cells in vitro and in FXN-deficient KIKO mice in vivo”, Neuropharmacology. 2017 Sep 1 ; 123:34-45.). In some embodiments, the gene expression construct encodes interferon gamma (see, e.g. US Patent No. 8,815,230, filed 8/30/2010, “Methods for treating Friedreich's ataxia with interferon gamma”).

DMD / Dystrophinopathies

[000457] A gene expression construct may encode a sequence of a dystrophin protein, a dystrophin fragment, a mini-dystrophin, a utrophin protein, or any protein that shares a common function with dystrophin. In some embodiments, the gene expression construct may be expressed, e.g., overexpressed, within the nucleus of a muscle cell. In some embodiments, the gene expression constructs encodes a protein that comprises at least one zinc finger. In some embodiments, the gene expression construct encodes a protein that promotes the expression of dystrophin or a protein that shares function with dystrophin, e.g., utrophin. In some embodiments, the gene expression construct encodes a gene editing enzyme. In some embodiments, the gene expression construct is as described in U.S. Patent Application Publication US20170368198A1, published December 28, 2017, entitled “Optimized mini dystrophin genes and expression cassettes and their use”; Duan D. “Myodys, a full-length dystrophin plasmid vector for Duchenne and Becker muscular dystrophy gene therapy.” Curr Opin Mol Ther 2008;10:86-94; and expression cassettes disclosed in Tang, Y. et al., “AAV- directed muscular dystrophy gene therapy” Expert Opin Biol Ther. 2010 Mar;10(3):395-408; the contents of each of which are incorporated herein by reference in their entireties.

C. Linkers

[000458] Complexes described herein generally comprise a linker that connects any one of the anti-TfR antibodies described herein to a molecular payload. A linker comprises at least one covalent bond. In some embodiments, a linker may be a single bond, e.g., a disulfide bond or disulfide bridge, that connects an anti-TfR antibody to a molecular payload. However, in some embodiments, a linker may connect any one of the anti-TfR antibodies described herein to a molecular payload through multiple covalent bonds. In some embodiments, a linker may be a cleavable linker. However, in some embodiments, a linker may be a non-cleavable linker. A linker is generally stable in vitro and in vivo, and may be stable in certain cellular environments. Additionally, generally a linker does not negatively impact the functional properties of either the anti-TfR antibody or the molecular payload. Examples and methods of synthesis of linkers are known in the art (see, e.g. Kline, T. et al. “Methods to Make Homogenous Antibody Drug Conjugates.” Pharmaceutical Research, 2015, 32:11, 3480- 3493.; Jain, N. et al. “Current ADC Linker Chemistry” Pharm Res. 2015, 32:11, 3526-3540.; McCombs, J.R. and Owen, S.C. “Antibody Drug Conjugates: Design and Selection of Linker, Payload and Conjugation Chemistry” AAPS J. 2015, 17:2, 339-351.).

[000459] A precursor to a linker typically will contain two different reactive species that allow for attachment to both the anti-TfR antibody and a molecular payload. In some embodiments, the two different reactive species may be a nucleophile and/or (e.g., and) an electrophile. In some embodiments, a linker is connected to an anti-TfR antibody via conjugation to a lysine residue or a cysteine residue of the anti-TfR antibody. In some embodiments, a linker is connected to a cysteine residue of an anti-TfR antibody via a maleimide-containing linker, wherein optionally the maleimide-containing linker comprises a maleimidocaproyl or maleimidomethyl cyclohexane- 1-carboxylate group. In some embodiments, a linker is connected to a cysteine residue of an anti-TfR antibody or thiol functionalized molecular payload via a 3-arylpropionitrile functional group. In some embodiments, a linker is connected to a lysine residue of an anti-TfR antibody. In some embodiments, a linker is connected to an anti-TfR antibody and/or (e.g., and) a molecular payload via an amide bond, a carbamate bond, a hydrazide, a trizaole, a thioether, or a disulfide bond. i. Cleavable Linkers [000460] A cleavable linker may be a protease-sensitive linker, a pH-sensitive linker, or a glutathione- sensitive linker. These linkers are generally cleavable only intracellularly and are preferably stable in extracellular environments, e.g. extracellular to a muscle cell.

[000461] Protease-sensitive linkers are cleavable by protease enzymatic activity. These linkers typically comprise peptide sequences and may be 2-10 amino acids, about 2-5 amino acids, about 5-10 amino acids, about 10 amino acids, about 5 amino acids, about 3 amino acids, or about 2 amino acids in length. In some embodiments, a peptide sequence may comprise naturally-occurring amino acids, e.g. cysteine, alanine, or non-naturally-occurring or modified amino acids. Non-naturally occurring amino acids include b-amino acids, homo amino acids, proline derivatives, 3-substituted alanine derivatives, linear core amino acids, N- methyl amino acids, and others known in the art. In some embodiments, a protease- sensitive linker comprises a valine-citmlline or alanine-citrulline dipeptide sequence. In some embodiments, a protease- sensitive linker can be cleaved by a lysosomal protease, e.g. cathepsin B, and/or (e.g., and) an endosomal protease.

[000462] A pH-sensitive linker is a covalent linkage that readily degrades in high or low pH environments. In some embodiments, a pH-sensitive linker may be cleaved at a pH in a range of 4 to 6. In some embodiments, a pH-sensitive linker comprises a hydrazone or cyclic acetal. In some embodiments, a pH-sensitive linker is cleaved within an endosome or a lysosome.

[000463] In some embodiments, a glutathione-sensitive linker comprises a disulfide moiety. In some embodiments, a glutathione- sensitive linker is cleaved by an disulfide exchange reaction with a glutathione species inside a cell. In some embodiments, the disulfide moiety further comprises at least one amino acid, e.g. a cysteine residue.

[000464] In some embodiments, the linker is a Val-cit linker (e.g., as described in US Patent 6,214,345, incorporated herein by reference). In some embodiments, before conjugation, the val-cit linker has a structure of:

[000465] In some embodiments, after conjugation, the val-cit linker has a structure of:

[000466] In some embodiments, the Val-cit linker is attached to a reactive chemical moiety (e.g., SPAAC for click chemistry conjugation). In some embodiments, before click chemistry conjugation, the val-cit linker attached to a reactive chemical moiety (e.g., SPAAC for click chemistry conjugation) has the structure of: wherein n is any number from 0-10. In some embodiments, n is 3.

[000467] In some embodiments, the val-cit linker attached to a reactive chemical moiety

(e.g., SPAAC for click chemistry conjugation) is conjugated (e.g., via a different chemical moiety) to a molecular payload (e.g., an oligonucleotide). In some embodiments, the val-cit linker attached to a reactive chemical moiety (e.g., SPAAC for click chemistry conjugation) and conjugated to a molecular payload (e.g., an oligonucleotide) has the structure of (before click chemistry conjugation): wherein n is any number from 0-10. In some embodiments, n is 3.

[000468] In some embodiments, after conjugation to a molecular payload (e.g., an oligonucleotide), the val-cit linker has a structure of: wherein n is any number from 0-10, and wherein m is any number from 0-10. In some embodiments, n is 3 and m is 4. ii. Non-Cleavable Linkers

[000469] In some embodiments, non-cleavable linkers may be used. Generally, a non- cleavable linker cannot be readily degraded in a cellular or physiological environment. In some embodiments, a non-cleavable linker comprises an optionally substituted alkyl group, wherein the substitutions may include halogens, hydroxyl groups, oxygen species, and other common substitutions. In some embodiments, a linker may comprise an optionally substituted alkyl, an optionally substituted alkylene, an optionally substituted arylene, a heteroarylene, a peptide sequence comprising at least one non-natural amino acid, a truncated glycan, a sugar or sugars that cannot be enzymatically degraded, an azide, an alkyne-azide, a peptide sequence comprising a LPXT sequence, a thioether, a biotin, a biphenyl, repeating units of polyethylene glycol or equivalent compounds, acid esters, acid amides, sulfamides, and/or (e.g., and) an alkoxy-amine linker. In some embodiments, sortase-mediated ligation will be utilized to covalently link an anti-TfR antibody comprising a LPXT sequence to a molecular payload comprising a (G) _n sequence (see, e.g. Proft T. Sortase-mediated protein ligation: an emerging biotechnology tool for protein modification and immobilization. Biotechnol Lett. 2010,

32(1): 1-10.).

[000470] In some embodiments, a linker may comprise a substituted alkylene, an optionally substituted alkenylene, an optionally substituted alkynylene, an optionally substituted cycloalkylene, an optionally substituted cycloalkenylene, an optionally substituted arylene, an optionally substituted heteroarylene further comprising at least one heteroatom selected from N, O, and S,; an optionally substituted heterocyclylene further comprising at least one heteroatom selected from N, O, and S,; an imino, an optionally substituted nitrogen species, an optionally substituted oxygen species O, an optionally substituted sulfur species, or a poly(alkylene oxide), e.g. polyethylene oxide or polypropylene oxide. iii. Linker conjugation

[000471] In some embodiments, a linker is connected to an anti-TfR antibody and/or (e.g., and) molecular payload via a phosphate, thioether, ether, carbon-carbon, carbamate, or amide bond. In some embodiments, a linker is connected to an oligonucleotide through a phosphate or phosphorothioate group, e.g. a terminal phosphate of an oligonucleotide backbone. In some embodiments, a linker is connected to an anti-TfR antibody, through a lysine or cysteine residue present on the anti-TfR antibody.

[000472] In some embodiments, a linker is connected to an anti-TfR antibody and/or (e.g., and) molecular payload by a cycloaddition reaction between an azide and an alkyne to form a triazole, wherein the azide and the alkyne may be located on the anti-TfR antibody, molecular payload, or the linker. In some embodiments, an alkyne may be a cyclic alkyne, e.g., a cyclooctyne. In some embodiments, an alkyne may be bicyclononyne (also known as bicyclo[6.1.0]nonyne or BCN) or substituted bicyclononyne. In some embodiments, a cyclooctane is as described in International Patent Application Publication WO2011136645, published on November 3, 2011, entitled, “ Fused Cyclooctyne Compounds And Their Use In Metal-free Click Reactions”. In some embodiments, an azide may be a sugar or carbohydrate molecule that comprises an azide. In some embodiments, an azide may be 6-azido-6- deoxygalactose or 6-azido-N-acetylgalactosamine. In some embodiments, a sugar or carbohydrate molecule that comprises an azide is as described in International Patent Application Publication W02016170186, published on October 27, 2016, entitled, “ Process For The Modification Of A Glycoprotein Using A Glycosyltransferase That Is Or Is Derived From A b(1 ,4)-N -Acetylgalactosaminyltr ansf erase” . In some embodiments, a cycloaddition reaction between an azide and an alkyne to form a triazole, wherein the azide and the alkyne may be located on the anti-TfR antibody, molecular payload, or the linker is as described in International Patent Application Publication WO2014065661, published on May 1, 2014, entitled, “ Modified antibody, antibody-conjugate and process for the preparation thereof or International Patent Application Publication W02016170186, published on October 27, 2016, entitled, “ Process For The Modification Of A Glycoprotein Using A Glycosyltransferase That Is Or Is Derived From A b(1, 4)-N-Acetylgalactosaminyltransf erase” .

[000473] In some embodiments, a linker further comprises a spacer, e.g., a polyethylene glycol spacer or an acyl/carbomoyl sulfamide spacer, e.g., a HydraSpace™ spacer. In some embodiments, a spacer is as described in Verkade, J.M.M. et ah, “A Polar Sulfamide Spacer Significantly Enhances the Manufacturability, Stability, and Therapeutic Index of Antibody- Drug Conjugates” , Antibodies, 2018, 7, 12.

[000474] In some embodiments, a linker is connected to an anti-TfR antibody and/or (e.g., and) molecular payload by the Diels-Alder reaction between a dienophile and a diene/hetero-diene, wherein the dienophile and the diene/hetero-diene may be located on the anti-TfR antibody, molecular payload, or the linker. In some embodiments a linker is connected to an anti-TfR antibody and/or (e.g., and) molecular payload by other pericyclic reactions, e.g. ene reaction. In some embodiments, a linker is connected to an anti-TfR antibody and/or (e.g., and) molecular payload by an amide, thioamide, or sulfonamide bond reaction. In some embodiments, a linker is connected to an anti-TfR antibody and/or (e.g., and) molecular payload by a condensation reaction to form an oxime, hydrazone, or semicarbazide group existing between the linker and the anti-TfR antibody and/or (e.g., and) molecular payload.

[000475] In some embodiments, a linker is connected to an anti-TfR antibody and/or (e.g., and) molecular payload by a conjugate addition reactions between a nucleophile, e.g. an amine or a hydroxyl group, carbonate, and an electrophile, e.g. a carboxylic acid or an aldehyde. In some embodiments, a nucleophile may exist on a linker and an electrophile may exist on an anti-TfR antibody or molecular payload prior to a reaction between a linker and an anti-TfR antibody or molecular payload. In some embodiments, an electrophile may exist on a linker and a nucleophile may exist on an anti-TfR antibody or molecular payload prior to a reaction between a linker and an anti-TfR antibody or molecular payload. In some embodiments, an electrophile may be an azide, pentafluorophenyl, a silicon centers, a carbonyl, a carboxylic acid, an anhydride, an isocyanate, a thioisocyanate, a succinimidyl ester, a sulfosuccinimidyl ester, a maleimide, an alkyl halide, an alkyl pseudohalide, an epoxide, an episulfide, an aziridine, an aryl, an activated phosphorus center, and/or (e.g., and) an activated sulfur center. In some embodiments, a nucleophile may be an optionally substituted alkene, an optionally substituted alkyne, an optionally substituted aryl, an optionally substituted heterocyclyl, a hydroxyl group, an amino group, an alkylamino group, an anilido group, or a thiol group.

[000476] In some embodiments, the val-cit linker attached to a reactive chemical moiety (e.g., SPAAC for click chemistry conjugation) is conjugated to the anti-TfR antibody by a structure of:

[000477] In some embodiments, the val-cit linker attached to a reactive chemical moiety (e.g., SPAAC for click chemistry conjugation) is conjugated to an anti-TfR antibody having a structure of: wherein m is any number from 0-10. In some embodiments, m is 4.

[000478] In some embodiments, the val-cit linker attached to a reactive chemical moiety (e.g., SPAAC for click chemistry conjugation) and conjugated to an anti-TfR antibody has a structure of: antibody wherein n is any number from 0-10, wherein m is any number from 0-10. In some embodiments, n is 3 and/or (e.g., and) m is 4.

[000479] In some embodiments, the val-cit linker that links the antibody and the molecular payload has a structure of:

wherein n is any number from 0-10, wherein m is any number from 0-10. In some embodiments, n is 3 and/or (e.g., and) m is 4. In some embodiments, n is 3 and/or (e.g., and) m is 4. In some embodiments, X is NH (e.g., NH from an amine group of a lysine), S (e.g., S from a thiol group of a cysteine), or O (e.g., O from a hydroxyl group of a serine, threonine, or tyrosine) of the antibody.

[000480] In some embodiments, the complex described herein has a structure of: wherein n is any number from 0-10, wherein m is any number from 0-10. In some embodiments, n is 3 and/or (e.g., and) m is 4.

[000481] In structures formula (A), (B), (C), and (D), LI, in some embodiments, is a spacer that is a substituted or unsubstituted aliphatic, substituted or unsubstituted heteroaliphatic, substituted or unsubstituted carbocyclylene, substituted or unsubstituted heterocyclylene, substituted or unsubstituted arylene, substituted or unsubstituted heteroarylene, -O-, -N(R ^A )-, -S-, -C(=0)-, -C(=0)0-, -C(=0)NR ^A -, -NR ^A C(=0)-, - NR ^A C(=0)R ^a -, -C(=0)R ^a -, -NR ^A C(=0)0-, -NR ^A C(=0)N(R ^a )-, -OC(=0)-, -0C(=0)0-, - OC(=0)N(R ^a )-, -S(0) ₂ NR ^a -, -NR ^A S(0) ₂ -, or a combination thereof. In some embodiments, LI is wherein the piperazine moiety links to the oligonucleotide, wherein L2 is wherein the piperazine moiety links to the oligonucleotide.

[000483] In some embodiments,

[000484] In some embodiments, LI is linked to a 5’ phosphate of the oligonucleotide.

[000485] In some embodiments, LI is optional (e.g., need not be present).

[000486] In some embodiments, any one of the complexes described herein has a structure of: m antibody wherein n is 0-15 (e.g., 3) and m is 0-15 (e.g., 4).

C. Examples of Antibody-Molecular Payload Complexes [000487] Further provided herein are non-limiting examples of complexes comprising any one the anti-TfR antibodies described herein covalently linked to any of the molecular payloads (e.g., an oligonucleotide) described herein. In some embodiments, the anti-TfR antibody (e.g., any one of the anti-TfR antibodies provided in Table 2) is covalently linked to a molecular payload (e.g., an oligonucleotide) via a linker. Any of the linkers described herein may be used. In some embodiments, if the molecular payload is an oligonucleotide, the linker is linked to the 5' end, the 3' end, or internally of the oligonucleotide. In some embodiments, the linker is linked to the anti-TfR antibody via a thiol-reactive linkage (e.g., via a cysteine in the anti-TfR antibody). In some embodiments, the linker (e.g., a Val-cit linker) is linked to the antibody (e.g., an anti-TfR antibody described herein) via an amine group (e.g., via a lysine in the antibody). In some embodiments, the molecular payload is an oligonucleotide (e.g., an oligonucleotide targeting a gene listed in Table 1).

[000488] An example of a structure of a complex comprising an anti-TfR antibody covalently linked to a molecular payload via a Val-cit linker is provided below: wherein the linker is linked to the antibody via a thiol-reactive linkage (e.g., via a cysteine in the antibody). In some embodiments, the molecular payload is an oligonucleotide (e.g., an oligonucleotide targeting a gene listed in Table 1). [000489] Another example of a structure of a complex comprising an anti-TfR antibody covalently linked to a molecular payload via a Val-cit linker is provided below: wherein n is a number between 0-10, wherein m is a number between 0-10, wherein the linker is linked to the antibody via an amine group (e.g., on a lysine residue), and/or (e.g., and) wherein the linker is linked to the oligonucleotide (e.g., at the 5’ end, 3’ end, or internally). In some embodiments, the linker is linked to the antibody via a lysine, the linker is linked to the oligonucleotide at the 5’ end, n is 3, and m is 4. In some embodiments, the molecular payload is an oligonucleotide comprising a sense strand and an antisense strand, and, the linker is linked to the sense strand or the antisense strand at the 5’ end or the 3’ end. In some embodiments, the molecular payload is an oligonucleotide (e.g., an oligonucleotide targeting a gene listed in Table 1).

[000490] It should be appreciated that antibodies can be linked to molecular payloads with different stochiometries, a property that may be referred to as a drug to antibody ratios (DAR) with the “drug” being the molecular payload. In some embodiments, one molecular payload is linked to an antibody (DAR = 1). In some embodiments, two molecular payloads are linked to an antibody (DAR = 2). In some embodiments, three molecular payloads are linked to an antibody (DAR = 3). In some embodiments, four molecular payloads are linked to an antibody (DAR = 4). In some embodiments, a mixture of different complexes, each having a different DAR, is provided. In some embodiments, an average DAR of complexes in such a mixture may be in a range of 1 to 3, 1 to 4, 1 to 5 or more. DAR may be increased by conjugating molecular payloads to different sites on an antibody and/or (e.g., and) by conjugating multimers to one or more sites on antibody. For example, a DAR of 2 may be achieved by conjugating a single molecular payload to two different sites on an antibody or by conjugating a dimer molecular payload to a single site of an antibody. [000491] In some embodiments, the complex described herein comprises an anti-TfR antibody described herein (e.g., the 3-A4, 3-M12, and 5-H12 antibodies provided in Table 2 in a IgG or Fab form) covalently linked to a molecular payload. In some embodiments, the complex described herein comprises an anti-TfR antibody described herein (e.g., the 3-A4, 3- M12, and 5-H12 antibodies provided in Table 2 in a IgG or Fab form) covalently linked to molecular payload via a linker (e.g., a Val-cit linker). In some embodiments, the linker (e.g., a Val-cit linker) is linked to the antibody (e.g., an anti-TfR antibody described herein) via a thiol-reactive linkage (e.g., via a cysteine in the antibody). In some embodiments, the linker (e.g., a Val-cit linker) is linked to the antibody (e.g., an anti-TfR antibody described herein) via an amine group (e.g., via a lysine in the antibody).

[000492] In some embodiments, in any one of the examples of complexes described herein, the molecular payload is an oligonucleotide targeting a gene listed in Table 1. In some embodiments, in any one of the examples of complexes described herein, the molecular payload is an oligonucleotide comprising a region of complementarity of at least 15 nucleotides to any one of the gene target sequences described in Table 1.

[000493] In some embodiments, the complex described herein comprises an anti-TfR antibody covalently linked to a molecular payload, wherein the anti-TfR antibody comprises a CDR-H1, a CDR-H2, and a CDR-H3 that are the same as the CDR-H1, CDR-H2, and CDR- H3 shown in Table 2; and a CDR-L1, a CDR-L2, and a CDR-L3 that are the same as the CDR- Ll, CDR-L2, and CDR-L3 shown in Table 2.

[000494] In some embodiments, the complex described herein comprises an anti-TfR antibody covalently linked to a molecular payload, wherein the anti-TfR antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 69, SEQ ID NO: 71, or SEQ ID NO: 72, and a VL comprising the amino acid sequence of SEQ ID NO: 70. In some embodiments, the molecular payload is an oligonucleotide (e.g., an oligonucleotide targeting a gene listed in Table 1).

[000495] In some embodiments, the complex described herein comprises an anti-TfR antibody covalently linked to a molecular payload, wherein the anti-TfR antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 73 or SEQ ID NO: 76, and a VL comprising the amino acid sequence of SEQ ID NO: 74. In some embodiments, the molecular payload is an oligonucleotide (e.g., an oligonucleotide targeting a gene listed in Table 1). [000496] In some embodiments, the complex described herein comprises an anti-TfR antibody covalently linked to a molecular payload, wherein the anti-TfR antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 73 or SEQ ID NO: 76, and a VL comprising the amino acid sequence of SEQ ID NO: 75. In some embodiments, the molecular payload is an oligonucleotide (e.g., an oligonucleotide targeting a gene listed in Table 1). [000497] In some embodiments, the complex described herein comprises an anti-TfR antibody covalently linked to a molecular payload, wherein the anti-TfR antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 77, and a VL comprising the amino acid sequence of SEQ ID NO: 78. In some embodiments, the molecular payload is an oligonucleotide (e.g., an oligonucleotide targeting a gene listed in Table 1).

[000498] In some embodiments, the complex described herein comprises an anti-TfR antibody covalently linked to a molecular payload, wherein the anti-TfR antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 77 or SEQ ID NO: 79, and a VL comprising the amino acid sequence of SEQ ID NO: 80. In some embodiments, the molecular payload is an oligonucleotide (e.g., an oligonucleotide targeting a gene listed in Table 1). [000499] In some embodiments, the complex described herein comprises an anti-TfR antibody covalently linked to a molecular payload, wherein the anti-TfR antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 84, SEQ ID NO: 86 or SEQ ID NO: 87 and a light chain comprising the amino acid sequence of SEQ ID NO: 85. In some embodiments, the molecular payload is an oligonucleotide (e.g., an oligonucleotide targeting a gene listed in Table 1).

[000500] In some embodiments, the complex described herein comprises an anti-TfR antibody covalently linked to a molecular payload, wherein the anti-TfR antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 88 or SEQ ID NO: 91, and a light chain comprising the amino acid sequence of SEQ ID NO: 89. In some embodiments, the molecular payload is an oligonucleotide (e.g., an oligonucleotide targeting a gene listed in Table 1).

[000501] In some embodiments, the complex described herein comprises an anti-TfR antibody covalently linked to a molecular payload, wherein the anti-TfR antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 88 or SEQ ID NO: 91, and a light chain comprising the amino acid sequence of SEQ ID NO: 90. In some embodiments, the molecular payload is an oligonucleotide (e.g., an oligonucleotide targeting a gene listed in Table 1).

[000502] In some embodiments, the complex described herein comprises an anti-TfR antibody covalently linked to a molecular payload, wherein the anti-TfR antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 92 or SEQ ID NO: 94, and a light chain comprising the amino acid sequence of SEQ ID NO: 95. In some embodiments, the molecular payload is an oligonucleotide (e.g., an oligonucleotide targeting a gene listed in Table 1).

[000503] In some embodiments, the complex described herein comprises an anti-TfR antibody covalently linked to a molecular payload, wherein the anti-TfR antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 92, and a light chain comprising the amino acid sequence of SEQ ID NO: 93. In some embodiments, the molecular payload is an oligonucleotide (e.g., an oligonucleotide targeting a gene listed in Table 1). [000504] In some embodiments, the complex described herein comprises an anti-TfR antibody covalently linked to a molecular payload,, wherein the anti-TfR antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 97, SEQ ID NO: 98, or SEQ ID NO: 99 and a VL comprising the amino acid sequence of SEQ ID NO: 85. In some embodiments, the molecular payload is an oligonucleotide (e.g., an oligonucleotide targeting a gene listed in Table 1).

[000505] In some embodiments, the complex described herein comprises an anti-TfR antibody covalently linked to a molecular payload, wherein the anti-TfR antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 100 or SEQ ID NO: 101 and a light chain comprising the amino acid sequence of SEQ ID NO: 89. In some embodiments, the molecular payload is an oligonucleotide (e.g., an oligonucleotide targeting a gene listed in Table 1).

[000506] In some embodiments, the complex described herein comprises an anti-TfR antibody covalently linked to a molecular payload, wherein the anti-TfR antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 100 or SEQ ID NO: 101 and a light chain comprising the amino acid sequence of SEQ ID NO: 90. In some embodiments, the molecular payload is an oligonucleotide (e.g., an oligonucleotide targeting a gene listed in Table 1).

[000507] In some embodiments, the complex described herein comprises an anti-TfR antibody covalently linked to a molecular payload, wherein the anti-TfR antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 102 and a light chain comprising the amino acid sequence of SEQ ID NO: 93. In some embodiments, the molecular payload is an oligonucleotide (e.g., an oligonucleotide targeting a gene listed in Table 1). [000508] In some embodiments, the complex described herein comprises an anti-TfR antibody covalently linked to a molecular payload, wherein the anti-TfR antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 102 or SEQ ID NO: 103 and a light chain comprising the amino acid sequence of SEQ ID NO: 95. In some embodiments, the molecular payload is an oligonucleotide (e.g., an oligonucleotide targeting a gene listed in Table 1).

[000509] In some embodiments, the complex described herein comprises an anti-TfR antibody covalently linked via a lysine to the 5’ end of an oligonucleotide, wherein the anti- TfR antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 84 and a light chain comprising the amino acid sequence of in SEQ ID NO: 85; wherein the complex has the structure of: wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is an oligonucleotide targeting a gene listed in Table 1.

[000510] In some embodiments, the complex described herein comprises an anti-TfR antibody covalently linked via a lysine to the 5’ end of an oligonucleotide, wherein the anti- TfR antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 86 and a light chain comprising the amino acid sequence of in SEQ ID NO: 85; wherein the complex has the structure of: wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is an oligonucleotide targeting a gene listed in Table 1. [000511] In some embodiments, the complex described herein comprises an anti-TfR antibody covalently linked via a lysine to the 5’ end of an oligonucleotide, wherein the anti- TfR antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 87 and a light chain comprising the amino acid sequence of in SEQ ID NO: 85; wherein the complex has the structure of: wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is an oligonucleotide targeting a gene listed in Table 1.

[000512] In some embodiments, the complex described herein comprises an anti-TfR antibody covalently linked via a lysine to the 5’ end of an oligonucleotide, wherein the anti- TfR antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 88 and a light chain comprising the amino acid sequence of in SEQ ID NO: 89; wherein the complex has the structure of: wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is an oligonucleotide targeting a gene listed in Table 1.

[000513] In some embodiments, the complex described herein comprises an anti-TfR antibody covalently linked via a lysine to the 5’ end of an oligonucleotide, wherein the anti- TfR antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 88 and a light chain comprising the amino acid sequence of in SEQ ID NO: 90; wherein the complex has the structure of: wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is an oligonucleotide targeting a gene listed in Table 1.

[000514] In some embodiments, the complex described herein comprises an anti-TfR antibody covalently linked via a lysine to the 5’ end of an oligonucleotide, wherein the anti- TfR antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 91 and a light chain comprising the amino acid sequence of in SEQ ID NO: 89; wherein the complex has the structure of: wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is an oligonucleotide targeting a gene listed in Table 1.

[000515] In some embodiments, the complex described herein comprises an anti-TfR antibody covalently linked via a lysine to the 5’ end of an oligonucleotide, wherein the anti- TfR antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 91 and a light chain comprising the amino acid sequence of in SEQ ID NO: 90; wherein the complex has the structure of: wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is an oligonucleotide targeting a gene listed in Table 1.

[000516] In some embodiments, the complex described herein comprises an anti-TfR antibody covalently linked via a lysine to the 5’ end of an oligonucleotide, wherein the anti- TfR antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 92 and a light chain comprising the amino acid sequence of in SEQ ID NO: 93; wherein the complex has the structure of: wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is an oligonucleotide targeting a gene listed in Table 1.

[000517] In some embodiments, the complex described herein comprises an anti-TfR antibody covalently linked via a lysine to the 5’ end of an oligonucleotide, wherein the anti- TfR antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 94 and a light chain comprising the amino acid sequence of in SEQ ID NO: 95; wherein the complex has the structure of: wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is an oligonucleotide targeting a gene listed in Table 1.

[000518] In some embodiments, the complex described herein comprises an anti-TfR antibody covalently linked via a lysine to the 5’ end of an oligonucleotide, wherein the anti- TfR antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 92 and a light chain comprising the amino acid sequence of in SEQ ID NO: 95; wherein the complex has the structure of: wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is an oligonucleotide targeting a gene listed in Table 1.

[000519] In some embodiments, the complex described herein comprises an anti-TfR Fab covalently linked via a lysine to the 5’ end of an oligonucleotide, wherein the anti-TfR Fab comprises a VH comprising the amino acid sequence of SEQ ID NO: 69 and a VL comprising the amino acid sequence of in SEQ ID NO: 70; wherein the complex has the structure of: wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is an oligonucleotide targeting a gene listed in Table 1.

[000520] In some embodiments, the complex described herein comprises an anti-TfR Fab covalently linked via a lysine to the 5’ end of an oligonucleotide, wherein the anti-TfR Fab comprises a VH comprising the amino acid sequence of SEQ ID NO: 71 and a VL comprising the amino acid sequence of in SEQ ID NO: 70; wherein the complex has the structure of: wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is an oligonucleotide targeting a gene listed in Table 1.

[000521] In some embodiments, the complex described herein comprises an anti-TfR Fab covalently linked via a lysine to the 5’ end of an oligonucleotide, wherein the anti-TfR Fab comprises a VH comprising the amino acid sequence of SEQ ID NO: 72 and a VL comprising the amino acid sequence of in SEQ ID NO: 70; wherein the complex has the structure of: wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is an oligonucleotide targeting a gene listed in Table 1.

[000522] In some embodiments, the complex described herein comprises an anti-TfR Fab covalently linked via a lysine to the 5’ end of an oligonucleotide, wherein the anti-TfR Fab comprises a VH comprising the amino acid sequence of SEQ ID NO: 73 and a VL comprising the amino acid sequence of in SEQ ID NO: 74; wherein the complex has the structure of: wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is an oligonucleotide targeting a gene listed in Table 1.

[000523] In some embodiments, the complex described herein comprises an anti-TfR Fab covalently linked via a lysine to the 5’ end of an oligonucleotide, wherein the anti-TfR Fab comprises a VH comprising the amino acid sequence of SEQ ID NO: 73 and a VL comprising the amino acid sequence of in SEQ ID NO: 75; wherein the complex has the structure of: wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is an oligonucleotide targeting a gene listed in Table 1.

[000524] In some embodiments, the complex described herein comprises an anti-TfR Fab covalently linked via a lysine to the 5’ end of an oligonucleotide, wherein the anti-TfR Fab comprises a VH comprising the amino acid sequence of SEQ ID NO: 76 and a VL comprising the amino acid sequence of in SEQ ID NO: 74; wherein the complex has the structure of: wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is an oligonucleotide targeting a gene listed in Table 1.

[000525] In some embodiments, the complex described herein comprises an anti-TfR Fab covalently linked via a lysine to the 5’ end of an oligonucleotide, wherein the anti-TfR Fab comprises a VH comprising the amino acid sequence of SEQ ID NO: 76 and a VL comprising the amino acid sequence of in SEQ ID NO: 75; wherein the complex has the structure of: wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is an oligonucleotide targeting a gene listed in Table 1.

[000526] In some embodiments, the complex described herein comprises an anti-TfR Fab covalently linked via a lysine to the 5’ end of an oligonucleotide, wherein the anti-TfR Fab comprises a VH comprising the amino acid sequence of SEQ ID NO: 77 and a VL comprising the amino acid sequence of in SEQ ID NO: 78; wherein the complex has the structure of: wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is an oligonucleotide targeting a gene listed in Table 1.

[000527] In some embodiments, the complex described herein comprises an anti-TfR Fab covalently linked via a lysine to the 5’ end of an oligonucleotide, wherein the anti-TfR Fab comprises a VH comprising the amino acid sequence of SEQ ID NO: 79 and a VL comprising the amino acid sequence of in SEQ ID NO: 80; wherein the complex has the structure of: wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is an oligonucleotide targeting a gene listed in Table 1.

[000528] In some embodiments, the complex described herein comprises an anti-TfR Fab covalently linked via a lysine to the 5’ end of an oligonucleotide, wherein the anti-TfR Fab comprises a VH comprising the amino acid sequence of SEQ ID NO: 77 and a VL comprising the amino acid sequence of in SEQ ID NO: 80; wherein the complex has the structure of: wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is an oligonucleotide targeting a gene listed in Table 1.

[000529] In some embodiments, the complex described herein comprises an anti-TfR Fab covalently linked via a lysine to the 5’ end of an oligonucleotide, wherein the anti-TfR Fab comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 97 and a light chain comprising the amino acid sequence of in SEQ ID NO: 85; wherein the complex has the structure of: wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is an oligonucleotide targeting a gene listed in Table 1.

[000530] In some embodiments, the complex described herein comprises an anti-TfR Fab covalently linked via a lysine to the 5’ end of an oligonucleotide, wherein the anti-TfR Fab comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 98 and a light chain comprising the amino acid sequence of in SEQ ID NO: 85; wherein the complex has the structure of: wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is an oligonucleotide targeting a gene listed in Table 1.

[000531] In some embodiments, the complex described herein comprises an anti-TfR Fab covalently linked via a lysine to the 5’ end of an oligonucleotide, wherein the anti-TfR Fab comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 99 and a light chain comprising the amino acid sequence of in SEQ ID NO: 85; wherein the complex has the structure of: wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is an oligonucleotide targeting a gene listed in Table 1.

[000532] In some embodiments, the complex described herein comprises an anti-TfR Fab covalently linked via a lysine to the 5’ end of an oligonucleotide, wherein the anti-TfR Fab comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 100 and a light chain comprising the amino acid sequence of in SEQ ID NO: 89; wherein the complex has the structure of: wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is an oligonucleotide targeting a gene listed in Table 1.

[000533] In some embodiments, the complex described herein comprises an anti-TfR Fab covalently linked via a lysine to the 5’ end of an oligonucleotide, wherein the anti-TfR Fab comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 100 and a light chain comprising the amino acid sequence of in SEQ ID NO: 90; wherein the complex has the structure of: wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is an oligonucleotide targeting a gene listed in Table 1.

[000534] In some embodiments, the complex described herein comprises an anti-TfR Fab covalently linked via a lysine to the 5’ end of an oligonucleotide, wherein the anti-TfR Fab comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 101 and a light chain comprising the amino acid sequence of in SEQ ID NO: 89; wherein the complex has the structure of: wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is an oligonucleotide targeting a gene listed in Table 1.

[000535] In some embodiments, the complex described herein comprises an anti-TfR Fab covalently linked via a lysine to the 5’ end of an oligonucleotide, wherein the anti-TfR Fab comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 101 and a light chain comprising the amino acid sequence of in SEQ ID NO: 90; wherein the complex has the structure of: wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is an oligonucleotide targeting a gene listed in Table 1.

[000536] In some embodiments, the complex described herein comprises an anti-TfR Fab covalently linked via a lysine to the 5’ end of an oligonucleotide, wherein the anti-TfR Fab comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 102 and a light chain comprising the amino acid sequence of in SEQ ID NO: 93; wherein the complex has the structure of: wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is an oligonucleotide targeting a gene listed in Table 1.

[000537] In some embodiments, the complex described herein comprises an anti-TfR Fab covalently linked via a lysine to the 5’ end of an oligonucleotide, wherein the anti-TfR Fab comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 103 and a light chain comprising the amino acid sequence of in SEQ ID NO: 95; wherein the complex has the structure of: wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is an oligonucleotide targeting a gene listed in Table 1.

[000538] In some embodiments, the complex described herein comprises an anti-TfR Fab covalently linked via a lysine to the 5’ end of an oligonucleotide, wherein the anti-TfR Fab comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 102 and a light chain comprising the amino acid sequence of in SEQ ID NO: 95; wherein the complex has the structure of:

[000539] wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is an oligonucleotide targeting a gene listed in Table 1.

[000540] In some embodiments, in any one of the examples of complexes described herein, LI is any one of the spacers described herein.

[000541] In some embodiments, LI is: wherein the piperazine moiety links to the oligonucleotide, wherein L2 is wherein the piperazine moiety links to the oligonucleotide.

[000543] In some embodiments,

[000544] In some embodiments, LI is linked to a 5’ phosphate of the oligonucleotide.

[000545] In some embodiments, LI is optional (e.g., need not be present).

III. Formulations

[000546] Complexes provided herein may be formulated in any suitable manner. Generally, complexes provided herein are formulated in a manner suitable for pharmaceutical use. For example, complexes can be delivered to a subject using a formulation that minimizes degradation, facilitates delivery and/or (e.g., and) uptake, or provides another beneficial property to the complexes in the formulation. In some embodiments, provided herein are compositions comprising complexes and pharmaceutically acceptable carriers. Such compositions can be suitably formulated such that when administered to a subject, either into the immediate environment of a target cell or systemically, a sufficient amount of the complexes enter target muscle cells. In some embodiments, complexes are formulated in buffer solutions such as phosphate-buffered saline solutions, liposomes, micellar structures, and capsids. [000547] It should be appreciated that, in some embodiments, compositions may include separately one or more components of complexes provided herein (e.g., muscle-targeting agents, linkers, molecular payloads, or precursor molecules of any one of them).

[000548] In some embodiments, complexes are formulated in water or in an aqueous solution (e.g., water with pH adjustments). In some embodiments, complexes are formulated in basic buffered aqueous solutions (e.g., PBS). In some embodiments, formulations as disclosed herein comprise an excipient. In some embodiments, an excipient confers to a composition improved stability, improved absorption, improved solubility and/or (e.g., and) therapeutic enhancement of the active ingredient. In some embodiments, an excipient is a buffering agent (e.g., sodium citrate, sodium phosphate, a tris base, or sodium hydroxide) or a vehicle (e.g., a buffered solution, petrolatum, dimethyl sulfoxide, or mineral oil).

[000549] In some embodiments, a complex or component thereof (e.g., oligonucleotide or antibody) is lyophilized for extending its shelf-life and then made into a solution before use (e.g., administration to a subject). Accordingly, an excipient in a composition comprising a complex, or component thereof, described herein may be a lyoprotectant (e.g., mannitol, lactose, polyethylene glycol, or polyvinyl pyrolidone), or a collapse temperature modifier (e.g., dextran, ficoll, or gelatin).

[000550] In some embodiments, a pharmaceutical composition is formulated to be compatible with its intended route of administration. Examples of routes of administration include parenteral, e.g., intravenous, intradermal, subcutaneous, administration. Typically, the route of administration is intravenous or subcutaneous. In some embodiments, the route of administration is extramuscular parenteral administration.

[000551] Pharmaceutical compositions suitable for injectable use include sterile aqueous solutions (where water soluble) or dispersions and sterile powders for the extemporaneous preparation of sterile injectable solutions or dispersions. The carrier can be a solvent or dispersion medium containing, for example, water, ethanol, polyol (for example, glycerol, propylene glycol, and liquid polyethylene glycol, and the like), and suitable mixtures thereof.

In some embodiments, formulations include isotonic agents, for example, sugars, polyalcohols such as mannitol, sorbitol, and sodium chloride in the composition. Sterile injectable solutions can be prepared by incorporating the complexes in a required amount in a selected solvent with one or a combination of ingredients enumerated above, as required, followed by filtered sterilization.

[000552] In some embodiments, a composition may contain at least about 0.1% of the a complex, or component thereof, or more, although the percentage of the active ingredient(s) may be between about 1 % and about 80% or more of the weight or volume of the total composition. Factors such as solubility, bioavailability, biological half-life, route of administration, product shelf life, as well as other pharmacological considerations will be contemplated by one skilled in the art of preparing such pharmaceutical formulations, and as such, a variety of dosages and treatment regimens may be desirable.

IV. Methods of Use / Treatment

[000553] Complexes comprising a muscle-targeting agent covalently linked to a molecular payload as described herein are effective in treating a muscle disease ( e.g a rare muscle disease). In some embodiments, complexes are effective in treating a muscle disease provided in Table 1. In some embodiments, a muscle disease is associated with a disease allele, for example, a disease allele for a particular muscle disease may comprise a genetic alteration in a corresponding gene listed in Table 1.

[000554] In some embodiments, a subject may be a human subject, a non-human primate subject, a rodent subject, or any suitable mammalian subject. In some embodiments, a subject may have a muscle disease provided in Table 1.

[000555] An aspect of the disclosure includes a methods involving administering to a subject an effective amount of a complex as described herein. In some embodiments, an effective amount of a pharmaceutical composition that comprises a complex comprising a muscle-targeting agent covalently linked to a molecular payload can be administered to a subject in need of treatment. In some embodiments, a pharmaceutical composition comprising a complex as described herein may be administered by a suitable route, which may include intravenous administration, e.g., as a bolus or by continuous infusion over a period of time. In some embodiments, intravenous administration may be performed by intramuscular, intraperitoneal, intracerebrospinal, subcutaneous, intra- articular, intrasynovial, or intrathecal routes. In some embodiments, a pharmaceutical composition may be in solid form, aqueous form, or a liquid form. In some embodiments, an aqueous or liquid form may be nebulized or lyophilized. In some embodiments, a nebulized or lyophilized form may be reconstituted with an aqueous or liquid solution.

[000556] Compositions for intravenous administration may contain various carriers such as vegetable oils, dimethylactamide, dimethyformamide, ethyl lactate, ethyl carbonate, isopropyl myristate, ethanol, and polyols (glycerol, propylene glycol, liquid polyethylene glycol, and the like). For intravenous injection, water soluble antibodies can be administered by the drip method, whereby a pharmaceutical formulation containing the antibody and a physiologically acceptable excipients is infused. Physiologically acceptable excipients may include, for example, 5% dextrose, 0.9% saline, Ringer’s solution or other suitable excipients. Intramuscular preparations, e.g., a sterile formulation of a suitable soluble salt form of the antibody, can be dissolved and administered in a pharmaceutical excipient such as Water-for- Injection, 0.9% saline, or 5% glucose solution.

[000557] In some embodiments, a pharmaceutical composition that comprises a complex comprising a muscle-targeting agent covalently linked to a molecular payload is administered via site-specific or local delivery techniques. Examples of these techniques include implantable depot sources of the complex, local delivery catheters, site specific carriers, direct injection, or direct application.

[000558] In some embodiments, a pharmaceutical composition that comprises a complex comprising a muscle-targeting agent covalently linked to a molecular payload is administered at an effective concentration that confers therapeutic effect on a subject. Effective amounts vary, as recognized by those skilled in the art, depending on the severity of the disease, unique characteristics of the subject being treated, e.g. age, physical conditions, health, or weight, the duration of the treatment, the nature of any concurrent therapies, the route of administration and related factors. These related factors are known to those in the art and may be addressed with no more than routine experimentation. In some embodiments, an effective concentration is the maximum dose that is considered to be safe for the patient. In some embodiments, an effective concentration will be the lowest possible concentration that provides maximum efficacy.

[000559] Empirical considerations, e.g. the half-life of the complex in a subject, generally will contribute to determination of the concentration of pharmaceutical composition that is used for treatment. The frequency of administration may be empirically determined and adjusted to maximize the efficacy of the treatment.

[000560] Generally, for administration of any of the complexes described herein, an initial candidate dosage may be about 1 to 100 mg/kg, or more, depending on the factors described above, e.g. safety or efficacy. In some embodiments, a treatment will be administered once. In some embodiments, a treatment will be administered daily, biweekly, weekly, bimonthly, monthly, or at any time interval that provide maximum efficacy while minimizing safety risks to the subject. Generally, the efficacy and the treatment and safety risks may be monitored throughout the course of treatment [000561] The efficacy of treatment may be assessed using any suitable methods. In some embodiments, the efficacy of treatment may be assessed by evaluation of observation of symptoms associated with a muscle disease.

[000562] In some embodiments, a pharmaceutical composition that comprises a complex comprising a muscle-targeting agent covalently linked to a molecular payload described herein is administered to a subject at an effective concentration sufficient to inhibit activity or expression of a target gene by at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90% or at least 95% relative to a control, e.g. baseline level of gene expression prior to treatment.

[000563] In some embodiments, a single dose or administration of a pharmaceutical composition that comprises a complex comprising a muscle-targeting agent covalently linked to a molecular payload described herein to a subject is sufficient to inhibit activity or expression of a target gene for at least 1-5, 1-10, 5-15, 10-20, 15-30, 20-40, 25-50, or more days. In some embodiments, a single dose or administration of a pharmaceutical composition that comprises a complex comprising a muscle-targeting agent covalently linked to a molecular payload described herein to a subject is sufficient to inhibit activity or expression of a target gene for at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 weeks. In some embodiments, a single dose or administration of a pharmaceutical composition that comprises a complex comprising a muscle-targeting agent covalently linked to a molecular payload described herein to a subject is sufficient to inhibit activity or expression of a target gene for at least 1, 2, 3, 4, 5, or 6 months.

[000564] In some embodiments, a pharmaceutical composition may comprises more than one complex comprising a muscle-targeting agent covalently linked to a molecular payload. In some embodiments, a pharmaceutical composition may further comprise any other suitable therapeutic agent for treatment of a subject, e.g. a human subject having a muscle disease (e.g., a muscle disease provided in Table 1). In some embodiments, the other therapeutic agents may enhance or supplement the effectiveness of the complexes described herein. In some embodiments, the other therapeutic agents may function to treat a different symptom or disease than the complexes described herein.

EXAMPLES

Example 1: Targeting DMPK with transfected antisense oligonucleotides [000565] A gapmer antisense oligonucleotide that targets both wild-type and mutant alleles of DMPK (AS 0300) was tested in vitro for its ability to reduce expression levels of DMPK in an immortalized cell line. Briefly, Hepa 1-6 cells were transfected with the AS0300 (100 nM) formulated with Lipofectamine 2000. DMPK expression levels were evaluated 72 hours following transfection. A control experiment was also performed in which vehicle (phosphate-buffered saline) was delivered to Hepa 1-6 cells in culture and the cells were maintained for 72 hours. As shown in FIG. 1, it was found that ASO300 reduced DMPK expression levels by about 90% compared with controls.

Example 2: Targeting DMPK with a muscle-targeting complex

[000566] A muscle-targeting complex was generated comprising the DMPK ASO used in Example 1 (ASO300) covalently linked, via a cathepsin cleavable linker, to DTX-A-002 (RI7 217 Fab), an anti-transferrin receptor antibody.

[000567] Briefly, a maleimidocaproyl-L-valine-L-citrulline-p-aminobenzyl alcohol p- nitrophenyl carbonate (MC-Val-Cit-PABC-PNP) linker molecule was coupled to NH2-C6- ASO300 using an amide coupling reaction. Excess linker and organic solvents were removed by gel permeation chromatography. The purified Val-Cit-linker-ASO300 was then coupled to a thiol on the anti-transferrin receptor antibody (DTX-A-002).

[000568] The product of the antibody coupling reaction was then subjected to hydrophobic interaction chromatography (HIC-HPLC). FIG. 2A shows a resulting HIC-HPLC trace, in which fractions B7-C2 of the trace (denoted by vertical lines) contained antibody- oligonucleotide complexes (referred to as DTX-C-008) comprising one or two DMPK ASO molecules covalently attached to DTX-A-002, as determined by SDS-PAGE. These HIC- HPLC fractions were combined and densitometry following additional purification confirmed that this sample of DTX-C-008 complexes had an average ASO to antibody ratio (DAR) of 1.48. SDS-PAGE analysis demonstrated that 86.4% of this sample of DTX-C-008 complexes comprised DTX-A-002 linked to either one or two DMPK ASO molecules (FIG. 2B).

[000569] Using the same methods as described above, a control complex was generated comprising the DMPK ASO used in Example 1 (ASO300) covalently linked via a Val-Cit linker to an IgG2a (Fab) antibody (DTX-C-007).

[000570] The purified RI7 217 Fab antibody- ASO complex (DTX-C-008) was then tested for cellular internalization and inhibition of DMPK. Hepa 1-6 cells, which have relatively high expression levels of transferrin receptor, were incubated in the presence of vehicle control, DTX-C-008 (100 nM), or DTX-C-007 (100 nM) for 72 hours. After the 72 hour incubation, the cells were isolated and assayed for expression levels of DMPK (FIG. 3). Cells treated with the DTX-C-008 demonstrated a reduction in DMPK expression by about 65% relative to the cells treated with the vehicle control. Meanwhile, cells treated with the DTX-C- 007 had DMPK expression levels comparable to the vehicle control (no reduction in DMPK expression). These data indicate that the anti-transferrin receptor antibody of the DTX-C-008 enabled cellular internalization of the complex, thereby allowing the DMPK ASO to inhibit expression of DMPK.

Example 3: Targeting DMPK in mouse muscle tissues with a muscle-targeting complex [000571] The muscle-targeting complex described in Example 2, RI7 217 Fab antibody- ASO complex DTX-C-008, was tested for inhibition of DMPK in mouse tissues. C57BL/6 wild-type mice were intravenously injected with a single dose of a vehicle control, naked ASO300 (3 mg/kg of ASO), DTX-C-008 (3 mg/kg of ASO, corresponding to 20 mg/kg antibody conjugate), or DTX-C-007 IgG2a Fab antibody-ASO complex (3 mg/kg of ASO, corresponding to 20 mg/kg antibody conjugate). Naked ASO300, the DMPK ASO as described in Example 1, was used as a control. Each experimental condition was replicated in three individual C57BL/6 wild-type mice. Following a seven-day period after injection, the mice were euthanized and segmented into isolated tissue types. Individual tissue samples were subsequently assayed for expression levels of DMPK (FIGs. 4A-4E and 5A-5B).

[000572] Mice treated with the DTX-C-008 complex demonstrated a reduction in DMPK expression in a variety of skeletal, cardiac, and smooth muscle tissues. For example, as shown in FIGs 4A-4E, DMPK expression levels were significantly reduced in gastrocnemius (50% reduction), heart (30% reduction), esophagus (45% reduction), tibialis anterior (47% reduction), and soleus (31% reduction) tissues, relative to the mice treated with the vehicle control. Meanwhile, mice treated with the DTX-C-007 complex had DMPK expression levels comparable to the vehicle control mice and mice treated with naked AS 0300 (no reduction in DMPK expression) for all assayed muscle tissue types.

[000573] Mice treated with the DTX-C-008 complex demonstrated no change in DMPK expression in non-muscle tissues such as spleen and brain tissues (FIGs. 5A and 5B).

[000574] These data indicate that the anti-transferrin receptor antibody of the DTX-C-008 enabled cellular internalization of the complex into muscle-specific tissues in an in vivo mouse model, thereby allowing the DMPK ASO to inhibit expression of DMPK. These data further demonstrate that the DTX-C-008 complex is capable of specifically targeting muscle tissues.

Example 4: Targeting DMPK in mouse muscle tissues with a muscle-targeting complex [000575] The muscle-targeting complex described in Example 2, RI7 217 Fab antibody- ASO complex DTX-C-008, was tested for dose-dependent inhibition of DMPK in mouse tissues. C57BL/6 wild-type mice were intravenously injected with a single dose of a vehicle control (phosphate-buffered saline, PBS), naked ASO300 (10 mg/kg of ASO), DTX-C-008 (3 mg/kg or 10 mg/kg of ASO, wherein 3 mg/kg corresponds to 20 mg/kg antibody conjugate), or DTX-C-007 IgG2a Fab antibody- ASO complex (3 mg/kg or 10 mg/kg of ASO, wherein 3 mg/kg corresponds to 20 mg/kg antibody conjugate). Naked ASO300, the DMPK ASO as described in Example 1, was used as a control. Each experimental condition was replicated in five individual C57BL/6 wild-type mice. Following a seven-day period after injection, the mice were euthanized and segmented into isolated tissue types. Individual tissue samples were subsequently assayed for expression levels of DMPK (FIGs. 6A-6F).

[000576] Mice treated with the DTX-C-008 complex demonstrated a reduction in DMPK expression in a variety of skeletal muscle tissues. As shown in FIGs 6A-6F, DMPK expression levels were significantly reduced in tibialis anterior (58% and 75% reduction for 3 mg/kg and 10 mg/kg DTX-C-008, respectively), soleus (55% and 66% reduction for 3 mg/kg and 10 mg/kg DTX-C-008, respectively), extensor digitorum longus (EDF) (52% and 72% reduction for 3 mg/kg and 10 mg/kg DTX-C-008, respectively), gastrocnemius (55% and 77% reduction for 3 mg/kg and 10 mg/kg DTX-C-008, respectively), heart (19% and 35% reduction for 3 mg/kg and 10 mg/kg DTX-C-008, respectively), and diaphragm (53% and 70% reduction for 3 mg/kg and 10 mg/kg DTX-C-008, respectively) tissues, relative to the mice treated with the vehicle control. Notably, all assayed muscle tissue types experienced dose-dependent inhibition of DMPK, with greater reduction in DMPK levels at 10 mg/kg antibody conjugate relative to 3 mg/kg antibody conjugate.

[000577] Meanwhile, mice treated with the control DTX-C-007 complex had DMPK expression levels comparable to the vehicle control (no reduction in DMPK expression) for all assayed muscle tissue types.

These data indicate that the anti-transferrin receptor antibody of the DTX-C-008 enabled cellular internalization of the complex into muscle- specific tissues in an in vivo mouse model, thereby allowing the DMPK ASO to inhibit expression of DMPK. These data further demonstrate that the DTX-C-008 complex is capable of specifically targeting muscle tissues for dose-dependent inhibition of DMPK.

Example 5: Targeting DMPK in cynomolgus monkey muscle tissues with a muscletargeting complex [000578] A muscle-targeting complex comprising ASO300 (DTX-C-012), was generated and purified using methods described in Example 2. DTX-C-012 is a complex comprising a human anti-transferrin receptor antibody covalently linked, via a cathepsin cleavable Val-Cit linker, to ASO300, an antisense oligonucleotide that targets DMPK. The anti-TfR antibody used in DTX-C-012 is cross -reactive with cynomolgus and human TfRl. Following HIC- HPLC purification and additional purification, densitometry confirmed that DTX-C-012 had an average ASO to antibody ratio of 1.32, and SDS-PAGE revealed a purity of 92.3%.

[000579] DTX-C-012 was tested for inhibition of DMPK in male cynomolgus monkey tissues. Male cynomolgus monkeys (19-31 months; 2-3 kg) were intravenously injected with a single dose of a saline control, naked ASO300 (10 mg/kg of ASO), or DTX-C-012 (10 mg/kg of ASO) on Day 0. Each experimental condition was replicated in three individual male cynomolgus monkeys. On Day 7 after injection, tissue biopsies (including muscle tissues) were collected. DMPK mRNA expression levels, ASO detection assays, serum clinical chemistries, tissue histology, clinical observations, and body weights were analyzed. The monkeys were euthanized on Day 14.

[000580] Significant knockdown (KD) of DMPK mRNA expression using DTX-C-012 was observed in soleus, deep flexor, and masseter muscles relative to saline control, with 39% KD, 62% KD, and 41% KD, respectively (FIGs. 7A-7C). Robust knockdown of DMPK mRNA expression by DTX-C-012 was further observed in gastrocnemius (62% KD; FIG. 7D), EDL (29% KD; FIG. 7E), tibialis anterior muscle (23% KD; FIG. 7F), diaphragm (54% KD; FIG. 7G), tongue (43% KD; FIG. 7H), heart muscle (36% KD; FIG. 71), quadriceps (58% KD; FIG. 7J), bicep (51% KD; FIG. 7K), and deltoid muscles (47% KD; FIG. 7F). Knockdown of DMPK mRNA expression by DTX-C-012 in smooth muscle was also observed in the intestine, with 63% KD at jejunum-duodenum ends (FIG. 8A) and 70% KD in ileum (FIG. 8B).

Notably, naked DMPK ASO300 (i.e., not linked to a muscle-targeting agent) had minimal effects on DMPK expression levels relative to the vehicle control (i.e., little or no reduction in DMPK expression) for most assayed muscle tissue types. Monkeys treated with the DTX-C- 012 complex demonstrated no change in DMPK expression in most non-muscle tissues, such as kidney, brain, and spleen tissues (FIGs. 9A-9D). Additional tissues were examined, as depicted in FIG. 10, which shows normalized DMPK mRNA tissue expression levels across several tissue types in cynomolgus monkeys. (N=3 male cynomolgus monkeys)

[000581] Prior to euthanization, all monkeys were tested for reticulocyte levels, platelet levels, hemoglobin expression, alanine aminotransferase (AFT) expression, aspartate aminotransferase (AST) expression, and blood urea nitrogen (BUN) levels on days 2, 7, and 14 after dosing. As shown in FIG. 12, monkeys dosed with antibody-oligonucleotide complex had normal reticulocyte levels, platelet levels and hemoglobin expression throughout the length of the experiment. Monkeys dosed with DTX-C-012 also had normal alanine aminotransferase (ALT) expression, aspartate aminotransferase (AST) expression, and blood urea nitrogen (BUN) levels throughout the length of the experiment. These data show that a single dose of a complex comprising ASO300 is safe and tolerated in cynomolgus monkeys.

[000582] These data demonstrate that the anti-transferrin receptor antibody of the DTX- C-012 complex enabled cellular internalization of the complex into muscle- specific tissues in an in vivo cynomolgus monkey model, thereby allowing the DMPK ASO (ASO300) to inhibit expression of DMPK. These data further demonstrate that the DTX-C-012 complex is capable of specifically targeting muscle tissues for dose-dependent inhibition of DMPK without substantially impacting non-muscle tissues. This is direct contrast with the limited ability of naked DMPK ASO300 (not linked to a muscle-targeting agent), to inhibit expression of DMPK in muscle tissues of an in vivo cynomolgus monkey model.

Example 6: Targeting DMPK in mouse muscle tissues with a muscle-targeting complex [000583] The RI7 217 Fab antibody- ASO muscle-targeting complex described in Example 2, DTX-C-008, was tested for time-dependent inhibition of DMPK in mouse tissues. C57BL/6 wild-type mice were intravenously injected with a single dose of a vehicle control (saline), naked ASO300 (10 mg/kg of ASO), or DTX-C-008 (10 mg/kg of ASO) and euthanized after a prescribed period of time, as described in Table 10. Following euthanization, the mice were segmented into isolated tissue types and tissue samples were subsequently assayed for expression levels of DMPK (FIGs. 11A-11B).

Table 10. Experimental conditions Mice treated with the DTX-C-008 complex demonstrated approximately 50% reduction in DMPK expression in gastrocnemius (FIG. 11 A) and tibialis anterior (FIG. 11B) muscles for all of Groups 9-12 (3-28 days between injection and euthanization), relative to vehicle. Mice treated with the naked ASO300 oligonucleotide did not demonstrate significant reduction in DMPK expression.

Example 7: Targeting DMPK in mouse muscle tissues with a muscle-targeting complex [000584] The RI7 217 Fab antibody- ASO muscle-targeting complex described in Example 2, DTX-C-008, was tested for time-dependent inhibition of DMPK in mouse tissues in vivo. C57BL/6 wild-type mice were intravenously injected with a single dose of a vehicle control (phosphate-buffered saline (PBS)), naked antisense oligonucleotide (ASO300) (10 mg/kg of ASO), DTX-C-007 IgG2a Fab antibody-ASO control complex (10 mg/kg of ASO), or DTX-C-008 10 mg/kg of ASO) on Day 0 and euthanized after a prescribed period of time, as described in Table 11. One group of mice in each experimental condition was subjected to a second dose (multi-dose groups) at four weeks (Day 28). Following euthanization, the mice were segmented into isolated tissue types and samples of tibialis anterior and gastrocnemius muscle tissues were subsequently assayed for expression levels of DMPK (FIGs. 13A-13B).

Table 11. Experimental conditions [000585] Mice treated with the RI7217 Fab antibody- ASO DTX-C-008 complex demonstrated about 50-60% reduction in DMPK expression in tibialis anterior muscle (FIG. 13A) and about 30-50% reduction in DMPK expression in gastrocnemius muscle (FIG. 13B) for all of Groups 16-20 (2-12 weeks between injection and euthanization), relative to vehicle. These data show that a single dose of the muscle-targeting complex DTX-C-008 reduces expression of DMPK for at least twelve weeks following administration of the complex. [000586] In contrast, mice treated with the naked antisense oligonucleotide or the control complex did not demonstrate significant inhibition of DMPK expression across all experimental groups and tissues.

[000587] These data demonstrate that a muscle-targeting complex as described herein is capable of providing persistent inhibition of DMPK expression in vivo for up to 12 weeks following a single dose or administration of said muscle targeting complex.

Example 8: A muscle-targeting complex can target gene expression in the nucleus [000588] The RI7 217 Fab antibody- ASO muscle-targeting complex as described in Example 2, DTX-C-008, was tested for inhibition of nuclear-retained DMPK RNA in mouse muscle tissues. The mice used for this Example have been engineered to express a human mutant DMPK gene (schematic shown in FIG. 14A) - DMPK with a 350 CTG repeat region and a downstream G-for-C single-nucleotide polymorphism. As shown in FIG. 14A, the human mutant DMPK RNA is retained in the nucleus, while the mouse wild-type DMPK RNA is located in the cytoplasm and the nucleus.

[000589] Mice were intravenously injected with a single dose of a vehicle control (saline), an IgG2a Fab-ASO control complex DTX-C-007 (10 mg/kg of ASO), naked ASO300 (10 mg/kg of ASO), or DTX-C-008 (10 mg/kg of ASO) and euthanized after 14 days. Six mice were treated in each experimental condition. Following euthanization, the mice were segmented into isolated tissue types and tissue samples were subsequently assayed for expression levels of mutant and wild-type DMPK (FIG. 14B).

[000590] Mice treated with the muscle-targeting complex DTX-C-008 demonstrated statistically significant reduction in both nuclear-retained mutant DMPK and wild-type DMPK. (p-value <0.05). These data demonstrate that a muscle-targeting complex as described herein is capable of targeting DMPK in the nucleus.

Example 9: A muscle-targeting complex reverses myotonia in HSA ^LR mouse model [000591] A muscle-targeting complex (DTX-Actin) was generated comprising an antisense oligonucleotide (ASO) that targets actin covalently linked, via a cathepsin cleavable linker, to DTX-A-002 (RI7 217 Fab), an anti-transferrin receptor antibody.

[000592] The actin-targeting ASO is an MOE 5-10-5 gapmer that comprises: 5'-NH ₂ - (CH ₂ ) ₆ -dA*oC*oC*oA*oT*oT*dT*dT*dC*dT*dT*dC*dC*dA*dC*dA*oG*oG *oG*oC*oT- 3 (SEQ ID NO: 131); wherein represents a PS linkage; ‘d’ represents a deoxynucleic acid; and ‘o’ represents a 2'-MOE.

[000593] DTX-Actin was then tested for its ability to reduce target gene expression (hACTAl) and reduce myotonia in HSA ^LR mice, a mouse model that has a functional myotonia phenotype similar to that observed in human DM1 patients. Details of the HSA ^LR mouse model are as described in Mankodi, A. et al. Science. 289: 1769, 2000. HSA ^LR mice were intravenously injected with a single dose of PBS or DTX-Actin (either 10 mg/kg or 20 mg/kg ASO equivalent). Each of these three experimental conditions were replicated in two individual mice. On Day 14 after injection, mice were euthanized and specific muscles were collected - quadriceps (quad), gastrocnemius (gastroc) and tibialis anterior (TA). The muscle tissues were analyzed for expression of hACTAl. DTX-Actin demonstrated reduction of hACTAl expression in all three muscle tissues relative to vehicle control (FIG. 15A).

[000594] On Day 14 after injection, and prior to the euthanasia and tissue collection described above, electromyography (EMG) was performed on specific muscles. EMG myotonic discharges were graded by a blinded examiner on a 4-point scale: 0, no myotonia; 1, occasional myotonic discharge in less than 50% of needle insertions; 2, myotonic discharge in greater than 50% of needle insertions; and 3: myotonic discharge with nearly every insertion. DTX-Actin demonstrated reduction in graded myotonia in all three muscle tissues relative to vehicle control (FIG. 15B). Mice treated with DTX-Actin at a dose of 20 mg/kg ASO equivalent demonstrated little-to-no myotonia in quadriceps and gastrocnemius muscles. [000595] These data demonstrate that a single dose of a muscle-targeting complex is capable of gene-specific targeting and reduction in functional myotonia in in the HSA ^LR mice, a mouse model that has a functional myotonia phenotype similar to that observed in human DM1 patients.

Example 10: A muscle-targeting complex can functionally correct arrhythmia in a DM1 mouse model

[000596] The RI7 217 Fab antibody- ASO muscle-targeting complex as described in Example 2, DTX-C-008, was tested for its ability to functionally correct arrhythmia in a DM1 mouse model. The mice used for this Example are the offspring of mice expressing myosin heavy chain reverse tet transactivator (MHCrtTA) and mice expressing a mutant form of human DMPK (CUG960). FIG. 16A shows the genomic structure of the mutant transgene. [000597] Doxycycline containing chow (2 g doxycycline/kg chow, Bio-Serv) was provided to the mice beginning at postnatal day 1, initially through the nursing dam and subsequently through chow after weaning, to induce selective expression of mutant DMPK in the heart. All mice were maintained on chow containing doxycycline throughout the entire course of the study except the “off Dox Control” group. At 12 weeks of age, all mice underwent a baseline pre-dose ECG evaluation. Mice were then treated intravenously with a single dose of either vehicle (saline), naked ASO300 (10 mg/kg), DTX-C-008 (10 mg/kg ASO equivalent) or DTX-C-008 (20 mg/kg ASO equivalent). Following baseline pre-dose ECG evaluation mice in the “off Dox Control” group were switched to chow without doxycycline. Post dose ECG evaluations were performed in all mice 7 and 14 days after treatment, or in the case of the “off Dox Control” group 7 and 14 days after reversion to chow without doxycycline. For each of the ECG spectra, QRS and QTc intervals were measured.

[000598] In this model, mice treated with doxycycline exhibit prolongation of QRS and QTC intervals driven by expression of mutant DMPK in the heart, similar to those reported in DM1 patients, and consistent with increased propensity for cardiac arrhythmia. Removal of doxycycline for the diet in the “Off Dox Control” group turns off expression of mutant DMPK, resulting in a normalization of QRS (FIG. 16B) and QTC (FIG. 16C) intervals. Mice maintained on doxycycline and treated with 20 mg/kg of the muscle-targeting complex DTX- C-008 demonstrated statistically significant reduction in their QTc intervals after 14 days despite continued expression of mutant DMPK in the heart (FIG. 16C). This reduction in QTc intervals represents a correction in cardiac arrhythmia in a DM1 mouse model. These data demonstrate that a muscle-targeting complex as described herein is capable of providing a phenotypic and therapeutic benefit in a DM1 model.

Example 11: A muscle-targeting complex can target DMPK and correct DMl-related gene splicing

[000599] In isolated muscles cells derived from human DM1 patients, the muscle targeting complex as described in Example 5, DTX-C-012, was tested for reduction of DMPK expression and subsequent correction of splicing defects in Binl, a downstream gene of DMPK. [000600] Briefly, patient cells were seeded at a density of 10k cells/well before being allowed to recover overnight. Cells were then treated with PBS (vehicle control), naked ASO300, or DTX-C-012 (500 nM; equivalent to 55.5 nM ASO). Cells were allowed to differentiate for 14 days. Expression levels of DMPK and %Binl exon- 11 inclusion were determined on Days 10, 11, 12, 13, and 14 post differentiation.

[000601] Treatment of DM1 patient cells with the DTX-C-012 complex leads to reduction of DMPK levels as early as Day 10 post differentiation (FIG. 17A). Treatment of DM1 patient cells with the DTX-C-012 complex also leads to a statistically significant time- dependent change in Bin 1 splicing (FIG. 17B). (**p<0.01, ***p<0.001). These data demonstrate that a muscle-targeting complex as described herein is capable of providing phenotypic and therapeutic benefit (increased correction of DM1 gene-specific splicing) in a DM1 model.

Example 12: A muscle-targeting complex enables cellular internalization and targeting of DUX4

[000602] A muscle-targeting complex (anti-TfR antibody-FMlO) was generated comprising the FM10 PMO covalently linked to an anti-transferrin receptor antibody.

[000603] Briefly, purified Val-Cit- linker- FM 10 was coupled to a functionalized 15G11 antibody generated through modifying e-amine on lysine of the antibody.

[000604] The product of the antibody coupling reaction was then subjected to hydrophobic interaction chromatography (HIC) and size exclusion chromatography (SEC) to isolate pure conjugate. Ultrafiltration was then used to concentrate the conjugate and densitometry confirmed that this sample of anti-TfR antibody-FMlO complexes had an average ASO to antibody ratio of 1.9.

[000605] FM 10 PMO comprises the sequence GGGC ATTTT A AT AT AT CTCT G A ACT (SEQ ID NO: 147).

[000606] Human U-2 OS cells were dosed with the complex. Briefly, U-2 OS cells were seeded at a density of 10k cells/well before being allowed to recover overnight. Cells were then treated with one of the following treatments - vehicle control (PBS), a siRNA that targets DUX4, naked FM10 PMO (1 mM), naked FM10 PMO (10 pM), or anti-TfR antibody-FMlO (1 pM; equivalent to 800 nM naked PMO). Cells were incubated for 72 hours before being harvested for total RNA. cDNA was then synthesized from the total RNA extracts and qPCR was performed to determine expression of downstream DUX4 genes (ZSCAN4, MBD3F2, TRIM43) in technical quadruplicate. All qPCR data were analyzed using a standard AACT method and were normalized to a plate-based negative control comprised of untreated cells (i.e., without any oligonucleotide). Results were then converted to fold change to evaluate efficacy.

[000607] As shown in FIG. 18, upregulation of DUX4 in FSHD leads to the upregulation of disease characteristic genes including ZSCAN4, MBD3L2, and TRIM43. In U-2 OS cells that express DUX4 and have elevated levels of ZSCAN4, MDB3L2 and TRIM43, mirroring pathologically relevant events in FSHD patient cells, treatment with naked FM10 at 1 mM fails to reduce ZSCAN4, MBD3L2, and TRIM43 expression. Increased concentration of naked FM10 (to 10 mM) leads to a modest reduction in ZSCAN4 and TRIM43 expression, but has no effect on MDB3L2 expression. In contrast, treatment with anti-TfR antibody-FMlO (1 mM concentration; equivalent to 800 nM of naked FM10) significantly reduced expression of MBD3L2, ZSCAN4 and TRIM43.

These data indicate that the anti-transferrin receptor antibody of the anti-TfR antibody-FMlO complex enabled cellular internalization of the complex into U-2 OS cells, thereby allowing the FM10 PMO to inhibit expression of DUX4.

Example 13: Targeting DMD with a muscle-targeting complex

[000608] A muscle-targeting complex (DTX-C-042) was generated comprising an exon- 23 PMO ASO covalently linked to DTX-A-002 (RI7 217 (Fab)), an anti-transferrin receptor antibody.

[000609] Briefly, a Bicyclo[6.1.0]nonyne-PEG3-L-valine-L-citmlline-pentafluoroph enyl ester (BCN-PEG3-Val-Cit-PFP) linker molecule was coupled to NH ₂ -C ₆ -(exon-23 PMO) using an amide coupling reaction. Excess linker and organic solvents were removed by gel permeation chromatography. The purified Val-Cit-linker-(exon-23 PMO) was then coupled to an azide functionalized anti-transferrin receptor antibody (DTX-A-002) generated through modifying e-amine on lysine with Azide-PEG4-PFP.

[000610] The product of the antibody coupling reaction was then purified and densitometry confirmed that this sample of DTX-C-042 complexes had an average ASO to antibody ratio of 1.9.

[000611] The PMO ASO that targets exon-23 of DMD used in this Example comprises a sequence consisting of GGCCAAACCUCGGCUUACCUGAAAU (SEQ ID NO: 148). [000612] DTX-C-042 was tested for its ability to induce exon skipping of exon 23 of the dystrophin gene, and to subsequently increase expression of dystrophin protein in targeted muscles relevant to DMD in vivo mdx mice, a DMD mouse model, were intravenously injected with a single dose of a vehicle control (saline); DTX-C-042 complex at a dose of 10 mg/kg ASO; DTX-C-042 complex at a dose of 20 mg/kg ASO; or DTX-C-042 complex at a dose of 30 mg/kg ASO. Each experimental condition was replicated in four mdx mice. Four wild-type mice were also dosed with vehicle control (saline) as a control experiment.

[000613] Fourteen days after treatment, mice were euthanized and targeted muscle tissues were collected. Individual muscle tissue samples were subsequently assayed for percent skipping of exon 23 of the dystrophin gene (FIG. 19). Additionally, dystrophin protein levels in targeted muscles were also quantified (quantification of dystrophin in quadriceps is shown in FIGs. 20A-20B).

[000614] Mice treated with the antibody- ASO complex demonstrated a dose-dependent increase in the percent exon skipping of exon 23 in quadriceps, diaphragm, and heart muscles. Mice treated with the antibody- ASO complex also demonstrated a dose-dependent increase in the expression of dystrophin protein in the quadriceps, with an average of >4% dystrophin protein in mice treated with 30 mg/kg ASO equivalent of DTX-C-042.

[000615] These data demonstrate that the anti-transferrin receptor antibody of the antibody- ASO complex enables cellular internalization of the complex into muscle-specific tissues in an in vivo mdx mouse model, thereby allowing the exon 23 PMO ASO to induce exon skipping of exon 23 of DMD. These data further demonstrate that the antibody- ASO complex is capable of specifically targeting muscle tissues.

Example 14: Targeting DMD with a muscle-targeting complex to demonstrate functional benefit in mdx mouse model

[000616] Mdx mice (DMD mouse model; diseased mice) were intravenously injected with a single dose of a vehicle control (saline); the MDX-ASO (naked exon 23 skipping PMO ASO, 30 mg/kg); or the DTX-C-042 complex as described in Example 13 (anti-transferrin receptor antibody RI7 217 Fab linked to exon 23 skipping PMO, 30 mg/kg ASO equivalent). Each experimental condition was replicated in five mdx mice. Five wild-type mice (healthy mice) were also dosed with vehicle control (saline).

[000617] Two and four weeks after injection, the functional activity of all treated mice was determined using an open field chamber experiment. The experiment involved three consecutive stages: (1) a 10-minute period during which each mouse was placed into an open field chamber; (2) a 10-minute period during which each mouse was subjected to a hind limb fatigue challenge; and (3) a 10-minute period during which each mouse was placed into an open field chamber. The total horizontal distances traveled during stages (1) and (3) were collected. The percent change in the total distance traveled between the first and second tests. As shown in FIG. 21 A, at the two week timepoint, the wild-type mice treated with saline traveled an average of about 20% less during stage (3) relative to stage (1); the mdx mice treated with saline traveled an average of about 70% less during stage (3) relative to stage (1); the mdx mice treated with MDX-ASO traveled an average of about 85% less during stage (3) relative to stage (1); and the mdx mice treated with DTX-C-042 traveled an average of about 40% less during stage (3) relative to stage (1). When compared to wild-type mice treated with saline, mdx mice treated with saline performed significantly worse (as indicated by a significant decrease in distance traveled in stage (3) relative to stage (1)). This observation is consistent with the impaired motor function experienced by DMD patients mdx mice treated with naked MDX-ASO showed the same compromised functional performance as those treated with vehicle. In contrast, the performance of mdx mice treated with DTX-C-042 was not statistically different from vehicle treated wild-type mice. As shown in FIG. 21B, at the four week timepoint, the wild-type mice treated with saline traveled an average of about 35% less during stage (3) relative to stage (1); the mdx mice treated with saline traveled an average of about 80% less during stage (3) relative to stage (1); the mdx mice treated with MDX-ASO traveled an average of about 55% less during stage (3) relative to stage (1); and the mdx mice treated with DTX-C-042 traveled an average of about 50% less during stage (3) relative to stage (1).

[000618] Two and four weeks after injection, the activity of all treated mice was determined using a cage running wheel test. Each mouse was individually placed into cages with a running wheel for a 24-hour period. The 24-hour period involved five hours of light on followed by thirteen hours of darkness, and ending with six hours of light. The total distance traveled (in meters, m) by each mouse on the running wheel was continuously collected throughout the 24-hour period and subsequently binned into discrete one-hour increments. As shown in FIG. 21C, at the two week timepoint, the distance traveled by the mdx mice treated with DTX-C-042 was higher than the distance traveled by the mdx mice treated with MDX- ASO or with saline, and approached the distance traveled by the wild-type mice at certain times. As shown in FIG. 2 ID, at the four week timepoint, the distance traveled by the mdx mice treated with DTX-C-042 complex closely mirrored the total distance traveled by the wild- type mice treated with saline during the dark period (i.e., when mice are active). This is in contrast to the mdx mice treated with either saline or MDX-ASO, which traveled considerably shorter distances during the dark period. [000619] All mice in this Example were further tested for creatine kinase activity levels two weeks and four weeks after injection. Wild-type mice do not secrete large amounts of creatine kinase from muscle tissues. Conversely, mdx mice (having diseased muscle tissues) do secrete high levels of creatine kinase, which can be observed by determination of creatine kinase enzymatic activities. As shown in FIG. 2 IE, the mdx mice that were treated with saline had approximately 9- and 10- fold more creatine kinase enzymatic activity relative to wild-type mice treated with saline after two and four weeks, respectively. Dosing with naked ASO provided no significant benefit to the mdx mice. However, dosing mdx mice with DTX-C-042 complex did provide a statistically significant reduction in levels of creatine kinase activity after both two and four weeks.

[000620] These surprising results show that the antibody- ASO complex is capable of providing functional benefits to mice suffering from a DMD phenotype {mdx mice), such that these mice have phenotypic indicators resembling healthy (wild-type) mice. The performance of the antibody- ASO complex relative to the naked PMO (MDX- ASO) demonstrates that the anti-transferrin receptor antibody of the antibody- ASO complex is responsible for providing the functional benefits shown in this Example.

Example 15: Selected antisense oligonucleotides provided dose-dependent reduction in DMPK expression in DM1 and NHP myotubes

[000621] Oligonucleotides against DMPK were assessed to identify oligos that are safe in vivo (e.g., as indicated by low immunogenicity as measured by cytokine induction), and further based on manufacturability and secondary structure considerations. Three antisense oligonucleotides, DMPK- ASO- 1 (SEQ ID NO: 149), DMPK-ASO-2 (SEQ ID NO: 150), and DMPK-ASO-3 (SEQ ID NO: 151) were selected. These oligonucleotides were then evaluated for their ability to reduce DMPK expression in DM1 myotubes and NHP myotubes in a dose- responsive manner. The tool compound ASO300 was used as control. Each of the antisense oligonucleotides were capable of dose-dependently reducing DMPK in DM1 and NHP myotubes (see FIGs. 22A-22C and FIGs. 23A-23B, respectively).

[000622] These data demonstrate that these antisense oligonucleotides are safe in vivo and are capable of dose-dependent reduction of DMPK in cellule , suggesting that muscle targeting complexes comprising these antisense oligonucleotides would be capable of targeting DMPK in muscle tissues in vivo.

Example 16: Binding Affinity of selected anti-TfRl antibodies to human TfRl [000623] Selected anti-TfRl antibodies were tested for their binding affinity to human TfRl for measurement of Ka (association rate constant), Kd (dissociation rate constant), and KD (affinity). Two known anti-TfRl antibodies were used as control, 15G11 and OKT9. The binding experiment was performed on Carterra LSA at 25°C. An anti-mouse IgG and anti human IgG antibody "lawn" was prepared on a HC30M chip by amine coupling. The IgGs were captured on the chip. Dilution series of hTfRl, cyTfRl, and hTfR2 were injected to the chip for binding (starting from 1000 nM, 1:3 dilution, 8 concentrations).

[000624] Binding data were referenced by subtracting the responses from a buffer analyte injection and globally fitting to a 1:1 Langmuir binding model for estimate of Ka (association rate constant), Kd (dissociation rate constant), and KD (affinity) using the CarterraTM Kinetics software. 5-6 concentrations were used for curve fitting.

[000625] The result showed that the mouse mAbs demonstrated binding to hTfRl with K _D values ranging from 13 pM to 50 nM. A majority of the mouse mAbs had K _D values in the single digit nanomolar to sub-nanomolar range. The tested mouse mAbs showed cross reactive binding to cyTfRl with K _D values ranging from 16 pM to 22 nM.

[000626] Ka, Kd, and K _D values of anti-TfRl antibodies are provided in Table 12.

Table 12. Ka, Kd, and K _D values of anti-TfRl antibodies

Example 17: Conjugation of anti-TfRl antibodies with oligonucleotides [000627] Complexes containing an anti-TfRl antibody covalently conjugated to an antisense oligonucleotide (ASO) targeting DMPK (ASO300) were generated. First, Fab fragments of anti-TfR antibody clones 3-A4, 3-M12, and 5-H12 were prepared by cutting the mouse monoclonal antibodies with an enzyme in or below the hinge region of the full IgG followed by partial reduction. The Fabs were confirmed to be comparable to mAbs in avidity or affinity.

[000628] Muscle-targeting complexes were generated by covalently linking the anti-TfR mAbs to ASO300 via a cathepsin cleavable linker. Briefly, a Bicyclo[6.1.0]nonyne-PEG3-L- valine-L-citrulline-pentafluorophenyl ester (BCN-PEG3-Val-Cit-PFP) linker molecule was coupled to ASO300 through a carbamate bond. Excess linker and organic solvents were removed by tangential flow filtration (TFF). The purified Val-Cit-linker-ASO was then coupled to an azide functionalized anti-transferrin receptor antibody generated through modifying e-amine on lysine with Azide-PEG4-PFP. A positive control muscle-targeting complex was also generated using 15G11.

[000629] The product of the antibody coupling reaction was then subjected to two purification methods to remove free antibody and free payload. Concentrations of the conjugates were determined by either Nanodrop A280 or BCA protein assay (for antibody) and Quant-It Ribogreen assay (for payload). Corresponding drug-antibody ratios (DARs) were calculated. DARs ranged between 0.8 and 2.0, and were standardized so that all samples receive equal amounts of payload.

[000630] The purified complexes were then tested for cellular internalization and inhibition of DMPK. Non-human primate (NHP) or DM1 (donated by DM1 patients) cells were grown in 96-well plates and differentiated into myotubes for 7 days. Cells were then treated with escalating concentrations (0.5 nM, 5 nM, 50 nM) of each complex for 72 hours. Cells were harvested, RNA was isolated, and reverse transcription was performed to generate cDNA. qPCR was performed using TaqMan kits specific for Ppib (control) and DMPK on the QuantS tudio 7. The relative amounts of remaining DMPK transcript in treated vs non-treated cells was were calculated and the results are shown in Table 13.

[000631] The results demonstrated that the anti-TfRl antibodies are able to target muscle cells, be internalized by the muscle cells with the molecular payload (ASO300), and that the molecular payload is able to target and knockdown the target gene (DMPK). Knockdown activity of a complex comprising the anti-TfRl antibody conjugated to a molecular payload (e.g., an oligonucleotide) targeting any of the other rare muscle disease genes listed in Table 1 can be tested using the same assay described herein.

Table 13. Binding Affinity of anti-TfRl Antibodies and Efficacy of Conjugates [000632] Interestingly, the DMPK knockdown results showed a lack of correlation between the binding affinity of the anti-TfR to transferrin receptor and efficacy in delivering a DMPK ASO to cells for DMPK knockdown. Surprisingly, the anti-TfR antibodies provided herein (e.g., at least 3-A4, 3-M12, and 5-H12) demonstrated superior activity in delivering a payload (e.g., DMPK ASO) to the target cells and achieving the biological effect of the molecular payload (e.g., DMPK knockdown) in either cyno cells or human DM1 patient cells, compared to the control antibody 15G11, despite the comparable binding affinity (or, in certain instances, such as 5-H12, lower binding affinity) to human or cyno transferrin receptor between these antibodies and the control antibody 15G11.

[000633] Top attributes such as high huTfRl affinity, >50% knockdown of DMPK in NHP and DM1 patient cell line, identified epitope binding with 3 unique sequences, low/no predicted PTM sites, and good expression and conjugation efficiency led to the selection of the top 3 clones for humanization, 3-A4, 3-M12, and 5-H12.

Example 18: Humanized anti-TfRl antibodies

[000634] The anti-TfR antibodies shown in Table 2 were subjected to humanization and mutagenesis to reduce manufacturability liabilities. The humanized variants were screened and tested for their binding properties and biological actives. Humanized variants of anti-TfRl heavy and light chain variable regions (5 variants each) were designed using Composite Human Technology. Genes encoding Fabs having these heavy and light chain variable regions were synthesized, and vectors were constructed to express each humanized heavy and light chain variant. Subsequently, each vector was expressed on a small scale and the resultant humanized anti-TfRl Fabs were analyzed. Humanized Fabs were selected for further testing based upon several criteria including Biocore assays of antibody affinity for the target antigen, relative expression, percent homology to human germline sequence, and the number of MHC class II predicted T cell epitopes (determined using iTope™ MCH class II in silico analysis). [000635] Potential liabilities were identified within the parental sequence of some antibodies by introducing amino acid substitutions in the heavy chain and light chain variable regions. These substitutions were chosen based on relative expression levels, iTope™ score and relative KD from Biacore single cycle kinetics analysis. The humanized variants were tested and variants were selected initially based upon affinity for the target antigen. Subsequently, the selected humanized Fabs were further screened based on a series of biophysical assessments of stability and susceptibility to aggregation and degradation of each analyzed variant, shown in Table 14 and Table 15. The selected Fabs were analyzed for their properties binding to TfRl by kinetic analysis. The results of these analyses are shown in Table 16. For conjugates shown in Table 14 and Table 15, the selected humanized Fabs were conjugated to a DMPK-targeting oligonucleotide ASO300. The selected Fabs are thermally stable, as indicated by the comparable binding affinity to human and cyno TfRl after been exposed to high temperature (40 °C) for 9 days, compared to before the exposure (see Table 16).

Table 14. Biophysical assessment data for humanized anti-TfR Fabs

*Regains cyno binding after conjugation;

Table 15. Thermal Stability for humanized anti-TfR Fabs and conjugates

Table 16. Kinetic analysis of humanized anti-TfR Fabs binding to TfRl

Binding of humanized anti-TfRl Fabs to TfRl (ELISA)

[000636] To measure binding of humanized anti-TfR antibodies to TfRl, ELISAs were conducted. High binding, black, flat bottom, 96 well plates (Coming# 3925) were first coated with 100 pL/well of recombinant huTfRl at 1 pg/mL in PBS and incubated at 4°C overnight. Wells were emptied and residual liquid was removed. Blocking was conducted by adding 200 pL of 1%BSA (w/w) in PBS to each well. Blocking was allowed to proceed for 2 hours at room temperature on a shaker at 300 rpm. After blocking, liquid was removed and wells were washed three times with 300 pL of TBST. Anti-TfRl antibodies were then added in 0.5% BSA/TBST in triplicate in an 8 point serial dilution (dilution range 5 pg/mL - 5 ng/mL). A positive control and isotype controls were also included on the ELISA plate. The plate was incubated at room temperature on an orbital shaker for 60 minutes at 300 rpm, and the plate was washed three times with 300 pL of TBST. Anti-(H+L)IgG-A488 (1:500) (Invitrogen #A11013) was diluted in 0.5% BSA in TBST, and 100 pL was added to each well. The plate was then allowed to incubate at room temperature for 60 minutes at 300 rpm on orbital shaker. The liquid was removed and the plate was washed four times with 300 pL of TBST. Absorbance was then measured at 495 nm excitation and 50 nm emission (with a 15 nm bandwidth) on a plate reader. Data was recorded and analyzed for EC50. The data for binding to human TfRl (hTfRl) for the humanized 3M12, 3A4 and 5H12 Fabs are shown in FIG. 25A, 25C, and 25E, respectively. ELISA measurements were conducted using cynomolgus monkey (Macaca fascicularis) TfRl (cTfRl) according to the same protocol described above for hTfRl, and results are shown in FIG. 25B, 25D, and 25F.

[000637] Results of these two sets of ELISA analyses for binding of the humanized anti- TfR Fabs to hTfRl and cTfRl demonstrate that humanized 3M12 Fabs show consistent binding to both hTfRl and cTfRl, and that humanized 3A4 Fabs show decreased binding to cTfRl relative to hTfRl.

[000638] Antibody-oligonucleotide conjugates were prepared using six humanized anti- TfR Fabs, each of which were conjugated to ASO300. Conjugation efficiency and down stream purification were characterized, and various properties of the product conjugates were measured. The results demonstrate that conjugation efficiency was robust across all 10 variants tested, and that the purification process (hydrophobic interaction chromatography followed by hydroxyapatite resin chromatography) were effective. The purified conjugates showed a >97% purity as analyzed by size exclusion chromatography.

[000639] Several humanized Fabs were tested in cellular uptake experiments to evaluate TfRl-mediated internalization. To measure such cellular uptake mediated by antibodies, humanized anti-TfR Fab conjugates were labeled with Cypher5e, a pH-sensitive dye. Rhabdomyosarcoma (RD) cells were treated for 4 hours with 100 nM of the conjugates, trypsinized, washed twice, and analyzed by flow cytometry. Mean Cypher5e fluorescence (representing uptake) was calculated using Attune NxT software. As shown in FIG. 26, the humanized anti-TfR Fabs show similar or greater endosomal uptake compared to a positive control anti-TfRl Fab (15G11). Similar internalization efficiencies were observed for different oligonucleotide payloads. An anti-mouse TfR antibody was used as the negative control. Cold (non-intemalizing) conditions abrogated the fluorescence signal of the positive control antibody-conjugate (data not shown), indicating that the positive signal in the positive control and humanized anti-TfR Fab-conjugates is due to internalization of the Fab-conjugates. [000640] Conjugates of six humanized anti-TfR Fabs of were also tested for binding to hTfRl and cTfRl by ELISA, and compared to the unconjugated forms of the humanized Fabs. Results demonstrate that humanized 3M12 and 5H12 Fabs maintain similar levels of hTfRl and cTfRl binding after conjugation relative to their unconjugated forms (3M12, FIG. 27A and 27B; 5H12, FIG. 27E and 27F). Interestingly, 3A4 clones show improved binding to cTfRl after conjugation relative to their unconjugated forms (FIG. 27C and 27D).

[000641] As used in this Example, the term ‘unconjugated’ indicates that the antibody was not conjugated to an oligonucleotide.

Example 19. Knockdown of DMPK mRNA level facilitated by oligonucleotides conjugates in vitro

[000642] DMPK-targeting oligonucleotides (e.g., ASO) were tested in rhabdomyosarcoma (RD) cells for knockdown of DMPK transcript expression. RD cells were cultured in a growth medium of DMEM with glutamine, supplemented with 10% FBS and penicillin/streptomycin until nearly confluent. Cells were then seeded into a 96 well plate at 20K cells per well and were allowed to recover for 24 hours. Cells were then treated with free DMPK-targeting oligonucleotides or by transfection of the oligonucleotides using 0.3 pL per well of Lipofectamine MessengerMAX transfection reagent. After 3 days, total RNA was collected from cells, cDNA was synthesized and DMPK expression was measured by qPCR. [000643] Results in FIG. 28 show that DMPK expression level was reduced in cells treated with each given DMPK-targeting oligonucleotide, relative to expression in PBS -treated cells. Several DMPK-oligonucleotides showed dose-dependent reduction of DMPK expression level. In FIG. 28, DMPK- ASO- 1 has the sequence

GCGUAGAAGGGCGU CU GCCC (SEQ ID NO: 149). DMPK-ASO-2 has the sequence CCCAGCGCCCACCAGUCACA (SEQ ID NO: 150). DMPK-ASO-3 has the sequence CCAUCUCGGCCGGAAUCCGC (SEQ ID NO: 151). ASO300 was also used in this experiment.

Example 20. Knockdown of DMPK mRNA level facilitated by antibody-oligonucleotide conjugates in vitro

[000644] Conjugates containing humanized anti-TfR Fabs 3M12(VH3/Vk2), 3M-12 (VH4/Vk3), and 3A4(VH3-N54S/Vk4) were conjugated to a DMPK-targeting oligonucleotide ASO300 and were tested in rhabdomyosarcoma (RD) cells for knockdown of DMPK transcript expression. Antibodies were conjugated to ASO300 via the linker shown in Formula (C). [000645] RD cells were cultured in a growth medium of DMEM with glutamine, supplemented with 10% FBS and penicillin/streptomycin until nearly confluent. Cells were then seeded into a 96 well plate at 20K cells per well and were allowed to recover for 24 hours. Cells were then treated with the conjugates for 3 days. Total RNA was collected from cells, cDNA was synthesized and DMPK expression was measured by qPCR.

[000646] Results in FIG. 29 show that DMPK expression level was reduced in cells treated with each indicated conjugate, relative to expression in PBS-treated cells, indicating that the humanized anti-TfR Fabs are able to mediate the uptake of the DMPK- targeting oligonucleotide by the RD cells and that the internalized DMPK-targeting oligonucleotide are effective in knocking down DMPK mRNA level.

Example 21. Splicing correction and functional efficacy in HSA-LR mouse model of DM1 [000647] Correction of splicing in the HSA-LR mouse model of DM1 was demonstrated with conjugates containing anti-TfR antibodies conjugated to oligonucleotides target human skeletal actin (ACTA1). The anti-TfRl antibody used in this study was RI7217. The oligonucleotide targeting ACTA1 is an MOE 5-10-5 gapmer that comprises: 5'-NH ₂ -(CH ₂ ) ₆ - dA*oC*oC*oA*oT*oT*dT*dT*dC*dT*dT*dC*dC*dA*dC*dA*oG*oG*oG*oC* oT-3 (SEQ ID NO: 131); wherein represents a PS linkage; ‘d’ represents a deoxynucleic acid; and ‘o’ represents a 2'-MOE.

[000648] The HSA-LR DM1 mouse model is a well-validated model of DM1 that exhibits pathologies that are very similar to human DM1 patients. The HSA-LR model uses the human skeletal actin (ACTA1) promoter to drive expression of CUG long repeats (LR). In this model, toxic DMPK RNA accumulates within the nucleus and sequesters proteins responsible for splicing, such as Muscleblind-like protein (MBNL), resulting in mis-splicing of multiple RNAs, including CLCN1 (chloride channel), ATP2al (calcium channel), and others. This mis- splicing causes the mice to also exhibit myotonia which is a hallmark of the DM1 clinical presentation in humans.

[000649] The anti-TfR-oligonucleotide conjugate delivered intravenously has been shown to have activity in dose-dependent correction of splicing in multiple RNAs and multiple muscles and was well tolerated by HSA-LR mice. In this study, the ability of the conjugates to correct splicing in more than 30 different RNAs was evaluated. In DM1, significant RNA mis- splicing of these RNAs reduces the ability of multiple muscles to function. The RNAs monitored are critical for contraction and relaxation of muscle in HSA-LR mice. Dose- dependent correction of splicing was observed.

[000650] FIG. 30 shows results for Atp2al, which encodes a calcium channel and contributes to muscle contraction and relaxation. The X-axis represents splice derangement with 1.00 representing severe mis-splicing and 0.00 representing a wild type (WT) splice pattern. Progression from right to left in the figure represents a correction of splicing. The Y- axis represents the percent of the gene spliced in (PSI). Severe mis-splicing of ATP2al is caused by exclusion of exon 22 in the ATP2al RNA. WT splicing reflects near complete inclusion of exon 22. Results demonstrate that the conjugate corrected splicing of ATP2al in a dose-dependent manner in the gastrocnemius muscle.

[000651] Data for the more than 30 different RNAs that were tested in this study are shown in FIGs. 31, 58 A, and 58B. Similar dose-dependent correction of splicing was achieved for all of the tested RNAs in gastrocnemius muscle (FIG. 31), tibialis anterior (FIG. 58A), and quadriceps (FIG. 58B). For some of these RNAs, correction of splicing is reflected by a decrease in PSI, as in FIG. 30, and for other RNAs correction is reflected by an increase in PSI. [000652] Similar dose-dependent improvements in splicing within the set of RNAs were observed in the quadriceps and tibialis anterior muscles, after treatment with the conjugate.

FIG. 32 shows composite levels of splicing derangement observed for saline and different doses of the Ab-ASO across the more than 30 RNAs that were tested in each muscle type. Doses of lOmg/kg and 20mg/kg were administered in this study.

[000653] In addition to reductions in splicing derangement across multiple genes in several muscles in the HSA-LR model, disease modification was observed in the HSA-LR model. The results in FIG. 33 show that almost complete reversal of myotonia was achieved after a single dose of the conjugate. The severity of myotonia on a four-point scale was evaluated 14 days following dosing with saline (PBS), naked oligonucleotide, or the conjugate. Grade 0 indicates no myotonia was observed, grade 1 indicates myotonic discharge was measured by electromyography (EMG) in less than 50% of needle insertions, grade 2 indicates myotonic discharge was measured in greater than 50% of needle insertions and grade 3 indicates myotonic discharge was measured with nearly every needle insertion.

Example 22. Anti-TfR-oligonucleotide conjugate treatment increased dystrophin expression in mdx mouse model of DMD

[000654] To test the effects of another oligonucleotide that induces DMD exon skipping in vivo , an oligonucleotide (PMO) that induces exon 23 skipping was administered as naked oligonucleotide or in conjugate with an anti-mouse TfR antibody to the mdx mouse model of DMD. Dystrophin expression was measured. The exon skipping promoted by the conjugate resulted in dose-dependent production of dystrophin protein as illustrated by western blot (FIG. 35) and quantified in FIG. 36. Alpha-actin was used as a loading control. [000655] A single dose of the exon 23-conjugate administered in the mdx mouse also restored dystrophin expression to the muscle cell membrane in addition to increasing overall dystrophin levels, as shown in FIG. 37. Immunofluorescence staining of dystrophin in quadricep muscles demonstrated that mdx mice treated with the conjugated had higher levels of dystrophin in their quadriceps than mice treated with naked oligonucleotide or saline.

Example 23. Oligonucleotide-mediated exon skipping in DMD myotubes [000656] Promoting the skipping of specific DMD exons in the nucleus could allow muscle cells to create more complete, functional dystrophin protein. An oligonucleotide (PMO) that induces skipping of DMD exon 51 was conjugated to an anti-TfRl Fab and the conjugated was tested in human DMD myotubes with a mutation amenable to Exon 51 skipping. Treatment with the conjugate resulted in a 50% increase in exon skipping as compared to a 25% increase in exon skipping following treatment with an equimolar dose of the naked oligonucleotide (p-value=0.001), as shown in FIG. 34. Similar results were observed in the mdx mouse model of DMD, such as those shown in FIG. 19.

Example 24. Functional activity of antibody-conjugated oligonucleotides targeting DUX4 for treating FSHD.

[000657] FSHD patient-derived myotubes were treated with FM10 conjugated to an anti- TfRl Fab or with naked FM10. FM10 has the sequence 5'-

GGGC ATTTT A AT AT AT CTCT G A ACT -3 ' (SEQ ID NO: 147). Expression of mRNA transcribed from three genes known to be only expressed following DUX4 activation was subsequently measured in the myotubes. Expression of these three DUX4-associated genes was reduced, as shown in FIG. 38A (naked oligonucleotide) and 38B (Ab-oligonucleotide). In addition, the half maximal concentration required to inhibit (IC50) values for the conjugate were up to 9.6 times lower than those observed for naked FM10, as shown in Table 7 below, demonstrating that the conjugates were up to 9.6 times more potent than naked FM10 in suppressing DUX4-associated gene expression.

[000658] Additional anti-DUX4 oligonucleotides that may also be used to suppress DUX4-as sociated genes are ACUGCGCGCAGGUCUAGCCAGGAAG (SEQ ID NO: 153) and UGCGCACUGCGCGCAGGUCUAGCCAGGAAG (SEQ ID NO: 154).

Table 7. IC50 values for inhibition of DUX4-as sociated genes.

Example 25. Serum stability of the linker linking the anti-TfR antibody and the molecular payload

[000659] Oligonucleotides which were linked to antibodies in examples were conjugated via a cleavable linker shown in Formula (C). It is important that the linker maintain stability in serum and provide release kinetics that favor sufficient payload accumulation in the targeted muscle cell. This serum stability is important for systemic intravenous administration, stability of the conjugated oligonucleotide in the bloodstream, delivery to muscle tissue and internalization of the therapeutic payload in the muscle cells. The linker has been confirmed to facilitate precise conjugation of multiple types of payloads (including ASOs, siRNAs and PMOs) to Fabs. This flexibility enabled rational selection of the appropriate type of payload to address the genetic basis of each muscle disease. Additionally, the linker and conjugation chemistry allowed the optimization of the ratio of payload molecules attached to each Fab for each type of payload, and enabled rapid design, production and screening of molecules to enable use in various muscle disease applications.

[000660] FIG. 24 shows serum stability of the linker in vivo , which was comparable across multiple species over the course of 72 hours after intravenous dosing. At least 75% stability was measured in each case at 72 hours after dosing.

Example 26. Exon-skipping activity of anti-TfR conjugates in DMD patient myotubes [000661] In this study, the exon-skipping activities of anti-TfR conjugates containing an anti-TfR Fab (3M12 VH3/VK2, 3M12 VH4/VK3, and 3A4 VH3 N54S/VK4) conjugated to a DMD exon 51 -skipping oligonucleotide were evaluated. Immortalized human myoblasts bearing an exon 52 deletion were thawed and seeded at a density of le6 cell/flask in Promocell Skeletal Cell Growth Media (with 5% FBS and lx Pen-Strep) and allowed to grow to confluency. Once confluent, cells were trypsinized and pelleted via centrifugation and resuspended in fresh Promocell Skeletal Cell Growth Media. The cell number was counted and cells were seeded into Matrigel-coated 96-well plates at a density of 50k cells/well. Cells were allowed to recover for 24 hours. Cells were induced to differentiate by aspirating the growth media and replacing with differentiation media with no serum. Cells were then treated with conjugated or unconjugated DMD exon skipping oligonucleotide at 10 mM. Cells were incubated with test articles for ten days then total RNA was harvested from the 96 well plates. cDNA synthesis was performed on 75 ng of total RNA, and mutation specific PCRs were performed to evaluate the degree of exon 51 skipping in each cell type. Mutation- specific PCR products were run on a 4% agarose gel and visualized using SYBR gold. Densitometry was used to calculate the relative amounts of the skipped and unskipped amplicon and exon skipping was determined as a ratio of the Exon 51 skipped amplicon divided by the total amount of amplicon present:

[000662] The data demonstrate that the conjugates with either 3M12 VH3/VK2 or 3M12 VH4/VK3 Fab conjugated to the DMD exon 51-skipping oligonucleotide resulted in enhanced exon skipping compared to the unconjugated DMD exon skipping oligonucleotide in patient myotubes (FIG. 39).

[000663] As used in this Example, the term ‘unconjugated’ indicates that the oligonucleotide was not conjugated to an antibody.

Example 27. In vivo activity of anti-TfR conjugates in hTfRl mice

[000664] In DM1, the higher than normal number of CUG repeats form large hairpin loops that remain trapped in the nucleus, forming nuclear foci that bind splicing proteins and inhibit the ability of splicing proteins to perform their normal function. When toxic nuclear

DMPK levels are reduced, the nuclear foci are diminished, releasing splicing proteins, allowing restoration of normal mRNA processing, and potentially stopping or reversing disease progression.

[000665] The in vivo activity of conjugates containing an anti-TfR Fab (control, 3M12 VH3/VK2, 3M12 VH4/VK3, 3A4 VH3 N54S/VK4) conjugated to the DMPK-targeting oligonucleotide ASO300 in reducing DMPK mRNA level in multiple muscle tissues following systemic intravenous administration in mice was evaluated.

[000666] Male and female C57BF/6 mice where one TfRl allele was replaced with a human TFR1 allele were administered between the ages of 5 and 15 weeks according to the dosing schedule outlined in Table 17 and in FIG. 40A. Mice were sacrificed 14 days after the first injection and selected muscles collected as indicated in Table 18.

[000667]

[000668] Total RNA was extracted on a Maxwell Rapid Sample Concentrator (RSC) Instrument using kits provided by the manufacturer (Promega). Purified RNA was reverse- transcribed and levels of Dmpk and Ppib transcripts determined by qRT-PCR with specific TaqMan assays (Thermo Fisher). Log fold changes in Dmpk expression were calculated according to the 2 ^{DD( T} method using Ppib as the reference gene and mice injected with vehicle as the control group. Statistical significance in differences of Dmpk expression between control mice and mice administered with the conjugates were determined by one-way ANOVA with Dunnet’s correction for multiple comparisons. As shown in FIGs. 40B-40E, the tested conjugates showed robust activity in reducing DMPK mRNA level in vivo in various muscle tissues.

Example 28. In vitro activity of anti-TfR conjugates in patient-derived cells [000669] An in vitro experiment was conducted to determine the activities of anti-TfR conjugates in reducing DMPK mRNA expression, correcting BIN1 splicing, and reducing nuclear foci in CM-DM1-32F primary cells expressing a mutant DMPK mRNA containing 380 CUG repeats. The CM-DM1-32F primary cell is an immortalized myoblastic cell line isolated from a DM1 patient (CL5 cells; Described in Arandel et ah, Dis Model Mech. 2017 Apr 1; 10(4): 487-497). Conjugate 1 contains an anti-TfR mAb conjugated to DMPK-targeting oligonucleotide (ASO300). Conjugate 2 contains an anti-TfR Fab conjugated to DMPK ASO- 1 (GCGUAGAAGGGCGUCUGCCC; SEQ ID NO: 149).

[000670] CL5 cells were seeded at a density of 156,000 cells/cm ² , allowed to recover for 24 hours, transferred to differentiation media to induce myotube formation, as described (Arandel et al. Dis Model Mech. (2017) 10(4):487-497) and subsequently exposed to conjugate 1 and conjugate 2 at a payload concentration of 500 nM. Parallel cultures exposed to vehicle PBS served as controls. Cells were harvested after 10 days of culture.

[000671] For analysis of gene expression, cells were collected with Qiazol for total RNA extraction with a Qiagen miRNAeasy kit. Purified RNA was reverse-transcribed and levels of DMPK, PPIB, BIN1 transcripts and of the BIN I mRNA isoform containing exon 11 determined by qRT-PCR with specific TaqMan assays (Thermo Fisher). Log fold changes in DMPK expression were calculated according to the 2 ^{DD( t} method using PPIB as the reference gene and cells exposed to vehicle as the control group. Log fold changes in the levels BIN1 isoform containing exon 11 were calculated according to the 2 ^AACT method using BIN I as the reference gene and cells exposed to vehicle as the control group.

[000672] To measure the area of mutant DMPK nuclear foci, cells were fixed in 4% formalin, permeabilized with 0.1% Triton X-100 and hybridized at 70 °C with a CAG peptide- nucleic acid probe conjugated to the Cy5 fluorophore. After multiple washes in hybridization buffer and 2xSSC solution, nuclei were counterstained with DAPI. Images were collected at a 400x magnification by confocal microscopy and foci area measured as the area of Cy5 signal contained within the area of DAPI signal. Data were expressed as foci area corrected for nuclear area.

[000673] The results show that a single dose of the conjugates containing an anti-TfR (IgG or Fab) conjugated to a DMPK-targeting oligonucleotide (ASO300 or DMPK ASO-1 (SEQ ID NO: 149)) resulted reduced mutant DMPK expression (FIG. 41A), corrected BIN1 splicing (FIG. 41B), and reduced nuclear foci by approximately 40% (FIG. 41C).

Example 29. Characterization of binding activities of anti-TfR Fab 3M12 VH4/Vk3 [000674] In vitro studies were performed to test the specificity of anti-TfR Fab 3M12 VH4/Vk3 for human and cynomolgus monkey TfRl binding and to confirm its selectivity for human TfRl vs TfR2. The binding affinity of anti-TfR Fab 3M12 VH4/Vk3 to TfRl from various species was determined using an enzyme-linked immunosorbent assay (ELISA). Serial dilutions of the Fab were added to plates precoated with recombinant human, cynomolgus monkey, mouse, or rat TfRl. After a short incubation, binding of the Fab was quantified by addition of a fluorescently tagged anti-(H-i-L) IgG secondary antibody and measurement of fluorescence intensity at 495nm excitation and 520nm emission. The Fab showed strong binding affinity to human and cynomolgus monkey TfRl, and no detectable binding of mouse or rat TfRl was observed (FIG. 42). Surface plasmon resonance (SPR) measurements were also conducted, and results are shown in Table 19. The K _d of the Fab against the human TfRl receptor was calculated to be 7.68xl0 ¹⁰ M and against the cynomolgus monkey TfRl receptor was calculated to be 5.18xl0 ⁹ M.

Table 19. Kinetic analysis of anti-TfR Fab 3M12 VH4/Vk3 binding to human and cynomolgus monkey TfRl or human TfR2, measured using surface plasmon resonance

ND = No detectable binding by SPR (lOpM - 100 uM)

[000675] To test for cross-reactivity of anti-TfR Fab 3M12 VH4/Vk3 to human TfR2, an ELISA was performed. Recombinant human TfR2 protein was plated overnight at 2 pg/mL and was blocked for 1 hour with 1% bovine serum albumin (BSA) in PBS. Serial dilutions of the Fab or a positive control anti-TfR2 antibody were added in 0.5% BSA/TBST for 1 hour. After washing, anti-(H-i-L) IgG-A488 (Invitrogen #MA5-25932) fluorescent secondary antibody was added at a 1:500 dilution in 0.5% BSA/TBST and the plate was incubated for 1 hour. Relative fluorescence was measured using a Biotek Synergy plate reader at 495nm excitation and 520nm emission. No binding of anti-TfR Fab 3M12 VH4/Vk3 to hTfR2 was observed (FIG. 43).

Example 30. Serum stability of anti-TfR Fab-ASO conjugate

[000676] Anti-TfR Fab VH4/Vk3 was conjugated to a control antisense oligonucleotide (ASO) via a linker as shown in Formula (C) and the resulting conjugate was tested for stability of the linker conjugating the Fab to the ASO. Serum stability was measured by incubating fluorescently labeled conjugate in PBS or in rat, mouse, cynomolgus monkey, or human serum and measuring relative fluorescence intensity over time, with higher fluorescence indicating more conjugate remaining intact. FIG. 44 shows serum stability was similar across multiple species and remained high after 72 hours.

Example 31. Exon skipping activity of anti-TfR Fab-ASO conjugate in vivo in cynomolgus monkeys

[000677] Anti-TfR Fab 3M12 VH4/Vk3 was conjugated to a dystrophin (DMD) exon 51- skipping antisense oligonucleotide (ASO) targeting an exonic splicing enhancer (ESE) sequence in DMD exon 51. The exon 51 skipping oligonucleotide is a phosphorodiamidate morpholino oligomer (PMO) of 30 nucleotides in length. The exon skipping activity of the conjugate was tested in vivo in healthy non-human primates. Naive male cynomolgus monkeys (n= 4-5 per group) were administered two doses of vehicle, 30 mg/kg ASO alone, or 122 mg/kg conjugate (30 mg/kg ASO equivalent) via intravenous infusion on days 1 and 8. Animals were sacrificed and tissues harvested either 2 weeks or 4 weeks after the first dose was administered. Total RNA was collected from tissue samples using a Promega Maxwell® RSC instrument and cDNA synthesis was performed using qScript cDNA SuperMix. Assessment of exon 51 skipping was performed using end-point PCR.

Capillary electrophoresis of the PCR products was used to assess exon skipping, and % exon 51 skipping was calculated using the following formula: 100.

Calculated exon 51 skipping results are shown in Table 20.

Table 20. Exon 51 skipping of dystrophin in cynomolgus monkey dystrophin ^a ASO = antisense oligonucleotide, ^b Conjugate doses are listed as mg/kg of anti-TfR Fab 3M12 VH4/Vk3-ASO conjugate. ^c ASO doses are listed as mg/kg ASO equivalent of the anti-TfR Fab 3M12 VH4/Vk3-ASO dose. ^d Exon skipping values are mean % exon 51 skipping with standard deviations (n=5) in parentheses. [000678] Tissue ASO accumulation was also quantified using a hybridization ELISA with a probe complementary to the ASO sequence. A standard curve was generated and ASO levels (in ng/g) were derived from a linear regression of the standard curve. The ASO was distributed to all tissues evaluated at a higher level following the administration of the anti-TfR Fab VH4/Vk3-ASO conjugate as compared to the administration of unconjugated ASO. Intravenous administration of unconjugated ASO resulted in levels of ASO that were close to background levels in all tissues evaluated at 2 and 4 weeks after the first does was administered. Administration of anti-TfR Fab VH4/Vk3-ASO conjugate resulted in distribution of ASO through the tissues evaluated with a rank order of heart>diaphragm>bicep>quadriceps>gastrocnemious& gt;tibialis anterior 2 weeks after first dosing. The duration of tissue concentration was also assessed. Concentrations of the ASO in quadriceps, bicep and diaphragm decreased by less than 50% over the time period evaluated (2 to 4 weeks), while levels of ASO in the heart, tibialis anterior, and gastrocnemius remained virtually unchanged (Table 21).

[000679] As used in this Example, the term ‘unconjugated’ indicates that the oligonucleotide was not conjugated to an antibody.

Table 21. Tissue distribution of DMD exon 51 skipping ASO in cynomolgus monkeys ^a ASO = Antisense oligonucleotide.

Conjugate doses are listed as mg/kg of anti-TfR Fab 3M12 VH4/Vk3 ASO conjugate. ^c ASO doses are listed as mg/kg ASO or ASO equivalent of the anti-TfR Fab 3M12 VH4/Vk3-ASO conjugate dose. ^d ASO values are mean concentrations of ASO in tissue as ng/g with standard deviations (n=5) in parentheses.

Example 32. Effects of conjugates containing an anti-TfR Fab conjugated to a DUX4- targeting oligonucleotide in FSHD patient-derived immortalized myoblasts [000680] An anti-TfR Fab 3M12 VH4/VK3 was conjugated to a DUX4-targeting oligonucleotide (SEQ ID NO: 147) via a cleavable Val-Cit linker to achieve enhanced muscle delivery of the oligonucleotide. The oligonucleoide is a PMO and targets the polyadenylation signal of the DUX4 transcript. The activity of the conjugate was evaluated in the C6(AB1080) immortalized FSHD1 cell line, which has significant levels of surface TfRl expression and activation of DUX4 transcriptome markers (MBD3L2, TRIM43, ZSCAN4). It is demonstrated that receptor-mediated delivery of the PMO (SEQ ID NO: 147) by the anti-TfR Fab into muscle cells resulted in about 75% reduction of DUX4 transcriptome biomarkers at an 8 nM PMO concentration, whereas equivalent unconjugated PMO shows no significant biomarker reduction compared to vehicle treated cells (FIG. 45). The results show that conjugating with anti-TfR Fab enhances delivery of therapeutic oligonucleotides to muscle cells for the treatment of FSHD.

[000681] As used in this Example, the term ‘unconjugated’ indicates that the oligonucleotide was not conjugated to an antibody

[000682] Additionally, a dose response curve for reduction of MBD3L2 mRNA is shown in FIG. 46A. The half maximal concentration required to inhibit (IC50) value for the conjugate was 189 pM. Dose response curves for reduction of MBD3L2, TRIM43, and ZSCAN4 mRNA are shown in FIG. 46B. The IC50 values for the conjugate inhibiting MBD3L2, TRIM43, and ZSCAN4 were 200 pM, 50 pM, and 200 pM, respectively.

Experimental Procedures for Example 32

Cell culture and test article treatment

[000683] C6 (AB1080) immortalized FSHD myoblasts were seeded to a density of 45,000 cells/well on a 96-well plate (ThermoFisher Scientific) in Skeletal Growth Media (CAT# C-23060, Promocell) with Supplementary mix (C-39365, Promocell) and 1% Penstrep (15140-122, Gibco). Growth media was replaced with differentiation media, NbActiv4 (Brainbits) and 1% Pen/Strep (Gibco), 24 hours later. The cells were treated with unconjugated DUX4-targeting oligonucleotde, the conjugate at a PMO concentration of 8 nM, vehicle in technical replicates for 4 hours prior to washout with 1XPBS (10010023, Gibco) one time. Conditioned differentiation media was immediately added back to wells and the cells were harvested 5 days later for downstream analyses.

[000684] For the dose response curves for MBD3L2, TRIM43, and ZSCAN4 knockdown, C6 (AB1080) immortalized FSHD myoblasts were treated as described above but with varying concentrations of the conjugates. RNA extraction and qPCR

[000685] Total RNA was extracted from cell monolayers with the RNeasy 96 Kit (Qiagen) in accordance with the manufacturer's instructions. The RNA was quantified with the Biotek Plate Reader and diluted to 50 ng per sample with Nuclease-Free Water (Qiagen) and reverse transcribed with qScript cDNA SuperMix (QuantaBio). Gene expression was analyzed by qPCR with specific TaqMan assays (ThermoFisher) by measuring levels of TRIM43 (Hs00299174_m 1 ), MBD3L2 (Hs00544743_ml), ZSCAN4 (Hs00537549_ml) and RPL13A (Hs04194366_gl) transcripts. Two-step amplification reactions and fluorescence measurements for Ct determination were conducted on a QuantStudio 7 instrument (Thermo Scientific). Log fold changes in the expression of transcripts of interest were calculated according to the 2- ^{DD( i} method using RPL13A as the reference gene and cells exposed to vehicle as the control group. Data are expressed as means ± S.D.

Example 33. Effect of a single dose of an anti-mouse TfRl Fab conjugated to an oligonucleotide (ASO) against the human ACTA1 mRNA in HSA ^LR mice, a model of DM1.

[000686] Six- to 8-week-old homozygous HSA ^LR mice were allocated randomly to one of five treatment groups and treated with vehicle, a naked oligonucleotide (ASO) targeting human ACTA1 mRNA at a dose of 10 mg/kg or 20 mg/kg, or conjugates containing anti-TfRl RI7217 Fab conjugated to the ASO (Ab-ASO) at a dose equivalent to 10 mg/kg or 20 mg/kg of ASO. [000687] Twenty-eight days after intravenous injections of vehicle, ASO, or Ab-ASO, EMG myotonic discharges in quadriceps (FIG. 47 A), gastrocnemius (FIG. 47B), and tibialis anterior (FIG. 47C), were graded by blinded examiner on a 4-point scale in which 0 indicated no myotonia; 1 indicated occasional myotonic discharge in less than 50% of needle insertions;

2 indicated myotonic discharge in greater than 50% of needle insertions; and 3 indicated myotonic discharge with nearly every insertion. A single dose of the conjugate, but not naked ASO, dose-dependently reversed myotonia in the HSA ^LR DM1 model.

[000688] Statistical significance of differences between vehicle-treated group and each experimental arm was determined by Kruskal-Wallis test with Dunn’s multiple comparisons test. Data are reported as means ± S.E.M.; *p < 0.05, **p < 0.01.

[000689] Additionally, fourteen days and twenty-eight days after the treatment mice were sacrificed and quadriceps (quad), gastrocnemius (gastroc) and tibialis anterior (TA) muscles were collected and analyzed for expression of ACTA1. Knockdown (KD) of ACTA1 expression using the Ab-ASO conjugate was observed in quadriceps (quad), gastrocnemius (gastroc) and tibialis anterior (TA) muscles relative to PBS control 14 days following a single administered dose, whereas naked ASO did not facilitate ACTA1 suppression in the same timeframe (FIG 48). Measurement of ACTA1 in muscle 28 days following the treatment showed that the, the Ab-ASO conjugate reduced ACTA1 expression relative to vehicle control at both tested doses (10 mg/kg ASO equivalent and 20 mg/kg ASO equivalent), whereas the same doses of naked ASO did not facilitate ACTA1 suppression (FIGs. 49A-49C; *p < 0.05,

**p < 0.01).

Example 34. Effect of conjugates containing an anti-TfRl Fab conjugated to an oligonucleotide that induces DMD exon 23 skipping on biomarker expression and muscle function in mdx mice

[000690] The objective of this study was to determine the effect of a single dose of anti mouse TfRl Fab conjugated to an antisense oligonucleotide (Ab-ASO) or of a single dose of the same naked ASO on dystrophin expression and muscle function in mdx mice. The complex used in this example was DTX-C-042 as described in Example 13.

[000691] Seven- week-old male mdx homozygous mice were allocated randomly to each of eight treatment groups. The mice were administered via tail vein a singled dose of ASO at 30 mg/kg, Ab-ASO at a dose equivalent to 30 mg/kg of ASO, or saline. Tissues were harvested and analyzed 2 weeks or 4 weeks following administration.

[000692]

[000693] Measurement of exon 23 skipping in muscles: Quantification of exon 23 skipping was performed using a single-step RT-PCR reaction using the Superscript® III (Thermo Fisher) with 75 ng total RNA input. The PCR primers used were 5’- CACATCTTTGATGGTGTGAGG (forward) (SEQ ID NO: 155) and 5’- CAACTTCAGCCATCCATTTCTG (reverse) (SEQ ID NO: 156). Capillary electrophoresis was used to quantitate the skipped and unskipped bands in the skeletal muscles of interest using the following equation:

Skipped Band

% Exon 23 Skipping = x 100

Skipped. Band 3- Unshipped Band

. The results demonstrate that a single administration of anti-TfRl Fab-oligonucleotide conjugate (Ab-ASO) facilitated significant increases in skipping of exon 23 in quadriceps (FIG. 50A), heart (FIG. 50B), and diaphragm (FIG. 50C) of mdx mice. By contrast, little or no exon 23 skipping was observed in the same muscle tissues in wild-type (WT) mice or in mdx mice treated with saline or naked ASO.

[000694] Measurement of dystrophin protein in muscles: Muscle tissue samples taken from the quadriceps were homogenized and protein concentrations were measured by BCA assay. Total protein (25 pg) was loaded onto a 3% to 8% Tris-acetate protein gel and run at 150 V for 1 hour. The gel was then transferred to a polyvinylidene difluoride membrane, and the membrane was cut, and the portion containing dystrophin was incubated overnight in anti dystrophin antibody (Abeam catalog # 15277) at 4°C, followed by goat anti-rabbit IgG (H+L) horseradish peroxidase conjugate (Bio-Rad) for 30 minutes at room temperature. As a control, the remaining portion of the blot was incubated overnight with anti- alpha- actinin antibody (Abeam catalog # 9465) at 4°C, followed by goat anti-mouse IgG (H+L) horseradish peroxidase conjugate (Bio-Rad) for 15 minutes at room temperature. The blot was developed using the ECL Western Detection Kit (Cytiva) and quantified using iBright analysis software (Thermo Fisher Scientific). Images of western blots are shown for muscle tissues collected two-weeks following injections in FIGs. 51A (quadriceps), 52A (heart), and 53A (diaphragm), and quantification of the western blot results are shown in FIGs. 5 IB (quadriceps), 52B (heart), and 53B (diaphragm). Images of western blots are shown for muscle tissues collected four- weeks following injections in FIGs. 51C (quadriceps), 52C (heart), and 53C (diaphragm), and quantification of the western blot results are shown in FIGs. 5 ID (quadriceps), 52D (heart), and 53D (diaphragm). In each western blot, the standard curve was generated using pooled protein from wild-type and mdx tissues, and the percentage wild-type (% WT) protein in each standard indicates the amount of wild-type protein in the sample. FIGs. 51A-51D demonstrate that two- and four-weeks following administration, Ab-ASO facilitated increases in dystrophin protein in quadriceps to a greater extent than naked ASO. FIGS. 52A-52D demonstrate that two- and four-weeks following administration, Ab-ASO facilitated increases in dystrophin protein in heart muscle, whereas little to no wild-type dystrophin was measured in heart muscle from mice treated with naked ASO. FIGs. 53A-53D demonstrate that two- and four-weeks following administration, Ab-ASO facilitated increases in dystrophin protein in diaphragm muscle, whereas little to no wild-type dystrophin was measured in diaphragm muscle from mice treated with naked ASO.

[000695] Measurement of ASO content within tissues. Enzyme-linked immunosorbent assay (ELISA) was performed by coating NeutrAvidin coated plates with a capture probe specific to the ASO of interest. Proteinase K digested tissue lysate was incubated on the coated plates to allow binding of the ASO of interest to the capture probe. Plates were then washed and unbound capture probe was digested with micrococcal nuclease, followed by further washing and blocking. A Digoxigenin HRP-conjugated antibody was added to bind to intact capture probe, then imaged using TMB substrate (R&D Systems, Inc.). Quantification was performed using a standard curve of known concentration diluted into skeletal muscle matrix. The results demonstrate that administration of the Fab conjugate is able to achieve substantial accumulation of ASO within quadriceps (FIG. 54A), diaphragm (FIG. 54B), and heart (FIG. 54C), whereas administration of naked ASO showed little or no ASO content in each muscle tissue. FIGs. 54A-54C demonstrate that little or no ASO was detected in muscle tissues of mice administered saline or naked ASO, whereas administration of Ab-ASO resulted in measurable quantities of ASO in each of the tissues tested two- and four-weeks following administration.

Example 35. Pharmacokinetic properties of antibody-oligonucleotide conjugate in nonhuman primates

[000696] A DUX4-targeting oligonucleotide (SEQ ID NO: 147) was administered intravenously to non-human primates, either naked or conjugated to an anti-TfRl antibody (3M12 VH4/Vk3 Fab). The naked oligonucleotide was administered at a dose of 30 mg/kg, and the conjugate was administered at a dose of 3 mg/kg, 10 mg/kg, or 30 mg/kg oligonucleotide equivalent. Plasma levels of the oligonucleotide measured over time are shown in FIG. 55. The results demonstrate that systemic exposure of the antibody-oligonucleotide conjugate shows linear pharmacokinetic properties, and achieves higher exposure relative to the naked oligonucleotide. The plasma measurements also demonstrate the antibody-oligonucleotide conjugate has a long serum half-life of about 60 hours. Furthermore, the antibody- oligonucleotide conjugate demonstrates a 58-fold increase in area under the curve compared to the naked oligonucleotide. These results are summarized in Table 22.

Table 22. Pharmacokinetic values calculated from plasma concentration measurements

[000697] Two-weeks following administration of the oligonucleotide or the antibody- oligonucleotied conjugate, necropsies were performed and muscle tissues from the non-human primates were collected and oligonucleotide levels were measured. In each muscle tissue tested (heart, orbicularius oris, zygomatic major, diaphragm, trapezius, deltoid, gastrocnemius, biceps, quadriceps, and tibialis anterior), tissue oligonucleotide levels were higher for each dose of antibody-oligonucleotide conjugate (3, 10, or 30 mg/kg oligonucleotide equivalent) compared to the naked oligonucleotide (30 mg/kg) (FIG. 56). As a control, tissue oligonucleotide levels were also measured in tissues collected from vehicle-treated animals, and no oligonucleotide was detected in any of the muscle tissues tested. These results demonstrate that the antibody-oligonucleotide conjugate achieves high exposure of the DUX4- targeting oligonucleotide to muscle tissue, and markedly higher than oligonucleotide administered naked.

[000698] To evaluate tissue accumulation of DUX4-targeting oligonucleotide over time, tissue oligonucleotide levels were measured in gastrocnemius biopsy samples collected one- week following administration and compared to the values measured in the necropsy samples collected two-weeks following administration. The oligonucleotide levels were markedly higher in the gastrocnemius biopsy samples collected from the animals administered 3, 10, or 30 mg/kg oligonucleotide equivalent of antibody- oligonucleotide conjugate than in the biopsy samples collected from the animals administered 30 mg/kg naked oligonucleotide, and the levels were even higher in the tissues collected two-weeks following administration (FIG. 57). No oligonucleotide was detected in tissue samples from vehicle-treated animals. These results demonstrate that the antibody-oligonucleotide conjugate achieves high exposure of the DUX4- targeting oligonucleotide to muscle tissue when compared to naked oligonucleotide, and that the conjugate continues to accumulate over time.

Example 35. Conjugation of DMD exon 53-skipping oligonucleotides to anti-TfRl antibodies improves their potency

[000699] To test the effect of anti-TfRl targeting on exon 53-skipping oligonucleotides, complexes were formed comprising an anti-TfRl Fab antibody (3M12 VH4/Vk3) covalently linked to exon 53-skipping PMOs via a linker having the structure of formula (C). Two exon 53-skipping PMOs were used in this Example: exon 53 PMO-A, comprising the sequence GTTGCCTCCGGTTCTGAAGGTGTTC (SEQ ID NO: 156), and exon 53 PMO-B, comprising the sequence CCTCCGGTTCTGAAGGTGTTC (SEQ ID NO: 157).

[000700] First, the exon 53-skipping PMOs alone were tested for their ability to facilitate skipping of exon 53 following gymnotic uptake (i.e., without transfection agent or modification to confer muscle targeting). KM1328 DMD patient cells which harbor a deletion of DMD exon 52 were treated with a range of concentrations of exon 53 PMO-A or exon 53 PMO-B, and exon 53 skipping was measured. As shown in FIG. 59, exon 53 PMO-A was about 2-fold more potent than exon 53 PMO-B. Based on the dose response curves, it was calculated that a concentration of 2.5 mM of exon 53 PMO-A or 4.7 mM of exon 53 PMO-B is required to achieve 50% skipping of exon 53.

[000701] Next, complexes comprising the anti-TfRl Fab covalently linked to either exon 53 PMO-A or exon 53 PMO-B (“anti-TfRl Fab-ASO complex”) were tested for their ability to facilitate skipping of exon 53 in KM1328 DMD patient cells in comparison with the same PMOs not linked to an antibody (“naked ASO”). Cells were treated with the naked ASO at concentrations of 0.16 pM, 0.32 pM, 0.63 pM, or 1.25 pM, or with the anti-TfRl Fab-ASO complex at ASO equivalent concentrations of 0.16 pM, 0.32 pM, 0.63 pM, or 1.25 pM. As shown in FIG. 60, the Fab-ASO complexes achieved greater exon 53 skipping than did the naked ASO at each of the tested concentrations, including achieving significantly improved exon 53 skipping by exon 53 PMO-A at the lower doses tested (0.16 pM, 0.32 pM, and 0.63 pM). These results demonstrate that covalently linking exon- skipping oligonucleotides to anti- TfRl antibodies can facilitate exon-skipping activity at lower doses, thereby enabling efficacy of the oligonucleotides at lower doses.

ADDITIONAL EMBODIMENTS

1. A method for treating a subject diagnosed as having a muscle disease associated with a gain-of-function disease allele, the method comprising administering to the subject a complex comprising a muscle-targeting agent covalently linked to a molecular payload configured to inhibit expression or activity of the disease allele, wherein the muscle-targeting agent specifically binds to an internalizing cell surface receptor on muscle cells of the subject, wherein the muscle targeting agent is a humanized antibody that binds to a transferrin receptor, wherein the antibody comprises:

(i) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 69; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 70;

(ii) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 71; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 70;

(iii) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 72; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 70;

(iv) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 73; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 74;

(v) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 73; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 75;

(vi) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 76; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 74;

(vii) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 76; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 75;

(viii) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 77; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 78; (ix) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 79; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 80; or

(x) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 77; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 80.

2. The method of embodiment 1, wherein the antibody comprises:

(i) a VH comprising the amino acid sequence of SEQ ID NO: 69 and a VL comprising the amino acid sequence of SEQ ID NO: 70;

(ii) a VH comprising the amino acid sequence of SEQ ID NO: 7 land a VL comprising the amino acid sequence of SEQ ID NO: 70;

(iii) a VH comprising the amino acid sequence of SEQ ID NO: 72 and a VL comprising the amino acid sequence of SEQ ID NO: 70;

(iv) a VH comprising the amino acid sequence of SEQ ID NO: 73 and a VL comprising the amino acid sequence of SEQ ID NO: 74;

(v) a VH comprising the amino acid sequence of SEQ ID NO: 73 and a VL comprising the amino acid sequence of SEQ ID NO: 75;

(vi) a VH comprising the amino acid sequence of SEQ ID NO: 76 and a VL comprising the amino acid sequence of SEQ ID NO: 74;

(vii) a VH comprising the amino acid sequence of SEQ ID NO: 76 and a VL comprising the amino acid sequence of SEQ ID NO: 75;

(viii) a VH comprising the amino acid sequence of SEQ ID NO: 77 and a VL comprising the amino acid sequence of SEQ ID NO: 78;

(ix) a VH comprising the amino acid sequence of SEQ ID NO: 79 and a VL comprising the amino acid sequence of SEQ ID NO: 80; or

(x) a VH comprising the amino acid sequence of SEQ ID NO: 77 and a VL comprising the amino acid sequence of SEQ ID NO: 80.

3. The method of embodiment 1 or embodiment 2, wherein the antibody is selected from the group consisting of a full-length IgG, a Fab fragment, a Fab' fragment, a F(ab’)2 fragment, a scFv, and a Fv.

4. The method of embodiment 3, wherein the antibody is a full-length IgG, optionally wherein the full-length IgG comprises a heavy chain constant region of the isotype IgGl, IgG2, IgG3, or IgG4. 5. The method of embodiment 4, wherein the antibody comprises:

(i) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 84; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 85;

(ii) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 86; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 85;

(iii) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 87; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 85;

(iv) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 88; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 89;

(v) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 88; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 90;

(vi) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 91; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 89;

(vii) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 91; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 90;

(viii) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 92; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 93;

(ix) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 94; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 95; or

(x) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 92; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 95.

6. The method of embodiment 3, wherein the antibody is a Fab fragment.

7. The method of embodiment 6, wherein the antibody comprises: (i) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 97; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 85;

(ii) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 98; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 85;

(iii) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 99; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 85;

(iv) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 100; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 89;

(v) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 100; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 90;

(vi) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 101; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 89;

(vii) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 101; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 90;

(viii) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 102; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 93;

(ix) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 103; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 95; or

(x) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 102; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 95.

8. The method of embodiment 6 or embodiment 7, wherein the antibody comprises:

(i) a heavy chain comprising the amino acid sequence of SEQ ID NO: 97; and a light chain comprising the amino acid sequence of SEQ ID NO: 85; (ii) a heavy chain comprising the amino acid sequence of SEQ ID NO: 98; and a light chain comprising the amino acid sequence of SEQ ID NO: 85;

(iii) a heavy chain comprising the amino acid sequence of SEQ ID NO: 99; and a light chain comprising the amino acid sequence of SEQ ID NO: 85;

(iv) a heavy chain comprising the amino acid sequence of SEQ ID NO: 100; and a light chain comprising the amino acid sequence of SEQ ID NO: 89;

(v) a heavy chain comprising the amino acid sequence of SEQ ID NO: 100; and a light chain comprising the amino acid sequence of SEQ ID NO: 90;

(vi) a heavy chain comprising the amino acid sequence of SEQ ID NO: 101; and a light chain comprising the amino acid sequence of SEQ ID NO: 89;

(vii) a heavy chain comprising the amino acid sequence of SEQ ID NO: 101; and a light chain comprising the amino acid sequence of SEQ ID NO: 90;

(viii) a heavy chain comprising the amino acid sequence of SEQ ID NO: 102; and a light chain comprising the amino acid sequence of SEQ ID NO: 93;

(ix) a heavy chain comprising the amino acid sequence of SEQ ID NO: 103; and a light chain comprising the amino acid sequence of SEQ ID NO: 95; or

(x) a heavy chain comprising the amino acid sequence of SEQ ID NO: 102; and a light chain comprising the amino acid sequence of SEQ ID NO: 95.

9. The method of any one of embodiments 1-8, wherein the muscle disease is hereditary.

10. The method of any one of embodiments 1-9, wherein the muscle disease exhibits increased severity in sequential family generations of the subject.

11. The method of any one of embodiments 1 to 10, wherein the subject was diagnosed as having the muscle disease based on a genetic analysis of the disease allele.

12. The method of any one of embodiments 1 to 11, wherein the subject exhibits progressive muscle weakness and/or sarcopenia prior to the administration.

13. The method of any one of embodiments 1 to 12, wherein the subject exhibits myotonia, e.g., measurable with electromyography, prior to the administration.

14. The method of any one of embodiments 1-13, wherein the equilibrium dissociation constant (K _D ) of binding of the antibody to the transferrin receptor is in a range from 10 ¹¹ M to 10 ⁶ M. 15. The method of any one of embodiments 1 to 14, wherein the antibody does not specifically bind to the transferrin binding site of the transferrin receptor and/or wherein the antibody does not inhibit binding of transferrin to the transferrin receptor.

16. The method of any one of embodiments 1 to 15, wherein the antibody is cross reactive with extracellular epitopes of two or more of a human, non-human primate and rodent transferrin receptor.

17. The method of any one of embodiments 1 to 16, wherein the method is configured to promote transferrin receptor mediated internalization of the molecular payload into a muscle cell.

18. The method of any one of embodiments 1 to 17, wherein the antibody is a chimeric antibody, optionally wherein the chimeric antibody is a humanized monoclonal antibody.

19. The method of any one of embodiments 1 to 18, wherein the antibody is in the form of a ScFv, a Fab fragment, Fab' fragment, F(ab')2 fragment, or Fv fragment.

20. The method of any one of embodiments 1 to 19, wherein the molecular payload is an oligonucleotide.

21. The method of embodiment 20, wherein the oligonucleotide comprises a region of complementarity to gene listed in Table 1 or mRNA encoded therefrom.

22. The method of embodiment 20 or 21, wherein the oligonucleotide is a gapmer oligonucleotide, a mixmer oligonucleotide, an antisense oligonucleotide, a RNAi oligonucleotide, a messenger RNA (mRNA), or a guide sequence.

23. The method of any one of embodiments 1 to 22, wherein the complex is administered to the subject by extramuscular parenteral administration.

24. The method of embodiment 23, wherein the complex is administered to the subject by intravenous administration.

25. The method of embodiment 23, wherein the complex is administered to the subject by subcutaneous administration of the complex.

26. A complex comprising a muscle-targeting agent linked to a single- stranded oligonucleotide, wherein the muscle-targeting agent specifically binds to an internalizing cell surface receptor on muscle cells, and wherein the oligonucleotide comprises a region of complementarity to a muscle disease gene, optinally wherein the muscle targeting agent is a humanized antibody that binds to a transferrin receptor and comprises:

(i) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 69; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 70;

(ii) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 71; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 70;

(iii) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 72; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 70;

(iv) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 73; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 74;

(v) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 73; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 75;

(vi) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 76; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 74;

(vii) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 76; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 75;

(viii) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 77; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 78;

(ix) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 79; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 80; or

(x) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 77; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 80.

27. A composition comprising a plurality of complexes, each complex comprising a muscle-targeting agent covalently linked to at least three oligonucleotides, wherein the muscle- targeting agent specifically binds to an internalizing cell surface receptor on muscle cells of a subject, and wherein each oligonucleotide comprises a region of complementarity to a muscle disease gene, optinally wherein the muscle targeting agent is a humanized antibody that binds to a transferrin receptor and comprises:

(i) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 69; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 70;

(ii) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 71; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 70;

(iii) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 72; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 70;

(iv) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 73; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 74;

(v) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 73; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 75;

(vi) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 76; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 74;

(vii) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 76; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 75;

(viii) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 77; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 78;

(ix) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 79; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 80; or

(x) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 77; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 80. 28. A complex comprising a muscle-targeting agent covalently linked to a molecular payload configured to modulate expression or activity of a muscle disease gene that encodes a non-secreted product that functions within muscle cells, wherein the muscle targeting agent specifically binds to an internalizing cell surface receptor on muscle cells, optionally wherein the muscle targeting agent is a humanized antibody that binds to a transferrin receptor and comprises:

(i) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 69; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 70;

(ii) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 71; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 70;

(iii) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 72; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 70;

(iv) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 73; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 74;

(v) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 73; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 75;

(vi) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 76; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 74;

(vii) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 76; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 75;

(viii) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 77; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 78;

(ix) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 79; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 80; or (x) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 77; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 80.

29. The complex of embodiment 28, wherein the antibody comprises:

(i) a VH comprising the amino acid sequence of SEQ ID NO: 69 and a VL comprising the amino acid sequence of SEQ ID NO: 70;

(ii) a VH comprising the amino acid sequence of SEQ ID NO: 7 land a VL comprising the amino acid sequence of SEQ ID NO: 70;

(iii) a VH comprising the amino acid sequence of SEQ ID NO: 72 and a VL comprising the amino acid sequence of SEQ ID NO: 70;

(iv) a VH comprising the amino acid sequence of SEQ ID NO: 73 and a VL comprising the amino acid sequence of SEQ ID NO: 74;

(v) a VH comprising the amino acid sequence of SEQ ID NO: 73 and a VL comprising the amino acid sequence of SEQ ID NO: 75;

(vi) a VH comprising the amino acid sequence of SEQ ID NO: 76 and a VL comprising the amino acid sequence of SEQ ID NO: 74;

(vii) a VH comprising the amino acid sequence of SEQ ID NO: 76 and a VL comprising the amino acid sequence of SEQ ID NO: 75;

(viii) a VH comprising the amino acid sequence of SEQ ID NO: 77 and a VL comprising the amino acid sequence of SEQ ID NO: 78;

(ix) a VH comprising the amino acid sequence of SEQ ID NO: 79 and a VL comprising the amino acid sequence of SEQ ID NO: 80; or

(x) a VH comprising the amino acid sequence of SEQ ID NO: 77 and a VL comprising the amino acid sequence of SEQ ID NO: 80.

30. The complex of embodiment 29 or embodiment 29, wherein the antibody is selected from the group consisting of a full-length IgG, a Fab fragment, a Fab' fragment, a F(ab’)2 fragment, a scFv, and a Fv.

31. The complex of embodiment 30, wherein the antibody is a full-length IgG, optionally wherein the full-length IgG comprises a heavy chain constant region of the isotype IgGl, IgG2, IgG3, or IgG4.

32. The complex of embodiment 31, wherein the antibody comprises: (i) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 84; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 85;

(ii) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 86; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 85;

(iii) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 87; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 85;

(iv) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 88; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 89;

(v) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 88; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 90;

(vi) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 91; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 89;

(vii) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 91; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 90;

(viii) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 92; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 93;

(ix) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 94; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 95; or

(x) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 92; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 95.

33. The complex of embodiment 30, wherein the antibody is a Fab fragment.

34. The complex of embodiment 33, wherein the antibody comprises: (i) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 97; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 85;

(ii) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 98; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 85;

(iii) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 99; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 85;

(iv) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 100; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 89;

(v) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 100; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 90;

(vi) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 101; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 89;

(vii) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 101; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 90;

(viii) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 102; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 93;

(ix) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 103; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 95; or

(x) a heavy chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 102; and/or a light chain comprising an amino acid sequence at least 85% identical to SEQ ID NO: 95.

35. The complex of embodiment 33 or embodiment 34, wherein the antibody comprises:

(i) a heavy chain comprising the amino acid sequence of SEQ ID NO: 97; and a light chain comprising the amino acid sequence of SEQ ID NO: 85; (ii) a heavy chain comprising the amino acid sequence of SEQ ID NO: 98; and a light chain comprising the amino acid sequence of SEQ ID NO: 85;

(iii) a heavy chain comprising the amino acid sequence of SEQ ID NO: 99; and a light chain comprising the amino acid sequence of SEQ ID NO: 85;

(iv) a heavy chain comprising the amino acid sequence of SEQ ID NO: 100; and a light chain comprising the amino acid sequence of SEQ ID NO: 89;

(v) a heavy chain comprising the amino acid sequence of SEQ ID NO: 100; and a light chain comprising the amino acid sequence of SEQ ID NO: 90;

(vi) a heavy chain comprising the amino acid sequence of SEQ ID NO: 101; and a light chain comprising the amino acid sequence of SEQ ID NO: 89;

(vii) a heavy chain comprising the amino acid sequence of SEQ ID NO: 101; and a light chain comprising the amino acid sequence of SEQ ID NO: 90;

(viii) a heavy chain comprising the amino acid sequence of SEQ ID NO: 102; and a light chain comprising the amino acid sequence of SEQ ID NO: 93;

(ix) a heavy chain comprising the amino acid sequence of SEQ ID NO: 103; and a light chain comprising the amino acid sequence of SEQ ID NO: 95; or

(x) a heavy chain comprising the amino acid sequence of SEQ ID NO: 102; and a light chain comprising the amino acid sequence of SEQ ID NO: 95.

36. The complex of any one of embodiments 28-35, wherein the equilibrium dissociation constant (K _D ) of binding of the muscle-targeting antibody to the transferrin receptor is in a range from 10 ¹¹ M to 10 ⁶ M.

37. The complex of any one of embodiments 28 to 36, wherein the antibody does not specifically bind to the transferrin binding site of the transferrin receptor and/or wherein the antibody does not inhibit binding of transferrin to the transferrin receptor.

38. The complex of any one of embodiments 28 to 37, wherein the antibody is cross-reactive with extracellular epitopes of two or more of a human, non-human primate and rodent transferrin receptor.

39. The complex of any one of embodiments 28 to 38, wherein the complex is configured to promote transferrin receptor mediated internalization of the molecular payload into a muscle cell.

40. The complex of any one of embodiments 28 to 39, wherein the antibody is a chimeric antibody. 41. The complex of embodiment 40, wherein the chimeric antibody is a humanized monoclonal antibody.

42. The complex of any one of embodiments 28 to 41, wherein the antibody is in the form of a ScFv, a Fab fragment, Fab' fragment, F(ab')2 fragment, or Fv fragment.

43. The complex of any one of embodiments 28 to 42, wherein the molecular payload is an oligonucleotide.

44. The complex of embodiment 43, wherein the oligonucleotide comprises a region of complementarity to a muscle disease gene having a gain-of-function disease allele.

45. The complex of any one of embodiments 28 to 42, wherein the molecular payload is a polypeptide.

46. The complex of embodiment 45, wherein the polypeptide is an E3 ubiquitin ligase inhibitor peptide.

47. The complex of embodiment 43 or 44, wherein the oligonucleotide comprises at least one modified internucleotide linkage.

48. The complex of embodiment 47, wherein the at least one modified intemucleotide linkage is a phosphorothioate linkage.

49. The complex of embodiment 48, wherein the oligonucleotide comprises phosphorothioate linkages in the Rp stereochemical conformation and/or in the Sp stereochemical conformation.

50. The complex of embodiment 49, wherein the oligonucleotide comprises phosphorothioate linkages that are all in the Rp stereochemical conformation or that are all in the Sp stereochemical conformation.

51. The complex of any one of embodiments 43, 44, or 47 to 50, wherein the oligonucleotide comprises one or more modified nucleotides.

52. The complex of embodiment 51, wherein the one or more modified nucleotides are 2 ’-modified nucleotides.

53. The complex of any one of embodiments 43, 44, or 47 to 52, wherein the oligonucleotide is a gapmer oligonucleotide that directs RNAse H-mediated cleavage of an mRNA transcript encoded by the muscle disease gene in a cell. 54. The complex of embodiment 53, wherein the gapmer oligonucleotide comprises a central portion of 5 to 15 deoxyribonucleotides flanked by wings of 2 to 8 modified nucleotides.

55. The complex of embodiment 54, wherein the modified nucleotides of the wings are 2 ’-modified nucleotides.

56. The complex of any one of embodiments 43, 44, or 47 to 52, wherein the oligonucleotide is a mixmer oligonucleotide.

57. The complex of embodiment 56, wherein the mixmer oligonucleotide comprises two or more different 2’ modified nucleotides.

58. The complex of any one of embodiments 43, 44, or 47 to 52, wherein the oligonucleotide is an RNAi oligonucleotide that promotes RNAi-mediated cleavage of a mRNA transcript encoded by the muscle disease gene.

59. The complex of embodiment 58, wherein the RNAi oligonucleotide is a double- stranded oligonucleotide of 19 to 25 nucleotides in length.

60. The complex of embodiment 58 or 59, wherein the RNAi oligonucleotide comprises at least one 2’ modified nucleotide.

61. The complex of any one of embodiments 52, 55, 57, or 60, wherein each 2’ modified nucleotide is selected from the group consisting of: 2'-0-methyl, 2'-fluoro (2'-F), 2'- O-methoxyethyl (2'-MOE), and 2', 4'-bridged nucleotides.

62. The complex of embodiment 51, wherein the one or more modified nucleotides are bridged nucleotides.

63. The complex of any one of embodiments 52, 55, 57, or 60, wherein at least one 2’ modified nucleotide is a 2 ’,4 ’-bridged nucleotide selected from: 2 ',4 '-constrained 2 '-O-ethyl (cEt) and locked nucleic acid (LNA) nucleotides.

64. The complex of any one of embodiments 43, 44, or 47 to 52, wherein the oligonucleotide comprises a guide sequence for a genome editing nuclease.

65. The complex of any one of embodiments 43, 44, or 47 to 52, wherein the oligonucleotide is phosphorodiamidite morpholino oligomer.

66. The complex of any one of embodiments 28 to 65, wherein the antibody is covalently linked to the molecular payload via a cleavable linker. 67. The complex of embodiment 66, wherein the cleavable linker is selected from: a protease-sensitive linker, pH-sensitive linker, and glutathione- sensitive linker.

68. The complex of embodiment 67, wherein the cleavable linker is a protease- sensitive linker.

69. The complex of embodiment 68, wherein the protease-sensitive linker comprises a sequence cleavable by a lysosomal protease and/or an endosomal protease.

70. The complex of embodiment 68, wherein the protease-sensitive linker comprises a valine-citrulline dipeptide sequence.

71. The complex of embodiment 67, wherein the linker is a pH-sensitive linker that is cleaved at a pH in a range of 4 to 6.

72. The complex of any one of embodiments 28 to 65, wherein the antibody is covalently linked to the molecular payload via a non-cleavable linker.

73. The complex of embodiment 72, wherein the non-cleavable linker is an alkane linker.

74. The complex of any one of embodiments 28 to 73, wherein the antibody comprises a non-natural amino acid to which the oligonucleotide is covalently linked.

75. The complex of any one of embodiments 28 to 74, wherein the antibody is covalently linked to the oligonucleotide via conjugation to a lysine residue or a cysteine residue of the antibody.

76. The complex of embodiment 75, wherein the antibody is conjugated to the cysteine via a maleimide-containing linker, optionally wherein the maleimide-containing linker comprises a maleimidocaproyl or maleimidomethyl cyclohexane- 1-carboxylate group.

77. The complex of any one of embodiments 28 to 76, wherein the antibody is a glycosylated antibody that comprises at least one sugar moiety to which the oligonucleotide is covalently linked.

78. The complex of embodiment 77, wherein the sugar moiety is a branched mannose.

79. The complex of embodiment 77 or 78, wherein the antibody is a glycosylated antibody that comprises one to four sugar moieties each of which is covalently linked to a separate oligonucleotide. 80. The complex of embodiment 77, wherein the antibody is a fully-glycosylated antibody.

81. The complex of embodiment 77, wherein the antibody is a partially- glycosylated antibody.

82. The complex of embodiment 81, wherein the partially-glycosylated antibody is produced via chemical or enzymatic means.

83. The complex of embodiment 81, wherein the partially-glycosylated antibody is produced in a cell, cell that is deficient for an enzyme in the N- or O- glycosylation pathway.

84. A method of delivering a molecular payload to a cell expressing transferrin receptor, the method comprising contacting the cell with the complex of any one of embodiments 29 to 83.

85. A method of inhibiting expression or activity of a muscle disease gene in a cell, the method comprising contacting the cell with the complex of any one of embodiments 29 to 83 in an amount effective for promoting internalization of the molecular payload to the cell.

86. The method of embodiment 85, wherein the cell is in vitro.

87. The method of embodiment 85, wherein the cell is in a subject.

88. The method of embodiment 87, wherein the subject is a human.

89. A method of treating a subject having a muscle disease, the method comprising administering to the subject an effective amount of the complex of any one of embodiments 29 to 83.

90. The method of embodiment 89, wherein the muscle disease is a disease listed in Table 1.

91. The method of embodiment 89, wherein the muscle disease is a disease selected from the group consisting of: Adult Pompe Disease, Centronuclear myopathy (CNM), Duchenne Muscular Dystrophy, Facioscapulohumeral Muscular Dystrophy (FSHD), Familial Hypertrophic Cardiomyopathy, Fibrodysplasia Ossificans Progressiva (FOP), Friedreich's Ataxia (FRDA), Inclusion Body Myopathy 2, Laing Distal Myopathy, Myofibrillar Myopathy, Myotonia Congenita (autosomal dominant form, Thomsen Disease), Myotonic Dystrophy Type I, Myotonic Dystrophy Type II, Myotubular Myopathy, Oculopharyngeal Muscular Dystrophy, and Paramyotonia Congenita. 92. A complex comprising an anti-transferrin receptor (TfR) antibody covalently linked to a molecular payload configured to modulate expression or activity of a muscle disease gene, wherein the antibody comprises:

(i) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 76; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 75;

(ii) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 69; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 70;

(iii) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 71; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 70;

(iv) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 72; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 70;

(v) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 73; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 74;

(vi) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 73; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 75;

(vii) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 76; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 74;

(viii) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 77; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 78;

(ix) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 79; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 80; or

(x) a heavy chain variable region (VH) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 77; and/or a light chain variable region (VL) comprising an amino acid sequence at least 85% identical to SEQ ID NO: 80. 93. A complex comprising an anti-transferrin receptor (TfR) antibody covalently linked to a molecular payload configured to modulate expression or activity of a muscle disease gene, wherein the anti-TfR antibody has undergone pyroglutamate formation resulting from a post-translational modification.

EQUIVALENTS AND TERMINOLOGY

[000702] The disclosure illustratively described herein suitably can be practiced in the absence of any element or elements, limitation or limitations that are not specifically disclosed herein. Thus, for example, in each instance herein any of the terms “comprising”, “consisting essentially of’, and “consisting of’ may be replaced with either of the other two terms. The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention that in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the disclosure. Thus, it should be understood that although the present disclosure has been specifically disclosed by preferred embodiments, optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this disclosure.

[000703] In addition, where features or aspects of the disclosure are described in terms of Markush groups or other grouping of alternatives, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group or other group.

[000704] It should be appreciated that, in some embodiments, sequences presented in the sequence listing may be referred to in describing the structure of an oligonucleotide or other nucleic acid. In such embodiments, the actual oligonucleotide or other nucleic acid may have one or more alternative nucleotides (e.g., an RNA counterpart of a DNA nucleotide or a DNA counterpart of an RNA nucleotide) and/or (e.g., and) one or more modified nucleotides and/or (e.g., and) one or more modified intemucleotide linkages and/or (e.g., and) one or more other modification compared with the specified sequence while retaining essentially same or similar complementary properties as the specified sequence.

[000705] The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms ( i.e ., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language ( e.g ., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. [000706] Embodiments of this invention are described herein. Variations of those embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description.

[000707] The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. Such equivalents are intended to be encompassed by the following claims.