CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US provisional patent application No. 62/661 ,871 filed on April 24, 2018, the specification of which is hereby incorporated by reference in its entirety.

BACKGROUND

(a) Field

[0002] The subject matter disclosed generally relates to antibodies or antigen-binding fragments that bind to serum albumin. More specifically, the subject matter relates to antibodies or antigen-binding fragments that bind to serum albumin for half-life extension of biologies, as well as compounds, pharmaceutical compositions, nucleic acid vectors, cells comprising the nucleic acid vectors, and methods of removing molecules from serum.

(b) Related Prior Art

[0003] Biologies of less than 40-50 kDa in size possess short serum half- lives due to rapid renal clearance. Strategies to prolong the serum half-life of various biologies (antibody fragments, single-domain antibodies, enzymes, growth factors, peptides) are critically important for efficacy. The half-life of biologies can be extended through various techniques, including, but not limited to PEGylation, PASylation, conjugation to carbohydrates, fusion to an IgG Fc domain, fusion to serum albumin, and fusion to an albumin binding domain or antibody binding domain that recognizes serum albumin. In the latter case, single-domain antibodies (referred to as sdAbs, VHHS, or nanobodies), which are naturally occurring autonomous binding domains found in Camelid species, are ideal agents for which to target serum albumin for half-life extension. The flexibility VHHS offer in terms of modularity and functionality allow for fusion to many biologies, in both N- and C-terminal orientations, without compensating target binding affinities or specificity.

[0004] The requirements for VhiH-based half-life extension of biologies are as follows: (i) high affinity binding and species cross-reactivity of the VHH to the relevant serum albumins (human, monkey, rat, mouse) at pH 7.4, (ii) high affinity binding and species cross-reactivity of the VHH to the relevant serum albumins (human, monkey, rat, mouse) at pH 5.5, (iii) the anti-serum albumin VHH cannot compete with FcRn for albumin binding, and (iv) the anti-serum albumin VHH must retain functionality when fused to biologies through linkers.

[0005] On the other hand, many harmful molecules (e.g., protein-based bacterial toxin or venoms) need to be removed as quickly as possible from the body. Increasing their rate of removal will have therapeutic effects and prevent disease. To remove harmful molecules from circulation, a direct neutralizing agent (e.g., antibody) can be used to neutralize the harmful effects of the toxic molecules. Presently, direct neutralization of many toxins is not efficacious enough (the toxic substance is not removed quickly enough from serum) leaving significant room for improvement of therapeutic antibody efficacy.

[0006] Therefore, there is a need for additional VHHS which target multiple serum albumin species, for the purpose of extending the serum half-life of biologies or removal of harmful molecules.

[0007] The following application describes the isolation, characterization, and in vivo testing of several llama-derived VHHS which target multiple serum albumin species, for the purpose of extending the serum half-life of biologies or removal of harmful molecules.

SUMMARY

[0008] According to an embodiment, there is provided an antibody or an antigen-binding fragment that binds to serum albumin comprising three complementarity determining regions (CDR1 , CDR2 and CDR3), wherein the CDR1 , CDR2 and CDR3 comprise an amino acid sequence comprising:

1 ) GFLLRSNTM (SEQ ID NO:1 ), IRPSGLT (SEQ ID NO:2), and

HTRPPFQRDS (SEQ ID NO:3) or ATRPPFQRDS (SEQ ID NO:4), respectively; or

2) GRTFIAYAM (SEQ ID NO:5), ITNFAGGTT (SEQ ID NO:6), and AAD RSAQTM RQVRPVLPY (SEQ ID NO:7), respectively; or

3) GRTFDNYVM (SEQ ID NO:8), ISGSGSIT (SEQ ID NO:9), and

AAGSRRTYYREPKFYPS (SEQ ID NO: 10), respectively; or

4) GSTFSSSSV (SEQ ID NO:11 ), ITSGGST (SEQ ID NO:12), and

NVAGRNWVPISRYSPGPY (SEQ ID NO:13) or AVAGRNWVPISRYSPGPY (SEQ ID NO: 14), respectively; or

5) GSIESINRM (SEQ ID NO:15), ISKGGST (SEQ ID NO:16), and

AAGPVWEQF (SEQ ID NO: 17), respectively; or

6) GRTISLYAV (SEQ ID NO:18), ISWTDSST (SEQ ID NO:19), and AADVSIRGLQKYEYDY (SEQ ID NO:20), respectively; or

7) TRTFSSYIM (SEQ ID NO:21 ), ISWSGRMT (SEQ ID NO:22), and AADRTTAWGAPRSQYDS (SEQ ID NO:23), respectively.

[0009] The antigen-binding fragment may be a single-domain antibody (sdAb).

[0010] The antibody may be an IgA, IgD, IgE, IgG, or IgM.

[0011] The CDR1 , CDR2 and CDR3 may comprise an amino acid sequence comprising GFLLRSNTM (SEQ ID NO:1 ), IRPSGLT (SEQ ID NO:2), and HTRPPFQRDS (SEQ ID NO:3) or ATRPPFQRDS (SEQ ID NO:4), respectively.

[0012] The CDR1 , CDR2 and CDR3 may comprise an amino acid sequence comprising GRTFIAYAM (SEQ ID NO:5), ITNFAGGTT (SEQ ID NO:6), and AADRSAQTMRQVRPVLPY (SEQ ID NO:7), respectively. [0013] The CDR1 , CDR2 and CDR3 may comprise an amino acid sequence comprising GRTFDNYVM (SEQ ID NO:8), ISGSGSIT (SEQ ID NO:9), and AAGSRRTYYREPKFYPS (SEQ ID NO:10), respectively.

[0014] The CDR1 , CDR2 and CDR3 may comprise an amino acid sequence comprising GSTFSSSSV (SEQ ID NO:11 ), ITSGGST (SEQ ID NO:12), and NVAGRNWVPISRYSPGPY (SEQ ID NO:13) or AVAGRNWVPISRYSPGPY (SEQ ID NO: 14), respectively.

[0015] The CDR1 , CDR2 and CDR3 may comprise an amino acid sequence comprising GSIESINRM (SEQ ID NO:15), ISKGGST (SEQ ID NO:16), and AAGPVWEQF (SEQ ID NO: 17), respectively.

[0016] The CDR1 , CDR2 and CDR3 may comprise an amino acid sequence comprising GRTISLYAV (SEQ ID NO: 18), ISWTDSST (SEQ ID NO:19), and AADVSIRGLQKYEYDY (SEQ ID NO:20), respectively.

[0017] The CDR1 , CDR2 and CDR3 may comprise an amino acid sequence comprising TRTFSSYIM (SEQ ID NO:21 ), ISWSGRMT (SEQ ID NO:22), and AADRTTAWGAPRSQYDS (SEQ ID NO:23), respectively.

[0018] The antibody or an antigen-binding fragment may be humanized or partially humanized.

[0019] According to another embodiment, there is provided a compound comprising an antibody or an antigen-binding fragment according to the present invention.

[0020] The antibody or an antigen-binding fragment may be linked to the compound via a linker.

[0021] The linker may be an amino acid sequence that allows for the functional linking of the compound to the antibody or an antigen-binding fragment. [0022] The amino acid sequence may comprise about 3 to about 40 amino acids.

[0023] The linker sequence may be (GGGGS)n, wherein n > 1 , or any suitable linker.

[0024] The antibody or an antigen-binding fragment may be fused to an antibody or an antigen-binding fragment, operable to bind a target epitope.

[0025] The antibody or an antigen-binding fragment may be linked to a peptide, a polypeptide, a protein, an enzyme, an antibody, an antibody fragment, or combinations thereof, wherein each of the antibody or an antigen-binding fragment and the linked peptide, polypeptide, protein, enzyme, antibody, antibody fragment, or combinations thereof are functional.

[0026] According to another embodiment, there is provided a composition comprising the compound of the present invention, and a pharmaceutically acceptable diluent, carrier or excipient.

[0027] According to another embodiment, there is provided a nucleic acid vector comprising a nucleotide sequence encoding a compound of the present invention.

[0028] According to another embodiment, there is provided a cell comprising the nucleic acid vector of the present invention for expressing the compound of the present invention.

[0029] According to another embodiment, there is provided a cell for expressing the compound of the present invention.

[0030] According to another embodiment, there is provided a method of removing a molecule from serum, comprising administering a compound according to the present invention specific to the molecule, wherein the antibody or an antigen-binding fragment comprises CDR1 , CDR2 and CDR3 comprising an amino acid sequence comprising GRTFDNYVM (SEQ ID NO:8), ISGSGSIT (SEQ ID NO:9), and AAGSRRTYYREPKFYPS (SEQ ID NO:10), respectively.

[0031] According to another embodiment, there is provided a use of a compound according to the present invention specific to a molecule for removing the molecule from serum, wherein the sdAb comprises CDR1 , CDR2 and CDR3 comprising an amino acid sequence comprising GRTFDNYVM (SEQ ID NO:8), ISGSGSIT (SEQ ID NO:9), and AAGSRRTYYREPKFYPS (SEQ ID NO:10), respectively.

[0032] According to another embodiment, there is provided a solid support for purification of albumin, derivatives thereof, or fragments thereof comprising a solid or semi-solid medium linked to an antibody or an antigen-binding fragment according to the present invention or a compound according to the present invention.

[0033] According to another embodiment, there is provided a method of purifying albumin comprising contacting an albumin containing sample with a solid support according to the present invention.

[0034] Features and advantages of the subject matter hereof will become more apparent in light of the following detailed description of selected embodiments, as illustrated in the accompanying figures. As will be realized, the subject matter disclosed and claimed is capable of modifications in various respects, all without departing from the scope of the claims. Accordingly, the drawings and the description are to be regarded as illustrative in nature, and not as restrictive and the full scope of the subject matter is set forth in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Further features and advantages of the present disclosure will become apparent from the following detailed description, taken in combination with the appended drawings, in which: [0036] Fig. 1 illustrates the results from immunization of a llama in order to generate serum albumin binding single domain antibodies (VHHS). An ELISA shows the llama serum response to various serum albumins day 42 post immunization with human serum albumin (HSA). Pre-immune serum drawn before the first immunization is shown as a control. RhSA: rhesus serum albumin; MSA: mouse serum albumin; RSA: rat serum albumin.

[0037] Fig. 2A illustrates the sequences of wild-type serum albumin binding VHFIS and their humanized variants. The sequences of isolated (llama, wild-type) and humanized VHFIS are shown. The international ImMunoGeneTics information (IMGT) numbering system is used to distinguish framework regions (FRs) and complementarity determining regions (CDRs). The sequences of (A) R11 VHFIS, (B) R28 VHFIS, (C) M75 VHFIS, (D) M79 VHFIS are provided.

[0038] Fig 2B provides sequences of wild-type serum albumin binding VHFIS and their humanized variants. The sequences of isolated (llama, wild-type) and humanized VHFIS are shown. The international ImMunoGeneTics information (IMGT) numbering system is used to distinguish framework regions (FRs) and complementarity determining regions (CDRs). The sequences of (E) FH 18 VHFIS, (F) Rh34 VHFIS, and (G) Rh46 VHFIS are provided.

[0039] Fig. 3 illustrates the biophysical characterization of serum albumin binding VHFIS. In this example, various assays are shown to characterize the VHFIS. (A) Representative size exclusion chromatography (SEC) profiles illustrating the VHFIS are strictly monomeric and non-aggregating. (B) Representative surface plasmon resonance (SPR) sensorgrams demonstrating the cross-reactive binding of VHFIS to various serum albumins at pFH 7.4. FISA: human serum albumin; RhSA: rhesus serum albumin; MSA: mouse serum albumin; RSA: rat serum albumin.

[0040] Fig. 4 illustrates the SPR binding analyses of serum albumin binding VHFIS at pFI 5.5. The representative SPR sensorgrams illustrate pFH- sensitive binding to various serum albumins. (A) M79 VHH binding to HSA, RSA and RhSA at pH 5.5. (B) M75 VHH (at a 100 nM injection) very weakly binds HSA and does not recognize RSA at pH 5.5. HSA: human serum albumin; RhSA: rhesus serum albumin; RSA: rat serum albumin.

[0041] Fig. 5 illustrates SPR-based epitope binning experiments. The SPR-based epitope binning experiments identified the different epitope bins targeted by the pool of serum albumin binding VHHS. (A) Representative SPR sensorgrams of VHH co-injection experiments of various VHH + VHH combinations. (B) Graphical representation of the three epitopes targeted by the serum albumin VHHS. R11 and M79 bind the same or a completely overlapping epitope, R28 binds an epitope that is partially overlapping with the R11/M79 epitope and M75 binds an epitope distinct from R11 , M79 and R28.

[0042] Fig. 6 illustrates SPR-based human FcRn (h-FcRn) binding assays. The assays are used to show that the serum albumin binding VHHS do not block the interaction of serum albumin with h-FcRn. (A) Graphical representation of the assay design. (B) Top panels showing that h-FcRn does not bind to immobilized HSA at pH 7.4, but does bind at pH 5.5. Lower panels showing R11 , R28 and M79 binding to immobilized to HSA at pH 5.5, then injection of h-FcRn illustrates h-FcRn is free to bind HSA, demonstrating the VHHS do not compete with h-FcRn binding to HSA.

[0043] Fig. 7 illustrates that serum albumin VHHS can be formatted as N- terminal or C-terminal fusions and remain functional. A representative VHH (B39, SEQ ID NO:74; Murase et al, 2014) was used to demonstrate that the serum albumin binding VHHS can be placed at either the N-terminus or C-terminus of the representative VHH (B39) and retain their ability to bind human serum albumin. (A) Schematic representation of construct designs. (B) SPR assays demonstrating functional binding of constructs to C. difficile toxin B ( via B39 VHH). (C) SPR assays demonstrating functional binding of constructs to human serum albumin ( via R11 , R28, M75 or M79 VHHS). [0044] Fig. 8 illustrates the half-life extension of a monovalent single domain antibody in rats. An anti-toxin B VHH B39 is fused to serum albumin binding VHHS and evaluated in vivo. (A) Design of VHH-VHH dimers that are either control or test articles. B39 is a C. difficile toxin B binding antibody. (B) Size exclusion chromatography profiles. (C) ELISA standard curves using toxin B coated on ELISA wells, VHH-VHH constructs added and detected with anti-HA- IgG HRP. (D) Rat in vivo half-life profiles of VHH-VHH fusions injected at 1 mg/kg. The data show that three VHHS (R11 , R28 and M79) significantly extend B39 half-life (31.1 - 46.1 h) and that the pH sensitive VHH (M75) increases B39 half- life (4.3 h) but to a lesser extent than the aforementioned VHHS. The half-life of unfused B39 and B39-A20.1 control constructs are ~ 0.5 h and 1.4 h, respectively.

[0045] Fig. 9 illustrates the half-life extension of a dimeric single domain antibody in rats. The anti-toxin A VHH-VHH dimer, consisting of anti-C. difficile toxin A VHHS A20 (SEQ ID NO:75) and A26 (SEQ ID NO:76) (Hussack et al 2011a), are fused to serum albumin binding VHHS and evaluated in vivo. (A) Design of VHH-VHH dimers that are either control or test articles. A20 and A26 bind unique C. difficile toxin A epitopes. (B) ELISA standard curves using toxin A coated on ELISA wells, VHH-VHH-VHH constructs added and detected with anti- His6-lgG HRP. This demonstrates the constructs retain binding to toxin A. (C) SPR assays demonstrating binding of the fusion proteins to human and rat serum albumin surfaces. (D) SPR co-injection assay demonstrating the A20-A26- M75 and A20-A26-M79 fusion proteins can simultaneously bind to toxin A on the SPR surface and to human serum albumin in solution. The control A20-A26 can only bind to toxin A and does not bind human serum albumin in solution, as expected. (E) Rat in vivo half-life profiles of VHH-VHH-VHH fusions injected at 1 mg/kg. The data show a half-life of 1.8 h for the A20-A26 control construct compared to half-lives of 6.8 h and 45.0 h for A20-A26 fused to M75 and M79, respectively. [0046] Fig. 10 illustrates the half-life extension of a growth factor binding protein. A growth factor CIBP2 (SEQ ID NO:77)(WO 2008019491 A1 ; UniProtKB ref # P18065) is fused to serum albumin binding VHHS and evaluated in vivo. (A) Design of CIBP2-VHHS that are either control or test articles. (B) Rat in vivo half- life profiles of CIBP2-VHH fusions injected at 1 mg/kg, as determined by MRM mass spectrometry analysis. The data show rapid clearance of the CIBP2 control construct (half-life could not be calculated) compared to half-lives of 4.9 h and 40.3 h for CIBP2 fused to M75 and M79, respectively.

[0047] Fig. 11 illustrates half-life extension of a blood brain barrier penetrating antibody FC5 (Muruganandam et al, 2002) fused to an amyloid-b binding peptide (ABP (SEQ ID NO:79); Chakravarthy et al, 2014) construct in rats. FC5-ABP is fused to serum albumin binding VHFIS and evaluated in vivo. (A) Design of FC5-ABP-VHFIS that are either control or test articles. (B) Rat in vivo half-life profiles of FC5-ABP-VHFI fusions injected at 1 mg/kg, as determined by MRM mass spectrometry analysis. The data show a half-life of 1.1 h for the FC5- ABP control compared to a half-life of 25.4 h for the FC5-ABP-M79 construct.

[0048] Fig. 12 illustrates the half-life extension of an enzyme. In this example, an enzyme (IDS, SEQ ID NO:80) important in lysosomal storage disease is fused to serum albumin binding VHFIS R28 and M79 and evaluated in vivo. (A) Design of IDS-VHFIS. (B) Size exclusion chromatography profiles. (C) SPR binding profiles of IDS-VHFIS to rat serum albumin with KDS of 55.7 nM and 339 nM for IDS-R28 and IDS-M79, respectively. (D) Rat in vivo half-life profiles of IDS-VHFI fusions. The data show a half-life of 0.9 h for the control IDS-C1 enzyme compared to half-lives ranging from 2.8 h to 4.4 h for various IDS-R28 and IDS-M79 constructs tested at different concentrations.

[0049] Fig. 13 illustrates the half-life extension of a monovalent single domain antibody in rats using humanized serum albumin binding VHFIS. In this example an anti-toxin B VHFI B39 is fused to three representative humanized serum albumin binding VHFIS (M75-H1 , SEQ ID NO: 41 ; R28-H5, SEQ ID NO: 38; R11-H6, SEQ ID NO: 31 ) and evaluated in vivo. (A) Schematic representation of constructs designed for testing. (B) ELISA standard curves using toxin B coated on ELISA wells, VHH-VHH constructs added and detected with anti-HA-lgG HRP. (C) Rat in vivo half-life profiles of B39-humanized VHH fusions injected at 1 mg/kg (or 0.5 mg/kg for B39-R11-H6). Serum antibody concentrations were determined by ELISA and obtained from standard curves. The data show a half-life of 3.8 h for B39-M75-H1 , 51.2 h for B39-R28-H5 and 41.4 h for B39-R11-H6. The unfused B39 half-life was determined to be 0.5 h (Fig. 8). The data show that all three humanized VHHS (M75-H1 , R28-H5 and R11-H6) extend B39 half-life and that the pH sensitive VHH (M75-H1) increases B39 half-life to a lesser extent. This trend is consistent with the half-life extension of the wild-type versions of these VHHS. Importantly, VHH humanization did not negatively impact VHH function as in vivo half-life in rats was essentially identical to the durations observed for wild-type VHHS (Table 2).

[0050] Fig. 14 illustrates crude domain mapping on HSA. Serum albumin is comprised of three major domains (domain 1 , Dl; domain 2, Dll; domain 3, Dill). These domains were expressed and purified from mammalian cells (HEK293 6E) either alone or as fusions (Dl, Dll, Dill, DI-DII, DII-DIII) to determine the location of VHH binding. (A) Schematic of HSA domains synthesized and cloned into the pTT5 expression vector. Numbers refer to amino acid positions of the mature human serum albumin after signal and pro-peptide cleavage. (B) SDS-PAGE of the constructs expressed and purified. Dl and Dill domains could not be expressed. (C) SPR sensorgrams demonstrating the response from injection of 100 nM of each anti-serum albumin VHH (M75, M79, R11 or R28) over amine-coupled surfaces of Dll, DI-DII or DII-DIII. (D) Summary of VHH reactivity for various serum albumin domains. From the domain mapping binding studies: M75 binds Dl, and M79, R11 and R28 all bind Dll of human serum albumin. This is consistent with previous FcRn competition experiments that showed VHHS did not interfere with FcRn binding to human serum albumin (in Dill). This is also consistent with epitope binning experiments that showed M75 bound an HSA epitope that was distinct from the M79/R11/R28 binding site.

[0051] Fig. 15 illustrates the impact of pH on the binding affinity of VHHS for human and rat serum albumin. (A) Affinity of VHHS for HSA at various pHs. (B) Affinity of M75 for HSA, HSA DI-DII and RSA at various pHs.

DETAILED DESCRIPTION

[0052] The present invention is directed to a technology for extending the serum half-life of biologies, or increasing the rate of removal and neutralization of harmful molecules. In embodiments there is disclosed an antibody or an antigen- binding fragment that binds to serum albumin comprising four framework regions (FR1 to FR4) and three complementarity determining regions (CDR1 , CDR2 and CDR3). According to an embodiment, the antibody or an antigen binding fragment may be a single domain antibody (sdAb) that binds to serum albumin comprising four framework regions (FR1 to FR4) and three complementarity determining regions (CDR1 , CDR2 and CDR3).

[0053] The CDR1 , CDR2 and CDR3 of the invention may comprise any one of the following amino acid sequence:

1 ) GFLLRSNTM (SEQ ID NO:1 ), IRPSGLT (SEQ ID NO:2), and HTRPPFQRDS (SEQ ID NO:3) or ATRPPFQRDS (SEQ ID NO:4), respectively; or

2) GRTFIAYAM (SEQ ID NO:5), ITNFAGGTT (SEQ ID NO:6), and AAD RSAQTM RQVRPVLPY (SEQ ID NO:7), respectively; or

3) GRTFDNYVM (SEQ ID NO:8), ISGSGSIT (SEQ ID NO:9), and AAGSRRTYYREPKFYPS (SEQ ID NO: 10), respectively; or

4) GSTFSSSSV (SEQ ID NO:11 ), ITSGGST (SEQ ID NO:12), and NVAGRNWVPISRYSPGPY (SEQ ID NO:13) or AVAGRNWVPISRYSPGPY (SEQ ID NO: 14), respectively; or 5) GSIESINRM (SEQ ID NO:15), ISKGGST (SEQ ID N0:16), and

AAGPVWEQF (SEQ ID NO: 17), respectively; or

6) GRTISLYAV (SEQ ID NO:18), ISWTDSST (SEQ ID NO:19), and

AADVSIRGLQKYEYDY (SEQ ID NO:20), respectively; or

7) TRTFSSYIM (SEQ ID NO:21), ISWSGRMT (SEQ ID NO:22), and

AADRTTAWGAPRSQYDS (SEQ ID NO:23), respectively.

[0054] According to embodiments, the sdAb of the present invention may be the R11 sdAb (SEQ ID NO:24), and humanized versions thereof (HO to H6) SEQ ID NOS:25 - 31 ); the R28 sdAb (SEQ ID NO:32), and humanized versions thereof (HO to H5) SEQ ID NOS:33 - 38); the M75 sdAb (SEQ ID NO:39), and humanized versions thereof (HO to H5) SEQ ID NOS:40 - 45); the M79 sdAb (SEQ ID NO:46), and humanized versions thereof (HO to H5) SEQ ID NOS:47 - 52); the H18 sdAb (SEQ ID NO:53), and humanized versions thereof (HO to H5) SEQ ID NOS:54 - 59); the Rh34 sdAb (SEQ ID NO:60), and humanized versions thereof (HO to H5) SEQ ID NOS:61 - 66); and the Rh46 sdAb (SEQ ID NO:67), and humanized versions thereof (HO to H5) SEQ ID NOS:68 - 73). See Tables 1 to Tables 3 below, and Figs. 2A and 2B.

TABLE 1 : Wild-type VHH affinities for serum albumins from various species.

Unless noted, all values were determined by single cycle kinetic (SCK) SPR measurements on a Biacore T200

# determined by ITC

not determined

n.b.: no binding

HSA: human serum albumin

RhSA: rhesus serum albumin

RSA: rat serum albumin

MSA: mouse serum albumin

h-FcRn: human neonatal Fc receptor

TABLE 2: In vivo serum half-lives of various anti-serum albumin V _H H-fusions in rat

*: Mean serum T (terminal half-life, in h, unless otherwise noted), from n = 3 rats per group, determined by non-compartmental analysis using PK Solver v2.0 (Zhang et al, 2010).

a: alpha half-life, b half-life could not be determined

#: determined by MRM analysis

BBB: blood brain barrier

n.d.: could not be determined

File No P4395PC00

TABLE 3: Biophysical characteristics of wild-type and humanized anti-serum albumin VHHS.

File No P4395PC00

[0055] According to other embodiments, the antibody or an antigen- binding fragment of the present invention may be sdAb having sequences substantially identical to sdAb R11 , R28, M75, M79, H18, Rh34 and Rh46, operable to bind to serum albumin from multiple species, including, but not limited to, human, monkey, rat, and mouse. A substantially identical sequence may comprise one or more conservative amino acid mutations. It is known in the art that one or more conservative amino acid mutation to a reference sequence may yield a mutant peptide with no substantial change in physiological, chemical, physico-chemical or functional properties compared to the reference sequence; in such a case, the reference and mutant sequences would be considered “substantially identical” polypeptides. A conservative amino acid substitution is defined herein as the substitution of an amino acid residue for another amino acid residue with similar chemical properties (e.g. size, charge, or polarity). According to one embodiment, these conservative amino acid mutations may be made to the framework regions of the sdAb while maintaining the CDR sequences listed above and the overall structure of the CDR of the antibody or fragment; thus the specificity and binding of the antibody are maintained. According to another embodiment, these conservative amino acid mutations may be made to the framework regions of the sdAb and the CDR sequence listed above while maintaining the antigen-binding function of the overall structure of the CDR of the antibody or fragment; thus the specificity and binding of the antibody are maintained.

[0056] In a non-limiting example, a conservative mutation may be an amino acid substitution. Such a conservative amino acid substitution may substitute a basic, neutral, hydrophobic, or acidic amino acid for another of the same group. By the term“basic amino acid” it is meant hydrophilic amino acids having a side chain pK value of greater than 7, which are typically positively charged at physiological pH. Basic amino acids include histidine (His or H), arginine (Arg or R), and lysine (Lys or K). By the term“neutral amino acid” (also “polar amino acid”), it is meant hydrophilic amino acids having a side chain that is uncharged at physiological pH, but which has at least one bond in which the pair of electrons shared in common by two atoms is held more closely by one of the atoms. Polar amino acids include serine (Ser or S), threonine (Thr or T), cysteine (Cys or C), tyrosine (Tyr or Y), asparagine (Asn or N), and glutamine (Gin or Q). The term“hydrophobic amino acid” (also“non-polar amino acid”) is meant to include amino acids exhibiting a hydrophobicity of greater than zero according to the normalized consensus hydrophobicity scale of Eisenberg (1984). Hydrophobic amino acids include proline (Pro or P), isoleucine (lie or I), phenylalanine (Phe or F), valine (Val or V), leucine (Leu or L), tryptophan (Trp or W), methionine (Met or M), alanine (Ala or A), and glycine (Gly or G).“Acidic amino acid” refers to hydrophilic amino acids having a side chain pK value of less than 7, which are typically negatively charged at physiological pH. Acidic amino acids include glutamate (Glu or E), and aspartate (Asp or D).

[0057] Sequence identity is used to evaluate the similarity of two sequences; it is determined by calculating the percent of residues that are the same when the two sequences are aligned for maximum correspondence between residue positions. Any known method may be used to calculate sequence identity; for example, computer software is available to calculate sequence identity. Without wishing to be limiting, sequence identity can be calculated by software such as NCBI BLAST2 service maintained by the Swiss Institute of Bioinformatics (and as found at ca.expasy.org/tools/blast/), BLAST-P, Blast-N, or FASTA-N, or any other appropriate software that is known in the art.

[0058] The substantially identical sequences of the present invention may be at least 90% identical; in another example, the substantially identical sequences may be at least 90, 91 , 92, 93, 94, 95, 96, 97, 98, 99, or 100% identical, or any percentage therebetween, at the amino acid level to sequences described herein. Importantly, the substantially identical sequences retain the activity and specificity of the reference sequence. In a non-limiting embodiment, the difference in sequence identity may be due to conservative amino acid mutation(s). In a non-limiting example, the present invention may be directed to an antibody or antigen-binding fragment comprising a sequence at least 95%, 98%, or 99% identical to that of the antibodies described herein.

[0059] The antibody or an antigen-binding fragment of the present invention may be used for example to improve the half-life of the compounds in serum, by targeting an albumin moiety. As used herein, the expression“targeting an albumin moiety” is intended to mean that the antibody or an antigen-binding fragment of the present invention are enabled to bind to serum albumin and particularly to human, rhesus, mouse and rat serum albumin.

[0060] The term“antibody”, also referred to in the art as“immunoglobulin” (Ig), as used herein refers to a protein constructed from paired heavy and light polypeptide chains; various Ig isotypes exist, including IgA, IgD, IgE, IgG, and IgM. When an antibody is correctly folded, each chain folds into a number of distinct globular domains joined by more linear polypeptide sequences. For example, the immunoglobulin light chain folds into a variable (VL) and a constant (CL) domain, while the heavy chain folds into a variable (VH) and three constant (CH1 , CH2, CH3) domains. Interaction of the heavy and light chain variable domains (VH and VL) results in the formation of an antigen binding region (Fv). Each domain has a well-established structure familiar to those of skill in the art.

[0061] The light and heavy chain variable regions are responsible for binding the target antigen and can therefore show significant sequence diversity between antibodies. The constant regions show less sequence diversity, and are responsible for binding a number of natural proteins to elicit important biochemical events. The variable region of an antibody contains the antigen- binding determinants of the molecule, and thus determines the specificity of an antibody for its target antigen. The majority of sequence variability occurs in six hypervariable regions, three each per variable heavy (VH) and light (VL) chain; the hypervariable regions combine to form the antigen-binding site, and contribute to binding and recognition of an antigenic determinant. The specificity and affinity of an antibody for its antigen is determined by the structure of the hypervariable regions, as well as their size, shape, and chemistry of the surface they present to the antigen. Various schemes exist for identification of the regions of hypervariability, the two most common being those of Kabat and of Chothia and Lesk. Kabat and Wu (1991) define the “complementarity- determining regions” (CDR) based on sequence variability at the antigen-binding regions of the VH and VL domains. Chothia and Lesk (1987) define the “hypervariable loops” (H or L) based on the location of the structural loop regions in the VH and VL domains. These individual schemes define CDR and hypervariable loop regions that are adjacent or overlapping, those of skill in the antibody art often utilize the terms “CDR” and “hypervariable loop” interchangeably, and they may be so used herein. The CDR/loops are identified herein according to the IMGT nomenclature scheme (i.e., CDR1 , 2 and 3, for each variable region).

[0062] An“antibody fragment” or“antigen-binding fragment” as referred to herein may include any suitable antigen-binding antibody fragment known in the art. The antibody fragment may be a naturally-occurring antibody fragment, or may be obtained by manipulation of a naturally-occurring antibody or by using recombinant methods. For example, an antibody fragment may include, but is not limited to a Fv, single-chain Fv (scFv; a molecule consisting of VL and VH connected with a peptide linker), Fab, F(ab’)2, single-domain antibody (sdAb; a fragment composed of a single VL or VH or a VHFI), and multivalent presentations of any of these. Antibody fragments such as those just described may require linker sequences, disulfide bonds, or other type of covalent bond to link different portions of the fragments; those of skill in the art will be familiar with the requirements of the different types of fragments and various approaches and various approaches for their construction. [0063] In a non-limiting example, the antigen-binding fragment of the present invention may be an sdAb derived from naturally-occurring sources (i.e. in effect, an additional sdAb as the albumin binding sdAb of the present invention). Heavy chain antibodies of camelid origin (Hamers-Casterman et al, 1993) lack light chains and thus their antigen binding sites consist of one domain, termed VHH . SdAbs have also been observed in shark and are termed VNAR (Nuttall et al, 2003). Other sdAbs may be engineered based on human Ig heavy and light chain sequences (Jespers et al, 2004; To et al, 2005). As used herein, the term“sdAb” includes those sdAb directly isolated from VH, VHH, VL, or VNAR reservoir of any origin through phage display or other technologies, sdAb derived from the aforementioned sdAb, recombinantly produced sdAb, as well as those sdAb generated through further modification of such sdAb by humanization, affinity maturation, stabilization, solubilization, camelization, or other methods of antibody engineering. Also encompassed by the present invention are homologues, derivatives, or fragments that retain the antigen-binding function and specificity of the sdAb.

[0064] SdAbs possess desirable properties for antibody molecules, such as high thermostability, high detergent resistance, relatively high resistance to proteases (Dumoulin et al, 2002) and high production yield (Arbabi-Ghahroudi et al, 1997); they can also be engineered to have very high affinity by isolation from an immune library (Li et al, 2009) or by in vitro affinity maturation (Davies & Riechmann, 1996). Further modifications to increase stability, such as the introduction of non-canonical disulfide bonds (Hussack et al, 2011 a, b; Kim et al, 2012), may also be brought to the sdAb.

[0065] A person of skill in the art would be well-acquainted with the structure of a single-domain antibody (see, for example, 3DWT, 2P42 in Protein Data Bank). An sdAb comprises a single immunoglobulin domain that retains the immunoglobulin fold; most notably, only three CDR/hypervariable loops form the antigen-binding site. However, and as would be understood by those of skill in the art, not all CDR may be required for binding the antigen. For example, and without wishing to be limiting, one, two, or three of the CDR may contribute to binding and recognition of the antigen by the sdAb of the present invention. The CDR of the sdAb or variable domain are referred to herein as CDR1 , CDR2, and CDR3.

[0066] The present invention further encompasses an antibody or an antigen-binding fragment that is "humanized" using any suitable method known in the art, for example, but not limited to CDR grafting and veneering. Humanization of an antibody or an antigen-binding fragment comprises replacing an amino acid in the sequence with its human counterpart, as found in the human consensus sequence, without loss of antigen-binding ability or specificity; this approach reduces immunogenicity of the antibody or antigen-binding fragment when introduced into human subjects. In the process of CDR grafting, one or more than one of the CDR defined herein may be fused or grafted to a human variable region (VH, or VL), to other human antibody (IgA, IgD, IgE, IgG, and IgM), to other human antibody fragment framework regions (Fv, scFv, Fab) or to other proteins of similar size and nature onto which CDR can be grafted (Nicaise et al, 2004). In such a case, the conformation of the one or more than one hypervariable loop is likely preserved, and the affinity and specificity of the antibody or an antigen-binding fragment for its target (i.e., human/rhesus/rat/mouse serum albumin, collectively referred to as serum albumin) is likely minimally affected. CDR grafting is known in the art and is described in at least the following: US Patent No. 6180370, US Patent No. 5693761 , US Patent No. 6054297, US Patent No. 5859205, and European Patent No. 626390. Veneering, also referred to in the art as "variable region resurfacing", involves humanizing solvent-exposed positions of the antibody or fragment; thus, buried nonhumanized residues, which may be important for CDR conformation, are preserved while the potential for immunological reaction against solvent-exposed regions is minimized. Veneering is known in the art and is described in at least the following: US Patent No. 5869619, US Patent No. 5766886, US Patent No. 5821123, and European Patent No. 519596. Persons of skill in the art would also be amply familiar with methods of preparing such humanized antibody fragments and humanizing amino acid positions.

[0067] The antibody or an antigen-binding fragment used with the present invention may also comprise additional sequences to aid in expression, detection or purification of a recombinant antibody or an antigen-binding fragment. Any such sequences or tags known to those of skill in the art may be used. For example, and without wishing to be limiting, the antibody or antigen-binding fragment may comprise a targeting or signal sequence (for example, but not limited to ompA or pelB), a detection/purification tag (for example, but not limited to c-Myc, HA, His5, or His6), or a combination thereof. In another example, the additional sequence may be a biotin recognition site such as that described by Cronan et al in WO 95/04069 or Voges et al in WO/2004/076670. As is also known to those of skill in the art, linker sequences may be used in conjunction with the additional sequences or tags, or may serve as a detection/purification tag.

[0068] In another embodiment, there is disclosed a compound comprising antibody or an antigen-binding fragment according to the present invention. In embodiments, the antibody or an antigen-binding fragment of the compound may be linked to the remainder of the compound via a linker (also known as a linker sequence. As known to those of skill in the art, linker sequences may be used in conjunction with the antibody or antigen-binding fragment of the present invention of the compound of the present invention. As used herein, the term “linker sequences” is intended to mean short peptide sequences that occur between protein domains. Linker sequences are often composed of flexible residues like glycine and serine so that the adjacent protein domains are free to move relative to one another. The linker sequence can be any linker sequence known in the art that would allow for the antibody and polypeptide of a compound, of the present invention to be operably linked for the desired function. The linker may be any sequence in the art (either a natural or synthetic linker) that allows for an operable fusion comprising an antibody or fragment linked to a polypeptide. For example, the linker sequence may be a linker sequence L such as (GGGGS)n, wherein n equal to or greater than 1 , or from about 1 to about 5, or from about 1 to 15, or n may be any number of linker that would allow for the operability of the compound of the present invention. In another example, the linker may be an amino acid sequence, for example, an amino acid sequence that comprises about 3 to about 40 amino acids, or about 5 to about 40 amino acids, or about 10 to about 40 amino acids, or about 15 to about 40 amino acids, or about 20 to about 40 amino acids, or about 25 to about 40 amino acids, or about 30 to about 40 amino acids, or about 35 to about 40 amino acids, or about 3 to about 35 amino acids, or about 5 to about 35 amino acids, or about 10 to about 35 amino acids, or about 15 to about 35 amino acids, or about 20 to about 35 amino acids, or about 25 to about 35 amino acids, or about 30 to about 35 amino acids, or about 3 to about 30 amino acids, or about 5 to about 30 amino acids, or about 10 to about 30 amino acids, or about 15 to about 30 amino acids, or about 20 to about 30 amino acids, or about 25 to about 30 amino acids, or about 3 to about 25 amino acids, or about 5 to about 25 amino acids, or about 10 to about 25 amino acids, or about 15 to about 25 amino acids, or about 20 to about 25 amino acids, or about 3 to about 20 amino acids, or about 5 to about 20 amino acids, or about 10 to about 20 amino acids, or about 15 to about 20 amino acids, or about 3 to about 15 amino acids, or about 5 to about 15 amino acids, or about 10 to about 15 amino acids, or about 15 to about 20 amino acids, or about 3 to about 10 amino acids, or about 5 to about 10 amino acids, or about 3 to about 5 amino acids, or about 3, 5, 10, 15, 20, 25, 30, 35, or 40 amino acids.

[0069] According to an embodiment, the antibody or an antigen-binding fragment of the compound may be fused to any one of a peptide, polypeptide (e.g. growth factor CIBP2, antimicrobial cyclic peptides), a protein, an enzyme or polypeptide [such as for example iduronate-2-sulfatase (IDS), acid beta- glucosidase (GCase), serine proteases, growth factors], an antibody or a fragment operable to bind a target epitope (e.g. anti-microbial antibodies, anti- inflammatory antibodies, intrabodies, BBB-crossing antibodies, neurodegeneration targets antibodies, ion channel targeting antibodies for pain, imaging, diagnostic, affinity purification reagents, anti-cancer targets, checkpoint inhibitors, GPCR targeting antibodies), or combinations thereof, in which both the antibody or an antigen-binding fragment and the rest of the compound remain functional for their intended purpose. In a preferred embodiment, the compound may be fused to an antibody or an antigen-binding fragment, operable to bind a target epitope.

[0070] The antibody or antigen-binding fragment of the present invention may also be in a multivalent display format, also referred to herein as multivalent presentation. Multimerization may be achieved by any suitable method of known in the art. For example, and without wishing to be limiting in any manner, multimerization may be achieved using self-assembly molecules such as those described in Zhang et al (2004a; 2004b) and W02003/046560, where pentabodies are produced by expressing a fusion protein comprising the antibody or antigen- binding fragment of the present invention and the pentamerization domain of the B-subunit of an AB5 toxin family (Merritt & Hoi, 1995). A multimer may also be formed using the multimerization domains described by Zhu et al. (2010); this form, referred to herein as a "combody" form, is a fusion of the antibody or fragment of the present invention with a coiled-coil peptide resulting in a multimeric molecule (Zhu et al., 2010). Other forms of multivalent display are also encompassed by the present invention. For example, and without wishing to be limiting, the antibody or antigen-binding fragment may be presented as a dimer, a trimer, or any other suitable oligomer. This may be achieved by methods known in the art (Spiess et al, 2015), for example direct linking connection (Nielsen et al, 2000), c-jun/Fos interaction (de Kruif & Logtenberg, 1996), "Knob into holes" interaction (Ridgway et al, 1996).

[0071] Another method known in the art for multimerization is to dimerize the antibody or antigen-binding fragment using an Fc domain, for example, but not limited to human Fc domains. The Fc domains may be selected from various classes including, but not limited to, IgG, IgM, or various subclasses including, but not limited to lgG1 , lgG2, etc. In this approach, the Fc gene in inserted into a vector along with the sdAb gene to generate a sdAb-Fc fusion protein (Bell et al, 2010; Iqbal et al, 2010); the fusion protein is recombinantly expressed then purified. For example, and without wishing to be limiting in any manner, multivalent display formats may encompass chimeric or humanized formats of antibodies VHFI of the present invention linked to an Fc domain, or bi or tri- specific antibody fusions with two or three antibodies VHFI recognizing unique epitopes. Such antibodies are easy to engineer and to produce, can greatly extend the serum half-life of sdAb, and may be excellent tumor imaging reagents (Bell et al., 2010).

[0072] The Fc domain in the multimeric complex as just described may be any suitable Fc fragment known in the art. The Fc fragment may be from any suitable source; for example, the Fc may be of mouse or human origin. In a specific, non-limiting example, the Fc may be the mouse Fc2b fragment or human Fc1 fragment (Bell et al, 2010; Iqbal et al, 2010). The Fc fragment may be fused to the N-terminal or C-terminal end of the VFHF-I or humanized versions of the present invention.

[0073] Each subunit of the multimers described above may comprise the same or different antibodies or antigen-binding fragments of the present invention, which may have the same or different specificity. Additionally, the multimerization domains may be linked to the antibody or antigen-binding fragment using a linker, as required; such a linker should be of sufficient length and appropriate composition to provide flexible attachment of the two molecules, but should not hamper the antigen-binding properties of the antibody. As defined above, the linker sequence can be any linker known in the art that would allow for the compound of the present invention to be prepared and be operable for the desired function. For example, such a linker sequence should be of sufficient length and appropriate composition to provide flexible attachment of the two molecules, but should not hamper the antigen-binding properties of the antibody.

[0074] According to another embodiment, the present invention also encompasses a composition comprising one or more than one of the compound as described herein. The composition may comprise a single sdAb and/or compound as described above, or may be a mixture of sdAb or compounds. Furthermore, in a composition comprising a mixture of sdAb or compounds of the present invention, the sdAb or compound may have the same specificity, or may differ in their specificities; for example, and without wishing to be limiting in any manner, the composition may comprise sdAb or compounds specific to albumin (same or different epitope).

[0075] The composition may also comprise a pharmaceutically acceptable diluent, excipient, or carrier. The diluent, excipient, or carrier may be any suitable diluent, excipient, or carrier known in the art, and must be compatible with other ingredients in the composition, with the method of delivery of the composition, and is not deleterious to the recipient of the composition. The composition may be in any suitable form; for example, the composition may be provided in suspension form, powder form (for example, but limited to lyophilised or encapsulated), capsule or tablet form. For example, and without wishing to be limiting, when the composition is provided in suspension form, the carrier may comprise water, saline, a suitable buffer, or additives to improve solubility and/or stability; reconstitution to produce the suspension is effected in a buffer at a suitable pH to ensure the viability of the antibody or antigen-binding fragment. Dry powders may also include additives to improve stability and/or carriers to increase bulk/volume; for example, and without wishing to be limiting, the dry powder composition may comprise sucrose or trehalose. In a specific, non- limiting example, the composition may be so formulated as to deliver the antibody or antigen-binding fragment to the gastrointestinal tract of the subject. Thus, the composition may comprise encapsulation, time release, or other suitable technologies for delivery of the sdAb or compounds of the present invention. It would be within the competency of a person of skill in the art to prepare suitable compositions comprising the present sdAb or compounds.

[0076] The invention also encompasses nucleic acid vector comprising a nucleotide sequence encoding a sdAb or a compound of the present invention, as well as cells comprising the nucleic acid vector, for expressing the sdAb or compound of the present invention, and cells for expressing the sdAb or compound of the present invention.

[0077] According to another embodiment, there is provided a method of removing a molecule from serum, comprising administering a compound according to the present invention, specific to the molecule, wherein the sdAb comprises CDR1 , CDR2 and CDR3 comprising an amino acid sequence comprising GRTFDNYVM (SEQ ID NO:8), ISGSGSIT (SEQ ID NO:9), and AAGSRRTYYREPKFYPS (SEQ ID NO: 10), respectively.

[0078] According to another embodiment, there is provided a use of a compound according to the present invention which is specific to a molecule, for removing the molecule from serum, wherein the sdAb comprises CDR1 , CDR2 and CDR3 comprising an amino acid sequence comprising GRTFDNYVM (SEQ ID NO:8), ISGSGSIT (SEQ ID NO:9), and AAGSRRTYYREPKFYPS (SEQ ID NO: 10), respectively.

[0079] According to another embodiment, there is provided a solid support for purification of albumin, derivatives thereof, or fragments thereof comprising a solid or semi-solid medium linked to an antibody or an antigen-binding fragment according to the present invention or a compound according to any one of claims 12 to 15.

[0080] According to another embodiment, there is provided a method of purifying albumin comprising contacting an albumin containing sample with a solid support according to the present invention.

[0081] The present invention will be more readily understood by referring to the following examples which are given to illustrate the invention rather than to limit its scope.

Serum albumin VHH isolation

EXAMPLE 1

Llama immunization

[0082] One male llama ( lama glama ) was immunized by Cedarlane (Burlington, ON, Canada) four times with 100 pg of human serum albumin (HSA; Sigma, Oakville, ON, Canada) in 1 mL of phosphate-buffered saline (PBS), pH 7.4, emulsified in an equal volume of Freund’s complete adjuvant for the priming immunization (day 0) or Freund’s incomplete adjuvant for the boosting immunizations (days 21 , 28 and 35). Pre-immune blood was drawn before the first injection on day 1 and served as a negative control. One week after the final immunization, serum and peripheral blood mononuclear cells (PBMCs) were obtained from the animal (day 42).

EXAMPLE 2

Fractionation of serum

[0083] Pre-immune and day 42 llama sera were fractionated by protein G and protein A chromatography (Hi Trap, GE Healthcare, Mississauga, ON, Canada) and eluted by acidic elution. Serum fractions A1 (HCAb), A2 (HCAb), G1 (HCAb), and G2 (clgG) were neutralized with Tris pH 8.8 and dialyzed against PBS pH 7.4 for storage at 4°C. IgG serum fractions were measured using 1.3 AbS280nm = 1 mg/mL.

EXAMPLE 3

ELISA of whole and fractionated serum

[0084] Total serum (pre-immune and day 42), as well as the resulting fractionated sera, A1 (HCAb), A2 (HCAb), G1 (HCAb), and G2 (conventional IgG), were analyzed for specific binding to serum albumins from human, rhesus, rat and mouse (HSA, RhSA, MSA and RSA, respectively) by ELISA. Wells of NUNC MaxiSorp™ microtiter plates were coated overnight at 4°C with 1.5 pg of each serum albumin in 100 pL PBS. The next day, wells were blocked with 300 pL of PBS containing 5% (w/v) skim milk and 0.05% (v/v) Tween-20 for 1.5 h at 37°C, then sera were diluted in PBS, added to wells and incubated for 1 h. Wells were washed 3* with PBS containing 0.1% Tween-20 (PBS-T), incubated with HRP-conjugated goat anti-llama IgG (Cedarlane) diluted to 1 :10000 in PBS, then washed again 3* with PBS-T. Wells were developed with 100 pL of tetramethylbenzidine substrate (Mandel Scientific, Guelph, ON, Canada) then after 5 min, the reaction was stopped with 100 pL of 1 M H2SO4 and the absorbance at 450 nm was measured using a Multiskan™ FC photometer (Thermo-Fisher, Ottawa, ON, Canada)(Fig. 1 ).

EXAMPLE 4

Library construction

[0085] A phage-displayed VHH library was constructed from the heavy- chain-only antibody repertoire of the immunized llama as described previously (Hussack et al, 2011a; Baral et al, 2013). Briefly, total cellular RNA was extracted from approximately 5*10 ⁷ peripheral blood mononuclear cells (PBMCs) using a PureLink ^® RNA Mini Kit (Life Technologies, Carlsbad, CA), pooled, then reverse transcribed using Superscript ^® VILO™ MasterMix (Life Technologies) as per the manufacturer’s instructions. Rearranged VHH genes were amplified using two rounds of semi-nested PCR and cloned into the pMED1 phagemid vector, and then phage were rescued from library-bearing Escherichia coli TG1 cells by superinfection with M13K07 helper phage (Life Technologies) and purified by polyethylene glycol precipitation, essentially as previously described (Hussack et al, 2011a).

EXAMPLE 5

Panning

[0086] The phage-displayed VHH library was panned, essentially as described (Hussack et al, 2011a; Baral et al, 2013), for a single round simultaneously against HSA, RhSA, MSA and RSA immobilized in separate wells. Briefly, wells of NUNC MaxiSorp™ microtiter plates (Thermo-Fisher) were coated overnight at 4°C with 5 pg of each serum albumin in 100 pL of PBS. The next day, wells were blocked for 1.5 h at 37°C with 300 pL of PBS containing 5% (w/v) skim milk and 0.05% (v/v) Tween-20, then ~10 ¹² phage particles (diluted in 100 pL PBS containing 20% (v/v) SuperBlock™ (Life Technologies)) were applied to each well and incubated at room temperature for 2 h. The wells were washed five times with PBS containing 0.05% (v/v) Tween-20 (PBS-T), five times with PBS and then bound phage were eluted sequentially with 100 pL of 100 mM triethylamine followed by 100 pL of 100 mM glycine, pH 2.0. Both high and low pH phage elutions were neutralized with 50 pL of 1 M Tris HCI, pH 8.0, pooled and titered. As a control, the library was panned against an antigen-free well containing only blocking solution.

EXAMPLE 6

Next generation DNA sequencing

[0087] The original library phage and the phage eluted from each panning (HSA, RhSA, MSA and RSA) were used directly as templates for next generation sequencing (NGS). Approximately 10 ⁶ phage particles were used as template in 25 mI_ PCR reactions containing 1x ABI Buffer II, 1.5 mM MgCL, 200 mM each dNTP (Thermo-Fisher), 5 pmol each of primers NGS-MJ7 (5’CGCTCTTCCGATCTCTGNNNNNGCCCAGCCGGCCATGGCC) and NGS- MJ8 (5TGCTCTTCCGATCTGACNNNNNTGAGGAGACGGTGACCTGG) and 1 U of AmpliTaq® Gold DNA polymerase (Life Technologies) and cycled as follows on an GeneAmp ^® PCR System 9700 thermal cycler (Applied BioSystems, Foster City, CA): 95°C for 7 min; 35 cycles of (94°C for 30 s, 55°C for 45 s, and 72°C for 2 min); 72°C for 10 min. The resulting amplicons were purified using PureLink ^® PCR purification kits (Life Technologies) with a >300 bp size cutoff according to the manufacturer’s instructions. Each sample was individually barcoded in a second“tagging” 50 pL PCR reaction containing 1x Phusion HF Buffer, 1 .5 mM MgC , 200 mM each dNTP, 10 pmol of each primer pair P5-seqF (5’AATGATACGGCGACCACCGAGATCTACACTCTTTCCCTACACGACGCTCT TCCGATCTCTG) and P7-index1-seqR (5’

CAAGCAGAAGACGGCATACGAGAT CGT GAT GT GACTGGAGTTCAGACGT GT GCTCTTCCGATCTGAC) sequences. 0.25 U Phusion High-Fidelity DNA polymerase (Thermo-Fisher) and 5 pL first-round PCR as template, then cycled as follows: 98°C for 30 s; 20 cycles of (98°C for 10 s, 65°C for 30 s, and 72°C for 30 s); 72°C for 5 min. The final five amplicons (derived from library phage, HSA output phage, RhSA output phage, MSA output phage and RSA output phage) were pooled and purified from 1 % (w/v) agarose gels using a QIAquick ^® gel extraction kit (QIAGEN, Toronto, ON, Canada), desalted using Agencourt AMPure XP beads (Beckman-Coulter, Pasadena, CA), then sequenced on a MiSeq Sequencing System (lllumina, San Diego, CA) using a 500-cycle MiSeq Reagent Kit V2 and a 5% PhiX genomic DNA spike. From each sample, 1 .8 - 2.4 million reads were generated, of which 0.4 - 1 .2 million were used for analysis after assembly using FLASH (default parameters; (Magoc and Salzberg, 201 1 ) and quality filtering using the FAST-X toolkit with a stringency of Q30 over >95% of each read (Schmieder and Edwards, 201 1 ). The DNA sequence of each VHH was then translated in silico, and the CDR3 sequence (IMGT positions 105-117) parsed using conserved N-terminal amino acid consensus sequences (YYC). For each panning, the set of CDR3 sequences derived from the output phage was compared to the set from the VHH library; for each shared CDR3 sequence, an enrichment score was calculated as the frequency in the output phage divided by the frequency in the library. This frequency score was used as a first-pass approximation of the binding behaviour of VHHS in the library and used for identification of putative serum albumin-binding VHHS with a range of predicted cross-species reactivity. A fold-enrichment of >10 was used as a cut-off for putative serum albumin binding.

EXAMPLE 7

Subcloning expression and purification

[0088] The DNA sequences of seven VHHS were synthesized commercially in the pSJF2 expression vector (GenScript, Piscataway, NJ) and each construct was produced in E. coli. Briefly, 1 L 2*YT cultures containing 100 pg/mL ampicillin, 0.1% (w/v) glucose and 0.5 mM IPTG were inoculated with single plasmid-bearing E. coli TG1 colonies and grown overnight at 37°C with 220 rpm shaking. The next morning, periplasmic proteins were extracted by osmotic shock. The resulting supernatant was dialyzed overnight into immobilized metal affinity chromatography buffer A (10 mM HEPES buffer pH7.0, 500 mM NaCI) and sterile filtered. Protein was purified by I MAC using 5 mL HiTrap™ Chelating HP IMAC columns (GE Healthcare), under the control of an AKTA™ Express (GE Healthcare). A step-wise gradient of 500 mM imidazole in the above buffer A was used for protein elution. Proteins were stored at 4°C.

EXAMPLE 8

Phage ELISA and soluble ELISA

[0089] Wells of NUNC MaxiSorp™ microtiter plates were coated overnight at 4°C with 1.5 pg of each serum albumin in 100 pL PBS. The next day, wells were blocked with 300 mI of PBS containing 5 % (w/v) skim milk and 0.05% (v/v) Tween-20 for 1.5 h at 37°C, then serially diluted VHHS or VhiH-bearing phage were added to wells and incubated for 1 h. Wells were washed 3* with PBS containing 0.1 % Tween-20 (PBS-T), then incubated in either horseradish peroxidase (HRP)-conjugated rabbit anti-His6 (Cedarlane) or anti-M13 (GE Healthcare) secondary antibody, respectively, both at a dilution of 1 :5,000., then washed again 3* with PBS-T and developed with 100 mI_ of tetramethylbenzidine substrate (Mandel Scientific, Guelph, ON, Canada). After 5 min, the reaction was stopped with 100 pL of 1 M H2SO4 and the absorbance at 450 nm was measured using a Multiskan™ FC photometer (Thermo-Fisher).

EXAMPLE 9

Size exclusion chromatography

[0090] VHHS were purified by size exclusion chromatography (SEC) using a Superdex™ 75 10/300 GL column (GE Healthcare) under the control of an AKTA™-FPLC (GE Healthcare). Briefly 250-500 pg of sample were applied at a flow rate of 0.5 mL/min in a mobile phase that consisted of phosphate buffered saline (PBS pH 7.0). Fractions of 0.5 mL of monomeric VHH were collected. The results are shown in Fig. 3A.

EXAMPLE 10

Isothermal Titration Calorimetry

[0091] ITC experiments were performed at 25°C using a MicroCal Auto- ITC200 (GE Healthcare). To avoid buffer artifacts all serum albumins and VHHS were buffer exchanged into PBS using SEC. Settings included 18 automatically defined injections of 2 pL over 5 s and a syringe stirring at 1000 rpm. Concentrations of 50 mM were used for the VHH titrants in the syringe and concentrations of 5 mM of the various serum albumins were in the cell. Data analysis was performed with the Origin software package (GE Healthcare). EXAMPLE 11

SPR binding assays at pH 7.4

[0092] For SPR, a total of 1362 - 1471 resonance units of each serum albumin protein were immobilized in 10 mM acetate buffer, pH 4.5, on CM5 or CM5 series S sensor chips (GE Healthcare) using an amine coupling kit (GE Healthcare). Kinetic analyses were carried out on a Biacore 3000 or Biacore T200 instrument (GE Healthcare) at 25°C by injecting VHHS at various concentration ranges, in HBS-EP+ buffer (10 mM HEPES buffer, pH 7.4 containing 150 mM NaCI, 3 mM EDTA and 0.005 % (v/v) surfactant P20) and at a flow rate of 20 pL/min. Data were analyzed using BIAevaluation software version 4.1 (GE Healthcare) and fitted to a 1 :1 binding model. Results are shown in Fig. 3B and Table 1.

EXAMPLE 12

SPR binding assays at pH 5.5

[0093] SPR experiments were repeated exactly as described above with the exception of the running buffer which was adjusted to pH 5.5 (HBSP-MES: 10 mM HEPES buffer, pH 5.5, 10 mM MES, 150 mM NaCI, 0.005% P20). SEC- purified fractions of monomeric VHHS were also buffer exchanged into the same pH 5.5 buffer before running the SPR experiments. The results are shown in Figs. 4A, 4B and Table 1.

EXAMPLE 13

SPR-based epitope binning

[0094] The SPR-based epitope binning experiments identified the different epitope bins targeted by the pool of VHHS. Fig. 5A shows SPR sensorgrams of VHH co-injection experiments of various VHH+VHH combinations (injected at 10- 20* KD concentrations). Fig. 5B shows a graphical representation of the three epitope bins targeted by the serum albumin VHHS. R11 and M79 bind the same epitope, R28 binds an epitope that is partially overlapping with the R11/M79 epitope and M75 binds an epitope distinct of R11 , M79 and R28.

EXAMPLE 14

SPR FcRn competition binding assay

[0095] All FcRn binding assays were performed at pH 5.5 using HBSP- MES running buffer. Briefly, human serum albumin was immobilized on a CM5 sensor chip as described above. Human FcRn (h-FcRn, produced recombinantly by NRC) was flowed over immobilized HSA at 2 mM in control experiments to demonstrate binding. To ensure anti-serum albumin VHHS did not compete with h-FcRn for albumin binding, a co-injection SPR assay was set up as follows. Serum albumin VHHS were first injected over the HSA surface at concentrations that were 10x their KD for 120 s at a flow rate of 20 pL/min. Immediately following the first 120 s injection, a second injection followed that contained the VHH and 2 pM h-FcRn. In cases where the VHH did not compete for albumin binding with h- FcRn, sensorgrams show two unique and additive binding responses. The results are shown in Figs. 6A and 6B.

Anti-serum albumin VHH fusion proteins

EXAMPLE 15

Synthesis of anti-serum albumin VHH fusion proteins

[0096] Anti-serum albumin VHHS were synthesized as fusion proteins to the C. difficile toxin B VHH (B39; Murase et al, 2014) by Genscript using a (GGGGSjs linker. A control construct consisting of a C. difficile toxin A VHH (A20; Hussak et al, 2011a) fused to B39 was synthesized as a control, as well as the B39 VHH monomer. Sequences were subcloned into the expression vector PSJF2H with N-terminal HA and 6 His tags. Plasmid DNA (5 pg) were diluted into 50 pi of nuclease-free water to produce DNA stocks (100 ng/pL) stored at -20°C. Fig. 7A illustrates the different constructs prepared. EXAMPLE 16

Expression and purification

[0097] Approximately 5 pL of Zymo Research Mix and Go TG1 E.coli competent cells (Cedarlane) were aliquoted into PCR tubes placed on ice. To this, 0.5 pL of DNA plasmid stock was added to cells and incubated on ice for 10 min. The cells were plated onto pre-warmed (at 37°C) 2YT+ampicillin plates for incubation overnight at 32°C. VHH fusions were expressed using a 5-day M9 minimal media method as previously described (Baral et al, 2013). After induction of protein expression, cell cultures were harvested at 5,000 rpm for 20 min (4°C), the supernatant was decanted, and the cell contents were extracted from the cell pellet by whole cell lysis. Briefly, each pellet was resuspended in 100 mL of ice- cold lysis buffer (50 mM Tris-HCI buffer, pH 8.0, 25 mM NaCI, 2 mM EDTA, pH 8.0) and frozen at -80°C for 1 h. Next, pellets were thawed at room temperature with the addition of DTT and PMSF (final of 1 mM and 2 mM, respectively). Freshly prepared lysozyme was added to each culture (150 pg/mL final concentration) and incubated for 30 min. DNAse was added (200 pL of 15 units/pL) for further 30 min incubation. The slurry was then centrifuged at 8,000 rpm for 30 min at 4°C. The resulting supernatant was dialyzed overnight into immobilized metal affinity chromatography (I MAC) buffer A (10 mM HEPES, pH 7.0, 500 mM NaCI) and sterile filtered. Protein was purified by I MAC using 5 mL HiTrap™ Chelating HP columns (GE Healthcare), under the control of an AKTA™ Express (GE Healthcare). A step-wise gradient of 500 mM imidazole in the above buffer was used for protein elution. Proteins were stored at 4°C.

EXAMPLE 17

Size exclusion chromatography and SPR

[0098] Size exclusion chromatography was performed on all purified VHH- VHH fusions with a Superdex 75™ column under the control of an AKTA™-FPLC (GE Healthcare) to determine their aggregation state and to provide samples for SPR analysis. Briefly, VHHS were applied at concentrations of 500 pg with a flow rate of 0.5 mL/min in a mobile phase that consisted of HBS-EP running buffer (10 mM HEPES, pH 7.4, 150 mM NaCI, 3 mM EDTA, and 0.005% (v/v) P20 surfactant)(GE Healthcare). Approximately 0.5 mL samples were collected and sent for SPR. A Biacore 3000 instrument was used to assess the functionality of VHH-VH H fusion proteins, essentially as described above with the exception that a single concentration injection of VHH-VHH over the human serum albumin and toxin B surfaces was performed. The results are shown in Figs. 7B and 7C.

EXAMPLE 18

Endotoxin removal

[0099] To remove endotoxins, affinity purified fusion proteins were concentrated to 5 mL volume for passage through a HiLoad 1660 S75 size exclusion column (GE Healthcare) under control of an AKTA™-FPLC. Briefly, the column was cleaned with 0.5 M NaOH followed by 50% isopropanol to remove endotoxins. VHH fusion protein samples (5 mL) were injected onto the column at 1 mL/min in PBS, pH 7.5, endotoxin-free buffer (Sigma). Collected samples were concentrated on Amicon spin columns (Millipore) to a 1 mL volume and filtered through 0.22 pM filter (Millipore). Samples were then processed on Proteus NoEndo™ Mini spin column kits (Generon, Berkshire, UK) as per the manufacturer’s instructions. Samples were tested for endotoxin levels prior to rat PK studies.

EXAMPLE 19

Rat PK studies

[00100] Male Wistar rats (-200 g) were injected (i.v.) with equimolar amounts of VHH fusion protein (-0.25 mg/mL) for a total dose of -1 mg/kg equivalent, with endotoxin levels in the range of 0.14-4 EU/mg. Groups of three rats per fusion protein were tested. Serum (50 pL) was collected at nine time points for up to 168 h. Serum samples were frozen at -20°C until analysis. The results are shown in Fig. 8A-D.

EXAMPLE 20

ELISA on PK serum samples

[00101] ELISAs were performed to determine the serum half-life of VHH fusion proteins in serum, using purified proteins and standard curves. The B39 VHH antigen, TcdB-RBD (Murase et al, 2014), was coated at 0.3 pg/well in PBS pH 7.4 overnight at 4°C. The next day, wells were blocked in 2% milk in PBS, pH 7.4, for 1 h at 37°C. Next, 100 pL of serum (diluted 1 :10, 1 :50 or 1 :250 in PBS, depending on serum time point) were added to wells in duplicate. Standard curves were also produced on each plate. Serum samples were incubated at room temperature for 1 h. Following three washes with PBS-Tween 20 (0.05%, v/v), a secondary antibody of anti-HA-HRP (1 :5000 dilution) in PBS pH 7.4 was added to each well and incubated for 1 h at room temperature. A final set of three washes preceded the addition of the HRP substrate tetramethylbenzidine (Mandel Scientific). The reaction was stopped with 1.5 M phosphoric acid, and the absorbance was measured using a plate reader at 450 nm. The results are shown in Fig. 8C.

Additional anti-serum albumin VHH fusion protein examples

EXAMPLE 21

Synthesis of additional anti-serum albumin VHH fusion constructs

[00102] DNA encoding the following nine constructs were synthesized and subcloned as described above. A20-A26, A20-A26-M75, A20-A26-M79, FC5- ABP, FC5-ABP-M75, FC5-ABP-M79, CIBP2, CIBP2-M75, and CIBP2-M79 were all subcloned into the mammalian expression vector pTT5™ (Durocher et al, 2002) with HA and His6 tags. Plasmid DNA (5 pg) were diluted into 50 pL of nuclease-free water to produce DNA stocks (100 ng/pL) stored at -20°C. lduronate-2-sulfatase (IDS; UniProtKB ref # P22304) enzyme-VHH conjugates, IDS-R28 and IDS-M79, were designed, expressed and purified by Oxyrane (Gent, Belgium). Figs. 9A, 10A, 11A and 12A illustrate the different constructs prepared.

EXAMPLE 22

Transformation and plasmid preparation

[00103] Approximately 5 pL of Zymo Research Mix and Go TG1 E.coli competent cells (Cedarlane) were aliquoted into PCR tubes placed on ice. To this, 0.5 pL of DNA plasmid stock was added to cells and incubated on ice for 10 min. The cells were plated onto pre-warmed (at 37°C) 2YT+ampicillin plates for incubation overnight at 32°C. Starter cultures of 5 mL of 2YT+ampicillin were inoculated with a single colony and grown at 37°C for 4 h at which point 1 mL was transferred into 200 mL of 2YT+ampicillin in 500 mL ultra-yield flasks with an air top seal for overnight incubation at 37°C. Plasmid extraction was performed using the endo-free plasmid Maxi prep kit (Thermo-Fisher, Ottawa, ON, Canada). Yields of 300-400 pg of plasmid were obtained for transfection into HEK293-6E cells.

EXAMPLE 23

Expression and purification

[00104] Mammalian expression was performed essentially as described previously (Durocher et al, 2002). HEK293-6E mammalian cells were cultured from frozen in enriched F17 media at 5 % CO2, 60 % humidity, 37°C and 100 rpm shaking. Cultures (100 mL) were transfected with 100 pg DNA/100 pL PEIpro transfection reagent (Polyplus, lllkirch, France) at a cell density of 1.5 x 10 ⁶ - 1.7 x 10 ⁶ cells/mL, 99% cell viability. Cells were fed after 24 h with 2% TNI in enriched F17 media and were then grown for 5 d before harvesting. Flarvested cultures were spun at 4000 rpm for 15 min on bench top centrifuge. Supernatants were filtered through a 0.22 pM filter (Millipore), dialyzed into endo-free PBS pH 7.4 (Sigma), then loaded onto an IMAC nickel affinity column (GE Flealthcare) on the AKTA system and purified as described earlier. Endotoxins were removed and measured as described above.

EXAMPLE 24

Rat PK studies

[00105] Rat PK studies were performed exactly as described above (1 mg/kg equivalent) for the other anti-serum albumin VHH fusion proteins. The results are shown in Figs. 9E, 10B, 11 B, 12D and 13B. One set of rats (Fig. 13B; B39-R11-FI6 test group) received 0.5 mg/kg equivalent.

EXAMPLE 25

ELISA analysis of A20-A26 PK serum samples

[00106] ELISA was performed to determine the serum half-life of A20-A26 fusion proteins (with or without fusion to an anti-serum albumin VHFI) in serum. The A20-A26 antigen, C. difficile toxin A (List Biological Laboratories, Campbell, CA) was coated at 0.1 pg/well in PBS, pH 7.4, overnight at 4°C. The next day, wells were blocked in 2% (w/v) milk in PBS, pH 7.5, for 1 h at 37°C. Next, serum samples (diluted 1 :100, 1 :1 ,000, 1 :5,000 or 1 :10,000 in PBS, depending on the fusion protein and time point) were added to wells in duplicate. ELISA plates were incubated at room temperature for 1 h. Following 3 washes with PBS- Tween 20 (0.05%, v/v), secondary antibody of anti-His-HRP (1 :5,000 dilution) in PBS, pH 7.4, was added to each well and incubated for 1 h at room temperature. A final set of three washes preceded the addition of the HRP substrate tetramethylbenzidine (Mandel). The reaction was stopped with 1.5 M sulfuric acid, and the absorbance was measured using a plate reader at 450 nm. Serial dilutions of purified proteins were run on the same plates to generate standard curves. The results are shown in Fig. 9B. EXAMPLE 26

SPR Analysis

[00107] SPR assays were used to demonstrate the binding of the fusion proteins to human and rat serum albumin surfaces (Fig. 9C). A SPR co-injection assay demonstrate that the A20-A26-M75 and A20-A26-M79 fusion proteins can simultaneously bind to toxin A on the surface and to human serum albumin in solution. The control A20-A26 can only bind to toxin A and does not bind human serum albumin in solution, as expected (Fig. 9D). The IDS-R28 and IDS-M79 constructs (Fig. 12A) were SEC purified (Fig. 12B) before confirming that they retain the ability to bind rat serum albumin in SP (Fig. 12C).

EXAMPLE 27

MRM mass spectrometry analysis of FC5-ABP, CIBP2 and IDS fusion proteins in rat serum

[00108] Using purified protein constructs as controls [CIBP2, CIBP2-M75, CIBP2-M79 (Fig. 10A), FC5-ABP, FC5-ABP-M75, FC5-ABP-M79 (Fig. 11A) and, and IDS, IDS-R28, IDS-M79 (Fig. 12A)], MRM mass spectrometry analysis was used to determine the serum concentrations of the above fusion proteins in rats, essentially as previously described (Flaqqani et al, 2013; Figs. 10B, 11 B and 12D).

EXAMPLE 28

Identification of lead humanized VHHs and in vivo testing

[00109] Flumanized VHFIS were designed (Figure 2), expressed in E. coli, purified by immobilized metal affinity chromatography and assessed by SEC, thermal unfolding (T _m ) and binding affinity at pH 7.4 and pH 5.5 for albumins from various species. Lead humanized VHHS were fused to B39 VHH for in vivo half- life extension studies in rats (Table 3, Fig. 13). Based on the biophysical properties described in Table 3 (expression yield, lack of aggregation, preservation of thermal stability and serum albumin binding affinities), the lead humanized version of each VHH identified are: M75-H1 (SEQ ID NO: 41 ), M79- H2 (SEQ ID NO: 49), R28-H5 (SEQ ID NO: 38) and R11-H6 (SEQ ID NO: 31 ). Of these, three examples were fused to the B39 VHH and the serum half-life evaluated in rats, confirming that humanization of the wild-type VHH sequences did not negatively impact half-life extension (Fig. 13C).

EXAMPLE 29

Human serum albumin domain mapping

[00110] To identify which domain of serum albumin the VHHS described bind, the three major domains of HSA were expressed in mammalian HEK293- 6E cells as either individual domains (Dl, Dll and Dill) or two neighboring domains (DI-DII and DII-DIII). HSA domains were purified by affinity chromatography, subjected to SEC, and used for SPR binding experiments (Fig. 14). The results demonstrated that M75 binds to HSA domain 1 (Dl) and R11 , R28 and M79 bind to HSA domain 2 (Dll). This data is consistent with FcRn competition assays in that none of the VHHS compete with FcRn for albumin binding that occurs in domain 3 of HSA.

EXAMPLE 30

Impact of pH on VHH affinities for serum albumin

[00111] VHH affinities (KDS) for human and rat serum albumin as a function of pH were determined (Fig. 15), to illustrate the unique pH sensitivity of the M75 VHH for HSA, HSA DI-DII and for RSA. The affinity of M75 for HSA drops significantly, from KD = 1.2 nM at pH 7.4 to KD = 735 nM at pH 5.5. The affinity of M75 for RSA is D = 315 nM at pH 7.4 while at pH 5.5 the affinity could not be measured because there was no evidence binding. In addition, flowing 50 mM of M75 VHH over RSA surfaces at pH 6.0 did not show a trace of binding. In comparison, the other three VHHS maintain nearly identical binding affinities for HSA at pHs 7.4 and 5.5. [00112] While preferred embodiments have been described above and illustrated in the accompanying drawings, it will be evident to those skilled in the art that modifications may be made without departing from this disclosure. Such modifications are considered as possible variants comprised in the scope of the disclosure.

SEQUENCES

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