FIELD OF THE INVENTION

[0001] The present invention relates to novel human sequence monoclonal antibodies, particularly to human monoclonal antibodies that specifically bind to PD-L1 with high affinities. In particular, the invention relates to the uses of such molecules in the treatment and diagnosis of human diseases.

BACKGROUND OF THE INVENTION

[0002] The protein Programmed Death 1 (PD-l) is an inhibitory member of the CD28 family of receptors, which also include CD28, CTLA-4, ICOS, and BTLA. PD-l is expressed on activated B cells, T cells, and myeloid cells (Bennett et al. 2003, J. Immunol. 170(2): 711-718.). Its ligand, programmed cell death-ligand 1 (PD-L1), is expressed on some tumor cells and by activated B cells and T cells, dendritic cells, macrophages, and fibroblasts cells (Hansen et al. 2009, Mol. Immunol. 46(3): 457-472). PD-L1 binds PD-l to attenuate cellular immune responses by inducing T-cell apoptosis or exhaustion. Blockade of the PD-1/PD-L1 pathway with monoclonal antibodies (against PD-l or PD-L1) is a promising therapeutic approach that is being explored in studies of many types of human cancers (Sanmamed and Chen 2014, Cancer J. 20(4): 256-261). The results of these studies suggest that PD-L1 plays an important role in helping tumors to escape immune systems by facilitating PD-l /PD-L 1 pathway activation.

[0003] PD-L1 expression has been observed in various solid tumors, including breast cancer, lung cancer, gastric cancer, colorectal cancer, hepatocellular carcinoma, renal cell carcinoma, testicular cancer and papillary thyroid cancer. Moreover, several meta-analyses have shown that PD-L1 overexpression signifies a poor prognosis in many cancer types. Therefore, there is a need for better antibodies against PD-L1 for the treatment or diagnosis of diseases or conditions mediated by PD-L1.

SUMMARY OF THE INVENTION

[0004] In one aspect, the present invention relates to antibodies that specifically bind to human PD-L1. An antibody of the invention comprises a heavy-chain variable region comprising three heavy-chain complementarity-determining regions, HCDR1, HCDR2, and HCDR3, with the sequences of SEQ ID NOs: 2-4, or 6-8, or 10-12, or 14-16, or 18-20, and a light-chain variable region comprising three light-chain complementarity-determining regions, LCDR1, LCDR2, and LCDR3, with the sequences of SEQ ID NOs: 22-24, or 26-28, or 30-32, or 34-36, or 38-40. [0005] In some embodiments, the HCDR1 sequence is GYIFISFWIH (SEQ ID NO: 2), the HCDR2 sequence is NIDP SD SETH YN QKFKD (SEQ ID NO:3), the HCDR3 sequence is LDGDYGRAY (SEQ ID NO:4); or the HCDR1 sequence is GYIFISFWIH (SEQ ID NO: 6), the HCDR2 sequence is NIDP SD SETHYNEKFRD (SEQ ID NO: 7), the HCDR3 sequence is LDGDYGRAY (SEQ ID NO: 8); or the HCDR1 sequence is GYAFSTSWIN (SEQ ID NO: 10), the HCDR2 sequence is RIYPGDGDINYNGKFKD (SEQ ID NO: 11), the HCDR3 sequence is SNHYYFDF (SEQ ID NO: 12); or the HCDR1 sequence is GYAFSTSWMN (SEQ ID NO: 14), the HCDR2 sequence is RIYPGDEDTNYNGNFKG (SEQ ID NO: 15), the HCDR3 sequence is SDNYYFDY (SEQ ID NO: 16); or the HCDR1 sequence is GFTFSDSGMH (SEQ ID NO: 18), the HCDR2 sequence is YISAGSYTIYYADIVKG (SEQ ID NO: 19), the HCDR3 sequence is GDWYFAV (SEQ ID NO: 20); wherein the HCDR sequences are defined according to the method of Chothia.

[0006] In accordance with embodiments of the invention, a heavy chain variable region sequence of a human anti-PD-Ll antibody has the sequence of SEQ ID NO: 1, 5, 9, 13, or 17 shown in FIGs. 1A-1E.

[0007] In another aspect, the present application relates to antibodies that specifically bind human PD-L1, comprising a light chain variable region having LCDR1, LCDR2 and LCDR3 sequences, wherein: the LCDR1 sequence is RASESVDSFGNSFMH (SEQ ID NO: 22), the LCDR2 sequence is LASNLES (SEQ ID NO: 23), the LCDR3 sequence is QQNNEDPLT (SEQ ID NO: 24), or the LCDR1 sequence is RASESVDSNGNSFMH (SEQ ID NO: 26), the LCDR2 sequence is LASNLES (SEQ ID NO: 27), the LCDR3 sequence is QQNNDDPWT (SEQ ID NO: 28); or the LCDR1 sequence is RASEDIRTYLN (SEQ ID NO: 30), the LCDR2 sequence is YTSRLHS (SEQ ID NO: 31), the LCDR3 sequence is QQVHTLPPWT (SEQ ID NO: 32); or the LCDR1 sequence is RASDDIRTYLN (SEQ ID NO: 34), the LCDR2 sequence is YTSRLHS (SEQ ID NO: 35), the LCDR3 sequence is QQVHTLPPWT (SEQ ID NO: 36); or the LCDR1 sequence is RSSQSLVHINGNTYLE (SEQ ID NO: 38), the LCDR2 sequence is KVSNRFS (SEQ ID NO: 39), the LCDR3 sequence is SQGSHVPWT (SEQ ID NO: 40); wherein the LCDR sequences are defined according to method of Chothia.

[0008] In accordance with some embodiments of the invention, a light-chain variable region of an antibody that specifically binds human PD-L1 has the sequence of SEQ ID NO: 21, 25, 29, 33, or 37, shown in FIGs. 2A-2E.

[0009] In another aspect, the present invention relates to an antibody that specifically binds human PD-L1, comprising a heavy chain variable region having HCDR1, HCDR2, and HCDR3 and a light chain variable region having LCDR1, LCDR2 and LCDR3, wherein the HCDR1 sequence is GYIFISFWIH (SEQ ID NO: 2), the HCDR2 sequence is NIDP SD SETH YN QKFKD (SEQ ID NO:3), the HCDR3 sequence is LDGDYGRAY (SEQ ID NO:4); or the HCDR1 sequence is GYIFISFWIH (SEQ ID NO: 6), the HCDR2 sequence is NIDP SD SETH YNEKFRD (SEQ ID NO: 7), the HCDR3 sequence is LDGDYGRAY (SEQ ID NO: 8); or the HCDR1 sequence is GYAFSTSWIN (SEQ ID NO: 10), the HCDR2 sequence is RIYPGDGDINYNGKFKD (SEQ ID NO: 11), the HCDR3 sequence is SNHYYFDF (SEQ ID NO: 12); or the HCDR1 sequence is GYAFSTSWMN (SEQ ID NO: 14), the HCDR2 sequence is RIYPGDEDTNYNGNFKG (SEQ ID NO: 15), the HCDR3 sequence is SDNYYFDY (SEQ ID NO: 16); or the HCDR1 sequence is GFTFSDSGMH (SEQ ID NO: 18), the HCDR2 sequence is YISAGSYTIYYADIVKG (SEQ ID NO: 19), the HCDR3 sequence is GDWYFAV (SEQ ID NO: 20), LCDR1 sequence is RASESVDSFGNSFMH (SEQ ID NO: 22), the LCDR2 sequence is LASNLES (SEQ ID NO: 23), the LCDR3 sequence is QQNNEDPLT (SEQ ID NO: 24), or the LCDR1 sequence is RASESVDSNGNSFMH (SEQ ID NO: 26), the LCDR2 sequence is LASNLES (SEQ ID NO: 27), the LCDR3 sequence is QQNNDDPWT (SEQ ID NO: 28); or the LCDR1 sequence is RASEDIRTYLN (SEQ ID NO: 30), the LCDR2 sequence is YTSRLHS (SEQ ID NO: 31), the LCDR3 sequence is QQVHTLPPWT (SEQ ID NO: 32); or the LCDR1 sequence is RASDDIRTYLN (SEQ ID NO: 34), the LCDR2 sequence is YTSRLHS (SEQ ID NO: 35), the LCDR3 sequence is QQVHTLPPWT (SEQ ID NO: 36); or the LCDR1 sequence is RSSQSLVHINGNTYLE (SEQ ID NO: 38), the LCDR2 sequence is KVSNRFS (SEQ ID NO: 39), the LCDR3 sequence is SQGSHVPWT (SEQ ID NO: 40); and wherein the HCDR and LCDR sequences are defined according to the method of Chothia.

[0010] In some embodiments, a heavy-chain variable region sequence of an antibody that specifically binds human PD-L1 has the sequence of SEQ ID NO: 1, 5, 9, 13, or 17, and a light- chain variable region sequence of the antibody that specifically binds human PD-L1 has the sequence of SEQ ID NO: 21, 25, 29, 33, or 37.

[0011] In some embodiments, a heavy-chain variable region sequence of an antibody that specifically binds human PD-L1 has the sequence of SEQ ID NO: 1, and a light-chain variable region sequence of the antibody that specifically binds human PD-L1 has the sequence of SEQ ID NO: 21. In some embodiments, a heavy-chain variable region sequence of an antibody that specifically binds human PD-L1 has the sequence of SEQ ID NO: 5, a light-chain variable region sequence of the antibody that specifically binds human PD-L1 has the sequence of SEQ ID NO: 25. In some embodiments, a heavy-chain variable region sequence of an antibody that specifically binds human PD-L1 has the sequence of SEQ ID NO: 9, and a light-chain variable region sequence of an antibody that specifically binds human PD-L1 has the sequence of SEQ ID NO: 29. In some embodiments, a heavy-chain variable region sequence of an antibody that specifically binds human PD-L1 has the sequence of SEQ ID NO: 13, and a light-chain variable region sequence of an antibody that specifically binds human PD-L1 has the sequence of SEQ ID NO: 33. In some embodiments, a heavy-chain variable region sequence of an antibody that specifically binds human PD-L1 has the sequence of SEQ ID NO: 17, and a light-chain variable region sequence of an antibody that specifically binds human PD-L1 has the sequence of SEQ ID NO: 37.

[0012] In some embodiments of the invention, an antibody that specifically binds human PD- Ll is a full antibody, an Fab fragment, an F(ab’)2 fragment, or an ScFv fragment. In some embodiments, an antibody that specifically binds human PD-LI is a fully human antibody. In some embodiments, an antibody that specifically binds human PD-L1 comprises a heavy chain constant region selected from IgGl, IgG2, or IgG4 isoforms and a light chain constant region selected from k subtype or l isoform.

[0013] In some embodiments, an antibody (or a binding fragment thereof) of the invention forms part of a bispecific or multi-specific antibody by conjugating with another specific binding domain for a second target. The other specific binding domain for the second target, for example, may be anti-CD3, anti-ICOS or anti-TIM3, etc. In some embodiments, an antibody (or a binding fragment thereof) of the invention forms part of an antibody-drug conjugate (ADC) by conjugating with a drug (payload). The drug or payload may be selected for its ability to modulate a function in the PD-L1 -expressing cells or PD- 1 -expression cells. Such drugs or payloads, for example, may include DM1, MMAE or MMAF.

[0014] Another aspect of the present invention relates to a pharmaceutical composition for use in treating and/or preventing a disease associated with PD-l and/or PD-L1 signaling, wherein the pharmaceutical composition comprises the above-described antibody, or a binding fragment thereof, that binds specifically to the human PD-L1. The PD-LI mediated disease may be a cancer. The cancers may include, but are not limited to: melanoma, non-small cell lung cancer, renal cancer, breast cancer, leukemia, cancer and other advanced solid tumors.

BRI EF DESCRIPTION OF DRAWINGS

[0015] FIGS. 1A-1E show composite, human heavy chain (FIG. 1A, 1E12; FIG. 1B, 3F11;

FIG. 1C, 3E10; and FIG. 1D, 8H3; FIG. 1E, 5E6) variable region sequences designed to correspond to that of the mouse anti-human PD-L1 antibody. [0016] FIGS. 2A-2E show composite, human light chain (FIG. 2A, 1E12; FIG. 2B, 3F11; FIG. 2C, 3E10; FIG. 2D, 8H3; FIG. 2E, 5E6) variable region sequences designed to correspond to that of the mouse anti-human PD-l antibody.

[0017] FIGS. 3A-3B illustrate the bindings of various antibodies to PD-L1. FIG. 3 A shows bindings of human anti-PD-Ll to PD-L1 using ELISA. FIG. 3B shows results of human anti- PD-L1 to PD-L1 using Biacore 2000 (GE Healthcare).

[0018] FIGS. 4A-4B illustrate abilities of the various antibodies to block binding of PD-L1 to PD-l. FIG. 4A shows antibodies 1E12 and 3F11; FIG. 4B shows antibodies 3E10, 8H3 and 5E6.

[0019] FIG. 5 illustrate the ability of the various antibodies to induce PD-1/PD-L1 blockade.

[0020] FIG. 6 show the anti-PDL-l antibodies binding to HCC827 cells assayed with Flow Cytometry.

[0021] FIGs. 7 A and 7B shows the anti-PDL-l antibodies binding and internalization assay in MDA-MB-231 cells using Flow Cytometry.

[0022] FIG. 8 shows anti-PD-Ll mAh 3F11 immunohistochemistry in human tissue specimens.

[0023] FIG. 9 shows the in vivo efficacy of anti-PD-Ll mAh treatment in the murine syngeneic MC38 colon cancer model.

DETAI LED DESCRIPTION OF THE I NVENTION

[0024] The present invention relates to novel antibodies that bind specifically to and have high affinities for PD-L1 and can deliver therapeutic benefits to a subject. The antibodies of the invention, which may be human or humanized, can be used as therapeutics for treating and/or diagnosing a variety of disorders mediated by PD-L1, which are more fully described herein.

[0025] Particularly, an antibody, or an antigen-binding fragment thereof, according to embodiments of the invention specifically binds to an epitope in human PD-L1 or a fragment thereof, wherein the human PD-L1 has the amino acid sequence of SEQ ID NO: 51, and the epitope comprises: the Lysine residue at position 178, and the threonine residue at position 179.

[0026] An antibody according to embodiments of the invention can be full-length (e.g., an IgGl or IgG4 antibody), or may comprise only an antigen-binding portion (e.g., a Fab, F(ab')2, or scFv fragment), and may be modified to affect functionalities as needed.

[0027] An antibody or antigen-binding fragment thereof according to embodiments of the invention specifically binds to human PD-L1. PD-L1, also known as CD274 or B7 homolog 1, is a 40kDa type 1 transmembrane protein that has been speculated to play a major role in suppressing the immune system during particular events, e.g., pregnancy, tissue allografts, autoimmune disease and other disease states. Normally, immune system reacts to foreign antigens associated with exogenous or endogenous danger signals, which trigger a proliferation of antigen-specific CD8+ T cells and/or CD4+ helper cells. The binding of PD-L1 to PD-l or B7.1 transmits an inhibitory signal that reduces the proliferation of these T cells and can also induce apoptosis, which is further mediated by a lower regulation of the gene Bcl-2.

[0028] The term "antibody" has its ordinary meaning and comprises two heavy (H) chains and two light (L) chains inter-connected by disulfide bonds. Each heavy chain comprises a heavy chain variable region (abbreviated herein as HCVR or VH) comprising three CDRs (HCDR1, HCDR2, and HCDR3) and four framework regions (FRs). Each light chain comprises a light chain variable region (abbreviated herein as LCVR or VL) comprising three CDRs (LCDR1, LCDR2, and LCDR3) and four FRs. In different embodiments of the invention, the FRs of the anti-PD-Ll antibody (or antigen-binding portion thereof) may be identical to the human germline sequences, or may be naturally or artificially modified. An amino acid consensus sequence may be defined based on a side-by-side analysis of two or more CDRs.

[0029] The term "antigen-binding fragment" of an antibody as used herein includes any fragment of an antibody that can specifically bind an antigen to form a complex. Non-limiting examples of an antigen-binding fragment includes: (i) Fab fragments; (ii) F(ab')2 fragments; (iii) Fd fragments; (iv) Fv fragments; (v) single-chain Fv (scFv) molecules; (vi) dAb fragments; and (vii) minimal recognition units consisting of the amino acid residues that mimic the hypervariable region of an antibody (e.g., an isolated CDR, e.g., a CDR3 peptide), or a constrained FR3-CDR3-FR4 peptide. Other engineered molecules, such as domain-specific antibodies, single domain antibodies, domain-deleted antibodies, chimeric antibodies, CDR- grafted antibodies, diabodies, triabodies, tetrabodies, minibodies, nanobodies (e.g. monovalent nanobodies, bivalent nanobodies, etc.), small modular immunopharmaceuticals (SMIPs), and shark variable IgNAR domains, are also "antigen-binding fragment," as used herein.

[0030] An antigen-binding fragment of an antibody typically comprises at least one variable domain. The variable domain may be of any size or amino acid composition and will generally comprise at least one CDR. In antigen-binding fragments having a VH domain associated with a VL domain, the VH and VL domains may be situated relative to one another in any suitable arrangement. For example, the variable region may be dimeric and contain VH-VH, VH-VL or VL-VL dimers. Alternatively, the antigen-binding fragment of an antibody may contain a monomeric VH or VL domain.

[0031] As with a full antibody molecule, an antigen-binding fragment may be monospecific or multispecific (e.g., bispecific). A multispecific antigen-binding fragment of an antibody will typically comprise at least two different variable domains, wherein each variable domain is capable of specifically binding to a separate antigen or to a different epitope on the same antigen. Any multispecific antibody format, including the exemplary bispecific antibody formats disclosed herein, may be adapted for use in the context of an antigen-binding fragment of an antibody of the present invention using routine techniques available in the art.

[0032] Antibodies of the invention may be used as antibody-drug conjugates (ADCs), which can specifically target PD-L1. The conjugates on the ADCs may modulate the immune cells that express PD-L1 or cells that interact with cells that express PD-L1 (e.g., PD-l expressing cells). These ADCs can use any antibody of the invention, or an antigen-binding fragment thereof. The drugs (payloads) that are conjugated to the antibody (or binding fragment) can be any that are commonly used in ADCs. The methods for conjugation can be those known in the art.

[0033] As applied to polypeptides, the term "substantial similarity" or "substantially similar" means that two peptide sequences, when optimally aligned, such as by the programs GAP or BESTFIT using default gap weights or by BLAST, share at least 95% sequence identity, even more preferably at least 98% or 99% sequence identity. According to embodiments of the invention, the Gap and Best fit program in GCG software was used with default parameters to determine sequence homology or sequence identity between closely related polypeptides.

[0034] In embodiments of the invention, an anti-PD-Ll antibody, or an antigen-binding fragment thereof, comprises a heavy chain variable region and a light chain variable region, wherein the heavy chain variable region comprises 3 CDR regions, CDRH1 (or HCDR1), CDRH2 (or HCDR2) and CDRH3 (or HCDR3) regions, and he light chain variable region comprises 3 CDR regions, CDRL1 (or LCDR1), CDRL2 (or LCDR2) and CDRL3 (or LCDR3) regions.

[0035] As used herein, the term“a disease mediated by PD-l or PD-L1” refers to a disease associated with PD-1/PD-L1 signaling leading to immune suppression or exhaustion. Such diseases include those associated with autoimmunity, neurological disorders, stroke, and cancer. (N. Kuol et al, Immunotherapy, 2018, 10(2): 149-160). As used herein,“treating” refers to alleviation of symptoms of a disease or condition; it does not have to be complete cure. [0036] Referring to FIGs. 1 A - 1E and 2A - 2E, in some embodiments of the invention, the CDRH1 region comprises the amino acid sequence of SEQ ID NO: 2, the CDRH2 region comprises the amino acid sequence of SEQ ID NO: 3, the CDRH3 region comprises the amino acid sequence of SEQ ID NO: 4, the CDRL1 region comprises the amino acid sequence of SEQ ID NO: 22, the CDRL2 region comprises the amino acid sequence of SEQ ID NO: 23, and the CDRL3 region comprises the amino acid sequence of SEQ ID NO: 24.

[0037] In some embodiments of the invention, the CDRH1 region comprises the amino acid sequence of SEQ ID NO: 6, the CDRH2 region comprises the amino acid sequence of SEQ ID NO: 7, the CDRH3 region comprises the amino acid sequence of SEQ ID NO: 8, the CDRL1 region comprises the amino acid sequence of SEQ ID NO: 26, the CDRL2 region comprises the amino acid sequence of SEQ ID NO: 27, and the CDRL3 region comprises the amino acid sequence of SEQ ID NO: 28.

[0038] In some embodiments of the invention, the CDRH1 region comprises the amino acid sequence of SEQ ID NO: 10, the CDRH2 region comprises the amino acid sequence of SEQ ID NO: 11, the CDRH3 region comprises the amino acid sequence of SEQ ID NO: 12, the CDRL1 region comprises the amino acid sequence of SEQ ID NO: 30, the CDRL2 region comprises the amino acid sequence of SEQ ID NO: 31, and the CDRL3 region comprises the amino acid sequence of SEQ ID NO: 32.

[0039] In some embodiments of the invention, the CDRH1 region comprises the amino acid sequence of SEQ ID NO: 14, the CDRH2 region comprises the amino acid sequence of SEQ ID NO: 15, the CDRH3 region comprises the amino acid sequence of SEQ ID NO: 16, the CDRL1 region comprises the amino acid sequence of SEQ ID NO: 34, the CDRL2 region comprises the amino acid sequence of SEQ ID NO: 35, and the CDRL3 region comprises the amino acid sequence of SEQ ID NO: 36.

[0040] In some embodiments of the invention, the CDRH1 region comprises the amino acid sequence of SEQ ID NO: 18, the CDRH2 region comprises the amino acid sequence of SEQ ID NO: 19, the CDRH3 region comprises the amino acid sequence of SEQ ID NO: 20, the CDRL1 region comprises the amino acid sequence of SEQ ID NO: 38, the CDRL2 region comprises the amino acid sequence of SEQ ID NO: 39, and the CDRL3 region comprises the amino acid sequence of SEQ ID NO: 40.

[0041] In some embodiments of the invention, an anti-PD-Ll antibody, or an antigen-binding fragment thereof, comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 1 and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 21. Preferably, the heavy chain variable region is encoded by the nucleic acid sequence of SEQ ID NO: 41, and the light chain variable region is encoded by the nucleic acid sequence of SEQ ID NO: 46.

[0042] In some embodiments of the invention, an anti-PD-Ll antibody, or an antigen-binding fragment thereof, comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 5 and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 25. Preferably, the heavy chain variable region is encoded by the nucleic acid sequence of SEQ ID NO: 45, and the light chain variable region is encoded by the nucleic acid sequence of SEQ ID NO: 47.

[0043] In some embodiments of the invention, an anti-PD-Ll antibody, or an antigen-binding fragment thereof, comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 9 and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 29. Preferably, the heavy chain variable region is encoded by the nucleic acid sequence of SEQ ID NO: 49, and the light chain variable region is encoded by the nucleic acid sequence of SEQ ID NO: 48.

[0044] In some embodiments of the invention, an anti-PD-Ll antibody, or an antigen-binding fragment thereof, comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 13 and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 33. Preferably, the heavy chain variable region is encoded by the nucleic acid sequence of SEQ ID NO: 44, and the light chain variable region is encoded by the nucleic acid sequence of SEQ ID NO: 43.

[0045] In some embodiments of the invention, an anti-PD-Ll antibody, or an antigen-binding fragment thereof, comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 17 and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 37. Preferably, the heavy chain variable region is encoded by the nucleic acid sequence of SEQ ID NO: 42, and the light chain variable region is encoded by the nucleic acid sequence of SEQ ID NO: 50.

[0046] Antibodies of the invention were confirmed to have specific bindings with PD-L1 via ELISA. Briefly, PD-L1 was coated on a 96-well ELISA plate (0.1 pg/well). After binding of anti-PD-Ll antibodies, a goat anti mouse IgG conjugated with horse radish peroxidase (HRP) was used as a second antibody and 3,3’,5,5’-Tetramethylbenzidine (TMB) was used as a substrate to assess the antibody-PD-Ll bindings. The OD405 was read to calculate the activities.

[0047] As shown in FIG. 3 A, several mouse hybridoma anti-human PD-L1 antibodies (mAbs 1E12, 3F11, 8H3, 3E10, and 5E6) all show specific and tight bindings with PD-L1. FIG. 3B shows the binding parameters and affinities of these antibodies as determined by BIAcore T200 (GE Healthcare). Briefly, a CM5 BIAcore chip was coated with human PD-L1 on the active channel. The active channels were injected with mouse hybridoma anti-human PD-L1 antibodies (mAbs 1E12, 3F11, 8H3, 3E10, and 5E6) or its variants sequentially at various concentrations, and a channel injected with buffer alone was used as a blank control. The affinities were determined with the method of single-cycle kinetics. The data was fitted with a 1 : 1 binding model using BIAcore T200 evaluation software to obtain the kinetics constants (K _a : association constant; ¾: dissociation constant; K _D = K _a /K _d ).

[0048] That antibodies of the invention can bind human PD-L1 tightly and specifically suggests that these antibodies should be able to interfere with the binding between PD-l and PD- Ll . The abilities of various antibodies of the invention to block the binding of PD-L 1 to PD-l were confirmed using ELISA. Briefly, 100 ng/well PD-Ll-Fc was coated on a 96-well plate. Then, 5ug/well PD-l -biotin and different concentrations of anti-human PD-L1 antibodies were added. The binding was allowed to proceed at 37°C for 1 hour. After washing with PBS, HRP- Conjugated Streptavidin was added, followed by addition of TMB (3, 3', 5,5'- tetramethylbenzidine). The amounts of biotinated PD-l binding to the PD-Ll-Fc were quantified with OD405 readings.

[0049] As shown in FIG. 4A, mAbs of the invention (e.g., 1E12 and 3F11) effectively blocked the bindings between PD-l and PD-L1, while the control mouse IgG did not. Similarly, FIG. 4B shows that mAbs 3E10, 8H3, and 5E6 could interfere with the interactions between PD-l and PD-L1, while the control mouse IgG could not.

[0050] While the above experiment tests the binding of antibodies of the invention to PD-L1 molecule in vitro, such binding was also tested with PD-l and PD-L1 respectively expressed on interaction cells. For example, the PD-1/PD-L1 blockage assay may use any commercial kit, such as the kit from Promega (Maddison, WI, EiSA). The Promega PD-l /PD-L 1 Blockade Bioassay is a bioluminescent cell-based assay. The assay kit consists of two genetically engineered ceil lines: PD-l Effector Cells, which are Jurkat T cells expressing human PD-l and a luciferase reporter driven by an NFAT response element (NFAT-RE), and PD- LI aAPC/CHO- Ki Cells, which are CHO-K1 cells expressing human PD-L1 and an engineered cell surface protein designed to activate cognate TCRs in an antigen-independent manner

[0051] When the two cell types are co-cultured, the PD~1/PD~L1 interaction inhibits TCR signaling and NFAT-RE-mediated luminescence. Addition of anti-PD-Ll antibodies of the invention that block the PD-1/PD-L1 interactions can release the inhibitory signal, leading to TCR activation and NF AT -RE-mediated luminescence. The bioluminescent signal can be detected and quantified using the Bio-Gio™ Luciferase Assay System and a standard luminometer, such as the GloMax® Discover System from Promega (Maddison, WI, USA).

[0052] As shown in FIG. 5, mAbs of the invention 1E12, 3F11, 3E10, and 8H3 all show specific and potent activities that block PD-1/PD-L1 interactions. Other antibodies of the invention also show similar activities. These results confirm that antibodies of the invention would be effective in relieving immune suppression mediated by PD-l and PD-L1 interactions on interacting cells. Therefore, antibodies of the invention should be useful as therapeutics for diseases arising from immune suppression or exhaustion due to PD-l and/or PD-L1 signaling. Such diseases include various cancers.

[0053] To further validate the utility of antibodies of the invention in cancer treatments, the abilities of these antibodies to bind PD-L1 expressed on cancer cells were assessed. For example, binding of anti-PD-Ll antibodies to PD-L1 expressing cells was assayed by Flow Cytometry using HCC827 cells (lung adenocarcinoma), which express high-level PD-L1. Briefly, HCC827 cells (PD-L1 high) were incubated with anit-PD-Ll antibodies for 1 hour, then analyzed using flow cytometry. As shown in FIG. 6, mAbs of the invention 1E12, 3E10, 3F11, and 8H3 all can bind HCC827 cells, indicating that these antibodies can recognize PD-L1 on the cancer cell surfaces. Other antibodies of the invention also show similar activities. Therefore, antibodies of the invention can be used to treat cancers by binding to PD-L1 expressed on cancer cells and thereby inhibiting PD-L1 mediated immune suppression or exhaustion.

[0054] In addition to blockade of PD-l /PD-L 1 interactions, antibodies binding to PD-L1 may also trigger receptor internalization/recycling. Receptor internalization or recycling would also make PD-L1 unavailable for interactions with PD-l . Thus, the abilities of anti-PDL-l antibodies of the invention to trigger PD-L1 internalization were investigated. Briefly, to explore these blocking/recycling processes of PD-L 1, MDA-MB-231 cells (an epithelial, human breast cancer cell line) were treated with 1 pg/mL anti-PD-Ll antibodies at 4°C and 37°C and monitored over 24 hours. Then, at various time points, the cells were analyzed with Flow Cytometry. [0055] As shown in FIGs. 7A and 7B, mAbs 1E12 and 3F11 could bind to MDA-MB-231 cells and became internalized. The internalization occurred at 37°C, but not at 4°C, in a time- dependent manner. These results indicate that antibodies of the invention can block PD-l/PD- Ll interactions by binding to PD-L1, as well as triggering internalization of PD-L1. Internalization makes PD-L1 unavailable and would be more effective (than simple blinding) in blocking PD-L1 mediated signaling pathway. Therefore, antibodies of the invention should be more effective in the treatment of cancers or diseases that are mediated by PD-L1.

[0056] Because anti-PD-Ll antibodies of the invention can bind PD-L1 specifically and tightly, it would be also useful for detection of PD-L1, which is highly expressed in several cancer cells. As shown in Fig. 8, anti-PD-Ll antibody 3F11 immunohistochemistry staining of human tissue specimens revealed only weak staining in normal tissues (e.g., tonsil and smooth muscle), whereas the staining of lung cancer tissue is very strong. These results indicate that anti-PD-Ll antibodies of the invention are useful for detection of cells or tissue that express PD- Ll, such as cancer cells. Therefore, these antibodies should be useful as diagnostic agents for the detection of cancers and for prognosis/monitoring of cancers during and/or after treatments.

[0057] The above examples clearly show that anti-PD-Ll antibodies of the invention can bind human PD-L1 specifically and tightly. These antibodies can also interfere with the interactions between PD-l and PD-L1 and block the PD-1/PD-L1 bindings. In addition, these antibodies can cause internalization of PD-L 1, rendering PD-L1 unavailable for binding with PD-l . As a result, antibodies of the invention should be effective therapeutics for treating diseases mediated by PD-1/PD-L1 interactions. Such diseases include, for example, cancers. Examples of cancers include, but are not limited to, lung cancer, breast cancer, prostate cancer, colorectal cancer, etc. In addition, antibodies of the invention may be used as reagents to detect PD-L1, which is useful in the diagnosis of PD-L1 expression or in the prognosis during treatments.

[0058] Some embodiments of the invention relate to methods for treating, or alleviating conditions/ symptoms of, a disease mediated by PD-l and/or PD-L1 signaling; such diseases may include cancers. To demonstrate the utility of antibodies of the invention in treating cancers, a murine syngeneic model was used. Briefly, MC38 cells (colon adenocarcinoma cells) were injected subcutaneously into C57BL/6 mice on day 0. On days 6, 9, and 13, the mice were treated with antibodies (e.g., 1E12, 3F11, 3E10, and 8H3) of the invention at 5mpk (mg/kg) each time. An IgG (not anti-PD-Ll) was used as a control. The tumor growths in various treatment groups were monitored until day 16. [0059] As shown in FIG. 9, anti-PD-Ll mAbs of the invention (e.g., 1E12, 3F11, 3E10, and 8H3) were effective in suppressing tumor growths in this in vivo colorectal cancer model. Other antibodies of the invention also have similar effects. These results clearly demonstrate that antibodies of the invention will be useful for clinical uses to treat cancers, such as lung cancer, breast cancer, prostate cancer, colorectal cancer, etc.

[0060] In addition, antibodies of the invention are highly specific for human PD-L1. they recognize unique epitopes with high specificities and affinities. These properties would make them more useful as therapeutics. Indeed, in a mouse xenograft model of MDA-MB231 breast cancer cells, antibody of the invention (3F11 and 1E12) homed in the tumor over time, i.e., the binding intensity increases with time up to 120 hours. In contrast, an FDA approved antibody, Atezolizumab, did not have sufficient binding avidity and appeared to be distributed throughout the animal. As a result, Atezolizumab was cleared by the system relatively fast and did not show much binding by 120 hours. Because the antibodies of the invention bind to the cancer cells tightly, very little of the antibodies appears in circulation to be cleared by the system. As a result, antibodies of the invention have much longer in vivo half-lives. Therefore, antibodies of the invention can be used in smaller doses and with less frequent administrations, substantially reducing the treatment costs and minimizing any potential adverse effects.

[0061] As compared to the prior art anti-PD-Ll antibodies, antibodies of the invention have more favorable pharmacokinetic properties (e.g., higher avidities and longer half-lives), which are likely due to binding to different epitopes on human PD-L1. Epitope mappings indicate that antibodies of the invention bind to human PD-L1 at epitopes located in the regions involving residues 171-180 and 206-210. These epitope regions are different from those of known antibodies. For example, critical residues involved in the bindings of prior art antibodies (e.g., atezolizumab and durvalumab) to PD-L1 involves E58 and R125 on PD-L1. (Lee et al, Scientific Reports, (2017), 7: 5532).

[0062] Further analysis of the epitopes for bindings of antibodies of the invention using alanine scanning revealed that residues 178 and 179 are particularly important for the bindings, as shown in the following Table:

Mapping of Anti-PD-Ll Antibody Binding to Human PD-L1 by Site-Directed Mutagenesis

O: no effect on binding

-: effect on binding

[0063] In sum, antibodies of the invention can bind PD-L1 specifically and tightly, including PD-L1 on cell surfaces. The PD-L1 expressing cells include cancer cells, such as lung cancer cells, colorectal cancer cells (e.g., MC38 cells), breast cancer cells (e.g., MDA-MB-231 cells), etc. These antibodies can interfere with the binding between PD-l and PD-L1, leading to blockade of PD-l and/or D-Ll signaling pathways. In addition, binding by antibodies of the invention also causes internalization of PD-L1, rendering it unavailable for interaction with PD- 1. As a result, antibodies of the invention can alleviate or reverse immune suppression or exhaustion caused by PD-l and/or D-Ll signaling. Therefore, antibodies of the invention are useful therapeutic agents for treating or alleviating conditions of diseases associated with immune suppression or exhaustion caused by PD-l and PD-L1 interactions.

[0064] Bindings of PD-L1 by antibodies of the invention involve hereto unknown epitopes on human PD-L1, and bindings to these new epitope result in unexpected high specificity and avidities, leading to more favorable pharmacokinetic properties (e.g., more focused binding on tumor cells, less free antibodies in circulation, and longer half-lives). As a result, antibodies of the invention can be used at lower doses and with less frequent administration, thereby reducing the costs and side effects and increasing patient compliance.

[0065] While embodiments of the invention have been illustrated with a limited number of examples, one skilled in the art would appreciate that other modifications and variations are possible. Therefore, the scope of protection of the invention should only be limited by the attached claims.