Anti-BCMA antibody-drug conjugates and methods of use

Abstract

Disclosed are antibodies, antigen-binding fragments, and conjugates (e.g., antibody-drug conjugates (ADCs), including those that include splicing modulators) that bind to BCMA. The disclosure further relates to methods and compositions for use in treating cancer by administering the compositions provided herein.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This disclosure claims the benefit of priority to U.S. Provisional Patent Application No. 62 / 704,997, filed June 5, 2020, which is incorporated herein by reference in its entirety.

[0002] This application contains a Sequence Listing that has been submitted electronically in ASCII format, which is incorporated herein by reference in its entirety. The ASCII copy created on May 28, 2021 is titled 15647_0012-00304_SL.txt and is 698,277 bytes in size.

[0003] The present disclosure relates to anti-B cell maturation antigen (BCMA) antibodies and antigen-binding fragments thereof, and conjugates such as antibody-drug conjugates (ADCs), including those that comprise splicing modulators, and uses thereof. [Background technology]

[0004] The majority of protein-coding genes in the human genome consist of multiple exons (including coding regions) separated by introns (non-coding regions). Gene expression results in precursor messenger RNA (pre-mRNA), which is then converted to mature messenger RNA (mRNA) through the removal of intron sequences in a process called splicing. Alternative splicing results in the inclusion of various combinations of exons, resulting in mRNAs that encode distinct protein isoforms.

[0005] RNA splicing is catalyzed by the spliceosome, a dynamic multiprotein-RNA complex composed of five small nuclear RNAs (snRNAs U1, U2, U4, U5, and U6) and associated proteins. The spliceosome assembles on pre-mRNAs and orchestrates a dynamic cascade of multiple RNA and protein interactions that catalyze intron excision and exon ligation (Matera and Wang (2014) Nat Rev Mol Cell Biol. 15(2):108-21). Growing evidence implicates human diseases in dysregulation of RNA splicing, affecting many genes (Scotti and Swanson (2016) Nat Rev Genet. 17(1):19-32). Several studies have now demonstrated alterations in the splicing profile of cancer cells, as well as in the splicing factors themselves (Agrawal et al. (2018) Curr Opin Genet Dev. 48:67-74). Alternative splicing can lead to exon inclusion / exclusion, intron retention, or differential cryptic splice site usage (Seiler et al. (2018) Cell Rep. 23(1):282-96). Collectively, these events describe functional alterations that may contribute to tumorigenesis or therapeutic resistance (Siegfried and Karni (2018) Curr Opin Genet Dev. 48:16-21).

[0006] Certain products can bind to the SF3b spliceosome complex. These small molecules modulate splicing by promoting intron retention and / or exon skipping (Teng et al. (2017) Nat Commun. 8:15522). A significant proportion of the resulting transcripts contain premature termination codons that trigger nonsense-mediated mRNA decay (NMD). Furthermore, impaired canonical splicing leads to a significant reduction in canonical transcripts, which can negatively impact cellular function and viability. Therefore, splicing modulators are a promising class of drugs for the treatment of cancer (Puthenveetil et al. (2016) Bioconjugate Chem. 27:1880-8). The current challenge in this field is to deliver these splicing modulators to relevant tumorigenic tissues while avoiding or minimizing potential toxicity. Therefore, improved targeting of small molecule splicing modulators would be desirable.

[0007] BCMA, also known as TNFRSF17 or CD269, is a member of the tumor necrosis factor receptor (TNFR) superfamily (Madry et al. (1998) Int Immunol. 10:1693-702; Sanchez et al. (2012) Br J Haematol. 158:727-38). BCMA ligands include B-cell activating factor (BAFF) and proliferation-inducing ligand (APRIL) (Rennert et al. (2000) J Exp Med. 192:1677-83). BCMA is preferentially expressed by mature B lymphocytes, but is minimally expressed in hematopoietic stem cells and non-hematopoietic tissues, where it plays a role in the survival of long-lived bone marrow plasma cells (PCs) (Novak et al. (2004) Blood. 103:689-94; O'Connor et al. (2004) 199:91-7). Summary of the Invention [Problem to be solved by the invention]

[0008] BCMA is highly expressed in malignant PCs from patients with multiple myeloma (MM) compared to normal bone marrow mononuclear cells (BMMCs) from healthy donors (Sanchez et al. (2012) Br J Haematol. 158:727-38). BCMA overexpression and activation are also associated with the progression of multiple myeloma in preclinical models and humans (Sanchez et al. (2012) Br J Haematol. 158:727-38; Tai et al. (2016) Blood. 127:3225-36; Sanchez et al. (2016) Clin Cancer Res. 22:3383-97). Mouse xenografts induced with BCMA overexpression grow faster than BCMA-negative controls, and similar results are observed after BCMA activation by APRIL induction in ex vivo human multiple myeloma cells (Tai et al. (2016) Blood. 127:3225-36). This BCMA overexpression and activation can lead to upregulation of canonical and non-canonical nuclear factor kappa-B (NFκB) pathways and enhanced expression of genes critical for survival, growth, adhesion, osteoclast activation, angiogenesis, metastasis, and immunosuppression. BCMA represents a promising antigen for targeting multiple myeloma and other B-cell / plasma cell malignancies and / or delivering novel cancer therapies (Shah et al. (2020) Leukemia. 34(4):985-1005). Nevertheless, improved methods for effectively targeting BCMA remain needed.

[0009] In particular, while the use of splicing modulators has been reported in the art, including in the context of ADCs, there remains a need for better targeted delivery of splicing modulators to specific tissues, e.g., cancer tissues that express BCMA. Similarly, there remains a need in the art for improved antibodies that bind to BCMA with superior properties, e.g., with respect to antigen binding and / or the ability to effectively deliver a payload, such as a splicing modulator, to target cells or tissues that express BCMA. [Means for solving the problem]

[0010] In various embodiments, the present disclosure provides, in part, novel antibodies and antigen-binding fragments that can be used alone, linked to one or more additional agents (e.g., as ADCs), or used as part of a larger macromolecule (e.g., bispecific or multispecific antibodies, alone or as part of a multispecific antibody linked to a payload in an ADC format), which may be administered as part of a pharmaceutical composition or combination therapy.

[0011] In some embodiments, the anti-BCMA antibodies and antigen-binding fragments disclosed herein are humanized. In some embodiments, the anti-BCMA antibodies and antigen-binding fragments disclosed herein have minimal sequence derived from a non-human (e.g., murine) antibody, retaining the reactivity of a non-human antibody while being less immunogenic in humans. In some embodiments, the anti-BCMA antibodies and antigen-binding fragments disclosed herein are capable of binding to BCMA. In some embodiments, the anti-BCMA antibodies and antigen-binding fragments disclosed herein bind to BCMA and possess one or more superior properties when compared to a reference anti-BCMA antibody or antigen-binding fragment. In some embodiments, the anti-BCMA antibodies and antigen-binding fragments disclosed herein have higher affinity for BCMA (e.g., as assessed in a binding assay using cancer cells with high or moderate BCMA expression levels) when compared to the reference anti-BCMA antibody or antigen-binding fragment. In some embodiments, ADCs comprising the anti-BCMA antibodies and antigen-binding fragments disclosed herein exhibit favorable drug loading, aggregation, stability, activity, and / or potency when compared to ADCs comprising the reference anti-BCMA antibody or antigen-binding fragment. In some embodiments, ADCs comprising the anti-BCMA antibodies and antigen-binding fragments disclosed herein demonstrate desirable properties for therapeutic ADCs. In some embodiments, such properties include, but are not limited to, effective levels of drug loading, low levels of aggregation, improved stability, retained affinity for BCMA-expressing cells comparable to that of an unconjugated antibody, potent cytotoxicity against BCMA-expressing cells, improved cytotoxic and / or cytostatic activity against non-dividing and / or slowly dividing cells, low levels of off-target cell killing, high levels of bystander killing, and / or effective in vivo anti-cancer activity, for example, when compared to a reference anti-BCMA antibody and / or reference anti-BCMA ADC. In some embodiments, the increased potency, cytotoxicity, and / or anti-cancer activity is in cancers that highly express the antigen targeted by the antibodies, antigen-binding fragments, or ADCs disclosed herein (e.g., high BCMA expression).In some embodiments, the increased potency, cytotoxicity, and / or anti-cancer activity is in cancers that moderately express the antigen targeted by the antibodies, antigen-binding fragments, or ADCs disclosed herein (e.g., moderately BCMA-expressing). In some embodiments, the antibodies, antigen-binding fragments, and / or ADCs may be useful in treating human cancer patients.

[0012] In some embodiments, the cancer to be treated with the antibodies, antigen-binding fragments, or ADCs disclosed herein is multiple myeloma. Most multiple myeloma patients eventually relapse. Without wishing to be bound by theory, myeloma patients may relapse, at least in part, due to the presence of "dormant" (e.g., non-dividing or slowly dividing) myeloma cells, such as those present in the skeletal microenvironment throughout the body (Figueroa-Vazquez et al. (2021) Mol Cancer Ther. 20(2):367-378; Franqui-Machin et al. (2015) Oncotarget. 6:40496-40506). Such dormant myeloma cells may be largely resistant to standard-of-care therapies, including many FDA-approved chemotherapeutics, which may exert their antiproliferative effects by inhibiting or deregulating cellular pathways required for DNA replication and cell division (Cheung-Ong et al. (2013) Chem Biol. 20(5):648-659). Thus, therapeutic agents that retain antiproliferative activity in non-dividing and / or slowly dividing cells may provide an effective means of treating both newly diagnosed and relapsed / refractory forms of multiple myeloma, as well as other B-cell / plasma cell malignancies. In some embodiments, the antibody, antigen-binding fragment, conjugate, and / or ADC compounds disclosed herein retain cytotoxic and / or cytostatic activity regardless of cell proliferative state. In some embodiments, the described antibodies, antigen-binding fragments, conjugates, and / or ADC compounds can target both actively dividing and dormant cells (e.g., actively dividing myeloma cells, non-dividing myeloma cells, and / or slowly dividing myeloma cells).

[0013] Certain cancer types may be particularly suitable for treatment with the antibody, antigen-binding fragment, conjugate, and / or ADC compounds disclosed herein based, for example, on genetic background, gene expression patterns, or other cancer-defining characteristics. In some embodiments, the increased potency, cytotoxicity, and / or anti-cancer activity of an antibody, antigen-binding fragment, or ADC disclosed herein (e.g., compared to a reference anti-BCMA antibody and / or reference anti-BCMA ADC) is in a cancer that highly or moderately expresses the antigen targeted by the antibody, antigen-binding fragment, or ADC (e.g., high or moderate BCMA expression). In some embodiments, the increased potency, cytotoxicity, and / or anti-cancer activity of an antibody, antigen-binding fragment, or ADC disclosed herein is in a cancer that comprises at least some dormant cells, e.g., non-dividing or slowly-dividing myeloma cells. In some embodiments, the increased potency, cytotoxicity, and / or anti-cancer activity of an antibody, antigen-binding fragment, or ADC disclosed herein is in multiple myeloma. In some embodiments, the increased potency, cytotoxicity, and / or anti-cancer activity of an antibody, antigen-binding fragment, or ADC disclosed herein is in a cancer that expresses MCL1, e.g., a cancer with high or moderate levels of MCL1 expression.

[0014] MCL1 is a member of the BCL2 gene family, a group of genes generally recognized as master regulators of apoptotic forms of programmed cell death. Three major alternatively spliced ​​isoforms of MCL1 have been described, with the longest isoform (MCL1-long, MCL1-L, MCL1L) acting as a potent pro-survival / anti-apoptotic factor that opposes the pro-death function of pore-forming BH3-only members of the family. In humans, MCL1 is ubiquitously expressed in most normal tissues under normal physiological conditions and is particularly enriched in myeloid cell types, including plasma B cells, the cell type that gives rise to myeloma. MCL1 expression is frequently upregulated by various mechanisms in many cancer types, including myeloma, and further increased expression following some standard-of-care regimens for myeloma has been shown to confer resistance to such therapies. Thus, without being bound by theory, therapeutic agents capable of inhibiting MCL1, e.g., MCL1L function and / or suppressing MCL, e.g., MCL1L expression, may provide clinical benefit to myeloma patients, particularly in relapsed / refractory forms of the disease associated with high MCL1L expression or dependence.

[0015] Without wishing to be bound by theory, delivery of splicing modulators to cancer cells, such as those expressing BCMA, can induce cell death by reducing or inhibiting MCL1 expression (Aird et al. (2019) Nat Commun 10:137). MCL1 mRNA and protein are relatively short-lived, each typically having a half-life of approximately 30 minutes in some human cancer cell lines. Genes encoding short-lived RNA transcripts and proteins may be particularly suitable for modulation by splicing modulators, as aberrantly spliced ​​transcripts may begin to accumulate while the existing pool of correctly spliced ​​RNA and protein products is rapidly degraded upon treatment. Such aberrant splicing events often introduce missense or nonsense mutations, resulting in little or no functional protein output. In addition to affecting overall gene expression, splicing modulator treatment can also result in the expression of protein products with novel functions or functions antagonistic to those of correctly spliced ​​genes. In contrast to payloads that disrupt microtubules or damage DNA, splicing modulators as used in the ADCs described herein can kill hard-to-treat cancer cells (e.g., myeloma cells) by disrupting MCL1 splicing and providing a pathway-specific apoptotic mechanism. By targeting the MCL1 splicing dependency of cancer cells, the described antibodies, antigen-binding fragments, conjugates, and / or ADC compounds may provide effective therapeutic solutions to current clinical challenges, such as overcoming drug resistance in multiple myeloma and other BCMA-expressing cancers.

[0016] More specifically, in various embodiments, the present disclosure relates to antibodies, antigen-binding fragments, and ADCs capable of binding to BCMA-expressing cancer cells. In various embodiments, the antibodies, antigen-binding fragments, and ADCs also have the ability to internalize into target cells after binding. ADCs are disclosed that include a linker connecting a splicing modulator to the antibody moiety. The antibody moiety (alone or as part of an ADC) can be a full-length antibody or an antigen-binding fragment thereof.

[0017] In some embodiments, the present disclosure provides an isolated antibody or antigen-binding fragment, which is capable of binding to BCMA; and (i) When defined by the Kabat numbering system, HCDR1 comprising the amino acid sequence of NYWIH (SEQ ID NO: 1); X1TYRX5X6SX8TX 10 YX 12 QKX 15 KS (SEQ ID NO: 67) X1 is A or G; X5 is S or I; X6 is H or Q; X8 is D or T; X 10 is Y or N; X 12 is N or A; and X 15 is F or Y) HCDR2 comprising the amino acid sequence of: GAX3YHGYDVIX 11 N (SEQ ID NO: 68) X3 is I or V; and X 11 is E or D) HCDR3 containing the amino acid sequence of RASQSISSYX 10 N (SEQ ID NO: 69) X 10 is L or I) LCDR1 containing the amino acid sequence of ATSNLQX7 (SEQ ID NO: 70), wherein: X7 is S or I) an LCDR2 comprising the amino acid sequence of QQX3RRX6PWX9 (SEQ ID NO: 71), wherein: X3 is F or Y; X6 is L or I; and X9 is T or S) LCDR3 containing the amino acid sequence three heavy chain complementarity determining regions (HCDRs) and three light chain complementarity determining regions (LCDRs); or (ii) When defined by the IMGT numbering system: GGTFX5NYW (SEQ ID NO: 72), wherein: X5 is S or T) HCDR1 containing the amino acid sequence of; TYRX4X5SX7T (SEQ ID NO: 73), wherein: X4 is S or I; X5 is H or Q; and X7 is D or T) HCDR2 comprising the amino acid sequence of: ARGAX5YHGYDVIX 13 N (SEQ ID NO: 74), wherein: X5 is I or V; and X 13 is D or E) HCDR3 containing the amino acid sequence of LCDR1 comprising the amino acid sequence of QSISSY (SEQ ID NO: 40); LCDR2 comprising the amino acid sequence of ATS (SEQ ID NO: 41); and QQX3RRX6PWX9 (SEQ ID NO: 75), wherein: X3 is Y or F; X6 is L or I; and X9 is T or S) LCDR3 containing the amino acid sequence three heavy chain complementarity determining regions (HCDRs) and three light chain complementarity determining regions (LCDRs), The present invention provides an antibody or antigen-binding fragment comprising:

[0018] In some embodiments, the present disclosure provides an isolated antibody or antigen-binding fragment, which is capable of binding to BCMA; and (a) When defined according to the Kabat numbering system, three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:2 (HCDR2), and SEQ ID NO:3 (HCDR3); and three LCDRs comprising the amino acid sequences of SEQ ID NO:4 (LCDR1), SEQ ID NO:5 (LCDR2), and SEQ ID NO:6 (LCDR3); or when defined according to the IMGT numbering system, three HCDRs comprising the amino acid sequences of SEQ ID NO:37 (HCDR1), SEQ ID NO:38 (HCDR2), and SEQ ID NO:39 (HCDR3); and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:42 (LCDR3); (b) three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:7 (HCDR2), and SEQ ID NO:8 (HCDR3), as defined by the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:9 (LCDR1), SEQ ID NO:10 (LCDR2), and SEQ ID NO:11 (LCDR3); or three HCDRs comprising the amino acid sequences of SEQ ID NO:43 (HCDR1), SEQ ID NO:44 (HCDR2), and SEQ ID NO:45 (HCDR3), as defined by the IMGT numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:46 (LCDR3); (c) three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:12 (HCDR2), and SEQ ID NO:13 (HCDR3), as defined by the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:14 (LCDR1), SEQ ID NO:15 (LCDR2), and SEQ ID NO:16 (LCDR3); or three HCDRs comprising the amino acid sequences of SEQ ID NO:47 (HCDR1), SEQ ID NO:48 (HCDR2), and SEQ ID NO:49 (HCDR3), as defined by the IMGT numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:50 (LCDR3); (d) three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:17 (HCDR2), and SEQ ID NO:18 (HCDR3), as defined by the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:19 (LCDR1), SEQ ID NO:20 (LCDR2), and SEQ ID NO:21 (LCDR3); or three HCDRs comprising the amino acid sequences of SEQ ID NO:51 (HCDR1), SEQ ID NO:52 (HCDR2), and SEQ ID NO:53 (HCDR3), as defined by the IMGT numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:54 (LCDR3); (e) three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:22 (HCDR2), and SEQ ID NO:23 (HCDR3), as defined by the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:24 (LCDR1), SEQ ID NO:25 (LCDR2), and SEQ ID NO:26 (LCDR3); or three HCDRs comprising the amino acid sequences of SEQ ID NO:55 (HCDR1), SEQ ID NO:56 (HCDR2), and SEQ ID NO:57 (HCDR3), as defined by the IMGT numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:58 (LCDR3); (f) three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:27 (HCDR2), and SEQ ID NO:28 (HCDR3), as defined by the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:29 (LCDR1), SEQ ID NO:30 (LCDR2), and SEQ ID NO:31 (LCDR3); or three HCDRs comprising the amino acid sequences of SEQ ID NO:59 (HCDR1), SEQ ID NO:60 (HCDR2), and SEQ ID NO:61 (HCDR3), as defined by the IMGT numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:62 (LCDR3); or (g) three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:32 (HCDR2), and SEQ ID NO:33 (HCDR3), as defined by the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:34 (LCDR1), SEQ ID NO:35 (LCDR2), and SEQ ID NO:36 (LCDR3); or three HCDRs comprising the amino acid sequences of SEQ ID NO:63 (HCDR1), SEQ ID NO:64 (HCDR2), and SEQ ID NO:65 (HCDR3), as defined by the IMGT numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:66 (LCDR3). The present invention provides an antibody or antigen-binding fragment comprising:

[0019] In some embodiments, the present disclosure provides an isolated antibody or antigen-binding fragment, which is capable of binding to BCMA; and (a) three HCDRs from a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 76 and three LCDRs from a light chain variable region comprising the amino acid sequence of SEQ ID NO: 77; (b) three HCDRs from a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 78 and three LCDRs from a light chain variable region comprising the amino acid sequence of SEQ ID NO: 79; (c) three HCDRs from a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 80 and three LCDRs from a light chain variable region comprising the amino acid sequence of SEQ ID NO: 81; (d) three HCDRs from a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 82 and three LCDRs from a light chain variable region comprising the amino acid sequence of SEQ ID NO: 83; (e) three HCDRs from a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 84 and three LCDRs from a light chain variable region comprising the amino acid sequence of SEQ ID NO: 85; (f) three HCDRs from a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 86 and three LCDRs from a light chain variable region comprising the amino acid sequence of SEQ ID NO: 87; or (g) three HCDRs from a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 88 and three LCDRs from a light chain variable region comprising the amino acid sequence of SEQ ID NO: 89 The present invention provides an antibody or antigen-binding fragment comprising:

[0020] In some embodiments, the antibodies or antigen-binding fragments disclosed herein comprise human heavy and light chain variable region frameworks, or human heavy and light chain variable region frameworks with one or more back mutations.

[0021] In some embodiments, the antibodies or antigen-binding fragments disclosed herein: (a) a heavy chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 76, and a light chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 77; (b) a heavy chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 78, and a light chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 79; (c) a heavy chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 80, and a light chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 81; (d) a heavy chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 82, and a light chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 83; (e) a heavy chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 84, and a light chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 85; (f) a heavy chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 86 and a light chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 87; or (g) a heavy chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 88, and a light chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 89. Includes.

[0022] In some embodiments, the antibodies or antigen-binding fragments disclosed herein: (a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 76, and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 77; (b) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 78, and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 79; (c) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 80, and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 81; (d) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 82, and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 83; (e) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 84, and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 85; (f) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 86 and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 87; or (g) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 88 and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 89 Includes.

[0023] In some embodiments, the antibodies or antigen-binding fragments disclosed herein: (a) three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:2 (HCDR2), and SEQ ID NO:3 (HCDR3), as defined by the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:4 (LCDR1), SEQ ID NO:5 (LCDR2), and SEQ ID NO:6 (LCDR3); or three HCDRs comprising the amino acid sequences of SEQ ID NO:37 (HCDR1), SEQ ID NO:38 (HCDR2), and SEQ ID NO:39 (HCDR3), as defined by the IMGT numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:42 (LCDR3); or (b) three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:22 (HCDR2), and SEQ ID NO:23 (HCDR3), as defined by the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:24 (LCDR1), SEQ ID NO:25 (LCDR2), and SEQ ID NO:26 (LCDR3); or three HCDRs comprising the amino acid sequences of SEQ ID NO:55 (HCDR1), SEQ ID NO:56 (HCDR2), and SEQ ID NO:57 (HCDR3), as defined by the IMGT numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:58 (LCDR3). Includes.

[0024] In some embodiments, the antibody or antigen-binding fragment comprises: (a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 76 and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 77; or (b) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 84 and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 85 Includes.

[0025] In some embodiments, the antibody or antigen-binding fragment disclosed herein comprises three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:22 (HCDR2), and SEQ ID NO:23 (HCDR3), when defined by the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:24 (LCDR1), SEQ ID NO:25 (LCDR2), and SEQ ID NO:26 (LCDR3); or three HCDRs comprising the amino acid sequences of SEQ ID NO:55 (HCDR1), SEQ ID NO:56 (HCDR2), and SEQ ID NO:57 (HCDR3), when defined by the IMGT numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:58 (LCDR3). In some embodiments, the antibody or antigen-binding fragment comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO:84, and a light chain variable region comprising the amino acid sequence of SEQ ID NO:85.

[0026] In some embodiments, the present disclosure provides an isolated antibody or antigen-binding fragment, which is capable of binding to BCMA; and (a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 119 modified to include an amino acid substitution at one or more of positions 30, 34, 50, 54, 55, 57, 59, 61, 64, 66, 101, 103, 108, and 109; and (b) a light chain variable region comprising the amino acid sequence of SEQ ID NO: 120 modified to include an amino acid substitution at one or more of positions 24, 28, 31, 33, 50, 55, 56, 91, 93, 94, and 97; The present invention provides an antibody or antigen-binding fragment comprising:

[0027] In some embodiments, the antibody or antigen-binding fragment comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 119 modified to include an amino acid substitution at one or more of positions 30, 34, 50, 54, 55, 57, 59, 61, 64, 66, 101, 103, 108, and 109, the amino acid at position 30 of SEQ ID NO: 119 is substituted with T; the amino acid at position 34 of SEQ ID NO: 119 is substituted with I; the amino acid at position 50 of SEQ ID NO: 119 is substituted with G; the amino acid at position 54 of SEQ ID NO: 119 is substituted with S or I; the amino acid at position 55 of SEQ ID NO: 119 is substituted with Q; the amino acid at position 57 of SEQ ID NO: 119 is substituted with T; the amino acid at position 59 of SEQ ID NO: 119 is substituted with N; the amino acid at position 61 of SEQ ID NO: 119 is substituted with A; the amino acid at position 64 of SEQ ID NO: 119 is substituted with Y; the amino acid at position 66 of SEQ ID NO: 119 is substituted with S; the amino acid at position 101 of SEQ ID NO: 119 is substituted with V; the amino acid at position 103 of SEQ ID NO: 119 is substituted with H; the amino acid at position 108 of SEQ ID NO: 119 is substituted with I; and / or It comprises a heavy chain variable region in which the amino acid at position 109 of SEQ ID NO: 119 is substituted with E.

[0028] In some embodiments, the antibody or antigen-binding fragment comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 119 modified to include an amino acid substitution at at least position 103. In some embodiments, the amino acid at position 103 of SEQ ID NO: 119 is substituted with H.

[0029] In some embodiments, the antibody or antigen-binding fragment comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 119 modified to contain at least four amino acid substitutions. In some embodiments, the antibody or antigen-binding fragment comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 119 modified to contain at least amino acid substitutions at positions 34, 66, 103, and 108. In some embodiments, the amino acid at position 34 of SEQ ID NO: 119 is substituted with I; the amino acid at position 66 of SEQ ID NO: 119 is substituted with S; the amino acid at position 103 of SEQ ID NO: 119 is substituted with H; and the amino acid at position 108 of SEQ ID NO: 119 is substituted with I.

[0030] In some embodiments, the antibody or antigen-binding fragment comprises a light chain variable region comprising the amino acid sequence of SEQ ID NO: 120 modified to include an amino acid substitution at one or more of positions 24, 28, 31, 33, 50, 55, 56, 91, 93, 94, and 97, the amino acid at position 24 of SEQ ID NO: 120 is substituted with R; the amino acid at position 28 of SEQ ID NO: 120 is substituted with S; the amino acid at position 31 of SEQ ID NO: 120 is substituted with S; the amino acid at position 33 of SEQ ID NO: 120 is substituted with I; the amino acid at position 50 of SEQ ID NO: 120 is substituted with A; the amino acid at position 55 of SEQ ID NO: 120 is substituted with Q; the amino acid at position 56 of SEQ ID NO: 120 is substituted with I; the amino acid at position 91 of SEQ ID NO: 120 is substituted with F; the amino acid at position 93 of SEQ ID NO: 120 is substituted with R; the amino acid at position 94 of SEQ ID NO: 120 is substituted with I; and / or It comprises a light chain variable region in which the amino acid at position 97 of SEQ ID NO: 120 is substituted with S.

[0031] In some embodiments, the antibody or antigen-binding fragment comprises a light chain variable region comprising the amino acid sequence of SEQ ID NO: 120 modified to contain at least six amino acid substitutions. In some embodiments, the antibody or antigen-binding fragment comprises a light chain variable region comprising the amino acid sequence of SEQ ID NO: 120 modified to contain at least amino acid substitutions at positions 24, 28, 31, 50, 55, and 93. In some embodiments, the amino acid at position 24 of SEQ ID NO: 120 is substituted with R; the amino acid at position 28 of SEQ ID NO: 120 is substituted with S; the amino acid at position 31 of SEQ ID NO: 120 is substituted with S; the amino acid at position 50 of SEQ ID NO: 120 is substituted with A; the amino acid at position 55 of SEQ ID NO: 120 is substituted with Q; and the amino acid at position 93 of SEQ ID NO: 120 is substituted with R.

[0032] In some embodiments, the antibody or antigen-binding fragment comprises: (a) a heavy chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 76, and a light chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 77; (b) a heavy chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 78, and a light chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 79; (c) a heavy chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 80, and a light chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 81; (d) a heavy chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 82, and a light chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 83; (e) a heavy chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 84, and a light chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 85; (f) a heavy chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 86 and a light chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 87; or (g) a heavy chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 88, and a light chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 89. Includes.

[0033] In some embodiments, the antibody or antigen-binding fragment comprises: (a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 76, and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 77; (b) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 78, and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 79; (c) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 80, and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 81; (d) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 82, and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 83; (e) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 84, and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 85; (f) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 86 and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 87; or (g) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 88 and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 89 Includes.

[0034] In some embodiments, the antibodies or antigen-binding fragments disclosed herein comprise a human IgG1 heavy chain constant region. In some embodiments, the antibodies or antigen-binding fragments comprise a heavy chain constant region comprising the amino acid sequence of SEQ ID NO: 90. In some embodiments, the heavy chain constant region further comprises a C-terminal lysine (K). In some embodiments, the antibodies or antigen-binding fragments disclosed herein comprise a human IgG4 heavy chain constant region.

[0035] In some embodiments, the antibodies or antigen-binding fragments disclosed herein comprise a human Igκ light chain constant region. In some embodiments, the antibodies or antigen-binding fragments comprise a light chain constant region comprising the amino acid sequence of SEQ ID NO: 91. In some embodiments, the antibodies or antigen-binding fragments disclosed herein comprise a human Igλ light chain constant region.

[0036] In some embodiments, the antibody or antigen-binding fragment disclosed herein comprises a heavy chain constant region comprising the amino acid sequence of SEQ ID NO:90, and a light chain constant region comprising the amino acid sequence of SEQ ID NO:91.

[0037] In some embodiments, the antibodies or antigen-binding fragments disclosed herein: (a) a heavy chain comprising the amino acid sequence of SEQ ID NO: 92, and a light chain comprising the amino acid sequence of SEQ ID NO: 93; (b) a heavy chain comprising the amino acid sequence of SEQ ID NO: 94, and a light chain comprising the amino acid sequence of SEQ ID NO: 95; (c) a heavy chain comprising the amino acid sequence of SEQ ID NO: 96, and a light chain comprising the amino acid sequence of SEQ ID NO: 97; (d) a heavy chain comprising the amino acid sequence of SEQ ID NO: 98, and a light chain comprising the amino acid sequence of SEQ ID NO: 99; (e) a heavy chain comprising the amino acid sequence of SEQ ID NO: 100, and a light chain comprising the amino acid sequence of SEQ ID NO: 101; (f) a heavy chain comprising the amino acid sequence of SEQ ID NO: 102 and a light chain comprising the amino acid sequence of SEQ ID NO: 103; or (g) a heavy chain comprising the amino acid sequence of SEQ ID NO: 104 and a light chain comprising the amino acid sequence of SEQ ID NO: 105 In some embodiments, the heavy chain further comprises a C-terminal lysine (K).

[0038] In some embodiments, the antibodies or antigen-binding fragments disclosed herein: (a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 76 and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 77; or (b) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 84 and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 85 Includes.

[0039] In some embodiments, the antibody or antigen-binding fragment comprises: (a) a heavy chain comprising the amino acid sequence of SEQ ID NO: 92 and a light chain comprising the amino acid sequence of SEQ ID NO: 93; or (b) a heavy chain comprising the amino acid sequence of SEQ ID NO: 100, and a light chain comprising the amino acid sequence of SEQ ID NO: 101. Includes.

[0040] In some embodiments, the antibody or antigen-binding fragment disclosed herein comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 84 and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 85. In some embodiments, the antibody or antigen-binding fragment comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 100 and a light chain comprising the amino acid sequence of SEQ ID NO: 101. In some embodiments, the heavy chain further comprises a C-terminal lysine (K).

[0041] In some embodiments, the antibody or antigen-binding fragment disclosed herein is conjugated to a therapeutic agent. In some embodiments, the therapeutic agent is a splicing modulator. In some embodiments, the therapeutic agent is a pladienolide or a pladienolide derivative. In some embodiments, the therapeutic agent is pladienolide D or a pladienolide D derivative.

[0042] In some embodiments, the therapeutic agent is D1: [ka] is.

[0043] In some embodiments, the therapeutic agent is D2: [ka] is.

[0044] In some embodiments, the antibody-drug conjugates (ADCs) disclosed herein have the formula (I): Ab-(LD) p (I) (In the formula, Ab is an antibody or antigen-binding fragment disclosed herein; D is a splicing modulator; L is a linker covalently linking Ab to D; and and p is an integer from 1 to 15.

[0045] In some embodiments, the linker is a cleavable linker.

[0046] In some embodiments, the linker comprises a cleavable peptide moiety. In some embodiments, the cleavable peptide moiety is cleavable by an enzyme. In some embodiments, the cleavable peptide moiety or linker comprises an amino acid unit. In some embodiments, the amino acid unit comprises valine-citrulline (Val-Cit). In some embodiments, the amino acid unit comprises valine-alanine (Val-Ala). In some embodiments, the amino acid unit comprises alanine-alanine-aspartic acid (Ala-Ala-Asp). In some embodiments, the amino acid unit comprises glutamine-valine-citrulline (Glu-Val-Cit).

[0047] In some embodiments, the linker comprises a cleavable glucuronide moiety. In some embodiments, the cleavable glucuronide moiety is cleavable by an enzyme. In some embodiments, the cleavable glucuronide moiety is cleavable by a glucuronidase. In some embodiments, the cleavable glucuronide moiety is cleavable by a β-glucuronidase. In some embodiments, the cleavable glucuronide moiety or linker comprises a β-glucuronide.

[0048] In some embodiments, the linker comprises a maleimide moiety. In some embodiments, the maleimide moiety comprises maleimidocaproyl (MC). In some embodiments, the maleimide moiety is reactive with cysteine ​​residues on the antibody or antigen-binding fragment. In some embodiments, the maleimide moiety is attached to the antibody or antigen-binding fragment via a cysteine ​​residue on the antibody or antigen-binding fragment.

[0049] In some embodiments, the linker comprises a maleimide moiety and a cleavable peptide moiety. In some embodiments, the cleavable peptide moiety comprises an amino acid unit. In some embodiments, the cleavable peptide moiety or amino acid unit comprises Val-Cit. In some embodiments, the cleavable peptide moiety or amino acid unit comprises Val-Ala. In some embodiments, the cleavable peptide moiety or amino acid unit comprises Ala-Ala-Asp. In some embodiments, the cleavable peptide moiety or amino acid unit comprises Glu-Val-Cit. In some embodiments, the linker comprises a maleimide moiety and a cleavable glucuronide moiety. In some embodiments, the cleavable glucuronide moiety comprises β-glucuronide.

[0050] In some embodiments, the linker comprises at least one spacer unit. In some embodiments, the spacer unit in the linker comprises a polyethylene glycol (PEG) moiety. In some embodiments, the PEG moiety is -(PEG) m-, and m is an integer from 1 to 10. In some embodiments, m is 2. In some embodiments, a spacer unit in a linker is attached to an antibody or antigen-binding fragment via a maleimide moiety (a "Mal-spacer unit"). In some embodiments, a Mal-spacer unit comprises a PEG moiety. In some embodiments, a Mal-spacer unit comprises MC.

[0051] In some embodiments, the linker comprises a Mal-spacer unit and a cleavable peptide moiety. In some embodiments, the cleavable peptide moiety comprises an amino acid unit. In some embodiments, the cleavable peptide moiety or amino acid unit comprises Val-Cit, Val-Ala, Ala-Ala-Asp, or Glu-Val-Cit. In some embodiments, the linker comprises a Mal-spacer unit and a cleavable glucuronide moiety. In some embodiments, the cleavable glucuronide moiety comprises a β-glucuronide.

[0052] In some embodiments, a maleimide moiety or Mal-spacer unit links the antibody or antigen-binding fragment to a cleavable moiety in the linker.

[0053] In some embodiments, the cleavable moiety in the linker comprises a cleavable peptide moiety. In some embodiments, the cleavable peptide moiety comprises an amino acid unit. In some embodiments, the cleavable peptide moiety or amino acid unit comprises Val-Cit, Val-Ala, Ala-Ala-Asp, or Glu-Val-Cit. In some embodiments, the linker comprises MC-Val-Cit. In some embodiments, the linker comprises MC-Val-Ala. In some embodiments, the linker comprises MC-Ala-Ala-Asp. In some embodiments, the linker comprises MC-Glu-Val-Cit. In some embodiments, the linker comprises MC-(PEG)2-Val-Cit.

[0054] In some embodiments, the cleavable moiety in the linker comprises a cleavable glucuronide moiety. In some embodiments, the cleavable glucuronide moiety comprises a β-glucuronide. In some embodiments, the linker comprises an MC-β-glucuronide.

[0055] In some embodiments, the cleavable moiety in the linker is directly linked to the splicing modulator. In some other embodiments, a spacer unit links the cleavable moiety in the linker to the splicing modulator. In some embodiments, cleavage of the conjugate releases the splicing modulator from the antibody or antigen-binding fragment and the linker. In some embodiments, the spacer unit linking the cleavable moiety in the linker to the splicing modulator is self-immolative.

[0056] In some embodiments, the spacer unit connecting the cleavable moiety in the linker to the splicing modulator comprises p-aminobenzyloxycarbonyl (pABC). In some embodiments, pABC connects the cleavable moiety in the linker to the splicing modulator. In some embodiments, the cleavable moiety in the linker comprises a cleavable peptide moiety. In some embodiments, the cleavable peptide moiety comprises an amino acid unit. In some embodiments, the cleavable peptide moiety or amino acid unit comprises Val-Cit, Val-Ala, Ala-Ala-Asp, or Glu-Val-Cit. In some embodiments, the linker comprises Val-Cit-pABC. In some embodiments, the linker comprises Val-Ala-pABC. In some embodiments, the linker comprises Ala-Ala-Asp-pABC. In some embodiments, the linker comprises Glu-Val-Cit-pABC. In some embodiments, the cleavable moiety in the linker comprises a cleavable glucuronide moiety. In some embodiments, the cleavable glucuronide moiety comprises a β-glucuronide. In some embodiments, the linker comprises β-glucuronide-pABC.

[0057] In some embodiments, the cleavable linker comprises MC-Val-Cit-pABC, MC-Val-Ala-pABC, MC-Ala-Ala-Asp-pABC, MC-Glu-Val-Cit-pABC, MC-(PEG)2-Val-Cit-pABC, or MC-β-glucuronide. In some embodiments, the cleavable linker comprises MC-Val-Cit-pABC. In some embodiments, the cleavable linker comprises MC-Val-Ala-pABC. In some embodiments, the cleavable linker comprises MC-Ala-Ala-Asp-pABC. In some embodiments, the cleavable linker comprises MC-Glu-Val-Cit-pABC. In some embodiments, the cleavable linker comprises MC-(PEG)2-Val-Cit-pABC. In some embodiments, the cleavable linker comprises MC-β-glucuronide.

[0058] In some embodiments, the linker is a non-cleavable linker.

[0059] In some embodiments, the splicing modulator comprises a modulator of the SF3b complex. In some embodiments, the splicing modulator comprises pladienolide or a pladienolide derivative. In some embodiments, the splicing modulator comprises pladienolide D or a pladienolide D derivative. In some embodiments, the splicing modulator comprises D1 or D2. In some embodiments, the splicing modulator comprises D1. In some embodiments, the splicing modulator comprises D2.

[0060] In some embodiments, p is 1 to 12. In some embodiments, p is 2 to 8. In some embodiments, p is 4 to 8. In some embodiments, p is 4. In some embodiments, p is 8.

[0061] In some embodiments, the ADCs disclosed herein have formula (I): Ab-(LD) p (I) (In the ceremony Ab is an antibody or antigen-binding fragment disclosed herein; D is D1; L is a linker covalently linking Ab to D; and and p is an integer from 1 to 15.

[0062] In some embodiments, the ADCs disclosed herein have formula (I): Ab-(LD) p (I) (In the ceremony Ab is an antibody or antigen-binding fragment disclosed herein; D is D2; L is a linker covalently linking Ab to D; and and p is an integer from 1 to 15.

[0063] In some embodiments, the antibody or antigen-binding fragment of the ADC disclosed herein (a) When defined according to the Kabat numbering system, three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:2 (HCDR2), and SEQ ID NO:3 (HCDR3); and three LCDRs comprising the amino acid sequences of SEQ ID NO:4 (LCDR1), SEQ ID NO:5 (LCDR2), and SEQ ID NO:6 (LCDR3); or when defined according to the IMGT numbering system, three HCDRs comprising the amino acid sequences of SEQ ID NO:37 (HCDR1), SEQ ID NO:38 (HCDR2), and SEQ ID NO:39 (HCDR3); and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:42 (LCDR3); (b) three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:7 (HCDR2), and SEQ ID NO:8 (HCDR3), as defined by the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:9 (LCDR1), SEQ ID NO:10 (LCDR2), and SEQ ID NO:11 (LCDR3); or three HCDRs comprising the amino acid sequences of SEQ ID NO:43 (HCDR1), SEQ ID NO:44 (HCDR2), and SEQ ID NO:45 (HCDR3), as defined by the IMGT numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:46 (LCDR3); (c) three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:12 (HCDR2), and SEQ ID NO:13 (HCDR3), as defined by the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:14 (LCDR1), SEQ ID NO:15 (LCDR2), and SEQ ID NO:16 (LCDR3); or three HCDRs comprising the amino acid sequences of SEQ ID NO:47 (HCDR1), SEQ ID NO:48 (HCDR2), and SEQ ID NO:49 (HCDR3), as defined by the IMGT numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:50 (LCDR3); (d) three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:17 (HCDR2), and SEQ ID NO:18 (HCDR3), as defined by the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:19 (LCDR1), SEQ ID NO:20 (LCDR2), and SEQ ID NO:21 (LCDR3); or three HCDRs comprising the amino acid sequences of SEQ ID NO:51 (HCDR1), SEQ ID NO:52 (HCDR2), and SEQ ID NO:53 (HCDR3), as defined by the IMGT numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:54 (LCDR3); (e) three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:22 (HCDR2), and SEQ ID NO:23 (HCDR3), as defined by the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:24 (LCDR1), SEQ ID NO:25 (LCDR2), and SEQ ID NO:26 (LCDR3); or three HCDRs comprising the amino acid sequences of SEQ ID NO:55 (HCDR1), SEQ ID NO:56 (HCDR2), and SEQ ID NO:57 (HCDR3), as defined by the IMGT numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:58 (LCDR3); (f) three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:27 (HCDR2), and SEQ ID NO:28 (HCDR3), as defined by the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:29 (LCDR1), SEQ ID NO:30 (LCDR2), and SEQ ID NO:31 (LCDR3); or three HCDRs comprising the amino acid sequences of SEQ ID NO:59 (HCDR1), SEQ ID NO:60 (HCDR2), and SEQ ID NO:61 (HCDR3), as defined by the IMGT numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:62 (LCDR3); or (g) three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:32 (HCDR2), and SEQ ID NO:33 (HCDR3), as defined by the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:34 (LCDR1), SEQ ID NO:35 (LCDR2), and SEQ ID NO:36 (LCDR3); or three HCDRs comprising the amino acid sequences of SEQ ID NO:63 (HCDR1), SEQ ID NO:64 (HCDR2), and SEQ ID NO:65 (HCDR3), as defined by the IMGT numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:66 (LCDR3). Includes.

[0064] In some embodiments, the antibody or antigen-binding fragment of the ADC comprises human heavy and light chain variable region frameworks, or human heavy and light chain variable region frameworks with one or more back mutations.

[0065] In some embodiments, the antibody or antigen-binding fragment of the ADC (a) a heavy chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 76, and a light chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 77; (b) a heavy chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 78, and a light chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 79; (c) a heavy chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 80, and a light chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 81; (d) a heavy chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 82, and a light chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 83; (e) a heavy chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 84, and a light chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 85; (f) a heavy chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 86 and a light chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 87; or (g) a heavy chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 88, and a light chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 89. Includes.

[0066] In some embodiments, the antibody or antigen-binding fragment of the ADC (a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 76, and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 77; (b) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 78, and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 79; (c) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 80, and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 81; (d) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 82, and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 83; (e) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 84, and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 85; (f) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 86 and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 87; or (g) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 88 and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 89 Includes.

[0067] In some embodiments, the antibody or antigen-binding fragment of the ADC disclosed herein (a) three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:2 (HCDR2), and SEQ ID NO:3 (HCDR3), as defined by the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:4 (LCDR1), SEQ ID NO:5 (LCDR2), and SEQ ID NO:6 (LCDR3); or three HCDRs comprising the amino acid sequences of SEQ ID NO:37 (HCDR1), SEQ ID NO:38 (HCDR2), and SEQ ID NO:39 (HCDR3), as defined by the IMGT numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:42 (LCDR3); or (b) three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:22 (HCDR2), and SEQ ID NO:23 (HCDR3), as defined by the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:24 (LCDR1), SEQ ID NO:25 (LCDR2), and SEQ ID NO:26 (LCDR3); or three HCDRs comprising the amino acid sequences of SEQ ID NO:55 (HCDR1), SEQ ID NO:56 (HCDR2), and SEQ ID NO:57 (HCDR3), as defined by the IMGT numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:58 (LCDR3). Includes.

[0068] In some embodiments, the antibody or antigen-binding fragment of the ADC (a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 76 and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 77; or (b) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 84 and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 85 Includes.

[0069] In some embodiments, the antibody or antigen-binding fragment of the ADC disclosed herein comprises three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:22 (HCDR2), and SEQ ID NO:23 (HCDR3), when defined by the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:24 (LCDR1), SEQ ID NO:25 (LCDR2), and SEQ ID NO:26 (LCDR3); or three HCDRs comprising the amino acid sequences of SEQ ID NO:55 (HCDR1), SEQ ID NO:56 (HCDR2), and SEQ ID NO:57 (HCDR3), when defined by the IMGT numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:58 (LCDR3). In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO:84 and a light chain variable region comprising the amino acid sequence of SEQ ID NO:85.

[0070] In some embodiments, the ADCs disclosed herein have formula (I): Ab-(LD) p (I) (In the ceremony Ab refers to an antibody or antigen-binding fragment thereof, which has the ability to bind to BCMA and comprises three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:22 (HCDR2), and SEQ ID NO:23 (HCDR3), as defined by the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:24 (LCDR1), SEQ ID NO:25 (LCDR2), and SEQ ID NO:26 (LCDR3); or three HCDRs comprising the amino acid sequences of SEQ ID NO:55 (HCDR1), SEQ ID NO:56 (HCDR2), and SEQ ID NO:57 (HCDR3), as defined by the IMGT numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:58 (LCDR3); D is D1; L is a linker covalently linking Ab to D; and and p is an integer from 1 to 15.

[0071] In some embodiments, the antibodies or antigen-binding fragments of the ADCs disclosed herein comprise human heavy and light chain variable region frameworks, or human heavy and light chain variable region frameworks with one or more back mutations.

[0072] In some embodiments, the antibody or antigen-binding fragment of the ADC disclosed herein comprises a heavy chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 84, and a light chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 85. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a heavy chain variable region that comprises the amino acid sequence of SEQ ID NO: 84, and a light chain variable region that comprises the amino acid sequence of SEQ ID NO: 85.

[0073] In some embodiments, the antibody or antigen-binding fragment of the ADC disclosed herein comprises a human IgG1 heavy chain constant region and a human Igκ light chain constant region. In some embodiments, the antibody or antigen-binding fragment of the ADC disclosed herein comprises a human IgG1 heavy chain constant region and a human Igλ light chain constant region. In some embodiments, the antibody or antigen-binding fragment of the ADC disclosed herein comprises a human IgG4 heavy chain constant region and a human Igκ light chain constant region. In some embodiments, the antibody or antigen-binding fragment of the ADC disclosed herein comprises a human IgG4 heavy chain constant region and a human Igλ light chain constant region. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a heavy chain constant region comprising the amino acid sequence of SEQ ID NO: 90 and a light chain constant region comprising the amino acid sequence of SEQ ID NO: 91. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 100 and a light chain comprising the amino acid sequence of SEQ ID NO: 101. In some embodiments, the heavy chain constant region or heavy chain further comprises a C-terminal lysine (K).

[0074] In some embodiments, the linker of the ADCs disclosed herein is a cleavable linker. In some embodiments, the cleavable linker comprises MC-Val-Cit-pABC. In some embodiments, the cleavable linker comprises MC-Val-Ala-pABC. In some embodiments, the cleavable linker comprises MC-Ala-Ala-Asp-pABC. In some embodiments, the cleavable linker comprises MC-Glu-Val-Cit-pABC. In some embodiments, the cleavable linker comprises MC-(PEG)2-Val-Cit-pABC. In some embodiments, the cleavable linker comprises MC-β-glucuronide.

[0075] In some embodiments, p of the ADCs disclosed herein is 1 to 12. In some embodiments, p is 2 to 8. In some embodiments, p is 4 to 8. In some embodiments, p is 4. In some embodiments, p is 8.

[0076] In some embodiments, the ADCs disclosed herein have formula (I): Ab-(LD) p (I) (In the ceremony Ab refers to an antibody or antigen-binding fragment thereof, which has the ability to bind to BCMA and comprises three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:22 (HCDR2), and SEQ ID NO:23 (HCDR3), as defined by the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:24 (LCDR1), SEQ ID NO:25 (LCDR2), and SEQ ID NO:26 (LCDR3); or three HCDRs comprising the amino acid sequences of SEQ ID NO:55 (HCDR1), SEQ ID NO:56 (HCDR2), and SEQ ID NO:57 (HCDR3), as defined by the IMGT numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:58 (LCDR3); D is D1; L is a linker (ADL1) comprising MC-Val-Cit-pABC; and and p is an integer from 1 to 15.

[0077] In some embodiments, the antibody or antigen-binding fragment of the ADC disclosed herein comprises human heavy and light chain variable region frameworks, or human heavy and light chain variable region frameworks with one or more backmutations. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 84 and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 85. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a human IgG1 heavy chain constant region and a human Igκ light chain constant region. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a heavy chain constant region comprising the amino acid sequence of SEQ ID NO: 90 and a light chain constant region comprising the amino acid sequence of SEQ ID NO: 91. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 100 and a light chain comprising the amino acid sequence of SEQ ID NO: 101. In some embodiments, the heavy chain constant region or heavy chain further comprises a C-terminal lysine (K). In some embodiments, p is 1 to 12. In some embodiments, p is 2 to 8. In some embodiments, p is 4 to 8. In some embodiments, p is 4. In some embodiments, p is 8.

[0078] In some embodiments, the ADCs disclosed herein have formula (I): Ab-(LD) p (I) (In the ceremony Ab is an antibody or antigen-binding fragment thereof that has the ability to bind to BCMA and that comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 84 and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 85; D is D1; L is a linker (ADL1) comprising MC-Val-Cit-pABC; and and p is an integer from 1 to 15.

[0079] In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a human IgG1 heavy chain constant region and a human Igκ light chain constant region. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a heavy chain constant region comprising the amino acid sequence of SEQ ID NO: 90 and a light chain constant region comprising the amino acid sequence of SEQ ID NO: 91. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 100 and a light chain comprising the amino acid sequence of SEQ ID NO: 101. In some embodiments, the heavy chain constant region or heavy chain further comprises a C-terminal lysine (K). In some embodiments, p is 1 to 12. In some embodiments, p is 2 to 8. In some embodiments, p is 4 to 8. In some embodiments, p is 4. In some embodiments, p is 8.

[0080] In various embodiments, provided herein are pharmaceutical compositions comprising the antibodies, antigen-binding fragments, conjugates, and / or ADCs described herein. In some embodiments, the pharmaceutical compositions comprise one or more antibodies, one or more antigen-binding fragments, and / or one or more ADCs described herein, together with at least a pharmaceutically acceptable carrier. In some embodiments, the pharmaceutical compositions comprise multiple copies of an antibody, antigen-binding fragment, and / or ADC. In some embodiments, the pharmaceutical compositions comprise multiple copies of an ADC disclosed herein, wherein the average p of the ADC in the composition is about 2 to about 8. In some embodiments, the average p of the ADC in the composition is about 4.

[0081] In some embodiments, provided herein are therapeutic methods and uses of the described antibodies, antigen-binding fragments, conjugates, and / or ADC compounds or compositions, e.g., in the treatment of cancer. In certain aspects, the disclosure provides methods of treating a subject having or suspected of having cancer by administering to the subject a therapeutically effective amount and / or regimen of any one of the antibodies, antigen-binding fragments, ADCs, and / or pharmaceutical compositions described herein. In certain aspects, the disclosure provides methods of reducing a cancer cell population or slowing its growth in a subject by administering to the subject a therapeutically effective amount and / or regimen of any one of the antibodies, antigen-binding fragments, ADCs, and / or pharmaceutical compositions described herein. In some embodiments, administration of the antibody, antigen-binding fragment, ADC, and / or pharmaceutical composition results in a reduction in the cancer cell population by at least about 10%, at least about 20%, at least about 50%, at least about 70%, at least about 80%, at least about 90%, at least about 95%, or at least about 99%. In some embodiments, administration of the antibody, antigen-binding fragment, ADC, and / or pharmaceutical composition slows the growth of a cancer cell population by at least about 10%, at least about 20%, at least about 50%, at least about 70%, at least about 80%, at least about 90%, at least about 95%, or at least about 99%. In some embodiments, the antibody, antigen-binding fragment, ADC, and / or pharmaceutical composition is administered in combination with one or more additional therapeutic agents. In some embodiments, the one or more additional therapeutic agents include a BCL2 inhibitor, a BCLxL inhibitor, a BCL2 / BCLxL inhibitor, and / or a gamma-secretase inhibitor.

[0082] In some embodiments of the therapeutic methods and uses disclosed herein, treatment with the described antibodies, antigen-binding fragments, ADCs, and / or pharmaceutical compositions induces bystander killing of cancer cells that do not express the target antigen but are adjacent to cancer cells that do express the target antigen. In some embodiments, a subject has one or more cancer cells that express the target antigen. In some embodiments, the target antigen is BCMA. In some embodiments, the described antibodies, antigen-binding fragments, ADCs, and / or pharmaceutical compositions induce increased levels of bystander killing of cancer cells when compared to a reference, e.g., another anti-BCMA ADC, such as AB200-ADL10-MMAF.

[0083] In some embodiments of the methods of treatment and uses disclosed herein, the cancer expresses BCMA. In some embodiments, the cancer is a plasma cell malignancy. In some embodiments, the plasma cell malignancy or cancer is a leukemia, lymphoma, plasmacytoma, or myeloma. In some embodiments, the plasma cell malignancy or cancer is multiple myeloma, diffuse large cell B-cell lymphoma, mantle cell lymphoma, plasmablastic lymphoma, plasmablastic myeloma, or Burkitt's lymphoma. In some embodiments, the plasma cell malignancy or cancer is multiple myeloma. In some embodiments, the plasma cell malignancy or cancer is relapsed / refractory multiple myeloma. In some embodiments, the plasma cell malignancy or cancer comprises actively dividing cells, dormant cells, or both. In some embodiments, the plasma cell malignancy or cancer comprises at least some dormant cells, e.g., non-dividing myeloma cells or slowly dividing myeloma cells. In some embodiments, the plasma cell malignancy or cancer expresses MCL1. In some embodiments, the plasma cell malignancy or cancer exhibits high or moderate MCL1 expression levels.

[0084] In some embodiments, provided herein are treatment methods and uses of the described antibodies, antigen-binding fragments, conjugates, and / or ADC compounds or compositions, e.g., in determining whether a subject having or suspected of having cancer (e.g., a BCMA-expressing cancer) will respond to treatment with an agent that targets BCMA, e.g., an antibody, antigen-binding fragment, ADC, and / or pharmaceutical composition described herein. In some embodiments, the method includes providing a biological sample from the subject; contacting the sample with an antibody or antigen-binding fragment disclosed herein; and detecting binding of the antibody or antigen-binding fragment to one or more cancer cells in the sample. In some embodiments, the one or more cancer cells express BCMA. In some embodiments, the cancer is a plasma cell malignancy. In some embodiments, the plasma cell malignancy or cancer is leukemia, lymphoma, plasmacytoma, or myeloma. In some embodiments, the plasma cell malignancy or cancer is multiple myeloma, diffuse large cell B-cell lymphoma, mantle cell lymphoma, plasmablastic lymphoma, plasmablastic myeloma, or Burkitt's lymphoma. In some embodiments, the plasma cell malignancy or cancer is multiple myeloma. In some embodiments, the plasma cell malignancy or cancer is relapsed / refractory multiple myeloma. In some embodiments, the biological sample is a blood sample or a bone marrow aspirate sample. In some embodiments, the blood sample is blood, a blood fraction, or one or more cells obtained from blood or a blood fraction.

[0085] In certain other aspects, the present disclosure provides pharmaceutical compositions comprising an antibody, antigen-binding fragment, conjugate, and / or ADC and a pharmaceutically acceptable diluent, carrier, and / or excipient. In some embodiments, one or more nucleic acids encoding the antibody or antigen-binding fragment of the present disclosure, or the antibody portion in the conjugate and / or ADC of the present disclosure, are also provided. The nucleic acid may be in the form of an isolated nucleic acid, a nucleic acid incorporated into an isolated vector, and / or an antibody or antigen-binding fragment expressed by a cell or cell population under conditions suitable for producing the antibody or antigen-binding fragment.

[0086] In yet another aspect, the present disclosure provides methods of making the described antibodies, antigen-binding fragments, conjugates, and / or ADC compounds or compositions. In some embodiments, the present disclosure provides methods of making antibodies or antigen-binding fragments by culturing a host cell or cell population modified to contain one or more nucleic acids encoding the antibodies or antigen-binding fragments described herein under conditions suitable for producing the antibodies or antigen-binding fragments. In some embodiments, the present disclosure provides methods of making ADCs by reacting an antibody or antigen-binding fragment described herein with a linker attached to a splicing modulator under conditions that allow conjugation. In some embodiments, the present disclosure provides methods of making ADCs by reacting an antibody or antigen-binding fragment described herein with a linker and a splicing modulator under conditions that allow conjugation.

[0087] In some embodiments, the methods disclosed herein comprise sequentially reacting an antibody or antigen-binding fragment with a linker and a splicing modulator, wherein the antibody or antigen-binding fragment is first reacted with the linker to form an antibody-linker intermediate, and then the antibody-linker intermediate is reacted with the splicing modulator. In some other embodiments, the methods disclosed herein comprise simultaneously reacting the antibody or antigen-binding fragment with the linker and the splicing modulator. In some embodiments, the linker is a cleavable linker. In some embodiments, the cleavable linker comprises MC-Val-Cit-pABC. In some embodiments, the cleavable linker comprises MC-Val-Ala-pABC. In some embodiments, the cleavable linker comprises MC-Ala-Ala-Asp-pABC. In some embodiments, the cleavable linker comprises MC-Glu-Val-Cit-pABC. In some embodiments, the cleavable linker comprises MC-(PEG)2-Val-Cit-pABC. In some embodiments, the cleavable linker comprises MC-β-glucuronide. In some embodiments, the splicing modulator comprises D1. In some embodiments, the splicing modulator comprises D2. [Brief explanation of the drawings]

[0088] [Figure 1] Figure 1 shows flow cytometry determination of anti-BCMA antibody binding affinity to the NCI-H929 human myeloma cell line (high BCMA expression). [Figure 2] Figure 1 shows flow cytometry determination of anti-BCMA antibody binding affinity to the OPM2 human myeloma cell line (moderate BCMA expression). [Figure 3] Figure 1 shows flow cytometry determination of anti-BCMA ADC binding affinity to the Raji human Burkitt's lymphoma cell line (low BCMA expression). [Figure 4] 1 shows flow cytometry determination of anti-BCMA ADC binding affinity to the NCI-H929 human myeloma cell line. [Figure 5]Possible mRNA splicing changes in genes affected by ADC treatment are shown. Without wishing to be bound by theory, these possible mRNA splicing changes may include the accumulation of premature mRNA (intron retention), exon skipping events, and / or expression of aberrant junctions (AJs), which may be accompanied by a decrease in expression of correctly spliced ​​(mature) mRNAs and mRNAs carrying canonical junctions (CJs). [Figure 6A] Figure 6 shows mRNA splicing regulation of four exemplary genes (FBXW5 (Figure 6A), PLEKHJ1 (Figure 6B), DYNLT1 (Figure 6C), and UBA2 (Figure 6D)) in OPM2 tumors treated with AB200 antibody or AB200-ADL5-D4. Counts of mature mRNAs (FBXW5-mat, PLEKHJ1-mat, and DYNLT1-mat), pre-mRNA species (FBXW5-pre, PLEKHJ1-pre_2, and DYNLT1-pre), mRNA with canonical splice sites (UBA2_CJ_1), and mRNA with aberrant splice sites (UBA2_AJ_4) are shown. [Figure 6B] Figure 6 shows mRNA splicing regulation of four exemplary genes (FBXW5 (Figure 6A), PLEKHJ1 (Figure 6B), DYNLT1 (Figure 6C), and UBA2 (Figure 6D)) in OPM2 tumors treated with AB200 antibody or AB200-ADL5-D4. Counts of mature mRNAs (FBXW5-mat, PLEKHJ1-mat, and DYNLT1-mat), pre-mRNA species (FBXW5-pre, PLEKHJ1-pre_2, and DYNLT1-pre), mRNA with canonical splice sites (UBA2_CJ_1), and mRNA with aberrant splice sites (UBA2_AJ_4) are shown. [Figure 6C]Figure 6 shows mRNA splicing regulation of four exemplary genes (FBXW5 (Figure 6A), PLEKHJ1 (Figure 6B), DYNLT1 (Figure 6C), and UBA2 (Figure 6D)) in OPM2 tumors treated with AB200 antibody or AB200-ADL5-D4. Counts of mature mRNAs (FBXW5-mat, PLEKHJ1-mat, and DYNLT1-mat), pre-mRNA species (FBXW5-pre, PLEKHJ1-pre_2, and DYNLT1-pre), mRNA with canonical splice sites (UBA2_CJ_1), and mRNA with aberrant splice sites (UBA2_AJ_4) are shown. [Figure 6D] Figure 6 shows mRNA splicing regulation of four exemplary genes (FBXW5 (Figure 6A), PLEKHJ1 (Figure 6B), DYNLT1 (Figure 6C), and UBA2 (Figure 6D)) in OPM2 tumors treated with AB200 antibody or AB200-ADL5-D4. Counts of mature mRNAs (FBXW5-mat, PLEKHJ1-mat, and DYNLT1-mat), pre-mRNA species (FBXW5-pre, PLEKHJ1-pre_2, and DYNLT1-pre), mRNA with canonical splice sites (UBA2_CJ_1), and mRNA with aberrant splice sites (UBA2_AJ_4) are shown. [Figure 7A] Figure 7 shows mRNA splicing regulation of four exemplary genes (FBXW5 (Figure 7A), PLEKHJ1 (Figure 7B), DYNLT1 (Figure 7C), and UBA2 (Figure 7D)) in MOLP8 tumors treated with AB200 antibody or AB200-ADL1-D2. Counts of mature mRNAs (FBXW5-mat, PLEKHJ1-mat, and DYNLT1-mat), pre-mRNA species (FBXW5-pre, PLEKHJ1-pre_2, and DYNLT1-pre), mRNA with canonical splice sites (UBA2_CJ_1), and mRNA with aberrant splice sites (UBA2_AJ_4) are shown. [Figure 7B]Figure 7 shows mRNA splicing regulation of four exemplary genes (FBXW5 (Figure 7A), PLEKHJ1 (Figure 7B), DYNLT1 (Figure 7C), and UBA2 (Figure 7D)) in MOLP8 tumors treated with AB200 antibody or AB200-ADL1-D2. Counts of mature mRNAs (FBXW5-mat, PLEKHJ1-mat, and DYNLT1-mat), pre-mRNA species (FBXW5-pre, PLEKHJ1-pre_2, and DYNLT1-pre), mRNA with canonical splice sites (UBA2_CJ_1), and mRNA with aberrant splice sites (UBA2_AJ_4) are shown. [Figure 7C] Figure 7 shows mRNA splicing regulation of four exemplary genes (FBXW5 (Figure 7A), PLEKHJ1 (Figure 7B), DYNLT1 (Figure 7C), and UBA2 (Figure 7D)) in MOLP8 tumors treated with AB200 antibody or AB200-ADL1-D2. Counts of mature mRNAs (FBXW5-mat, PLEKHJ1-mat, and DYNLT1-mat), pre-mRNA species (FBXW5-pre, PLEKHJ1-pre_2, and DYNLT1-pre), mRNA with canonical splice sites (UBA2_CJ_1), and mRNA with aberrant splice sites (UBA2_AJ_4) are shown. [Figure 7D] Figure 7 shows mRNA splicing regulation of four exemplary genes (FBXW5 (Figure 7A), PLEKHJ1 (Figure 7B), DYNLT1 (Figure 7C), and UBA2 (Figure 7D)) in MOLP8 tumors treated with AB200 antibody or AB200-ADL1-D2. Counts of mature mRNAs (FBXW5-mat, PLEKHJ1-mat, and DYNLT1-mat), pre-mRNA species (FBXW5-pre, PLEKHJ1-pre_2, and DYNLT1-pre), mRNA with canonical splice sites (UBA2_CJ_1), and mRNA with aberrant splice sites (UBA2_AJ_4) are shown. [Figure 8A]Figure 8 shows mRNA splicing regulation of four exemplary genes (FBXW5 (Figure 8A), PLEKHJ1 (Figure 8B), DYNLT1 (Figure 8C), and UBA2 (Figure 8D)) in OPM2 tumors treated with AB200 antibody, AB212-ADL1-D1, or AB212-ADL1-D2. Counts of mature mRNAs (FBXW5-mat, PLEKHJ1-mat, and DYNLT1-mat), pre-mRNA species (FBXW5-pre, PLEKHJ1-pre_2, and DYNLT1-pre), mRNA with canonical splice sites (UBA2_CJ_1), and mRNA with aberrant splice sites (UBA2_AJ_4) are shown. [Figure 8B] Figure 8 shows mRNA splicing regulation of four exemplary genes (FBXW5 (Figure 8A), PLEKHJ1 (Figure 8B), DYNLT1 (Figure 8C), and UBA2 (Figure 8D)) in OPM2 tumors treated with AB200 antibody, AB212-ADL1-D1, or AB212-ADL1-D2. Counts of mature mRNAs (FBXW5-mat, PLEKHJ1-mat, and DYNLT1-mat), pre-mRNA species (FBXW5-pre, PLEKHJ1-pre_2, and DYNLT1-pre), mRNA with canonical splice sites (UBA2_CJ_1), and mRNA with aberrant splice sites (UBA2_AJ_4) are shown. [Figure 8C] Figure 8 shows mRNA splicing regulation of four exemplary genes (FBXW5 (Figure 8A), PLEKHJ1 (Figure 8B), DYNLT1 (Figure 8C), and UBA2 (Figure 8D)) in OPM2 tumors treated with AB200 antibody, AB212-ADL1-D1, or AB212-ADL1-D2. Counts of mature mRNAs (FBXW5-mat, PLEKHJ1-mat, and DYNLT1-mat), pre-mRNA species (FBXW5-pre, PLEKHJ1-pre_2, and DYNLT1-pre), mRNA with canonical splice sites (UBA2_CJ_1), and mRNA with aberrant splice sites (UBA2_AJ_4) are shown. [Figure 8D]Figure 8 shows mRNA splicing regulation of four exemplary genes (FBXW5 (Figure 8A), PLEKHJ1 (Figure 8B), DYNLT1 (Figure 8C), and UBA2 (Figure 8D)) in OPM2 tumors treated with AB200 antibody, AB212-ADL1-D1, or AB212-ADL1-D2. Counts of mature mRNAs (FBXW5-mat, PLEKHJ1-mat, and DYNLT1-mat), pre-mRNA species (FBXW5-pre, PLEKHJ1-pre_2, and DYNLT1-pre), mRNA with canonical splice sites (UBA2_CJ_1), and mRNA with aberrant splice sites (UBA2_AJ_4) are shown. [Figure 9] 1 shows the in vivo anti-cancer activity of an exemplary anti-BCMA antibody (AB214) in an OPM2 xenograft model (Study 1). [Figure 10] 1 shows the in vivo anti-cancer activity of exemplary anti-BCMA antibodies (AB212, AB217, and AB218) in the OPM2 xenograft model (Study 2). [Figure 11] 1 shows the in vivo anti-cancer activity of exemplary anti-BCMA ADCs in an OPM2 xenograft model (Study 1). [Figure 12] 1 shows the in vivo anti-cancer activity of exemplary anti-BCMA ADCs in an OPM2 xenograft model (Study 2). [Figure 13] 1 shows the in vivo anti-cancer activity of exemplary anti-BCMA ADCs in an OPM2 xenograft model (Study 3). [Figure 14] 1 shows the in vivo anti-cancer activity of exemplary anti-BCMA ADCs in an OPM2 xenograft model (Study 4). [Figure 15] 1 shows the in vivo anti-cancer activity of exemplary anti-BCMA ADCs in a MOLP8 xenograft model (Study 1). [Figure 16] 1 shows the in vivo anti-cancer activity of exemplary anti-BCMA ADCs in a MOLP8 xenograft model (Study 2). [Figure 17A]Figures 17A-D show the in vitro cytotoxicity of AB216-ADL1-D1 (y-axis) and AB200-ADL10-MMAF (x-axis) in a panel of 11 human myeloma cell lines. The GI, LD, area under the curve (AUC), and maximum reduction in viable cells (RminAve) values ​​are shown in Figures 17A-D, respectively. [Figure 17B] Figures 17A-D show the in vitro cytotoxicity of AB216-ADL1-D1 (y-axis) and AB200-ADL10-MMAF (x-axis) in a panel of 11 human myeloma cell lines. The GI, LD, area under the curve (AUC), and maximum reduction in viable cells (RminAve) values ​​are shown in Figures 17A-D, respectively. [Figure 17C] Figures 17A-D show the in vitro cytotoxicity of AB216-ADL1-D1 (y-axis) and AB200-ADL10-MMAF (x-axis) in a panel of 11 human myeloma cell lines. The GI, LD, area under the curve (AUC), and maximum reduction in viable cells (RminAve) values ​​are shown in Figures 17A-D, respectively. [Figure 17D] Figures 17A-D show the in vitro cytotoxicity of AB216-ADL1-D1 (y-axis) and AB200-ADL10-MMAF (x-axis) in a panel of 11 human myeloma cell lines. The GI, LD, area under the curve (AUC), and maximum reduction in viable cells (RminAve) values ​​are shown in Figures 17A-D, respectively. [Figure 18] 1 shows the determination of AB216-ADL1-D1 and AB200-ADL10-MMAF activity in a 6-day CellTiter-Glo® cell viability assay under normal serum conditions in NCI-H929 human myeloma cells. [Figure 19A]Figure 19A shows biological repeats of 6-day CellTiter-Glo® cell viability determinations of AB216-ADL1-D1 and AB200-ADL10-MMAF under low serum conditions in NCI-H929 human myeloma cells. Figure 19A (experimental replicate #1) and Figure 19B (experimental replicate #2) show the relative proliferation of NCI-H929 human myeloma cells treated with AB216-ADL1-D1 or AB200-ADL10-MMAF under low serum conditions, respectively, as a percentage of the time-matched untreated control on day 6. [Figure 19B] Figure 19A shows biological repeats of 6-day CellTiter-Glo® cell viability determinations of AB216-ADL1-D1 and AB200-ADL10-MMAF under low serum conditions in NCI-H929 human myeloma cells. Figure 19A (experimental replicate #1) and Figure 19B (experimental replicate #2) show the relative proliferation of NCI-H929 human myeloma cells treated with AB216-ADL1-D1 or AB200-ADL10-MMAF under low serum conditions, respectively, as a percentage of the time-matched untreated control on day 6. [Figure 20] 1 shows the determination of AB216-ADL1-D1 and AB200-ADL10-MMAF activity in a 6-day CellTiter-Glo® cell viability assay under normal serum conditions in OPM2 human myeloma cells. [Figure 21A] Figure 21A (experimental replicate #1) and Figure 21B (experimental replicate #2) show the relative proliferation of OPM2 human myeloma cells treated with AB216-ADL1-D1 or AB200-ADL10-MMAF under low serum conditions, respectively, as a percentage of the time-matched untreated control on day 6. [Figure 21B]Figure 21A (experimental replicate #1) and Figure 21B (experimental replicate #2) show the relative proliferation of OPM2 human myeloma cells treated with AB216-ADL1-D1 or AB200-ADL10-MMAF under low serum conditions, respectively, as a percentage of the time-matched untreated control on day 6. [Figure 22] 1 shows mRNA levels of the long pro-survival isoform of MCL1 (MCL1L) in NCI-H929 human myeloma cells treated with 5, 50, or 500 nM of AB216-ADL1-D1 or AB200-ADL10-MMAF for 24 or 96 hours. [Figure 23] 1 shows immunoblot analysis of MCL1 expression in NCI-H929 human myeloma cells treated with 5, 50, or 500 nM of AB216-ADL1-D1 or AB200-ADL10-MMAF for 24 or 96 hours. DETAILED DESCRIPTION OF THE INVENTION

[0089] The disclosed compositions and methods may be more readily understood by reference to the following detailed description.

[0090] Throughout this document, the description refers to compositions and methods of using those compositions. When this disclosure describes or claims features or embodiments related to a composition, such features or embodiments are equally applicable to the method of using that composition. Similarly, when this disclosure describes or claims features or embodiments related to the method of using a composition, such features or embodiments are equally applicable to that composition.

[0091] When a range of values ​​is expressed, it includes embodiments using any specific value within that range. Moreover, reference to values ​​stated in ranges includes every value within that range. All ranges are inclusive of their endpoints and are combinable. When values ​​are expressed as approximations, by use of the antecedent "about," it will be understood that the particular value forms another embodiment. Reference to a particular numerical value includes at least that particular value, unless the context clearly dictates otherwise. The use of "or" is intended to mean "and / or" unless the specific context of its use dictates otherwise.

[0092] It is to be understood that certain features of the compositions and methods of the present disclosure, which are, for clarity, described herein in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the compositions and methods of the present disclosure, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any subcombination.

[0093] All references cited herein are incorporated by reference for all purposes. In the event of a conflict between a reference and the present specification, the present specification shall control.

[0094] Throughout this specification and claims, various terms are used with respect to aspects of the present description. Unless otherwise indicated, such terms should be given their ordinary meaning within the art. Other specifically defined terms should be construed consistent with the definition provided herein.

[0095] As used herein, the singular forms "a," "an," and "the" include the plural forms unless the context clearly dictates otherwise.

[0096] The term "about" or "approximately" in the context of numerical values ​​and ranges refers to a value or range that approximates or is close to the recited value or range such that the embodiment will work as intended, such as having a desired amount of nucleic acid or polypeptide in a reaction mixture, as will be apparent to one of skill in the art from the teachings contained herein. In some embodiments, "about" means ±10% of a numerical amount.

[0097] The term "antibody" is used in its broadest sense to refer to an immunoglobulin molecule that recognizes and specifically binds to a target, such as a protein, polypeptide, carbohydrate, polynucleotide, lipid, or a combination thereof, via at least one antigen recognition site within the variable region of the immunoglobulin molecule. The heavy chain of an antibody is composed of a heavy chain variable region (VH) and a heavy chain constant region (CH). The light chain is composed of a light chain variable region (VL) and a light chain constant region (CL). For purposes of this application, mature heavy and light chain variable regions each contain three complementarity-determining regions (CDR1, CDR2, and CDR3) within four framework regions (FR1, FR2, FR3, and FR4), arranged N-terminus to C-terminus: FR1, CDR1, FR2, CDR2, FR3, CDR3, and FR4. An "antibody" may be naturally occurring or artificial, such as a monoclonal antibody produced by conventional hybridoma technology. An antibody may comprise one or more heavy and / or light chains. The term "antibody" includes full-length monoclonal and polyclonal antibodies, as well as antibody fragments such as Fab, Fab', F(ab')2, Fv, and single-chain antibodies. An antibody may belong to any one of the five major immunoglobulin classes: IgA, IgD, IgE, IgG, and IgM, or their subclasses (e.g., isotypes IgG1, IgG2, IgG3, IgG4). The term also encompasses human antibodies, chimeric antibodies, humanized antibodies, and any modified immunoglobulin molecule having an antigen recognition site, so long as it exhibits one or more desired biological activities (e.g., binding to a target antigen (e.g., BCMA), internalization into a target antigen-expressing cell, etc.).

[0098] Numbering systems for describing the locations of CDR and FR regions of antibodies have been defined by various groups. Any numbering system known in the art and / or described herein can be used to define the CDR and FR regions in the antibodies and antigen-binding fragments of the present disclosure.

[0099] In some embodiments, antibodies and antigen-binding fragments of the present disclosure comprise CDR and FR regions as defined by the Kabat numbering system (see, e.g., Kabat et al., "Sequences of Proteins of Immunological Interest," Diane Publishing Company (1992); see also, Kabat et al., "Sequences of Proteins of Immunological Interest," USDapartment of Health and Human Services, US Government Printing Office (1987 and 1991)). Exemplary CDR sequences as defined by the Kabat numbering system are shown in Table 3 and can be used in any of the exemplary antibodies and antigen-binding fragments disclosed herein. The Kabat numbering system can also be used in some embodiments to describe one or more individual amino acids at a position within a CDR and / or FR region. In some embodiments, the Kabat numbering system is used in addition to, or instead of, describing one or more amino acids with their absolute position in an antibody or antigen-binding fragment. In some embodiments, amino acids and / or amino acid modifications in the antibodies or antigen-binding fragments disclosed herein may be referred to by their Kabat position. For example, in some embodiments, the antibodies or antigen-binding fragments disclosed herein comprise a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 119 modified to include an amino acid substitution at at least position 103 (i.e., absolute position 103). In some embodiments, position 103 of SEQ ID NO: 119 may be referred to by its Kabat position, i.e., as Kabat position 99 of SEQ ID NO: 119. In some embodiments, the amino acid at position 103 of SEQ ID NO: 119 (corresponding to Kabat position 99) is substituted with H.

[0100] In some embodiments, the antibodies and antigen-binding fragments of the present disclosure comprise CDR and FR regions as defined by the IMGT numbering system (International ImMunoGeneTics Information System (IMGT®)). Exemplary CDR sequences as defined by the IMGT numbering system are shown in Table 4 and can be used in any of the exemplary antibodies and antigen-binding fragments disclosed herein.

[0101] Additional numbering systems, such as the Chothia numbering system (see, e.g., Al-Lazikani et al. J Mol Biol. 1997;273:927-48) and the Chemical Computing Group (CCG) numbering system (see, e.g., Molecular Operating Environment (MOE), 2013.08; Chemical Computing Group ULC, Montreal, QC, Canada, H3A 2R7, 2018), are known in the art and may be used to define the CDR and FR regions in the antibodies and antigen-binding fragments of the present disclosure. In some embodiments, the antibodies and antigen-binding fragments of the present disclosure comprise CDR sequences that match with 100% homology to the CDR sequences described herein.

[0102] The term "monoclonal antibody," as used herein, refers to an antibody obtained from a population of substantially homogeneous antibodies; i.e., the individual antibodies comprising the population are identical except for possible minor naturally occurring mutations. Monoclonal antibodies are highly specific, directed against a single antigenic epitope. In contrast, conventional (polyclonal) antibody preparations typically include a large number of antibodies directed against (or specific for) different epitopes. The modifier "monoclonal" indicates the character of the antibody as being obtained from a substantially homogeneous antibody population and should not be construed as requiring that the antibody have been produced by any particular method. For example, monoclonal antibodies to be used in the present disclosure may be produced by the hybridoma method first described by Kohler et al. (1975) Nature 256:495, or may be produced by recombinant DNA methods (see, e.g., U.S. Pat. No. 4,816,567). Monoclonal antibodies may also be isolated from phage antibody libraries using, for example, the techniques described in Clackson et al. (1991) Nature 352:624-8 and Marks et al. (1991) J Mol Biol. 222:581-97.

[0103] The monoclonal antibodies described herein specifically include "chimeric" antibodies in which a portion of the heavy and / or light chain is identical to or homologous to corresponding sequences in antibodies from a particular species or belonging to a particular antibody class or subclass, while the remainder of the chain is identical to or homologous to corresponding sequences in antibodies from another species or belonging to another antibody class or subclass, as well as fragments of such antibodies, so long as they specifically bind to the target antigen and / or exhibit the desired biological activity.

[0104] The term "human antibody," as used herein, refers to an antibody produced by a human or an antibody having the amino acid sequence of an antibody produced by a human.

[0105] The term "chimeric antibody," as used herein, refers to an antibody in which (a) the constant region has been modified, substituted, or exchanged to link the antigen-binding site (variable region) to a constant region of a different or modified class, effector function, and / or species; and / or (b) the variable region, or a portion thereof, has been modified, substituted, or exchanged with a variable region, or a portion thereof, having a different or modified antigen specificity. To create a chimeric antibody, in some embodiments, variable region sequences from a non-human donor antibody (e.g., a mouse, rabbit, or rat donor antibody) can be linked to a human constant region using methods known in the art (see, e.g., U.S. Pat. No. 4,816,567 (Cabilly et al.)). For example, a mouse anti-BCMA antibody can be modified by replacing its constant region with a constant region from a human immunoglobulin. Due to the replacement with a human constant region, the chimeric antibody can exhibit reduced immunogenicity in humans compared to the original mouse antibody, while retaining its specificity in recognizing human BCMA.

[0106] As used herein, the term "humanized antibody" refers to a form of antibody having at least some human sequence and at least some non-human sequence. Typically, the antibody has human sequence and a small amount of non-human sequence that confers binding specificity for the target antigen. Such antibodies are chimeric antibodies that have minimal sequence derived from non-human antibodies and retain the reactivity of non-human antibodies while being less immunogenic in humans. Typically, humanized antibodies are generated by replacing hypervariable region sequences from a human acceptor antibody with hypervariable region sequences from a non-human donor antibody (e.g., a mouse, rabbit, or rat donor antibody) that binds to the antigen of interest (e.g., BCMA). In some cases, framework region sequences of the acceptor antibody may also be replaced (e.g., by backmutation) with the corresponding sequences of the donor antibody. In addition to the sequences derived from the donor and acceptor antibodies, humanized antibodies can be further modified by substitution of residues either in the framework regions and / or within the replaced non-human residues, as discussed herein, to refine and optimize antibody specificity, selectivity, affinity, and / or activity.

[0107] In some embodiments, the antibodies and antigen-binding fragments disclosed herein are humanized. In some embodiments, the disclosed antibodies and antigen-binding fragments have minimal sequence derived from a non-human antibody, such as the murine antibody CA8 (see, e.g., U.S. Pat. No. 9,273,141, incorporated herein by reference for exemplary non-human antibody sequences). In some embodiments, the disclosed antibodies and antigen-binding fragments retain the affinity of the non-human antibody but include modifications to one or more CDRs and / or frameworks. In some embodiments, the disclosed antibodies and antigen-binding fragments also exhibit one or more desirable properties not exhibited by non-human antibodies, including, but not limited to, low immunogenicity and reduced toxicity. In some embodiments, the non-human antibody is a murine antibody. In some embodiments, the non-human antibody is a murine anti-BCMA antibody. In some embodiments, a non-human antibody, or antigen-binding fragment or antigen-binding domain thereof, is used as a comparator or "reference" antibody, antigen-binding fragment, or antigen-binding domain, e.g., to assess comparative binding affinity. In other embodiments, a non-human antibody, or a variant (e.g., a humanized variant) of its antigen-binding fragment or antigen-binding domain is used as a control or "reference" antibody, antigen-binding fragment, or antigen-binding domain.

[0108] In some embodiments, the reference antibody, or antigen-binding fragment or antigen-binding domain thereof, is a humanized anti-BCMA antibody comprising a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 119 and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 120 (see, e.g., U.S. Pat. No. 9,273,141, which is incorporated herein by reference for exemplary reference antibody sequences). Such a reference antibody, antigen-binding fragment, and / or antigen-binding domain may be referred to herein as "AB200."

[0109] The term "antigen-binding fragment" or "antigen-binding portion" of an antibody, as used herein, refers to one or more fragments of an antibody or protein that retain the ability to specifically bind to an antigen (e.g., BCMA). An antigen-binding fragment may also retain the ability to internalize into antigen-expressing cells. In some embodiments, an antigen-binding fragment also retains immune effector activity. It has been shown that fragments of a full-length antibody can perform the antigen-binding function of the full-length antibody. Examples of binding fragments encompassed within the term "antigen-binding fragment" or "antigen-binding portion" of an antibody include: (i) a Fab fragment, which is a monovalent fragment consisting of the VL, VH, CL, and CH1 domains; (ii) an F(ab')2 fragment, which is a bivalent fragment comprising two Fab fragments linked by a disulfide bridge at the hinge region; (iii) an Fd fragment consisting of the VH and CH1 domains; (iv) an Fv fragment consisting of the VL and VH domains of a single arm of an antibody; (v) a dAb fragment comprising a single variable domain, such as a VH domain (see, e.g., Ward et al. (1989) Nature 341:544-6; and WO 1990 / 005144); and (vi) isolated complementarity-determining regions (CDRs). Furthermore, although the two domains of the Fv fragment, VL and VH, are encoded by separate genes, recombinant methods can be used to join them with a synthetic linker, allowing them to be produced as a single protein chain (known as a single-chain Fv (scFv)) in which the VL and VH regions pair to form a monovalent molecule. See, e.g., Bird et al. (1988) Science 242:423-6; and Huston et al. (1988) Proc Natl Acad Sci. USA 85:5879-83. Such single chain antibodies are also intended to be encompassed within the term "antigen-binding fragment" or "antigen-binding portion" of an antibody, and are known in the art as an exemplary type of binding fragment that can be internalized into cells upon binding (see, e.g., Zhu et al. (2010) 9:2131-41; He et al. (2010) J Nucl Med. 51:427-32; and Fitting et al. (2015) MAbs 7:390-402).In certain embodiments, scFv molecules may be incorporated into fusion proteins. Other forms of single-chain antibodies, such as diabodies, are also encompassed. Diabodies are bivalent, bispecific antibodies in which the VH and VL domains are expressed on a single polypeptide chain but use a linker that is too short to allow pairing between the two domains on the same chain, thereby forcing them to pair with complementary domains on separate chains to create two antigen-binding sites (see, e.g., Holliger et al. (1993) Proc Natl. Acad Sci. USA 90:6444-8; and Poljak et al. (1994) Structure 2:1121-3). Antigen-binding fragments can be obtained using conventional techniques known to those skilled in the art, and such binding fragments are screened for utility (e.g., binding affinity, internalization) in the same manner as intact antibodies. Antigen-binding fragments may also be prepared by cleaving the intact protein, for example, by protease or chemical cleavage.

[0110] The terms "antibody-drug conjugate," "antibody conjugate," "immunoconjugate," and "ADC" are used interchangeably and refer to one or more therapeutic compounds (e.g., splicing modulators) linked to one or more antibodies or antigen-binding fragments, and are defined by the general formula: Ab-(LD)p (Formula I), where Ab = antibody or antigen-binding fragment, L = linker moiety, D = drug moiety (e.g., splicing modulator), and p = number of drug moieties per antibody or antigen-binding fragment. ADCs containing splicing modulators may also be more specifically referred to herein as "splice modulator-loaded antibodies" or "SMLAs." In ADCs containing splicing modulator drug moieties, "p" refers to the number of splicing modulators linked to the antibody or antigen-binding fragment. In some embodiments, the linker L can include a cleavable moiety between the antibody or antigen-binding fragment and the splicing modulator. In some embodiments, the linker L can comprise a cleavable moiety that can be attached to either or both of the antibody or antigen-binding fragment and the splicing modulator via one or more spacer units. In some embodiments, when a spacer unit attaches the cleavable moiety to the splicing modulator, it is a self-immolative spacer unit. In other embodiments, the linker L does not comprise a cleavable moiety and is a non-cleavable linker. In some embodiments, the linker L can comprise at least one spacer unit that can be attached directly to the antibody or antigen-binding fragment and the splicing modulator. Exemplary cleavable and non-cleavable linkers are described herein.

[0111] The term "internalizing," as used herein in reference to an antibody or antigen-binding fragment, refers to an antibody or antigen-binding fragment that, upon binding to a cell, has the ability to penetrate the lipid bilayer membrane of the cell and be taken up into an internal compartment, typically a degradative compartment of the cell (i.e., be "internalized"). For example, an internalizing anti-BCMA antibody is one that has the ability to be taken up into the cell after binding to BCMA on the cell membrane. In some embodiments, the antibody or antigen-binding fragment used in the ADCs disclosed herein targets a cell surface antigen (e.g., BCMA) and is an internalizing antibody or internalizing antigen-binding fragment (i.e., the ADC translocates through the cell membrane after antigen binding). In some embodiments, the internalizing antibody or antigen-binding fragment binds to a receptor on the cell surface. An internalizing antibody or internalizing antigen-binding fragment that targets a receptor on the cell membrane can induce receptor-mediated endocytosis. In some embodiments, the internalizing antibody or internalizing antigen-binding fragment is taken up into the cell by receptor-mediated endocytosis.

[0112] The term "B-cell maturation antigen" or "BCMA," as used herein, refers to any native form of human BCMA. BCMA may also be referred to as "tumor necrosis factor receptor superfamily member 17 (TNFRSF17)" or "CD269." The term "BCMA" encompasses full-length BCMA (e.g., NCBI GenBank Reference Sequence: BAB60895.1; UniProt Reference Sequence: Q02223; SEQ ID NO: 106), as well as any form of human BCMA that may result from cellular expression or processing (e.g., alternative splicing events, different promoter usage, post-transcriptional modifications, post-translational modifications, etc.). The term also encompasses functional variants or fragments of human BCMA that retain one or more biological functions of human BCMA, including, but not limited to, splice variants, allelic variants, and isoforms (i.e., variants and fragments are included unless the context dictates that the term is used to refer only to the wild-type protein). BCMA can be isolated from humans or produced recombinantly or by synthetic methods. The term may also encompass any synthetic variant to which an anti-BCMA antibody, such as an antibody or antigen-binding fragment disclosed herein, can specifically bind.

[0113] The term "anti-BCMA antibody" or "antibody that binds to BCMA" refers to any form of antibody or antigen-binding fragment thereof that binds, e.g., specifically binds, to BCMA. This encompasses monoclonal antibodies (including full-length monoclonal antibodies), polyclonal antibodies, and antibody fragments that are biologically functional so long as they bind, e.g., specifically bind, to BCMA. More specifically, in some embodiments, the anti-BCMA antibodies or antigen-binding fragments disclosed herein may bind, e.g., specifically bind, to one or more amino acids in the extracellular domain of BCMA. In some embodiments, the extracellular domain of BCMA comprises amino acids 1-54 of SEQ ID NO: 106 (Table 8).

[0114] As used herein, the terms "specific," "specifically binds," and "binds specifically" refer to a binding reaction between an antibody or antigen-binding fragment (e.g., an anti-BCMA antibody) and a target antigen (e.g., BCMA) in a heterogeneous population of proteins and other biological substances. An antibody can be tested for binding specificity by comparing binding to the appropriate antigen with binding to another antigen or mixture of antigens under a given set of conditions. An antibody is considered specific if it binds to the appropriate antigen with at least 2-, 5-, 7-, 10-fold or more greater affinity than another antigen or mixture of antigens. A "specific antibody" or "target-specific antibody" is one that binds only to a target antigen (e.g., BCMA) and does not bind (or exhibits minimal binding) to other antigens. In certain embodiments, an antibody or antigen-binding fragment that specifically binds to a target antigen (e.g., BCMA) also has a KD for that target of less than 1×10 M, less than 1×10 M, less than 1×10 M, less than 1×10 M, less than 1×10 M, less than 1×10 M, less than 1×10 M, or less than 1×10 M. In certain embodiments, the KD is between 1 pM and 500 pM. In some embodiments, the KD is between 500 pM and 1 μM, between 1 μM and 100 nM, or between 100 mM and 10 nM.

[0115] The term "epitope" refers to a portion of an antigen that has the ability to be recognized and specifically bound by an antibody. When the antigen is a polypeptide, the epitope may be formed by contiguous amino acids, or by non-contiguous amino acids that are adjacent to each other when the polypeptide folds into a tertiary structure. The epitope bound by an antibody may be identified using any epitope mapping technique known in the art, including X-ray crystallography for epitope identification by direct visualization of the antigen-antibody complex, and monitoring the binding of antibody to fragments or mutant variants of the antigen, or monitoring the solvent accessibility of various portions of the antibody and antigen. Exemplary strategies used to map antibody epitopes include, but are not limited to, array-based oligopeptide scanning, limited proteolysis, site-directed mutagenesis, high-throughput mutagenesis mapping, hydrogen-deuterium exchange, and mass spectrometry (see, e.g., Gershoni et al. (2007) 21:145-56; and Hager-Braun and Tomer (2005) Expert Rev Proteomics 2:745-56).

[0116] Competitive binding and epitope binning can also be used to determine antibodies that share the same or overlapping epitopes. Competitive binding can be determined using a cross-blocking assay, such as the assay described in "Antibodies, A Laboratory Manual," Cold Spring Harbor Laboratory, Harlow and Lane (1st edition 1988, 2nd edition 2014). In some embodiments, competitive binding is identified when binding to a target antigen, such as BCMA, by a reference antibody or binding protein is reduced by a test antibody or binding protein (e.g., a binding protein comprising a CDR and / or variable region selected from those identified in Tables 3-5) by at least about 50% (e.g., 50%, 60%, 70%, 80%, 90%, 95%, 99%, 99.5%, or more, or any percentage in between) in a cross-blocking assay, and / or vice versa. In some embodiments, competitive binding can be due to shared or similar (e.g., partially overlapping) epitopes, or can be due to steric hindrance of antibodies or binding proteins binding to nearby epitopes (see, e.g., Tzartos, Methods in Molecular Biology (Morris, ed. (1998) vol. 66, pp. 55-66)). In some embodiments, competitive binding can be used to group binding proteins that share similar epitopes. For example, binding proteins that compete for binding can be "binned" into a group of binding proteins with overlapping or nearby epitopes, while those that do not compete are separated into another group of binding proteins with no overlapping or nearby epitopes.

[0117] The term "p" or "drug loading" or "drug:antibody ratio" or "drug-antibody ratio" or "DAR" refers to the number of drug moieties per antibody or antigen-binding fragment, i.e., the number of -LD moieties per antibody or antigen-binding fragment in an ADC disclosed herein (e.g., an ADC of Formula (I)). In an ADC that includes a splicing modulator drug moiety, "p" refers to the number of splicing modulators linked to the antibody or antigen-binding fragment. For example, if two splicing modulators (e.g., two compounds each having the structure D1) are linked to the antibody or antigen-binding fragment, then p=2. In a composition that includes multiple copies of an ADC (e.g., an ADC of Formula (I)), the "average p" refers to the average number of -LD moieties per antibody or antigen-binding fragment, also referred to as the "average drug loading."

[0118] "Linker" or "linker moiety" is used herein to refer to any chemical moiety capable of covalently tethering a compound, usually a drug moiety such as a splicing modulator, to another moiety, such as an antibody or antigen-binding fragment. The linker may be susceptible to or substantially resistant to acid-induced cleavage, peptidase-induced cleavage, light-based cleavage, esterase-induced cleavage, and / or disulfide bond cleavage, provided that the compound or antibody remains active.

[0119] The term "agent" is used herein to refer to a chemical compound, a mixture of chemical compounds, a biological macromolecule, or an extract made from biological materials. The terms "therapeutic agent" or "drug" refer to an agent capable of modulating a biological process and / or having biological activity. The splicing modulator compounds described herein are exemplary therapeutic agents.

[0120] The term "chemotherapeutic agent" or "anti-cancer agent" is used herein to refer to any agent effective in treating cancer, regardless of mechanism of action. Inhibition of metastasis or angiogenesis is frequently a property of chemotherapeutic agents. Chemotherapeutic agents include antibodies, biomolecules, and small molecules, including the splicing modulator compounds described herein. Chemotherapeutic agents can be cytotoxic or cytostatic. The term "cytostatic agent" refers to an agent that inhibits or suppresses cell growth and / or proliferation. The term "cytotoxic agent" refers to a substance that causes cell death primarily by interfering with cellular expression activity and / or function.

[0121] As used herein, the terms "splice modulating agent," "spliceosome modulating agent," and "splice modulator" refer to compounds that exhibit anti-cancer activity by interacting with components of the spliceosome. In some embodiments, splicing modulating agents alter the rate or type of splicing in target cells. For example, splicing modulating agents that function as inhibitory agents can reduce uncontrolled cell proliferation. In some embodiments, splicing modulating agents can act by binding to the SF3b spliceosome complex. Such modulating agents can be naturally occurring or synthetic compounds. Non-limiting examples of splicing modulators and categories of such modulators include pladienolides (e.g., pladienolide D or pladienolide B), pladienolide derivatives (e.g., pladienolide D or pladienolide B derivatives), herboxidiene, herboxidiene derivatives, splicostatin, splicostatin derivatives, sudemycin, and sudemycin derivatives. As used herein, the terms "derivative" and "analog," when referring to splicing modulators and the like, refer to any such compound that retains essentially the same, similar, or enhanced biological function or activity as the original compound but has an altered chemical or biological structure. In some embodiments, the splicing modulator is a pladienolide or a pladienolide derivative.

[0122] As used herein, "pladienolide derivatives" refer to compounds structurally related to members of the family of natural products known as pladienolides, but retain one or more biological functions of the starting compound. Pladienolides were originally identified in the bacterium Streptomyces platensis (Mizui et al. (2004) J Antibiot. 57:188-96) as potentially cytotoxic compounds that cause cell cycle arrest in the G1 and G2 / M phases of the cell cycle (e.g., Bonnal et al. (2012) Nat Rev Drug Dis 11:847-59). There are seven naturally occurring pladienolides, pladienolides A through G (Mizui et al. (2004) J Antibiot. 57:188-96; Sakai et al. (2004) J Antibiotics 57:180-7). U.S. Patent Nos. 7,884,128 and 7,816,401 describe exemplary synthetic methods for pladienolides B and D, and are each incorporated herein by reference for such methods. Pladienolides B and D may also be synthesized using the exemplary method described in Kanada et al. ((2007) Angew Chem Int Ed. 46:4350-5). Kanada et al. and WO 2003 / 099813 describe an exemplary synthetic method for E7107 (D11) (compound 45 in WO 2003 / 099813) from pladienolide D (11107D in WO 2003 / 099813). The corresponding U.S. patent number is U.S. Patent No. 7,550,503 to Kotake et al. Each of these references is incorporated herein by reference for the synthetic methods described.

[0123] As used herein, "splice modulator drug moiety" refers to the component of an ADC or composition that provides the structure of the splice modulator compound, e.g., the splice modulator (D) component in an ADC of Formula (I).

[0124] As used herein, "spliceosome" refers to a ribonucleoprotein complex that removes introns from one or more RNA segments, such as pre-mRNA segments.

[0125] The term "homologue" refers to a molecule that exhibits homology to another molecule, for example, by having sequences of chemical residues that are the same or similar at corresponding positions.

[0126] The terms "inhibit" or "inhibition of," as used herein, mean to reduce by a measurable amount and can include, but need not necessarily, complete prevention or inhibition.

[0127] The terms "target negative," "target antigen negative," and "antigen negative" refer to the absence (or below detectable levels) of target antigen expression by a cell or tissue. The terms "target positive," "target antigen positive," and "antigen positive" refer to the presence (or detectable levels) of target antigen expression. For example, a cell or cell line that does not express a target antigen may be described as target negative, while a cell or cell line that expresses the target antigen may be described as target positive.

[0128] The terms "bystander killing" and "bystander effect" refer to the killing of target-negative cells in the presence of target-positive cells, where killing of target-negative cells is not observed in the absence of target-positive cells. Cell-to-cell contact, or at least proximity, between target-positive and target-negative cells allows for bystander killing. This type of killing can be distinguished from "off-target killing," which refers to the indiscriminate killing of target-negative cells. "Off-target killing" can be observed even in the absence of target-positive cells.

[0129] As used herein, the terms "cancer," "neoplasm," and "tumor," whether singular or plural, are used interchangeably and refer to cells that have undergone malignant transformation and become pathological to the host organism. Primary cancer cells can be readily distinguished from noncancerous cells by well-established techniques, such as histological examination. As used herein, the definition of a cancer cell includes not only primary cancer cells but also any cell derived from a cancer cell ancestor. This includes metastasized cancer cells, as well as in vitro cultures and cell lines derived from cancer cells. Cancer may manifest as a solid tumor, e.g., a tumor detectable based on tumor burden and / or by manual techniques such as computed tomography (CT) scan, magnetic resonance imaging (MRI), X-ray, ultrasound, or palpation during a medical examination, and / or by the expression of one or more cancer-specific antigens in a sample available from the patient. Tumors may also be hematopoietic (or hematologic or hematological or blood-related) cancers, such as cancers derived from blood cells or immune cells, which are sometimes referred to as "liquid tumors." Specific examples of hematological tumor-based clinical conditions include leukemias such as chronic myelocytic leukemia, acute myelocytic leukemia, chronic lymphocytic leukemia, and acute lymphocytic leukemia; plasma cell malignancies such as multiple myeloma, monoclonal gammopathy of undetermined (or unknown or uncertain) significance (MGUS), and Waldenstrom's macroglobulinemia; lymphomas such as non-Hodgkin's lymphoma and Hodgkin's lymphoma.

[0130] In some embodiments, the cancers described herein may be any blood cancer. Blood cancers include both lymphoid and myeloid malignancies, as well as plasma cell disorders or cancers, such as multiple myeloma, MGUS, plasmacytoma (bone, extramedullary), lymphoplasmacytic lymphoma (LPL), Waldenstrom's macroglobulinemia, plasma cell leukemia, and primary amyloidosis (AL). Blood cancers may also include cancers of other types of hematopoietic cells, including polymorphonuclear leukocytes (or neutrophils), basophils, eosinophils, dendritic cells, platelets, erythrocytes, and natural killer cells. Tissues that contain hematopoietic cells are sometimes referred to as "hematopoietic cell tissues" and include bone marrow; peripheral blood; thymus; and peripheral lymphoid tissues, such as the spleen, lymph nodes, lymphoid tissues associated with mucous membranes (such as gut-associated lymphoid tissue), tonsils, Peyer's patches and appendix, and lymphoid tissues associated with other mucous membranes, such as the bronchial lining.

[0131] Specific examples of BCMA cancers described herein include plasma cell cancers. In some embodiments, the cancer is a plasma cell malignancy. In some embodiments, the plasma cell malignancy or cancer is a leukemia, lymphoma, plasmacytoma, or myeloma. In some embodiments, the plasma cell malignancy or cancer is multiple myeloma, diffuse large cell B-cell lymphoma, mantle cell lymphoma, plasmablastic lymphoma, plasmablastic myeloma, or Burkitt's lymphoma. In some embodiments, the plasma cell malignancy or cancer is multiple myeloma. In some embodiments, the plasma cell malignancy or cancer is relapsed / refractory multiple myeloma. In some embodiments, the plasma cell malignancy or cancer comprises actively dividing cells, dormant cells, or both. In some embodiments, the plasma cell malignancy or cancer comprises at least some dormant cells, e.g., non-dividing myeloma cells or slowly dividing myeloma cells.

[0132] The term "quiescent," when used to describe cells, refers to cells that are either not dividing or dividing at a slower rate than normal (e.g., the rate observed under low serum conditions). See, e.g., Khoo et al. (2019) Blood. 134(1):30-43. This term encompasses both non-dividing (quiescent) cells and slowly dividing cells. The term "quiescent" refers to cells in a reversible state in which they are not dividing but retain the ability to re-enter the cell division process. Quiescent cells may be identified by low RNA content, the absence of cell proliferation markers, and / or low cell turnover. In some embodiments, quiescent cells are quiescent cancer cells. In contrast to "dormant" cells, "actively dividing" cells are cells that are either in the process of dividing or actively preparing to divide at a normal rate (e.g., the rate observed under normal serum conditions).

[0133] The terms "subject" and "patient" are used interchangeably herein to refer to any animal, such as any mammal, including, but not limited to, humans, non-human primates, rodents, etc. In some embodiments, the subject or patient is a mammal. In some embodiments, the subject or patient is human.

[0134] The term "co-administration" or administration "in combination with" one or more therapeutic agents includes simultaneous and consecutive administration in any order.

[0135] A "pharmaceutical composition" refers to a preparation in a form that allows for administration and subsequently provides the intended biological activity of one or more active ingredients and / or achieves a therapeutic effect, and that does not contain additional components that are unacceptably toxic to the subject to whom the formulation will be administered. The pharmaceutical composition may be sterile.

[0136] "Pharmaceutical excipients" include materials such as adjuvants, carriers, pH adjusting and buffering agents, tonicity adjusting agents, wetting agents, preservatives, and the like.

[0137] The term "pharmaceutically acceptable" means approved or expected to be approved by a federal or state regulatory agency for use in animals, and more particularly in humans, or listed in the United States Pharmacopoeia or other generally recognized pharmacopeia.

[0138] A "pharmaceutically acceptable salt" is a salt that retains the desired biological activity of the parent compound and does not impart undesired toxicological effects. Examples of such salts are (a) acid addition salts formed with inorganic acids such as hydrochloric acid, hydrobromic acid, sulfuric acid, phosphoric acid, nitric acid, and the like; and salts formed with organic acids such as acetic acid, oxalic acid, tartaric acid, succinic acid, maleic acid, fumaric acid, gluconic acid, citric acid, malic acid, ascorbic acid, benzoic acid, tannic acid, palmitic acid, alginic acid, polyglutamic acid, naphthalenesulfonic acid, methanesulfonic acid, p-toluenesulfonic acid, naphthalenedisulfonic acid, polygalacturonic acid, and the like; and (b) salts formed from elemental anions such as chlorine, bromine, and iodine. See, for example, Haynes et al., "Commentary: Occurrence of Pharmaceutically Acceptable Anions and Cations in the Cambridge Structural Database," J Pharmaceutical Sciences, vol. 94, no. 10 (2005), and Berge et al., "Pharmaceutical Salts," J Pharmaceutical Sciences, vol. 66, no. 1 (1977), which are incorporated herein by reference.

[0139] For example, an "effective amount" of an antibody, antigen-binding fragment, and / or ADC disclosed herein is an amount sufficient to achieve a specifically stated purpose, e.g., an amount sufficient to produce a therapeutic effect after administration, such as a reduction in tumor growth rate or tumor volume, a reduction in symptoms of cancer, or some other indicator of therapeutic efficacy. The term "therapeutically effective amount" refers to the amount of an antibody, antigen-binding fragment, and / or ADC effective to treat a disease or disorder of interest. In the case of cancer, a therapeutically effective amount of an antibody, antigen-binding fragment, and / or ADC can reduce the number of cancer cells, reduce tumor size, inhibit (e.g., slow or stop) tumor metastasis, inhibit (e.g., slow or stop) tumor growth, and / or alleviate one or more symptoms. A "prophylactically effective amount" refers to an amount effective, at dosages and for periods of time necessary, to achieve the desired prophylactic result. Typically, because a prophylactic dose is used prior to or at an earlier stage of disease in a subject, the prophylactically effective amount will be less than the therapeutically effective amount.

[0140] As used herein, the terms "treat" or "treatment" or "therapeutic" (and grammatically related terms) refer to any improvement in any outcome of a disease, such as prolonged survival, reduced morbidity, and / or reduced side effects resulting from alternative treatment modalities. As is readily understood in the art, complete eradication of the disease is encompassed, but is not required for therapeutic action. The terms "treat" or "treatment," as used herein, can also refer to administration of the described antibodies, antigen-binding fragments, and / or ADCs to a subject, e.g., a patient having or suspected of having cancer. Treatment can be curing, relieving, alleviating, altering, ameliorating, palliating, improving, or affecting a disease, a symptom of a disease, or a predisposition to a disease, e.g., cancer. In some embodiments, in addition to treating a subject with a condition, the compositions disclosed herein can also be provided prophylactically to prevent or reduce the likelihood of the condition developing.

[0141] In some embodiments, labeled antibodies, antigen-binding fragments, and / or ADCs are used. Suitable "labels" include radionuclides, enzymes, substrates, cofactors, inhibitors, fluorescent moieties, chemiluminescent moieties, magnetic particles, and the like.

[0142] The term "protein," as used herein, refers to at least two covalently linked amino acids. This term encompasses polypeptides, oligopeptides, and peptides. In some embodiments, the two or more covalently linked amino acids are linked by a peptide bond. For example, when a protein is made recombinantly using an expression system and a host cell, the protein may be composed of naturally occurring amino acids and peptide bonds. Alternatively, the protein may contain synthetic amino acids (e.g., homophenylalanine, citrulline, ornithine, and norleucine). A "recombinant protein" is a protein made using recombinant technology, i.e., through the expression of a recombinant nucleic acid, using any techniques and methods known in the art. Methods and techniques for making recombinant proteins are well known in the art.

[0143] The terms "amino acid" and "residue," as used herein, refer to naturally occurring and synthetic amino acids, as well as amino acid analogs and amino acid mimetics that function similarly to naturally occurring amino acids. Naturally occurring amino acids are those encoded by the genetic code, as well as those that are later modified in vivo, such as hydroxyproline, γ-carboxyglutamate, and O-phosphoserine. Amino acid analogs refer to compounds that have the same basic chemical structure as a naturally occurring amino acid, i.e., an α-carbon bonded to a hydrogen, a carboxyl group, an amino group, and an R group, such as selenocysteine, homoserine, norleucine, and methionine sulfoxide. Such analogs can have modified R groups (e.g., selenocysteine, norleucine) or modified peptide backbones (e.g., homoserine), but retain the same basic chemical structure as a naturally occurring amino acid. Amino acid mimetics refer to chemical compounds that have a structure that differs from the general chemical structure of an amino acid, but that function similarly to a naturally occurring amino acid. Exemplary three-letter and one-letter amino acid codes are provided in Table 1.

[0144] [Table 1]

[0145] With respect to amino acid sequences, the terms "identity" or "homology" refer to a relationship between the sequences of two or more polypeptides, as determined by comparing the sequences. The term "identity" also refers to the degree of sequence relatedness between polypeptides, as determined by the number of matches between stretches of two or more amino acid residues. The percent "identity" between two sequences is a function of the number of identical positions shared by the two sequences, taking into account the number of gaps that need to be introduced for optimal alignment of the two sequences and the length of each gap (i.e., percent identity equals the number of identical positions / total number of positions × 100). Comparison of sequences and determination of percent identity between two sequences can be accomplished using a mathematical algorithm. For sequence comparison, typically, one sequence acts as a reference sequence, to which a test sequence is compared. When using a sequence comparison algorithm, test and reference sequences are entered into a computer, subsequence coordinates are designated, if necessary, and sequence algorithm program parameters are designated. Default program parameters can be used, or alternative parameters can be designated. The sequence comparison algorithm then calculates the percent sequence identity for the test sequence(s) relative to the reference sequence, based on the program parameters. Additionally, or alternatively, the protein sequences of the disclosure can be further utilized as a "query sequence" in performing a search against public databases, e.g., to identify related sequences. For example, such a search can be performed using the BLAST program of Altschul et al. ((1990) J Mol Biol. 215(3):403-10).

[0146] Generally, the amino acid identity or homology between the proteins disclosed herein and variants thereof, including variants of target antigens (such as BCMA) and variants of antibody variable domains (including individual variant CDRs), will be at least 80% identical or homologous to the sequences set forth herein, for example at least 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, nearly 100%, or 100% identical or homologous.

[0147] Similarly, percent "nucleic acid sequence identity" with respect to nucleic acid sequences encoding the antibodies and other proteins identified herein is defined as the percentage of nucleotide residues in a candidate sequence that are identical with the nucleotide residues in the coding sequence of the antigen-binding protein. An exemplary method utilizes the BLASTN module of WU-BLAST-2 set to default parameters, with overlap span and overlap fraction set to 1 and 0.125, respectively.

[0148] Anti-BCMA antibodies and antigen-binding fragments The present disclosure relates, in various embodiments, to antibodies and antigen-binding fragments thereof capable of binding to and / or killing cancer cells (e.g., BCMA-expressing cancer cells), and their use in conjugates (e.g., ADCs) and therapeutic compositions.

[0149] In some embodiments, the antibodies and antigen-binding fragments disclosed herein may be used alone, administered as part of a pharmaceutical composition or combination therapy, and / or as the antibody portion of an ADC. In some embodiments, the antibodies and antigen-binding fragments are capable of binding to BCMA. In some embodiments, the anti-BCMA antibodies and antigen-binding fragments disclosed herein are useful as is (i.e., in unconjugated form) and as the antibody portion of an ADC.

[0150] In some embodiments, the anti-BCMA antibodies and antigen-binding fragments disclosed herein are humanized. In some embodiments, the anti-BCMA antibodies and antigen-binding fragments have minimal sequence derived from a non-human (e.g., murine) antibody and retain the reactivity of the non-human antibody while being less immunogenic in humans. In some embodiments, the anti-BCMA antibodies and antigen-binding fragments offer one or more improvements in binding affinity, stability, ease of formulation, and / or therapeutic efficacy, and / or reduced aggregation and / or off-target toxicity, when compared to one or more anti-BCMA antibodies known in the art.

[0151] In some embodiments, the anti-BCMA antibodies and antigen-binding fragments disclosed herein, whether used alone or as part of a larger molecule such as an ADC, provide improved binding affinity when compared to a reference anti-BCMA antibody or antigen-binding fragment (e.g., a reference including AB200). In some embodiments, the disclosed antibodies and antigen-binding fragments have higher affinity for BCMA (e.g., human BCMA) when compared to a reference anti-BCMA antibody or antigen-binding fragment. In some embodiments, the disclosed antibodies and antigen-binding fragments have higher affinity for human BCMA, monkey BCMA, or both when compared to a reference anti-BCMA antibody or antigen-binding fragment. In some embodiments, the binding affinity of an antibody or antigen-binding fragment to BCMA (e.g., human BCMA and / or monkey BCMA) may be determined, for example, by an Octet binding assay using the extracellular domain of human BCMA and / or monkey BCMA. In some embodiments, the binding affinity of an antibody or antigen-binding fragment to BCMA (e.g., human BCMA) may be determined, for example, by one or more binding assays using cancer cells with high or moderate levels of BCMA expression.

[0152] In some embodiments, the anti-BCMA antibodies and antigen-binding fragments disclosed herein, whether used alone or as part of a larger molecule such as an ADC, provide improved stability when compared to a reference anti-BCMA antibody or antigen-binding fragment (e.g., a reference including AB200). In some embodiments, the disclosed antibodies and antigen-binding fragments exhibit increased thermal stability when compared to a reference anti-BCMA antibody or antigen-binding fragment. In some embodiments, the disclosed antibodies and antigen-binding fragments have a higher melting temperature (Tm) when compared to a reference anti-BCMA antibody or antigen-binding fragment. In some embodiments, the stability (e.g., thermal stability) of an antibody or antigen-binding fragment may be determined, for example, by a temperature-based stability assay, such as differential scanning calorimetry (DSC) or a ThermoFluor assay.

[0153] By virtue of some or all of these improved properties, the disclosed antibodies and antigen-binding fragments (alone or as part of an ADC) may be useful as therapeutic agents, e.g., for the treatment, prevention, and / or diagnosis of cancer (e.g., BCMA-expressing cancers).

[0154] In some embodiments, the antibodies and antigen-binding fragments disclosed herein bind to (e.g., specifically bind to) BCMA, e.g., as expressed on cancer cells. The antibodies or antigen-binding fragments may bind to BCMA with a dissociation constant (KD) of 1 mM or less, 100 nM or less, or 10 nM or less, as measured, e.g., by flow cytometry analysis, or any value therebetween. In some embodiments, the KD is between 0.5 nM and 10 nM, as measured, e.g., by flow cytometry analysis.

[0155] In some embodiments, the antibody or antigen-binding fragment is a four-chain antibody (also called an immunoglobulin) comprising two heavy chains and two light chains. In some embodiments, the antibody or antigen-binding fragment is a two-chain half antibody (one light chain and one heavy chain) or an antigen-binding fragment of an immunoglobulin. In some embodiments, the antibody or antigen-binding fragment is an antigen-binding fragment of an immunoglobulin that retains the ability to bind to a target cancer antigen (e.g., BCMA) and / or provide an immunoglobulin function.

[0156] In some embodiments, the antibody or antigen-binding fragment disclosed herein is an internalizing antibody or internalizing antigen-binding fragment thereof. In some embodiments, the internalizing antibody or internalizing antigen-binding fragment thereof binds to a target cancer antigen expressed on the surface of a cell and enters the cell upon binding. In some embodiments, the antibody or antigen-binding fragment is linked to a splicing modulator drug moiety as an ADC, and the splicing modulator drug moiety of the ADC is released from the antibody or antigen-binding fragment of the ADC after the ADC has entered and is present in a cell expressing the target cancer antigen (i.e., after the ADC has been internalized), for example, by cleavage, degradation of the antibody or antigen-binding fragment, or any other suitable release mechanism.

[0157] In some embodiments, an antibody or antigen-binding fragment disclosed herein may comprise a paired heavy and light chain variable region taken from those listed in Table 5, or a set of six CDR sequences from a paired heavy and light chain set, e.g., a set of CDRs listed in Table 3 or Table 4. In some embodiments, the antibody or antigen-binding fragment further comprises human heavy and light chain frameworks (optionally containing one or more back mutations to improve binding affinity) and / or human heavy and light chain constant regions or fragments thereof. For example, the antibody or antigen-binding fragment may comprise a human IgG heavy chain constant region (such as IgG1 or IgG4) and a human kappa or lambda light chain constant region. In some embodiments, the antibody or antigen-binding fragment comprises a human immunoglobulin G subtype 1 (IgG1) heavy chain constant region together with a human Igκ light chain constant region. In some embodiments, the antibody or antigen-binding fragment comprises a human IgG1 heavy chain constant region together with a human Igλ light chain constant region. In some embodiments, the antibody or antigen-binding fragment comprises a human immunoglobulin G subtype 4 (IgG4) heavy chain constant region in combination with a human Igκ light chain constant region, hi some embodiments, the antibody or antigen-binding fragment comprises a human IgG4 heavy chain constant region in combination with a human Igλ light chain constant region.

[0158] The amino acid sequences of exemplary antibodies of the disclosure are shown in Tables 3-7. The amino acid sequences of exemplary target antigens and exemplary reference antibodies are shown in Tables 8 and 9, respectively.

[0159] [Table 2]

[0160] [Table 3]

[0161] [Table 4]

[0162] [Table 5]

[0163] [Table 6]

[0164] [Table 7]

[0165] [Table 8]

[0166] [Table 9]

[0167] [Table 10]

[0168] [Table 11]

[0169] Table 12

[0170] Table 13

[0171] Table 14

[0172] Table 15

[0173] Table 16

[0174] Table 17

[0175] Table 18

[0176] Table 19

[0177] Table 20

[0178] In some embodiments, the antibodies, antigen-binding fragments, or antibody portions of the ADCs disclosed herein may comprise any pair of heavy and light chain variable regions listed in the table above, or a set of six CDR sequences from that set of heavy and light chains, e.g., by grafting the six CDRs onto a human donor antibody framework of choice. In some embodiments, the antibodies, antigen-binding fragments, or antibody portions of the ADCs disclosed herein may comprise amino acid sequences homologous to those listed in the table above, so long as the antibody, antigen-binding fragment, or antibody portion retains the ability to bind to its target cancer antigen (e.g., with a KD of less than 1 x 10-8 M) and / or retains one or more functional properties of the antibodies, antigen-binding fragments, and antibody portions disclosed herein (e.g., the ability to internalize, the ability to modulate RNA splicing, etc.).

[0179] In some embodiments, the anti-BCMA antibody or antigen-binding fragment thereof comprises three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:2 (HCDR2), and SEQ ID NO:3 (HCDR3), when defined according to the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:4 (LCDR1), SEQ ID NO:5 (LCDR2), and SEQ ID NO:6 (LCDR3); or three HCDRs comprising the amino acid sequences of SEQ ID NO:37 (HCDR1), SEQ ID NO:38 (HCDR2), and SEQ ID NO:39 (HCDR3), when defined according to the IMGT numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:42 (LCDR3).

[0180] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises three HCDRs and three LCDRs as follows: when defined by the Kabat numbering system, an HCDR1 consisting of SEQ ID NO: 1, an HCDR2 consisting of SEQ ID NO: 2, and an HCDR3 consisting of SEQ ID NO: 3; and an LCDR1 consisting of SEQ ID NO: 4, an LCDR2 consisting of SEQ ID NO: 5, and an LCDR3 consisting of SEQ ID NO: 6; or when defined by the IMGT numbering system, an HCDR1 consisting of SEQ ID NO: 37, an HCDR2 consisting of SEQ ID NO: 38, and an HCDR3 consisting of SEQ ID NO: 39; and an LCDR1 consisting of SEQ ID NO: 40, an LCDR2 consisting of SEQ ID NO: 41, and an LCDR3 consisting of SEQ ID NO: 42.

[0181] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 76, and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 77. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region amino acid sequence of SEQ ID NO: 76 and a light chain variable region amino acid sequence of SEQ ID NO: 77, or sequences at least 90% identical to these disclosed sequences. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region at least 90% identical to the amino acid sequence of SEQ ID NO: 76, and a light chain variable region at least 90% identical to the amino acid sequence of SEQ ID NO: 77. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:76; and / or a light chain variable region amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:77.

[0182] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises human heavy and light chain variable region frameworks, or human heavy and light chain variable region frameworks with one or more back mutations, hi some embodiments, the anti-BCMA antibody or antigen-binding fragment is an internalizing antibody or internalizing antigen-binding fragment.

[0183] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human IgG1 heavy chain constant region and / or a human Igκ light chain constant region. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human IgG1 heavy chain constant region and / or a human Igλ light chain constant region. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human IgG4 heavy chain constant region and / or a human Igκ light chain constant region. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human IgG4 heavy chain constant region and / or a human Igλ light chain constant region. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain constant region comprising the amino acid sequence of SEQ ID NO: 90 and a light chain constant region comprising the amino acid sequence of SEQ ID NO: 91. In some embodiments, the heavy chain constant region further comprises a C-terminal lysine (K).

[0184] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 92, and a light chain comprising the amino acid sequence of SEQ ID NO: 93. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain at least 90% identical to the amino acid sequence of SEQ ID NO: 92, and a light chain at least 90% identical to the amino acid sequence of SEQ ID NO: 93. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO: 92; and / or a light chain amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO: 93. In some embodiments, the heavy chain further comprises a C-terminal lysine (K). In some embodiments, the anti-BCMA antibody or antigen-binding fragment is AB212.

[0185] In some embodiments, the anti-BCMA antibody or antigen-binding fragment thereof comprises three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:7 (HCDR2), and SEQ ID NO:8 (HCDR3), when defined according to the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:9 (LCDR1), SEQ ID NO:10 (LCDR2), and SEQ ID NO:11 (LCDR3); or three HCDRs comprising the amino acid sequences of SEQ ID NO:43 (HCDR1), SEQ ID NO:44 (HCDR2), and SEQ ID NO:45 (HCDR3), when defined according to the IMGT numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:46 (LCDR3).

[0186] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises three HCDRs and three LCDRs as follows: when defined by the Kabat numbering system, HCDR1 consisting of SEQ ID NO: 1, HCDR2 consisting of SEQ ID NO: 7, and HCDR3 consisting of SEQ ID NO: 8; and LCDR1 consisting of SEQ ID NO: 9, LCDR2 consisting of SEQ ID NO: 10, and LCDR3 consisting of SEQ ID NO: 11; or when defined by the IMGT numbering system, HCDR1 consisting of SEQ ID NO: 43, HCDR2 consisting of SEQ ID NO: 44, and HCDR3 consisting of SEQ ID NO: 45; and LCDR1 consisting of SEQ ID NO: 40, LCDR2 consisting of SEQ ID NO: 41, and LCDR3 consisting of SEQ ID NO: 46.

[0187] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 78, and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 79. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region amino acid sequence of SEQ ID NO: 78 and a light chain variable region amino acid sequence of SEQ ID NO: 79, or sequences at least 90% identical to these disclosed sequences. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region at least 90% identical to the amino acid sequence of SEQ ID NO: 78, and a light chain variable region at least 90% identical to the amino acid sequence of SEQ ID NO: 79. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:78; and / or a light chain variable region amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:79.

[0188] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises human heavy and light chain variable region frameworks, or human heavy and light chain variable region frameworks with one or more back mutations, hi some embodiments, the anti-BCMA antibody or antigen-binding fragment is an internalizing antibody or internalizing antigen-binding fragment.

[0189] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human IgG1 heavy chain constant region and / or a human Igκ light chain constant region. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human IgG1 heavy chain constant region and / or a human Igλ light chain constant region. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human IgG4 heavy chain constant region and / or a human Igκ light chain constant region. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human IgG4 heavy chain constant region and / or a human Igλ light chain constant region. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain constant region comprising the amino acid sequence of SEQ ID NO: 90 and a light chain constant region comprising the amino acid sequence of SEQ ID NO: 91. In some embodiments, the heavy chain constant region further comprises a C-terminal lysine (K).

[0190] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 94 and a light chain comprising the amino acid sequence of SEQ ID NO: 95. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain at least 90% identical to the amino acid sequence of SEQ ID NO: 94 and a light chain at least 90% identical to the amino acid sequence of SEQ ID NO: 95. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO: 94; and / or a light chain amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO: 95. In some embodiments, the heavy chain further comprises a C-terminal lysine (K). In some embodiments, the anti-BCMA antibody or antigen-binding fragment is AB213.

[0191] In some embodiments, the anti-BCMA antibody or antigen-binding fragment thereof comprises three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:12 (HCDR2), and SEQ ID NO:13 (HCDR3), when defined according to the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:14 (LCDR1), SEQ ID NO:15 (LCDR2), and SEQ ID NO:16 (LCDR3); or three HCDRs comprising the amino acid sequences of SEQ ID NO:47 (HCDR1), SEQ ID NO:48 (HCDR2), and SEQ ID NO:49 (HCDR3), when defined according to the IMGT numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:50 (LCDR3).

[0192] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises three HCDRs and three LCDRs as follows: when defined by the Kabat numbering system, HCDR1 consisting of SEQ ID NO: 1, HCDR2 consisting of SEQ ID NO: 12, and HCDR3 consisting of SEQ ID NO: 13; and LCDR1 consisting of SEQ ID NO: 14, LCDR2 consisting of SEQ ID NO: 15, and LCDR3 consisting of SEQ ID NO: 16; or when defined by the IMGT numbering system, HCDR1 consisting of SEQ ID NO: 47, HCDR2 consisting of SEQ ID NO: 48, and HCDR3 consisting of SEQ ID NO: 49; and LCDR1 consisting of SEQ ID NO: 40, LCDR2 consisting of SEQ ID NO: 41, and LCDR3 consisting of SEQ ID NO: 50.

[0193] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 80, and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 81. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region amino acid sequence of SEQ ID NO: 80 and a light chain variable region amino acid sequence of SEQ ID NO: 81, or sequences at least 90% identical to these disclosed sequences. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region at least 90% identical to the amino acid sequence of SEQ ID NO: 80, and a light chain variable region at least 90% identical to the amino acid sequence of SEQ ID NO: 81. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:80; and / or a light chain variable region amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:81.

[0194] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises human heavy and light chain variable region frameworks, or human heavy and light chain variable region frameworks with one or more back mutations, hi some embodiments, the anti-BCMA antibody or antigen-binding fragment is an internalizing antibody or internalizing antigen-binding fragment.

[0195] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human IgG1 heavy chain constant region and / or a human Igκ light chain constant region. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human IgG1 heavy chain constant region and / or a human Igλ light chain constant region. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human IgG4 heavy chain constant region and / or a human Igκ light chain constant region. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human IgG4 heavy chain constant region and / or a human Igλ light chain constant region. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain constant region comprising the amino acid sequence of SEQ ID NO: 90 and a light chain constant region comprising the amino acid sequence of SEQ ID NO: 91. In some embodiments, the heavy chain constant region further comprises a C-terminal lysine (K).

[0196] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 96, and a light chain comprising the amino acid sequence of SEQ ID NO: 97. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain at least 90% identical to the amino acid sequence of SEQ ID NO: 96, and a light chain at least 90% identical to the amino acid sequence of SEQ ID NO: 97. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO: 96; and / or a light chain amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO: 97. In some embodiments, the heavy chain further comprises a C-terminal lysine (K). In some embodiments, the anti-BCMA antibody or antigen-binding fragment is AB214.

[0197] In some embodiments, the anti-BCMA antibody or antigen-binding fragment thereof comprises three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:17 (HCDR2), and SEQ ID NO:18 (HCDR3), when defined according to the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:19 (LCDR1), SEQ ID NO:20 (LCDR2), and SEQ ID NO:21 (LCDR3); or three HCDRs comprising the amino acid sequences of SEQ ID NO:51 (HCDR1), SEQ ID NO:52 (HCDR2), and SEQ ID NO:53 (HCDR3), when defined according to the IMGT numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:54 (LCDR3).

[0198] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises three HCDRs and three LCDRs as follows: when defined by the Kabat numbering system, HCDR1 consisting of SEQ ID NO: 1, HCDR2 consisting of SEQ ID NO: 17, and HCDR3 consisting of SEQ ID NO: 18; and LCDR1 consisting of SEQ ID NO: 19, LCDR2 consisting of SEQ ID NO: 20, and LCDR3 consisting of SEQ ID NO: 21; or when defined by the IMGT numbering system, HCDR1 consisting of SEQ ID NO: 51, HCDR2 consisting of SEQ ID NO: 52, and HCDR3 consisting of SEQ ID NO: 53; and LCDR1 consisting of SEQ ID NO: 40, LCDR2 consisting of SEQ ID NO: 41, and LCDR3 consisting of SEQ ID NO: 54.

[0199] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 82, and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 83. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region amino acid sequence of SEQ ID NO: 82 and a light chain variable region amino acid sequence of SEQ ID NO: 83, or sequences at least 90% identical to these disclosed sequences. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region at least 90% identical to the amino acid sequence of SEQ ID NO: 82, and a light chain variable region at least 90% identical to the amino acid sequence of SEQ ID NO: 83. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:82; and / or a light chain variable region amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:83.

[0200] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises human heavy and light chain variable region frameworks, or human heavy and light chain variable region frameworks with one or more back mutations, hi some embodiments, the anti-BCMA antibody or antigen-binding fragment is an internalizing antibody or internalizing antigen-binding fragment.

[0201] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human IgG1 heavy chain constant region and / or a human Igκ light chain constant region. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human IgG1 heavy chain constant region and / or a human Igλ light chain constant region. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human IgG4 heavy chain constant region and / or a human Igκ light chain constant region. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human IgG4 heavy chain constant region and / or a human Igλ light chain constant region. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain constant region comprising the amino acid sequence of SEQ ID NO: 90 and a light chain constant region comprising the amino acid sequence of SEQ ID NO: 91. In some embodiments, the heavy chain constant region further comprises a C-terminal lysine (K).

[0202] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 98, and a light chain comprising the amino acid sequence of SEQ ID NO: 99. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain at least 90% identical to the amino acid sequence of SEQ ID NO: 98, and a light chain at least 90% identical to the amino acid sequence of SEQ ID NO: 99. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO: 98; and / or a light chain amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO: 99. In some embodiments, the heavy chain further comprises a C-terminal lysine (K). In some embodiments, the anti-BCMA antibody or antigen-binding fragment is AB215.

[0203] In some embodiments, the anti-BCMA antibody or antigen-binding fragment thereof comprises three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:22 (HCDR2), and SEQ ID NO:23 (HCDR3), when defined according to the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:24 (LCDR1), SEQ ID NO:25 (LCDR2), and SEQ ID NO:26 (LCDR3); or three HCDRs comprising the amino acid sequences of SEQ ID NO:55 (HCDR1), SEQ ID NO:56 (HCDR2), and SEQ ID NO:57 (HCDR3), when defined according to the IMGT numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:58 (LCDR3).

[0204] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises three HCDRs and three LCDRs as follows: when defined by the Kabat numbering system, an HCDR1 consisting of SEQ ID NO: 1, an HCDR2 consisting of SEQ ID NO: 22, and an HCDR3 consisting of SEQ ID NO: 23; and when defined by the IMGT numbering system, an HCDR1 consisting of SEQ ID NO: 24, an LCDR2 consisting of SEQ ID NO: 25, and an LCDR3 consisting of SEQ ID NO: 26; or when defined by the IMGT numbering system, an HCDR1 consisting of SEQ ID NO: 55, an HCDR2 consisting of SEQ ID NO: 56, and an HCDR3 consisting of SEQ ID NO: 57; and when defined by the IMGT numbering system, an LCDR1 consisting of SEQ ID NO: 40, an LCDR2 consisting of SEQ ID NO: 41, and an LCDR3 consisting of SEQ ID NO: 58.

[0205] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 84, and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 85. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region amino acid sequence of SEQ ID NO: 84 and a light chain variable region amino acid sequence of SEQ ID NO: 85, or sequences at least 90% identical to these disclosed sequences. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region at least 90% identical to the amino acid sequence of SEQ ID NO: 84, and a light chain variable region at least 90% identical to the amino acid sequence of SEQ ID NO: 85. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:84; and / or a light chain variable region amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:85.

[0206] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises human heavy and light chain variable region frameworks, or human heavy and light chain variable region frameworks with one or more back mutations, hi some embodiments, the anti-BCMA antibody or antigen-binding fragment is an internalizing antibody or internalizing antigen-binding fragment.

[0207] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human IgG1 heavy chain constant region and / or a human Igκ light chain constant region. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human IgG1 heavy chain constant region and / or a human Igλ light chain constant region. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human IgG4 heavy chain constant region and / or a human Igκ light chain constant region. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human IgG4 heavy chain constant region and / or a human Igλ light chain constant region. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain constant region comprising the amino acid sequence of SEQ ID NO: 90 and a light chain constant region comprising the amino acid sequence of SEQ ID NO: 91. In some embodiments, the heavy chain constant region further comprises a C-terminal lysine (K).

[0208] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 100, and a light chain comprising the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain that is at least 90% identical to the amino acid sequence of SEQ ID NO: 100, and a light chain that is at least 90% identical to the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain amino acid sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO: 100; and / or a light chain amino acid sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO: 101. In some embodiments, the heavy chain further comprises a C-terminal lysine (K). In some embodiments, the anti-BCMA antibody or antigen-binding fragment is AB216.

[0209] In some embodiments, the anti-BCMA antibody or antigen-binding fragment thereof comprises three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:27 (HCDR2), and SEQ ID NO:28 (HCDR3), when defined according to the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:29 (LCDR1), SEQ ID NO:30 (LCDR2), and SEQ ID NO:31 (LCDR3), when defined according to the IMGT numbering system; or three HCDRs comprising the amino acid sequences of SEQ ID NO:59 (HCDR1), SEQ ID NO:60 (HCDR2), and SEQ ID NO:61 (HCDR3), and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:62 (LCDR3), when defined according to the IMGT numbering system.

[0210] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises three HCDRs and three LCDRs as follows: when defined by the Kabat numbering system, an HCDR1 consisting of SEQ ID NO: 1, an HCDR2 consisting of SEQ ID NO: 27, and an HCDR3 consisting of SEQ ID NO: 28; and an LCDR1 consisting of SEQ ID NO: 29, an LCDR2 consisting of SEQ ID NO: 30, and an LCDR3 consisting of SEQ ID NO: 31; or when defined by the IMGT numbering system, an HCDR1 consisting of SEQ ID NO: 59, an HCDR2 consisting of SEQ ID NO: 60, and an HCDR3 consisting of SEQ ID NO: 61; and an LCDR1 consisting of SEQ ID NO: 40, an LCDR2 consisting of SEQ ID NO: 41, and an LCDR3 consisting of SEQ ID NO: 62.

[0211] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 86, and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 87. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region amino acid sequence of SEQ ID NO: 86 and a light chain variable region amino acid sequence of SEQ ID NO: 87, or sequences at least 90% identical to these disclosed sequences. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region at least 90% identical to the amino acid sequence of SEQ ID NO: 86, and a light chain variable region at least 90% identical to the amino acid sequence of SEQ ID NO: 87. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:86; and / or a light chain variable region amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:87.

[0212] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises human heavy and light chain variable region frameworks, or human heavy and light chain variable region frameworks with one or more back mutations, hi some embodiments, the anti-BCMA antibody or antigen-binding fragment is an internalizing antibody or internalizing antigen-binding fragment.

[0213] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human IgG1 heavy chain constant region and / or a human Igκ light chain constant region. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human IgG1 heavy chain constant region and / or a human Igλ light chain constant region. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human IgG4 heavy chain constant region and / or a human Igκ light chain constant region. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human IgG4 heavy chain constant region and / or a human Igλ light chain constant region. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain constant region comprising the amino acid sequence of SEQ ID NO: 90 and a light chain constant region comprising the amino acid sequence of SEQ ID NO: 91. In some embodiments, the heavy chain constant region further comprises a C-terminal lysine (K).

[0214] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 102, and a light chain comprising the amino acid sequence of SEQ ID NO: 103. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain that is at least 90% identical to the amino acid sequence of SEQ ID NO: 102, and a light chain that is at least 90% identical to the amino acid sequence of SEQ ID NO: 103. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain amino acid sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO: 102; and / or a light chain amino acid sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO: 103. In some embodiments, the heavy chain further comprises a C-terminal lysine (K). In some embodiments, the anti-BCMA antibody or antigen-binding fragment is AB217.

[0215] In some embodiments, the anti-BCMA antibody or antigen-binding fragment thereof comprises three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:32 (HCDR2), and SEQ ID NO:33 (HCDR3), when defined according to the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:34 (LCDR1), SEQ ID NO:35 (LCDR2), and SEQ ID NO:36 (LCDR3), when defined according to the IMGT numbering system; or three HCDRs comprising the amino acid sequences of SEQ ID NO:63 (HCDR1), SEQ ID NO:64 (HCDR2), and SEQ ID NO:65 (HCDR3), and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:66 (LCDR3), when defined according to the IMGT numbering system.

[0216] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises three HCDRs and three LCDRs as follows: when defined by the Kabat numbering system, an HCDR1 consisting of SEQ ID NO: 1, an HCDR2 consisting of SEQ ID NO: 32, and an HCDR3 consisting of SEQ ID NO: 33; and an LCDR1 consisting of SEQ ID NO: 34, an LCDR2 consisting of SEQ ID NO: 35, and an LCDR3 consisting of SEQ ID NO: 36; or when defined by the IMGT numbering system, an HCDR1 consisting of SEQ ID NO: 63, an HCDR2 consisting of SEQ ID NO: 64, and an HCDR3 consisting of SEQ ID NO: 65; and an LCDR1 consisting of SEQ ID NO: 40, an LCDR2 consisting of SEQ ID NO: 41, and an LCDR3 consisting of SEQ ID NO: 66.

[0217] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 88, and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 89. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region amino acid sequence of SEQ ID NO: 88 and a light chain variable region amino acid sequence of SEQ ID NO: 89, or sequences at least 90% identical to these disclosed sequences. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region at least 90% identical to the amino acid sequence of SEQ ID NO: 88, and a light chain variable region at least 90% identical to the amino acid sequence of SEQ ID NO: 89. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:88; and / or a light chain variable region amino acid sequence at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO:89.

[0218] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises human heavy and light chain variable region frameworks, or human heavy and light chain variable region frameworks with one or more back mutations, hi some embodiments, the anti-BCMA antibody or antigen-binding fragment is an internalizing antibody or internalizing antigen-binding fragment.

[0219] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human IgG1 heavy chain constant region and / or a human Igκ light chain constant region. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human IgG1 heavy chain constant region and / or a human Igλ light chain constant region. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human IgG4 heavy chain constant region and / or a human Igκ light chain constant region. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human IgG4 heavy chain constant region and / or a human Igλ light chain constant region. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain constant region comprising the amino acid sequence of SEQ ID NO: 90 and a light chain constant region comprising the amino acid sequence of SEQ ID NO: 91. In some embodiments, the heavy chain constant region further comprises a C-terminal lysine (K).

[0220] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 104, and a light chain comprising the amino acid sequence of SEQ ID NO: 105. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain that is at least 90% identical to the amino acid sequence of SEQ ID NO: 104, and a light chain that is at least 90% identical to the amino acid sequence of SEQ ID NO: 105. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain amino acid sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO: 104; and / or a light chain amino acid sequence that is at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% identical to SEQ ID NO: 105. In some embodiments, the heavy chain further comprises a C-terminal lysine (K). In some embodiments, the anti-BCMA antibody or antigen-binding fragment is AB218.

[0221] The antibodies and antigen-binding fragments disclosed herein may include further modifications (e.g., one or more amino acid substitutions, deletions, and / or insertions) while retaining the ability to bind to BCMA. In some embodiments, the antibody or antigen-binding fragment includes a specified modification (e.g., compared to a reference antibody), and optionally includes up to about 1, about 2, about 3, about 4, about 5, about 6, about 7, about 8, about 9, or about 10 amino acid modifications in addition to the specified modification. In some embodiments, the antibody or antigen-binding fragment includes a heavy chain variable region that includes up to about 2, up to about 5, or up to about 10 amino acid modifications (e.g., compared to a reference antibody) in addition to any specified amino acid modifications. In some embodiments, the antibody or antigen-binding fragment includes a light chain variable region that includes up to about 2, up to about 5, or up to about 10 amino acid modifications in addition to any specified amino acid modifications.

[0222] In some embodiments, amino acid substitutions are single residue substitutions. Insertions typically range from about 1 to about 20 amino acid residues, although much larger insertions can be tolerated as long as biological function (e.g., binding to BCMA) is maintained. Deletions typically range from about 1 to about 20 amino acid residues, although in some cases deletions can be much larger. Substitutions, deletions, insertions, or any combination thereof can be used to arrive at the final derivative or variant. Generally, these changes are made to a few amino acids to minimize alteration of the immunogenicity and specificity of the molecule, particularly the antigen-binding protein. However, larger changes can be tolerated in certain circumstances. Conservative substitutions are generally made based on tables providing functionally similar amino acids, such as the exemplary table shown below as Table 10 and other tables known in the art.

[0223] [Table 21]

[0224] In various embodiments, substantial alterations in function or immunological identity can be made by selecting substitutions that are less conservative than those shown in Table 10. For example, substitutions can be made that have a greater effect on the structure of the polypeptide backbone, e.g., α-helical or β-sheet structure, the charge or hydrophobicity of the molecule at the target site, or the bulkiness of the side chain. In general, the substitutions that are likely to produce the greatest changes in the properties of a polypeptide are those in which a hydrophilic residue, e.g., seryl or threonyl, is substituted for (or by) a hydrophobic residue, e.g., leucyl, isoleucyl, phenylalanyl, valyl, or alanyl; (b) cysteine ​​or proline is substituted for (or by) any other residue; (c) a residue with an electropositive side chain, e.g., lysyl, arginyl, or histidyl, is substituted for (or by) an electronegative residue, e.g., glutamyl or aspartyl; or (d) a residue with a bulky side chain, e.g., phenylalanine, is substituted for (or by) one without a side chain, e.g., glycine.

[0225] In some embodiments in which variant antibody sequences are used in antibodies, antigen-binding fragments, or ADCs, the variants will typically exhibit the same qualitative biological activity and elicit the same immune response, although variants that modify the properties of the antigen-binding protein may also be selected, if desired. In addition to modifications made within the framework or CDR regions, antibodies of the disclosure may also be engineered to contain modifications within the Fc region, typically to modify one or more functional properties of the antibody or antigen-binding fragment, such as serum half-life, complement fixation, Fc receptor binding, and / or antigen-dependent cellular cytotoxicity. Furthermore, antibodies of the disclosure may, in some embodiments, be chemically modified (e.g., one or more chemical moieties can be attached to the antibody) or to modify its glycosylation, e.g., to modify one or more functional properties of the antibody or antigen-binding fragment.

[0226] Amino acid substitutions described herein may be designated by listing the absolute residue position followed by the three-letter or one-letter code of the substituted (i.e., replacing) amino acid. For example, a substitution of threonine for serine at position 30 of SEQ ID NO: 119 may be represented as "Ser30Thr" or "S30T." In this example, serine is the "replaced" amino acid and threonine is the "substituted" or "replacing" amino acid.

[0227] In some embodiments, the amino acid substitutions described herein may be referred to using the absolute position of the substitution in the antibody or antigen-binding fragment, the Kabat numbering system, or another numbering system known in the art. Unless otherwise specified, amino acid substitutions are referred to using the absolute position of the substitution in the antibody or antigen-binding fragment. However, in some embodiments, amino acid substitutions in the antibodies or antigen-binding fragments disclosed herein may be referred to by their Kabat position. In some embodiments, the antibodies or antigen-binding fragments disclosed herein comprise a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 119 modified to include an amino acid substitution at at least position 103 (i.e., absolute position 103). In some embodiments, position 103 of SEQ ID NO: 119 may be referred to by its Kabat position, i.e., as Kabat position 99 of SEQ ID NO: 119. In some embodiments, the amino acid at position 103 of SEQ ID NO: 119 (corresponding to Kabat position 99) is substituted with H. Without being bound by theory, in some embodiments, an antibody or antigen-binding fragment comprising a substitution of histidine for aspartic acid at position 103 (corresponding to Kabat position 99) of SEQ ID NO: 119 may demonstrate higher affinity for BCMA when compared to an antibody or antigen-binding fragment lacking this substitution. In some embodiments, the D103H (Kabat D99H) substitution may improve the binding affinity of the antibody or antigen-binding fragment to human BCMA, monkey BCMA, or both. In some embodiments, the D103H (Kabat D99H) substitution may improve the binding affinity of the antibody or antigen-binding fragment to both human BCMA and monkey BCMA, as determined, for example, by an Octet binding assay.

[0228] In some embodiments, the antibodies or antigen-binding fragments disclosed herein: (a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 119 modified to include an amino acid substitution at one or more of positions 30, 34, 50, 54, 55, 57, 59, 61, 64, 66, 101, 103, 108, and 109; and (b) a light chain variable region comprising the amino acid sequence of SEQ ID NO: 120 modified to include an amino acid substitution at one or more of positions 24, 28, 31, 33, 50, 55, 56, 91, 93, 94, and 97; Includes.

[0229] In some embodiments, the antibody or antigen-binding fragment comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 119 modified to include an amino acid substitution at one or more of positions 30, 34, 50, 54, 55, 57, 59, 61, 64, 66, 101, 103, 108, and 109, wherein: the amino acid at position 30 of SEQ ID NO: 119 is substituted with T; The amino acid at position 34 of SEQ ID NO: 119 is substituted with I; the amino acid at position 50 of SEQ ID NO: 119 is substituted with G; the amino acid at position 54 of SEQ ID NO: 119 is substituted with S or I; the amino acid at position 55 of SEQ ID NO: 119 is substituted with Q; the amino acid at position 57 of SEQ ID NO: 119 is substituted with T; the amino acid at position 59 of SEQ ID NO: 119 is substituted with N; The amino acid at position 61 of SEQ ID NO: 119 is substituted with A; the amino acid at position 64 of SEQ ID NO: 119 is substituted with Y; the amino acid at position 66 of SEQ ID NO: 119 is substituted with S; the amino acid at position 101 of SEQ ID NO: 119 is substituted with V; The amino acid at position 103 of SEQ ID NO: 119 is substituted with H; the amino acid at position 108 of SEQ ID NO: 119 is substituted with I; and / or The amino acid at position 109 of SEQ ID NO: 119 is substituted with E.

[0230] In some embodiments, the antibody or antigen-binding fragment comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 119 modified to include an amino acid substitution at least at position 103. In some embodiments, the amino acid at position 103 (corresponding to Kabat position 99) of SEQ ID NO: 119 is substituted with H.

[0231] In some embodiments, the antibody or antigen-binding fragment comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 119 modified to contain at least four amino acid substitutions. In some embodiments, the antibody or antigen-binding fragment comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 119 modified to contain at least amino acid substitutions at positions 34, 66, 103, and 108. In some embodiments, the amino acid at position 34 of SEQ ID NO: 119 is substituted with I; the amino acid at position 66 of SEQ ID NO: 119 is substituted with S; the amino acid at position 103 of SEQ ID NO: 119 is substituted with H; and the amino acid at position 108 of SEQ ID NO: 119 is substituted with I.

[0232] In some embodiments, the antibody or antigen-binding fragment comprises a light chain variable region comprising the amino acid sequence of SEQ ID NO: 120 modified to include an amino acid substitution at one or more of positions 24, 28, 31, 33, 50, 55, 56, 91, 93, 94, and 97, wherein: The amino acid at position 24 of SEQ ID NO: 120 is substituted with R; The amino acid at position 28 of SEQ ID NO: 120 is substituted with S; The amino acid at position 31 of SEQ ID NO: 120 is substituted with S; The amino acid at position 33 of SEQ ID NO: 120 is substituted with I; The amino acid at position 50 of SEQ ID NO: 120 is substituted with A; the amino acid at position 55 of SEQ ID NO: 120 is substituted with Q; The amino acid at position 56 of SEQ ID NO: 120 is substituted with I; The amino acid at position 91 of SEQ ID NO: 120 is substituted with F; The amino acid at position 93 of SEQ ID NO: 120 is substituted with R; the amino acid at position 94 of SEQ ID NO: 120 is substituted with I; and / or The amino acid at position 97 of SEQ ID NO: 120 is substituted with S.

[0233] In some embodiments, the antibody or antigen-binding fragment comprises a light chain variable region comprising the amino acid sequence of SEQ ID NO: 120 modified to include at least six amino acid substitutions. In some embodiments, the antibody or antigen-binding fragment comprises a light chain variable region comprising the amino acid sequence of SEQ ID NO: 120 modified to include at least amino acid substitutions at positions 24, 28, 31, 50, 55, and 93. In some embodiments, the amino acid at position 24 of SEQ ID NO: 120 is substituted with R; the amino acid at position 28 of SEQ ID NO: 120 is substituted with S; the amino acid at position 31 of SEQ ID NO: 120 is substituted with S; the amino acid at position 50 of SEQ ID NO: 120 is substituted with A; the amino acid at position 55 of SEQ ID NO: 120 is substituted with Q; and the amino acid at position 93 of SEQ ID NO: 120 is substituted with R. In various embodiments, any of the modified heavy and light chains can be paired among the antibodies or antigen-binding fragments or ADCs disclosed herein.

[0234] In some embodiments, the antibodies or antigen-binding fragments disclosed herein may be useful alone (e.g., as an antibody or antigen-binding fragment), linked to one or more additional agents (e.g., as an ADC), or as part of a larger macromolecule (e.g., a bispecific or multispecific antibody). For example, in some embodiments, the antibody or antigen-binding fragment is and / or is part of an antigen-binding domain in a bispecific or multispecific antibody. In some embodiments, the antigen-binding domain is an antigen-binding fragment. In some embodiments, the antigen-binding domain and / or antigen-binding fragment is a single-chain variable fragment (scFv) or a Fab fragment. In some embodiments, the antibodies and antigen-binding fragments disclosed herein for use alone or as part of a larger macromolecule may include further modifications (e.g., one or more amino acid substitutions, deletions, and / or insertions) while retaining BCMA-binding function.

[0235] In some embodiments, the antibody or antigen-binding fragment disclosed herein is conjugated to a therapeutic agent. In some embodiments, the therapeutic agent is a splicing modulator. In some embodiments, the therapeutic agent is pladienolide or a pladienolide derivative. In some embodiments, the therapeutic agent is pladienolide D or a pladienolide D derivative. In some embodiments, the therapeutic agent is D1, D2, or another exemplary splicing modulator described herein or incorporated by reference. In some embodiments, the therapeutic agent is D1. In some embodiments, the therapeutic agent is D2.

[0236] In some embodiments, the present disclosure provides isolated and / or substantially purified nucleic acid molecules (also referred to as polynucleotides) encoding polypeptides including full-length polypeptides or segments thereof of the antibodies and antigen-binding fragments described herein. As used herein, "isolated" means removed from one or more components previously found in the nucleic acid's normal environment. In some embodiments, a single nucleic acid may contain coding sequences for both the heavy chain variable region and the light chain variable region, and optionally also contain coding sequences for one or more constant regions of the antibodies or antigen-binding fragments disclosed herein. Alternatively, some or all of these coding sequences may be on separate nucleic acid molecules. When expressed from an appropriate expression vector, the polypeptides encoded by these polynucleotides have the ability to bind to BCMA (e.g., human BCMA).

[0237] Also provided herein are polynucleotides that encode at least one CDR region, and typically all three CDR regions, from the heavy and / or light chain of an exemplary anti-BCMA antibody or antigen-binding fragment of the present disclosure. Further provided herein are polynucleotides that encode all or substantially all of the variable region sequences of the heavy and / or light chain of an exemplary anti-BCMA antibody or antigen-binding fragment of the present disclosure. Due to the degeneracy of the genetic code, a variety of nucleic acid sequences will encode each of the exemplary amino acid sequences disclosed herein.

[0238] Also provided herein are expression vectors, host cells, and methods for making the anti-BCMA antibodies and antigen-binding fragments of the disclosure.

[0239] An exemplary embodiment is an isolated nucleic acid encoding an antibody or antigen-binding fragment disclosed herein. Another exemplary embodiment is an isolated vector comprising an isolated nucleic acid encoding an antibody or antigen-binding fragment disclosed herein. Another exemplary embodiment is an isolated cell or cell population comprising an isolated nucleic acid encoding an antibody or antigen-binding fragment disclosed herein, or a vector comprising the isolated nucleic acid. Another exemplary embodiment is a method of producing an antibody or antigen-binding fragment by culturing a host cell or cell population modified to contain one or more nucleic acid sequences encoding an antibody or antigen-binding fragment described herein under conditions suitable for producing the antibody or antigen-binding fragment. In some embodiments, the method further comprises isolating, purifying, and / or recovering the produced antibody or antigen-binding fragment.

[0240] The term "vector" is intended to refer to a polynucleotide molecule capable of transporting and / or controlling the expression of another polynucleotide linked to it. One type of vector is a "plasmid," which refers to a circular double-stranded DNA loop into which additional DNA segments can be ligated. Another type of vector is a viral vector, into which additional DNA segments can be ligated. Certain vectors are capable of autonomous replication in a host cell into which they are introduced (e.g., bacterial vectors having a bacterial origin of replication and episomal mammalian vectors). Other vectors (e.g., non-episomal mammalian vectors) can be integrated into the genome of a host cell upon introduction into the host cell, and thus are replicated along with the host genome. Moreover, certain vectors are capable of directing the expression of genes to which they are operatively linked. Such vectors are referred to herein as "expression vectors" or "recombinant expression vectors." In general, expression vectors of utility in recombinant DNA techniques are often in the form of plasmids. The present disclosure is intended to include other forms of expression vectors, such as plasmids and viral vectors (e.g., replication defective retroviruses or lentiviruses, adenoviruses and adeno-associated viruses), which serve equivalent functions.

[0241] The vectors to be used to receive sequences encoding the anti-BCMA antibody heavy and / or light chain variable regions sometimes also encode the constant regions or portions thereof. Such vectors allow for expression of the variable regions as fusion proteins with the constant regions, thus leading to the production of full-length antibodies or antigen-binding fragments thereof. Generally, such constant regions are human. In some embodiments, the constant region is a human IgG1 heavy chain constant region. In some embodiments, the constant region is a human IgG4 heavy chain constant region. In some embodiments, the constant region is a human Igκ light chain constant region. In some embodiments, the constant region is a human Igλ light chain constant region.

[0242] The term "host cell" refers to a cell (or population of cells) that has been artificially engineered to contain a nucleic acid encoding a peptide sequence, which will transcribe, translate, and optionally secrete the peptide into the cell growth medium. If recombinant production is the goal, the nucleic acid encoding the peptide's amino acid sequence will typically be synthesized or cloned by conventional methods and incorporated into an expression vector. The term "host cell" refers not only to the particular subject cell, but also to the progeny of such a cell. Because certain modifications may occur in successive generations, either due to mutation or environmental influences, such progeny may not, in fact, be identical to the parent cell, but are still included within the scope of the term as used herein.

[0243] Host cells that harbor and express nucleic acids encoding anti-BCMA antibody chains or antigen-binding fragments can be prokaryotic or eukaryotic. In some embodiments, mammalian host cells are used to express and produce the anti-BCMA polypeptides of the present disclosure. For example, they can be hybridoma cell lines expressing endogenous immunoglobulin genes or mammalian cell lines harboring exogenous expression vectors. These include any normal mortal or normal or abnormal immortal animal or human cells. For example, several suitable host cell lines capable of secreting intact immunoglobulins have been developed, including CHO cell lines, various COS cell lines, HeLa cells, myeloma cell lines, transformed B cells, and hybridomas. Exemplary host cells include, but are not limited to, Chinese hamster ovary (CHO) cells, human embryonic kidney (HEK) cells (e.g., 293T), monkey kidney (COS) cells (e.g., COS-1, COS-7), baby hamster kidney (BHK) cells (e.g., BHK-21), African green monkey kidney cells (e.g., BSC-1), HeLa cells, human hepatocellular carcinoma cells (e.g., Hep G2), myeloma cells (e.g., NS0, 653, SP2 / 0), and lymphoma cells, or any derivative, immortalized, or transformed cells thereof.

[0244] In some embodiments, one or more nucleic acid molecules encoding the heavy and / or light chains of an anti-BCMA antibody or antigen-binding fragment, or one or more expression vectors comprising such nucleic acid molecules, can be introduced into a suitable host cell using any method appropriate for the host cell of choice (e.g., transformation, transfection, electroporation, infection) to create a recombinant host cell, whereby the nucleic acid molecule is operably linked to one or more expression control elements (e.g., in a vector, in a construct generated by a cellular process, integrated into the host cell genome). In some embodiments, the resulting recombinant host cell can be maintained under conditions suitable for expression or production (e.g., in the presence of an inducer, in a suitable non-human animal, in a suitable culture medium supplemented with appropriate salts, growth factors, antibiotics, nutritional supplements, etc.), thereby producing the encoded polypeptide. If desired, the encoded protein can be isolated or recovered (e.g., from the animal, the host cell, or the medium). This process includes expression in host cells of a transgenic non-human animal (see, e.g., WO 1992 / 003918). Furthermore, expression of antibody chains or antigen-binding fragments from production cell lines can be enhanced using known techniques. For example, the glutamine synthetase and DHFR gene expression systems are commonly used methods to enhance expression under certain conditions. High-expressing cell clones can be identified using conventional techniques, such as limiting dilution cloning, gel microdroplet technology, or any other method known in the art.

[0245] Antibody-drug conjugates Antibody-drug conjugates (ADCs) of the present disclosure include those with anti-cancer activity. In particular, ADCs include antibodies or antigen-binding fragments conjugated (e.g., covalently attached by a linker) to a drug moiety (e.g., a splicing modulator), where the drug moiety has a cytotoxic or cytostatic effect when not conjugated to the antibody or antigen-binding fragment. In various embodiments, the drug moiety is capable of binding to and / or interacting with the SF3b spliceosome complex when not conjugated to the antibody or antigen-binding fragment. In various embodiments, the drug moiety is capable of modulating RNA splicing in vitro and / or in vivo when not conjugated to the antibody or antigen-binding fragment. The drug moieties and ADCs disclosed herein, in various embodiments, provide potent anti-proliferative agents by targeting RNA splicing. In various embodiments, the drug moieties and ADCs disclosed herein can target both actively dividing and dormant cells (e.g., actively dividing, non-dividing, and / or slowly dividing myeloma cells).

[0246] In various embodiments, the present disclosure is based, at least in part, on the discovery that the novel antibodies and antigen-binding fragments disclosed herein can provide improved properties when linked to certain biologically active splicing modulators and used in ADCs. While a splicing modulator may desirably exhibit improved characteristics (e.g., robust SF3b spliceosome complex binding, potent RNA splicing modulation) when used alone, its ability to preferentially target diseased tissues may be limited. Also, in various embodiments, a splicing modulator may exhibit less of its desirable characteristics when conjugated to some antibodies or antigen-binding fragments. Thus, the development and production of ADCs for use as human therapeutics, e.g., oncology agents, may require more than identifying an antibody that binds to a desired target or targets and has the ability to link to a drug used alone to treat cancer. Linking an antibody to a drug can have significant effects on the activity of one or both of the antibody and the drug, and the effects may vary depending on the type of linker and / or drug chosen. Thus, in some embodiments, the components of the ADC are selected so that (i) they retain one or more therapeutic properties exhibited by the antibody and drug moiety alone, (ii) they maintain the specific binding properties of the antibody or antigen-binding fragment; (iii) they optimize drug loading and drug-to-antibody ratio; (iv) they enable stable association of the drug moiety with the antibody or antigen-binding fragment, for example, intracellular delivery; (v) they maintain the stability of the ADC as an intact conjugate until transported or delivered to the target site; (vi) they minimize aggregation of the ADC before or after administration; (vii) they achieve the therapeutic effect, e.g., cytotoxic effect, of the drug moiety after cleavage or other release mechanism in the cellular environment; (viii) they exhibit in vivo anti-cancer therapeutic efficacy that is comparable to or superior to that of the antibody and drug moiety alone; (ix) they minimize off-target killing by the drug moiety; and / or (x) they exhibit desirable pharmacokinetic and pharmacodynamic properties, ease of formulation, and toxicological / immunological profile.Some or each of these properties may be necessary for the identification of improved ADCs for therapeutic use (Ab et al. (2015) Mol Cancer Ther. 14:1605-13).

[0247] In various embodiments, the ADCs disclosed herein exhibit unexpectedly advantageous properties in some or each of the above-listed categories. For example, in some embodiments, the ADC constructs disclosed herein exhibit unexpectedly favorable drug loading, aggregation, and / or stability profiles, and / or maintain or improve antibody binding function, drug activity, and / or bystander killing activity, while reducing off-target killing, when compared to ADCs comprising another antibody, linker, and / or drug moiety (e.g., another antibody (e.g., a reference antibody) and / or another splicing modulator). In some embodiments, the ADC constructs disclosed herein exhibit improved cytotoxic and / or cytostatic activity against non-dividing and / or slowly-dividing cells when compared to ADCs comprising another antibody, linker, and / or drug moiety (e.g., another antibody (e.g., a reference antibody) and / or another splicing modulator). In some embodiments, the ADC constructs disclosed herein demonstrate higher affinity for BCMA and / or greater stability, activity, potency, or other effect (measured in vivo or in vitro) when compared to an ADC that uses a different antibody, linker, and / or drug moiety (e.g., a different antibody (e.g., a reference antibody) and / or a different splicing modulator). In some embodiments, the comparator or reference ADC is an ADC that includes the same linker and / or splicing modulator payload, but includes a different antibody (e.g., AB200 or another exemplary anti-BCMA antibody).

[0248] In some embodiments, the ADC constructs disclosed herein demonstrate improved binding affinity, e.g., when compared to an ADC comprising the same linker and / or splicing modulator payload but another antibody (e.g., AB200 or another exemplary anti-BCMA antibody). In some embodiments, the disclosed ADCs have higher affinity for BCMA (e.g., human BCMA) when compared to an ADC comprising the same linker and / or splicing modulator payload but another antibody. In some embodiments, the disclosed ADCs comprise an exemplary anti-BCMA antibody or antigen-binding fragment, a linker, and a splicing modulator payload. In some embodiments, the anti-BCMA antibody or antigen-binding fragment is any one of antibodies AB212, AB213, AB214, AB215, AB216, AB217, or AB218 (e.g., AB212 or AB216, e.g., AB216). In some embodiments, the reference ADC is an ADC that includes the same linker and the same splicing modulator payload (e.g., ADL1-D2) as the disclosed ADC, but includes a different antibody (e.g., AB200). In some embodiments, the binding affinity of the ADC to BCMA (e.g., human BCMA) may be determined by one or more binding assays using, for example, cancer cells with high or moderate levels of BCMA expression.

[0249] In some embodiments, the ADC constructs disclosed herein demonstrate improved cytotoxic and / or cytostatic activity, e.g., when compared to an ADC comprising the same linker and / or splicing modulator payload but another antibody (e.g., AB200 or other exemplary anti-BCMA antibody). In some embodiments, the disclosed ADCs exhibit increased potency against BCMA-expressing cells (e.g., NCI-H929 and / or OPM2 cells) when compared to an ADC comprising the same linker and / or splicing modulator payload but another antibody. In some embodiments, the disclosed ADCs are cell cycle independent for activity. In some embodiments, the disclosed ADCs retain cytotoxic and / or cytostatic activity independent of cell proliferative state. In some embodiments, the disclosed ADCs can target both actively dividing and dormant cells. In some embodiments, the disclosed ADCs exhibit increased potency against dormant cells (e.g., non-dividing and / or slowly-dividing myeloma cells) when compared to another anti-BCMA ADC (e.g., an anti-BCMA ADC comprising another antibody, linker, and / or payload, e.g., AB200-ADL10-MMAF). In some embodiments, the disclosed ADCs do not inhibit the growth of and / or kill cells that do not express BCMA (e.g., BCMA-negative cells, e.g., Jurkat cells). In some embodiments, the disclosed ADCs comprise an exemplary anti-BCMA antibody or antigen-binding fragment, a linker, and a splicing modulator payload. In some embodiments, the anti-BCMA antibody or antigen-binding fragment is any one of antibodies AB212, AB213, AB214, AB215, AB216, AB217, or AB218 (e.g., AB212 or AB216, e.g., AB216). In some embodiments, the reference ADC is an ADC that includes the same linker and the same splicing modulator payload as the disclosed ADC, but includes a different antibody (e.g., AB200).In some embodiments, the cytotoxic and / or cytostatic activity of an ADC may be determined by an in vitro activity assay using, for example, cancer cells with high or moderate levels of BCMA expression.

[0250] In some embodiments, the ADC constructs disclosed herein demonstrate improved in vivo anti-cancer activity, e.g., when compared to an ADC comprising the same linker and / or splicing modulator payload but another antibody (e.g., AB200 or other exemplary anti-BCMA antibodies). In some embodiments, the disclosed ADCs exhibit increased tumor growth inhibition against BCMA-expressing tumors (e.g., OPM2 and / or MOLP8 tumors) when compared to an ADC comprising the same linker and / or splicing modulator payload but another antibody. In some embodiments, the disclosed ADCs comprise an exemplary anti-BCMA antibody or antigen-binding fragment, a linker, and a splicing modulator payload. In some embodiments, the anti-BCMA antibody or antigen-binding fragment is any one of antibodies AB212, AB213, AB214, AB215, AB216, AB217, or AB218 (e.g., AB212 or AB216, e.g., AB216). In some embodiments, the reference ADC is an ADC that includes the same linker and the same splicing modulator payload (e.g., ADL1-D2) as the disclosed ADC, but includes a different antibody (e.g., AB200). In some embodiments, the in vivo anti-cancer activity of the ADC may be determined, for example, by activity assays in xenograft models with high or moderate BCMA expression levels.

[0251] In some embodiments, the ADC constructs disclosed herein demonstrate desirable properties for a therapeutic ADC, including, but not limited to, effective levels of drug loading, low levels of aggregation, stability, retained affinity for BCMA-expressing cells comparable to unconjugated antibodies, potent cytotoxicity against BCMA-expressing cells, low levels of off-target cell killing, and / or effective in vivo anti-cancer activity. In some embodiments, the ADC constructs disclosed herein exhibit in vivo therapeutic efficacy when administered as a single dose.

[0252] The disclosed ADC compounds can selectively deliver effective doses of cytotoxic or cytostatic agents to cancer cells. In some embodiments, the disclosed ADCs have potent cytotoxic and / or cytostatic activity against cells expressing a target antigen (e.g., BCMA). In some embodiments, the cytotoxic and / or cytostatic activity of the ADC depends on the cellular expression of the target antigen. In some embodiments, the disclosed ADCs are particularly effective at killing cancer cells that highly express a target antigen compared to cancer cells that express the same antigen at low levels. In some embodiments, the disclosed ADCs are particularly effective at killing cancer cells that moderately express a target antigen compared to cancer cells that express the same antigen at low levels. Exemplary highly BCMA-expressing cancer cells include, but are not limited to, human myeloma NCI-H929 cells. Exemplary moderately BCMA-expressing cancer cells include, but are not limited to, human myeloma OPM2 cells and human myeloma MOLP8 cells. In some embodiments, the disclosed ADCs are particularly effective at killing cancer cells that express the target antigen while minimizing off-target killing, hi some embodiments, the disclosed ADCs do not exhibit cytotoxic and / or cytostatic effects against cancer cells that do not express the target antigen.

[0253] In some embodiments, cleavage of the ADC releases the splicing modulator from the antibody or antigen-binding fragment and linker. In some embodiments, the linker and / or splicing modulator are designed to facilitate bystander killing (killing of neighboring cells). In some embodiments, the linker and / or splicing modulator are designed to facilitate bystander killing through cleavage after cellular internalization and diffusion of the linker-splicing modulator moiety and / or the splicing modulator moiety alone to neighboring cells. In some embodiments, the linker promotes cellular internalization. In some embodiments, the linker is designed to minimize cleavage in the extracellular environment, thereby reducing toxicity to off-target cells or tissues (e.g., non-cancerous cells or tissues), while maintaining bystander killing of ADC binding to target cells or tissues and / or cancerous tissues surrounding the target cancerous tissue that do not express the antigen targeted by the antibody or antigen-binding fragment of the ADC, but that do express the antigen. In some embodiments, the drug moiety, or the catabolic product of the drug moiety, resulting from cleavage of the ADC is designed for ease of uptake by the target cell or by neighboring cells (i.e., cell permeability). Such splicing modifier drug moieties and catabolic products may be referred to as having "bystander activity," while drug moieties or catabolic products with reduced cell permeability may be referred to as having "no bystander activity."

[0254] In some embodiments, the disclosed ADCs also demonstrate bystander killing activity. Without being bound by theory, the bystander killing activity of an ADC may be particularly beneficial when its penetration into solid tumors is limited and / or target antigen expression is heterogeneous among tumor cells. In some embodiments, the ADCs disclosed herein exhibit improved solubility and target cell penetration compared to the drug moiety itself. In some embodiments, the ADCs disclosed herein exhibit improved cytotoxicity compared to the drug moiety itself. In some embodiments, the ADCs disclosed herein use drug moieties that exhibit low cytotoxicity when evaluated as independent drugs, yet are surprisingly better than ADCs comprising other drug moieties that have higher cytotoxicity when evaluated as independent drugs. In some embodiments, cleavage and release of the splicing modulator improves the cytotoxicity of the ADC compared to comparable treatment with an ADC comprising a non-cleavable linker. In other embodiments, cleavage and release of the splicing modulator is not required for the ADC to possess the desired biological activity.

[0255] Provided herein are ADCs comprising an antibody or antigen-binding fragment thereof (Ab) capable of binding to BCMA, a splicing modulator drug moiety (D), and a linker moiety (L) covalently linking the Ab to D. In some embodiments, the antibody or antigen-binding fragment can bind to BCMA with high specificity and high affinity. In some embodiments, the antibody or antigen-binding fragment is internalized into the target cell upon binding, e.g., into a degradative compartment of the cell. In some embodiments, ADCs may be used that kill cancer cells by internalizing upon binding to the target cell and undergoing degradation to release the splicing modulator drug moiety. The splicing modulator drug moiety may be released from the antibody and / or linker moiety of the ADC by enzymatic action, hydrolysis, oxidation, or any other mechanism.

[0256] An exemplary ADC has formula (I): Ab-(LD)p (I) where Ab = antibody or antigen-binding fragment, L = linker moiety, D = splicing modulator drug moiety, and p = number of splicing modulator drug moieties per antibody or antigen-binding fragment.

[0257] In some embodiments, the antibody or antigen-binding fragment (Ab) used in the described ADCs and compositions is an anti-BCMA antibody or antigen-binding fragment disclosed herein.

[0258] Linker In some embodiments, the linker in the ADCs disclosed herein is sufficiently stable outside a cell to be therapeutically effective. In some embodiments, because the linker is stable outside a cell, the ADC remains intact when present in extracellular conditions (e.g., before transport or delivery into a cell). The term "intact," as used in the context of an ADC, means that the antibody or antigen-binding fragment remains attached to the drug moiety (e.g., a splicing modulator). As used herein, "stable," in the context of a linker or an ADC that includes a linker, means that no more than about 20%, no more than about 15%, no more than about 10%, no more than about 5%, no more than about 3%, or no more than about 1% (or any percentage therebetween) of the linkers present in a sample of the ADC are cleaved (or otherwise not intact, in the case of the entire ADC) when the ADC is present under extracellular conditions. In some embodiments, the linkers and / or ADCs disclosed herein are surprisingly stable compared to ADCs having alternative linkers and / or alternative linkers and / or splicing modulator payloads, hi some embodiments, the ADCs disclosed herein can remain intact for greater than about 48 hours, greater than 60 hours, greater than about 72 hours, greater than about 84 hours, or greater than about 96 hours.

[0259] Whether a linker is stable extracellularly can be determined, for example, by placing the ADC in plasma for a predetermined period of time (e.g., 2, 4, 6, 8, 16, 24, 48, or 72 hours) and then quantifying the amount of free drug moiety present in the plasma. Stability may allow sufficient time for the ADC to localize to target cancer cells and prevent premature release of the drug moiety (which could reduce the therapeutic index of the ADC by indiscriminately damaging both normal and cancer cells). In some embodiments, the linker is stable outside the target cell and, once inside the cell, releases the drug moiety from the ADC, allowing the drug to bind to its target (e.g., to the SF3b spliceosome complex). Thus, in some embodiments, an effective linker will (i) maintain the specific binding properties of the antibody or antigen-binding fragment; (ii) allow for delivery of the drug moiety, e.g., intracellular delivery, through stable association with the antibody or antigen-binding fragment; (iii) remain stable and intact until the ADC has been transported or delivered to its target site; and (iv) achieve the therapeutic effect, e.g., cytotoxic effect, of the drug moiety after cleavage or another release mechanism.

[0260] Linkers can affect the physicochemical properties of ADCs. Many cytotoxic agents are inherently hydrophobic, and linking them to antibodies with additional hydrophobic moieties can lead to aggregation. ADC aggregates are insoluble and often limit the drug loading achievable on the antibody, which can adversely affect ADC efficacy. Protein aggregates in biologics are also commonly associated with increased immunogenicity. As shown below, the linkers disclosed herein result in ADCs with low levels of aggregation and desirable drug loading levels.

[0261] The linkers described in PCT / US2019 / 035015 (WO 2019 / 232449) may be used with the ADCs disclosed herein, which is incorporated by reference for all exemplary linkers and linker attachment points to the antibody.

[0262] Linkers may be "cleavable" or "non-cleavable" (Ducry and Stump (2010) Bioconjugate Chem. 21:5-13). Cleavable linkers are designed to release the drug moiety (e.g., a splicing modulator) when subjected to certain environmental factors, such as when internalized within a target cell, whereas non-cleavable linkers generally rely on degradation of the antibody or antigen-binding fragment itself.

[0263] In some embodiments, the linker is a non-cleavable linker. In some embodiments, the splicing modulator drug moiety of the ADC is released by degradation of the antibody or antigen-binding fragment. Non-cleavable linkers tend to remain covalently associated with at least one amino acid of the antibody and drug, even upon internalization by and degradation within the target cell. Numerous exemplary non-cleavable linkers are described herein, and others are known in the art. Exemplary non-cleavable linkers may include thioether, cyclohexyl, N-succinimidyl 4-(N-maleimidomethyl)cyclohexane-1 carboxylate (SMCC), or N-hydroxysuccinimide (NHS), one or more polyethylene glycol (PEG) moieties (e.g., 1, 2, 3, 4, 5, or 6 PEG moieties), or one or more alkyl moieties (e.g., 1, 2, 3, 4, 5, or 6 alkyl moieties).

[0264] In some other embodiments, the linker is a cleavable linker. A cleavable linker refers to any linker that includes a cleavable moiety. As used herein, the term "cleavable moiety" refers to any chemical bond that can be cleaved. Suitable cleavable chemical bonds are well known in the art and include, but are not limited to, acid-labile bonds, protease / peptidase-labile bonds, photolabile bonds, disulfide bonds, and esterase-labile bonds. A linker that includes a cleavable moiety may allow for release of the splicing modulator drug moiety from the ADC upon cleavage at a specific site in the linker.

[0265] In some embodiments, the linker is cleavable under intracellular conditions such that cleavage of the linker is sufficient to release the splicing modulator drug moiety from the antibody or antigen-binding fragment in the intracellular environment to activate the drug and / or render the drug therapeutically effective. In some embodiments, the splicing modulator drug moiety is not cleaved from the antibody or antigen-binding fragment until the ADC is inside a cell that expresses an antigen specific for the antibody or antigen-binding fragment of the ADC, upon which the splicing modulator drug moiety is cleaved from the antibody or antigen-binding fragment. In some embodiments, the linker comprises a cleavable moiety positioned such that upon cleavage, no portion of the linker or antibody or antigen-binding fragment remains attached to the splicing modulator drug moiety. Exemplary cleavable linkers include acid-labile linkers, protease / peptidase-sensitive linkers, photolabile linkers, dimethyl-containing, disulfide-containing, or sulfonamide-containing linkers.

[0266] In some embodiments, the linker is a pH-sensitive linker, which is sensitive to hydrolysis at a specific pH value. Typically, pH-sensitive linkers are cleavable under acidic conditions. This cleavage strategy generally takes advantage of the lower pH of intracellular compartments, such as endosomes (pH approximately 5-6) and lysosomes (pH approximately 4.8), compared to the cytosol (pH approximately 7.4), to induce hydrolysis of an acid-labile group in the linker, such as a hydrazone (Jain et al. (2015) Pharm Res 32:3526-40). In some embodiments, the linker is an acid-labile and / or hydrolyzable linker. For example, an acid-labile linker that is hydrolyzable in the lysosome and contains an acid-labile group (e.g., hydrazone, semicarbazone, thiosemicarbazone, cis-aconitic acid amide, orthoester, acetal, ketal, etc.) can be used. See, e.g., U.S. Patent Nos. 5,122,368; 5,824,805; 5,622,929; Dubowchik and Walker (1999) Pharm Therapeutics 83:67-123; Neville et al. (1989) Biol Chem. 264:14653-61. Such linkers are relatively stable under neutral pH conditions, such as those found in blood, but become unstable below pH 5.5 or 5.0, which approximates the pH of lysosomes. In some embodiments, the hydrolyzable linker is a thioether linker (e.g., a thioether attached to a therapeutic agent via an acylhydrazone bond) (see, e.g., U.S. Patent No. 5,622,929).

[0267] In some embodiments, the linker is cleavable under reducing conditions. In some embodiments, the linker is cleavable in the presence of a reducing agent such as glutathione or dithiothreitol. In some embodiments, the linker is a cleavable disulfide linker or a cleavable sulfonamide linker.

[0268] In some embodiments, the linker is a cleavable disulfide linker. A variety of disulfide linkers are known in the art, including, for example, SATA (N-succinimidyl-5-acetylthioacetate), SPDP (N-succinimidyl-3-(2-pyridyldithio)propionate), SPDB (N-succinimidyl-3-(2-pyridyldithio)butyrate), and SMPT (N-succinimidyloxycarbonyl-α-methyl-α-(2-pyridyldithio)toluene), including those that can be formed using SPDB and SMPT. See, e.g., Thorpe et al. (1987) Cancer Res. 47:5924-31; Wawrzynczak et al., In Immunoconjugates: Antibody Conjugates in Radioimagery and Therapy of Cancer (C.W. Vogel ed., Oxford U. Press, 1987). See also U.S. Pat. No. 4,880,935. Disulfide linkers are typically used to take advantage of the abundance of intracellular thiols that can facilitate cleavage of the disulfide bond. The intracellular concentration of the most abundant intracellular thiol, reduced glutathione, is generally in the 1-10 nM range, approximately 1,000-fold higher than the most abundant small thiol (i.e., cysteine) in blood, which is approximately 5 μM (Goldmacher et al., In Cancer Drug Discovery and Development: Antibody-Drug Conjugates and Immunotoxins (GLP Hillips ed., Springer, 2013)). Intracellular enzymes of the protein disulfide isomerase family can also contribute to the intracellular cleavage of disulfide linkers. As used herein, a cleavable disulfide linker refers to any linker that contains a cleavable disulfide moiety. The term "cleavable disulfide moiety" refers to a disulfide bond that can be cleaved and / or reduced, for example, by a thiol or an enzyme.

[0269] In some embodiments, the linker is a cleavable sulfonamide linker. As used herein, a cleavable sulfonamide linker refers to any linker that includes a cleavable sulfonamide moiety. The term "cleavable sulfonamide moiety" refers to a sulfonamide group, i.e., a sulfonyl group connected to an amine group, where the sulfur-nitrogen bond can be cleaved.

[0270] In some embodiments, the linker may be a dendritic linker that covalently links two or more drug moieties to an antibody or antigen-binding fragment via a branched, multifunctional linker moiety. See, e.g., Sun et al. (2002) Bioorg Med Chem Lett. 12:2213-5; Sun et al. (2003) Bioorg Med Chem. 11:1761-8. Dendritic linkers can increase the drug-to-antibody molar ratio, i.e., drug loading, which is related to the potency of the ADC. Thus, for example, if an antibody or antigen-binding fragment bears only one reactive cysteine ​​thiol group, multiple splicing modulator drug moieties may be attached via a dendritic linker. In some embodiments, linker moieties or linker-drug moieties may be attached to the antibody or antigen-binding fragment via reduced disulfide crosslinking chemistry or lysine-restricted utilization techniques. See, e.g., WO 2013 / 173391 and WO 2013 / 173393.

[0271] In some embodiments, the linker is cleavable by a cleaving agent, e.g., an enzyme, present in the intracellular environment (e.g., in a lysosome or endosome or caveolae). The linker may be, for example, a peptide linker that is cleaved by an intracellular peptidase or protease enzyme, including, but not limited to, a lysosomal or endosomal protease. In some embodiments, the linker comprises a cleavable peptide moiety. In some embodiments, the linker comprises a cleavable glucuronide moiety.

[0272] In some embodiments, the linker is a cleavable peptide linker. As used herein, a cleavable peptide linker refers to any linker comprising a cleavable peptide moiety. The term "cleavable peptide moiety" refers to any chemically linked amino acids (natural or synthetic amino acid derivatives) that can be cleaved by an agent present in the intracellular environment. In some embodiments, the cleavable peptide moiety is enzymatically cleavable. For example, the linker may comprise a valine-alanine (Val-Ala) sequence or a valine-citrulline (Val-Cit) sequence that is cleavable by a peptidase such as a cathepsin, e.g., cathepsin B. In some embodiments, the linker may comprise an alanine-alanine-aspartic acid (Ala-Ala-Asp) sequence. In some embodiments, the linker may comprise a glutamic acid-valine-citrulline (Glu-Val-Cit) sequence. In some embodiments, the linker is an enzyme-cleavable linker, and the cleavable peptide moiety in the linker is enzymatically cleavable. In some embodiments, the cleavable peptide moiety is cleavable by a lysosomal enzyme, e.g., a cathepsin. In some embodiments, the linker is a cathepsin-cleavable linker. In some embodiments, the cleavable peptide moiety in the linker is cleavable by a lysosomal cysteine ​​cathepsin, such as cathepsin B, C, F, H, K, L, O, S, V, X, or W. In some embodiments, the cleavable peptide moiety is cleavable by cathepsin B. An exemplary dipeptide that can be cleaved by cathepsin B is valine-citrulline (Val-Cit) (Dubowchik et al. (2002) Bioconjugate Chem. 13:855-69).

[0273] In some embodiments, the linker or cleavable peptide moiety in the linker comprises an amino acid unit. In some embodiments, the amino acid unit allows for protease cleavage of the linker, thereby facilitating release of the splicing modulator drug moiety from the ADC upon exposure to one or more intracellular proteases, such as one or more lysosomal enzymes (Doronina et al. (2003) Nat Biotechnol. 21:778-84; Dubowchik and Walker (1999) Pharm Therapeutics 83:67-123). Exemplary amino acid units include, but are not limited to, dipeptides, tripeptides, tetrapeptides, and pentapeptides. Exemplary dipeptides include, but are not limited to, valine-alanine (Val-Ala), valine-citrulline (Val-Cit), alanine-asparagine (Ala-Asn), alanine-phenylalanine (Ala-Phe), phenylalanine-lysine (Phe-Lys), alanine-lysine (Ala-Lys), alanine-valine (Ala-Val), valine-lysine (Val-Lys), lysine-lysine (Lys-Lys), phenylalanine-citrulline (Phe-Cit), leucine-citrulline (Leu-Cit), isoleucine-citrulline (Ile-Cit), tryptophan-citrulline (Trp-Cit), and phenylalanine-alanine (Phe-Ala). Exemplary tripeptides include, but are not limited to, alanine-alanine-asparagine (Ala-Ala-Asn), glycine-valine-citrulline (Gly-Val-Cit), glycine-glycine-glycine (Gly-Gly-Gly), phenylalanine-phenylalanine-lysine (Phe-Phe-Lys), alanine-alanine-aspartic acid (Ala-Ala-Asp), glutamic acid-valine-citrulline (Glu-Val-Cit) (see Anami et al. (2018) Nat Comm. 9:2512), and glycine-phenylalanine-lysine (Gly-Phe-Lys).Other exemplary amino acid units include, but are not limited to, Gly-Phe-Gly-Gly (SEQ ID NO: 125), Gly-Phe-Leu-Gly (SEQ ID NO: 126), Ala-Leu-Ala-Leu (SEQ ID NO: 127), Phe-N9-tosyl-Arg, and Phe-N9-nitro-Arg, as described, for example, in U.S. Patent No. 6,214,345. In some embodiments, the amino acid unit in the linker comprises Val-Ala. In some embodiments, the amino acid unit in the linker comprises Val-Cit. In some embodiments, the amino acid unit in the linker comprises Ala-Ala-Asp. In some embodiments, the amino acid unit in the linker comprises Glu-Val-Cit. The amino acid unit may comprise naturally occurring amino acid residues and / or minor amino acids and / or non-naturally occurring amino acid analogs, such as citrulline. The amino acid units can be designed and optimized for enzymatic cleavage by a particular enzyme, for example, a tumor-associated protease, a lysosomal protease such as cathepsin B, C, D, or S, or a plasmin protease.

[0274] In some embodiments, the linker is a cleavable glucuronide linker. As used herein, a cleavable glucuronide linker refers to any linker that includes a cleavable glucuronide moiety. In some embodiments, the cleavable glucuronide moiety can be cleaved by an enzyme. An exemplary cleavable glucuronide linker has the structure: [ka] Includes.

[0275] The term "cleavable glucuronide moiety" refers to a glycosidic bond that can be cleaved by an agent having glucuronidase activity. In some embodiments, the cleavable glucuronide moiety is cleavable by glucuronidase. In some embodiments, the cleavable glucuronide moiety is cleavable by β-glucuronidase. In some embodiments, the cleavable glucuronide moiety or linker comprises a β-glucuronide, i.e., a glycosidic bond that can be cleaved by β-glucuronidase. β-glucuronidase is a UDP-glucuronosyltransferase that catalyzes the hydrolysis of glycosidic bonds of glucuronides having a β-configuration.

[0276] In some embodiments, the ADCs disclosed herein comprise a cleavable β-glucuronide moiety in the linker that is cleavable by an enzyme. In some embodiments, the cleavable β-glucuronide moiety in the linker is cleavable by a lysosomal enzyme, such as β-glucuronidase. In some embodiments, the linker is a β-glucuronidase-cleavable linker. In some embodiments, the cleavable β-glucuronide moiety in the linker allows cleavage of the linker by β-glucuronidase after internalization of the ADC, thereby facilitating release of the drug moiety from the ADC in the cellular environment.

[0277] In some embodiments, the linker in the ADCs disclosed herein comprises a maleimide moiety. The term "Mal" or "maleimide moiety," as used herein, refers to a compound that contains a maleimide group and is reactive with sulfhydryl groups, such as the sulfhydryl groups of cysteine ​​residues on antibodies or antigen-binding fragments. Other functional groups reactive with sulfhydryl groups (thiols) include, but are not limited to, iodoacetamide, bromoacetamide, vinylpyridine, disulfide, pyridyl disulfide, isocyanate, and isothiocyanate. In some embodiments, the maleimide moiety comprises maleimidocaproyl (MC). In some embodiments, the maleimide moiety is reactive with cysteine ​​residues on antibodies or antigen-binding fragments. In some embodiments, the maleimide moiety is attached to an antibody or antigen-binding fragment via a cysteine ​​residue on the antibody or antigen-binding fragment.

[0278] In some embodiments, the linker comprises a maleimide moiety and a cleavable peptide moiety. In some embodiments, the cleavable peptide moiety comprises an amino acid unit. In some embodiments, the cleavable peptide moiety or amino acid unit comprises Val-Cit. In some embodiments, the cleavable peptide moiety or amino acid unit comprises Val-Ala. In some embodiments, the cleavable peptide moiety or amino acid unit comprises Ala-Ala-Asp. In some embodiments, the cleavable peptide moiety or amino acid unit comprises Glu-Val-Cit. In some embodiments, the linker comprises a maleimide moiety and a cleavable glucuronide moiety. In some embodiments, the cleavable glucuronide moiety comprises β-glucuronide.

[0279] In some embodiments, the linker in the ADCs disclosed herein may comprise at least one spacer unit that links the antibody or antigen-binding fragment to the drug moiety (e.g., a splicing modulator drug moiety). In some embodiments, the spacer unit between the antibody or antigen-binding fragment and the cleavable moiety, if present, links the cleavage site in the linker (e.g., a cleavable peptide moiety or a cleavable glucuronide moiety) to the antibody or antigen-binding fragment. In some embodiments, the spacer unit between the drug moiety and the cleavable moiety, if present, links the cleavage site in the linker (e.g., a cleavable peptide moiety or a cleavable glucuronide moiety) to the drug moiety. In some embodiments, the cleavage site is not present, and a spacer unit is used to link the antibody or antigen-binding fragment to the drug moiety.

[0280] In some embodiments, the linker and / or the spacer unit in the linker are substantially hydrophilic. The use of a hydrophilic linker can reduce the extent to which the drug can be extruded from resistant cancer cells by multidrug resistance (MDR) or functionally similar transporters. In some embodiments, the hydrophilic linker can include one or more polyethylene glycol (PEG) moieties, for example, 1, 2, 3, 4, 5, or 6 PEG moieties.

[0281] In some embodiments, the spacer unit in the linker comprises at least one PEG moiety. In some embodiments, the PEG moiety or spacer unit comprises one or more -(PEG)m-, where m is an integer from 1 to 10 (i.e., m can be 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10). In some embodiments, m ranges from 1 to 10; 2 to 8; 2 to 6; 2 to 5; 2 to 4; or 2 to 3. In some embodiments, m is 2. In some embodiments, the PEG moiety or spacer unit comprises (PEG)2, (PEG)3, (PEG)4, (PEG)5, (PEG)6, (PEG)7, (PEG)8, (PEG)9, or (PEG)10. In some embodiments, the PEG moiety or spacer unit comprises (PEG)2.

[0282] In some embodiments, the spacer unit in the linker comprises an alkyl moiety. In some embodiments, the alkyl moiety or spacer unit comprises one or more -(CH2)n-, where n is an integer from 1 to 10 (i.e., n can be 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10). In some embodiments, n ranges from 1 to 10; 2 to 8; 2 to 6; 2 to 5; 2 to 4; or 2 to 3. In some embodiments, n is 2. In some embodiments, n is 5. In some embodiments, n is 6. In some embodiments, the spacer unit comprises (CH2), (CH2), (CH2), (CH2), (CH2), (CH2), (CH2), (CH2), (CH2), or (CH2). In some embodiments, the alkyl moiety or spacer unit comprises (CH2)2 ("Et"). In some embodiments, the alkyl moiety or spacer unit comprises (CH2)6 ("Hex"). In some embodiments, the alkyl moiety or spacer unit comprises (CH2)2-O-(CH2)2 ("Et-O-Et").

[0283] A spacer unit can be used, for example, to link an antibody or antigen-binding fragment to a drug moiety either directly or indirectly. In some embodiments, the spacer unit directly links the antibody or antigen-binding fragment to the splicing modulator drug moiety. In some embodiments, the antibody or antigen-binding fragment and the splicing modulator drug moiety are linked via a spacer unit comprising one or more PEG moieties (e.g., (PEG)2) or one or more alkyl moieties (e.g., (CH2)2, (CH2)6, or (CH2)2-O-(CH2)2). In some embodiments, the spacer unit indirectly links the antibody or antigen-binding fragment to the splicing modulator drug moiety. In some embodiments, the spacer unit indirectly links the antibody or antigen-binding fragment to the splicing modulator drug moiety through a cleavable moiety (e.g., a cleavable peptide or a cleavable β-glucuronide) and / or a linking moiety, e.g., a maleimide moiety, for joining the spacer unit to the antibody or antigen-binding fragment.

[0284] In various embodiments, the spacer unit is attached to the antibody or antigen-binding fragment (i.e., antibody or antigen-binding fragment) via a maleimide moiety. A spacer unit that is attached to the antibody or antigen-binding fragment via a maleimide moiety is referred to herein as a "Mal-spacer unit." In some embodiments, the Mal-spacer unit comprises a PEG moiety. In some embodiments, the Mal-spacer unit comprises an alkyl moiety. In some embodiments, the Mal-spacer unit comprises maleimidocaproyl (MC).

[0285] In some embodiments, the linker comprises the structure: Mal-spacer unit. In some embodiments, the Mal-spacer unit or linker comprises MC. In some embodiments, the linker comprises the structure: MC. In some embodiments, the linker comprises the structure: Mal-(CH2)2 ("Mal-Et"). In some embodiments, the linker comprises the structure: Mal-(CH2)6 ("Mal-Hex"). In some embodiments, the linker comprises the structure: Mal-(CH2)2-O-(CH2)2 ("Mal-Et-O-Et"). In some embodiments, the linker comprises the structure: Mal-(PEG)2. In some embodiments, the linker comprises the structure: Mal-(PEG)2-CO.

[0286] In some embodiments, the linker comprises a Mal-spacer unit and a cleavable peptide moiety. In some embodiments, the cleavable peptide moiety comprises an amino acid unit. In some embodiments, the cleavable peptide moiety or amino acid unit comprises Val-Cit, Val-Ala, Ala-Ala-Asp, or Glu-Val-Cit. In some embodiments, the cleavable peptide moiety or amino acid unit comprises Val-Cit. In some embodiments, the cleavable peptide moiety or amino acid unit comprises Val-Ala. In some embodiments, the cleavable peptide moiety or amino acid unit comprises Ala-Ala-Asp. In some embodiments, the cleavable peptide moiety or amino acid unit comprises Glu-Val-Cit. In some embodiments, the linker comprises a Mal-spacer unit and a cleavable glucuronide moiety. In some embodiments, the cleavable glucuronide moiety comprises a β-glucuronide.

[0287] In some embodiments, a maleimide moiety or Mal-spacer unit links the antibody or antigen-binding fragment to the cleavable moiety in the linker. In some embodiments, the cleavable moiety in the linker comprises a cleavable peptide moiety. In some embodiments, the cleavable peptide moiety comprises an amino acid unit. In some embodiments, the cleavable peptide moiety or amino acid unit comprises Val-Cit, Val-Ala, Ala-Ala-Asp, or Glu-Val-Cit. In some embodiments, the cleavable moiety in the linker comprises a cleavable glucuronide moiety. In some embodiments, the cleavable glucuronide moiety comprises a β-glucuronide.

[0288] In some embodiments, a Mal-spacer unit links the antibody or antigen-binding fragment to the cleavable peptide moiety. In some embodiments, the linker comprises a Mal-spacer unit-peptide.

[0289] In some embodiments, the linker comprises the structure: Mal-spacer unit-Val-Cit. In some embodiments, the Mal-spacer unit comprises MC. In some embodiments, the linker comprises MC-Val-Cit. In some embodiments, the linker comprises MC-(PEG)2-Val-Cit.

[0290] In some embodiments, the linker comprises the structure: Mal-spacer unit-Val-Ala. In some embodiments, the Mal-spacer unit comprises MC. In some embodiments, the linker comprises MC-Val-Ala.

[0291] In some embodiments, the linker comprises the structure: Mal-spacer unit-Ala-Ala-Asp. In some embodiments, the Mal-spacer unit comprises MC. In some embodiments, the linker comprises MC-Ala-Ala-Asp.

[0292] In some embodiments, the linker comprises the structure: Mal-spacer unit-Glu-Val-Cit. In some embodiments, the Mal-spacer unit comprises MC. In some embodiments, the linker comprises MC-Glu-Val-Cit.

[0293] In some embodiments, a Mal-spacer unit links the antibody or antigen-binding fragment to a cleavable glucuronide moiety. In some embodiments, the linker comprises the structure: Mal-spacer unit-β-glucuronide. In some embodiments, the Mal-spacer unit comprises MC. In some embodiments, the linker comprises MC-β-glucuronide.

[0294] In some embodiments, the cleavable moiety in the linker is directly linked to the splicing modulator drug moiety. In other embodiments, a spacer unit links the cleavable moiety in the linker to the splicing modulator drug moiety. In some embodiments, the splicing modulator is linked to the cleavable moiety in the linker by a spacer unit.

[0295] A spacer unit may be "self-immolative" or "non-self-immolative." A "non-self-immolative" spacer unit is one in which some or all of the spacer unit remains attached to the splicing modulator drug moiety upon cleavage of the linker. Examples of non-self-immolative spacer units include, but are not limited to, a glycine spacer unit and a glycine-glycine spacer unit. A non-self-immolative spacer unit may eventually degrade over time, but does not immediately release the entire linked native drug moiety, even under cellular conditions. A "self-immolative" spacer unit allows for release of the native drug moiety under intracellular conditions. A "native drug" or "native drug moiety" is one in which no part of the spacer unit or other chemical modification remains after cleavage / degradation of the spacer unit.

[0296] Self-immolative chemistries are known in the art and can be readily selected for the disclosed ADCs. In some embodiments, the spacer unit connecting the cleavable moiety in the linker to the splicing modulator drug moiety is self-immolative and undergoes self-immolation simultaneously with, or immediately before or after, cleavage of the cleavable moiety under intracellular conditions. In some embodiments, cleavage of the conjugate releases the splicing modulator from the antibody or antigen-binding fragment and the linker.

[0297] In some embodiments, the spacer unit connecting the cleavable moiety in the linker to the splicing modulator is self-immolative. In certain embodiments, the splicing modulator is connected to the cleavable moiety of the linker by a self-immolative spacer unit, the cleavable moiety comprises Val-Cit, and an MC joins the cleavable moiety to the antibody or antigen-binding fragment. In certain embodiments, the splicing modulator is connected to the cleavable moiety in the linker by a self-immolative spacer unit, the cleavable moiety comprises Val-Cit, and an MC-(PEG)2 joins the cleavable moiety to the antibody or antigen-binding fragment. In certain embodiments, the splicing modulator is connected to the cleavable moiety in the linker by a self-immolative spacer unit, the cleavable moiety comprises Val-Ala, and an MC joins the cleavable moiety to the antibody or antigen-binding fragment. In certain embodiments, the splicing modulator is connected to the cleavable moiety in the linker by a self-immolative spacer unit, the cleavable moiety comprises Ala-Ala-Asp, and an MC joins the cleavable moiety to the antibody or antigen-binding fragment. In certain embodiments, the splicing modulator is linked to the cleavable moiety in the linker by a self-immolative spacer unit, the cleavable moiety comprises Glu-Val-Cit, and an MC joins the cleavable moiety to the antibody or antigen-binding fragment. In certain embodiments, the splicing modulator is linked to the cleavable moiety in the linker by a self-immolative spacer unit, the cleavable moiety comprises a β-glucuronide, and an MC joins the cleavable moiety to the antibody or antigen-binding fragment.

[0298] In some embodiments, the spacer unit (e.g., self-immolative spacer unit) that connects the cleavable moiety in the linker to the splicing modulator comprises a p-aminobenzyl unit. In some embodiments, p-aminobenzyl alcohol (pABOH) is connected to the amino acid unit or other cleavable moiety in the linker via an amide bond, creating a carbamate, methylcarbamate, or carbonate between the pABOH and the drug moiety (Hamann et al. (2005) Expert Opin Ther Patents 15:1087-103).

[0299] In some embodiments, the spacer unit (e.g., a self-immolative spacer unit) in the linker that connects the cleavable moiety to the splicing modulator is or includes p-aminobenzyloxycarbonyl (pABC). Without being bound by theory, the self-immolation of pABC is believed to involve a spontaneous 1,6-elimination reaction (Jain et al. (2015) Pharm Res. 32:3526-40). In some embodiments, the spacer unit (e.g., a self-immolative spacer unit) in the linker that connects the cleavable moiety to the splicing modulator is or includes p-aminobenzyl (pAB). In some embodiments, the self-immolation of pAB involves a spontaneous 1,6-elimination reaction.

[0300] In various embodiments, a self-immolative spacer unit connects the cleavable moiety in the linker to the splicing modulator, hi some embodiments, the self-immolative spacer unit in the linker comprises a p-aminobenzyl unit.

[0301] In some embodiments, the self-immolative spacer unit in the linker consists of or comprises pABC. In some embodiments, pABC links the cleavable moiety in the linker to the splicing modulator. In some embodiments, pABC undergoes self-immolation upon cleavage of the cleavable moiety, releasing the splicing modulator from the ADC in its native, active form.

[0302] In some embodiments, the structure of pABC used in the disclosed ADCs is shown below: [ka]

[0303] In some embodiments, the cleavable moiety in the linker comprises a cleavable peptide moiety. In some embodiments, the cleavable peptide moiety comprises an amino acid unit. In some embodiments, the linker comprises the amino acid unit-pABC. In some embodiments, the cleavable peptide moiety or amino acid unit comprises Val-Cit, Val-Ala, Ala-Ala-Asp, or Glu-Val-Cit. In some embodiments, the linker comprises Val-Cit-pABC. In some embodiments, the linker comprises Val-Ala-pABC. In some embodiments, the linker comprises Ala-Ala-Asp-pABC. In some embodiments, the linker comprises Glu-Val-Cit-pABC. In some embodiments, the cleavable moiety in the linker comprises a cleavable glucuronide moiety. In some embodiments, the cleavable glucuronide moiety comprises a β-glucuronide. In some embodiments, the linker comprises a β-glucuronide-pABC.

[0304] In some embodiments, the antibody or antigen-binding fragment of the ADC is conjugated to the splicing modulator drug moiety via a linker, where the linker comprises a Mal-spacer unit (e.g., MC, MC-(PEG)2), a cleavable amino acid unit, and pABC. In some embodiments, the spacer unit comprises a PEG moiety. In some embodiments, the Mal-spacer unit comprises MC. In some embodiments, the cleavable linker comprises Mal-spacer unit-amino acid unit-pABC. In some embodiments, the cleavable linker comprises MC-amino acid unit-pABC. In some embodiments, the cleavable linker comprises MC-Val-Cit-pABC, MC-Val-Ala-pABC, MC-Ala-Ala-Asp-pABC, MC-Glu-Val-Cit-pABC, or MC-(PEG)2-Val-Cit-pABC. In some embodiments, the cleavable linker comprises MC-Val-Cit-pABC. In some embodiments, the cleavable linker comprises MC-Val-Ala-pABC. In some embodiments, the cleavable linker comprises MC-Ala-Ala-Asp-pABC. In some embodiments, the cleavable linker comprises MC-Glu-Val-Cit-pABC. In some embodiments, the cleavable linker comprises MC-(PEG)2-Val-Cit-pABC.

[0305] In some embodiments, the antibody or antigen-binding fragment of the ADC is conjugated to the splicing modulator drug moiety via a linker, where the linker comprises a Mal-spacer unit (e.g., MC), a cleavable β-glucuronide, and pABC. In some embodiments, the Mal-spacer unit comprises MC. In some embodiments, the cleavable linker comprises Mal-spacer unit-β-glucuronide-pABC. In some embodiments, the cleavable linker comprises MC-β-glucuronide-pABC.

[0306] In some embodiments, the anti-BCMA antibody or antigen-binding fragment is tethered to the splicing modulator by a linker comprising MC-Val-Cit-pABC. In some embodiments, the anti-BCMA antibody or antigen-binding fragment is tethered to the splicing modulator by a linker comprising MC-Val-Ala-pABC. In some embodiments, the anti-BCMA antibody or antigen-binding fragment is tethered to the splicing modulator by a linker comprising MC-Ala-Ala-Asp-pABC. In some embodiments, the anti-BCMA antibody or antigen-binding fragment is tethered to the splicing modulator by a linker comprising MC-Glu-Val-Cit-pABC. In some embodiments, the anti-BCMA antibody or antigen-binding fragment is tethered to the splicing modulator by a linker comprising MC-(PEG)2-Val-Cit-pABC. In some embodiments, the anti-BCMA antibody or antigen-binding fragment is tethered to the splicing modulator by a linker comprising MC-β-glucuronide-pABC.

[0307] In some embodiments, the self-immolative spacer unit in the linker consists of or comprises p-aminobenzyl (pAB). In some embodiments, pAB links the cleavable moiety in the linker to the splicing modulator. In some embodiments, pAB undergoes self-immolation upon cleavage of the cleavable moiety, releasing the splicing modulator from the ADC in its native, active form.

[0308] In some embodiments, the structure of pAB used in the disclosed ADCs is shown below: [ka]

[0309] In some embodiments, the cleavable moiety in the linker comprises a cleavable peptide moiety. In some embodiments, the cleavable peptide moiety comprises an amino acid unit. In some embodiments, the linker comprises the amino acid unit -pAB. In some embodiments, the cleavable peptide moiety or amino acid unit comprises Val-Cit, Val-Ala, Ala-Ala-Asp, or Glu-Val-Cit. In some embodiments, the linker comprises Val-Cit-pAB. In some embodiments, the linker comprises Val-Ala-pAB. In some embodiments, the linker comprises Ala-Ala-Asp-pAB. In some embodiments, the linker comprises Glu-Val-Cit-pAB. In some embodiments, the cleavable moiety in the linker comprises a cleavable glucuronide moiety. In some embodiments, the cleavable glucuronide moiety comprises a β-glucuronide. In some embodiments, the linker comprises a β-glucuronide-pAB.

[0310] In some embodiments, the antibody or antigen-binding fragment of the ADC is conjugated to the splicing modulator drug moiety via a linker, where the linker comprises a Mal-spacer unit (e.g., MC, MC-(PEG)2), a cleavable amino acid unit, and pAB. In some embodiments, the spacer unit comprises a PEG moiety. In some embodiments, the Mal-spacer unit comprises MC. In some embodiments, the cleavable linker comprises Mal-spacer unit-amino acid unit-pAB. In some embodiments, the cleavable linker comprises MC-Val-Cit-pAB, MC-Val-Ala-pAB, MC-Ala-Ala-Asp-pAB, MC-Glu-Val-Cit-pAB, or MC-(PEG)2-Val-Cit-pAB. In some embodiments, the cleavable linker comprises MC-Val-Cit-pAB. In some embodiments, the cleavable linker comprises MC-Val-Ala-pAB. In some embodiments, the cleavable linker comprises MC-Ala-Ala-Asp-pAB. In some embodiments, the cleavable linker comprises MC-Glu-Val-Cit-pAB. In some embodiments, the cleavable linker comprises MC-(PEG)2-Val-Cit-pAB.

[0311] In some embodiments, the antibody or antigen-binding fragment of the ADC is conjugated to the splicing modulator drug moiety via a linker, where the linker comprises a Mal-spacer unit (e.g., MC), a cleavable β-glucuronide, and pAB. In some embodiments, the Mal-spacer unit comprises MC. In some embodiments, the cleavable linker comprises Mal-spacer unit-β-glucuronide-pAB. In some embodiments, the cleavable linker comprises MC-β-glucuronide-pAB.

[0312] In some embodiments, the anti-BCMA antibody or antigen-binding fragment is tethered to the splicing modulator by a linker comprising MC-Val-Cit-pAB. In some embodiments, the anti-BCMA antibody or antigen-binding fragment is tethered to the splicing modulator by a linker comprising MC-Val-Ala-pAB. In some embodiments, the anti-BCMA antibody or antigen-binding fragment is tethered to the splicing modulator by a linker comprising MC-Ala-Ala-Asp-pAB. In some embodiments, the anti-BCMA antibody or antigen-binding fragment is tethered to the splicing modulator by a linker comprising MC-Glu-Val-Cit-pAB. In some embodiments, the anti-BCMA antibody or antigen-binding fragment is tethered to the splicing modulator by a linker comprising MC-(PEG)2-Val-Cit-pAB. In some embodiments, the anti-BCMA antibody or antigen-binding fragment is tethered to the splicing modulator by a linker comprising MC-β-glucuronide-pAB.

[0313] In some embodiments, a splicing modulator is coupled to an antibody or antigen-binding fragment via a Val-Cit cleavable moiety and a Mal-spacer unit in a linker coupled to a pABC or pAB self-immolative spacer unit. In some other embodiments, a splicing modulator is coupled to an antibody or antigen-binding fragment via a Val-Ala cleavable moiety and a Mal-spacer unit in a linker coupled to a pABC or pAB self-immolative spacer unit. In some other embodiments, a splicing modulator is coupled to an antibody or antigen-binding fragment via an Ala-Ala-Asp cleavable moiety and a Mal-spacer unit in a linker coupled to a pABC or pAB self-immolative spacer unit. In some other embodiments, a splicing modulator is coupled to an antibody or antigen-binding fragment via a Glu-Val-Cit cleavable moiety and a Mal-spacer unit in a linker coupled to a pABC or pAB self-immolative spacer unit. In some other embodiments, the splicing modulator is conjugated to the antibody or antigen-binding fragment via a Mal-spacer unit in a linker conjugated to a β-glucuronide cleavable moiety and a pABC or pAB self-immolative spacer unit. In some embodiments, the spacer unit comprises a PEG moiety. In some embodiments, the Mal-spacer unit comprises MC. In some embodiments, the Mal-spacer unit comprises MC and a PEG moiety. In some embodiments, the Mal-spacer unit comprises MC-(PEG)m-, where m is an integer between 1 and 10 (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10). In some embodiments, the Mal-spacer unit comprises MC-(PEG)2.

[0314] In some other embodiments, the splicing modulator is coupled to the antibody or antigen-binding fragment via a Mal-spacer unit in a linker coupled to a Val-Cit cleavable moiety and a non-self-immolative spacer unit. In some other embodiments, the splicing modulator is coupled to the antibody or antigen-binding fragment via a Mal-spacer unit in a linker coupled to a Val-Ala cleavable moiety and a non-self-immolative spacer unit. In some other embodiments, the splicing modulator is coupled to the antibody or antigen-binding fragment via a Mal-spacer unit in a linker coupled to an Ala-Ala-Asp cleavable moiety and a non-self-immolative spacer unit. In some other embodiments, the splicing modulator is coupled to the antibody or antigen-binding fragment via a Mal-spacer unit in a linker coupled to a Glu-Val-Cit cleavable moiety and a non-self-immolative spacer unit. In some other embodiments, the splicing modulator is conjugated to the antibody or antigen-binding fragment via a Mal-spacer unit in a linker conjugated to a β-glucuronide cleavable moiety and a non-self-immolative spacer unit. In some embodiments, the spacer unit comprises a PEG moiety. In some embodiments, the Mal-spacer unit comprises MC. In some embodiments, the Mal-spacer unit comprises MC and a PEG moiety. In some embodiments, the Mal-spacer unit comprises MC-(PEG)m-, where m is an integer between 1 and 10 (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10). In some embodiments, the Mal-spacer unit comprises MC-(PEG)2.

[0315] In some embodiments, the ADC of the disclosure has formula (I): Ab-(LD)p (I) (In the ceremony Ab is an antibody or antigen-binding fragment capable of binding to BCMA; D is a splicing modulator; L is a linker covalently linking Ab to D; and p is an integer from 1 to 15. Includes.

[0316] In some embodiments, the antibody or antigen-binding fragment (Ab) of the ADC is conjugated to the splicing modulator drug moiety via a linker, where the linker is any of the linkers disclosed herein or incorporated by reference, or comprises one or more components of any of the linkers disclosed herein or incorporated by reference.

[0317] In some embodiments, the linker is a non-cleavable linker. In some embodiments, the linker comprises at least one spacer unit that connects the antibody or antigen-binding fragment to the drug moiety. In some embodiments, the spacer unit comprises at least one alkyl moiety. In some embodiments, the spacer unit comprises at least one PEG moiety.

[0318] In some embodiments, the spacer unit in the linker is attached to the antibody or antigen-binding fragment via a maleimide moiety ("Mal-spacer unit"). In some embodiments, the Mal-spacer unit comprises at least one alkyl moiety. In some embodiments, the Mal-spacer unit comprises at least one PEG moiety. In some embodiments, the Mal-spacer unit comprises MC. In some embodiments, the Mal-spacer unit attaches the antibody or antigen-binding fragment to the drug moiety.

[0319] In some embodiments, the Mal-spacer unit or linker comprises Mal-(PEG)2, Mal-(PEG)3, Mal-(PEG)4, Mal-(PEG)5, Mal-(PEG)6, Mal-(PEG)7, or Mal-(PEG)8. In some embodiments, the Mal-spacer unit or linker comprises Mal-(PEG)2. In some embodiments, the Mal-spacer unit or linker comprises Mal-(PEG)2-CO, Mal-(PEG)3-CO, Mal-(PEG)4-CO, Mal-(PEG)5-CO, Mal-(PEG)6-CO, Mal-(PEG)7-CO, or Mal-(PEG)8-CO. In some embodiments, the Mal-spacer unit or linker comprises Mal-(PEG)2-CO. In some embodiments, the Mal-spacer unit or linker comprises MC. In some embodiments, the Mal-spacer unit or linker comprises Mal-(CH2)6 ("Mal-Hex"). In some embodiments, the Mal-spacer unit or linker comprises Mal-(CH2)2 ("Mal-Et"). In some embodiments, the Mal-spacer unit or linker comprises Mal-(CH2)2-O-(CH2)2 ("Mal-Et-O-Et").

[0320] In some embodiments, the Mal-spacer unit or linker comprises Mal-(PEG)2-CO. In some embodiments, the Mal-spacer unit or linker comprises Mal-(PEG)2-CO and at least one additional spacer unit. In some embodiments, Mal-(PEG)2-CO links the antibody or antigen-binding fragment to the drug moiety. In some embodiments, the linker comprises or consists of Mal-(PEG)2-CO. An example of a "Mal-(PEG)2-CO" linker is also referred to herein as an "ADL2" or "ADL2" linker.

[0321] In some embodiments, the Mal-spacer unit or linker comprises MC. In some embodiments, the Mal-spacer unit or linker comprises MC and at least one additional spacer unit. In some embodiments, the MC connects the antibody or antigen-binding fragment to the drug moiety. In some embodiments, the linker comprises or consists of MC. Examples of "MC" linkers are also referred to herein as "ADL10" or "ADL10" linkers.

[0322] In some embodiments, the Mal-spacer unit or linker comprises Mal-(CH2)6 ("Mal-Hex"). In some embodiments, the Mal-spacer unit or linker comprises Mal-Hex and at least one additional spacer unit. In some embodiments, the Mal-Hex connects the antibody or antigen-binding fragment to the drug moiety. In some embodiments, the linker comprises Mal-Hex. An example of a "Mal-Hex" linker is also referred to herein as an "ADL12" or "ADL12" linker.

[0323] In some embodiments, the Mal-spacer unit or linker comprises Mal-(CH2)2 ("Mal-Et"). In some embodiments, the Mal-spacer unit or linker comprises Mal-Et and at least one additional spacer unit. In some embodiments, Mal-Et connects the antibody or antigen-binding fragment to the drug moiety. In some embodiments, the linker comprises Mal-Et. An example of a "Mal-Et" linker is also referred to herein as an "ADL14" or "ADL14" linker.

[0324] In some embodiments, the Mal-spacer unit or linker comprises Mal-(CH2)2-O-(CH2)2 ("Mal-Et-O-Et"). In some embodiments, the Mal-spacer unit or linker comprises Mal-Et-O-Et and at least one additional spacer unit. In some embodiments, Mal-Et-O-Et connects the antibody or antigen-binding fragment to the drug moiety. In some embodiments, the linker comprises Mal-Et-O-Et. An example of a "Mal-Et-O-Et" linker is also referred to herein as an "ADL15" or "ADL15" linker.

[0325] In some other embodiments, the Mal-spacer unit links the antibody or antigen-binding fragment to the cleavable moiety in the linker. In some embodiments, the cleavable moiety in the linker is a cleavable peptide moiety, such as an amino acid unit. In some embodiments, the cleavable peptide moiety is an amino acid unit. In some embodiments, the cleavable peptide moiety or amino acid unit is Val-Cit, Val-Ala, Ala-Ala-Asp, or Glu-Val-Cit. In some embodiments, the cleavable moiety in the linker is a cleavable glucuronide moiety, such as a β-glucuronide. In some embodiments, the cleavable glucuronide moiety is a β-glucuronide. In some embodiments, the Mal-spacer unit comprises MC. In some embodiments, the Mal-spacer unit comprises MC and a PEG moiety. In some embodiments, the Mal-spacer unit comprises MC-(PEG)m-, where m is an integer from 1 to 10 (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10). In some embodiments, the Mal-spacer unit comprises MC-(PEG)2.

[0326] In some embodiments, the linker comprises MC-Val-Cit. In some embodiments, the linker comprises MC-(PEG)2-Val-Cit. In some embodiments, the linker comprises MC-Val-Ala. In some embodiments, the linker comprises MC-Ala-Ala-Asp. In some embodiments, the linker comprises MC-Glu-Val-Cit. In some embodiments, the linker comprises MC-β-glucuronide.

[0327] In some embodiments, a spacer unit in the linker that links the cleavable moiety to the splicing regulator, hi some embodiments, the spacer unit that links the cleavable moiety to the splicing regulator is self-immolative.

[0328] In some embodiments, the spacer unit connecting the cleavable moiety in the linker to the splicing modulator comprises pABC. In some embodiments, pABC connects the cleavable moiety to the splicing modulator. In some embodiments, the cleavable moiety is a cleavable peptide moiety, e.g., an amino acid unit. In some embodiments, the cleavable peptide moiety is an amino acid unit. In some embodiments, the linker comprises the amino acid unit-pABC. In some embodiments, the amino acid unit comprises Val-Cit, Val-Ala, Ala-Ala-Asp, or Glu-Val-Cit. In some embodiments, the linker comprises Val-Cit-pABC. In some embodiments, the linker comprises Val-Ala-pABC. In some embodiments, the linker comprises Ala-Ala-Asp-pABC. In some embodiments, the linker comprises Glu-Val-Cit-pABC. In some embodiments, the cleavable moiety is a cleavable glucuronide moiety, e.g., a β-glucuronide. In some embodiments, the cleavable glucuronide moiety is a β-glucuronide. In some embodiments, the linker comprises β-glucuronide-pABC.

[0329] In some embodiments, the linker comprises Val-Cit-pABC. In some embodiments, the linker comprises Val-Cit-pABC and an MC Mal-spacer unit that joins the linker to the antibody or antigen-binding fragment. In some embodiments, the linker comprises MC-Val-Cit-pABC. In some embodiments, the linker comprises MC-Val-Cit-pABC and at least one additional spacer unit. An example of an MC-Val-Cit-pABC linker is also referred to herein as "ADL1" or the "ADL1" linker. The structure of ADL1 and other exemplary linkers are shown in Table 13.

[0330] In some embodiments, the linker comprises Val-Ala-pABC. In some embodiments, the linker comprises Val-Ala-pABC and an MC Mal-spacer unit that joins the linker to the antibody or antigen-binding fragment. In some embodiments, the linker comprises MC-Val-Ala-pABC. In some embodiments, the linker comprises MC-Val-Ala-pABC and at least one additional spacer unit. An example of an MC-Val-Ala-pABC linker is also referred to herein as "ADL6" or the "ADL6" linker. The structure of ADL6 and other exemplary linkers are shown in Table 13.

[0331] In some embodiments, the linker comprises β-glucuronide-pABC. In some embodiments, the linker comprises β-glucuronide-pABC and an MC Mal-spacer unit that joins the linker to the antibody or antigen-binding fragment. In some embodiments, the linker comprises MC-β-glucuronide-pABC. In some embodiments, the linker comprises MC-β-glucuronide-pABC and at least one additional spacer unit. An example of MC-β-glucuronide-pABC is also referred to herein as "ADL13" or an "ADL13" linker. The structure of ADL13 and other exemplary linkers are shown in Table 13.

[0332] In some embodiments, the linker comprises Ala-Ala-Asp-pABC. In some embodiments, the linker comprises Ala-Ala-Asp-pABC and an MC Mal-spacer unit that joins the linker to the antibody or antigen-binding fragment. In some embodiments, the linker comprises MC-Ala-Ala-Asp-pABC. In some embodiments, the linker comprises MC-Ala-Ala-Asp-pABC and at least one additional spacer unit. An example of an MC-Ala-Ala-Asp-pABC linker is also referred to herein as "ADL21" or the "ADL21" linker. The structure of ADL21 and other exemplary linkers are shown in Table 13.

[0333] In some embodiments, the linker comprises Val-Cit-pABC. In some embodiments, the linker comprises Val-Cit-pABC and an MC-(PEG)2Mal-spacer unit connecting the linker to the antibody or antigen-binding fragment. In some embodiments, the linker comprises MC-(PEG)2-Val-Cit-pABC. In some embodiments, the linker comprises MC-(PEG)2-Val-Cit-pABC and at least one additional spacer unit. An example of an MC-(PEG)2-Val-Cit-pABC linker is also referred to herein as "ADL22" or the "ADL22" linker. The structure of ADL22 and other exemplary linkers are shown in Table 13.

[0334] In some embodiments, the linker comprises Glu-Val-Cit-pABC. In some embodiments, the linker comprises Glu-Val-Cit-pABC and an MC Mal-spacer unit that joins the linker to the antibody or antigen-binding fragment. In some embodiments, the linker comprises MC-Glu-Val-Cit-pABC. In some embodiments, the linker comprises MC-Glu-Val-Cit-pABC and at least one additional spacer unit. An example of an MC-Glu-Val-Cit-pABC linker is also referred to herein as "ADL23" or the "ADL23" linker. The structure of ADL23 and other exemplary linkers are shown in Table 13.

[0335] In some embodiments, the spacer unit in the linker linking the cleavable moiety to the splicing modulator comprises pAB. In some embodiments, pAB links the cleavable moiety to the splicing modulator. In some embodiments, the cleavable moiety is a cleavable peptide moiety, e.g., an amino acid unit. In some embodiments, the cleavable peptide moiety is an amino acid unit. In some embodiments, the linker comprises the amino acid unit-pAB. In some embodiments, the amino acid unit comprises Val-Cit, Val-Ala, Ala-Ala-Asp, or Glu-Val-Cit. In some embodiments, the linker comprises Val-Cit-pAB. In some embodiments, the linker comprises Val-Ala-pAB. In some embodiments, the linker comprises Ala-Ala-Asp-pAB. In some embodiments, the linker comprises Glu-Val-Cit-pAB. In some embodiments, the cleavable moiety is a cleavable glucuronide moiety, e.g., a β-glucuronide. In some embodiments, the cleavable glucuronide moiety is a β-glucuronide. In some embodiments, the linker comprises β-glucuronide-pAB.

[0336] In some embodiments, the linker comprises Val-Ala-pAB. In some embodiments, the linker comprises Val-Ala-pAB and an MC Mal-spacer unit that joins the linker to the antibody or antigen-binding fragment. In some embodiments, the linker comprises MC-Val-Ala-pAB. In some embodiments, the linker comprises MC-Val-Ala-pAB and at least one additional spacer unit. An example of an MC-Val-Ala-pAB linker is also referred to herein as an "ADL5" or "ADL5" linker.

[0337] In some embodiments, the linker comprises Val-Cit-pAB. In some embodiments, the linker comprises Val-Cit-pAB and an MC Mal-spacer unit that joins the linker to the antibody or antigen-binding fragment. In some embodiments, the linker comprises MC-Val-Cit-pAB. In some embodiments, the linker comprises MC-Val-Cit-pAB and at least one additional spacer unit. An example of an MC-Val-Cit-pAB linker is also referred to herein as an "ADL7" or "ADL7" linker.

[0338] In some embodiments, the antibody or antigen-binding fragment is conjugated to the splicing modulator drug moiety via an ADL1, ADL2, ADL5, ADL6, ADL7, ADL10, ADL12, ADL13, ADL14, ADL15, ADL21, ADL22, or ADL23 linker. In some embodiments, the antibody or antigen-binding fragment is conjugated to the splicing modulator drug moiety via an ADL1, ADL6, ADL13, ADL21, ADL22, or ADL23 linker. In various embodiments, it has been discovered that ADCs comprising an ADL1, ADL6, ADL13, ADL21, ADL22, or ADL23 linker (e.g., an ADL1 linker) and a splicing modulator drug moiety disclosed herein demonstrate desirable properties for therapeutic ADCs. In some embodiments, such properties include, but are not limited to, effective levels of drug loading, low levels of aggregation, stability under storage conditions or while circulating in the body (e.g., serum stability), retention of affinity for target antigen-expressing cells comparable to unconjugated antibodies, potent cytotoxicity against target antigen-expressing cells, low levels of off-target cell killing, and / or effective in vivo anti-cancer activity, all when compared to ADCs that use other linker-payloads.

[0339] In some embodiments, the ADC comprises an ADL1-splice modulator and an antibody or antigen-binding fragment capable of binding to BCMA. In some embodiments, the ADC comprises an ADL2-splice modulator and an antibody or antigen-binding fragment capable of binding to BCMA. In some embodiments, the ADC comprises an ADL5-splice modulator and an antibody or antigen-binding fragment capable of binding to BCMA. In some embodiments, the ADC comprises an ADL6-splice modulator and an antibody or antigen-binding fragment capable of binding to BCMA. In some embodiments, the ADC comprises an ADL7-splice modulator and an antibody or antigen-binding fragment capable of binding to BCMA. In some embodiments, the ADC comprises an ADL10-splice modulator and an antibody or antigen-binding fragment capable of binding to BCMA. In some embodiments, the ADC comprises an ADL12-splice modulator and an antibody or antigen-binding fragment capable of binding to BCMA. In some embodiments, the ADC comprises an ADL13-splice modulator and an antibody or antigen-binding fragment capable of binding to BCMA. In some embodiments, the ADC comprises an ADL14-splice modulator and an antibody or antigen-binding fragment capable of binding to BCMA. In some embodiments, the ADC comprises an ADL15-splice modulator and an antibody or antigen-binding fragment capable of binding to BCMA. In some embodiments, the ADC comprises an ADL21-splice modulator and an antibody or antigen-binding fragment capable of binding to BCMA. In some embodiments, the ADC comprises an ADL22-splice modulator and an antibody or antigen-binding fragment capable of binding to BCMA. In some embodiments, the ADC comprises an ADL23-splice modulator and an antibody or antigen-binding fragment capable of binding to BCMA. In some embodiments, the ADC retains the ability to target and internalize in BCMA-expressing cancer cells.

[0340] In some embodiments, the antibody or antigen-binding fragment of the ADC disclosed herein is an internalizing antibody or internalizing antigen-binding fragment. In some embodiments, the antibody or antigen-binding fragment is capable of binding to BCMA and comprises three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:2 (HCDR2), and SEQ ID NO:3 (HCDR3), as defined by the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:4 (LCDR1), SEQ ID NO:5 (LCDR2), and SEQ ID NO:6 (LCDR3); or three HCDRs comprising the amino acid sequences of SEQ ID NO:37 (HCDR1), SEQ ID NO:38 (HCDR2), and SEQ ID NO:39 (HCDR3), as defined by the IMGT numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:42 (LCDR3).

[0341] In some embodiments, the ADC has formula (I): Ab-(LD)p (I) (In the ceremony Ab refers to an antibody or antigen-binding fragment thereof, which has the ability to bind to BCMA and comprises, as defined by the Kabat numbering system, three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:2 (HCDR2), and SEQ ID NO:3 (HCDR3); and three LCDRs comprising the amino acid sequences of SEQ ID NO:4 (LCDR1), SEQ ID NO:5 (LCDR2), and SEQ ID NO:6 (LCDR3); or, as defined by the IMGT numbering system, three HCDRs comprising the amino acid sequences of SEQ ID NO:37 (HCDR1), SEQ ID NO:38 (HCDR2), and SEQ ID NO:39 (HCDR3); and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:42 (LCDR3); D is a splicing modulator; L is a linker comprising ADL1, ADL6, ADL13, ADL21, ADL22, or ADL23; and and p is an integer of 1 to 15.

[0342] In some embodiments, the antibody or antigen-binding fragment of the ADC comprises human heavy and light chain variable region frameworks, or human heavy and light chain variable region frameworks with one or more backmutations. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 76 and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 77. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a human IgG1 heavy chain constant region and a human Igκ light chain constant region. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a human IgG1 heavy chain constant region and a human Igλ light chain constant region. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a human IgG4 heavy chain constant region and a human Igκ light chain constant region. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a human IgG4 heavy chain constant region and a human Igλ light chain constant region. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a heavy chain constant region comprising the amino acid sequence of SEQ ID NO: 90 and a light chain constant region comprising the amino acid sequence of SEQ ID NO: 91. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 92 and a light chain comprising the amino acid sequence of SEQ ID NO: 93. In some embodiments, the heavy chain constant region or heavy chain further comprises a C-terminal lysine (K). In some embodiments, the antibody or antigen-binding fragment of the ADC is AB212. In some embodiments, p is an integer from 1 to 12, 1 to 10, 2 to 8, or 4 to 8. In some embodiments, p is 4. In some embodiments, p is 8.

[0343] In some embodiments, the antibody or antigen-binding fragment of the ADC disclosed herein is an internalizing antibody or internalizing antigen-binding fragment. In some embodiments, the antibody or antigen-binding fragment is capable of binding to BCMA and comprises three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:7 (HCDR2), and SEQ ID NO:8 (HCDR3), as defined by the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:9 (LCDR1), SEQ ID NO:10 (LCDR2), and SEQ ID NO:11 (LCDR3), as defined by the IMGT numbering system; or three HCDRs comprising the amino acid sequences of SEQ ID NO:43 (HCDR1), SEQ ID NO:44 (HCDR2), and SEQ ID NO:45 (HCDR3), and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:46 (LCDR3), as defined by the IMGT numbering system.

[0344] In some embodiments, the ADC has formula (I): Ab-(LD)p (I) (In the ceremony Ab refers to an antibody or antigen-binding fragment thereof, which has the ability to bind to BCMA and comprises, as defined by the Kabat numbering system, three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:7 (HCDR2), and SEQ ID NO:8 (HCDR3); and three LCDRs comprising the amino acid sequences of SEQ ID NO:9 (LCDR1), SEQ ID NO:10 (LCDR2), and SEQ ID NO:11 (LCDR3); or, as defined by the IMGT numbering system, three HCDRs comprising the amino acid sequences of SEQ ID NO:43 (HCDR1), SEQ ID NO:44 (HCDR2), and SEQ ID NO:45 (HCDR3); and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:46 (LCDR3); D is a splicing modulator; L is a linker comprising ADL1, ADL6, ADL13, ADL21, ADL22, or ADL23; and and p is an integer of 1 to 15.

[0345] In some embodiments, the antibody or antigen-binding fragment of the ADC comprises human heavy and light chain variable region frameworks, or human heavy and light chain variable region frameworks with one or more backmutations. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 78 and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 79. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a human IgG1 heavy chain constant region and a human Igκ light chain constant region. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a human IgG1 heavy chain constant region and a human Igλ light chain constant region. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a human IgG4 heavy chain constant region and a human Igκ light chain constant region. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a human IgG4 heavy chain constant region and a human Igλ light chain constant region. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a heavy chain constant region comprising the amino acid sequence of SEQ ID NO: 90 and a light chain constant region comprising the amino acid sequence of SEQ ID NO: 91. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 94 and a light chain comprising the amino acid sequence of SEQ ID NO: 95. In some embodiments, the heavy chain constant region or heavy chain further comprises a C-terminal lysine (K). In some embodiments, the antibody or antigen-binding fragment of the ADC is AB213. In some embodiments, p is an integer from 1 to 12, 1 to 10, 2 to 8, or 4 to 8. In some embodiments, p is 4. In some embodiments, p is 8.

[0346] In some embodiments, the antibody or antigen-binding fragment of the ADC disclosed herein is an internalizing antibody or internalizing antigen-binding fragment. In some embodiments, the antibody or antigen-binding fragment is capable of binding to BCMA and comprises three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:12 (HCDR2), and SEQ ID NO:13 (HCDR3), as defined by the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:14 (LCDR1), SEQ ID NO:15 (LCDR2), and SEQ ID NO:16 (LCDR3), as defined by the IMGT numbering system; or three HCDRs comprising the amino acid sequences of SEQ ID NO:47 (HCDR1), SEQ ID NO:48 (HCDR2), and SEQ ID NO:49 (HCDR3), and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:50 (LCDR3), as defined by the IMGT numbering system.

[0347] In some embodiments, the ADC has formula (I): Ab-(LD)p (I) (In the ceremony Ab refers to an antibody or antigen-binding fragment thereof, which has the ability to bind to BCMA and comprises, as defined by the Kabat numbering system, three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:12 (HCDR2), and SEQ ID NO:13 (HCDR3); and three LCDRs comprising the amino acid sequences of SEQ ID NO:14 (LCDR1), SEQ ID NO:15 (LCDR2), and SEQ ID NO:16 (LCDR3); or, as defined by the IMGT numbering system, three HCDRs comprising the amino acid sequences of SEQ ID NO:47 (HCDR1), SEQ ID NO:48 (HCDR2), and SEQ ID NO:49 (HCDR3); and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:50 (LCDR3); D is a splicing modulator; L is a linker comprising ADL1, ADL6, ADL13, ADL21, ADL22, or ADL23; and and p is an integer of 1 to 15.

[0348] In some embodiments, the antibody or antigen-binding fragment of the ADC comprises human heavy and light chain variable region frameworks, or human heavy and light chain variable region frameworks with one or more backmutations. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 80 and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 81. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a human IgG1 heavy chain constant region and a human Igκ light chain constant region. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a human IgG1 heavy chain constant region and a human Igλ light chain constant region. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a human IgG4 heavy chain constant region and a human Igκ light chain constant region. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a human IgG4 heavy chain constant region and a human Igλ light chain constant region. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a heavy chain constant region comprising the amino acid sequence of SEQ ID NO: 90 and a light chain constant region comprising the amino acid sequence of SEQ ID NO: 91. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 96 and a light chain comprising the amino acid sequence of SEQ ID NO: 97. In some embodiments, the heavy chain constant region or heavy chain further comprises a C-terminal lysine (K). In some embodiments, the antibody or antigen-binding fragment of the ADC is AB214. In some embodiments, p is an integer from 1 to 12, 1 to 10, 2 to 8, or 4 to 8. In some embodiments, p is 4. In some embodiments, p is 8.

[0349] In some embodiments, the antibody or antigen-binding fragment of the ADC disclosed herein is an internalizing antibody or internalizing antigen-binding fragment. In some embodiments, the antibody or antigen-binding fragment is capable of binding to BCMA and comprises three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:17 (HCDR2), and SEQ ID NO:18 (HCDR3), as defined by the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:19 (LCDR1), SEQ ID NO:20 (LCDR2), and SEQ ID NO:21 (LCDR3), as defined by the IMGT numbering system; or three HCDRs comprising the amino acid sequences of SEQ ID NO:51 (HCDR1), SEQ ID NO:52 (HCDR2), and SEQ ID NO:53 (HCDR3), and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:54 (LCDR3), as defined by the IMGT numbering system.

[0350] In some embodiments, the ADC has formula (I): Ab-(LD)p (I) (In the ceremony Ab refers to an antibody or antigen-binding fragment thereof, which has the ability to bind to BCMA and comprises, as defined by the Kabat numbering system, three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:17 (HCDR2), and SEQ ID NO:18 (HCDR3); and three LCDRs comprising the amino acid sequences of SEQ ID NO:19 (LCDR1), SEQ ID NO:20 (LCDR2), and SEQ ID NO:21 (LCDR3); or, as defined by the IMGT numbering system, three HCDRs comprising the amino acid sequences of SEQ ID NO:51 (HCDR1), SEQ ID NO:52 (HCDR2), and SEQ ID NO:53 (HCDR3); and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:54 (LCDR3); D is a splicing modulator; L is a linker comprising ADL1, ADL6, ADL13, ADL21, ADL22, or ADL23; and and p is an integer of 1 to 15.

[0351] In some embodiments, the antibody or antigen-binding fragment of the ADC comprises human heavy and light chain variable region frameworks, or human heavy and light chain variable region frameworks with one or more backmutations. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 82 and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 83. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a human IgG1 heavy chain constant region and a human Igκ light chain constant region. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a human IgG1 heavy chain constant region and a human Igλ light chain constant region. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a human IgG4 heavy chain constant region and a human Igκ light chain constant region. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a human IgG4 heavy chain constant region and a human Igλ light chain constant region. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a heavy chain constant region comprising the amino acid sequence of SEQ ID NO: 90 and a light chain constant region comprising the amino acid sequence of SEQ ID NO: 91. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 98 and a light chain comprising the amino acid sequence of SEQ ID NO: 99. In some embodiments, the heavy chain constant region or heavy chain further comprises a C-terminal lysine (K). In some embodiments, the antibody or antigen-binding fragment of the ADC is AB215. In some embodiments, p is an integer from 1 to 12, 1 to 10, 2 to 8, or 4 to 8. In some embodiments, p is 4. In some embodiments, p is 8.

[0352] In some embodiments, the antibody or antigen-binding fragment of the ADC disclosed herein is an internalizing antibody or internalizing antigen-binding fragment. In some embodiments, the antibody or antigen-binding fragment is capable of binding to BCMA and comprises three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:22 (HCDR2), and SEQ ID NO:23 (HCDR3), as defined by the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:24 (LCDR1), SEQ ID NO:25 (LCDR2), and SEQ ID NO:26 (LCDR3), as defined by the IMGT numbering system; or three HCDRs comprising the amino acid sequences of SEQ ID NO:55 (HCDR1), SEQ ID NO:56 (HCDR2), and SEQ ID NO:57 (HCDR3), and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:58 (LCDR3), as defined by the IMGT numbering system.

[0353] In some embodiments, the ADC has formula (I): Ab-(LD)p (I) (In the ceremony Ab refers to an antibody or antigen-binding fragment thereof, which has the ability to bind to BCMA and comprises three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:22 (HCDR2), and SEQ ID NO:23 (HCDR3), as defined by the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:24 (LCDR1), SEQ ID NO:25 (LCDR2), and SEQ ID NO:26 (LCDR3); or three HCDRs comprising the amino acid sequences of SEQ ID NO:55 (HCDR1), SEQ ID NO:56 (HCDR2), and SEQ ID NO:57 (HCDR3), as defined by the IMGT numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:58 (LCDR3); D is a splicing modulator; L is a linker comprising ADL1, ADL6, ADL13, ADL21, ADL22, or ADL23; and and p is an integer of 1 to 15.

[0354] In some embodiments, the antibody or antigen-binding fragment of the ADC comprises human heavy and light chain variable region frameworks, or human heavy and light chain variable region frameworks with one or more backmutations. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 84 and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 85. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a human IgG1 heavy chain constant region and a human Igκ light chain constant region. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a human IgG1 heavy chain constant region and a human Igλ light chain constant region. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a human IgG4 heavy chain constant region and a human Igκ light chain constant region. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a human IgG4 heavy chain constant region and a human Igλ light chain constant region. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a heavy chain constant region comprising the amino acid sequence of SEQ ID NO: 90 and a light chain constant region comprising the amino acid sequence of SEQ ID NO: 91. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 100 and a light chain comprising the amino acid sequence of SEQ ID NO: 101. In some embodiments, the heavy chain constant region or heavy chain further comprises a C-terminal lysine (K). In some embodiments, the antibody or antigen-binding fragment of the ADC is AB216. In some embodiments, p is an integer from 1 to 12, 1 to 10, 2 to 8, or 4 to 8. In some embodiments, p is 4. In some embodiments, p is 8.

[0355] In some embodiments, the antibody or antigen-binding fragment of the ADC disclosed herein is an internalizing antibody or internalizing antigen-binding fragment. In some embodiments, the antibody or antigen-binding fragment is capable of binding to BCMA and comprises three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:27 (HCDR2), and SEQ ID NO:28 (HCDR3), as defined by the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:29 (LCDR1), SEQ ID NO:30 (LCDR2), and SEQ ID NO:31 (LCDR3), as defined by the IMGT numbering system; and three HCDRs comprising the amino acid sequences of SEQ ID NO:59 (HCDR1), SEQ ID NO:60 (HCDR2), and SEQ ID NO:61 (HCDR3), and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:62 (LCDR3), as defined by the IMGT numbering system.

[0356] In some embodiments, the ADC has formula (I): Ab-(LD)p (I) (In the ceremony Ab refers to an antibody or antigen-binding fragment thereof, which has the ability to bind to BCMA and comprises, as defined by the Kabat numbering system, three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:27 (HCDR2), and SEQ ID NO:28 (HCDR3); and three LCDRs comprising the amino acid sequences of SEQ ID NO:29 (LCDR1), SEQ ID NO:30 (LCDR2), and SEQ ID NO:31 (LCDR3); or, as defined by the IMGT numbering system, three HCDRs comprising the amino acid sequences of SEQ ID NO:59 (HCDR1), SEQ ID NO:60 (HCDR2), and SEQ ID NO:61 (HCDR3); and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:62 (LCDR3); D is a splicing modulator; L is a linker comprising ADL1, ADL6, ADL13, ADL21, ADL22, or ADL23; and and p is an integer of 1 to 15.

[0357] In some embodiments, the antibody or antigen-binding fragment of the ADC comprises human heavy and light chain variable region frameworks, or human heavy and light chain variable region frameworks with one or more backmutations. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 86 and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 87. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a human IgG1 heavy chain constant region and a human Igκ light chain constant region. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a human IgG1 heavy chain constant region and a human Igλ light chain constant region. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a human IgG4 heavy chain constant region and a human Igκ light chain constant region. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a human IgG4 heavy chain constant region and a human Igλ light chain constant region. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a heavy chain constant region comprising the amino acid sequence of SEQ ID NO: 90 and a light chain constant region comprising the amino acid sequence of SEQ ID NO: 91. In some embodiments, the antibody or antigen-binding fragment of the ADC comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 102 and a light chain comprising the amino acid sequence of SEQ ID NO: 103. In some embodiments, the heavy chain constant region or heavy chain further comprises a C-terminal lysine (K). In some embodiments, the antibody or antigen-binding fragment of the ADC is AB217. In some embodiments, p is an integer from 1 to 12, 1 to 10, 2 to 8, or 4 to 8. In some embodiments, p is 4. In some embodiments, p is 8.

[0358] In some embodiments, the antibody or antigen-binding fragment of the ADC disclosed he...

Claims

1. an isolated antibody or antigen-binding fragment, having the ability to bind to B-cell maturation antigen (BCMA); and When defined by the Kabat numbering system: three heavy chain complementarity determining regions (HCDRs) comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:22 (HCDR2), and SEQ ID NO:23 (HCDR3); and three light chain complementarity determining regions (LCDRs) comprising the amino acid sequences of SEQ ID NO:24 (LCDR1), SEQ ID NO:25 (LCDR2), and SEQ ID NO:26 (LCDR3); or As defined by the IMGT numbering system, three HCDRs comprising the amino acid sequences of SEQ ID NO:55 (HCDR1), SEQ ID NO:56 (HCDR2), and SEQ ID NO:57 (HCDR3); and three LCDRs comprising the amino acid sequences of SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:58 (LCDR3).

1. An isolated antibody or antigen-binding fragment comprising:

2. The antibody or antigen-binding fragment thereof a heavy chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 84, and a light chain variable region that is at least 90% identical to the amino acid sequence of SEQ ID NO: 85, optionally a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 84, and a light chain variable region comprising the amino acid sequence of SEQ ID NO: 85 2. The antibody or antigen-binding fragment of claim 1, comprising:

3. The antibody or antigen-binding fragment thereof (i) a heavy chain constant region comprising the amino acid sequence of SEQ ID NO: 90, or (ii) a light chain constant region comprising the amino acid sequence of SEQ ID NO: 91, or (iii) (i) and (ii).

2. The antibody or antigen-binding fragment of claim 1, comprising: Claim 4: The antibody or antigen-binding fragment thereof a heavy chain comprising the amino acid sequence of SEQ ID NO: 100, and a light chain comprising the amino acid sequence of SEQ ID NO: 101; 2. The antibody or antigen-binding fragment of claim 1, comprising:

5. The antibody or antigen-binding fragment of claim 4, wherein the heavy chain further comprises a C-terminal lysine (K).

6. 2. The antibody or antigen-binding fragment of claim 1, wherein the antibody or antigen-binding fragment is conjugated to a therapeutic agent or a pharmaceutically acceptable salt thereof, optionally wherein the therapeutic agent or a pharmaceutically acceptable salt thereof is a splicing modulator, optionally wherein the therapeutic agent or a pharmaceutically acceptable salt thereof is a pladienolide or a pladienolide derivative, and optionally wherein the therapeutic agent or a pharmaceutically acceptable salt thereof is pladienolide D or a pladienolide D derivative.

7. Antibody-drug conjugates of formula (I): Ab-(L-D) ｐ (I) (In the formula, Ab is an antibody or antigen-binding fragment according to any one of claims 1 to 5; D is a splicing modulator or a pharmaceutically acceptable salt thereof; L is a linker that covalently links Ab to D; and and p is an integer from 1 to 15.

8. (LD) is a compound of formula (II-A): 【Chemistry 1】 wherein Z′ is 【Chemistry 2】 Selected from: R １ Is absent, hydrogen, C １ ~C ６ Alkyl group, C １ ~C ６ Alkylalkoxy group, C １ ~C ６ Alkylamino group, C １ ~C ６ Alkylcarboxylic acid group, C １ ~C ６ Alkylhydroxy group, C ３ ~C ８ Cycloalkyl group, benzyl group, C ３ ~C ８ Heterocyclyl group, —O—C(═O)—(C １ ~C ６ alkyl) group, and -CD ３ Selected from: R ３ is hydrogen, C １ ~C ６ Alkyl group, C １ ~C ６ Alkylalkoxy group, C １ ~C ６ Alkylamino group, C １ ~C ６ Alkylcarboxylic acid group, C １ ~C ６ Alkylhydroxy group, C ３ ~C ８ Cycloalkyl group, benzyl group, C ３ ~C ８ Heterocyclyl groups, and —O—C(═O)—(C １ ~C ６ alkyl) groups; and R ４ , R ５ , and R ８ are each independently hydrogen, hydroxyl, —O—(C １ ~C ６ alkyl) group, —O—C(═O)—(C １ ~C ６ alkyl) groups, and C １ ~C ６ alkyl groups; R ６ and R ７ are each independently hydrogen, -O-R １７ , -OC(=O)-R １７ , -OC(=O)-NR １５ R １６ , C １ ~C ６ Alkyl groups, and -NR １５ R １６ Selected from: R １５ and R １６ are each independently hydrogen, R １７ , —C(═O)—R １７ and —C(═O)—O—R １７ Selected from: R １７ is hydrogen, C １ ~C ６ Alkyl group, C ３ ~C ８ Cycloalkyl groups, benzyl groups, and C ３ ~C ８ heterocyclyl groups; and In the formula, R １ , R ３ , R ４ , R ５ , R ６ , R ７ , R ８ , R １５ , R １６ , and R １７ are each independently a halogen, a hydroxyl, or a C １ ~C ６ alkyl group, —O—(C １ ~C ６ alkyl group, —NR １５ R １６ , C ３ ~C ８ Cycloalkyl group, C １ ~C ６ Alkylhydroxy group, C １ ~C ６ Alkylalkoxy group, benzyl group, and C ３ ~C ８ substituted with 0 to 3 groups independently selected from heterocyclyl groups; In the formula, R ６ and R ７ or a pharmaceutically acceptable salt thereof, wherein at least one of:

9. (LD) is a compound of formula (IV-A): 【Transformation 3】 [In the formula, R １ Is absent, hydrogen, C １ ~C ６ Alkyl group, C １ ~C ６ Alkylalkoxy group, C １ ~C ６ Alkylamino group, C １ ~C ６ Alkylcarboxylic acid group, C １ ~C ６ Alkylhydroxy group, C ３ ~C ８ Cycloalkyl group, benzyl group, C ３ ~C ８ Heterocyclyl group, —O—C(═O)—(C １ ~C ６ alkyl) group, and -CD ３ Selected from: R ３ is hydrogen, C １ ~C ６ Alkyl group, C １ ~C ６ Alkylalkoxy group, C １ ~C ６ Alkylamino group, C １ ~C ６ Alkylcarboxylic acid group, C １ ~C ６ Alkylhydroxy group, C ３ ~C ８ Cycloalkyl group, benzyl group, C ３ ~C ８ Heterocyclyl groups, and —O—C(═O)—(C １ ~C ６ alkyl) groups; and R ４ , R ５ , and R ８ are each independently hydrogen, hydroxyl, —O—(C １ ~C ６ alkyl) group, —O—C(═O)—(C １ ~C ６ alkyl) groups, and C １ ~C ６ alkyl groups; R ６ and R ７ are each independently hydrogen, -O-R １７ , -OC(=O)-R １７ , -OC(=O)-NR １５ R １６ , C １ ~C ６ Alkyl groups, and -NR １５ R １６ Selected from: R １５ and R １６ are each independently hydrogen, R １７ , —C(═O)—R １７ and —C(═O)—O—R １７ is selected from: R １７ is hydrogen, C １ ~C ６ Alkyl group, C ３ ~C ８ Cycloalkyl groups, benzyl groups, and C ３ ~C ８ heterocyclyl groups; In the formula, R １ , R ３ , R ４ , R ５ , R ６ , R ７ and R8 are each independently a halogen, a hydroxyl, C １ ~C ６ alkyl group, —O—(C １ ~C ６ alkyl group, —NR １５ R １６ , C ３ ~C ８ Cycloalkyl group, C １ ~C ６ Alkylhydroxy group, C １ ~C ６ Alkylalkoxy group, benzyl group, and C ３ ~C ８ substituted with 0 to 3 groups independently selected from heterocyclyl groups; In the formula, R ６ and R ７ or a pharmaceutically acceptable salt thereof, wherein at least one of:

10. (LD) is a compound of formula (VI-A): 【Chemistry 4】 [In the formula, R １ and R ９ are each independently absent, hydrogen, C １ ~C ６ Alkyl group, C １ ~C ６ Alkylalkoxy group, C １ ~C ６ Alkylamino group, C １ ~C ６ Alkylcarboxylic acid group, C １ ~C ６ Alkylhydroxy group, C ３ ~C ８ Cycloalkyl group, benzyl group, C ３ ~C ８ Heterocyclyl group, —O—C(═O)—(C １ ~C ６ alkyl) group, and -CD ３ Selected from: R ３ is hydrogen, C １ ~C ６ Alkyl group, C １ ~C ６ Alkylalkoxy group, C １ ~C ６ Alkylamino group, C １ ~C ６ Alkylcarboxylic acid group, C １ ~C ６ Alkylhydroxy group, C ３ ~C ８ Cycloalkyl group, benzyl group, C ３ ~C ８ Heterocyclyl groups, and —O—C(═O)—(C １ ~C ６ alkyl) groups; R ４ , R ５ , and R ８ are each independently hydrogen, hydroxyl, —O—(C １ ~C ６ alkyl) group, —O—C(═O)—(C １ ~C ６ alkyl) groups, and C １ ~C ６ alkyl groups; R ６ and R ７ are each independently hydrogen, -O-R １７ , -OC(=O)-R １７ , -OC(=O)-NR １５ R １６ , C １ ~C ６ Alkyl groups, and -NR １５ R16 is selected from: R １０ is hydrogen, C １ ~C ６ Alkyl group, —C(═O)—(C １ ~C ６ alkyl) group, and -CD ３ Selected from: R １５ and R １６ are each independently hydrogen, R １７ , —C(═O)—R １７ and —C(═O)—O—R １７ Selected from: R １７ is hydrogen, C １ ~C ６ Alkyl group, C ３ ~C ８ Cycloalkyl groups, benzyl groups, and C ３ ~C ８ heterocyclyl groups; and a is 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10; In the formula, R １ , R ３ , R ４ , R ５ , R ６ , R ７ , R ８ , R ９ and R10 are each independently a halogen, a hydroxyl, １ ~C ６ alkyl group, —O—(C １ ~C ６ alkyl group, —NR １５ R １６ , C ３ ~C ８ Cycloalkyl group, C １ ~C ６ Alkylhydroxy group, C １ ~C ６ Alkylalkoxy group, benzyl group, and C ３ ~C ８ substituted with 0 to 3 groups independently selected from heterocyclyl groups; In the formula, R ６ and R ７ at least one of is hydrogen; and In the formula, R １ and R ９ and both of them cannot be absent, or a pharmaceutically acceptable salt thereof.

11. (LD) is the formula (VIII-A): 【Transformation 5】 [In the formula, R １ Is absent, hydrogen, C １ ~C ６ Alkyl group, C １ ~C ６ Alkylalkoxy group, C １ ~C ６ Alkylamino group, C １ ~C ６ Alkylcarboxylic acid group, C １ ~C ６ Alkylhydroxy group, C ３ ~C ８ Cycloalkyl group, benzyl group, C ３ ~C ８ Heterocyclyl group, —O—C(═O)—(C １ ~C ６ alkyl) group, and -CD ３ Selected from: R ３ is hydrogen, C １ ~C ６ Alkyl group, C １ ~C ６ Alkylalkoxy group, C １ ~C ６ Alkylamino group, C １ ~C ６ Alkylcarboxylic acid group, C １ ~C ６ Alkylhydroxy group, C ３ ~C ８ Cycloalkyl group, benzyl group, C ３ ~C ８ Heterocyclyl groups, and —O—C(═O)—(C １ ~C ６ alkyl) groups; R ４ is hydrogen, hydroxyl, —O—(C １ ~C ６ alkyl) group, —O—C(═O)—(C １ ~C ６ alkyl) groups, and C １ ~C ６ alkyl groups; and R １０ is selected from a 3- to 10-membered carbocycle and a 3- to 10-membered heterocycle, each of which is selected from 0 to 3 R ａ wherein each R ａ are independently halogen, C １ ~C ６ alkyl group, —O—(C １ -C ６ ) alkyl group, C １ ~C ６ Alkylalkoxy group, C １ ~C ６ Alkylhydroxy group, —S(═O) ｗ -(4- to 7-membered heterocycle), 4- to 7-membered carbocycle, and 4- to 7-membered heterocycle; R １５ and R １６ are each independently hydrogen, R １７ , —C(═O)—R １７ and —C(═O)—O—R １７ is selected from: R １７ is hydrogen, C １ ~C ６ Alkyl group, C ３ ~C ８ Cycloalkyl groups, benzyl groups, and C ３ ~C ８ heterocyclyl groups; In the formula, R １ , R ３ , R ４ and R10 are each independently a halogen, a hydroxyl, １ ~C ６ alkyl group, —O—(C １ ~C ６ alkyl group, —NR １５ R １６ , C ３ ~C ８ Cycloalkyl group, C １ ~C ６ Alkylhydroxy group, C １ ~C ６ Alkylalkoxy group, benzyl group, and C ３ ~C ８ substituted with 0 to 3 groups independently selected from heterocyclyl groups; and In the formula, each R ａ are independently halogen, hydroxyl, -NR １５ R １６ , C １ ~C ６ Alkyl group, -(C=O)-(C １ ~C ６ alkyl) group, -(C=O)-(C １ ~C ６ alkyl)-(C ３ ~C １０ heterocyclyl groups), and C １ ~C ６ Alkylcarboxylic acid groups (each of which may contain halogen, hydroxyl, -NR １５ R １６ , and C １ ~C ３ substituted with 0 to 3 groups independently selected from alkyl; and w is 0, 1, or 2, or a pharmaceutically acceptable salt thereof.

12. The splicing regulator D 【Transformation 6】 【Transformation 7】 【Transformation 8】 【Chemistry 9】 【Chemistry 10】 【Chemistry 11】 【Chemistry 12】 【Chemistry 13】 【Chemistry 14】 8. The antibody-drug conjugate of claim 7, wherein the compound is selected from the group consisting of the compounds:

13. Splicing regulator D 【Chemistry 15】 or a pharmaceutically acceptable salt thereof; and 【Chemistry 16】 or a pharmaceutically acceptable salt thereof.

14. wherein the linker L comprises a cleavable moiety, and the cleavable moiety is (i) a cleavable peptide moiety, optionally wherein said cleavable peptide moiety comprises valine-citrulline (Val-Cit), valine-alanine (Val-Ala), alanine-alanine-asparagine (Ala-Ala-Asn) or glutamic acid-valine-citrulline (Glu-Val-Cit); or (ii) a cleavable glucuronide moiety, optionally said cleavable glucuronide moiety is enzymatically cleavable, optionally said cleavable glucuronide moiety is cleavable by a glucuronidase, optionally said cleavable glucuronide moiety is cleavable by a β-glucuronidase; The antibody-drug conjugate of claim 7, comprising:

15. 15. The antibody-drug conjugate of claim 14, wherein the linker L comprises a maleimide moiety, optionally wherein the maleimide moiety comprises maleimidocaproyl (MC), and further optionally wherein the linker L comprises MC-Val-Cit, MC-Val-Ala, MC-Ala-Ala-Asn, or MC-Glu-Val-Cit.

16. The linker L comprises at least one spacer unit, and optionally, the at least one spacer unit is (a) a polyethylene glycol (PEG) moiety, wherein the PEG moiety is -(PEG) ｍ -, where m is an integer from 1 to 10 or 4 to 8, further optionally 4, 7, or 8; or (b) an alkyl moiety, said alkyl moiety being —(CH ２ ) ｎ -, and n is an integer from 1 to 10; The antibody-drug conjugate of claim 14.

17. The antibody-drug conjugate of claim 14, wherein the linker L comprises a spacer unit that links the cleavable moiety in the linker L to the splicing regulator D, and optionally, the spacer unit that links the cleavable moiety in the linker L to the splicing regulator D is self-immolative.

18. The spacer unit connecting the cleavable moiety in the linker L to the splicing modulator D comprises p-aminobenzyl (pAB) or p-aminobenzyloxycarbonyl (pABC), optionally the linker L comprises Val-Cit-pAB, Val-Ala-pAB, Ala-Ala-Asn-pAB, Glu-Val-Cit-pAB, Val-Cit-pABC, Val-Ala-pABC, Ala-Ala-Asn-pABC or Glu-Val-Cit-pABC, optionally the linker L comprises MC-Val-Cit-pAB, MC-Val-Ala-pAB, MC-Ala-Ala-Asn-pAB, MC-Glu-Val-Cit-pAB, MC-(PEG) ２ -Val-Cit-pAB, MC-Val-Cit-pABC, MC-Val-Ala-pABC, MC-Ala-Ala-Asn-pABC, MC-Glu-Val-Cit-pABC, MC-(PEG) ２ 18. The antibody-drug conjugate of claim 17, comprising -Val-Cit-pABC or MC-β-glucuronide.

19. The linker L is 【Chemistry 17】 or [Chemistry 18] The antibody-drug conjugate of claim 7, comprising:

20. The antibody-drug conjugate of claim 7 , wherein the linker L is covalently bound to a cysteine ​​residue of the antibody Ab.

21. 8. The antibody-drug conjugate of claim 7, wherein p is an integer from 1 to 12, optionally p is an integer from 2 to 8, further optionally p is an integer from 4 to 8, further optionally p is 4, 7, or 8.

22. the antibody or antigen-binding fragment: (i) three HCDRs comprising the amino acid sequences of SEQ ID NO:1 (HCDR1), SEQ ID NO:22 (HCDR2), and SEQ ID NO:23 (HCDR3), as defined by the Kabat numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO:24 (LCDR1), SEQ ID NO:25 (LCDR2), and SEQ ID NO:26 (LCDR3); (ii) three HCDRs comprising the amino acid sequences of SEQ ID NO: 55 (HCDR1), SEQ ID NO: 56 (HCDR2), and SEQ ID NO: 57 (HCDR3), as defined by the IMGT numbering system; and three LCDRs comprising the amino acid sequences of SEQ ID NO: 40 (LCDR1), SEQ ID NO: 41 (LCDR2), and SEQ ID NO: 58 (LCDR3); or (iii) a heavy chain variable region at least 90% identical to the amino acid sequence of SEQ ID NO: 84, and a light chain variable region at least 90% identical to the amino acid sequence of SEQ ID NO: 85; Including, D is 【Chemistry 19】 or a pharmaceutically acceptable salt thereof; and 【Chemistry 20】 or a pharmaceutically acceptable salt thereof; L contains MC-Val-Cit-pABC, The antibody-drug conjugate of claim 7.

23. An isolated nucleic acid encoding the antibody or antigen-binding fragment of any one of claims 1 to 5; an isolated vector comprising said isolated nucleic acid; or an isolated cell or cell population comprising said isolated nucleic acid or isolated vector.

24. A pharmaceutical composition comprising the antibody or antigen-binding fragment of any one of claims 1 to 5, or the antibody-drug conjugate of any one of claims 7 to 22, and a pharmaceutically acceptable carrier.

25. 25. The pharmaceutical composition of claim 24, wherein the pharmaceutical composition comprises multiple copies of the antibody-drug conjugate, and wherein the average p of the antibody-drug conjugates in the composition is from about 2 to about 8, and optionally, the average p of the antibody-drug conjugates in the composition is about 4.

26. 25. The pharmaceutical composition of claim 24 for use in a method of treating a subject having or suspected of having a BCMA-expressing cancer.

27. 27. The pharmaceutical composition of claim 26, wherein the cancer is a plasma cell malignancy.

28. The cancer (a) myeloma, optionally multiple myeloma, optionally relapsed / refractory multiple myeloma; (b) Leukemia; (c) lymphoma, optionally diffuse large B-cell lymphoma, mantle cell lymphoma, plasmablastic lymphoma, or Burkitt lymphoma; or (d) plasmacytoma or myeloma; 27. The pharmaceutical composition of claim 26.

29. 27. The pharmaceutical composition of claim 26, administered in combination with one or more additional therapeutic agents, optionally wherein the one or more additional therapeutic agents comprise a BCL2 inhibitor, a BCLxL inhibitor, a BCL2 / BCLxL inhibitor, or a gamma secretase inhibitor.

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