Anti-BCMA antibody-drug conjugates and their usage

Abstract

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

Description

[0001] This disclosure claims the priority benefit of 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 list of sequences that have been submitted electronically in ASCII format and incorporated herein by reference in their entirety. The ASCII copy created on May 28, 2021, is named 15647_0012-00304_SL.txt and is 698,277 bytes in size.

[0003] This disclosure relates to anti-B cell maturation antigen (BCMA) antibodies and their antigen-binding fragments, as well as conjugates such as antibody-drug conjugates (ADCs), such as those containing splicing modulators, and their uses.

[0004] Most protein-coding genes in the human genome consist of multiple exons (including coding regions) separated by introns (non-coding regions). Gene expression produces pre-mRNA. Subsequently, intron sequences are removed from the pre-mRNA through a process called splicing, producing mature messenger RNA (mRNA). By including different combinations of exons, alternative splicing can produce mRNAs encoding different protein isoforms.

[0005] RNA splicing is catalyzed by the spliceosome, a dynamic multi-protein-RNA complex composed of five small nuclear RNAs (snRNAs U1, U2, U4, U5, and U6) and associated proteins. The spliceosome assembles on pre-mRNA to establish a dynamic cascade of multiple RNA and protein interactions that catalyze intron excision and exon conjugation (Matera and Wang (2014) Nat Rev Mol Cell Biol. [Nature Review of Molecular and Cell Biology] 15(2):108-21). Increasing evidence links human diseases to aberrant regulation of RNA splicing affecting many genes (Scotti and Swanson (2016) Nat Rev Genet. [Nature Reviews Genetics] 17(1):19-32). Several studies have now documented alterations in cancer cell splicing profiles and in autosplicing factors (Agrawal et al. (2018) Curr Opin Genet Dev. [Recent Perspectives on Genetics and Development] 48:67-74). Alternative splicing can cause differential exon inclusion / exclusion, intron retention, or the use of hidden splice sites (Seiler et al. (2018) Cell Rep. 23(1):282-96). In summary, these events result in functional alterations that may contribute to tumorigenesis or resistance to therapy (Siegfried and Karni (2018) Curr Opin GenetDev. 48:16-21).

[0006] Some products can bind to the SF3b spliceosome complex. These small molecules regulate splicing by promoting intron retention and / or exon skipping (Teng et al. (2017) Nat Commun. [Nature Communications] 8:15522). A significant portion of the resulting transcripts contain premature stop codons, triggering nonsense-mediated mRNA decay (NMD). Furthermore, due to impaired typical splicing, typical transcripts are significantly reduced, which can adversely affect cell function and viability. For this reason, splice regulators have become a promising class of drugs for cancer treatment (Puthenveetil et al. (2016) Bioconjugate Chem. [Bioconjugate Chemistry] 27:1880-8). Delivering these splice regulators to relevant carcinogenic tissues while avoiding or minimizing potential toxicity remains an ongoing challenge in this field. Therefore, improving the targeting of small molecule splice regulators is promising.

[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. [International Journal of Immunology] 10:1693-702; Sanchez et al. (2012) Br J Haematol. [British Journal of Hematology] 158:727-38). BCMA ligands include B cell activating factor (BAFF) and proliferation-inducing ligand (APRIL) (Rennert et al. (2000) J Exp Med. [Journal of Experimental Medicine] 192:1677-83). BCMA is preferentially expressed by mature B lymphocytes, with minimal expression in hematopoietic stem cells and non-hematopoietic tissues, and plays a role in the survival of long-lived bone marrow plasma cells (PCs) (Novak et al. (2004) Blood. [Blood] 103:689-94; O'Connor et al. (2004) 199:91-7).

[0008] Compared with normal bone marrow mononuclear cells (BMMCs) from healthy donors, BCMA is highly expressed in malignant PCs collected from multiple myeloma (MM) patients (Sanchez et al. (2012) Br J Haematol. [British Journal of Hematology] 158:727-38). BCMA overexpression and activation are also associated with the progression of multiple myeloma in preclinical models and in humans (Sanchez et al. (2012) Br J Haematol. [British Journal of Hematology] 158:727-38; Tai et al. (2016) Blood. [Blood] 127:3225-36; Sanchez et al. (2016) Clin Cancer Res. [Clinical Cancer Research] 22:3383-97). Mouse xenografts with induced BCMA overexpression grew faster than BCMA-negative controls, and similar results were observed after APRIL-induced activation of BCMA in ex vivo human multiple myeloma cells (Tai et al. (2016) Blood. [Blood] 127:3225-36). This overexpression and activation of BCMA may lead to upregulation of both classical and non-classical nuclear factor κ-B (NFKB) pathways, as well as enhanced expression of genes crucial for survival, growth, adhesion, osteoclast activation, angiogenesis, metastasis, and immunosuppression. BCMA represents a promising antigen that could be used to target multiple myeloma and other B-cell / plasma cell malignancies and / or to provide novel cancer therapies (Shah et al. (2020) Leukemia. [Leukemia] 34(4):985-1005). However, improved and effective methods for targeting BCMA are still needed.

[0009] In particular, while the use of splice modulators has been reported in the art (including in the context of ADCs), there remains a need for better targeted delivery of splice modulators to specific tissues, such as cancerous tissues expressing BCMA. Similarly, there remains a need in the art for improved BCMA-binding antibodies with superior properties, such as the ability to bind antigens and / or efficiently deliver payloads (e.g., splice modulators) to target cells or tissues expressing BCMA.

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

[0011] In some embodiments, the anti-BCMA antibody and antigen-binding fragments disclosed herein are humanized. In some embodiments, the anti-BCMA antibody and antigen-binding fragments disclosed herein contain a minimal sequence derived from a non-human (e.g., mouse) antibody and retain the reactivity of the non-human antibody while exhibiting low immunogenicity in humans. In some embodiments, the anti-BCMA antibody and antigen-binding fragments disclosed herein are capable of binding to BCMA. In some embodiments, the anti-BCMA antibody and antigen-binding fragments disclosed herein bind to BCMA and have one or more superior properties compared to a reference anti-BCMA antibody or antigen-binding fragment. In some embodiments, the anti-BCMA antibody and antigen-binding fragments disclosed herein have a higher affinity for BCMA compared to a reference anti-BCMA antibody or antigen-binding fragment (e.g., as assessed in binding assays using cancer cells with high or moderate levels of BCMA expression). In some embodiments, ADCs containing the anti-BCMA antibody and antigen-binding fragments disclosed herein exhibit favorable drug loading, aggregation, stability, activity, and / or potency compared to ADCs containing a reference anti-BCMA antibody or antigen-binding fragment. In some embodiments, ADCs containing the anti-BCMA antibody and antigen-binding fragments disclosed herein exhibit the properties required for a therapeutic ADC. In some embodiments, compared to a reference anti-BCMA antibody and / or a reference anti-BCMA ADC, these properties include, but are not limited to, effective drug loading levels, low aggregation levels, improved stability, residual affinity for BCMA-expressing cells comparable to unconjugated antibodies, effective cytotoxicity against BCMA-expressing cells, improved cytotoxicity and / or cell growth inhibitory 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 anticancer activity. In some embodiments, the increased potency, cytotoxicity, and / or anticancer activity are observed in cancers expressing high levels of the antibodies, antigen-binding fragments, or ADC-targeted antigens (e.g., high BCMA expression) disclosed herein. In some embodiments, the increased potency, cytotoxicity, and / or anticancer activity are observed in cancers expressing moderate levels of the antibodies, antigen-binding fragments, or ADC-targeted antigens (e.g., moderate BCMA expression) disclosed herein. In some embodiments, these antibodies, antigen-binding fragments, and / or ADCs may be used to treat 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 patients with multiple myeloma eventually relapse. Without being bound by theory, patients with myeloma 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 bone niches throughout the body (Figueroa-Vazquez et al. (2021) Mol Cancer Ther. [Molecular Cancer Therapeutics] 20(2):367-378; Franqui-Machin et al. (2015) Oncotarget. [Tumor Targeting] 6:40496-40506). These dormant myeloma cells may be largely resistant to standard care therapies (including many FDA-approved chemotherapy therapies), which exert their antiproliferative effects by inhibiting or aberrantly regulating cellular pathways required for DNA replication and cell division (Cheung-Ong et al. (2013) Chem Biol. [Chemical Biology] 20(5):648-659). Therefore, therapeutic agents that retain antiproliferative activity in non-dividing and / or slowly dividing cells can provide an effective means of treating newly diagnosed and relapsed / refractory forms of multiple myeloma, as well as other B-cell / plasma cell malignancies. In some embodiments, the antibodies, antigen-binding fragments, conjugates, and / or ADC complexes disclosed herein retain cytotoxic and / or cell growth-inhibiting activity independent of cell proliferation status. In some embodiments, the antibodies, antigen-binding fragments, conjugates, and / or ADC complexes can target actively dividing and dormant cells (e.g., actively dividing, non-dividing, and / or slowly dividing myeloma cells).

[0013] Based on factors such as genetic background, gene expression profiles, or other defining characteristics of cancer, certain cancer types may be particularly well-suited for treatment with the antibodies, antigen-binding fragments, conjugates, and / or ADC compounds disclosed herein. In some embodiments, the increased potency, cytotoxicity, and / or anticancer activity (e.g., compared to a reference anti-BCMA antibody and / or a reference anti-BCMA ADC) of the antibodies, antigen-binding fragments, or ADCs disclosed herein is present in cancers expressing high or moderate levels of antigens 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 anticancer activity of the antibodies, antigen-binding fragments, or ADCs disclosed herein is present in cancers containing at least some dormant cells (e.g., non-dividing or slowly dividing myeloma cells). In some embodiments, the increased potency, cytotoxicity, and / or anticancer activity of the antibodies, antigen-binding fragments, or ADCs disclosed herein is present in multiple myeloma. In some embodiments, the increased potency, cytotoxicity, and / or anticancer activity of the antibodies, antigen-binding fragments, or ADCs disclosed herein are present in cancers expressing MCL1, for example, in cancers with high or moderate levels of MCL1 expression.

[0014] MCL1 is a member of the BCL2 gene family, which are generally considered major regulators of the apoptotic form of programmed cell death. Three major alternative splicing isoforms of MCL1 have been described, with the longest isoform (MCL1-long, MCL1-L, MCL1L) acting as a potent pro-survival / anti-apoptotic factor, counteracting the pro-death function of pore-forming and BH3-only family members. In humans, MCL1 is widely expressed in most normal tissues under normal physiological conditions and is particularly rich in bone marrow cell types (including plasma B cells, which lead to myeloma). MCL1 expression is frequently upregulated by various mechanisms in many cancer types, including myeloma, and has been shown to increase further after some standard care regimens in myeloma, thus conferring resistance to such therapies. Therefore, without being bound by theory, therapeutic agents capable of inhibiting MCL1 (e.g., MCL1L function) and / or inhibiting MCL (e.g., MCL1L expression) could provide clinical benefit to patients with myeloma, especially in relapsed / refractory forms of the disease with high or dependent MCL1L expression.

[0015] Without being bound by theory, delivering splicing regulators to cancer cells (e.g., those expressing BCMA) can induce cell death by reducing or inhibiting MCL1 expression (Aird et al. (2019) Nat Commun [Nature Communications] 10:137). MCL1 mRNA and protein have relatively short lifespans, typically around 30 minutes each in several human cancer cell lines. Genes encoding short-lived RNA transcripts and proteins may be particularly well-suited for regulation by splicing regulators, as pre-existing pools of correctly spliced ​​RNA and protein products may rapidly degrade after treatment, while aberrantly spliced ​​transcripts begin to accumulate. These 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 regulator treatment can also lead to the expression of protein products with novel functions or functions that oppose those of correctly spliced ​​genes. Compared to payloads that disrupt microtubules or damage DNA, the splicing regulators used in the ADCs described herein disrupt MCL1 splicing and provide pathway-specific apoptosis mechanisms to kill refractory cancer cells (e.g., myeloma cells). By targeting cancer cells' dependence on MCL1 splicing, the antibodies, antigen-binding fragments, conjugates, and / or ADC complexes can provide effective treatment options for current clinical challenges, such as overcoming drug resistance in multiple myeloma and other BCMA-expressing cancers.

[0016] In various embodiments, this disclosure more specifically relates to antibodies, antigen-binding fragments, and ADCs capable of binding to cancer cells expressing BCMA. In various embodiments, these antibodies, antigen-binding fragments, and ADCs are also capable of internalization into target cells after binding. ADCs comprising a linker are disclosed that connect a splicing regulator to an antibody moiety. The antibody moiety (alone or as part of an ADC) may be a full-length antibody or its antigen-binding fragment.

[0017] In some embodiments, this disclosure provides isolated antibody or antigen-binding fragments, wherein the antibody or antigen-binding fragment is capable of binding BCMA and comprises:

[0018] (i) Three heavy chain complementarity determinants (HCDRs) and three light chain complementarity determinants (LCDRs), as defined by the Kabat numbering system, include:

[0019] HCDR1 contains the following amino acid sequence: NYWIH (SEQ ID NO:1);

[0020] HCDR2 contains the following amino acid sequence:

[0021] X1TYRX5X6SX8TX 10 YX 12 QKX15 KS(SEQ ID NO:67), where:

[0022] X1 is either A or G;

[0023] X5 is either S or I;

[0024] X6 is either H or Q;

[0025] X8 is either D or T;

[0026] X 10 It is either Y or N;

[0027] X 12 It is N or A; and

[0028] X 15 It is either F or Y;

[0029] HCDR3 contains the following amino acid sequence:

[0030] GAX3YHGYDVIX 11 N(SEQ ID NO:68), where:

[0031] X3 is either I or V; and

[0032] X 11 It is either E or D;

[0033] LCDR1 contains the following amino acid sequence:

[0034] RASQSISSYX 10 N(SEQ ID NO:69), where:

[0035] X 10 It is L or I;

[0036] LCDR2 contains the following amino acid sequence:

[0037] ATSNLQX7 (SEQ ID NO:70), where:

[0038] X7 is either S or I; and

[0039] LCDR3 contains the following amino acid sequence:

[0040] QQX3RRX6PWX9(SEQ ID NO:71), where:

[0041] X3 is either F or Y;

[0042] X6 is either L or I; and

[0043] X9 is either T or S; or

[0044] (ii) Three heavy chain complementarity determinant regions (HCDRs) and three light chain complementarity determinant regions (LCDRs), as defined by the IMGT numbering system, include:

[0045] HCDR1 contains the following amino acid sequence:

[0046] GGTFX5NYW (SEQ ID NO:72), where:

[0047] X5 is either S or T;

[0048] HCDR2 contains the following amino acid sequence:

[0049] TYRX4X5SX7T (SEQ ID NO:73), wherein:

[0050] X4 is either S or I;

[0051] X5 is either H or Q; and

[0052] X7 is either D or T;

[0053] HCDR3 contains the following amino acid sequence:

[0054] ARGAX5YHGYDVIX 13 N(SEQ ID NO:74), where:

[0055] X5 is either I or V; and

[0056] X 13 It is either D or E;

[0057] LCDR1 contains the following amino acid sequence: QSISSY (SEQ ID NO:40);

[0058] LCDR2, which contains the following amino acid sequence: ATS (SEQ ID NO:41); and

[0059] LCDR3 contains the following amino acid sequence:

[0060] QQX3RRX6PWX9(SEQ ID NO:75), where:

[0061] X3 is either Y or F;

[0062] X6 is either L or I; and

[0063] X9 is either T or S.

[0064] In some embodiments, this disclosure provides isolated antibody or antigen-binding fragments, wherein the antibody or antigen-binding fragment is capable of binding BCMA and comprises:

[0065] (a) Three HCDRs comprising the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:2 (HCDR2), and SEQ ID NO:3 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:4 (LCDR1), SEQ ID NO:5 (LCDR2), and SEQ ID NO:6 (LCDR3), as defined by the Kabat numbering system; or three HCDRs comprising the following amino acid sequences: SEQ ID NO:37 (HCDR1), SEQ ID NO:38 (HCDR2), and SEQ ID NO:39 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:42 (LCDR3), as defined by the IMGT numbering system;

[0066] (b) Three HCDRs comprising the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:7 (HCDR2), and SEQ ID NO:8 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:9 (LCDR1), SEQ ID NO:10 (LCDR2), and SEQ ID NO:11 (LCDR3), as defined by the Kabat numbering system; or three HCDRs comprising the following amino acid sequences: SEQ ID NO:43 (HCDR1), SEQ ID NO:44 (HCDR2), and SEQ ID NO:45 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:46 (LCDR3), as defined by the IMGT numbering system;

[0067] (c) Three HCDRs comprising the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:12 (HCDR2), and SEQ ID NO:13 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:14 (LCDR1), SEQ ID NO:15 (LCDR2), and SEQ ID NO:16 (LCDR3), as defined by the Kabat numbering system; or three HCDRs comprising the following amino acid sequences: SEQ ID NO:47 (HCDR1), SEQ ID NO:48 (HCDR2), and SEQ ID NO:49 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:50 (LCDR3), as defined by the IMGT numbering system;

[0068] (d) Three HCDRs comprising the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:17 (HCDR2), and SEQ ID NO:18 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:19 (LCDR1), SEQ ID NO:20 (LCDR2), and SEQ ID NO:21 (LCDR3), as defined by the Kabat numbering system; or three HCDRs comprising the following amino acid sequences: SEQ ID NO:51 (HCDR1), SEQ ID NO:52 (HCDR2), and SEQ ID NO:53 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:54 (LCDR3), as defined by the IMGT numbering system;

[0069] (e) Three HCDRs comprising the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:22 (HCDR2), and SEQ ID NO:23 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:24 (LCDR1), SEQ ID NO:25 (LCDR2), and SEQ ID NO:26 (LCDR3), as defined by the Kabat numbering system; or three HCDRs comprising the following amino acid sequences: SEQ ID NO:55 (HCDR1), SEQ ID NO:56 (HCDR2), and SEQ ID NO:57 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:58 (LCDR3), as defined by the IMGT numbering system;

[0070] (f) Three HCDRs comprising the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:27 (HCDR2), and SEQ ID NO:28 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:29 (LCDR1), SEQ ID NO:30 (LCDR2), and SEQ ID NO:31 (LCDR3), as defined by the Kabat numbering system; or three HCDRs comprising the following amino acid sequences: SEQ ID NO:59 (HCDR1), SEQ ID NO:60 (HCDR2), and SEQ ID NO:61 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:62 (LCDR3), as defined by the IMGT numbering system; or

[0071] (g) Three HCDRs comprising the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:32 (HCDR2), and SEQ ID NO:33 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:34 (LCDR1), SEQ ID NO:35 (LCDR2), and SEQ ID NO:36 (LCDR3), as defined by the Kabat numbering system; or three HCDRs comprising the following amino acid sequences: SEQ ID NO:63 (HCDR1), SEQ ID NO:64 (HCDR2), and SEQ ID NO:65 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:66 (LCDR3), as defined by the IMGT numbering system.

[0072] In some embodiments, this disclosure provides isolated antibody or antigen-binding fragments, wherein the antibody or antigen-binding fragment is capable of binding BCMA and comprises:

[0073] (a) Three HCDRs from the heavy chain variable region containing the amino acid sequence of SEQ ID NO:76, and three LCDRs from the light chain variable region containing the amino acid sequence of SEQ ID NO:77;

[0074] (b) Three HCDRs from the heavy chain variable region containing the amino acid sequence of SEQ ID NO:78, and three LCDRs from the light chain variable region containing the amino acid sequence of SEQ ID NO:79;

[0075] (c) Three HCDRs from the heavy chain variable region containing the amino acid sequence of SEQ ID NO:80, and three LCDRs from the light chain variable region containing the amino acid sequence of SEQ ID NO:81;

[0076] (d) Three HCDRs from the heavy chain variable region containing the amino acid sequence of SEQ ID NO:82, and three LCDRs from the light chain variable region containing the amino acid sequence of SEQ ID NO:83;

[0077] (e) Three HCDRs from the heavy chain variable region containing the amino acid sequence of SEQ ID NO:84, and three LCDRs from the light chain variable region containing the amino acid sequence of SEQ ID NO:85;

[0078] (f) Three HCDRs from the heavy chain variable region containing the amino acid sequence of SEQ ID NO:86, and three LCDRs from the light chain variable region containing the amino acid sequence of SEQ ID NO:87; or

[0079] (g) Three HCDRs from the heavy chain variable region containing the amino acid sequence of SEQ ID NO:88, and three LCDRs from the light chain variable region containing the amino acid sequence of SEQ ID NO:89.

[0080] In some embodiments, the antibody or antigen-binding fragment disclosed herein comprises a human heavy chain and light chain variable region framework, or a human heavy chain and light chain variable region framework having one or more reversion mutations.

[0081] In some embodiments, the antibody or antigen-binding fragment disclosed herein comprises:

[0082] (a) a heavy chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:76, and a light chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:77;

[0083] (b) a heavy chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:78, and a light chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:79;

[0084] (c) The heavy chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:80, and the light chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:81;

[0085] (d) The heavy chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:82, and the light chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:83;

[0086] (e) a heavy chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:84, and a light chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:85;

[0087] (f) a heavy chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:86, and a light chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:87; or

[0088] (g) The heavy chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:88, and the light chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:89.

[0089] In some embodiments, the antibody or antigen-binding fragment disclosed herein comprises:

[0090] (a) The heavy chain variable region containing the amino acid sequence of SEQ ID NO:76 and the light chain variable region containing the amino acid sequence of SEQ ID NO:77;

[0091] (b) The heavy chain variable region containing the amino acid sequence of SEQ ID NO:78 and the light chain variable region containing the amino acid sequence of SEQ ID NO:79;

[0092] (c) The heavy chain variable region containing the amino acid sequence of SEQ ID NO:80 and the light chain variable region containing the amino acid sequence of SEQ ID NO:81;

[0093] (d) The heavy chain variable region containing the amino acid sequence of SEQ ID NO:82 and the light chain variable region containing the amino acid sequence of SEQ ID NO:83;

[0094] (e) The heavy chain variable region containing the amino acid sequence of SEQ ID NO:84 and the light chain variable region containing the amino acid sequence of SEQ ID NO:85.

[0095] (f) The heavy chain variable region containing the amino acid sequence of SEQ ID NO:86 and the light chain variable region containing the amino acid sequence of SEQ ID NO:87; or

[0096] (g) The heavy chain variable region containing the amino acid sequence of SEQ ID NO:88 and the light chain variable region containing the amino acid sequence of SEQ ID NO:89.

[0097] In some embodiments, the antibody or antigen-binding fragment disclosed herein comprises:

[0098] (a) Three HCDRs comprising the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:2 (HCDR2), and SEQ ID NO:3 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:4 (LCDR1), SEQ ID NO:5 (LCDR2), and SEQ ID NO:6 (LCDR3), as defined by the Kabat numbering system; or three HCDRs comprising the following amino acid sequences: SEQ ID NO:37 (HCDR1), SEQ ID NO:38 (HCDR2), and SEQ ID NO:39 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:42 (LCDR3), as defined by the IMGT numbering system; or

[0099] (b) Three HCDRs comprising the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:22 (HCDR2), and SEQ ID NO:23 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:24 (LCDR1), SEQ ID NO:25 (LCDR2), and SEQ ID NO:26 (LCDR3), as defined by the Kabat numbering system; or three HCDRs comprising the following amino acid sequences: SEQ ID NO:55 (HCDR1), SEQ ID NO:56 (HCDR2), and SEQ ID NO:57 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:58 (LCDR3), as defined by the IMGT numbering system.

[0100] In some embodiments, the antibody or antigen-binding fragment comprises:

[0101] (a) The heavy chain variable region containing the amino acid sequence of SEQ ID NO:76 and the light chain variable region containing the amino acid sequence of SEQ ID NO:77; or

[0102] (b) The heavy chain variable region containing the amino acid sequence of SEQ ID NO:84 and the light chain variable region containing the amino acid sequence of SEQ ID NO:85.

[0103] In some embodiments, the antibody or antigen-binding fragment disclosed herein comprises three HCDRs containing the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:22 (HCDR2), and SEQ ID NO:23 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:24 (LCDR1), SEQ ID NO:25 (LCDR2), and SEQ ID NO:26 (LCDR3), as defined by the Kabat numbering system; or three HCDRs containing the following amino acid sequences: SEQ ID NO:55 (HCDR1), SEQ ID NO:56 (HCDR2), and SEQ ID NO:57 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:58 (LCDR3), as defined by the IMGT numbering system. In some embodiments, the antibody or antigen-binding fragment comprises a heavy chain variable region containing the amino acid sequence of SEQ ID NO:84 and a light chain variable region containing the amino acid sequence of SEQ ID NO:85.

[0104] In some embodiments, this disclosure provides isolated antibody or antigen-binding fragments, wherein the antibody or antigen-binding fragment is capable of binding BCMA and comprises:

[0105] (a) A heavy chain variable region containing the amino acid sequence of SEQ ID NO:119, wherein the amino acid sequence is modified by substitution of amino acids at one or more of positions 30, 34, 50, 54, 55, 57, 59, 61, 64, 66, 101, 103, 108, and 109; and

[0106] (b) A light chain variable region containing the amino acid sequence of SEQ ID NO:120, wherein the amino acid sequence is modified to be replaced by an amino acid at one or more of positions 24, 28, 31, 33, 50, 55, 56, 91, 93, 94 and 97.

[0107] In some embodiments, the antibody or antigen-binding fragment comprises a heavy chain variable region containing the amino acid sequence of SEQ ID NO:119, which is modified by substitution of amino acids at one or more of positions 30, 34, 50, 54, 55, 57, 59, 61, 64, 66, 101, 103, 108, and 109, wherein:

[0108] The amino acid at position 30 of SEQ ID NO:119 is replaced by T;

[0109] The amino acid at position 34 of SEQ ID NO:119 is replaced by I;

[0110] The amino acid at position 50 of SEQ ID NO:119 is replaced by G;

[0111] The amino acid at position 54 of SEQ ID NO:119 is replaced by S or I;

[0112] The amino acid at position 55 of SEQ ID NO:119 is replaced by Q;

[0113] The amino acid at position 57 of SEQ ID NO:119 is replaced by T;

[0114] The amino acid at position 59 of SEQ ID NO:119 is replaced by N;

[0115] The amino acid at position 61 of SEQ ID NO:119 is replaced by A;

[0116] The amino acid at position 64 of SEQ ID NO:119 is replaced by Y;

[0117] The amino acid at position 66 of SEQ ID NO:119 is replaced by S;

[0118] The amino acid at position 101 of SEQ ID NO:119 is replaced by V;

[0119] The amino acid at position 103 of SEQ ID NO:119 is replaced by H;

[0120] The amino acid at position 108 of SEQ ID NO:119 is replaced by I; and / or

[0121] The amino acid at position 109 of SEQ ID NO:119 is replaced by E.

[0122] In some embodiments, the antibody or antigen-binding fragment comprises a heavy chain variable region containing the amino acid sequence of SEQ ID NO: 119, which is modified to include at least one amino acid substituted at position 103. In some embodiments, the amino acid at position 103 of SEQ ID NO: 119 is substituted with H.

[0123] In some embodiments, the antibody or antigen-binding fragment comprises a heavy chain variable region containing the amino acid sequence of SEQ ID NO: 119, which is modified to include at least four amino acid substitutions. In some embodiments, the antibody or antigen-binding fragment comprises a heavy chain variable region containing the amino acid sequence of SEQ ID NO: 119, which is modified to include at least one amino acid substitution 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.

[0124] In some embodiments, the antibody or antigen-binding fragment comprises a light chain variable region containing the amino acid sequence of SEQ ID NO:120, which is modified by substitution of amino acids at one or more of positions 24, 28, 31, 33, 50, 55, 56, 91, 93, 94, and 97, wherein:

[0125] The amino acid at position 24 of SEQ ID NO:120 is replaced by R;

[0126] The amino acid at position 28 of SEQ ID NO:120 is replaced by S;

[0127] The amino acid at position 31 of SEQ ID NO:120 is replaced by S;

[0128] The amino acid at position 33 of SEQ ID NO:120 is replaced by I;

[0129] The amino acid at position 50 of SEQ ID NO:120 is replaced by A;

[0130] The amino acid at position 55 of SEQ ID NO:120 is replaced by Q;

[0131] The amino acid at position 56 of SEQ ID NO:120 is replaced by I;

[0132] The amino acid at position 91 of SEQ ID NO:120 is replaced by F;

[0133] The amino acid at position 93 of SEQ ID NO:120 is replaced by R;

[0134] The amino acid at position 94 of SEQ ID NO:120 is substituted with I; and / or

[0135] The amino acid at position 97 of SEQ ID NO:120 is replaced by S.

[0136] In some embodiments, the antibody or antigen-binding fragment comprises a light chain variable region containing the amino acid sequence of SEQ ID NO: 120, which is modified to include at least six amino acid substitutions. In some embodiments, the antibody or antigen-binding fragment comprises a light chain variable region containing the amino acid sequence of SEQ ID NO: 120, which is modified to include at least one amino acid substitution 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.

[0137] In some embodiments, the antibody or antigen-binding fragment comprises:

[0138] (a) a heavy chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:76, and a light chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:77;

[0139] (b) a heavy chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:78, and a light chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:79;

[0140] (c) The heavy chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:80, and the light chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:81;

[0141] (d) The heavy chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:82, and the light chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:83;

[0142] (e) a heavy chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:84, and a light chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:85;

[0143] (f) a heavy chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:86, and a light chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:87; or

[0144] (g) The heavy chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:88, and the light chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:89.

[0145] In some embodiments, the antibody or antigen-binding fragment comprises:

[0146] (a) The heavy chain variable region containing the amino acid sequence of SEQ ID NO:76 and the light chain variable region containing the amino acid sequence of SEQ ID NO:77;

[0147] (b) The heavy chain variable region containing the amino acid sequence of SEQ ID NO:78 and the light chain variable region containing the amino acid sequence of SEQ ID NO:79;

[0148] (c) The heavy chain variable region containing the amino acid sequence of SEQ ID NO:80 and the light chain variable region containing the amino acid sequence of SEQ ID NO:81;

[0149] (d) The heavy chain variable region containing the amino acid sequence of SEQ ID NO:82 and the light chain variable region containing the amino acid sequence of SEQ ID NO:83;

[0150] (e) The heavy chain variable region containing the amino acid sequence of SEQ ID NO:84 and the light chain variable region containing the amino acid sequence of SEQ ID NO:85.

[0151] (f) The heavy chain variable region containing the amino acid sequence of SEQ ID NO:86 and the light chain variable region containing the amino acid sequence of SEQ ID NO:87; or

[0152] (g) The heavy chain variable region containing the amino acid sequence of SEQ ID NO:88 and the light chain variable region containing the amino acid sequence of SEQ ID NO:89.

[0153] In some embodiments, the antibody or antigen-binding fragment disclosed herein comprises a human IgG1 heavy chain constant region. In some embodiments, the antibody or antigen-binding fragment comprises a heavy chain constant region containing 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 antibody or antigen-binding fragment disclosed herein comprises a human IgG4 heavy chain constant region.

[0154] In some embodiments, the antibody or antigen-binding fragment disclosed herein comprises a human Igκ light chain constant region. In some embodiments, the antibody or antigen-binding fragment comprises a light chain constant region containing the amino acid sequence of SEQ ID NO:91. In some embodiments, the antibody or antigen-binding fragment disclosed herein comprises a human Igλ light chain constant region.

[0155] In some embodiments, the antibody or antigen-binding fragment disclosed herein comprises a heavy chain constant region containing the amino acid sequence of SEQ ID NO:90 and a light chain constant region containing the amino acid sequence of SEQ ID NO:91.

[0156] In some embodiments, the antibody or antigen-binding fragment disclosed herein comprises:

[0157] (a) A heavy chain containing the amino acid sequence of SEQ ID NO:92 and a light chain containing the amino acid sequence of SEQ ID NO:93;

[0158] (b) A heavy chain containing the amino acid sequence of SEQ ID NO:94 and a light chain containing the amino acid sequence of SEQ ID NO:95;

[0159] (c) A heavy chain containing the amino acid sequence of SEQ ID NO:96 and a light chain containing the amino acid sequence of SEQ ID NO:97;

[0160] (d) A heavy chain containing the amino acid sequence of SEQ ID NO:98 and a light chain containing the amino acid sequence of SEQ ID NO:99;

[0161] (e) A heavy chain containing the amino acid sequence of SEQ ID NO:100 and a light chain containing the amino acid sequence of SEQ ID NO:101;

[0162] (f) A heavy chain containing the amino acid sequence of SEQ ID NO:102, and a light chain containing the amino acid sequence of SEQ ID NO:103; or

[0163] (g) A heavy chain containing the amino acid sequence of SEQ ID NO:104, and a light chain containing the amino acid sequence of SEQ ID NO:105. In some embodiments, the heavy chain further comprises a C-terminal lysine (K).

[0164] In some embodiments, the antibody or antigen-binding fragment disclosed herein comprises:

[0165] (a) The heavy chain variable region containing the amino acid sequence of SEQ ID NO:76 and the light chain variable region containing the amino acid sequence of SEQ ID NO:77; or

[0166] (b) The heavy chain variable region containing the amino acid sequence of SEQ ID NO:84 and the light chain variable region containing the amino acid sequence of SEQ ID NO:85.

[0167] In some embodiments, the antibody or antigen-binding fragment comprises:

[0168] (a) A heavy chain containing the amino acid sequence of SEQ ID NO:92, and a light chain containing the amino acid sequence of SEQ ID NO:93; or

[0169] (b) A heavy chain containing the amino acid sequence of SEQ ID NO:100, and a light chain containing the amino acid sequence of SEQ ID NO:101.

[0170] In some embodiments, the antibody or antigen-binding fragment disclosed herein comprises a heavy chain variable region containing the amino acid sequence of SEQ ID NO:84 and a light chain variable region containing the amino acid sequence of SEQ ID NO:85. In some embodiments, the antibody or antigen-binding fragment comprises a heavy chain containing the amino acid sequence of SEQ ID NO:100 and a light chain containing the amino acid sequence of SEQ ID NO:101. In some embodiments, the heavy chain further comprises a C-terminal lysine (K).

[0171] 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 prasadiene lactone or a prasadiene lactone derivative. In some embodiments, the therapeutic agent is prasadiene lactone D or a prasadiene lactone D derivative.

[0172] In some embodiments, the therapeutic agent is D1:

[0173]

[0174] In some embodiments, the therapeutic agent is D2:

[0175]

[0176] In some embodiments, the antibody-drug conjugates (ADCs) disclosed herein include formula (I):

[0177] Ab-(LD) p (I)

[0178] in

[0179] Ab is the antibody or antigen-binding fragment disclosed in this article;

[0180] D is a splice modifier;

[0181] L is the connector that covalently links Ab to D; and

[0182] p is an integer from 1 to 15.

[0183] In some embodiments, the connector is a detachable connector.

[0184] In some embodiments, the linker comprises a cleavable peptide moiety. In some embodiments, the cleavable peptide moiety may be enzymatically cleaved. 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).

[0185] In some embodiments, the connector includes a cleavable glucuronide moiety. In some embodiments, the cleavable glucuronide moiety may be cleaved by an enzyme. In some embodiments, the cleavable glucuronide moiety may be cleaved by a glucuronidase. In some embodiments, the cleavable glucuronide moiety may be cleaved by a β-glucuronidase. In some embodiments, the cleavable glucuronide moiety or connector includes a β-glucuronide.

[0186] In some embodiments, the connector includes a maleimide portion. In some embodiments, the maleimide portion includes a maleimide hexanoyl (MC) group. In some embodiments, the maleimide portion reacts with a cysteine ​​residue on an antibody or antigen-binding fragment. In some embodiments, the maleimide portion is linked to the antibody or antigen-binding fragment via a cysteine ​​residue on the antibody or antigen-binding fragment.

[0187] In some embodiments, the connector comprises a maleimide portion and a cleavable peptide portion. In some embodiments, the cleavable peptide portion comprises an amino acid unit. In some embodiments, the cleavable peptide portion or amino acid unit comprises Val-Cit. In some embodiments, the cleavable peptide portion or amino acid unit comprises Val-Ala. In some embodiments, the cleavable peptide portion or amino acid unit comprises Ala-Ala-Asp. In some embodiments, the cleavable peptide portion or amino acid unit comprises Glu-Val-Cit. In some embodiments, the connector comprises a maleimide portion and a cleavable glucuronide portion. In some embodiments, the cleavable glucuronide portion comprises β-glucuronide.

[0188] In some embodiments, the connector includes at least one spacer subunit. In some embodiments, the spacer subunit in the connector includes a polyethylene glycol (PEG) portion. In some embodiments, the PEG portion includes -(PEG) m - And m is an integer from 1 to 10. In some embodiments, m is 2. In some embodiments, the spacer subunit in the connector is linked to an antibody or antigen-binding fragment via a maleimide portion (“Mal-spacer subunit”). In some embodiments, the Mal-spacer subunit includes a PEG portion. In some embodiments, the Mal-spacer subunit includes MC.

[0189] In some embodiments, the connector comprises a Mal-spacer unit and a cleavable peptide portion. In some embodiments, the cleavable peptide portion comprises an amino acid unit. In some embodiments, the cleavable peptide portion or the amino acid unit comprises Val-Cit, Val-Ala, Ala-Ala-Asp, or Glu-Val-Cit. In some embodiments, the connector comprises a Mal-spacer unit and a cleavable glucuronide portion. In some embodiments, the cleavable glucuronide portion comprises β-glucuronide.

[0190] In some embodiments, the maleimide portion or Mal-spacer unit connects an antibody or antigen-binding fragment to a cleavable portion in the adapter.

[0191] In some embodiments, the cleavable portion of the linker comprises a cleavable peptide portion. In some embodiments, the cleavable peptide portion comprises an amino acid unit. In some embodiments, the cleavable peptide portion 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.

[0192] In some embodiments, the cleavable portion of the connector comprises a cleavable glucuronide portion. In some embodiments, the cleavable glucuronide portion comprises β-glucuronide. In some embodiments, the connector comprises MC-β-glucuronide.

[0193] In some embodiments, the cleavable portion of the connector is directly connected to the splicing modulator. In some other embodiments, a spacer unit connects the cleavable portion of the connector to the splicing modulator. In some embodiments, cleavage of the conjugate releases the splicing modulator from the antibody or antigen-binding fragment and the connector. In some embodiments, the spacer unit connecting the cleavable portion of the connector to the splicing modulator is self-immolative.

[0194] In some embodiments, the spacer subunit connecting the cleavable portion of the connector to the splicing modulator comprises a p-aminobenzyloxycarbonyl group (pABC). In some embodiments, the pABC connects the cleavable portion of the connector to the splicing modulator. In some embodiments, the cleavable portion of the connector comprises a cleavable peptide portion. In some embodiments, the cleavable peptide portion comprises an amino acid unit. In some embodiments, the cleavable peptide portion or amino acid unit comprises Val-Cit, Val-Ala, Ala-Ala-Asp, or Glu-Val-Cit. In some embodiments, the connector comprises Val-Cit-pABC. In some embodiments, the connector comprises Val-Ala-pABC. In some embodiments, the connector comprises Ala-Ala-Asp-pABC. In some embodiments, the connector comprises Glu-Val-Cit-pABC. In some embodiments, the cleavable portion of the connector comprises a cleavable glucuronide portion. In some embodiments, the cleavable glucuronide portion comprises β-glucuronide. In some embodiments, the connector comprises β-glucuronide-pABC.

[0195] 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.

[0196] In some embodiments, the connector is a non-breakable connector.

[0197] In some embodiments, the splice modifier comprises a modifier of the SF3b complex. In some embodiments, the splice modifier comprises prasadiene lactone or a prasadiene lactone derivative. In some embodiments, the splice modifier comprises prasadiene lactone D or a prasadiene lactone D derivative. In some embodiments, the splice modifier comprises D1 or D2. In some embodiments, the splice modifier comprises D1. In some embodiments, the splice modifier comprises D2.

[0198] 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.

[0199] In some embodiments, the ADC disclosed herein includes formula (I):

[0200] Ab-(LD) p (I)

[0201] in

[0202] Ab is the antibody or antigen-binding fragment disclosed in this article;

[0203] D is D1;

[0204] L is the connector that covalently links Ab to D; and

[0205] p is an integer from 1 to 15.

[0206] In some embodiments, the ADC disclosed herein includes formula (I):

[0207] Ab-(LD) p (I)

[0208] in

[0209] Ab is the antibody or antigen-binding fragment disclosed in this article;

[0210] D is D2;

[0211] L is the connector that covalently links Ab to D; and

[0212] p is an integer from 1 to 15.

[0213] In some embodiments, the antibody or antigen-binding fragment of the ADC disclosed herein comprises:

[0214] (a) Three HCDRs comprising the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:2 (HCDR2), and SEQ ID NO:3 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:4 (LCDR1), SEQ ID NO:5 (LCDR2), and SEQ ID NO:6 (LCDR3), as defined by the Kabat numbering system; or three HCDRs comprising the following amino acid sequences: SEQ ID NO:37 (HCDR1), SEQ ID NO:38 (HCDR2), and SEQ ID NO:39 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:42 (LCDR3), as defined by the IMGT numbering system;

[0215] (b) Three HCDRs comprising the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:7 (HCDR2), and SEQ ID NO:8 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:9 (LCDR1), SEQ ID NO:10 (LCDR2), and SEQ ID NO:11 (LCDR3), as defined by the Kabat numbering system; or three HCDRs comprising the following amino acid sequences: SEQ ID NO:43 (HCDR1), SEQ ID NO:44 (HCDR2), and SEQ ID NO:45 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:46 (LCDR3), as defined by the IMGT numbering system;

[0216] (c) Three HCDRs comprising the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:12 (HCDR2), and SEQ ID NO:13 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:14 (LCDR1), SEQ ID NO:15 (LCDR2), and SEQ ID NO:16 (LCDR3), as defined by the Kabat numbering system; or three HCDRs comprising the following amino acid sequences: SEQ ID NO:47 (HCDR1), SEQ ID NO:48 (HCDR2), and SEQ ID NO:49 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:50 (LCDR3), as defined by the IMGT numbering system;

[0217] (d) Three HCDRs comprising the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:17 (HCDR2), and SEQ ID NO:18 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:19 (LCDR1), SEQ ID NO:20 (LCDR2), and SEQ ID NO:21 (LCDR3), as defined by the Kabat numbering system; or three HCDRs comprising the following amino acid sequences: SEQ ID NO:51 (HCDR1), SEQ ID NO:52 (HCDR2), and SEQ ID NO:53 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:54 (LCDR3), as defined by the IMGT numbering system;

[0218] (e) Three HCDRs comprising the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:22 (HCDR2), and SEQ ID NO:23 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:24 (LCDR1), SEQ ID NO:25 (LCDR2), and SEQ ID NO:26 (LCDR3), as defined by the Kabat numbering system; or three HCDRs comprising the following amino acid sequences: SEQ ID NO:55 (HCDR1), SEQ ID NO:56 (HCDR2), and SEQ ID NO:57 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:58 (LCDR3), as defined by the IMGT numbering system;

[0219] (f) Three HCDRs comprising the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:27 (HCDR2), and SEQ ID NO:28 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:29 (LCDR1), SEQ ID NO:30 (LCDR2), and SEQ ID NO:31 (LCDR3), as defined by the Kabat numbering system; or three HCDRs comprising the following amino acid sequences: SEQ ID NO:59 (HCDR1), SEQ ID NO:60 (HCDR2), and SEQ ID NO:61 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:62 (LCDR3), as defined by the IMGT numbering system; or

[0220] (g) Three HCDRs comprising the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:32 (HCDR2), and SEQ ID NO:33 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:34 (LCDR1), SEQ ID NO:35 (LCDR2), and SEQ ID NO:36 (LCDR3), as defined by the Kabat numbering system; or three HCDRs comprising the following amino acid sequences: SEQ ID NO:63 (HCDR1), SEQ ID NO:64 (HCDR2), and SEQ ID NO:65 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:66 (LCDR3), as defined by the IMGT numbering system.

[0221] In some embodiments, the antibody or antigen-binding fragment in the ADC comprises a human heavy chain and light chain variable region framework, or a human heavy chain and light chain variable region framework having one or more reversion mutations.

[0222] In some embodiments, the antibody or antigen-binding fragment in the ADC comprises:

[0223] (a) a heavy chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:76, and a light chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:77;

[0224] (b) a heavy chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:78, and a light chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:79;

[0225] (c) The heavy chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:80, and the light chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:81;

[0226] (d) The heavy chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:82, and the light chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:83;

[0227] (e) a heavy chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:84, and a light chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:85;

[0228] (f) a heavy chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:86, and a light chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:87; or

[0229] (g) The heavy chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:88, and the light chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:89.

[0230] In some embodiments, the antibody or antigen-binding fragment in the ADC comprises:

[0231] (a) The heavy chain variable region containing the amino acid sequence of SEQ ID NO:76 and the light chain variable region containing the amino acid sequence of SEQ ID NO:77;

[0232] (b) The heavy chain variable region containing the amino acid sequence of SEQ ID NO:78 and the light chain variable region containing the amino acid sequence of SEQ ID NO:79;

[0233] (c) The heavy chain variable region containing the amino acid sequence of SEQ ID NO:80 and the light chain variable region containing the amino acid sequence of SEQ ID NO:81;

[0234] (d) The heavy chain variable region containing the amino acid sequence of SEQ ID NO:82 and the light chain variable region containing the amino acid sequence of SEQ ID NO:83;

[0235] (e) The heavy chain variable region containing the amino acid sequence of SEQ ID NO:84 and the light chain variable region containing the amino acid sequence of SEQ ID NO:85.

[0236] (f) The heavy chain variable region containing the amino acid sequence of SEQ ID NO:86 and the light chain variable region containing the amino acid sequence of SEQ ID NO:87; or

[0237] (g) The heavy chain variable region containing the amino acid sequence of SEQ ID NO:88 and the light chain variable region containing the amino acid sequence of SEQ ID NO:89.

[0238] In some embodiments, the antibody or antigen-binding fragment of the ADC disclosed herein comprises:

[0239] (a) Three HCDRs comprising the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:2 (HCDR2), and SEQ ID NO:3 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:4 (LCDR1), SEQ ID NO:5 (LCDR2), and SEQ ID NO:6 (LCDR3), as defined by the Kabat numbering system; or three HCDRs comprising the following amino acid sequences: SEQ ID NO:37 (HCDR1), SEQ ID NO:38 (HCDR2), and SEQ ID NO:39 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:42 (LCDR3), as defined by the IMGT numbering system; or

[0240] (b) Three HCDRs comprising the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:22 (HCDR2), and SEQ ID NO:23 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:24 (LCDR1), SEQ ID NO:25 (LCDR2), and SEQ ID NO:26 (LCDR3), as defined by the Kabat numbering system; or three HCDRs comprising the following amino acid sequences: SEQ ID NO:55 (HCDR1), SEQ ID NO:56 (HCDR2), and SEQ ID NO:57 (HCDR3); and three LCDRs comprising the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:58 (LCDR3), as defined by the IMGT numbering system.

[0241] In some embodiments, the antibody or antigen-binding fragment in the ADC comprises:

[0242] (a) The heavy chain variable region containing the amino acid sequence of SEQ ID NO:76 and the light chain variable region containing the amino acid sequence of SEQ ID NO:77; or

[0243] (b) The heavy chain variable region containing the amino acid sequence of SEQ ID NO:84 and the light chain variable region containing the amino acid sequence of SEQ ID NO:85.

[0244] In some embodiments, the antibody or antigen-binding fragment of the ADC disclosed herein comprises three HCDRs containing the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:22 (HCDR2), and SEQ ID NO:23 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:24 (LCDR1), SEQ ID NO:25 (LCDR2), and SEQ ID NO:26 (LCDR3), as defined by the Kabat numbering system; or three HCDRs containing the following amino acid sequences: SEQ ID NO:55 (HCDR1), SEQ ID NO:56 (HCDR2), and SEQ ID NO:57 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:58 (LCDR3), as defined by the IMGT numbering system. In some embodiments, the antibody or antigen-binding fragment in the ADC includes a heavy chain variable region containing the amino acid sequence of SEQ ID NO:84 and a light chain variable region containing the amino acid sequence of SEQ ID NO:85.

[0245] In some embodiments, the ADC disclosed herein includes formula (I):

[0246] Ab-(LD) p (I)

[0247] in

[0248] Ab is an antibody or antigen-binding fragment capable of binding BCMA and comprising three HCDRs containing the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:22 (HCDR2), and SEQ ID NO:23 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:24 (LCDR1), SEQ ID NO:25 (LCDR2), and SEQ ID NO:26 (LCDR3), as defined by the Kabat numbering system; or three HCDRs containing the following amino acid sequences: SEQ ID NO:55 (HCDR1), SEQ ID NO:56 (HCDR2), and SEQ ID NO:57 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:58 (LCDR3), as defined by the IMGT numbering system;

[0249] D is D1;

[0250] L is the connector that covalently links Ab to D; and

[0251] p is an integer from 1 to 15.

[0252] In some embodiments, the antibody or antigen-binding fragment of the ADC disclosed herein comprises a human heavy chain and light chain variable region framework, or a human heavy chain and light chain variable region framework having one or more reversion mutations.

[0253] In some embodiments, the antibody or antigen-binding fragment of the ADC disclosed herein comprises a heavy chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:84 and a light chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:85. In some embodiments, the antibody or antigen-binding fragment in the ADC comprises a heavy chain variable region containing the amino acid sequence of SEQ ID NO:84 and a light chain variable region containing the amino acid sequence of SEQ ID NO:85.

[0254] 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 in the ADC comprises a heavy chain constant region containing the amino acid sequence of SEQ ID NO:90 and a light chain constant region containing the amino acid sequence of SEQ ID NO:91. In some embodiments, the antibody or antigen-binding fragment in the ADC comprises a heavy chain containing the amino acid sequence of SEQ ID NO:100 and a light chain containing 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).

[0255] In some embodiments, the connector of the ADC disclosed herein is a cleavable connector. In some embodiments, the cleavable connector comprises MC-Val-Cit-pABC. In some embodiments, the cleavable connector comprises MC-Val-Ala-pABC. In some embodiments, the cleavable connector comprises MC-Ala-Ala-Asp-pABC. In some embodiments, the cleavable connector comprises MC-Glu-Val-Cit-pABC. In some embodiments, the cleavable connector comprises MC-(PEG)2-Val-Cit-pABC. In some embodiments, the cleavable connector comprises MC-β-glucuronide.

[0256] In some embodiments, p of the ADC 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.

[0257] In some embodiments, the ADC disclosed herein includes formula (I):

[0258] Ab-(LD) p (I)

[0259] in

[0260] Ab is an antibody or antigen-binding fragment capable of binding BCMA and comprising three HCDRs containing the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:22 (HCDR2), and SEQ ID NO:23 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:24 (LCDR1), SEQ ID NO:25 (LCDR2), and SEQ ID NO:26 (LCDR3), as defined by the Kabat numbering system; or three HCDRs containing the following amino acid sequences: SEQ ID NO:55 (HCDR1), SEQ ID NO:56 (HCDR2), and SEQ ID NO:57 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:58 (LCDR3), as defined by the IMGT numbering system;

[0261] D is D1;

[0262] L is a connector that includes MC-Val-Cit-pABC (ADL1); and

[0263] p is an integer from 1 to 15.

[0264] In some embodiments, the antibody or antigen-binding fragment in the ADC disclosed herein comprises a human heavy chain and light chain variable region framework, or a human heavy chain and light chain variable region framework having one or more reversion mutations. In some embodiments, the antibody or antigen-binding fragment in the ADC comprises a heavy chain variable region containing the amino acid sequence of SEQ ID NO:84 and a light chain variable region containing the amino acid sequence of SEQ ID NO:85. In some embodiments, the antibody or antigen-binding fragment in 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 in the ADC comprises a heavy chain constant region containing the amino acid sequence of SEQ ID NO:90 and a light chain constant region containing the amino acid sequence of SEQ ID NO:91. In some embodiments, the antibody or antigen-binding fragment in the ADC comprises a heavy chain containing the amino acid sequence of SEQ ID NO:100 and a light chain containing 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.

[0265] In some embodiments, the ADC disclosed herein includes formula (I):

[0266] Ab-(LD) p (I)

[0267] in

[0268] Ab is an antibody or antigen-binding fragment, wherein the antibody or antigen-binding fragment is capable of binding BCMA and includes a heavy chain variable region containing the amino acid sequence of SEQ ID NO:84 and a light chain variable region containing the amino acid sequence of SEQ ID NO:85.

[0269] D is D1;

[0270] L is a connector that includes MC-Val-Cit-pABC (ADL1); and

[0271] p is an integer from 1 to 15.

[0272] In some embodiments, the antibody or antigen-binding fragment in 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 in the ADC comprises a heavy chain constant region containing the amino acid sequence of SEQ ID NO:90 and a light chain constant region containing the amino acid sequence of SEQ ID NO:91. In some embodiments, the antibody or antigen-binding fragment in the ADC comprises a heavy chain containing the amino acid sequence of SEQ ID NO:100 and a light chain containing 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.

[0273] In various embodiments, this document provides pharmaceutical compositions comprising the antibodies, antigen-binding fragments, conjugates, and / or ADCs described herein. In some embodiments, the pharmaceutical composition comprises one or more antibodies, one or more antigen-binding fragments, and / or one or more ADCs described herein, and at least one pharmaceutically acceptable carrier. In some embodiments, the pharmaceutical composition comprises multiple copies of the antibody, antigen-binding fragment, and / or ADC. In some embodiments, the pharmaceutical composition comprises multiple copies of the ADC disclosed herein, wherein the average p-value of the ADC in the composition is from about 2 to about 8. In some embodiments, the average p-value of the ADC in the composition is about 4.

[0274] In some embodiments, this document provides treatment methods and uses for the described antibodies, antigen-binding fragments, conjugates, and / or ADC complexes or compositions, such as for treating cancer. In some aspects, this disclosure provides methods for treating a subject who has or is suspected of having cancer, these methods being carried out by administering to the subject a therapeutically effective amount and / or a therapeutically effective regimen of any of the antibodies, antigen-binding fragments, ADCs, and / or pharmaceutical compositions described herein. In some aspects, this disclosure provides methods for reducing or slowing the growth of a cancer cell population in a subject, these methods being carried out by administering to the subject a therapeutically effective amount and / or a therapeutically effective regimen of any of the antibodies, antigen-binding fragments, ADCs, and / or pharmaceutical compositions described herein. In some embodiments, the administration of the antibody, antigen-binding fragment, ADC, and / or pharmaceutical composition reduces 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 an 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, one or more additional therapeutic agents include BCL2 inhibitors, BCLxL inhibitors, BCL2 / BCLxL inhibitors, and / or γ-secretase inhibitors.

[0275] In some embodiments of the treatments and uses disclosed herein, treatment with the antibody, antigen-binding fragment, ADC, and / or pharmaceutical composition induces bystander killing of cancer cells that do not express the target antigen but are adjacent to cancer cells that express the target antigen. In some embodiments, the subject has one or more cancer cells expressing the target antigen. In some embodiments, the target antigen is BCMA. In some embodiments, the antibody, antigen-binding fragment, ADC, and / or pharmaceutical composition induces increased levels of bystander killing of cancer cells compared to a reference, such as an alternative anti-BCMA ADC (e.g., AB200-ADL10-MMAF).

[0276] In some embodiments of the treatments 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 leukemia, lymphoma, plasmacytoma, or myeloma. In some embodiments, the plasma cell malignancy or cancer is multiple myeloma, diffuse large B-cell lymphoma, mantle cell lymphoma, plasmablastic lymphoma, plasmablastic myeloma, or Burkitt 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 includes actively dividing cells, dormant cells, or both. In some embodiments, the plasma cell malignancy or cancer comprises at least some dormant cells, such as non-dividing 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 has high or intermediate levels of MCL1 expression.

[0277] In some embodiments, this document provides treatment methods and uses for the antibodies, antigen-binding fragments, conjugates, and / or ADC complexes or compositions described herein, such as for determining whether a subject with or suspected of having cancer (e.g., cancer expressing BCMA) will respond to treatment with an agent targeting BCMA (e.g., the antibodies, antigen-binding fragments, ADCs, and / or pharmaceutical compositions described herein). In some embodiments, the method includes providing a biological sample from a subject; contacting the sample with an antibody or antigen-binding fragment disclosed herein; and detecting the binding of the antibody or antigen-binding fragment to one or more cancer cells in the sample. In some embodiments, one or more cancer cells express BCMA. In some embodiments, the cancer is a plasma cell malignancy. In some embodiments, a plasma cell malignancy or cancer is leukemia, lymphoma, plasmacytoma, or myeloma. In some embodiments, a plasma cell malignancy or cancer is multiple myeloma, diffuse large B-cell lymphoma, mantle cell lymphoma, plasmablastic lymphoma, plasmablastic myeloma, or Burkitt lymphoma. In some embodiments, a plasma cell malignancy or cancer is multiple myeloma. In some embodiments, plasma cell malignancy or cancer is relapsed / refractory multiple myeloma. In some embodiments, the biological sample is a blood sample or a bone marrow aspiration sample. In some embodiments, the blood sample is blood, blood components, or one or more cells obtained from blood or blood components.

[0278] In some other aspects, this disclosure provides pharmaceutical compositions comprising antibodies, antigen-binding fragments, conjugates, and / or ADCs, as well as pharmaceutically acceptable diluents, carriers, and / or excipients. In some embodiments, one or more nucleic acids encoding the antibody or antigen-binding fragment of this disclosure, or the antibody portion of the conjugate and / or ADC of this disclosure, are also provided. These nucleic acids may be in the form of isolated nucleic acids, nucleic acids incorporated into isolated carriers, and / or antibody or antigen-binding fragments expressed by cells or cell populations under conditions suitable for generating antibody or antigen-binding fragments.

[0279] In other aspects, this disclosure provides methods for generating the antibodies, antigen-binding fragments, conjugates, and / or ADC complexes or compositions described herein. In some embodiments, this disclosure provides a method for generating antibodies or antigen-binding fragments by culturing host cells or cell populations modified to contain one or more nucleic acids encoding the antibodies or antigen-binding fragments described herein under conditions suitable for generating antibodies or antigen-binding fragments. In some embodiments, this disclosure provides a method for generating ADCs by reacting the antibody or antigen-binding fragments described herein with a linker connected to a splicing modulator under conditions allowing conjugation. In some embodiments, this disclosure provides a method for generating ADCs by reacting the antibody or antigen-binding fragments described herein with a linker and a splicing modulator under conditions allowing conjugation.

[0280] In some embodiments, the methods disclosed herein include 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 include simultaneously reacting an antibody or antigen-binding fragment with a linker and a 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. Attached Figure Description

[0281] Figure 1The flow cytometry was used to assess the binding affinity of the anti-BCMA antibody to the NCI-H929 human myeloma cell line (high BCMA expression).

[0282] Figure 2 The flow cytometry was used to assess the binding affinity of the anti-BCMA antibody to the OPM2 human myeloma cell line (with moderate BCMA expression).

[0283] Figure 3 The flow cytometry was used to assess the binding affinity of the anti-BCMA ADC to the Raji human Burkitt lymphoma cell line (low BCMA expression).

[0284] Figure 4 The flow cytometry was used to assess the binding affinity of anti-BCMA ADC to the NCI-H929 human myeloma cell line.

[0285] Figure 5 This diagram illustrates possible mRNA splicing changes in genes affected by ADC treatment. Without being bound by theory, these possible mRNA splicing changes may include increased accumulation of pre-matured mRNA (intron retention), exon skipping events, and / or aberrant junctions (AJs), accompanied by decreased expression of properly spliced ​​(mature) mRNAs and mRNAs with canonical junctions (CJs).

[0286] Figures 6A-6D This shows four exemplary genes (FBXW5) in OPM2 tumors treated with AB200 antibody or AB200-ADL5-D4. Figure 6A ), PLEKHJ1 ( Figure 6B ), DYNLT1 ( Figure 6C ) and UBA2 ( Figure 6D The regulation of mRNA splicing is shown. Mature mRNAs (FBXW5-mat, PLEKHJ1-mat, and DYNLT1-mat), pre-mRNA species (FBXW5-pre, PLEKHJ1-pre_2, and DYNLT1-pre), mRNAs with canonical splicing sites (UBA2_CJ_1) and mRNAs with aberrant splicing sites (UBA2_AJ_4) are shown.

[0287] Figures 7A-7D This shows four exemplary genes (FBXW5) in MOLP8 tumors treated with AB200 antibody or AB200-ADL1-D2. Figure 7A ), PLEKHJ1 ( Figure 7B ), DYNLT1 ( Figure 7C ) and UBA2 ( Figure 7DThe regulation of mRNA splicing is shown. Mature mRNAs (FBXW5-mat, PLEKHJ1-mat, and DYNLT1-mat), pre-mRNA species (FBXW5-pre, PLEKHJ1-pre_2, and DYNLT1-pre), mRNAs with canonical splicing sites (UBA2_CJ_1) and mRNAs with aberrant splicing sites (UBA2_AJ_4) are shown.

[0288] Figures 8A-8D This shows four exemplary genes (FBXW5) in OPM2 tumors treated with AB200 antibody, AB212-ADL1-D1, or AB212-ADL1-D2. Figure 8A ), PLEKHJ1 ( Figure 8B ), DYNLT1 ( Figure 8C ) and UBA2 ( Figure 8D The regulation of mRNA splicing is shown. Mature mRNAs (FBXW5-mat, PLEKHJ1-mat, and DYNLT1-mat), pre-mRNA species (FBXW5-pre, PLEKHJ1-pre_2, and DYNLT1-pre), mRNAs with canonical splicing sites (UBA2_CJ_1) and mRNAs with aberrant splicing sites (UBA2_AJ_4) are shown.

[0289] Figure 9 This study demonstrates the in vivo anticancer activity of an exemplary anti-BCMA antibody (AB214) in an OPM2 xenograft model (Study 1).

[0290] Figure 10 This study demonstrates the in vivo anticancer activity of exemplary anti-BCMA antibodies (AB212, AB217, and AB218) in an OPM2 xenograft model (Study 2).

[0291] Figure 11 This study demonstrates the in vivo anticancer activity of an exemplary anti-BCMA ADC in an OPM2 xenograft model (Study 1).

[0292] Figure 12 This study demonstrates the in vivo anticancer activity of an exemplary anti-BCMA ADC in an OPM2 xenograft model (Study 2).

[0293] Figure 13 This study demonstrates the in vivo anticancer activity of an exemplary anti-BCMA ADC in an OPM2 xenograft model (Study 3).

[0294] Figure 14 This demonstrates the in vivo anticancer activity of an exemplary anti-BCMA ADC in an OPM2 xenograft model (Study 4).

[0295] Figure 15 This study demonstrates the in vivo anticancer activity of an exemplary anti-BCMA ADC in a MOLP8 xenograft model (Study 1).

[0296] Figure 16 This study demonstrates the in vivo anticancer activity of an exemplary anti-BCMA ADC in a MOLP8 xenograft model (Study 2).

[0297] Figures 17A-17D The in vitro cytotoxicity of AB216-ADL1-D1 (y-axis) and AB200-ADL10-MMAF (x-axis) against a group of 11 human myeloma cell lines is shown. 50 LD 50 Area under the curve (AUC) and maximum percentage reduction in viable cells (R²) min The values ​​of Ave are displayed respectively. Figures 17A-17D middle.

[0298] Figure 18 The results showed that under normal serum conditions, in NCI-H929 human myeloma cells, after 6 days... The activities of AB216-ADL1-D1 and AB200-ADL10-MMAF were evaluated in the cell viability assay.

[0299] Figures 19A-19B The results showed that under low serum conditions, AB216-ADL1-D1 and AB200-ADL10-MMAF were effective for 6 days in NCI-H929 human myeloma cells. Biological replication of cell viability assessment. Figure 19A (Experiment repeated #1) and Figure 19B (Experimental Replication #2) Each shows the relative proliferation of NCI-H929 human myeloma cells treated with AB216-ADL1-D1 or AB200-ADL10-MMAF on day 6 under low serum conditions, as the percentage (%) of the time-matched untreated control.

[0300] Figure 20 The results showed that under normal serum conditions, in OPM2 human myeloma cells, after 6 days... The activities of AB216-ADL1-D1 and AB200-ADL10-MMAF were evaluated in the cell viability assay.

[0301] Figures 21A-21B The results showed that under low serum conditions, AB216-ADL1-D1 and AB200-ADL10-MMAF were effective for 6 days in OPM2 human myeloma cells. Biological replication of cell viability assessment. Figure 21A (Experiment repeated #1) and Figure 21B(Experimental Replication #2) Each shows the relative proliferation of OPM2 human myeloma cells treated with AB216-ADL1-D1 or AB200-ADL10-MMAF on day 6 under low serum conditions, as the percentage (%) of the time-matched untreated control.

[0302] Figure 22 The mRNA levels of MCL1 pro-survival, long isoform (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 were shown.

[0303] Figure 23 Immunoblot analysis showing MCL1 expression in NCI-H929 human myeloma cells treated with 5, 50, or 500 nM AB216-ADL1-D1 or AB200-ADL10-MMAF for 24 or 96 hours. Detailed Implementation

[0304] The disclosed compositions and methods can be more easily understood with reference to the following detailed description.

[0305] Throughout this document, descriptions relate to compositions and methods of using such compositions. When this disclosure describes or claims features or embodiments associated with a composition, such features or embodiments equally apply to methods of using the composition. Similarly, when this disclosure describes or claims features or embodiments associated with methods of using the composition, such features or embodiments equally apply to the composition.

[0306] When a range of values ​​is indicated, it includes embodiments using any particular value within that range. Furthermore, references to values ​​stated by range include every value within that range. All ranges include their endpoints and are composable. When a value is indicated as an approximation by the preceding use of "about," it should be understood that the particular value forms another embodiment. Unless the context explicitly indicates otherwise, references to a particular numerical value include at least that particular value. Unless otherwise indicated regarding its specific use, the use of "or" means "and / or."

[0307] It should be understood that some features of the compositions and methods disclosed herein, described in the case of individual embodiments for clarity, may also be provided in combination with individual embodiments. Conversely, various features of the disclosed compositions and methods, described in the case of individual embodiments for simplicity, may also be provided individually or in any sub-combination.

[0308] All references cited herein are incorporated by way of reference for any purpose. In the event of any discrepancy between the references and this specification, this specification shall prevail.

[0309] Throughout this specification and claims, various terms related to the described aspects are used. Unless otherwise indicated, such terms will be given their ordinary meaning in the art. Other specially defined terms will be interpreted in a manner consistent with the definitions provided herein.

[0310] As used herein, the singular forms “a / an” and “the” include the plural forms unless the context explicitly indicates otherwise.

[0311] As will be apparent to those skilled in the art from the teachings contained herein, in the context of numerical values ​​and ranges, the terms “about” or “approximately” refer to a value or range that is approximately or close to the stated value or range, such that the embodiment can be performed as intended, such as having the desired amount of nucleic acid or polypeptide in the reaction mixture. In some embodiments, “about” means an index value ±10%.

[0312] The term "antibody" in its broadest sense refers to an immunoglobulin molecule that recognizes and specifically binds to a target such as a protein, polypeptide, carbohydrate, polynucleotide, lipid, or a combination of the foregoing via at least one antigen recognition site within the variable region of an immunoglobulin molecule. The heavy chain of an antibody consists of a heavy chain variable region (V... H ) and heavy chain constant region (C H The light chain is composed of the light chain variable region (V). L ) and light chain constant region (C L The mature heavy and light chain variable regions each comprise three complementarity-determining regions (CDR1, CDR2, and CDR3) within four framework regions (FR1, FR2, FR3, and FR4) arranged from the N-terminus to the C-terminus: FR1, CDR1, FR2, CDR2, FR3, CDR3, and FR4. An "antibody" can be naturally occurring or artificial, such as a monoclonal antibody produced by conventional hybridoma techniques. An antibody can contain one or more heavy and / or light chains. The term "antibody" includes full-length monoclonal antibodies and full-length polyclonal antibodies, as well as antibody fragments such as Fab, Fab', F(ab')2, Fv, and single-chain antibodies. An antibody can be any of the five major classes of immunoglobulins: IgA, IgD, IgE, IgG, and IgM, or their subclasses (e.g., isotypes IgG1, IgG2, IgG3, and IgG4). The term further encompasses human antibodies, chimeric antibodies, humanized antibodies, and any modified immunoglobulin molecule containing an antigen recognition site, provided that it exhibits one or more of the desired biological activities (e.g., binding to a target antigen (e.g., BCMA) or internalization within a cell expressing the target antigen).

[0313] Numbering systems describing the locations of CDR and FR regions in antibodies have been defined by different 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 disclosed herein.

[0314] In some embodiments, the antibody and antigen binding fragments disclosed herein comprise CDR and FR regions defined by the Kabat numbering system (see, for example, Kabat et al., “Sequences of Proteins of Immunological Interest”, Diane Publishing Company (1992); also see, Kabat et al., “Sequences of Proteins of Immunological Interest”, U.S. Department of Health and Human Services, U.S. Government Printing Office (1987 and 1991)). Exemplary CDR sequences defined by the Kabat numbering system are listed in Table 3 and may be used in any of the exemplary antibody and antigen binding fragments disclosed herein. In some embodiments, the Kabat numbering system may also be used to describe one or more individual amino acids at positions within the CDR and / or FR regions. In some embodiments, the Kabat numbering system is used in addition to (or as an alternative to) describing one or more amino acids using their absolute positions within the antibody or antigen binding fragment. In some embodiments, the amino acids and / or amino acid modifications in the antibody or antigen-binding fragments disclosed herein can be identified by their Kabat positions. For example, in some embodiments, the antibody 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 at least one amino acid substitution at position 103 (i.e., at absolute position 103). In some embodiments, position 103 of SEQ ID NO:119 can be identified by its Kabat position (i.e., 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.

[0315] In some embodiments, the antibody and antigen binding fragments disclosed herein comprise numbers generated by the IMGT numbering system (International Immunogenetic Information System). The CDR and FR regions are defined by the IMGT numbering system. Exemplary CDR sequences defined by the IMGT numbering system are listed in Table 4 and may be used in any exemplary antibody and antigen-binding fragments disclosed herein.

[0316] Other numbering systems, such as the Chothia numbering system (see, for example, Al-Lazikani et al. J Mol Biol. [Journal of Molecular Biology] 1997; 273: 927-48) and the Chemical Computing Group (CCG) numbering system (see, for example, Molecular Operating Environment (MOE), 2013.08; Chemical Computing Group ULC, Montreal, QC, Canada, H3A 2R7, 2018), are known in the art and can be used to define the CDR and FR regions in the antibody and antigen binding fragments disclosed herein. In some embodiments, the antibody and antigen binding fragments disclosed herein comprise a CDR sequence that is 100% homologous to the CDR sequence described herein.

[0317] As used herein, the term "monoclonal antibody" refers to an antibody obtained from a substantially homogeneous population of antibodies, meaning that the individual antibodies constituting that population are identical except for the possible small number of naturally occurring mutations. Monoclonal antibodies are highly specific for a single antigenic epitope. In contrast, conventional (polyclonal) antibody formulations typically comprise multiple antibodies that target or are specific to different epitopes. The modifier "monoclonal" indicates the characteristic of an antibody obtained from a substantially homogeneous population of antibodies and should not be construed as requiring the antibody to be produced by any particular method. For example, monoclonal antibodies used according to this disclosure may be manufactured by a hybridoma method first described by Kohler et al. (1975) Nature 256:495, or by a recombinant DNA method (see, for example, U.S. Patent No. 4,816,567). Monoclonal antibodies can also be isolated from phage antibody libraries using techniques described, for example, those described in Clackson et al. (1991) Nature 352:624-8 and Marks et al. (1991) J Mol Biol. 222:581-97.

[0318] The monoclonal antibodies described herein specifically include “chimeric” antibodies, wherein a portion of the heavy chain and / or light chain is identical or homologous to a corresponding sequence in an antibody derived from a particular species or belonging to a particular antibody class or subclass, while the remainder of the chain is identical or homologous to a corresponding sequence in an antibody derived from another species or belonging to another antibody class or subclass, and in fragments of such antibodies; provided that they specifically bind to the target antigen and / or exhibit the desired biological activity.

[0319] As used herein, the term "human antibody" refers to an antibody produced by a human or an antibody having the amino acid sequence of an antibody produced by a human.

[0320] As used herein, the term "chimeric antibody" refers to an antibody in which (a) a constant region is altered, replaced, or exchanged such that the antigen-binding site (variable region) is linked to a constant region of a different or altered class, effector function, and / or species; and / or (b) a variable region or a portion thereof is altered, replaced, or exchanged for a variable region or a portion thereof of a different or altered antigen specificity. To generate chimeric antibodies, in some embodiments, a variable region sequence from a non-human donor antibody (e.g., mouse, rabbit, or rat donor antibody) can be linked to a human constant region using methods known in the art (see, for example, U.S. Patent No. 4,816,567 (Cabilly et al.)). For example, a mouse anti-BCMA antibody can be modified by replacing the mouse constant region with a constant region derived from a human immunoglobulin. Due to the replacement with a human constant region, the chimeric antibody can retain its specificity for recognizing human BCMA while exhibiting reduced immunogenicity in humans compared to the original mouse antibody.

[0321] As used herein, the term "humanized antibody" refers to an antibody form comprising at least some human sequences and at least some non-human sequences. Typically, an antibody comprises a human sequence conferring binding specificity to a target antigen and a small subset of non-human sequences. Such antibodies are chimeric antibodies, which comprise a minimal sequence derived from a non-human antibody and retain the reactivity of the non-human antibody while exhibiting lower immunogenicity in humans. Typically, humanized antibodies are generated by replacing the hypervariable region sequence of a human receptor antibody with a hypervariable region sequence of a non-human donor antibody (e.g., a mouse, rabbit, or rat donor antibody) that binds to the target antigen (e.g., BCMA). In some cases, the frame region sequence of the receptor antibody may also be replaced with a corresponding sequence of the donor antibody (e.g., via a reversion mutation). In addition to sequences derived from the donor and receptor antibodies, humanized antibodies may also be modified by residue substitution within the frame region and / or the replaced non-human residues to improve and optimize antibody specificity, selectivity, affinity, and / or activity as discussed herein.

[0322] In some embodiments, the antibody and antigen-binding fragments disclosed herein are humanized. In some embodiments, the disclosed antibody and antigen-binding fragments contain a minimal sequence derived from a nonhuman antibody, such as mouse antibody CA8 (see, for example, U.S. Patent No. 9,273,141, which relates to exemplary nonhuman antibody sequences and is incorporated herein by reference). In some embodiments, the disclosed antibody and antigen-binding fragments retain the affinity of the nonhuman antibody but include modifications in one or more CDRs and / or frames. In some embodiments, the disclosed antibody and antigen-binding fragments also exhibit one or more desired properties not exhibited by the nonhuman antibody, including but not limited to lower immunogenicity and reduced toxicity. In some embodiments, the nonhuman antibody is a mouse antibody. In some embodiments, the nonhuman antibody is a mouse anti-BCMA antibody. In some embodiments, a nonhuman antibody or its antigen-binding fragment or antigen-binding domain is used as a comparative or “reference” antibody, antigen-binding fragment, or antigen-binding domain, for example, to assess comparable binding affinity. In other embodiments, a variant of a nonhuman antibody or its antigen-binding fragment or antigen-binding domain (e.g., a humanized variant) is used as a comparative or “reference” antibody, antigen-binding fragment, or antigen-binding domain.

[0323] In some embodiments, the reference antibody or its antigen-binding fragment or antigen-binding domain is a humanized anti-BCMA antibody comprising a heavy chain variable region and a light chain variable region, the heavy chain variable region comprising the amino acid sequence of SEQ ID NO:119 and the light chain variable region comprising the amino acid sequence of SEQ ID NO:120 (see, for example, U.S. Patent No. 9,273,141, which is incorporated herein by reference with respect to an exemplary reference antibody sequence). Such reference antibodies, antigen-binding fragments, and / or antigen-binding domains may be referred to herein as “AB200”.

[0324] As used herein, the term "antigen-binding fragment" or "antigen-binding moiety" of an antibody refers to one or more fragments of an antibody or protein that retain the ability to specifically bind to an antigen (e.g., BCMA). Antigen-binding fragments may also retain the ability to be internalized into cells expressing the antigen. In some embodiments, antigen-binding fragments also retain immune effector activity. It has been shown that fragments of a full-length antibody can perform the antigen-binding function of a full-length antibody. Examples of binding fragments encompassed within the term "antigen-binding fragment" or "antigen-binding moiety" of an antibody include (i) Fab fragments, i.e., fragments composed of V... L Structural domain, V H Domain, C L Domain and C H1 (ii) a monovalent segment composed of structural domains; (iii) a F(ab')2 segment, i.e., a divalent segment containing two Fab segments connected by disulfide bridges at the hinge region; (iv) a segment composed of V H Domain and CH1 (iv) The Fd fragment composed of the binding domain; L Domain and V H Fv segments composed of structural domains; (v)dAb segments containing a single variable structural domain, such as V. H The structural domains (see, for example, Ward et al. (1989) Nature 341:544-6; and International Publication No. WO 1990 / 005144); and (vi) the separated complementarity-determining regions (CDRs). Furthermore, although the two structural domains V of the Fv segment... L and V H Encoded by individual genes, but which can be conjugated using recombination methods by enabling them to be made into synthetic linkers in the form of single protein chains, where V L District and V H Regions pair to form a monovalent molecule (called a single-chain Fv (scFv)). See, for example, 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 antibody, and are known in the art to be exemplary types of binding fragments that can be internalized into cells when bound (see, for example, 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 some embodiments, scFv molecules may be incorporated into fusion proteins. Other forms of single-chain antibodies, such as bifunctional antibodies, are also covered. Biantibodies are bivalent bispecific antibodies, where V... H and V L Domains are expressed on a single polypeptide chain, but a linker that is too short to allow pairing between two domains on the same chain is used, thereby forcing these domains to pair with complementary domains on another chain and creating two antigen-binding sites (see, for example, Holliger et al. (1993) Proc Natl Acad Sci. USA [Proceedings of the National Academy of Sciences] 90:6444-8; and Poljak et al. (1994) Structure [Structure] 2:1121-3). Antigen-binding fragments are obtained using conventional techniques known to those skilled in the art, and the fragments are screened for utility (e.g., binding affinity, internalization) in the same manner as the intact antibody. Antigen-binding fragments can be prepared by cleaving the intact protein, for example by protease or chemical cleavage.

[0325] 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 following general formula: Ab-(LD) p (Formula I), where Ab = antibody or antigen-binding fragment, L = linker portion, D = drug portion (e.g., splicing modulator), and p = number of drug portions / antibody or antigen-binding fragment. ADCs containing splicing modulators may also be more specifically referred to herein as “antibody loaded with splicing modulator” or “SMLA”. In ADCs containing splicing modulator drug portions, “p” refers to the number of splicing modulators linked to the antibody or antigen-binding fragment. In some embodiments, the linker L may include a cleavable portion located between the antibody or antigen-binding fragment and the splicing modulator. In some embodiments, the linker L may include a cleavable portion that can be linked to either or both of the antibody or antigen-binding fragment and the splicing modulator via one or more spacer subunits. In some embodiments, when the spacer subunit links the cleavable portion to the splicing modulator, it is a self-ablating spacer subunit. In other embodiments, the linker L does not include a cleavable portion and is a non-cleavable linker. In some embodiments, the linker L may include at least one spacer subunit that can be directly linked to the antibody or antigen-binding fragment and the splicing modulator. Exemplary cleavable and non-cleavable linkers are described herein.

[0326] As used herein with respect to antibody or antigen-binding fragments, "internalization" refers to the ability of an antibody or antigen-binding fragment to cross the lipid bilayer membrane of a cell after binding to it (i.e., "internalization"), typically into the degradation compartments within the cell. For example, an internalizing anti-BCMA antibody is an antibody that is absorbed 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 is transferred across the cell membrane after antigen binding). In some embodiments, the internalizing antibody or antigen-binding fragment binds to a receptor on the cell surface. Internalizing antibodies or internalizing antigen-binding fragments targeting receptors on the cell membrane can induce receptor-mediated endocytosis. In some embodiments, the internalizing antibody or internalizing antigen-binding fragment is absorbed into the cell via receptor-mediated endocytosis.

[0327] As used herein, the term “B cell maturation antigen” or “BCMA” refers to any natural 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 can be produced by cellular expression or processing (e.g., alternative splicing events, alternative promoter use, post-transcriptional modification, post-translational modification, etc.). The term also encompasses functional variants or fragments of human BCMA, including but not limited to splice variants, allelic variants, and isotypes that retain one or more biological functions of human BCMA (i.e., variants and fragments are included unless the context indicates that the term is used only to refer to wild-type proteins). BCMA can be isolated from humans or can be produced recombinantly or synthetically. The term may also include any synthetic variant to which anti-BCMA antibodies (e.g., antibodies or antigen-binding fragments disclosed herein) can specifically bind.

[0328] The term "anti-BCMA antibody" or "BCMA-binding antibody" refers to any form of antibody or antigen-binding fragment thereof that binds, for example, specifically to BCMA. It encompasses monoclonal antibodies (including full-length monoclonal antibodies), polyclonal antibodies, and biologically functional antibody fragments, provided they bind, for example, specifically to BCMA. More specifically, in some embodiments, the anti-BCMA antibody or antigen-binding fragment disclosed herein may bind one or more amino acids in, for example, an extracellular domain that specifically binds BCMA. In some embodiments, the extracellular domain of BCMA comprises amino acids 1-54 of SEQ ID NO:106 (Table 8).

[0329] As used herein, the terms "specificity," "specifically binds," and "binds specifically" refer to the 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 products. The binding specificity of an antibody can be tested by comparing binding to an appropriate antigen with binding to an alternative antigen or a mixture of antigens under a given set of conditions. An antibody is considered specific if it binds to an appropriate antigen and has an affinity at least 2, 5, 7, 10, or more times greater than that with an alternative antigen or a mixture of antigens. A "specific antibody" or "target-specific antibody" is an antibody that binds only to a target antigen (e.g., BCMA) but not to other antigens (or exhibits minimal binding to other antigens). In some embodiments, an antibody or antigen-binding fragment that specifically binds to a target antigen (e.g., BCMA) has a K0 of the target.D Less than 1×10 -6 M, less than 1×10 -7 M, less than 1×10 -8 M, less than 1×10 -9 M, less than 1×10 -10 M, less than 1×10 -11 M, less than 1×10 -12 M or less than 1×10 -13 M. In some embodiments, K D It ranges from 1pM to 500pM. In some embodiments, K D Between 500 pM and 1 μM, 1 μM and 100 nM, or 100 mM and 10 nM.

[0330] The term "epitope" refers to a portion of an antigen that can be recognized and specifically bound by an antibody. When the antigen is a polypeptide, the epitope can be formed from consecutive amino acids or discontinuous amino acids adjacent to each other via the tertiary folding of the polypeptide. Epitopes bound by antibodies can be identified using any epitope localization technique known in the art, including X-ray crystallography for epitope identification (which involves direct visual inspection of the antigen-antibody complex), monitoring the binding of the antibody to fragments or mutant variants of the antigen, or monitoring the solvent accessibility of different portions of the antibody and antigen. Exemplary strategies for mapping antibody epitopes include, but are not limited to, array-based oligopeptide scanning, restriction proteolysis, site-directed mutagenesis, high-throughput mutagenesis mapping, hydrogen-deuterium exchange, and mass spectrometry (see, for example, Gershoni et al. (2007) 21:145-56; and Hager-Braun and Tomer (2005) Expert Rev Proteomics 2:745-56).

[0331] Competitive binding and epitope binning can also be used to identify antibodies sharing the same or overlapping epitopes. Competitive binding can be assessed using cross-blocking assays, such as those 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, in a cross-blocking assay, the antibody or binding protein tested reduces the binding of a reference antibody or binding protein (e.g., binding proteins containing a CDR and / or selected from the variable regions identified in Tables 3-5) to a target antigen (e.g., BCMA) by at least about 50% (e.g., 50%, 60%, 70%, 80%, 90%, 95%, 99%, 99.5%, or higher, or any percentage between thereof). In some embodiments, competitive binding may be attributed to shared or similar (e.g., partially overlapping) epitopes, or due to steric hindrance where the antibody or binding protein binds at a neighboring epitope (see, for example, Tzartos, Methods in Molecular Biology (Morris, ed., Vol. 66, pp. 55-66)). In some embodiments, competitive binding may be used to sort groups of binding proteins that share similar epitopes. For example, competitively binding proteins may be “boxed” into groups of binding proteins with overlapping or neighboring epitopes, while non-competitive binding proteins may be grouped into different groups of binding proteins that do not have overlapping or neighboring epitopes.

[0332] The term "p" or "drug load" or "drug:antibody ratio" or "drug to antibody ratio" or "DAR" refers to the number of drug portions per antibody or antigen-binding fragment, i.e., the number of -LD portions per antibody or antigen-binding fragment in the ADC disclosed herein (e.g., an ADC having formula (I)). In an ADC containing a splice modulator drug portion, "p" refers to the number of splice modulators linked to an antibody or antigen-binding fragment. For example, if there are two splice modulators (e.g., two compounds each having a D1 structure) linked to an antibody or antigen-binding fragment, then p = 2. In a composition containing multiple copies of an ADC (e.g., an ADC having formula (I)), "average p" refers to the average number of -LD portions per antibody or antigen-binding fragment, also known as "average drug load".

[0333] In this document, the term "connector" or "connector part" is used to refer to any chemical part capable of covalently attaching a compound (typically a pharmaceutical part, such as a splicing modulator) to another part (such as an antibody or antigen-binding fragment). A connector may be readily resistant to acid-induced cleavage, peptidase-induced cleavage, light-based cleavage, esterase-induced cleavage, and / or disulfide bond cleavage, under conditions that keep the compound or antibody active.

[0334] The term "pharmaceutical" is used herein to refer to a compound, a mixture of compounds, a biological macromolecule, or an extract made from biological material. The terms "therapeutic agent" or "drug" refer to a pharmaceutical agent capable of modulating biological processes and / or possessing biological activity. The splice modulator compounds described herein are exemplary therapeutic agents.

[0335] The terms "chemotherapy agent" or "anticancer agent" are used herein to refer to all agents that are effective in treating cancer regardless of their mechanism of action. Inhibition of metastasis or angiogenesis is often a characteristic of chemotherapy agents. Chemotherapy agents include antibodies, biomolecules, and small molecules, and encompass the splicing regulator compounds described herein. Chemotherapy agents can be cytotoxic agents or cell growth inhibitors. The term "cell growth inhibitor" refers to an agent that inhibits or suppresses cell growth and / or cell proliferation. The term "cytotoxic agent" refers to a substance that causes cell death primarily by interfering with the expression activity and / or function of cells.

[0336] As used herein, the terms "splicing modulator," "splicing body modulator," and "splice modulator" refer to compounds that exhibit anticancer activity through interaction with components of the spliceosome. In some embodiments, splicing modulators alter the rate or form of splicing in target cells. Splicing modulators that act as inhibitors, for example, can reduce uncontrolled cell proliferation. In some embodiments, splicing modulators may act by binding to the SF3b spliceosome complex. Such modulators can be naturally occurring or synthetic compounds. Non-limiting examples of splicing modulators and classes of such modulators include prasadiene lactones (e.g., prasadiene lactone D or prasadiene lactone B), prasadiene lactone derivatives (e.g., prasadiene lactone D or prasadiene lactone B derivatives), herboxidiene, herboxidiene derivatives, spliceostatin, spliceostatin derivatives, sudemycin, and sudemycin derivatives. As used herein, when referring to splice modulators or analogues, the terms “derivative” and “analyte” mean any such compound that retains substantially the same, similar, or enhanced biological function or activity as the original compound but has a modified chemical or biological structure. In some embodiments, the splice modulator is prasadiene lactone or a prasadiene lactone derivative.

[0337] As used herein, “pradoadienolide derivatives” refers to compounds that are structurally related to members of the natural product family called pradoadienolides and retain one or more biological functions of the starting compound. Pradoadienolides were first identified in the bacterium *Streptomyces platensis* (Mizui et al. (2004) J Antibiot. [Journal of Antibiotics] 57:188-96) as having potent cytotoxicity and causing cell cycle arrest at the G1 and G2 / M phases (e.g., Bonnal et al. (2012) Nat Rev Drug Dis [Nature Reviews: Drug Discovery] 11:847-59). There are seven naturally occurring pradoadienolides, namely pradoadienolide AG (Mizui et al. (2004) J Antibiot. [Journal of Antibiotics] 57:188-96; Sakai et al. (2004) J Antibiotics. [Journal of Antibiotics] 57:180-7). U.S. Patent Nos. 7,884,128 and 7,816,401 describe exemplary methods for the synthesis of prasadiene lactones B and D, and these references, each relating to such methods, are incorporated herein by reference. The synthesis of prasadiene lactones B and D can also be carried out using the exemplary methods described in Kanada et al. ((2007) Angew Chem Int Ed. [Applied Chemistry International Edition] 46:4350-5). Kanada et al. and International Publication No. WO 2003 / 099813 describe an exemplary method for the synthesis of E7107(D11) (compound 45 of WO 2003 / 099813) from prasadiene lactone D (11107D of WO 2003 / 099813). The corresponding U.S. Patent No. is 7,550,503 by Kotake et al. Each of these references relating to the described synthetic methods is incorporated herein by reference.

[0338] As used herein, “splicing modulator drug portion” refers to the component in an ADC or composition that provides the structure of a splicing modulator compound, such as the splicing modulator (D) component in an ADC having formula (I).

[0339] As used herein, a "splicing complex" refers to a ribonucleoprotein complex from which an intron is removed from one or more RNA segments, such as a pre-mRNA segment.

[0340] The term "homology" refers to a molecule that exhibits homology with another molecule by having, for example, the same or similar sequence of chemical residues at corresponding positions.

[0341] As used herein, the term “inhibit or inhibition of” means a reduction in a measurable amount and may include, but does not require, complete prevention or inhibition.

[0342] The terms "target negative," "target antigen negative," and "antigen negative" refer to the absence of target antigen expression (or a lack of detectable levels) in cells or tissues. The terms "target positive," "target antigen positive," and "antigen positive" refer to the presence of target antigen expression (or a detectable level). For example, cells or cell lines that do not express the target antigen can be described as target negative, while cells or cell lines that express the target antigen can be described as target positive.

[0343] The term "bystander killing" or "bystander effect" refers to the killing of target negative cells in the presence of target positive cells, where no killing of target negative cells is observed in the absence of target positive cells. Cell-to-cell contact, or at least the proximity between target positive and target negative cells, enables 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 in the absence of target positive cells.

[0344] As used herein, the terms “cancer,” “vesicle,” and “tumor” are used interchangeably and in the singular or plural form to refer to cells that have undergone malignant transformation, making them pathogenic to the host organism. Primary cancer cells can be readily distinguished from non-cancer cells using 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 cells derived from a cancer cell ancestor. This includes metastatic cancer cells, as well as in vitro cultures and cell lines derived from cancer cells. Cancer can manifest as a solid tumor, such as a tumor detectable by procedures such as computed tomography (CT) scans, magnetic resonance imaging (MRI), X-rays, ultrasound, or physical examination palpation, and / or a tumor detectable by the expression of one or more cancer-specific antigens in a sample obtainable from the patient. Tumors can also be hematopoietic (or hematologic or blood-related) cancers, such as cancers originating from blood cells or immune cells, which may be referred to as “liquid tumors.” Specific examples of clinical conditions based on hematologic malignancies include leukemias such as chronic myeloid leukemia, acute myeloid leukemia, chronic lymphocytic leukemia, and acute lymphoblastic leukemia; plasma cell malignancies such as multiple myeloma, monoclonal gammopathy of undetermined significance (MGUS), and Waldenström macroglobulinemia; lymphomas such as non-Hodgkin lymphoma and Hodgkin lymphoma; and so on.

[0345] In some embodiments, the cancers described herein can be any blood cancer. Blood cancers include malignancies of the lymph nodes and bone marrow, as well as plasma cell diseases or cancers such as multiple myeloma, MGUS, plasmacytoma (bone, extramedullary), lymphoplasmacytic lymphoma (LPL), Waldenström macroglobulinemia, plasma cell leukemia, and primary amyloidosis (AL). Blood cancers can 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 containing hematopoietic cells may be referred to as “hematopoietic tissues” and include bone marrow; peripheral blood; thymus; and peripheral lymphoid tissues such as the spleen, lymph nodes, mucosa-associated lymphoid tissues (such as intestinal-associated lymphoid tissue), tonsils, Peyer's cluster lymph nodes, and appendix, as well as other mucosa-associated lymphoid tissues (e.g., bronchial endothelium).

[0346] Specific examples of BCMA cancers described herein include plasma cell carcinoma. In some embodiments, the cancer is a plasma cell malignancy. In some embodiments, a plasma cell malignancy or cancer is leukemia, lymphoma, plasmacytoma, or myeloma. In some embodiments, a plasma cell malignancy or cancer is multiple myeloma, diffuse large B-cell lymphoma, mantle cell lymphoma, plasmablastic lymphoma, plasmablastic myeloma, or Burkitt lymphoma. In some embodiments, a plasma cell malignancy or cancer is multiple myeloma. In some embodiments, a plasma cell malignancy or cancer is relapsed / refractory multiple myeloma. In some embodiments, a plasma cell malignancy or cancer includes actively dividing cells, dormant cells, or both. In some embodiments, a plasma cell malignancy or cancer comprises at least some dormant cells, such as non-dividing or slowly dividing myeloma cells.

[0347] When used to describe cells, the term “dormant” refers to a cell that does not divide or divides at a rate below normal (e.g., the rate observed under low serum conditions). See, for example, Khoo et al. (2019) Blood. [Blood] 134(1):30-43. The term covers both non-dividing (stationary) and slowly dividing cells. The term “stationary” refers to a cell in a reversible state, where the cell does not divide but retains the ability to re-enter the cell division process. Stationary cells can be identified by low RNA content, lack of cell proliferation markers, and / or low levels of cell renewal. In some embodiments, stationary cells are stationary cancer cells. In contrast to “dormant” cells, “actively dividing” cells are cells that are in the process of dividing or are actively preparing to divide at a normal rate (e.g., the rate observed under normal serum conditions).

[0348] 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 a human.

[0349] The terms “co-administration” or “combination” refer to the administration of one or more therapeutic agents, including simultaneous administration as well as sequential administration in any order.

[0350] "Pharmaceutical composition" means a formulation which is permitted to administer an active ingredient and subsequently provides the intended biological activity and / or achieves a therapeutic effect of one or more active ingredients, and which does not contain any additional components that would have unacceptable toxicity to a subject administering the formulation. Pharmaceutical compositions may be sterile.

[0351] "Drug excipients" include substances such as adjuvants, carriers, pH adjusters and buffers, tension modifiers, wetting agents, preservatives, etc.

[0352] The term “pharmaceutical acceptable” means approved or permitted by a federal regulatory agency or state government, or listed in the United States Pharmacopeia or other generally recognized pharmacopoeia for use in animals and more specifically in humans.

[0353] "Pharmaceutically acceptable salts" are salts that retain the desired biological activity of the parent compound without conferring unwanted toxicological effects. Examples of such salts include: (a) acid addition salts formed with inorganic acids (e.g., hydrochloric acid, hydrobromic acid, sulfuric acid, phosphoric acid, nitric acid, etc.); and salts formed with organic acids (e.g., 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, etc.); and (b) salts formed from elemental anions (e.g., 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.

[0354] For example, the “effective amount” of antibodies, antigen-binding fragments, and / or ADCs disclosed herein is an amount sufficient to perform the purpose specifically stated (e.g., to produce a therapeutic effect upon administration, such as reducing tumor growth rate or tumor volume, reducing cancer symptoms, or certain other indicators of therapeutic efficacy). The term “therapeutic effective amount” refers to the amount of antibody, antigen-binding fragment, and / or ADC that effectively treats a subject’s disease or disorder. In the case of cancer, a therapeutically effective amount of 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 “preventative effective amount” refers to the amount that effectively achieves the desired preventative outcome at the necessary dose and time period. Typically, because the preventative dose is administered to the subject before or in an early stage of the disease, the preventative effective amount will be less than the therapeutic effective amount.

[0355] As used herein, the terms "treat" or "treatment" refer to any improvement in any outcome of the disease, such as prolonged survival, lower morbidity, and / or reduction of side effects resulting from an alternative mode of treatment. As readily understood in the art, a treatment procedure encompasses, but does not require, complete eradication of the disease. As used herein, the term "treat" may also refer to the administration of the antibody, antigen-binding fragment, and / or ADC to a subject, such as a patient with or suspected of having cancer. Treatment may be used to cure, heal, alleviate, relieve, alter, remedy, improve, mitigate, improve, or influence a disease (e.g., cancer), its symptoms, or a predisposition to the disease. In some embodiments, in addition to treating a subject with the condition, the compositions disclosed herein may be provided prophylactically to prevent or reduce the likelihood of developing the condition.

[0356] In some embodiments, labeled antibodies, antigen-binding fragments, and / or ADCs are used. Suitable “labels” include radionuclides, enzymes, receptors, cofactors, inhibitors, fluorescent portions, chemiluminescent portions, magnetic particles, etc.

[0357] As used herein, the term "protein" refers to at least two covalently linked amino acids. This term encompasses polypeptides, oligopeptides, and peptides. In some embodiments, two or more covalently linked amino acids are linked by peptide bonds. Proteins may consist of naturally occurring amino acids and peptide bonds, as is the case, for example, when proteins are recombinantly produced using an expression system and host cells. Alternatively, proteins may include synthetic amino acids (e.g., homophenylalanine, citrulline, ornithine, and leucine). "Recombinant protein" is a protein produced using recombinant technology, employing any techniques and methods known in the art, i.e., by expressing recombinant nucleic acids. Methods and techniques for producing recombinant proteins are well known in the art.

[0358] As used herein, the terms “amino acid” and “residue” refer to naturally occurring and synthetic amino acids, together with amino acid analogs and amino acid mimics that function in a manner similar to that of naturally occurring amino acids. Naturally occurring amino acids are those encoded by the genetic code, together with those subsequently modified in vivo, such as hydroxyproline, γ-carboxyglutamic acid, and α-phosphoserine. Amino acid analogs are compounds that have the same basic chemical structure as naturally occurring amino acids, namely, an α-carbon bound to hydrogen, a carboxyl group, an amino group, and an R group, such as selenocysteine, homoserine, ortholeucine, and methionine sulfoxide. Such analogs may have modified R groups (e.g., selenocysteine, ortholeucine) or modified peptide backbones, but retain the same basic chemical structure as natural amino acids. Amino acid mimics are compounds whose structure differs from the general chemical structure of amino acids, but which function in a manner similar to that of naturally occurring amino acids. Three-letter and single-letter codes for exemplary amino acids are provided in Table 1.

[0359] Table 1. Three-letter and single-letter codes for exemplary amino acids

[0360]

[0361]

[0362] For amino acid sequences, the term "identity" or "homology" refers to the relationship between two or more polypeptide sequences determined by comparing their sequences. The term "identity" also implies the degree of sequence relevance between polypeptides, such as that determined by the number of matches between strings of two or more amino acid residues. The percentage of identity between two sequences is a function of the number of shared positions (i.e., percentage of identity equals number of shared positions / total number of positions x 100). Taking into account the number of gaps and the length of each gap, gaps need to be introduced for optimal alignment of the two sequences. Sequence comparison and the determination of the percentage of identity between two sequences can be accomplished using mathematical algorithms. For sequence comparison, typically one sequence serves as a reference sequence, and the test sequence is compared to this reference sequence. When using a sequence comparison algorithm, the test and reference sequences are input into the computer, subsequence coordinates are specified if necessary, and sequence algorithm program parameters are specified. Default program parameters can be used, or alternative parameters can be specified. The sequence comparison algorithm then calculates the percentage of sequence identity of the test sequence relative to the reference sequence based on the program parameters. Alternatively or concurrently, the protein sequences disclosed herein can be further used as “query sequences” for searching public databases, such as to identify relevant sequences. For example, such a search can be performed using the BLAST program of Altschul et al. ((1990) J Mol Biol. [Journal of Molecular Biology] 215(3):403-10).

[0363] Typically, the amino acid identity or homology between the protein disclosed herein and its variants (including variants of target antigens (such as BCMA) and variants of antibody variable domains (including single variants CDR)) is at least 80% identity or homology with the sequence described herein, for example, at least 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, almost 100%, or 100% identity or homology.

[0364] Similarly, the "percentage of nucleic acid sequence identity" for nucleic acid sequences encoding the antibodies and other proteins identified in this paper is defined as the percentage of nucleotide residues in candidate sequences that are identical to those in the coding sequence of the antigen-binding protein. The specific method utilizes the BLASTN module of WU-BLAST-2 with default parameters set, where the overlap interval and overlap fraction are set to 1 and 0.125, respectively.

[0365] Anti-BCMA antibody and antigen-binding fragment

[0366] In various embodiments, this disclosure relates to antibodies and antigen-binding fragments thereof capable of binding to and / or killing cancer cells (e.g., cancer cells expressing BCMA), and their use in conjugates (e.g., ADCs) and therapeutic compositions.

[0367] In some embodiments, the antibody and antigen-binding fragments disclosed herein may be used alone, administered as part of a pharmaceutical composition or combination therapy, and / or administered as the antibody portion of an ADC. In some embodiments, the antibody and antigen-binding fragments are capable of binding BCMA. In some embodiments, the anti-BCMA antibody and antigen-binding fragments disclosed herein may be used alone (i.e., in unconjugated form) and as the antibody portion of an ADC.

[0368] In some embodiments, the anti-BCMA antibody and antigen-binding fragments disclosed herein are humanized. In some embodiments, the anti-BCMA antibody and antigen-binding fragments contain a minimal sequence derived from a non-human (e.g., mouse) antibody and retain the reactivity of the non-human antibody while exhibiting lower immunogenicity in humans. In some embodiments, these anti-BCMA antibody and antigen-binding fragments provide one or more improvements in binding affinity, stability, formulaability, and / or therapeutic efficacy, and / or provide reduced aggregation and / or off-target toxicity, compared to one or more anti-BCMA antibodies known in the art.

[0369] In some embodiments, the anti-BCMA antibody and antigen-binding fragment disclosed herein provide improved binding affinity compared to a reference anti-BCMA antibody or antigen-binding fragment (e.g., a reference containing AB200), whether used alone or as part of a larger molecule (such as an ADC). In some embodiments, the disclosed antibody and antigen-binding fragment have a higher affinity for BCMA (e.g., human BCMA) compared to a reference anti-BCMA antibody or antigen-binding fragment. In some embodiments, the disclosed antibody and antigen-binding fragment have a higher affinity for human BCMA, monkey BCMA, or both compared to a reference anti-BCMA antibody or antigen-binding fragment. In some embodiments, the binding affinity of the antibody or antigen-binding fragment for BCMA (e.g., human BCMA and / or monkey BCMA) can be determined, for example, by an Octet binding assay using the extracellular domains of human BCMA and / or monkey BCMA. In some embodiments, the binding affinity of the antibody or antigen-binding fragment for BCMA (e.g., human BCMA) can be determined, for example, by one or more binding assays using cancer cells with high or moderate BCMA expression levels.

[0370] In some embodiments, the anti-BCMA antibody and antigen-binding fragment disclosed herein provide improved stability compared to a reference anti-BCMA antibody or antigen-binding fragment (e.g., a reference containing AB200), whether used alone or as part of a larger molecule (such as an ADC). In some embodiments, the disclosed antibody and antigen-binding fragment exhibit increased thermal stability compared to a reference anti-BCMA antibody or antigen-binding fragment. In some embodiments, the disclosed antibody and antigen-binding fragment have a higher melting temperature (T0) compared to a reference anti-BCMA antibody or antigen-binding fragment. m In some embodiments, the stability (e.g., thermal stability) of the antibody or antigen-binding fragment can be determined, for example, by temperature-based stability assays, such as differential scanning calorimetry (DSC) or ThermoFluor assays.

[0371] With some or all of these improved properties, the disclosed antibody and antigen-binding fragments (alone or as part of an ADC) can be used as therapeutic agents, for example, for the treatment, prevention, and / or diagnosis of cancer (e.g., cancers expressing BCMA).

[0372] In some embodiments, the antibody and antigen-binding fragments disclosed herein bind (e.g., specifically bind) BCMA (e.g., as expressed on cancer cells). The antibody or antigen-binding fragment may bind to BCMA, wherein the dissociation constant (K0) is... D ≤1 mM, ≤100 nM, or ≤10 nM, or any amount in between, as measured by, for example, flow cytometry analysis. In some embodiments, K D Between 0.5 nM and 10 nM, as measured by, for example, flow cytometry analysis.

[0373] In some embodiments, the antibody or antigen-binding fragment is a four-chain antibody (also referred to as an immunoglobulin) comprising two heavy chains and two light chains. In some embodiments, the antibody or antigen-binding fragment is a double-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 provides the function of an immunoglobulin.

[0374] In some embodiments, the antibody or antigen-binding fragment disclosed herein is an internalizing antibody or an internalizing antigen-binding fragment thereof. In some embodiments, the internalizing antibody or its internalizing antigen-binding fragment binds to a target cancer antigen expressed on a cell surface and enters the cell after binding. In some embodiments, the antibody or antigen-binding fragment is linked to a splice modulator drug portion in the form of an ADC, and after the ADC has entered and is present in the cell expressing the target cancer antigen (i.e., after the ADC has been internalized), the splice modulator drug portion of the ADC is released from the antibody or antigen-binding fragment in the ADC, for example by lysis, by degradation of the antibody or antigen-binding fragment, or by any other suitable release mechanism.

[0375] In some embodiments, the antibody or antigen-binding fragment disclosed herein may comprise a pair of heavy and light chain variable regions listed in Table 5, or a group of six CDR sequences from a pair of heavy and light chain regions, such as a group 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 having one or more reversion mutations to enhance 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 κ or λ 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 and a human Igκ light chain constant region. In some embodiments, the antibody or antigen-binding fragment 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 comprises a human immunoglobulin G subtype 4 (IgG4) heavy chain constant region and a human Igκ light chain constant region. In some embodiments, the antibody or antigen-binding fragment comprises a human IgG4 heavy chain constant region and a human Igλ light chain constant region.

[0376] Tables 3-7 list the amino acid sequences of the exemplary antibodies disclosed herein. Tables 8 and 9 list the amino acid sequences of exemplary target antigens and exemplary reference antibodies, respectively.

[0377] Table 2. Anti-BCMA antibodies

[0378] mAb type target AB212 Humanization BCMA AB213 Humanization BCMA AB214 Humanization BCMA AB215 Humanization BCMA AB216 Humanization BCMA AB217 Humanization BCMA AB218 Humanization BCMA

[0379] Table 3. Amino acid sequence of Kabat CDR for anti-BCMA antibody

[0380]

[0381]

[0382]

[0383] Table 4. Amino acid sequence of IMGT CDR of anti-BCMA antibody

[0384]

[0385]

[0386] Table 5. Amino acid sequence of the variable region of anti-BCMA antibody

[0387]

[0388]

[0389]

[0390] Table 6. Amino acid sequence of the constant region of anti-BCMA antibody

[0391]

[0392]

[0393]

[0394]

[0395]

[0396]

[0397] Table 7. Amino acid sequence of the full-length Ig chain of anti-BCMA antibody

[0398]

[0399]

[0400]

[0401]

[0402]

[0403]

[0404] Table 8. Amino acid sequences of exemplary target antigens

[0405]

[0406] *The underlined part indicates an extracellular domain.

[0407] Table 9. Amino acid sequences of exemplary reference antibodies

[0408]

[0409]

[0410] In some embodiments, the antibody, antigen-binding fragment, or antibody portion of the ADC disclosed herein may comprise any group of heavy and light chain variable regions listed in the table above, or, for example, a group of six CDR sequences from the heavy and light chain groups obtained by grafting six CDRs into a selected human donor antibody framework. In some embodiments, the antibody, antigen-binding fragment, or antibody portion of the ADC disclosed herein may comprise amino acid sequences homologous to the sequences listed in the table above, provided that the antibody, antigen-binding fragment, or antibody portion retains the ability to bind its target cancer antigen (e.g., K). D Less than 1x10 -8 The ability of M) and / or retention of one or more functional properties of the antibody, antigen-binding fragment or antibody portion disclosed herein (e.g., the ability to internalize, regulate RNA splicing, etc.) is sufficient.

[0411] In some embodiments, the anti-BCMA antibody or its antigen-binding fragment comprises three HCDRs containing the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:2 (HCDR2), and SEQ ID NO:3 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:4 (LCDR1), SEQ ID NO:5 (LCDR2), and SEQ ID NO:6 (LCDR3), as defined by the Kabat numbering system; or three HCDRs containing the following amino acid sequences: SEQ ID NO:37 (HCDR1), SEQ ID NO:38 (HCDR2), and SEQ ID NO:39 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:42 (LCDR3), as defined by the IMGT numbering system.

[0412] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises three HCDRs and three LCDRs as follows: HCDR1 consisting of SEQ ID NO:1, HCDR2 consisting of SEQ ID NO:2, and HCDR3 consisting of SEQ ID NO:3; and LCDR1 consisting of SEQ ID NO:4, LCDR2 consisting of SEQ ID NO:5, and LCDR3 consisting of SEQ ID NO:6, as defined by the Kabat numbering system; or HCDR1 consisting of SEQ ID NO:37, HCDR2 consisting of SEQ ID NO:38, and HCDR3 consisting of SEQ ID NO:39; and LCDR1 consisting of SEQ ID NO:40, LCDR2 consisting of SEQ ID NO:41, and LCDR3 consisting of SEQ ID NO:42, as defined by the IMGT numbering system.

[0413] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region containing the amino acid sequence of SEQ ID NO:76 and a light chain variable region containing the amino acid sequence of SEQ ID NO:77. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises the heavy chain variable region amino acid sequence SEQ ID NO:76 and the light chain variable region amino acid sequence SEQ ID NO:77, or a sequence having at least 90% identity with the disclosed sequence. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:76 and a light chain variable region having at least 90% identity with 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 having 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% identity with SEQ ID NO:76; and / or a light chain variable region amino acid sequence having 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% identity with SEQ ID NO:77.

[0414] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human heavy chain and light chain variable region framework, or a human heavy chain and light chain variable region framework having one or more reversion mutations. In some embodiments, the anti-BCMA antibody or antigen-binding fragment is an internalizing antibody or an internalizing antigen-binding fragment.

[0415] 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 heavy chain constant region containing the amino acid sequence of SEQ ID NO: 90 and a light chain constant region containing the amino acid sequence of SEQ ID NO: 91. In some embodiments, the heavy chain constant region further comprises a C-terminal lysine (K).

[0416] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain containing the amino acid sequence of SEQ ID NO:92 and a light chain containing the amino acid sequence of SEQ ID NO:93. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain having at least 90% identity with the amino acid sequence of SEQ ID NO:92 and a light chain having at least 90% identity with 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 having 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% identity with SEQ ID NO:92; and / or a light chain amino acid sequence having 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% identity with 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.

[0417] In some embodiments, the anti-BCMA antibody or its antigen-binding fragment comprises three HCDRs containing the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:7 (HCDR2), and SEQ ID NO:8 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:9 (LCDR1), SEQ ID NO:10 (LCDR2), and SEQ ID NO:11 (LCDR3), as defined by the Kabat numbering system; or three HCDRs containing the following amino acid sequences: SEQ ID NO:43 (HCDR1), SEQ ID NO:44 (HCDR2), and SEQ ID NO:45 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:46 (LCDR3), as defined by the IMGT numbering system.

[0418] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises three HCDRs and three LCDRs as follows: 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, as defined by the Kabat numbering system; or 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, as defined by the IMGT numbering system.

[0419] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region containing the amino acid sequence of SEQ ID NO:78 and a light chain variable region containing the amino acid sequence of SEQ ID NO:79. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises the heavy chain variable region amino acid sequence SEQ ID NO:78 and the light chain variable region amino acid sequence SEQ ID NO:79, or a sequence having at least 90% identity with the disclosed sequence. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:78 and a light chain variable region having at least 90% identity with 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 having 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% identity with SEQ ID NO:78; and / or a light chain variable region amino acid sequence having 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% identity with SEQ ID NO:79.

[0420] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human heavy chain and light chain variable region framework, or a human heavy chain and light chain variable region framework having one or more reversion mutations. In some embodiments, the anti-BCMA antibody or antigen-binding fragment is an internalizing antibody or an internalizing antigen-binding fragment.

[0421] 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 heavy chain constant region containing the amino acid sequence of SEQ ID NO: 90 and a light chain constant region containing the amino acid sequence of SEQ ID NO: 91. In some embodiments, the heavy chain constant region further comprises a C-terminal lysine (K).

[0422] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain containing the amino acid sequence of SEQ ID NO:94 and a light chain containing the amino acid sequence of SEQ ID NO:95. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain having at least 90% identity with the amino acid sequence of SEQ ID NO:94 and a light chain having at least 90% identity with 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 having 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% identity with SEQ ID NO:94; and / or a light chain amino acid sequence having 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% identity with 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.

[0423] In some embodiments, the anti-BCMA antibody or its antigen-binding fragment comprises three HCDRs containing the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:12 (HCDR2), and SEQ ID NO:13 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:14 (LCDR1), SEQ ID NO:15 (LCDR2), and SEQ ID NO:16 (LCDR3), as defined by the Kabat numbering system; or three HCDRs containing the following amino acid sequences: SEQ ID NO:47 (HCDR1), SEQ ID NO:48 (HCDR2), and SEQ ID NO:49 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:50 (LCDR3), as defined by the IMGT numbering system.

[0424] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises three HCDRs and three LCDRs as follows: 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, as defined by the Kabat numbering system; or 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, as defined by the IMGT numbering system.

[0425] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region containing the amino acid sequence of SEQ ID NO:80 and a light chain variable region containing the amino acid sequence of SEQ ID NO:81. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises the heavy chain variable region amino acid sequence of SEQ ID NO:80 and the light chain variable region amino acid sequence of SEQ ID NO:81, or a sequence having at least 90% identity with the disclosed sequence. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:80 and a light chain variable region having at least 90% identity with 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 having 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% identity with SEQ ID NO:80; and / or a light chain variable region amino acid sequence having 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% identity with SEQ ID NO:81.

[0426] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human heavy chain and light chain variable region framework, or a human heavy chain and light chain variable region framework having one or more reversion mutations. In some embodiments, the anti-BCMA antibody or antigen-binding fragment is an internalizing antibody or an internalizing antigen-binding fragment.

[0427] 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 heavy chain constant region containing the amino acid sequence of SEQ ID NO: 90 and a light chain constant region containing the amino acid sequence of SEQ ID NO: 91. In some embodiments, the heavy chain constant region further comprises a C-terminal lysine (K).

[0428] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain containing the amino acid sequence of SEQ ID NO:96 and a light chain containing the amino acid sequence of SEQ ID NO:97. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain having at least 90% identity with the amino acid sequence of SEQ ID NO:96 and a light chain having at least 90% identity with 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 having 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% identity with SEQ ID NO:96; and / or a light chain amino acid sequence having 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% identity with 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.

[0429] In some embodiments, the anti-BCMA antibody or its antigen-binding fragment comprises three HCDRs containing the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:17 (HCDR2), and SEQ ID NO:18 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:19 (LCDR1), SEQ ID NO:20 (LCDR2), and SEQ ID NO:21 (LCDR3), as defined by the Kabat numbering system; or three HCDRs containing the following amino acid sequences: SEQ ID NO:51 (HCDR1), SEQ ID NO:52 (HCDR2), and SEQ ID NO:53 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:54 (LCDR3), as defined by the IMGT numbering system.

[0430] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises three HCDRs and three LCDRs as follows: 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, as defined by the Kabat numbering system; or 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, as defined by the IMGT numbering system.

[0431] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region containing the amino acid sequence of SEQ ID NO:82 and a light chain variable region containing the amino acid sequence of SEQ ID NO:83. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises the heavy chain variable region amino acid sequence of SEQ ID NO:82 and the light chain variable region amino acid sequence of SEQ ID NO:83, or a sequence having at least 90% identity with the disclosed sequence. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:82 and a light chain variable region having at least 90% identity with 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 having 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% identity with SEQ ID NO:82; and / or a light chain variable region amino acid sequence having 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% identity with SEQ ID NO:83.

[0432] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human heavy chain and light chain variable region framework, or a human heavy chain and light chain variable region framework having one or more reversion mutations. In some embodiments, the anti-BCMA antibody or antigen-binding fragment is an internalizing antibody or an internalizing antigen-binding fragment.

[0433] 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 heavy chain constant region containing the amino acid sequence of SEQ ID NO: 90 and a light chain constant region containing the amino acid sequence of SEQ ID NO: 91. In some embodiments, the heavy chain constant region further comprises a C-terminal lysine (K).

[0434] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain containing the amino acid sequence of SEQ ID NO:98 and a light chain containing the amino acid sequence of SEQ ID NO:99. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain having at least 90% identity with the amino acid sequence of SEQ ID NO:98 and a light chain having at least 90% identity with 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 having 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% identity with SEQ ID NO:98; and / or a light chain amino acid sequence having 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% identity with 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.

[0435] In some embodiments, the anti-BCMA antibody or its antigen-binding fragment comprises three HCDRs containing the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:22 (HCDR2), and SEQ ID NO:23 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:24 (LCDR1), SEQ ID NO:25 (LCDR2), and SEQ ID NO:26 (LCDR3), as defined by the Kabat numbering system; or three HCDRs containing the following amino acid sequences: SEQ ID NO:55 (HCDR1), SEQ ID NO:56 (HCDR2), and SEQ ID NO:57 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:58 (LCDR3), as defined by the IMGT numbering system.

[0436] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises three HCDRs and three LCDRs as follows: HCDR1 consisting of SEQ ID NO:1, HCDR2 consisting of SEQ ID NO:22, and HCDR3 consisting of SEQ ID NO:23; and LCDR1 consisting of SEQ ID NO:24, LCDR2 consisting of SEQ ID NO:25, and LCDR3 consisting of SEQ ID NO:26, as defined by the Kabat numbering system; or HCDR1 consisting of SEQ ID NO:55, HCDR2 consisting of SEQ ID NO:56, and HCDR3 consisting of SEQ ID NO:57; and LCDR1 consisting of SEQ ID NO:40, LCDR2 consisting of SEQ ID NO:41, and LCDR3 consisting of SEQ ID NO:58, as defined by the IMGT numbering system.

[0437] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region containing the amino acid sequence of SEQ ID NO:84 and a light chain variable region containing the amino acid sequence of SEQ ID NO:85. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises the heavy chain variable region amino acid sequence SEQ ID NO:84 and the light chain variable region amino acid sequence SEQ ID NO:85, or a sequence having at least 90% identity with the disclosed sequence. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:84 and a light chain variable region having at least 90% identity with 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 having 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% identity with SEQ ID NO:84; and / or a light chain variable region amino acid sequence having 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% identity with SEQ ID NO:85.

[0438] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human heavy chain and light chain variable region framework, or a human heavy chain and light chain variable region framework having one or more reversion mutations. In some embodiments, the anti-BCMA antibody or antigen-binding fragment is an internalizing antibody or an internalizing antigen-binding fragment.

[0439] 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 heavy chain constant region containing the amino acid sequence of SEQ ID NO: 90 and a light chain constant region containing the amino acid sequence of SEQ ID NO: 91. In some embodiments, the heavy chain constant region further comprises a C-terminal lysine (K).

[0440] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain containing the amino acid sequence of SEQ ID NO:100 and a light chain containing the amino acid sequence of SEQ ID NO:101. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain having at least 90% identity with the amino acid sequence of SEQ ID NO:100 and a light chain having at least 90% identity with 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 having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identity with SEQ ID NO:100; and / or a light chain amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identity with 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.

[0441] In some embodiments, the anti-BCMA antibody or its antigen-binding fragment comprises three HCDRs containing the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:27 (HCDR2), and SEQ ID NO:28 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:29 (LCDR1), SEQ ID NO:30 (LCDR2), and SEQ ID NO:31 (LCDR3), as defined by the Kabat numbering system; or three HCDRs containing the following amino acid sequences: SEQ ID NO:59 (HCDR1), SEQ ID NO:60 (HCDR2), and SEQ ID NO:61 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:62 (LCDR3), as defined by the IMGT numbering system.

[0442] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises three HCDRs and three LCDRs as follows: HCDR1 consisting of SEQ ID NO:1, HCDR2 consisting of SEQ ID NO:27, and HCDR3 consisting of SEQ ID NO:28; and LCDR1 consisting of SEQ ID NO:29, LCDR2 consisting of SEQ ID NO:30, and LCDR3 consisting of SEQ ID NO:31, as defined by the Kabat numbering system; or HCDR1 consisting of SEQ ID NO:59, HCDR2 consisting of SEQ ID NO:60, and HCDR3 consisting of SEQ ID NO:61; and LCDR1 consisting of SEQ ID NO:40, LCDR2 consisting of SEQ ID NO:41, and LCDR3 consisting of SEQ ID NO:62, as defined by the IMGT numbering system.

[0443] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region containing the amino acid sequence of SEQ ID NO:86 and a light chain variable region containing the amino acid sequence of SEQ ID NO:87. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises the heavy chain variable region amino acid sequence SEQ ID NO:86 and the light chain variable region amino acid sequence SEQ ID NO:87, or a sequence having at least 90% identity with the disclosed sequence. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:86 and a light chain variable region having at least 90% identity with 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 having 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% identity with SEQ ID NO:86; and / or a light chain variable region amino acid sequence having 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% identity with SEQ ID NO:87.

[0444] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human heavy chain and light chain variable region framework, or a human heavy chain and light chain variable region framework having one or more reversion mutations. In some embodiments, the anti-BCMA antibody or antigen-binding fragment is an internalizing antibody or an internalizing antigen-binding fragment.

[0445] 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 heavy chain constant region containing the amino acid sequence of SEQ ID NO: 90 and a light chain constant region containing the amino acid sequence of SEQ ID NO: 91. In some embodiments, the heavy chain constant region further comprises a C-terminal lysine (K).

[0446] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain containing the amino acid sequence of SEQ ID NO:102 and a light chain containing the amino acid sequence of SEQ ID NO:103. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain having at least 90% identity with the amino acid sequence of SEQ ID NO:102 and a light chain having at least 90% identity with 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 having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identity with SEQ ID NO:102; and / or a light chain amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identity with 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.

[0447] In some embodiments, the anti-BCMA antibody or its antigen-binding fragment comprises three HCDRs containing the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:32 (HCDR2), and SEQ ID NO:33 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:34 (LCDR1), SEQ ID NO:35 (LCDR2), and SEQ ID NO:36 (LCDR3), as defined by the Kabat numbering system; or three HCDRs containing the following amino acid sequences: SEQ ID NO:63 (HCDR1), SEQ ID NO:64 (HCDR2), and SEQ ID NO:65 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:66 (LCDR3), as defined by the IMGT numbering system.

[0448] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises three HCDRs and three LCDRs as follows: HCDR1 consisting of SEQ ID NO:1, HCDR2 consisting of SEQ ID NO:32, and HCDR3 consisting of SEQ ID NO:33; and LCDR1 consisting of SEQ ID NO:34, LCDR2 consisting of SEQ ID NO:35, and LCDR3 consisting of SEQ ID NO:36, as defined by the Kabat numbering system; or HCDR1 consisting of SEQ ID NO:63, HCDR2 consisting of SEQ ID NO:64, and HCDR3 consisting of SEQ ID NO:65; and LCDR1 consisting of SEQ ID NO:40, LCDR2 consisting of SEQ ID NO:41, and LCDR3 consisting of SEQ ID NO:66, as defined by the IMGT numbering system.

[0449] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region containing the amino acid sequence of SEQ ID NO:88 and a light chain variable region containing the amino acid sequence of SEQ ID NO:89. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises the heavy chain variable region amino acid sequence SEQ ID NO:88 and the light chain variable region amino acid sequence SEQ ID NO:89, or a sequence having at least 90% identity with the disclosed sequence. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:88 and a light chain variable region having at least 90% identity with 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 having 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% identity with SEQ ID NO:88; and / or a light chain variable region amino acid sequence having 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% identity with SEQ ID NO:89.

[0450] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a human heavy chain and light chain variable region framework, or a human heavy chain and light chain variable region framework having one or more reversion mutations. In some embodiments, the anti-BCMA antibody or antigen-binding fragment is an internalizing antibody or an internalizing antigen-binding fragment.

[0451] 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 heavy chain constant region containing the amino acid sequence of SEQ ID NO: 90 and a light chain constant region containing the amino acid sequence of SEQ ID NO: 91. In some embodiments, the heavy chain constant region further comprises a C-terminal lysine (K).

[0452] In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain containing the amino acid sequence of SEQ ID NO:104 and a light chain containing the amino acid sequence of SEQ ID NO:105. In some embodiments, the anti-BCMA antibody or antigen-binding fragment comprises a heavy chain having at least 90% identity with the amino acid sequence of SEQ ID NO:104 and a light chain having at least 90% identity with 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 having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identity with SEQ ID NO:104; and / or a light chain amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identity with 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.

[0453] The antibody and antigen-binding fragments disclosed herein may include additional modifications (e.g., one or more amino acid substitutions, deletions, and / or insertions) while maintaining the ability to bind BCMA. In some embodiments, the antibody or antigen-binding fragment includes a specified modification (e.g., relative 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 modifications. In some embodiments, the antibody or antigen-binding fragment includes a heavy chain variable region that includes up to about 2, about 5, or up to about 10 amino acid modifications (e.g., relative 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, about 5, or up to about 10 amino acid modifications in addition to any specified amino acid modifications.

[0454] In some embodiments, amino acid substitutions have a single residue. Insertions are typically on the order of about 1 to about 20 amino acid residues, but significantly larger insertions are permissible as long as biological function (e.g., binding to BCMA) is maintained. Deletions are typically in the range of about 1 to about 20 amino acid residues, but in some cases, deletions may be much larger. Substitutions, deletions, insertions, or any combination thereof can be used to obtain the final derivative or variant. Typically, these changes are made to several amino acids to minimize alterations to the immunogenicity and specificity of the molecule, particularly antigen-binding proteins. However, in some cases, more variations are permissible. Conservative substitutions are typically made according to a table providing functionally similar amino acids (an exemplary table described below as Table 10), and other substitutions are known in the art.

[0455] Table 10

[0456]

[0457]

[0458] In various embodiments, substantial changes in functional or immune properties can be made by selecting substitutions with lower conservation than those shown in Table 10. For example, substitutions can be made that more significantly affect: the structure of the polypeptide backbone in the region, such as α-helical or β-sheet structures; the charge or hydrophobicity of the molecule at the target site; or the volume of the side chains. The substitutions that typically produce the greatest changes in peptide properties are the following substitutions, in which: (a) a hydrophilic residue (e.g., serine or threonine) is substituted with (or substituted by) a hydrophobic residue (e.g., leucine, isoleucine, phenylalanine, valine, or alanine); (b) cysteine ​​or proline is substituted with (or substituted by) any other residue; (c) a residue with a positively charged side chain (e.g., lysine, arginine, or histidine) is substituted with (or substituted by) a negatively charged residue (e.g., glutamyl or aspartic); or (d) a residue with a bulky side chain (e.g., phenylalanine) is substituted with (or substituted by) a residue without a side chain (e.g., glycine).

[0459] In some embodiments where the variant antibody sequence is used in antibodies, antigen-binding fragments, or ADCs, the variants typically exhibit the same qualitative biological activity and elicit the same immune response, but variants may also be selected as needed to modify the characteristics of the antigen-binding protein. In addition to modifications within the frame region or CDR region, the antibodies disclosed herein may be engineered to include modifications within the Fc region, typically to alter one or more functional properties of the antibody or antigen-binding fragment, such as serum half-life, complement binding, Fc receptor binding, and / or antigen-dependent cytotoxicity. Furthermore, in some embodiments, the antibodies disclosed herein may be chemically modified (e.g., one or more chemical portions may be linked to the antibody) or modified to alter their glycosylation, for example, to change one or more functional properties of the antibody or antigen-binding fragment.

[0460] Amino acid substitutions described herein can be represented by listing the absolute residue position followed by a three-letter or one-letter code for the substituted (i.e., replaced) amino acid. For example, the substitution of serine at position 30 of SEQ ID NO:119 with threonine can be represented as "Ser30Thr" or "S30T". In this example, serine is the "substituted" amino acid, and threonine is the "replaced" or "substituted" amino acid.

[0461] In some embodiments, the amino acid substitutions described herein may be designated 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 stated, the absolute position of the substitution in the antibody or antigen-binding fragment is used to designate the amino acid substitution. However, in some embodiments, the amino acid substitution in the antibody or antigen-binding fragment disclosed herein may be designated by its Kabat position. 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:119 modified to include at least one amino acid substitution at position 103 (i.e., at absolute position 103). In some embodiments, position 103 of SEQ ID NO:119 may be designated by its Kabat position (i.e., 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. Unbound by theory, in some embodiments, antibody or antigen-binding fragments containing histidine substituted for aspartic acid at position 103 (corresponding to Kabat position 99) in SEQ ID NO: 119 may exhibit higher affinity for BCMA compared to antibody or antigen-binding fragments lacking the substitutions described below. In some embodiments, D103H (Kabat D99H) substitution may increase the binding affinity of the antibody or antigen-binding fragment for human BCMA, monkey BCMA, or both. In some embodiments, D103H (Kabat D99H) substitution increases the binding affinity of the antibody or antigen-binding fragment for both human BCMA and monkey BCMA, as determined by, for example, an Octet binding assay.

[0462] In some embodiments, the antibody or antigen-binding fragment disclosed herein comprises:

[0463] (a) A heavy chain variable region containing the amino acid sequence of SEQ ID NO:119, wherein the amino acid sequence is modified by substitution of amino acids at one or more of positions 30, 34, 50, 54, 55, 57, 59, 61, 64, 66, 101, 103, 108, and 109; and

[0464] (b) A light chain variable region containing the amino acid sequence of SEQ ID NO:120, wherein the amino acid sequence is modified to be replaced by an amino acid at one or more of positions 24, 28, 31, 33, 50, 55, 56, 91, 93, 94 and 97.

[0465] In some embodiments, the antibody or antigen-binding fragment comprises a heavy chain variable region containing the amino acid sequence of SEQ ID NO:119, which is modified by substitution of amino acids at one or more of positions 30, 34, 50, 54, 55, 57, 59, 61, 64, 66, 101, 103, 108, and 109, wherein:

[0466] The amino acid at position 30 of SEQ ID NO:119 is replaced by T;

[0467] The amino acid at position 34 of SEQ ID NO:119 is replaced by I;

[0468] The amino acid at position 50 of SEQ ID NO:119 is replaced by G;

[0469] The amino acid at position 54 of SEQ ID NO:119 is replaced by S or I;

[0470] The amino acid at position 55 of SEQ ID NO:119 is replaced by Q;

[0471] The amino acid at position 57 of SEQ ID NO:119 is replaced by T;

[0472] The amino acid at position 59 of SEQ ID NO:119 is replaced by N;

[0473] The amino acid at position 61 of SEQ ID NO:119 is replaced by A;

[0474] The amino acid at position 64 of SEQ ID NO:119 is replaced by Y;

[0475] The amino acid at position 66 of SEQ ID NO:119 is replaced by S;

[0476] The amino acid at position 101 of SEQ ID NO:119 is replaced by V;

[0477] The amino acid at position 103 of SEQ ID NO:119 is replaced by H;

[0478] The amino acid at position 108 of SEQ ID NO:119 is replaced by I; and / or

[0479] The amino acid at position 109 of SEQ ID NO:119 is replaced by E.

[0480] In some embodiments, the antibody or antigen-binding fragment comprises a heavy chain variable region containing the amino acid sequence of SEQ ID NO: 119, which is modified to include at least one amino acid substituted at position 103. In some embodiments, the amino acid at position 103 of SEQ ID NO: 119 (corresponding to Kabat position 99) is substituted with H.

[0481] In some embodiments, the antibody or antigen-binding fragment comprises a heavy chain variable region containing the amino acid sequence of SEQ ID NO: 119, which is modified to include at least four amino acid substitutions. In some embodiments, the antibody or antigen-binding fragment comprises a heavy chain variable region containing the amino acid sequence of SEQ ID NO: 119, which is modified to include at least one amino acid substitution 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.

[0482] In some embodiments, the antibody or antigen-binding fragment comprises a light chain variable region containing the amino acid sequence of SEQ ID NO:120, which is modified by substitution of amino acids at one or more of positions 24, 28, 31, 33, 50, 55, 56, 91, 93, 94, and 97, wherein:

[0483] The amino acid at position 24 of SEQ ID NO:120 is replaced by R;

[0484] The amino acid at position 28 of SEQ ID NO:120 is replaced by S;

[0485] The amino acid at position 31 of SEQ ID NO:120 is replaced by S;

[0486] The amino acid at position 33 of SEQ ID NO:120 is replaced by I;

[0487] The amino acid at position 50 of SEQ ID NO:120 is replaced by A;

[0488] The amino acid at position 55 of SEQ ID NO:120 is replaced by Q;

[0489] The amino acid at position 56 of SEQ ID NO:120 is replaced by I;

[0490] The amino acid at position 91 of SEQ ID NO:120 is replaced by F;

[0491] The amino acid at position 93 of SEQ ID NO:120 is replaced by R;

[0492] The amino acid at position 94 of SEQ ID NO:120 is substituted with I; and / or

[0493] The amino acid at position 97 of SEQ ID NO:120 is replaced by S.

[0494] In some embodiments, the antibody or antigen-binding fragment comprises a light chain variable region containing the amino acid sequence of SEQ ID NO: 120, which is modified to include at least six amino acid substitutions. In some embodiments, the antibody or antigen-binding fragment comprises a light chain variable region containing the amino acid sequence of SEQ ID NO: 120, which is modified to include at least one amino acid substitution 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 modified heavy and light chains may be paired in the antibody or antigen-binding fragment or ADC disclosed herein.

[0495] In some embodiments, the antibody or antigen-binding fragments disclosed herein may be used alone (e.g., as an antibody or antigen-binding fragment), linked to one or more other pharmaceutical 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 an antigen-binding domain in a bispecific or multispecific antibody and / or part of 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 antibody and antigen-binding fragments disclosed herein (used alone or as part of a larger macromolecule) may include additional modifications (e.g., one or more amino acid substitutions, deletions, and / or insertions) while retaining BCMA binding functionality.

[0496] 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 prasadiene lactone or a prasadiene lactone derivative. In some embodiments, the therapeutic agent is prasadiene lactone D or a prasadiene lactone D derivative. In some embodiments, the therapeutic agent is D1, D2, or another exemplary splicing modulator described herein or incorporated herein by reference. In some embodiments, the therapeutic agent is D1. In some embodiments, the therapeutic agent is D2.

[0497] In some embodiments, this disclosure provides isolated and / or substantially purified nucleic acid molecules (also referred to as polynucleotides) encoding full-length polypeptides comprising the antibody and antigen-binding fragments described herein, or polypeptides comprising segments of the antibody and antigen-binding fragments described herein. As used herein, “isolated” means removed from one or more components found in the normal environment of nucleic acids prior to intervention. In some embodiments, a single nucleic acid may comprise coding sequences for the heavy chain variable region and light chain variable region of the antibody or antigen-binding fragment disclosed herein, and optionally also comprise coding sequences for one or more constant regions thereof. Alternatively, some or all of these coding sequences may be located on a separate nucleic acid molecule. When expressed from a suitable expression vector, the polypeptides encoded by these polynucleotides are able to bind BCMA (e.g., human BCMA).

[0498] This document also provides polynucleotides encoding at least one CDR region and typically all three CDR regions of the heavy and / or light chains of the exemplary anti-BCMA antibody or antigen-binding fragment disclosed herein. This document further provides polynucleotides encoding all or substantially all of the variable region sequences of the heavy and / or light chains of the exemplary anti-BCMA antibody or antigen-binding fragment disclosed herein. Due to the degeneracy of the genetic code, multiple nucleic acid sequences will encode each of the exemplary amino acid sequences disclosed herein.

[0499] This article also provides expression vectors, host cells, and methods for generating the anti-BCMA antibodies and antigen-binding fragments disclosed herein.

[0500] An exemplary embodiment is an isolated nucleic acid encoding an antibody or antigen-binding fragment disclosed herein. Another exemplary embodiment is an isolated vector containing an isolated nucleic acid encoding an antibody or antigen-binding fragment disclosed herein. Another exemplary embodiment is an isolated cell or cell population containing an isolated nucleic acid encoding an antibody or antigen-binding fragment disclosed herein, or containing a vector containing an isolated nucleic acid. Another exemplary embodiment is a method for generating an antibody or antigen-binding fragment, the method being carried out by culturing host cells or cell populations modified to contain one or more nucleic acid sequences encoding the antibody or antigen-binding fragments described herein under conditions suitable for generating the antibody or antigen-binding fragment. In some embodiments, the method further includes the steps of isolating, purifying, and / or recovering the generated antibody or antigen-binding fragment.

[0501] The term "vector" is intended to refer to a polynucleotide molecule capable of transporting another polynucleotide linked to it and / or controlling the expression of that linked polynucleotide. One type of vector is a "plasmid," which is a circular double-stranded DNA loop into which an additional DNA segment can be linked. Another type of vector is a viral vector, in which an additional DNA segment can be linked to a viral genome. Some vectors (e.g., bacterial vectors with bacterial origins of replication and episodic mammalian vectors) are capable of autonomous replication in the host cell to which they are introduced. Other vectors (e.g., non-episodic mammalian vectors) can integrate into the host cell genome once introduced into the host cell and thereby replicate along with the host genome. Furthermore, some vectors can direct the expression of genes operatively linked to them. Such vectors are referred to herein as "expression vectors" or "recombinant expression vectors." Typically, expression vectors useful in recombinant DNA technologies are in the form of plasmids. This disclosure is intended to include plasmids, as well as other forms of expression vectors that perform equivalent functions, such as viral vectors (e.g., replication-defective retroviruses or lentiviruses, adenoviruses, and adeno-associated viruses).

[0502] Vectors used to receive sequences encoding variable regions of the heavy and / or light chains of anti-BCMA antibodies sometimes also encode constant regions or portions thereof. Such vectors allow the expression of the variable regions as fusion proteins with constant regions, resulting in the production of full-length antibodies or antigen-binding fragments thereof. Typically, such constant regions are human constant regions. In some embodiments, the constant region is the human IgG1 heavy chain constant region. In some embodiments, the constant region is the human IgG4 heavy chain constant region. In some embodiments, the constant region is the human Igκ light chain constant region. In some embodiments, the constant region is the human Igλ light chain constant region.

[0503] The term "host cell" refers to cells (or cell populations) that have been engineered to contain nucleic acids encoding peptide sequences, and which are transcribed and translated, and optionally secrete peptides into cell growth media. For recombinant production purposes, nucleic acids encoding amino acid sequences of peptides are typically synthesized or cloned using conventional methods and integrated into expression vectors. The term "host cell" refers not only to a specific subject cell but also to its progeny. Because certain modifications can occur in subsequent generations due to mutations or environmental influences, these progeny cells may actually differ from the parent cells but are still included within the scope of this terminology as used herein.

[0504] The host cell carrying and expressing nucleic acid encoding an anti-BCMA antibody chain or antigen-binding fragment can be a prokaryotic or eukaryotic cell. In some embodiments, mammalian host cells are used to express and produce the anti-BCMA peptide disclosed herein. For example, they can be hybridoma cell lines expressing endogenous immunoglobulin genes or mammalian cell lines carrying exogenous expression vectors. These include any normal morbid animal or human cells or normal or abnormal immortalized animal or human cells. For example, many 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), young 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 derived, immortalized, or transformed cells thereof.

[0505] In some embodiments, one or more nucleic acid molecules encoding heavy and / or light chains of anti-BCMA antibodies or antigen-binding fragments, or one or more expression vectors containing such nucleic acid molecules, may be introduced into suitable host cells using any method suitable for the selected host cells (e.g., transformation, transfection, electroporation, infection) to produce recombinant host cells, such that the nucleic acid molecules are operatively linked to one or more expression control elements (e.g., in a vector, in a construct created by a process within the cell, integrated into the host cell genome). In some embodiments, the resulting recombinant host cells may 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 suitable salts, growth factors, antibiotics, nutritional supplements, etc.), thereby producing the encoded polypeptide. If desired, the encoded protein may be isolated or recovered (e.g., from the animal, host cell, culture medium). This process includes expression in the host cells of a transgenic non-human animal (see, for example, International Publication No. WO 1992 / 003918). Furthermore, the expression of antibody chains or antigen-binding fragments from production cell lines can be enhanced using known techniques. For example, glutamine synthase and DHFR gene expression systems are commonly used methods to enhance expression under certain conditions. Highly expressed cell clones can be identified using conventional techniques such as limiting dilution cloning, gel microdroplet technology, or any other method known in the art.

[0506] Antibody-drug conjugates

[0507] The antibody-drug conjugates (ADCs) disclosed herein include those conjugates possessing anticancer activity. Specifically, these ADCs include an antibody or antigen-binding fragment conjugated (i.e., covalently linked via a linker) to a drug moiety (e.g., a splicing modulator), wherein the drug moiety, when not conjugated to the antibody or antigen-binding fragment, has cytotoxic or cell growth-inhibiting effects. In various embodiments, the drug moiety, when not conjugated to the antibody or antigen-binding fragment, is capable of binding to and / or interacting with the SF3b spliceosome complex. In various embodiments, the drug moiety, when not conjugated to the antibody or antigen-binding fragment, is capable of modulating in vitro and / or in vivo RNA splicing. In various embodiments, by targeting RNA splicing, the drug moiety and ADC disclosed herein provide potent antiproliferative agents. In various embodiments, the drug moiety and ADC disclosed herein can target actively dividing and dormant cells (e.g., actively dividing, non-dividing, and / or slowly dividing myeloma cells).

[0508] In various embodiments, this disclosure is based, at least in part, on the finding that the novel antibody and antigen-binding fragments disclosed herein can provide improved properties when conjugated to certain bioactive splice modulators and used in ADCs. While splice modulators may exhibit the desired improved characteristics when used alone (e.g., strong SF3b spliceosome complex binding, efficient regulation of RNA splicing), their ability to preferentially target diseased tissues may be limited. Moreover, in various embodiments, splice modulators may exhibit fewer of the desired characteristics when conjugated to some antibody or antigen-binding fragments. Therefore, the development and production of ADCs for use as human therapeutics (e.g., as oncology agents) may require more than just identifying antibodies capable of binding to one or more desired targets and conjugated to drugs used alone to treat cancer. The conjugation of an antibody to a drug can have a significant impact on the activity of one or both of the antibody and the drug, and this impact will vary depending on the type of linker and / or drug selected. Therefore, in some embodiments, the components of the ADC are selected to (i) maintain one or more therapeutic properties exhibited by the separated antibody and drug portions; (ii) maintain the specific binding properties of the antibody or antigen-binding fragment; (iii) optimize the drug load and drug-to-antibody ratio; (iv) allow delivery of the drug portion via stable linkage to the antibody or antigen-binding fragment (e.g., intracellular delivery); (v) maintain the stability of the ADC as a complete conjugate until transported or delivered to the target site; (vi) minimize aggregation of the ADC before or after administration; (vii) allow the therapeutic effects of the drug portion, such as cytotoxic effects, to be achieved following lysis or other release mechanisms in the cellular environment; (viii) exhibit in vivo anticancer therapeutic efficacy similar to or superior to that of the separated antibody and drug portions; (ix) minimize off-target killing caused by the drug portion; and / or (x) exhibit the desired pharmacokinetic and pharmacodynamic properties, reproducibility, and toxicological / immunological characteristics. Some or all of these properties may be needed to identify improved ADCs for therapeutic use (Ab et al. (2015) Mol Cancer Ther. [Molecular Cancer Therapeutics] 14:1605-13).

[0509] In various embodiments, the ADCs disclosed herein exhibit some or all of the unexpectedly advantageous properties listed above. For example, in some embodiments, the ADC constructs disclosed herein exhibit surprisingly advantageous drug loading, aggregation, and / or stability characteristics, and / or maintain or improve antibody binding function, drug activity, and / or bystander killing activity, while reducing off-target killing, compared to ADCs comprising alternative antibodies, adapters, and / or drug portions (e.g., alternative antibodies (e.g., reference antibodies) and / or alternative splicing modulators). In some embodiments, the ADC constructs disclosed herein exhibit improved cytotoxic and / or cell growth inhibitory activity against non-dividing and / or slowly dividing cells compared to ADCs comprising alternative antibodies, adapters, and / or drug portions (e.g., alternative antibodies (e.g., reference antibodies) and / or alternative splicing modulators). In some embodiments, the ADC constructs disclosed herein exhibit higher affinity for BCMA and / or superior stability, activity, potency, or other effects (measured in vivo or in vitro) compared to ADCs using alternative antibodies, linkers, and / or pharmaceutical portions (e.g., alternative antibodies (e.g., reference antibodies) and / or alternative splicing modulators). In some embodiments, the comparative or reference ADC is an ADC containing the same linker and / or splicing modulator payload but containing an alternative antibody (e.g., AB200 or other exemplary anti-BCMA antibodies).

[0510] In some embodiments, the ADC constructs disclosed herein exhibit improved binding affinity compared to ADCs containing, for example, the same linker and / or splice modulator payload but containing an alternative antibody (e.g., AB200 or other exemplary anti-BCMA antibody). In some embodiments, the disclosed ADC has a higher affinity for BCMA (e.g., human BCMA) compared to ADCs containing the same linker and / or splice modulator payload but containing an alternative antibody. In some embodiments, the disclosed ADC contains an exemplary anti-BCMA antibody or antigen-binding fragment, a linker, and a splice modulator payload. In some embodiments, the anti-BCMA antibody or antigen-binding fragment is any one of antibody AB212, AB213, AB214, AB215, AB216, AB217, or AB218 (e.g., AB212 or AB216, such as AB216). In some embodiments, a reference ADC is an ADC containing the same linker and the same splice modulator payload as the disclosed ADC (e.g., ADL1-D2) but containing an alternative antibody (e.g., AB200). In some embodiments, the binding affinity of the ADC to BCMA (e.g., human BCMA) can be determined, for example, by using one or more binding assays on cancer cells with high or moderate BCMA expression levels.

[0511] In some embodiments, the ADC constructs disclosed herein exhibit improved cytotoxic and / or cell growth inhibitory activity compared to ADCs containing, for example, the same linker and / or splicing regulator payload but containing an alternative 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) compared to ADCs containing the same linker and / or splicing regulator payload but containing an alternative antibody. In some embodiments, the activity of the disclosed ADCs is independent of the cell cycle. In some embodiments, the disclosed ADCs retain cytotoxic and / or cell growth inhibitory activity independent of cell proliferation 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) compared to alternative anti-BCMA ADCs (e.g., anti-BCMA ADCs containing an alternative antibody, linker, and / or payload, such as AB200-ADL10-MMAF). In some embodiments, the disclosed ADC does not inhibit the growth of cells that do not express BCMA (e.g., BCMA-negative cells, such as Jurkat cells) and / or does not kill them. In some embodiments, the disclosed ADC comprises 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, such as AB216). In some embodiments, a reference ADC is an ADC that contains the same linker and the same splicing modulator payload as the disclosed ADC but contains an alternative antibody (e.g., AB200). In some embodiments, the cytotoxic and / or cell growth-inhibiting activity of the ADC can be determined, for example, by using an in vitro activity assay with cancer cells having high or moderate BCMA expression levels.

[0512] In some embodiments, the ADC constructs disclosed herein exhibit improved in vivo anticancer activity compared to ADCs containing, for example, the same linker and / or splice modulator payload but containing an alternative antibody (e.g., AB200 or other exemplary antiBCMA antibodies). In some embodiments, the disclosed ADCs exhibit increased tumor growth inhibition against BCMA-expressing tumors (e.g., OPM2 and / or MOLP8 tumors) compared to ADCs containing the same linker and / or splice modulator payload but containing an alternative antibody. In some embodiments, the disclosed ADCs contain an exemplary antiBCMA antibody or antigen-binding fragment, a linker, and a splice modulator payload. In some embodiments, the antiBCMA antibody or antigen-binding fragment is any one of antibodies AB212, AB213, AB214, AB215, AB216, AB217, or AB218 (e.g., AB212 or AB216, such as AB216). In some embodiments, a reference ADC is an ADC that contains the same linker and the same splicing modulator payload as the disclosed ADC (e.g., ADL1-D2) but contains an alternative antibody (e.g., AB200). In some embodiments, the in vivo anticancer activity of an ADC can be determined, for example, by activity assays in xenograft models with high or moderate BCMA expression levels.

[0513] In some embodiments, the ADC constructs disclosed herein exhibit the properties required for a therapeutic ADC. In some embodiments, these properties include, but are not limited to, effective drug loading levels, low aggregation levels, stability, residual affinity for BCMA-expressing cells comparable to unconjugated antibodies, strong cytotoxicity to BCMA-expressing cells, low levels of off-target cell killing, and / or effective in vivo anticancer activity. In some embodiments, the ADC constructs disclosed herein exhibit in vivo therapeutic efficacy upon single-dose administration.

[0514] The disclosed ADC can selectively deliver an effective dose of a cytotoxic agent or cell growth inhibitor to cancer cells. In some embodiments, the disclosed ADC has effective cytotoxic and / or cell growth inhibitory activity against cells expressing a target antigen (e.g., BCMA). In some embodiments, the cytotoxic and / or cell growth inhibitory activity of the ADC depends on the expression of the target antigen in the cells. In some embodiments, the disclosed ADC is particularly effective in killing cancer cells expressing high levels of the target antigen compared to cancer cells expressing low levels of the same antigen. In some embodiments, the disclosed ADC is particularly effective in killing cancer cells expressing intermediate levels of the target antigen compared to cancer cells expressing low levels of the same antigen. Exemplary cancer cells that highly express BCMA include, but are not limited to, human myeloma NCI-H929 cells. Exemplary cancer cells that moderately express BCMA include, but are not limited to, human myeloma OPM2 cells and human myeloma MOLP8 cells. In some embodiments, the disclosed ADC is particularly effective in killing cancer cells expressing the target antigen while minimizing off-target killing. In some embodiments, the disclosed ADC does not exhibit cytotoxic and / or cell growth inhibitory effects on cancer cells that do not express the target antigen.

[0515] In some embodiments, cleavage of the ADC releases the splicing regulator from the antibody or antigen-binding fragment and the linker. In some embodiments, the linker and / or splicing regulator are designed to promote bystander killing (killing of neighboring cells). In some embodiments, the linker and / or splicing regulator are designed to promote bystander killing via cleavage after internalization and diffusion of the linker-splicing regulator portion and / or the individual splicing regulator portion to neighboring cells. In some embodiments, the linker promotes internalization. In some embodiments, the linker is designed to minimize cleavage in the extracellular environment and thereby reduce toxicity to off-target cells or tissues (e.g., non-cancerous cells or tissues) while maintaining ADC binding to target cells or tissues and / or bystander killing of cancerous tissues (which do not express the antigen targeted by the antibody or antigen-binding fragment of the ADC but surround target cancerous tissues expressing that antigen). In some embodiments, the drug portion or catabolic metabolites of the drug portion resulting from ADC cleavage are designed to promote uptake by target cells or neighboring cells (i.e., cell-permeable). Such splice modulators and their catabolites can be termed "bystander active," while drug moieties or catabolites that reduce cell permeability can be termed "bystander inactive."

[0516] In some embodiments, the disclosed ADCs also exhibit bystander-killing activity. Unbound by theory, bystander-killing activity of ADCs can be particularly beneficial when ADC penetration into solid tumors is limited and / or when target antigen expression in tumor cells is heterogeneous. In some embodiments, the ADCs disclosed herein exhibit improved solubility and target cell penetration compared to the drug portion alone. In some embodiments, the ADCs disclosed herein exhibit improved cytotoxicity compared to the drug portion alone. In some embodiments, the ADCs disclosed herein use a drug portion that exhibits lower cytotoxicity when evaluated as a drug alone, but which unexpectedly outperforms ADCs containing other drug portions that have higher cytotoxicity when evaluated as a drug alone. In some embodiments, cleavage and release of the splice modulator improve the cytotoxicity of the ADC relative to comparable treatments with an ADC containing a non-cleavable linker. In other embodiments, cleavage and release of the splice modulator are not required for the ADC to have the desired biological activity.

[0517] This document provides an ADC comprising an antibody or antigen-binding fragment (Ab) capable of binding BCMA, a splicing modulator drug portion (D), and a linker portion (L) covalently linking the Ab to the D. In some embodiments, the antibody or antigen-binding fragment can bind BCMA with high specificity and high affinity. In some embodiments, the antibody or antigen-binding fragment is internalized into the target cell after binding, for example, into a degradation compartment within the cell. In some embodiments, an ADC that internalizes upon binding to a target cell, undergoes degradation, and releases the splicing modulator drug portion to kill cancer cells can be used. The splicing modulator drug portion can be released from the antibody and / or linker portion in the ADC via enzymatic action, hydrolysis, oxidation, or any other mechanism.

[0518] An exemplary ADC has equation (I):

[0519] Ab-(LD) p (I)

[0520] Where Ab = antibody or antigen-binding fragment, L = linker portion, D = splice modulator drug portion, and p = number of splice modulator drug portions / antibody or antigen-binding fragment.

[0521] In some embodiments, the antibody or antigen-binding fragment (Ab) used in the ADC and the composition is the anti-BCMA antibody or antigen-binding fragment disclosed herein.

[0522] connector

[0523] In some embodiments, the linkers in the ADCs disclosed herein are extracellularly stable in a manner sufficient to achieve therapeutic efficacy. In some embodiments, the linkers are stable outside the cells such that the ADC remains intact when present in extracellular conditions (e.g., prior to transport or delivery to cells). 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, in the case of a linker or an ADC containing a linker, “stable” means that no more than 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 between these) of the linker in the ADC sample is cleaved (or the overall ADC is otherwise incomplete) when the ADC is present in extracellular conditions. In some embodiments, the linkers and / or ADCs disclosed herein are remarkably stable compared to alternative linkers and / or ADCs having alternative linker and / or splicing modulator payloads. In some embodiments, the ADCs disclosed herein can remain intact for more than about 48 hours, more than 60 hours, more than about 72 hours, more than about 84 hours, or more than about 96 hours.

[0524] Extracellular stability of the linker can be determined, for example, by including the ADC in plasma for a predetermined time period (e.g., 2, 4, 6, 8, 16, 24, 48, or 72 hours) and subsequently quantifying the amount of free drug fraction present in the plasma. Stability allows the ADC time to localize to target cancer cells and prevents premature release of the drug fraction, 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 releases the drug fraction from the ADC once inside the cell, allowing the drug to bind to its target (e.g., to the SF3b splice complex). Thus, in some embodiments, an effective linker will: (i) maintain the specific binding properties of the antibody or antigen-binding fragment; (ii) allow delivery (e.g., intracellular delivery) of the drug fraction via stable attachment to the antibody or antigen-binding fragment; (iii) maintain stability and integrity until the ADC has been transported or delivered to the target site; and (iv) allow the therapeutic effects of the drug fraction, such as cytotoxic effects, following cleavage or alternative release mechanisms.

[0525] Connectors can influence the physicochemical properties of ADCs. Since many cytotoxic agents are inherently hydrophobic, linking them to antibodies with an additional hydrophobic moiety can lead to aggregation. ADC aggregates are insoluble and typically limit the drug loading achievable on the antibody, which can adversely affect the efficacy of the ADC. Protein aggregates in biologics are also often associated with increased immunogenicity. As shown below, the connectors disclosed herein enable ADCs to achieve low aggregation levels and the desired drug loading levels.

[0526] The adapters described in International Application No. PCT / US 2019 / 035015 (Publication No. WO 2019 / 232449) can be used with the ADC disclosed herein. For all exemplary adapters and adapter-antibody connection points, International Application No. PCT / US 2019 / 035015 (Publication No. WO 2019 / 232449) is incorporated herein by reference.

[0527] Linkers can be “cleavable” or “non-cleavable” (Ducry and Stump (2010) Bioconjugate Chem. [Bioconjugate Chemistry] 21:5-13). Cleavable linkers are designed to release drug moieties (e.g., splicing regulators) when subjected to certain environmental factors (e.g., when internalized into target cells), while non-cleavable linkers typically rely on the degradation of the antibody or antigen-binding fragment itself.

[0528] In some embodiments, the linker is a non-cleavable linker. In some embodiments, the splicing modulator drug portion of the ADC is released via the degradation of the antibody or antigen-binding fragment. Upon internalization and degradation within the target cell, the non-cleavable linker tends to maintain covalent association with at least one amino acid of the antibody and the drug. Several exemplary non-cleavable linkers are described herein, and other non-cleavable linkers are known in the art. Exemplary non-cleavable linkers may comprise a thioether, cyclohexyl, N-succinimide-4-(N-maleimide-methyl)cyclohexane-1-carboxylate (SMCC) or N-hydroxysuccinimide (NHS), one or more polyethylene glycol (PEG) portions (e.g., 1, 2, 3, 4, 5, or 6 PEG portions) or one or more alkyl portions (e.g., 1, 2, 3, 4, 5, or 6 alkyl portions).

[0529] In some other embodiments, the connector is a cleavable connector. A cleavable connector refers to any connector containing a cleavable portion. As used herein, the term "cleavable portion" 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-instable bonds, protease / peptidase-instable bonds, light-instable bonds, disulfide bonds, and esterase-instable bonds. A connector containing a cleavable portion allows the release of the splice modulator drug portion from the ADC via cleavage at a specific site within the connector.

[0530] In some embodiments, the linker can be cleaved under intracellular conditions, and the cleavage of the linker allows the splicing modulator drug portion to be fully released from the antibody or antigen-binding fragment in the intracellular environment to activate the drug and / or make the drug therapeutically effective. In some embodiments, the splicing modulator drug portion is not cleaved from the antibody or antigen-binding fragment until the ADC enters a cell expressing an antigen specific to the antibody or antigen-binding fragment in the ADC, and the splicing modulator drug portion cleaves from the antibody or antigen-binding fragment after entering the cell. In some embodiments, the linker includes a cleavable portion that is fixed in place such that no portion of the linker or the antibody or antigen-binding fragment remains bound to the splicing modulator drug portion after cleavage. Exemplary cleavable linkers include acid-instable linkers, protease / peptidase-sensitive linkers, photostable linkers, dimethyl-containing linkers, disulfide-containing linkers, or sulfonamide-containing linkers.

[0531] In some embodiments, the linker is a pH-sensitive linker and is sensitive to hydrolysis at certain pH values. Typically, pH-sensitive linkers can be hydrolyzed under acidic conditions. This cleavage strategy generally utilizes a lower pH compared to the cytosol (pH about 7.4) in the intracellular compartment of the endosome (pH about 5-6) and the intracellular compartment of the lysosome (pH about 4.8) to trigger the hydrolysis of acid-instable groups in linkers such as hydrazones (Jain et al. (2015) Pharm Res [Pharmaceutical Research] 32:3526-40). In some embodiments, the linker is an acid-instable linker and / or a hydrolyzable linker. For example, acid-instable linkers that can be hydrolyzed in lysosomes and contain acid-instable groups (e.g., hydrazones, hemicarbazones, thiohemicarbazones, cis-aconitamide, orthoesters, acetals, ketals, or analogs thereof) can be used. See, for example, 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. These types of linkers are relatively stable under neutral pH conditions (such as the pH of blood) but unstable below pH 5.5 or 5.0 (the approximate pH of lysosomes). In some embodiments, the hydrolyzable linker is a thioether linker (e.g., a thioether linked to a therapeutic agent via an acylhydrazone bond) (see, for example, U.S. Patent No. 5,622,929).

[0532] In some embodiments, the connector may be cleaved under reducing conditions. In some embodiments, the connector may be cleaved in the presence of a reducing agent such as glutathione or dithiothreitol. In some embodiments, the connector is a cleavable disulfide connector or a cleavable sulfonamide connector.

[0533] In some embodiments, the connector is a pyrolytic disulfide connector. Various disulfide connectors are known in the art, including, for example, disulfide connectors formed using 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-pyridyl-dithio)toluene), SPDB, and SMPT. See, for example, Thorpe et al. (1987) Cancer Res. 47:5924-31; Wawrzynczak et al., Immunoconjugates: Antibody Conjugates in Radioimagery and Therapy of Cancer (edited by CW Vogel, Oxford U. Press, 1987). See also U.S. Patent No. 4,880,935. Disulfide linkers are commonly used to develop the abundance of intracellular thiols, which promotes the cleavage of their disulfide bonds. The intracellular concentrations of the most abundant intracellular thiols and reduced glutathione are typically in the range of 1–10 nM, approximately 1,000 times higher than the intracellular concentration of the most abundant low-molecular-weight thiols in the blood (i.e., cysteine), which is approximately 5 μM (Goldmacher et al., in Cancer Drug Discovery and Development: Antibody-Drug Conjugates and Immunotoxins [edited by GL Phillips, Springer, 2013]). Intracellular enzymes of the protein disulfide isomerase family can also promote the intracellular cleavage of disulfide linkers. As used herein, a cleavable disulfide linker refers to any linker containing 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 enzyme.

[0534] In some embodiments, the connector is a cleavable sulfonamide connector. As used herein, a cleavable sulfonamide connector refers to any connector containing a cleavable sulfonamide moiety. The term "cleavable sulfonamide moiety" refers to a sulfonamide group, i.e., a sulfonyl group attached to an amine group, wherein the sulfur-nitrogen bond is cleavable.

[0535] In some embodiments, the linker may be a dendritic linker for covalently linking more than one drug moiety to an antibody or antigen-binding fragment via a branched, multifunctional linker portion. See, for example, 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 molar ratio of drug to antibody, i.e., the drug loading, which is related to the potency of the ADC. Therefore, in cases where the antibody or antigen-binding fragment has only one reactive cysteine ​​thiol group, multiple splice modulator drug moieties, for example, can be linked via a dendritic linker. In some embodiments, the linker portion or linker-drug portion may be linked to the antibody or antigen-binding fragment via a reduced disulfide bridging chemical or a restricted lysine utilization technique. See, for example, International Publications WO 2013 / 173391 and WO 2013 / 173393.

[0536] In some embodiments, the linker may be cleaved by a cleaving agent (e.g., an enzyme) present in the intracellular environment (e.g., lysosomes, endosomes, or crypts). The linker may be a peptide linker cleaved, for example, by an intracellular peptidase or protease (including, but not limited to, lysosomal or endosomal proteases). In some embodiments, the linker comprises a cleavable peptide moiety. In some embodiments, the linker comprises a cleavable glucuronide moiety.

[0537] In some embodiments, the linker is a cleavable peptide linker. As used herein, a cleavable peptide linker refers to any linker containing a cleavable peptide moiety. The term "cleavable peptide moiety" refers to any chemically bonded amino acid (natural or synthetic amino acid derivative) that can be cleaved by an agent present in the intracellular environment. In some embodiments, the cleavable peptide moiety can be cleaved by an enzyme. For example, the linker may contain a valine-alanine (Val-Ala) sequence or a valine-citrulline (Val-Cit) sequence, which can be cleaved by peptidases (such as cathepsins, e.g., cathepsin B). In some embodiments, the linker may contain an alanine-alanine-aspartic acid (Ala-Ala-Asp) sequence. In some embodiments, the linker may contain 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 can be cleaved by an enzyme. In some embodiments, the cleavable peptide moiety can be cleaved by a lysosomal enzyme (e.g., cathepsin). In some embodiments, the linker is a cathepsin-cleavable linker. In some embodiments, the cleavable peptide moiety in the linker can be cleaved by lysosomal cysteine ​​cathepsins (such as cathepsins B, C, F, H, K, L, O, S, V, X, or W). In some embodiments, the cleavable peptide moiety can be cleaved by cathepsin B. An exemplary dipeptide that can be cleaved by cathepsin B is valine-citrulline (Val-Cit) (Dubowchik et al. (2002) Bioconjugate Chem. [Bioconjugate Chemistry] 13:855-69).

[0538] In some embodiments, the linker or the cleavable peptide portion within the linker comprises an amino acid unit. In some embodiments, this amino acid unit makes the linker cleavable by a protease, thereby promoting the release of the splicing regulator drug portion from the ADC upon exposure to one or more intracellular proteases, such as one or more lysosomal enzymes (Doronina et al. (2003) Nat Biotechnol. [Nature Biotechnology] 21:778-84; Dubowchik and Walker (1999) Pharm Therapeutics [Pharmacology and 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. [Nature Communications] 9:2512) and glycine-phenylalanine-lysine (Gly-Phe-Lys). Other exemplary amino acid units include, for example, Gly-Phe-Gly-Gly (SEQ ID NO: 125), Gly-Phe-Leu-Gly (SEQ ID NO: 126), Ala-Leu-Ala-Leu (SEQ ID NO: 127), and Phe-N as described in U.S. Patent No. 6,214,345. 9 -Toluenesulfonyl-Arg and Phe-N 9-Nitro-Arg. 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 secondary amino acids and / or non-naturally occurring amino acid analogs (such as citrulline). The amino acid unit may be targeted to a specific enzyme (e.g., tumor-associated proteases, lysosomal proteases (such as cathepsin B, C, D, or S) or plasminase).

[0539] In some embodiments, the connector is a cleavable glucuronide connector. As used herein, a cleavable glucuronide connector refers to any connector containing a cleavable glucuronide moiety. In some embodiments, the cleavable glucuronide moiety can be cleaved by an enzyme. An exemplary cleavable glucuronide connector comprises the following structure:

[0540]

[0541] 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 can be cleaved by glucuronidase. In some embodiments, the cleavable glucuronide moiety can be cleaved 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-glucuronyltransferase that catalyzes the hydrolysis of the glycosidic bond of a glucuronide having a β-configuration.

[0542] In some embodiments, the ADC disclosed herein comprises a cleavable β-glucuronide moiety in a cleavable linker. In some embodiments, the cleavable β-glucuronide moiety in the linker may be cleaved by a lysosomal enzyme (e.g., 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 the linker to be cleaved by β-glucuronidase after ADC internalization, thereby facilitating the release of the drug moiety from the ADC in the cellular environment.

[0543] In some embodiments, the linker in the ADC disclosed herein comprises a maleimide moiety. As used herein, the term “Mal” or “maleimide moiety” means a compound containing a maleimide group and capable of reacting with a thiohydride group (e.g., a thiohydride group of a cysteine ​​residue on an antibody or antigen-binding fragment). Other functional groups capable of reacting with a thiohydride group (thiol) include, but are not limited to, iodoacetamide, bromoacetamide, vinylpyridine, disulfides, pyridyl disulfides, isocyanates, and isothiocyanates. In some embodiments, the maleimide moiety comprises a maleimide hexanoyl (MC). In some embodiments, the maleimide moiety reacts with a cysteine ​​residue on an antibody or antigen-binding fragment. In some embodiments, the maleimide moiety is linked to the antibody or antigen-binding fragment via a cysteine ​​residue on the antibody or antigen-binding fragment.

[0544] In some embodiments, the connector comprises a maleimide portion and a cleavable peptide portion. In some embodiments, the cleavable peptide portion comprises an amino acid unit. In some embodiments, the cleavable peptide portion or amino acid unit comprises Val-Cit. In some embodiments, the cleavable peptide portion or amino acid unit comprises Val-Ala. In some embodiments, the cleavable peptide portion or amino acid unit comprises Ala-Ala-Asp. In some embodiments, the cleavable peptide portion or amino acid unit comprises Glu-Val-Cit. In some embodiments, the connector comprises a maleimide portion and a cleavable glucuronide portion. In some embodiments, the cleavable glucuronide portion comprises β-glucuronide.

[0545] In some embodiments, the connector in the ADC disclosed herein may include at least one spacer subunit that binds an antibody or antigen-binding fragment to a drug portion (e.g., a splicing modulator drug portion). In some embodiments, the spacer subunit located between the antibody or antigen-binding fragment and the cleavable portion, when present, binds a cleavage site (e.g., a cleavable peptide portion) in the connector to the antibody or antigen-binding fragment. In some embodiments, the spacer subunit located between the drug portion and the cleavable portion, when present, binds a cleavage site (e.g., a cleavable peptide portion or a cleavable glucuronide) in the connector to the drug portion. In some embodiments, a cleavage site is absent, and the spacer subunit is used to connect the antibody or antigen-binding fragment to the drug portion.

[0546] In some embodiments, the connector and / or the spacer subunits within the connector are substantially hydrophilic. Hydrophilic connectors can be used to reduce the extent to which drugs can be pumped out of drug-resistant cancer cells via multidrug resistance (MDR) transporters or functionally similar transporters. In some embodiments, the hydrophilic connector may include one or more polyethylene glycol (PEG) portions, such as 1, 2, 3, 4, 5, or 6 PEG portions.

[0547] In some embodiments, the spacer subunit in the connector includes at least one PEG portion. In some embodiments, the PEG portion or spacer subunit includes one or more -(PEG) portions. m - and 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 is in the range of 1 to 10; in the range of 2 to 8; in the range of 2 to 6; in the range of 2 to 5; in the range of 2 to 4; or in the range of 2 to 3. In some embodiments, m is 2. In some embodiments, the PEG portion or spacer subunit 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 portion or spacer subunit comprises (PEG)2.

[0548] In some embodiments, the spacer subunits in the connector comprise alkyl portions. In some embodiments, the alkyl portions or spacer subunits comprise one or more -(CH2) groups. n - and 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 is in the range of 1 to 10; in the range of 2 to 8; in the range of 2 to 6; in the range of 2 to 5; in the range of 2 to 4; or in the range of 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 subunit comprises (CH2)2, (CH2)3, (CH2)4, (CH2)5, (CH2)6, (CH2)7, (CH2)8, (CH2)9, or (CH2) 10 In some embodiments, the alkyl moiety or spacer subunit comprises (CH2)2 (“Et”). In some embodiments, the alkyl moiety or spacer subunit comprises (CH2)6 (“Hex”). In some embodiments, the alkyl moiety or spacer subunit comprises (CH2)2-O-(CH2)2 (“Et-O-Et”).

[0549] Spacer units can be used, for example, to directly or indirectly connect antibody or antigen-binding fragments to a drug portion. In some embodiments, the spacer unit directly connects the antibody or antigen-binding fragment to the splice modulator drug portion. In some embodiments, the antibody or antigen-binding fragment and the splice modulator drug portion are connected via a spacer unit comprising one or more PEG portions (e.g., (PEG)2) or one or more alkyl portions (e.g., (CH2)2, (CH2)6, or (CH2)2-O-(CH2)2). In some embodiments, the spacer unit indirectly connects the antibody or antigen-binding fragment to the splice modulator drug portion. In some embodiments, the spacer unit indirectly connects the antibody or antigen-binding fragment to the splice modulator drug portion via a cleavable portion (e.g., a cleavable peptide or a cleavable β-glucuronide) and / or a connecting portion (e.g., a maleimide portion) for attaching the spacer unit to the antibody or antigen-binding fragment.

[0550] In various embodiments, the spacer subunit is linked to an antibody or antigen-binding fragment (i.e., an antibody or antigen-binding fragment) via a maleimide portion. The spacer subunit linked to the antibody or antigen-binding fragment via a maleimide portion is referred to herein as a "Mal-spacer subunit". In some embodiments, the Mal-spacer subunit comprises a PEG portion. In some embodiments, the Mal-spacer subunit comprises an alkyl portion. In some embodiments, the Mal-spacer subunit comprises a maleimide-hexanoyl (MC).

[0551] In some embodiments, the connector includes the following structure: Mal-spacer subunit. In some embodiments, the Mal-spacer subunit or connector includes MC. In some embodiments, the connector includes the following structure: MC. In some embodiments, the connector includes the following structure: Mal-(CH2)2 (“Mal-Et”). In some embodiments, the connector includes the following structure: Mal-(CH2)6 (“Mal-Hex”). In some embodiments, the connector includes the following structure: Mal-(CH2)2-O-(CH2)2 (“Mal-Et-O-Et”). In some embodiments, the connector includes the following structure: Mal-(PEG)2. In some embodiments, the connector includes the following structure: Mal-(PEG)2-CO.

[0552] In some embodiments, the connector comprises a Mal-spacer unit and a cleavable peptide portion. In some embodiments, the cleavable peptide portion comprises an amino acid unit. In some embodiments, the cleavable peptide portion or amino acid unit comprises Val-Cit, Val-Ala, Ala-Ala-Asp, or Glu-Val-Cit. In some embodiments, the cleavable peptide portion or amino acid unit comprises Val-Cit. In some embodiments, the cleavable peptide portion or amino acid unit comprises Val-Ala. In some embodiments, the cleavable peptide portion or amino acid unit comprises Ala-Ala-Asp. In some embodiments, the cleavable peptide portion or amino acid unit comprises Glu-Val-Cit. In some embodiments, the connector comprises a Mal-spacer unit and a cleavable glucuronide portion. In some embodiments, the cleavable glucuronide portion comprises β-glucuronide.

[0553] In some embodiments, the maleimide portion or Mal-spacer unit links an antibody or antigen-binding fragment to a cleavable portion in the adapter. In some embodiments, the cleavable portion in the adapter comprises a cleavable peptide portion. In some embodiments, the cleavable peptide portion comprises an amino acid unit. In some embodiments, the cleavable peptide portion or amino acid unit comprises Val-Cit, Val-Ala, Ala-Ala-Asp, or Glu-Val-Cit. In some embodiments, the cleavable portion in the adapter comprises a cleavable glucuronide portion. In some embodiments, the cleavable glucuronide portion comprises β-glucuronide.

[0554] In some embodiments, the Mal-spacer subunit links an antibody or antigen-binding fragment to a cleavable peptide portion. In some embodiments, the adapter comprises a Mal-spacer subunit-peptide.

[0555] In some embodiments, the connector comprises the following structure: Mal-spacer subunit-Val-Cit. In some embodiments, the Mal-spacer subunit comprises MC. In some embodiments, the connector comprises MC-Val-Cit. In some embodiments, the connector comprises MC-(PEG)2-Val-Cit.

[0556] In some embodiments, the connector includes the following structure: Mal-spacer subunit-Val-Ala. In some embodiments, the Mal-spacer subunit includes MC. In some embodiments, the connector includes MC-Val-Ala.

[0557] In some embodiments, the connector comprises the following structure: Mal-spacer subunit-Ala-Ala-Asp. In some embodiments, the Mal-spacer subunit comprises MC. In some embodiments, the connector comprises MC-Ala-Ala-Asp.

[0558] In some embodiments, the connector comprises the following structure: Mal-spacer subunit-Glu-Val-Cit. In some embodiments, the Mal-spacer subunit comprises MC. In some embodiments, the connector comprises MC-Glu-Val-Cit.

[0559] In some embodiments, the Mal-spacer unit links an antibody or antigen-binding fragment to a cleavable glucuronide portion. In some embodiments, the adapter comprises the following structure: Mal-spacer unit-β-glucuronide. In some embodiments, the Mal-spacer unit comprises MC. In some embodiments, the adapter comprises MC-β-glucuronide.

[0560] In some embodiments, the pyrolytic portion of the connector is directly connected to the splice modulator drug portion. In other embodiments, a spacer subunit connects the pyrolytic portion of the connector to the splice modulator drug portion. In some embodiments, the splice modulator is connected to the pyrolytic portion of the connector via a spacer subunit.

[0561] Spacer units can be either "self-ablating" or "non-self-ablating." A "non-self-ablating" spacer unit is one in which part or all of the splicing modulator drug portion remains bound during linker cleavage. Examples of non-self-ablating spacer units include, but are not limited to, glycine spacer units and glycine-glycine spacer units. Non-self-ablating spacer units may eventually degrade over time, but do not readily and completely release the attached natural drug portion under cellular conditions. "Self-ablating" spacer units allow for the release of the natural drug portion under intracellular conditions. "Natural drug" or "natural drug portion" refers to a portion of the spacer unit that does not retain the spacer unit or any other chemical modifications after spacer unit cleavage / degradation.

[0562] Self-ablating chemicals are known in the art and can be readily selected for the disclosed ADC. In some embodiments, the spacer subunit connecting the cleavable portion of the connector to the splice modulator drug portion is self-ablating and undergoes self-ablation simultaneously with or shortly before / after cleavage of the cleavable portion under intracellular conditions. In some embodiments, cleavage of the conjugate releases the splice modulator from the antibody or antigen-binding fragment and the connector.

[0563] In some embodiments, the spacer subunit connecting the cleavable portion in the connector to the splice modulator is self-ablating. In some embodiments, the splice modulator is connected to the cleavable portion in the connector via a self-ablating spacer subunit, the cleavable portion comprising Val-Cit, and MC binds the cleavable portion to an antibody or antigen-binding fragment. In some embodiments, the splice modulator is connected to the cleavable portion in the connector via a self-ablating spacer subunit, the cleavable portion comprising Val-Cit, and MC-(PEG)2 binds the cleavable portion to an antibody or antigen-binding fragment. In some embodiments, the splice modulator is connected to the cleavable portion in the connector via a self-ablating spacer subunit, the cleavable portion comprising Val-Ala, and MC binds the cleavable portion to an antibody or antigen-binding fragment. In some embodiments, the splice modulator is connected to the cleavable portion in the connector via a self-ablating spacer subunit, the cleavable portion comprising Ala-Ala-Asp, and MC binds the cleavable portion to an antibody or antigen-binding fragment. In some embodiments, the splicing modulator is connected to a cleavable portion in the adapter via a self-ablating spacer subunit, the cleavable portion comprising Glu-Val-Cit, and the MC binds the cleavable portion to an antibody or antigen-binding fragment. In some embodiments, the splicing modulator is connected to a cleavable portion in the adapter via a self-ablating spacer subunit, the cleavable portion comprising β-glucuronide, and the MC binds the cleavable portion to an antibody or antigen-binding fragment.

[0564] In some embodiments, the spacer subunit (e.g., a self-ablating spacer subunit) connecting the cleavable portion in the connector to the splice modulator comprises a p-aminobenzyl unit. In some embodiments, p-aminobenzyl alcohol (pABOH) is connected via an amide bond to an amino acid unit or other cleavable portion in the connector, and a carbamate, methyl carbamate, or carbonate is formed between pABOH and the drug portion (Hamann et al. (2005) Expert Opin Ther Patents. [Therapeutic Agent Patent Expert Review] 15:1087-103).

[0565] In some embodiments, the spacer subunit (e.g., a self-ablating spacer subunit) connecting the cleavable portion of the connector to the splice modifier is or contains a p-aminobenzyloxycarbonyl group (pABC). Without being bound by theory, it is considered that the self-ablating of pABC involves a spontaneous 1,6-elimination reaction (Jain et al. (2015) Pharm Res. [Pharmaceutical Research] 32:3526-40). In some embodiments, the spacer subunit (e.g., a self-ablating spacer subunit) connecting the cleavable portion of the connector to the splice modifier is or contains a p-aminobenzyl group (pAB). In some embodiments, the self-ablating of pAB involves a spontaneous 1,6-elimination reaction.

[0566] In various embodiments, the self-ablating spacer subunit connects the pyrolytic portion of the joint to the shear modifier. In some embodiments, the self-ablating spacer subunit in the joint comprises a p-aminobenzyl unit.

[0567] In some embodiments, the self-ablating spacer subunit in the connector comprises or is composed of a pABC. In some embodiments, the pABC connects a pyrolytic portion in the connector to a splice modulator. In some embodiments, the pABC undergoes self-ablation after the pyrolytic portion pyrolyzes, and the splice modulator is released from the ADC in its native, active form.

[0568] In some embodiments, the structure of the pABC used in the disclosed ADC is shown below:

[0569]

[0570] In some embodiments, the cleavable portion of the connector comprises a cleavable peptide portion. In some embodiments, the cleavable peptide portion comprises an amino acid unit. In some embodiments, the connector comprises an amino acid unit -pABC. In some embodiments, the cleavable peptide portion or amino acid unit comprises Val-Cit, Val-Ala, Ala-Ala-Asp, or Glu-Val-Cit. In some embodiments, the connector comprises Val-Cit-pABC. In some embodiments, the connector comprises Val-Ala-pABC. In some embodiments, the connector comprises Ala-Ala-Asp-pABC. In some embodiments, the connector comprises Glu-Val-Cit-pABC. In some embodiments, the cleavable portion of the connector comprises a cleavable glucuronide portion. In some embodiments, the cleavable glucuronide portion comprises β-glucuronide. In some embodiments, the connector comprises β-glucuronide-pABC.

[0571] In some embodiments, an antibody or antigen-binding fragment in an ADC is conjugated to a splicing modulator drug portion via a linker comprising a Mal-spacer subunit (e.g., MC, MC-(PEG)2), a cleavable amino acid unit, and a pABC. In some embodiments, the spacer subunit comprises a PEG portion. In some embodiments, the Mal-spacer subunit comprises MC. In some embodiments, the cleavable linker comprises a Mal-spacer subunit-amino acid unit-pABC. In some embodiments, the cleavable linker comprises an 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 pyrolytic connector comprises MC-Glu-Val-Cit-pABC. In some embodiments, the pyrolytic connector comprises MC-(PEG)2-Val-Cit-pABC.

[0572] In some embodiments, an antibody or antigen-binding fragment in an ADC is conjugated to a splicing modulator drug portion via a linker, wherein 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 a Mal-spacer unit-β-glucuronide-pABC. In some embodiments, the cleavable linker comprises MC-β-glucuronide-pABC.

[0573] In some embodiments, an anti-BCMA antibody or antigen-binding fragment binds to a splicing modulator via a linker comprising MC-Val-Cit-pABC. In some embodiments, an anti-BCMA antibody or antigen-binding fragment binds to a splicing modulator via a linker comprising MC-Val-Ala-pABC. In some embodiments, an anti-BCMA antibody or antigen-binding fragment binds to a splicing modulator via a linker comprising MC-Ala-Ala-Asp-pABC. In some embodiments, an anti-BCMA antibody or antigen-binding fragment binds to a splicing modulator via a linker comprising MC-Glu-Val-Cit-pABC. In some embodiments, an anti-BCMA antibody or antigen-binding fragment binds to a splicing modulator via a linker comprising MC-(PEG)2-Val-Cit-pABC. In some embodiments, an anti-BCMA antibody or antigen-binding fragment binds to a splicing modulator via a linker comprising MC-β-glucuronide-pABC.

[0574] In some embodiments, the self-ablating spacer subunit in the connector comprises or is composed of p-aminobenzyl (pAB). In some embodiments, pAB connects the cleavable portion of the connector to the splice modifier. In some embodiments, pAB undergoes self-ablation after the cleavable portion cleaves, and the splice modifier is released from the ADC in its native, active form.

[0575] In some embodiments, the structure of the pAB used in the disclosed ADC is shown below:

[0576]

[0577] In some embodiments, the cleavable portion of the connector comprises a cleavable peptide portion. In some embodiments, the cleavable peptide portion comprises an amino acid unit. In some embodiments, the connector comprises an amino acid unit -pAB. In some embodiments, the cleavable peptide portion or amino acid unit comprises Val-Cit, Val-Ala, Ala-Ala-Asp, or Glu-Val-Cit. In some embodiments, the connector comprises Val-Cit-pAB. In some embodiments, the connector comprises Val-Ala-pAB. In some embodiments, the connector comprises Ala-Ala-Asp-pAB. In some embodiments, the connector comprises Glu-Val-Cit-pAB. In some embodiments, the cleavable portion of the connector comprises a cleavable glucuronide portion. In some embodiments, the cleavable glucuronide portion comprises β-glucuronide. In some embodiments, the connector comprises β-glucuronide-pAB.

[0578] In some embodiments, an antibody or antigen-binding fragment in an ADC is conjugated to a splicing modulator drug portion via a linker comprising a Mal-spacer subunit (e.g., MC, MC-(PEG)2), a cleavable amino acid unit, and pAB. In some embodiments, the spacer subunit comprises a PEG portion. In some embodiments, the Mal-spacer subunit comprises MC. In some embodiments, the cleavable linker comprises a Mal-spacer subunit-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 pyrolytic connector comprises MC-(PEG)2-Val-Cit-pAB.

[0579] In some embodiments, an antibody or antigen-binding fragment in an ADC is conjugated to a splicing modulator drug portion via a linker, wherein the linker comprises a Mal-spacer subunit (e.g., MC), a cleavable β-glucuronide, and pAB. In some embodiments, the Mal-spacer subunit comprises MC. In some embodiments, the cleavable linker comprises a Mal-spacer subunit-β-glucuronide-pAB. In some embodiments, the cleavable linker comprises MC-β-glucuronide-pAB.

[0580] In some embodiments, an anti-BCMA antibody or antigen-binding fragment binds to a splicing modulator via a linker comprising MC-Val-Cit-pAB. In some embodiments, an anti-BCMA antibody or antigen-binding fragment binds to a splicing modulator via a linker comprising MC-Val-Ala-pAB. In some embodiments, an anti-BCMA antibody or antigen-binding fragment binds to a splicing modulator via a linker comprising MC-Ala-Ala-Asp-pAB. In some embodiments, an anti-BCMA antibody or antigen-binding fragment binds to a splicing modulator via a linker comprising MC-Glu-Val-Cit-pAB. In some embodiments, an anti-BCMA antibody or antigen-binding fragment binds to a splicing modulator via a linker comprising MC-(PEG)2-Val-Cit-pAB. In some embodiments, an anti-BCMA antibody or antigen-binding fragment binds to a splicing modulator via a linker comprising MC-β-glucuronide-pAB.

[0581] In some embodiments, the splicing modulator binds to an antibody or antigen-binding fragment via a Mal-spacer subunit in a connector, the connector binding to a Val-Cit cleavable portion and a pABC or pAB self-ablating spacer subunit. In some other embodiments, the splicing modulator binds to an antibody or antigen-binding fragment via a Mal-spacer subunit in a connector, the connector binding to a Val-Ala cleavable portion and a pABC or pAB self-ablating spacer subunit. In some other embodiments, the splicing modulator binds to an antibody or antigen-binding fragment via a Mal-spacer subunit in a connector, the connector binding to an Ala-Ala-Asp cleavable portion and a pABC or pAB self-ablating spacer subunit. In some other embodiments, the splicing modulator binds to an antibody or antigen-binding fragment via a Mal-spacer subunit in a connector, the connector binding to a Glu-Val-Cit cleavable portion and a pABC or pAB self-ablating spacer subunit. In some other embodiments, the splicing modulator binds to the antibody or antigen-binding fragment via a Mal-spacer subunit in a linker that binds to a β-glucuronide cleavable portion and a pABC or pAB self-ablating spacer subunit. In some embodiments, the spacer subunit comprises a PEG portion. In some embodiments, the Mal-spacer subunit comprises MC. In some embodiments, the Mal-spacer subunit comprises both MC and PEG portions. In some embodiments, the Mal-spacer subunit comprises MC-(PEG). m - and 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, the Mal-spacer subunit comprises MC-(PEG)2.

[0582] In some other embodiments, the splicing modulator binds to an antibody or antigen-binding fragment via a Mal-spacer subunit in a connector, the connector binding to the Val-Cit cleavable portion and a non-self-ablating spacer subunit. In some other embodiments, the splicing modulator binds to an antibody or antigen-binding fragment via a Mal-spacer subunit in a connector, the connector binding to the Val-Ala cleavable portion and a non-self-ablating spacer subunit. In some other embodiments, the splicing modulator binds to an antibody or antigen-binding fragment via a Mal-spacer subunit in a connector, the connector binding to the Ala-Ala-Asp cleavable portion and a non-self-ablating spacer subunit. In some other embodiments, the splicing modulator binds to an antibody or antigen-binding fragment via a Mal-spacer subunit in a connector, the connector binding to the Glu-Val-Cit cleavable portion and a non-self-ablating spacer subunit. In some other embodiments, the splicing modulator binds to an antibody or antigen-binding fragment via a Mal-spacer subunit in a connector, the connector binding to the β-glucuronide cleavable portion and a non-self-ablating spacer subunit. In some embodiments, the spacer subunit includes a PEG portion. In some embodiments, the Mal-spacer subunit includes an MC portion. In some embodiments, the Mal-spacer subunit includes both an MC and a PEG portion. In some embodiments, the Mal-spacer subunit includes MC-(PEG). m - and 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, the Mal-spacer subunit comprises MC-(PEG)2.

[0583] In some embodiments, the ADC disclosed herein includes formula (I):

[0584] Ab-(LD) p (I)

[0585] in

[0586] Ab is an antibody or antigen-binding fragment that can bind to BCMA;

[0587] D is a splice modifier;

[0588] L is the connector that covalently links Ab to D; and

[0589] p is an integer from 1 to 15.

[0590] In some embodiments, an antibody or antigen-binding fragment (Ab) in the ADC is conjugated to the splice modulator drug portion via a linker, wherein the linker is any of the linkers disclosed or incorporated herein by reference, or comprises one or more components of any of the linkers disclosed or incorporated herein by reference.

[0591] In some embodiments, the connector is a non-cleavable connector. In some embodiments, the connector includes at least one spacer subunit for attaching an antibody or antigen-binding fragment to a drug moiety. In some embodiments, the spacer subunit includes at least one alkyl portion. In some embodiments, the spacer subunit includes at least one PEG portion.

[0592] In some embodiments, the spacer subunit in the connector is linked to an antibody or antigen-binding fragment via a maleimide portion (“Mal-spacer subunit”). In some embodiments, the Mal-spacer subunit comprises at least one alkyl portion. In some embodiments, the Mal-spacer subunit comprises at least one PEG portion. In some embodiments, the Mal-spacer subunit comprises MC. In some embodiments, the Mal-spacer subunit links an antibody or antigen-binding fragment to a pharmaceutical portion.

[0593] In some embodiments, the Mal-spacer subunit or connector 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 subunit or connector comprises Mal-(PEG)2. In some embodiments, the Mal-spacer subunit or connector 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. 8- CO. In some embodiments, the Mal-spacer subunit or connector comprises Mal-(PEG)2-CO. In some embodiments, the Mal-spacer subunit or connector comprises MC. In some embodiments, the Mal-spacer subunit or connector comprises Mal-(CH2)6 (“Mal-Hex”). In some embodiments, the Mal-spacer subunit or connector comprises Mal-(CH2)2 (“Mal-Et”). In some embodiments, the Mal-spacer subunit or connector comprises Mal-(CH2)2-O-(CH2)2 (“Mal-Et-O-Et”).

[0594] In some embodiments, the Mal-spacer subunit or adapter comprises Mal-(PEG)2-CO. In some embodiments, the Mal-spacer subunit or adapter comprises Mal-(PEG)2-CO and at least one additional spacer subunit. In some embodiments, Mal-(PEG)2-CO links an antibody or antigen-binding fragment to a drug moiety. In some embodiments, the adapter comprises or is composed of Mal-(PEG)2-CO. Examples of the “Mal-(PEG)2-CO” adapter are also referred to herein as “ADL2” or “ADL2 adapter”.

[0595] In some embodiments, the Mal-spacer subunit or adapter comprises an MC. In some embodiments, the Mal-spacer subunit or adapter comprises an MC and at least one additional spacer subunit. In some embodiments, the MC links an antibody or antigen-binding fragment to a drug portion. In some embodiments, the adapter comprises or is composed of an MC. Examples of “MC” adapters are also referred to herein as “ADL10” or “ADL10 adapter”.

[0596] In some embodiments, the Mal-spacer subunit or adapter comprises Mal-(CH2)6 (“Mal-Hex”). In some embodiments, the Mal-spacer subunit or adapter comprises Mal-Hex and at least one additional spacer subunit. In some embodiments, Mal-Hex links an antibody or antigen-binding fragment to a drug moiety. In some embodiments, the adapter comprises Mal-Hex. Examples of the “Mal-Hex” adapter are also referred to herein as “ADL12” or the “ADL12 adapter”.

[0597] In some embodiments, the Mal-spacer unit or adapter comprises Mal-(CH2)2 (“Mal-Et”). In some embodiments, the Mal-spacer unit or adapter comprises Mal-Et and at least one additional spacer unit. In some embodiments, Mal-Et links an antibody or antigen-binding fragment to a drug moiety. In some embodiments, the adapter comprises Mal-Et. Examples of the “Mal-Et” adapter are also referred to herein as “ADL14” or the “ADL14 adapter”.

[0598] In some embodiments, the Mal-spacer unit or adapter comprises Mal-(CH2)2-O-(CH2)2 (“Mal-Et-O-Et”). In some embodiments, the Mal-spacer unit or adapter comprises Mal-Et-O-Et and at least one additional spacer unit. In some embodiments, Mal-Et-O-Et links an antibody or antigen-binding fragment to a drug moiety. In some embodiments, the adapter comprises Mal-Et-O-Et. Examples of the “Mal-Et-O-Et” adapter are also referred to herein as “ADL15” or the “ADL15” adapter.

[0599] In some other embodiments, the Mal-spacer subunit links an antibody or antigen-binding fragment to a cleavable portion in the adapter. In some embodiments, the cleavable portion in the adapter is a cleavable peptide portion, such as an amino acid unit. In some embodiments, the cleavable peptide portion is an amino acid unit. In some embodiments, the cleavable peptide portion or amino acid unit is Val-Cit, Val-Ala, Ala-Ala-Asp, or Glu-Val-Cit. In some embodiments, the cleavable portion in the adapter is a cleavable glucuronide portion, such as β-glucuronide. In some embodiments, the cleavable glucuronide portion is β-glucuronide. In some embodiments, the Mal-spacer subunit comprises MC. In some embodiments, the Mal-spacer subunit comprises MC and a PEG portion. In some embodiments, the Mal-spacer subunit comprises MC-(PEG). m - and 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, the Mal-spacer subunit comprises MC-(PEG)2.

[0600] In some embodiments, the connector comprises MC-Val-Cit. In some embodiments, the connector comprises MC-(PEG)2-Val-Cit. In some embodiments, the connector comprises MC-Val-Ala. In some embodiments, the connector comprises MC-Ala-Ala-Asp. In some embodiments, the connector comprises MC-Glu-Val-Cit. In some embodiments, the connector comprises MC-β-glucuronide.

[0601] In some embodiments, the spacer subunit connects the detachable portion of the connector to the shear modifier. In some embodiments, the spacer subunit connecting the detachable portion to the shear modifier is self-ablating.

[0602] In some embodiments, the spacer subunit connecting the cleavable portion of the connector to the splicing regulator comprises a pABC. In some embodiments, the pABC connects the cleavable portion to the splicing regulator. In some embodiments, the cleavable portion is a cleavable peptide portion, such as an amino acid unit. In some embodiments, the cleavable peptide portion is an amino acid unit. In some embodiments, the connector comprises an 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 connector comprises Val-Cit-pABC. In some embodiments, the connector comprises Val-Ala-pABC. In some embodiments, the connector comprises Ala-Ala-Asp-pABC. In some embodiments, the connector comprises Glu-Val-Cit-pABC. In some embodiments, the cleavable portion is a cleavable glucuronide portion, such as β-glucuronide. In some embodiments, the cleavable glucuronide portion is β-glucuronide. In some embodiments, the connector comprises β-glucuronide-pABC.

[0603] In some embodiments, the connector comprises Val-Cit-pABC. In some embodiments, the connector comprises Val-Cit-pABC and an MC Mal-spacer subunit for attaching the connector to an antibody or antigen-binding fragment. In some embodiments, the connector comprises MC-Val-Cit-pABC. In some embodiments, the connector comprises MC-Val-Cit-pABC and at least one additional spacer subunit. Examples of the MC-Val-Cit-pABC connector are also referred to herein as “ADL1” or “ADL1 connector”. The structures of ADL1 and other exemplary connectors are shown in Table 13.

[0604] In some embodiments, the connector comprises Val-Ala-pABC. In some embodiments, the connector comprises Val-Ala-pABC and an MC Mal-spacer subunit for attaching the connector to an antibody or antigen-binding fragment. In some embodiments, the connector comprises MC-Val-Ala-pABC. In some embodiments, the connector comprises MC-Val-Ala-pABC and at least one additional spacer subunit. Examples of the MC-Val-Ala-pABC connector are also referred to herein as “ADL6” or the “ADL6” connector. The structures of ADL6 and other exemplary connectors are shown in Table 13.

[0605] In some embodiments, the adapter comprises β-glucuronide-pABC. In some embodiments, the adapter comprises β-glucuronide-pABC and an MC-Mal-spacer subunit for attaching the adapter to an antibody or antigen-binding fragment. In some embodiments, the adapter comprises MC-β-glucuronide-pABC. In some embodiments, the adapter comprises MC-β-glucuronide-pABC and at least one additional spacer subunit. Examples of MC-β-glucuronide-pABC are also referred to herein as “ADL13” or “ADL13” adapters. The structures of ADL13 and other exemplary adapters are shown in Table 13.

[0606] In some embodiments, the connector comprises Ala-Ala-Asp-pABC. In some embodiments, the connector comprises Ala-Ala-Asp-pABC and an MC Mal-spacer subunit for attaching the connector to an antibody or antigen-binding fragment. In some embodiments, the connector comprises MC-Ala-Ala-Asp-pABC. In some embodiments, the connector comprises MC-Ala-Ala-Asp-pABC and at least one additional spacer subunit. Examples of the MC-Ala-Ala-Asp-pABC connector are also referred to herein as “ADL21” or “ADL21” connectors. The structures of ADL21 and other exemplary connectors are shown in Table 13.

[0607] In some embodiments, the adapter comprises Val-Cit-pABC. In some embodiments, the adapter comprises Val-Cit-pABC and MC-(PEG)2Mal-spacer subunits that bind the adapter to an antibody or antigen-binding fragment. In some embodiments, the adapter comprises MC-(PEG)2-Val-Cit-pABC. In some embodiments, the adapter comprises MC-(PEG)2-Val-Cit-pABC and at least one additional spacer subunit. Examples of the MC-(PEG)2-Val-Cit-pABC adapter are also referred to herein as “ADL22” or “ADL22” adapters. The structures of ADL22 and other exemplary adapters are shown in Table 13.

[0608] In some embodiments, the connector comprises Glu-Val-Cit-pABC. In some embodiments, the connector comprises Glu-Val-Cit-pABC and an MC Mal-spacer subunit for attaching the connector to an antibody or antigen-binding fragment. In some embodiments, the connector comprises MC-Glu-Val-Cit-pABC. In some embodiments, the connector comprises MC-Glu-Val-Cit-pABC and at least one additional spacer subunit. Examples of the MC-Glu-Val-Cit-pABC connector are also referred to herein as “ADL23” or the “ADL23” connector. The structures of ADL23 and other exemplary connectors are shown in Table 13.

[0609] In some embodiments, the spacer subunit connecting the cleavable portion of the connector to the splicing modulator comprises a pAB. In some embodiments, the pAB connects the cleavable portion to the splicing modulator. In some embodiments, the cleavable portion is a cleavable peptide portion, such as an amino acid unit. In some embodiments, the cleavable peptide portion is an amino acid unit. In some embodiments, the connector comprises an 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 connector comprises Val-Cit-pAB. In some embodiments, the connector comprises Val-Ala-pAB. In some embodiments, the connector comprises Ala-Ala-Asp-pAB. In some embodiments, the connector comprises Glu-Val-Cit-pAB. In some embodiments, the cleavable portion is a cleavable glucuronide portion, such as β-glucuronide. In some embodiments, the cleavable glucuronide portion is β-glucuronide. In some embodiments, the connector comprises β-glucuronide-pAB.

[0610] In some embodiments, the connector comprises Val-Ala-pAB. In some embodiments, the connector comprises Val-Ala-pAB and an MC Mal-spacer subunit for attaching the connector to an antibody or antigen-binding fragment. In some embodiments, the connector comprises MC-Val-Ala-pAB. In some embodiments, the connector comprises MC-Val-Ala-pAB and at least one additional spacer subunit. Examples of the MC-Val-Ala-pAB connector are also referred to herein as “ADL5” or the “ADL5” connector.

[0611] In some embodiments, the connector comprises Val-Cit-pAB. In some embodiments, the connector comprises Val-Cit-pAB and an MC Mal-spacer subunit for attaching the connector to an antibody or antigen-binding fragment. In some embodiments, the connector comprises MC-Val-Cit-pAB. In some embodiments, the connector comprises MC-Val-Cit-pAB and at least one additional spacer subunit. Examples of the MC-Val-Cit-pAB connector are also referred to herein as “ADL7” or the “ADL7” connector.

[0612] In some embodiments, an antibody or antigen-binding fragment is conjugated to the splice modulator drug portion via a linker of ADL1, ADL2, ADL5, ADL6, ADL7, ADL10, ADL12, ADL13, ADL14, ADL15, ADL21, ADL22, or ADL23. In some embodiments, an antibody or antigen-binding fragment is conjugated to the splice modulator drug portion via a linker of ADL1, ADL6, ADL13, ADL21, ADL22, or ADL23. It has been found that, in various embodiments, ADCs comprising a linker of ADL1, ADL6, ADL13, ADL21, ADL22, or ADL23 (e.g., an ADL1 linker) and the splice modulator drug portion disclosed herein exhibit the characteristics required for a therapeutic ADC. In some embodiments, these properties include, but are not limited to, effective drug loading level, low aggregation level, stability under storage conditions or when circulating in vivo (e.g., serum stability), retention affinity for cells expressing the target antigen comparable to that of unconjugated antibodies, strong cytotoxicity to cells expressing the target antigen, low levels of off-target cell killing, and / or effective in vivo anticancer activity, all of which are compared to ADCs using other linker-payloads.

[0613] In some embodiments, the ADC comprises an ADL1 splice modulator and an antibody or antigen-binding fragment capable of binding BCMA. In some embodiments, the ADC comprises an ADL2 splice modulator and an antibody or antigen-binding fragment capable of binding BCMA. In some embodiments, the ADC comprises an ADL5 splice modulator and an antibody or antigen-binding fragment capable of binding BCMA. In some embodiments, the ADC comprises an ADL6 splice modulator and an antibody or antigen-binding fragment capable of binding BCMA. In some embodiments, the ADC comprises an ADL7 splice modulator and an antibody or antigen-binding fragment capable of binding BCMA. In some embodiments, the ADC comprises an ADL10 splice modulator and an antibody or antigen-binding fragment capable of binding BCMA. In some embodiments, the ADC comprises an ADL12 splice modulator and an antibody or antigen-binding fragment capable of binding BCMA. In some embodiments, the ADC comprises an ADL13 splice modulator and an antibody or antigen-binding fragment capable of binding BCMA. In some embodiments, the ADC comprises an ADL14 splice modulator and an antibody or antigen-binding fragment capable of binding BCMA. In some embodiments, the ADC comprises an ADL15 splice modulator and an antibody or antigen-binding fragment capable of binding BCMA. In some embodiments, the ADC comprises an ADL21 splice regulator and an antibody or antigen-binding fragment capable of binding BCMA. In some embodiments, the ADC comprises an ADL22 splice regulator and an antibody or antigen-binding fragment capable of binding BCMA. In some embodiments, the ADC comprises an ADL23 splice regulator and an antibody or antigen-binding fragment capable of binding BCMA. In some embodiments, the ADC retains the ability to target and internalize BCMA-expressing cancer cells.

[0614] In some embodiments, the antibody or antigen-binding fragment in the ADC disclosed herein is an internalizing antibody or an internalizing antigen-binding fragment. In some embodiments, the antibody or antigen-binding fragment is capable of binding BCMA and comprises three HCDRs containing the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:2 (HCDR2), and SEQ ID NO:3 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:4 (LCDR1), SEQ ID NO:5 (LCDR2), and SEQ ID NO:6 (LCDR3), as defined by the Kabat numbering system; or three HCDRs containing the following amino acid sequences: SEQ ID NO:37 (HCDR1), SEQ ID NO:38 (HCDR2), and SEQ ID NO:39 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:42 (LCDR3), as defined by the IMGT numbering system.

[0615] In some embodiments, the ADC has equation (I):

[0616] Ab-(LD) p (I)

[0617] in

[0618] Ab is an antibody or antigen-binding fragment capable of binding BCMA and comprising three HCDRs containing the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:2 (HCDR2), and SEQ ID NO:3 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:4 (LCDR1), SEQ ID NO:5 (LCDR2), and SEQ ID NO:6 (LCDR3), as defined by the Kabat numbering system; or three HCDRs containing the following amino acid sequences: SEQ ID NO:37 (HCDR1), SEQ ID NO:38 (HCDR2), and SEQ ID NO:39 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:42 (LCDR3), as defined by the IMGT numbering system;

[0619] D is a splice modifier;

[0620] L is a connector that includes ADL1, ADL6, ADL13, ADL21, ADL22, or ADL23; and

[0621] p is an integer from 1 to 15.

[0622] In some embodiments, the antibody or antigen-binding fragment in the ADC comprises a human heavy chain and light chain variable region framework, or a human heavy chain and light chain variable region framework having one or more reversion mutations. In some embodiments, the antibody or antigen-binding fragment in the ADC comprises a heavy chain variable region containing the amino acid sequence of SEQ ID NO:76 and a light chain variable region containing the amino acid sequence of SEQ ID NO:77. In some embodiments, the antibody or antigen-binding fragment in 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 in 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 in 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 in 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 in the ADC comprises a heavy chain constant region containing the amino acid sequence of SEQ ID NO:90 and a light chain constant region containing the amino acid sequence of SEQ ID NO:91. In some embodiments, the antibody or antigen-binding fragment in the ADC comprises a heavy chain containing the amino acid sequence of SEQ ID NO:92 and a light chain containing 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 in 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.

[0623] In some embodiments, the antibody or antigen-binding fragment in the ADC disclosed herein is an internalizing antibody or an internalizing antigen-binding fragment. In some embodiments, the antibody or antigen-binding fragment is capable of binding BCMA and comprises three HCDRs containing the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:7 (HCDR2), and SEQ ID NO:8 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:9 (LCDR1), SEQ ID NO:10 (LCDR2), and SEQ ID NO:11 (LCDR3), as defined by the Kabat numbering system; or three HCDRs containing the following amino acid sequences: SEQ ID NO:43 (HCDR1), SEQ ID NO:44 (HCDR2), and SEQ ID NO:45 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:46 (LCDR3), as defined by the IMGT numbering system.

[0624] In some embodiments, the ADC has equation (I):

[0625] Ab-(LD) p (I)

[0626] in

[0627] Ab is an antibody or antigen-binding fragment capable of binding BCMA and comprising three HCDRs containing the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:7 (HCDR2), and SEQ ID NO:8 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:9 (LCDR1), SEQ ID NO:10 (LCDR2), and SEQ ID NO:11 (LCDR3), as defined by the Kabat numbering system; or three HCDRs containing the following amino acid sequences: SEQ ID NO:43 (HCDR1), SEQ ID NO:44 (HCDR2), and SEQ ID NO:45 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:46 (LCDR3), as defined by the IMGT numbering system;

[0628] D is a splice modifier;

[0629] L is a connector that includes ADL1, ADL6, ADL13, ADL21, ADL22, or ADL23; and

[0630] p is an integer from 1 to 15.

[0631] In some embodiments, the antibody or antigen-binding fragment in the ADC comprises a human heavy chain and light chain variable region framework, or a human heavy chain and light chain variable region framework having one or more reversion mutations. In some embodiments, the antibody or antigen-binding fragment in the ADC comprises a heavy chain variable region containing the amino acid sequence of SEQ ID NO:78 and a light chain variable region containing the amino acid sequence of SEQ ID NO:79. In some embodiments, the antibody or antigen-binding fragment in 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 in 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 in 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 in 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 in the ADC comprises a heavy chain constant region containing the amino acid sequence of SEQ ID NO:90 and a light chain constant region containing the amino acid sequence of SEQ ID NO:91. In some embodiments, the antibody or antigen-binding fragment in the ADC comprises a heavy chain containing the amino acid sequence of SEQ ID NO:94 and a light chain containing 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 in 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.

[0632] In some embodiments, the antibody or antigen-binding fragment in the ADC disclosed herein is an internalizing antibody or an internalizing antigen-binding fragment. In some embodiments, the antibody or antigen-binding fragment is capable of binding BCMA and comprises three HCDRs containing the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:12 (HCDR2), and SEQ ID NO:13 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:14 (LCDR1), SEQ ID NO:15 (LCDR2), and SEQ ID NO:16 (LCDR3), as defined by the Kabat numbering system; or three HCDRs containing the following amino acid sequences: SEQ ID NO:47 (HCDR1), SEQ ID NO:48 (HCDR2), and SEQ ID NO:49 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:50 (LCDR3), as defined by the IMGT numbering system.

[0633] In some embodiments, the ADC has equation (I):

[0634] Ab-(LD) p (I)

[0635] in

[0636] Ab is an antibody or antigen-binding fragment capable of binding BCMA and comprising three HCDRs containing the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:12 (HCDR2), and SEQ ID NO:13 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:14 (LCDR1), SEQ ID NO:15 (LCDR2), and SEQ ID NO:16 (LCDR3), as defined by the Kabat numbering system; or three HCDRs containing the following amino acid sequences: SEQ ID NO:47 (HCDR1), SEQ ID NO:48 (HCDR2), and SEQ ID NO:49 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:50 (LCDR3), as defined by the IMGT numbering system;

[0637] D is a splice modifier;

[0638] L is a connector that includes ADL1, ADL6, ADL13, ADL21, ADL22, or ADL23; and

[0639] p is an integer from 1 to 15.

[0640] In some embodiments, the antibody or antigen-binding fragment in the ADC comprises a human heavy chain and light chain variable region framework, or a human heavy chain and light chain variable region framework having one or more reversion mutations. In some embodiments, the antibody or antigen-binding fragment in the ADC comprises a heavy chain variable region containing the amino acid sequence of SEQ ID NO:80 and a light chain variable region containing the amino acid sequence of SEQ ID NO:81. In some embodiments, the antibody or antigen-binding fragment in 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 in 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 in 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 in 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 in the ADC comprises a heavy chain constant region containing the amino acid sequence of SEQ ID NO:90 and a light chain constant region containing the amino acid sequence of SEQ ID NO:91. In some embodiments, the antibody or antigen-binding fragment in the ADC comprises a heavy chain containing the amino acid sequence of SEQ ID NO:96 and a light chain containing 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 in 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.

[0641] In some embodiments, the antibody or antigen-binding fragment in the ADC disclosed herein is an internalizing antibody or an internalizing antigen-binding fragment. In some embodiments, the antibody or antigen-binding fragment is capable of binding BCMA and comprises three HCDRs containing the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:17 (HCDR2), and SEQ ID NO:18 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:19 (LCDR1), SEQ ID NO:20 (LCDR2), and SEQ ID NO:21 (LCDR3), as defined by the Kabat numbering system; or three HCDRs containing the following amino acid sequences: SEQ ID NO:51 (HCDR1), SEQ ID NO:52 (HCDR2), and SEQ ID NO:53 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:54 (LCDR3), as defined by the IMGT numbering system.

[0642] In some embodiments, the ADC has equation (I):

[0643] Ab-(LD) p (I)

[0644] in

[0645] Ab is an antibody or antigen-binding fragment capable of binding BCMA and comprising three HCDRs containing the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:17 (HCDR2), and SEQ ID NO:18 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:19 (LCDR1), SEQ ID NO:20 (LCDR2), and SEQ ID NO:21 (LCDR3), as defined by the Kabat numbering system; or three HCDRs containing the following amino acid sequences: SEQ ID NO:51 (HCDR1), SEQ ID NO:52 (HCDR2), and SEQ ID NO:53 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:54 (LCDR3), as defined by the IMGT numbering system;

[0646] D is a splice modifier;

[0647] L is a connector that includes ADL1, ADL6, ADL13, ADL21, ADL22, or ADL23; and

[0648] p is an integer from 1 to 15.

[0649] In some embodiments, the antibody or antigen-binding fragment in the ADC comprises a human heavy chain and light chain variable region framework, or a human heavy chain and light chain variable region framework having one or more reversion mutations. In some embodiments, the antibody or antigen-binding fragment in the ADC comprises a heavy chain variable region containing the amino acid sequence of SEQ ID NO:82 and a light chain variable region containing the amino acid sequence of SEQ ID NO:83. In some embodiments, the antibody or antigen-binding fragment in 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 in 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 in 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 in 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 in the ADC comprises a heavy chain constant region containing the amino acid sequence of SEQ ID NO:90 and a light chain constant region containing the amino acid sequence of SEQ ID NO:91. In some embodiments, the antibody or antigen-binding fragment in the ADC comprises a heavy chain containing the amino acid sequence of SEQ ID NO:98 and a light chain containing 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 in 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.

[0650] In some embodiments, the antibody or antigen-binding fragment in the ADC disclosed herein is an internalizing antibody or an internalizing antigen-binding fragment. In some embodiments, the antibody or antigen-binding fragment is capable of binding BCMA and comprises three HCDRs containing the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:22 (HCDR2), and SEQ ID NO:23 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:24 (LCDR1), SEQ ID NO:25 (LCDR2), and SEQ ID NO:26 (LCDR3), as defined by the Kabat numbering system; or three HCDRs containing the following amino acid sequences: SEQ ID NO:55 (HCDR1), SEQ ID NO:56 (HCDR2), and SEQ ID NO:57 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:58 (LCDR3), as defined by the IMGT numbering system.

[0651] In some embodiments, the ADC has equation (I):

[0652] Ab-(LD) p (I)

[0653] in

[0654] Ab is an antibody or antigen-binding fragment capable of binding BCMA and comprising three HCDRs containing the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:22 (HCDR2), and SEQ ID NO:23 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:24 (LCDR1), SEQ ID NO:25 (LCDR2), and SEQ ID NO:26 (LCDR3), as defined by the Kabat numbering system; or three HCDRs containing the following amino acid sequences: SEQ ID NO:55 (HCDR1), SEQ ID NO:56 (HCDR2), and SEQ ID NO:57 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:58 (LCDR3), as defined by the IMGT numbering system;

[0655] D is a splice modifier;

[0656] L is a connector that includes ADL1, ADL6, ADL13, ADL21, ADL22, or ADL23; and

[0657] p is an integer from 1 to 15.

[0658] In some embodiments, the antibody or antigen-binding fragment in the ADC comprises a human heavy chain and light chain variable region framework, or a human heavy chain and light chain variable region framework having one or more reversion mutations. In some embodiments, the antibody or antigen-binding fragment in the ADC comprises a heavy chain variable region containing the amino acid sequence of SEQ ID NO:84 and a light chain variable region containing the amino acid sequence of SEQ ID NO:85. In some embodiments, the antibody or antigen-binding fragment in 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 in 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 in 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 in 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 in the ADC comprises a heavy chain constant region containing the amino acid sequence of SEQ ID NO:90 and a light chain constant region containing the amino acid sequence of SEQ ID NO:91. In some embodiments, the antibody or antigen-binding fragment in the ADC comprises a heavy chain containing the amino acid sequence of SEQ ID NO: 100 and a light chain containing 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 in 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.

[0659] In some embodiments, the antibody or antigen-binding fragment in the ADC disclosed herein is an internalizing antibody or an internalizing antigen-binding fragment. In some embodiments, the antibody or antigen-binding fragment is capable of binding BCMA and comprises three HCDRs containing the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:27 (HCDR2), and SEQ ID NO:28 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:29 (LCDR1), SEQ ID NO:30 (LCDR2), and SEQ ID NO:31 (LCDR3), as defined by the Kabat numbering system; or three HCDRs containing the following amino acid sequences: SEQ ID NO:59 (HCDR1), SEQ ID NO:60 (HCDR2), and SEQ ID NO:61 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:62 (LCDR3), as defined by the IMGT numbering system.

[0660] In some embodiments, the ADC has equation (I):

[0661] Ab-(LD) p (I)

[0662] in

[0663] Ab is an antibody or antigen-binding fragment capable of binding BCMA and comprising three HCDRs containing the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:27 (HCDR2), and SEQ ID NO:28 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:29 (LCDR1), SEQ ID NO:30 (LCDR2), and SEQ ID NO:31 (LCDR3), as defined by the Kabat numbering system; or three HCDRs containing the following amino acid sequences: SEQ ID NO:59 (HCDR1), SEQ ID NO:60 (HCDR2), and SEQ ID NO:61 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:62 (LCDR3), as defined by the IMGT numbering system;

[0664] D is a splice modifier;

[0665] L is a connector that includes ADL1, ADL6, ADL13, ADL21, ADL22, or ADL23; and

[0666] p is an integer from 1 to 15.

[0667] In some embodiments, the antibody or antigen-binding fragment in the ADC comprises a human heavy chain and light chain variable region framework, or a human heavy chain and light chain variable region framework having one or more reversion mutations. In some embodiments, the antibody or antigen-binding fragment in the ADC comprises a heavy chain variable region containing the amino acid sequence of SEQ ID NO:86 and a light chain variable region containing the amino acid sequence of SEQ ID NO:87. In some embodiments, the antibody or antigen-binding fragment in 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 in 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 in 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 in 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 in the ADC comprises a heavy chain constant region containing the amino acid sequence of SEQ ID NO:90 and a light chain constant region containing the amino acid sequence of SEQ ID NO:91. In some embodiments, the antibody or antigen-binding fragment in the ADC comprises a heavy chain containing the amino acid sequence of SEQ ID NO: 102 and a light chain containing 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 in 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.

[0668] In some embodiments, the antibody or antigen-binding fragment in the ADC disclosed herein is an internalizing antibody or an internalizing antigen-binding fragment. In some embodiments, the antibody or antigen-binding fragment is capable of binding BCMA and comprises three HCDRs containing the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:32 (HCDR2), and SEQ ID NO:33 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:34 (LCDR1), SEQ ID NO:35 (LCDR2), and SEQ ID NO:36 (LCDR3), as defined by the Kabat numbering system; or three HCDRs containing the following amino acid sequences: SEQ ID NO:63 (HCDR1), SEQ ID NO:64 (HCDR2), and SEQ ID NO:65 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:40 (LCDR1), SEQ ID NO:41 (LCDR2), and SEQ ID NO:66 (LCDR3), as defined by the IMGT numbering system.

[0669] In some embodiments, the ADC has equation (I):

[0670] Ab-(LD) p (I)

[0671] in

[0672] Ab is an antibody or antigen-binding fragment capable of binding BCMA and comprising three HCDRs containing the following amino acid sequences: SEQ ID NO:1 (HCDR1), SEQ ID NO:32 (HCDR2), and SEQ ID NO:33 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:34 (LCDR1), SEQ ID NO:35 (LCDR2), and SEQ ID NO:36 (LCDR3), as defined by the Kabat numbering system; or three HCDRs containing the following amino acid sequences: SEQ ID NO:63 (HCDR1), SEQ ID NO:64 (HCDR2), and SEQ ID NO:65 (HCDR3); and three LCDRs containing the following amino acid sequences: SEQ ID NO:40 (LCDR...

Claims

1. An isolated antibody or antigen-binding fragment, wherein the antibody or antigen-binding fragment is capable of binding B cell maturation antigen (BCMA) and comprises three HCDRs and three LCDRs. Wherein, HCDR1 consists of the amino acid sequence of SEQ ID NO:1, HCDR2 consists of the amino acid sequence of SEQ ID NO:22, HCDR3 consists of the amino acid sequence of SEQ ID NO:23, LCDR1 consists of the amino acid sequence of SEQ ID NO:24, LCDR2 consists of the amino acid sequence of SEQ ID NO:25, and LCDR3 consists of the amino acid sequence of SEQ ID NO:26, as defined by the Kabat numbering system; or HCDR1 consists of the amino acid sequence of SEQ ID NO:55, HCDR2 consists of the amino acid sequence of SEQ ID NO:56, HCDR3 consists of the amino acid sequence of SEQ ID NO:57, LCDR1 consists of the amino acid sequence of SEQ ID NO:40, LCDR2 consists of the amino acid sequence of SEQ ID NO:41, and LCDR3 consists of the amino acid sequence of SEQ ID NO:58, as defined by the IMGT numbering system.

2. The antibody or antigen-binding fragment of claim 1, wherein the antibody or antigen-binding fragment comprises: a heavy chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:84, and a light chain variable region having at least 90% identity with the amino acid sequence of SEQ ID NO:

85.

3. The antibody or antigen-binding fragment of claim 2, wherein the antibody or antigen-binding fragment comprises: a heavy chain variable region containing the amino acid sequence of SEQ ID NO:84, and a light chain variable region containing the amino acid sequence of SEQ ID NO:

85.

4. The antibody or antigen-binding fragment of claim 1, wherein the antibody or antigen-binding fragment comprises a constant region of the human IgG1 heavy chain.

5. The antibody or antigen-binding fragment of claim 1, wherein the antibody or antigen-binding fragment comprises a heavy chain constant region containing the amino acid sequence of SEQ ID NO:

90.

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

7. The antibody or antigen-binding fragment of claim 1, wherein the antibody or antigen-binding fragment comprises a constant region of the human Igκ light chain.

8. The antibody or antigen-binding fragment of claim 1, wherein the antibody or antigen-binding fragment comprises a light chain constant region containing the amino acid sequence of SEQ ID NO:

91.

9. The antibody or antigen-binding fragment of claim 1, wherein the antibody or antigen-binding fragment comprises: a heavy chain containing the amino acid sequence of SEQ ID NO:100, and a light chain containing the amino acid sequence of SEQ ID NO:

101.

10. The antibody or antigen-binding fragment of claim 9, wherein the heavy chain further comprises a C-terminal lysine (K).

11. The antibody or antigen-binding fragment of claim 1, wherein the antibody or antigen-binding fragment is conjugated to a therapeutic agent.

12. The antibody or antigen-binding fragment of claim 11, wherein the therapeutic agent is a splicing modulator.

13. The antibody or antigen-binding fragment of claim 12, wherein the splicing regulator is D1:

14. The antibody or antigen-binding fragment of claim 12, wherein the splicing regulator is D2:

15. An antibody-drug conjugate having formula (I): Ab-(L-D) p (I) in Ab is an antibody or antigen-binding fragment as described in any one of claims 1 to 10; D is a splice modifier; L is the connector that covalently links Ab to D; and p is an integer from 1 to 15.

16. The antibody-drug conjugate of claim 15, wherein the (LD) comprises a compound having formula (II-A): Or its pharmaceutically acceptable salt, wherein: Z' is selected from R 1 Selected from non-existent, hydrogen, C1-C6 alkyl group, C1-C6 alkylalkoxy group, C1-C6 alkylamino group, C1-C6 alkylcarboxylic acid group, C1-C6 alkylhydroxy group, C3-C8 cycloalkyl group, benzyl group, C3-C8 heterocyclic group, -OC(=O)-(C1-C6 alkyl) group and -CD3; R 3 Selected from hydrogen, C1-C6 alkyl groups, C1-C6 alkylalkoxy groups, C1-C6 alkylamino groups, C1-C6 alkylcarboxylic acid groups, C1-C6 alkylhydroxy groups, C3-C8 cycloalkyl groups, benzyl groups, C3-C8 heterocyclic groups, and -OC(=O)-(C1-C6 alkyl) groups; and R 4 R 5 and R 8 Each is independently selected from hydrogen, hydroxyl, -O-(C1-C6 alkyl) group, -OC(=O)-(C1-C6 alkyl) group and C1-C6 alkyl group; R 6 and R 7 Each is independently selected from hydrogen, -OR 17 、-OC(=O)-R 17 、-OC(=O)-NR 15 R 16 C1-C6 alkyl groups and -NR 15 R 16 ; R 15 and R 16 Each is independently selected from hydrogen, R 17 -C(=O)-R 17 and -C(=O)-OR 17 ; R 17 Selected from hydrogen, C1-C6 alkyl groups, C3-C8 cycloalkyl groups, benzyl groups, and C3-C8 heterocyclic groups; and where R 1 R 3 R 4 R 5 R 6 R 7 and R 8 Each is independently substituted by 0 to 3 groups independently selected from the following: halogen, hydroxyl, C1-C6 alkyl group, -O-(C1-C6 alkyl) group, -NR 15 R 16 C3-C8 cycloalkyl groups, C1-C6 alkylhydroxy groups, C1-C6 alkylalkoxy groups, benzyl groups, and C3-C8 heterocyclic groups, and where R 6 and R 7 At least one of them is hydrogen.

17. The antibody-drug conjugate of claim 15, wherein the (LD) comprises a compound having formula (IV-A): Or its pharmaceutically acceptable salt, wherein: R 1 Selected from non-existent, hydrogen, C1-C6 alkyl group, C1-C6 alkylalkoxy group, C1-C6 alkylamino group, C1-C6 alkylcarboxylic acid group, C1-C6 alkylhydroxy group, C3-C8 cycloalkyl group, benzyl group, C3-C8 heterocyclic group, -OC(=O)-(C1-C6 alkyl) group and -CD3; R 3 Selected from hydrogen, C1-C6 alkyl groups, C1-C6 alkylalkoxy groups, C1-C6 alkylamino groups, C1-C6 alkylcarboxylic acid groups, C1-C6 alkylhydroxy groups, C3-C8 cycloalkyl groups, benzyl groups, C3-C8 heterocyclic groups, and -OC(=O)-(C1-C6 alkyl) groups; and R 4 R 5 and R 8 Each is independently selected from hydrogen, hydroxyl, -O-(C1-C6 alkyl) group, -OC(=O)-(C1-C6 alkyl) group and C1-C6 alkyl group; R 6 and R 7 Each is independently selected from hydrogen, -OR 17 、-OC(=O)-R 17 、-OC(=O)-NR 15 R 16 C1-C6 alkyl groups and -NR 15 R 16 ; R 15 and R 16 Each is independently selected from hydrogen, R 17 -C(=O)-R 17 and -C(=O)-OR 17 ;and R 17 Selected from hydrogen, C1-C6 alkyl groups, C3-C8 cycloalkyl groups, benzyl groups, and C3-C8 heterocyclic groups; where R 1 R 3 R 4 R 5 R 6 R 7 and R 8 Each is independently substituted by 0 to 3 groups independently selected from the following: halogen, hydroxyl group, C1-C6 alkyl group, -O-(C1-C6 alkyl) group, -NR 15 R 16 C3-C8 cycloalkyl groups, C1-C6 alkylhydroxy groups, C1-C6 alkylalkoxy groups, benzyl groups, and C3-C8 heterocyclic groups, and where R 6 and R 7 At least one of them is hydrogen.

18. The antibody-drug conjugate of claim 15, wherein the (LD) comprises a compound having formula (VI-A): Or its pharmaceutically acceptable salt, wherein: R 1 and R 9 Each is independently selected from the absence of, hydrogen, C1-C6 alkyl group, C1-C6 alkylalkoxy group, C1-C6 alkylamino group, C1-C6 alkylcarboxylic acid group, C1-C6 alkylhydroxy group, C3-C8 cycloalkyl group, benzyl group, C3-C8 heterocyclic group, -OC(=O)-(C1-C6 alkyl) group and -CD3; R 3 Selected from hydrogen, C1-C6 alkyl groups, C1-C6 alkylalkoxy groups, C1-C6 alkylamino groups, C1-C6 alkylcarboxylic acid groups, C1-C6 alkylhydroxy groups, C3-C8 cycloalkyl groups, benzyl groups, C3-C8 heterocyclic groups and -OC(=O)-(C1-C6 alkyl) groups; R 4 R 5 and R 8 Each group is independently selected from hydrogen, hydroxyl groups, -O-(C1-C6 alkyl) groups, -OC(=O)-(C1-C6 alkyl) groups, and C1-C6 alkyl groups; R 6 and R 7 Each is independently selected from hydrogen, -OR 17 、-OC(=O)-R 17 、-OC(=O)-NR 15 R 16 C1-C6 alkyl groups and -NR 15 R 16 ; R 10 Selected from hydrogen, C1-C6 alkyl groups, -C(=O)-(C1-C6 alkyl) groups, and -CD3; R 15 and R 16 Each is independently selected from hydrogen, R 17 -C(=O)-R 17 and -C(=O)-OR 17 ; R 17 Selected from hydrogen, C1-C6 alkyl groups, C3-C8 cycloalkyl groups, benzyl groups, and C3-C8 heterocyclic groups; and a is 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10; where R 1 R 3 R 4 R 5 R 6 R 7 R 8 R 9 and R 10 Each is independently substituted by 0 to 3 groups independently selected from the following: halogen, hydroxyl group, C1-C6 alkyl group, -O-(C1-C6 alkyl) group, -NR 15 R 16 C3-C8 cycloalkyl groups, C1-C6 alkylhydroxy groups, C1-C6 alkylalkoxy groups, benzyl groups, and C3-C8 heterocyclic groups; where R 6 and R 7 At least one of them is hydrogen; and where R 1 and R 9 They cannot both be absent at the same time.

19. The antibody-drug conjugate of claim 15, wherein the (LD) comprises a compound having formula (VIII-A): Or its pharmaceutically acceptable salt, wherein: R 1 Selected from non-existent, hydrogen, C1-C6 alkyl group, C1-C6 alkylalkoxy group, C1-C6 alkylamino group, C1-C6 alkylcarboxylic acid group, C1-C6 alkylhydroxy group, C3-C8 cycloalkyl group, benzyl group, C3-C8 heterocyclic group, -OC(=O)-(C1-C6 alkyl) group and -CD3; R 3 Selected from hydrogen, C1-C6 alkyl groups, C1-C6 alkylalkoxy groups, C1-C6 alkylamino groups, C1-C6 alkylcarboxylic acid groups, C1-C6 alkylhydroxy groups, C3-C8 cycloalkyl groups, benzyl groups, C3-C8 heterocyclic groups and -OC(=O)-(C1-C6 alkyl) groups; R 4 Selected from hydrogen, hydroxyl groups, -O-(C1-C6 alkyl) groups, -OC(=O)-(C1-C6 alkyl) groups, and C1-C6 alkyl groups; and R 10 Selected from 3- to 10-membered carbon rings and 3- to 10-membered heterocycles, each of which is composed of 0 to 3 R... a Replace, where each R a Independently selected from halogens, C1-C6 alkyl groups, -O-(C1-C6)alkyl groups, C1-C6 alkylalkoxy groups, C1-C6 alkylhydroxy groups, and -S (=O). w -(4- to 7-membered heterocycles), 4- to 7-membered carbon rings and 4- to 7-membered heterocycles; R 15 and R 16 Each is independently selected from hydrogen, R 17 -C(=O)-R 17 and -C(=O)-OR 17 ;and R 17 Selected from hydrogen, C1-C6 alkyl groups, C3-C8 cycloalkyl groups, benzyl groups, and C3-C8 heterocyclic groups; where R 1 R 3 R 4 and R 10 Each is independently substituted by 0 to 3 groups independently selected from the following: halogen, hydroxyl group, C1-C6 alkyl group, -O-(C1-C6 alkyl) group, -NR 15 R 16 C3-C8 cycloalkyl groups, C1-C6 alkylhydroxy groups, C1-C6 alkylalkoxy groups, benzyl groups, and C3-C8 heterocyclic groups; Each R a Independently substituted by 0 to 3 groups independently selected from the following: halogen, hydroxyl group, -NR 15 R 16 C1-C6 alkyl groups, -(C=O)-(C1-C6 alkyl) groups, -(C=O)-(C1-C6 alkyl)-(C3-C 10 Heterocyclic groups and C1-C6 alkylcarboxylic acid groups, each substituted by 0, 1, or 2 independently selected groups from the following: halogen, hydroxyl group, -NR 15 R 16 and C1-C3 alkyl groups; and w is 0, 1, or 2.

20. The antibody-drug conjugate of claim 15, wherein the splicing regulator D comprises a compound selected from: And its pharmaceutically acceptable salts.

21. The antibody-drug conjugate of claim 15, wherein the linker L is a cleavable linker comprising a cleavable portion.

22. The antibody-drug conjugate of claim 21, wherein the cleavable portion of the linker L comprises a cleavable peptide portion.

23. The antibody-drug conjugate of claim 22, wherein the cleavable peptide moiety comprises valine-citrulline (Val-Cit).

24. The antibody-drug conjugate of claim 22, wherein the cleavable peptide moiety comprises valine-alanine (Val-Ala).

25. The antibody-drug conjugate of claim 22, wherein the cleavable peptide moiety comprises alanine-alanine-asparagine (Ala-Ala-Asn).

26. The antibody-drug conjugate of claim 22, wherein the cleavable peptide moiety comprises glutamic acid-valine-citrulline (Glu-Val-Cit).

27. The antibody-drug conjugate of claim 21, wherein the linker L comprises a cleavable glucuronide moiety.

28. The antibody-drug conjugate of claim 27, wherein the cleavable glucuronide moiety is cleavable by an enzyme.

29. The antibody-drug conjugate of claim 28, wherein the cleavable glucuronide moiety is cleaved by glucuronidase.

30. The antibody-drug conjugate of claim 29, wherein the cleavable glucuronide moiety is cleaved by β-glucuronidase.

31. The antibody-drug conjugate of claim 21, wherein the linker L comprises a maleimide moiety.

32. The antibody-drug conjugate of claim 31, wherein the maleimide moiety comprises a maleimide hexanoyl group.

33. The antibody-drug conjugate of claim 32, wherein the maleimide moiety is linked to the antibody or antigen-binding fragment via a cysteine ​​residue on the antibody or antigen-binding fragment.

34. The antibody-drug conjugate of claim 15, wherein the linker L comprises at least one spacer subunit.

35. The antibody-drug conjugate of claim 34, wherein the at least one spacer subunit in the connector L comprises a polyethylene glycol (PEG) portion.

36. The antibody-drug conjugate of claim 35, wherein the PEG moiety comprises -(PEG). m - And m is an integer from 1 to 10.

37. The antibody-drug conjugate of claim 36, wherein m is an integer from 4 to 8.

38. The antibody-drug conjugate of claim 36, wherein m is 2, 4, 7 or 8.

39. The antibody-drug conjugate of claim 34, wherein the at least one spacer subunit in the connector L is linked to the antibody or antigen-binding fragment via a maleimide portion.

40. The antibody-drug conjugate of claim 39, wherein the at least one spacer subunit in the connector L is linked to the antibody or antigen-binding fragment via a maleimide portion comprising a maleimide hexanoyl group.

41. The antibody-drug conjugate of claim 40, wherein the linker L comprises the maleimide hexanoyl group linked to Val-Cit.

42. The antibody-drug conjugate of claim 40, wherein the linker L comprises the maleimide hexanoyl group linked to Val-Ala.

43. The antibody-drug conjugate of claim 40, wherein the linker L comprises the maleimide hexanoyl group linked to Ala-Ala-Asn.

44. The antibody-drug conjugate of claim 40, wherein the linker L comprises the maleimide hexanoyl group linked to Glu-Val-Cit.

45. The antibody-drug conjugate of claim 40, wherein the linker L comprises the maleimide hexanoyl group linked to (PEG)2-Val-Cit.

46. ​​The antibody-drug conjugate of claim 40, wherein the linker L comprises the maleimide hexanoyl group linked to β-glucuronide.

47. The antibody-drug conjugate of claim 21, wherein the cleavable portion of the linker L is directly connected to the splicing regulator D.

48. The antibody-drug conjugate of claim 21, wherein the linker L comprises a self-ablating spacer subunit, wherein the self-ablating spacer subunit connects the cleavable portion of the linker L to the splice modulator D.

49. The antibody-drug conjugate of claim 48, wherein the self-ablating spacer subunit of the linker L connected to the splice modulator D comprises a p-aminobenzyloxycarbonyl group (pABC).

50. The antibody-drug conjugate of claim 49, wherein the pABC connects the cleavable portion of the linker L to the splicing regulator D.

51. The antibody-drug conjugate of claim 50, wherein the linker L comprises Val-Cit-pABC.

52. The antibody-drug conjugate of claim 50, wherein the linker L comprises Val-Ala-pABC.

53. The antibody-drug conjugate of claim 50, wherein the linker L comprises Ala-Ala-Asn-pABC.

54. The antibody-drug conjugate of claim 50, wherein the linker L comprises Glu-Val-Cit-pABC.

55. The antibody-drug conjugate of claim 48, wherein the self-ablating spacer subunit of the linker L connected to the splice modulator D comprises p-aminobenzyl (pAB).

56. The antibody-drug conjugate of claim 55, wherein the pAB connects the cleavable portion of the linker L to the splice modulator D.

57. The antibody-drug conjugate of claim 56, wherein the linker L comprises Val-Cit-pAB.

58. The antibody-drug conjugate of claim 56, wherein the linker L comprises Val-Ala-pAB.

59. The antibody-drug conjugate of claim 56, wherein the linker L comprises Ala-Ala-Asn-pAB.

60. The antibody-drug conjugate of claim 56, wherein the linker L comprises Glu-Val-Cit-pAB.

61. The antibody-drug conjugate of claim 50, wherein the linker L comprises β-glucuronide-pABC.

62. The antibody-drug conjugate of claim 56, wherein the linker L comprises β-glucuronide-pAB.

63. The antibody-drug conjugate of claim 15, wherein the linker L comprises a maleimide hexanoyl group linked to Val-Cit-pABC, Val-Ala-pABC, Ala-Ala-Asn-pABC, Glu-Val-Cit-pABC, (PEG)2-Val-Cit-pABC, β-glucuronide-pABC, Val-Cit-pAB, Val-Ala-pAB, Ala-Ala-Asn-pAB, Glu-Val-Cit-pAB, (PEG)2-Val-Cit-pAB, or β-glucuronide-pAB.

64. The antibody-drug conjugate of claim 63, wherein the linker L comprises a maleimide hexanoyl group linked to Val-Cit-pABC.

65. The antibody-drug conjugate of claim 63, wherein the linker L comprises a maleimide hexanoyl group linked to Val-Ala-pABC.

66. The antibody-drug conjugate of claim 63, wherein the linker L comprises a maleimide hexanoyl group linked to Ala-Ala-Asn-pABC.

67. The antibody-drug conjugate of claim 63, wherein the linker L comprises a maleimide hexanoyl group linked to Glu-Val-Cit-pABC.

68. The antibody-drug conjugate of claim 63, wherein the linker L comprises a maleimide hexanoyl group linked to (PEG)2-Val-Cit-pABC.

69. The antibody-drug conjugate of claim 63, wherein the linker L comprises a maleimide hexanoyl group linked to β-glucuronide-pABC.

70. The antibody-drug conjugate of claim 63, wherein the linker L comprises a maleimide hexanoyl group linked to Val-Cit-pAB.

71. The antibody-drug conjugate of claim 63, wherein the linker L comprises a maleimide hexanoyl group linked to Val-Ala-pAB.

72. The antibody-drug conjugate of claim 63, wherein the linker L comprises a maleimide hexanoyl group linked to Ala-Ala-Asn-pAB.

73. The antibody-drug conjugate of claim 63, wherein the linker L comprises a maleimide hexanoyl group linked to Glu-Val-Cit-pAB.

74. The antibody-drug conjugate of claim 63, wherein the linker L comprises a maleimide hexanoyl group linked to (PEG)2-Val-Cit-pAB.

75. The antibody-drug conjugate of claim 63, wherein the linker L comprises a maleimide hexanoyl group linked to β-glucuronide-pAB.

76. The antibody-drug conjugate of claim 15, wherein the linker L is a non-cleavable linker.

77. The antibody-drug conjugate of claim 15, wherein p is an integer from 1 to 12.

78. The antibody-drug conjugate of claim 15, wherein p is an integer from 2 to 8.

79. The antibody-drug conjugate of claim 15, wherein p is an integer from 4 to 8.

80. The antibody-drug conjugate of claim 15, wherein p is 4.

81. The antibody-drug conjugate of claim 15, wherein p is 8.

82. The antibody-drug conjugate of claim 15, wherein the splicing regulator is D1:

83. The antibody-drug conjugate of claim 15, wherein the splicing regulator is D2:

84. An antibody-drug conjugate having formula (I): Ab-(L-D) p (I) in Ab is an antibody or antigen-binding fragment that can bind to BCMA and contains three HCDRs and three LCDRs. Wherein, HCDR1 consists of the amino acid sequence of SEQ ID NO:1, HCDR2 consists of the amino acid sequence of SEQ ID NO:22, HCDR3 consists of the amino acid sequence of SEQ ID NO:23, LCDR1 consists of the amino acid sequence of SEQ ID NO:24, LCDR2 consists of the amino acid sequence of SEQ ID NO:25, and LCDR3 consists of the amino acid sequence of SEQ ID NO:26, as defined by the Kabat numbering system; or HCDR1 consists of the amino acid sequence of SEQ ID NO:55, HCDR2 consists of the amino acid sequence of SEQ ID NO:56, HCDR3 consists of the amino acid sequence of SEQ ID NO:57, LCDR1 consists of the amino acid sequence of SEQ ID NO:40, LCDR2 consists of the amino acid sequence of SEQ ID NO:41, and LCDR3 consists of the amino acid sequence of SEQ ID NO:58, as defined by the IMGT numbering system; D is the splice modifier D1: L is a cleavable linker that covalently links Ab to D, wherein the cleavable linker contains a maleimide hexanoyl group linked to Val-Cit-pABC or Val-Cit-pAB; and p is an integer from 4 to 8.

85. The antibody-drug conjugate of claim 84, wherein p is 4, 7 or 8.

86. An antibody-drug conjugate having formula (I): Ab-(L-D) p (I) in Ab is an antibody or antigen-binding fragment, wherein the antibody or antigen-binding fragment is capable of binding BCMA and includes a heavy chain variable region containing the amino acid sequence of SEQ ID NO:84 and a light chain variable region containing the amino acid sequence of SEQ ID NO:

85. D is the splice modifier D1: L is a cleavable linker that covalently links Ab to D, wherein the cleavable linker contains a maleimide hexanoyl group linked to Val-Cit-pABC or Val-Cit-pAB; and p is an integer from 4 to 8.

87. The antibody-drug conjugate of claim 86, wherein p is 4, 7 or 8.

88. An antibody-drug conjugate having formula (I): Ab-(L-D) p (I) in Ab is an antibody or antigen-binding fragment, wherein the antibody or antigen-binding fragment is capable of binding BCMA and comprises a heavy chain containing the amino acid sequence of SEQ ID NO:100 and a light chain containing the amino acid sequence of SEQ ID NO:

101. D is the splice modifier D1: L is a cleavable linker that covalently links Ab to D, wherein the cleavable linker contains a maleimide hexanoyl group linked to Val-Cit-pABC or Val-Cit-pAB; and p is an integer from 4 to 8.

89. The antibody-drug conjugate of claim 88, wherein p is 4, 7 or 8.

90. An antibody-drug conjugate having formula (I): Ab-(L-D) p (I) in Ab is an antibody or antigen-binding fragment that can bind to BCMA and contains three HCDRs and three LCDRs. Wherein, HCDR1 consists of the amino acid sequence of SEQ ID NO:1, HCDR2 consists of the amino acid sequence of SEQ ID NO:22, HCDR3 consists of the amino acid sequence of SEQ ID NO:23, LCDR1 consists of the amino acid sequence of SEQ ID NO:24, LCDR2 consists of the amino acid sequence of SEQ ID NO:25, and LCDR3 consists of the amino acid sequence of SEQ ID NO:26, as defined by the Kabat numbering system; or HCDR1 consists of the amino acid sequence of SEQ ID NO:55, HCDR2 consists of the amino acid sequence of SEQ ID NO:56, HCDR3 consists of the amino acid sequence of SEQ ID NO:57, LCDR1 consists of the amino acid sequence of SEQ ID NO:40, LCDR2 consists of the amino acid sequence of SEQ ID NO:41, and LCDR3 consists of the amino acid sequence of SEQ ID NO:58, as defined by the IMGT numbering system; D is the splice modifier D2: L is a cleavable linker that covalently links Ab to D, wherein the cleavable linker contains a maleimide hexanoyl group linked to Val-Cit-pABC or Val-Cit-pAB; and p is an integer from 4 to 8.

91. The antibody-drug conjugate of claim 90, wherein p is 4, 7 or 8.

92. An antibody-drug conjugate having formula (I): Ab-(L-D) p (I) in Ab is an antibody or antigen-binding fragment, wherein the antibody or antigen-binding fragment is capable of binding BCMA and includes a heavy chain variable region containing the amino acid sequence of SEQ ID NO:84 and a light chain variable region containing the amino acid sequence of SEQ ID NO:

85. D is the splice modifier D2: L is a cleavable linker that covalently links Ab to D, wherein the cleavable linker contains a maleimide hexanoyl group linked to Val-Cit-pABC or Val-Cit-pAB; and p is an integer from 4 to 8.

93. The antibody-drug conjugate of claim 92, wherein p is 4, 7 or 8.

94. An antibody-drug conjugate having formula (I): Ab-(L-D) p (I) in Ab is an antibody or antigen-binding fragment, wherein the antibody or antigen-binding fragment is capable of binding BCMA and comprises a heavy chain containing the amino acid sequence of SEQ ID NO:100 and a light chain containing the amino acid sequence of SEQ ID NO:

101. D is the splice modifier D2: L is a cleavable linker that covalently links Ab to D, wherein the cleavable linker contains a maleimide hexanoyl group linked to Val-Cit-pABC or Val-Cit-pAB; and p is an integer from 4 to 8.

95. The antibody-drug conjugate of claim 94, wherein p is 4, 7 or 8.

96. A pharmaceutical composition comprising an antibody or antigen-binding fragment as described in any one of claims 1 to 14 and a pharmaceutically acceptable carrier.

97. Use of the pharmaceutical composition of claim 96 in the manufacture of a medicament for treating a subject suffering from a plasma cell malignancy.

98. A pharmaceutical composition comprising the antibody-drug conjugate as described in claim 15 and a pharmaceutically acceptable carrier.

99. The pharmaceutical composition of claim 98, wherein the pharmaceutical composition comprises a plurality of copies of the antibody-drug conjugate.

100. The pharmaceutical composition of claim 98, wherein the pharmaceutical composition comprises multiple copies of the antibody-drug conjugate, wherein the average p of the antibody-drug conjugate in the pharmaceutical composition is 2 to 8.

101. The pharmaceutical composition of claim 100, wherein the average p of the antibody-drug conjugate in the pharmaceutical composition is 4.

102. Use of the pharmaceutical composition of claim 98 in the manufacture of a medicament for treating a subject suffering from a plasma cell malignancy.

103. The use as described in claim 102, wherein the plasma cell malignancy is plasma cell leukemia.

104. Use of the pharmaceutical composition of claim 98 in the manufacture of a medicament for treating a subject suffering from lymphoma, plasmacytoma, or myeloma.

105. The use as described in claim 104, wherein the lymphoma is diffuse large B-cell lymphoma, mantle cell lymphoma, plasmablastic lymphoma, or Burkitt lymphoma.

106. The use as described in claim 104, wherein the myeloma is plasmablastic myeloma.

107. The use as described in claim 104, wherein the myeloma is multiple myeloma.

108. The use as described in claim 107, wherein the myeloma is a relapsed / refractory multiple myeloma.

109. A pharmaceutical composition comprising an antibody-drug conjugate as described in any one of claims 84 to 95 and a pharmaceutically acceptable carrier.

110. Use of the pharmaceutical composition of claim 109 in the manufacture of a medicament for treating a subject suffering from cancer, wherein the cancer is a plasma cell malignancy.

111. Use of the pharmaceutical composition of claim 109 in the manufacture of a medicament for treating a subject suffering from cancer, wherein the cancer is lymphoma, plasmacytoma, or myeloma.

112. An isolated nucleic acid that encodes an antibody or antigen-binding fragment as described in any one of claims 1 to 10.

113. An isolated vector comprising the nucleic acid as described in claim 112.

114. An isolated cell or cell population comprising the nucleic acid as described in claim 112.

115. A method for generating an antibody or antigen-binding fragment, wherein the method comprises culturing the cells or cell populations as described in claim 114 under conditions suitable for generating the antibody or antigen-binding fragment.

116. A method for generating an antibody-drug conjugate, wherein the method comprises reacting an antibody or antigen-binding fragment as described in any one of claims 1 to 10 with a linker connected to a splicing modulator under conditions that allow conjugation.

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