Antibody-drug conjugate, pharmaceutical composition, use thereof, and antibody or antigen-binding fragment thereof that binds specifically to human cells expressing STEAP2.

Abstract

The protein known as prostate transmembrane epithelial antigen six 2 (STEAP2) is highly expressed in prostate cancer and is associated with the expression of other prostate cancer-associated genes. The present invention provides full-length human IgG antibodies that bind to human STEAP2 (monospecific antibodies). The present invention: (i) provides bispecific antibodies (BSABs) that bind both STEAP2 and CD3 and activate T cells via CD3 complex in the presence of tumors expressing STEAP2; (ii) provides bispecific antigen-binding molecules comprising a first antigen-binding domain that specifically binds human and monkey CD3 and a second antigen-binding molecule that specifically binds human STEAP2; (iii) includes STEAP2 antibody-drug conjugates that inhibit tumor growth in vivo. The bispecific antigen-binding molecules of the present invention are capable of inhibiting the growth of tumors expressing STEAP2.The bispecific antigen-binding molecules of the invention are useful for treating prostate diseases and disorders in which an upregulated or induced immune response directed at STEAP2 is desired and / or therapeutically beneficial. For example, the bispecific antibodies of the invention are useful for treating prostate cancers, including castration-resistant prostate cancer.

Description

1 / 163 “ANTIBODY-DRUG CONJUGATE, PHARMACEUTICAL COMPOSITION, USE THEREOF AND ANTIBODY OR ANTIGEN-BINDING FRAGMENT THEREOF THAT SPECIFICALLY BINDS TO HUMAN CELLS EXPRESSING STEAP2” REFERENCE TO A LISTING OF SEQUENCES

[0001] This request incorporates by reference the Listing of Sequences displayed in Computer Readable Form as file 10296WO01-Sequence.txt, created on September 22, 2017 and containing 739,964 bytes. FIELD OF THE INVENTION

[0002] The present invention relates to antibodies and antigen-binding fragments thereof that are specific for prostate six-transmembrane epithelial antigen 2 (STEAP2) and to methods of using them. The present invention also relates to bispecific antigen-binding molecules that bind STEAP2 and CD3, and methods of using them. The present invention further relates to antibody-drug conjugates comprising an antiSTEAP2 antibody or a fragment thereof and a therapeutic agent (e.g., a cytotoxic agent). BACKGROUND

[0003] Prostate six-transmembrane epithelial antigen 2 (STEAP2), also known as STEAP2, STEAP2 metalloreductase, prostate cancer-associated protein 1, upregulated protein in metastatic prostate cancer, prostate six-transmembrane protein 1 (STAMP1), and 098P4B6, is an integral six-transmembrane protein that is upregulated in normal and malignant prostate cells. STEAP2, which acts as a vehicle between the Golgi complex and the plasma membrane, is a metalloreductase that reduces iron and copper, facilitating their import. Petition 870260043419, dated 08 / 05 / 2026, page 9 / 353 2 / 163 for the cell. STEAP2 is primarily located in prostate epithelial cells. STEAP2 is also expressed in normal heart, brain, pancreas, ovary, skeletal muscle, mammary gland, testicle, uterus, kidney, lung, trachea, colon, and liver. STEAP2 is overexpressed in cancerous tissues, including tumors of the prostate, bladder, cervix, lung, colon, kidney, breast, pancreas, stomach, uterus, and ovaries (Gomes, IM et al., 2012, Mol. Cancer Res. 10:573-587; Challita-Eid- PM, et al., 2003, WO 03 / 087306; Emtage, PCR, 2005, WO 2005 / 079490).

[0004] CD3 is a homodimeric or heterodimeric antigen expressed on T cells in association with the T cell receptor complex (TCR) and is required for T cell activation. Functional CD3 is formed from the dimeric association of two of four different chains: epsilon, zeta, delta, and gamma. The dimeric arrangements of CD3 include gamma / epsilon, delta / epsilon, and zeta / zeta. Antibodies against CD3 have been shown to bind CD3 to T cells, thereby causing T cell activation in a manner similar to the binding of the TCR by peptide-laden MHC molecules. Thus, anti-CD3 antibodies have been proposed for therapeutic purposes involving T cell activation. Additionally, bispecific antibodies capable of binding CD3 to a target antigen have been proposed for therapeutic uses involving targeted T cell immune responses to tissues and cells expressing the target antigen.

[0005] Antigen-binding molecules that target STEAP2, including antibody-drug conjugates, as well as bispecific antigen-binding molecules that bind both STEAP2 and CD3, would be useful in therapeutic protocols where specific targeting and T cell-mediated killing of STEAP2-expressing cells are desired. BRIEF SUMMARY OF THE INVENTION Petition 870260043419, dated 08 / 05 / 2026, p. 10 / 353 3 / 163

[0006] In a first aspect, the present invention provides antibodies and antigen-binding fragments thereof that bind to human STEAP2. The antibodies according to this aspect of the invention are useful, inter alia, for targeting cells expressing STEAP2. The present invention also provides bispecific antibodies and antigen-binding fragments thereof that bind human STEAP2 and human CD3. The bispecific antibodies according to this aspect of the invention are useful, inter alia, for targeting CD3-expressing T cells and for stimulating T cell activation, for example, in circumstances where T cell-mediated death of STEAP2-expressing cells is beneficial or desirable. For example, the bispecific antibodies can direct CD3-mediated T cell activation to specific STEAP2-expressing cells, such as prostate tumor cells.

[0007] Exemplary anti-STEAP2 antibodies of the present invention are listed in Tables 1 and 2 of this document. Table 1 establishes the amino acid sequence identifiers of the heavy chain variable regions (HCVRs) and light chain variable regions (LCVRs), as well as heavy chain complementarity-determining regions (HCDR1, HCDR2, and HCDR3) and light chain complementarity-determining regions (LCDR1, LCDR2, and LCDR3) of the exemplary anti-STEAP2 antibodies. Table 2 establishes the nucleic acid molecule sequence identifiers of the HCVRs, LCVRs, HCDR1, HCDR2, HCDR3, LCDR1, LCDR2, and LCDR3 of the exemplary anti-STEAP2 antibodies.

[0008] The present invention provides antibodies, or antigen-binding fragments thereof, comprising an HCVR comprising an amino acid sequence selected from any of the HCVR amino acid sequences listed in Table 1, or a substantially similar sequence thereof that has Petition 870260043419, dated 08 / 05 / 2026, p. 11 / 353 4 / 163 at least 90%, at least 95%, at least 98%, or at least 99% sequence identity.

[0009] The present invention also provides antibodies or antigen-binding fragments thereof comprising an LCVR comprising an amino acid sequence selected from any of the LCVR amino acid sequences listed in Table 1, or a substantially similar sequence having at least 90%, at least 95%, at least 98% or at least 99% sequence identity.

[0010] The present invention also provides antibodies, or antigen-binding fragments thereof, comprising an HCVR and an LCVR amino acid sequence pair (HCVR / LCVR) comprising any of the HCVR amino acid sequences listed in Table 1 paired with any of the LCVR amino acid sequences listed in Table 1. According to certain embodiments, the present invention provides antibodies, or antigen-binding fragments thereof, comprising an HCVR / LCVR amino acid sequence pair contained in any of the exemplary anti-STEAP antibodies listed in Table 1. In certain embodiments, the HCVR / LCVR amino acid sequence pair is selected from the group consisting of SEQ ID NOs: 250 / 258 (e.g., H2M11162N).

[0011] The present invention also provides antibodies, or antigen-binding fragments thereof, comprising a CDR1 heavy chain (HCDR1) comprising an amino acid sequence selected from any of the HCDR1 amino acid sequences listed in Table 1 or a substantially similar sequence thereof containing at least 90%, at least 95%, at least 98% or at least 99% sequence identity. Petition 870260043419, dated 08 / 05 / 2026, p. 12 / 353 5 / 163

[0012] The present invention also provides antibodies, or antigen-binding fragments thereof, comprising a CDR2 heavy chain (HCDR2) comprising an amino acid sequence selected from any of the HCDR2 amino acid sequences listed in Table 1 or a substantially similar sequence thereof containing at least 90%, at least 95%, at least 98% or at least 99% sequence identity.

[0013] The present invention also provides antibodies, or antigen-binding fragments thereof, comprising a CDR3 heavy chain (HCDR3) comprising an amino acid sequence selected from any of the HCDR3 amino acid sequences listed in Table 1 or a substantially similar sequence thereof containing at least 90%, at least 95%, at least 98% or at least 99% sequence identity.

[0014] The present invention also provides antibodies, or antigen-binding fragments thereof, comprising a CDR1 light chain (LCDR1) comprising an amino acid sequence selected from any of the LCDR1 amino acid sequences listed in Table 1 or a substantially similar sequence thereof containing at least 90%, at least 95%, at least 98% or at least 99% sequence identity.

[0015] The present invention also provides antibodies, or antigen-binding fragments thereof, comprising a CDR2 light chain (LCDR2) comprising an amino acid sequence selected from any of the LCDR2 amino acid sequences listed in Table 1 or a substantially similar sequence thereof containing at least 90%, Petition 870260043419, dated 08 / 05 / 2026, p. 13 / 353 6 / 163 at least 95%, at least 98%, or at least 99% sequence identity.

[0016] The present invention also provides antibodies, or antigen-binding fragments thereof, comprising a CDR3 light chain (LCDR3) comprising an amino acid sequence selected from any of the LCDR3 amino acid sequences listed in Table 1 or a substantially similar sequence thereof containing at least 90%, at least 95%, at least 98% or at least 99% sequence identity.

[0017] The present invention also provides antibodies, or antigen-binding fragments thereof, comprising an HCDR3 and an LCDR3 amino acid sequence pair (HCDR3 / LCDR3) comprising any of the HCDR3 amino acid sequences listed in Table 1 paired with any of the LCDR3 amino acid sequences listed in Table 1. According to certain embodiments, the present invention provides antibodies, or antigen-binding fragments thereof, comprising an HCDR3 / LCDR3 amino acid sequence pair contained in any of the exemplary anti-STEAP antibodies listed in Table 1. In certain embodiments, the HCDR3 / LCDR3 amino acid sequence pair is selected from the group consisting of SEQ ID NOs: 256 / 264 (e.g., H2M11162N).

[0018] The present invention also provides antibodies, or antigen-binding fragments thereof, comprising a set of six CDRs (i.e., HCDR1-HCDR2-HCDR3-LCDR1LCDR2-LCDR3) contained in any of the examples of anti-STEAP2 antibodies listed in Table 1. In certain embodiments, the amino acid sequence set HCDR1-HCDR2-HCDR3LCDR1-LCDR2-LCDR3 is selected from the group consisting of Petition 870260043419, dated 08 / 05 / 2026, p. 14 / 353 7 / 163 SEQ ID Nos: 252-254-256-260-262-264 (e.g., H2M11162N).

[0019] In a related embodiment, the present invention provides antibodies, or antigen-binding fragments thereof, comprising a set of six CDRs (i.e., HCDR1-HCDR2-HCDR3-LCDR1-LCDR2-LCDR3) contained in an HCVR / LCVR amino acid sequence pair as defined by any of the exemplary anti-STEAP2 antibodies listed in Table 1. For example, the present invention includes antibodies, or antigen-binding fragments thereof, comprising the amino acid sequences HCDR1-HCDR2-HCDR3-LCDR1-LCDR2-LCDR3 contained in an HCVR / LCVR amino acid sequence pair selected from the group consisting of SEQ ID NOs: 250 / 258 (e.g., H2M11162N). The methods and techniques for identifying CDRs in the amino acid sequences of HCVR and LCVR are well known in the art and can be used to identify CDRs within the specified HCVR and / or LCVR amino acid sequences described in this document.Exemplary conventions that can be used to identify the boundaries of CDRs include, for example, the Kabat definition, the Chothia definition, and the AbM definition. Broadly speaking, the Kabat definition is based on sequence variability, the Chothia definition is based on the location of structural loop regions, and the AbM definition is a consensus between the Kabat and Chothia approaches. See, for example, Kabat, “Sequences of Proteins of Immunological Interest”, National Institutes of Health, Bethesda, Md. (1991); Al-Lazikani et al., J. Mol. Biol. 273:927-948 (1997); and Martin et al., Proc. Natl. Acad. Sci. USA 86: 9268-9272 (1989). Public databases are also available for identifying CDR sequences within an antibody.

[0020] The present invention also provides nucleic acid molecules encoding anti-STEAP2 antibodies or portions thereof. Petition 870260043419, dated 08 / 05 / 2026, p. 15 / 353 8 / 163 For example, the present invention provides nucleic acid molecules encoding any of the HCVR amino acid sequences listed in Table 1; in certain embodiments, the nucleic acid molecule comprises a polynucleotide sequence selected from any of the HCVR nucleic acid sequences listed in Table 2, or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98%, or at least 99% sequence identity to them.

[0021] The present invention also provides nucleic acid molecules encoding any of the LCVR amino acid sequences listed in Table 1; in certain embodiments, the nucleic acid molecule comprises a polynucleotide sequence selected from any of the LCVR nucleic acid sequences listed in Table 2, or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98%, or at least 99% sequence identity to the same.

[0022] The present invention also provides nucleic acid molecules encoding any of the HCDR1 amino acid sequences listed in Table 1; in certain embodiments, the nucleic acid molecule comprises a polynucleotide sequence selected from any of the HCDR1 nucleic acid sequences listed in Table 2, or a substantially similar sequence among the same that has at least 90%, at least 95%, at least 98%, or at least 99% sequence identity.

[0023] The present invention also provides nucleic acid molecules encoding any of the HCDR2 amino acid sequences listed in Table 1; in certain embodiments, the nucleic acid molecule comprises a polynucleotide sequence selected from any of the nucleic acid sequences. Petition 870260043419, dated 08 / 05 / 2026, p. 16 / 353 9 / 163 of the HCDR2 nucleic acid listed in Table 2, or a substantially similar sequence thereof that has at least 90%, at least 95%, at least 98%, or at least 99% sequence identity to it.

[0024] The present invention also provides nucleic acid molecules encoding any of the HCDR3 amino acid sequences listed in Table 1; in certain embodiments, the nucleic acid molecule comprises a polynucleotide sequence selected from any of the HCDR3 nucleic acid sequences listed in Table 2, or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98%, or at least 99% sequence identity to them.

[0025] The present invention also provides nucleic acid molecules encoding any of the LCDR1 amino acid sequences listed in Table 1; in certain embodiments, the nucleic acid molecule comprises a polynucleotide sequence selected from any of the LCDR1 nucleic acid sequences listed in Table 2, or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98%, or at least 99% sequence identity to them.

[0026] The present invention also provides nucleic acid molecules encoding any of the LCDR2 amino acid sequences listed in Table 1; in certain embodiments, the nucleic acid molecule comprises a polynucleotide sequence selected from any of the LCDR2 nucleic acid sequences listed in Table 2, or a substantially similar sequence thereof that has at least 90%, at least 95%, at least 98%, or at least 99% identity. Petition 870260043419, dated 08 / 05 / 2026, p. 17 / 353 10 / 163 sequence for them.

[0027] The present invention also provides nucleic acid molecules encoding any of the LCDR3 amino acid sequences listed in Table 1; in certain embodiments, the nucleic acid molecule comprises a polynucleotide sequence selected from any of the LCDR3 nucleic acid sequences listed in Table 2, or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98%, or at least 99% sequence identity to them.

[0028] The present invention also provides nucleic acid molecules encoding an HCVR, wherein the HCVR comprises a set of three CDRs (i.e., HCDR1-HCDR2-HCDR3), wherein the amino acid sequence set HCDR1-HCDR2-HCDR3 is as defined by any of the exemplary anti-STEAP2 antibodies listed in Table 1.

[0029] The present invention also provides nucleic acid molecules encoding an LCVR, wherein the LCVR comprises a set of three CDRs (i.e., LCDR1-LCDR2-LCDR3), wherein the amino acid sequence set LCDR1-LCDR2-LCDR3 is as defined by any of the exemplary anti-STEAP2 antibodies listed in Table 1.

[0030] The present invention also provides nucleic acid molecules encoding both an HCVR and an LCVR, wherein the HCVR comprises an amino acid sequence from any of the HCVR amino acid sequences listed in Table 1, and wherein the LCVR comprises an amino acid sequence from any of the LCVR amino acid sequences listed in Table 1. In certain embodiments, the nucleic acid molecule comprises a polynucleotide sequence selected from any of the nucleic acid sequences. Petition 870260043419, dated 08 / 05 / 2026, p. 18 / 353 11 / 163 nucleic acid sequence of HCVR listed in Table 2, or a substantially similar sequence thereof that has at least 90%, at least 95%, at least 98% or at least 99% sequence identity to the same, and a polynucleotide sequence selected from any of the nucleic acid sequences of LCVR listed in Table 2, or a substantially similar sequence thereof that has at least 90%, at least 95%, at least 98% or at least 99% sequence identity to them. In certain embodiments according to this aspect of the invention, the nucleic acid molecule encodes an HCVR and an LCVR, wherein the HCVR and the LCVR are both derived from the same antiSTEAP2 antibody listed in Table 1.

[0031] The present invention also provides recombinant expression vectors capable of expressing a polypeptide comprising a variable heavy or light chain region of an antiSTEAP2 antibody. For example, the present invention includes recombinant expression vectors comprising any of the nucleic acid molecules mentioned above, i.e., nucleic acid molecules encoding any of the HCVR, LCVR and / or CDR sequences, as set forth in Table 1. Furthermore, the scope of the present invention includes host cells into which such vectors have been introduced, as well as methods for producing the antibodies or portions thereof by culturing the host cells under conditions that permit the production of the antibodies or antibody fragments and recovering the antibodies and antibody fragments thus produced.

[0032] The present invention includes anti-STEAP2 antibodies having a modified glycosylation pattern. In some embodiments, it may be useful to modify them to remove undesirable glycosylation sites or to have an antibody lacking a fucose moiety present in the chain. Petition 870260043419, dated 08 / 05 / 2026, page 19 / 353 12 / 163 oligosaccharide, for example, to enhance antibody-dependent cellular cytotoxicity function (see Shield et al. (2002) JBC 277:26733). In other applications, a galactosylation modification can be made in order to modify complement-dependent cytotoxicity (CDC).

[0033] In another aspect, the invention provides a pharmaceutical composition comprising a recombinant human antibody or fragment thereof that specifically binds STEAP2 and a pharmaceutically acceptable carrier. In a related aspect, the invention presents a composition which is a combination of an anti-STEAP2 antibody and a second therapeutic agent. In one embodiment, the second therapeutic agent is any agent that is advantageously combined with an anti-STEAP2 antibody. Additional combination therapies and co-formulations involving the anti-STEAP2 antibodies of the present invention are further disclosed herein.

[0034] In another aspect, the invention provides therapeutic methods for targeting / killing STEAP2-expressing tumor cells using an anti-STEAP2 antibody of the invention, wherein the therapeutic methods comprise administering a therapeutically effective amount of a pharmaceutical composition comprising an anti-STEAP2 antibody of the invention to an individual in need thereof. In some cases, the anti-STEAP2 antibodies (or antigen-binding fragments thereof) can be used to treat prostate cancer, or can be modified to be more cytotoxic by methods including, but not limited to, modified Fc domains to increase ADCC (see, for example, Shield et al. (2002) JBC 277:26733), radioimmunotherapy, antibody-drug conjugates, or other methods to increase the efficiency of tumor ablation.

[0035] The present invention also includes the use of an antibody Petition 870260043419, dated 08 / 05 / 2026, page 20 / 353 13 / 163 anti-STEAP2 of the invention in the manufacture of a medicament for the treatment of a disease or disorder (e.g., cancer) related to or caused by cells expressing STEAP2. In one aspect, the invention relates to a compound comprising an anti-STEAP2 antibody or antigen-binding fragment, or a bispecific STEAP2xCD3 antibody, as disclosed herein, for use in medicine. In another aspect, the invention relates to a compound comprising an antibody-drug conjugate (ADC) as disclosed herein, for use in medicine.

[0036] In yet another aspect, the invention provides monospecific anti-STEAP2 antibodies for diagnostic applications, such as, for example, imaging reagents.

[0037] In yet another aspect, the invention provides therapeutic methods for stimulating T cell activation using an anti-CD3 antibody or antigen-binding portion of an antibody of the invention, wherein the therapeutic methods comprise administering a therapeutically effective amount of a pharmaceutical composition comprising an antibody.

[0038] In another aspect, the present invention provides an isolated antibody or antigen-binding fragment thereof that binds to C4-2 cells expressing STEAP2 with an EC50 of less than 50 nm, as measured by FACS analysis. In another aspect, the present invention provides an isolated antibody or antigen-binding fragment thereof that binds to and is internalized by C42 cells expressing STEAP2.

[0039] The invention further provides an antibody or antigen-binding fragment that competes for binding to human STEAP2 with a reference antibody comprising an HCVR / LCVR amino acid sequence pair as set out in Table 1. In another aspect, the invention provides an antibody or antigen-binding fragment Petition 870260043419, dated 08 / 05 / 2026, p. 21 / 353 14 / 163 to the antigen that competes for binding to human STEAP2 with a reference antibody comprising a pair of amino acid sequences of HCVR / LCVR selected from the group consisting of SEQ ID NOs: 2 / 10; 18 / 26; 34 / 42; 50 / 58; 66 / 58; 74 / 58; 82 / 58; 90 / 58; 98 / 58; 106 / 114; 122 / 130; 138 / 146; 154 / 162; 170 / 178; 186 / 194; 202 / 210; 218 / 226; 234 / 242; 250 / 258; 266 / 274; 282 / 290; 298 / 306; 314 / 322; 330 / 338; 346 / 354; 362 / 370; and 378 / 386.

[0040] The invention further provides an antibody or antigen-binding fragment wherein the antibody or antigen-binding fragment thereto binds to the same epitope in human STEAP2 as a reference antibody comprising an HCVR / LCVR amino acid sequence pair as set forth in Table 1. In another aspect, the antibody or antigen-binding fragment binds to the same epitope in human STEAP2 as a reference antibody comprising an HCVR / LCVR amino acid sequence pair selected from the group consisting of SEQ ID NOs: 2 / 10; 18 / 26; 34 / 42; 50 / 58; 66 / 58; 74 / 58; 82 / 58; 90 / 58; 98 / 58; 106 / 114; 122 / 130; 138 / 146; 154 / 162; 170 / 178; 186 / 194; 202 / 210; 218 / 226; 234 / 242; 250 / 258; 266 / 274; 282 / 290; 298 / 306; 314 / 322; 330 / 338; 346 / 354; 362 / 370; and 378 / 386.

[0041] The invention further provides an isolated antibody or antigen-binding fragment thereof that binds human STEAP2, characterized in that the antibody or antigen-binding fragment comprises: the complementarity-determining regions (CDRs) of a heavy chain variable region (HCVR) having an amino acid sequence as set forth in Table 1; and the CDRs of a light chain variable region (LCVR) having an amino acid sequence as set forth in Table 1. In another aspect, the isolated antibody or antigen-binding fragment comprises the heavy and light chain CDRs of a sequence pair of Petition 870260043419, dated 08 / 05 / 2026, page 22 / 353 15 / 163 amino acids from HCVR / LCVR selected from the group consisting of SEQ ID NOs: 2 / 10; 18 / 26; 34 / 42; 50 / 58; 66 / 58; 74 / 58; 82 / 58; 90 / 58; 98 / 58; 106 / 114; 122 / 130; 138 / 146; 154 / 162; 170 / 178; 186 / 194; 202 / 210; 218 / 226; 234 / 242; 250 / 258; 266 / 274; 282 / 290; 298 / 306; 314 / 322; 330 / 338; 346 / 354; 362 / 370; and 378 / 386. In yet another aspect, the isolated antibody or antigen-binding fragment comprises HCDR1-HCDR2-HCDR3-LCDR1-LCDR2-LCDR3 domains, respectively, selected from the group consisting of: SEQ ID NOs: 4-6-8-12-14-16; 20-22-24-28-30-32; 36-38-40-44-46-48; 52-54-56-60-62-64; 68-70-72-60-62-64; 76-78-80-60-62-64; 84-86-88-60-62-64; 92-94-96-60-62-64; 100-102-104-60-62-64; 108-110-112-116-118-120; 124-126-128-132-134-136; 140-142-144-148-150-152; 156-158-160-164-166-168; 172-174-176-180-182-184; 188-190-192-196-198-200; 204-206-208-212-214-216; 220-222-224-228-230-232; 236-238-240-244-246-248; 252-254-256-260-262-264; 268-270-272-276-278-280; 284-286-288-292-294-296; 300-302-304-308-310-312; 316-318-320-324-326-328; 332-334-336-340-342-344; 348-350-352-356-358-360; 364-366-368-372-374-376; and 380-382-384-388-390-392.

[0042] In another aspect, the invention provides an isolated antibody or antigen-binding fragment thereof that binds human STEAP2, wherein the antibody or antigen-binding fragment comprises: (a) a heavy chain variable region (HCVR) having an amino acid sequence selected from the group consisting of SEQ ID NOs: 2, 18, 34, 50, 66, 74, 82, 90, 98, 106, 122, 138, 154, 170, 186, 202, 218, 234, 250, 266, 282, 298, 314, 330, 346, 362 and 378; and (b) a light chain variable region (LCVR) having an amino acid sequence selected from the group consisting of SEQ ID NOs: 10; 26; 42; 58; 114; 130; 146; 162; 178; 194; 210; 226, 242; 258; 274; 290; 306; 322; 338; 354; 370; and 386. In an additional aspect, the isolated antibody or antigen-binding fragment of Petition 870260043419, dated 08 / 05 / 2026, p. 23 / 353 16 / 163 claim 10, wherein the antibody or antigen-binding fragment comprises a pair of HCVR / LCVR amino acid sequences selected from the group consisting of SEQ ID NOs: 2 / 10; 18 / 26; 34 / 42; 50 / 58; 66 / 58; 74 / 58; 82 / 58; 90 / 58; 98 / 58; 106 / 114; 122 / 130; 138 / 146; 154 / 162; 170 / 178; 186 / 194; 202 / 210; 218 / 226; 234 / 242; 250 / 258; 266 / 274; 282 / 290; 298 / 306; 314 / 322; 330 / 338; 346 / 354; 362 / 370; and 378 / 386.

[0043] According to another aspect, the present invention provides antibody-drug conjugates comprising an anti-STEAP2 antibody or an antigen-binding fragment thereof and a therapeutic agent (e.g., a cytotoxic agent). In some embodiments, the antibody or antigen-binding fragment and the cytotoxic agent are covalently linked via a linker, as discussed herein. In several embodiments, the anti-STEAP2 antibody or antigen-binding fragment may be any of the antibodies or anti-STEAP2 fragments described herein.

[0044] In some embodiments, the cytotoxic agent is selected from an auristatin, a maytansinoid, a tubulisin, a tomaimycin derivative, or a dolastatin derivative. In some cases, the cytotoxic agent is an auristatin selected from MMAE or MMAF or a maytansinoid selected from DM1 or DM4. In some embodiments, the cytotoxic agent is a maytansinoid having the structure of Formula (I) or Formula (II), as discussed herein.

[0045] In some forms, the cytotoxic agent is a maytansinoid having the following structure: Petition 870260043419, dated 08 / 05 / 2026, p. 24 / 353 17 / 163

[0046] In some forms, the cytotoxic agent is a maytansinoid having the following structure:

[0047] In some embodiments, the antibody-drug conjugate comprises an anti-STEAP2 antibody or a fragment thereof, and where * is a link to or a fragment of the anti-STEAP2 antibody.

[0048] In some embodiments, the antibody-drug conjugate comprises an anti-STEAP2 antibody or a fragment thereof, and where * is a link to or a fragment of the anti-STEAP2 antibody.

[0049] In some embodiments, the antibody-drug conjugate comprises an anti-STEAP2 antibody or a fragment thereof, and Petition 870260043419, dated 08 / 05 / 2026, p. 25 / 353 18 / 163 where « is a link to the anti-STEAP2 antibody or a fragment thereof.

[0050] In some embodiments, the binding contacts the antibody or a fragment thereof via a sulfur constituent of a cysteine ​​residue.

[0051] In some embodiments, the antibody-drug conjugate comprises an anti-STEAP2 antibody or a fragment thereof, and a mixture of them, where " is a link to the anti-STEAP2 antibody or a fragment thereof.

[0052] In some embodiments, the binding contacts the antibody or a fragment thereof via a nitrogenous constituent of a lysine residue.

[0053] In any of the various conjugate forms Petition 870260043419, dated 08 / 05 / 2026, p. 26 / 353 19 / 163 antibody-drug conjugate discussed above or here, the antibody-drug conjugate may comprise from 1 to 4 cytotoxic agents per anti-STEAP2 antibody or fragment thereof.

[0054] According to another aspect, the present invention provides bispecific antigen-binding molecules (e.g., antibodies) that bind STEAP2 and CD3. Such antigen-binding molecules are also referred to herein as “anti-STEAP2 / anti-CD3 bispecific molecules” or “anti-CD3 / anti-STEAP2 bispecific molecules” or “STEAP2xCD3 bsAbs”. The anti-STEAP2 portion of the anti-STEAP2 / anti-CD3 bispecific molecule is useful for targeting cells (e.g., tumor cells) that express STEAP2 (e.g., prostate tumors), and the anti-CD3 portion of the bispecific molecule is useful for activating T cells. The simultaneous binding of STEAP2 to a tumor cell and CD3 to a T cell facilitates the directed killing (cell lysis) of the target tumor cell by the activated T cell. The bispecific anti-STEAP2 / anti-CD3 molecules of the invention are therefore useful, inter alia, for treating diseases and disorders related to or caused by tumors that express STEAP2 (e.g., prostate cancers).

[0055] The bispecific antigen-binding molecules according to this aspect of the present invention comprise a first antigen-binding domain that specifically binds human CD3 and a second antigen-binding domain that specifically binds STEAP2. The present invention includes bispecific anti-STEAP2 / anti-CD3 molecules (e.g., bispecific antibodies) in which each antigen-binding domain comprises a heavy chain variable region (HCVR) paired with a light chain variable region (LCVR). In certain exemplary embodiments of the invention, the anti-CD3 antigen-binding domain and the anti-STEAP2 antigen-binding domain each comprise different HCVRs, Petition 870260043419, dated 08 / 05 / 2026, page 27 / 353 20 / 163 distinct paired with a common LCVR. For example, as illustrated in Example 4 here, bispecific antibodies have been constructed comprising a first antigen-binding domain that specifically binds CD3, wherein the first antigen-binding domain comprises an HCVR derived from an anti-CD3 antibody paired with an LCVR derived from an anti-STEAP2 antibody (e.g., the same LCVR that is included in the anti-STEAP2 antigen-binding domain); and a second antigen-binding domain that specifically binds STEAP2, wherein the second antigen-binding domain comprises an HCVR / LCVR derived from an anti-STEAP2 antibody. In other words, in the exemplary molecules disclosed here, the pairing of an HCVR from an anti-CD3 antibody with an LCVR from an anti-STEAP2 antibody creates an antigen-binding domain that specifically binds CD3 (but does not bind STEAP2).In such embodiments, the first and second antigen-binding domains comprise distinct anti-CD3 and anti-STEAP2 HCVRs, but share a common anti-STEAP2 LCVR. In other embodiments, the bispecific antigen-binding molecules comprise distinct anti-CD3 and anti-STEAP2 HCVRs, but share a common LCVR. The amino acid sequence of this LCVR is shown, for example, in SEQ ID NO: 1890, and the amino acid sequences of the corresponding CDRs (i.e., LCDR1-LCDR2LCDR3) are shown in SEQ ID NOs: 1892, 1894, and 1896, respectively. Genetically modified mice can be used to produce fully human bispecific antigen-binding molecules comprising two different heavy chains that associate with an identical light chain comprising a variable domain derived from one of two gene segments of the different human light chain variable region.Alternatively, variable heavy chains can be paired with a light chain. Petition 870260043419, dated 08 / 05 / 2026, page 28 / 353 21 / 163 common and recombinantly expressed in host cells. As such, the antibodies of the invention may comprise immunoglobulin heavy chains associated with a single rearranged light chain. In some embodiments, the light chain comprises a variable domain derived from a segment of the human Vk1-39 gene or a segment of the Vk3-20 gene. In other embodiments, the light chain comprises a variable domain derived from a segment of the human Vk1-39 gene rearranged with a human Jk5 or a segment of the human Jk1 gene.

[0056] The present invention provides bispecific anti-CD3 / anti-STEAP2 molecules, wherein the first antigen-binding domain that specifically binds CD3 comprises any of the amino acid sequences of HCVR, any of the amino acid sequences of LCVR, any of the amino acid sequence pairs of HCVR / LCVR, any of the heavy chain amino acid sequences of CDR1-CDR2-CDR3, or any of the light chain amino acid sequences of CDR1-CDR2-CDR3 as set forth in US Publication 2014 / 0088295 published on March 27, 2014 and PCT / US2016 / 044732 filed on July 29, 2016.

[0057] In addition, the present invention provides bispecific anti-CD3 / anti-STEAP2 molecules, wherein the first antigen-binding domain that specifically binds CD3 comprises any of the HCVR amino acid sequences as set forth in Tables 9, 11 and 15 of the application. The first antigen-binding domain that specifically binds CD3 may also comprise any of the LCVR amino acid sequences as set forth in Tables 1, 9, 12 and 17 of the application. According to certain embodiments, the first antigen-binding domain that specifically binds CD3 comprises any of the HCVR / LCVR amino acid sequence pairs as set forth in Petition 870260043419, dated 08 / 05 / 2026, p. 29 / 353 22 / 163 Tables 9, 11, 12, 15 and 17 of the application. The present invention also provides bispecific anti-CD3 / anti-STEAP2 molecules, wherein the first antigen-binding domain that specifically binds CD3 comprises any of the CDR1-CDR2-CDR3 amino acid sequences as set forth in Tables 9, 11 and 15 herein and / or any of the CDR1-CDR2-CDR3 light chain amino acid sequences as set forth in Tables 1, 9, 12 and 17 of the application.

[0058] According to certain embodiments, the present invention provides bispecific anti-CD3 / anti-STEAP molecules, wherein the first antigen-binding domain that specifically binds CD3 comprises a heavy chain variable region (HCVR) having an amino acid sequence as set forth in Tables 9, 11 and 15 of the application or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98% or at least 99% sequence identity.

[0059] The present invention also provides bispecific anti-CD3 / anti-STEAP molecules, wherein the first antigen-binding domain that specifically binds CD3 comprises a light chain variable region (LCVR) having an amino acid sequence as set out in Tables 1, 9, 12 and 17 of the application or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98% or at least 99% sequence identity.

[0060] The present invention also provides bispecific anti-CD3 / anti-STEAP2 molecules, wherein the first antigen-binding domain that specifically binds CD3 comprises an amino acid sequence pair of HCVR and LCVR (HCVR / LCVR) as set forth in Tables 9, 11, 12, 15 and 17 of the application.

[0061] The present invention also provides bispecific anti-CD3 / anti-STEAP molecules, in which the first domain of Petition 870260043419, dated 08 / 05 / 2026, p. 30 / 353 23 / 163 antigen-binding CD3 comprises a heavy chain CDR3 domain (HCDR3) having an amino acid sequence as set forth in Tables 9, 11 and 15 of the application, or a substantially similar sequence thereto having at least 90%, at least 95%, at least 98% or at least 99% sequence identity; and a light chain CDR3 domain (LCVR) having an amino acid sequence as set forth in Tables 1, 9, 12 and 17 of the application or a substantially similar sequence thereto having at least 90%, at least 95%, at least 98% or at least 99% sequence identity.

[0062] In certain embodiments, the first antigen-binding domain that specifically binds CD3 comprises an HCDR3 / LCDR3 amino acid sequence pair as set forth in Tables 9, 11, 12, 15 and 17 of the application.

[0063] The present invention also provides bispecific anti-CD3 / anti-STEAP2 antigen-binding molecules, wherein the first antigen-binding domain that specifically binds CD3 comprises a heavy chain CDR1 (HCDR1) domain having an amino acid sequence as set forth in Tables 9, 11 and 15 of the application, or a substantially similar sequence thereto having at least 90%, at least 95%, at least 98% or at least 99% sequence identity; a heavy chain CDR2 (HCDR2) domain having an amino acid as set forth in Tables 9, 11 and 15 or a substantially similar sequence thereto having at least 90%, at least 95%, at least 98% or at least 99% sequence identity;a heavy chain CDR3 (HCDR3) domain having an amino acid sequence as set out in Tables 9, 11 and 15 or a substantially similar sequence having at least 90%, at least 95%, at least 98% or at least 99% identity; Petition 870260043419, dated 08 / 05 / 2026, page 31 / 353 24 / 163 sequence; a CDR1 light chain domain (LCDR1) having an amino acid sequence as set out in Tables 1, 9, 12 and 17 herein or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98% or at least 99% sequence identity; a CDR2 light chain domain (LCDR2) having an amino acid sequence as set forth in Tables 1, 9, 12 and 17 of the application or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98% or at least 99% sequence identity and a CDR3 light chain domain (LCDR3) having an amino acid sequence as set forth in Tables 1, 9, 12 and 17 of the application or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98% or at least 99% sequence identity.

[0064] Certain exemplary non-limiting bispecific anti-CD3 / anti-STEAP2 antigen-binding molecules of the invention include a first antigen-binding domain that specifically binds CD3 comprising HCDR1-HCDR2-HCDR3-LCDR1-LCDR2LCDR3 domains, respectively having the amino acid sequences as set forth in Tables 9, 11, 12, 15 and 17 of the application.

[0065] The present invention further provides a bispecific antigen-binding molecule, wherein the first antigen-binding domain that specifically binds human CD3 comprises heavy chain complementarity-determining regions (HCDR1, HCDR2 and HCDR3) of a heavy chain variable region (HCVR) comprising an amino acid sequence as set forth in Table 9, 11 or 15 and light chain complementarity-determining regions (LCDR1, LCDR2 and LCDR3) of a light chain variable region (LCVR) comprising an amino acid sequence as set forth in Table 1, 9, 12 or 17. Petition 870260043419, dated 08 / 05 / 2026, page 32 / 353 25 / 163

[0066] In another aspect, the invention provides a bispecific antigen-binding molecule wherein the first antigen-binding domain that specifically binds human CD3 comprises heavy chain complementarity-determining regions (HCDR1, HCDR2 and HCDR3) of a variable heavy chain region (HCVR) selected from the group consisting of SEQ ID NOs: 1730, 1762 and 1866 and light chain complementarity-determining regions (LCDR1, LCDR2 and LCDR3) of a variable light chain region (LCVR) comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 258.

[0067] The invention further provides a bispecific antigen-binding molecule, wherein the first antigen-binding domain that specifically binds human CD3 comprises three heavy chain complementarity-determining regions (A1-HCDR1, A1-HCDR2 and A1-HCDR3) and three light chain complementarity-determining regions (A1-LCDR1, A1-LCDR2 and A1LCDR3), wherein A1-HCDR1 comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 1732, 1764 and 1868; A1-HCDR2 comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 1734, 1766 and 1870; A1-HCDR3 comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 1736, 1768 and 1872; A1-LCDR1 comprises an amino acid sequence with SEQ ID NO: 260; A1LCDR2 comprises an amino acid sequence with SEQ ID NO: 262 and A1-LCDR3 comprises an amino acid sequence with SEQ ID NO: 264.

[0068] In a further aspect, the invention provides a bispecific antigen-binding molecule, wherein the first antigen-binding domain that specifically binds human CD3 comprises the heavy and light chain CDRs of a sequence pair of Petition 870260043419, dated 08 / 05 / 2026, p. 33 / 353 26 / 163 amino acids from HCVR / LCVR selected from the group consisting of: SEQ ID NOs: 1730 / 258, 1762 / 258 and 1866 / 258.

[0069] In another aspect, the invention provides a bispecific antigen-binding molecule, wherein the first antigen-binding domain that specifically binds human CD3 comprises three heavy chain complementarity-determining regions (A1-HCDR1, A1-HCDR2 and A1-HCDR3) and three light chain complementarity-determining regions (A1-LCDR1, A1-LCDR2 and A1-LCDR3) and wherein the second antigen-binding domain that specifically binds human STEAP2 comprises three heavy chain complementarity-determining regions (A2-HCDR1, A2-HCDR2 and A2-HCDR3) and three light chain complementarity-determining regions (A2-LCDR1, A2-LCDR2 and A2-LCDR3); wherein A1-HCDR1 comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 1732, 1764 and 1868; A1-HCDR2 comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 1734, 1766 and 1870;A1-HCDR3 comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 1736, 1768 and 1872; A1-LCDR1 comprises an amino acid sequence of SEQ ID NO: 260; A1LCDR2 comprises an amino acid sequence of SEQ ID NO: 262 and A1-LCDR3 comprises an amino acid sequence of SEQ ID NO: 264; and where A2-HCDR1 comprises an amino acid sequence of SEQ ID NO: 252; A2-HCDR2 comprises an amino acid sequence of SEQ ID NO: 254; A2-HCDR3 comprises an amino acid sequence of SEQ ID NO: 256; A2-LCDR1 comprises an amino acid sequence of SEQ ID NO: 260; A2-LCDR2 comprises an amino acid sequence of SEQ ID NO: 262; and A2LCDR3 comprises an amino acid sequence of SEQ ID NO: 264.

[0070] Certain bispecific antigen-binding molecules Petition 870260043419, 08 / 05 / 2026, p. 34 / 353; 27 / 163 CD3 / anti-STEAP2 exemplars, not limiting to the invention, include a first antigen-binding domain that specifically binds CD3 comprising a heavy chain comprising variable domain framework regions having an amino acid sequence selected from FR1 (SEQ ID NO: 1903), FR2 (SEQ ID NO: 1904), FR3 (SEQ ID NO: 1905) and FR4 (SEQ ID NO: 1906).

[0071] In embodiments, exemplary bispecific anti-CD2 / anti-STEAP2 antigen-binding molecules of the invention include a bispecific antigen-binding molecule wherein the first antigen-binding domain that specifically binds human CD3 comprises an HCVR comprising HCDR1-HCDR2-HCDR3 having amino acid sequences of SEQ ID NOs: 1907-1908-1909

[0072] The present invention also provides bispecific anti-CD3 / anti-STEAP2 molecules, wherein the second antigen-binding domain that specifically binds STEAP2 comprises a variable heavy chain region (HCVR) having the selected amino acid sequence from the group consisting of SEQ ID NOs: 2, 18, 34, 50, 66, 74, 82, 90, 98, 106, 122, 138, 154, 170, 186, 202, 218, 234, 250, 266, 282, 298, 314, 330, 346, 362 and 378 or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98% or at least 99% sequence identity.

[0073] The present invention also provides bispecific anti-CD3 / anti-STEAP2 molecules, wherein the second antigen-binding domain that specifically binds STEAP2 comprises a light chain variable region (LCVR) having the selected amino acid sequence from the group consisting of SEQ ID NOs: 10; 26; 42; 58; 114; 130; 146; 162; 178; 194; 210; 226, 242; 258; 274; 290; 306; 322; 338; 354; 370; and 386 or a substantially similar sequence thereof having at least 90%, at least 95%, at least Petition 870260043419, dated 08 / 05 / 2026, p. 35 / 353 28 / 163 minus 98% or at least 99% sequence identity.

[0074] The present invention also provides bispecific anti-CD3 / anti-STEAP2 molecules, wherein the second antigen-binding domain that specifically binds STEAP2 comprises an amino acid sequence pair of HCVR and LCVR (HCVR / LCVR) with SEQ ID NO: 250 / 258.

[0075] The present invention also provides bispecific anti-CD3 / anti-STEAP2 molecules, wherein the second antigen-binding domain that specifically binds STEAP2 comprises a heavy chain CDR3 domain (HCDR3) having an amino acid sequence of SEQ ID NO:256 or a substantially similar sequence thereto having at least 90%, at least 95%, at least 98% or at least 99% sequence identity; and a light chain CDR3 domain (LCDR3) having an amino acid sequence of SEQ ID NO:264 or a substantially similar sequence thereto having at least 90%, at least 95%, at least 98% or at least 99% sequence identity.

[0076] In certain embodiments, the second antigen-binding domain that specifically binds STEAP2 comprises an amino acid sequence pair of HCDR3 / LCDR3 selected from the group consisting of SEQ ID NOs: 256 / 264.

[0077] The present invention also provides bispecific anti-CD3 / anti-STEAP2 antigen-binding molecules, wherein the second antigen-binding domain that specifically binds STEAP2 comprises a heavy chain CDR1 domain (HCDR1) having an amino acid sequence selected from the group consisting of SEQ ID NOs: 4, 20, 36, 52, 68, 76, 84, 92, 100, 108, 124, 140, 156, 172, 188, 204, 220, 236, 252, 268, 284, 300, 316, 332, 348, 364 and 380; or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98% or at least 99% of Petition 870260043419, dated 08 / 05 / 2026, p. 36 / 353 29 / 163 sequence identity; a heavy chain CDR2 (HCDR2) domain having an amino acid sequence selected from the group consisting of SEQ ID NOs: 6, 22, 38, 54, 70, 78, 86, 94, 102, 110, 126, 142, 158, 174, 190, 206, 222, 238, 254, 270, 286, 302, 318, 334, 350, 366 and 382 or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98% or at least 99% sequence identity; a heavy chain CDR3 (HCDR3) domain having an amino acid sequence selected from the group consisting of SEQ ID NOs: 8, 24, 40, 56, 72, 80, 88, 96, 104, 112, 128, 144, 160, 176, 182, 208, 224, 240, 256, 272, 288, 304, 320, 336, 352, 368 and 384 or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98% or at least 99% sequence identity;a CDR1 light chain domain (LCDR1) having an amino acid sequence selected from the group consisting of SEQ ID NOs: 12, 28, 44, 60, 116, 132, 148, 164, 180, 196, 212, 228, 244, 260, 276, 292, 308, 324, 340, 356, 372 and 388 or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98% or at least 99% sequence identity; a CDR2 light chain domain (LCDR2) having an amino acid sequence selected from the group consisting of SEQ ID NOs: 14, 30, 46, 62, 118, 134, 150, 166, 182, 198, 214, 230, 246, 262, 278, 294, 310, 326, 342, 358, 374 and 390 or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98% or at least 99% sequence identity;and a CDR3 light chain domain (LCDR3) having an amino acid sequence selected from the group consisting of SEQ ID NOs: 16, 32, 48, 64, 120, 136, 152, 168, 184, 200, 216, 232, 248, 264, 280, 296, 312, 328, 344, 360, 376 and 392 or a substantially similar sequence thereof having at least 90%, at least 95%, of the same; Petition 870260043419, dated 08 / 05 / 2026, page 37 / 353 30 / 163 minus 98% or at least 99% sequence identity.

[0078] Certain exemplary non-limiting bispecific antigen-binding molecules of the invention include a second antigen-binding domain that specifically binds STEAP2 comprising domains HCDR1-HCDR2-HCDR3-LCDR1LCDR2-LCDR3, respectively having selected amino acid sequences from the group consisting of: SEQ ID NOs: 252-254-256-260262-264.

[0079] In a related embodiment, the invention includes bispecific anti-CD3 / anti-STEAP2 antigen-binding molecules, wherein the second antigen-binding domain that specifically binds STEAP2 comprises the heavy and light chain domains of CDR contained within the heavy and light chain variable region (HCVR / LCVR) sequences selected from the group consisting of: SEQ ID NOs: 250 / 258.

[0080] In another aspect, the invention provides a bispecific antigen-binding molecule comprising a first antigen-binding domain that binds human CD3 and a second antigen-binding domain that binds human STEAP2, wherein the second antigen-binding domain is derived from the antibody or antigen-binding fragment of any of the anti-STEAP2 antibodies of the invention. In a further aspect, the invention provides a bispecific antigen-binding molecule comprising a first antigen-binding domain that specifically binds human CD3 and a second antigen-binding domain that specifically binds human STEAP2.

[0081] The invention further provides a bispecific antigen-binding molecule that binds human cells expressing human CD3 and cynomolgus monkey cells expressing cynomolgus CD3. In another aspect, the antigen-binding molecule Petition 870260043419, dated 08 / 05 / 2026, page 38 / 353 31 / 163 bispecific ligation binds to human cells expressing human STEAP2.

[0082] In another aspect, the invention provides a bispecific antigen-binding molecule which inhibits tumor growth in immunocompromised mice bearing human prostate cancer xenografts.

[0083] In certain embodiments, the anti-CD3 antibodies of the invention, the antigen-binding fragments and the bispecific antibodies thereof were made by replacing amino acid residues of a parent in a stepwise manner based on the differences between the germline sequence and the parental antibody sequence.

[0084] In some embodiments, the invention provides a bispecific antigen-binding molecule, wherein the second antigen-binding domain competes for binding to human STEAP2 with a reference antigen-binding protein comprising three heavy chain complementarity-determining regions (A2-HCDR1, A2-HCDR2 and A2-HCDR3) and three light chain complementarity-determining regions (A2-LCDR1, A2LCDR2 and A2-LCDR3), wherein A2-HCDR1 comprises an amino acid sequence selected from the group consisting of SEQ ID NO: 252; A2-HCDR2 comprises an amino acid sequence of SEQ ID NO: 254; A2-HCDR3 comprises an amino acid sequence of SEQ ID NO: 256; A2-LCDR1 comprises an amino acid sequence of SEQ ID NO: 260; A2-LCDR2 comprises an amino acid sequence of SEQ ID NO: 262; A2-LCDR3 comprises an amino acid sequence with SEQ ID NO: 264.In some embodiments, the invention provides a bispecific antigen-binding molecule, wherein the second antigen-binding domain competes for binding to human STEAP2 with a reference antigen-binding protein comprising a heavy chain variable region (HCVR) comprising a sequence of... Petition 870260043419, dated 08 / 05 / 2026, page 39 / 353 32 / 163 amino acid of SEQ ID NO: 250; and a light chain variable region (LCVR) comprising an amino acid sequence of SEQ ID NO: 258.

[0085] In some embodiments, the invention provides a bispecific antigen-binding molecule, wherein the first antigen-binding domain competes for binding to human CD3 with a reference antigen-binding protein comprising three heavy chain complementarity-determining regions (A1-HCDR1, A1-HCDR2 and A1-HCDR3) and three light chain complementarity-determining regions (A1-LCDR1, A1-LCDR2 and A1LCDR3), wherein A1-HCDR1 comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 1732, 1764 and 1868; A1-HCDR2 comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 1734, 1766 and 1870; A1-HCDR3 comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 1736, 1768 and 1872; A1-LCDR1 comprises an amino acid sequence with SEQ ID NO: 260; A1LCDR2 comprises an amino acid sequence with SEQ ID NO: 262 and A1-LCDR3 comprises an amino acid sequence with SEQ ID NO: 264.In some embodiments, the invention provides a bispecific antigen-binding molecule, wherein the first antigen-binding domain competes for binding to human CD3 with a reference antigen-binding protein comprising a heavy chain variable region (HCVR) comprising an amino acid sequence of SEQ ID NOs: 1730, 1762 and 1866 and a light chain variable region (LCVR) comprising an amino acid sequence of SEQ ID NO: 258.

[0086] In some embodiments, the invention provides a bispecific antigen-binding molecule, wherein the first antigen-binding domain competes for binding to human CD3. Petition 870260043419, dated 08 / 05 / 2026, page 40 / 353 33 / 163 with a reference antigen-binding protein comprising a heavy chain variable region (HCVR) comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 1730, 1762 and 1866 and a light chain variable region (LCVR) comprising an amino acid sequence of SEQ ID NO: 258; and wherein the second antigen-binding domain competes for binding to human STEAP2 with a reference antigen-binding protein comprising a heavy chain variable region (HCVR) comprising an amino acid sequence of SEQ ID NO: 250 and a light chain variable region (LCVR) comprising an amino acid sequence of SEQ ID NO: 258.

[0087] In one aspect, the invention provides a pharmaceutical composition comprising an anti-STEAP2 antigen-binding molecule or a bispecific anti-STEAP2 / anti-CD3 antigen-binding molecule and a pharmaceutically acceptable vehicle or diluent. The invention further provides a method for treating cancer in an individual, the method comprising administering to the individual the pharmaceutical composition comprising an anti-STEAP2 antigen-binding molecule or a bispecific anti-STEAP2 / anti-CD3 antigen-binding molecule and a pharmaceutically acceptable vehicle or diluent. In some embodiments, the cancer is selected from the group consisting of prostate cancer, bladder cancer, cervical cancer, lung cancer, colon cancer, kidney cancer, breast cancer, pancreatic cancer, stomach cancer, uterine cancer, and ovarian cancer. In some cases, the cancer is prostate cancer. In some cases, the prostate cancer is castration-resistant prostate cancer.

[0088] In another aspect, the present invention provides nucleic acid molecules encoding any of the HCVR, LCVR, or CDR sequences of the antigen-binding molecules. Petition 870260043419, dated 08 / 05 / 2026, p. 41 / 353 34 / 163 bispecific anti-CD3 / anti-STEAP2 antibodies disclosed herein, including nucleic acid molecules comprising the polynucleotide sequences as set forth in Tables 2, 10, 13, 14, 16 and 18, as well as nucleic acid molecules comprising two or more of the polynucleotide sequences as set forth in Tables 2, 10, 13, 14, 16 and 18 in any functional combination or arrangement thereof. Recombinant expression vectors, therefore the nucleic acids of the invention and host cells into which these vectors have been introduced, are also encompassed by the invention, as are methods for producing the antibodies by culturing the host cells under conditions that permit the production of the antibodies and recovery of the antibodies produced.

[0089] The present invention includes bispecific anti-CD3 / anti-STEAP2 antigen-binding molecules in which any of the aforementioned antigen-binding domains that specifically bind CD3 is combined, linked, or otherwise associated with any of the aforementioned antigen-binding domains that specifically bind STEAP2 to form a bispecific antigen-binding molecule that binds CD3 and STEAP2.

[0090] The present invention includes bispecific anti-CD3 / anti-STEAP2 antigen-binding molecules having a modified glycosylation pattern. In some applications, modification to remove undesirable glycosylation sites may be useful for an antibody lacking a fucose moiety present in the oligosaccharide chain, for example, to enhance antibody-dependent cellular cytotoxicity (ADCC) function (see Shield et al. (2002) JBC 277:26733). In other applications, a galactosylation modification may be made in order to modify complement-dependent cytotoxicity (CDC).

[0091] In another aspect, the invention provides a pharmaceutical composition comprising an antigen-binding molecule. Petition 870260043419, dated 08 / 05 / 2026, page 42 / 353 35 / 163 bispecific anti-CD3 / anti-STEAP2 antigen-binding molecule as disclosed herein and a pharmaceutically acceptable carrier. In a related aspect, the invention provides a composition which is a combination of a bispecific anti-CD3 / anti-STEAP2 antigen-binding molecule and a second therapeutic agent. In one embodiment, the second therapeutic agent is any agent that is advantageously combined with a bispecific anti-CD3 / anti-STEAP2 antigen-binding molecule. Exemplary agents that can be advantageously combined with a bispecific anti-CD3 / anti-STEAP2 antigen-binding molecule are discussed in detail elsewhere herein.

[0092] In yet another aspect, the invention provides therapeutic methods of targeting / killing STEAP2-expressing tumor cells using a bispecific anti-CD3 / anti-STEAP2 antigen-binding molecule of the invention, wherein the therapeutic methods comprise administering a therapeutically effective amount of a pharmaceutical composition comprising a bispecific anti-CD3 / anti-STEAP2 antigen-binding molecule of the invention to an individual in need thereof.

[0093] The present invention also includes the use of a bispecific anti-CD3 / anti-STEAP2 antigen-binding molecule of the invention in the manufacture of a medicament for the treatment of a disease or disorder related to or caused by cells expressing STEAP2.

[0094] Other modalities will become apparent from a review of the detailed description below. BRIEF DESCRIPTION OF THE FIGURES

[0095] Figure 1 shows the efficacy of H1H7814N-7 in a STEAP2-positive prostate cancer xenograft model (SCID mice implanted with C4-2 cells) at a dose of 10, 20, or 40 mg / kg of H1H7814N-7 administered on day 13 after implantation. Petition 870260043419, dated 08 / 05 / 2026, page 43 / 353 36 / 163

[0096] Figure 2 shows the efficacy of H1H7814N-7 in a STEAP2-positive prostate cancer xenograft model (SCID mice implanted with C4-2 cells) at a dose of 20 mg / kg of H1H7814N-7 administered on day 14 after implantation.

[0097] Figure 3 shows the efficacy of H1H7814N-7 in a STEAP2-positive prostate cancer xenograft model (SCID mice implanted with C4-2 cells) at a dose of 150 pg / kg of H1H7814N-7 administered on day 17 after implantation.

[0098] Figure 4 shows the efficacy of H1H7814N-60 in a STEAP2-positive prostate cancer xenograft model (SCID mice implanted with C4-2 cells) at a dose of 2.5 mg / kg (DAR 3.6 TV) of H1H7814N-7 administered on day 29 after implantation.

[0099] Figure 5 shows the binding of bispecific antibodies STEAP2xCD3 Jurkat cells.

[00100] Figure 6 shows the binding of bispecific antibodies STEAP2xCD3 is a human prostate cancer cell line (PC3) engineered to express a chimeric STEAP2 / 1 construct.

[00101] Figures 7 and 8 show the binding of bispecific STEAP2xCD3 antibodies to Cynomolgus T cells.

[00102] Figure 9 shows the induction of human PBMC proliferation by STEAP2xCD3 bispecific antibodies.

[00103] Figure 10 shows the induction of cynomolgus PBMC proliferation by STEAP2xCD3 bispecific antibodies.

[00104] Figure 11 shows the depletion of C4-2 cells (STEAP2-bearing target cells) in a cytotoxicity assay with representative STEAP2xCD3 bispecific antibodies in the presence of human PBMCs.

[00105] Figure 12 shows activation of human T cells by representative STEAP2xCD3 bispecific antibodies that Petition 870260043419, dated 08 / 05 / 2026, page 44 / 353 37 / 163 correlates with the observed target cell lysis, shown in Figure 11. DETAILED DESCRIPTION

[00106] Before the present invention is described, it is to be understood that this invention is not limited to the particular methods and experimental conditions described, as such methods and conditions may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments and is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims.

[00107] Unless defined otherwise, all technical and scientific terms used in this document have the same meaning as commonly understood by one skilled in the art to which this invention pertains. As used herein, the term “about,” when used in reference to a particular recited numerical value, means that the value may vary from the recited value by no more than 1%. For example, as used herein, the expression “about 100” includes 99 and 101 and all values ​​between them (e.g., 99.1, 99.2, 99.3, 99.4, etc.).

[00108] Although any methods and materials similar or equivalent to those described herein may be used in the practice or testing of the present invention, the preferred methods and materials are described herein. All patents, applications and non-patent publications mentioned in this descriptive report are incorporated herein by reference in their entirety. Definitions

[00109] The term “CD3”, as used herein, refers to an antigen that is expressed on T cells as part of the multimolecular T cell receptor (TCR) and that consists of a homodimer or Petition 870260043419, dated 08 / 05 / 2026, p. 45 / 353 38 / 163 heterodimer formed from the association of two of four receptor chains: CD3-epsilon, CD3-delta, CD3-zeta, and CD3-gamma. Human CD3-epsilon comprises the amino acid sequence as set forth in SEQ ID NO: 1897; human CD3-delta comprises the amino acid sequence as set forth in SEQ ID NO: 1898. All references to proteins, polypeptides, and protein fragments herein are intended to refer to the human version of the respective protein, polypeptide, or protein fragment, unless explicitly specified as being from a non-human species. Thus, the expression “CD3” means human CD3, unless specified as being from a non-human species, for example, “mouse CD3”, “monkey CD3”, etc.

[00110] As used herein, “a CD3-binding antibody” or an “anti-CD3 antibody” includes antibodies and antigen-binding fragments thereof that specifically recognize a single CD3 subunit (e.g., epsilon, delta, gamma, or zeta), as well as antibodies and antigen-binding fragments thereof that specifically recognize a dimeric complex of two CD3 subunits (e.g., CD3 gamma / epsilon, delta / epsilon, and zeta / zeta dimers). The antibodies and antigen-binding fragments of the present invention may bind soluble CD3 and / or CD3 expressed on the cell surface. Soluble CD3 includes natural CD3 proteins as well as recombinant CD3 protein variants such as, for example, monomeric and dimeric CD3 constructs that lack a transmembrane domain or are otherwise not associated with a cell membrane.

[00111] As used herein, the expression “CD3 expressed on the cell surface” means one or more CD3 proteins that are expressed on the surface of a cell in vitro or in vivo, such that at least a portion of a CD3 protein is exposed on the side Petition 870260043419, dated 08 / 05 / 2026, p. 46 / 353 39 / 163 extracellular matrix of the cell membrane and be accessible to an antigen-binding portion of an antibody. “CD3 expressed on the cell surface” includes CD3 proteins contained within the context of a functional T cell receptor on the membrane of a cell. The expression “CD3 expressed on the cell surface” includes CD3 protein expressed as part of a homodimer or heterodimer on the surface of a cell (e.g., CD3 gamma / epsilon, delta / epsilon, and zeta / zeta dimers). The expression “CD3 expressed on the cell surface” also includes a CD3 chain (e.g., CD3-epsilon, CD3-delta, or CD3-gamma) that is expressed on its own, without other types of CD3 chains on the surface of a cell. A “CD3 expressed on the cell surface” may comprise or consist of a CD3 protein expressed on the surface of a cell that normally expresses the CD3 protein.Alternatively, "CD3 expressed on the cell surface" may comprise or consist of CD3 protein expressed on the surface of a cell that does not normally express human CD3 on its surface, but has been artificially engineered to express CD3 on its surface.

[00112] The expression “STEAP2”, as used herein, refers to prostate six-transmembrane epithelial antigen 2. STEAP2 is a six-transmembrane integral protein highly expressed in prostate epithelial cells and is a cell surface marker for prostate cancer; for example, STEAP2 has been found to be expressed at significant levels in the LNCaP prostate cell line (Porkka, et al. Lab Invest 2002, 82:1573-1582). STEAP2 (UniProtKB / Swiss-Prot: Q8NFT2.3) is a 490-amino acid protein encoded by the STEAP2 gene located in the chromosomal region 7q21 in humans; see, for example, the amino acid sequence of human STEAP2 as established in SEQ ID NO: 1899.

[00113] As used herein, “an antibody that binds STEAP2” or a Petition 870260043419, dated 08 / 05 / 2026, p. 47 / 353 40 / 163 “anti-STEAP2 antibody” includes antibodies and antigen-binding fragments thereof that specifically recognize STEAP2.

[00114] The term “antigen-binding molecule” includes antibodies and antigen-binding fragments including, for example, bispecific antibodies.

[00115] The term “antibody,” as used herein, means any antigen-binding molecule or molecular complex comprising at least one complementarity-determining region (CDR) that specifically binds to, or interacts with, a particular antigen (e.g., STEAP2 or CD3). The term “antibody” includes immunoglobulin molecules comprising four polypeptide chains, two heavy chains (H) and two light chains (L) interconnected by disulfide bonds, as well as multimers thereof (e.g., IgM). Each heavy chain comprises a variable heavy chain region (abbreviated herein HCVR or VH) and a constant heavy chain region. The constant heavy chain region comprises three domains, CH1, CH2, and CH3. Each light chain comprises a variable light chain region (abbreviated LCVR or VL) and a constant light chain region. The constant light chain region comprises one domain (CL1).The VH and VL regions can be further subdivided into regions of hypervariability, called complementarity-determining regions (CDRs), interspersed with more conserved regions, called structural regions (FRs). Each VH and VL is composed of three CDRs and four FRs, arranged from the amino terminal to the carboxy terminal in the following order: FR1, CDR1, FR2, CDR2, FR3, CDR3, FR4. In different embodiments of the invention, the FRs of the anti-STEAP2 antibody or anti-CD3 antibody (or antigen-binding portion thereof) may be identical to human germline sequences or may be naturally or artificially modified. A sequence. Petition 870260043419, dated 08 / 05 / 2026, p. 48 / 353 A consensus amino acid ratio (41 / 163) can be defined based on a side-by-side analysis of two or more CDRs.

[00116] The term “antibody,” as used herein, also includes antigen-binding fragments of complete antibody molecules. The terms “antigen-binding portion of an antibody,” “antigen-binding fragment” of an antibody, and the like, as used herein, include any naturally occurring, enzymatically obtainable, synthetic, or genetically engineered polypeptide or glycoprotein that specifically binds an antigen to form a complex. Antigen-binding fragments of an antibody may be derived, for example, from complete antibody molecules using any suitable standard techniques, such as proteolytic digestion or recombinant genetic modification techniques involving the manipulation and expression of DNA encoding variable and, optionally, constant antibody domains.This DNA is known and / or readily available, for example, from commercial sources, DNA libraries (including, for example, phage-antibody libraries), or it can be synthesized. The DNA can be sequenced and manipulated chemically or using molecular biology techniques, for example, to arrange one or more variable and / or constant domains into a suitable configuration, or to introduce codons, create cysteine ​​residues, modify, add or delete amino acids, etc.

[00117] Non-limiting examples of antigen-binding fragments include: (i) Fab fragments; (ii) F(ab')2 fragments; (iii) Fd fragments; (iv) Fv fragments; (v) single-chain Fv molecules (scFv); (vi) dAb fragments; and (vii) minimal recognition units consisting of amino acid residues that mimic the hypervariable region of an antibody (e.g., an isolated complementarity-determining region (CDR) such as a Petition 870260043419, dated 08 / 05 / 2026, page 49 / 353 42 / 163 CDR3 peptide) or a restricted FR3-CDR3-FR4 peptide. Other manipulated molecules, such as domain-specific antibodies, single-domain antibodies, domain-deleted antibodies, chimeric antibodies, CDR-grafted antibodies, diabodies, triabodies, tetrabodies, minibodies, nanobodies (e.g., monovalent nanobodies, bivalent nanobodies, etc.), small modular immunopharmaceuticals (SMIPs), and shark variable IgNAR domains, are also encompassed by the antigen-binding fragment expression as used herein.

[00118] An antigen-binding fragment of an antibody will typically comprise at least one variable domain. The variable domain may be of any size or amino acid composition and will generally comprise at least one CDR that is adjacent to or in line with one or more structural sequences. In antigen-binding fragments that possess a VH domain associated with a VL domain, the VH and VL domains may be situated relative to each other in any suitable arrangement. For example, the variable region may be dimeric and contain VH-VH, VH-VL, or VL-VL dimers. Alternatively, the antigen-binding fragment of an antibody may contain a monomeric VH or VL domain.

[00119] In certain embodiments, an antigen-binding fragment of an antibody may contain at least one variable domain covalently linked to at least one constant domain. Non-limiting exemplary configurations of variable and constant domains that may be found within an antigen-binding fragment of an antibody of the present invention include: (i) VH-CH1; (ii) VH-CH2; (iii) VH-CH3; (iv) VH-CH1-CH2; (v) VH-CH1-CH2CH3; (vi) VH-CH2-CH3; (vii) VH-CL; (viii) VL-CH1; (ix) VL-CH2; (x) VLCH3; (xi) VL-CH1-CH2; (xii) VL-CH1-CH2-CH3; (xiii) VL-CH2-CH3; and Petition 870260043419, dated 08 / 05 / 2026, page 50 / 353 43 / 163 (xiv) VL-CL. In any variable and constant domain configuration, including any of the exemplary configurations listed above, the variable and constant domains may be directly linked to each other or may be linked by a partial region of the linker or hinge. A hinge region may consist of at least 2 (e.g., 5, 10, 15, 20, 40, 60 or more) amino acids resulting in a flexible or semi-flexible linkage between adjacent variable and / or constant domains in a polypeptide molecule. Furthermore, an antigen-binding fragment of an antibody of the present invention may comprise a homodimer or heterodimer (or other multimer) of any of the variable and constant domain configurations listed above in non-covalent association with each other and / or with one or more monomeric VH or VL domains (e.g., by disulfide linkage(s)).

[00120] As with complete antibody molecules, antigen-binding fragments can be monospecific or multispecific (e.g., bispecific). A multispecific antigen-binding fragment of an antibody will typically comprise at least two different variable domains, wherein each variable domain is capable of specifically binding to a separate antigen or to a different epitope on the same antigen. Any multispecific antibody format, including the exemplary bispecific antibody formats disclosed herein, can be adapted for use in the context of an antigen-binding fragment of an antibody of the present invention using routine techniques available in the art.

[00121] The antibodies of the present invention can function through complement-dependent cytotoxicity (CDC) or antibody-dependent cell-mediated cytotoxicity (ADCC). “Complement-dependent cytotoxicity” (CDC) refers to the lysis of Petition 870260043419, dated 08 / 05 / 2026, p. 51 / 353 44 / 163 cells expressing antigen by an antibody of the invention in the presence of complement. “Antibody-dependent cell-mediated cytotoxicity” (ADCC) refers to a cell-mediated reaction in which non-specific cytotoxic cells expressing Fc receptors (FcRs) (e.g., Natural Killer (NK) cells, neutrophils, and macrophages) recognize antibody bound to a target cell and thereby lead to lysis of the target cell. CDC and ADCC can be measured using assays that are well-known and available in the art. (See, for example, U.S. Patent 5,500,362 and 5,821,337, and Clynes et al. (1998) Proc. Natl. Acad. Sci. (USA) 95:652656). The constant region of an antibody is important in the ability of an antibody to fix complement and mediate cell-dependent cytotoxicity. Thus, the isotype of an antibody can be selected based on whether it is desirable for the antibody to mediate cytotoxicity.

[00122] In certain embodiments of the invention, the monospecific anti-STEAP2 antibodies or bispecific anti-STEAP2 / anti-CD3 antibodies of the invention are human antibodies. The term “human antibody,” as used herein, is intended to include antibodies that have variable and constant regions derived from human germline immunoglobulin sequences. The human antibodies of the invention may include amino acid residues not encoded by human germline immunoglobulin sequences (e.g., mutations introduced by random site-specific mutagenesis in vitro or by somatic mutation in vivo), for example, in CDRs and, in particular, in CDR3. However, the term “human antibody,” as used herein, is not intended to include antibodies in which germline-derived CDR sequences from another mammalian species, such as a mouse, have been grafted onto human structural sequences. Petition 870260043419, dated 08 / 05 / 2026, p. 52 / 353 45 / 163

[00123] The antibodies of the invention may, in some embodiments, be recombinant human antibodies. The term “recombinant human antibody,” as used herein, is intended to include all human antibodies that are prepared, expressed, created, or isolated by recombinant means, such as antibodies expressed using a recombinant expression vector transfected into a host cell (described further below), antibodies isolated from a recombinant human antibody library, combinatorial antibodies (described further below), antibodies isolated from an animal (e.g., a mouse) that is transgenic for human immunoglobulin genes (see, for example, Taylor et al., 1992) Nucl. Acids Res. 20:6287-6295), or antibodies prepared, expressed, created, or isolated by any other means involving splicing of human immunoglobulin gene sequences to other DNA sequences.These recombinant human antibodies have variable and constant regions derived from human germline immunoglobulin sequences. In certain embodiments, however, such recombinant human antibodies are subject to in vitro mutagenesis (or, when a transgenic animal is used for human Ig sequences, in vivo somatic mutagenesis) and thus the amino acid sequences of the VH and VL regions of the recombinant antibodies are sequences that, although derived from and related to the human germline VH and VL sequences, may not naturally exist within the human germline antibody repertoire in vivo.

[00124] Human antibodies can exist in two forms that are associated with hinge heterogeneity. In one form, an immunoglobulin molecule comprises a stable four-chain construct of approximately 150-160 kDa, in which the dimers are held together by a chain disulfide bond. Petition 870260043419, dated 08 / 05 / 2026, page 53 / 353 46 / 163 heavy interchain. In a second form, the dimers are not linked through interchain disulfide bonds and a molecule of about 75-80 kDa is formed, composed of a covalently coupled light and heavy chain (half antibody). These forms have been extremely difficult to separate, even after affinity purification.

[00125] The frequency of appearance of the second form in various intact IgG isotypes is due to, but not limited to, structural differences associated with the isotype of the antibody hinge region. A single amino acid substitution in the hinge region of human IgG4 can significantly reduce the appearance of the second form (Angal et al. (1993) Molecular Immunology 30:105) to levels typically observed using a human IgG1 hinge. The present invention encompasses antibodies having one or more mutations in the hinge, CH2 or CH3 region which may be desirable, for example, in production, to improve the yield of the desired antibody form.

[00126] The antibodies of the invention may be isolated antibodies. An “isolated antibody,” as used herein, means an antibody that has been identified and separated and / or recovered from at least one component of its natural environment. For example, an antibody that has been separated or removed from at least one component of an organism, or from a tissue or cell in which the antibody naturally exists or is naturally produced, is an “isolated antibody” for the purposes of the present invention. An isolated antibody also includes an antibody in situ within a recombinant cell. Isolated antibodies are antibodies that have undergone at least one purification or isolation step. According to certain embodiments, an isolated antibody may be substantially free of other cellular material and / or chemicals. Petition 870260043419, dated 08 / 05 / 2026, p. 54 / 353 47 / 163

[00127] The present invention also includes single-arm antibodies that bind STEAP2. As used herein, a “single-arm antibody” means an antigen-binding molecule comprising a single antibody heavy chain and a single antibody light chain. The single-arm antibodies of the present invention may comprise any of the amino acid sequences of HCVR / LCVR or CDR, as set forth in Table 1.

[00128] The anti-STEAP2 or anti-STEAP2 / anti-CD3 antibodies disclosed herein may comprise one or more amino acid substitutions, insertions and / or deletions in the structure and / or CDR regions of the variable heavy and light chain domains compared to the corresponding germline sequences from which the antibodies were derived. Such mutations can be readily determined by comparing the amino acid sequences disclosed herein to available germline sequences, for example, from public antibody sequence databases.The present invention includes antibodies, and antigen-binding fragments thereof, which are derived from any of the amino acid sequences disclosed herein, wherein one or more amino acids within one or more structural regions and / or CDRs are mutated to the corresponding residue (or residues) of the germline sequence from which the antibody was derived or to the corresponding residue (or residues) of another human germline sequence, or to a conservative amino acid substitution of the corresponding germline residue (or residues) (such sequence changes are collectively referred to herein as “germline mutations”). A person skilled in the art, beginning with the variable region sequences. Petition 870260043419, dated 08 / 05 / 2026, p. 55 / 353 The 48 / 163 heavy and light chain mutations disclosed in this document can readily produce numerous antibodies and antigen-binding fragments thereof comprising one or more individual germline mutations or combinations thereof. In certain embodiments, all structural and / or CDR residues within the VH and / or VL domains mutate back to the residues found in the original germline sequence from which the antibody was derived. In other embodiments, only certain residues mutate back to the original germline sequence, for example, only the mutated residues found in the first 8 amino acids of FR1 or the last 8 amino acids of FR4, or only the mutated residues found in CDR1, CDR2, or CDR3.In other embodiments, one or more of the structure and / or CDR residues mutate to the corresponding residue (or residues) of a different germline sequence (i.e., a germline sequence that is different from the germline sequence from which the antibody originally derived). Furthermore, the antibodies of the present invention may contain any combination of two or more germline mutations within the structure and / or CDR regions, for example, where certain individual residues mutate to the corresponding residue of a given germline sequence while some other residues that are different from the original germline sequence are retained or mutate to the corresponding residue of a different germline sequence.Once obtained, antibodies and their antigen-binding fragments containing one or more germline mutations can be easily tested for one or more desired properties, such as... Petition 870260043419, dated 08 / 05 / 2026, page 56 / 353 49 / 163 improved binding specificity, higher binding affinity, enhanced or amplified antagonistic or agonistic biological properties (as the case may be), reduced immunogenicity, etc. Antibodies and antigen-binding fragments obtained in this manner are generally covered by the present invention.

[00129] The present invention also includes anti-STEAP2 or anti-STEAP2 / anti-CD3 antibodies comprising variants of any of the HCVR, LCVR and / or CDR amino acid sequences disclosed herein having one or more conservative substitutions. For example, the present invention includes anti-STEAP2 or anti-STEAP2 / anti-CD3 antibodies having HCVR, LCVR and / or CDR amino acid sequences with, for example, 10 or fewer, 8 or fewer, 6 or fewer, 4 or fewer, etc. conservative amino acid substitutions with respect to any of the HCVR, LCVR and / or CDR amino acid sequences set forth in Table 1 herein or as described in Tables 9, 11, 12, 15 and 16 herein.

[00130] The term “epitope” refers to an antigenic determinant that interacts with a specific antigen-binding site in the variable region of an antibody molecule known as a paratope. A single antigen can have more than one epitope.Thus, different antibodies can bind to different areas of an antigen and may have different biological effects. Epitopes can be either conformational or linear. A conformational epitope is produced by spatially juxtaposed amino acids from different segments of the linear polypeptide chain. A linear epitope is produced by adjacent amino acid residues in a polypeptide chain. Under certain circumstances, an epitope may include saccharide fragments, phosphoryl groups, or sulfonyl groups in the antigen.

[00131] The term substantial identity or substantially identical, when referring to a nucleic acid or fragment thereof, indicates that, when ideally aligned with insertions or Petition 870260043419, dated 08 / 05 / 2026, p. 57 / 353 50 / 163 appropriate nucleotide deletions with another nucleic acid (or complementary strand thereof), there is nucleotide sequence identity in at least about 95% and, more preferably, at least about 96%, 97%, 98% or 99% of the nucleotide bases, as measured by any well-known sequence identity algorithm, such as FASTA, BLAST or Gap, as discussed below. A nucleic acid molecule that has substantial identity with a reference nucleic acid molecule may, in certain cases, encode a polypeptide that has the same or substantially similar amino acid sequence to the polypeptide encoded by the reference nucleic acid molecule.

[00132] When applied to polypeptides, the term substantial similarity or substantially similar means that two peptide sequences, when optimally aligned, such as by GAP or BESTFIT programs using standard interval weights, share at least 95% sequence identity, even more preferably at least 98% or 99% sequence identity. Preferably, the residue positions that are not identical are differing by conservative amino acid substitutions. A “conservative amino acid substitution” is one in which an amino acid residue is replaced by another amino acid residue having a side chain (R group) with similar chemical properties (e.g., charge or hydrophobicity). In general, a conservative amino acid substitution will not substantially change the functional properties of a protein.In cases where two or more amino acid sequences differ from each other by conservative substitutions, the percentage of sequence identity or degree of similarity can be adjusted upward to correct for the conservative nature of the substitution. Methods for making this adjustment are well known to those skilled in the art. See, for example... Petition 870260043419, dated 08 / 05 / 2026, p. 58 / 353 51 / 163 example, Pearson (1994) Methods Mol. Biol. 24: 307-331, incorporated here by reference. Examples of groups of amino acids that have side chains with similar chemical properties include (1) aliphatic side chains: glycine, alanine, valine, leucine, and isoleucine; (2) aliphatic hydroxyl side chains: serine and threonine; (3) amide-containing side chains: asparagine and glutamine; (4) aromatic side chains: phenylalanine, tyrosine, and tryptophan; (5) basic side chains: lysine, arginine, and histidine; (6) acidic side chains: aspartate and glutamate; and (7) sulfur-containing side chains: cysteine ​​and methionine. Preferred conservative amino acid substitution groups are: valine-leucine-isoleucine, phenylalanine-tyrosine, lysine-arginine, alanine-valine, glutamate-aspartate, and asparagine-glutamine.Alternatively, a conservative substitution is any change having a positive value in the PAM250 log-probability matrix disclosed in Gonnet et al. (1992) Science 256: 1443-1445, incorporated here by reference. A “moderately conservative” substitution is any change having a non-negative value in the PAM250 log-probability matrix.

[00133] Sequence similarity for polypeptides, also referred to as sequence identity, is typically measured using sequence analysis software. Protein analysis software matches similar sequences using similarity measures attributed to various substitutions, deletions, and other modifications, including conservative amino acid substitutions. For example, the GCG software contains programs, such as Gap and Bestfit, that can be used with standard parameters to determine sequence homology or sequence identity between closely related polypeptides, such as homologous polypeptides from different species of organisms or between a wild-type protein and a wild-type mutain. See, for example, GCG Version 6.1. Sequences of Petition 870260043419, dated 08 / 05 / 2026, page 59 / 353 52 / 163 polypeptides can also be compared using FASTA using default or recommended parameters, a program in GCG Version 6.1. FASTA (e.g., FASTA2 and FASTA3) provides alignments and percentage of sequence identity of the best overlap regions between query and search sequences (Pearson (2000) supra). Another preferred algorithm when a sequence of the invention is compared to a database containing a large number of sequences from different organisms is the BLAST computer program, especially BLASTP or TBLASTN, using default parameters. See, for example, Altschul et al. (1990) J. Mol. Biol. 215: 403-410 and Altschul et al. (1997) Nucleic Acids Res. 25:3389402, each incorporated herein by reference. Germline Mutations

[00134] The anti-CD3 antibodies disclosed here may comprise one or more amino acid substitutions, insertions and / or deletions in the structure and / or CDR regions of the variable heavy chain domains compared to the corresponding germline sequences from which the antibodies were derived.

[00135] The present invention also includes antibodies, and antigen-binding fragments thereof, which are derived from any of the amino acid sequences disclosed herein, wherein one or more amino acids within one or more structural regions and / or CDRs are mutated to the corresponding residue (or residues) of the germline sequence from which the antibody was derived or to the corresponding residue (or residues) of another human germline sequence, or to a conservative amino acid substitution of the corresponding germline residue (or residues) (such sequence changes are referred to herein collectively as “strainline mutations”). Petition 870260043419, dated 08 / 05 / 2026, p. 60 / 353 53 / 163 germ cell antibodies”) and having weak or undetectable binding to a CD3 antigen. Several of these exemplary antibodies that recognize CD3 are described in Tables 12 and 18.

[00136] Furthermore, the antibodies of the present invention may contain any combination of two or more germline mutations within the structure and / or CDR regions, for example, wherein certain individual residues mutate to the corresponding residue of a given germline sequence while some other residues that are different from the original germline sequence are retained or mutate to the corresponding residue of a different germline sequence. Once obtained, the antibodies and antigen-binding fragments thereof containing one or more germline mutations may be tested for one or more desired properties, such as improved binding specificity, weak or reduced binding affinity, improved or enhanced pharmacokinetic properties, reduced immunogenicity, etc.The antibodies and antigen-binding fragments obtained in this general manner, given the orientation of the present disclosure, are encompassed within the present invention.

[00137] The present invention also includes anti-CD3 antibodies comprising variants of any of the HCVR, LCVR and / or CDR amino acid sequences disclosed herein having one or more conservative substitutions. For example, the present invention includes anti-CD3 antibodies having HCVR, LCVR and / or CDR amino acid sequences with, for example, 10 or fewer, 8 or fewer, 6 or fewer, 4 or fewer, etc. conservative amino acid substitutions with respect to any of the HCVR, LCVR and / or CDR amino acid sequences set forth in Tables 1, 9, 11, 12, 15 and 16 herein. The antibodies and bispecific antigen-binding molecules of the present invention Petition 870260043419, dated 08 / 05 / 2026, p. 61 / 353 54 / 163 comprise one or more amino acid substitutions, insertions, and / or deletions in the structure and / or CDR regions of the variable heavy and light chain domains compared to the corresponding germline sequences from which the individual antigen-binding domains were derived, while maintaining or improving the desired weak to undetectable binding to the CD3 antigen. A “conservative amino acid substitution” is one in which an amino acid residue is replaced by another amino acid residue having a side chain (R group) with similar chemical properties (e.g., charge or hydrophobicity). In general, a conservative amino acid substitution will not substantially change the functional properties of a protein; that is, the amino acid substitution maintains or improves the desired weak to undetectable binding affinity in the case of anti-CD3 binding molecules.Examples of amino acid groups that have side chains with similar chemical properties include (1) aliphatic side chains: glycine, alanine, valine, leucine, and isoleucine; (2) aliphatic hydroxyl side chains: serine and threonine; (3) amide-containing side chains: asparagine and glutamine; (4) aromatic side chains: phenylalanine, tyrosine, and tryptophan; (5) basic side chains: lysine, arginine, and histidine; (6) acidic side chains: aspartate and glutamate; and (7) sulfur-containing side chains: cysteine ​​and methionine. Preferred conservative amino acid substitution groups are: valine-leucine-isoleucine, phenylalanine-tyrosine, lysine-arginine, alaninavalin, glutamate-aspartate, and asparagine-glutamine. Alternatively, a conservative substitution is any change having a positive value in the PAM250 log-probability matrix disclosed in Gonnet et al. (1992) Science 256: 1443-1445.A "moderately conservative" substitution is any change having a non-negative value in the PAM250 log-probability matrix. Petition 870260043419, dated 08 / 05 / 2026, page 62 / 353 55 / 163

[00138] The present invention also includes antigen-binding molecules comprising an antigen-binding domain with an HCVR and / or CDR amino acid sequence that is substantially identical to any of the HCVR and / or CDR amino acid sequences disclosed herein, while maintaining or improving the desired weak affinity for the CD3 antigen. The term “substantial identity” or “substantially identical,” referring to an amino acid sequence, means that two amino acid sequences, when optimally aligned, such as by GAP or BESTFIT programs using default range weights, share at least 95% sequence identity, even more preferably at least 98% or 99% sequence identity. Preferably, the residue positions that are not identical are differing by conservative amino acid substitutions.In cases where two or more amino acid sequences differ from each other by conservative substitutions, the percentage of sequence identity or degree of similarity can be adjusted upward to correct for the conservative nature of the substitution. Methods for making this adjustment are well known to those skilled in the art. See, for example, Pearson (1994) Methods Mol. Biol. 24: 307-331.

[00139] Sequence similarity for polypeptides, also referred to as sequence identity, is typically measured using sequence analysis software. Protein analysis software matches similar sequences using similarity measures attributed to various substitutions, deletions, and other modifications, including conservative amino acid substitutions. For example, the GCG software contains programs, such as Gap and Bestfit, that can be used with standard parameters to determine sequence homology or sequence identity between closely related polypeptides, such as homologous polypeptides of different Petition 870260043419, dated 08 / 05 / 2026, page 63 / 353 56 / 163 species of organisms or between a wild-type protein and a mutant of the same. See, for example, GCG Version 6.1. Polypeptide sequences can also be compared using FASTA using default or recommended parameters, a program in GCG Version 6.1. FASTA (e.g., FASTA2 and FASTA3) provides alignments and percentage of sequence identity of the best overlap regions between query and search sequences (Pearson (2000) supra). Another preferred algorithm when a sequence of the invention is compared to a database containing a large number of sequences from different organisms is the BLAST computer program, especially BLASTP or TBLASTN, using default parameters. See, for example, Altschul et al. (1990) J. Mol. Biol. 215:403-410 and Altschul et al. (1997) Nucleic Acids Res. 25:3389402.

[00140] Once obtained, antigen-binding domains containing one or more germline mutations were tested for decreased binding affinity using one or more in vitro assays. Although antibodies recognizing a particular antigen are typically screened for their purpose by testing for high (i.e., strong) antigen-binding affinity, the antibodies of the present invention exhibit weak or undetectable binding. Bispecific antigen-binding molecules comprising one or more antigen-binding domains obtained in this manner are also encompassed within the present invention and have been considered advantageous as avidity-directed tumor therapies.

[00141] Unexpected benefits, for example, improved pharmacokinetic properties and low patient toxicity, can be achieved from the methods described herein. Antibody Binding Properties

[00142] As used herein, the term “connection”, in the context of Petition 870260043419, dated 08 / 05 / 2026, p. 64 / 353 57 / 163 The binding of an antibody, immunoglobulin, antibody-binding fragment, or Fc-containing protein to any one of, for example, a predetermined antigen, such as a cell surface protein or a fragment thereof, typically refers to an interaction or association between a minimum of two entities or molecular structures, such as an antibody-antigen interaction.

[00143] For example, binding affinity typically corresponds to a KD value of about 10-7 M or less, such as about 108 M or less, such as about 10-9 M or less when determined, for example, by surface plasmon resonance (SPR) technology on a BIAcore 3000 instrument using the antigen as the ligand and the antibody, Ig, antibody-binding fragment or Fc-containing protein as the analyte (or antiligand). Cell-based binding strategies, such as fluorescence-activated cell separation (FACS) binding assays, are also routinely used, and FACS data correlate well with other methods, such as radioligand competition binding and SPR (Benedict, CA, J Immunol Methods. 1997, 201(2):223-31; Geuijen, CA, et al. J Immunol Methods. 2005, 302(12):68-77).

[00144] Therefore, the antibody or antigen-binding protein of the invention binds to the predetermined antigen or cell surface molecule (receptor) having an affinity corresponding to a KD value that is at least ten times lower than its affinity for binding to a non-specific antigen (e.g., BSA, casein). According to the present invention, an antibody affinity corresponding to a KD value that is equal to or less than ten times lower than that of a non-specific antigen can be considered undetectable binding; however, such an antibody can be paired with a second antigen-binding arm to produce an antibody. Petition 870260043419, dated 08 / 05 / 2026, p. 65 / 353 58 / 163 bispecific of the invention.

[00145] The term “KD” (M) refers to the dissociation equilibrium constant of a particular antibody-antigen interaction, or the dissociation equilibrium constant of an antibody or antibody-binding fragment for an antigen. There is an inverse relationship between KD and binding affinity, therefore, the lower the KD value, the higher, i.e., the stronger, the affinity. Thus, the terms “higher affinity” or “stronger affinity” refer to a higher ability to form an interaction and therefore a lower KD value, and conversely, the terms “lower affinity” or “weaker affinity” refer to a lower ability to form an interaction and therefore a higher KD value.In some circumstances, a higher binding affinity (or KD) of a particular molecule (e.g., antibody) for its interacting partner molecule (e.g., antigen X) compared to the binding affinity of the molecule (e.g., antibody) for another interacting partner molecule (e.g., antigen Y) can be expressed as a binding ratio determined by dividing the higher KD value (lower or weaker affinity) by the lower KD value (higher or stronger affinity), for example expressed as a binding affinity 5 times or 10 times greater, as the case may be.

[00146] The term “kd” (s-1 or 1 / s) refers to the dissociation rate constant of a particular antibody-antigen interaction, or the dissociation rate constant of an antibody or antibody-binding fragment. This value is also referred to as the koff value.

[00147] The term “ka” (M-1 x s-1 or 1 / M) refers to the association rate constant of a particular antibody-antigen interaction, or the association rate constant of an antibody or antibody-binding fragment. Petition 870260043419, dated 08 / 05 / 2026, p. 66 / 353 59 / 163

[00148] The term “KA” (M-1 or 1 / M) refers to the association equilibrium constant of a particular antibody-antigen interaction, or the association equilibrium constant of an antibody or antibody-binding fragment. The association equilibrium constant is obtained by dividing ka by kd.

[00149] The term “EC50” or “EC50” refers to half the maximum effective concentration, which includes the concentration of an antibody that induces a response halfway between baseline and at maximum after a specified exposure time. EC50 essentially represents the concentration of an antibody where 50% of its maximum effect is observed. In certain embodiments, the EC50 value is equal to the concentration of an antibody of the invention that gives a half-maximum binding to cells expressing CD3 or tumor-associated antigen, as determined by, for example, a FACS binding assay. Thus, reduced or weaker binding is observed with a high EC50, or half the maximum effective concentration value.

[00150] In one embodiment, reduced binding can be defined as a high EC50 antibody concentration that allows binding to the mid-maximum amount of target cells.

[00151] In another embodiment, the EC50 value represents the concentration of an antibody of the invention that elicits half-maximal depletion of target cells by T-cell cytotoxic activity. Thus, high cytotoxic activity (e.g., T-cell mediated tumor cell death) is observed with a decreased EC50 or half-maximal effective concentration value. Bispecific Antigen-Binding Molecules

[00152] The antibodies of the present invention may be monospecific, bispecific, or multispecific. Multispecific antibodies may be specific for different epitopes of a target polypeptide or may contain antigen-binding domains. Petition 870260043419, dated 08 / 05 / 2026, page 67 / 353 60 / 163 specific for more than one target polypeptide. See, for example, Tutt et al., 1991, J. Immunol. 147:60-69; Kufer et al., 2004, Trends Biotechnol. 22:238-244. The monospecific anti-STEAP2 antibodies or the bispecific anti-STEAP2 / anti-CD3 antibodies of the present invention can be linked or co-expressed with another functional molecule, for example, another peptide or another protein. For example, an antibody or fragment thereof can be functionally linked (e.g., by chemical coupling, genetic fusion, non-covalent association or otherwise) to one or more other molecular entities, such as another antibody or antibody fragment, to produce a bispecific or multispecific antibody with a second or additional binding specificity.

[00153] The use of the expression “anti-CD3 antibody” or “anti-STEAP2 antibody” herein is intended to include both monospecific anti-CD3 or anti-STEAP2 antibodies, as well as bispecific antibodies comprising a CD3-binding arm and a STEAP2-binding arm. Thus, the present invention includes bispecific antibodies in which one arm of an immunoglobulin binds human CD3 and the other arm of the immunoglobulin is specific for human STEAP2. The CD3-binding arm may comprise any of the amino acid sequences of HCVR / LCVR or CDR as set forth in Tables 1, 9, 11, 12, 15 and 17 herein.

[00154] In certain embodiments, the CD3-binding arm binds to human CD3 and induces activation of human T cells. In certain embodiments, the CD3-binding arm binds weakly to human CD3 and induces activation of human T cells. In other embodiments, the CD3-binding arm binds weakly to human CD3 and induces death of antigen-expressing tumor-associated cells in the context of a bispecific or multispecific antibody. In other embodiments, the CD3-binding arm binds or associates weakly with human and CD3. Petition 870260043419, dated 08 / 05 / 2026, p. 68 / 353 61 / 163 cynomolgus (monkey), however the binding interaction is not detectable by in vitro assays known in the art. The STEAP2 binding arm may comprise any of the amino acid sequences of HCVR / LCVR or CDR as set out in Table 1.

[00155] According to certain exemplary embodiments, the present invention includes bispecific antigen-binding molecules that specifically bind CD3 and STEAP2. Such molecules may be referred to herein as, for example, bispecific “anti-CD3 / anti-STEAP2” or “anti-CD3xSTEAP2” or “CD3xSTEAP2” molecules, or other similar terminology (e.g., anti-STEAP2 / anti-CD3).

[00156] The term “STEAP2”, as used herein, refers to human STEAP2 protein, unless specified as being from a non-human species (e.g., “mouse STEAP2”, “monkey STEAP2”, etc.). The human STEAP2 protein has the amino acid sequence shown in SEQ ID NO:1899.

[00157] The bispecific antigen-binding molecules mentioned above that specifically bind CD3 and STEAP2 may comprise an anti-CD3 antigen-binding molecule that binds CD3 with a weak binding affinity, such as exhibiting a KD greater than about 40 nM, as measured by an in vitro affinity binding assay. In some cases, the CD3-binding arm binds CD3 with a KD or EC50 greater than about 100 nM, greater than about 200 nM, greater than about 300 nM, greater than about 400 nM, greater than about 500 nM, or greater than about 1 μM (e.g., as measured in a surface plasmon resonance assay). In some cases, the first antigen-binding domain specifically binds CD3 (e.g., either or both human CD3 or cynomolgus CD3 with weak affinity or no measurable affinity).

[00158] As used here, the expression “binding molecule to Petition 870260043419, dated 08 / 05 / 2026, p. 69 / 353 62 / 163 antigen” means a protein, a polypeptide, or a molecular complex comprising or consisting of at least one complementarity-determining region (CDR) that alone, or in combination with one or more additional CDRs and / or structural regions (FRs), specifically binds to a particular antigen. In certain embodiments, an antigen-binding molecule is an antibody or a fragment of an antibody, as those terms are defined elsewhere herein.

[00159] As used herein, the expression “bispecific antigen-binding molecule” means a protein, polypeptide, or molecular complex comprising at least one first antigen-binding domain and a second antigen-binding domain. Each antigen-binding domain within the bispecific antigen-binding molecule comprises a CDR that alone, or in combination with one or more additional CDRs and / or FRs, specifically binds to a particular antigen. In the context of the present invention, the first antigen-binding domain specifically binds to a first antigen (e.g., CD3) and the second antigen-binding domain specifically binds to a distinct second antigen (e.g., STEAP2).

[00160] In certain exemplary embodiments of the present invention, the bispecific antigen-binding molecule is a bispecific antibody. Each antigen-binding domain of a bispecific antibody comprises a heavy chain variable domain (HCVR) and a light chain variable domain (LCVR). In the context of a bispecific antigen-binding molecule comprising a first and a second antigen-binding domain (e.g., a bispecific antibody), the CDRs of the first antigen-binding domain may be designated with the prefix “A1” and the CDRs of the second antigen-binding domain may be designated with the prefix “A2”. Petition 870260043419, dated 08 / 05 / 2026, page 70 / 353 63 / 163 prefix “A2”. Thus, the CDRs of the first antigen-binding domain can be referred to here as A1-HCDR1, A1-HCDR2 and A1-HCDR3; and the CDRs of the second antigen-binding domain can be referred to here as A2-HCDR1, A2-HCDR2 and A2-HCDR3.

[00161] The first antigen-binding domain and the second antigen-binding domain can be directly or indirectly connected to each other to form a bispecific antigen-binding molecule of the present invention. Alternatively, the first antigen-binding domain and the second antigen-binding domain can each be connected to a separate multimerization domain. The association of one multimerization domain with another multimerization domain facilitates the association between the two antigen-binding domains, thereby forming a bispecific antigen-binding molecule. As used herein, a “multimerization domain” is any macromolecule, protein, polypeptide, peptide, or amino acid that has the ability to associate with a second multimerization domain of the same or similar structure or constitution.For example, a multimerization domain can be a polypeptide comprising an immunoglobulin CH3 domain. A non-limiting example of a multimerization component is an Fc portion of an immunoglobulin (comprising a CH2-CH3 domain), for example, an Fc domain of an IgG selected from IgG1, IgG2, IgG3, and IgG4 isotypes, as well as any allotype within each isotype group.

[00162] Bispecific antigen-binding molecules of the present invention will typically comprise two multimerization domains, for example, two Fc domains, each of which is individually part of a separate antibody heavy chain. The first and second multimerization domains may be of the same IgG isotype, such as, for example, IgG1 / IgG1, IgG2 / IgG2, Petition 870260043419, dated 08 / 05 / 2026, page 71 / 353 64 / 163 IgG4 / IgG4. Alternatively, the first and second multimerization domains may be of different IgG isotypes, such as, for example, IgG1 / IgG2, IgG1 / IgG4, IgG2 / IgG4, etc.

[00163] In certain embodiments, the multimerization domain is an Fc fragment or an amino acid sequence of 1 to about 200 amino acids in length containing at least one cysteine ​​residue. In other embodiments, the multimerization domain is a cysteine ​​residue or a short cysteine-containing peptide. Other multimerization domains include peptides or polypeptides comprising or consisting of a leucine zipper, a helix-loop motif, or a spiral-coil motif.

[00164] Any bispecific antibody format or technology can be used to make the bispecific antigen-binding molecules of the present invention. For example, an antibody or fragment thereof having a first antigen-binding specificity can be functionally linked (e.g., by chemical coupling, gene fusion, non-covalent association, or otherwise) to one or more other molecular entities, such as another antibody or antibody fragment having a second antigen-binding specificity, to produce a bispecific antigen-binding molecule. Specific exemplary bispecific formats that can be used in the context of the present invention include, without limitation, for example, bispecific or scFv-based formats, IgG-scFv fusions, dual variable domain (DVD)-Ig, Quadrome, knobs-into-holes type packaging, common light chain (e.g., common light chain with knobs-into-holes, etc.).), CrossMab, CrossFab, (SEED)body, leucine zipper, Duobody, IgG1 / IgG2, (DAF)Dual-action Fab IgG and bispecific Mab2 formats (see, for example, Klein et al. 2012, mAbs 4:6, 1-11 and references cited therein for a review of the previous formats). Petition 870260043419, dated 08 / 05 / 2026, p. 72 / 353 65 / 163

[00165] In the context of bispecific antigen-binding molecules of the present invention, the multimerization domains, for example, Fc domains, may comprise one or more amino acid changes (e.g., insertions, deletions, or substitutions) compared to the naturally occurring wild-type version of the Fc domain. For example, the invention includes bispecific antigen-binding molecules comprising one or more modifications to the Fc domain that result in a modified Fc domain having a modified (e.g., enhanced or diminished) binding interaction between Fc and FcRn. In one embodiment, the bispecific antigen-binding molecule comprises a modification in a CH2 or CH3 region, wherein the modification increases the affinity of the Fc domain to FcRn in an acidic environment (e.g., in an endosome where the pH ranges from about 5.5 to about 6.0).Non-limiting examples of such Fc modifications include, for example, a modification at position 250 (e.g., E or Q); 250 and 428 (e.g., L or F); 252 (e.g., L / Y / F / W or T), 254 (e.g., S or T) and 256 (e.g., S / R / Q / E / D or T); or a modification at position 428 and / or 433 (e.g., L / R / S / P / Q or K) and / or 434 (e.g., H / F or Y); or a modification at position 250 and / or 428; or a modification at position 307 or 308 (e.g., 308F, V308F) and 434. In one embodiment, the modification comprises a 428L modification (e.g., M428L) and a 434S modification (e.g., N434S); a 428L, 259I (e.g., V259I) and 308F (e.g., V308F) modification; a 433K (e.g., H433K) and a 434 (e.g., 434Y) modification; a 252, 254 and 256 (e.g., 252Y, 254T and 256E) modification; a 250Q and 428L (e.g., T250Q and M428L) modification; and a 307 and / or 308 (e.g., 308F or 308P) modification.

[00166] The present invention also includes molecules for binding to Petition 870260043419, dated 08 / 05 / 2026, p. 73 / 353 66 / 163 Bispecific antigens comprising a first CH3 domain and a second CH3 domain of Ig, wherein the first and second CH3 domains of Ig differ from each other by at least one amino acid and wherein at least one amino acid difference reduces the binding of the bispecific antibody to Protein A compared with a bispecific antibody lacking the amino acid difference. In one embodiment, the first CH3 domain of Ig binds to Protein A and the second CH3 domain of Ig contains a mutation that reduces or abolishes binding to Protein A, such as an H95R modification (by exon numbering IMGT; H435R by exon numbering EU). The second CH3 may further comprise a Y96F modification (by exon numbering IMGT; Y436F by exon numbering EU). See, for example, US Patent 8,586,713.Additional modifications that may be found within the second CH3 include: D16E, L18M, N44S, K52N, V57M, and V82I (by IMGT; D356E, L358M, N384S, K392N, V397M, and V422I by EU) in the case of IgG1 antibodies; N44S, K52N, and V82I (IMGT; N384S, K392N, and V422I by EU) in the case of IgG2 antibodies; and Q15R, N44S, K52N, V57M, R69K, E79Q, and V82I (by IMGT; Q355R, N384S, K392N, V397M, R409K, E419Q, and V422I by EU) in the case of IgG4 antibodies.

[00167] In certain embodiments, the Fc domain may be chimeric, combining Fc sequences derived from more than one immunoglobulin isotype. For example, a chimeric Fc domain may comprise part or all of a CH2 sequence derived from a CH2 region of human IgG1, human IgG2, or human IgG4 and part or all of a CH3 sequence derived from a human IgG1, human IgG2, or human IgG4. A chimeric Fc domain may also contain a chimeric hinge region. For example, a chimeric hinge may comprise a “top hinge” sequence derived from a hinge region of human IgG1, human IgG2, or human IgG4 combined with a sequence of Petition 870260043419, dated 08 / 05 / 2026, page 74 / 353 67 / 163 “lower hinge” derived from a hinge region of human IgG1, human IgG2, or human IgG4. A particular example of a chimeric Fc domain that can be included in any of the antigen-binding molecules set forth herein comprises, from the N-terminus to the C-terminus: [IgG4 CH1] - [IgG4 upper hinge] - [IgG2 lower hinge] - [IgG4 CH2] - [IgG4CH3]. Another particular example of a chimeric Fc domain that can be included in any of the antigen-binding molecules set forth herein comprises, from the N-terminus to the C-terminus: [IgG1 CH1] - [IgG1 upper hinge] - [IgG2 lower hinge] - [IgG4 CH2] - [IgG1 CH3]. These and other examples of chimeric Fc domains that can be included in any of the antigen-binding molecules of the present invention are described in US publication 2014 / 0243504, published August 28, 2014, which is incorporated herein in its entirety.Chimeric Fc domains, having these general structural arrangements and variants thereof, may have altered Fc receptor binding which, in turn, affects Fc effector function.

[00168] In certain embodiments, the invention provides an antibody heavy chain wherein the constant region of the heavy chain (CH) region comprises an amino acid sequence at least 95%, at least 96%, at least 97%, at least 98%, at least 99% identical to any one of SEQ ID NO: 1911, SEQ ID NO: 1912, SEQ ID NO: 1913, SEQ ID NO: 1914, SEQ ID NO: 1915, SEQ ID NO: 1916, SEQ ID NO: 1917, SEQ ID NO: 1918, SEQ ID NO: 1919 or SEQ ID NO: 1920. In some embodiments, the constant region of the heavy chain (CH) comprises an amino acid sequence selected from the group consisting of SEQ ID NO: 1911, SEQ ID NO: 1912, SEQ ID NO: 1913, SEQ ID NO: 1914, SEQ ID NO: 1915, SEQ ID NO: 1916, SEQ ID NO: 1917, SEQ ID NO: 1918, SEQ ID NO: 1919 and SEQ ID NO: 1920.

[00169] In other embodiments, the invention provides a chain Petition 870260043419, dated 08 / 05 / 2026, p. 75 / 353 68 / 163 heavy antibody in which the Fc domain comprises an amino acid sequence that is at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identical to any of SEQ ID NO: 1921, SEQ ID NO: 1922, SEQ ID NO: 1923, SEQ ID NO: 1924, SEQ ID NO: 1925, SEQ ID NO: 1926, SEQ ID NO: 1927, SEQ ID NO: 1928, SEQ ID NO: 1929, or SEQ ID NO: 1930. In some embodiments, the Fc domain comprises an amino acid sequence selected from the group consisting of SEQ ID NO: 1921, SEQ ID NO: 1922, SEQ ID NO: 1923, SEQ ID NO: 1924, SEQ ID NO: 1925, SEQ ID NO: 1926, SEQ ID NO: 1927, SEQ ID NO: 1928, SEQ ID NO: 1929 and SEQ ID NO: 1930. Sequence Variants

[00170] The bispecific antibodies and antigen-binding molecules of the present invention may comprise one or more amino acid substitutions, insertions and / or deletions in the structure and / or CDR regions of the variable heavy and light chain domains compared to the corresponding germline sequences from which the individual antigen-binding domains were derived. Such mutations can be readily determined by comparing the amino acid sequences disclosed herein to available germline sequences, for example, from public antibody sequence databases.The antigen-binding molecules of the present invention may comprise antigen-binding domains that are derived from any of the amino acid sequences disclosed herein, wherein one or more amino acids within one or more structure and / or CDR regions are mutated to the corresponding residue(s) of the germline sequence from which the antibody was derived or to the corresponding residue(s) of another human germline sequence, or to a conservative amino acid substitution of the germline residue(s). Petition 870260043419, dated 08 / 05 / 2026, p. 76 / 353 69 / 163 corresponding (such sequence changes are collectively referred to herein as “germline mutations”). A person skilled in the art, beginning with the sequences of variable heavy and light chain regions disclosed herein, can readily produce numerous antibodies and antigen-binding fragments thereof comprising one or more individual germline mutations or combinations thereof. In certain embodiments, all framework and / or CDR residues within the VH and / or VL domains mutate back to the residues found in the original germline sequence from which the antigen-binding domain was originally derived.In other embodiments, only certain residues mutate back to the original germline sequence, for example, only the mutated residues found in the first 8 amino acids of FR1 or the last 8 amino acids of FR4, or only the mutated residues found in CDR1, CDR2, or CDR3. In other embodiments, one or more of the structure and / or CDR residues mutate to the corresponding residue (or residues) of a different germline sequence (i.e., a germline sequence that is different from the germline sequence from which the antigen-binding domain was originally derived).Furthermore, antigen-binding domains can contain any combination of two or more germline mutations within the structure and / or CDR regions, for example, where certain individual residues mutate to the corresponding residue of a given germline sequence while some other residues that are different from the original germline sequence are retained or mutate to the corresponding residue of a different germline sequence. Petition 870260043419, dated 08 / 05 / 2026, page 77 / 353 70 / 163 Once obtained, antigen-binding domains containing one or more germline mutations can be easily tested for one or more desired properties, such as improved binding specificity, higher binding affinity, enhanced or amplified antagonistic or agonistic biological properties (as the case may be), reduced immunogenicity, etc. Bispecific antigen-binding molecules comprising one or more antigen-binding domains obtained in this manner are generally encompassed within the present invention.

[00171] The present invention also includes antigen-binding molecules in which one or both antigen-binding domains comprise variants of any of the HCVR, LCVR, and / or CDR amino acid sequences disclosed herein having one or more conservative substitutions. For example, the present invention includes antigen-binding molecules comprising an antigen-binding domain having HCVR, LCVR, and / or CDR amino acid sequences with, for example, 10 or fewer, 8 or fewer, 6 or fewer, 4 or fewer, etc. conservative amino acid substitutions with respect to any of the HCVR, LCVR, and / or CDR amino acid sequences described herein. A “conservative amino acid substitution” is one in which an amino acid residue is replaced by another amino acid residue having a side chain (R group) with similar chemical properties (e.g., charge or hydrophobicity).In general, a conservative amino acid substitution will not substantially change the functional properties of a protein. Examples of amino acid groups that have side chains with similar chemical properties include (1) aliphatic side chains: glycine, alanine, valine, leucine, and isoleucine; (2) aliphatic hydroxyl side chains: serine and threonine; (3) amide-containing side chains: asparagine and glutamine; (4) side chains. Petition 870260043419, dated 08 / 05 / 2026, p. 78 / 353 71 / 163 aromatic: phenylalanine, tyrosine, and tryptophan; (5) basic side chains: lysine, arginine, and histidine; (6) acidic side chains: aspartate and glutamate; and (7) sulfur-containing side chains: cysteine ​​and methionine. Preferred conservative amino acid substitution groups are: valine-leucine-isoleucine, phenylalanine-tyrosine, lysine-arginine, alanine-valine, glutamate-aspartate, and asparagine-glutamine. Alternatively, a conservative substitution is any change having a positive value in the PAM250 log-probability matrix disclosed in Gonnet et al. (1992) Science 256: 1443-1445, incorporated here by reference. A "moderately conservative" substitution is any change having a non-negative value in the PAM250 log-probability matrix.

[00172] The present invention also includes antigen-binding molecules comprising an antigen-binding domain with an amino acid sequence of HCVR, LCVR and / or CDR that is substantially identical to any of the HCVR, LCVR and / or CDR amino acid sequences disclosed herein. The term “substantial identity” or “substantially identical”, referring to an amino acid sequence, means that two amino acid sequences, when optimally aligned, such as by GAP or BESTFIT programs using default range weights, share at least 95% sequence identity, even more preferably at least 98% or 99% sequence identity. Preferably, the residue positions that are not identical are different by conservative amino acid substitutions.In cases where two or more amino acid sequences differ from each other by conservative substitutions, the percentage of sequence identity or degree of similarity can be adjusted upward to correct for the conservative nature of the substitution. Methods for making this adjustment are well known to those skilled in the art. See, for example, Pearson. Petition 870260043419, dated 08 / 05 / 2026, p. 79 / 353 72 / 163 (1994) Methods Mol. Biol. 24: 307-331, incorporated herein by reference.

[00173] Sequence similarity for polypeptides, also referred to as sequence identity, is typically measured using sequence analysis software. Protein analysis software matches similar sequences using similarity measures attributed to various substitutions, deletions, and other modifications, including conservative amino acid substitutions. For example, the GCG software contains programs, such as Gap and Bestfit, that can be used with standard parameters to determine sequence homology or sequence identity between closely related polypeptides, such as homologous polypeptides from different species of organisms or between a wild-type protein and a wild-type mutain. See, for example, GCG Version 6.1.Polypeptide sequences can also be compared using FASTA using default or recommended parameters, a program in GCG Version 6.1. FASTA (e.g., FASTA2 and FASTA3) provides alignments and percentage of sequence identity of the best overlap regions between query and search sequences (Pearson (2000) supra). Another preferred algorithm when a sequence of the invention is compared to a database containing a large number of sequences from different organisms is the BLAST computer program, especially BLASTP or TBLASTN, using default parameters. See, for example, Altschul et al. (1990) J. Mol. Biol. 215: 403-410 and Altschul et al. (1997) Nucleic Acids Res. 25:3389402, each incorporated herein by reference. pH-Dependent Bonding

[00174] The present invention includes anti-STEAP2 antibodies and bispecific anti-CD3 / anti-STEAP2 antigen-binding molecules with pH-dependent binding characteristics. For example, an anti-STEAP2 antibody of the present invention may exhibit binding. Petition 870260043419, dated 08 / 05 / 2026, p. 80 / 353 73 / 163 reduced to STEAP2 at acidic pH compared to neutral pH. Alternatively, anti-STEAP2 antibodies of the invention may exhibit enhanced binding to STEAP2 at acidic pH compared to neutral pH. The term “acidic pH” includes pH values ​​less than about 6.2, for example, about 6.0, 5.95, 5.9, 5.85, 5.8, 5.75, 5.7, 5.65, 5.6, 5.55, 5.5, 5.45, 5.4, 5.35, 5.3, 5.25, 5.2, 5.15, 5.1, 5.05, 5.0 or less. As used herein, the term “neutral pH” means a pH of about 7.0 to about 7.4. The term "neutral pH" includes pH values ​​of approximately 7.0, 7.05, 7.1, 7.15, 7.2, 7.25, 7.3, 7.35, and 7.4.

[00175] In certain cases, “reduced binding ... at acidic pH compared to neutral pH” is expressed in terms of a ratio of the KD value of the antibody binding to its antigen at acidic pH to the KD value of the antibody binding to its antigen at neutral pH (or vice versa). For example, an antibody or antigen-binding fragment thereof may be considered as exhibiting “reduced STEAP2 binding at acidic pH compared to neutral pH” for the purposes of the present invention if the antibody or antigen-binding fragment thereof exhibits an acidic / neutral KD ratio of about 3.0 or greater. In certain exemplary embodiments, the acid / neutral KD ratio for an antibody or antigen-binding fragment of the present invention may be about 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10.0, 10.5, 11.0, 11.5, 12.0, 12.5, 13.0, 13.5, 14.0, 14.5, 15.0, 20.0, 25.0, 30.0, 40.0, 50.0, 60.0, 70.0, 100.0 or greater.

[00176] Antibodies with pH-dependent binding characteristics can be obtained, for example, by screening a population of antibodies for reduced (or enhanced) binding to a particular antigen at acidic pH compared to neutral pH. Additionally, modifications of the antigen-binding domain at the amino acid level can yield antibodies with pH-dependent characteristics. For example, by replacing one or more amino acids in a binding domain to Petition 870260043419, dated 08 / 05 / 2026, page 81 / 353 74 / 163 antigen (e.g., within a CDR) by a histidine residue, an antibody with reduced antigen binding can be obtained at acidic pH compared to neutral pH. Antibodies Comprising Fc Variants

[00177] According to certain embodiments of the present invention, anti-STEAP2 antibodies and bispecific anti-CD3 / anti-STEAP2 antigen-binding molecules are provided comprising an Fc domain comprising one or more mutations that enhance or diminish the binding of the antibody to the FcRn receptor, for example, at acidic pH compared to neutral pH. For example, the present invention includes antibodies comprising a mutation in the CH2 or CH3 region of the Fc domain, wherein the mutation(s) increase(s) the affinity of the Fc domain for FcRn in an acidic environment (for example, in an endosome where the pH ranges from about 5.5 to about 6.0). Such mutations may result in an increased serum half-life of the antibody when administered to an animal.Non-limiting examples of such Fc modifications include, for example, a modification at position 250 (e.g., E or Q); 250 and 428 (e.g., L or F); 252 (e.g., L / Y / F / W or T), 254 (e.g., S or T) and 256 (e.g., S / R / Q / E / D or T); or a modification at position 428 and / or 433 (e.g., H / L / R / S / P / Q or K) and / or 434 (e.g., H / F or Y); or a modification at position 250 and / or 428; or a modification at position 307 or 308 (e.g., 308F, V308F) and 434. In one embodiment, the modification comprises a 428L modification (e.g., M428L) and a 434S modification (e.g., N434S); a modification 428L, 259I (e.g., V259I) and 308F (e.g., V308F); a modification 433K (e.g., H433K) and a modification 434 (e.g., 434Y); a modification 252, 254 and 256 (e.g., 252Y, 254T and 256E); a modification 250Q and 428L (e.g., T250Q and M428L); and a modification 307 and / or 308 (e.g., Petition 870260043419, dated 08 / 05 / 2026, page 82 / 353 75 / 163 example, 308F or 308P).

[00178] For example, the present invention includes anti-STEAP2 antibodies and bispecific anti-CD3 / anti-STEAP2 antigen-binding molecules comprising one or more pairs or groups of mutations selected from the group consisting of: 250Q and 248L (e.g., T250Q and M248L); 252Y, 254T and 256E (e.g., M252Y, S254T and T256E); 428L and 434S (e.g., M428L and N434S); and 433K and 434F (e.g., H433K and N434F). All possible combinations of the preceding Fc domain mutations, and other mutations within the antibody variable domains disclosed herein, are contemplated within the scope of the present invention. Biological Characteristics of Antibodies and Bispecific Antigen-Binding Molecules

[00179] The present invention includes antibodies and antigen-binding fragments thereof that bind human STEAP2 with high affinity (e.g., sub-nanomolar KD values).

[00180] The present invention also includes bispecific anti-CD3 / anti-STEAP2 antigen-binding molecules which inhibit tumor growth in immunocompromised mice bearing human prostate cancer xenografts. (see, for example, Example 5).

[00181] The present invention includes antibodies and antigen-binding fragments thereof that bind human CD3 with high affinity. The present invention also includes antibodies and antigen-binding fragments thereof that bind human CD3 with medium or low affinity depending on the therapeutic context and the particular target properties that are desired. For example, in the context of a bispecific antigen-binding molecule, where one arm binds CD3 and the other arm binds a target antigen (e.g., STEAP2), it may be desirable that the antigen-binding arm of Petition 870260043419, dated 08 / 05 / 2026, p. 83 / 353 The 76 / 163 target arm binds the target antigen with high affinity, while the anti-CD3 arm binds CD3 with only moderate or low affinity. In this way, preferential targeting of the antigen-binding molecule to cells expressing the target antigen can be achieved, while avoiding general / non-targeted CD3 binding and the consequent adverse side effects associated with it.

[00182] The present invention includes bispecific antigen-binding molecules (e.g., bispecific antibodies) that are capable of simultaneously binding to human CD3 and a human STEAP2. The binding arm that interacts with cells expressing CD3 may have weak to undetectable binding, as measured in a suitable in vitro binding assay. The extent to which a bispecific antigen-binding molecule binds cells expressing CD3 and / or STEAP2 can be assessed by fluorescence-activated cell sorting (FACS).

[00183] The present invention also includes antibodies, antigen-binding fragments and bispecific antibodies thereof that bind to cells and cell lines expressing STEAP2 (e.g., CA-2 cells), with an EC50 value between about 1 nM and 50 nM, as determined using a FACS binding assay as set out in Example 2 or a substantially similar assay. In certain embodiments, antibodies, antigen-binding fragments, and bispecific antibodies thereof that bind cells and cell lines expressing STEAP2 (e.g., CA-2 cells), with an EC50 value of about 50 nM, to about 40 nM, to about 30 nM, to about 20 nM, to about less than about 15 nM, to about 10 nM, to about 5 nM, to about 4 nM, to about 3 nM, or to about 2 nM, to about 1 nM, as determined using a FACS binding assay as set forth in Example 2 or a substantially similar assay. Petition 870260043419, dated 08 / 05 / 2026, p. 84 / 353 77 / 163

[00184] The present invention includes antibodies, antigen-binding fragments and bispecific antibodies thereof that bind human CD3 with weak (i.e., low) affinity or even no detectable affinity. According to certain embodiments, the present invention includes antibodies and antibody antigen-binding fragments that bind human CD3 (e.g., at 37°C) with a KD of less than about 11 nM, as measured by surface plasmon resonance. In certain embodiments, the antibodies or antigen-binding fragments of the present invention bind CD3 with a KD greater than about 15 nM, greater than about 20 nM, greater than about 25 nM, greater than about 30 nM, greater than about 35 nM, greater than about 40 nM, greater than about 45 nM, greater than about 50 nM, greater than about 55 nM, greater than about 60 nM, greater than about 65 nM, greater than about 70 nM, greater than about 75 nM, at least 80 nM, greater than about 90 nM, greater than about 100 nM,greater than about 110 nM, at least 120 nM, greater than about 130 nM, greater than about 140 nM, greater than about 150 nM, at least 160 nM, greater than about 170 nM, greater than about 180 nM, greater than about 190 nM, greater than about 200 nM, greater than about 250 nM, greater than about 300 nM, greater than about 400 nM, greater than about 500 nM, or greater than about 1 pM, or with no detectable affinity as measured by surface plasmon resonance (e.g., mAb capture or antigen capture format) or a substantially similar assay.

[00185] The present invention includes antibodies, antigen-binding fragments and bispecific antibodies thereof that bind human monkey CD3 (i.e., cynologus) with weak (i.e., low) affinity or even no detectable affinity.

[00186] The present invention includes bispecific anti-CD3 / anti-STEAP2 antigen-binding molecules that bind and are internalized Petition 870260043419, dated 08 / 05 / 2026, p. 85 / 353 78 / 163 by cells expressing human STEAP2 (e.g., CA-2 cells), as measured by an assay format as defined by Example 3 herein or a substantially similar assay. The present invention includes bispecific anti-CD3 / anti-STEAP2 antigen-binding molecules that are specific for binding to human STEAP2. In certain embodiments, the bispecific anti-CD3 / anti-STEAP2 antigen-binding molecules of the present invention bind transiently expressed human STEAP2 on HEK293 cells, as measured by an assay format as defined by Example 3 herein or a substantially similar assay. In certain embodiments, the bispecific anti-CD3 / anti-STEAP2 antigen-binding molecules of the present invention do not bind transiently expressed human STEAP1, human STEAP2, or human STEAP4 on HEK293 cells, as measured by an assay format as defined by Example 3 herein or a substantially similar assay.

[00187] The present invention includes bispecific anti-CD3 / anti-STEAP2 antigen-binding molecules that are capable of inhibiting C4-2 tumor growth (see, for example, Example 5). For example, according to certain embodiments, bispecific anti-CD3 / anti-STEAP2 antigen-binding molecules are provided, wherein a single administration, for example, at a dose of about 0.1 mg / kg or about 0.01 mg / kg) causes a reduction in tumor size compared to animals to which a bispecific isotype control antibody was administered, when measured 46 days post-tumor implantation, as detected in an individual using standard gauge measurement methods, for example, as set out in Example 5 herein.

[00188] The present invention also includes anti-STEAP2 antibody-drug conjugates which inhibit tumor growth in STEAP2-positive prostate cancer xenograft models in vivo. Petition 870260043419, dated 08 / 05 / 2026, p. 86 / 353 79 / 163 (see, for example, Example 7 or a substantially similar assay). In certain embodiments, anti-STEAP2 antibody-drug conjugates with Compound 7 are provided, wherein a dose of 10, 20, or 40 mg / kg administered on day 13 after tumor implantation inhibits C4-2 tumor growth in STEAP2-positive prostate cancer xenograft models in vivo. In certain embodiments, anti-STEAP2 antibody-drug conjugates with Compound 7 are provided, wherein a dose of 5 or 20 mg / kg administered on day 14 after implantation inhibits C4-2 tumor growth in STEAP2-positive prostate cancer xenograft models in vivo. In certain embodiments, anti-STEAP2 antibody-drug conjugates with Compound 7 are provided, wherein a dose of 150 pg / kg administered on day 17 after implantation inhibits C4-2 tumor growth in prostate cancer xenograft models. positive STEAP2 in vivo.In other embodiments, anti-STEAP2 antibody-drug conjugates with Compound 60 are provided, where a dose of at least 2.5 pg / kg administered on day 29 after implantation inhibits C4-2 tumor growth in STEAP2-positive prostate cancer xenograft models in vivo. Epitope Mapping and Related Technologies

[00189] The epitope on CD3 and / or STEAP2 to which the antigen-binding molecules of the present invention bind may consist of a single contiguous sequence of 3 or more amino acids (e.g., 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more) of a CD3 or STEAP2 protein. Alternatively, the epitope may consist of a plurality of non-contiguous amino acids (or amino acid sequences) of CD3 or STEAP2. The antibodies of the invention may interact with amino acids contained in a single CD3 chain (e.g., CD3-epsilon, CD3-delta, or CD3-gamma), or they may interact with amino acids in two or more different CD3 chains. The term Petition 870260043419, dated 08 / 05 / 2026, p. 87 / 353 80 / 163 “Epitope,” as used herein, refers to an antigenic determinant that interacts with a specific antigen-binding site in the variable region of an antibody molecule known as a paratope. A single antigen may have more than one epitope. Thus, different antibodies may bind to different areas of an antigen and may have different biological effects. Epitopes can be either conformational or linear. A conformational epitope is produced by spatially juxtaposed amino acids from different segments of the linear polypeptide chain. A linear epitope is produced by adjacent amino acid residues in a polypeptide chain. Under certain circumstances, an epitope may include saccharide moieties, phosphoryl groups, or sulfonyl groups in the antigen.

[00190] Several techniques known to those skilled in the art can be used to determine whether an antigen-binding domain of an antibody “interacts with one or more amino acids” within a polypeptide or protein. Exemplary techniques include, for example, routine cross-blocking assays, such as those described in Antibodies, Harlow and Lane (Cold Spring Harbor Press, Cold Spring Harb., NY), alanine scan mutational analysis, peptide blot analysis (Reineke, 2004, Methods Mol Biol 248:443-463), and peptide cleavage analysis. Additionally, methods such as epitope excision, epitope extraction, and chemical modification of antigens can be employed (Tomer (2000), Protein Science 9: 487-496). Another method that can be used to identify the amino acids within a polypeptide with which an antibody's antigen-binding domain interacts is hydrogen / deuterium exchange detected by mass spectrometry.In general terms, the hydrogen / deuterium exchange method involves labeling the protein of interest with deuterium, followed by the binding of the antibody to the deuterium-labeled protein. Then, the complex... Petition 870260043419, dated 08 / 05 / 2026, page 88 / 353 81 / 163 The protein / antibody is transferred to water to allow hydrogen-deuterium exchange to occur at all residues except those protected by the antibody (which remain labeled with deuterium). After antibody dissociation, the target protein is subjected to protease cleavage analysis and mass spectrometry, thus revealing the deuterium-labeled residues that correspond to the specific amino acids with which the antibody interacts. See, for example, Ehring (1999) Analytical Biochemistry 267(2):252-259; Engen and Smith (2001) Anal. Chem. 73:256A-265A. X-ray crystallography of the antigen / antibody complex can also be used for epitope mapping purposes.

[00191] The present invention further includes anti-STEAP2 antibodies that bind to the same epitope as any of the specific exemplary antibodies described herein (for example, antibodies comprising any of the amino acid sequences as set forth in Table 1 herein). Similarly, the present invention also includes anti-STEAP2 antibodies that compete for STEAP2 binding with any of the specific exemplary antibodies described herein (for example, antibodies comprising any of the amino acid sequences as set forth in Table 1 herein).

[00192] The present invention also includes bispecific antigen-binding molecules comprising a first antigen-binding domain that specifically binds human CD3 and / or cynomolgus CD3 with low or detectable binding affinity and a second antigen-binding domain that specifically binds human STEAP2, wherein the first antigen-binding domain binds to the same epitope on CD3 as any of the exemplary CD3-specific antigen-binding domains described herein and / or wherein the second antigen-binding domain binds to the same epitope on STEAP2 as any of the antigen-binding domains described herein. Petition 870260043419, dated 08 / 05 / 2026, page 89 / 353 82 / 163 specific STEAP2 examples described here.

[00193] Similarly, the present invention also includes bispecific antigen-binding molecules comprising a first antigen-binding domain that specifically binds human CD3 and a second antigen-binding domain that specifically binds human STEAP2, wherein the first antigen-binding domain competes for binding to CD3 with any of the specific exemplary CD3 antigen-binding domains described herein and / or wherein the second antigen-binding domain competes for binding to STEAP2 with any of the specific exemplary STEAP2 antigen-binding domains described herein.

[00194] It can be easily determined whether a particular antigen-binding molecule (e.g., antibody) or antigen-binding domain of the same binds to the same epitope or competes for binding with a reference antigen-binding molecule of the present invention using routine methods known in the art. For example, to determine whether a test antibody binds to the same epitope on STEAP2 (or CD3) as a bispecific reference antigen-binding molecule of the present invention, the bispecific reference molecule is first allowed to bind to a STEAP2 protein (or CD3 protein). Then, the ability of a test antibody to bind to the STEAP2 (or CD3) molecule is evaluated.If the test antibody is able to bind to STEAP2 (or CD3) following saturation binding with the bispecific reference antigen-binding molecule, it can be concluded that the test antibody binds to a different STEAP2 (or CD3) epitope than the bispecific reference antigen-binding molecule. Conversely, if the test antibody is unable to bind to the STEAP2 (or CD3) molecule following saturation binding with the binding molecule... Petition 870260043419, dated 08 / 05 / 2026, p. 90 / 353 83 / 163 to the bispecific reference antigen, then the test antibody can bind to the same STEAP2 (or CD3) epitope as the epitope bound by the bispecific antigen-binding molecule of the invention. Further routine experimentation (e.g., peptide mutation and binding analyses) can then be performed to confirm whether the observed absence of binding of the test antibody is, in fact, due to binding to the same epitope as the bispecific reference antigen-binding molecule or whether steric blocking (or other phenomenon) is responsible for the observed lack of binding. Experiments of this type can be performed using ELISA, RIA, Biacore, flow cytometry, or any other quantitative or qualitative antibody binding assay available in the art.According to certain embodiments of the present invention, two antigen-binding proteins bind to the same (or overlap) epitope if, for example, a 1, 5, 10, 20, or 100-fold excess of one antigen-binding protein inhibits binding of the other by at least 50%, but preferably 75%, 90%, or even 99%, as measured in a competitive binding assay (see, for example, Junghans et al., Cancer Res. 1990:50:1495-1502). Alternatively, two antigen-binding proteins are considered to bind to the same epitope if essentially all amino acid mutations in the antigen that reduce or eliminate the binding of one antigen-binding protein do so. Two antigen-binding proteins are considered to have “overlapping epitopes” if only a subset of the amino acid mutations that reduce or eliminate the binding of one antigen-binding protein reduce or eliminate the binding of the other.

[00195] To determine whether an antibody or its antigen-binding domain competes for binding with a reference antigen-binding molecule, the binding methodology described above is performed in two orientations: In the first orientation, the molecule Petition 870260043419, dated 08 / 05 / 2026, page 91 / 353 In a second orientation, the test antibody is allowed to bind to a STEAP2 (or CD3) molecule under saturation conditions, followed by evaluation of the binding of the test antibody to the STEAP2 (or CD3) molecule. In a second orientation, the test antibody is allowed to bind to a STEAP2 (or CD3) molecule under saturation conditions, followed by evaluation of the binding of the reference antigen-binding molecule to the STEAP2 (or CD3) molecule. If, in both orientations, only the first (saturating) antigen-binding molecule is able to bind to the STEAP2 (or CD3) molecule, then it is concluded that the test antibody and the reference antigen-binding molecule compete for binding to STEAP2 (or CD3).As one skilled in the art will observe, an antibody that competes for binding with a reference antigen-binding molecule may not necessarily bind to the same epitope as the reference antibody, but may sterically block the binding of the reference antibody by binding to an overlapping or adjacent epitope. Preparation of Antigen-Binding Domains and Construction of Bispecific Molecules

[00196] Antigen-binding domains specific for particular antigens can be prepared by any antibody generation technology known in the art. Once obtained, two different antigen-binding domains, specific for two different antigens (e.g., CD3 and STEAP2), can be appropriately arranged relative to each other to produce a bispecific antigen-binding molecule of the present invention using routine methods. (A discussion of exemplary bispecific antibody formats that can be used to construct the bispecific antigen-binding molecules of the present invention is provided elsewhere. In certain embodiments, one or more of the individual components (e.g., heavy and light chains) of the molecules of Petition 870260043419, dated 08 / 05 / 2026, page 92 / 353 85 / 163 The multispecific antigen-binding antibodies of the invention are derived from chimeric, humanized, or fully human antibodies. The methods for making these antibodies are well known in the art. For example, one or more of the heavy and / or light chains of the bispecific antigen-binding molecules of the present invention can be prepared using VELOCIMMUNE™ technology. Using VELOCIMMUNE™ technology (or any other human antibody generation technology), high-affinity chimeric antibodies for a particular antigen (e.g., CD3 or STEAP2) are initially isolated having a human variable region and a mouse constant region. The antibodies are characterized and selected for desirable characteristics, including affinity, selectivity, epitope, etc.The mouse constant regions are replaced by a desired human constant region to generate fully human heavy and / or light chains that can be incorporated into the bispecific antigen-binding molecules of the present invention.

[00197] Genetically engineered animals can be used to make bispecific human antigen-binding molecules. For example, a genetically modified mouse can be used that is unable to rearrange and express an endogenous mouse immunoglobulin light chain variable sequence, wherein the mouse expresses only one or two human light chain variable domains encoded by human immunoglobulin sequences operationally linked to the mouse kappa constant gene at the endogenous mouse kappa locus. These genetically modified mice can be used to produce fully human bispecific antigen-binding molecules comprising two different heavy chains that associate with an identical light chain comprising a derived variable domain. Petition 870260043419, dated 08 / 05 / 2026, p. 93 / 353 86 / 163 of one of two gene segments from the variable region of the human light chain. (See, for example, US 2011 / 0195454). Fully human refers to an antibody, or antigen-binding fragment or immunoglobulin domain thereof, comprising an amino acid sequence encoded by DNA derived from a human sequence throughout the length of each polypeptide of the antibody or antigen-binding fragment or immunoglobulin domain thereof. In some cases, the fully human sequence is derived from a protein endogenous to a human. In other cases, the fully human protein or protein sequence comprises a chimeric sequence in which each component sequence is derived from the human sequence.Although not limited by any theory, chimeric proteins or chimeric sequences are generally designed to minimize the creation of immunogenic epitopes at the junctions of component sequences, for example, compared to any wild-type human immunoglobulin regions or domains. Bioequivalents

[00198] The present invention encompasses antigen-binding molecules having amino acid sequences that vary from those of the exemplary molecules described herein, but which retain the ability to bind CD3 and / or STEAP2. Such variant molecules may comprise one or more amino acid additions, deletions, or substitutions when compared to the parental sequence, but exhibit biological activity that is essentially equivalent to that of the bispecific antigen-binding molecules described.

[00199] The present invention includes antigen-binding molecules that are bioequivalent to any of the exemplary antigen-binding molecules set forth herein. Two antigen-binding proteins, or antibodies, are considered bioequivalent if, by Petition 870260043419, dated 08 / 05 / 2026, p. 94 / 353 87 / 163 For example, they are pharmaceutical equivalents or pharmaceutical alternatives whose rate and extent of absorption do not show a significant difference when administered at the same molar dose under similar experimental conditions, whether single dose or multiple dose. Some antigen-binding proteins will be considered pharmaceutical equivalents or alternatives if they are equivalent in the extent of their absorption but not in their rate of absorption and may still be considered bioequivalent because these differences in the rate of absorption are intentional and are reflected in the labeling, are not essential for achieving effective drug concentrations in the body, for example, in chronic use, and are considered medically insignificant for the particular drug product studied.

[00200] In one embodiment, two antigen-binding proteins are bioequivalent if there is no clinically significant difference in their safety, purity, and potency.

[00201] In one embodiment, two antigen-binding proteins are bioequivalent if a patient can switch one or more times between the reference product and the biologic product without an expected increase in the risk of adverse effects, including a clinically significant change in immunogenicity or decreased efficacy, compared with continued therapy without such switching.

[00202] In one embodiment, two antigen-binding proteins are bioequivalent if they both act by a common mechanism or mechanisms of action for the condition or conditions of use, to the extent that such mechanisms are known.

[00203] Bioequivalence can be demonstrated by in vivo and in vitro methods. Bioequivalence measures include, for example, (a) an in vivo test in humans or other mammals in which the concentration of the antibody or its metabolites is measured in blood, plasma, serum or Petition 870260043419, dated 08 / 05 / 2026, page 95 / 353 88 / 163 another biological fluid as a function of time; (b) an in vitro test that has been correlated with and is reasonably predictive of in vivo bioavailability data in humans; (c) an in vivo test in humans or other mammals in which the appropriate acute pharmacological effect of the antibody (or its target) is measured as a function of time; and (d) in a well-controlled clinical trial that establishes the safety, efficacy, or bioavailability or bioequivalence of an antigen-binding protein.

[00204] Bioequivalent variants of the exemplary bispecific antigen-binding molecules set forth herein may be constructed, for example, by making various substitutions of residues or sequences or by deleting terminal or internal residues or sequences not required for biological activity. For example, cysteine ​​residues not essential for biological activity may be deleted or replaced with other amino acids to prevent the formation of unnecessary or incorrect intramolecular disulfide bridges by renaturation. In other contexts, bioequivalent antigen-binding proteins may include variants of the exemplary bispecific antigen-binding molecules set forth herein comprising amino acid changes that modify the glycosylation characteristics of the molecules, for example, mutations that eliminate or remove glycosylation. Species Selectivity and Species Cross-Reactivity

[00205] According to certain embodiments of the invention, antigen-binding molecules are provided that bind human CD3 but not CD3 of another species. Antigen-binding molecules are also provided that bind human STEAP2 but not STEAP2 of another species. The present invention also includes antigen-binding molecules that bind human CD3 and CD3 of one or more non-human species; and / or antigen-binding molecules that Petition 870260043419, dated 08 / 05 / 2026, p. 96 / 353 89 / 163 link human STEAP2 and STEAP2 from one or more non-human species.

[00206]

[0001] According to certain exemplary embodiments of the invention, antigen-binding molecules are provided which bind to human CD3 and / or human STEAP2 and may or may not bind, as the case may be, to one or more CD3 and / or STEAP2 from mouse, rat, guinea pig, hamster, gerbil, pig, cat, dog, rabbit, goat, sheep, cow, horse, camel, cynomolgus, marmoset, rhesus or chimpanzee. For example, in a particular exemplary embodiment of the present invention, bispecific antigen-binding molecules are provided comprising a first antigen-binding domain that binds human CD3 and cynomolgus CD3 and a second antigen-binding domain that specifically binds human STEAP2. Antibody-Drug Conjugates (ADCs)

[00207] The present invention provides antibody-drug conjugates (ADCs) comprising an anti-STEAP2 antibody or an antigen-binding fragment thereof conjugated to a therapeutic fraction, such as a cytotoxic agent, a chemotherapeutic drug, an immunosuppressant or a radioisotope. In general terms, ADCs comprise: A - [L - P]y, where A is an antigen-binding molecule, for example, an anti-STEAP2 antibody or a fragment thereof (for example, a fragment comprising at least one HCDR3 selected from any of the HCDR3 amino acid sequences listed in Table 1), L is a ligand, P is the payload or therapeutic fraction (for example, cytotoxic agent), and y is an integer from 1 to 30. In several embodiments, the ADC comprises an anti-STEAP2 antibody or an antigen-binding fragment thereof comprising the CDRs of an HCVR and an LCVR having the amino acid sequences of the SEQ ID NOs (for example, SEQ ID NOs: 2 and 10) set in Petition 870260043419, dated 08 / 05 / 2026, p. 97 / 353 90 / 163 Table 1, or specific HCVR / LCVR pairs (e.g., SEQ ID NOs: 2 / 10). In some cases, the anti-STEAP2 antibody or fragment comprises CDRs with the amino acid sequences of SEQ ID NOs (e.g., SEQ ID NOs: 4-6-8-12-14-16) established in Table 1. In some cases, the anti-STEAP2 antibody or fragment comprises an HCVR and an LCVR having the amino acid sequences of SEQ ID NOs (e.g., SEQ ID NOs: 2 and 10) established in Table 1, or specific amino acid sequence pairs (e.g., SEQ ID NOs: 2 / 10).

[00208] Cytotoxic agents include any agent that is detrimental to the growth, viability, or propagation of cells. The antigen-binding molecules or antibodies of the invention deliver these cytotoxic agents, referred to herein as “payloads,” to the target cells. Examples of cytotoxic agents and chemotherapeutic agents for forming ADCs are known in the art.

[00209] Examples of suitable cytotoxic agents and chemotherapeutic agents that can be conjugated with anti-STEAP2 antibodies according to this aspect of the invention include, for example, 1-(2-chloroethyl)-1,2-dimethanesulfonylhydrazide, 1,8-dihydroxy-bicyclo[7.3.1]trideca-4,9-dieno-2,6-di-ino-13-one, 1-desidrotestosterone, 5-fluorouracil, 6-mercaptopurine, 6-thioguanine, 9-amino-camptothecin, actinomycin D, amanitins, aminopterin, anguidin, anthracycline, anthramycin (AMC), auristatins (monomethyl auristatin E or monomethyl auristatin F), bleomycin, bussulfan, butyric acid, caliquheamicins, camptothecin, carminomycins, carmustine, cemadotins, cisplatin, colchicine, combretastatins, cyclophosphamide, cytarabine, cytochalasin B, dactinomycin, daunorrubicin, decarbazine, diacetoxypentyldoxorrubicin, dibromomanitol, di-hidróxi anthracina diona, disorrazóis, dolastatin, doxorrubicin, duocarmycin, equinomycins, eleuterobinas, emetine, epotilonas, esperamycin, estramustinas,. Petition 870260043419, 08 / 05 / 2026, pág. 98 / 353 91 / 163 ethidium bromide, etoposide, fluorouracils, geldanamycins, gramicidin D, glucocorticoids, irinotecans, leptomycins, leurosins, lidocaine, lomustine (CCNU), maitansinoids, mechlorethamine, melphalan, mercatopurines, metopterines, methotrexate, mithramycin, mitomycin, mitoxantrone, N8-acetylspermidine, podophyllotoxins, procaine, propranolol, pteridines, puromycin, rhizoxins, streptozotocin, thalisomycins, taxol, tenoposide, tetracaine, thioepa chlorambucil, tomaimycins, topotecans, tubulisin, vinblastine, vincristine, vindesine, vinorelbines and derivatives of any of the foregoing.

[00210] According to certain embodiments, the cytotoxic agent that is conjugated with an anti-STEAP2 antibody is an auristatin, such as monomethyl auristatin E (MMAE) or monomethyl auristatin F (MMAF), a tubulisin, such as TUB-OH or TUB-OMOM, a tomaimycin derivative, a dolastatin derivative, or a maytansinoid, such as DM1 or DM4. In some embodiments, the cytotoxic agent is a maytansinoid having the structure of Formula (I) including stereoisomers of the compounds of Formula (I): H OH,OCH3 ?H3CK. N o ch3(Formula I) where A is arylene or heteroarylene.

[00211] In some embodiments, A is a divalent radical of benzene, pyridine, naphthalene or quinolone, which is optionally substituted.

[00212] In some forms, A is arylene.

[00213] In some modalities, A is: Petition 870260043419, dated 08 / 05 / 2026, p. 99 / 353 92 / 163 in which: R1 is, independently, in each occurrence, alkyl, alkenyl, alkynyl, aryl, alkaryl, aralkyl, halo, heteroaryl, heterocycloalkyl, hydroxyl, cyano, nitro, ^'orA, ψδο2κA, -^-rA, or azido, where RA is an alkyl or heteroalkyl group; n is an integer from 0 to 4; m is an integer from 0 to 3; p is an integer between 0 and 6; eq is an integer from 0 to 5.

[00214] In some forms, the Formula 1 compound is selected from the group consisting of: Petition 870260043419, dated 08 / 05 / 2026, p. 100 / 353 93 / 163 Petition 870260043419, dated 08 / 05 / 2026, p. 101 / 353 94 / 163 Petition 870260043419, dated 08 / 05 / 2026, p. 102 / 353 95 / 163

[00216] In some embodiments, the maytansinoid of Formula (I) is conjugated with an anti-STEAP2 antibody or antigen-binding fragment thereof via a linker, as shown in Formula (IA) below: Petition 870260043419, dated 08 / 05 / 2026, p. 103 / 353 96 / 163 (Formula IA) where: A is arylene or heteroarylene as discussed above in relation to Formula (I); L is a ligand; BA is an anti-STEAP2 antibody or antigen-binding fragment thereof; ek is an integer from 1 to 30.

[00217] In several modalities, L is: THE 4-SP-AA1-AA2-^where: SP is a spacer; -f§are one or more links to the anti-STEAP2 antibody or a fragment thereof; AA1 is an amino acid; and AA2 is an amino acid.

[00218] In some embodiments, AA1-AA2 is: valine-citrulline, citrulline-valine, lysine-phenylalanine, phenylalanine-lysine, valine-asparagine, asparagine-valine, threonine-asparagine, asparagine-threonine, serine-asparagine, asparagine-serine, phenylalanine-asparagine, asparagine-phenylalanine, leucine-asparagine, asparagine-leucine, isoleucine-asparagine, asparagine-isoleucine, glycine-asparagine, asparagine-glycine, glutamic acid-asparagine, asparagine-glutamic acid, citrulline-asparagine, asparagine-citrulline, alanine-asparagine or Petition 870260043419, dated 08 / 05 / 2026, page 104 / 353 97 / 163 asparagine-alanine.

[00219] In some modalities, SP is: oo N-(CH2)b^O or in which: « is a link to the anti-STEAP2 antibody or a fragment thereof; eb is an integer from 2 to 8. In other modalities, L is: in which: -f« is a link to the anti-STEAP2 antibody or a fragment thereof; eb is an integer from 2 to 8.

[00220] In one embodiment, the compound of Formula (IA), including the ligand, which is linked to the anti-STEAP2 antibody or antigen-binding fragment thereof is: where « is a link to the anti-STEAP2 antibody or a fragment thereof. In some cases, this fragment is called Petition 870260043419, dated 08 / 05 / 2026, p. 105 / 353 98 / 163 “Compound 10”.

[00221] In one embodiment, the compound of Formula (IA), including the ligand, which is linked to the anti-STEAP2 antibody or antigen-binding fragment thereof is: where « is a link to the anti-STEAP2 antibody or a fragment thereof. In some cases, this fragment is called “Compound 60”.

[00222] In some embodiments, the cytotoxic agent is a maytansinoid having the structure of Formula (II) including stereoisomers of the compounds of Formula (II): (Formula II) where: A3a is an amino acid, a peptide having 2 to 20 amino acids, an alkyl, an alkynyl, an alkenyl, a cycloalkyl, an aryl, a heteroaryl, a heterocyclyl, -CR5R6-, -O-, -C(=O)-, -OC(=O)-, -C(=O)-O-, -OC(=O)-O-, -C(=O)-(CHx)p1-, -C(=O)-O-(CHx)p1-(CHx)p1-C(=O)-, -(CHx)p1-C(=O)-O-, -(O-(CH2)p2-)p3-,-((CH2)p2-O-)p3-, C(=S)-, -C(=S)-S-, -C(=S)-NH-, -SC(=S)-, -SC(=S)-S-, -S-, -SO-, -SO2-, Petition 870260043419, dated 08 / 05 / 2026, p. 106 / 353 99 / 163 -NR4-, -N(R4)-C(=O)-N(R8)-, -N(R4)-C(=O)O-, -N(R4)-C(=O)-, -C(=O)- N(R4)-, -C(=O)-N(R4)-C(=O)-, or -OC(=O)-NR4-, where alkyl, alkynyl, alkenyl, cycloalkyl, aryl, heteroaryl and heterocyclyl are optionally substituted; and p1, p2 and p3 are each independently 0 or an integer from 1 to 100; x is 0, 1 or 2; R4, R5, R6 and Rs are each independently H, either substituted or unsubstituted: alkyl, alkenyl, alkynyl, aryl, heteroaryl or heterocyclyl; and R4a is either substituted or unsubstituted: alkyl, alkenyl, alkynyl, aryl, heteroaryl, or heterocyclyl.

[00223] In some forms, the compound of Formula (II) is selected from the group consisting of: hohPch3 X OX OX<CHM Cl H3C'' N η / ^OCh ÇH3 ÇH3 Ó H3C Cl HNX Ã Y 2 o O ch3 H0HPCH3 9H3 Ο £1 H3C'' \K> z N^v^oc CH3 0' H3C Cl AX H2N Y o ch3 e H OH PCH3 nX^och33 HN Χ|Ί CH3 O H3C ci ΟΑΛγΝ^Αθ 0 ch3 , , Petition 870260043419, dated 08 / 05 / 2026, p. 107 / 353 100 / 163

[00225] In some embodiments, the maytansinoid of Formula (II) is conjugated with an anti-STEAP2 antibody or antigen-binding fragment thereof via a ligand, as shown in Formula (IIA), below: R17 BA+-Z2—AWXA^ (Formula IIA) where: BA is an anti-STEAP2 antibody or antigen-binding fragment of the same; a is an integer from 1 to 30; Z2 is represented by the following structural formula: -Z2A-Z2B-Z2C-Z2D, where Z2A, Z2B, Z2C, and Z2D are each independently absent, an amino acid, a peptide having 2 to 20 amino acids, an alkyl group, a Petition 870260043419, dated 08 / 05 / 2026, p. 108 / 353 101 / 163 alkynyl, an alkenyl, a cycloalkyl, an aryl, a heteroaryl, a heterocyclyl, -CR5R6-, -O-, -C(=O)-, -OC(=O)-, -C(=O)-O-,-OC(=O)-O-, -C(=O)-(CHx)p1, -C(=O)-O-(CHx)p1, -(CHx)p1-C(=O)-, -(CHx)p1-C(=O)-O-, (O-(CH2)p2-)p3-, -((CH2)p2-O-)p3-, -C(=S)-, -C(=S)-S-, -C(=S)-NH-, -S- C(=S)-, -SC(=S)-S-, -S-, -SO-, -SO2-, -NR4-, -N(R4)-C(=O)-N(R8)-, -N(R4)-C(=O)O-, -N(R4)-C(=O)-, C(=O)-N(R4)-, -C(=O)-N(R4)-C(=O)-, -OC(=O)-N(R4), -OC(=S)-N(R4)-, -C(=S)-N(R4)-, -N=C=S, o no N^\ -N=C=O, ο· or 0; A is a natural or unnatural amino acid, or a peptide comprising 2 to 20 amino acids; W is -O-, -S-, -CR5R6- or -NR4-; X is aryl, heteroaryl, cycloalkyl or heterocyclyl, wherein aryl, heteroaryl, cycloalkyl and heterocyclyl are optionally substituted; wherein A1, A3, and R1 are each independently an amino acid, a peptide having 2 to 20 amino acids, an alkyl, an alkynyl, an alkenyl, a cycloalkyl, an aryl, a heteroaryl, a heterocyclyl, -CR5R6-, -O-, -C(=O)-, -OC(=O)-, -C(=O)-O-, -OC(=O)-O -C(=O)-(CHx)pi-, -C(=O)-O-(CHx)pi-, -(CHx)pi-C(=O)-, -(CHx)pi-C(=O)-O -(O-(CH2)p2-)p3-, -((CH2)p2-O-)p3-, -C(=S)-, -C(=S)-S-, -SC(=S)-, -C(=S)NH-, -SC(=S)-S-, -S-, -SO-, -SO2-, -NR4-, -N(R4)-C(=O)-N(R8)-, -N(R4)C(=O)O-, -N(R4)-C(=O)-, -C(=O)-N(R4)-, -C(=O)-N(R4)-C(=O)-, or -OC(=O)-NR4, where alkyl, alkynyl, alkenyl, cycloalkyl, aryl, heteroaryl and Petition 870260043419, dated 08 / 05 / 2026, p. 109 / 353 102 / 163 heterocyclyl groups are optionally replaced; R17 is selected from the group consisting of O, S, NR18 and CR5R6; R18 is selected from the group consisting of H, alkyl, alkynyl, alkenyl, cycloalkyl, aryl, heteroaryl, heterocyclyl and acyl, in which alkyl, alkynyl, alkenyl, cycloalkyl, aryl, heteroaryl, heterocyclyl and acyl are optionally substituted; R4, R5, R6 and R8 are each independently H, either substituted or unsubstituted: alkyl, alkenyl, alkynyl, aryl, heteroaryl or heterocyclyl; R4a is a substituted or unsubstituted group: alkyl, alkenyl, alkynyl, aryl, heteroaryl, or heterocyclyl; p1, p2, and p3 are each independently 0 or an integer from 1 to 100; ex is 0, 1, or 2.

[00226] In some embodiments of Formula (IIA), A is a peptide selected from the group consisting of valine-citrulline, citrulline-valine, lysine-phenylalanine, phenylalanine-lysine, valine-asparagine, asparagine-valine, threonine-asparagine, asparagine-threonine, serine-asparagine, asparagine-serine, phenylalanine-asparagine, asparagine-phenylalanine, leucine-asparagine, asparagine-leucine, isoleucine-asparagine, asparagine-isoleucine, glycine-asparagine, asparagine-glycine, glutamic acid-asparagine, asparagine-glutamic acid, citrulline-asparagine, asparagine-citrulline, alanine-asparagine and asparagine-alanine.

[00227] In one embodiment, the compound of Formula (IIA) that is linked to the anti-STEAP2 antibody or antigen-binding fragment thereof is: Petition 870260043419, dated 08 / 05 / 2026, page 110 / 353 103 / 163 where « is a link to or a fragment of the anti-STEAP2 antibody. In some cases, this fragment is called “Compound 7”.

[00228] In some embodiments, the cytotoxic agent that is conjugated with an anti-STEAP2 antibody or fragment thereof is a pure or substantially pure DM1 diastereomer: (DM1) ey is an integer 1 to 0.

[00229] In another modality, the ADC comprises an “A” structure. - [L - P]y” where A is an anti-STEAP2 antibody or antigen-binding fragment thereof; and [L - P] is: Petition 870260043419, dated 08 / 05 / 2026, p. 111 / 353 104 / 163 a mixture of them, where y is an integer from 1 to 30, and « is a link to the anti-STEAP2 antibody or a fragment thereof.

[00230] Other maitansinoid derivatives are discussed in WO 2014 / 145090, WO2016 / 160615 and WO 2015 / 031396, each of which is hereby incorporated by reference in its entirety.

[00231] In some embodiments, the cytotoxic agent that is conjugated with an anti-STEAP2 antibody or fragment thereof is MMAE or MMAF.

[00232] Other cytotoxic agents known in the art are contemplated within the scope of the present invention including, for example, protein toxins such as ricin, C. difficile toxin, Pseudomonas exotoxin, diphtheria toxin, botulinum toxin, briodin, saporin, pokeweed toxins (i.e., phytoalkatoxin and phytolacigenin) and others such as those set forth in Sapra et al., Pharmacol. & Therapeutics, 2013, 138:452-469.

[00233] Cytotoxic agents (“payloads”) can be attached to an anti-STEAP2 antigen-binding molecule or antibody of the present invention by means of a chemical linker that covalently links the payload compound to the protein molecule (i.e., antibody). Exemplary embodiments of specific linkers are discussed above. More generally, and as used herein, the term “linker” refers to any divalent group or moiety that binds, connects, or links a binding agent (e.g., an antibody or a Petition 870260043419, dated 08 / 05 / 2026, p. 112 / 353 105 / 163 antigen-binding fragment of the same) with a payload compound set forth herein. Generally, suitable binding agent ligands for the antibody conjugates described herein are those that are sufficiently stable to exploit the circulating half-life of the antibody and, at the same time, capable of releasing their payload after antigen-mediated internalization of the conjugate. Ligands may be cleavable or non-cleavable. Cleavable ligands are ligands that are cleaved by intracellular metabolism following internalization, for example, cleavage via hydrolysis, reduction, or enzymatic reaction. Non-cleavable ligands are ligands that release a payload via lysosomal degradation of the antibody following internalization. Suitable ligands include, but are not limited to, acid-labile ligands, hydrolysis-labile ligands, enzymatically cleavable ligands, reduction-labile ligands, autoimmolating ligands, and non-cleavable ligands.Suitable ligands also include, but are not limited to, those that are or comprise peptides, glucuronides, succinimide-thioethers, polyethylene glycol (PEG) units, hydrazones, mal-caproyl units, dipeptide units, valine-citrulline units, and para-aminobenzyl (PAB) units. In some cases, the ligand is able to bind to the antibody or antigen-binding fragment via a lysine residue or a cysteine ​​residue (e.g., via cleavage of a disulfide group of the antibody or fragment, or via an engineered cysteine ​​residue in the antibody or fragment). In some cases, the ligand is able to bind to the antibody or fragment via a glutamine residue, including those derived via transglutaminase-mediated conjugation.

[00234] Exemplary ligands that can be used in the context of the present invention include ligands comprising or consisting of, for example, MC (6-maleimidocaproyl), MCC (maleimidomethylcyclohexane-1-carboxylate), MP (maleimidopropanoyl), val-cit (valine. Petition 870260043419, dated 08 / 05 / 2026, page 113 / 353 106 / 163 citrulline), val-ala (valine-alanine), ala-phe (alanine-phenylalanine), phe-lys (phenylalanine-lysine), dipeptide site in protease-cleavable ligand, PAB (p-aminobenzyloxycarbonyl), SPP (N-succinimidyl 4-(2-pyridylthio)pentanoate), SMCC (N-Succinimidyl 4-(N-maleimidomethyl)cyclohexane1-carboxylate), SIAB (N-Succinimidyl (4-iodoacetyl)aminobenzoate) and variants and combinations thereof. Additional examples of ligands that can be used in the context of the present invention are disclosed, for example, in US Patent 7,754,681 and in Ducry, Bioconjugate Chem., 2010, 21:5-13, and the references cited therein, the content of which is incorporated herein by reference in its entirety. In some cases, the ligand is or contains a self-immolating spacer, such as those discussed in Jin, et al., Bioorganic & Medicinal Chemistry, 2012, 20:3465-3469, and Wu, et al., Bioorganic & Medicinal Chemistry, 2016, 24:2697-2706.

[00235] Payloads can be attached to the antibody or anti-STEAP2 antigen-binding fragment via attachment to a particular amino acid within the antibody or antigen-binding molecule. Exemplary amino acid fixations that can be used in the context of this aspect of the invention include, for example, lysine (see, for example, US Patent 5,208,020; US 2010 / 0129314; Hollander et al., Bioconjugate Chem., 2008, 19:358-361; WO 2005 / 089808; US Patent 5,714,586; US 2013 / 0101546; and US 2012 / 0585592), cysteine ​​(see, for example, US 2007 / 0258987; WO 2013 / 055993; WO 2013 / 055990; WO 2013 / 053873; WO 2013 / 053872; WO 2011 / 130598; US 2013 / 0101546 and US Patent 7,750,116), selenocysteine ​​(see, for example, WO 2008 / 122039; and Hofer et al., Proc. Natl. Acad. Sci., USA, 2008, 105:12451-12456), formyl glycine (see, for example, Carrico et al., Nat. Chem. Biol., 2007, 3:321-322; Agarwal et al., Proc. Natl. Acad. Sci. USA, 2013, 110:46-51, and Rabuka et al., Nat.Protocols, 2012, 10: 1052-1067), non-natural amino acids (see, for example, WO 2013 / 068874 and WO 2012 / 166559) and acidic amino acids (see, for example, WO. Petition 870260043419, dated 08 / 05 / 2026, p. 114 / 353 107 / 163 2012 / 05982). The ligands can also be conjugated with an antigen-binding protein via carbohydrate attachment (see, for example, US 2008 / 0305497 and Ryan et al., Food & Agriculture Immunol., 2001, 13: 127-130) and disulfide ligands (see, for example, WO 2013 / 085925, WO 2010 / 010324, WO 2011 / 018611 and Shaunak et al., Nat. Chem. Biol., 2006, 2:312-313).

[00236] The drug-to-antibody ratio (DAR) is the average number of drugs conjugated to the antibody or antigen-binding fragment that has a significant effect on the efficacy, potency, and pharmacokinetics of the ADC. In various embodiments, the DAR is 1, 2, 3, 4, 5, 6, 7, or 8 drug molecules per antibody. In some embodiments, the DAR is 1 to 4. In certain embodiments, the DAR is 2 to 4. In some cases, the DAR is 2 to 3. In certain cases, the DAR is 3 to 4. In some embodiments, the DAR is 1 to 10, 1 to 20, or 1 to 30 (i.e., 1 to 30 drug molecules per antibody or antigen-binding fragment thereof). Therapeutic Formulation and Administration

[00237] The present invention provides pharmaceutical compositions comprising the antigen-binding molecules of the present invention. The pharmaceutical compositions of the invention are formulated with suitable carriers, excipients, and other agents to provide improved transfer, distribution, tolerability, and the like. A multitude of suitable formulations can be found in the formulary known to all pharmaceutical chemists: Remington's Pharmaceutical Sciences, Mack Publishing Company, Easton, PA. These formulations include, for example, powders, pastes, ointments, gels, waxes, oils, lipids, lipid-containing vesicles (cationic or anionic) (such as LIPOFECTIN™, Life Technologies, Carlsbad, CA), DNA conjugates, anhydrous absorption pastes, oil-in-water and water-in-oil emulsions, and carbowax emulsions. Petition 870260043419, dated 08 / 05 / 2026, page 115 / 353 108 / 163 (polyethylene glycols of various molecular weights), semi-solid gels and semi-solid mixtures containing carbowax. See also Powell et al. Compendium of excipients for parenteral formulations PDA (1998) J Pharm Sci Technol 52:238-311.

[00238] The dose of antigen-binding molecule administered to a patient may vary depending on the patient's age and size, target disease, conditions, route of administration, and the like. The preferred dose is typically calculated according to body weight or body surface area. When a bispecific antigen-binding molecule of the present invention is used for therapeutic purposes in an adult patient, it may be advantageous to administer the bispecific antigen-binding molecule of the present invention intravenously, typically at a single dose of about 0.01 to about 20 mg / kg of body weight, more preferably about 0.02 to about 7, about 0.03 to about 5, or about 0.05 to about 3 mg / kg of body weight. Depending on the severity of the condition, the frequency and duration of treatment may be adjusted.Effective dosages and timing for administering a bispecific antigen-binding molecule can be determined empirically; for example, patient progress can be monitored by periodic assessment and the dose adjusted accordingly. Furthermore, interspecies dose escalation can be performed using methods well-known in the art (e.g., Mordenti et al., 1991, Pharmaceut. Res. 8: 1351).

[00239] Several delivery systems are known and can be used to administer the pharmaceutical composition of the invention, for example, encapsulation in liposomes, microparticles, microcapsules, recombinant cells capable of expressing mutant viruses, receptor-mediated endocytosis (see, for example, Wu et al., 1987, J. Biol. Chem. 262:4429-4432). Methods of delivery include, but are not limited to, intradermal, intramuscular, intraperitoneal, intravenous, subcutaneous routes, Petition 870260043419, dated 08 / 05 / 2026, page 116 / 353 109 / 163 intranasal, epidural and oral. The composition can be administered by any convenient route, for example, by infusion or bolus injection, by absorption through epithelial or mucocutaneous linings (e.g., oral mucosa, rectal and intestinal mucosa, etc.) and can be administered together with other biologically active agents. Administration can be systemic or local.

[00240] A pharmaceutical composition of the present invention can be dispensed subcutaneously or intravenously using a standard needle and syringe. Furthermore, regarding subcutaneous dispensing, a pen dispensing device readily has applications in dispensing a pharmaceutical composition of the present invention. Such a pen dispensing device can be reusable or disposable. A reusable pen dispensing device generally uses a replaceable cartridge containing a pharmaceutical composition. Once all the pharmaceutical composition within the cartridge has been administered, and the cartridge is empty, the empty cartridge can be readily discarded and replaced with a new cartridge containing the pharmaceutical composition. The pen dispensing device can be reused. In a disposable pen dispensing device, there is no replaceable cartridge.Conversely, the disposable pen dispensing device comes pre-loaded with the pharmaceutical composition held in a reservoir inside the device. After the reservoir is emptied of the pharmaceutical composition, the entire device is discarded.

[00241] Numerous reusable pen and autoinjector delivery devices have applications in the subcutaneous delivery of a pharmaceutical composition of the present invention. Examples include, but are not limited to, AUTOPEN™ (Owen Mumford, Inc., Woodstock, United Kingdom), DISETRONIC™ pen (Disetronic Medical Systems, Berghdorf, Switzerland), HUMALOG MIX 75 / 25™ pen, HUMALOG™ pen, HUMALIN 70 / 30™ (Eli Lilly and Co., Indianapolis, IN), Petition 870260043419, dated 08 / 05 / 2026, page 117 / 353 110 / 163 NOVOPEN™ I, II and III (Novo Nordisk, Copenhagen, Denmark), NOVOPEN JUNIOR™ (Novo Nordisk, Copenhagen, Denmark), BD™ pen (Becton Dickinson, Franklin Lakes, NJ), OPTIPEN™, OPTIPEN PRO™, OPTIPEN STARLET™ and OPTICLIK™ (sanofi-aventis, Frankfurt, Germany), to name a few. Examples of disposable pen delivery devices that have applications in the subcutaneous delivery of a pharmaceutical composition of the present invention include, but are not limited to, the SOLOSTAR™ pen (Sanofi-Aventis), the FLEXPEN™ (Novo Nordisk) and the KWIKPEN™ (Eli Lilly), the SURECLICK™ autoinjector (Amgen, Thousand Oaks, CA), the PENLET™ (Haselmeier, Stuttgart, Germany), the EPIPEN (Dey, LP) and the HUMIRA™ Pen (Abbott Labs, Abbott Park, IL), to name a few.

[00242] In certain situations, the pharmaceutical composition can be delivered in a controlled-release system. In one embodiment, a pump may be used (see Langer, supra; Sefton, 1987, CRC Crit. Ref. Biomed. Eng. 14:201). In another embodiment, polymeric materials may be used; see Medical Applications of Controlled Release, Langer and Wise (eds.), 1974, CRC Pres., Boca Raton, Florida. In yet another embodiment, a controlled-release system may be placed close to the target of the composition, thus requiring only a fraction of the systemic dose (see, for example, Goodson, 1984, in Medical Applications of Controlled Release, supra, vol. 2, pp. 115-138). Other controlled-release systems are discussed in the review by Langer, 1990, Science 249:1527-1533.

[00243] Injectable preparations may include dosage forms for intravenous, subcutaneous, intracutaneous, and intramuscular injections, drip infusions, etc. These injectable preparations may be prepared by publicly known methods. For example, injectable preparations may be prepared, for instance, by dissolving, suspending, or emulsifying the antibody or its salt described above in a sterile aqueous medium or in an oily medium conventionally used for injections. As aqueous media for injections, there are, for example, physiological saline, an isotonic solution containing glucose, and others. Petition 870260043419, dated 08 / 05 / 2026, page 118 / 353 111 / 163 auxiliary agents etc., which may be used in combination with a suitable solubilizing agent, such as an alcohol (e.g., ethanol), a polyalcohol (e.g., propylene glycol, polyethylene glycol), a non-ionic surfactant [e.g., polysorbate 80, HCO-50 (polyoxyethylene (50 mol) hydrogenated castor oil adduct)] etc. As an oily medium, sesame oil, soybean oil etc., are employed, for example, which may be used in combination with a solubilizing agent such as benzyl benzoate, benzyl alcohol etc. The injection thus prepared is preferably filled into a suitable ampoule.

[00244] Advantageously, the pharmaceutical compositions for oral or parenteral use described above are prepared in dosage forms in a unit dose suitable for delivering a dose of the active ingredients. Such dosage forms in a unit dose include, for example, tablets, pills, capsules, injections (ampoules), suppositories, etc. The amount of the aforementioned antibody contained is generally from about 5 to about 500 mg per dosage form in a unit dose; especially in the injection form, it is preferred that the aforementioned antibody be contained in about 5 to about 100 mg and in about 10 to about 250 mg for the other dosage forms. Therapeutic Uses of Antigen-Binding Molecules

[00245] The present invention includes methods comprising administering to an individual in need thereof a therapeutic composition comprising an anti-STEAP2 antibody or antigen-binding fragment, or a bispecific antigen-binding molecule that specifically binds CD3 and STEAP2. The pharmaceutical composition may comprise any of the antibodies or bispecific antigen-binding molecules as disclosed herein and a pharmaceutically acceptable vehicle or diluent. As used herein, the expression "an individual in need thereof" means a human or non-human animal exhibiting one or more Petition 870260043419, dated 08 / 05 / 2026, page 119 / 353 112 / 163 symptoms or signs of cancer (for example, an individual expressing a tumor or suffering from any of the cancers mentioned below) or who would otherwise benefit from an inhibition or reduction in STEAP2 activity or a depletion of STEAP2+ cells (for example, prostate cancer cells).

[00246] The antibodies and bispecific antigen-binding molecules of the invention (and therapeutic compositions comprising the same) are useful, inter alia, for the treatment of any disease or disorder in which stimulation, activation and / or targeting of an immune response would be beneficial. In particular, the anti-STEAP2 antibodies or bispecific anti-CD3 / anti-STEAP2 antigen-binding molecules of the present invention can be used for the treatment, prevention and / or improvement of any disease or disorder associated with or mediated by STEAP2 expression or activity or STEAP2+ cell activity or proliferation. The mechanism of action by which the therapeutic methods of the invention are achieved includes changing STEAP2-expressing cells in the presence of effector cells, for example, by CDC, apoptosis, ADCC, phagocytosis or by a combination of two or more of these mechanisms.Cells expressing STEAP2 that can be inhibited or killed using the bispecific antigen-binding molecules of the invention include, for example, prostate tumor cells.

[00247] The antigen-binding molecules of the present invention can be used to treat, for example, primary and / or metastatic tumors arising in the prostate, bladder, cervix, lung, colon, kidney, breast, pancreas, stomach, uterus and / or ovary. In certain embodiments, the bispecific antigen-binding molecules of the invention are used to treat one or more of the following cancers: prostate cancer, bladder cancer, cervical cancer, lung cancer, colon cancer, kidney cancer, breast cancer, cancer Petition 870260043419, dated 08 / 05 / 2026, page 120 / 353 113 / 163 pancreatic, stomach, uterine, and ovarian cancer. According to certain embodiments of the present invention, anti-STEAP2 antibodies or bispecific anti-STEAP2 / anti-CD3 antibodies are useful for treating a patient afflicted with castration-resistant prostate cancer. According to other related embodiments of the invention, methods are provided comprising administering an anti-STEAP2 antibody or a bispecific anti-CD3 / anti-STEAP2 antigen-binding molecule as disclosed herein to a patient afflicted with castration-resistant prostate cancer. Analytical / diagnostic methods known in the art, such as tumor scanning, etc., can be used to confirm whether a patient harbors a tumor that is castration-resistant.

[00248] The present invention also includes methods for treating residual cancer in an individual.As used herein, the term "residual cancer" means the existence or persistence of one or more cancerous cells in an individual following treatment with an anticancer therapy.

[00249] In certain aspects, the present invention provides methods for treating a disease or disorder associated with STEAP2 expression (e.g., prostate cancer) comprising administering one or more of the anti-STEAP2 or bispecific antigen-binding molecules described elsewhere herein to an individual after the individual has been determined to have prostate cancer (e.g., castration-resistant prostate cancer). For example, the present invention includes methods for treating prostate cancer comprising administering an anti-STEAP2 antibody or a bispecific anti-CD3 / anti-STEAP2 antigen-binding molecule to a patient 1 day, 2 days, 3 days, 4 days, 5 days, 6 days, 1 week, 2 weeks, 3 weeks or 4 weeks, 2 months, 4 months, 6 months, 8 months, 1 year, or more after the individual has received therapy. Petition 870260043419, dated 08 / 05 / 2026, page 121 / 353 114 / 163 hormonal (e.g., antiandrogen therapy). Combination Therapies and Formulations

[00250] The present invention provides methods comprising administering a pharmaceutical composition comprising any of the exemplary antibodies and bispecific antigen-binding molecules described herein, in combination with one or more additional therapeutic agents. Additional exemplary therapeutic agents that can be combined or administered in combination with an antigen-binding molecule of the present invention include, for example, an EGFR antagonist (e.g., an anti-EGFR antibody [e.g., cetuximab or panitumumab] or a small molecule EGFR inhibitor [e.g., gefitinib or erlotinib]), an antagonist of another member of the EGFR family, such as Her2 / ErbB2, ErbB3, or ErbB4 (e.g., anti-ErbB2, anti-ErbB3, or anti-ErbB4 antibody or small molecule inhibitor of ErbB2, ErbB3, or ErbB4 activity), an EGFRvIII antagonist (e.g., an antibody that specifically binds EGFRvIII), a cMET antagonist (e.g.,an anti-cMET antibody), an IGF1R antagonist (e.g., an anti-IGF1R antibody), a B-raf inhibitor (e.g., vemurafenib, sorafenib, GDC-0879, PLX-4720), a PDGFR-α inhibitor (e.g., an anti-PDGFR-α antibody), a PDGFR-β inhibitor (e.g., an anti-PDGFR-β antibody), a VEGF antagonist (e.g., a VEGF-Trap, see, for example, US 7,087,411 (also referred to herein as a “VEGF fusion protein inhibitor”), an anti-VEGF antibody (e.g., bevacizumab), a VEGF receptor small molecule kinase inhibitor (e.g., sunitinib, sorafenib, or pazopanib)), a DLL4 antagonist (e.g., an anti-DLL4 antibody disclosed in the US). 2009 / 0142354, as REGN421), an Ang2 antagonist (for example, an anti-Ang2 antibody disclosed in US 2011 / 0027286, as H1H685P), a, Petition 870260043419, dated 08 / 05 / 2026, p. 122 / 353 115 / 163 FOLH1 (PSMA) antagonist, a PRLR antagonist (e.g., an anti-PRLR antibody), a STEAP1 or STEAP2 antagonist (e.g., an anti-STEAP1 antibody or an anti-STEAP2 antibody), a TMPRSS2 antagonist (e.g., an anti-TMPRSS2 antibody), an MSLN antagonist (e.g., an anti-MSLN antibody), a CA9 antagonist (e.g., an anti-CA9 antibody), a uroplakin antagonist (e.g., an anti-uroplakin antibody), etc. Other agents that may be beneficially administered in combination with the antigen-binding molecules of the invention include cytokine inhibitors, including small molecule cytokine inhibitors and antibodies that bind to cytokines such as IL-1, IL-2, IL-3, IL-4, IL-5, IL-6, IL-8, IL-9, IL-11, IL-12, IL-13, IL-17, IL-18 or their respective receptors.The pharmaceutical compositions of the present invention (for example, pharmaceutical compositions comprising a bispecific anti-CD3 / anti-STEAP2 antigen-binding molecule as disclosed herein) can also be administered as part of a therapeutic regimen comprising one or more therapeutic combinations selected from “ICE”: ifosfamide (e.g., Ifex®), carboplatin (e.g., Paraplatina®), etoposide (e.g., Etopophos®, Toposar®, VePesid®, VP-16); “DHAP”: dexamethasone (e.g., Decadron®), cytarabine (e.g., Cytosar-U®, cytosine arabinoside, ara-C), cisplatin (e.g., Platinol®-AQ); and “ESHAP”: etoposide (e.g., Etopophos®, Toposar®, VePesid®, VP-16), methylprednisolone (e.g., Medrol®), high-dose cytarabine, cisplatin (e.g., Platinol®-AQ).

[00251] The present invention also includes therapeutic combinations comprising any of the antigen-binding molecules mentioned herein and an inhibitor of one or more of VEGF, Ang2, DLL4, EGFR, ErbB2, ErbB3, ErbB4, EGFRvIII, cMet, IGF1R, B Petition 870260043419, dated 08 / 05 / 2026, page 123 / 353 116 / 163 raf, PDGFR-α, PDGFR-β, FOLH1 (PSMA), PRLR, STEAP1, STEAP2, TMPRSS2, MSLN, CA9, uroplakin, or any of the aforementioned cytokines, wherein the inhibitor is an aptamer, an antisense molecule, a ribozyme, a siRNA, a pepticobody, a nanobody, or an antibody fragment (e.g., Fab fragment; F(ab')2 fragment; Fd fragment; Fv fragment; scFv; dAb fragment; or other engineered molecules, such as diantibodies, triantibodies, tetraantibodies, miniantibodies, and minimal recognition units). The antigen-binding molecules of the invention may also be administered and / or co-formulated in combination with antivirals, antibiotics, analgesics, corticosteroids, and / or NSAIDs. The antigen-binding molecules of the invention can also be administered as part of a treatment regimen that also includes conventional radiation and / or chemotherapy.

[00252] The additional therapeutically active component(s) may be administered immediately before, simultaneously with, or immediately after the administration of an antigen-binding molecule of the present invention; (for the purposes of this disclosure, these administration regimens are considered to be the administration of an antigen-binding molecule “in combination with” an additional therapeutically active component).

[00253] The present invention includes pharmaceutical compositions in which an antigen-binding molecule of the present invention is co-formulated with one or more of the additional therapeutically active components, as described elsewhere herein. Management Regimes

[00254] According to certain embodiments of the present invention, multiple doses of an antigen-binding molecule (for example, an anti-STEAP2 antibody or a bispecific antigen-binding molecule that specifically binds STEAP2 and CD3) can be Petition 870260043419, dated 08 / 05 / 2026, p. 124 / 353 117 / 163 administered to an individual over a defined period of time. The methods according to this aspect of the invention comprise sequentially administering to an individual multiple doses of an antigen-binding molecule of the invention. As used herein, “sequentially administering” means that each dose of an antigen-binding molecule is administered to the individual at a different point in time, for example, on different days separated by a predetermined interval (e.g., hours, days, weeks, or months). The present invention includes methods comprising sequentially administering to the patient a single initial dose of an antigen-binding molecule followed by one or more secondary doses of the antigen-binding molecule and, optionally, followed by one or more tertiary doses of the antigen-binding molecule.

[00255] The terms “initial dose,” “secondary doses,” and “tertiary doses” refer to the temporal sequence of administration of the antigen-binding molecule. Thus, the “initial dose” is the dose administered at the beginning of the treatment regimen (also called the “base dose”); “secondary doses” are the doses administered after the initial dose; and “tertiary doses” are the doses administered after the secondary doses. The initial, secondary, and tertiary doses may all contain the same amount of antigen-binding molecule, but they may generally differ from one another in terms of frequency of administration. However, in certain modalities, the amount of an antigen-binding molecule contained in the initial, secondary, and / or tertiary doses varies from one another (e.g., adjusted upwards or downwards, as appropriate) during the course of treatment.In certain modalities, two or more (e.g., 2, 3, 4, or 5) doses are administered at the start of the treatment regimen as “doses of. Petition 870260043419, dated 08 / 05 / 2026, page 125 / 353 118 / 163 loading” followed by subsequent doses that are administered on a less frequent basis (e.g., “maintenance doses”).

[00256] In an exemplary embodiment of the present invention, each secondary and / or tertiary dose is administered 1 to 26 (e.g., 1, 1½, 2, 2½, 3, 3½, 4, 4½, 5, 5½, 6, 6½, 7, 7½, 8, 8½, 9, 9½, 10, 10½, 21, 21½). The phrase “the immediately preceding dose,” as used herein, means, in a sequence of multiple administrations, the dose of antigen-binding molecule that is administered to a patient before the administration of the next dose in the sequence without intervening doses.

[00257] The methods according to this aspect of the invention may comprise administering to a patient any number of secondary and / or tertiary doses of an antigen-binding molecule (for example, an anti-STEAP2 antibody or a bispecific antigen-binding molecule that specifically binds STEAP2 and CD3). For example, in certain embodiments, only a single secondary dose is administered to the patient. In other embodiments, two or more secondary doses (for example, 2, 3, 4, 5, 6, 7, 8 or more) are administered to the patient. Similarly, in certain embodiments, only a single tertiary dose is administered to the patient. In other embodiments, two or more tertiary doses (for example, 2, 3, 4, 5, 6, 7, 8 or more) are administered to the patient.

[00258] In modalities involving multiple secondary doses, each secondary dose may be administered with the same frequency as other secondary doses. For example, each secondary dose may be administered to the patient 1 to 2 weeks after the dose. Petition 870260043419, dated 08 / 05 / 2026, p. 126 / 353 119 / 163 immediately preceding. Similarly, in modalities involving multiple tertiary doses, each tertiary dose may be administered with the same frequency as the other tertiary doses. For example, each tertiary dose may be administered to the patient 2 to 4 weeks after the immediately preceding dose. Alternatively, the frequency with which secondary and / or tertiary doses are administered to a patient may vary throughout the course of the treatment regimen. The frequency of administration may also be adjusted during the course of treatment by a physician, depending on the individual patient's needs after clinical examination. Diagnostic Uses of Antibodies

[00259] The anti-STEAP2 antibodies of the present invention can also be used to detect and / or measure STEAP2 or STEAP2-expressing cells in a sample, for example, for diagnostic purposes. For example, an anti-STEAP2 antibody, or a fragment thereof, can be used to diagnose a condition or disease characterized by aberrant expression (e.g., overexpression, underexpression, lack of expression, etc.) of STEAP2. Exemplary diagnostic assays for STEAP2 may comprise, for example, contacting a sample, obtained from a patient, with an anti-STEAP2 antibody of the invention, wherein the anti-STEAP2 antibody is labeled with a detectable marker or reporter molecule. Alternatively, an unlabeled anti-STEAP2 antibody can be used in diagnostic applications in combination with a secondary antibody that is itself detectably labeled.The detectable marker or reporter molecule may be a radioisotope, such as 3H, 14C, 32P, 35S, or 125I; a fluorescent or chemiluminescent unit, such as fluorescein isothiocyanate or rhodamine; or an enzyme such as alkaline phosphatase, beta-galactosidase, horseradish peroxidase, or luciferase. Another use of... Petition 870260043419, dated 08 / 05 / 2026, p. 127 / 353 120 / 163 Exemplary diagnostic of the anti-STEAP2 antibodies of the invention includes labeled 89Zr antibodies, such as 89Zr-desferrioxamine-labeled antibodies, for the purpose of non-invasive identification and tracking of tumor cells in an individual (e.g., positron emission tomography (PET) imaging). (See, for example, Tavare, R. et al. Cancer Res. 2016 Jan 1;76(1):73-82; and Azad, BB. et al. Oncotarget. 2016 Mar 15;7(11):12344-58.) Specific exemplary assays that can be used to detect or measure STEAP2 in a sample include enzyme-linked immunosorbent assay (ELISA), radioimmunoassay (RIA), and fluorescence-activated cell separation (FACS).

[00260] Samples that can be used in STEAP2 diagnostic assays according to the present invention include any tissue or fluid sample OBTAINABLE from a patient containing detectable amounts of STEAP2 protein or fragments thereof under normal or pathological conditions. In general, STEAP2 levels in a particular sample obtained from a healthy patient (e.g., a patient not afflicted with a disease or condition associated with abnormal STEAP2 levels or activity) will be measured to initially establish a baseline or standard STEAP2 level. This baseline STEAP2 level can then be compared with STEAP2 levels measured in samples obtained from individuals suspected of having a STEAP2-related disease (e.g., a tumor containing STEAP2-expressing cells) or condition. EXAMPLES

[00261] The following examples are presented so as to provide those skilled in the art with a complete disclosure and description of how to make and use the methods and compositions of the invention and are not intended to limit the scope of what the inventors consider to be their invention. Efforts have been made to ensure accuracy with Petition 870260043419, dated 08 / 05 / 2026, page 128 / 353 121 / 163 Regarding the numbers used (e.g., quantities, temperature, etc.), however, some experimental errors and deviations must be considered. Unless otherwise indicated, parts are parts by weight, molecular weight is the average molecular weight, temperature is in degrees Celsius, and pressure is at or near atmospheric pressure. Example 1: Generation of Anti-STEAP2 Antibodies

[00262] Anti-STEAP2 antibodies were obtained by immunizing a genetically modified mouse with a human STEAP2 antigen or by immunizing an engineered mouse comprising DNA encoding variable regions of human immunoglobulin heavy and light chains with a human STEAP2 antigen.

[00263] Genetically modified mice were immunized with hSTEAP2 antigen (SEQ ID:1899). After immunization, splenocytes were harvested from each mouse and (1) fused with mouse myeloma cells to preserve their viability and form hybridoma cells and screened for STEAP2 specificity or (2) separated from B cells (as described in US 2007 / 0280945A1) using a human STEAP2 fragment as the sorting reagent that binds and identifies reactive antibodies (antigen-positive B cells).

[00264] Chimeric antibodies to STEAP2 were initially isolated having a human variable region and a mouse constant region. The antibodies were characterized and selected for desirable characteristics, including affinity, selectivity, etc. If necessary, mouse constant regions were replaced with a desired human constant region, for example, wild-type or modified IgG1 or IgG4 constant region, to generate a fully human anti-STEAP2 antibody. Although the selected constant region may vary according to the specific use, the Petition 870260043419, dated 08 / 05 / 2026, page 129 / 353 122 / 163 high-affinity antigen binding and target-specificity characteristics reside in the variable region. Antibody name designations, such as H1H11243N and H1M7804N, denote fully human “H1H” antibodies or chimeric mouse constant region / human variable region “H1M” antibodies. Antibodies identified by the hybridoma method are indicated with antibody ID numbers ending with “N” or “N2”; antibodies identified by the B-cell sorting method are indicated with antibody ID numbers ending with “P” or “P2”.

[00265] Certain biological properties of the exemplary anti-STEAP2 antibodies generated according to the methods of this Example are described in detail in the Examples set out below. Amino acid and nucleic acid sequences of variable region heavy and light chains of anti-STEAP2 antibodies.

[00266] Table 1 sets forth amino acid sequence identifiers of the variable heavy and light chain regions and CDRs of selected anti-STEAP2 antibodies of the invention. The corresponding nucleic acid sequence identifiers are set forth in Table 2. Table 1: Amino Acid Sequence Identifiers SEQ ID Nos: Antibody Designation HCV R HCD R1 HCD R2 HCD R3 LCV R LCD R1 LCD R2 LCD R3 H1H11243 N 2 4 6 8 10 12 14 16 H1H11878 P 18 20 22 24 26 28 30 32 H1H11880 P 34 36 38 40 42 44 46 48 H1H11888 50 52 54 56 58 60 62 64 Petition 870260043419, dated 08 / 05 / 2026, p. 130 / 353 123 / 163 P2 H1H11892 P2 66 68 70 72 58 60 62 64 H1H11893 P2 74 76 78 80 58 60 62 64 H1H11894 P2 82 84 86 88 58 60 60 62 195 H1H189 92 94 96 58 60 62 64 H1H11896 P2 98 100 102 104 58 60 62 64 H1H11897 P2 106 108 110 112 114 116 118 118 HPH128 126 127 126 128 130 132 134 136 H1H7969P 138 140 142 144 146 148 150 152 H1H7970P 154 156 158 160 162 164 164 1616 HPH7978 172 174 176 178 180 182 184 H1H7972P 186 188 190 192 194 196 198 200 H1M7804 N 202 204 204 206 208 210 210 212 212 NM 214 784 218 220 222 224 226 228 230 232 H1M7832 N 234 236 238 240 242 244 246 248 H2M11162 N 250 252 254 256 286 2626 H2M11163 N 266 268 270 272 274 276 278 280 H2M11164 N 282 284 286 288 290 292 294 296 H2M7806 N 312 Petition 870260043419, of 08 / 05 / 2026, p. 131 / 353 124 / 163 H2M7807 N 314 316 318 320 322 324 326 328 360 H2M7811 N362 364 366 368 370 372 374 376 H2M7812 N 378 380 382 384 386 388 390 392 Table 2: Nucleic Acid Sequence Identifiers SEQ ID NOs: Antibody Designation HCV R HCD R1 HCD R2 HCD R3 LCV R LCD R1 LCD R2 LCD R3 H1H11243 N 1 3 5 7 9 11 13 15 H1H11878 P 17 19 21 23 25 27 29 31 H1H11880 P 33 35 37 39 41 43 45 47 H1H11888 P2 49 51 53 55 57 59 61 63 H1H11892 P2 65 67 69 71 57 59 61 63 H1H11893 P2 73 75 77 79 57 59 61 63 H1H11894 P2 81 83 85 87 57 59 61 63 H1H11895 P2 89 91 93 95 57 59 61 63 H1H11896 97 99 101 103 57 59 61 63 Petition 870260043419, dated 08 / 05 / 2026, page 132 / 353 125 / 163 P2 H1H11897 P2 105 107 109 111 113 115 117 119 H1H7968P 121 123 125 127 129 131 133 135 H1H7969P 137 139 141 143 145 147 149 151 H1H7970P 153 155 157 159 161 163 165 167 H1H7971P 169 171 173 175 177 179 181 183 H1H7972P 185 187 189 191 193 195 197 199 H1M7804 N 201 203 205 207 209 211 213 215 247 H2M11162 N249 251 253 255 257 259 261 263 H2M11163 N265 267 269 271 273 275 277 279 291 293 295 H2M7806 N 297 299 301 303 305 307 309 311 343 H2M7810 N 345 ​​347 349 351 353 355 357 359 H2M7811 N 361 363 365 367 369 371 373 375 Example 2: Human anti-STEAP2 antibodies bind Petition 870260043419, dated 08 / 05 / 2026, pp. 133 / 353 126 / 163 Selectively targeting STEAP2-expressing cell lines via FACS

[00267] The ability of anti-STEAP2 antibodies to selectively bind to cell lines endogenously expressing human six-transmembrane epithelial prostate antigen 2 (STEAP2) was determined by FACS analysis.

[00268] Briefly, 1x10⁵ cells were incubated with 10 pg / mL of anti-STEAP2 antibodies, or isotype control antibodies, for 30 minutes on ice in antibody dilution buffer. After a wash with antibody dilution buffer, the cells were incubated with 10 pg / mL of PE-conjugated anti-human or anti-mouse Fc secondary antibodies for 30 min on ice. After a further wash, the samples were incubated with Cytofix (1% formaldehyde) for 20 minutes. After a final wash, the samples were filtered through a 96-well Pall filtration block, passed through a Hypercyt® cytometer, and analyzed on ForeCyt™ (IntelliCyt, Albuquerque, NM). Mean fluorescence intensities (MFI) were expressed as change in times above unstained (background) levels. The average number of times above the background antibody concentrations of 100–300 nM was determined.For the determination of cell binding EC50, mAb concentrations ranged from 300 nM to 5 pM, and EC50 values ​​were determined from a four-parameter logistic equation along a 12-point response curve (GraphPad Prism). Tables 3A and 3B: FACS Binding Properties of anti-STEAP2 Antibodies to STEAP2-expressing and STEAP2-negative Cell Lines Petition 870260043419, dated 08 / 05 / 2026, page 134 / 353 127 / 163 Table 3A: Binding Properties of Selected Human-Fc Anti-STEAP2 Antibodies STEAP2 Expression STEAP2 Negative Cell Line HEK293 C4-2 FADU SKBR3 Raji Antibody Average FAB Average FAB Average EC50 (nM) Average FAB Average FAB Average FAB H1H7809N 31 89 >50 21 37 3 H1H7810N 3 26 ND 3 3 2 H1H7811N 5 65 >50 3 5 4 H1H7814N 2 96 4 2 2 2 H1H7972P 4 119 9 2 3 59 H1H11162N 10 104 1 3 3 2 H1H11163N 6 90 3 2 3 2 H1H11164N 10 117 2 3 2 2 H1H11243N 3 41 ND 2 3 2 H1H11878P 5 27 >50 ND ND ND H1H11880P 7 6 5 ND ND ND H1H11888P2 9 6 3 ND ND ND H1H11892P2 3 4 ND ND ND ND H1H11893P2 3 9 21 ND ND ND H1H11894P2 4 7 ND ND ND ND H1H11895P2 4 6 16 ND ND ND H1H11896P2 7 6 21 ND ND ND H1H11897P2 16 29 >50 ND ND ND Control isotype hIgG1 -I 1 2 ND 1 2 4 Control of hIgG1-II isotype 1.7 ± 0.5 2 ND 3 2 ND Anti-human PE 1.1 ± 0.1 1 ND 1 2 1 No staining 1 ± 0 1 ND 1 1 ND Petition 870260043419, dated 08 / 05 / 2026, pages 135 / 353 128 / 163 FAB: Times Above Bottom; ND: Not Detected Table 3B: Binding Properties of Anti-STEAP2 Hybridoma-Generated Antibodies STEAP2 Expression STEAP2 Negative Cell Line HEK293 C4-2 FADU SKBR3 Raji Antibody Average FAB Average FAB Average EC50 (nM) Average FAB Average FAB Average FAB H1M11243N ND 116 23 ND ND ND H1M11249N ND 11 ND ND ND ND H2M11160N ND 8 ND ND ND ND H2M11162N ND 365 4.9 ND ND ND H2M11163N ND 256 13 ND ND ND H2M11164N ND 360 3.7 ND ND ND H2M11166N ND 12 ND ND ND ND H2M11168N ND 9 ND ND ND ND H2M11245N ND 18 ND ND ND ND H2M11246N ND 11 ND ND ND ND H2M11247N ND 482 18 ND ND ND H2M11248N ND 50 >50 ND ND ND H3M11161N ND 5 ND ND ND ND H3M11165N ND 13 ND ND ND ND H3M11167N ND 14 ND ND ND ND H3M11244N ND 2 ND ND ND ND mIgG1 Isotype Control ND 2 ND ND ND mIgG2 Isotype Control ND 3 ND ND ND ND Isotype Control mIgG3 ND 4 ND ND ND ND Petition 870260043419, dated 08 / 05 / 2026, page 136 / 353 129 / 163 PE anti-human 1.1 ± 0.1 1 ND 1 2 1 No staining 1 ± 0 1 ND 1 1 ND FAB: Times Above Bottom; ND: Not Detected

[00269] As the results in Tables 3A and 3B demonstrate, several anti-STEAP2 antibodies specifically bound to C4-2 prostate adenocarcinoma cell lines expressing high STEAP2 levels greater than 50 times above background, with low nM EC50s via FACS. Some anti-STEAP2 antibodies also bound weakly to HEK293 cells expressing low STEAP2. Negligible binding was observed for most anti-STEAP2 antibodies to STEAP2-negative FADU, SK-BR-3, and Raji cells. This example illustrates the ability of several anti-STEAP2 antibodies of this invention to specifically and selectively bind to high STEAP2 expression cell lines. Example 3: Anti-human anti-STEAP2 antibodies show potent internalization and specificity for human STEAP2.

[00270] The ability of the anti-STEAP2 antibodies of this invention to selectively bind to STEAP2-expressing cell lines has been described (see Example 2 - FACS binding). Subsequently, the internalization properties of the anti-STEAP2 antibodies of this invention were also evaluated.

[00271] In summary, 20,000 C4-2 cells were seeded in 96-well plates coated with PDL. The following day, the cells were incubated with anti-human STEAP2 antibodies (10 pg / mL) for 30 min on ice followed by two washes with PBS. The cells were then incubated with Alexa 488-conjugated anti-hFc Fab secondary antibody for 30 minutes on ice, followed by two additional washes with PBS. The antibodies were allowed to internalize for 1 h at 37°C in internalization buffer (PBS + 2% FBS) or were kept at 4°C. The cells were fixed in formaldehyde. Petition 870260043419, dated 08 / 05 / 2026, page 137 / 353 130 / 163 at 4%, the nuclei were stained with DRAQ5 (cell signaling) and images were acquired on ImageXpress micro XL (Molecular Devices).

[00272] A qualitative visual assessment of the total binding intensity and the intensity of antibodies that had internalized into vesicles was performed and scored according to the following criteria: - (no internalization or binding), + (weak internalization or binding), ++ (moderate internalization or binding) and +++ (robust internalization or binding).

[00273] As the results in Table 4 illustrate, several antibodies showed robust internalization capabilities in the C4-2 cell line. In general, robust internalization correlated with higher levels of total binding intensity.

[00274] Selected STEAP2 antibodies were then tested for binding to other members of the human STEAP family (h) (STEAP1, STEAP3, and STEAP4). To assess the specificity of anti-STEAP2 antibody, plasmid constructs expressing hSTEAP1, hSTEAP2, hSTEAP3, or hSTEAP4 fused with Green Fluorescent Protein (GFP) were transiently introduced into HEK293 cells using a lipofectamine 2000-based methodology. After 48 h, the transiently transfected cells were stained with anti-STEAP2 antibodies and imaged as described above for the internalization assay. Wells with GFP-positive cells that bound to anti-STEAP2 antibodies were classified as positive (+) and those that did not bind to anti-STEAP2 antibodies were classified as negative (-). All antibodies tested bound hSTEAP2-GFP positive cells, but did not bind STEAP1GFP, STEAP3-GFP, or STEAP4-GFP positive cells, confirming the specificity of binding to human STEAP2.The results are summarized in Table 5. Petition 870260043419, dated 08 / 05 / 2026, page 138 / 353 131 / 163

[00275] In summary, several anti-STEAP2 antibodies of this invention demonstrate potent internalization capability and are specific ligands for human STEAP2. Table 4. Qualitative evaluation of internalization and total binding properties of anti-STEAP2 antibodies in a C42 cell line with high STEAP2 expression. Internalization (37°C, 1h) Total Binding (4°C) Antibody Qualitative Score Qualitative Score H1H7814N + + H1H11162N +++ +++ H1H11163N ++ ++ H1H11164N +++ +++ H1H11878P + + H1H11880P + + H1H11888P2 + + H1H11892P2 + / - + / - H1H11893P2 + / - + / - H1H11894P2 + / - + H1H11895P2 + + H1H11896P2 + + H1H11897P2 - - H1H7972P + + H1M11243N + + H2M11162N +++ +++ H2M11163N ++ ++ H2M11164N +++ +++ H2M11247N +++ +++ higG1 Isotype Control (Ab to irrelevant antigen) - - Petition 870260043419, dated 08 / 05 / 2026, pp. 139 / 353 132 / 163 Table 5. Specificity of anti-STEAP2 antibodies: Evaluation of binding to hSTEAP1, hSTEAP2, hSTEAP3, or hSTEAP4 fused to GFP. HEK293 Cells Transfected with STEAP / GFP Fusion Plasmids Antibodies hSTEAP1 hSTEAP2 hSTEAP3 hSTEAP4 H2M7807 - + - - H2M7810 - + - - H2M7811 - + - - H1M7814 - + - - H1H7972 - + - - Example 4: Generation of Bispecific Antibodies that Bind STEAP2 and CD3

[00276] The present invention provides bispecific antigen-binding molecules that bind to CD3 and STEAP2; such bispecific antigen-binding molecules are also referred to herein as “anti-STEAP2 / anti-CD3 or anti-STEAP2xCD3 bispecific molecules”. The anti-STEAP2 portion of the bispecific anti-STEAP2 / anti-CD3 molecule is useful for targeting tumor cells expressing prostate epithelial six-transmembrane antigen 2 (STEAP2), and the anti-CD3 portion of the bispecific molecule is useful for activating T cells. The simultaneous binding of STEAP2 to a tumor cell and CD3 to a T cell facilitates the directed killing (cell lysis) of the target tumor cell by the activated T cell.

[00277] Bispecific antibodies comprising a specific anti-STEAP2-binding domain and a specific anti-CD3-binding domain recombinantly constructed by standard molecular cloning methodologies and expressed in CHO cells, wherein the anti-STEAP2 antigen-binding domain and the anti-CD3 antigen-binding domain each comprise distinct different HCVRs paired with a common LCVR. In bispecific antibodies Petition 870260043419, dated 08 / 05 / 2026, pp. 140 / 353 133 / 163 exemplified, the molecules were constructed using a heavy chain of an anti-CD3 antibody, a heavy chain of an anti-STEAP2 antibody, and a common light chain of the anti-STEAP2 antibody and expressed in CHO cells. In some cases, bispecific antibodies can be constructed using a heavy chain of an anti-CD3 antibody, a heavy chain of an anti-STEAP2 antibody, and a light chain of an anti-CD3 antibody, or a light chain of an antibody known to be promiscuous or to effectively pair with a variety of heavy chain arms, such as VK1-39JK5 or VK3-20JK1.

[00278] The bispecific antibodies described in the following examples consist of anti-CD3 binding arms having binding affinities for human soluble heterodimeric hCD3s / β protein (as described in Example 12 herein); and human STEAP2 (see Examples 1-2 above). Exemplary bispecific antibodies have been manufactured having a modified (chimeric) IgG4 Fc domain as set forth in US Patent Application Publication US20140243504A1, published August 28, 2014.

[00279] A summary of the component parts of the antigen-binding domains of the various bispecific antiSTEAP2xCD3 antibodies constructed is set out in Table 6. Table 6: Construction of STEAP2xCD3 Bispecific Antibodies Bispecific Antibody Identifier Anti-STEAP2 Antigen-Binding Domain Anti-CD3 Antigen-Binding Domain Common Light Chain Variable Region Heavy Chain Variable Region Heavy Chain Variable Region BSSTEAP2 / CD3- H2M11162N CD3-VH-G H2M11162N Petition 870260043419, dated 08 / 05 / 2026, page 141 / 353 134 / 163 001 (SEQ ID NO:250) (SEQ ID NO: 1730) (SEQ ID NO:258) BSSTEAP2 / CD3- 002 CD3-VH-G5 (SEQ ID NO: 1762) BSSTEAP2 / CD3- 003 CD3-VH-G20 (SEQ ID NO:1866) BSSTEAP2 / CD3- 004 H1H7814N (SEQ ID NO:218) H1H7251P (SEQ ID NO:1570) H1H7814N (SEQ ID NO:226) BSSTEAP2 / CD3- 005 H1H11162 (SEQ ID NO:250) H1H7208P (SEQ ID NO:1490) H1H11162 (SEQ ID NO:226). NO:258) BSSTEAP2 / CD3- 006 CD3-VH-P (SEQ ID NO:1882) BSSTEAP2 / CD3- 007 H1H7195P (SEQ ID NO:1450) BSSTEAP2 / CD3- 008 H1H11163 (SEQ ID NO:266) H1H7208P (SEQ ID NO:1450). NO:1490) H1H11163 (SEQ ID NO:274) BSSTEAP2 / CD3- 009 H1H11164 (SEQ ID NO:282) H1H7208P (SEQ ID NO:1490) H1H11164 (SEQ ID NO:290) BSSTEAP2 / CD3- 010 H1H7809N (SEQ ID NO:1490). NO:330) H1H7198P (SEQ ID NO:1466) H1H7809N (SEQ ID NO:339) BSSTEAP2 / CD3- 011 H1H7203P (SEQ ID NO:1466). Petition 870260043419, 08 / 05 / 2026, p. 142 / 3 135 / 1 NO:1474)

[00280] The light chains listed in Table 6 were common to both the CD3 and STEAP2 target arms of bispecific antibodies. Tables 1 and 2 establish amino acid and nucleic acid sequence identifiers, respectively, for the various variable heavy chain regions and their corresponding CDRs, of the anti-STEAP2 arms (i.e., HCVR and LCVR are derived from H2M11162N) to construct the bispecific antibodies in this Example. Tables 15 and 16 establish amino acid and nucleic acid sequence identifiers, respectively, for the various variable heavy chain regions and their corresponding CDRs, of the anti-CD3 arms of the bispecific antibodies in this Example. Example 5: Bispecific anti-STEAP2 / anti-CD3 antibodies They exhibit potent anti-tumor efficacy in vivo.

[00281] To determine the efficacy of exemplary bispecific antiSTEAP2 / anti-CD3 antibodies in vivo, studies were performed in immunocompromised mice bearing prostate cancer xenografts. Efficacy of bispecific anti-STEAP2 / anti-CD3 antibodies in human tumor xenograft models.

[00282] To evaluate the in vivo efficacy of bispecific antiSTEAP2 / anti-CD3 antibodies in human tumor xenograft studies, NOD scid gamma (NSG) mice (Jackson Laboratories, Bar Harbor, Maine) were co-implanted with human peripheral blood mononuclear cells (PBMCs; ReachBio LLC., Seattle, WA) along with human prostate cancer C4-2 cells (MD Anderson Cancer Center, Houston, TX) that endogenously express STEAP2.

[00283] In summary, 5.0x106 C4-2 cells were co-implanted Petition 870260043419, dated 08 / 05 / 2026, pp. 143 / 353 136 / 163 subcutaneously (sc) with 1.25x10⁶ human PBMCs in a 50:50 mixture of Matrigel matrix (BD Biosciences, San Jose, CA) in the right flank of male NSG mice. Mice were treated intraperitoneally (ip) on the day of implantation (immediate treatment model) with bispecific anti-STEAP2 / anti-CD3 BSSTEAP2 / CD3-001, BSSTEAP2 / CD3-002, or BSSTEAP2 / CD3-003, or an isotype control, at a dose of 0.1 or 0.01 mg / kg (N=5 mice / group).

[00284] Tumor size was measured twice a week using calipers and tumor volume was calculated as Volume = (length x width2) / 2. Data are shown as tumor size (mm3) at the study endpoint, 46 days post-tumor implantation (Table 7). Table 7: Efficacy of Bispecific anti-STEAP2 / anti-CD3 Antibodies in an Immunocompromised Xenograft Model: Immediate Dosage Tumor Model / Mouse Strain Bispecific Antibody Identifier Dose (mg / kg) N Tumor Size (mm3) 46 d post-tumor implantation (mean ± SD) C4-2 / ​​NSG BSSTEAP2 / CD3-001 0.1 5 18.0 ± 14.0 0.01 5 23.0 ± 220 BSSTEAP2 / CD3-002 0.1 5 15.0 ± 12.0 0.01 5 17.0 ± 8.0 BSSTEAP2 / CD3-003 0.1 5 19.0 ± 12.0 0.01 5 25.0 ± 21.0 Bispecific Control 0.1 5 1020.0 ± 922.0

[00285] As the results in Table 7 show, BSSTEAP2 / CD3 Petition 870260043419, dated 08 / 05 / 2026, page 144 / 353 137 / 163 001, BSSTEAP2 / CD3-002, and BSSTEAP2 / CD3-003 significantly suppressed tumor growth compared to an isotype control when tumor sizes were measured at the study endpoint. Importantly, the bispecific anti-STEAP2 / anti-CD3 antibodies were effective in inhibiting C4-2 tumor growth even at the lowest dose of 0.1 mg / kg. Example 6: Conjugate Preparation and Characterization

[00286] All monoclonal antibodies were expressed in CHO cells and purified by Protein A. An isotype control was also prepared similarly. The non-binding isotype control antibody was derived from an immunological antigen having no relation to oncology.

[00287] The antibody (10 mg / mL) in 50 mM HEPES, 150 mM NaCl, pH 7.5, was treated with 1 mM dithiothreitol at 37°C for 30 min. After filtration through a gel (G-25, pH 4.5 sodium acetate), the maleimide ligand payload derivative Compound 7 (1.2 equivalents / SH group) in DMSO (10 mg / mL) was added to the reduced antibody and the mixture adjusted to pH 7.0 with 1 M HEPES (pH 7.4). Compound 7 and the methods for making the compound are described in PCT Publication WO2014 / 145090, published on September 18, 2014, which is incorporated herein by reference. After 1 h the reaction was quenched with excess N-ethylmaleimide. The conjugates were purified by size exclusion chromatography and filtered sterile. Protein and ligand payload concentrations were determined by UV spectral analysis.Size-exclusion HPLC established that all conjugates used were >95% monomeric, and RP-HPLC established that there was <0.5% unconjugated ligand payload. Yields are presented in Table 8 based on protein titer determination. All conjugated antibodies were analyzed by UV for loading values. Petition 870260043419, dated 08 / 05 / 2026, pages 145 / 353 138 / 163 payload of the ligand according to Hamblett et al, Cancer Res 2004 10 7063. The results are summarized in Table 8.

[00288] A conjugate comprising Compound 60 can be prepared by a similar method. Compound 60 and methods for making the compound are described in PCT Publication W02016 / 160615 (Example 20) published on October 6, 2016, which is incorporated herein by reference in its entirety. Compound 60 is Maitansin-N-methyl-Lalanine-(3-methoxy-4-amino)benzamido-Cit-Val-Cap-Mal. Table 8: Summary of Payload Parameters (Chemotoxic Drug) and Antibody-Drug Conjugate Compound ε252 nm (cm⁻¹ M⁻¹) ε280 nm (cm⁻¹ M⁻¹) 7 [Maitansin-3-N-methyl-L-(S)alanine-propanamidyl-3-N-methyl-N-[4-(amino-citrullinavalin-hexanamide-6-maleimidi / )benzyl]carbamate] 50600 8100 Antibody ε252 nm (cm⁻¹ M⁻¹) ε280 nm (cm⁻¹ M⁻¹) H1H7814N 110440 212400 Isotype Control 75113 218360 Antibody Conjugate Payload: Antibody (UV) Yield % H1H7814N-7 2.7 48 Isotype Control-7 3.0 48 Example 7: Anti-STEAP2 drug-antibody conjugates (ADCs) are potent inhibitors of tumor growth in vivo in STEAP2-positive prostate cancer xenograft models. Petition 870260043419, dated 08 / 05 / 2026, pp. 146 / 353 139 / 163

[00289] A. To determine the in vivo efficacy of antiSTEAP2 antibodies conjugated with Compound 7, studies were conducted in immunocompromised mice bearing STEAP2-positive prostate cancer xenografts.

[00290] For these studies, male SCID mice (Taconic, Hudson, NY) were implanted with C4-2 cells endogenously expressing STEAP2. Once the tumors had reached a mean volume of 200-250 mm3 (~Day 13-17), the mice were randomly assigned to treatment groups and dosed with either STEAP2-conjugated antibodies, a non-binding antibody conjugate, or vehicle. In these in vivo studies, antibodies were dosed once, and then tumors were monitored until a mean tumor size of approximately 1,500-2,000 mm3 was reached in the vehicle-only cohort (~40-50 days). Treatment groups showing efficacy were maintained for a longer period of time (80-110 days).

[00291] In an initial study, an exemplary anti-STEAP2 antibody conjugated with Compound 7 was examined for efficacy in reducing C4-2 tumor volume. Mice received a single dose of anti-STEAP2 and control ADCs at 10, 20, or 40 mg / kg on day 13 post-implantation. As summarized in Figure 1, H1H7841N-7 (DAR 2.92) potentially inhibited tumor growth at all doses tested. At the highest dose (40 mg / kg), H1H784N-7 efficiently reduced tumor size, although the non-binding control antibody (40 mg / kg) also showed an effect on tumor volume. At all doses investigated, H1H784N-7 reduced tumor size more potently than the control conjugate antibody.

[00292] In a second study, anti-STEAP2 ADC was administered at 5 and 20 mg / kg and the control antibody at 20 mg / kg on day 14 after implantation. As summarized in Figure 2, H1H7841N-7 (DAR 2.92) Petition 870260043419, dated 08 / 05 / 2026, pp. 147 / 353 140 / 163 potently inhibited tumor growth at a dose of 20 mg / kg, as in the previous experiment, but showed reduced efficacy at a dose of 5 mg / kg. The control antibody at a dose of 20 mg / kg showed no difference from the vehicle control.

[00293] In a further study, H1H7841N-7 (DAR 2.7) and the control antibody were dosed at μg / kg drug equivalents based on drug ADC:antibody ratios (“DAR”). The dose was 150 pg / kg administered on day 17 post-implantation (Figure 3). H1H7841N-7 potentially inhibited tumor growth at the 150 pg / kg dose, showing tumor regression up to 42 days post-implantation and 25 days post-injection. At this point, tumor growth began to recover. Tumor growth with the control antibody at this dose was not different from the vehicle control.

[00294] B. In analogous studies, male SCID mice (Taconic, Hudson, NY) were implanted with C4-2 cells endogenously expressing STEAP2. An exemplary anti-STEAP2 antibody (H1H7814N) conjugated with Compound 60 was examined for efficacy in C4-2 tumor regression. Mice received a single dose of anti-STEAP2 ADC, isotype control ADC (binding to irrelevant antigen), or vehicle (PBS) at 2.5 mg / kg on day 29 post-implantation. Tumor volume and body weight were recorded on day 0 (day of injection) and on days 4, 6, 8, 12, 14, and 20 post-injection. As summarized in Figure 4, H1H7814N-60 (DAR 3.6) potentially inhibited tumor growth at the tested dose, showing tumor regression up to 20 days after injection (49 days after implantation).The percent change in body weight for the test ADC was no greater than -2.01% by day 14 (after H1H7814N-60 injection) compared with mice treated with the Control AbADC for which the percent change in body weight was observed from -4.02% to -11.55% by day 14. Petition 870260043419, dated 08 / 05 / 2026, pp. 148 / 353 141 / 163 Example 8: Generation of Anti-CD3 Antibodies

[00295] Anti-CD3 antibodies were obtained by immunizing an engineered mouse comprising DNA encoding variable regions of human immunoglobulin kappa heavy and light chains with cells expressing CD3 or with CD3-encoding DNA. The antibody immune response was monitored by a CD3-specific immunoassay. When a desired immune response was achieved, splenocytes were harvested and fused with mouse myeloma cells to preserve their viability and form hybridoma cell lines. The hybridoma cell lines were researched and screened to identify cell lines that produce CD3-specific antibodies. Using this technique, several chimeric anti-CD3 antibodies (i.e., antibodies possessing both human variable domains and mouse constant domains) were obtained.Furthermore, several fully human anti-CD3 antibodies have been isolated directly from antigen-positive B cells without fusion to myeloma cells, as described in US 2007 / 0280945A1.

[00296] Certain biological properties of the exemplary anti-CD3 antibodies generated according to the methods in this Example are described in detail in the Examples herein. Example 9: Amino Acid and Nucleic Acid Sequences with Variable Heavy and Light Chain Regions

[00297] Table 9 sets forth the amino acid sequence identifiers of the variable heavy and light chain regions and CDRs of selected anti-CD3 antibodies of the invention. The corresponding nucleic acid sequence identifiers are set forth in Table 10. The methods for making the anti-CD3 antibodies disclosed herein can also be found in US publication 2014 / 0088295 published on March 27, 2014. Petition 870260043419, dated 08 / 05 / 2026, pp. 149 / 353 142 / 163 Table 9: Amino Acid Sequence Identifiers SEQ ID Nos: Antibody Designation HCV R HCD R1 HCD R2 HCD R3 LCV R LCD R1 LCD R2 LCD R3 H1H2712N 402 404 406 408 410 412 414 416 H1M2692 N 418 420 422 424 426 428 430 432 H1M3542 N 434 436 438 440 442 444 446 448 H1M3544 N 450 452 454 456 458 460 462 464 H1M3549 N 466 468 470 472 474 476 478 480 H1M3613 N 482 484 486 488 490 492 494 496 528 H2M2691 N530 532 534 536 538 540 542 544 H2M2704 N546 548 550 552 554 556 558 560 574 576 H2M2706 N 578 580 582 584 586 588 590 592 624 Petition 870260043419, dated 08 / 05 / 2026, pages 150 / 353 143 / 163 H2M2709 N 626 628 630 632 634 636 638 640 H2M2710 N 642 644 646 648 650 652 654 656 H2M2711 N 658 660 662 664 666 668 670 672 H2M2774 N 674 676 678 680 682 684 686 688 H2M2775 N 690 692 694 696 698 700 702 704 H2M2776 N 706 708 710 712 714 716 718 720 H2M2777 N 722 724 726 728 730 732 734 736 H2M2778 N 738 740 742 744 746 748 750 752 H2M2779 N 754 756 758 760 762 764 766 768 H2M2789 N 770 772 774 776 778 780 782 784 H2M2862 N 786 788 790 792 794 796 798 800 H2M2885 N 802 804 806 808 810 812 814 816 H2M2886 N 818 820 822 824 826 828 830 832 H2M3540 N 834 836 838 840 842 844 846 848 H2M3541 N 850 852 854 856 858 860 862 864 H2M3543 N 866 868 870 872 874 876 878 880 Petition 870260043419, on 05 / 08 / 2026, page. 151 / 353 144 / 163 H2M3547 N 882 884 886 888 890 892 894 896 H2M3548 N 898 900 902 904 906 908 910 912 H2M3563 N 914 916 918 920 922 924 926 928 H1H5751P 930 932 934 936 938 940 942 944 H1H5752P 946 948 950 952 954 956 958 960 H1H5753B 962 964 966 968 970 972 974 976 H1H5754B 978 980 982 984 986 988 990 992 H1H5755B 994 996 998 1000 1002 1004 1006 1008 H1H5756B 1010 1012 1014 1016 1018 1020 1022 1024 H1H5757B 1026 1028 1030 1032 1034 1036 1038 1040 H1H5758B 1042 1044 1046 1048 1050 1052 1054 1056 H1H5761P 1058 1060 1062 1064 1066 1068 1070 1072 H1H5763P 1074 1076 1078 1080 1082 1084 1086 1088 H1H5764P 1090 1092 1094 1096 1098 1100 1102 1104 H1H5769P 1106 1108 1110 1112 1114 1116 1118 1120 H1H5771P 1122 1124 1126 1128 1130 1132 1134 1136 H1H5772P 1138 1140 1142 1144 1146 1148 1150 1152 H1H5777P 1154 1156 1158 1160 1162 1164 1166 1168 H1H5778P 1170 1172 1174 1176 1178 1180 1182 1184 H1H5780P 1186 1188 1190 1192 1194 1196 1198 1200 H1H5781P 1202 1204 1206 1208 1210 1212 1214 1216 H1H5782P 1218 1220 12221224 1226 1228 1230 1232 H1H5785B 1234 1236 1238 1240 1242 1244 1246 1248 H1H5786B 1250 1252 1254 1256 1258 1260 1262 1264 H1H5788P 1266 1268 1270 1272 1274 1276 1278 1280 H1H5790B 1282 1284 1286 1288 1290 1292 1294 1296 H1H5791B 1298 1300 1302 1304 1306 1308 1310 1312 H1H5792B 1314 1316 1318 1320 1322 1324 1326 1328 H1H5793B 1330 1332 1334 1336 1338 1340 1342 1344 Petition 870260043419, dated 08 / 05 / 2026, pages 152 / 353 145 / 163 H1H5795B 1346 1348 1350 1352 1354 1356 1358 1360 H1H5796B 1362 1364 1366 1368 1370 1372 1374 1376 H1H5797B 1378 1380 1382 1384 1386 1388 1390 1392 H1H5798B 1394 1396 1398 1400 1402 1404 1406 1408 H1H5799P 1410 1412 1414 1416 1418 1420 1422 1424 H1H5801B 1426 1428 1430 1432 1434 1436 1438 1440 H1H7194B 1442 1444 1446 1448 1634 1636 1638 1640 H1H7195B 1450 1452 1454 1456 1634 1636 1638 1640 H1H7196B 1458 1460 1462 1464 1634 1636 1638 1640 H1H7198B 1466 1468 1470 1472 1634 1636 1638 1640 H1H7203B 1474 1476 1478 1480 1634 1636 1638 1640 H1H7204B 1482 1484 1486 1488 1634 1636 1638 1640 H1H7208B 1490 1492 1494 1496 1634 1636 1638 1640 H1H7211B 1498 1500 1502 1504 1634 1636 1638 1640 H1H7221B 1506 1508 1510 1512 1634 1636 1638 1640 H1H7223B 1514 1516 1518 1520 1634 1636 1638 1640 H1H7226B 1522 1524 1526 1528 1634 1636 1638 1640 H1H7232B 1530 1532 1534 1536 1634 1636 1638 1640 H1H7233B 1538 1540 1542 1544 1634 1636 1638 1640 H1H7241B 1546 1548 1550 1552 1634 1636 1638 1640 H1H7242B 1554 15561558 1560 1634 1636 1638 1640 H1H7250B 1638 1640 H1H7254B 1578 1580 1582 1584 1634 1636 1638 1640 H1H7258B 1586 1588 1590 1592 1634 1636 1638 1640 H1H7269B 1594 1596 1598 1600 1634 1636 1638 1640 H1H7279B 1602 1604 1606 1608 1634 1636 1638 1640 H1xH7221 G 1610 1612 1614 1616 1634 1636 1638 1640 H1xH7221 G3 1618 1620 1622 1624 1634 1636 1638 1640 H1xH7221 1626 1628 1630 1632 1634 1636 1638 1640 Petition 870260043419, dated 08 / 05 / 2026, pages 153 / 353 146 / 163 G5 Table 10: Nucleic Acid Sequence Identifiers SEQ ID Nos: Antibody Designation HCV R HCD R1 HCD R2 HCD R3 LCV R LCD R1 LCD R2 LCD R3 H1H2712N 401 403 405 407 409 411 413 415 H1M2692 N 417 419 421 423 425 427 429 431 H1M3542 N 433 435 437 439 441 443 445 447 H1M3544 N 449 451 453 455 457 459 461 463 H1M3549 N 465 467 469 471 473 475 477 479 H1M3613 N 481 483 485 487 489 491 493 495 527 H2M2691 N529 531 533 535 537 539 541 543 H2M2704 N545 547 549 551 553 555 557 559 573 575 H2M2706 N 577 579 581 583 585 587 589 591 623 Petition 870260043419, dated 08 / 05 / 2026, pages 154 / 353 147 / 163 N H2M2709 N 625 627 629 631 633 635 637 639 H2M2710 N 641 643 645 647 649 651 653 655 H2M2711 N 657 659 661 663 665 667 669 671 H2M2774 N 673 675 677 679 681 683 685 687 H2M2775 N 689 691 693 695 697 699 701 703 H2M2776 N 705 707 709 711 713 715 717 719 H2M2777 N 721 723 725 727 729 731 733 735 H2M2778 N 737 739 741 743 745 747 749 751 H2M2779 N 753 755 757 759 761 763 765 767 H2M2789 N 769 771 773 775 777 779 781 783 H2M2862 N 785 787 789 791 793 795 797 799 H2M2885 N 801 803 805 807 809 811 813 815 H2M2886 N 817 819 821 823 825 827 829 831 H2M3540 N 833 835 837 839 841 843 845 847 H2M3541 N 849 851 853 855 857 859 861 863 H2M3543 865 867 869 871 873 875 877 879 Petition 870260043419, on 05 / 08 / 2026, page. 155 / 353 148 / 163 N H2M3547 N 881 883 885 887 889 891 893 895 H2M3548 N 897 899 901 903 905 907 909 911 H2M3563 N 913 915 917 919 921 923 925 927 H1H5751P 929 931 933 935 937 939 941 943 H1H5752P 945 947 949 951 953 955 957 959 H1H5753B 961 963 965 967 969 971 973 975 H1H5754B 977 979 981 983 985 987 989 991 H1H5755B 993 995 997 999 1001 1003 1005 1007 H1H5756B 1009 1011 1013 1015 1017 1019 1021 1023 H1H5757B 1025 1027 1029 1031 1033 1035 1037 1039 H1H5758B 1041 1043 1045 1047 1049 1051 1053 1055 H1H5761P 1057 1059 1061 1063 1065 1067 1069 1071 H1H5763P 1073 1075 1077 1079 1081 1083 1085 1087 H1H5764P 1089 1091 1093 1095 1097 1099 1101 1103 H1H5769P 1105 1107 1109 1111 1113 1115 1117 1119 H1H5771P 1121 1123 1125 1127 1129 1131 1133 1135 H1H5772P 1137 1139 1141 1143 1145 1147 1149 1151 H1H5777P 1153 1155 1157 1159 1161 1163 1165 1167 H1H5778P 1169 1171 1173 1175 1177 1179 1181 1183 H1H5780P 1185 1187 1189 1191 1193 1195 1197 1199 H1H5781P 1201 1203 1205 1207 1209 1211 1213 1215 H1H5782P 1217 1219 12211223 1225 1227 1229 1231 H1H5785B 1233 1235 1237 1239 1241 1243 1245 1247 H1H5786B 1249 1251 1253 1255 1257 1259 1261 1263 H1H5788P 1265 1267 1269 1271 1273 1275 1277 1279 H1H5790B 1281 1283 1285 1287 1289 1291 1293 1295 H1H5791B 1297 1299 1301 1303 1305 1307 1309 1311 H1H5792B 1313 1315 1317 1319 1321 1323 1325 1327 Petition 870260043419, dated 08 / 05 / 2026, pages 156 / 353 149 / 163 H1H5793B 1329 1331 1333 1335 1337 1339 1341 1343 H1H5795B 1345 1347 1349 1351 1353 1355 1357 1359 H1H5796B 1361 1363 1365 1367 1369 1371 1373 1375 H1H5797B 1377 1379 1381 1383 1385 1387 1389 1391 H1H5798B 1393 1395 1397 1399 1401 1403 1405 1407 H1H5799P 1409 1411 1413 1415 1417 1419 1421 1423 H1H5801B 1425 1427 1429 1431 1433 1435 1437 1439 H1H7194B 1441 1443 1445 1447 1633 1635 1637 1639 H1H7195B 1449 1451 1453 1455 1633 1635 1637 1639 H1H7196B 1457 1459 1461 1463 1633 1635 1637 1639 H1H7198B 1465 1467 1469 1471 1633 1635 1637 1639 H1H7203B 1473 1475 1477 1479 1633 1635 1637 1639 H1H7204B 1481 1483 1485 1487 1633 1635 1637 1639 H1H7208B 1489 1491 1493 1495 1633 1635 1637 1639 H1H7211B 1497 1499 1501 1503 1633 1635 1637 1639 H1H7221B 1505 1507 1509 1511 1633 1635 1637 1639 H1H7223B 1513 1515 1517 1519 1633 1635 1637 1639 H1H7226B 1521 1523 1525 1527 1633 1635 1637 1639 H1H7232B 1529 1531 1533 1535 1633 1635 1637 1639 H1H7233B 1537 1539 1541 1543 1633 1635 1637 1639 H1H7241B 1545 15471549 1551 1633 1635 1637 1639 H1H7242B 1637 1639 H1H7251B 1569 1571 1573 1575 1633 1635 1637 1639 H1H7254B 1577 1579 1581 1583 1633 1635 1637 1639 H1H7258B 1585 1587 1589 1591 1633 1635 1637 1639 H1H7269B 1593 1595 1597 1599 1633 1635 1637 1639 H1H7279B 1601 1603 1605 1607 1633 1635 1637 1639 H1xH7221G 1609 1611 1613 1615 1633 1635 1637 1639 Petition 870260043419, dated 08 / 05 / 2026, pages 157 / 353 150 / 163 H1xH7221 G5 1625 1627 1629 1631 1633 1635 1637 1639

[00298] Antibodies are typically designated herein according to the following nomenclature: Fc prefix (e.g., “H1H”, “H1M”, “H2M”, etc.) followed by a numerical identifier (e.g., “2712”, “2692”, etc., as shown in Table 1) followed by a suffix “P”, “N”, or “B”. Thus, according to this nomenclature, an antibody may be referred to herein as, for example, “H1H2712N”, “H1M2692N”, “H2M2689N”, etc. The H1H, H1M, and H2M prefixes in the antibody designations used herein indicate the particular Fc region isotope of the antibody. For example, an “H1H” antibody has a human IgG1 Fc pattern, an “H1M” antibody has a mouse IgG1 Fc pattern, and an “H2M” antibody has a mouse IgG2 Fc pattern (all variable regions are fully human as denoted by the first “H” in the antibody designation).As will be observed by one skilled in the art, an antibody having a particular Fc isotype can be converted into an antibody with a different Fc isotype (for example, an antibody with a mouse IgG1 Fc can be converted into an antibody with a human IgG4, etc.) however, in any case, the variable domains (including the CDRs) - which are indicated by the numerical identifiers shown in Table 1 - will remain the same and the antigen-binding properties are expected to be substantially similar regardless of the nature of the Fc domain.

[00299] Tables 11 and 12 establish the amino acid sequence identifiers for variable heavy chain regions (Table 13) and variable light chain regions (Table 14) and their corresponding CDRs of additional anti-CD3 HCVRs and LCVRs useful in bispecific anti-STEAP2 x anti-CD3 antibodies of the invention. Petition 870260043419, dated 08 / 05 / 2026, pages 158 / 353 151 / 163 Table 11 (Amino Acid Sequences of Variable Region of Heavy Chain SEQ ID Nos: Heavy Chain Identifier HCVR HCDR1 HCDR2 HCDR3 CD3-VH-AA 1642 1644 1646 1648 CD3-VH-B 1658 1660 1662 1664 CD3-VH-C 1674 1676 1678 1680 CD3-VH-D 1690 1692 1694 1696 CD3-VH-E 1706 1708 1710 1712 CD3-VH-F# 1721 1722 1723 1724 Table 12 (Amino Acid Sequences of the Variable Region of Light Chain SEQ ID NOs: Light Current Identifier LCVR LCDR1 LCDR2 LCDR3 CD3-VL-AA 1650 1652 1654 1656 CD3-VL-B 1666 1668 1670 1672 CD3-VL-C 1682 1684 1686 1688 CD3-VL-D 1698 1700 1702 1704 CD3-VL-E 1714 1716 1718 1720 CD3-VL-F# 1725 1726 1727 1728

[00300] The variable heavy and light chain regions of CD3-VH-F and CD3-VL-F were derived from the anti-CD3 antibody designated “L2K” as established in WO2004 / 106380.

[00301] In addition, Tables 13 and 14 establish the sequence identifiers for the nucleotide sequences encoding the heavy chain variable regions (Table 13) and light chain variable regions (Table 14) and their corresponding CDRs, of additional anti-CD3 HCVRs and LCVRs useful in bispecific anti-STEAP2 x anti-CD3 antibodies of the invention. Petition 870260043419, dated 08 / 05 / 2026, pp. 159 / 353 152 / 163 Table 13 (Nucleotide Sequences Encoding Heavy Chain Variable Region Sequences) SEQ ID Nos: Heavy Chain Identifier HCVR HCDR1 HCDR2 HCDR3 CD3-VH-AA 1641 1643 1645 1647 CD3-VH-B 1657 1659 1661 1663 CD3-VH-C 1673 1675 1677 1679 CD3-VH-D 1689 1691 1693 1695 CD3-VH-E 1705 1707 1709 1711 Table 14 (Nucleotide Sequences Encoding Variable Light Chain Region Sequences) SEQ ID NOs: Light Current Identifier LCVR LCDR1 LCDR2 LCDR3 CD3-VL-AA 1649 1651 1653 1655 CD3-VL-B 1665 1667 1669 1671 CD3-VL-C 1681 1683 1685 1687 CD3-VL-D 1697 1699 1701 1703 CD3-VL-E 1713 1715 1717 1719 Control Structures Used in the Examples Below

[00302] Several control constructs (anti-CD3 antibodies) were included in the following experiments for comparative purposes: “OKT-3”, a mouse monoclonal antibody against human T cell surface antigens available from the American Type Culture Collection (ATCC) under catalog number CRL-8001; and “SP34”, a commercially available mouse monoclonal antibody obtained, for example, from Biolegend, San Diego, CA (Cat. No. 302914) or BD Pharmagen, Cat. 55052, reactive against the epsilon chain of the T3 complex in human T lymphocyte cells. Example 10: Generation of Additional Anti-CD3 Antibodies Petition 870260043419, dated 08 / 05 / 2026, p. 160 / 353 153 / 163

[00303] The following procedures were aimed at identifying antibodies that specifically recognized CD3 (T cell coreceptor) as an antigen.

[00304] A pool of anti-CD3 antibodies was derived from a genetically modified mouse. Briefly, mice were immunized with a CD3 antigen and generated B cells comprising a diversity of human VH rearrangements in order to express a diverse repertoire of high-affinity antigen-specific antibodies. The antibodies described in Tables 15-18 have the same VK1-39JK5 light chain sequence (LCVR established in SEQ ID NO: 1890).

[00305] Generated antibodies were tested for affinity to human and monkey cynomolgus CD3 antigen in an in vitro binding assay and, for example, a CD3 antibody designated CD3-VH-P (HCVR established in SEQ ID NO: 1882) was identified, among several others, that were found to bind to both human and cynomolgus CD3 having an EC50 between 1 and 40 nM affinity, as determined by a FACS titration of Jurkat cells and cynomolgus T cells, respectively. See, for example, FACS binding experiments outlined in Example 12 and in PCT / US2016 / 044732, filed July 29, 2016.

[00306] The amino acid residues of the CD3VH-P germline were subsequently identified, and an antibody designated “CD3-VH-L” was engineered to contain only germline structures. Other antibody derivatives were engineered using well-known molecular cloning techniques to replace amino acid residues in a stepwise manner based on the differences between the germline sequence and the CD3-VH-P sequence. Each antibody derivative is given a number designation, “CD3-VH-G”. See Table 15. Petition 870260043419, dated 08 / 05 / 2026, p. 161 / 353 154 / 163

[00307] Although CD3-VH-L and some other engineered antibodies retained their binding affinity as observed in FACS assays, several anti-CD3 antibodies in a bispecific format bound to human or cynomolgus CD3 in vitro with weak or unmeasurable binding affinity, such as greater than 100 nM EC50. Binding affinities, binding kinetics, and other biological properties to elucidate toxicity and pharmacokinetic (pK) profiles were subsequently further investigated as bispecific antibodies comprising the exemplary anti-CD3 antibodies were generated according to the methods of this Example. Example 11: Variable Heavy and Light Chain Regions (Amino Acid and Nucleic Acid Sequences of CDRs)

[00308] Table 15 sets forth the amino acid sequence identifiers of the variable heavy chain regions and CDRs of selected anti-CD3 antibodies of the invention. The corresponding nucleic acid sequence identifiers are set forth in Table 16.

[00309] Amino acid and nucleic acid sequences were determined for each antibody heavy chain sequence. Each antibody heavy chain derived from the germline sequence (SEQ ID NO: 1910) was assigned a “G” number designation for consistent nomenclature. Table 15 sets forth the amino acid sequence identifiers of the variable regions of the heavy chain and CDRs of engineered anti-CD3 antibodies of the invention. The corresponding nucleic acid sequence identifiers are set forth in Table 16. The amino acid and nucleic acid sequence identifiers of the variable region of the light chain and CDR are also identified below in Tables 17 and 18, respectively. Petition 870260043419, dated 08 / 05 / 2026, p. 162 / 353 155 / 163 Table 15: Heavy Chain Amino Acid Sequence Identifiers Antibody Designation CD3-VH SEQ ID NOs: HCVR CDR1 CDR2 CDR3 CD3-VH-G 1730 1732 1734 1736 CD3-VH-G2 1738 1740 1742 1744 CD3-VH-G3 1746 1748 1750 1752 CD3-VH-G4 1754 1756 1758 1760 CD3-VH-G5 1762 1764 1766 1768 CD3-VH-G8 1770 1772 1774 1776 CD3-VH-G9 1778 1780 1782 1784 CD3-VH-G10 1786 1788 1790 1792 CD3-VH-G11 1794 1796 1798 1800 CD3-VH-G12 1802 1804 1806 1808 CD3-VH-G13 1810 1812 1814 1816 CD3-VH-G14 1818 1820 1822 1824 CD3-VH-G15 1826 1828 1830 1832 CD3-VH-G16 1834 1836 1838 1840 CD3-VH-G17 1842 1844 1846 1848 CD3-VH-G18 1850 1852 1854 1856 CD3-VH-G19 1858 1860 1862 1864 CD3-VH-G20 1866 1868 1870 1872 CD3-VH-G21 1874 1876 1878 1880 CD3-VH-P 1882 1884 1886 1888 Petition 870260043419, dated 08 / 05 / 2026, page 163 / 353 156 / 163 Table 16: Heavy Chain Nucleic Acid Sequence Identifiers Antibody Designation CD3-VH SEQ ID NOs: HCVR CDR1 CDR2 CDR3 CD3-VH-G 1729 1731 1733 1735 CD3-VH-G2 1737 1739 1741 1743 CD3-VH-G3 1745 1747 1749 1751 CD3-VH-G4 1753 1755 1757 1759 CD3-VH-G5 1761 1763 1765 1767 CD3-VH-G8 1769 1771 1773 1775 CD3-VH-G9 1777 1779 1781 1783 CD3-VH-G10 1785 1787 1789 1791 CD3-VH-G11 1793 1795 1797 1799 CD3-VH-G12 1801 1803 1805 1807 CD3-VH-G13 1809 1811 1813 1815 CD3-VH-G14 1817 1819 1821 1823 CD3-VH-G15 1825 1827 1829 1831 CD3-VH-G16 1833 1835 1837 1839 CD3-VH-G17 1841 1843 1845 1847 CD3-VH-G18 1849 1851 1853 1855 CD3-VH-G19 1857 1859 1861 1863 CD3-VH-G20 1865 1867 1869 1871 CD3-VH-G21 1873 1875 1877 1879 CD3-VH-P 1881 1883 1885 1887 Table 17: Light Chain Amino Acid Sequence Identifiers Antibody Designation SEQ ID Nos: LCVR CDR1 CDR2 CDR3 VK1-39JK5 1890 1892 1894 1896 Petition 870260043419, dated 08 / 05 / 2026, page 164 / 353 157 / 163 Table 18: Light Chain Nucleic Acid Sequence Identifiers Antibody Designation SEQ ID Nos: LCVR CDR1 CDR2 CDR3 VK1-39JK5 1889 1891 1893 1895

[00310] Control antibody 1 designated “CD3-L2K” was constructed based on a known anti-CD3 antibody (i.e., the anti-CD3 antibody “L2K” as established in WO2004 / 106380).

[00311] Isotype Control Antibody, referred to here in the Examples, is a combined isotype antibody (modified IgG4) that interacts with an irrelevant antigen, i.e., FelD1 antigen. Example 12: In vitro and in vivo studies on human anti-CD3 monoclonal antibodies.

[00312] In vivo and in vitro studies on human anti-CD3 monoclonal antibodies were conducted as described in US publication 2014 / 0088295, published on March 27, 2014, and PCT / US2016 / 044732, filed on July 29, 2016, which are incorporated herein by reference.

[00313] Some human monoclonal anti-CD3 antibodies of the present invention bind soluble heterodimeric CD3 protein in either antibody-capture or antigen-capture formats with high affinity. Soluble heterodimeric CD3 protein (hCD3epsilon / hCD3-delta; SEQ ID NOs:1900 / 1901) was prepared with either a human Fc marker (hFcΔAdp / hFc; SEQ ID NOs:1931 / 1932) or a mouse Fc marker (mFcΔAdp / mFc; SEQ ID NOs:1933 / 1934). Heterodimeric CD3 protein was purified using the method described in Davis et al. (US2010 / 0331527).

[00314] Some human monoclonal anti-CD3 antibodies of the invention bound human T cells and induced cell proliferation. Petition 870260043419, dated 08 / 05 / 2026, pp. 165 / 353 158 / 163 T. Some human monoclonal anti-CD3 antibodies of the invention bound CD2+CD4+ monkey T cells and induced their proliferation. Some human monoclonal anti-CD3 antibodies supported redirected T cell-mediated killing via Fc / FcR interaction in a calcein-based U937 killing assay. The observed killing, believed to be dependent on antibody Fc engagement with the Fc receptor on U937 cells leading to CD3 clustering on adjacent T cells, was silenced by the addition of non-specific human IgG (data not shown). Example 13: In vitro studies in human STEAP2xCD3 bispecific antibodies.

[00315]

[0002] FACS Binding Titration in Jurkat Cells, PC3_STEAP2 / 1 and Cynomolgus T cells: Flow cytometry analysis was used to determine the binding of bispecific STEAP2xCD3 antibodies to Jurkat, chimeric PC3_STEAP2 / 1, and Cynomolgus T cells, followed by detection with a phycoerythrin-(PE)-labeled anti-human IgG antibody. Briefly, 2x10⁵ cells / well were incubated for 30 minutes at 4°C with a serial dilution of bispecific STEAP2xCD3 antibodies or a control antibody (a human IgG1 antibody that binds to a feline antigen without cross-reactivity to STEAP2 or human or Cynomolgus CD3) ranging from 66.6 nM to 0.001 nM. After incubation, the cells were washed twice with cold PBS containing 1% filtered FBS, and a PE-conjugated anti-human secondary antibody was added to the cells and incubated for an additional 30 minutes. Wells containing no antibody or only secondary antibody were used as a control.After incubation, the cells were washed, resuspended in 200 µL of cold PBS containing 1% filtered FBS, and analyzed by flow cytometry on a BD FACS Canto II. Petition 870260043419, dated 08 / 05 / 2026, page 166 / 353 159 / 163 Table 19: FACS binding of selected STEAP2xCD3 bispecific antibodies to Jurkat, PC3_STEAP2 / 1 and cynomolgus T cells Bispecific Antibody Designation FACS Jurkat EC50(M) FACS PC3_STEAP2 / 1 EC50 [M] Cynomolgus T Cells EC50(M) BSSTEAP2 / CD3- 0010 1.36E-08 No binding Very weak BSSTEAP2 / CD3- 004 6.88E-10 7.91E-08 1.99E-09 BSSTEAP2 / CD3- 0011 8.63E-09 No binding No binding BSSTEAP2 / CD3- 005 1.41E-08 3.18E-08 No binding BSSTEAP2 / CD3- 001 7.19E-09 3.44E-09 7.27E-09 BSSTEAP2 / CD3- 006 3.98E-09 1.22E-08 7.99E-09 BSSTEAP2 / CD3-007 6.15E-10 5.37E-09 1.73E-08 BSSTEAP2 / CD3-008 1.52E-09 6.88E-08 1.66E-08 BSSTEAP2 / CD3-009 4.14E-09 4.21E-08 No connection

[00316] Jurkat cells are derived from a lymphoblastic T cell line expressing human CD3. All bispecific antibodies tested (Table 19 and Figure 5) bound Jurkat cells with EC50 ranging from 1.41E-08 M to 6.15E-10 M. PC3 cells, a human prostate cancer cell line, were engineered to express a chimeric STEAP2 / 1 construct. Several bispecific antibodies bound PC3_STEAP2 / 1 cells, with EC50 ranging from 7.91E-08 M to 3.44E-09 M (Table 19 and Figure 6). Petition 870260043419, dated 08 / 05 / 2026, page 167 / 353 160 / 163

[00317] The binding of bispecific STEAP2xCD3 antibodies to the surface of purified Cynomolgus T cells was also tested. Several bispecific antibodies bound EC50 ranging from 1.73E-08 M to 7.27E-09 M. Control antibodies did not bind to any cell line. See Table 19 and Figures 7 and 8.

[00318] T-Cell Proliferation Assay: Freshly isolated thawed human or monkey PBMCs (50,000 cells / well) were incubated with 3-fold (human, concentration range: 5E-10M to 2.82E-15M; cynomolgus, concentration range: 1E-09M to 4.57E-13M) serial dilutions of bispecific STEAP2xCD3 or isotype control in complete medium (RPMI supplemented with 10% FBS, 100 U / mL penicillin, 100 pg / mL streptomycin, 292 pg / mL L-glutamine) and a fixed concentration (human: 200 ng / mL, cyano: 500 ng / mL) of a commercial anti-CD28 antibody (Biolegend, (Catalog#302914) in white 96-well flat-bottom plates for 72 hours at 37°C. Isolated monkey PBMCs were from two donors (identified as mk8781M or mk9381M). After incubation, CellTiter Glo® (Promega, Cat#7573) was added and luminescence, as a readout for cell viability, was measured using a VICTOR X5 multi-label plate reader.The cell titer was calculated by dividing the luminescence of stimulated cells by the baseline luminescence of unstimulated cells.

[00319]

[0003] All bispecific aSTEAP2xaCD3 antibodies induce human PBMC proliferation in the presence of a co-stimulatory anti-CD28 antibody (See Table 20 and Figure 9). PBMCs were incubated with a serial dilution of bispecific antibodies or the control antibody and a fixed concentration of anti-CD28 for 72 hours, and cell viability was measured in a luminescence assay to detect live cells. Proliferation was determined by comparing the luminescence of cells stimulated by bispecific antibodies. Petition 870260043419, dated 08 / 05 / 2026, page 168 / 353 161 / 163 with cells without antibody. EC50 values ​​(defined as the antibody concentration required to generate half the maximum proliferation) ranged from 3.68E-13M to 1.60E-10M. In contrast, the Control antibody did not exhibit activity under the same conditions. Table 20: T cell activation proliferation induced by Selected STEAP2xCD3 Bispecific Antibodies Designation of Bispecific Antibody hPBMC Proliferation [M] Cyno PBMC Proliferation [M] (donor) BSSTEAP2 / CD3-0010 6.55E-12 7.034E-13 (mk8781M) BSSTEAP2 / CD3-004 7.10E-13 [++] (mk8781M) [-] (mk9381M) BSSTEAP2 / CD3-011 8.62E-12 3.597E-12 (mk8781M) BSSTEAP2 / CD3-005 2.76E-12 [-] (mk9381M) (mk8781M) BSSTEAP2 / CD3-001 1.60E-10 4.592E-12 (mk9381M) [+] (mk8781M) BSSTEAP2 / CD3-006 8.14E-13 1.532E-11 (mk9381M) [+] (mk8781M) BSSTEAP2 / CD3-007 8.26E-11 [+ / -] (mk9381M) [+] (mk8781M) BSSTEAP2 / CD3-008 7.76E-12 [+ / -] (mk9381M) [+] (mk8781M) BSSTEAP2 / CD3-009 3.68E-13 [-] (mk9381M) (mk8781M)

[00320] Bispecific antibodies BSSTEAP2 / CD3-0010 and BSSTEAP2 / CD3-011 also induced cynomolgus PBMC proliferation (with donor mk8781 M) exhibiting EC50s of 7E-13 and 3.6E-12, respectively. The activity of BSSTEAP2 / CD3-004 was donor-dependent. Two additional bispecific antibodies, BSSTEAP2 / CD3001 and BSSTEAP2 / CD3-006, induced robust cynomolgus PBMC proliferation in all donors tested. EC50 values Petition 870260043419, dated 08 / 05 / 2026, page 169 / 353 162 / 163 using donor mk9381M were 4.6E-12M and 1.53E-11M, respectively (see Table 20 and Figure 10).

[00321]

[0004] BSSTEAP2 / CD3-007 Activity and BSSTEAP2 / CD3-008 was donor-dependent. In contrast, BSSTEAP2 / CD3-005, BSSTEAP2 / CD3-009, and the isotype control exhibited no activity.

[00322] Cytotoxicity assay targeting C4-2 cells in the presence of bispecific anti-STEAP2xCD3 antibodies and human T cells: In order to monitor the specific killing of STEAP2-bearing target cells by flow cytometry, C4-2 cells were labeled with 1μM of the fluorescent tracking dye Violet Cell Tracker (Life Technologies kit, #C34557). After labeling, the cells were plated overnight at 37°C. Separately, human PBMCs were plated in RPMI medium supplemented at 1x10⁶ cells / mL and incubated overnight at 37°C in order to enrich them for lymphocytes depleting adherent macrophages, dendritic cells, and some monocytes. The following day, target cells were co-incubated with naive PBMCs depleted of adherent cells (4:1 Effector / Target cell ratio) and a serial dilution of STEAP2xCD3 bispecific antibodies or an IgG1 control antibody (non-STEAP2 binding) (concentration range: 66.7 nM to 0.25 pM) for 48 hours at 37°C.Cells were removed from cell culture plates using an enzyme-free cell dissociation buffer and analyzed by FACS. For FACS analysis, cells were stained with a dead / alive far-red cell tracer (Invitrogen). 5 x 10⁵ bead counts were added to each well immediately before FACS analysis. 1 x 10⁵ beads were collected for each sample. For death specificity assessment, cells were blocked in populations labeled with live Violet. The percentage of the live population was recorded and used for survival calculation. Petition 870260043419, dated 08 / 05 / 2026, page 170 / 353 163 / 163 standardized.

[00323] T cell activation was assessed by incubating cells with antibodies directly conjugated to CD2 and CD69 and reporting the percentage of activated T cells (CD69+) out of total T cells (CD2+). Several bispecific anti-STEAP2xCD3 antibodies were tested for their ability to induce naive T cells to kill target cells expressing human STEAP2 (see Table 21 and Figure 11). All antibodies tested activated and directed human T cells to deplete C4-2 cells (human prostate adenocarcinoma subline derived from LnCap cells). Target cell death was only observed in the presence of the bispecific antibodies, with C4-2 cells depleted in a dose-dependent manner with pM EC50s. Additionally, the observed target cell lysis was associated with the upregulation of CD69 cells to CD2+ T cells with pM EC50s (see Table 21 and Figure 12). Table 21: Cytotoxicity and T cell activation properties of Selected STEAP2xCD3 Bispecific Antibodies Bispecific Antibody Designation C4-2 cell depletion EC50 [M] T cell activation EC50 [M] BSSTEAP2 / CD3-004 3.11E-12 9.40E-13 BSSTEAP2 / CD3-005 7.29E-12 +++ BSSTEAP2 / CD3-001 4.68E-12 1.61E-12 BSSTEAP2 / CD3-006 3.93E-12 +++ BSSTEAP2 / CD3-007 8.11E-12 +++ BSSTEAP2 / CD3-008 4.11E-12 +++ BSSTEAP2 / CD3-009 2.73E-12 +++

[00324] The present invention does not

Claims

1 / 6 CLAIMS 1. Antibody-drug conjugate (ADC), characterized in that it comprises an antibody or antigen-binding fragment thereof that specifically binds to human six-transmembrane epithelial prostate antigen 2 (STEAP2), and a cytotoxic agent, wherein the cytotoxic agent is a maytansinoid, in which the antibody or antigen-binding fragment thereof and the cytotoxic agent are covalently linked via a ligand, and wherein the antibody or antigen-binding fragment thereof comprises the complementarity-determining regions HCDR1-HCDR2-HCDR3-LCDR1-LCDR2-LCDR3 comprising the amino acid sequences of SEQ ID NOs: 220-222-224-228-230-232, respectively, wherein the ADC is internalized by cells expressing human STEAP2.

2. ADC, according to claim 1, characterized in that the antibody or antigen-binding fragment thereof comprises a heavy chain variable region (HCVR) comprising the amino acid sequence of SEQ ID NO: 218 and a light chain variable region (LCVR) comprising the amino acid sequence of SEQ ID NO:

226.

3. ADC, according to claim 1 or 2, characterized in that the antibody or antigen-binding fragment thereof is fully human.

4. ADC, according to any one of claims 1 to 3, characterized in that maytansinoid is DM1.

5. ADC, according to any one of claims 1 to 3, characterized in that the maytansinoid is DM4.

6. ADC, according to any one of claims 1 to 3, characterized in that the maytansinoid is: Petition 870260043419, dated 08 / 05 / 2026, page 172 / 353 2 / 6 0 CH3 ; or the CH3 ; or the CH3 7. ADC, according to any one of claims 1 to 3, characterized in that it comprises the antibody or antigen-binding fragment thereof, and: wherein "is an antibody-binding fragment or antigen-binding fragment thereof." 8. ADC, according to any one of claims 1 to 3, characterized in that it comprises the antibody or antigen-binding fragment thereof, and Petition 870260043419, dated 08 / 05 / 2026, page 173 / 353 3 / 6 where it is an antibody-binding fragment or antigen-binding fragment thereof.

9. ADC, according to any one of claims 1 to 3, characterized in that it comprises the antibody or antigen-binding fragment thereof, and -fem that « is an antibody-binding fragment or antigen-binding fragment thereof.

10. ADC, according to any one of claims 7 to 9, characterized in that the binding contacts the antibody or a fragment thereof via a sulfur constituent of a cysteine ​​residue.

11. ADC, according to any one of claims 1 to 3, characterized in that it comprises the antibody or antigen-binding fragment thereof, and Petition 870260043419, dated 08 / 05 / 2026, page 174 / 353 4 / 6 a mixture thereof, wherein "it is an antibody-binding fragment or antigen-binding fragment thereof." 12. ADC, according to claim 11, characterized in that the binding contacts the antibody or antigen-binding fragment thereof via a nitrogenous constituent of a lysine residue.

13. ADC, according to any one of claims 1 to 12, characterized in that it comprises 1 to 4 cytotoxic agents per antibody or antigen-binding fragment thereof.

14. Pharmaceutical composition, characterized in that it comprises the antibody-drug conjugate, as defined in any one of claims 1 to 13, and a pharmaceutically acceptable vehicle or diluent.

15. Antibody or antigen-binding fragment thereof that specifically binds to human cells expressing six-transmembrane epithelial prostate antigen 2 (STEAP2), Petition 870260043419, dated 08 / 05 / 2026, page 175 / 353 5 / 6, characterized in that the antibody or antigen-binding fragment thereof comprises the complementarity-determining regions HCDR1-HCDR2-HCDR3-LCDR1-LCDR2-LCDR3 comprising the amino acid sequences SEQ ID NOs: 220-222-224-228-230-232, respectively, wherein the antibody or antigen-binding fragment thereof is internalized by cells expressing human STEAP2.

16. Antibody or antigen-binding fragment thereof, according to claim 15, characterized in that the antibody comprises a heavy chain variable region (HCVR) comprising the amino acid sequence of SEQ ID NO: 218 and a light chain variable region (LCVR) comprising the amino acid sequence of SEQ ID NO:

226.

17. Antibody or antigen-binding fragment thereof, according to claim 15 or 16, characterized in that it is wholly human.

18. Pharmaceutical composition, characterized in that it comprises the antibody or antigen-binding fragment thereof, as defined in any one of claims 15 to 17, and a pharmaceutically acceptable vehicle or diluent.

19. Use of the antibody-drug conjugate (ADC), as defined in any one of claims 1 to 13, or of the pharmaceutical composition, as defined in claim 14, characterized in that it is for the manufacture of a medicament to treat a cancer that expresses STEAP2 in an individual.

20. Use, according to claim 19, characterized in that the cancer is selected from the group consisting of prostate cancer, bladder cancer, cervical cancer, lung cancer, colon cancer, kidney cancer, breast cancer, pancreatic cancer, stomach cancer, uterine cancer, and ovarian cancer. Petition 870260043419, dated 08 / 05 / 2026, p. 176 / 353 6 / 6 21. Use, according to claim 20, characterized in that the cancer is prostate cancer. Petition 870260043419, dated 08 / 05 / 2026, p. 177 / 353

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