5T4 ANTIBODY-DRUG CONJUGATES AND METHODS OF THEIR USE

Abstract

Treatments for cancer using 5T4 ADCs, optionally in combination with a PD-L1 / PD-1 inhibitor such as pembrolizumab, are presented. Cancers eligible for treatment include breast cancer, endometrial cancer, head and neck cancer, pancreatic cancer, lung cancer, prostate cancer, cervical cancer, bladder cancer, renal cell carcinoma (RCC), hepatocellular carcinoma (HCC), and colorectal cancer.

Description

Attorney Docket No.14529-168-228 5T4 ANTIBODY DRUG CONJUGATES AND METHODS OF THEIR USE 1. CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Patent Application Nos. 63 / 599,497, filed November 15, 2023, and 63 / 608,755, filed December 11, 2023, the disclosure of each of which is incorporated by reference herein in its entirety. 2. SEQUENCE LISTING

[0002] This application contains an electronic Sequence Listing which has been submitted in XML file format with this application, the entire content of which is incorporated by reference herein in its entirety. The Sequence Listing XML file submitted with this application is entitled “14529-168-228_SEQ_LISTING.xml”, was created on November 12, 2024, and is 146,919 bytes in size. 3. FIELD

[0003] The present disclosure relates generally to a 5T4 antibody drug conjugate and methods of its use in treating cancer. 4. BACKGROUND

[0004] 5T4, also known as Wnt-Activated Inhibitory Factor 1 or WAIF1, is an N- glycosylated transmembrane 72 kDa glycoprotein containing eight leucine-rich repeats.5T4 is often referred to as an oncofetal antigen due to its expression in fetal trophoblast (where it was first discovered) or as trophoblast glycoprotein (TPBG).5T4 is found in various tumors. Although its confined expression would appear to give 5T4 the potential to be a target in cancer therapy, therapeutic success with antibodies, ADCs, and vaccines targeting 5T4 has not yet been achieved.

[0005] There remains a need in the art for ADCs that can target 5T4 to treat, prevent, or alleviate 5T4-mediated diseases, disorders, or conditions, such as those involving tumor cells expressing 5T4. 5. SUMMARY

[0006] Provided is a method for treating cancer in a subject. The method comprises administering an ADC to the subject. The cancer is any one or more of breast cancer, endometrial cancer (EC), head and neck cancer, pancreatic cancer, lung cancer, prostate cancer, cervical cancer, bladder cancer, renal cell carcinoma (RCC), hepatocellular carcinoma (HCC), or colorectal cancer. In some embodiments, the cancer is triple-negative breast cancer (TNBC). In some embodiments, the cancer is hormone-receptor positive breast cancer (HR+ 1 NAI-1541858741BC). In some embodiments, the cancer is pancreatic ductal adenocarcinoma (PDAC). In some embodiments, the cancer is non-small cell lung cancer (NSCLC). In some embodiments, the cancer is head and neck squamous cell carcinoma (HNSCC). In some embodiments, the cancer is endometrial cancer (EC).

[0007] In some embodiments, the ADC is represented by Formula (I’):(I’), wherein the Ab is a 5T4 antibody or an antigen binding fragment thereof, and wherein the Ab comprises: (1) a heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), and a heavy chain complementarity determining region 3 (HCDR3) as set forth in a heavy chain variable region (VH) comprising the amino acid sequence of SEQ ID NO: 11, and (2) a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and a light chain complementarity determining region 3 (LCDR3) as set forth in a light chain variable region (VL) comprising the amino acid sequence of SEQ ID NO: 12; wherein the Ab further comprises one or more fGly’, wherein fGly’ is a formylglycine amino acid residue to which the non-Ab part of Formula (I’) is attached; wherein the MMAE is monomethyl auristatin E and represented by Formula (III):wherein * indicates the point of attachment in Formula (I’); and wherein n is an integer. In further embodiments, n is an integer selected from any one of 1 to 10. In yet further embodiments, n is 2.

[0008] In some embodiments, the ADC is represented by Formula (I): 2 NAI-1541858741(I), wherein the Ab is a 5T4 antibody or an antigen binding fragment thereof, and wherein the Ab comprises: (1) a heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), and a heavy chain complementarity determining region 3 (HCDR3) as set forth in a heavy chain variable region (VH) comprising the amino acid sequence of SEQ ID NO: 11, and (2) a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and a light chain complementarity determining region 3 (LCDR3) as set forth in a light chain variable region (VL) comprising the amino acid sequence of SEQ ID NO: 12; wherein the Ab further comprises one or more fGly’, wherein the MMAE is monomethyl auristatin E and represented by Formula (III):(III), wherein * indicates the point of attachment in Formula (I) and wherein fGly’ is a formylglycine amino acid residue to which the non-Ab part of Formula (I) is attached.

[0009] In some embodiments, the ADC comprises an antibody (Ab) conjugated to a monomethyl auristatin E (MMAE) by a linker (L-1):(L-1), 3 NAI-1541858741wherein the wavy line indicates the point of attachment to the Ab and the ## indicates the point of attachment to the MMAE; wherein the MMAE is represented by Formula (III):wherein * indicates the point of attachment to (L-1); wherein the Ab is a 5T4 antibody or an antigen binding fragment thereof, and wherein the Ab comprises: (1) a heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), and a heavy chain complementarity determining region 3 (HCDR3) as set forth in a heavy chain variable region (VH) comprising the amino acid sequence of SEQ ID NO: 11, and (2) a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and a light chain complementarity determining region 3 (LCDR3) as set forth in a light chain variable region (VL) comprising the amino acid sequence of SEQ ID NO: 12; and wherein the Ab further comprises one or more fGly’ and wherein fGly’ is a formylglycine amino acid residue to which linker (L-1) is attached. In further embodiments, one Ab is conjugated to one to ten MMAEs and each MMAE is conjugated to Ab by one linker (L-1). In yet further embodiments, one Ab is conjugated to two MMAEs and each MMAE is conjugated to Ab by one linker (L-1).

[0010] In some embodiments, the ADC is produced by conjugating an antibody (Ab) to a linker-drug comprising a pre-conjugate linker (L-1a’) and a monomethyl auristatin E (MMAE):(L-1a’), wherein the ## indicates the point of attachment to the MMAE; wherein the MMAE is represented by Formula (III): 4 NAI-1541858741(III), wherein * indicates the point of attachment to (L-1a’); wherein the Ab is a 5T4 antibody or an antigen binding fragment thereof, and wherein the Ab comprises: (1) a heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), and a heavy chain complementarity determining region 3 (HCDR3) as set forth in a heavy chain variable region (VH) comprising the amino acid sequence of SEQ ID NO: 11, and (2) a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and a light chain complementarity determining region 3 (LCDR3) as set forth in a light chain variable region (VL) comprising the amino acid sequence of SEQ ID NO: 12; and wherein the Ab further comprises one or more fGly’ and wherein fGly’ is a formylglycine amino acid residue to which linker (L-1a’) is attached after conjugating the Ab and the linker-drug. In further embodiments, one Ab is conjugated to one to ten linker-drugs. In yet further embodiments, one Ab is conjugated to two linker-drugs.

[0011] In any of the embodiments as disclosed herein, for example, in the ADCs represented by Formula (I’) or Formula (I), or the ADCs comprising (L-1), or the ADCs produced by conjugating (L-1a’), the Ab comprises one to ten fGly’. In further embodiments, the Ab comprises two fGly’.

[0012] In any of the embodiments as disclosed herein, for example, in the ADCs represented by Formula (I’) or Formula (I), or the ADCs comprising (L-1), or the ADCs produced by conjugating (L-1a’), the Ab comprises a motif of X1(fGly’)X2Z2X3Z3(SEQ ID NO: 67), wherein: Z2is either a proline (P) or alanine (A) residue; Z3is a basic amino acid residue or an aliphatic amino acid residue; X1is present or absent and, when present, is any amino acid residue, with the proviso that when the sequence of SEQ ID NO: 67 is at the N- terminus of the antibody Ab, X1is present; and X2and X3independently is any amino acid residue. In some embodiments, the basic amino acid residue is selected from the group consisting of: arginine (R), lysine (K), and histidine (H). Additionally or alternatively, the aliphatic amino acid residue is selected from the group consisting of: alanine (A), glycine (G), leucine (L), valine (V), isoleucine (I), and proline (P). In some embodiments, the motif of SEQ ID NO: 67 is selected from the group consisting of: L(fGly’)TPSR (SEQ ID NO: 1), 5 NAI-1541858741M(fGly’)TPSR (SEQ ID NO: 45), V(fGly’)TPSR (SEQ ID NO: 46), L(fGly’)SPSR (SEQ ID NO: 47), L(fGly’)APSR (SEQ ID NO: 48), L(fGly’)VPSR (SEQ ID NO: 49), L(fGly’)GPSR (SEQ ID NO: 50), I(fGly’)TPAR (SEQ ID NO: 51), L(fGly’)TPSK (SEQ ID NO: 52), M(fGly’)TPSK (SEQ ID NO: 53), V(fGly’)TPSK (SEQ ID NO: 54), L(fGly’)SPSK (SEQ ID NO: 55), L(fGly’)APSK (SEQ ID NO: 56), L(fGly’)VPSK (SEQ ID NO: 57), L(fGly’)GPSK (SEQ ID NO: 58), L(fGly’)TPSA (SEQ ID NO: 59), I(fGly’)TPAA (SEQ ID NO: 60), M(fGly’)TPSA (SEQ ID NO: 61), V(fGly’)TPSA (SEQ ID NO: 62), L(fGly’)SPSA (SEQ ID NO: 63), L(fGly’)APSA (SEQ ID NO: 64), L(fGly’)VPSA (SEQ ID NO: 65), and L(fGly’)GPSA (SEQ ID NO: 66).

[0013] In any of the embodiments as disclosed herein, for example, in the ADCs represented by Formula (I’) or Formula (I), or the ADCs comprising (L-1), or the ADCs produced by conjugating (L-1a’), the Ab comprises two heavy chains and two light chains, and wherein each of the heavy chains comprises a motif of SEQ ID NO: 67. In any of the embodiments as disclosed herein, for example, in the ADCs represented by Formula (I’) or Formula (I), or the ADCs comprising (L-1), or the ADCs produced by conjugating (L-1a’), the Ab comprises an amino acid sequence of L(fGly’)TPSR (SEQ ID NO: 1). In further embodiments, the Ab comprises two heavy chains and two light chains, and wherein each of the heavy chains comprises a motif of L(fGly’)TPSR (SEQ ID NO: 1). In some embodiments, the fGly’ of the motif is located in the heavy chain at a position corresponding to the 453rdamino acid residue of SEQ ID NO: 2.

[0014] In any of the embodiments as disclosed herein, for example, in the ADCs represented by Formula (I’) or Formula (I), or the ADCs comprising (L-1), or the ADCs produced by conjugating (L-1a’), the Ab is a 5T4 antibody or antigen binding fragment thereof as disclosed herein.

[0015] In some embodiments, the Ab comprises HCDR1 comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 13, 19, 24, 25, and 30; HCDR2 comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 14, 20, 26, 31, and 36; HCDR3 comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 15, 21, 27, and 32; LCDR1 comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 16, 22, 28, and 33; LCDR2 comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 17, 23, and 34; and LCDR3 comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 18, 29, and 35. 6 NAI-1541858741

[0016] In some embodiments, HCDR1 comprises the amino acid sequence of SEQ ID NO: 13, HCDR2 comprises the amino acid sequence of SEQ ID NO: 14, HCDR3 comprises the amino acid sequence of SEQ ID NO: 15, LCDR1 comprises the amino acid sequence of SEQ ID NO: 16, LCDR2 comprises the amino acid sequence of SEQ ID NO: 17, and LCDR3 comprises the amino acid sequence of SEQ ID NO: 18. In some embodiments, HCDR1 comprises the amino acid sequence of SEQ ID NO: 19, HCDR2 comprises the amino acid sequence of SEQ ID NO: 20, HCDR3 comprises the amino acid sequence of SEQ ID NO: 21, LCDR1 comprises the amino acid sequence of SEQ ID NO: 22, LCDR2 comprises the amino acid sequence of SEQ ID NO: 23, and LCDR3 comprises the amino acid sequence of SEQ ID NO: 18. In some embodiments, HCDR1 comprises the amino acid sequence of SEQ ID NO: 24, HCDR2 comprises the amino acid sequence of SEQ ID NO: 14, HCDR3 comprises the amino acid sequence of SEQ ID NO: 15, LCDR1 comprises the amino acid sequence of SEQ ID NO: 16, LCDR2 comprises the amino acid sequence of SEQ ID NO: 17, and LCDR3 comprises the amino acid sequence of SEQ ID NO: 18. In some embodiments, HCDR1 comprises the amino acid sequence of SEQ ID NO: 25, HCDR2 comprises the amino acid sequence of SEQ ID NO: 26, HCDR3 comprises the amino acid sequence of SEQ ID NO: 27, LCDR1 comprises the amino acid sequence of SEQ ID NO: 28, LCDR2 comprises the amino acid sequence of SEQ ID NO: 23, and LCDR3 comprises the amino acid sequence of SEQ ID NO: 29. In some embodiments, HCDR1 comprises the amino acid sequence of SEQ ID NO: 30, HCDR2 comprises the amino acid sequence of SEQ ID NO: 31, HCDR3 comprises the amino acid sequence of SEQ ID NO: 32, LCDR1 comprises the amino acid sequence of SEQ ID NO: 33, LCDR2 comprises the amino acid sequence of SEQ ID NO: 34, and LCDR3 comprises the amino acid sequence of SEQ ID NO: 35. In some embodiments, HCDR1 comprises the amino acid sequence of SEQ ID NO: 13, HCDR2 comprises the amino acid sequence of SEQ ID NO: 36, HCDR3 comprises the amino acid sequence of SEQ ID NO: 15, LCDR1 comprises the amino acid sequence of SEQ ID NO: 16, LCDR2 comprises the amino acid sequence of SEQ ID NO: 17, and LCDR3 comprises the amino acid sequence of SEQ ID NO: 18.

[0017] In some embodiments, the Ab comprises a VH comprising the amino acid sequence of SEQ ID NO: 11 and a VL comprising the amino acid sequence of SEQ ID NO: 12. In further embodiments, the Ab comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 2 and a light chain comprising the amino acid sequence of SEQ ID NO: 3. 7 NAI-1541858741

[0018] In some embodiments, a method of administering an ADC as disclosed herein is combined with administrating to the subject means for inhibiting interaction between PD-1 and PD-L1, such as a PD-L1 / PD-1 inhibitor. One example of such means for inhibiting interaction between PD-1 and PD-L1 is pembrolizumab. In some embodiments, the method as disclosed herein further comprises administrating to the subject means for inhibiting interaction between PD-1 and PD-L1. In some embodiments, the ADC is administered concurrently with the means for inhibiting interaction between PD-1 and PD-L1. In some embodiments, the ADC is administered after the means for inhibiting interaction between PD-1 and PD-L1. In some embodiments, the ADC is administered before the means for inhibiting interaction between PD-1 and PD-L1.

[0019] In some embodiments, a method of administering an ADC as disclosed herein is combined with administrating to the subject a PD-L1 / PD-1 inhibitor. In some embodiments, the method as disclosed herein further comprises administrating to the subject a PD-L1 / PD-1 inhibitor. In some embodiments, the ADC is administered concurrently with the PD-L1 / PD-1 inhibitor. In some embodiments, the ADC is administered after the PD-L1 / PD-1 inhibitor. In some embodiments, the ADC is administered before the PD-L1 / PD-1 inhibitor. Additionally or alternatively, in some embodiments, the PD-L1 / PD-1 inhibitor is an antibody or an antigen binding fragment thereof comprising HCDR1, HCDR2, HCDR3, LCDR1, LCDR2, and LCDR3 of pembrolizumab. In further embodiments, the PD-L1 / PD-1 inhibitor is pembrolizumab. In yet further embodiments, the PD-L1 / PD-1 inhibitor is administered to the subject at a dose of about 200 mg. Additionally or alternatively, in some embodiments, the PD-L1 / PD-1 inhibitor is administered intravenously. Additionally or alternatively, in some embodiments, the PD-L1 / PD-1 inhibitor is administered once every 3 weeks (q3w).

[0020] In any of the embodiments as disclosed herein, for example, in the ADCs represented by Formula (I’) or Formula (I), or the ADCs comprising (L-1), or the ADCs produced by conjugating (L-1a’), the ADC is administered intravenously. Additionally or alternatively, in some embodiments, the ADC is administered once every 3 weeks (q3w).

[0021] In some embodiments, wherein the subject is human. 6. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG.1 provides a method for synthesizing the ADC as disclosed herein (such as 5T4-ADC-1) according to Example 1.

[0023] FIG.2 depicts a schematic of the BOIN design. 8 NAI-1541858741

[0024] FIG.3 depicts a scheme depicting the BOIN design for the Dose Escalation Stage described in the Examples.

[0025] FIGs.4A-4B show in vitro cytotoxic activities of 5T4-ADC-1 in MCF-7 (FIG. 4A) and MDA-MB-468 (FIG.4B) breast cancer cell lines, as further illustrated in Example 3.5T4-ADC-1 mediated in vitro cytotoxicity was observed in both tumor cell lines that were used for in vivo xenograft studies. In both cell lines, 5T4-ADC-1 demonstrated improved potency and similar maximal inhibition compared with the positive control (5T4-targeting mafodotin ADC).

[0026] FIGs.5A-5E show in vivo tumor growth inhibition and survival curves following IV administration of 5T4-ADC-1 in the MCF-7 (FIGs.5A-5D) and MDA-MB-468 (FIG. 5E) murine breast cancer xenograft models, as further illustrated in Example 3. Dose response study with either a single dose (FIG.5A) or once per week for two weeks (QWx2) dosing (FIG.5B) of 5T4-ADC-1 was performed. Survival curves for single dose (FIG.5C) and QWx2 dose (FIG.5D) studies were plotted.5T4-ADC-1 led to dose-related tumor volume suppression and longer survival (right-shifted curves) compared with vehicle following either dosing regimen. As shown in FIG.5E, 5T4-ADC-1 produced maximal and durable suppression starting at 20 days post dose. Survival curves were not generated for this study as only 2 / 8 animals in the vehicle reached the prespecified survival outcome. SEM, standard error of the mean.

[0027] FIGs.6A-6B show combinatorial efficacy for 5T4-ADC-1 and anti-PD-1 checkpoint inhibitor in a mouse syngeneic MC38-h5T4 model, as further illustrated in Example 3. Combination of 5T4-ADC-1 and anti-PD-1 reagent enhanced anti-tumor activity and improved survival compared with either agent administered alone. BIW, twice-weekly; i.v., intravenous; PD-1, programmed cell death protein 1; SEM, standard error of the mean.

[0028] FIGs.7A-7C show in vivo tumor growth inhibition following single dose IV administration of 5T4-ADC-1 (10 mg / kg) in murine PDX models of HNSCC (FIG.7A), NSCLC (FIG.7B), and breast cancer (non-TNBC) (FIG.7C), as further illustrated in Example 3. IV, intravenous; NSCLC, non-small cell lung cancer; SEM, standard error of the mean; HNSCC, squamous cell cancer of the head and neck; TGI, tumor growth inhibition.

[0029] FIGs.8A-8B plot 5T4 expression of patient tumor tissue samples (FIG.8A, HScores; FIG.8B, percentages of 5T4 positive tumor cells), as further illustrated in Example 4. 9 NAI-15418587417. DETAILED DESCRIPTION

[0030] In one aspect, provided herein is a method for treating a cancer in a subject, the method comprising administering an ADC to the subject at a therapeutically effective dose, wherein the ADC is represented by Formula (I’) or Formula (I).

[0031] In some embodiments, the ADC is represented by Formula (I’):(I’), wherein the Ab is a 5T4 antibody or an antigen binding fragment thereof, and wherein the Ab comprises: (1) a heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), and a heavy chain complementarity determining region 3 (HCDR3) as set forth in a heavy chain variable region (VH) comprising the amino acid sequence of SEQ ID NO: 11, and (2) a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and a light chain complementarity determining region 3 (LCDR3) as set forth in a light chain variable region (VL) comprising the amino acid sequence of SEQ ID NO: 12; wherein the Ab further comprises one or more fGly’, wherein fGly’ is a formylglycine amino acid residue to which the non-Ab part of Formula (I’) is attached; wherein the MMAE is monomethyl auristatin E and represented by Formula (III):wherein * indicates the point of attachment in Formula (I’); and wherein n is an integer. In further embodiments, n is an integer selected from any one of 1 to 10. In yet further embodiments, n is 2. 10 NAI-1541858741

[0032] In some embodiments, the ADC is represented by Formula (I) and comprises an Ab conjugated to a monomethyl auristatin E (MMAE) by a linker (L-1):(I), wherein the Ab is a 5T4 antibody or an antigen binding fragment thereof and comprises a heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), a heavy chain complementarity determining region 3 (HCDR3), a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and a light chain complementarity determining region 3 (LCDR3) of an antibody designated mAbA15, wherein the Ab further comprises two motifs, each of which is L(fGly’)TPSR (SEQ ID NO: 1), wherein fGly’ is the amino acid residue to which a linker-drug comprising (L-1) is attached, and wherein mAbA15 comprises: a) a heavy chain comprising an amino acid sequence of: EVQLVESGGGLVQPGGSLRLSCAASGFTFSSYYIHWVRQAPGKGLEWVAYITSTGSY TEYADSVKGRFTISADTSKNTAYLQMNSLRAEDTAVYYCARYDRSTRYSGLDYWG QGTLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTS GVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDK THTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVD GVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTI SKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKT TPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGSL (fGly’)TPSRGS (SEQ ID NO: 2); and b) a light chain comprising an amino acid sequence of: DIQMTQSPSSLSASVGDRVTITCRASQSVSSAVAWYQQKPGKAPKLLIYSASSLYSGV PSRFSGSRSGTDFTLTISSLQPEDFATYYCQQAYATPVTFGQGTKVEIKRTVAAPSVFI FPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTY SLSSTLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 3); 11 NAI-1541858741wherein L-1 is:wherein the wavy line indicates the point of attachment to the Ab and the ## indicates the point of attachment to the MMAE; and wherein the MMAE is represented by Formula (III):wherein * indicates the point of attachment to (L-1).

[0033] In some embodiments, the ADC is represented by Formula (I): wherein the Ab is a 5T4 antibody or an antigen binding fragment thereof, and wherein the Ab comprises: (1) a heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), and a heavy chain complementarity determining region 3 (HCDR3) as set forth in a heavy chain variable region (VH) comprising the amino acid sequence of SEQ ID NO: 11, and (2) a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and a light chain complementarity determining region 3 (LCDR3) as set forth in a light chain variable region (VL) comprising the amino acid sequence of SEQ ID NO: 12; wherein the Ab further comprises one or more fGly’, wherein the MMAE is monomethyl auristatin E and represented by Formula (III).

[0034] In certain embodiments, the cancer is any one or more of breast cancer, endometrial cancer, head and neck cancer, pancreatic cancer, lung cancer, prostate cancer, cervical cancer, or bladder cancer. In certain embodiments, the cancer is pancreatic adenocarcinoma (PDAC, also referred to herein as pancreatic ductal adenocarcinoma). In certain embodiments, the cancer is lung adenocarcinoma or squamous cell lung carcinoma. In certain embodiments, the cancer is non-small cell lung cancer (NSCLC). In certain embodiments, the cancer is head and neck cancer. In certain embodiments, the cancer is head 12 NAI-1541858741and neck squamous cell carcinoma (HNSCC). In certain embodiments, the cancer is renal cell carcinoma (RCC), hepatocellular carcinoma (HCC), or colorectal cancer.

[0035] In certain embodiments, the ADC is administered to the subject at a dose of about 0.1 mg / kg to about 10.0 mg / kg. In certain embodiments, the ADC is administered to the subject at a dose of about 0.3 mg / kg to about 6.0 mg / kg, or about 0.3 mg / kg to about 2.0 mg / kg. In certain embodiments, the ADC is administered to the subject at a dose of about 0.3 mg / kg, about 0.6 mg / kg, about 1.0 mg / kg, about 1.5 mg / kg, or about 2.0 mg / kg.

[0036] In certain embodiments, the Ab comprises two heavy chains (HCs) and two light chains (LCs), and wherein each of the HCs comprises one motif of L(fGly’)TPSR (SEQ ID NO: 1).

[0037] In certain embodiments, the ADC is administered to the subject on the first day of a treatment cycle for one or more treatment cycles. In certain embodiments, each treatment cycle is 3 weeks ± 3 days. In certain embodiments, the ADC is administered to the subject once every three weeks (q3w). In certain embodiments, the ADC is administered to the subject intravenously.

[0038] In certain embodiments, the method comprises administering to the subject a PD- L1 / PD-1 inhibitor. In certain embodiments, the PD-L1 / PD-1 inhibitor is administered to the subject once every three weeks (q3w). In certain embodiments, the PD-L1 / PD-1 inhibitor is administered to the subject intravenously. In certain embodiments, the PD-L1 / PD-1 inhibitor is pembrolizumab. In certain embodiments, the PD-L1 / PD-1 inhibitor is administered to the subject at a dose of about 200 mg.

[0039] In certain embodiments, the subject is human.

[0040] In another aspect, provided herein is a method of treating a cancer for two or more treatment cycles in a subject experiencing an adverse event when administered an ADC, the method comprising: (i) administering the ADC to the subject at a dose of about 0.1 mg / kg to about 10.0 mg / kg in a first treatment cycle; (ii) delaying a further administration of the ADC to the subject upon the subject having an adverse event after the first treatment cycle and before the second treatment cycle; and (iii) resuming the administration of the ADC in a second treatment cycle, wherein the ADC is represented by Formula (I) and comprises an Ab conjugated to a monomethyl auristatin E (MMAE) by a linker (L-1): 13 NAI-1541858741wherein the Ab is a 5T4 antibody or an antigen binding fragment thereof and comprises a heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), a heavy chain complementarity determining region 3 (HCDR3), a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and a light chain complementarity determining region 3 (LCDR3) of an antibody designated mAbA15, wherein the Ab further comprises two motifs, each of which is L(fGly’)TPSR (SEQ ID NO: 1), wherein fGly’ is the amino acid residue to which a linker-drug comprising (L-1) is attached, and wherein mAbA15 comprises: a) a heavy chain comprising an amino acid sequence of: EVQLVESGGGLVQPGGSLRLSCAASGFTFSSYYIHWVRQAPGKGLEWVAYITSTGSY TEYADSVKGRFTISADTSKNTAYLQMNSLRAEDTAVYYCARYDRSTRYSGLDYWG QGTLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTS GVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDK THTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVD GVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTI SKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKT TPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGSL (fGly’)TPSRGS (SEQ ID NO: 2); and b) a light chain comprising an amino acid sequence of: DIQMTQSPSSLSASVGDRVTITCRASQSVSSAVAWYQQKPGKAPKLLIYSASSLYSGV PSRFSGSRSGTDFTLTISSLQPEDFATYYCQQAYATPVTFGQGTKVEIKRTVAAPSVFI FPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTY SLSSTLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 3); wherein (L-1) is: 14 NAI-1541858741wherein the wavy line indicates the point of attachment to the Ab and the ## indicates the point of attachment to the MMAE; and wherein the MMAE is represented by Formula (III):wherein * indicates the point of attachment to (L-1).

[0041] In certain embodiments, the administration is resumed in step (iii) once the adverse event is alleviated or recovered. In certain embodiments, the administration of the second treatment cycle is at the dose of the first treatment cycle. In certain embodiments, the administration of the second treatment cycle is at a dose lower than that of the first treatment cycle.

[0042] In a further aspect, provided herein is a method of treating a cancer for two or more treatment cycles in a subject experiencing an adverse event when administered an ADC, the method comprising: i) administering the ADC to the subject at a first dose of about 0.1 mg / kg to about 10.0 mg / kg in a first treatment cycle; ii) in a second treatment cycle, administering the ADC to the subject at a second dose which is lower than the first dose upon the subject having an adverse event, wherein the ADC is represented by Formula (I) and comprises an Ab conjugated to a monomethyl auristatin E (MMAE) by a: 15 NAI-1541858741wherein the Ab is a 5T4 antibody or an antigen binding fragment thereof and comprises a heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), a heavy chain complementarity determining region 3 (HCDR3), a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and a light chain complementarity determining region 3 (LCDR3) of an antibody designated mAbA15, wherein the Ab further comprises two motifs, each of which is L(fGly’)TPSR (SEQ ID NO: 1), wherein fGly’ is the amino acid residue to which a linker-drug comprising (L-1) is attached, and wherein mAbA15 comprises: a) a heavy chain comprising an amino acid sequence of: EVQLVESGGGLVQPGGSLRLSCAASGFTFSSYYIHWVRQAPGKGLEWVAYITSTGSY TEYADSVKGRFTISADTSKNTAYLQMNSLRAEDTAVYYCARYDRSTRYSGLDYWG QGTLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTS GVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDK THTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVD GVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTI SKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKT TPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGSL (fGly’)TPSRGS (SEQ ID NO: 2); and b) a light chain comprising an amino acid sequence of: DIQMTQSPSSLSASVGDRVTITCRASQSVSSAVAWYQQKPGKAPKLLIYSASSLYSGV PSRFSGSRSGTDFTLTISSLQPEDFATYYCQQAYATPVTFGQGTKVEIKRTVAAPSVFI FPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTY SLSSTLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 3); wherein (L-1) is: 16 NAI-1541858741wherein the wavy line indicates the point of attachment to the Ab and the ## indicates the point of attachment to the MMAE; and wherein the MMAE is represented by Formula (III):indicates the point of attachment to (L-1).

[0043] In certain embodiments, the subject is administered at the second dose in step (ii) once the adverse event is alleviated or recovered. In certain embodiments, the adverse event is selected from the group consisting of Grade 3 thrombocytopenia with clinically significant bleeding, Grade 4 thrombocytopenia, Grade 3 or higher neutropenia with a measured fever of at least 38.3°C, Grade 3 or higher neutropenia with a sustained fever of at least 38°C for at least an hour, Grade 4 neutropenia for greater than 7 days, Grade 4 anemia, alanine transaminase or aspartate transaminase levels that are greater than 3 times the upper limit of normal and a total bilirubin level that is greater than 2 times the upper limit of normal in the absence of biliary obstruction or other explanation for liver abnormality (such as viral hepatitis, alcohol or autoimmune hepatitis, Gilbert Syndrome, or treatment with other hepatotoxic drug), and a Grade 5 adverse event. 7.1 Definitions

[0044] Unless defined otherwise, all technical and scientific terms used herein have the meaning commonly understood by a person skilled in the art of the present disclosure. As used herein, the following terms have the meanings ascribed to them below, unless specified otherwise.

[0045] In some embodiments, chemical structures are disclosed with a corresponding chemical name. In case of conflict, the chemical structure controls the meaning, rather than the name. 17 NAI-1541858741

[0046] Unless specifically stated or obvious from context, as used herein, the term "or" is understood to be inclusive. Unless specifically stated or obvious from context otherwise, as used herein, the terms “a,” “an,” and “the” are understood to be singular or plural.

[0047] The terms “about” and “approximately” mean within 20%, within 15%, within 10%, within 9%, within 8%, within 7%, within 6%, within 5%, within 4%, within 3%, within 2%, within 1%, or less variation of a given value or range.

[0048] In some embodiments, the terms “first,” “second,” “third,” “fourth” and similar in a component name are used to distinguish and identify more than one component sharing certain identity in their names. For example, “first antibody” and “second antibody” are used to distinguish two antibodies.

[0049] It is understood that wherever embodiments are described herein with the term “comprising” otherwise analogous embodiments described in terms of “consisting of” and / or “consisting essentially of” are also provided. It is also understood that wherever embodiments are described herein with the phrase “consisting essentially of” otherwise analogous embodiments described in terms of “consisting of” are also provided.

[0050] The term “between” as used in a phrase as such “between A and B” or “between A-B” refers to a range including both A and B or any subranges thereof.

[0051] As used herein, a range of A to B includes both A and B or any numbers or subranges thereof.

[0052] The term “and / or” as used in a phrase such as “A and / or B” herein is intended to include both A and B; A or B; A (alone); and B (alone). Likewise, the term “and / or” as used in a phrase such as “A, B, and / or C” is intended to encompass each of the following embodiments: A, B, and C; A, B, or C; A or C; A or B; B or C; A and C; A and B; B and C; A (alone); B (alone); and C (alone).

[0053] The term “optional” or “optionally” means that the subsequently described circumstance may or may not occur, so that the description includes instances wherein the circumstance occurs, and the instances wherein the circumstance does not occur.

[0054] The term “patient” and “subject” are used interchangeably and refer to human and non-human subjects, especially mammalian subjects. In one embodiment, the patient or subject is a human.

[0055] Dosing of the 5T4 ADCs as disclosed herein are provided in units of milligrams of ADC per kilogram of subject weight (mg / kg). However, dosing may also be specified having a unit of milligrams of ADC per square meters of body surface (mg / m2). One of skill in the art will readily be able to convert a dose in mg / kg to a dose in mg / m2using the Km ratio for 18 NAI-1541858741humans (1.62 m2for a 60 kg human or 37 kg / m2). That is, a dose in mg / kg can be converted to a dose in mg / m2by multiplying by 37 kg / m2. In a human subject, a dose of about 0.3 mg / kg is equal to a dose of about 11 mg / m2. A dose of 5 mg / kg ADC is equal to a dose of 185 mg / m2in a human.

[0056] The term “treating” or “treatment” as used herein means the treating or treatment of a disease or medical condition in a subject, such as a mammal (particularly a human) that includes: (a) preventing the disease or medical condition from occurring, such as, prophylactic treatment of a subject; (b) ameliorating the disease or medical condition, such as, eliminating or causing regression of the disease or medical condition in a subject; (c) suppressing the disease or medical condition, for example by, slowing or arresting the development of the disease or medical condition in a subject; or (d) alleviating a symptom of the disease or medical condition in a subject. In some embodiments, the term “treating,” or “treatment” excludes a prophylactic treatment. In some embodiments, the term “treating” or “treatment” as it relates to the treating or treatment of cancer may include reversing tumor progression (e.g., reducing tumor size), slowing tumor progression, or halting tumor progression. In one embodiment, tumor progression is determined by the response assessment criteria selected for the clinical trial.

[0057] The term “tumor,” in any embodiment herein, refers to any neoplastic cell growth or proliferation, whether malignant or benign, and to all pre-cancerous and cancerous cells and tissues.

[0058] The terms “cancer” and “cancerous” refer to or describe the physiological condition in mammals that is typically characterized by unregulated cell growth. Cancers that may be treated according to the methods disclosed herein include, but are not limited to, breast cancer (e.g., triple-negative breast cancer (TNBC) or hormone-receptor positive breast cancer (HR+ BC)), endometrial cancer, head and neck cancer (e.g., head and neck squamous cell carcinoma (HNSCC)), pancreatic cancer (e.g., pancreatic adenocarcinoma (PDAC, also referred to herein as pancreatic ductal adenocarcinoma)), lung cancer (e.g., non-small cell lung cancer (NSCLC)), prostate cancer, cervical cancer, or bladder cancer. In certain embodiments, the cancer is lung adenocarcinoma or squamous cell lung carcinoma. In certain embodiments, the NSCLC is characterized by a mutation selected from the group consisting of an EGFR sensitizing mutation, an ALK rearrangement, a ROS1 rearrangement, a BRAF V600E mutation, a MET Exon 14 skipping mutation, and a RET rearrangement. In certain embodiments, the cancer is renal cell carcinoma (RCC), hepatocellular carcinoma (HCC), or colorectal cancer. In some embodiments, the cancer is a genitourinary cancer. In some 19 NAI-1541858741embodiments, the cancer is a gastrointestinal cancer. In some embodiments, the cancer is a gynecological cancer. Additionally or alternatively, the cancer is previously untreatable. Additionally or alternatively, the cancer is recurrent. Additionally or alternatively, the cancer is metastatic. Additionally or alternatively, the cancer is advanced, for example locally advanced. Additionally or alternatively, the cancer is inoperable.

[0059] As used herein, “EGFR sensitizing mutation” includes Exon 19 deletions and Exon 21 point mutations. Exon 19 Deletions destabilize the inactive form of EGFR, causing it to remain in the active conformation. These deletions account for around 45% of all EGFR mutations. The most common frame shift deletion is delE756-A750, followed by delL747_P753insS and delL747_A750insP. Exon 21 Point Mutations lock EGFR in a constitutively active conformation and account for 40% of EGFR mutations. The most common exon 21 mutation is L858R.

[0060] As used herein, “ALK rearrangement” or “alk-positive” includes any rearrangement of the ALK gene with another gene that results in a fusion gene. The most comment ALK rearrangement is rearrangement of the EML4 gene and the ALK (anaplastic lymphoma kinase) gene that results in a fusion oncogene EML4-ALK.

[0061] As used herein, “ROS1 rearrangement”, refers to the fusion of the ROS1 gene with a part of another gene.

[0062] As used herein, “BRAF V600E mutation,” refers to a mutation of the BRAF gene from a valine to a glutamic acid at amino acid 600.

[0063] As used herein, “MET Exon 14 skipping mutation” refers to a presence of a splice site mutation that results in a loss of transcription of exon 14 of the MET gene.

[0064] As used herein “RET rearrangement,” refers to the fusion of the RET gene with a part of another gene.

[0065] The term “therapeutically effective amount” as used herein refers to the amount of an antibody or ADC described herein that is sufficient to reduce and / or ameliorate the severity and / or duration of a given disease, disorder, or condition, and / or a symptom related thereto. A therapeutically effective amount of an agent, including a therapeutic agent, can be an amount necessary for (i) reduction or amelioration of the advancement or progression of a given disease, disorder, or condition, (ii) reduction or amelioration of the recurrence, development or onset of a given disease, disorder or conditions, and / or (iii) to improve or enhance the therapeutic effect of another therapy (e.g., a therapy other than the administration of an antibody or ADC described herein). A “therapeutically effective amount” of a substance / molecule / agent of the present disclosure (e.g., a 5T4 antibody or ADC) can vary 20 NAI-1541858741based on a number of factors such as the disease state, age, sex, and weight of the individual, and the ability of the substance / molecule / agent, to elicit a desired response in the individual. A therapeutically effective amount encompasses an amount in which any toxic or detrimental effects of the substance / molecule / agent are outweighed by the therapeutically beneficial effects. In some embodiments, the term “therapeutically effective amount” refers to an amount of an antibody or other agent (e.g., or drug) effective to “treat” a disease, disorder, or condition, in a subject or mammal.

[0066] The term “pharmaceutically acceptable” as used herein means being approved by a regulatory agency of the federal or a state government, or listed in the U.S. Pharmacopeia, European Pharmacopeia, or other generally recognized Pharmacopeia for use in animals, and more particularly in humans.

[0067] “Excipients” include carriers, excipients, preservatives, or stabilizers that are nontoxic to the cell or mammal being exposed thereto at the dosages and concentrations employed and can be included, for example, to affect stability, bulk up formulations, or to confer a therapeutic enhancement on the active ingredient in the final dosage form (e.g., facilitating absorption, reducing viscosity, enhancing solubility). An "excipient" can be an organic or inorganic ingredient, natural or synthetic with which the active ingredient is combined to facilitate the use of the active ingredient, e.g., the administration of the active ingredient to a subject. Examples of excipients include buffers such as phosphate, citrate, and other organic acids; antioxidants such as ascorbic acid; low molecular weight (e.g., less than about ten amino acid residues) polypeptide; proteins, such as serum albumin, gelatin, or immunoglobulins; hydrophilic polymers such as polyvinylpyrrolidone; amino acids such as glycine, glutamine, asparagine, arginine or lysine; monosaccharides, disaccharides, and other carbohydrates such as glucose, mannose, or dextrins; chelating agents such as EDTA; sugar alcohols such as mannitol or sorbitol; salt-forming counterions such as sodium; and / or nonionic surfactants such as TWEEN™, polyethylene glycol (PEG), and PLURONICS™. The term “excipient” can also refer to a diluent, adjuvant (e.g., Freund’s adjuvant (complete or incomplete)), excipient, or vehicle with which the therapeutic is administered. Such excipients can be sterile liquids, such as water and oils, such as those of petroleum, animal, vegetable, or synthetic origin, such as peanut oil, soybean oil, mineral oil, sesame oil, and the like. Water is an exemplary excipient when a composition (e.g., a pharmaceutical composition) is administered intravenously. Saline solutions and aqueous dextrose and glycerol solutions can also be employed as liquid excipients, particularly for injectable solutions. Suitable excipients (e.g., pharmaceutical excipients) include starch, glucose, 21 NAI-1541858741lactose, sucrose, gelatin, malt, rice, flour, chalk, silica gel, sodium stearate, glycerol monostearate, talc, sodium chloride, dried skim milk, glycerol, propylene, glycol, water, ethanol, and the like. The composition, in any embodiment, can also contain minor amounts of wetting or emulsifying agents, or pH buffering agents. Compositions can take the form of solutions, suspensions, emulsion, tablets, pills, capsules, powders, sustained-release formulations, and the like. Oral compositions, such as formulations, can include standard excipients such as pharmaceutical grades of mannitol, lactose, starch, magnesium stearate, sodium saccharine, cellulose, magnesium carbonate, and the like. Examples of suitable excipients are described in Remington: The Science and Practice of Pharmacy (2020) (Elsevier Science, Amsterdam, Netherlands), including pharmaceutical compounds, can contain an effective amount or therapeutically effective amount of a 5T4 ADC, for example, in isolated or purified form, together with a suitable amount of excipient to provide the form for proper administration to the subject. The formulation should suit the mode of administration.

[0068] The term "5T4" refers to a polypeptide (“polypeptide” and “protein” are used interchangeably herein) or any native 5T4 from any vertebrate source, including mammals such as primates (e.g., humans, cynomolgus monkey (cyno)), dogs, and rodents (e.g., mice and rats), unless otherwise indicated.5T4, also known as "5T4 Oncofetal Trophoblast Glycoprotein" or "Wnt-Activated Inhibitory Factor 1" or "5T4 Oncotrophoblast Glycoprotein" or "5T4 Oncofetal Antigen" or "WAIF1" or "M6P1" or "5T4-AG" or "5T4AG" or "TPBG" is a glycoprotein encoded by the TPBG gene. The term 5T4 encompasses “full-length,” 5T4, as well as any form of 5T4 or any fragment thereof that results from processing in the cell. In some embodiments, the 5T4 comprises a signal sequence. In some embodiments, the 5T4 does not include a signal sequence. In some embodiments, the term 5T4 refers to a fragment of the full-length 5T4, which comprises a 5T4 extracellular domain. The term 5T4 also encompasses naturally occurring variants of 5T4, such as SNP variants, splice variants and allelic variants. The full-length amino acid sequence of human 5T4 is provided below (exemplary signal sequence = italic text; exemplary extracellular domain = underlined text): MPGGCSRGPA AGDGRLRLAR LALVLLGWVS SSSPTSSASS FSSSAPFLAS AVSAQPPLPD QCPALCECSE AARTVKCVNR NLTEVPTDLP AYVRNLFLTG NQLAVLPAGA FARRPPLAEL AALNLSGSRL DEVRAGAFEH LPSLRQLDLS HNPLADLSPF AFSGSNASVS APSPLVELIL NHIVPPEDER QNRSFEGMVV AALLAGRALQ GLRRLELASN HFLYLPRDVL AQLPSLRHLD LSNNSLVSLT YVSFRNLTHL ESLHLEDNAL KVLHNGTLAE LQGLPHIRVF LDNNPWVCDC 22 NAI-1541858741HMADMVTWLK ETEVVQGKDR LTCAYPEKMR NRVLLELNSA DLDCDPILPP SLQTSYVFLG IVLALIGAIF LLVLYLNRKG IKKWMHNIRD ACRDHMEGYH YRYEINADPR LTNLSSNSDV (SEQ ID NO: 4).

[0069] The full-length amino acid sequence of cynomolgus monkey (cyno) 5T4 is provided below (exemplary signal sequence = italic text; exemplary extracellular domain = underlined text): MPGGCSRGPA AGDGRLRLAR LALVLLGWVS SSSSTSSASS SSSSAPFLAS AASAQPPLPD QCPALCECSE AARTVKCVNR NLTEVPTDLP LYVRNLFLTG NQLAVLPAGA FARRPPLAEL AALNLSGSRL DEVRGGAFEH LPSLRQLDLS HNPLAYLSPF AFSGSNASIS APSPLVELIL NHIVPPDDKR QNRSFEGMVA AALVAGRALQ GLHLLELASN HFLYLPRDVL AQLPSLRYLD LSNNSLVSLT YVSFRNLTHL ESLHLEDNAL KVLHNGTLAE LQGLPHVRVF LDNNPWVCDC HMADMVTWLK QTGVVQGKDR LTCAFPEKMR NRVLLELNSA DLDCDPILPP SLQTSYVFLG IVLALIGAIF LLVLYLNRKG IKKWMHNIRD ACRDHMEGYH YRYEINADPR LTNLSSNSDV (SEQ ID NO: 5).

[0070] The full-length amino acid sequence of mouse 5T4 is provided below (exemplary signal sequence = italic text; exemplary extracellular domain = underlined text): MPGAGSRGPS AGDGRLRLAR LALVLLGWVS ASAPSSSVPS SSTSPAAFLA SGSAQPPPAE RCPAACECSE AARTVKCVNR NLLEVPADLP PYVRNLFLTG NQMTVLPAGA FARQPPLADL EALNLSGNHL KEVCAGAFEH LPGLRRLDLS HNPLTNLSAF AFAGSNASVS APSPLEELIL NHIVPPEDQR QNGSFEGMVA FEGMVAAALR SGLALRGLTR LELASNHFLF LPRDLLAQLP SLRYLDLRNN SLVSLTYASF RNLTHLESLH LEDNALKVLH NSTLAEWHGL AHVKVFLDNN PWVCDCYMAD MVAWLKETEV VPDKARLTCA FPEKMRNRGL LDLNSSDLDC DAVLPQSLQT SYVFLGIVLA LIGAIFLLVL YLNRKGIKKW MHNIRDACRD HMEGYHYRYE INADPRLTNL SSNSDV (SEQ ID NO: 6).

[0071] The terms “constant region” and “constant domain” are used interchangeably herein, are well-known antibody terms of art, and refer to an antibody portion, for example, a carboxyl terminal portion of a light and / or heavy chain which is not directly involved in binding of an antibody to an antigen, but which can exhibit various effector functions, such as interaction with an Fc receptor. The term includes the portion of an immunoglobulin molecule having a generally more conserved amino acid sequence relative to an immunoglobulin variable region.

[0072] The terms “antibody,” “immunoglobulin,” or “Ig” are used interchangeably herein and are used in the broadest sense and specifically covers, for example polyclonal antibodies, monoclonal antibodies (including agonist, antagonist, neutralizing antibodies, full length monoclonal antibodies), antibody compositions with polyepitopic or monoepitopic 23 NAI-1541858741specificity, recombinantly produced antibodies, single domain antibodies, monospecific antibodies, multispecific antibodies (including bispecific antibodies), synthetic antibodies, chimeric antibodies, humanized antibodies, or human versions of antibodies having full length heavy and / or light chains. Antibodies also include single antibody domains as well as antibody fragments (and / or polypeptides that comprise antibody fragments) that retain 5T4 binding characteristics (also referred to herein as antigen binding fragment). Non-limiting examples of antibody fragments include antigen-binding regions and / or effector regions of the antibody, e.g., Fab, Fab’, F(ab’)2, Fv, scFv, (scFv)2, single-chain antibody molecule, dual variable domain antibody, single variable domain antibody, linear antibody, V region, a multispecific antibody formed from antibody fragments, F(ab)2, Fd, Fc, diabody, di-diabody, disulfide-linked Fvs (dsFv), single-domain antibody (e.g., nanobody) or other fragments (e.g., fragments consisting of the variable regions of the heavy and light chains that are non- covalently coupled). In general terms, a variable (V) region can be any suitable arrangement of immunoglobulin heavy (VH) and / or light (VL) variable regions. For example, antibodies also include tetrameric antibodies comprising two heavy chain and two light chain molecules, an antibody light chain monomer, and an antibody heavy chain monomer. Thus, for example, the V region can be dimeric and contain VH-VH, VH-VL, or VL-VL dimers that bind 5T4. In any embodiment, a VH region and a VL region can be covalently coupled either directly or through a linker to form a single-chain Fv (scFv). For ease of reference, scFv proteins are referred to herein as included in the category “antibody fragments.” Another form of an antibody fragment is a peptide comprising one or more complementarity determining regions (CDRs) of an antibody. CDRs (also termed “minimal recognition units” or “hypervariable regions”) can be obtained by constructing polynucleotides that encode one or more CDRs of interest. Such polynucleotides are prepared, for example, by using the polymerase chain reaction to synthesize the variable region using mRNA of antibody-producing cells as a template (see, for example, Larrick et al., Methods: A Companion to Methods in Enzymology, 2:106 (1991); Courtenay-Luck, “Genetic Manipulation of Monoclonal Antibodies,” in Monoclonal Antibodies Production, Engineering and Clinical Application, Ritter et al. (eds.), page 166, Cambridge University Press (1995); and Ward et al., “Genetic Manipulation and Expression of Antibodies,” in Monoclonal Antibodies: Principles and Applications, Birch et al., (eds.), page 137, Wiley-Liss, Inc. (1995)). Antibody fragments can be incorporated, for example, into single domain antibodies, maxibodies, minibodies, intrabodies, diabodies, triabodies, tetrabodies, variable regions of new antigen receptors (v- NAR), and bis-single-chain Fv regions (see, e.g., Hollinger and Hudson, Nature 24 NAI-1541858741Biotechnology, 23(9):1126-1136, 2005). In some embodiments, antibodies comprising a VH and / or VL contain a light chain and / or a heavy chain constant region, such as one or more constant regions, including one or more IgG1, IgG2, IgG3 and / or IgG4 constant regions. In some embodiments, antibodies can include epitope-binding fragments of any of the above. The antibodies described herein can be of any class (e.g., IgG, IgE, IgM, IgD, and IgA) or any subclass (e.g., IgG1, IgG2, IgG3, IgG4, IgA1, and IgA2) of immunoglobulin molecule.

[0073] The terms “variable region” and “variable domain” are used interchangeably to refer to a portion of the light and heavy chains of an antibody that are generally located at the amino-terminal of the light and heavy chain, has a length of about 120 to 130 amino acids in the heavy chain, about 100 to 110 amino acids in the light chain, and is used in the binding and specificity of each antibody for its antigen. The variable region of the heavy chain is referred to herein as “VH.” The variable region of the light chain is referred to herein as “VL.” The term “variable” refers to the fact that certain segments of the variable regions differ extensively in sequence among antibodies. The V region mediates antigen binding and defines specificity of a particular antibody for its antigen. However, the variability is not evenly distributed across the 110-amino acid span of the variable regions. Instead, the V regions consist of less variable (e.g., relatively invariant) stretches called framework regions (FRs) of about 15-30 amino acids separated by shorter regions of greater variability (e.g., extreme variability) called “hypervariable regions” or alternatively called “complementarity determining regions.” The variable regions of heavy and light chains each comprise four frameworks (FR1, FR2, FR3 and FR4), largely adopting a β sheet configuration, connected by three hypervariable regions, which form loops connecting, and in some cases forming part of, the β sheet structure. The hypervariable regions in each chain are held together in proximity by the frameworks and, with the hypervariable regions from the other chain, contribute to the formation of the antigen-binding site of antibodies (see, e.g., Kabat et al., Sequences of Proteins of Immunological Interest, 5th Ed. Public Health Service, National Institutes of Health, Bethesda, MD, (1991)). The constant regions are not involved directly in binding an antibody to an antigen, but exhibit various effector functions, such as participation of the antibody in antibody dependent cellular cytotoxicity (ADCC) and complement dependent cytotoxicity (CDC). The variable regions differ extensively in sequence between different antibodies. The variability in sequence is concentrated in the CDRs while the less variable portions in the variable region are referred to as framework regions (FR). The CDRs of the light and heavy chains are primarily responsible for the interaction of the antibody with antigen. In specific embodiments, the variable region is a human variable region. 25 NAI-1541858741

[0074] The term “heavy chain” when used in reference to an antibody refers to a polypeptide chain of about 50-70 kDa, wherein the amino-terminal portion includes a variable region of about 120 to 130 or more amino acids, and a carboxy-terminal portion includes one or more constant regions. The “heavy chain” can refer to any distinct types, e.g., for example, alpha (α), delta (δ), epsilon (ε), gamma (γ) and mu (µ), based on the amino acid sequence of the constant region, which give rise to IgA, IgD, IgE, IgG and IgM classes of antibodies, respectively, including subclasses of IgG, e.g., IgG1, IgG2, IgG3 and IgG4.

[0075] As used herein, the term “light chain” when used in reference to an antibody can refer to a polypeptide chain of about 25 kDa, wherein the amino-terminal portion includes a variable region of about 100 to about 110 or more amino acids, and a carboxy-terminal portion includes a constant region. The approximate length of a light chain is 211 to 217 amino acids. There are two distinct types, e.g., kappa (κ) or lambda (λ) based on the amino acid sequence of the constant regions. Light chain amino acid sequences are well known in the art.

[0076] The terms “identical” or percent “identity” in the context of two or more nucleic acids or polypeptides, refer to two or more sequences or subsequences that are the same or have a specified percentage of nucleotides or amino acid residues that are the same, when compared and aligned (introducing gaps, if necessary) for maximum correspondence, not considering any conservative amino acid substitutions as part of the sequence identity. The percent identity can be measured using sequence comparison software or algorithms or by visual inspection. Various algorithms and software that can be used to obtain alignments of amino acid or nucleotide sequences are well known in the art. These include, but are not limited to, basic local alignment search tool (BLAST), ALIGN, MegAlign, BestFit, GCG Wisconsin Package, and variants thereof. In some embodiments, two nucleic acids or polypeptides are substantially identical, meaning they have at least 70%, at least 75%, at least 80%, at least 85%, or at least 90%, and in some embodiments, at least 95%, 96%, 97%, 98%, or 99% nucleotide or amino acid residue identity, when compared and aligned for maximum correspondence, as measured using a sequence comparison algorithm or by visual inspection. In some embodiments, identity exists over a region of the amino acid sequences that is at least about ten residues, at least about 20 residues, at least about 40-60 residues, at least about 60-80 residues in length or any integral value there between. In some embodiments, identity exists over a longer region than 60-80 residues, such as at least about 80-100 residues, and in some embodiments, the sequences are substantially identical over the full-length of the sequences being compared, such as the coding region of a target protein or an antibody. In 26 NAI-1541858741some embodiments, identity exists over a region of the nucleotide sequences that is at least about ten bases, at least about 20 bases, at least about 40-60 bases, at least about 60-80 bases in length or any integral value there between. In some embodiments, identity exists over a longer region than 60-80 bases, such as at least about 80-1000 bases or more, and in some embodiments, the sequences are substantially identical over the full length of the sequences being compared, such as a nucleotide sequence encoding a protein of interest.

[0077] A “conservative amino acid substitution” is one in which one amino acid residue is replaced with another amino acid residue having a side chain with similar chemical characteristics. Families of amino acid residues having similar side chains have been generally defined in the art, including basic side chains (e.g., lysine, arginine, histidine), acidic side chains (e.g., aspartic acid, glutamic acid), uncharged polar side chains (e.g., glycine, asparagine, glutamine, serine, threonine, tyrosine, cysteine), nonpolar side chains (e.g., alanine, valine, leucine, isoleucine, proline, phenylalanine, methionine, tryptophan), beta-branched side chains (e.g., threonine, valine, isoleucine) and aromatic side chains (e.g., tyrosine, phenylalanine, tryptophan, histidine). For example, substitution of a phenylalanine for a tyrosine is a conservative substitution. Generally, conservative substitutions in the sequences of the polypeptides, soluble proteins, and / or antibodies of the disclosure do not abrogate the binding of the polypeptide, soluble protein, or antibody containing the amino acid sequence, to the target binding site. Methods of identifying amino acid conservative substitutions that do not eliminate binding are well known in the art.

[0078] The term “polypeptide” refers to a polymer of amino acids of any length. The polymer can be linear or branched, it can comprise modified amino acids, and it can include (e.g., be substituted with) non-amino acids. The terms also encompass an amino acid polymer that has been modified naturally or by intervention; for example, disulfide bond formation, glycosylation, lipidation, acetylation, phosphorylation, or any other manipulation or modification, such as linkage to or conjugation with (directly or indirectly) a moiety such as a labeling component or a drug (e.g., toxin). Also included within the definition are, for example, polypeptides containing one or more analogs of an amino acid (including, for example, unnatural amino acids), as well as other modifications known in the art. It is understood that, because the polypeptides of this disclosure can be based upon antibodies or other members of the immunoglobulin superfamily, in some embodiments, the polypeptides can occur as single chains or dimers of single chains.

[0079] As used herein, a first amino acid residue in a first peptide corresponding to a second amino acid residue in a second peptide refers to the first amino acid residue aligned to 27 NAI-1541858741the second amino acid residue in a sequence alignment between the first peptide and the second peptide. Alignment methods are available to one of skilled in the art, such as BLAST as disclosed herein and / or Clustal Omega.

[0080] As used herein, an “antigen” is a moiety or molecule that contains an epitope to which an antibody can bind. As such, an antigen can be bound by an antibody. In some embodiments, the antigen to which an antibody described herein binds is 5T4 (e.g., human 5T4), or a fragment thereof, such as a fragment that comprises one or more regions of 5T4.

[0081] As used herein, an “epitope” is a term in the art and refers to a localized region of an antigen to which an antibody can bind. An epitope can be a linear epitope or a conformational, non-linear, or discontinuous epitope. In the case of a polypeptide antigen, for example, an epitope can be contiguous amino acids of the polypeptide (a “linear” epitope), or an epitope can comprise amino acids from two or more non-contiguous regions of the polypeptide (a “conformational,” “non-linear” or “discontinuous” epitope), e.g., human 5T4. It will be appreciated by one of skill in the art that, in general, a linear epitope may or may not be dependent on secondary, tertiary, or quaternary structure. For example, in some embodiments, an antibody binds to a group of amino acids regardless of whether they are folded in a natural three-dimensional protein structure. In other embodiments, an antibody requires amino acid residues making up the epitope to exhibit a particular conformation (e.g., bend, twist, turn or fold) in order to recognize and bind the epitope.

[0082] An antibody binds “an epitope,” “essentially the same epitope,” or “the same epitope” as a reference antibody. The most widely used and rapid methods for determining whether two antibodies bind to identical, overlapping, or adjacent epitopes in a three- dimensional space are competition assays, which can be configured in a number of different formats, for example, using either labeled antigen or labeled antibody. In some assays, the antigen is immobilized on a 96-well plate, or expressed on a cell surface, and the ability of unlabeled antibodies to block the binding of labeled antibodies is measured using radioactive, fluorescent or enzyme labels.

[0083] The term “Fc region” herein is used to define a C-terminal region of an immunoglobulin heavy chain, including, for example, native sequence Fc regions, recombinant Fc regions, and variant Fc regions. Although the boundaries of the Fc region of an immunoglobulin heavy chain might vary, the human IgG heavy chain Fc region is often defined to stretch from an amino acid residue at position Cys226 (of the EU numbering system) or from Pro230 (of the EU numbering system) to the carboxyl-terminus thereof. The C-terminal lysine (residue 447 of the EU numbering system) of the Fc region can be 28 NAI-1541858741removed, for example, during production or purification of the antibody, or by recombinantly engineering the nucleic acid encoding a heavy chain of the antibody. An exemplary Fc region sequence is provided below (CH2 domain = bold text; CH3 domain = underlined text): CPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNA KTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVY TLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLT VDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 7).

[0084] A “functional Fc region” possesses an “effector function” of a native sequence Fc region. Exemplary “effector functions” include C1q binding; complement dependent cytotoxicity (CDC); Fc receptor binding; antibody-dependent cell-mediated cytotoxicity (ADCC); phagocytosis; down regulation of cell surface receptors (e.g., B cell receptor; BCR), and the like. Such effector functions generally require the Fc region to be combined with a binding region or binding domain (e.g., an antibody variable region or domain) and can be assessed using various assays as disclosed.

[0085] A “native sequence Fc region” comprises an amino acid sequence identical to the amino acid sequence of an Fc region found in nature, and not manipulated, modified, and / or changed (e.g., isolated, purified, selected, including, or combining with other sequences such as variable region sequences) by a human. Native sequence human Fc regions include a native sequence human IgG1 Fc region (non-A and A allotypes); native sequence human IgG2 Fc region; native sequence human IgG3 Fc region; and native sequence human IgG4 Fc region; as well as naturally occurring variants thereof.

[0086] A “variant Fc region” comprises an amino acid sequence that differs from that of a native sequence Fc region by virtue of at least one amino acid modification, (e.g., substituting, addition, or deletion) preferably one or more amino acid substitution(s). In some embodiments, the variant Fc region has at least one amino acid substitution compared to a native sequence Fc region or to the Fc region of a parent polypeptide, for example, from about one to about ten amino acid substitutions, and preferably from about one to about five amino acid substitutions in a native sequence Fc region or in the Fc region of the parent polypeptide. The variant Fc region described herein can possess at least about 80% homology with a native sequence Fc region and / or with an Fc region of a parent polypeptide, or at least about 90% homology therewith, for example, at least about 95% homology therewith. The variant Fc region herein described herein can have a loss of effector function (e.g., silent Fc). An exemplary variant Fc region (“silent Fc”) sequence is provided below (CH2 domain = bold text with amino acid changes underlined; CH3 domain = underlined text): 29 NAI-1541858741CPPCPAPEAAGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNA KTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALKAPIEKTISKAKGQPREPQVY TLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLT VDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 8).

[0087] The terms “antigen binding fragment,” “antigen binding domain,” “antigen binding region,” and similar terms refer to a portion of an antibody that comprises amino acid residues that interact with an antigen and confer on the binding fragment or region its specificity and affinity for the antigen (e.g., the CDRs). “Antigen binding fragment” as used herein includes “antibody fragment,” which comprises a portion of an antibody including one or more CDRs, such as the antigen binding or variable region of the antibody.

[0088] Antibodies described herein include, but are not limited to, synthetic antibodies, monoclonal antibodies, recombinantly produced antibodies, multispecific antibodies (e.g., including bispecific antibodies), human antibodies, humanized antibodies, chimeric antibodies, intrabodies, single-chain Fvs (scFv) (e.g., including monospecific, bispecific, and the like), camelized antibodies, Fab fragments, F(ab’) fragments, disulfide-linked Fvs (sdFv), anti-idiotypic (anti-Id) antibodies, and epitope-binding fragments of any of the above.

[0089] In some embodiments, antibodies described herein include immunoglobulin molecules and immunologically active portions of immunoglobulin molecules, such as molecules that contain one or more antigen binding sites that bind to 5T4.

[0090] A 5T4 antibody, as described herein, can be of any type (e.g., IgG, IgE, IgM, IgD, IgA or IgY), any class (e.g., IgG1, IgG2, IgG3, IgG4, IgA1 or IgA2), or any subclass (e.g., IgG2a or IgG2b) of immunoglobulin molecule. In some embodiments, a 5T4 antibody, as described herein, is an IgG antibody (e.g., human IgG), or a class (e.g., human IgG1, IgG2, IgG3, or IgG4) or a subclass thereof. In some embodiments, a 5T4 antibody is an IgG1 antibody. Additionally or alternatively, a 5T4 antibody is a kappa antibody.

[0091] In some embodiments, a 5T4 antibody is a 4-chain antibody unit comprising two heavy (H) chain / light (L) chain pairs, wherein the amino acid sequences of the H chains are identical and the amino acid sequences of the L chains are identical. In some embodiments, the H and / or L chains comprise constant regions, for example, human constant regions. In some embodiments, the L chain constant region of a 5T4 antibody is a kappa or lambda light chain constant region, for example, a human kappa or lambda light chain constant region. In some embodiments, the L chain constant region of a 5T4 antibody is a kappa light chain constant region, for example, a human kappa light chain constant region. Additionally or alternatively, in some embodiments, the H chain constant region of a 5T4 antibody comprises 30 NAI-1541858741a gamma heavy chain constant region, for example, a human gamma heavy chain constant region. In some embodiments, a 5T4 antibody comprises an IgG constant region, for example, human IgG constant regions (e.g., IgG1, IgG2, IgG3, and / or IgG4 constant regions). In some embodiments, a 5T4 antibody comprises an IgG1 constant region. In some embodiments, a 5T4 antibody comprises an IgG1 heavy chain constant region and a kappa light chain constant region.

[0092] As used herein, “5T4 antibody” and “antibody that binds to 5T4” are used interchangeably and refer to an antibody that preferentially binds to 5T4. An antibody or fragment thereof can preferentially bind to 5T4, such as human 5T4, which means that the antibody or fragment thereof binds to 5T4, such as human 5T4, with greater affinity than it binds to an unrelated control protein. For example, the antibody or fragment thereof can specifically recognize and bind to 5T4 or a portion thereof. “Specific binding” means that the 5T4 antibody or fragment thereof binds to 5T4 with an affinity that is at least 5, 10, 15, 20, 25, 50, 100, 250, 500, 1000, or 10,000 times greater than the affinity for an unrelated control protein (e.g., hen egg white lysozyme). In some embodiments, the 5T4 antibody or fragment thereof can bind 5T4 substantially exclusively (e.g., is able to distinguish 5T4 from other known polypeptides, for example, by virtue of measurable differences in binding affinity). In some embodiments, a 5T4 antibody can react with 5T4 sequences other than human 5T4 sequences (e.g., cynomolgus 5T4 sequences).

[0093] The terms “hypervariable region,” “HVR,” “HV,” “complementarity determining region,” and “CDR” when used herein refer to the regions of an antibody variable region that are hypervariable in sequence and / or form structurally defined loops. Generally, antibodies comprise six hypervariable regions: three in the VH (H1 or VH CDR1 or HCDR1, H2 or VH CDR2 or HCDR2, and H3 or VH CDR3 or HCDR3), and three in the VL (L1 or VL CDR1 or LCDR1, L2 or VL CDR2 or LCDR2, and L3 or VL CDR3 or LCDR3). Several hypervariable region delineations are in use and are encompassed herein. The Kabat CDRs are based on sequence variability and are the most used (see, e.g., Kabat et al., Sequences of Proteins of Immunological Interest, 5th Ed. Public Health Service, National Institutes of Health, Bethesda, MD. (1991)). Chothia refers instead to the location of the structural loops (see, e.g., Chothia and Lesk, J. Mol. Biol.196:901-917 (1987)). The end of the Chothia CDR- H1 loop when numbered using the Kabat numbering convention varies between H32 and H34 depending on the length of the loop (this is because the Kabat numbering scheme places the insertions at H35A and H35B; if neither 35A nor 35B is present, the loop ends at 32; if only 35A is present, the loop ends at 33; if both 35A and 35B are present, the loop ends at 34). 31 NAI-1541858741The AbM hypervariable regions represent a compromise between the Kabat CDRs and Chothia structural loops and are used by Oxford Molecular’s AbM antibody modeling software (see, e.g., Martin, in Antibody Engineering, Vol.2, Chapter 3, Springer Verlag). The “contact” hypervariable regions are based on an analysis of the available complex crystal structures. The residues from each of these hypervariable regions or CDRs are noted below.

[0094] A universal numbering system has been developed and widely adopted, ImMunoGeneTics (IMGT®) Information System (Lefranc et al., Dev. Comp. Immunol. 27(1):55-77 (2003)). IMGT®is an integrated information system specializing in immunoglobulins (IG), T cell receptors (TR) and major histocompatibility complex (MHC) of human and other vertebrates. Herein, the CDRs are referred to in terms of both the amino acid sequence and the location within the light or heavy chain. As the “location” of the CDRs within the structure of the immunoglobulin variable region is conserved between species and present in structures called loops, by using numbering systems that align variable region sequences of structural features, CDR and framework residues are readily identified. This information can be used in grafting and replacement of CDR residues from immunoglobulins of one species into an acceptor framework from, typically, a human antibody. An additional numbering system (AHon) has been developed by Honegger and Plückthun, J. Mol. Biol. 309: 657-670 (2001). Correspondence between the numbering system, including, for example, the Kabat numbering and the IMGT®unique numbering system, is well known to one skilled in the art (see, e.g., Kabat, supra; Chothia and Lesk, supra; Martin, supra; Lefranc et al., supra) and is also illustrated below. Various systems known in the art or described herein represent different ways of delineating CDRs, and when they are used to define the same antibody, they are often considered equivalent. An exemplary system, shown herein, combines Kabat and Chothia.

[0095] Hypervariable regions can comprise “extended hypervariable regions” as follows: 24-36 or 24-34 (L1), 46-56 or 50-56 (L2) and 89-97 or 89-96 (L3) in the VL and 26-35 or 26- 35A (H1), 50-65 or 49-65 (H2) and 93-102, 94-102, or 95-102 (H3) in the VH. As used 32 NAI-1541858741herein, the terms “hypervariable region,” “HVR,” “HV,” “complementarity determining region,” or “CDR” are used interchangeably.

[0096] As used herein, “chemotherapeutic” refers to drugs that are cytotoxic drugs that can destroy or inhibit the growth and division of malignant cells in the treatment of cancer.

[0097] As used herein, “PD-L1 inhibitor,” “PD-1 inhibitor,” “PD-1 / PD-L1 inhibitor,” and “PD-L1 / PD-1 inhibitor” are used interchangeably and refer to a group of checkpoint inhibitor anticancer drugs that block the activity of PD-1 and PD-L1 immune checkpoint proteins present on the surface of cells. Non-limiting examples of PD-L1 / PD-1 inhibitors include nivolumab, pembrolizumab, atezolizumab, avelumab, durvalumab, cemiplimab, dostarlimab, and retifanlimab. See, for example US8354509B2 which is incorporated herein by reference in its entirety.

[0098] Pembrolizumab is a humanized monoclonal immunoglobulin G4 (IgG4) kappa antibody specific for PD-1 cell surface membrane receptor that has demonstrated the ability to generate increased antitumor immune responses and improvements in survival of cancer patients. In some embodiments, Pembrolizumab comprises or consists of two heavy chains and two light chains. In further embodiments, each of the heavy chains of Pembrolizumab comprises or consists of an amino acid sequence as set forth below: QVQLVQSGVEVKKPGASVKVSCKASGYTFTNYYMYWVRQAPGQGLEWMGGINPSNGGTNFNE KFKNRVTLTTDSSTTTAYMELKSLQFDDTAVYYCARRDYRFDMGFDYWGQGTTVTVSSASTK GPSVFPLAPCSRSTSESTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLS SVVTVPSSSLGTKTYTCNVDHKPSNTKVDKRVESKYGPPCPPCPAPEFLGGPSVFLFPPKPK DTLMISRTPEVTCVVVDVSQEDPEVQFNWYVDGVEVHNAKTKPREEQFNSTYRVVSVLTVLH QDWLNGKEYKCKVSNKGLPSSIEKTISKAKGQPREPQVYTLPPSQEEMTKNQVSLTCLVKGF YPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSRLTVDKSRWQEGNVFSCSVMHEALHN HYTQKSLSLSLGK (SEQ ID NO: 9). In yet further embodiments, each of the light chains of Pembrolizumab comprises or consists of an amino acid sequence as set forth below: EIVLTQSPATLSLSPGERATLSCRASKGVSTSGYSYLHWYQQKPGQAPRLLIYLASYLESGV PARFSGSGSGTDFTLTISSLEPEDFAVYYCQHSRDLPLTFGGGTKVEIKRTVAAPSVFIFPP SDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLS KADYEKHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 10). In some embodiments, Pembrolizumab is described in any one or more of the following: KEGG Entry: D10574, CAS: 1374853-91-4, or PubChem: 254741536, PubChem 377483934, and DrugBank Accession Number: DB09037, each of which is incorporated herein by reference in its entirety. 33 NAI-1541858741

[0099] As used herein, the term “cytopenia” means a deficiency in the number of blood cells and / or a deficiency in the number of a given type of blood cell. Cytopenia includes anemia, leukopenia, neutropenia, thrombocytopenia, and pancytopenia.

[0100] As used herein, the term “neutropenia” means a deficiency in the number of circulating neutrophils, for example, an absolute neutrophil count (ANC) less than 1,500 cells / µl (Grades 2 or higher). As used herein, the following grades of neutropenia are: Grade 0: ANC ≥ 2,000 cells / µL; Grade 1: ANC ≥ 1,500 cells / µL to < 2,000 cells / µL; Grade 2: ANC ≥ 1,000 cells / µL to < 1,500 cells / µL; Grade 3: ANC ≥ 500 cells / µL to < 1,000 / µL; Grade 4: ANC < 500 cells / µL. See, e.g., Common Terminology Criteria for Adverse Events (CTCAE), Version 5.0, November 2017, National Institutes of Health, National Cancer Institute, incorporated herein by reference in its entirety. It will be understood by those skilled in the art that Grade 0 neutropenia indicates the absence of neutropenia, that is, where there is no deficiency in the number of circulating neutrophils.

[0101] As used herein, the term “thrombocytopenia” means a deficiency in the number of circulating platelets, for example, a platelet count of less than 100,000 cells / µL. As used herein, the following grades of thrombocytopenia are: Grade 0: platelet count ≥ 150,000 cells / µL; Grade 1: platelet count ≥ 75,000 cells / µL to < 150,000 cells / µL; Grade 2: platelet count ≥ 50,000 cells / µL to < 75,000 cells / µL; Grade 3: platelet count ≥ 25,000 cells / µL to < 50,000 / µL; Grade 4: platelet count < 25,000 cells / µL. See, e.g., Common Terminology Criteria for Adverse Events (CTCAE), Version 5.0, November 2017, National Institutes of Health, National Cancer Institute. Grade 1 thrombocytopenia may also be categorized as Grade 1A: platelet count ≥ 100,000 cells / µL to < 150,000 cells / µL; and Grade 1B: platelet count ≥ 75,000 cells / µL to < 100,000 cells / µL. It will be understood by those skilled in the art that Grade 0 thrombocytopenia indicates the absence of thrombocytopenia, that is, where there is no deficiency in the number of circulating platelets.

[0102] As used herein, the term “absolute neutrophil count (ANC)” means the total number of neutrophils in the white blood cell count. Those skilled in the art will know how to calculate ANC. As an example, ANC may be calculated as follows: ANC = WBC (cells / µL) x [percent (PMNs + bands) ÷ 100]; where “WBC” is the white blood cell count, “PMNs” is the percent of neutrophils, and “bands” are young neutrophils.

[0103] The disclosure can be understood more fully by reference to the following detailed description and illustrative examples, which are intended to exemplify non-limiting embodiments. 34 NAI-15418587417.2 5T4 ANTIBODIES

[0104] 5T4 ADCs described herein comprise a drug and 5T4 antibody conjugated thereto. In some embodiments, a 5T4 antibody refers to an antibody, specifically binding to 5T4, such as a 5T4 protein, a 5T4 polypeptide, a 5T4 polypeptide fragment, a 5T4 peptide, or a 5T4 epitope. In some embodiments, the 5T4 antibody is a human or humanized antibody (e.g., comprising human constant regions) that binds to 5T4. In some embodiments, a 5T4 antibody can bind to 5T4 which is expressed on the surface of a mammalian (e.g., human) cell, including a 5T4-expressing tumor cell. In some embodiments, a 5T4 antibody binds a 5T4 extracellular epitope expressed on a cell such as a tumor cell (e.g., an extracellular 5T4 epitope). In some embodiments, 5T4 is a human 5T4. An exemplary amino acid sequence of human 5T4 is described herein.

[0105] In some embodiments, the 5T4 antibody competes for binding to 5T4 with a reference 5T4 antibody that comprises a VH region, VL region, HCDR1, HCDR2, HCDR3, LCDR1, LCDR2, and / or LCDR3 of any one of the antibodies described herein, such as an amino acid sequence of a VH region, VL region, HCDR1, HCDR2, HCDR3, LCDR1, LCDR2, and / or LCDR3 as described in Table 1. Accordingly, in some embodiments, the 5T4 antibody competes for binding to 5T4 with a reference 5T4 antibody that comprises one, two, and / or three VH CDRs and / or one, two, and / or three VL CDRs of the antibody designated as mAbA15. In some embodiments, a 5T4 ADC comprises a drug conjugated (directly or indirectly) to a 5T4 antibody that competes for binding to 5T4 with a reference 5T4 antibody that comprises one, two, and / or three VH CDRs and one, two, and / or three VL CDRs from the antibody designated as mAbA15. In some embodiments, the 5T4 antibody competes for binding to 5T4 with a reference 5T4 antibody that comprises a VH region and VL region of the antibody designated as mAbA15. In some embodiments, the 5T4 antibody competes for binding to 5T4 with a reference 5T4 antibody that comprises: a VH region comprising the amino acid sequence of SEQ ID NO: 11 and a VL region comprising the amino acid sequence of SEQ ID NO: 12.

[0106] In some embodiments, the 5T4 antibody comprises a VH region, VL region, HCDR1, HCDR2, HCDR3, LCDR1, LCDR2, and / or LCDR3 of any one of the antibodies described herein, such as an amino acid sequence of a VH region, VL region, HCDR1, HCDR2, HCDR3, LCDR1, LCDR2, and / or LCDR3 as described in Table 1. Accordingly, in some embodiments, the 5T4 antibody comprises one, two, and / or three heavy chain CDRs and / or one, two, and / or three light chain CDRs from the antibody designated as mAbA15. In 35 NAI-1541858741some embodiments, the 5T4 antibody comprises one, two, and / or three heavy chain CDRs and one, two, and / or three light chain CDRs from the antibody designated as mAbA15.

[0107] In some embodiments, the 5T4 antibody comprises a VH region, which comprises one or more (such as one, two, or three) of VH CDR1, VH CDR2, and VH CDR3 as described herein, such as in Table 1; and / or a VL region, which comprises one or more (such as one, two, or three) of VL CDR1, VL CDR2, and VL CDR3 as described herein, such as in Table 1.

[0108] The antibody designated as mAbA15 comprises a VH comprising an amino acid sequence of SEQ ID NO: 11 and a VL comprising an amino acid sequence of SEQ ID NO: 12. In further embodiments, the antibody designated as mAbA15 comprises a heavy chain comprising an amino acid sequence of SEQ ID NO: 2 and a light chain comprising an amino acid sequence of SEQ ID NO: 3. 36 NAI-1541858741)H3)6Y I1 ET3 D )5A)6)7)8R Q L1V1 1T1 LSQCSQSGET Q S Q QSQ ASQAQPDK GSS(TEISR E(DS(AESEQ (S(QES AI PY YR (QRQEK YSQ V(Q )9)0D ) ) ) )WSSY L1 2 3 T8HIW Y1 2 G 2 2 2 1 VY: T : : : :V:A OYOSO APYTSNSNYN SO O NSNTO NYV V SFTDG IT D RSTD V D AASS LA TSF GQS ISIETS I SDIYDI F SSIQREQQQ QA)QQ TG F QV2(SDE(YRSE(SE(S(QES(GSGSQ1:SO A AW AYA N) )Y) ) ) ) DRDCS LCDIH3I1A41 D51A6 7 T8L GTI QY:Y: L :V1:YOEOGO A S OS1SNTGNSNSN Y:V1: S TEOPORL YVS(SYLNTNFDSK Y RV SA:eSR: RcGTeDKITIGV DFQETS I TDSQESI SDRQ QI SDSQ AIYDSQAInQQeGScuP RnDeGEuVV GS(TISES AESESQESqQq SKY(D Y( R ( ( (eSVYReATd LASdSLG 12 3 1 iGCi SQ R DR R R2R3RcAGcGY ASGFCDCDC D C D DoSYoPS T 14H H HLCLCLni EVnmVAiQV78mTPT 58HR. . AL TAM14VDqCeL RSVDqCeSHQDVVE EQA51-ALVIY D AIA N

[0109] In some embodiments, the 5T4 antibody comprises a VH region. In some embodiments, the 5T4 antibody comprises a VL region. In some embodiments, the 5T4 antibody has a combination of (i) a VH region; and (ii) a VL region.

[0110] In some embodiments, the 5T4 antibody comprises a heavy chain having a combination of (i) a VH as described herein, such as in Table 1, and (ii) one or more heavy chain constant regions (e.g., CH1, hinge, CH2, and CH3). An exemplary IgG heavy chain can comprise any VH amino acid sequence as described herein and the following CH1, hinge, CH2, and CH3 amino acid sequence: ASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSL SSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKP KDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQD WLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDI AVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLS LSPGK (SEQ ID NO: 37). Another exemplary IgG heavy chain can comprise any VH amino acid sequence as described herein and the following CH1, hinge, CH2, and CH3 amino acid sequence: ASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSL SSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPEAAGGPSVFLFPPKP KDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQD WLNGKEYKCKVSNKALKAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDI AVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLS LSPGK (SEQ ID NO: 38).

[0111] In some embodiments, a 5T4 antibody comprises a light chain having a combination of (i) a VL region as described herein, such as in Table 1; and (ii) a light chain constant region (CL). An exemplary light chain (e.g., for pairing with an IgG heavy chain) can comprise any VL amino acid sequence described herein and the following CL amino acid sequence: RTVAAPSVFIFPPSDSQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDST YSLSSTLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 39).

[0112] In some embodiments, the 5T4 antibody comprises (a) a heavy chain having a combination of (i) a VH as described herein, such as in Table 1, and (ii) one or more heavy chain constant regions (e.g., CH1, hinge, CH2, and CH3); and (b) a light chain having a combination of (i) a VL as described herein, such as in Table 1, and (ii) a light chain constant region in an IgG format (CL). 38 NAI-1541858741

[0113] In some embodiments, an antibody that binds to 5T4 comprises a heavy chain having an amino acid sequence of EVQLVESGGGLVQPGGSLRLSCAASGFTFSSYYIHWVRQAPGKGLEWVAYITSTGSYTEYADSVK GRFTISADTSKNTAYLQMNSLRAEDTAVYYCARYDRSTRYSGLDYWGQGTLVTVSSASTKGPSVF PLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSS SLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRT PEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKC KVSNKALPAPIEKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQ PENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGSLCTP SRGS (SEQ ID NO: 40), and a light chain having an amino acid sequence of DIQMTQSPSSLSASVGDRVTITCRASQSVSSAVAWYQQKPGKAPKLLIYSASSLYSGVPSRFSGS RSGTDFTLTISSLQPEDFATYYCQQAYATPVTFGQGTKVEIKRTVAAPSVFIFPPSDEQLKSGTA SVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACE VTHQGLSSPVTKSFNRGEC (SEQ ID NO: 3).

[0114] In some embodiments, the antibody that binds to 5T4 comprises a heavy chain which has been modified to include a formyl glycine residue and therefore have the amino acid sequence of EVQLVESGGGLVQPGGSLRLSCAASGFTFSSYYIHWVRQAPGKGLEWVAYITSTGSYTEYADSVK GRFTISADTSKNTAYLQMNSLRAEDTAVYYCARYDRSTRYSGLDYWGQGTLVTVSSASTKGPSVF PLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSS SLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRT PEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKC KVSNKALPAPIEKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQ PENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGSL(fGl y)TPSRGS (SEQ ID NO: 41), wherein f(Gly) is the formylglycine residue. In further embodiments, the antibody that binds to 5T4 further comprises a light chain having an amino acid sequence of DIQMTQSPSSLSASVGDRVTITCRASQSVSSAVAWYQQKPGKAPKLLIYSASSLYSGVPSRFSGS RSGTDFTLTISSLQPEDFATYYCQQAYATPVTFGQGTKVEIKRTVAAPSVFIFPPSDEQLKSGTA SVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACE VTHQGLSSPVTKSFNRGEC (SEQ ID NO: 3).

[0115] In some embodiments, a 5T4 ADC comprises a heavy chain having an amino acid sequence of EVQLVESGGGLVQPGGSLRLSCAASGFTFSSYYIHWVRQAPGKGLEWVAYITSTGSYTEYADSVK 39 NAI-1541858741GRFTISADTSKNTAYLQMNSLRAEDTAVYYCARYDRSTRYSGLDYWGQGTLVTVSSASTKGPSVF PLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSS SLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRT PEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKC KVSNKALPAPIEKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQ PENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGSL (fGly’)TPSRGS (SEQ ID NO: 2), wherein (fGly’) is an amino acid (formylglycine) conjugated to (such as by having its side chain replaced by) a linker-drug as disclosed herein. In further embodiments, the antibody that binds to 5T4 further comprises a light chain having an amino acid sequence of DIQMTQSPSSLSASVGDRVTITCRASQSVSSAVAWYQQKPGKAPKLLIYSASSLYSGVPSRFSGS RSGTDFTLTISSLQPEDFATYYCQQAYATPVTFGQGTKVEIKRTVAAPSVFIFPPSDEQLKSGTA SVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACE VTHQGLSSPVTKSFNRGEC (SEQ ID NO: 3).

[0116] As described herein, to produce the conjugate, the polypeptide containing the fGly residue may be conjugated to a drug or active agent by reaction of the fGly with a reactive moiety (e.g., hydrazinyl-indolyl or a hydrazinyl-pyrrolo-pyridinyl coupling moiety, as described herein) of a linker attached to the drug or active agent to produce an fGly’-containing sulfatase motif. As used herein, the term fGly’ refers to the amino acid residue of the sulfatase motif that is coupled to the drug or active agent through a linker as described herein.

[0117] In some embodiments, a 5T4 ADC comprises a heavy chain having an amino acid sequence of EVQLVESGGGLVQPGGSLRLSCAASGFTFSSYYIHWVRQAPGKGLEWVAYITSTGSYTEYADSVK GRFTISADTSKNTAYLQMNSLRAEDTAVYYCARYDRSTRYSGLDYWGQGTLVTVSSASTKGPSVF PLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSS SLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRT PEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKC KVSNKALPAPIEKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQ PENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGSLnTP SRGS (SEQ ID NO: 42), wherein n is an amino acid (formylglycine) conjugated to (such as by having its side chain replaced by) a linker-drug as disclosed herein. In some embodiments, the amino acid n refers to fGly’. In further embodiments, the antibody that binds to 5T4 further comprises a light chain having an amino acid sequence of DIQMTQSPSSLSASVGDRVTITCRASQSVSSAVAWYQQKPGKAPKLLIYSASSLYSGVPSRFSGS 40 NAI-1541858741RSGTDFTLTISSLQPEDFATYYCQQAYATPVTFGQGTKVEIKRTVAAPSVFIFPPSDEQLKSGTA SVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACE VTHQGLSSPVTKSFNRGEC (SEQ ID NO: 3).

[0118] In some embodiments, a 5T4 antibody comprises one or more CDRs (e.g., one, two, three, four, five, or six CDRs), for example, an HCDR1, HCDR2, HCDR3, LCDR1, LCDR2, and / or LCDR3 as described in Table 1.

[0119] In some embodiments, a 5T4 antibody comprises one or more CDRs (e.g., one, two, or three VH CDRs), for example, an HCDR1, HCDR2, HCDR3, as described in Table 1. In some embodiments, a 5T4 antibody comprises one or more CDRs (e.g., one, two, or three VL CDRs), for example, an LCDR1, LCDR2, and / or LCDR3, as described in Table 1. In some embodiments, a 5T4 antibody comprises one or more CDRs (e.g., one, two, or three VH CDRs), for example, an HCDR1, HCDR2, HCDR3, as described in Table 1, and one or more CDRs (e.g., one, two, or three VL CDRs), for example, an LCDR1, LCDR2, and / or LCDR3, as described in Table 1.

[0120] In some embodiments, a 5T4 antibody comprises a heavy chain variable region (VH) comprising: (1) an HCDR1 comprising an amino acid sequence of any one of: (i) SEQ ID NO: 13, (ii) SEQ ID NO: 19, (iii) SEQ ID NO: 24, (iv) SEQ ID NO: 25, and (v) SEQ ID NO: 30; (2) an HCDR2 comprising an amino acid sequence of any one of: (i) SEQ ID NO: 14, (ii) SEQ ID NO: 20, (iii) SEQ ID NO: 26, (iv) SEQ ID NO: 31, and (v) SEQ ID NO: 36; and (3) an HCDR3 comprising an amino acid sequence of any one of: (i) SEQ ID NO: 15, (ii) SEQ ID NO: 21, (iii) SEQ ID NO: 27, and (iv) SEQ ID NO: 32; and / or a VL region comprising: (1) a VCDR1 comprising an amino acid sequence of any one of: (i) SEQ ID NO: 16, (ii) SEQ ID NO: 22, (iii) SEQ ID NO: 28, and (iv) SEQ ID NO: 33; (2) an LCDR2 comprising an amino acid sequence of any one of: (i) SEQ ID NO: 17, (ii) SEQ ID NO: 23, and (iii) SEQ ID NO: 34; and (3) an LCDR3 comprising an amino acid sequence of any one of: (i) SEQ ID NO: 18, (ii) SEQ ID NO: 29, and (iii) SEQ ID NO: 35.

[0121] In some embodiments, a 5T4 antibody comprises a VH region comprising: (1) an HCDR1 comprising an amino acid sequence of any one of: (i) SEQ ID NO: 13, (ii) SEQ ID NO: 19, (iii) SEQ ID NO: 24, (iv) SEQ ID NO: 25, and (v) SEQ ID NO: 30; (2) an HCDR2 comprising an amino acid sequence of any one of: (i) SEQ ID NO: 14, (ii) SEQ ID NO: 20, (iii) SEQ ID NO: 26, (iv) SEQ ID NO: 31, and (v) SEQ ID NO: 36; and (3) an HCDR3 comprising an amino acid sequence of any one of: (i) SEQ ID NO: 15, (ii) SEQ ID NO: 21, (iii) SEQ ID NO: 27, and (iv) SEQ ID NO: 32. 41 NAI-1541858741

[0122] In some embodiments, a 5T4 antibody comprises a VL region comprising: (1) an LCDR1 comprising an amino acid sequence of any one of: (i) SEQ ID NO: 16, (ii) SEQ ID NO: 22, (iii) SEQ ID NO: 28, and (iv) SEQ ID NO: 33; (2) an LCDR2 comprising an amino acid sequence of any one of: (i) SEQ ID NO: 17, (ii) SEQ ID NO: 23, and (iii) SEQ ID NO: 34; and (3) an LCDR3 comprising an amino acid sequence of any one of: (i) SEQ ID NO: 18, (ii) SEQ ID NO: 29, and (iii) SEQ ID NO: 35.

[0123] In some embodiments, a 5T4 ADC comprises an antibody that binds to 5T4, wherein the antibody comprises all three heavy chain CDRs and / or all three light chain CDRs from the antibody designated as mAbA15 that comprises a VH amino acid sequence of SEQ ID NO: 11 and a VL amino acid sequence of SEQ ID NO: 12. In some embodiments, a 5T4 ADC comprises a 5T4 antibody, wherein the 5T4 antibody comprises all three heavy chain CDRs and / or all three light chain CDRs from the antibody designated as mAbA15.

[0124] In some embodiments, a 5T4 ADC comprises an antibody that binds to 5T4, wherein the antibody comprises: (a) a VH region comprising an HCDR1, an HCDR2, and an HCDR3 amino acid sequence as described herein, such as in Table 1; and / or (b) a VL region comprising an LCDR1, an LCDR2, and an LCDR3 amino acid sequence as described herein, such as in Table 1. In some embodiments, a 5T4 ADC comprises an antibody that binds to 5T4 wherein the antibody comprises: a VH region comprising an HCDR1, an HCDR2, and an HCDR3 amino acid sequence as described herein, such as in Table 1. In some embodiments, a 5T4 ADC comprises an antibody that binds to 5T4, wherein the antibody comprises a VL region comprising an LCDR1, an LCDR2, and an LCDR3 amino acid sequence as described herein, such as in Table 1.

[0125] In some embodiments, a 5T4 ADC comprises an antibody that binds to 5T4, wherein the antibody comprises a VH region and / or VL region described herein, and wherein the VH and / or VL comprises human framework sequences. In some embodiments, the VH region and / or VL region comprises a framework 1 (FR1), a framework 2 (FR2), a framework 3 (FR3) and / or a framework 4 (FR4) sequence, such as a human FR1, a human FR2, a human FR3 and / or a human FR4.

[0126] In some embodiments, CDRs of a 5T4 antibody can be determined by the Kabat system (Kabat et al. (1971) Ann. NY Acad. Sci.190:382-391 and, Kabat et al. (1991) Sequences of Proteins of Immunological Interest, Fifth Edition, U.S. Department of Health and Human Services, NIH Publication No.91-3242).

[0127] In some embodiments, CDRs of a 5T4 antibody can be determined by the Chothia system, which will be referred to herein as the “Chothia CDRs” (see, e.g., Chothia and Lesk, 42 NAI-15418587411987, J. Mol. Biol., 196:901-917; Al-Lazikani et al., 1997, J. Mol. Biol., 273:927-948; Chothia et al., 1992, J. Mol. Biol., 227:799-817; Tramontano A. et al., 1990, J. Mol. Biol.215(1):175-82; and U.S. Patent No.7,709,226).

[0128] In some embodiments, CDRs of a 5T4 antibody can be determined by the ImMunoGeneTics (IMGT®) system, for example, as described in Lefranc, M.-P., 1999, The Immunologist, 7:132-136 and Lefranc, M.-P. et al., 1999, Nucleic Acids Res., 27:209-212 (“IMGT®CDRs”).

[0129] In some embodiments, CDRs of a 5T4 antibody can be determined by the AbM system, which will be referred to herein as the “AbM CDRs,” for example as described in MacCallum et al., 1996, J. Mol. Biol., 262:732-745. See also, e.g., Martin, A., “Protein Sequence and Structure Analysis of Antibody Variable Domains,” in Antibody Engineering, Kontermann and Dübel, eds., Chapter 31, pp.422-439, Springer-Verlag, Berlin (2001).

[0130] In some embodiments, CDRs of a 5T4 antibody can be determined by the Contact system, which will be referred to herein as the “Contact CDRs” (see, e.g., MacCallum RM et al., 1996, J Mol Biol 5: 732-745). The Contact CDRs are based on an analysis of the available complex crystal structures.

[0131] In some embodiments, the position of one or more (e.g., one, two, three) CDRs along the VH (e.g., CDR1, CDR2, or CDR3) and / or VL (e.g., CDR1, CDR2, or CDR3) region of a 5T4 antibody can vary by one, two, three, four, five, or six amino acid positions provided that binding to 5T4 (e.g., human 5T4) is maintained (e.g., substantially maintained, for example, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, or at least 95%). For example, in some embodiments, the position defining a CDR of Table 1 can vary by shifting the N-terminal and / or C-terminal boundary of the CDR by one, two, three, four, five, or six amino acids, relative to the current CDR position, provided that binding to 5T4 (e.g., human 5T4) is maintained (e.g., substantially maintained, for example, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, or at least 95%). Additionally or alternatively, in some embodiments, the length of one or more (e.g., one, two, three) CDRs along the VH (e.g., CDR1, CDR2, or CDR3) and / or VL (e.g., CDR1, CDR2, or CDR3) region of a 5T4 antibody (e.g., a human 5T4 antibody) described herein can vary (e.g., be shorter or longer) by one, two, three, four, five, or more amino acids, provided that binding to 5T4 (e.g., human 5T4) is maintained (e.g., substantially maintained, for example, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, or at least 95%). For example, in some embodiments, a VH and / or VL CDR1, CDR2, and / or CDR3 can be one, two, three, four, five or more amino acids shorter than one or more of the CDRs described by SEQ ID NOs:13-36, provided that binding to 5T4 (e.g., human 5T4) is maintained (e.g., substantially 43 NAI-1541858741maintained, for example, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, or at least 95%). In other embodiments, a VH and / or VL CDR1, CDR2, and / or CDR3 can be one, two, three, four, five or more amino acids longer than one or more of the CDRs described by SEQ ID NOs: 13-36, provided that binding to 5T4 (e.g., human 5T4) is maintained (e.g., substantially maintained, for example, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, or at least 95%). Additionally or alternatively, in some embodiments, the amino terminus of a VH and / or VL CDR1, CDR2, and / or CDR3 can be extended by one, two, three, four, five or more amino acids compared to one or more of the CDRs described by SEQ ID NOs: 13-36, provided that binding to 5T4 (e.g., human 5T4) is maintained (e.g., substantially maintained, for example, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, or at least 95%). Additionally or alternatively, in some embodiments, the carboxy terminus of a VH and / or VL CDR1, CDR2, and / or CDR3 can be extended by one, two, three, four, five or more amino acids compared to one or more of the CDRs described by SEQ ID NOs: 13-36, provided that binding to 5T4 (e.g., human 5T4) is maintained (e.g., substantially maintained, for example, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, or at least 95%). Additionally or alternatively, in some embodiments, the amino terminus of a VH and / or VL CDR1, CDR2, and / or CDR3 can be shortened by one, two, three, four, five or more amino acids compared to one or more of the CDRs described by SEQ ID NOs: 13-36, provided that binding to 5T4 (e.g., human 5T4) is maintained (e.g., substantially maintained, for example, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, or at least 95%). In some embodiments, the carboxy terminus of a VH and / or VL CDR1, CDR2, and / or CDR3 can be shortened by one, two, three, four, five or more amino acids compared to one or more of the CDRs described by SEQ ID NOs: 13-36, provided that binding to 5T4 (e.g., human 5T4) is maintained (e.g., substantially maintained, for example, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, or at least 95%). Any method known in the art can be used to ascertain whether binding to 5T4 (e.g., human 5T4) is maintained, such as those disclosed in WO2023220620 and WO2023220626, each of which is enclosed herein by reference in its entirety. 7.3 ANTIBODY DRUG CONJUGATES AND CONJUGATION METHODS

[0132] In some embodiments, the antibody can be modified before conjugation to the linker- drug. Modification of the antibody can produce a modified antibody that contains one or more reactive groups suitable for conjugation to the linker-drug.

[0133] In some embodiments, the antibody can be modified at one or more amino acid residues to provide one or more reactive groups suitable for conjugation to the linker-drug. For 44 NAI-1541858741example, carbonyl groups introduced into a polypeptide can be selectively reacted with α- nucleophiles, such as aminooxy- and hydrazide-bearing compounds. Chemistries selective for carbonyl functional groups on a protein with enhanced kinetics, site selectivity and conjugate stability can result in improved bioconjugates.

[0134] In some embodiments, the antibody can be modified to include a reactive aldehyde group (e.g., a reactive aldehyde). A reactive aldehyde can be included in an “aldehyde tag” or “ald-tag,” which is meant to refer to an amino acid sequence derived from a sulfatase motif that has been converted by action of a formylglycine generating enzyme (FGE) to contain a 2- formylglycine residue (referred to herein as “fGly”). The fGly residue generated by an FGE is also referred to in the literature as a “formylglycine.” Stated differently, the term “aldehyde tag” is used herein to refer to an amino acid sequence comprising a “converted” sulfatase motif (e.g., a sulfatase motif in which the cysteine or the serine residue has been converted to fGly by action of an FGE, e.g., L(fGly)TPSR (SEQ ID NO: 43)). A converted sulfatase motif can be derived from an amino acid sequence comprising an “unconverted” sulfatase motif (e.g., a sulfatase motif in which the cysteine or serine residues has not been converted to fGly by an FGE, but is capable of being converted, e.g., an unconverted sulfatase motif with the sequence: L(C / S)TPSR (SEQ ID NO: 44)). “Conversion,” used in the context of action of a formylglycine generating enzyme (FGE) on a sulfatase motif, refers to biochemical modification of a cysteine or serine residue in a sulfatase motif to a formylglycine (fGly) residue (e.g., Cys to fGly, or Ser to fGly). As used herein, an aldehyde-tagged antibody refers to an antibody where a cysteine or serine residue has been modified to form a formylglycine residue. Additional aspects of aldehyde tags and uses thereof in site-specific protein modification are described in U.S.7,985,783, U.S.8,729,232, WO2008036350, and WO2009120611, the disclosures of which are each incorporated herein by reference. Accordingly, the fGly residue conjugated to the linker or linker-drug as disclosed herein is referred to herein as fGly’.

[0135] Conversion of a polypeptide to include fGly can be accomplished by cell-based (in vivo) or cell-free methods (in vitro). Similarly, modification of a polypeptide to produce a polypeptide suitable for conjugation (e.g., modification to produce a polypeptide containing a reactive group suitable for conjugation) can be accomplished by cell-based (in vivo) or cell-free methods (in vitro).

[0136] The amino acid sequence of an antibody can be modified to include a sulfatase motif that contains a serine or cysteine residue that is capable of being converted (oxidized) to an fGly residue by action of an FGE either in vivo (e.g., at the time of translation of an aldehyde tag- containing protein in a cell) or in vitro (e.g., by contacting an aldehyde tag-containing protein 45 NAI-1541858741with an FGE in a cell-free system). Such sulfatase motifs may also be referred to herein as an FGE-modification site. A 5T4 antibody used to generate a 5T4 ADC includes at least an Ig constant region, e.g., an Ig heavy chain constant region (e.g., at least a CH1 domain; at least a CH1 and a CH2 domain; a CH1, a CH2, and a CH3 domain; or a CH1, a CH2, a CH3, and a CH4 domain), or an Ig light chain constant region.

[0137] A sulfatase motif can be introduced into any convenient site in the antibody. As noted herein, in some embodiments, the extent of modification of the native amino acid sequence of the target polypeptide is minimized, to minimize the number of amino acid residues that are inserted, deleted, substituted (replaced), and / or added (e.g., to the N- or C-terminus). Minimizing the extent of amino acid sequence modification of the target antibody can minimize the impact such modifications can have upon antibody function and / or structure.

[0138] In some embodiments, an aldehyde-tagged antibody comprises an aldehyde-tagged Ig heavy chain constant region (e.g., at least a CH1 domain; at least a CH1 and a CH2 domain; a CH1, a CH2, and a CH3 domain; or a CH1, a CH2, a CH3, and a CH4 domain). The aldehyde- tagged Ig heavy chain constant region can include heavy chain constant region sequences of an IgA, IgM, IgD, IgE, IgG1, IgG2, IgG3, or IgG4 isotype heavy chain or any allotypic variant of same, e.g., human heavy chain constant region sequences or mouse heavy chain constant region sequences, a hybrid heavy chain constant region, a synthetic heavy chain constant region, or a consensus heavy chain constant region sequence, and the like, modified to include at least one sulfatase motif that can be modified by an FGE to generate an fGly-modified Ig polypeptide. See, e.g., WO2012097333 and WO2018169953, each of which is incorporated herein by reference in its entirety. Allotypic variants of Ig heavy chains are known in the art. See, e.g., Jefferis and Lefranc (2009) MAbs 1:4.

[0139] In some embodiments, an aldehyde-tagged antibody comprises an aldehyde-tagged Ig light chain constant region. The aldehyde-tagged Ig light chain constant region can include constant region sequences of a kappa light chain, a lambda light chain, e.g., kappa or lambda light chain constant regions, a hybrid light chain constant region, a synthetic light chain constant region, or a consensus light chain constant region sequence, and the like, modified to include at least one sulfatase motif that can be modified by an FGE to generate an fGly-modified antibody. See, e.g., WO2012097333 and WO2017189432, each of which is incorporated herein by reference in its entirety.

[0140] Alternatively, isolated, unmodified polypeptides can be isolated following recombinant production in a host cell lacking a suitable enzyme or by synthetic production. The isolated polypeptide can then be contacted with a suitable enzyme under conditions to provide for 46 NAI-1541858741the desired modification of the polypeptide to include fGly. The polypeptide can be unfolded by methods known in the art (e.g., using heat, adjustment of pH, chaotropic agents, (e.g., urea, and the like), organic solvents (e.g., hydrocarbons: octane, benzene, chloroform), and the like) and the denatured protein contacted with a suitable enzyme. The modified polypeptide can then be refolded under suitable conditions.

[0141] In some embodiments, the modified antibody containing the fGly residue can be conjugated to a linker-drug by reaction of the fGly with a coupling moiety on the linker-drug, such as a hydrazinyl-pyrrolo coupling moiety as described herein. For example, an fGly- containing antibody can be isolated from a production source (e.g., recombinant host cell production, synthetic production), and contacted with a reactive partner-containing drug or other moiety (e.g., detectable label) under conditions suitable to provide for conjugation of the drug or other moiety to the 5T4 antibody. For example, the reactive partner-containing drug or other moiety can include a conjugating moiety (e.g., a hydrazinyl-pyrrolo coupling moiety as described herein). The hydrazinyl-pyrrolo-containing drug can be reacted with the antibody to produce a 5T4 ADC, as described herein. See, e.g., WO2014078566 and WO2015081282, each of which is incorporated herein by reference in its entirety.

[0142] A general scheme for coupling an antibody to a pyridazine-pyrrolo coupling moiety is shown below.azaHIPS antibody with fGly residue pyridazine-pyrrolo coupling moiety

[0143] A hydrazinyl-pyrrolo coupling moiety, which can interchangeably be referred to herein as an aza-hydrazino-iso-Pictet-Spengler (azaHIPS) coupling moiety, upon conjugation to a formyl-glycine, forms a pyridazine-pyrrolo coupling moiety, such as that shown above. A 5T4 antibody can include a 2-formylglycine residue (fGly) that is reacted with azaHIPS coupling moiety, thus conjugating the two together. To generate a 5T4 ADC, a drug can be coupled directly or indirectly (e.g., through a linker moiety) to the azaHIPS moiety at any location of the azaHIPs moiety (e.g., R16, Y1, Y2, Y3, or Q4). R2and R3can each independently be any desired substituent, such as, but not limited to, hydrogen, alkyl, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, alkoxy, substituted alkoxy, amino, substituted amino, 47 NAI-1541858741carboxyl, carboxyl ester, acyl, acyloxy, acyl amino, amino acyl, alkylamide, substituted alkylamide, sulfonyl, thioalkoxy, substituted thioalkoxy, aryl, substituted aryl, heteroaryl, substituted heteroaryl, cycloalkyl, substituted cycloalkyl, heterocyclyl, or substituted heterocyclyl.

[0144] A minimal sulfatase motif of an aldehyde tag is usually 5 or 6 amino acid residues in length, usually no more than 6 amino acid residues in length. Sulfatase motifs provided in an Ig polypeptide are at least 5 or 6 amino acid residues, and can be, for example, from 5 to 16, 6-16, 5-15, 6-15, 5-14, 6-14, 5-13, 6-13, 5-12, 6-12, 5-11, 6-11, 5-10, 6-10, 5-9, 6-9, 5-8, or 6-8 amino acid residues in length, so as to define a sulfatase motif of less than 16, 15, 14, 13, 12, 11, 10, 9, 8, 7 or 6 amino acid residues in length.

[0145] In certain embodiments, 5T4 antibodies of interest include those where one or more amino acid residues, such as 2 or more, or 3 or more, or 4 or more, or 5 or more, or 6 or more, or 7 or more, or 8 or more, or 9 or more, or 10 or more, or 11 or more, or 12 or more, or 13 or more, or 14 or more, or 15 or more, or 16 or more, or 17 or more, or 18 or more, or 19 or more, or 20 or more amino acid residues have been inserted, deleted, substituted (replaced) relative to the native amino acid sequence to provide for a sequence of a sulfatase motif in the 5T4 antibody. In certain embodiments, the 5T4 antibody includes a modification (insertion, addition, deletion, and / or substitution / replacement) of less than 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3 or 2 amino acid residues of the amino acid sequence relative to the native amino acid sequence of the 5T4 antibody (such as a light chain of SEQ ID NO: 3 and / or a heavy chain comprising a VH of SEQ ID NO: 11 and a Fc region). Where an amino acid sequence native to the 5T4 antibody contains one or more residues of the desired sulfatase motif, the total number of modifications of residues can be reduced, e.g., by site-specification modification (insertion, addition, deletion, substitution / replacement) of amino acid residues flanking the native amino acid residues to provide a sequence of the desired sulfatase motif. In certain embodiments, the extent of modification of the native amino acid sequence of the target antibody is minimized, so as to minimize the number of amino acid residues that are inserted, deleted, substituted (replaced), or added (e.g., to the N- or C-terminus). Minimizing the extent of amino acid sequence modification of the target antibody may minimize the impact such modifications may have upon antibody function and / or structure.

[0146] It should be noted that while aldehyde tags of particular interest are those comprising at least a minimal sulfatase motif (also referred to a “consensus sulfatase motif”), it will be readily appreciated that longer aldehyde tags are both contemplated and encompassed by the present disclosure and can find use in the compositions and methods of the present disclosure. 48 NAI-1541858741Aldehyde tags can thus comprise a minimal sulfatase motif of 5 or 6 residues or can be longer and comprise a minimal sulfatase motif which can be flanked at the N- and / or C-terminal sides of the motif by additional amino acid residues. Aldehyde tags of, for example, 5 or 6 amino acid residues are contemplated, as well as longer amino acid sequences of more than 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more amino acid residues.

[0147] An aldehyde tag can be present at or near the C-terminus of an Ig heavy chain; e.g., an aldehyde tag can be present within 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acids of the C-terminus of a native, wild-type Ig heavy chain. An aldehyde tag can be present within a CH1 domain of an Ig heavy chain. An aldehyde tag can be present within a CH2 domain of an Ig heavy chain. An aldehyde tag can be present within a CH3 domain of an Ig heavy chain. An aldehyde tag can be present in an Ig light chain constant region, e.g., in a kappa light chain constant region or a lambda light chain constant region.

[0148] In some embodiments, the 5T4 antibody as disclosed herein comprises a sulfatase motif.

[0149] In certain embodiments, the sulfatase motif used may be described by: X1Z1X2Z2X3Z3(SEQ ID NO: 68) wherein: Z1is cysteine or serine (which can also be represented by (C / S)); Z2is either a proline or alanine residue (which can also be represented by (P / A)); Z3is a basic amino acid (e.g., arginine (R), and may be lysine (K) or histidine (H), e.g., lysine), or an aliphatic amino acid (alanine (A), glycine (G), leucine (L), valine (V), isoleucine (I), or proline (P), e.g., A, G, L, V, or I; X1is present or absent and, when present, can be any amino acid, e.g., an aliphatic amino acid, a sulfur-containing amino acid, or a polar, uncharged amino acid, (e.g., other than an aromatic amino acid or a charged amino acid), e.g., L, M, V, S or T, e.g., L, M, S or V, with the proviso that when the sulfatase motif is at the N-terminus of the target 5T4 antibody, X1is present; and X2and X3independently can be any amino acid, though usually an aliphatic amino acid, a polar, uncharged amino acid, or a sulfur containing amino acid (e.g., other than an aromatic amino acid or a charged amino acid), e.g., S, T, A, V, G or C, e.g., S, T, A, V or G.

[0150] The amino acid sequence of an antibody heavy and / or light chain can be modified to provide a sequence of at least 5 amino acids of X1Z1X2Z2X3Z3(SEQ ID NO: 68) wherein: 49 NAI-1541858741Z1is cysteine or serine; Z2is a proline or alanine residue; Z3is an aliphatic amino acid or a basic amino acid; X1is present or absent and, when present, is any amino acid, with the proviso that when the heterologous sulfatase motif is at an N-terminus of the 5T4 antibody, X1is present; X2and X3are each independently any amino acid.

[0151] The sulfatase motif is generally selected so as to be capable of conversion by a selected FGE, e.g., an FGE present in a host cell in which the aldehyde-tagged antibody is expressed or an FGE which is to be contacted with the aldehyde-tagged antibody in a cell-free in vitro method.

[0152] For example, where the FGE is a eukaryotic FGE (e.g., a mammalian FGE, including a human FGE), the sulfatase motif can be of: X1CX2PX3Z3(SEQ ID NO: 69) wherein: X1may be present or absent and, when present, can be any amino acid, e.g., an aliphatic amino acid, a sulfur-containing amino acid, or a polar, uncharged amino acid, (e.g., other than an aromatic amino acid or a charged amino acid), e.g., L, M, S or V, with the proviso that when the sulfatase motif is at the N-terminus of the target 5T4 antibody, X1is present; X2and X3independently can be any amino acid, e.g., an aliphatic amino acid, a sulfur- containing amino acid, or a polar, uncharged amino acid, (e.g., other than an aromatic amino acid or a charged amino acid), e.g., S, T, A, V, G, or C, e.g., S, T, A, V or G; and Z3is a basic amino acid (e.g., arginine (R), and may be lysine (K) or histidine (H), e.g., lysine), or an aliphatic amino acid (alanine (A), glycine (G), leucine (L), valine (V), isoleucine (I), or proline (P), e.g., A, G, L, V, or I.

[0153] Specific examples of sulfatase motifs include LCTPSR (SEQ ID NO: 70), MCTPSR (SEQ ID NO: 71), VCTPSR (SEQ ID NO: 72), LCSPSR (SEQ ID NO: 73), LCAPSR (SEQ ID NO: 74), LCVPSR (SEQ ID NO: 75), LCGPSR (SEQ ID NO: 76), ICTPAR (SEQ ID NO: 77), LCTPSK (SEQ ID NO: 78), MCTPSK (SEQ ID NO: 79), VCTPSK (SEQ ID NO: 80), LCSPSK (SEQ ID NO: 81), LCAPSK (SEQ ID NO: 82), LCVPSK (SEQ ID NO: 83), LCGPSK (SEQ ID NO: 84), LCTPSA (SEQ ID NO: 85), ICTPAA (SEQ ID NO: 86), MCTPSA (SEQ ID NO: 87), VCTPSA (SEQ ID NO: 88), LCSPSA (SEQ ID NO: 89), LCAPSA (SEQ ID NO: 90), LCVPSA (SEQ ID NO: 91), and LCGPSA (SEQ ID NO: 92).

[0154] In some embodiments, the 5T4 antibody prior to conjugating to a linker or a linker- drug as disclosed herein as disclosed herein comprises a fGly-containing sulfatase motif. 50 NAI-1541858741

[0155] Upon action of FGE on the antibody heavy and / or light chain, the serine or the cysteine in the sulfatase motif is modified to fGly. Thus, the fGly-containing sulfatase motif can be o: X1(fGly)X2Z2X3Z3(SEQ ID NO: 93) wherein: fGly is the formylglycine residue; Z2is either a proline or alanine residue (which can also be represented by (P / A)); Z3is a basic amino acid (e.g., arginine (R), and may be lysine (K) or histidine (H), usually lysine), or an aliphatic amino acid (alanine (A), glycine (G), leucine (L), valine (V), isoleucine (I), or proline (P), e.g., A, G, L, V, or I; X1may be present or absent and, when present, can be any amino acid, e.g., an aliphatic amino acid, a sulfur-containing amino acid, or a polar, uncharged amino acid, (e.g., other than an aromatic amino acid or a charged amino acid), e.g., L, M, V, S or T, e.g., L, M or V, with the proviso that when the sulfatase motif is at the N-terminus of the target 5T4 antibody, X1is present; and X2and X3independently can be any amino acid, e.g., an aliphatic amino acid, a sulfur- containing amino acid, or a polar, uncharged amino acid, (e.g., other than an aromatic amino acid or a charged amino acid), e.g., S, T, A, V, G or C, e.g., S, T, A, V or G.

[0156] Specific examples of fGly-containing sulfatase motifs include L(fGly)TPSR (SEQ ID NO: 94), M(fGly)TPSR (SEQ ID NO: 95), V(fGly)TPSR (SEQ ID NO: 96), L(fGly)SPSR (SEQ ID NO: 97), L(fGly)APSR (SEQ ID NO: 98), L(fGly)VPSR (SEQ ID NO: 99), L(fGly)GPSR (SEQ ID NO: 100), I(fGly)TPAR (SEQ ID NO: 101), L(fGly)TPSK (SEQ ID NO: 102), M(fGly)TPSK (SEQ ID NO: 103), V(fGly)TPSK (SEQ ID NO: 104), L(fGly)SPSK (SEQ ID NO: 105), L(fGly)APSK (SEQ ID NO: 106), L(fGly)VPSK (SEQ ID NO: 107), L(fGly)GPSK (SEQ ID NO: 108), L(fGly)TPSA (SEQ ID NO: 109), I(fGly)TPAA (SEQ ID NO: 110), M(fGly)TPSA (SEQ ID NO: 111), V(fGly)TPSA (SEQ ID NO: 112), L(fGly)SPSA (SEQ ID NO: 113), L(fGly)APSA (SEQ ID NO: 114), L(fGly)VPSA (SEQ ID NO: 115), and L(fGly)GPSA (SEQ ID NO: 116).

[0157] In some embodiments, the 5T4 antibody as disclosed herein comprises a fGly’- containing sulfatase motif. In some embodiments, the 5T4 antibody as disclosed herein comprises at least one fGly’-containing sulfatase motif.

[0158] As described above, to produce the conjugate, the 5T4 antibody containing the fGly residue may be conjugated to a drug or active agent by reaction of the fGly with a reactive moiety (e.g., a hydrazinyl-indolyl or a hydrazinyl-pyrrolo-pyridinyl conjugation moiety, as described 51 NAI-1541858741above) of a linker attached to the drug or active agent to produce an fGly’-containing sulfatase motif. As used herein, the term fGly’ refers to the amino acid residue of the sulfatase motif that is coupled to the drug or active agent through a linker (e.g., a branched linker) as described herein. Thus, the fGly’-containing sulfatase motif can be of: X1(fGly’)X2Z2X3Z3(SEQ ID NO: 67) wherein: fGly’ is the amino acid residue coupled to the drug or active agent through a linker (e.g., a branched linker) as described herein; Z2is either a proline or alanine residue (which can also be represented by (P / A)); Z3is a basic amino acid (e.g., arginine (R), and may be lysine (K) or histidine (H), usually lysine), or an aliphatic amino acid (alanine (A), glycine (G), leucine (L), valine (V), isoleucine (I), or proline (P), e.g., A, G, L, V, or I; X1may be present or absent and, when present, can be any amino acid, e.g., an aliphatic amino acid, a sulfur-containing amino acid, or a polar, uncharged amino acid, (e.g., other than an aromatic amino acid or a charged amino acid), e.g., L, M, V, S or T, e.g., L, M or V, with the proviso that when the sulfatase motif is at the N-terminus of the target 5T4 antibody, X1is present; and X2and X3independently can be any amino acid, e.g., an aliphatic amino acid, a sulfur- containing amino acid, or a polar, uncharged amino acid, (e.g., other than an aromatic amino acid or a charged amino acid), e.g., S, T, A, V, G or C, e.g., S, T, A, V or G.

[0159] Specific examples of fGly’-containing sulfatase motifs include L(fGly’)TPSR (SEQ ID NO: 1), M(fGly’)TPSR (SEQ ID NO: 45), V(fGly’)TPSR (SEQ ID NO: 46), L(fGly’)SPSR (SEQ ID NO: 47), L(fGly’)APSR (SEQ ID NO: 48), L(fGly’)VPSR (SEQ ID NO: 49), L(fGly’)GPSR (SEQ ID NO: 50), I(fGly’)TPAR (SEQ ID NO: 51), L(fGly’)TPSK (SEQ ID NO: 52), M(fGly’)TPSK (SEQ ID NO: 53), V(fGly’)TPSK (SEQ ID NO: 54), L(fGly’)SPSK (SEQ ID NO: 55), L(fGly’)APSK (SEQ ID NO: 56), L(fGly’)VPSK (SEQ ID NO: 57), L(fGly’)GPSK (SEQ ID NO: 58), L(fGly’)TPSA (SEQ ID NO: 59), I(fGly’)TPAA (SEQ ID NO: 60), M(fGly’)TPSA (SEQ ID NO: 61), V(fGly’)TPSA (SEQ ID NO: 62), L(fGly’)SPSA (SEQ ID NO: 63), L(fGly’)APSA (SEQ ID NO: 64), L(fGly’)VPSA (SEQ ID NO: 65), and L(fGly’)GPSA (SEQ ID NO: 66).

[0160] As noted above, the amino acid sequence of an antibody is modified to include a sulfatase motif that contains a serine or cysteine residue that is capable of being converted (oxidized) to an fGly residue by action of an FGE either in vivo (e.g., at the time of translation of an aldehyde tag-containing protein in a cell) or in vitro (e.g., by contacting an aldehyde tag- 52 NAI-1541858741containing protein with an FGE in a cell-free system). The antibody used to generate a conjugate of the present disclosure include at least an Ig constant region, e.g., an Ig heavy chain constant region (e.g., at least a CH1 domain; at least a CH1 and a CH2 domain; a CH1, a CH2, and a CH3 domain; or a CH1, a CH2, a CH3, and a CH4 domain), or an Ig light chain constant region. Such Ig antibodies are referred to herein as “target Ig polypeptides” or “target antibodies.”

[0161] The site in an antibody into which a sulfatase motif is introduced can be any convenient site. As noted above, in some instances, the extent of modification of the native amino acid sequence of the target polypeptide is minimized, so as to minimize the number of amino acid residues that are inserted, deleted, substituted (replaced), and / or added (e.g., to the N- or C-terminus). Minimizing the extent of amino acid sequence modification of the target antibody may minimize the impact such modifications may have upon antibody function and / or structure.

[0162] An antibody heavy chain constant region can include Ig constant regions of any heavy chain isotype, non-naturally occurring Ig heavy chain constant regions (including consensus Ig heavy chain constant regions). An Ig constant region amino acid sequence can be modified to include an aldehyde tag, where the aldehyde tag is present in or adjacent a solvent-accessible loop region of the Ig constant region. An Ig constant region amino acid sequence can be modified by insertion and / or substitution of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or 16 amino acids, or more than 16 amino acids, to provide an amino acid sequence of a sulfatase motif as described above.

[0163] In some cases, an aldehyde-tagged antibody comprises an aldehyde-tagged Ig heavy chain constant region (e.g., at least a CH1 domain; at least a CH1 and a CH2 domain; a CH1, a CH2, and a CH3 domain; or a CH1, a CH2, a CH3, and a CH4 domain). The aldehyde-tagged Ig heavy chain constant region can include heavy chain constant region sequences of an IgA, IgM, IgD, IgE, IgG1, IgG2, IgG3, or IgG4 isotype heavy chain or any allotypic variant of same, e.g., human heavy chain constant region sequences or mouse heavy chain constant region sequences, a hybrid heavy chain constant region, a synthetic heavy chain constant region, or a consensus heavy chain constant region sequence, etc., modified to include at least one sulfatase motif that can be modified by an FGE to generate an fGly-modified Ig polypeptide. Allotypic variants of Ig heavy chains are known in the art. See, e.g., Jefferis and Lefranc (2009) MAbs 1:4.

[0164] In some cases, an aldehyde-tagged antibody comprises an aldehyde-tagged Ig light chain constant region. The aldehyde-tagged Ig light chain constant region can include constant region sequences of a kappa light chain, a lambda light chain, e.g., human kappa or lambda light chain constant regions, a hybrid light chain constant region, a synthetic light chain constant 53 NAI-1541858741region, or a consensus light chain constant region sequence, etc., modified to include at least one sulfatase motif that can be modified by an FGE to generate an fGly-modified antibody. Exemplary constant regions include human gamma 1 and gamma 3 regions. With the exception of the sulfatase motif, a constant region may have a wild-type amino acid sequence, or it may have an amino acid sequence that is at least 70% identical (e.g., at least 80%, at least 90% or at least 95% identical) to a wild-type amino acid sequence.

[0165] In some embodiments the sulfatase motif is at a position other than, or in addition to, the C-terminus of the Ig polypeptide heavy chain. As noted above, an isolated aldehyde-tagged antibody can comprise a heavy chain constant region amino acid sequence modified to include a sulfatase motif as described above, where the sulfatase motif is in or adjacent to a surface- accessible loop region of the antibody heavy chain constant region.

[0166] A sulfatase motif can be provided within or adjacent to one or more of these amino acid sequences of such modification sites of an Ig heavy chain. For example, an Ig heavy chain polypeptide amino acid sequence can be modified (e.g., where the modification includes one or more amino acid residue insertions, deletions, and / or substitutions) at one or more of these amino acid sequences to provide a sulfatase motif adjacent and N-terminal and / or adjacent and C- terminal to these modification sites. Alternatively, or in addition, an Ig heavy chain polypeptide amino acid sequence can be modified (e.g., where the modification includes one or more amino acid residue insertions, deletions, and / or substitutions) at one or more of these amino acid sequences to provide a sulfatase motif between any two residues of the Ig heavy chain modifications sites. In some embodiments, an Ig heavy chain polypeptide amino acid sequence may be modified to include two motifs, which may be adjacent to one another, or which may be separated by one, two, three, four or more (e.g., from about 1 to about 25, from about 25 to about 50, or from about 50 to about 100, or more, amino acids. Alternatively, or in addition, where a native amino acid sequence provides for one or more amino acid residues of a sulfatase motif sequence, selected amino acid residues of the modification sites of an Ig heavy chain polypeptide amino acid sequence can be modified (e.g., where the modification includes one or more amino acid residue insertions, deletions, and / or substitutions) so as to provide a sulfatase motif at the modification site.

[0167] An antibody used in an antibody-drug conjugate of the present disclosure can have any of a variety of antigen-binding specificities, including but not limited to, e.g., an antigen present on a cancer cell; an antigen present on an autoimmune cell; an antigen present on a pathogenic microorganism; an antigen present on a virus-infected cell (e.g., a human immunodeficiency virus-infected cell); an antigen present on a diseased cell; and the like. For example, an antibody 54 NAI-1541858741conjugate can bind an antigen, where the antigen is present on the surface of the cell. An antibody conjugate of the present disclosure can bind antigen with a suitable binding affinity, e.g., from 5 x 10-6M to 10-7M, from 10-7M to 5 x 10-7M, from 5 x 10-7M to 10-8M, from 10-8M to 5 x 10-8M, from 5 x 10-8M to 10-9M, or a binding affinity greater than 10-9M.

[0168] As non-limiting examples, a subject antibody conjugate can bind an antigen present on a cancer cell (e.g., a tumor-specific antigen; an antigen that is over-expressed on a cancer cell; etc.), and the conjugated moiety can be a drug, such as a cytotoxic compound (e.g., a cytotoxic small molecule, a cytotoxic synthetic peptide, etc.). For example, a subject antibody conjugate can be specific for an antigen on a cancer cell, where the conjugated moiety is a drug, such as a cytotoxic compound (e.g., a cytotoxic small molecule, a cytotoxic synthetic peptide, etc.).

[0169] The modified 5T4 antibody containing the fGly residue can be conjugated to a linker- drug comprising an aza-hydrazino-iso-Pictet-Spengler (azaHIPS) coupling moiety, e.g., such as in linker (L-1), as shown below in SCHEME 1:SCHEME 1 wherein W is Formula (L-2):wherein # represents the point of conjugation to azaHIPS moiety and ## indicates the point of attachment to the MMAE; and wherein the MMAE is represented by Formula (III): 55 NAI-1541858741wherein * indicates the point of attachment to (L-2).

[0170] More particularly, one or more fGly modifications on the 5T4 antibody may be reacted with the azaHIPS moiety on a linker-drug comprising pre-conjugate linker (L-1a), shown below, to generate a 5T4 antibody comprising one more conjugated linker-drugs comprising linker (L-1):wherein ## indicates the point of attachment to the MMAE; and wherein the MMAE is represented by Formula (III):wherein * indicates the point of attachment to (L-1a).

[0171] More particularly, one or more fGly modifications on the 5T4 antibody may be reacted with the azaHIPS moiety on a linker-drug comprising pre-conjugate linker (L-1a’), shown below, to generate a 5T4 antibody comprising one more conjugated linker-drugs comprising linker (L-1):wherein ## indicates the point of attachment to the MMAE; and wherein the MMAE is represented by Formula (III): 56 NAI-1541858741wherein * indicates the point of attachment to (L-1a’).

[0172] In some embodiments, (L-1a’) refers to (2S,3S,4S,5R,6S)-6-(5-((5S,8S,11S,12R)-11- ((S)-sec-butyl)-12-(2-((S)-2-((1R,2R)-3-(((1S,2R)-1-hydroxy-1-phenylpropan-2-yl)amino)-1- methoxy-2-methyl-3-oxopropyl)pyrrolidin-1-yl)-2-oxoethyl)-5,8-diisopropyl-4,10-dimethyl- 3,6,9-trioxo-2,13-dioxa-4,7,10-triazatetradecyl)-2-((2S,5S,18R)-22-(2-((1,2- dimethylhydrazineyl)methyl)-1H-pyrrolo[2,3-b]pyridin-1-yl)-5-isopropyl-2-methyl-4,7,17,20- tetraoxo-18-(sulfomethyl)-10,13-dioxa-3,6,16,19-tetraazadocosanamido)phenoxy)-3,4,5- trihydroxytetrahydro-2H-pyran-2-carboxylic acid. In some embodiments, (L-1a’) has a Chemical Abstracts Service (CAS) Registry Number of 2773415-17-9.

[0173] In one embodiment, one or more amino acids in one or both of the heavy chain constant regions and light chain constant regions is conjugated to a linker-drug comprising a linker of (L-1):wherein represents the point of conjugation to Ab and ## indicates the point of attachment to the MMAE; and wherein the MMAE is represented by Formula (III):the point of attachment to (L-1). In one embodiment, the linker-drug comprising pre-conjugate linker (L-1a’) or (L-1a) is a linker-drug of Formula (II): 57 NAI-1541858741wherein the wavy line indicates the point of attachment to the Ab and MMAE is represented by Formula (III):wherein * indicates the point of attachment in Formula (II).

[0174] In one embodiment, one or more amino acids in one or both of the heavy chain constant region and light chain constant region is conjugated to a linker-drug comprising a linker of (L-1). In one embodiment, one amino acid in both of the heavy chain constant regions is conjugated to a linker-drug comprising a linker of (L-1). A composition comprising such 5T4 ADCs may exhibit a drug-to-antibody ratio (“DAR”) of about 1 to about 2. In other words, each 5T4 antibody is conjugated to one or two linker-drugs. Methods to determine DAR are well known to the skilled person and include methods using Reverse Phase Chromatography, or HPLC-MS, for example, those disclosed in WO2023220620, which is incorporated herein by reference in its entirety.

[0175] In one embodiment, provided herein is a 5T4 ADC as disclosed, e.g., in International Patent Publication No. WO 2023 / 220620 A2 (International Patent Application No. PCT / US2023 / 066811), incorporated herein by reference in its entirety. In one embodiment, the 5T4 ADC is represented by Formula (I), comprising an Ab conjugated to a monomethyl auristatin E (MMAE) by a linker-drug comprising linker (L-1):58 NAI-1541858741wherein Ab is a 5T4 antibody or an antigen binding fragment thereof. In one embodiment, the 5T4 ADC comprises a 5T4 antibody or an antigen binding fragment thereof comprising a VH region, VL region, heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), a heavy chain complementarity determining region 3 (HCDR3), a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and / or a light chain complementarity determining region 3 (LCDR3) as described in Table 1. In one embodiment, the 5T4 ADC comprises a 5T4 antibody or an antigen binding fragment thereof comprising a VH region comprising the amino acid sequence of SEQ ID NO: 11 and a VL region comprising the amino acid sequence of SEQ ID NO: 12. In one embodiment, the 5T4 antibody comprises a light chain having an amino acid sequence of: DIQMTQSPSSLSASVGDRVTITCRASQSVSSAVAWYQQKPGKAPKLLIYSASSLYSGVPSRFSGS RSGTDFTLTISSLQPEDFATYYCQQAYATPVTFGQGTKVEIKRTVAAPSVFIFPPSDEQLKSGTA SVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACE VTHQGLSSPVTKSFNRGEC (SEQ ID NO: 3).

[0176] In one embodiment, a linker-drug comprising linker (L-1) is conjugated to each of the heavy chain constant regions in the 5T4 antibody (e.g., the 5T4 antibody is conjugated to two linker-drugs). In one embodiment, a linker-drug comprising linker (L-1) is conjugated to each of the heavy chains in the 5T4 antibody (e.g., the 5T4 antibody is conjugated to two linker-drugs). In one embodiment, a linker-drug comprising linker (L-1) is conjugated to the CH3 region in each of the heavy chain constant regions in the 5T4 antibody. In one embodiment, a linker-drug comprising linker (L-1) is conjugated to the CH3 region in each of the heavy chains in the 5T4 antibody. In a further embodiment, a linker-drug comprising linker (L-1) is conjugated to the aldehyde in the formylglycine at C453 of each heavy chain of an anti-5T4 aldehyde-containing antibody (the formylglycine amino acid residue corresponding to the 453rdamino acid residue of C in SEQ ID NO: 40, also referred to herein as “C453”). In one embodiment, a linker-drug comprising linker (L-1) is conjugated to the aldehyde in the formylglycine corresponding to the 453rdamino acid residue of fGly in SEQ ID NO: 41). In one embodiment, a linker-drug comprising linker (L-1) is conjugated to the aldehyde in the formylglycine corresponding to the 453rdamino acid residue of fGly’ in SEQ ID NO: 2). In such embodiments, each 5T4 ADC comprises two MMAE drugs. A composition comprising such ADCs will exhibit a DAR of 2. In some embodiments, a 5T4 ADC comprises a 5T4 antibody comprising a light chain comprising the amino acid sequence of 59 NAI-1541858741DIQMTQSPSSLSASVGDRVTITCRASQSVSSAVAWYQQKPGKAPKLLIYSASSLYSGVPSRFSGS RSGTDFTLTISSLQPEDFATYYCQQAYATPVTFGQGTKVEIKRTVAAPSVFIFPPSDEQLKSGTA SVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACE VTHQGLSSPVTKSFNRGEC (SEQ ID NO: 3) and a heavy chain having an amino acid sequence of: EVQLVESGGGLVQPGGSLRLSCAASGFTFSSYYIHWVRQAPGKGLEWVAYITSTGSYTEYADSVK GRFTISADTSKNTAYLQMNSLRAEDTAVYYCARYDRSTRYSGLDYWGQGTLVTVSSASTKGPSVF PLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSS SLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRT PEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKC KVSNKALPAPIEKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQ PENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGSLnTP SRGS (SEQ ID NO: 42), wherein n is an amino acid having its side chain replaced by a linker- drug comprising linker (L-1):wherein represents the point of conjugation to Ab and ## indicates the point of attachment to the MMAE; and wherein the MMAE is represented by Formula (III):wherein * indicates the point of attachment to (L-1). In some embodiments, the amino acid n in SEQ ID NO: 42 refers to fGly’ as described herein.

[0177] In one embodiment, a 5T4 ADC is produced by conjugating a pre-conjugate linker (L-1a’) to the aldehyde in the formylglycine, such as at C453, of each heavy chain of an anti-5T4 aldehyde-containing antibody, wherein Ab is a 5T4 antibody or an antigen binding fragment thereof. In one embodiment, the 5T4 ADC comprises a 5T4 antibody or an antigen binding 60 NAI-1541858741fragment thereof comprising a VH region, VL region, heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), a heavy chain complementarity determining region 3 (HCDR3), a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and / or a light chain complementarity determining region 3 (LCDR3) as described in Table 1. In one embodiment, the 5T4 ADC comprises a 5T4 antibody or an antigen binding fragment thereof as disclosed herein. In one embodiment, the 5T4 ADC comprises a 5T4 antibody or an antigen binding fragment thereof comprising a VH region comprising the amino acid sequence of SEQ ID NO: 11 and a VL region comprising the amino acid sequence of SEQ ID NO: 12. In one embodiment, the 5T4 antibody comprises a light chain having an amino acid sequence of SEQ ID NO: 3. In some embodiments, a 5T4 ADC comprises a 5T4 antibody comprising a light chain comprising the amino acid sequence of SEQ ID NO: 3 and a heavy chain having an amino acid sequence of SEQ ID NO: 2.

[0178] In further embodiments, the antibody of the 5T4 ADC (e.g., those of Formula (I) or Formula (I’), or the ADCs comprising (L-1), or the ADCs produced by conjugating (L-1a’)) comprises two heavy chains (HCs) and two light chains (LCs), and wherein each of the HCs comprises one motif of L(fGly’)TPSR (SEQ ID NO: 1). Accordingly, each 5T4 ADC comprises two MMAE drugs, and a composition comprising such ADCs exhibits a DAR of about 1 to about 2, such as 2.

[0179] In some embodiments, a 5T4 ADC comprises an antibody that binds to 5T4, wherein the antibody comprises: (a) a VH region comprising: (1) an HCDR1 comprising an amino acid sequence of any one of: (i) SEQ ID NO: 13, (ii) SEQ ID NO: 19, (iii) SEQ ID NO: 24, (iv) SEQ ID NO: 25, and (v) SEQ ID NO: 30; (2) an HCDR2 comprising an amino acid sequence of any one of: (i) SEQ ID NO: 14, (ii) SEQ ID NO: 20, (iii) SEQ ID NO: 26, (iv) SEQ ID NO: 31, and (v) SEQ ID NO: 36; and (3) an HCDR3 comprising an amino acid sequence of any one of: (i) SEQ ID NO: 15, (ii) SEQ ID NO: 21, (iii) SEQ ID NO: 27, and (iv) SEQ ID NO: 32; and / or a VL region comprising: (1) an LCDR1 comprising an amino acid sequence of any one of: (i) SEQ ID NO: 16, (ii) SEQ ID NO: 22, (iii) SEQ ID NO: 28, and (iv) SEQ ID NO: 33; (2) an LCDR2 comprising an amino acid sequence of any one of: (i) SEQ ID NO: 17, (ii) SEQ ID NO: 23, and (iii) SEQ ID NO: 34; and (3) an LCDR3 comprising an amino acid sequence of any one of: (i) SEQ ID NO: 18, (ii) SEQ ID NO: 29, and (iii) SEQ ID NO: 35.

[0180] In some embodiments, a 5T4 ADC comprises an antibody that binds to 5T4, wherein the antibody comprises a VH region comprising: (1) an HCDR1 comprising an amino acid sequence of any one of: (i) SEQ ID NO: 13, (ii) SEQ ID NO: 19, (iii) SEQ ID NO: 24, (iv) SEQ 61 NAI-1541858741ID NO: 25, and (v) SEQ ID NO: 30; (2) an HCDR2 comprising an amino acid sequence of any one of: (i) SEQ ID NO: 14, (ii) SEQ ID NO: 20, (iii) SEQ ID NO: 26, (iv) SEQ ID NO: 31, and (v) SEQ ID NO: 36; and (3) an HCDR3 comprising an amino acid sequence of any one of: (i) SEQ ID NO: 15, (ii) SEQ ID NO: 21, (iii) SEQ ID NO: 27, and (iv) SEQ ID NO: 32

[0181] In some embodiments, a 5T4 ADC comprises an antibody that binds to 5T4, wherein the antibody comprises a VL region comprising: (1) an LCDR1 comprising an amino acid sequence of any one of: (i) SEQ ID NO: 16, (ii) SEQ ID NO: 22, (iii) SEQ ID NO: 28, and (iv) SEQ ID NO: 33; (2) an LCDR2 comprising an amino acid sequence of any one of: (i) SEQ ID NO: 17, (ii) SEQ ID NO: 23, and (iii) SEQ ID NO: 34; and (3) an LCDR3 comprising an amino acid sequence of any one of: (i) SEQ ID NO: 18, (ii) SEQ ID NO: 29, and (iii) SEQ ID NO: 35.

[0182] In some embodiments, a 5T4 ADC comprises an antibody that binds to 5T4, wherein the antibody comprises: (a) a VH region comprising: (1) an HCDR1 comprising an amino acid sequence of SEQ ID NO: 13; (2) an HCDR2 comprising an amino acid sequence of SEQ ID NO: 14; and (3) an HCDR3 comprising an amino acid sequence of SEQ ID NO: 15; and (b) a VL region comprising: (1) a VL CDR1 comprising an amino acid sequence of SEQ ID NO: 16; (2) an LCDR2 comprising an amino acid sequence of SEQ ID NO: 17; and (3) an LCDR3 comprising an amino acid sequence of SEQ ID NO: 18.

[0183] In some embodiments, a 5T4 ADC comprises an antibody that binds to 5T4, wherein the antibody comprises: (a) a VH region comprising: (1) an HCDR1 comprising an amino acid sequence of SEQ ID NO: 19; (2) an HCDR2 comprising an amino acid sequence of SEQ ID NO: 20; and (3) an HCDR3 comprising an amino acid sequence of SEQ ID NO: 21; and (b) a VL region comprising: (1) an LCDR1 comprising an amino acid sequence of SEQ ID NO: 22; (2) an LCDR2 comprising an amino acid sequence of SEQ ID NO: 23; and (3) an LCDR3 comprising an amino acid sequence of SEQ ID NO: 18.

[0184] In some embodiments, a 5T4 ADC comprises an antibody that binds to 5T4, wherein the antibody comprises: (a) a VH region comprising: (1) an HCDR1 comprising an amino acid sequence of SEQ ID NO: 24; (2) an HCDR2 comprising an amino acid sequence of SEQ ID NO: 14; and (3) an HCDR3 comprising an amino acid sequence of SEQ ID NO: 15; and (b) a VL region comprising: (1) an LCDR1 comprising an amino acid sequence of SEQ ID NO: 16; (2) an LCDR2 comprising an amino acid sequence of SEQ ID NO: 17; and (3) an LCDR3 comprising an amino acid sequence of SEQ ID NO: 18.

[0185] In some embodiments, a 5T4 ADC comprises an antibody that binds to 5T4, wherein the antibody comprises: (a) a VH region comprising: (1) an HCDR1 comprising an amino acid sequence of SEQ ID NO: 25; (2) an HCDR2 comprising an amino acid sequence of SEQ ID NO: 62 NAI-154185874126; and (3) an HCDR3 comprising an amino acid sequence of SEQ ID NO: 27; and (b) a VL region comprising: (1) an LCDR1 comprising an amino acid sequence of SEQ ID NO: 28; (2) an LCDR2 comprising an amino acid sequence of SEQ ID NO: 23; and (3) an LCDR3 comprising an amino acid sequence of SEQ ID NO: 29.

[0186] In some embodiments, a 5T4 ADC comprises an antibody that binds to 5T4, wherein the antibody comprises: (a) a VH region comprising: (1) an HCDR1 comprising an amino acid sequence of SEQ ID NO: 30; (2) an HCDR2 comprising an amino acid sequence of SEQ ID NO: 31; and (3) an HCDR3 comprising an amino acid sequence of SEQ ID NO: 32; and (b) a VL region comprising: (1) an LCDR1 comprising an amino acid sequence of SEQ ID NO: 33; (2) an LCDR2 comprising an amino acid sequence of SEQ ID NO: 34; and (3) an LCDR3 comprising an amino acid sequence of SEQ ID NO: 35.

[0187] In some embodiments, a 5T4 ADC comprises an antibody that binds to 5T4, wherein the antibody comprises: (a) a VH region comprising: (1) an HCDR1 comprising an amino acid sequence of SEQ ID NO: 13; (2) an HCDR2 comprising an amino acid sequence of SEQ ID NO: 36; and (3) an HCDR3 comprising an amino acid sequence of SEQ ID NO: 15; and (b) a VL region comprising: (1) an LCDR1 comprising an amino acid sequence of SEQ ID NO: 16; (2) an LCDR2 comprising an amino acid sequence of SEQ ID NO: 17; and (3) an LCDR3 comprising an amino acid sequence of SEQ ID NO: 18.

[0188] In some embodiments, a 5T4 ADC can comprise a 5T4 antibody that comprises one or more (e.g., one, two, three, four, or more) conservative sequence modifications. With respect to polypeptides that are 5T4 antibodies, such as human 5T4 antibodies, conservative sequence modifications include conservative amino acid substitutions in which an amino acid residue is replaced with an amino acid residue having a similar side chain. Families of amino acid residues having similar side chains have been defined in the art. These families are disclosed herein. Thus, in some embodiments, a predicted nonessential amino acid residue in a 5T4 antibody can be replaced with another amino acid residue from the same side chain family. Methods of identifying amino acid conservative substitutions which do not eliminate antigen binding and nucleotides encoding thereof are well known in the art (see, e.g., Brummell et al., Biochem. 32:1180-1187 (1993); Kobayashi et al. Protein Eng.12(10):879-884 (1999); and Burks et al. Proc. Natl. Acad. Sci. USA 94:412-417 (1997)). In some embodiments, the conservative sequence modifications described herein modify the amino acid sequences of a 5T4 antibody (e.g., a human 5T4 antibody) by 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 98%, or 99%. In some embodiments, the amino acid sequence modifications refer to at most one, two, three, four, five, or six amino acid substitutions to the CDRs, such as those described in Table 1. 63 NAI-1541858741Thus, for example, each such CDR can contain up to five conservative amino acid substitutions, for example up to (not more than) four conservative amino acid substitutions, for example up to (not more than) three conservative amino acid substitutions, for example up to (not more than) two conservative amino acid substitutions, or no more than one conservative amino acid substitution. In some embodiments, a 5T4 ADC comprises a 5T4 antibody that contains one or more, (e.g., one, two, three, four, five, or six CDRs) having at least 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identity to the CDRs of mAbA15 (see, e.g., Table 1). In some embodiments, a 5T4 ADC comprises a 5T4 antibody that contains a VH and a VL comprising CDRs identical to those of mAbA15 (see, e.g., Table 1). In some embodiments, the amino acid sequence modifications do not include any modification within a specificity determining residue (SDR). In some embodiments, the amino acid sequence modifications do not include any modification within a CDR (such as CDR1, CDR2, CDR3, or any combination thereof). In further embodiments, the amino acid sequence modifications are in the framework or constant region.

[0189] In some embodiments, the antibody in a 5T4 ADC comprises a VH comprising an amino acid sequence having at least 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 11 and a VL comprising an amino acid sequence having at least 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 12, and the binding of the antibody to 5T4 (e.g., human 5T4) is maintained (e.g., substantially maintained, for example, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, or at least 95%). In further embodiments, the antibody in a 5T4 ADC comprises CDRs identical to those of mAbA15 (see, e.g., Table 1).

[0190] In some embodiments, the antibody in a 5T4 ADC comprises a heavy chain comprising an amino acid sequence having at least 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 2 and a light chain comprising an amino acid sequence having at least 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 3, and the binding of the antibody to 5T4 (e.g., human 5T4) is maintained (e.g., substantially maintained, for example, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, or at least 95%). In further embodiments, the antibody in a 5T4 ADC comprises CDRs identical to those of mAbA15 (see, e.g., Table 1). In yet further embodiments, the motif of L(fGly’)TPSR (SEQ ID NO: 1) in the heavy chain is maintained.

[0191] In some embodiments, a 5T4 ADC can be represented by Formula (I) or Formula (I’), or comprise (L-1), or be produced by conjugating (L-1a’), wherein Ab is an antibody that binds to 5T4 as disclosed herein. In some embodiments, the antibody comprises a VH comprising 64 NAI-1541858741one or more (such as one, two, or three) CDRs identical or substantially identical to the CDRs as described herein, such as in Table 1. Additionally or alternatively, in some embodiments, the antibody comprises a VL comprising one or more (such as one, two, or three) CDRs identical or substantially identical to the CDRs as described herein, such as in Table 1.

[0192] In some embodiments, a 5T4 ADC can be represented by Formula (I) or Formula (I’), or comprise (L-1), or be produced by conjugating (L-1a’), wherein Ab is an antibody that binds to 5T4 as disclosed herein. In some embodiments, the antibody comprises a VH identical or substantially identical to a VH as described herein, such as in Table 1. Additionally or alternatively, in some embodiments, the antibody comprises a VL identical or substantially identical to a VL as described herein, such as in Table 1.

[0193] In some embodiments, a 5T4 ADC can be represented by Formula (I) or Formula (I’), or comprise (L-1), or be produced by conjugating (L-1a’), wherein Ab is an antibody that binds to 5T4. In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 11 and a VL comprising the amino acid sequence of SEQ ID NO: 12.

[0194] In some embodiments, a 5T4 ADC can be represented by Formula (I) or Formula (I’), or comprise (L-1), or be produced by conjugating (L-1a’), wherein Ab is an antibody that binds to 5T4 and comprises (a) a VH region comprising: (1) an HCDR1 comprising an amino acid sequence of any one SEQ ID NOs:13, 19, 24, 25, and 30; (2) an HCDR2 comprising an amino acid sequence of any one SEQ ID NOs:14, 20, 26, 31, and 36; and (3) an HCDR3 comprising an amino acid sequence of any one SEQ ID NOs:15, 21, 27, and 32; and (b) a VL region comprising: (1) an LCDR1 comprising an amino acid sequence of any one SEQ ID NOs:16, 22, 28, and 33; (2) an LCDR2 comprising an amino acid sequence of any one SEQ ID NOs:17, 23, and 34; and (3) an LCDR3 comprising an amino acid sequence of any one SEQ ID NOs:18, 29, and 35.

[0195] In some embodiments, a 5T4 ADC can be represented by Formula (I) or Formula (I’), or comprise (L-1), or be produced by conjugating (L-1a’), wherein Ab is an antibody that binds to 5T4. In some embodiments, the Ab comprises: (a) a VH region comprising: (1) an HCDR1 comprising an amino acid sequence of SEQ ID NO: 13; (2) an HCDR2 comprising an amino acid sequence of SEQ ID NO: 14; and (3) an HCDR3 comprising an amino acid sequence of SEQ ID NO: 15; and (b) a VL region comprising: (1) a VL CDR1 comprising an amino acid sequence of SEQ ID NO: 16; (2) an LCDR2 comprising an amino acid sequence of SEQ ID NO: 17; and (3) an LCDR3 comprising an amino acid sequence of SEQ ID NO: 18. In some embodiments, the Ab comprises: (a) a VH region comprising: (1) an HCDR1 comprising an amino acid sequence of SEQ ID NO: 19; (2) an HCDR2 comprising an amino acid sequence of 65 NAI-1541858741SEQ ID NO: 20; and (3) an HCDR3 comprising an amino acid sequence of SEQ ID NO: 21; and (b) a VL region comprising: (1) an LCDR1 comprising an amino acid sequence of SEQ ID NO: 22; (2) an LCDR2 comprising an amino acid sequence of SEQ ID NO: 23; and (3) an LCDR3 comprising an amino acid sequence of SEQ ID NO: 18. In some embodiments, the Ab comprises: (a) a VH region comprising: (1) an HCDR1 comprising an amino acid sequence of SEQ ID NO: 24; (2) an HCDR2 comprising an amino acid sequence of SEQ ID NO: 14; and (3) an HCDR3 comprising an amino acid sequence of SEQ ID NO: 15; and (b) a VL region comprising: (1) an LCDR1 comprising an amino acid sequence of SEQ ID NO: 16; (2) an LCDR2 comprising an amino acid sequence of SEQ ID NO: 17; and (3) an LCDR3 comprising an amino acid sequence of SEQ ID NO: 18. In some embodiments, the Ab comprises: (a) a VH region comprising: (1) an HCDR1 comprising an amino acid sequence of SEQ ID NO: 25; (2) an HCDR2 comprising an amino acid sequence of SEQ ID NO: 26; and (3) an HCDR3 comprising an amino acid sequence of SEQ ID NO: 27; and (b) a VL region comprising: (1) an LCDR1 comprising an amino acid sequence of SEQ ID NO: 28; (2) an LCDR2 comprising an amino acid sequence of SEQ ID NO: 23; and (3) an LCDR3 comprising an amino acid sequence of SEQ ID NO: 29. In some embodiments, the Ab comprises: (a) a VH region comprising: (1) an HCDR1 comprising an amino acid sequence of SEQ ID NO: 30; (2) an HCDR2 comprising an amino acid sequence of SEQ ID NO: 31; and (3) an HCDR3 comprising an amino acid sequence of SEQ ID NO: 32; and (b) a VL region comprising: (1) an LCDR1 comprising an amino acid sequence of SEQ ID NO: 33; (2) an LCDR2 comprising an amino acid sequence of SEQ ID NO: 34; and (3) an LCDR3 comprising an amino acid sequence of SEQ ID NO: 35. In some embodiments, the Ab comprises: (a) a VH region comprising: (1) an HCDR1 comprising an amino acid sequence of SEQ ID NO: 13; (2) an HCDR2 comprising an amino acid sequence of SEQ ID NO: 36; and (3) an HCDR3 comprising an amino acid sequence of SEQ ID NO: 15; and (b) a VL region comprising: (1) an LCDR1 comprising an amino acid sequence of SEQ ID NO: 16; (2) an LCDR2 comprising an amino acid sequence of SEQ ID NO: 17; and (3) an LCDR3 comprising an amino acid sequence of SEQ ID NO: 18.

[0196] In some embodiments, a 5T4 ADC can be represented by Formula (I) or Formula (I’), or comprise (L-1), or be produced by conjugating (L-1a’), wherein Ab is an antibody that binds to 5T4. In some embodiments, the antibody further comprises a framework 1 (FR1), a framework 2 (FR2), a framework 3 (FR3) and / or a framework 4 (FR4) sequence as set forth in any one of SEQ ID NOs: 11 and 12.

[0197] In some embodiments, a 5T4 ADC can be represented by Formula (I) or Formula (I’), or comprise (L-1), or be produced by conjugating (L-1a’), wherein Ab is an antibody that 66 NAI-1541858741binds to 5T4. In some embodiments, the Ab is mAbA15. In some embodiments, the Ab comprises a heavy chain comprising an amino acid sequence as set forth in SEQ ID NO: 2 and a light chain comprising an amino acid sequence as set forth in SEQ ID NO: 3. In some embodiments, the Ab comprises a heavy chain comprising an amino acid sequence as set forth in SEQ ID NO: 42 and a light chain comprising an amino acid sequence as set forth in SEQ ID NO: 3.

[0198] In one embodiment, the 5T4 ADC comprises an Ab conjugated to a monomethyl auristatin E (MMAE) by linker (L-1) and is represented by Formula (I) below:wherein the Ab is a 5T4 antibody or an antigen binding fragment thereof and comprises a heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), a heavy chain complementarity determining region 3 (HCDR3), a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and a light chain complementarity determining region 3 (LCDR3) of an antibody designated mAbA15, wherein the Ab further comprises two motifs, each of which is L(fGly’)TPSR (SEQ ID NO: 1), wherein fGly’ is the amino acid residue to which a linker-drug comprising linker (L-1) is attached, and wherein mAbA15 comprises: a) a heavy chain comprising an amino acid sequence of: EVQLVESGGGLVQPGGSLRLSCAASGFTFSSYYIHWVRQAPGKGLEWVAYITSTGSYTEYADSVK GRFTISADTSKNTAYLQMNSLRAEDTAVYYCARYDRSTRYSGLDYWGQGTLVTVSSASTKGPSVF PLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSS SLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRT PEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKC KVSNKALPAPIEKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQ PENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGSL (fGly’)TPSRGS (SEQ ID NO: 2); and b) a light chain comprising an amino acid sequence of: 67 NAI-1541858741DIQMTQSPSSLSASVGDRVTITCRASQSVSSAVAWYQQKPGKAPKLLIYSASSLYSGVPSRFSGS RSGTDFTLTISSLQPEDFATYYCQQAYATPVTFGQGTKVEIKRTVAAPSVFIFPPSDEQLKSGTA SVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACE VTHQGLSSPVTKSFNRGEC (SEQ ID NO: 3).

[0199] In one embodiment, the 5T4 ADC is represented by Formula (I) below:wherein Ab is a 5T4 antibody comprising: a) a heavy chain comprising an amino acid sequence of: EVQLVESGGGLVQPGGSLRLSCAASGFTFSSYYIHWVRQAPGKGLEWVAYITSTGSYTEYADSVK GRFTISADTSKNTAYLQMNSLRAEDTAVYYCARYDRSTRYSGLDYWGQGTLVTVSSASTKGPSVF PLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSS SLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRT PEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKC KVSNKALPAPIEKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQ PENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGSL (fGly’)TPSRGS (SEQ ID NO: 2); and b) a light chain comprising an amino acid sequence of: DIQMTQSPSSLSASVGDRVTITCRASQSVSSAVAWYQQKPGKAPKLLIYSASSLYSGVPSRFSGS RSGTDFTLTISSLQPEDFATYYCQQAYATPVTFGQGTKVEIKRTVAAPSVFIFPPSDEQLKSGTA SVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACE VTHQGLSSPVTKSFNRGEC (SEQ ID NO: 3). In some embodiments, linker (L-1) is: 68 NAI-1541858741wherein the wavy line indicates the point of attachment to the Ab at (fGly’) and ## indicates the point of attachment to the MMAE; and wherein the MMAE is represented by Formula (III):wherein * indicates the point of attachment to (L-1). In one embodiment, a linker-payload of Formula (II) is conjugated to the Ab at (fGly’):wherein the wavy line indicates the point of attachment to the Ab and MMAE is represented by Formula (III):wherein * indicates the point of attachment in Formula (II). This ADC is also referred to herein as “5T4-ADC-1.”

[0200] In some embodiments, the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4- ADC-1), carries two MMAE drug molecules per antibody component, resulting in a drug-to- antibody ratio (DAR) of 2:1. 69 NAI-1541858741

[0201] The ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’), was evaluated in a 13-week, Good Laboratory Practice (GLP)-compliant, toxicology, toxicokinetic, and safety pharmacology study in a pharmacologically relevant species, cynomolgus monkeys. In some embodiments, the 5T4 ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L- 1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1),carries two MMAE payload molecules per antibody component, resulting in a drug-to-antibody ratio (DAR) of 2:1. Without wishing to be bound by theory, it is believed that, mechanistically, the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1), binds to 5T4 expressed on the surface of tumor cells and is subsequently internalized by the tumor cell. Subsequent enzymatic cleavage of the linker- payload from the antibody releases the MMAE cytotoxin. Free MMAE works inside the tumor cell to block polymerization of tubulin cell division but is also released from the initial tumor cell into the extracellular space to enter surrounding cells, including tumor cells, to inhibit cell division in those surrounding cells (commonly known as the bystander effect). This bystander effect efficiently kills both 5T4-expressing tumor cells and 5T4-negative tumor cells existing alongside 5T4-expressing cells.

[0202] Antibodies targeting the PD-1, a T-cell inhibitory checkpoint protein, have been demonstrated to enhance the immune response against tumor cells and are part of standard of care for a variety of cancers. Pembrolizumab is a humanized monoclonal immunoglobulin G4 (IgG4) kappa antibody specific for PD-1 / PD-L1 cell surface membrane receptor that has demonstrated the ability to generate increased antitumor immune responses and improvements in survival of cancer patients. Pembrolizumab has been approved in multiple cancer types in the US and Europe (Keytruda US Prescribing Information [USPI] and European Medicines Agency [EMA] Summary of Product Characteristics [SmPC]). As illustrated in the Examples, combining a PD-L1 inhibitor or a PD-1 inhibitor, such as pembrolizumab, with the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1), enhances the anticancer effect of the ADC, which may be particularly useful in patients with advanced tumors or for those patients where other available therapies are ineffective and / or not well-tolerated. As such, in one aspect, the present disclosure also provides methods of using a combination of the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1), and a PD-L1 / PD-1 inhibitor, such as pembrolizumab, in the treatment of cancer. 70 NAI-1541858741

[0203] In some embodiments, the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4- ADC-1) ,is provided in the form of a pharmaceutical composition for administration to a subject. Such a pharmaceutical composition comprises a therapeutically effective amount of the ADC and one or more pharmaceutically acceptable excipients.

[0204] Accordingly, provided herein is a pharmaceutical composition comprising a 5T4 ADC as disclosed herein, such as 5T4-ADC-1, and one or more pharmaceutically acceptable excipients.

[0205] Examples of suitable pharmaceutically acceptable excipients include solid or liquid fillers, diluents, other excipients, or encapsulating substances that are suitable for administration into a human or veterinary subject (e.g., a physiologically acceptable and / or pharmacologically acceptable). The pharmaceutically acceptable excipient can be co-mingled with one or more of the active components, e.g., a hybrid molecule, and with each other, when more than one pharmaceutically acceptable excipient is present in the pharmaceutical composition, in a manner so as not to substantially impair the desired pharmaceutical efficacy. Pharmaceutically acceptable materials typically are capable of administration to a subject without the production of significant undesirable physiological effects such as nausea, dizziness, rash, or gastric upset. It is, for example, desirable for a composition comprising a pharmaceutically acceptable excipient not to be immunogenic when administered to a human subject for therapeutic purposes.

[0206] In some embodiments, a pharmaceutical composition comprising the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1), additionally contains suitable buffering agents, including, for example, acetic acid in a salt, citric acid in a salt, boric acid in a salt, and phosphoric acid in a salt. In some embodiments, a pharmaceutical composition comprising the ADC also optionally contains suitable preservatives, such as benzalkonium chloride, chlorobutanol, parabens, and thimerosal. In some embodiments, a pharmaceutical composition comprising the ADC is provided in unit dosage form and can be prepared by any suitable method, many of which are well known in the art of pharmacy.

[0207] In some embodiments, a pharmaceutical composition comprising the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1), that is suitable for parenteral administration is in the form of a sterile aqueous preparation of the ADC, which preferably is isotonic with the blood of the recipient. In some embodiments, this aqueous preparation is formulated using known methods using suitable dispersing or wetting agents and suspending 71 NAI-1541858741agents. In some embodiments, a sterile injectable preparation is also a sterile injectable solution or suspension in a non-toxic parenterally acceptable diluent or solvent, for example, as a solution in 1,3-butane diol. Non-limiting examples of suitable vehicles and solvents include water, Ringer's solution, and isotonic sodium chloride solution. In some embodiments, sterile, fixed oils is employed as a solvent or suspending medium. For this purpose, any bland fixed oil can be employed, such as synthetic mono-or di-glycerides. In addition, fatty acids, such as oleic acid, can be used in the preparation of an injectable formulation of the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1).

[0208] In some embodiments, a pharmaceutical composition of the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) is suitably packaged, e.g., in a vial, pouch, ampoule, and / or any like and appropriate container. In one embodiment, a pharmaceutical composition comprising the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) is provided as a concentrate, which can be further diluted prior to use. In one embodiment, a pharmaceutical composition comprising the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) is provided as a such as a lyophilizate, which can be reconstitute prior to use. In one embodiment, a pharmaceutical composition comprising the ADC of as disclosed herein, for example those Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) is provided at the concentration intended for use. In some embodiments, a pharmaceutical composition comprising the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) is provided in unit dosage form in sterilized containers, e.g., as part of a kit, each container having a desired amount and concentration of the ADC. 7.4 METHODS, ADMINISTRATION, AND DOSING

[0209] In one aspect, provided herein is a method for treating cancer in a subject, the method comprising administering an ADC to the subject.

[0210] In some embodiments, the cancer is any one or more of breast cancer, endometrial cancer, head and neck cancer, pancreatic cancer, lung cancer, prostate cancer, cervical cancer, bladder cancer, renal cell carcinoma (RCC), hepatocellular carcinoma (HCC), or colorectal cancer. 72 NAI-1541858741

[0211] In some embodiments, the ADC is represented by Formula (I’):(I’), wherein the Ab is a 5T4 antibody or an antigen binding fragment thereof, and wherein the Ab comprises: (1) a heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), and a heavy chain complementarity determining region 3 (HCDR3) as set forth in a heavy chain variable region (VH) comprising the amino acid sequence of SEQ ID NO: 11, and (2) a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and a light chain complementarity determining region 3 (LCDR3) as set forth in a light chain variable region (VL) comprising the amino acid sequence of SEQ ID NO: 12.

[0212] In some embodiments, the Ab further comprises one or more fGly’, wherein fGly’ is a formylglycine amino acid residue to which the non-Ab part of Formula (I’) is attached.

[0213] In some embodiments, wherein the MMAE is monomethyl auristatin E and represented by Formula (III):wherein * indicates the point of attachment in Formula (I’).

[0214] In some embodiments, n is an integer. In further embodiments, n is an integer selected from any one of 1 to 10. In yet further embodiments, n is 2. In other embodiments, n is 1. 73 NAI-1541858741

[0215] In some embodiments, administered is a population of ADCs comprising a multiplicity of DAR species. In further embodiments, the population comprises a first ADC represented by Formula (I’) wherein its n is 1 and a second ADC represented by Formula (I’) wherein its n is 2.

[0216] In some embodiments, a pharmaceutical composition comprising a first ADC represented by Formula (I’) and a pharmaceutically acceptable excipient is administered to the subject. In further embodiments, the pharmaceutical composition comprises a second ADC represented by Formula (I’), wherein a first n in the first ADC is different from the second n of the second ADC. In yet further embodiments, the first n is 2. Additionally or alternatively, the second n is 1. In some embodiments, such a pharmaceutical composition exhibits a drug-to- antibody ratio (“DAR”) of about 1 to about 2. In further embodiments, the pharmaceutical composition exhibits a DAR of 1.8.

[0217] In some embodiments, the Ab in Formula (I’) comprises at least one fGly’. In some embodiments, the Ab in Formula (I’) further comprises one or more (such as one to ten) fGly. In further embodiments, the Ab in Formula (I’) further comprises one or more (such as one to ten) motif of SEQ ID NO: 93.

[0218] In another aspect, the ADC is represented by Formula (I):wherein the * in Formula (III) indicates the point of attachment in Formula (I) and wherein fGly’ is a formylglycine amino acid residue to which the non-Ab part of Formula (I) is attached.

[0219] In some embodiments, the ADC comprises an antibody (Ab) conjugated to a monomethyl auristatin E (MMAE) by a linker (L-1): 74 NAI-1541858741(L-1), wherein the wavy line indicates the point of attachment to the Ab and the ## indicates the point of attachment to the MMAE.

[0220] In some embodiments, the MMAE is represented by Formula (III):wherein * indicates the point of attachment to (L-1). wherein the Ab is a 5T4 antibody or an antigen binding fragment thereof, and wherein the Ab comprises: (1) a heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), and a heavy chain complementarity determining region 3 (HCDR3) as set forth in a heavy chain variable region (VH) comprising the amino acid sequence of SEQ ID NO: 11, and (2) a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and a light chain complementarity determining region 3 (LCDR3) as set forth in a light chain variable region (VL) comprising the amino acid sequence of SEQ ID NO: 12; and wherein the Ab further comprises one or more fGly’ and wherein fGly’ is a formylglycine amino acid residue to which linker (L-1) is attached.

[0221] In some embodiments, one Ab is conjugated to one to ten MMAEs and wherein each MMAE is conjugated to Ab by one linker (L-1).

[0222] In some embodiments, one Ab is conjugated to two MMAEs and wherein each MMAE is conjugated to Ab by one linker (L-1). 75 NAI-1541858741

[0223] In yet another aspect, provided is a method for treating cancer in a subject, the method comprising administering an ADC to the subject, wherein the cancer is any one or more of breast cancer, endometrial cancer, head and neck cancer, pancreatic cancer, lung cancer, prostate cancer, cervical cancer, bladder cancer, renal cell carcinoma (RCC), hepatocellular carcinoma (HCC), or colorectal cancer, wherein the ADC is produced by conjugating an antibody (Ab) to a linker-drug comprising a pre-conjugate linker (L-1a’) and a monomethyl auristatin E (MMAE):(L-1a’), wherein the ## indicates the point of attachment to the MMAE; wherein the MMAE is represented by Formula (III):wherein * indicates the point of attachment to (L-1a’); wherein the Ab is a 5T4 antibody or an antigen binding fragment thereof, and wherein the Ab comprises: (1) a heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), and a heavy chain complementarity determining region 3 (HCDR3) as set forth in a heavy chain variable region (VH) comprising the amino acid sequence of SEQ ID NO: 11, and (2) a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and a light chain complementarity determining region 3 (LCDR3) as set forth in a light chain variable region (VL) comprising the amino acid sequence of SEQ ID NO: 12; and 76 NAI-1541858741wherein the Ab further comprises one or more fGly’ and wherein fGly’ is a formylglycine amino acid residue to which linker (L-1a’) is attached after conjugating the Ab and the linker-drug. In some embodiments, the Ab prior to conjugating to the linker- drug comprises a heavy chain comprising an amino acid sequence of SEQ ID NO: 41 and a light chain comprising an amino acid sequence of SEQ ID NO: 3.

[0224] In any of the embodiments and aspects as disclosed herein, one Ab is conjugated to one to ten linker-drugs.

[0225] In any of the embodiments and aspects as disclosed herein, one Ab is conjugated to two linker-drugs.

[0226] In any of the embodiments and aspects as disclosed herein, the Ab comprises one to ten fGly’.

[0227] In any of the embodiments and aspects as disclosed herein, the Ab comprises two fGly’.

[0228] In any of the embodiments and aspects as disclosed herein, the Ab comprises a motif of X1(fGly’)X2Z2X3Z3(SEQ ID NO: 67), wherein: Z2is either a proline (P) or alanine (A) residue; Z3is a basic amino acid residue optionally selected from the group consisting of: arginine (R), lysine (K), and histidine (H), or an aliphatic amino acid residue optionally selected from the group consisting of: alanine (A), glycine (G), leucine (L), valine (V), isoleucine (I), and proline (P); X1is present or absent and, when present, is any amino acid residue, with the proviso that when the sequence of SEQ ID NO: 67 is at the N-terminus of the antibody Ab, X1is present; and X2and X3independently is any amino acid residue, optionally wherein, the motif of SEQ ID NO: 67 is selected from the group consisting of: L(fGly’)TPSR (SEQ ID NO: 1), M(fGly’)TPSR (SEQ ID NO: 45), V(fGly’)TPSR (SEQ ID NO: 46), L(fGly’)SPSR (SEQ ID NO: 47), L(fGly’)APSR (SEQ ID NO: 48), L(fGly’)VPSR (SEQ ID NO: 49), L(fGly’)GPSR (SEQ ID NO: 50), I(fGly’)TPAR (SEQ ID NO: 51), L(fGly’)TPSK (SEQ ID NO: 52), M(fGly’)TPSK (SEQ ID NO: 53), V(fGly’)TPSK (SEQ ID NO: 54), L(fGly’)SPSK (SEQ ID NO: 55), L(fGly’)APSK (SEQ ID NO: 56), L(fGly’)VPSK (SEQ ID NO: 57), L(fGly’)GPSK (SEQ ID NO: 58), 77 NAI-1541858741L(fGly’)TPSA (SEQ ID NO: 59), I(fGly’)TPAA (SEQ ID NO: 60), M(fGly’)TPSA (SEQ ID NO: 61), V(fGly’)TPSA (SEQ ID NO: 62), L(fGly’)SPSA (SEQ ID NO: 63), L(fGly’)APSA (SEQ ID NO: 64), L(fGly’)VPSA (SEQ ID NO: 65), and L(fGly’)GPSA (SEQ ID NO: 66).

[0229] In any of the embodiments and aspects as disclosed herein, the Ab comprises two heavy chains and two light chains, and wherein each of the heavy chains comprises a motif of SEQ ID NO: 67.

[0230] In any of the embodiments and aspects as disclosed herein, the Ab comprises an amino acid sequence of L(fGly’)TPSR (SEQ ID NO: 1).

[0231] In any of the embodiments and aspects as disclosed herein, the Ab comprises two heavy chains and two light chains, and wherein each of the heavy chains comprises a motif of L(fGly’)TPSR (SEQ ID NO: 1)

[0232] In any of the embodiments and aspects as disclosed herein, the fGly’ of the motif is located in the heavy chain at a position corresponding to the 453rdamino acid residue of SEQ ID NO: 2 (also referred to herein as C453).

[0233] In any of the embodiments and aspects as disclosed herein, (1) HCDR1 comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 13, 19, 24, 25, and 30, (2) HCDR2 comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 14, 20, 26, 31, and 36, (3) HCDR3 comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 15, 21, 27, and 32, (4) LCDR1 comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 16, 22, 28, and 33, (5) LCDR2 comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 17, 23, and 34, and (6) LCDR3 comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 18, 29, and 35.

[0234] In any of the embodiments and aspects as disclosed herein, (i) HCDR1 comprises the amino acid sequence of SEQ ID NO: 13, HCDR2 comprises the amino acid sequence of SEQ ID NO: 14, HCDR3 comprises the amino acid sequence of SEQ ID NO: 15, LCDR1 comprises the amino acid sequence of SEQ ID NO: 78 NAI-154185874116, LCDR2 comprises the amino acid sequence of SEQ ID NO: 17, and LCDR3 comprises the amino acid sequence of SEQ ID NO: 18; or (ii) HCDR1 comprises the amino acid sequence of SEQ ID NO: 19, HCDR2 comprises the amino acid sequence of SEQ ID NO: 20, HCDR3 comprises the amino acid sequence of SEQ ID NO: 21, LCDR1 comprises the amino acid sequence of SEQ ID NO: 22, LCDR2 comprises the amino acid sequence of SEQ ID NO: 23, and LCDR3 comprises the amino acid sequence of SEQ ID NO: 18; or (iii) HCDR1 comprises the amino acid sequence of SEQ ID NO: 24, HCDR2 comprises the amino acid sequence of SEQ ID NO: 14, HCDR3 comprises the amino acid sequence of SEQ ID NO: 15, LCDR1 comprises the amino acid sequence of SEQ ID NO: 16, LCDR2 comprises the amino acid sequence of SEQ ID NO: 17, and LCDR3 comprises the amino acid sequence of SEQ ID NO: 18; or (iv) HCDR1 comprises the amino acid sequence of SEQ ID NO: 25, HCDR2 comprises the amino acid sequence of SEQ ID NO: 26, HCDR3 comprises the amino acid sequence of SEQ ID NO: 27, LCDR1 comprises the amino acid sequence of SEQ ID NO: 28, LCDR2 comprises the amino acid sequence of SEQ ID NO: 23, and LCDR3 comprises the amino acid sequence of SEQ ID NO: 29; or (v) HCDR1 comprises the amino acid sequence of SEQ ID NO: 30, HCDR2 comprises the amino acid sequence of SEQ ID NO: 31, HCDR3 comprises the amino acid sequence of SEQ ID NO: 32, LCDR1 comprises the amino acid sequence of SEQ ID NO: 33, LCDR2 comprises the amino acid sequence of SEQ ID NO: 34, and LCDR3 comprises the amino acid sequence of SEQ ID NO: 35; or (vi) HCDR1 comprises the amino acid sequence of SEQ ID NO: 13, HCDR2 comprises the amino acid sequence of SEQ ID NO: 36, HCDR3 comprises the amino acid sequence of SEQ ID NO: 15, LCDR1 comprises the amino acid sequence of SEQ ID NO: 16, LCDR2 comprises the amino acid sequence of SEQ ID NO: 17, and LCDR3 comprises the amino acid sequence of SEQ ID NO: 18.

[0235] In any of the embodiments and aspects as disclosed herein, the Ab comprises a VH comprising the amino acid sequence of SEQ ID NO: 11 and a VL comprising the amino acid sequence of SEQ ID NO: 12.

[0236] In any of the embodiments and aspects as disclosed herein, the Ab comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 2 and a light chain comprising the amino acid sequence of SEQ ID NO: 3. Accordingly, the Ab prior to being conjugated to a linker 79 NAI-1541858741or linker-drug comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 41 and a light chain comprising the amino acid sequence of SEQ ID NO: 3.

[0237] In any of the embodiments and aspects as disclosed herein, the cancer is triple- negative breast cancer (TNBC) or hormone-receptor positive breast cancer (HR+ BC).

[0238] In any of the embodiments and aspects as disclosed herein, the cancer is pancreatic ductal adenocarcinoma (PDAC).

[0239] In any of the embodiments and aspects as disclosed herein, the cancer is non-small cell lung cancer (NSCLC).

[0240] In any of the embodiments and aspects as disclosed herein, the cancer is head and neck squamous cell carcinoma (HNSCC).

[0241] In any of the embodiments and aspects as disclosed herein, the method further comprises administrating to the subject means for inhibiting interaction between PD-1 and PD- L1. Exemplary means for inhibiting interaction between PD-1 and PD-L1 include a PD-L1 / PD-1 inhibitor as disclosed herein, such as a pembrolizumab.

[0242] In any of the embodiments and aspects as disclosed herein, the ADC is administered concurrently with, after, or before the means for inhibiting interaction between PD-1 and PD-L1.

[0243] In any of the embodiments and aspects as disclosed herein, the method further comprises administering to the subject a PD-L1 / PD-1 inhibitor.

[0244] In any of the embodiments and aspects as disclosed herein, the ADC is administered concurrently with, after, or before the PD-L1 / PD-1 inhibitor.

[0245] In any of the embodiments and aspects as disclosed herein, the PD-L1 / PD-1 inhibitor is an antibody or an antigen binding fragment thereof comprising HCDR1, HCDR2, HCDR3, LCDR1, LCDR2, and LCDR3 of pembrolizumab.

[0246] In any of the embodiments and aspects as disclosed herein, the PD-L1 / PD-1 inhibitor is pembrolizumab.

[0247] In any of the embodiments and aspects as disclosed herein, the PD-L1 / PD-1 inhibitor is administered to the subject at a dose of about 200 mg.

[0248] In any of the embodiments and aspects as disclosed herein, the PD-L1 / PD-1 inhibitor is administered intravenously.

[0249] In any of the embodiments and aspects as disclosed herein, the PD-L1 / PD-1 inhibitor is administered once every 3 weeks (q3w).

[0250] In any of the embodiments and aspects as disclosed herein, the ADC is administered intravenously. 80 NAI-1541858741

[0251] In any of the embodiments and aspects as disclosed herein, the ADC is administered once every 3 weeks (q3w).

[0252] In any of the embodiments and aspects as disclosed herein, the subject is human.

[0253] In any of the embodiments and aspects as disclosed herein, the ADC also refers to its stereoisomer, solvate, or salt.

[0254] In any of the embodiments and aspects as disclosed herein, a pharmaceutical composition comprising an ADC as described and a pharmaceutically acceptable excipient is administered to the subject. In further embodiments, the pharmaceutical composition comprises a multiplicity of DAR species of the ADC. In some embodiments, the average DAR of the pharmaceutical composition is about 1 to about 2. In further embodiments, the average DAR of the pharmaceutical composition is 1.8. In some embodiments, the pharmaceutical composition exhibits a DAR of about 1 to about 2. In further embodiments, the pharmaceutical composition exhibits a DAR of 1.8.

[0255] In any of the embodiments and aspects as disclosed herein, a pharmaceutical composition comprising a first ADC as described and a pharmaceutically acceptable excipient is administered to the subject. In some embodiments, the pharmaceutical composition comprises a second ADC as disclosed herein, wherein the two ADCs are different in the number of drugs, such as MMAEs, directly or indirectly conjugated to each Ab. In yet further embodiments, two drugs, such as MMAEs, are directly or indirectly conjugated to the Ab in the first ADC and one drug, such as MMAE, is directly or indirectly conjugated to the Ab in the second ADC. In some embodiments, such a pharmaceutical composition exhibits a drug-to-antibody ratio (“DAR”) of about 1 to about 2. In further embodiments, the pharmaceutical composition exhibits a DAR of 1.8. In yet further embodiments, each 5T4 antibody is conjugated to one or two linker-drugs.

[0256] In any of the embodiments and aspects as disclosed herein, a population of the ADCs is administered to the subject. In further embodiments, such an ADC population exhibits a drug- to-antibody ratio (“DAR”) of about 1 to about 2. In yet further embodiments, the ADC population exhibits a DAR of 1.8. In yet further embodiments, each 5T4 antibody is conjugated to one or two linker-drugs.

[0257] In some embodiments, the ADCs as disclosed herein (such as 5T4-ADC-1) are represented by the illustration below. In further embodiments, the wavy line in the lower panel separates the Ab (illustrated as four bars forming a Y shape in the upper panel) and the linker- drug (illustrated as a solid star in both panels). 81 NAI-1541858741

[0258] The present disclosure provides methods of treating cancer in a subject comprising administering a therapeutically effective dose of a 5T4 ADC as disclosed herein, such as an ADC of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (for example, 5T4-ADC-1).

[0259] In one embodiment, the 5T4 ADC is represented by Formula (I) below:(I)wherein Ab is a 5T4 antibody or an antigen binding fragment thereof. In one embodiment, the 5T4 ADC comprises a 5T4 antibody or an antigen binding fragment thereof, wherein the 5T4 antibody or antigen binding fragment thereof comprises a VH region, VL region, heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), a heavy chain complementarity determining region 3 (HCDR3), a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and / or a light chain complementarity determining region 3 (LCDR3) as described in Table 1. In one embodiment, the Ab is a 5T4 antibody as disclosed herein. In one embodiment, the 5T4 ADC comprises a 5T4 antibody comprising a VH region comprising the amino acid sequence of SEQ ID NO: 11 and a VL region comprising the amino acid sequence of 82 NAI-1541858741SEQ ID NO: 12. In one embodiment, the 5T4 antibody comprises a light chain having an amino acid sequence of: DIQMTQSPSSLSASVGDRVTITCRASQSVSSAVAWYQQKPGKAPKLLIYSASSLYSGVPSRFSGS RSGTDFTLTISSLQPEDFATYYCQQAYATPVTFGQGTKVEIKRTVAAPSVFIFPPSDEQLKSGTA SVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACE VTHQGLSSPVTKSFNRGEC (SEQ ID NO: 3).

[0260] In one embodiment, a linker-drug comprising linker (L-1) is conjugated to each of the heavy chain constant regions in the 5T4 antibody (e.g., the 5T4 antibody is conjugated to two linker-drugs). In one embodiment, a linker-drug comprising linker (L-1) is conjugated to each of the heavy chains in the 5T4 antibody (e.g., the 5T4 antibody is conjugated to two linker-drugs). In one embodiment, a linker-drug comprising linker (L-1) is conjugated to the CH3 region in each of the heavy chain constant regions in the 5T4 antibody. In one embodiment, a linker-drug comprising linker (L-1) is conjugated to the CH3 region in each of the heavy chains in the 5T4 antibody. In a further embodiment, a linker-drug comprising linker (L-1) is conjugated to the aldehyde in the formylglycine at C453 of each heavy chain of an anti-5T4 aldehyde-containing antibody. In such embodiments, each 5T4 ADC comprises two MMAE drugs. A composition comprising such ADCs will exhibit a DAR of 2. In some embodiments, a 5T4 ADC comprises a 5T4 antibody comprising a light chain comprising the amino acid sequence of DIQMTQSPSSLSASVGDRVTITCRASQSVSSAVAWYQQKPGKAPKLLIYSASSLYSGVPSRFSGS RSGTDFTLTISSLQPEDFATYYCQQAYATPVTFGQGTKVEIKRTVAAPSVFIFPPSDEQLKSGTA SVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACE VTHQGLSSPVTKSFNRGEC (SEQ ID NO: 3) and a heavy chain having an amino acid sequence of: EVQLVESGGGLVQPGGSLRLSCAASGFTFSSYYIHWVRQAPGKGLEWVAYITSTGSYTEYADSVK GRFTISADTSKNTAYLQMNSLRAEDTAVYYCARYDRSTRYSGLDYWGQGTLVTVSSASTKGPSVF PLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSS SLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRT PEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKC KVSNKALPAPIEKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQ PENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGSLnTP SRGS (SEQ ID NO: 42), wherein n is an amino acid conjugated to (e.g., by having its side chain replaced by) a linker-drug comprising linker (L-1): 83 NAI-1541858741wherein represents the point of conjugation to Ab and ## indicates the point of attachment to MMAE; and wherein the MMAE is represented by Formula (III):wherein * indicates the point of attachment to (L-1). In some embodiments, the amino acid n in SEQ ID NO: 42 refers to fGly’ as described herein. In some embodiments, n is an amino acid having its side chain replaced by Formula (II):wherein the wavy line indicates the point of attachment to the Ab and MMAE is represented by Formula (III):wherein * indicates the point of attachment in Formula (II). 84 NAI-1541858741

[0261] In one embodiment, the ADC is represented by Formula (I):wherein Ab is a 5T4 antibody comprising: a) a heavy chain having an amino acid sequence of: EVQLVESGGGLVQPGGSLRLSCAASGFTFSSYYIHWVRQAPGKGLEWVAYITSTGSYTEYADSVK GRFTISADTSKNTAYLQMNSLRAEDTAVYYCARYDRSTRYSGLDYWGQGTLVTVSSASTKGPSVF PLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSS SLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRT PEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKC KVSNKALPAPIEKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQ PENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGSLnTP SRGS (SEQ ID NO: 42), wherein n is the amino acid to which a linker-drug comprising linker (L-1), as described herein, is attached:wherein the wavy line indicates the point of attachment to the Ab at (fGly’) and ## indicates the point of attachment to the MMAE; and wherein the MMAE is represented by Formula (III):wherein * indicates the point of attachment to linker (L-1); and b) a light chain having an amino acid sequence of: 85 NAI-1541858741DIQMTQSPSSLSASVGDRVTITCRASQSVSSAVAWYQQKPGKAPKLLIYSASSLYSGVPSRFSGS RSGTDFTLTISSLQPEDFATYYCQQAYATPVTFGQGTKVEIKRTVAAPSVFIFPPSDEQLKSGTA SVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACE VTHQGLSSPVTKSFNRGEC (SEQ ID NO: 3). In some embodiments, the amino acid n in SEQ ID NO: 42 refers to fGly’ as described herein.

[0262] In some embodiments, a therapeutically effective dose of a PD-L1 inhibitor is administered to the subject in combination with the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1). In one embodiment, the PD-L1 inhibitor is pembrolizumab. In one embodiment, the therapeutically effective dose of the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4- ADC-1) is administered to the subject in a pharmaceutical composition, as described herein in Section 7.3.

[0263] In one embodiment, the cancer is a cancer selected from the group consisting of breast cancer, endometrial cancer, head and neck cancer, pancreatic cancer, lung cancer, prostate cancer, cervical cancer, or bladder cancer. In one embodiment, the cancer is TNBC. In one embodiment, the cancer is HR+ BC. In one embodiment, the cancer is PDAC. In certain embodiments, the cancer is lung adenocarcinoma or squamous cell lung carcinoma. In one embodiment, the cancer is NSCLC. In some embodiments, the cancer is head and neck cancer. In one embodiment, the cancer is HNSCC. In one embodiment, the NSCLC is characterized by a mutation selected from the group consisting of an EGFR sensitizing mutation, an ALK rearrangement, a ROS1 rearrangement, a BRAF V600E mutation, a MET Exon 14 skipping mutation, and a RET rearrangement. In certain embodiments, the cancer is renal cell carcinoma (RCC), hepatocellular carcinoma (HCC), or colorectal cancer. In some embodiments, the cancer is a genitourinary cancer. In some embodiments, the cancer is a gastrointestinal cancer. In some embodiments, the cancer is a gynecological cancer. Additionally or alternatively, the cancer is previously untreatable. Additionally or alternatively, the cancer is recurrent. Additionally or alternatively, the cancer is metastatic. Additionally or alternatively, the cancer is advanced, for example locally advanced. Additionally or alternatively, the cancer is inoperable.

[0264] A number of therapeutically effective administration and dosing regimens for treating cancer in a subject are contemplated and described herein below.

[0265] In one aspect, provided is a method for treating a cancer in a subject comprising administering an ADC as disclosed herein, e.g., according to any embodiment in Section 7.3, to the subject at a dose of about 0.1 mg / kg to about 10.0 mg / kg. In one embodiment, the ADC is 86 NAI-1541858741represented by Formula (I) and comprises an Ab conjugated to a monomethyl auristatin E (MMAE) by linker (L-1) as disclosed herein:

[0266] In further embodiments, the Ab is a 5T4 antibody or an antigen binding fragment thereof and comprises a heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), a heavy chain complementarity determining region 3 (HCDR3), a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and a light chain complementarity determining region 3 (LCDR3) of an antibody designated mAbA15. In some embodiments, the Ab further comprises two motifs, each of which is L(fGly’)TPSR (SEQ ID NO: 1). In further embodiments, fGly’ is the amino acid residue to which a linker-drug comprising linker (L-1), as disclosed herein, is attached. In some embodiments, mAbA15 comprises: a) a heavy chain comprising an amino acid sequence of: EVQLVESGGGLVQPGGSLRLSCAASGFTFSSYYIHWVRQAPGKGLEWVAYITSTGSYTEYADSVK GRFTISADTSKNTAYLQMNSLRAEDTAVYYCARYDRSTRYSGLDYWGQGTLVTVSSASTKGPSVF PLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSS SLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRT PEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKC KVSNKALPAPIEKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQ PENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGSL (fGly’)TPSRGS (SEQ ID NO: 2); and b) a light chain comprising an amino acid sequence of:

[0267] DIQMTQSPSSLSASVGDRVTITCRASQSVSSAVAWYQQKPGKAPKLLIYSASSLYSG VPSRFSGSRSGTDFTLTISSLQPEDFATYYCQQAYATPVTFGQGTKVEIKRTVAAPSVFIFPPSD EQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYE KHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 3). In some embodiments, the ADC is 5T4-ADC-1. In some embodiments, the cancer is any one or more of breast cancer, endometrial cancer, head and neck cancer, pancreatic cancer, lung cancer, prostate cancer, cervical cancer, or bladder cancer. In certain embodiments, the cancer is pancreatic adenocarcinoma (PDAC, also 87 NAI-1541858741referred to herein as pancreatic ductal adenocarcinoma). In certain embodiments, the cancer is lung adenocarcinoma or squamous cell lung carcinoma. In certain embodiments, the cancer is non-small cell lung cancer (NSCLC). In some embodiments, the cancer is head and neck cancer. In certain embodiments, the cancer is head and neck squamous cell carcinoma (HNSCC). In certain embodiments, the cancer is renal cell carcinoma (RCC), hepatocellular carcinoma (HCC), or colorectal cancer. In some embodiments, the cancer is a genitourinary cancer. In some embodiments, the cancer is a gastrointestinal cancer. In some embodiments, the cancer is a gynecological cancer. Additionally or alternatively, the cancer is previously untreatable. Additionally or alternatively, the cancer is recurrent. Additionally or alternatively, the cancer is metastatic. Additionally or alternatively, the cancer is advanced, for example locally advanced. Additionally or alternatively, the cancer is inoperable.

[0268] Also provided herein is a method for treating cancer in a subject comprising administering a 5T4 ADC as disclosed herein to the subject. In some embodiments, the cancer is any one or more of breast cancer, endometrial cancer, head and neck cancer, pancreatic cancer, lung cancer, prostate cancer, cervical cancer, or bladder cancer. In certain embodiments, the cancer is pancreatic adenocarcinoma (PDAC, also referred to herein as pancreatic ductal adenocarcinoma). In certain embodiments, the cancer is lung adenocarcinoma or squamous cell lung carcinoma. In certain embodiments, the cancer is non-small cell lung cancer (NSCLC). In some embodiments, the cancer is head and neck cancer. In certain embodiments, the cancer is head and neck squamous cell carcinoma (HNSCC). In certain embodiments, the cancer is renal cell carcinoma (RCC), hepatocellular carcinoma (HCC), or colorectal cancer. In some embodiments, the cancer is a genitourinary cancer. In some embodiments, the cancer is a gastrointestinal cancer. In some embodiments, the cancer is a gynecological cancer. Additionally or alternatively, the cancer is previously untreatable. Additionally or alternatively, the cancer is recurrent. Additionally or alternatively, the cancer is metastatic. Additionally or alternatively, the cancer is advanced, for example locally advanced. Additionally or alternatively, the cancer is inoperable.

[0269] In some embodiments, the ADC is represented by Formula (I) and comprises an Ab conjugated to a monomethyl auristatin E (MMAE) by linker (L-1): 88 NAI-1541858741In further embodiments, the Ab is a 5T4 antibody or an antigen binding fragment thereof and comprises a heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), a heavy chain complementarity determining region 3 (HCDR3), a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and a light chain complementarity determining region 3 (LCDR3) of an antibody designated mAbA15. In some embodiments, the Ab further comprises two motifs, each of which is L(fGly’)TPSR (SEQ ID NO: 1). In further embodiments, fGly’ is the amino acid residue to which a linker-drug comprising (L-1) is attached. In some embodiments, mAbA15 comprises: a) a heavy chain comprising an amino acid sequence of: EVQLVESGGGLVQPGGSLRLSCAASGFTFSSYYIHWVRQAPGKGLEWVAYITSTGSYTEYADSVK GRFTISADTSKNTAYLQMNSLRAEDTAVYYCARYDRSTRYSGLDYWGQGTLVTVSSASTKGPSVF PLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSS SLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRT PEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKC KVSNKALPAPIEKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQ PENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGSL (fGly’)TPSRGS (SEQ ID NO: 2); and b) a light chain comprising an amino acid sequence of: DIQMTQSPSSLSASVGDRVTITCRASQSVSSAVAWYQQKPGKAPKLLIYSASSLYSGVPSRFSGS RSGTDFTLTISSLQPEDFATYYCQQAYATPVTFGQGTKVEIKRTVAAPSVFIFPPSDEQLKSGTA SVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACE VTHQGLSSPVTKSFNRGEC (SEQ ID NO: 3). Additionally or alternatively, fGly’ is attached to a linker-drug of Formula (II): 89 NAI-1541858741wherein the wavy line indicates the point of attachment to the Ab and MMAE is represented by Formula (III):wherein * indicates the point of attachment in Formula (II). In some embodiments, the ADC is 5T4-ADC-1. In further embodiments, the ADC is administered to the subject at a dose of about 0.1 mg / kg to about 10.0 mg / kg.

[0270] In some embodiments, the Ab comprises two heavy chains (HCs) and two light chains (LCs), and each of the HCs comprises one motif of L(fGly’)TPSR (SEQ ID NO: 1). In some embodiments, the Ab is mAbA15.

[0271] In some embodiments, the ADC is administered to the subject on the first day of a treatment cycle for one or more treatment cycles. In further embodiments, each treatment cycle is 3 weeks ± 3 days.

[0272] In some embodiments, the ADC is administered to the subject once every three weeks (q3w).

[0273] In some embodiments, the ADC is administered to the subject intravenously.

[0274] In some embodiments, a method as disclosed herein further comprises administering to the subject a PD-L1 / PD-1 inhibitor. Additionally or alternatively, the subject is administered a PD-L1 / PD-1 inhibitor. In some embodiments, the ADC is administered concurrently with the PD-L1 / PD-1 inhibitor. In some embodiments, the ADC is administered after the PD-L1 / PD-1 inhibitor. In some embodiments, the ADC is administered before the PD-L1 / PD-1 inhibitor. In some embodiments, the ADC is administered on the same day with the PD-L1 / PD-1 inhibitor. In some embodiments, the administration of the ADC and the PD-L1 / PD-1 inhibitor is at least about 30 minutes apart or at least about 1 hour apart. In some embodiments, the PD-L1 / PD-1 inhibitor is administered to the subject on the first day of a treatment cycle for one or more treatment cycles. In further embodiments, each treatment cycle is 3 weeks ± 3 days. In some embodiments, 90 NAI-1541858741the PD-L1 / PD-1 inhibitor is administered to the subject once every three weeks (q3w). In some embodiments, the PD-L1 / PD-1 inhibitor is administered to the subject intravenously. In some embodiments, the PD-L1 / PD-1 inhibitor is an antibody or an antigen binding fragment thereof comprising HCDR1, HCDR2, HCDR3, LCDR1, LCDR2, and LCDR3 of pembrolizumab. In further embodiments, the PD-L1 / PD-1 inhibitor is pembrolizumab. In some embodiments, the PD-L1 / PD-1 inhibitor is administered to the subject at a dose of about 200 mg.

[0275] In some embodiments, the ADC as disclosed herein is administered to the subject at a dose of about 0.1 mg / kg to about 10.0 mg / kg. In some embodiments, the ADC is administered to the subject at a dose of about 0.1 mg / kg to about 9.5 mg / kg, about 0.1 mg / kg to about 9.0 mg / kg, about 0.1 mg / kg to about 8.5 mg / kg, about 0.1 mg / kg to about 8.0 mg / kg, about 0.1 mg / kg to about 7.5 mg / kg, about 0.1 mg / kg to about 7.0 mg / kg, about 0.1 mg / kg to about 6.5 mg / kg, about 0.1 mg / kg to about 6.0 mg / kg, about 0.1 mg / kg to about 5.5 mg / kg, about 0.1 mg / kg to about 5.0 mg / kg, about 0.1 mg / kg to about 4.5 mg / kg, about 0.1 mg / kg to about 4.0 mg / kg, about 0.1 mg / kg to about 3.5 mg / kg, about 0.1 mg / kg to about 3.0 mg / kg, about 0.1 mg / kg to about 2.5 mg / kg, about 0.1 mg / kg to about 2.0 mg / kg, about 0.1 mg / kg to about 1.5 mg / kg, about 0.1 mg / kg to about 1.0 mg / kg, about 0.1 mg / kg to about 0.5 mg / kg, or about 0.1 mg / kg to about 0.3 mg / kg. In some embodiments, the ADC is administered to the subject at a dose of about 0.3 mg / kg to about 9.5 mg / kg, about 0.3 mg / kg to about 9.0 mg / kg, about 0.3 mg / kg to about 8.5 mg / kg, about 0.3 mg / kg to about 8.0 mg / kg, about 0.3 mg / kg to about 7.5 mg / kg, about 0.3 mg / kg to about 7.0 mg / kg, about 0.3 mg / kg to about 6.5 mg / kg, about 0.3 mg / kg to about 6.0 mg / kg, about 0.3 mg / kg to about 5.5 mg / kg, about 0.3 mg / kg to about 5.0 mg / kg, about 0.3 mg / kg to about 4.5 mg / kg, about 0.3 mg / kg to about 4.0 mg / kg, about 0.3 mg / kg to about 3.5 mg / kg, about 0.3 mg / kg to about 3.0 mg / kg, about 0.3 mg / kg to about 2.5 mg / kg, about 0.3 mg / kg to about 2.0 mg / kg, about 0.3 mg / kg to about 1.5 mg / kg, about 0.3 mg / kg to about 1.0 mg / kg, or about 0.3 mg / kg to about 0.5 mg / kg. In some embodiments, the ADC is administered to the subject at a dose of about 0.5 mg / kg to about 9.5 mg / kg, about 0.5 mg / kg to about 9.0 mg / kg, about 0.5 mg / kg to about 8.5 mg / kg, about 0.5 mg / kg to about 8.0 mg / kg, about 0.5 mg / kg to about 7.5 mg / kg, about 0.5 mg / kg to about 7.0 mg / kg, about 0.5 mg / kg to about 6.5 mg / kg, about 0.5 mg / kg to about 6.0 mg / kg, about 0.5 mg / kg to about 5.5 mg / kg, about 0.5 mg / kg to about 5.0 mg / kg, about 0.5 mg / kg to about 4.5 mg / kg, about 0.5 mg / kg to about 4.0 mg / kg, about 0.5 mg / kg to about 3.5 mg / kg, about 0.5 mg / kg to about 3.0 mg / kg, about 0.5 mg / kg to about 2.5 mg / kg, about 0.5 mg / kg to about 2.0 mg / kg, about 0.5 mg / kg to about 1.5 mg / kg, or about 0.5 mg / kg to about 1.0 mg / kg. In some embodiments, the ADC is administered to the subject at a dose of about 1.0 mg / kg to about 9.5 mg / kg, about 1.0 mg / kg to about 9.0 91 NAI-1541858741mg / kg, about 1.0 mg / kg to about 8.5 mg / kg, about 1.0 mg / kg to about 8.0 mg / kg, about 1.0 mg / kg to about 7.5 mg / kg, about 1.0 mg / kg to about 7.0 mg / kg, about 1.0 mg / kg to about 6.5 mg / kg, about 1.0 mg / kg to about 6.0 mg / kg, about 1.0 mg / kg to about 5.5 mg / kg, about 1.0 mg / kg to about 5.0 mg / kg, about 1.0 mg / kg to about 4.5 mg / kg, about 1.0 mg / kg to about 4.0 mg / kg, about 1.0 mg / kg to about 3.5 mg / kg, about 1.0 mg / kg to about 3.0 mg / kg, about 1.0 mg / kg to about 2.5 mg / kg, about 1.0 mg / kg to about 2.0 mg / kg, or about 1.0 mg / kg to about 1.5 mg / kg. In some embodiments, the ADC is administered to the subject at a dose of about 1.5 mg / kg to about 9.5 mg / kg, about 1.5 mg / kg to about 9.0 mg / kg, about 1.5 mg / kg to about 8.5 mg / kg, about 1.5 mg / kg to about 8.0 mg / kg, about 1.5 mg / kg to about 7.5 mg / kg, about 1.5 mg / kg to about 7.0 mg / kg, about 1.5 mg / kg to about 6.5 mg / kg, about 1.5 mg / kg to about 6.0 mg / kg, about 1.5 mg / kg to about 5.5 mg / kg, about 1.5 mg / kg to about 5.0 mg / kg, about 1.5 mg / kg to about 4.5 mg / kg, about 1.5 mg / kg to about 4.0 mg / kg, about 1.5 mg / kg to about 3.5 mg / kg, about 1.5 mg / kg to about 3.0 mg / kg, about 1.5 mg / kg to about 2.5 mg / kg, or about 1.5 mg / kg to about 2.0 mg / kg. In some embodiments, the ADC is administered to the subject at a dose of about 2.0 mg / kg to about 9.5 mg / kg, about 2.0 mg / kg to about 9.0 mg / kg, about 2.0 mg / kg to about 8.5 mg / kg, about 2.0 mg / kg to about 8.0 mg / kg, about 2.0 mg / kg to about 7.5 mg / kg, about 2.0 mg / kg to about 7.0 mg / kg, about 2.0 mg / kg to about 6.5 mg / kg, about 2.0 mg / kg to about 6.0 mg / kg, about 2.0 mg / kg to about 5.5 mg / kg, about 2.0 mg / kg to about 5.0 mg / kg, about 2.0 mg / kg to about 4.5 mg / kg, about 2.0 mg / kg to about 4.0 mg / kg, about 2.0 mg / kg to about 3.5 mg / kg, about 2.0 mg / kg to about 3.0 mg / kg, or about 2.0 mg / kg to about 2.5 mg / kg. In some embodiments, the ADC is administered to the subject at a dose of about 2.5 mg / kg to about 9.5 mg / kg, about 2.5 mg / kg to about 9.0 mg / kg, about 2.5 mg / kg to about 8.5 mg / kg, about 2.5 mg / kg to about 8.0 mg / kg, about 2.5 mg / kg to about 7.5 mg / kg, about 2.5 mg / kg to about 7.0 mg / kg, about 2.5 mg / kg to about 6.5 mg / kg, about 2.5 mg / kg to about 6.0 mg / kg, about 2.5 mg / kg to about 5.5 mg / kg, about 2.5 mg / kg to about 5.0 mg / kg, about 2.5 mg / kg to about 4.5 mg / kg, about 2.5 mg / kg to about 4.0 mg / kg, about 2.5 mg / kg to about 3.5 mg / kg, or about 2.5 mg / kg to about 3.0 mg / kg. In some embodiments, the ADC is administered to the subject at a dose of about 3.0 mg / kg to about 9.5 mg / kg, about 3.0 mg / kg to about 9.0 mg / kg, about 3.0 mg / kg to about 8.5 mg / kg, about 3.0 mg / kg to about 8.0 mg / kg, about 3.0 mg / kg to about 7.5 mg / kg, about 3.0 mg / kg to about 7.0 mg / kg, about 3.0 mg / kg to about 6.5 mg / kg, about 3.0 mg / kg to about 6.0 mg / kg, about 3.0 mg / kg to about 5.5 mg / kg, about 3.0 mg / kg to about 5.0 mg / kg, about 3.0 mg / kg to about 4.5 mg / kg, about 3.0 mg / kg to about 4.0 mg / kg, or about 3.0 mg / kg to about 3.5 mg / kg. In some embodiments, the ADC is administered to the subject at a dose of about 3.5 mg / kg to about 9.5 mg / kg, about 3.5 mg / kg to about 9.0 92 NAI-1541858741mg / kg, about 3.5 mg / kg to about 8.5 mg / kg, about 3.5 mg / kg to about 8.0 mg / kg, about 3.5 mg / kg to about 7.5 mg / kg, about 3.5 mg / kg to about 7.0 mg / kg, about 3.5 mg / kg to about 6.5 mg / kg, about 3.5 mg / kg to about 6.0 mg / kg, about 3.5 mg / kg to about 5.5 mg / kg, about 3.5 mg / kg to about 5.0 mg / kg, about 3.5 mg / kg to about 4.5 mg / kg, or about 3.5 mg / kg to about 4.0 mg / kg. In some embodiments, the ADC is administered to the subject at a dose of about 4.0 mg / kg to about 9.5 mg / kg, about 4.0 mg / kg to about 9.0 mg / kg, about 4.0 mg / kg to about 8.5 mg / kg, about 4.0 mg / kg to about 8.0 mg / kg, about 4.0 mg / kg to about 7.5 mg / kg, about 4.0 mg / kg to about 7.0 mg / kg, about 4.0 mg / kg to about 6.5 mg / kg, about 4.0 mg / kg to about 6.0 mg / kg, about 4.0 mg / kg to about 5.5 mg / kg, about 4.0 mg / kg to about 5.0 mg / kg, or about 4.0 mg / kg to about 4.5 mg / kg. In some embodiments, the ADC is administered to the subject at a dose of about 4.5 mg / kg to about 9.5 mg / kg, about 4.5 mg / kg to about 9.0 mg / kg, about 4.5 mg / kg to about 8.5 mg / kg, about 4.5 mg / kg to about 8.0 mg / kg, about 4.5 mg / kg to about 7.5 mg / kg, about 4.5 mg / kg to about 7.0 mg / kg, about 4.5 mg / kg to about 6.5 mg / kg, about 4.5 mg / kg to about 6.0 mg / kg, about 4.5 mg / kg to about 5.5 mg / kg, or about 4.5 mg / kg to about 5.0 mg / kg. In some embodiments, the ADC is administered to the subject at a dose of about 5.0 mg / kg to about 9.5 mg / kg, about 5.0 mg / kg to about 9.0 mg / kg, about 5.0 mg / kg to about 8.5 mg / kg, about 5.0 mg / kg to about 8.0 mg / kg, about 5.0 mg / kg to about 7.5 mg / kg, about 5.0 mg / kg to about 7.0 mg / kg, about 5.0 mg / kg to about 6.5 mg / kg, about 5.0 mg / kg to about 6.0 mg / kg, about 5.0 mg / kg to about 5.5 mg / kg. In some embodiments, the ADC is administered to the subject at a dose of about 5.5 mg / kg to about 9.5 mg / kg, about 5.5 mg / kg to about 9.0 mg / kg, about 5.5 mg / kg to about 8.5 mg / kg, about 5.5 mg / kg to about 8.0 mg / kg, about 5.5 mg / kg to about 7.5 mg / kg, about 5.5 mg / kg to about 7.0 mg / kg, about 5.5 mg / kg to about 6.5 mg / kg, or about 5.5 mg / kg to about 6.0 mg / kg. In some embodiments, the ADC is administered to the subject at a dose of about 6.0 mg / kg to about 9.5 mg / kg, about 6.0 mg / kg to about 9.0 mg / kg, about 6.0 mg / kg to about 8.5 mg / kg, about 6.0 mg / kg to about 8.0 mg / kg, about 6.0 mg / kg to about 7.5 mg / kg, about 6.0 mg / kg to about 7.0 mg / kg, or about 6.0 mg / kg to about 6.5 mg / kg.

[0276] In some embodiments, the ADC as disclosed herein is administered to the subject at a dose of about 0.3 mg / kg to about 6.0 mg / kg.

[0277] In some embodiments, the ADC as disclosed herein is administered to the subject at a dose of about 0.3 mg / kg to about 2.0 mg / kg.

[0278] In some embodiments, the ADC as disclosed herein is administered to the subject at a dose of about 0.3 mg / kg, about 0.6 mg / kg, about 1.0 mg / kg, about 1.5 mg / kg, about 2.0 mg / kg, about 2.5 mg / kg, about 3.0 mg / kg, about 3.5 mg / kg, about 4.0 mg / kg, about 4.5 mg / kg, about 5.0 93 NAI-1541858741mg / kg, about 5.5 mg / kg, about 6.0 mg / kg, about 6.5 mg / kg, about 7.0 mg / kg, about 7.5 mg / kg, about 8.0 mg / kg, about 8.5 mg / kg, about 9.0 mg / kg, about 9.5 mg / kg, about 10.0 mg / kg.

[0279] As it would be understood by one of skill in the art, an equivalent dose, such as a dose as disclosed herein converted to ADC amount per body surface area, is also included herein. Methods of such a conversion can be found, for example, Nair AB, Jacob S. J Basic Clin Pharm. 2016 Mar;7(2):27-31, which is incorporated herein by reference in its entirety.

[0280] In some embodiments, the cancer is triple-negative breast cancer (TNBC) or hormone-receptor positive breast cancer (HR+ BC).

[0281] In some embodiments, the cancer is pancreatic adenocarcinoma (PDAC, also referred to herein as pancreatic ductal adenocarcinoma).

[0282] In some embodiments, the cancer is prostate cancer.

[0283] In some embodiments, the cancer is cervical cancer.

[0284] In some embodiments, the cancer is bladder cancer.

[0285] In some embodiments, the cancer is colorectal cancer.

[0286] In some embodiments, the cancer is non-small cell lung cancer (NSCLC). In some embodiments, the subject has one or more mutations selected from the group consisting of an EGFR sensitizing mutation, an ALK rearrangement, a ROS1 rearrangement, a BRAF V600E mutation, a MET Exon 14 skipping mutation, and a RET rearrangement. In some embodiments, the cancer of the subject has one or more mutations selected from the group consisting of an EGFR sensitizing mutation, an ALK rearrangement, a ROS1 rearrangement, a BRAF V600E mutation, a MET Exon 14 skipping mutation, and a RET rearrangement. In certain embodiments, the cancer is lung adenocarcinoma or squamous cell lung carcinoma.

[0287] In some embodiments, the cancer is head and neck squamous cell carcinoma (HNSCC).

[0288] In some embodiments, the ADC as disclosed herein is administered to the subject for about four to about twenty-four months. In some embodiments, the ADC is administered to the subject for about four to about eighteen months. In some embodiments, the ADC is administered to the subject for about four to about twelve months. In some embodiments, the ADC is administered to the subject for about four to about six months.

[0289] In some embodiments, the subject is human. 7.4.1 Monotherapy

[0290] In one embodiment, the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) 94 NAI-1541858741is administered at a therapeutically effective dose to a subject as a single agent (e.g., not in combination with any other chemotherapeutic agents) to treat a cancer. In one embodiment, the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L- 1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) is administered periodically to a subject (e.g., once every treatment cycle) at a therapeutically effective dose, when the periodic administration is continued for a length of time (“length of treatment”) and / or a certain number of treatment cycles.

[0291] In one embodiment, a method for treating cancer in a subject comprises administering the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) to the subject at a dose of about 0.3 mg / kg to about 5.0 mg / kg for one or more treatment cycles. In one embodiment, each dose of the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) is administered to the subject on the first day of each treatment cycle. Additionally or alternatively, each treatment cycle only contains one administration. In one embodiment, the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) is administered to the subject intravenously. In one embodiment, each treatment cycle is 3 weeks ± 3 days. Additionally or alternatively, the subject undergoes 1, or 2, or 3 or more treatment cycles and receives one administration on the first day of each treatment cycle. In one embodiment, the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) is administered to the subject at least 19 days apart. In one embodiment, a method of treating cancer in a subject comprises administering the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4- ADC-1) to the subject at a dose of about 0.3 mg / kg to about 3.5 mg / kg of the ADC. In one embodiment, a method of treating cancer in a subject comprises administering the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) to the subject at a dose of about 1 mg / kg to about 3.5 mg / kg of the ADC. In one embodiment, a method of treating cancer in a subject comprises administering the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) to the subject at a dose of about 0.3 mg / kg to about 2.0 mg / kg of the ADC. In one embodiment, a method of treating cancer in a subject comprises administering the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating 95 NAI-1541858741(L-1a’) (such as 5T4-ADC-1) to the subject at a dose of about 0.3 mg / kg of the ADC. In one embodiment, a method of treating cancer in a subject comprises administering the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) to the subject at a dose of about 0.6 mg / kg of the ADC. In one embodiment, a method of treating cancer in a subject comprises administering the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) to the subject at a dose of about 1 mg / kg of the ADC. In one embodiment, a method of treating cancer in a subject comprises administering the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) to the subject at a dose of about 1.5 mg / kg of the ADC. In one embodiment, a method of treating cancer in a subject comprises administering the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) to the subject at a dose of about 2 mg / kg of the ADC. As it would be understood by one of skill in the art, an equivalent dose, such as a dose as disclosed herein converted to ADC amount per body surface area, is also included herein. Methods of such a conversion can be found, for example, Nair AB, Jacob S. J Basic Clin Pharm.2016 Mar;7(2):27-31, which is incorporated herein by reference in its entirety. In one embodiment, the length of treatment during which the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’), is administered to the subject is about four to about twenty-four months. In one embodiment, the length of treatment is about four to about eighteen months. In one embodiment, the length of treatment is about four to about twelve months. In one embodiment, the length of treatment is about four to about six months.

[0292] In one embodiment, the cancer treated by the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) is a cancer selected from the group consisting of breast cancer, endometrial cancer, head and neck cancer, pancreatic cancer, lung cancer, prostate cancer, cervical cancer, or bladder cancer. In one embodiment, the cancer is TNBC. In one embodiment, the cancer is HR+ BC. In one embodiment, the cancer is PDAC. In certain embodiments, the cancer is lung adenocarcinoma or squamous cell lung carcinoma. In one embodiment, the cancer is NSCLC. In some embodiments, the cancer is head and neck cancer. In one embodiment, the cancer is HNSCC. In one embodiment, the NSCLC is characterized by a mutation selected from the group consisting of an EGFR sensitizing mutation, an ALK rearrangement, a ROS1 rearrangement, a BRAF V600E mutation, a MET Exon 14 skipping mutation, and a RET 96 NAI-1541858741rearrangement. In certain embodiments, the cancer is renal cell carcinoma (RCC), hepatocellular carcinoma (HCC), or colorectal cancer. In some embodiments, the cancer is a genitourinary cancer. In some embodiments, the cancer is a gastrointestinal cancer. In some embodiments, the cancer is a gynecological cancer. Additionally or alternatively, the cancer is previously untreatable. Additionally or alternatively, the cancer is recurrent. Additionally or alternatively, the cancer is metastatic. Additionally or alternatively, the cancer is advanced, for example locally advanced. Additionally or alternatively, the cancer is inoperable. 7.4.2 Combination Therapy

[0293] In one embodiment, the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) is administered at a therapeutically effective dose to a subject in combination with a therapeutically effective dose of a second chemotherapeutic agent to treat a cancer. In one embodiment, the second chemotherapeutic agent is a PD-1 / PD-L1 inhibitor. In one embodiment, the PD-1 / PD-L1 inhibitor is pembrolizumab. In one embodiment, the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) and the second therapeutic agent, e.g., a PD-1 / PD-L1 inhibitor or pembrolizumab, is administered periodically to the subject (e.g., once every treatment cycle) at a therapeutically effective dose, when the periodic administration is continued for a certain length of time (“length of treatment”) and / or certain number of treatment cycles. In one embodiment, 200 mg of pembrolizumab is administered to the subject in combination with a therapeutically effective amount of the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4- ADC-1).

[0294] In one embodiment, a method for treating cancer in a subject comprises administering the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) to the subject at a dose of about 0.3 mg / kg to about 5.0 mg / kg and a PD-1 / PD-L1 inhibitor, such as 200 mg pembrolizumab, for one or more treatment cycles. In one embodiment, each dose of the ADC is administered to the subject on the first day of each treatment cycle. In one embodiment, the PD-1 / PD-L1 inhibitor, e.g., 200 mg pembrolizumab, is administered to the subject on the same day of each treatment cycle as the ADC. In one embodiment, the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) is administered to the subject intravenously. In one embodiment, pembrolizumab is 97 NAI-1541858741administered to the subject intravenously. In one embodiment, each treatment cycle is 3 weeks ± 3 days. In one embodiment, the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) is administered to the subject at least 19 days apart. In one embodiment, the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) is administered to the subject at a dose of about 0.3 mg / kg to about 3.5 mg / kg. In one embodiment, the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) is administered to the subject at a dose of about 1 mg / kg to about 3.5 mg / kg. In one embodiment, the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) is administered to the subject at a dose of about 0.3 mg / kg to about 2.0 mg / kg. In one embodiment, the method of treating cancer in a subject comprises administering the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) to the subject at a dose of about 0.3 mg / kg of the ADC. In one embodiment, the method of treating cancer in a subject comprises administering the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L- 1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) to the subject at a dose of about 0.6 mg / kg of the ADC. In one embodiment, the method of treating cancer in a subject comprises administering the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) to the subject at a dose of about 1 mg / kg of the ADC. In one embodiment, the method of treating cancer in a subject comprises administering the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) to the subject at a dose of about 1.5 mg / kg of the ADC. In one embodiment, the method of treating cancer in a subject comprises administering the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) to the subject at a dose of about 2 mg / kg of the ADC. As it would be understood by one of skill in the art, an equivalent dose, such as a dose as disclosed herein converted to ADC amount per body surface area, is also included herein. Methods of such a conversion can be found, for example, Nair AB, Jacob S. J Basic Clin Pharm.2016 Mar;7(2):27- 31, which is incorporated herein by reference in its entirety. In one embodiment, the length of treatment during which the ADC (such as 5T4-ADC-1) is administered to the subject is about four to about twenty-four months. In one embodiment, the length of treatment is about four to 98 NAI-1541858741about eighteen months. In one embodiment, the length of treatment is about four to about twelve months. In one embodiment, the length of treatment is about six months.

[0295] In one embodiment, the cancer treated by the combination of the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) and pembrolizumab is a cancer selected from the group consisting of breast cancer, endometrial cancer, head and neck cancer, pancreatic cancer, lung cancer, prostate cancer, cervical cancer, or bladder cancer. In one embodiment, the cancer is TNBC. In one embodiment, the cancer is HR+ BC. In one embodiment, the cancer is PDAC. In certain embodiments, the cancer is lung adenocarcinoma or squamous cell lung carcinoma. In one embodiment, the cancer is NSCLC. In some embodiments, the cancer is head and neck cancer. In one embodiment, the cancer is HNSCC. In one embodiment, the NSCLC is characterized by a mutation selected from the group consisting of an EGFR sensitizing mutation, an ALK rearrangement, a ROS1 rearrangement, a BRAF V600E mutation, a MET Exon 14 skipping mutation, and a RET rearrangement. In certain embodiments, the cancer treated by the combination of the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) and pembrolizumab is a cancer selected from the group consisting of renal cell carcinoma (RCC), hepatocellular carcinoma (HCC), or colorectal cancer. In some embodiments, the cancer is a genitourinary cancer. In some embodiments, the cancer is a gastrointestinal cancer. In some embodiments, the cancer is a gynecological cancer. Additionally or alternatively, the cancer is previously untreatable. Additionally or alternatively, the cancer is recurrent. Additionally or alternatively, the cancer is metastatic. Additionally or alternatively, the cancer is advanced, for example locally advanced. Additionally or alternatively, the cancer is inoperable. 7.4.3 Adverse Events

[0296] A subject that has been administered the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) and / or pembrolizumab according to any dosing regimen disclosed herein (e.g., any as disclosed in any of sections 7.4.1 through 7.4.2) may, in any embodiment, undergo monitoring for adverse events (AEs). A subject may experience one or more treatment-related AEs due to the ADC and / or pembrolizumab. As such, it may be prudent to adjust the dose of the ADC and / or discontinue administration of the ADC and / or pembrolizumab until the subject recovers from the adverse event. 99 NAI-1541858741

[0297] AEs are characterized as one of five grades—grade 1 is a mild AE; grade 2 is a moderate AE; grade 3 is a severe AE; grade 4 is a life-threatening or disabling AE; and grade 5 is death related to AE. The grading of AEs is based on the guidelines provided in the CTCAE version 6.0. Non-limiting examples of adverse events that may prompt dose adjustment and / or discontinuation of administration include Grade 3 thrombocytopenia with clinically significant bleeding, Grade 4 thrombocytopenia, Grade 3 or higher neutropenia with a measured fever of at least 38.3°C, Grade 3 or higher neutropenia with a sustained fever of at least 38°C for at least an hour, Grade 4 neutropenia for greater than 7 days, Grade 4 anemia, alanine transaminase or aspartate transaminase levels that are greater than 3 times the upper limit of normal and a total bilirubin level that is greater than 2 times the upper limit of normal in the absence of biliary obstruction or other explanation for liver abnormality (such as viral hepatitis, alcohol or autoimmune hepatitis, Gilbert Syndrome, or treatment with other hepatotoxic drug), and any Grade 5 adverse event.

[0298] In one embodiment, the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) is administered at a therapeutically effective dose optionally in combination with pembrolizumab for one or more treatment cycles to a subject to treat a cancer according to any dosing regimen disclosed herein (e.g., any as disclosed in any of sections 7.4.1 through 7.4.2) and the subject experiences an AE. Administration of the ADC to the subject is then interrupted until such time as the subject has recovered from the AE, at which time the administration of the ADC is resumed. In some embodiments, when the subject is administered the ADC in combination with pembrolizumab, only administration of the ADC is interrupted until such time as the subject has recovered from the AE, at which time the administration of the ADC is resumed.

[0299] In one embodiment, the ADC as disclosed herein, for example those of Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’) (such as 5T4-ADC-1) is administered at a therapeutically effective dose optionally in combination with pembrolizumab for one or more treatment cycles to a subject to treat a cancer according to any dosing regimen disclosed herein (e.g., any as disclosed in any of sections 7.4.1 through 7.4.2) and the subject experiences an AE. The dose of the ADC is then reduced in one or more subsequent treatment cycles until such time as the subject has recovered from the AE, at which time the administration of the ADC at the dose that was administered prior to the AE is resumed. In some embodiments, when the subject is administered the ADC in combination with pembrolizumab, the dose of the ADC is reduced until such time as the subject has recovered from the AE, at which time the administration of the ADC at the dose that was administered prior to the AE is resumed. 100 NAI-1541858741

[0300] Recovery from the AE may be assessed by measurements, such as by measure of subject’s body temperature, alanine transaminase or aspartate transaminase levels, total bilirubin level, and / or blood counts (e.g., absolute neutrophil count (ANC) and / or platelet count). For example, a subject may be considered to have recovered from an AE when their ANC reaches a certain threshold, e.g., ≥ 1,500 cells / µL, ≥ 1,000 cells / µL, or ≥ 500 cells / µL, and / or their platelet count reaches a certain threshold, e.g., ≥ 100,000 cells / μL, ≥ 75,000 cells / μL, ≥ 50,000 cells / μL, or ≥ 25,000 cells / μL, for up to 14 days.

[0301] In one aspect, provided is a method of treating a cancer for two or more treatment cycles in a subject experiencing an adverse event when administered an ADC. The method comprises: (i) administering the ADC to the subject at a dose of about 0.1 mg / kg to about 10.0 mg / kg in a first treatment cycle; (ii) delaying a further administration of the ADC to the subject upon the subject having an adverse event after the first treatment cycle and before the second treatment cycle; and (iii) resuming the administration of the ADC in a second treatment cycle. In some embodiments, the ADC is as disclosed herein, for example those represented by Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’). Additionally or alternatively, the ADC comprises an Ab conjugated to a monomethyl auristatin E (MMAE) by linker (L-1).In some embodiments, the Ab is a 5T4 antibody or an antigen binding fragment thereof and comprises a heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), a heavy chain complementarity determining region 3 (HCDR3), a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and a light chain complementarity determining region 3 (LCDR3) of an antibody designated mAbA15. In some embodiments, the Ab further comprises two motifs, each of which is L(fGly’)TPSR (SEQ ID NO: 1), wherein fGly’ is the amino acid residue to which a linker-drug comprising linker (L-1) is attached. In some embodiments, mAbA15 comprises: a) a heavy chain comprising an amino acid sequence of: EVQLVESGGGLVQPGGSLRLSCAASGFTFSSYYIHWVRQAPGKGLEWVAYITSTGSYTEYADSVK 101 NAI-1541858741GRFTISADTSKNTAYLQMNSLRAEDTAVYYCARYDRSTRYSGLDYWGQGTLVTVSSASTKGPSVF PLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSS SLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRT PEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKC KVSNKALPAPIEKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQ PENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGSL (fGly’)TPSRGS (SEQ ID NO: 2); and b) a light chain comprising an amino acid sequence of: DIQMTQSPSSLSASVGDRVTITCRASQSVSSAVAWYQQKPGKAPKLLIYSASSLYSGVPSRFSGS RSGTDFTLTISSLQPEDFATYYCQQAYATPVTFGQGTKVEIKRTVAAPSVFIFPPSDEQLKSGTA SVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACE VTHQGLSSPVTKSFNRGEC (SEQ ID NO: 3). In some embodiments, the Ab is mAbA15. Additionally or alternatively, fGly’ is the amino acid residue to which a linker-drug of Formula (II) is attached:wherein the wavy line indicates the point of attachment to the Ab and MMAE is represented by Formula (III):wherein * indicates the point of attachment in Formula (II). In some embodiments, the ADC is 5T4-ADC-1. In some embodiments, the administration is resumed in step (iii) once the adverse event is alleviated or recovered. In some embodiments, the administration of the second treatment cycle is at the dose of the first treatment cycle. In some embodiments, the administration of the second treatment cycle is at a dose lower than that of the first treatment cycle.

[0302] In one aspect, provided is a method of treating a cancer for two or more treatment cycles in a subject experiencing an adverse event when administered an ADC. The method comprises: i) administering the ADC to the subject at a first dose of about 0.1 mg / kg to about 10.0 mg / kg in a first treatment cycle; ii) in a second treatment cycle, administering the ADC to 102 NAI-1541858741the subject at a second dose which is lower than the first dose upon the subject having an adverse event. In some embodiments, the ADC is as disclosed herein, for example those represented by Formula (I) or Formula (I’), or comprising (L-1), or produced by conjugating (L-1a’). In some embodiments, the ADC comprises an Ab conjugated to a monomethyl auristatin E (MMAE) by linker (L-1) (also illustrated as (L-1’)).In some embodiments, the Ab is a 5T4 antibody or an antigen binding fragment thereof and comprises a heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), a heavy chain complementarity determining region 3 (HCDR3), a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and a light chain complementarity determining region 3 (LCDR3) of an antibody designated mAbA15. In some embodiments, the Ab further comprises two motifs, each of which is L(fGly’)TPSR (SEQ ID NO: 1), wherein fGly’ is the amino acid residue to which a linker-drug comprising linker (L-1) is attached. In some embodiments, mAbA15 comprises: a) a heavy chain comprising an amino acid sequence of: EVQLVESGGGLVQPGGSLRLSCAASGFTFSSYYIHWVRQAPGKGLEWVAYITSTGSYTEYADSVK GRFTISADTSKNTAYLQMNSLRAEDTAVYYCARYDRSTRYSGLDYWGQGTLVTVSSASTKGPSVF PLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSS SLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRT PEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKC KVSNKALPAPIEKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQ PENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGSL (fGly’)TPSRGS (SEQ ID NO: 2); and b) a light chain comprising an amino acid sequence of: DIQMTQSPSSLSASVGDRVTITCRASQSVSSAVAWYQQKPGKAPKLLIYSASSLYSGVPSRFSGS RSGTDFTLTISSLQPEDFATYYCQQAYATPVTFGQGTKVEIKRTVAAPSVFIFPPSDEQLKSGTA SVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACE VTHQGLSSPVTKSFNRGEC (SEQ ID NO: 3). In some embodiments, the Ab is mAbA15. 103 NAI-1541858741Additionally or alternatively, fGly’ is the amino acid residue to which a linker-drug of Formula (II) is attached:wherein the wavy line indicates the point of attachment to the Ab and MMAE is represented by Formula (III):wherein * indicates the point of attachment in Formula (II). In some embodiments, the ADC is 5T4-ADC-1. In some embodiments, the subject is administered at the second dose in step (ii) once the adverse event is alleviated or recovered. In some embodiments, the subject is administered with the ADC once every 3 weeks (q3w).

[0303] In some embodiments, the adverse event is selected from the group consisting of Grade 3 thrombocytopenia with clinically significant bleeding, Grade 4 thrombocytopenia, Grade 3 or higher neutropenia with a measured fever of at least 38.3°C, Grade 3 or higher neutropenia with a sustained fever of at least 38°C for at least an hour, Grade 4 neutropenia for greater than 7 days, Grade 4 anemia, alanine transaminase or aspartate transaminase levels that are greater than 3 times the upper limit of normal and a total bilirubin level that is greater than 2 times the upper limit of normal in the absence of biliary obstruction or other explanation for liver abnormality (such as viral hepatitis, alcohol or autoimmune hepatitis, Gilbert Syndrome, or treatment with other hepatotoxic drug), and a Grade 5 adverse event.

[0304] In some embodiments, the Ab comprises two heavy chains (HCs) and two light chains (LCs), and wherein each of the HCs comprises one motif of L(fGly’)TPSR (SEQ ID NO: 1). In some embodiments, the Ab is mAbA15.

[0305] In some embodiments, the ADC is administered to the subject on the first day of each treatment cycle. In further embodiments, each treatment cycle is 3 weeks ± 3 days.

[0306] In some embodiments, the ADC is administered to the subject intravenously. 104 NAI-1541858741

[0307] In some embodiments, the method further comprises administering to the subject a PD-L1 / PD-1 inhibitor. In some embodiments, the subject is administered with a PD-L1 / PD-1 inhibitor. In some embodiments, the ADC is administered concurrently with the PD-L1 / PD-1 inhibitor. In some embodiments, the ADC is administered after the PD-L1 / PD-1 inhibitor. In some embodiments, the ADC is administered before the PD-L1 / PD-1 inhibitor. In some embodiments, the ADC is administered on the same day with the PD-L1 / PD-1 inhibitor. In some embodiments, the administrations of the ADC and the PD-L1 / PD-1 inhibitor is at least about 30 minutes apart or at least about 1 hour apart. In some embodiments, the PD-L1 / PD-1 inhibitor is administered to the subject on the first day of each treatment cycle. In some embodiments, the PD-L1 / PD-1 inhibitor is administered to the subject once every three weeks (q3w). In some embodiments, the PD-L1 / PD-1 inhibitor is administered to the subject intravenously. In some embodiments, the PD-L1 / PD-1 inhibitor is an antibody or an antigen binding fragment thereof comprising HCDR1, HCDR2, HCDR3, LCDR1, LCDR2, and LCDR3 of pembrolizumab. In some embodiments, the PD-L1 / PD-1 inhibitor is pembrolizumab. In some embodiments, the PD- L1 / PD-1 inhibitor is administered to the subject at a dose of about 200 mg.

[0308] In some embodiments, the ADC is administered to the subject in the first treatment cycle at a dose of about 0.3 mg / kg to about 6.0 mg / kg. In some embodiments, the ADC is administered to the subject in the first treatment cycle at a dose of about 0.3 mg / kg to about 2.0 mg / kg. In some embodiments, the ADC is administered to the subject in the first treatment cycle at a dose of about 0.3 mg / kg, about 0.6 mg / kg, about 1.0 mg / kg, about 1.5 mg / kg, or about 2.0 mg / kg.

[0309] In some embodiments, the cancer is breast cancer, endometrial cancer, head and neck cancer, pancreatic cancer, lung cancer, prostate cancer, cervical cancer, or bladder cancer. In some embodiments, the cancer is triple-negative breast cancer (TNBC) or hormone-receptor positive breast cancer (HR+ BC). In some embodiments, the cancer is pancreatic adenocarcinoma (PDAC, also referred to herein as pancreatic ductal adenocarcinoma). In certain embodiments, the cancer is lung adenocarcinoma or squamous cell lung carcinoma. In some embodiments, the cancer is non-small cell lung cancer (NSCLC). In further embodiments, the subject has one or more mutations selected from the group consisting of an EGFR sensitizing mutation, an ALK rearrangement, a ROS1 rearrangement, a BRAF V600E mutation, a MET Exon 14 skipping mutation, and a RET rearrangement. In some embodiments, the cancer of the subject has one or more mutations selected from the group consisting of an EGFR sensitizing mutation, an ALK rearrangement, a ROS1 rearrangement, a BRAF V600E mutation, a MET Exon 14 skipping mutation, and a RET rearrangement. In some embodiments, the cancer is head and neck cancer. 105 NAI-1541858741In some embodiments, the cancer is head and neck squamous cell carcinoma (HNSCC). In certain embodiments, the cancer is renal cell carcinoma (RCC), hepatocellular carcinoma (HCC), or colorectal cancer. In some embodiments, the cancer is a genitourinary cancer. In some embodiments, the cancer is a gastrointestinal cancer. In some embodiments, the cancer is a gynecological cancer. Additionally or alternatively, the cancer is previously untreatable. Additionally or alternatively, the cancer is recurrent. Additionally or alternatively, the cancer is metastatic. Additionally or alternatively, the cancer is advanced, for example locally advanced. Additionally or alternatively, the cancer is inoperable.

[0310] In some embodiments, the ADC is administered to the subject for about four to about twenty-four months. In some embodiments, the ADC is administered to the subject for about four to about eighteen months. In some embodiments, the ADC is administered to the subject for about four to about twelve months. In some embodiments, the ADC is administered to the subject for about four to about six months.

[0311] In some embodiments, the subject is human. 8. EMBODIMENTS

[0312] 1. A method for treating cancer in a subject, the method comprising administering an ADC to the subject, wherein the cancer is any one or more of breast cancer, endometrial cancer, head and neck cancer, pancreatic cancer, lung cancer, prostate cancer, cervical cancer, bladder cancer, renal cell carcinoma (RCC), hepatocellular carcinoma (HCC), or colorectal cancer; wherein the ADC is represented by Formula (I’):(I’), wherein the Ab is a 5T4 antibody or an antigen binding fragment thereof, and wherein the Ab comprises: (1) a heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), and a heavy chain complementarity determining region 3 (HCDR3) as set forth in a heavy chain variable region (VH) comprising the 106 NAI-1541858741amino acid sequence of SEQ ID NO: 11, and (2) a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and a light chain complementarity determining region 3 (LCDR3) as set forth in a light chain variable region (VL) comprising the amino acid sequence of SEQ ID NO: 12; wherein the Ab further comprises one or more fGly’, wherein fGly’ is a formylglycine amino acid residue to which the non-Ab part of Formula (I’) is attached; wherein the MMAE is monomethyl auristatin E and represented by Formula (III):wherein * indicates the point of attachment in Formula (I’); and wherein n is an integer.

[0313] 2. The method of embodiment 1, wherein n is an integer selected from any one of 1 to 10.

[0314] 3. The method of embodiment 1 or 2, wherein n is 2 and wherein the ADC is represented by Formula (I):wherein the * in Formula (III) indicates the point of attachment in Formula (I) and wherein fGly’ is a formylglycine amino acid residue to which the non-Ab part of Formula (I) is attached.

[0315] 4. A method for treating cancer in a subject, the method comprising administering an ADC to the subject, wherein the cancer is any one or more of breast cancer, endometrial cancer, head and neck cancer, pancreatic cancer, lung cancer, prostate cancer, cervical cancer, bladder cancer, renal cell carcinoma (RCC), hepatocellular carcinoma (HCC), or colorectal cancer, wherein the ADC is represented by Formula (I): 107 NAI-1541858741wherein the Ab is a 5T4 antibody or an antigen binding fragment thereof and comprises a heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), a heavy chain complementarity determining region 3 (HCDR3), a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and a light chain complementarity determining region 3 (LCDR3) of an antibody designated mAbA15, wherein the Ab further comprises two motifs, each of which is L(fGly’)TPSR (SEQ ID NO: 1), wherein fGly’ is the amino acid residue to which the non-Ab part of the ADC represented by Formula (I) is attached, and wherein mAbA15 comprises: a) a heavy chain comprising an amino acid sequence of: EVQLVESGGGLVQPGGSLRLSCAASGFTFSSYYIHWVRQAPGKGLEWVAYITSTGSYTEYADSVK GRFTISADTSKNTAYLQMNSLRAEDTAVYYCARYDRSTRYSGLDYWGQGTLVTVSSASTKGPSVF PLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSS SLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRT PEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKC KVSNKALPAPIEKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQ PENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGSL(fGl y’)TPSRGS (SEQ ID NO: 2); and b) a light chain comprising an amino acid sequence of: DIQMTQSPSSLSASVGDRVTITCRASQSVSSAVAWYQQKPGKAPKLLIYSASSLYSGVPSRFSGS RSGTDFTLTISSLQPEDFATYYCQQAYATPVTFGQGTKVEIKRTVAAPSVFIFPPSDEQLKSGTA SVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACE VTHQGLSSPVTKSFNRGEC (SEQ ID NO: 3); and wherein the MMAE is monomethyl auristatin E and represented by Formula (III): 108 NAI-1541858741wherein * indicates the point of attachment in Formula (I).

[0316] 5. A method for treating cancer in a subject, the method comprising administering an ADC to the subject, wherein the cancer is any one or more of breast cancer, endometrial cancer, head and neck cancer, pancreatic cancer, lung cancer, prostate cancer, cervical cancer, bladder cancer, renal cell carcinoma (RCC), hepatocellular carcinoma (HCC), or colorectal cancer; wherein the ADC comprises an antibody (Ab) conjugated to a monomethyl auristatin E (MMAE) by a linker (L-1):(L-1), wherein the wavy line indicates the point of attachment to the Ab and the ## indicates the point of attachment to the MMAE; wherein the MMAE is represented by Formula (III):wherein * indicates the point of attachment to (L-1); wherein the Ab is a 5T4 antibody or an antigen binding fragment thereof, and wherein the Ab comprises: (1) a heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), and a heavy chain complementarity determining region 3 (HCDR3) as set forth in a heavy chain variable region (VH) comprising the amino acid sequence of SEQ ID NO: 11, and (2) a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and a light 109 NAI-1541858741chain complementarity determining region 3 (LCDR3) as set forth in a light chain variable region (VL) comprising the amino acid sequence of SEQ ID NO: 12; and wherein the Ab further comprises one or more fGly’ and wherein fGly’ is a formylglycine amino acid residue to which linker (L-1) is attached.

[0317] 6. The method of embodiment 5, wherein one Ab is conjugated to one to ten MMAEs and wherein each MMAE is conjugated to Ab by one linker (L-1).

[0318] 7. The method of embodiment 5 or 6, wherein one Ab is conjugated to two MMAEs and wherein each MMAE is conjugated to Ab by one linker (L-1).

[0319] 8. A method for treating cancer in a subject, the method comprising administering an ADC to the subject, wherein the cancer is any one or more of breast cancer, endometrial cancer, head and neck cancer, pancreatic cancer, lung cancer, prostate cancer, cervical cancer, bladder cancer, renal cell carcinoma (RCC), hepatocellular carcinoma (HCC), or colorectal cancer, wherein the ADC comprises an antibody (Ab) conjugated to a monomethyl auristatin E (MMAE) by a linker (L-1):(L-1), wherein the wavy line indicates the point of attachment to the Ab and the ## indicates the point of attachment to the MMAE; wherein the MMAE is represented by Formula (III):wherein * indicates the point of attachment to (L-1); and wherein the Ab is a 5T4 antibody or an antigen binding fragment thereof and comprises a heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), a heavy chain complementarity determining region 3 (HCDR3), a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and a light chain complementarity determining region 3 110 NAI-1541858741(LCDR3) of an antibody designated mAbA15, wherein the Ab further comprises two motifs, each of which is L(fGly’)TPSR (SEQ ID NO: 1), wherein fGly’ is the amino acid residue to which linker (L-1) is attached, and wherein mAbA15 comprises a heavy chain comprising an amino acid sequence of SEQ ID NO: 2 and a light chain comprising an amino acid sequence of SEQ ID NO: 3.

[0320] 9. A method for treating cancer in a subject, the method comprising administering an ADC to the subject, wherein the cancer is any one or more of breast cancer, endometrial cancer, head and neck cancer, pancreatic cancer, lung cancer, prostate cancer, cervical cancer, bladder cancer, renal cell carcinoma (RCC), hepatocellular carcinoma (HCC), or colorectal cancer, wherein the ADC is produced by conjugating an antibody (Ab) to a linker-drug comprising a pre- conjugate linker (L-1a’) and a monomethyl auristatin E (MMAE):(L-1a’), wherein the ## indicates the point of attachment to the MMAE; wherein the MMAE is represented by Formula (III):wherein * indicates the point of attachment to (L-1a’); wherein the Ab is a 5T4 antibody or an antigen binding fragment thereof, and wherein the Ab comprises: (1) a heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), and a heavy chain complementarity determining region 3 (HCDR3) as set forth in a heavy chain variable region (VH) comprising the amino acid sequence of SEQ ID NO: 11, and (2) a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and a light 111 NAI-1541858741chain complementarity determining region 3 (LCDR3) as set forth in a light chain variable region (VL) comprising the amino acid sequence of SEQ ID NO: 12; and wherein the Ab further comprises one or more fGly’ and wherein fGly’ is a formylglycine amino acid residue to which linker (L-1a’) is attached after conjugating the Ab and the linker-drug.

[0321] 10. The method of embodiment 9, wherein one Ab is conjugated to one to ten linker- drugs.

[0322] 11. The method of embodiment 9 or 10, wherein one Ab is conjugated to two linker- drugs.

[0323] 12. A method for treating cancer in a subject, the method comprising administering an ADC to the subject, wherein the cancer is any one or more of breast cancer, endometrial cancer, head and neck cancer, pancreatic cancer, lung cancer, prostate cancer, cervical cancer, bladder cancer, renal cell carcinoma (RCC), hepatocellular carcinoma (HCC), or colorectal cancer, wherein the ADC is produced by conjugating an antibody (Ab) to a linker-drug comprising a pre- conjugate linker (L-1a’) and a monomethyl auristatin E (MMAE):wherein the ## indicates the point of attachment to the MMAE; wherein the MMAE is represented by Formula (III):wherein * indicates the point of attachment to (L-1a’); and wherein the Ab is a 5T4 antibody or an antigen binding fragment thereof and comprises a heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), a heavy chain complementarity determining region 3 (HCDR3), a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and a light chain complementarity determining region 3 (LCDR3) of an antibody designated mAbA15, wherein the Ab further comprises two motifs, each of which is L(fGly’)TPSR (SEQ ID NO: 1), wherein fGly’ is the amino acid residue to 112 NAI-1541858741which (L-1a’) is attached after the conjugation, and wherein mAbA15 comprises a heavy chain comprising an amino acid sequence of SEQ ID NO: 2 and a light chain comprising an amino acid sequence of SEQ ID NO: 3.

[0324] 13. The method of any one of embodiments 1-12, wherein the ADC is administered to the subject at a dose of about 0.1 mg / kg to about 10.0 mg / kg.

[0325] 14. A method for treating cancer in a subject, the method comprising administering an ADC to the subject at a dose of about 0.1 mg / kg to about 10.0 mg / kg, wherein the ADC is represented by Formula (I’):(I’), wherein the Ab is a 5T4 antibody or an antigen binding fragment thereof, and wherein the Ab comprises: (1) a heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), and a heavy chain complementarity determining region 3 (HCDR3) as set forth in a heavy chain variable region (VH) comprising the amino acid sequence of SEQ ID NO: 11, and (2) a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and a light chain complementarity determining region 3 (LCDR3) as set forth in a light chain variable region (VL) comprising the amino acid sequence of SEQ ID NO: 12; wherein the Ab further comprises one or more fGly’, wherein fGly’ is a formylglycine amino acid residue to which the non-Ab part of Formula (I’) is attached; wherein the MMAE is monomethyl auristatin E and represented by Formula (III):wherein * indicates the point of attachment in Formula (I’); and wherein n is an integer. 113 NAI-1541858741

[0326] 15. The method of embodiment 14, wherein n is an integer selected from any one of 1 to 10.

[0327] 16. The method of embodiment 14 or 15, wherein n is 2 and wherein the ADC is represented by Formula (I):wherein the * in Formula (III) indicates the point of attachment in Formula (I) and wherein fGly’ is a formylglycine amino acid residue to which the non-Ab part of Formula (I) is attached.

[0328] 17. A method for treating cancer in a subject, the method comprising administering an ADC to the subject at a dose of about 0.1 mg / kg to about 10.0 mg / kg, wherein the ADC is represented by Formula (I):wherein the Ab is a 5T4 antibody or an antigen binding fragment thereof and comprises a heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), a heavy chain complementarity determining region 3 (HCDR3), a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and a light chain complementarity determining region 3 (LCDR3) of an antibody designated mAbA15, wherein the Ab further comprises two motifs, each of which is L(fGly’)TPSR (SEQ ID NO: 1), wherein fGly’ is the amino acid residue to which the non-Ab part of the ADC represented by Formula (I) is attached, and wherein mAbA15 comprises: a) a heavy chain comprising an amino acid sequence of: 114 NAI-1541858741EVQLVESGGGLVQPGGSLRLSCAASGFTFSSYYIHWVRQAPGKGLEWVAYITSTGSYTEY ADSVKGRFTISADTSKNTAYLQMNSLRAEDTAVYYCARYDRSTRYSGLDYWGQGTLVTVS SASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQS SGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLG GPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQY NSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRE EMTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSR WQQGNVFSCSVMHEALHNHYTQKSLSLSPGSL(fGly’)TPSRGS (SEQ ID NO: 2); and b) a light chain comprising an amino acid sequence of: DIQMTQSPSSLSASVGDRVTITCRASQSVSSAVAWYQQKPGKAPKLLIYSASSLYSGVPS RFSGSRSGTDFTLTISSLQPEDFATYYCQQAYATPVTFGQGTKVEIKRTVAAPSVFIFPP SDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLT LSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 3); and wherein the MMAE is monomethyl auristatin E and represented by Formula (III):wherein * indicates the point of attachment in Formula (I).

[0329] 18. A method for treating cancer in a subject, the method comprising administering an ADC to the subject at a dose of about 0.1 mg / kg to about 10.0 mg / kg, wherein the ADC comprises an antibody (Ab) conjugated to a monomethyl auristatin E (MMAE) by a linker (L-1):(L-1), wherein the wavy line indicates the point of attachment to the Ab and the ## indicates the point of attachment to the MMAE; wherein the MMAE is represented by Formula (III): 115 NAI-1541858741wherein * indicates the point of attachment to (L-1); wherein the Ab is a 5T4 antibody or an antigen binding fragment thereof, and wherein the Ab comprises: (1) a heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), and a heavy chain complementarity determining region 3 (HCDR3) as set forth in a heavy chain variable region (VH) comprising the amino acid sequence of SEQ ID NO: 11, and (2) a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and a light chain complementarity determining region 3 (LCDR3) as set forth in a light chain variable region (VL) comprising the amino acid sequence of SEQ ID NO: 12; and wherein the Ab further comprises one or more fGly’ and wherein fGly’ is a formylglycine amino acid residue to which linker (L-1) is attached.

[0330] 19. The method of embodiment 18, wherein one Ab is conjugated to one to ten MMAEs and wherein each MMAE is conjugated to Ab by one linker (L-1).

[0331] 20. The method of embodiment 18 or 19, wherein one Ab is conjugated to two MMAEs and wherein each MMAE is conjugated to Ab by one linker (L-1).

[0332] 21. A method for treating cancer in a subject, the method comprising administering an ADC to the subject at a dose of about 0.1 mg / kg to about 10.0 mg / kg, wherein the ADC comprises an antibody (Ab) conjugated to a monomethyl auristatin E (MMAE) by a linker (L-1):(L-1), wherein the wavy line indicates the point of attachment to the Ab and the ## indicates the point of attachment to the MMAE; wherein the MMAE is represented by Formula (III): 116 NAI-1541858741wherein * indicates the point of attachment to (L-1); and wherein the Ab is a 5T4 antibody or an antigen binding fragment thereof and comprises a heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), a heavy chain complementarity determining region 3 (HCDR3), a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and a light chain complementarity determining region 3 (LCDR3) of an antibody designated mAbA15, wherein the Ab further comprises two motifs, each of which is L(fGly’)TPSR (SEQ ID NO: 1), wherein fGly’ is the amino acid residue to which linker (L-1) is attached, and wherein mAbA15 comprises a heavy chain comprising an amino acid sequence of SEQ ID NO: 2 and a light chain comprising an amino acid sequence of SEQ ID NO: 3.

[0333] 22. A method for treating cancer in a subject, the method comprising administering an ADC to the subject at a dose of about 0.1 mg / kg to about 10.0 mg / kg, wherein the ADC is produced by conjugating an antibody (Ab) to a linker-drug comprising a pre-conjugate linker (L- 1a’) and a monomethyl auristatin E (MMAE):(L-1a’), wherein the ## indicates the point of attachment to the MMAE; wherein the MMAE is represented by Formula (III):wherein * indicates the point of attachment to (L-1a’); 117 NAI-1541858741wherein the Ab is a 5T4 antibody or an antigen binding fragment thereof, and wherein the Ab comprises: (1) a heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), and a heavy chain complementarity determining region 3 (HCDR3) as set forth in a heavy chain variable region (VH) comprising the amino acid sequence of SEQ ID NO: 11, and (2) a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and a light chain complementarity determining region 3 (LCDR3) as set forth in a light chain variable region (VL) comprising the amino acid sequence of SEQ ID NO: 12; and wherein the Ab further comprises one or more fGly’ and wherein fGly’ is a formylglycine amino acid residue to which linker (L-1a’) is attached after conjugating the Ab and the linker-drug.

[0334] 23. The method of embodiment 22, wherein one Ab is conjugated to one to ten linker- drugs.

[0335] 24. The method of embodiment 22 or 23, wherein one Ab is conjugated to two linker- drugs.

[0336] 25. A method for treating cancer in a subject, the method comprising administering an ADC to the subject at a dose of about 0.1 mg / kg to about 10.0 mg / kg, wherein the ADC is produced by conjugating an antibody (Ab) to a linker-drug comprising a pre-conjugate linker (L- 1a’) and a monomethyl auristatin E (MMAE):(L-1a’), wherein the ## indicates the point of attachment to the MMAE; wherein the MMAE is represented by Formula (III):wherein * indicates the point of attachment to (L-1a’); and 118 NAI-1541858741wherein the Ab is a 5T4 antibody or an antigen binding fragment thereof and comprises a heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), a heavy chain complementarity determining region 3 (HCDR3), a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and a light chain complementarity determining region 3 (LCDR3) of an antibody designated mAbA15, wherein the Ab further comprises two motifs, each of which is L(fGly’)TPSR (SEQ ID NO: 1), wherein fGly’ is the amino acid residue to which (L-1a’) is attached after conjugating the Ab and the linker-drug, and wherein mAbA15 comprises a heavy chain comprising an amino acid sequence of SEQ ID NO: 2 and a light chain comprising an amino acid sequence of SEQ ID NO: 3.

[0337] 26. A method of treating cancer for two or more treatment cycles in a subject experiencing an adverse event when or after being administered an ADC, the method comprising: (i) administering the ADC to the subject at a dose of about 0.1 mg / kg to about 10.0 mg / kg in a first treatment cycle; (ii) delaying a further administration of the ADC to the subject upon the subject having an adverse event after the first treatment cycle and before a second treatment cycle; and (iii) resuming the administration of the ADC in the second treatment cycle, wherein the ADC is represented by Formula (I):wherein the Ab is a 5T4 antibody or an antigen binding fragment thereof and comprises a heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), a heavy chain complementarity determining region 3 (HCDR3), a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and a light chain complementarity determining region 3 (LCDR3) of an antibody designated mAbA15, wherein the Ab further comprises two motifs, each of which is L(fGly’)TPSR (SEQ ID NO: 1), wherein fGly’ is the amino acid residue to which the non-Ab part of the ADC represented by Formula (I) is attached, and wherein mAbA15 comprises: 119 NAI-1541858741a) a heavy chain comprising an amino acid sequence of: EVQLVESGGGLVQPGGSLRLSCAASGFTFSSYYIHWVRQAPGKGLEWVAYITSTGSYTEY ADSVKGRFTISADTSKNTAYLQMNSLRAEDTAVYYCARYDRSTRYSGLDYWGQGTLVTVS SASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQS SGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLG GPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQY NSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRE EMTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSR WQQGNVFSCSVMHEALHNHYTQKSLSLSPGSL(fGly’)TPSRGS (SEQ ID NO: 2); and b) a light chain comprising an amino acid sequence of: DIQMTQSPSSLSASVGDRVTITCRASQSVSSAVAWYQQKPGKAPKLLIYSASSLYSGVPS RFSGSRSGTDFTLTISSLQPEDFATYYCQQAYATPVTFGQGTKVEIKRTVAAPSVFIFPP SDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLT LSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 3); and wherein the MMAE is monomethyl auristatin E and represented by Formula (III):wherein * indicates the point of attachment in Formula (I).

[0338] 27. The method of embodiment 26, wherein the administration is resumed in step (iii) once the adverse event is alleviated or recovered.

[0339] 28. The method of embodiment 26 or 27, wherein the administration of the second treatment cycle is at the dose of the first treatment cycle.

[0340] 29. The method of embodiment 26 or 27, wherein the administration of the second treatment cycle is at a dose lower than that of the first treatment cycle.

[0341] 30. A method of treating cancer for two or more treatment cycles in a subject experiencing an adverse event when or after being administered an ADC, the method comprising: i) administering the ADC to the subject at a first dose of about 0.1 mg / kg to about 10.0 mg / kg in a first treatment cycle; ii) in a second treatment cycle, administering the ADC to the subject at a second dose which is lower than the first dose upon the subject having an adverse event, wherein the ADC is represented by Formula (I): 120 NAI-1541858741wherein the Ab is a 5T4 antibody or an antigen binding fragment thereof and comprises a heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), a heavy chain complementarity determining region 3 (HCDR3), a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and a light chain complementarity determining region 3 (LCDR3) of an antibody designated mAbA15, wherein the Ab further comprises two motifs, each of which is L(fGly’)TPSR (SEQ ID NO: 1), wherein fGly’ is the amino acid residue to which the non-Ab part of the ADC represented by Formula (I) is attached, and wherein mAbA15 comprises: a) a heavy chain comprising an amino acid sequence of: EVQLVESGGGLVQPGGSLRLSCAASGFTFSSYYIHWVRQAPGKGLEWVAYITSTGSYTEY ADSVKGRFTISADTSKNTAYLQMNSLRAEDTAVYYCARYDRSTRYSGLDYWGQGTLVTVS SASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQS SGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLG GPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQY NSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRE EMTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSR WQQGNVFSCSVMHEALHNHYTQKSLSLSPGSL(fGly’)TPSRGS (SEQ ID NO: 2); and b) a light chain comprising an amino acid sequence of: DIQMTQSPSSLSASVGDRVTITCRASQSVSSAVAWYQQKPGKAPKLLIYSASSLYSGVPS RFSGSRSGTDFTLTISSLQPEDFATYYCQQAYATPVTFGQGTKVEIKRTVAAPSVFIFPP SDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLT LSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 3); and wherein the MMAE is monomethyl auristatin E and represented by Formula (III): 121 NAI-1541858741wherein * indicates the point of attachment in Formula (I).

[0342] 31. The method of embodiment 30, wherein the subject is administered at the second dose in step (ii) once the adverse event is alleviated or recovered.

[0343] 32. The method of any one of embodiments 26-31, wherein the adverse event is selected from the group consisting of Grade 3 thrombocytopenia with clinically significant bleeding, Grade 4 thrombocytopenia, Grade 3 or higher neutropenia with a measured fever of at least 38.3°C, Grade 3 or higher neutropenia with a sustained fever of at least 38°C for at least an hour, Grade 4 neutropenia for greater than 7 days, Grade 4 anemia, alanine transaminase or aspartate transaminase levels that are greater than 3 times the upper limit of normal and a total bilirubin level that is greater than 2 times the upper limit of normal in the absence of biliary obstruction or other explanation for liver abnormality (such as viral hepatitis, alcohol or autoimmune hepatitis, Gilbert Syndrome, or treatment with other hepatotoxic drug), and a Grade 5 adverse event.

[0344] 33. The method of any one of embodiments 26-32, wherein the ADC comprises the Ab conjugated to the MMAE by a linker (L-1):(L-1), wherein the wavy line indicates the point of attachment to the Ab and the ## indicates the point of attachment to the MMAE.

[0345] 34. The method of any one of embodiments 14-33, wherein the cancer is any one or more of breast cancer, endometrial cancer, head and neck cancer, pancreatic cancer, lung cancer, prostate cancer, cervical cancer, or bladder cancer, renal cell carcinoma (RCC), hepatocellular carcinoma (HCC), or colorectal cancer.

[0346] 35. The method of any one of embodiments 1, 2, 5, 6, 9, 10, 13-15, 18, 19, 22, 23, and 35, wherein the Ab comprises one to ten fGly’. 122 NAI-1541858741

[0347] 36. The method of any one of embodiments 1-35, wherein the Ab comprises two fGly’.

[0348] 37. The method of any one of embodiments 1-36, wherein the Ab comprises a motif of X1(fGly’)X2Z2X3Z3(SEQ ID NO: 67), wherein: Z2is either a proline (P) or alanine (A) residue; Z3is a basic amino acid residue optionally selected from the group consisting of: arginine (R), lysine (K), and histidine (H), or an aliphatic amino acid residue optionally selected from the group consisting of: alanine (A), glycine (G), leucine (L), valine (V), isoleucine (I), and proline (P); X1is present or absent and, when present, is any amino acid residue, with the proviso that when the sequence of SEQ ID NO: 67 is at the N-terminus of the antibody Ab, X1is present; and X2and X3independently is any amino acid residue, optionally wherein, the motif of SEQ ID NO: 67 is selected from the group consisting of: L(fGly’)TPSR (SEQ ID NO: 1), M(fGly’)TPSR (SEQ ID NO: 45), V(fGly’)TPSR (SEQ ID NO: 46), L(fGly’)SPSR (SEQ ID NO: 47), L(fGly’)APSR (SEQ ID NO: 48), L(fGly’)VPSR (SEQ ID NO: 49), L(fGly’)GPSR (SEQ ID NO: 50), I(fGly’)TPAR (SEQ ID NO: 51), L(fGly’)TPSK (SEQ ID NO: 52), M(fGly’)TPSK (SEQ ID NO: 53), V(fGly’)TPSK (SEQ ID NO: 54), L(fGly’)SPSK (SEQ ID NO: 55), L(fGly’)APSK (SEQ ID NO: 56), L(fGly’)VPSK (SEQ ID NO: 57), L(fGly’)GPSK (SEQ ID NO: 58), L(fGly’)TPSA (SEQ ID NO: 59), I(fGly’)TPAA (SEQ ID NO: 60), M(fGly’)TPSA (SEQ ID NO: 61), V(fGly’)TPSA (SEQ ID NO: 62), L(fGly’)SPSA (SEQ ID NO: 63), L(fGly’)APSA (SEQ ID NO: 64), L(fGly’)VPSA (SEQ ID NO: 65), and L(fGly’)GPSA (SEQ ID NO: 66).

[0349] 38. The method of embodiment 37, wherein the Ab comprises two heavy chains and two light chains, and wherein each of the heavy chains comprises a motif of SEQ ID NO: 67.

[0350] 39. The method of any one of embodiments 1-38, wherein the Ab comprises an amino acid sequence of L(fGly’)TPSR (SEQ ID NO: 1).

[0351] 40. The method of any one of embodiments 1-39, wherein the Ab comprises two heavy chains (HCs) and two light chains (LCs), and wherein each of the HCs comprises one motif of L(fGly’)TPSR (SEQ ID NO: 1). 123 NAI-1541858741

[0352] 41. The method of embodiment 38 or 40, wherein the fGly’ of the motif is located in the heavy chain at a position corresponding to the 453rdamino acid residue (fGly’) of SEQ ID NO: 2.

[0353] 42. The method of any one of embodiments 1-41, wherein (1) HCDR1 comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 13, 19, 24, 25, and 30, (2) HCDR2 comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 14, 20, 26, 31, and 36, (3) HCDR3 comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 15, 21, 27, and 32, (4) LCDR1 comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 16, 22, 28, and 33, (5) LCDR2 comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 17, 23, and 34, and (6) LCDR3 comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 18, 29, and 35.

[0354] 43. The method of any one of embodiments 1-42, wherein: (i) HCDR1 comprises the amino acid sequence of SEQ ID NO: 13, HCDR2 comprises the amino acid sequence of SEQ ID NO: 14, HCDR3 comprises the amino acid sequence of SEQ ID NO: 15, LCDR1 comprises the amino acid sequence of SEQ ID NO: 16, LCDR2 comprises the amino acid sequence of SEQ ID NO: 17, and LCDR3 comprises the amino acid sequence of SEQ ID NO: 18; or (ii) HCDR1 comprises the amino acid sequence of SEQ ID NO: 19, HCDR2 comprises the amino acid sequence of SEQ ID NO: 20, HCDR3 comprises the amino acid sequence of SEQ ID NO: 21, LCDR1 comprises the amino acid sequence of SEQ ID NO: 22, LCDR2 comprises the amino acid sequence of SEQ ID NO: 23, and LCDR3 comprises the amino acid sequence of SEQ ID NO: 18; or (iii) HCDR1 comprises the amino acid sequence of SEQ ID NO: 24, HCDR2 comprises the amino acid sequence of SEQ ID NO: 14, HCDR3 comprises the amino acid sequence of SEQ ID NO: 15, LCDR1 comprises the amino acid sequence of SEQ ID NO: 16, LCDR2 comprises the amino acid sequence of SEQ ID NO: 17, and LCDR3 comprises the amino acid sequence of SEQ ID NO: 18; or (iv) HCDR1 comprises the amino acid sequence of SEQ ID NO: 25, HCDR2 comprises the amino acid sequence of SEQ ID NO: 26, HCDR3 comprises the amino acid sequence of SEQ ID 124 NAI-1541858741NO: 27, LCDR1 comprises the amino acid sequence of SEQ ID NO: 28, LCDR2 comprises the amino acid sequence of SEQ ID NO: 23, and LCDR3 comprises the amino acid sequence of SEQ ID NO: 29; or (v) HCDR1 comprises the amino acid sequence of SEQ ID NO: 30, HCDR2 comprises the amino acid sequence of SEQ ID NO: 31, HCDR3 comprises the amino acid sequence of SEQ ID NO: 32, LCDR1 comprises the amino acid sequence of SEQ ID NO: 33, LCDR2 comprises the amino acid sequence of SEQ ID NO: 34, and LCDR3 comprises the amino acid sequence of SEQ ID NO: 35; or (vi) HCDR1 comprises the amino acid sequence of SEQ ID NO: 13, HCDR2 comprises the amino acid sequence of SEQ ID NO: 36, HCDR3 comprises the amino acid sequence of SEQ ID NO: 15, LCDR1 comprises the amino acid sequence of SEQ ID NO: 16, LCDR2 comprises the amino acid sequence of SEQ ID NO: 17, and LCDR3 comprises the amino acid sequence of SEQ ID NO: 18.

[0355] 44. The method of any one of embodiments 1-43, wherein the Ab comprises a VH comprising the amino acid sequence of SEQ ID NO: 11 and a VL comprising the amino acid sequence of SEQ ID NO: 12.

[0356] 45. The method of any one of embodiments 1-44, wherein the Ab comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 2 and a light chain comprising the amino acid sequence of SEQ ID NO: 3.

[0357] 46. The method of any one of embodiments 1-45, wherein the Ab is mAbA15.

[0358] 47. The method of any one of embodiments 1-46, wherein the ADC is administered to the subject on the first day of a treatment cycle for one or more treatment cycles.

[0359] 48. The method of embodiment 47, wherein each treatment cycle is 3 weeks ± 3 days.

[0360] 49. The method of any one of embodiments 1-48, wherein the ADC is administered to the subject once every three weeks (q3w).

[0361] 50. The method of any one of embodiments 1-49, wherein the ADC is administered to the subject intravenously.

[0362] 51. The method of embodiments 1-50, further comprising administrating to the subject means for inhibiting interaction between PD-1 and PD-L1.

[0363] 52. The method of embodiments 1-51, wherein the subject is administrated with means for inhibiting interaction between PD-1 and PD-L1.

[0364] 53. The method of embodiment 51 or 52, wherein the ADC is administered concurrently with the means for inhibiting interaction between PD-1 and PD-L1. 125 NAI-1541858741

[0365] 54. The method of embodiment 51 or 52, wherein the ADC is administered after the means for inhibiting interaction between PD-1 and PD-L1.

[0366] 55. The method of embodiment 51 or 52, wherein the ADC is administered before the means for inhibiting interaction between PD-1 and PD-L1.

[0367] 56. The method of embodiment 54 or 55, wherein the ADC is administered on the same day with the means for inhibiting interaction between PD-1 and PD-L1.

[0368] 57. The method of embodiment 56, wherein the administration of the ADC and the means for inhibiting interaction between PD-1 and PD-L1 is at least about 30 minutes apart or at least about 1 hour apart.

[0369] 58. The method of any one of embodiments 51-57, wherein the means for inhibiting interaction between PD-1 and PD-L1 are administered to the subject on the first day of a treatment cycle for one or more treatment cycles.

[0370] 59. The method of embodiment 58, wherein each treatment cycle is 3 weeks ± 3 days.

[0371] 60. The method of any one of embodiments 51-59, wherein the means for inhibiting interaction between PD-1 and PD-L1 are administered to the subject once every three weeks (q3w).

[0372] 61. The method of any one of embodiments 51-60, wherein the means for inhibiting interaction between PD-1 and PD-L1 are administered to the subject intravenously.

[0373] 62. The method of any one of embodiments 1-50, further comprising administering to the subject a PD-L1 / PD-1 inhibitor.

[0374] 63. The method of any one of embodiments 1-50, wherein the subject is administered with a PD-L1 / PD-1 inhibitor.

[0375] 64. The method of embodiment 62 or 63, wherein the ADC is administered concurrently with the PD-L1 / PD-1 inhibitor.

[0376] 65. The method of embodiment 62 or 63, wherein the ADC is administered after the PD-L1 / PD-1 inhibitor.

[0377] 66. The method of embodiment 62 or 63, wherein the ADC is administered before the PD-L1 / PD-1 inhibitor.

[0378] 67. The method of embodiment 65 or 66, wherein the ADC is administered on the same day with the PD-L1 / PD-1 inhibitor.

[0379] 68. The method of embodiment 67, wherein the administration of the ADC and the PD-L1 / PD-1 inhibitor is at least about 30 minutes apart or at least about 1 hour apart. 126 NAI-1541858741

[0380] 69. The method of any one of embodiments 62-68, wherein the PD-L1 / PD-1 inhibitor is administered to the subject on the first day of a treatment cycle for one or more treatment cycles.

[0381] 70. The method of embodiment 69, wherein each treatment cycle is 3 weeks ± 3 days.

[0382] 71. The method of any one of embodiments 62-70, wherein the PD-L1 / PD-1 inhibitor is administered to the subject once every three weeks (q3w).

[0383] 72. The method of any one of embodiments 62-71, wherein the PD-L1 / PD-1 inhibitor is administered to the subject intravenously.

[0384] 73. The method of any one of embodiments 62-72, wherein the PD-L1 / PD-1 inhibitor is an antibody or an antigen binding fragment thereof comprising HCDR1, HCDR2, HCDR3, LCDR1, LCDR2, and LCDR3 of pembrolizumab.

[0385] 74. The method of embodiment 73, wherein the PD-L1 / PD-1 inhibitor is pembrolizumab.

[0386] 75. The method of embodiment 73 or 74, wherein the PD-L1 / PD-1 inhibitor is administered to the subject at a dose of about 200 mg.

[0387] 76. The method of any one of embodiments 1-75, wherein the ADC is administered to the subject at a dose of about 0.3 mg / kg to about 6.0 mg / kg.

[0388] 77. The method of any one of embodiments 1-76, wherein the ADC is administered to the subject at a dose of about 0.3 mg / kg to about 2.0 mg / kg.

[0389] 78. The method of any one of embodiments 1-77, wherein the ADC is administered to the subject at a dose of about 0.3 mg / kg, about 0.6 mg / kg, about 1.0 mg / kg, about 1.5 mg / kg, or about 2.0 mg / kg.

[0390] 79. The method of any one of embodiments 1-78, wherein the cancer is triple- negative breast cancer (TNBC) or hormone-receptor positive breast cancer (HR+ BC).

[0391] 80. The method of any one of embodiments 1-78, wherein the cancer is pancreatic ductal adenocarcinoma (PDAC).

[0392] 81. The method of any one of embodiments 1-78, wherein the cancer is non-small cell lung cancer (NSCLC).

[0393] 82. The method of embodiment 81, wherein the subject has one or more mutations selected from the group consisting of an EGFR sensitizing mutation, an ALK rearrangement, a ROS1 rearrangement, a BRAF V600E mutation, a MET Exon 14 skipping mutation, and a RET rearrangement.

[0394] 83. The method of any one of embodiments 1-78, wherein the cancer is head and neck squamous cell carcinoma (HNSCC). 127 NAI-1541858741

[0395] 84. The method of any one of embodiments 1-83, wherein the ADC is administered to the subject for about four to about twenty-four months.

[0396] 85. The method of any one of embodiments 1-84, wherein the ADC is administered to the subject for about four to about eighteen months.

[0397] 86. The method of any one of embodiments 1-85, wherein the ADC is administered to the subject for about four to about twelve months.

[0398] 87. The method of any one of embodiments 1-86, wherein the ADC is administered to the subject for about four to about six months.

[0399] 88. The method of any one of embodiments 1-87, wherein the ADC also refers to its stereoisomer, solvate, or salt.

[0400] 89. The method of any one of embodiments 1-88, wherein a pharmaceutical composition comprising the ADC and a pharmaceutically acceptable excipient is administered to the subject.

[0401] 90. The method of embodiment 89, the pharmaceutical composition comprises a multiplicity of DAR species of the ADC.

[0402] 91. The method of embodiment 90, wherein the pharmaceutical composition exhibits a drug-to-antibody ratio (DAR) of about 2.

[0403] 92. The method of embodiment 90 or 91, wherein the pharmaceutical composition exhibits a DAR of 1.8.

[0404] 93. The method of any preceding embodiment, wherein the subject is human. 9. EXAMPLES Example 1: Synthesis of the 5T4 ADC of Formula (I)

[0405] 1.1 Synthesis of Linker-Payload

[0406] The synthesis of the linker-drug pre-conjugate of Compound (IIa) (e.g., a form of Formula (II) ready to be conjugated to the 5T4 antibody) is shown in FIG.1.

[0407] Compound I-1 and 2,3,4,5,6-pentafluorophenol were obtained commercially from Shanghai Medicilon and used as received. Monomethyl auristatin E (MMAE) was purchased from BroadPharm (San Diego, CA, USA). All other reagents were obtained from commercial sources and used without purification.

[0408] Compound I-1 (1.33 g, 1.67 mmol) was combined with 2,3,4,5,6-pentafluorophenol (1.23 g, 6.68 mmol) in 6.5 mL of anhydrous DMF. This mixture was treated with 1-ethyl-3-(3- dimethylaminopropyl)carbodiimide (“EDCI-HCl,” 0.64 g, 3.34 mmol) in one portion at room temperature and stirred for 20 hours until Compound I-1 was fully consumed, as evidenced by 128 NAI-1541858741HPLC analysis. The reaction mixture was loaded onto a C18 column (BIOTAGE®, 60 g with a samplet) and eluted with a 0-80% gradient (10 column volumes) of ACN / water + 0.05% TFA. Pure fractions were combined, concentrated on a rotary evaporator until slightly murky, and lyophilized to give intermediate I-2 (1.40 g, 1.46 mmol, 87% yield) as a tan powder, which was stored under nitrogen at -20 °C until further use. LRMS (ESI) analysis of the tan powder revealed a peak at m / z 961.2 [M+H]+, as expected for C44H45F5N6O11S.

[0409] In a 20 mL glass vial, MMAE (720 mg, 1.0 mmol), 5 mL of anhydrous DMF, and 0.35 mL of DIPEA (2.0 mmol) were combined at room temperature. The resulting mixture was stirred and treated with compound I-3 (1014 mg, 1.0 mmol) as a solid in a few small portions, followed by the addition of HOAt (136 mg, 1.0 mmol) in one portion at room temperature. The reaction mixture was stirred for 6 hours until the reaction was complete, as evidenced by HPLC analysis. The reaction mixture was poured into 30 mL of water. The resulting white precipitate was separated by spinning and collected, washed with 5 mL of water, and dried briefly under high vacuum to give 1.87 g of intermediate I-4 as a yellow solid, which was further reacted according to the disclosure below without purification.

[0410] A solution of intermediate I-4 (1.87 g) in 15 mL of THF was cooled down to 0 °C in an ice bath and treated slowly with 1 M aqueous lithium hydroxide solution (3 mL). The reaction mixture was stirred at 0 °C for 3 hours, then warmed up to ambient temperature, treated with 3 mL of 1 M aqueous lithium hydroxide and diluted with 3 mL of methanol. The resulting mixture was stirred at room temperature for 3 hours until hydrolysis was complete, as evidenced by HPLC analysis. The reaction was then quenched by adding 1 M aqueous HCl solution to bring the reaction mixture to a pH of 7. The reaction mixture was then concentrated under reduced pressure and washed with 10 mL of methyl tert-butyl ether (“MTBE”). The aqueous layer was purified by reversed-phase chromatography (C18 column, 0-40% acetonitrile-water + 0.05% TFA). Pure product fractions were combined, concentrated under reduced pressure, and lyophilized to give intermediate I-5 as a white powder (735 mg, 0.60 mmol, 60% yield over two steps). LRMS (ESI) analysis of the white powder revealed a peak at m / z 1229.7 [M+H]+, as expected for C61H96N8O18.

[0411] DIPEA (0.21 mL, 1.2 mmol) and a solution of intermediate I-2 (575 mg, 0.60 mmol) in 2 mL of DMA were added to a stirred solution of intermediate I-5 (735 mg, 0.60 mmol) in 3 mL of anhydrous DMA at room temperature.1-Hydroxy-7-azabenzotriazole (“HOAt,” 84 mg, 0.60 mmol) was then added. The resulting mixture was stirred for 30 minutes until coupling was complete, as evidenced by HPLC. The reaction mixture was then treated with 1.2 mL of piperidine at room temperature. After 15 minutes, the reaction mixture was purified by reversed- 129 NAI-1541858741phase chromatography (C18 column, 0-40% gradient of acetonitrile-water). Pure fractions were combined, concentrated under reduced pressure and room temperature, and lyophilized to give Formula (IIa) (808 mg, 0.45 mmol, 75% yield) as a white fluffy powder. LRMS (ESI) analysis of the white powder revealed a peak at 1783.9 [M+H]+, as expected for C84H130N14O26S m / z.

[0412] 1.2 Synthesis of the 5T4 Antibody

[0413] The gene encoding heavy chain and light chains of the 5T4 antibody in the ADC were cloned separately into mammalian expression vectors for expression as a full-length IgG in mammalian cells. The IgG antibody was purified from culture supernatant using Protein A resin. Tagged 5T4 antibody was prepared according to methods known in the art, such as those described in Rabuka D. et al., “Site-specific chemical protein conjugation using genetically encoded aldehyde tags,” Nat Protoc., 2012; 7(6):1052-1067 and in U.S. Patent No.7,985,783 B2, each of which is incorporated in its entirety herein by reference. Briefly, the 5T4 antibody, which contained a heterologous sulfatase motif was contacted with a formylglycine-generating enzyme to convert the cysteine in the motif to a formylglycine having an aldehyde moiety to generate an “aldehyde-tagged antibody.”

[0414] 1.3 Conjugation

[0415] The 5T4 aldehyde-tagged antibody described in section 1.1 above (15 mg / mL) was conjugated to the synthesized linker-drug pre-conjugate IIa (8 mol. equivalents drug:antibody) by reacting the linker-drug and aldehyde-tagged antibody for 72 hours at 37 °C in 20 mM sodium citrate, pH 5.5, 50 mM sodium chloride containing 0.85% DMA. After conjugation, residual free drug was removed by diafiltration using a 115V Labscale Tangential Flow Filtration (TFF) system (Millipore, Cat. No. XX42LSS11) with a 30 kDa TFF cassette (Sigma-Aldrich, Cat. No. P3C030C00) and exchanging for 12 diavolumes (600 mL) into 20 mM sodium citrate, pH 5.5, 50 mM NaCl. Alternatively, residual free drug can also be removed using multiple rounds of dilution into 20 mM sodium citrate, pH 5.5, 50 mM sodium chloride and concentration using AMICON® 0.5 mL 30 kD molecular weight cut off (MWCO) centrifugal filters (Millipore Sigma, Cat. No. #UFC5030BK) or ZEBA® desalting columns (Fisher Scientific, Cat. No. PI87766). 130 NAI-1541858741Example 2: A Dose-Escalation and Expansion Study of the ADC of Example 1 as a Single Agent and in Combination Therapy in Subjects with Locally Advanced or Metastatic Solid Tumors

[0416] 2.1 Dose Escalation Stage

[0417] Subjects with advanced solid tumors are treated with the ADC of Example 1 (5T4- ADC-1) in escalating doses either as a single agent (Single Agent Dose Escalation Cohort) or in combination with 200 mg pembrolizumab (Combination Dose Escalation Cohort). The starting dose of the ADC is 0.3 mg / kg body weight administered intravenously once every three weeks (q3w). For subjects with a body weight > 120 kg, the maximum total dose is calculated based on 120 kg body weight. In the “Combination Dose Escalation Cohort,” pembrolizumab is also administered intravenously at the same time as the ADC.

[0418] Escalating dosing is determined using the Bayesian optimal interval (BOIN) design. The 3-week period following administration of the starting dose comprises a DLT-Evaluation Period. Escalated doses are initially based on a modified Fibonacci progression (increments of 100%, 67%, 50%, and then 33% over the prior dose), but smaller escalating doses may be instituted between cohorts based on evaluation of safety and PK results from the current and previous cohorts.

[0419] In this study, the target toxicity rate for the maximum tolerated dose (MTD) is ϕ= 0.25 and the maximum sample size is 45. The total number of subjects enrolled under the BOIN design, shown in FIG.2, depends on the number of dose levels required to determine the MTD and / or recommended dose (RD). Enrollment cohorts of sizes up to 5 subjects are treated and observed. Subjects are deemed evaluable for purposes of making dose-escalation / de-escalation decisions if they experience a dose-limiting toxicity (DLT) or complete the DLT-Evaluation Period without experiencing a DLT.

[0420] Subjects who do not experience a DLT and do not complete the DLT-Evaluation Period for reasons other than safety are not considered evaluable. Given the DLT rate among the evaluable subjects at the dose level, the BOIN design uses the following rule, optimized to minimize the probability of incorrect dose assignment to guide dose-escalation / de-escalation.

[0421] According to FIG.2: • If the observed DLT rate at the current dose is ≤ 0.197, the dose is escalated to the next higher dose level; • If the observed DLT rate at the current dose is > 0.298, the dose is de-escalated to the next lower dose level; 131 NAI-1541858741• Otherwise, the current dose is continued.

[0422] For the purpose of overdose control, doses ^^ and higher levels are eliminated from further examination if Pr (^^^^ > 0.25 | data) > 0.95 and at least 3 evaluable subjects have been treated at dose level ^^, where ^^^^ is the true DLT rate of dose level ^^. This posterior probability isevaluated based on the beta-binomial model ^^^^∣^^^^∼binomial (^^^^) with ^^^^∼uniform (0, 1), where^^^^ is the number of subjects experiencing DLT at dose level ^^. When the lowest dose iseliminated, stop the trial for safety. The probability cutoff 0.95 is chosen to be consistent with the common practice that when the target DLT rate ≤ 1 / 6, a dose with 2 out of 3 subjects experiencing DLT is eliminated. The above dose-escalation / de-escalation and elimination rule can be equivalently presented in Table 2, which is used to conduct the trial. Table 2: Dose Escalation and De-Escalation Rules for the BOIN Design

[0423] Accrual to a Dose-Escalation Stage ends when either 12 evaluable subjects have already been observed in the dose level indicated as the next step in the enrollment algorithm or a total of 45 evaluable subjects have been treated and observed in the stage for a regimen, whichever comes first. Additional subjects may also be added at any dose level lower than the safe dose, simultaneously.

[0424] The following stopping rules are employed during the study, including in the dose escalation stages and expansion stages: • Two or more Grade 5 treatment-related AEs that occur within one cohort (in nonrandomized cohorts) or within one treatment arm (in randomized cohorts); • More than 30% of subjects within one cohort that discontinue study treatment due to treatment-related AE; • More than 70% of subjects within one cohort that experience a ≥ Grade 3 treatment- related AE. 132 NAI-1541858741MTD Determination:

[0425] Determination of the MTD is based on isotonic regression as specified in Liu and Yuan, 2015, “Bayesian Optimal Interval Designs for Phase I Clinical Trials,” Journal of the Royal Statistical Society, 64(3):507-523. This computation is implemented by the Shiny app "BOIN" (Zhou et al., 2020, “BOIN Suite: A Software Platform to Design and Implement Novel Early-Phase Clinical Trials,” JCO Clin Cancer Inform., 5:91-10, available at http: / / www.trialdesign.org). Specifically, the dose selected as the MTD is the maximum isotonic estimate of the toxicity rate closest to the target toxicity rate. If there are ties, if the isotonic estimate is lower than the target toxicity rate, the higher dose level is selected. If the isotonic estimate is greater than or equal to the target toxicity rate, the lower dose level is selected.

[0426] The BOIN design (Liu and Yuan 2015; Yuan et al 2016) is used to identify the MTD of the ADC of Example 1. In this study, the target toxicity rate for the MTD is ϕ= 0.25. The maximum sample size is 45 for single-agent ADC based on up to 7 dose levels, and 30 in combination of pembrolizumab based on up to 4 dose levels. The total number of subjects enrolled under the BOIN design depends on the number of dose levels required to determine the MTD and / or RD. RD Determination:

[0427] Independent of MTD determination, and upon review of all available safety, PK, and preliminary clinical activity data, the Cohort Review Committee chooses one RD level for the ADC at which the corresponding expansion cohort subjects are treated. The RD for the ADC is the MTD or a lower dose level at the Cohort Review Committee’s discretion. Magnitude of Dose-Escalation:

[0428] Dose-escalation to the next higher dose level proceeds only if at least 3 subjects enrolled under the BOIN design have been evaluated at the current dose level and a reason for discontinuing enrollment is not reached as discussed above. When selecting new higher dose levels for evaluation, dose-escalation is based on a modified Fibonacci progression, but the Cohort Review Committee may decide to institute a smaller escalation between cohorts (e.g., dose for the next cohort may be less than that recommended by the Fibonacci sequence) based on evaluation of safety and PK results from the current and previous cohorts. Intra-subject Dose-Escalation:

[0429] Prior to establishing the MTD, the Cohort Review Committee can allow an intra- subject dose-escalation of a subject to a safe ADC dose level (that is, DLT-evaluation has been completed for at least 3 subjects). Subjects who are allowed to dose-escalate do contribute to the DLT evaluation at that higher dose. 133 NAI-1541858741Intermediate Dose Level Cohorts:

[0430] Intermediate dose level cohorts can be inserted between previously opened dose levels and evaluated at the request of the Cohort Review Committee based on emerging safety and PK data. The total sample size can be expanded by up to 6 subjects per additional intermediate dose (a maximum of 2 intermediate doses may be explored). Data from intermediate dose levels is included in final regression models to determine the MTD. Regimen Re-evaluation:

[0431] If the Cohort Review Committee is unable to select an acceptable RD for further evaluation of a regimen in the Cohort-Expansion Stage (e.g., early termination for safety, insufficient toxicity data), alternative treatment schedules can be evaluated in a new Dose- Escalation Stage...

Claims

CLAIMS What is claimed is:

1. A method for treating cancer in a subject, the method comprising administering an ADC to the subject, wherein the cancer is any one or more of breast cancer, endometrial cancer, head and neck cancer, pancreatic cancer, lung cancer, prostate cancer, cervical cancer, bladder cancer, renal cell carcinoma (RCC), hepatocellular carcinoma (HCC), or colorectal cancer; wherein the ADC is represented by Formula (I’):(I’), wherein the Ab is a 5T4 antibody or an antigen binding fragment thereof, and wherein the Ab comprises: (1) a heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), and a heavy chain complementarity determining region 3 (HCDR3) as set forth in a heavy chain variable region (VH) comprising the amino acid sequence of SEQ ID NO: 11, and (2) a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and a light chain complementarity determining region 3 (LCDR3) as set forth in a light chain variable region (VL) comprising the amino acid sequence of SEQ ID NO: 12; wherein the Ab further comprises one or more fGly’, wherein fGly’ is a formylglycine amino acid residue to which the non-Ab part of Formula (I’) is attached; 173 NAI-1541858741wherein the MMAE is monomethyl auristatin E and represented by Formula (III):wherein * indicates the point of attachment in Formula (I’); and wherein n is an integer.

2. The method of claim 1, wherein n is an integer selected from any one of 1 to 10.

3. The method of claim 1 or 2, wherein n is 2 and wherein the ADC is represented by Formula (I):(I), wherein the * in Formula (III) indicates the point of attachment in Formula (I) and wherein fGly’ is a formylglycine amino acid residue to which the non-Ab part of Formula (I) is attached.

4. A method for treating cancer in a subject, the method comprising administering an ADC to the subject, wherein the cancer is any one or more of breast cancer, endometrial cancer, head and neck cancer, pancreatic cancer, lung cancer, prostate cancer, cervical cancer, bladder cancer, renal cell carcinoma (RCC), hepatocellular carcinoma (HCC), or colorectal cancer; wherein the ADC comprises an antibody (Ab) conjugated to a monomethyl auristatin E (MMAE) by a linker (L-1): 174 NAI-1541858741(L-1), wherein the wavy line indicates the point of attachment to the Ab and the ## indicates the point of attachment to the MMAE; wherein the MMAE is represented by Formula (III):wherein * indicates the point of attachment to (L-1); wherein the Ab is a 5T4 antibody or an antigen binding fragment thereof, and wherein the Ab comprises: (1) a heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), and a heavy chain complementarity determining region 3 (HCDR3) as set forth in a heavy chain variable region (VH) comprising the amino acid sequence of SEQ ID NO: 11, and (2) a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and a light chain complementarity determining region 3 (LCDR3) as set forth in a light chain variable region (VL) comprising the amino acid sequence of SEQ ID NO: 12; and wherein the Ab further comprises one or more fGly’ and wherein fGly’ is a formylglycine amino acid residue to which linker (L-1) is attached.

5. The method of claim 4, wherein one Ab is conjugated to one to ten MMAEs and wherein each MMAE is conjugated to Ab by one linker (L-1).

6. The method of claim 4 or 5, wherein one Ab is conjugated to two MMAEs and wherein each MMAE is conjugated to Ab by one linker (L-1). 175 NAI-15418587417. A method for treating cancer in a subject, the method comprising administering an ADC to the subject, wherein the cancer is any one or more of breast cancer, endometrial cancer, head and neck cancer, pancreatic cancer, lung cancer, prostate cancer, cervical cancer, bladder cancer, renal cell carcinoma (RCC), hepatocellular carcinoma (HCC), or colorectal cancer, wherein the ADC is produced by conjugating an antibody (Ab) to a linker- drug comprising a pre-conjugate linker (L-1a’) and a monomethyl auristatin E (MMAE):(L-1a’), wherein the ## indicates the point of attachment to the MMAE; wherein the MMAE is represented by Formula (III):wherein the Ab is a 5T4 antibody or an antigen binding fragment thereof, and wherein the Ab comprises: (1) a heavy chain complementarity determining region 1 (HCDR1), a heavy chain complementarity determining region 2 (HCDR2), and a heavy chain complementarity determining region 3 (HCDR3) as set forth in a heavy chain variable region (VH) comprising the amino acid sequence of SEQ ID NO: 11, and (2) a light chain complementarity determining region 1 (LCDR1), a light chain complementarity determining region 2 (LCDR2), and a light chain 176 NAI-1541858741complementarity determining region 3 (LCDR3) as set forth in a light chain variable region (VL) comprising the amino acid sequence of SEQ ID NO: 12; and wherein the Ab further comprises one or more fGly’ and wherein fGly’ is a formylglycine amino acid residue to which linker (L-1a’) is attached after conjugating the Ab and the linker-drug.

8. The method of claim 7, wherein one Ab is conjugated to one to ten linker-drugs.

9. The method of claim 7 or 8, wherein one Ab is conjugated to two linker-drugs.

10. The method of any one of claims 1, 2, 4, 5, 7, and 8, wherein the Ab comprises one to ten fGly’.

11. The method of any one of claims 1-10, wherein the Ab comprises two fGly’.

12. The method of any one of claims 1-11, wherein the Ab comprises a motif of X1(fGly’)X2Z2X3Z3(SEQ ID NO: 67), wherein: Z2is either a proline (P) or alanine (A) residue; Z3is a basic amino acid residue optionally selected from the group consisting of: arginine (R), lysine (K), and histidine (H), or an aliphatic amino acid residue optionally selected from the group consisting of: alanine (A), glycine (G), leucine (L), valine (V), isoleucine (I), and proline (P); X1is present or absent and, when present, is any amino acid residue, with the proviso that when the sequence of SEQ ID NO: 67 is at the N-terminus of the antibody Ab, X1is present; and X2and X3independently is any amino acid residue, optionally wherein, the motif of SEQ ID NO: 67 is selected from the group consisting of: L(fGly’)TPSR (SEQ ID NO: 1), M(fGly’)TPSR (SEQ ID NO: 45), V(fGly’)TPSR (SEQ ID NO: 46), L(fGly’)SPSR (SEQ ID NO: 47), L(fGly’)APSR (SEQ ID NO: 48), L(fGly’)VPSR (SEQ ID NO: 49), L(fGly’)GPSR (SEQ ID NO: 50), I(fGly’)TPAR (SEQ ID NO: 51), L(fGly’)TPSK (SEQ ID NO: 52), M(fGly’)TPSK (SEQ ID NO: 53), V(fGly’)TPSK (SEQ ID NO: 54), L(fGly’)SPSK (SEQ ID NO: 55), L(fGly’)APSK (SEQ ID NO: 56), L(fGly’)VPSK (SEQ ID NO: 57), L(fGly’)GPSK (SEQ ID NO: 58), L(fGly’)TPSA (SEQ ID NO: 59), I(fGly’)TPAA (SEQ ID NO: 60), M(fGly’)TPSA (SEQ ID NO: 61), V(fGly’)TPSA (SEQ ID NO: 62), L(fGly’)SPSA 177 NAI-1541858741(SEQ ID NO: 63), L(fGly’)APSA (SEQ ID NO: 64), L(fGly’)VPSA (SEQ ID NO: 65), and L(fGly’)GPSA (SEQ ID NO: 66).

13. The method of claim 12, wherein the Ab comprises two heavy chains and two light chains, and wherein each of the heavy chains comprises a motif of SEQ ID NO:

67.

14. The method of any one of claims 1-13, wherein the Ab comprises an amino acid sequence of L(fGly’)TPSR (SEQ ID NO: 1).

15. The method of any one of claims 1-14, wherein the Ab comprises two heavy chains and two light chains, and wherein each of the heavy chains comprises a motif of L(fGly’)TPSR (SEQ ID NO: 1) 16. The method of claim 13 or 15, wherein the fGly’ of the motif is located in the heavy chain at a position corresponding to the 453rdamino acid residue of SEQ ID NO:

2.

17. The method of any one of claims 1-16, wherein (1) HCDR1 comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 13, 19, 24, 25, and 30, (2) HCDR2 comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 14, 20, 26, 31, and 36, (3) HCDR3 comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 15, 21, 27, and 32, (4) LCDR1 comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 16, 22, 28, and 33, (5) LCDR2 comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 17, 23, and 34, and (6) LCDR3 comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 18, 29, and 35.

18. The method of any one of claims 1-17, wherein: (i) HCDR1 comprises the amino acid sequence of SEQ ID NO: 13, HCDR2 comprises the amino acid sequence of SEQ ID NO: 14, HCDR3 comprises the amino acid sequence of SEQ ID NO: 15, LCDR1 comprises the amino acid sequence of SEQ ID NO: 16, LCDR2 comprises the amino acid sequence of SEQ ID NO: 17, and LCDR3 comprises the amino acid sequence of SEQ ID NO: 18; or (ii) HCDR1 comprises the amino acid sequence of SEQ ID NO: 19, HCDR2 comprises the amino acid sequence of SEQ ID NO: 20, HCDR3 comprises the amino 178 NAI-1541858741acid sequence of SEQ ID NO: 21, LCDR1 comprises the amino acid sequence of SEQ ID NO: 22, LCDR2 comprises the amino acid sequence of SEQ ID NO: 23, and LCDR3 comprises the amino acid sequence of SEQ ID NO: 18; or (iii) HCDR1 comprises the amino acid sequence of SEQ ID NO: 24, HCDR2 comprises the amino acid sequence of SEQ ID NO: 14, HCDR3 comprises the amino acid sequence of SEQ ID NO: 15, LCDR1 comprises the amino acid sequence of SEQ ID NO: 16, LCDR2 comprises the amino acid sequence of SEQ ID NO: 17, and LCDR3 comprises the amino acid sequence of SEQ ID NO: 18; or (iv) HCDR1 comprises the amino acid sequence of SEQ ID NO: 25, HCDR2 comprises the amino acid sequence of SEQ ID NO: 26, HCDR3 comprises the amino acid sequence of SEQ ID NO: 27, LCDR1 comprises the amino acid sequence of SEQ ID NO: 28, LCDR2 comprises the amino acid sequence of SEQ ID NO: 23, and LCDR3 comprises the amino acid sequence of SEQ ID NO: 29; or (v) HCDR1 comprises the amino acid sequence of SEQ ID NO: 30, HCDR2 comprises the amino acid sequence of SEQ ID NO: 31, HCDR3 comprises the amino acid sequence of SEQ ID NO: 32, LCDR1 comprises the amino acid sequence of SEQ ID NO: 33, LCDR2 comprises the amino acid sequence of SEQ ID NO: 34, and LCDR3 comprises the amino acid sequence of SEQ ID NO: 35; or (vi) HCDR1 comprises the amino acid sequence of SEQ ID NO: 13, HCDR2 comprises the amino acid sequence of SEQ ID NO: 36, HCDR3 comprises the amino acid sequence of SEQ ID NO: 15, LCDR1 comprises the amino acid sequence of SEQ ID NO: 16, LCDR2 comprises the amino acid sequence of SEQ ID NO: 17, and LCDR3 comprises the amino acid sequence of SEQ ID NO:

18.

19. The method of any one of claims 1-18, wherein the Ab comprises a VH comprising the amino acid sequence of SEQ ID NO: 11 and a VL comprising the amino acid sequence of SEQ ID NO:

12.

20. The method of any one of claims 1-19, wherein the Ab comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 2 and a light chain comprising the amino acid sequence of SEQ ID NO:

3.

21. The method of any one of claims 1-20, wherein the cancer is triple-negative breast cancer (TNBC) or hormone-receptor positive breast cancer (HR+ BC). 179 NAI-154185874122. The method of any one of claims 1-20, wherein the cancer is pancreatic ductal adenocarcinoma (PDAC).

23. The method of any one of claims 1-20, wherein the cancer is non-small cell lung cancer (NSCLC).

24. The method of any one of claims 1-20, wherein the cancer is head and neck squamous cell carcinoma (HNSCC).

25. The method of any one of claims 1-24, further comprising administrating to the subject means for inhibiting interaction between PD-1 and PD-L1.

26. The method of claim 25, wherein the ADC is administered concurrently with, after, or before the means for inhibiting interaction between PD-1 and PD-L1.

27. The method of any one of claims 1-24, further comprising administering to the subject a PD-L1 / PD-1 inhibitor.

28. The method of claim 27, wherein the ADC is administered concurrently with, after, or before the PD-L1 / PD-1 inhibitor.

29. The method of claim 27 or 28, wherein the PD-L1 / PD-1 inhibitor is an antibody or an antigen binding fragment thereof comprising HCDR1, HCDR2, HCDR3, LCDR1, LCDR2, and LCDR3 of pembrolizumab.

30. The method of any one of claims 27-29, wherein the PD-L1 / PD-1 inhibitor is pembrolizumab.

31. The method of claim 29 or 30, wherein the PD-L1 / PD-1 inhibitor is administered to the subject at a dose of about 200 mg.

32. The method of any one of claims 27-31, wherein the PD-L1 / PD-1 inhibitor is administered intravenously.

33. The method of any one of claims 27-32, wherein the PD-L1 / PD-1 inhibitor is administered once every 3 weeks (q3w).

34. The method of any one of claims 1-33, wherein the ADC is administered intravenously.

35. The method of any one of claims 1-34, wherein the ADC is administered once every 3 weeks (q3w). 180 NAI-154185874136. The method of any one of claims 1-35, wherein the subject is human. 181 NAI-1541858741

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