Multimeric bispecific binding molecules specific for CD20 and CD3

1. A dimeric or pentameric binding molecule comprising two or five bivalent binding units and a modified J-chain, wherein each binding unit comprises two heavy chain constant regions, each associated with an antigen-binding domain, wherein at least three antigen binding domains of the binding molecule are identical CD20 antigen binding domains comprising six immunoglobulin complementarity determining regions HCDR1, HCDR2, HCDR3, LCDR1, LCDR2, and LCDR3, wherein the HCDR1 comprises the amino acid sequence of SEQ ID NO: 39; the HCDR2 comprises the amino acid sequence of SEQ ID NO: 40; the HCDR3 comprises the amino acid sequence of SEQ ID NO: 41; the LCDR1 comprises the amino acid sequence of SEQ ID NO: 43; the LCDR2 comprises the amino acid sequence of SEQ ID NO: 44; and the LCDR3 comprises the amino acid sequence of SEQ ID NO: 45, wherein the modified J-chain comprises a J-chain and a heterologous polypeptide, wherein the heterologous polypeptide comprises an scFv fragment that can specifically bind to CD3E, wherein the heterologous polypeptide is directly or indirectly fused to the J-chain, and wherein the binding molecule can direct complement-mediated, T-cell-mediated, or both complement-mediated and T-cell-mediated killing of a CD20-expressing cell at higher potency than an equivalent amount of a monospecific, bivalent IgG1 antibody comprising a VH having the amino acid sequence SEQ ID NO: 38 and a VL having the amino acid sequence SEQ ID NO: 42.

2. The binding molecule of claim 1 , which is a dimeric binding molecule comprising two bivalent IgA binding units or fragments thereof, wherein each binding unit comprises two IgA heavy chain constant regions each comprising at least a Cα3-tp domain, and each associated with an antigen-binding domain.

3. The binding molecule of claim 2 , wherein the IgA heavy chain constant regions or fragments thereof each further comprise a Cα1 domain and a Cα2 domain.

4. The binding molecule of claim 1 , which is a pentameric binding molecule comprising five bivalent IgM binding units, wherein each binding unit comprises two IgM heavy chain constant regions each comprising at least a Cμ4-tp domain and each associated with an antigen-binding domain.

5. The binding molecule of claim 4 , wherein the IgM heavy chain constant regions further comprise a Cμ3 domain, a Cμ2 domain, a Cμ1 domain, or any combination thereof.

6. The binding molecule of claim 1 , wherein the J-chain comprises the amino acid sequence SEQ ID NO: 49.

7. The binding molecule of claim 1 , wherein the heterologous polypeptide is fused to the J-chain via a peptide linker, wherein the peptide linker comprises at least 5 amino acids, but no more than 25 amino acids, and wherein the heterologous polypeptide is fused to the N-terminus of the J-chain, the C-terminus of the J-chain, or to both the N-terminus and C-terminus of the J-chain.

8. The binding molecule of claim 1 , wherein the modified J-chain comprises the amino acid sequence SEQ ID NO: 64 (V15J) or SEQ ID NO: 66 (J15V).

9. The binding molecule of claim 5 , wherein the IgM heavy chain constant regions are human IgM constant regions, and wherein each binding unit comprises two identical IgM heavy chains each comprising a VH situated amino terminal to the IgM constant region, and two identical immunoglobulin light chains each comprising a VL situated amino terminal to an immunoglobulin light chain constant region.

10. The binding molecule of claim 9 , wherein each IgM heavy chain comprises the amino acid sequence SEQ ID NO: 56, and wherein each light chain comprises the amino acid sequence SEQ ID NO: 58.

11. The binding molecule of claim 1 , wherein the CD20-expressing cell is a lymphoma cell line.

12. The binding molecule of claim 1 , wherein the CD20-expressing cell is a malignant B cell in a subject with cancer.

13. The binding molecule of claim 12 , wherein the cancer is minimally responsive or non-responsive to rituximab therapy.

14. The binding molecule of claim 12 , wherein the subject is human.

15. A composition comprising the binding molecule claim 1 , and a carrier.

16. The binding molecule of claim 1 , wherein the at least three identical CD20 antigen binding domains each comprise an antibody heavy chain variable region (VH) and an antibody light chain variable region (VL), wherein the VH comprises an amino acid sequence at least at least 90% identical to SEQ ID NO: 38, and the VL comprises an amino acid sequence at least 90% identical to SEQ ID NO: 42.

17. The binding molecule of claim 16 , wherein the VH comprises the amino acid sequence of SEQ ID NO: 38 and the VL comprises the amino acid sequence of SEQ ID NO: 42.

18. The binding molecule of claim 8 , wherein the IgM heavy chain constant regions are human IgM constant regions, and wherein each binding unit comprises two identical IgM heavy chains each comprising a VH situated amino terminal to the IgM constant region, and two identical immunoglobulin light chains each comprising a VL situated amino terminal to an immunoglobulin light chain constant region.

19. The binding molecule of claim 18 , wherein each IgM heavy chain comprises the amino acid sequence SEQ ID NO: 56, and wherein each light chain comprises the amino acid sequence SEQ ID NO: 58.

20. The binding molecule of claim 16 , wherein the heterologous polypeptide is fused to the J-chain via a peptide linker, wherein the peptide linker comprises at least 5 amino acids, but no more than 25 amino acids, and wherein the heterologous polypeptide is fused to the N-terminus of the J-chain, the C-terminus of the J-chain, or to both the N-terminus and C-terminus of the J-chain.

21. The binding molecule of claim 16 , wherein the modified J-chain comprises the amino acid sequence SEQ ID NO: 64 (V15J) or SEQ ID NO: 66 (J15V).

22. The binding molecule of claim 17 , wherein the heterologous polypeptide is fused to the J-chain via a peptide linker, wherein the peptide linker comprises at least 5 amino acids, but no more than 25 amino acids, and wherein the heterologous polypeptide is fused to the N-terminus of the J-chain, the C-terminus of the J-chain, or to both the N-terminus and C-terminus of the J-chain.

23. The binding molecule of claim 17 , wherein the modified J-chain comprises the amino acid sequence SEQ ID NO: 64 (V15J) or SEQ ID NO: 66 (J15V).

24. The binding molecule of claim 4 , wherein the at least three identical CD20 antigen binding domains each comprise an antibody heavy chain variable region (VH) and an antibody light chain variable region (VL), wherein the VH comprises an amino acid sequence at least at least 90% identical to SEQ ID NO: 38, and the VL comprises an amino acid sequence at least 90% identical to SEQ ID NO: 42.

25. The binding molecule of claim 4 , wherein the VH comprises the amino acid sequence of SEQ ID NO: 38 and the VL comprises the amino acid sequence of SEQ ID NO: 42.

26. The binding molecule of claim 25 , wherein the heterologous polypeptide is fused to the J-chain via a peptide linker, wherein the peptide linker comprises at least 5 amino acids, but no more than 25 amino acids, and wherein the heterologous polypeptide is fused to the N-terminus of the J-chain, the C-terminus of the J-chain, or to both the N-terminus and C-terminus of the J-chain.

27. The binding molecule of claim 25 , wherein the modified J-chain comprises the amino acid sequence SEQ ID NO: 64 (V15J) or SEQ ID NO: 66 (J15V).

28. The binding molecule of claim 5 , wherein the at least three identical CD20 antigen binding domains each comprise an antibody heavy chain variable region (VH) and an antibody light chain variable region (VL), wherein the VH comprises an amino acid sequence at least at least 90% identical to SEQ ID NO: 38, and the VL comprises an amino acid sequence at least 90% identical to SEQ ID NO: 42.

29. The binding molecule of claim 5 , wherein the VH comprises the amino acid sequence of SEQ ID NO: 38 and the VL comprises the amino acid sequence of SEQ ID NO: 42.

30. The binding molecule of claim 29 , wherein the heterologous polypeptide is fused to the J-chain via a peptide linker, wherein the peptide linker comprises at least 5 amino acids, but no more than 25 amino acids, and wherein the heterologous polypeptide is fused to the N-terminus of the J-chain, the C-terminus of the J-chain, or to both the N-terminus and C-terminus of the J-chain.

31. The binding molecule of claim 29 , wherein the modified J-chain comprises the amino acid sequence SEQ ID NO: 64 (V15J) or SEQ ID NO: 66 (J15V).