Binding molecules with modified J-chain

1. A polymeric antibody comprising two or five immunoglobulin monomers and a modified J-chain, wherein the modified J-chain comprises a moiety introduced into a J-chain, wherein each immunoglobulin monomer comprises two heavy chains, and wherein each heavy chain comprises a tail-piece domain and a heavy chain constant domain, wherein the moiety comprises an albumin protein.

2. The polymeric antibody of claim 1 , wherein the J-chain is a native human J-chain.

3. The polymeric antibody of claim 2 , wherein the native human J-chain comprises SEQ ID NO: 1.

4. The polymeric antibody of claim 3 , wherein the moiety is introduced into the J-chain by indirect fusion through a peptide linker.

5. The polymeric antibody of claim 4 , wherein the peptide linker is located at or around the C- or N-terminus of the moiety.

6. The polymeric antibody of claim 4 , wherein the moiety is introduced at the C-terminus of the J-chain.

7. The polymeric antibody of claim 4 , wherein the moiety is introduced at the N-terminus of the J-chain.

8. The polymeric antibody of claim 4 , wherein the peptide linker is about 10 to 20 amino acids long.

9. The polymeric antibody of claim 4 , wherein the peptide linker is 15 amino acids long.

10. The polymeric antibody of claim 4 , wherein the modified J chain further comprising a binding moiety.

11. The polymeric antibody of claim 10 , wherein the binding moiety is a polypeptide introduced into the J-chain by direct or indirect fusion.

12. The polymeric antibody of claim 10 , wherein the moiety is located at an N-terminus of the modified J-chain, and the binding moiety is located at a C-terminus of the modified J-chain.

13. The polymeric antibody of claim 10 , wherein the moiety is located at a C-terminus of the modified J-chain, and the binding moiety is located at an N-terminus of the modified J-chain.

14. The polymeric antibody of claim 10 , wherein the binding moiety binds human CD3.

15. The polymeric antibody of claim 14 , wherein the binding moiety comprises a human CD3-binding scFv.

16. The polymeric antibody of claim 1 , which comprises five immunoglobulin monomers to form a pentamer, wherein the two heavy chains of each immunoglobulin monomer comprise an IgM tail-piece (μtp) and a Cμ4 domain.

17. The polymeric antibody of claim 16 , wherein the two heavy chains of each immunoglobulin monomer each further comprise a Cμ1 domain, a Cμ2 domain, and a Cμ3 domain.

18. The polymeric antibody of claim 1 , wherein each immunoglobulin monomer further comprises two light chains associated with the two heavy chains.

19. The polymeric antibody of claim 16 , wherein the two heavy chains of immunoglobulin monomer are hybrid heavy chains further comprising one or more heavy chain constant region domains of a non-IgM isotype.

20. The polymeric antibody of claim 19 , wherein the non-IgM isotype is IgG.

21. The polymeric antibody of claim 1 , which comprises two immunoglobulin monomers to form a dimer, wherein each immunoglobulin monomer comprise an IgA tail-piece (αtp) and a Cα3 domain.

22. The polymeric antibody of claim 21 , wherein the two heavy chains of each immunoglobulin monomer each further comprise a Cα1 domain, and a Cα2 domain.

23. The polymeric antibody of claim 22 , wherein the two heavy chains of each immunoglobulin monomer comprise a heavy chain variable domain (VH), and wherein each heavy chain comprises, starting at the N-terminus, the VH, the Cα1 domain, the Cα2 domain, the Cα3 domain, and the αtp.

24. The polymeric antibody of claim 23 , wherein each immunoglobulin monomer further comprises two light chains associated with the two heavy chains.

25. The polymeric antibody of claim 21 , wherein the two heavy chains of immunoglobulin monomer are hybrid heavy chains further comprising one or more heavy chain constant region domains of a non-IgA isotype.

26. The polymeric antibody of claim 25 , wherein the non-IgA isotype is IgG.

27. The polymeric antibody of claim 1 , wherein the albumin protein is human serum albumin.