The synergistic effects of the VH families and CH regions of multimeric IgM on its interaction with FcμR, and antigen

As the primary response antibody with increasing interest as a therapeutic antibody format, IgM is also the largest antibody structure among the five major human isotypes. Spontaneously forming pentamer and hexamers, IgM has avidity effects that could compensate for weaker interactions, although steric hindrances can occur for certain epitopes. With recent evidence of the heavy chain constant region affecting antigen binding and the VH families of the V-regions affecting FcR engagement found on other isotypes, we investigated CDR-grafted Trastuzumab and Pertuzumab VH1-7 IgMs for biolayer interferometry. From our panel of the 14 IgM variants, the V-regions holistically affected FcμR binding, and the IgM C-region modulated Her2 engagements with contributions from the V-regions and influences from protein L binding at the Vκ. These findings revealed the oligomerization effect of IgMs to play a significant role in both FcμR and antigen binding that is distinct from the other isotypes that can guide the development and protein en-gineering of IgM therapeutics.