Characterization of new recombinant Immunoglobulins type-M binding to C1q by Biolayer Interferometry

The Immunoglobulins type-M (IgMs) are one of the first antibody classes mobilized during immune responses against pathogens and tumor cells. Binding to specific target antigens enables the interaction with the C1q complex which strongly activates the classical complement pathway. This biological function is the base for the huge therapeutic potential of IgMs but due to their high oligomeric complexity, in vitro production as well as biochemical and biophysical characterizations are challenging. In the present study, we present new attempts of recombinant production of two IgM models (IgM617 and IgM012) and the evaluation of their polymer distribution using biophysical methods (AUC, SEC-MALLS, Mass Photometry, transmission EM). Each IgM has an individual specific expression yield with different protein quality likely due to intrinsic IgM properties and patterning. Despite the presence of additional oligomeric states, purified recombinant IgMs retain their ability to activate complement in a C1q dependent manner. More importantly, a new method to evaluate their functional quality attribute by characterizing the kinetics of C1q binding to recombinant IgM has been developed using BioLayer Interferometry (BLI). We show that recombinant IgMs possess similar C1q binding properties as IgMs purified from human plasma.