Sheathless CE-MS as a tool for monitoring exchange efficiency and stability of bispecific antibodies.

Bispecific monoclonal antibodies (BsAbs) are receiving great attention due to their extensive benefits as biopharmaceuticals and their involvement in IgG4 mediated autoimmune diseases. While the production of BsAbs is getting more accessible, their analytical characterization remains challenging. We explored the potential of sheathless CE-MS for monitoring exchange efficiency and stability of in-house produced bispecific antibodies. Two IgG4 bispecific antibodies with different molecular characteristics were prepared using controlled Fragment antigen binding (Fab)-arm exchange. Separation of BsAbs from their parent monospecific antibodies was achieved using a polyethyleniimine (PEI)-coated capillary and acidic background electrolytes permitting reliable assessment of the exchange efficiency. This was especially valuable for a Fab-glycosylated BsAb where the high glycan heterogeneity resulted in an overlap of masses with the monospecific parent antibody, hindering their discrimination by MS only. The method showed also good capabilities to monitor the stability of the generated BsAbs under different storage conditions. The levels of degradation products were different for the studied antibodies indicating pronounced differences in stability. Overall, the proposed method represents a useful analytical tool for exchange efficiency and stability studies of bispecific antibodies.