The aim of this study was to characterize the product variants of a therapeutic T-cell bispecific humanized monoclonal antibody (TCB Mab, ∼200 kDa, asymmetric) and to develop an online cation-exchange chromatography native electrospray mass spectrometry method (CEC-UV-MS) for direct TCB Mab charge variant monitoring during bioprocess and formulation development. For the identification and functional evaluation of the diverse and complex TCB Mab charge variants, offline fractionation combined with comprehensive analytical testing was applied. The offline fractionation of abundant product variant peaks enabled identification of coeluting acid charge variants such as asparagine deamidation, primary and secondary Fab glycosylation (with and without sialic acid), and the presence of O-glycosylation in the G4S-linker region. Consequently, a new nonconsensus N-glycosylation motif (N-338-FG) in the heavy chain CDR region was discovered. Functional evaluation by cell-based potency testing demonstrated a clear and negative impact of both asparagine deamidations, whereas the O-glycosylation did not affect the TCB Mab biological activity. We established an online native CEC-UV-MS method, with an ammonium acetate buffer and pH gradient, to directly monitor the TCB Mab charge variants. All abundant chemical degradations and post-translational amino acid modifications already identified by offline fraction experiments and liquid chromatography mass spectrometry peptide mapping could also be monitored by the online CEC-UV-MS method. The herein reported online native CEC-UV-MS methodology represents a complementary or even alternative approach for multiattribute monitoring of biologics, offering multiple benefits, including increased throughput and reduced sample handling and intact protein information in the near-native state.
Keywords: Fab glycosylation; bispecific antibodies; cation-exchange chromatography; critical quality attributes; fragmentation; multiattribute monitoring; native mass spectrometry; online HPLC; product variants.