Bispecific antibodies (bsAbs) are often composed of more than two component chains, such as Fabs-in-tandem immunoglobin (FIT-Ig) comprising three different component chains, which bring challenges for generating a high proportion of the correctly assembled bsAbs in a stable cell line. During the CHO-K1 stable cell line construction of a FIT-Ig, we investigated the FIT-Ig component chain ratio in transfection, where two sets of expression vectors were designed. Both designs utilized two vectors for co-transfection. Multiple transfections with plasmid ratio adjustment were applied, and the resultant minipools were evaluated for expression titer and quality of produced FIT-Ig. The results suggested that abundant outer Fab short chains (twofold chain genes versus other chains) can promote complete FIT-Ig assembly and therefore reduce the fragmental impurities of FIT-Ig. This adjustment of the component chain ratios at the beginning is beneficial to FIT-Ig stable cell line generation and brings favorable clones to process development.
[This corrects the article DOI: 10.1093/abt/tbad009.].
As the most abundant immunoglobulin in blood and the most common human isotype used for therapeutic monoclonal antibodies, the engagement and activation of its Fc receptors by IgGs are crucial for antibody function. Assumed to be relatively constant within subtypes, recent studies reveal that antibody variable regions exert distal effects of modulating antibody-receptor interactions on antibody isotypes. These variable (V)-region distal effects are also expected for the IgG subtypes. With an in-depth understanding of the V-region effects, researchers can make a more informed antibody engineering approach and antibody purification strategy accounting for the functions of microbial immune evasion . In this study, we created a panel of IgG2/IgG3/IgG4 antibodies by changing the VH family (VH1-7) frameworks while retaining the complementary determining regions of pertumuzab and measured their interactions with FcγRIa, FcγRIIaH167, FcγRIIaR167, FcγRIIb/c, FcγRIIIaF176, FcγRIIIaV176, FcγRIIIbNA1 and FcγRIIIbNA2 receptors alongside B-cell superantigens Protein L and G using biolayer interferometry. The panel of 21 IgGs demonstrated that the VH frameworks influenced receptor binding sites on the constant region in a non-canonical manner. However, there was minimal influence on the binding of bacterial B-cell superantigens Proteins L and Protein G on the IgGs, showing their robustness against V-region effects. These results demonstrate the role of V-regions during the humanization of therapeutic antibodies that can influence FcR-dependent immune responses while retaining binding by bacterial B-cell superantigens for antibody purification. These in vitro measurements provide a clue to detailed antibody engineering and understanding of antibody superantigen functions that would be relevant with in vivo validation.