Removing half antibody byproduct by Protein A chromatography during the purification of a bispecific antibody.

Half antibody (one half of an antibody which comprises a heavy chain and a light chain) is a common byproduct in bispecific antibody (bsAb) production and in many cases it represents the major product-related impurity. As half antibody contains only one Fc-domain, it binds Protein A resin weaker than the target bsAb, which contains the full Fc-region. Indeed, Protein A chromatography provides certain resolution between half antibody and the intact bsAb under linear pH gradient elution. Nevertheless, separation between these two species is far from complete under this condition. In this study, we demonstrated that adding salt additive to Protein A mobile phase can significantly improve resolution between half antibody and the intact bsAb, allowing most of the half antibody impurity in the load to be removed by this capture step. Having the majority of half antibody byproduct removed at this early stage is a big advantage as it improves the overall robustness of the downstream process.