pH-dependent antigen-binding antibodies as a novel therapeutic modality.

Monoclonal antibodies have become a general modality in therapeutic development. However, even with infinite binding affinity to an antigen, a conventional antibody is limited in that it can bind to the antigen only once, and this results in antigen-mediated antibody clearance when the a membrane-bound antigen is targeted, or in antibody-mediated antigen accumulation when a soluble antigen is targeted. Recently, a pH-dependent antigen-binding antibody that binds to an antigen in plasma at neutral pH and dissociates from the antigen in endosome at acidic pH has been reported to overcome this limitation and to reduce antigen-mediated antibody clearance and antibody-mediated antigen accumulation. A pH-dependent binding antibody against a soluble antigen can be further improved by Fc engineering to enhance the Fc receptor binding. Various approaches, including histidine-based engineering, direct cloning from immunized animals, and synthetic and combinatorial libraries, have been successfully applied to generate pH-dependent binding antibodies against various antigens. This review discusses the features, approaches, advantages, and challenges of developing a pH-dependent binding antibody as a novel therapeutic modality. This article is part of a Special Issue entitled: Recent advances in molecular engineering of antibody.