Subclass switching enhances protective efficacy of a non-neutralizing H7N9 avian influenza antibody

Non-neutralizing antibodies contribute to protection against the H7N9 subtype avian influenza virus through Fc effector functions. Antibody subclass plays a critical role in determining binding affinity to Fc receptors (FcR) and downstream Fc effector functions. In this study, to assess whether antibody subclass switching can enhance antibody protective efficacy, subclass of a non-neutralizing monoclonal antibody (mAb) against the hemagglutinin of H7N9 virus was switched from IgG1 to IgG2a, and their activity and protective efficacy were assessed. Subclass switching caused no significant changes in antigen binding, hemagglutination-inhibition and virus neutralizing activities of the antibody. The hybridoma-derived mAb conferred no protection against H7N9 virus infection. Interestingly, both IgG2a and IgG1 antibodies produced in CHO cells provided full protection against mortality caused by a sublethal H7N9 virus challenge. Upon lethal challenge, IgG2a antibody conferred 70% protection, whereas its IgG1 counterpart only provided 30% protection. However, both antibodies did not decrease virus loads in mouse lungs. Moreover, compared to the IgG1 antibody, affinity of the subclass-switched IgG2a antibody to FcR was significantly increased, as evidenced by enhanced binding of the antibody to recombinant murine FcγRI and to FcRs on murine macrophages. Our findings highlighted a benefit of subclass-engineering to antibody modification and development of therapeutic antibodies.