8. 4.2 Mode of Action Nivolumab is a fully human monoclonal immunoglobulin (Ig) G4 antibody that binds to the PD - 1 cell surface membrane receptor, a negative regulatory molecule expressed by activated T and B lymphocytes. Inhibition of the interaction between PD - 1 and its lig ands promotes immune responses and antigen - specific T cell responses to both f oreign antigens as well as self - antigens. J1790 / Version 7.0 / December 10, 2020 52 8.