This is a bispecific monoclonal antibody directed against both the immunosuppressive ligand, programmed cell death 1 ligand 1 (PDL1, cluster of differentiation 274, CD274), and cytotoxic T-lymphocyte-associated antigen 4 (CTLA4), with potential immune checkpoint inhibitory and antineoplastic activities. Upon administration, erfonrilimab targets and binds to both PDL1 expressed on tumor cells and CTLA4 expressed on T cells. It prevents the binding of PDL1 to its receptor, programmed cell death protein 1 (PD1, CD279), and inhibits the PD1 and CTLA4-mediated downregulation of T-cell activation and proliferation. This restores immune function and activates a sustained cytotoxic T-lymphocyte (CTL)-mediated immune response against tumor cells. Both PDL1, which is overexpressed in many human cancer cell types, and CTLA4, an inhibitory T-cell receptor, play a role in the downregulation of the immune system and tumor evasion from host immunity.