PDCD1 and cancer: Nivolumab (BMS-936558) is a fully human IgG4 programmed cell death 1 (PD-1) immune checkpoint inhibitor that enhances the immune T cell response by blocking the interaction between the PD-1, an inhibitory receptor on activated T lymphocytes, and the programmed cell death ligand 1 (PD-L1) expressed on cancer cells.