PDCD1 and neoplasm: Nivolumab is a programmed cell death protein 1 (PD-1) immune checkpoint inhibitor antibody that selectively blocks the interaction between PD-1, which is expressed on activated T cells, and programmed death-ligand 1 (PD-L1) and PD-L2, which are expressed on immune cells and tumor cells.[6] This inhibition of binding between PD-1 and its ligands by nivolumab stimulates the apoptosis of activated T cells, resulting in antitumor effects.