PDCD1 and neoplasm: Nivolumab, a human immunoglobulin G4 (IgG4) monoclonal antibody, specifically blocks the binding of PD-1 to its ligands PD-L1 and PD-L2, relieving the immune suppression of tumor cells on T-cells and restoring the T-cell’s ability to recognize and attack tumor cells, thereby enhancing the anti-tumor immune response (3).