PDCD1 and neoplasm: Programmed death-1 (PD-1), which is expressed on T cells, B cells, and myeloid cells, and its ligands programmed death-ligand 1 (PD-L1) and programmed death-ligand 2 (PD-L2), which are expressed on tumor cells and APCs, inhibit T-cell activation and proliferation when bound, reduce cytokine production, and impair cytotoxic functions (Figure 1) [12,13].