CD8A and neoplasm: Programmed cell death 1 (PD-1), encoded by the PDCD1 gene, and its ligands PD-L1 (also known as CD274) and PD-L2 (also known as PDCD1LG2 or CD273), plays a crucial role in maintaining self-tolerance and are associated with immune escape in cancer by inhibiting the direct cytotoxic activities of effector CD8+ T cells on tumor cells (34).