PD-1, also known as CD279 [6], suppresses the inflammatory activity of T lymphocytes, which prevents autoimmune diseases through a series of apoptosis-related mechanisms: (1) Promotion of apoptosis of antigen-specific effector T cells (Teffs) that become tumor-infiltrating lymphocytes (TILs) at tumor sites; and (2) reduction of the apoptosis of regulatory T cells (Tregs), which plays the opposite role of Teffs by decreasing the proliferation of effector T cells. Here, PDCD1 is linked to neoplasm.