PDCD1 and neoplasm: Immune exhaustion and dysfunction of cytotoxic T cells and NK cells are fatal to the host with cancer, since multiple immune inhibitory molecular expressions, including CTLA4, PD1, TIM3, LAG3, and TIGIT, are abundantly induced for braking of the activation signals followed by a decrease in anti-tumor effector molecules, such as IL2, IFNγ, TNFα, and granzyme B (GZMB) [129].