PDCD1 and cancer: Immune cells conferring tumor tolerance include myeloid-derived suppressor cells, regulatory T cells (Treg), Th17 cells, and M2 macrophages; different immune checkpoint molecules (such as programmed cell death protein 1 [PD-1], cytotoxic T-lymphocyte antigen 4 [CTLA-4], and TIM3), along with other molecules and cytokines (such as LAG3, CD137, MHC class II, FASLG, IL-10, IL-23, TGF-β, INF-γ, scavenger receptor A, arginase, and CD40) may also be susceptible targets for anti-cancer immune modulation [92].