PDCD1 and cancer: During chronic infections and in cancer, T lymphocytes are exposed to persistent inflammatory stimuli that lead cells to a deteriorating reversible process called “exhaustion”, which is associated with loss of T cell function and the expression of inhibitory receptors [5] such as Cytotoxic T-Lymphocyte Antigen 4 (CTLA-4), programmed cell death-1 (PD-1), lymphocyte activation gene-3 (LAG-3), CD244, CD160, CD39, T cell immunoglobulin, and mucin domain-containing protein 3 (TIM-3) [6].