T cell exhaustion within the tumor microenvironment (TME) is a newly discovered phenomenon resulting from persistent antigen stimulation from chronic virus infection or tumors, in which tumor-infiltrated CD8+ T cells experience gradual alterations in their functional capacity while highly expressing multiple inhibitory receptors, including PD1, TIM3, LAG3, CTLA4, and TIGIT (Wherry and Kurachi, 2015; Blank et al., 2019). The gene discussed is PDCD1; the disease is neoplasm.