Exhausted T cells have the following two characteristics: (1) high expression of immune checkpoint molecules under persistent infection or antigen stimulation, such as programmed cell death protein 1 (PD1) [12–14], lymphocyte activating 3 (LAG3) [15], cytotoxic T-lymphocyte associated protein 4 (CTLA4) [16], T-cell immunoreceptor with Ig and ITIM domains (TIGIT) [17], CD160 [18], TNF receptor superfamily member 9 (TNFRSF9) [19], and hepatitis A virus cellular receptor 2 (HAVCR2) [20]; and (2) decreased proliferation, viability, and the loss of cytotoxic activity against tumours in vitro [21]. This evidence concerns the gene PDCD1 and neoplasm.