Activated T cells are primary mediators of immune functions, and express multiple inhibitory immune checkpoint receptors molecules including CTLA-4, PD-1, LAG3, TIM-3, BTLA4, killer immunoglobulin-like receptors (KIR), the T-cell immunoglobulin and ITIM domain (TIGIT), tumor necrosis factor receptor (TNFR) superfamily, V-domain Ig suppressor of T cell activation (VISTA), and Indoleamine 2, 3-dioxygenase 1 (IDO1), which regulate the T cell responses to tumor antigens [17]. This evidence concerns the gene IDO1 and neoplasm.