IDO1 and neoplasm: Second, tumor cells and other cells from the tumor microenvironment can promote an immune privilege status by secretion of immunosuppressive cytokines—such as IL-1, IL-6, IL-10, TGFβ, TNFα, or VEGF [11,12,13,14,15,16,17,18]—or modulation of the expression of immunoregulatory molecules to induce T cell anergy or tolerance, such as the immune checkpoints molecules of the B7 family (PD1/PDL1, B7-1, B7-2/CTLA4, B7-H4), A2AR, LAG-3, galectin-9/TIM-3, IDO, and VISTA [19,20,21,22].