IDO1 and cancer: Amongst more than 200 genes induced by IFN-γ [82], many of those genes are the molecules involved in cancer cell immune evasion, such as PD-L1, PD-L2, CTLA-4, CIITA, non-classical MHC class Ib antigens, IDO1, CXCL12 etc. [18,19,83].