Blockade of the PD-1/PD-L1 axis results in antitumor activity due to its ability, in part, to inhibit interferon-induced adaptive immune resistance characterized by interferon-induced JAK-STAT signaling that results in activation of interferon regulatory factor 1 (IRF1) and expression of PD-L1 and IDO that allow for cancer cell immune evasion [67]. This evidence concerns the gene IDO1 and cancer.