IDO1 and neoplasm: Recent studies have shown that several potential molecules and pathways, such as suppressive cytokines IL-10 and TGF-β, as well as the inhibitor molecules PD-1 and IDO, are utilized by tumor cells to induce immunosuppression and immune escape (Croci et al, 2007; Uyttenhove et al, 2003; Whiteside, 2008).