IDO1 and neoplasm: Successful immune escape of tumor cells includes also the production of soluble factors in the microenvironment by tumor cells (TGF-β, LDH5), the induction of co-inhibitory molecules (PD-1, LAG-3 and TIM-3) and the release of immunosuppressive factors (CSF-1, VEGF, PGE2, NO, Arg I, IDO and Gal-1) (64).