IDO1 and acute myeloid leukemia: IFN-γ is a prototypical inducer of indoleamine 2,3-dioxygenase-1 (IDO1) [96], which catabolizes the essential amino acid tryptophan to immune suppressive intermediates, collectively referred to as kynurenines, and is over-expressed by a variety of solid tumors and hematological malignancies, including 50% of patients with newly diagnosed AML [97,98,99,100,101].