IDO1 and acute myeloid leukemia: Overall, treatment with IFN-γ for 72 hours translated into the up-regulation of functional IDO1 (Figure 1A) and into the long-term maintenance of IDO enzyme activity in 51% of AML cases, as reflected by heightened production of kynurenine (median 22.05 μM/L, range 6.0-36.0, in IFN-γ-stimulated cultures compared with 0.85 μM/L, range 0.4-1.7, in unstimulated cultures; p<0.0001) and by concomitant depletion of tryptophan (median 4.6 μM, range 1-22.6, in IFN-γ-stimulated cultures compared with 39.1 μM, range 18.2-51.0 in unstimulated cultures; p<0.0001; Figure 1B and 1C).