IFN-γ levels in the BM of IDO-expressing AML cases (n=7; median 3.9 ng/ml, range 0.72-8.74) exceeded those measured in IDO-nonexpressing AML samples (n=4; median 0.97 ng/ml, range 0.8-3.68; p=0.047) and in BM blasts from a cohort of 7 children with ALL, used as controls (median 1.32 ng/ml, range 0.09-2.05; p=0.039). Here, IDO1 is linked to acute lymphoblastic leukemia.