CD4 and acute myeloid leukemia: IDO1 constitutively expressing AML cells co-cultured with T cells and DCs can inhibit CD4+and CD8+T cell proliferation, promote Tregs proliferation, impair DCs maturation, and eventually suppress anti-tumor immune response [34–36].Despite the fact that 3 clinical studies (NCT03491579, NCT03444649, NCT02835729) have been conducted to explore the efficacy of combination of epacadostat and chemotherapy in AML [11], the role of IDO1 in AML and its underlying mechanism is still uncertain.