IDO1 and neoplasm: They promote tumor progression, angiogenesis, metastasis, and release indoleamine 2,3-dioxygenase (IDO), NOS2, ARG1, TGF-β, and IL-10 leading to the activation of M2 macrophage and Treg, and suppression of T-cell proliferation (Park et al., 2018; Wang and Mooney, 2018).