IDO1 and neoplasm: For example, constitutively activated KIT signaling in GI tumors can lead to overexpression of indoleamine-2,3-dioxygenase (IDO), thus increasing Treg cell infiltration and promoting tumor growth; furthermore, melanoma cells activated by β-catenin/Wnt signaling can inhibit DC-mediated antigen presentation and prevent CD8+ T cell infiltration (78).