IDO1 and neoplasm: The activated MSCs robustly support tumor progression and metastasis directly by inducing EMT, and indirectly through the production of numerous immunomodulatory molecules, such as TGFβ, PGE2, IL6, IL8, VEGF, TNFα, IL1β, IDO, and FSTL1, to generate and expand Tregs, MDSCs, and DCregs [109,110].