IDO1 and neoplasm: Indeed, MSC can interfere with the recognition of tumor cells by immune system producing and releasing immunoregulatory factors as TGFβ, prostaglandin E2 (PGE2), tumor necrosis factor α (TNFα), indolamine 2, 3-dioxygenase (IDO), hemeoxygenase (HO), NOS2, ARG1–2, IL10 [29–32].