IDO2 and neoplasm: Myeloid-derived suppressor cells (MDSCs), which are not present in healthy individuals, expand in tumor-bearing hosts and contribute to tumor immune evasion through various mechanisms, including oxidative stress and nutrient depletion via inducible nitric oxide synthase (iNOS) and arginase, transforming growth factor-beta (TGFβ), IL-10, cyclooxygenase-2 (COX2), and indoleamine 2,3-dioxygenase (IDO) production (49, 50).