IDO1 and neoplasm: Alternatively, inhibiting glutamine metabolism of the MDSCs themselves not only led to activation-induced cell death and conversion of MDSCs to inflammatory macrophages, also impaired suppressive function of MDSCs via inhibiting IDO expression in the tumor and MDSCs, that resulted in a marked decrease in kynurenine levels, and rendered checkpoint blockade-resistant tumors susceptible to immunotherapy in tumor-bearing mice (132).