1-methyl-l-tryptophan (1-MT, also known as Indoximod), the inhibitor of IDO1, was effective with combined TMZ in animal models of malignant gliomas (exclusively corresponding to WHO grade IV gliomas) [215], hence several phase I/II trails exploring the safety and efficacy of combined 1-MT and chemotherapy in both pediatric and adult patients with gliomas are ongoing. Here, IDO1 is linked to central nervous system cancer.