This is a first-in-children phase 1 trial using indoximod, an inhibitor of the immune "checkpoint" pathway indoleamine 2,3-dioxygenase (IDO), in combination with temozolomide-based therapy to treat pediatric brain tumors. Using a preclinical glioblastoma model, it was recently shown that adding IDO-blocking drugs to temozolomide plus radiation significantly enhanced survival by driving a vigorous, tumordirected inflammatory response. This data provided the rationale for the companion adult phase 1 trial using indoximod (IND#120813) plus temozolomide to treat adults with glioblastoma, which is currently open (NCT02052648). The goal of this pediatric study is to bring IDO-based immunotherapy into the clinic for children with brain tumors. This study will provide a foundation for future pediatric trials testing indoximod combined with radiation and temozolomide in the up-front setting for patients with newly diagnosed central nervous system tumors.