Peds CHAMP1ON - Hematopoietic Stem Cell And Monoclonal Antibody PD-1 Blockade for RecurreNt Pediatric High-Grade Glioma

Inclusion Criteria: * Patients must have a histologically confirmed diagnosis of a non-brainstem high-grade glioma (NB-HGG, WHO Grade III or IV astrocytoma, oligodendrogliomas, oligoastrocytomas, ependymomas) that is recurrent, progressive or refractory following radiotherapy with or without chemotherapy. Patients must be candidates for standard of care surgical resection or biopsy. * Patients must have measurable disease, defined as at least one lesion that can be accurately measured in two dimensions. * Patients must have recovered from the acute treatment related toxicities (defined as ≤ grade 2 if not defined in eligibility criteria) of all prior chemotherapy, immunotherapy, radiotherapy or any other treatment modality prior to entering this study. * Patients must have received their last dose of known myelosuppressive anticancer therapy greater than 21 days prior to enrollment. * Patients must have received their last dose of the investigational or biologic agent ≥ 7 days prior to study enrollment. * For agents that have known adverse events occurring beyond 7 days after administration, this period must be extended beyond the time during which adverse events are known to occur. The duration must be discussed with and approved by the study chair. * Monoclonal antibody treatment and/or agents with prolonged half-lives: At least three half-lives must have elapsed prior to enrollment. * Patients must have had their last fraction of: * Craniospinal irradiation ≥ 3 mo…