Fourth Ventricular Administration of Immune Checkpoint Inhibitor (Nivolumab) and Methotrexate or 5-Azacytidine for Recurrent Medulloblastoma, Ependymoma, and Other CNS Malignancies

The goal of this clinical trial is to assess the safety, toxicity, and antitumor activity of fourth ventricular infusions of nivolumab plus 5-azacytidine for recurrent ependymoma and nivolumab plus methotrexate for recurrent medulloblastoma and other CNS malignancies. Additionally, the study will explore immunologic responses to nivolumab. The hypothesis is that local administration of nivolumab, an immune checkpoint inhibitor, is safe and will lead to even more robust treatment responses when administered following 5-azacytidine in patients with recurrent ependymoma or methotrexate in patients with medulloblastoma or other CNS tumors.