B7-H3.CD28Z.CART in CNS Neoplasms

Pre-screening Inclusion Criteria: * Participants must have histologically and/or molecularly confirmed CNS embryonal tumor (see eligible tumor types below), OR ependymoma that is recurrent/progressive following standard of care treatment. --Eligible CNS embryonal tumor types include: * Medulloblastoma * Atypical Teratoid Rhabdoid Tumor (ATRT) * Embryonal Tumor with Multilayered Rosettes (ETMR) Pineoblastoma * Other CNS embryonal tumor types, at the discretion of the study chair (or designee) * Participants must have adequate pre-trial tumor material available to determine B7- H3 expression status. Tumor tissue from the most recent resection or biopsy of recurrent disease is preferred. If unavailable, tumor tissue from prior recurrences or from time of initial diagnosis is acceptable. Biopsies will not be performed for participation in this research trial or for research purposes. * Pre-screening IHC Consent: All participants ≥ 18 years of age must be able to give informed consent. For participants \<18 years of age, their legal authorized representative (LAR) (i.e. parent or guardian) must give informed consent. Pediatric participants will be included in age-appropriate discussion and written assent will be obtained for those ≥10 years of age, where appropriate. If a minor becomes of age during participation of this study, they will be asked to reconsent as an adult. Inclusion Criteria: * Participants must have histologically and/or molecularly confirmed CNS embryonal tumor (see eligible tumor types below), OR ependymoma that is recurrent/progressive following standard of care treatment. --Eligible CNS embryonal tumor types include: * Medulloblastoma * Atypical Teratoid Rhabdoid Tumor (ATRT) * Embryonal Tumor with Multilayered Rosettes (ETMR) * Pineoblastoma * Other CNS embryonal tumor types, at the discretion of the study chair (or designee) * B7-H3 expression: Demonstration of B7-H3 expression with H score greater than 100 by immunohistochemistry (IHC) is required. * Age: greater than or equal to two (2) years of age and less than or equal to 21 years of age. The first participant treated at each dose level within each stratum (Standard Risk and High Risk) will be ≥ 6 years of age when feasible. * Disease status: Participants must have evaluable disease in the central nervous system to be eligible. Evaluable disease includes either measurable OR non-measurable disease, defined as follows: --Measurable disease (contrast-enhancing or non-enhancing tumor) * Clearly defined lesional margins with two perpendicular diameters of at least 10mm, OR * At least two times (in both perpendicular diameters) the MRI slice thickness, plus the interslice gap --Non-measurable disease (tumor that is too small to be accurately measured) * Lesion that is measurable in only one perpendicular dimension, OR * Lesion that is less than 10mm in at least one perpendicular dimension, OR * Lesion that is less than two times the MRI slice thickness, plus the interslice gap * Note: Leptomeningeal (LM) disease is considered non-measurable but evaluable. * Performance status: Karnofsky performance status ≥60% for participants ≥16 years of age and Lansky performance status ≥60% for participants \<16 years of age (see APPENDIX A PERFORMANCE STATUS CRITERIA). NOTE: Participants with neurologic deficits must have a stable neurologic exam for seven (7) days prior to enrollment. Participants who are unable to walk because of paralysis, but who are up in a wheelchair, will be considered ambulatory for the purpose of assessing the performance score. * Life expectancy of greater than 12 weeks * Prior therapy: Participants must have received prior standard of care therapy, including maximal safe surgical resection, radiation therapy and/or standard chemotherapy, and is recovered from all acute treatment-related toxicities (defined as ≤ Grade 1 or stable) from all prior therapy before entering this study There is no upper limit to the number of prior therapies allowed, but must have received all standard curative options for their tumor type. * Participants must meet the following washouts prior to enrollment: * Radiation therapy - Participants must have had their last fraction of: ---Craniospinal irradiation, whole brain radiation therapy, or radiation therapy to \>50% of the pelvis or spine \>28 days prior to enrollment ---Focal irradiation (small port) \>14 days prior to enrollment * At least 14 days since any prior cytotoxic chemotherapy * At least 7 days since any biologic antineoplastics, tyrosine kinase inhibitor, targeted agent * At least 21 days or 5 half-lives (whichever is shorter) since any investigational antineoplastic or disease-directed agent (but at least 28 days from prior investigational antineoplastic vaccine therapy) * At least 21 days since any monoclonal antibody therapy * At least 90 days since any systemic inhibitor/stimulatory immune checkpoint therapy * At least 28 days from prior autologous stem cell transplantation, with no ongoing toxicities * At least 14 days after peg-filgrastim and 7 days for hematopoietic growth factor support * Steroid use: Must not require concurrent systemic steroid therapy, although physiologic corticosteroid replacement therapy for management of pituitary/adrenal insufficiency and/or topical administration (e.g. inhaled or dermatologic) is allowed. Use of topical, ocular, intranasal, or inhaled corticosteroids are permitted per PI discretion. * Participants must have adequate organ function, as defined below --Adequate bone marrow function * Hemoglobin ≥ 8 g/dL * Absolute neutrophil count (ANC) ≥ 1000 cells/uL * Absolute lymphocyte count (ALC) ≥ 150 cells/uL * Platelets ≥100,000/uL (unsupported, defined as no platelet transfusion within 4 days) * Adequate renal function defined as creatinine within normal limits for age OR creatinine clearance (as estimated by Cockcroft Gault Equation for