Atypical Teratoid/Rhabdoid Tumor

The purpose of this study is to evaluate the investigational oral drug AMXT 1501 in combination with oral eflornithine (DFMO). An investigational drug is one that has not been approved by the U.S. Food \& Drug Administration (FDA), or any other regulatory authorities around the world for use alone or in combination with any drug, for the condition or illness it is being used to treat. The goals of this part of the study are: * Establish a recommended dose of AMXT 1501 in combination with DFMO * Test the safety and tolerability of AMXT 1501 in combination with DFMO * To determine the activity of study treatments chosen based on: * How each subject responds to the study treatment * How long a subject lives without their disease returning/progressing

Loc3CAR is a Phase I clinical trial evaluating the use of autologous B7-H3-CAR T cells for participants ≤ 21 years old with primary CNS neoplasms. B7-H3-CAR T cells will be locoregionally administered via a CNS reservoir catheter. Study participants will be divided into two cohorts: cohort A with B7-H3-positive relapsed/refractory non-brainstem primary CNS tumors, and cohort B with diffuse midline gliomas (DMG). Participants will receive four (4) B7-H3-CAR T cell infusions over a 4 week period. The purpose of this study is to find the maximum (highest) dose of B7-H3-CAR T cells that are safe to give patients with primary brain tumors. Primary objectives * To determine the safety, maximum tolerated dose (MTD) and recommended phase 2 dose (RP2D) for the locoregional delivery of autologous B7-H3-CAR T cells in patients ≤ 21 years of age with recurrent/refractory B7-H3+ primary CNS tumors (Cohort A) or DMG (Cohort B). Secondary objectives * To assess the efficacy, defined as sustained objective response, a partial response (PR) or complete response (CR) observed anytime on active treatment with B7-H3-CAR T cells in patients with relapsed/refractory B7-H3+ primary CNS tumors (Cohort A) or DMG (Cohort B). * To characterize and monitor neurologic toxicities in patients while on study (Cohort A and B).

This is a Phase 1 study of central nervous system (CNS) locoregional adoptive therapy with autologous CD4+ and CD8+ T cells lentivirally transduced to express a B7H3-specific chimeric antigen receptor (CAR) and EGFRt. CAR T cells are delivered via an indwelling catheter into the tumor resection cavity or ventricular system in children and young adults with diffuse intrinsic pontine glioma (DIPG), diffuse midline glioma (DMG), and recurrent or refractory CNS tumors. A child or young adult meeting all eligibility criteria, including having a CNS catheter placed into the tumor resection cavity or into their ventricular system, and meeting none of the exclusion criteria, will have their T cells collected. The T cells will then be bioengineered into a second-generation CAR T cell that targets B7H3-expressing tumor cells. Patients will be assigned to one of 3 treatment arms based on location or type of their tumor. Patients with supratentorial tumors will be assigned to Arm A, and will receive their treatment into the tumor cavity. Patients with either infratentorial or metastatic/leptomeningeal tumors will be assigned to Arm B, and will have their treatment delivered into the ventricular system. The first 3 patients enrolled onto the study must be at least 15 years of age and assigned to Arm A or Arm B. Patients with DIPG will be assigned to Arm C and have their treatment delivered into the ventricular system. The patient's newly engineered T cells will be administered via the indwelling catheter for two courses. In the first course patients in Arms A and B will receive a weekly dose of CAR T cells for three weeks, followed by a week off, an examination period, and then another course of weekly doses for three weeks. Patients in Arm C will receive a dose of CAR T cells every other week for 3 weeks, followed by a week off, an examination period, and then dosing every other week for 3 weeks. Following the two courses, patients in all Arms will undergo a series of studies including MRI to evaluate the effect of the CAR T cells and may have the opportunity to continue receiving additional courses of CAR T cells if the patient has not had adverse effects and if more of their T cells are available. The hypothesis is that an adequate amount of B7H3-specific CAR T cells can be manufactured to complete two courses of treatment with 3 or 2 doses given on a weekly schedule followed by one week off in each course. The other hypothesis is that B7H3-specific CAR T cells can safely be administered through an indwelling CNS catheter or delivered directly into the brain via indwelling catheter to allow the T cells to directly interact with the tumor cells for each patient enrolled on the study. Secondary aims of the study will include evaluating CAR T cell distribution with the cerebrospinal fluid (CSF), the extent to which CAR T cells egress or traffic into the peripheral circulation or blood stream, and, if tissues samples from multiple timepoints are available, also evaluate disease response to B7-H3 CAR T cell locoregional therapy.

The purpose of this research study is to test the safety and effectiveness of a cell therapy at different doses for children and young adults with recurrent or progressive brain tumors. Recurrent/recurred means a tumor that has gone away and then came back. This cell therapy is called B7- H3.CD28Z.CART, referred to as B7-H3 CAR T cells. B7-H3 is a protein that is over-expressed on many tumor cells, making it a good target for cancer cell therapy. The names of the study investigational therapies involved in this study are: * Fludarabine (a type of chemotherapy) * Cyclophosphamide (a type of chemotherapy) * B7-H3 CAR T cells (a type of cellular therapy)