CD19x22 Chimeric Antigen Receptor T-cell Therapy (CAR T) in Pediatric B-ALL

This is an open-label Phase I trial consisting of 2 cohorts to determine the safety and tolerability of CD19x22 CAR T in Pediatric Patients with R/R B-ALL. This trial will include two parallel cohorts based on disease burden prior to lymphodepleting chemotherapy, Cohort 1: high disease burden cohort: defined as \>=25% bone marrow lymphoblasts and/or non-CNS extramedullary disease, and Cohort 2: low disease burden cohort: defined as \<25% bone marrow lymphoblasts and no non-CNS extramedullary disease. Dose escalation will proceed independently within each cohort using the Bayesian Optimal Interval (BOIN) design. This trial will enroll up to 53 patients with 21 patients in each cohort receiving treatment with lymphodepleting chemotherapy followed by CD19x22 CAR T cell infusion, with a total of up to 42 treated patients overall. Patients will be assessed for dose limiting toxicities (up to 28 days from infusion) to determine a maximum tolerated dose (MTD) and for preliminary efficacy through morphological remission rate and measurable residual disease (MRD) levels.