RecruitingBiological interventionAutologous HuCART19 T Cells Manufactured Using the CliniMACS Prodigy Platform for Pediatric B-ALL (huCART19 Prodigy)This study will determine the safety and efficacy of moving to a second-generation manufacturing process using the CliniMACS Prodigy platform to manufacture huCART19 cells for patients with B cell Acute Lymphoblastic Leukemia (B-ALL).