A Study Evaluating the Safety and Efficacy of Brexucabtagene Autoleucel (KTE-X19) in Adult Subjects With Relapsed/Refractory B-precursor Acute Lymphoblastic Leukemia (ZUMA-3)

Bridging therapy could be administered at the discretion of the investigator and is recommended for participants with high disease burden at baseline (M3 marrow \[\> 25% leukemic blasts\] or ≥ 1,000 blasts/mm\^3 in the peripheral circulation) to control participant's disease prior to conditioning chemotherapy. Bridging therapy includes: Attenuated VAD: Vincristine non-liposomal (1-2 mg IV weekly) or liposomal (2.25 mg/m\^2 IV weekly), and dexamethasone 20-40 mg IV or oral administration (PO) daily x 3-4 days per week. Optional doxorubicin 50 mg/m\^2 IV x 1 (first week only). Mercaptopurine (6-MP): 50-75 mg/m\^2/day by mouth (administer at bedtime on an empty stomach to improve absorption). Hydroxyurea: Doses titrated between 15-50 mg/kg/day (rounded to the nearest 500 mg capsule and given as a single daily oral dose on a continuous basis). DOMP: Dexamethasone 6 mg/m\^2/day PO (or IV) divided twice daily (BID) Days 1-5, vincristine 1.5 mg/m\^2 (maximum dose 2 mg) IV on Day 1, methotrexate 20 mg/m\^2 PO weekly, 6-MP 50- 75mg/m\^2/day PO daily. Attenuated FLAG/FLAG-IDA: fludarabine 30 mg/m\^2 IV days 1-2, cytarabine 2 g/m\^2 IV days 1-2, G-CSF 5 μg/kg subcutaneously (SC) or IV starts on Day 3 and can continue until day before the start of conditioning chemotherapy. With or without idarubicin 6 mg/m\^2 IV Days 1-2. Mini-hyper CVAD (courses A and/or B): * Course A: Cyclophosphamide 150 mg/m\^2 every 12 hours x 3 days, dexamethasone 20 mg/d IV or PO daily Days 1-4 and 11-14, vincristine 2 mg IV x 1 * Course B: Methotrexate 250 mg/m\^2 IV over 24 hours on Day 1,cytarabine 0.5 g/m\^2 IV every 12 hours x 4 doses on Days 2 and 3. After completion of the Month 24 visit, subjects who received an infusion of KTE-X19 will complete the remainder of the 15 year follow-up assessments in a separate long-term follow-up study, KT-US-982-5968