• Subject eligibility criteria include individuals who are under the age of 25 at the time of SNUH-CD19-CAR-T administration. Confirmation of B-cell acute lymphoblastic leukemia diagnosed at the initial assessment by a treating physician for the first diagnosis is required. Immunophenotypic analysis of CD19 expression on leukemia cells must be confirmed through immune profiling at the time of the initial diagnosis of B-cell acute lymphoblastic leukemia. In patients experiencing hematologic relapse of B-cell acute lymphoblastic leukemia, CD19 expression should also be confirmed at the time of relapse confirmation.

‣ Patients must achieve hematologic complete remission defined as less than 5% blasts in the bone marrow after the first-line or second-line chemotherapy (first salvage therapy). Eligible patients for hematopoietic stem cell transplantation, defined by indications for transplantation, include those meeting at least one of the following criteria:

⁃ Philadelphia chromosome-positive due to t(9;22)(q34;q11) translocation.

⁃ Hypodiploidy defined by fewer than 44 chromosomes.

⁃ E2A-HLF gene fusion due to t(17;19) translocation.

⁃ Detection of minimal residual disease (MRD) positive at 0.01% or higher by next-generation sequencing confirmed after consolidation therapy and maintenance therapy.

⁃ Failure of the first-line therapy.

⁃ Cases not meeting any of the above criteria but deemed eligible for hematopoietic stem cell transplantation based on the investigator's judgment.