• Age ≥14 years, gender is not limited;

• Patients with clinically diagnosed relapsed/refractory B-ALL (except those presenting with extramedullary disease only), including any of the following:

∙ Failure to obtain CR after 2 cycles of standard chemotherapy;

‣ First induction of CR, but duration of CR is ≤12 months;

‣ Relapsed/refractory B-ALL that has failed to respond to the first or multiple salvage treatments;

‣ Relapse after hematopoietic stem cell transplantation, including hematological relapse and positive micro residual disease (MRD).

• Cytological or histological confirmation of tumor cell immunophenotyping as CD19 positive;

• Bone marrow with a ratio of ≥5% primitive/naïve lymphocytes (morphology);

• Expected survival time of more than 3 months;

• Eastern Cooperative Oncology Group (ECOG) score of 0-2;

• Vital organ function meets the following requirements: left ventricular ejection fraction ≥50% on echocardiography; serum creatinine≤1.5 × upper limit of normal range (ULN); glutamine aminotransferase, aspartate aminotransferase ≤3 times ULN, total bilirubin ≤1.5 times ULN;

• Pregnancy tests for women of childbearing age should be negative, and both men and women should agree to use effective contraception during treatment and for the following 1 year.

• Toxicity of prior antitumor therapy ≤ grade 1 (according to CTCAE version 5.0) or acceptable inclusion/exclusion criteria level.

⁃ No significant hereditary disease;

⁃ Be able to understand the requirements and matters of the trial and be willing to participate in the clinical study as required;

⁃ Sign the trial informed consent form.