Clinical Study of Universal CD19 CAR-γδ T Cell Infusion in the Treatment of Relapsed/Refractory Acute B Lymphoblastic Leukemia

Inclusion Criteria: * Age \> 14 years, gender unrestricted; * Clinically diagnosed with relapsed/refractory acute B-lymphoblastic leukemia, with bone marrow blast/immature lymphocyte proportion ≥5% (morphology) (excluding cases with isolated extramedullary involvement), meeting any of the following criteria: 1. Failure to achieve CR after 2 cycles of standard chemotherapy; 2. Initial induction achieved CR, but CR duration ≤12 months; 3. Relapsed/refractory B-ALL refractory to first or multiple salvage therapies; 4. Post-hematopoietic stem cell transplantation relapse, including hematological relapse and minimal residual disease (MRD) positivity; 5. Patients for whom no standard therapy exists. * Cytology or histology confirms tumor cell immunophenotype as CD19-positive; * Expected survival time exceeding 3 months; * Eastern Cooperative Oncology Group (ECOG) performance status score of 0-2; * Key organ functions meeting the following criteria: left ventricular ejection fraction ≥50% by echocardiography; serum creatinine ≤1.5 × upper limit of normal (ULN); alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤3 × ULN; total bilirubin ≤1.5 × ULN; * Negative pregnancy test for women of childbearing potential; both males and females agree to use effective contraception during treatment and for 1 year thereafter; * Toxicity from prior anti-tumor therapy ≤ Grade 1 (according to CTCAE v5.0) or at an acceptable level per inclusion/exclusion criteria; * No significant hereditary diseases; * Able to comprehend the trial requirements and procedures, and willing to participate in the clinical study as required; * Signed informed consent form for the trial Exclusion Criteria: * Presence of central nervous system (CNS) involvement or a clinically significant history of CNS diseases, such as epilepsy and cerebrovascular diseases; * Pregnant or lactating women, or women who disagree to use effective contraception during treatment and within 1 year after treatment; * Other malignancies that are not in remission; * Patients with primary immunodeficiency or autoimmune diseases requiring immunosuppressive therapy; * Patients who have received allogeneic immune cell therapy within 6 months before enrollment, or donor lymphocyte infusion within 6 weeks before enrollment; * Confirmed positive anti-FMC63 and DSA responses in the patient's serum; * Patients who have participated in other clinical trials within 4 weeks before enrollment; * Uncontrolled infectious diseases or other serious conditions, including but not limited to infections (human immunodeficiency virus, acute or chronic active hepatitis B or C), congestive heart failure, unstable angina, arrhythmia, or conditions considered by the treating physician to pose unpredictable risks; * History of stroke or intracranial hemorrhage within 3 months before enrollment; * Major surgery or trauma within 28 days before enrollment, or main side effects not yet recovered; * History of allergy to any component of the cell product; * Inability to understand or unwillingness to sign the informed consent form; * Other reasons deemed by the researchers as unsuitable for the clinical trial.