Assessment of Senl_B19 CAR-T Cells in Relapsed/Refractory CD19+ B-ALL

Inclusion Criteria: * 1.Sign the informed consent and be willing and able to comply with the visit, treatment regimen, laboratory examination and other requirements of the study as stipulated in the trial flow chart; 2.Male or female subjects. Age between 3 and 25 years (inclusive) at the time of ICF signing； 3.Confirmed diagnosis of relapsed/refractory B-ALL at ICF signing; 4.\>5% blasts on screening bone marrow biopsy/aspirate; 5.CD19+ malignant cells by flow cytometry (bone marrow or peripheral blood) at screening; 6.Patients with Ph+ ALL are eligible if they meet the relapsed/refractory criteria and have either: failed ≥2 TKI regimens (unless they have a T315I mutation), demonstrated TKI intolerance, or have a contraindication to TKIs; 7.Estimated survival time\>3 months. Exclusion Criteria: * 1.Relapse of isolated extramedullary disease; 2.Burkitt lymphoma/leukemia； 3.Active acute or moderate-to-severe chronic GVHD within 4 weeks prior to ICF signing. Or, any systemic GVHD treatment within 4 weeks prior to infusion; 4.No uncontrolled active infection at the time of ICF signing or apheresis.; 5.Prior receipt of any CAR-T therapy or other cellular/gene therapy before screening; 6.Received investigational drugs or systemic anti-tumor therapy within 4 weeks or 5 half-lives (whichever longer) prior to apheresis; 7.Active interstitial lung disease/pneumonitis at the time of ICF signing; 8.Subjects whom the Investigator considers unable to comply with the study protocol or who are otherwise not an appropriate candidate for the study for any reason;