CD19 Targeted CAR T Cell Therapy in Patients With Relapsed/ Refractory B Cell Acute Lymphoblastic Leukaemia (ALL)

Inclusion Criteria: CD19+ ALL patients with any of the following: 1. Relapsed or Refractory CD19 positive B-cell acute lymphoblastic leukemia (R/R B-ALL) A. Primary refractory disease despite at least 2 cycles of an intensive chemotherapy regimen designed to induce remission B. Refractory disease despite salvage therapy C. 2nd or greater relapse D. Any relapse after allogeneic hematopoietic stem cell transplantation 2. Informed consent explained to and signed by patient/parents or legal guardian. 3. The Karnofsky (age ≥10 years)/Lansky (age \<10 years) performance status score over 50 points. 4. Expected to survive for more than 3 months. 5. Patients with a history of prior allogeneic hematopoietic stem cell transplant (HSCT) must be at least 3 months from HSCT at the time of CD19 CAR-T cells infusion and also have not received a donor lymphocyte infusion (DLI) within the 28 days prior to apheresis. 6. Important organ function is satisfied: Heart ultrasound indicates cardiac ejection fraction ≥ 50%, no obvious abnormality in ECG; Adequate pulmonary function defined as forced vital capacity (FVC) ≥ 50% of predicted value; or pulse oximetry ≥ 92% on room air if the patient is unable to perform pulmonary function testing; creatinine clearance calculated by Cockcroft-Gault formula ≥ 50 ml/min/1.73m2; Alanine aminotransferase (ALT) or aspartate aminotransferase (AST) ≤ 5 times the upper limit of normal for age; Total Bilirubin ≤ 3 times the upper limit of normal for age. 7. Absolute lymphocyte count ≥ 0.5 x 10⁹/L. 8. Hemoglobin ≥ 8 g/dl (can be transfused). 9. Platelet count ≥ 20,000/μL (can be transfused). 10. Meets eligibility criteria to undergo autologous apheresis. Exclusion Criteria: 1. Isolated extra-medullary disease relapse. 2. Active CNS involvement of ALL (CNS Grade 3 per National Comprehensive Cancer Network guidelines). 3. Severe, uncontrolled bacterial, fungal or viral infections (Active hepatitis B or C, history of HIV infection) 4. Pre-existing significant neurological disorder. 5. Active significant acute graft versus host disease (GVHD) or moderate/severe chronic GVHD requiring systemic steroids or other immunosuppressants within 4 weeks of enrolment. 6. Pregnant or lactating female. 7. The patient did not agree to use effective contraception during the treatment period and for the following 1 year. 8. A history of other malignant tumors. 9. Receiving systemic steroids therapy exceeding the equivalent of 0.5 mg/ kg/day of methylprednisolone, in the 7 days prior to CAR T-cell infusion 10. Receiving systemic immunosuppressive therapy in the 14 days prior to CAR T-cell infusion 11. Receiving intrathecal chemotherapy in the 7 days prior to CAR T-cell infusion