CD19/CD22 CAR-T Cell Therapy in MRD-Positive B-lineage Acute Lymphoblastic Leukemia in Children.

Inclusion Criteria: 1. Parents or legal guardians fully understand, are informed of this study and sign the informed consent form (ICF); are willing to follow and can complete all test procedures. 2. Chinese children aged 1-18 years old at the time of screening, regardless of gender, with a body weight ≥ 10 kg. 3. Bone marrow examination confirms that MRD is still positive on the 46th day after induction remission. 4. Tumor cells in the bone marrow (BM) or peripheral blood (PB) express CD19/CD22 within 3 months before screening. 5. Good organ function, which needs to meet the following criteria: (1)ALT ≤ 5 times the upper limit of normal value (ULN); (2)total bilirubin ≤ 2 times ULN (Gilbert's syndrome ≤ 3 times ULN); (3)without \> grade 1 dyspnea when not inhaling oxygen, and oxygen saturation \> 95%; (4)left ventricular ejection fraction (LVEF) ≥ 50%; (5)serum creatinine ≤ 1.5 times ULN. 6. Karnofsky score (≥ 16 years old) ≥ 70 or Lansky (\< 16 years old) score ≥ 50. 7. Expected survival period of at least 12 weeks. 8. Have sufficient venous access (for apheresis or venous blood sampling), and have no other contraindications for blood cell separation. Exclusion Criteria: 1. Have genetic diseases, except Down syndrome. 2. Have a history of other malignancies or have other malignancies simultaneously. 3. Meet any of the following conditions: (1)hepatitis B surface antigen (HBsAg) positive or HBV DNA quantification higher than the upper limit of normal value; (2)hepatitis C antibody (HCV Ab) positive and HCV RNA quantification higher than the upper limit of normal value; (3)human immunodeficiency virus antibody (HIV-Ab) positive; (4)Treponema pallidum antibody (TP-Ab) positive; (5)EBV DNA higher than the upper limit of normal value; (6)cytomegalovirus DNA higher than the upper limit of normal value. 4. Have or are suspected to have uncontrolled or require intravenous drug treatment for fungal, bacterial, viral or other infections. 5. Long-acting G-CSF is prohibited within 21 days before screening, and short-acting G-CSF is prohibited within 7 days before screening. 6. Have active central nervous system leukemia. 7. Are allergic to albumin and aminoglycoside antibiotics. 8. Have undergone organ transplantation (except hematopoietic stem cell transplantation). 9. Have participated in other interventional clinical studies within 3 months before screening (received active test drug treatment), or intend to participate in another clinical trial or receive anti-tumor treatment other than that specified in the protocol during the entire study period. 10. Cannot tolerate chemotherapy and cytokine storm due to impaired function of important organs. 11. Other situations that the investigator deems not suitable for participating in this clinical trial.