Bridging Allogeneic Hematopoietic Stem Cell Transplantation or Not After CD19 CAR - T (S1904) Cell Therapy for r/r B-cell Acute Lymphoblastic Leukemia

Inclusion Criteria:

1. The subject or guardian understands and voluntarily signs the Informed Consent Form (ICF);

2. Male or female, aged 12-65 years (including the cutoff value) when signing theinformed consent form;

3. Expected survival period is not less than 12 weeks;

4. ECOG physical performance score is 0-1 when signing the ICF;

5. The subject must be diagnosed with relapsed/refractory B-cell acute lymphoblasticleukemia when signing the ICF, and at least one of the following must be met:

6. Relapse: including relapse within 12 months after the first remission, 2 ormore relapses;

7. Refractory: including primary refractory, failure to achieve remission after atleast 2 courses of induction therapy, or failure to achieve remission after atleast 1 course of salvage therapy after the first relapse.

8. For patients with Philadelphia chromosome-positive ALL (Ph+ ALL), in addition tomeeting the above relapse or refractory criteria, they should have failed at leasttwo tyrosine kinase inhibitor (TKI) treatments (except for those with T315Imutations), or be unable to tolerate TKI treatment, or have contraindications to TKItreatment;

9. Bone marrow morphology examination at screening showed that the proportion ofprimitive immature lymphocytes in the bone marrow was >5%;

10. Tumor cells in the bone marrow or peripheral blood were CD19 positive by flowcytometry at screening;

11. Major organ functions must meet the following requirements:

12. Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) ≤2.5×upperlimit of normal (ULN);

13. Total bilirubin ≤2×ULN;

14. Serum creatinine clearance of adult subjects ≥60 mL/min (Cockcroft-Gaultformula) or creatinine ≤1.5×upper limit of normal (ULN);

15. Serum creatinine for children: no more than 1.2 mg/dL for 10 to 13 years old,no more than 1.5 mg/dL for males aged 13 to 16 years old, no more than 1.4mg/dL for females aged 13 years and above, and no more than 1.7 mg/dL for malesaged 16 years and above.

16. Blood oxygen saturation>92%;

17. Males and females of childbearing age with fertility must agree to use effectivecontraceptive measures from the signing of the informed consent form until 2 yearsafter the use of the study drug. Females of childbearing age include premenopausalwomen and women within 2 years after menopause. The blood pregnancy test of femalesof childbearing age must be negative at the time of screening.

Exclusion Criteria:

1. Isolated extramedullary relapse;

2. Burkitt's lymphoma/leukemia;

3. Previous history of CNS disease, including but not limited to epilepsy, paralysis,aphasia, stroke, severe brain injury, dementia, Parkinson's disease, neuropathy (except inactive CNS leukemia);

4. Previous hematopoietic stem cell transplantation;

5. History of autoimmune disease requiring systemic immunosuppressive drug treatmentwithin 2 years before signing the ICF (including but not limited to Crohn's disease,rheumatoid arthritis, systemic lupus erythematosus, systemic sclerosis, inflammatorybowel disease, vasculitis, psoriasis);

6. Any uncontrolled active infection at the time of signing the ICF or within 4 weeksbefore apheresis, requiring antibiotic, antiviral or antifungal treatment;

7. Previous cell therapy targeting CD19 (autologous or allogeneic);

8. Received CAR-T therapy or other cell/gene therapy before screening;

9. Those who tested positive for hepatitis B surface antigen (HBsAg) during screeningneed to be excluded; if HBsAg is negative but hepatitis B core antibody (HBcAb) ispositive, those with peripheral blood hepatitis B virus (HBV) DNA above thedetection limit need to be excluded; those who tested positive for hepatitis C virus (HCV) antibody and HCV RNA need to be excluded; those who tested positive for humanimmunodeficiency virus (HIV) antibody; those who tested positive for cytomegalovirus (CMV) DNA; those who tested positive for human lymphotropic herpes virus (EBV) DNA;those who tested positive for both Treponema pallidum-specific and non-specificantibodies;

10. Clinically significant cardiovascular disease, including any of the following:

11. QTc interval ≥470 ms after heart rate correction (QTc interval calculated byFridericia formula);

12. New York Heart Association (NYHA) grade II or above heart failure;

13. Unstable angina or acute myocardial infarction within 6 months before signingthe ICF;

14. Left ventricular ejection fraction (LVEF) < 50%;

15. Poorly controlled hypertension (systolic blood pressure ≥ 150 mm Hg and/ordiastolic blood pressure ≥ 95 mm Hg);

16. Arrhythmias with clinical significance or requiring antiarrhythmic treatment (such as sustained ventricular tachycardia, ventricular fibrillation, torsadede pointes tachycardia and complete left bundle branch block, etc.);

17. Allergic to any drug component to be used in this study, including but not limitedto S1904, clearing drugs (cyclophosphamide, fludarabine), etc.;

18. Received any study drug treatment or other systemic anti-tumor treatment within 4weeks before apheresis (or 5 half-lives of the drug, whichever is more appropriateas determined by the researcher);

19. Received extensive radiotherapy within 4 weeks before signing the ICF, except forlocal radiotherapy of non-target lesions for symptom relief within 2 weeks beforesigning the ICF or expected during the study period;

20. At the time of signing the ICF, except for alopecia and pigmentation, the toxicitycaused by previous anti-tumor treatment has not recovered to grade 1 or baselinelevel (according to NCI-CTCAE version 5.0);

21. Patients who need to receive systemic corticosteroids (dose equivalent to or higherthan 10 mg/day of prednisone) or other immunosuppressive drugs within 2 weeks beforesigning the ICF or within 2 weeks before apheresis or during the study, except forthe following:

22. Intranasal, inhaled, local steroids or local steroid injections (such asintra-articular injections), or

23. Systemic corticosteroid treatment not exceeding 10 mg/day of prednisone or itsequivalent physiological dose, or

24. Steroids as a preventive medication for allergic reactions (such aspretreatment before computed tomography [CT]), or

25. Used for symptomatic treatment of adverse reactions after reinfusion;

26. Subjects who have undergone major surgery (except routine biopsy) within 4 weeksbefore signing the ICF, or are expected to undergo major surgery during the study;

27. Subjects with a history of active tuberculosis infection within 1 year beforesigning the ICF (except for subjects with a history of active tuberculosis infectionmore than 1 year ago who are judged by the investigator to have no evidence ofactive tuberculosis);

28. Subjects with clinically significant thyroid dysfunction as judged by theinvestigator;

29. Subjects with or with a history of interstitial lung disease or interstitialpneumonia;

30. Subjects with a history of other primary malignant tumors within 5 years beforesigning the ICF, except for the following:

31. Cervical carcinoma in situ that has been fully treated and cured;

32. Localized basal cell carcinoma or squamous cell carcinoma of the skin;

33. Subjects who have received attenuated/inactivated vaccines within 4 weeks beforesigning the ICF, or subjects who are planned to receive attenuated/inactivatedvaccines during the screening period;

34. The researcher believes that the subject's complications or other conditions mayaffect compliance with the protocol or may be unsuitable for participation in thisstudy;

35. Pregnancy or lactation.