This is a single-arm, open-label, dose-escalation phase I clinical study to explore the safety, tolerability, and cytokinetic characteristics of MC-1-50 cell formulation, and to preliminarily observe the efficacy of MC-1-50 cell formulation in subjects with relapsed/refractory CD19-positive B Cell Acute Lymphoblastic Leukemia.

Based on the specific CD19-targeting CAR-T developed on the PrimeCARTM platform, the cell preparation time is about 3 days, which can greatly shorten the waiting time of patients, improve production efficiency and reduce production costs. At the same time, MC-1-50 products have a high proportion of T naive cells, which can play a therapeutic effect at a very low infusion dose to improve safety. In this study, a "3+3" design was adopted, and three dose groups were set up with 1×10^5/kg, 3×10^5/kg, and 5×10^5/kg CAR-positive cells, respectively (the upper limit of the total number of cells was not more than 5×10^7 CAR-positive cells). All subjects received only one infusion of MC-1-50 cells.

Inclusion Criteria:

1. The patient or their guardian agrees to participate in this clinical trial and sign the ICF, indicating their understanding of the purpose and procedures of this clinical trial and willingness to participate in the study;

2. Age ≥ 18 years old (including threshold), gender not limited;

3. Diagnosed with B-cell acute lymphoblastic leukemia and meeting one of the following conditions:

   1. Refractory B-ALL: Early refractory patients who have not achieved complete remission of bone marrow after two courses of first-line systemic therapy upon initial diagnosis;

   2. Relapsed B-ALL:

      ① Early relapsed after complete remission (< 12 months);

      ② Late relapsed after complete remission (≥ 12 months) requires systemic therapy again, but if complete remission is not achieved or early treatment response is poor;

      ③ Having experienced 2 or more times bone marrow relapse;

      ④ Relapsed after allogeneic hematopoietic stem cell transplantation;

   3. Individuals with Philadelphia chromosome positive (Ph+) disease are eligible if they have relapsed/refractory disease despite treatment with at least 2 different tyrosine kinase inhibitors (TKIs); (Note: Except for those who are intolerant to TKI therapy, or have T315i mutations);

4. Flow cytometry confirms the expression of CD19 in leukemia cells in the bone marrow. In individuals previously treated with targeted CD19 antibodies (such as blinatumomab), the proportion of CD19 positive cells in leukemia cells must be ≥ 90%;

5. Morphological disease in the bone marrow (≥ 5% blasts);

6. ECOG score 0-1;

7. Expected survival time of more than 12 weeks;

8. Adequate renal, hepatic, pulmonary and cardiac function defined as:

   1. Cardiac function: Echocardiography indicates left ventricular ejection fraction ≥ 50%;
   2. Renal function: serum creatinine ≤ 2.0 × ULN, or creatinine clearance rate ≥ 60ml/min (Cockcroft Gault formula);
   3. Hepatic function: ALT and AST ≤ 3.0 × ULN (may be relaxed to ≤ 5.0 × ULN in cases of combined liver infiltration);
   4. Total bilirubin ≤ 2.0 × ULN (Gilbert syndrome requires total bilirubin ≤ 3.0 × ULN);
   5. Pulmonary function: Blood oxygen saturation is ≥ 92% in non oxygen state.

9. No serious mental disorders;

10. Meet standards for apheresis or venous blood collection, and no other cell collection contraindications;

11. Women of childbearing age who have a negative blood pregnancy test and all subjects agree to use reliable and effective contraceptive methods (excluding safe period contraception) for contraception within one year after receiving MC-1-50 cell infusion from the time of signing the informed consent form. Including but not limited to: abstinence, implantable progestogen contraceptives that can inhibit ovulation; Intrauterine device (IUD); Intrauterine hormone release system; Spouse vasectomy; Compound hormone contraceptives that can inhibit ovulation (oral, vaginal, and transdermal); Progesterone contraceptives (oral or injectable) that can inhibit ovulation; When male subjects have sex with fertile women, they must agree to use barrier contraception (such as condom plus spermicidal foam/gel/film/emulsion/suppository). At the same time, participants should commit not to donate eggs (oocytes, oocytes) or sperm for assisted reproduction within one year after cell infusion.

Exclusion Criteria:

1. Isolated extramedullary disease;

2. Central nervous system abnormalities: defined as CNS-2 and 3 according to NCCN guidelines (note: CNS-2 and 3 can be screened, but must be treated and recovered to CNS-1 before lymphodepleting chemotherapy and infusion);

3. Transformation of chronic myeloid leukemia to acute biphenotypic leukemia;

4. Individuals who have received CAR-T therapy or other gene modified cell therapies;

5. Prior to apheresis, the following anti-tumor treatments have been received: chemotherapy, targeted therapy, and other drug treatments within 14 days or at least 5 half lives (whichever is shorter); Received radiation therapy within 14 days;

6. HBsAg or HBcAb positive and HBV DNA is greater than the normal range; HCV antibody is positive and HCV RNA greater than the normal range; HIV antibody positive; syphilis positive; CMV DNA positive;HBsAg or HBcAb positive and HBV DNA is greater than the normal range; HCV antibody is positive and HCV RNA greater than the normal range; HIV antibody positive; syphilis positive;

7. Suffered from any of the following heart diseases:

   1. New York Heart Association (NYHA) stage III or IV congestive heart failure;
   2. Within the 6 months prior to enrollment, there has been a myocardial infarction, or a coronary artery bypass grafting (CABG) or stent implantation surgery has been performed;
   3. History of ventricular arrhythmias requiring treatment or unexplained syncope (excluding cases caused by vasovagal or dehydration);
   4. History of severe non-ischemic cardiomyopathy;

8. Uncontrollable infection in the 2 weeks before enrollment;

9. Acute grade 2-4 graft-versus-host disease (GVHD) or moderate to severe chronic GVHD within the first 4 weeks of enrollment;

10. If a cerebrovascular accident or seizure occurs within the first 6 months of enrollment;

11. Active autoimmune diseases;

12. Deep vein or deep artery embolism event within the past 6 months prior to enrollment;

13. Poor control of hypertension during screening is defined as systolic blood pressure ≥ 160mmHg and/or diastolic blood pressure ≥ 100mmHg (blood pressure values are measured based on the average of three readings taken at least 2 minutes apart. Patients with blood pressure ≥ 160/100mmHg at the initial screening can receive antihypertensive treatment, and if good control is achieved after treatment and blood pressure<160/100mmHg, enrollment can be performed);

14. History of malignancy other than fully treated cervical carcinoma in situ, basal cell or squamous cell carcinoma of the skin, local prostate cancer after radical surgery, and ductal carcinoma in situ of the breast after radical surgery;

15. (attenuated) Live vaccine ≤ 4 weeks prior to enrollment;

16. Have participated in other clinical trials within one month or five drug half lives (whichever is shorter) before enrollment;

17. Women who are pregnant or breastfeeding, and male or female subjects who plan to have children within 1 year after receiving MC-1-50 cell infusion;

18. Other situations considered by the investigator to be unsuitable to participate in the study.