Blinatumomab Intensification for MRD-Negative Acute B-Cell Lymphoblastic Leukemia Before Allogeneic Hematopoietic Stem Cell Transplantation

Inclusion Criteria: 1\. Diagnosed with B-cell acute lymphoblastic leukemia (B-ALL) according to the 2022 WHO classification. 2\. Age between 18 and 65 years. 3. Meets the National Comprehensive Cancer Network (NCCN) criteria for high-risk B-ALL, based on clinical or cytogenetic/molecular features: 1. Clinical high-risk features (any of the following): 1. Age \> 35 years 2. Peripheral WBC count \> 30 × 10⁹/L 3. Cytogenetic/molecular high-risk features (any of the following): 2. Cytogenetic and molecular high-risk features (at least one of the following): 1. Hypodiploidy (\<44 chromosomes) 2. TP53 mutation 3. KMT2A rearrangement 4. MLL rearrangement 5. HLF rearrangement 6. ZNF384 rearrangement 7. MEF2D rearrangement 8. MYC rearrangement 9. BCR-ABL1-like (Ph-like) ALL, including: 10. JAK pathway rearrangements (CRLF2r, EPORr, JAK1/2/3r, TYK2r, SH2B3 mutation, IL7R mutation, JAK1/2/3 mutations) 11. ABL-class rearrangements (ABL1, ABL2, PDGFRA, PDGFRB, FGFR1) 12. Other kinase fusions (e.g., NTRK3r, FLT3r, LYNr, PTK2Br) 13. PAX5alt 14. t(9;22)(q34.1;q11.2); BCR-ABL1 with IKZF1 mutation and/or prior chronic myeloid leukemia (CML) 15. Intrachromosomal amplification of chromosome 21 (iAMP21) 16. IKZF1 alteration 17. Complex karyotype (≥5 chromosomal abnormalities) 4. CD19-positive by immunophenotyping. 5. BCR::ABL1-negative. 6. Achieved complete remission (CR) after induction therapy. 7. Measurable residual disease (MRD)-negative by flow cytometry (FCM). 8. Availability of a matched sibling donor, haploidentical related donor, or matched/unmatched unrelated donor. 9\. ECOG performance status score of 0-2. 10. Creatinine clearance ≥ 60 mL/min (by Cockcroft-Gault formula). 11. AST and ALT ≤ 3 × upper limit of normal (ULN); total bilirubin ≤ 2 × ULN. 12. Left ventricular ejection fraction (LVEF) ≥ 50% by echocardiography. 13. Expected survival \> 8 weeks. 14. Signed written informed consent, with ability to understand and comply with the study protocol. Exclusion Criteria: 1. Prior exposure to blinatumomab, chimeric antigen receptor (CAR) T-cell therapy, or anti-CD22 immunotoxins. 2. Clinically significant cardiovascular disease, including uncontrolled arrhythmia, uncontrolled hypertension, congestive heart failure, NYHA class III or IV heart disease, or myocardial infarction within 3 months prior to screening. 3. Other severe comorbidities that may limit participation in the trial (e.g., severe infection, renal failure). 4. Known HIV infection or uncontrolled severe viral hepatitis. 5. Pregnant or breastfeeding women.