Effectiveness and Safety of Blinatumomab and Donor Lymphocyte Infusion in Maintenance Therapy After Allogeneic Hematopoietic Stem Cell Transplantation for High-risk Ph Negative B Cell Acute Lymphoblastic Leukemia

"Blinatumomab dosage:~Cycle 1 (starting at day 60 post-transplant):Days 1-3: 9 μg/day，Days 4-14: 28 μg/day Cycles 2-4:Days 1-14: 28 μg/day Administration method: Continuous 24-hour intravenous infusion, one cycle every 3 months.~DLI eligibility criteria:No history of grade III-IV acute GVHD (aGVHD).No active aGVHD or chronic GVHD (cGVHD) at the time of infusion~DLI dosage:Administered at day 120 post-HSCT, CD3+ cell dose: 1 × 10⁷/kg"