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

Inclusion Criteria: 1. Age 14-65 years (inclusive), regardless of gender. 2. Newly diagnosed B-ALL with CD19 expression on leukemic cells (regardless of CD19 positivity rate). 3. Ph-negative B-ALL with high-risk features post-allo-HSCT . 4. ≥2 months post-transplant with hematopoietic reconstitution. 5. Bone marrow morphology in remission and MRD-negative before enrollment. 6. ECOG performance status \<3 and Karnofsky score ≥70. 7. No history of grade III/IV graft-versus-host disease (GVHD) and no active GVHD at enrollment. 8. Adequate organ function:AST and ALT ≤3× upper limit of normal (ULN), total bilirubin ≤2×ULN.Serum creatinine ≤2×ULN or creatinine clearance ≥50 mL/min (calculated by Cockcroft-Gault formula).Left ventricular ejection fraction (LVEF) ≥50% by echocardiography (ECHO). 9. Expected survival \>3 months. 10. Voluntary provision of written informed consent, with ability to understand and comply with study requirements. Exclusion Criteria: 1. History of hypersensitivity or severe adverse reactions to the study drug or structurally similar compounds, as assessed by the investigator to preclude participation. 2. Pregnant or lactating women, or women of childbearing potential unwilling to use effective contraception. 3. Severe cardiac dysfunction, including:Left ventricular ejection fraction (EF) \<60%.Clinically significant arrhythmias (e.g., ventricular tachycardia, atrial fibrillation, second-degree heart block).Prolonged QTc interval (men \>450 ms; women \>470 ms).Myocardial infarction within the past year.Symptomatic coronary artery disease requiring medication. 4. Severe pulmonary dysfunction (obstructive and/or restrictive ventilatory impairment). 5. Severe hepatic impairment:ALT or total bilirubin (TBIL) \>3× upper limit of normal (ULN). 6. Severe renal impairment:Serum creatinine (Cr) \>2× ULN.24-hour creatinine clearance (Ccr) \<50 mL/min. 7. Active infection or uncontrolled bleeding, as assessed by the investigator to preclude safe administration of the study drug. 8. History of thrombosis, embolism, cerebral hemorrhage, or other significant vascular events within the past year. 9. Psychiatric disorders or other conditions that impair the ability to provide informed consent or comply with study procedures. 10. Major organ surgery within the past six weeks. 11. Drug abuse or chronic alcoholism that may interfere with study assessments. 12. Prior organ transplantation (excluding hematopoietic stem cell transplantation). 13. Other conditions deemed by the investigator to make the patient unsuitable for participation.