Blinatumomab as Maintenance Therapy in Patients With High-risk B-lineage Acute Lymphoblastic Leukemia Post Allogeneic Hematopoietic Cell Transplantation

Inclusion Criteria: * 1．Age ≥ 14 years, male or female; 2．CD19 + acute B lymphoblastic leukemia treated with allogeneic hematopoietic stem cell transplantation \[Patients, the types of transplantation include fully matched sibling transplantation, haploidentical related donor transplantation and unrelated donor transplantation; 3．CD19 + acute B-lymphoblastic leukemia at risk of relapse before transplantation \[including but not limited to: refractory leukemia: failure to achieve complete remission (CR)/CR with partial hematological recovery (CRh)/CR with incomplete hematological recovery (CRi) or CR/CRh/CRi after the end of induction therapy (generally refers to 4-week regimen or Hyper-CVAD regimen), but still positive for measurable residual disease (MRD); relapsed leukemia: patients who have achieved CR have blasts in peripheral blood or bone marrow (proportion \> 5%), or extramedullary disease; onset of white blood cells \> 30 × 109/L; patients with poor prognosis cytogenetic abnormalities; patients with positive residual leukemia before transplantation, etc.\] 4．The disease is in complete remission, and residual leukemia is negative, absolute neutrophil count ≥ 1.0 × 109/L, platelet count ≥ 50 × 109/L, lasting for more than a week; 5．Freedom from ≥ Grade 3 acute GVHD or uncontrolled moderate to severe chronic GVHD within 30 days prior to enrollment; Awareness and willingness to sign written informed consent. Exclusion Criteria: * 1.Patients with hematological relapse or minimal residual disease relapse of B-ALL after transplantation; 2.Presence of serious uncontrolled active infection (e.g., sepsis, pulmonary infection, etc.). 3.Markedly abnormal screening laboratory tests: A) Alanine aminotransferase (ALT) ≥ 5 × ULN (upper limit of normal); B) Aspartate aminotransferase (AST) ≥ 5 × ULN; C) Total bilirubin (TBIL) ≥ 3 × ULN; D) Creatinine clearance \< 70 mL/min at screening; Patients with active hepatitis B (hepatitis B surface antigen positive and peripheral blood hepatitis B virus deoxyribonucleic acid (HBV DNA) ≥ 1 × 102 copies/mL); F) Hepatitis C antibody positive; G) Human immunodeficiency virus (HIV) positive; h) Treponema pallidum antibody positive; 4.ECOG performance status ≥ 3 5.Estimated survival less than 3 months This study may not be completed for other reasons, or the investigator considers it inappropriate to participate in this study.