Salvage Haploidentical Allogeneic Hematopoietic Stem Cell Transplantation Combined With Post-transplant Relapse Prevention Strategies for Relapsed/Refractory Acute Myeloid Leukemia (AML): A Prospective Observational Study

This is a prospective, single-center, observational study to evaluate the efficacy and safety of salvage haploidentical allogeneic hematopoietic stem cell transplantation (haplo-HSCT) combined with post-transplant relapse prevention strategies in patients with relapsed/refractory acute myeloid leukemia (R/R AML).

Eligible patients are adults aged 18-65 years with active AML (bone marrow blasts >5% or extramedullary disease) and HCT-CI score ≤5. All patients will receive a uniform conditioning regimen consisting of fludarabine, busulfan, and MECCNU, with addition of targeted agents (such as sorafenib, midostaurin, or venetoclax) according to mutation status. Graft-versus-host disease (GVHD) prophylaxis includes reduced-dose ATG (6 mg/kg), FK506, MMF, and basiliximab. Post-transplant maintenance with targeted therapy or azacitidine and prophylactic donor lymphocyte infusion (DLI) will be administered to reduce relapse risk.

The primary endpoints are cumulative incidence of relapse (CIR), overall survival (OS), and progression-free survival (PFS). Secondary endpoints include incidence of acute and chronic GVHD, CMV/EBV reactivation, non-relapse mortality (NRM), and GVHD-free, relapse-free survival. Patients will be followed for 24 months after transplantation. This study aims to explore an optimized transplant strategy to improve long-term survival in this high-risk population.