Introduction: Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is considered the only cure for acute myeloid leukemia (AML) or high-risk myelodysplastic syndrome (MDS), but the high mortality rate from relapse after transplantation remains a concern. Systematic monitoring and evaluation of measurable residual disease (MRD) post-allo-HSCT can identify subclinical levels of leukemia cells before clinical relapse, enabling the effective pre-emptive interventions. The promising efficacy of venetoclax-based treatment in newly diagnosed AML also promoted its use in post transplantation of myeloid malignancies. In this prospective study, we aimed to determine whether MRD-guided pre-emptive treatment with azacitidine combined with venetoclax (Ven/Aza) could prevent relapse in these patients (NCT04809181).

Methods: Patients with advanced MDS or AML achieving complete remission after allo-HSCT were prospectively screened for MRD using multiflow cytometry (MFC) and donor chimerism. For patients with leukemia-specific fusion genes or mutations, molecular MRD was assessed by real-time quantitative PCR (qPCR) or digital PCR (dPCR). For those with high baseline WT1 or EVI1 expression, bone marrow cell mRNA levels were measured. MRD positivity was defined as: Leukaemia-associated immunophenotypes (LAIPs) ≥0.1% by MFC, or Fusion genes >0.1%, or WT1 >0.6%, or Gene mutation positivity (NPM1 ≥2%, others >1% by qPCR or >0.2% by dPCR). Upon MRD detection, immunosuppressive agents were promptly tapered and discontinued. All patients received pre-emptive therapy with azacitidine (75 mg/m² days 1-7) plus venetoclax (400 mg days 1-14), administered every 4-8 weeks for 6 cycles. Therapy was discontinued for: Treatment intolerance or Grade II-IV aGVHD or severe cGVHD or Disease progression after two cycles. Response Definitions: Major Response Met ≥1 criteria: LAIPs <0.01%; ≥1-log reduction in gene expression or negativity. Minor Response Met ≥1 criteria: LAIPs reduction <60%; <1-log reduction in gene expression; No Response: Failure to meet major or minor response criteria.

Results: A total of 44 patients were enrolled, with a median age of 47 years (range: 17–66). Among them, 30 patients (68.2%) were diagnosed with AML, and 13 patients (29.5%) were diagnosed with MDS. Regarding donor type, 36 patients (81.8%) received HLA-haploidentical transplants. Pre-transplant conditioning regimens included BuCY-based regimen for 32 patients (72.7%), BuFlu-based regimen for 6 patients (13.6%), and Ven+Flu+Mel+ATG for 6 patients (13.6%). Among MRD-positive patients, 9 (20.5%) had MFC-positive MRD, 10 (22.7%) had fusion gene-positive MRD, 10 (22.7%) had mutation-positive MRD, and 5 (11.4%) had gene expression-positive MRD. Additionally, 10 patients (22.7%) were concurrently positive for two or more MRD markers.

The median time from transplantation to therapy initiation was 286 days (IQR, 186–657 days). After the first cycle, the major response rate was 62.8%, with 16.3% showing minor responses and 20.9% showing no response. By the third cycle, the major response rate peaked at 67.4%, and the overall response rate reached a peak of 81.4%. During a median follow-up of 549 days, 18 patients (40.9%) relapsed, with a 2-year cumulative incidence of relapse (CIR) of 46.4%. At 2 years, overall survival (OS), progression-free survival (PFS), and non-relapse mortality (NRM) were 73.5%, 48.6%, and 4.9%, respectively.In multivariate Cox regression analysis for progression-free survival (PFS), response to Ven/Aza treatment was identified as a significant protective factor (HR = 0.02, p < 0.001), whereas WT1 positivity (HR = 9.67, p= 0.001) and having MDS as the underlying disease (HR = 2.97, p = 0.059) were associated with inferior PFS.

The most common grade 3-4 adverse events were neutropenia (54.5%), leukopenia (45.5%), and thrombocytopenia (27.3%). All adverse events were reversible with supportive care and clinically manageable. During follow-up, acute graft-versus-host disease (aGVHD) developed in 27.3% of patients; half of these cases (50.0%) were grade III-IV. Additionally, 27.3% of patients developed moderate-to-severe chronic graft-versus-host disease (cGVHD).

In conclusion, pre-emptive azacitidine plus venetoclax is a safe and effective strategy to prevent disease progression in AML/MDS patients with MRD positivity after allo-HSCT.

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2025
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