HLA-mismatched/haploidentical hematopoietic stem cell transplantation without in vitro T cell depletion for chronic myeloid leukemia: Improved outcomes in patients in accelerated phase and blast crisis phase

Background. Allogeneic hematopoietic stem cell transplantation (allo-HSCT) remains the only proven curative therapy for chronic myeloid leukemia (CML), but lack of human leukocyte antigen (HLA)-matched sibling or unrelated donors has restricted its application. Recently, we developed an effective method for haploidentical allo-HSCT achieving comparable outcomes to HLA-identical transplantation. Aim. To evaluate the outcomes of CML patients who underwent haploidentical allo-HSCT. Methods. Ninety-three patients were treated with a modified busulfan (BU)/cyclophosphamide (CY)2 regimen, including antithymocyte globulin followed by unmanipulated blood and marrow transplantation. Results. Our data showed that the cumulative incidence of acute graft-versus-host disease (GVHD) was 64.52%, and grade III-IV was 26.45%, 61.79% had chronic GVHD, and 28.93% had extensive chronic GVHD. Non-relapse mortality varied at 8.72% (100 days), 20.72% (1 year) and 20.72% (2 years). Probability of 1-year and 4-year leukemia-free survival was similar in chronic phase (CP) 1, CP2/CR2, accelerated phase, and blast crisis patients. Probability of 4-year overall survival varied as 76.5% (CP1), 85.7% (CP2/CR2), 73.3% (accelerated phase), and 61.5% (blast crisis). Multivariate analysis indicated that factors affecting transplantation outcomes were HLA-B+DR mismatches versus others for II-III acute GVHD and III-IV acute GVHD, the stage of disease at transplantation for relapse, and the time from diagnosis to transplantation for leukemia-free survival, overall survival, and transplantation-related mortality. In our protocol, survival of HSCT for advanced CML was similar to stable stage. Conclusions. For patients lacking an HLA-identical related donor, haploidentical relatives are alternative HSCT donors.