Haploidentical Bone Marrow Transplantation for Sickle Cell Disease

Related human leukocyte antigen (HLA)-haploidentical bone marrow transplantation (BMT) with posttransplant cyclophosphamide may be curative for sickle cell disease. However, graft failure, severe graft-versus-host disease (GVHD), infections, and mortality remain a concern. We evaluated a novel conditioning regimen followed by related HLA-haploidentical BMT in adults with sickle cell disease. In a phase 2, open-label, single-arm, multicenter study, 54 eligible participants from 19 U.S. centers were enrolled. Of these, 42 (78%) received transplantation with conditioning including antithymocyte globulin, fludarabine, cyclophosphamide, thiotepa, and total body irradiation. GVHD prophylaxis included posttransplant cyclophosphamide, mycophenolate mofetil, and sirolimus. The primary outcome was event-free survival at 2 years, while secondary outcomes included overall survival and other transplant-related end points. The median age at enrollment was 22.8 years (range, 15.5 to 43.2), and the median follow-up period was 37.2 months (range, 20.4 to 56.4). The 2-year event-free and overall survival rates were 88.0% (95% confidence interval [CI], 73.5 to 94.8%) and 95.0% (95% CI, 81.5 to 98.7%), respectively. Two participants experienced primary and another secondary graft failure. The incidence of grade-3-to-4 acute GVHD at day 100 was 4.8% (95% CI, 0.9 to 14.4%), while the 2-year chronic GVHD rate was 22.4% (95% CI, 10.9 to 36.4%). Two of the four reported deaths were due to early infectious complications. HLA-haploidentical BMT is an accessible and potentially curative therapy for adults with sickle cell disease. Adverse events were those anticipated from this procedure, including GVHD. (Funded by the National Heart, Lung, and Blood Institute and the National Cancer Institute; BMT CTN 1507; ClinicalTrials.gov number, NCT03263559).