HLA haploidentical peripheral blood stem cell transplantation using reduced dose of posttransplantation cyclophosphamide for poor-prognosis or refractory leukemia and myelodysplastic syndrome

Nonmyeloablative, human leukocyte antigen (HLA) haploidentical, T-cell-replete bone marrow transplantation followed by high-dose posttransplantation cyclophosphamide (PT/Cy) has recently been developed. This transplantation milieu has resulted in favorable outcomes with low transplantation-related mortality, owing to a low incidence of graft-versus-host disease (GVHD), without increased infectious complications. However, the high relapse rate remains a major concern. We therefore performed a prospective pilot study of HLA haploidentical peripheral blood stem cell transplantation (PBSCT) with intensified conditioning, followed by two lower doses of PT/Cy. A total of 20 patients with refractory or poor-prognosis myelodysplastic syndrome (MDS) and leukemia were enrolled in the study. A trend toward a lower incidence of grade III-IV acute GVHD at day 100 in the group receiving 25 mg/kg × 2 doses of PT/Cy, compared with the group receiving 25 mg/kg of PT/Cy (9.1% vs. 33%, p = 0.20), was noted. However, the cumulative incidence of chronic GVHD was low, at 10% irrespective of PT/Cy dose. The number of infused CD34+ cells significantly correlated with the grade of acute GVHD (p = 0.004). In addition, the occurrence of BK virus hemorrhagic cystitis was significantly more common in the double-dose PT/Cy group (25% vs. 0%, p = 0.043), especially when combined with busulfan. The probability of overall survival at 1 year in the double-dose group tended to be better compared with that in the single-dose group (64% vs. 44%, respectively; p = 0.20). In conclusion, HLA haploidentical, T-cell-replete PBSCT with 25 mg/kg × 2 doses of PT/Cy might be a feasible option for treating high-risk leukemia and MDS.