We evaluated the efficacy of in vivo T-cell depletion with alemtuzumab in two prospective studies according to the International Conference on Harmonisation (ICH)-Good Clinical Practice (ICH-GCP) guidelines; one was for patients with aplastic anemia (AA study) and the other was for patients who were undergoing hematopoietic stem cell transplantation (HSCT) from a 2- or 3-antigen-mismatched haploidentical donor (MM study). The final dose of alemtuzumab in these studies was 0.16 mg/kg/day for 6 days. At this dose, all of the 12 and 11 patients in the AA and MM studies, respectively, achieved initial engraftment and the incidences of Grade II-IV acute graft-versus-host disease (GVHD) were 0% and 18%. While cytomegalovirus (CMV) frequently reactivated, none of the patients developed fatal CMV disease. Transplantation-related mortality within 1 year after HSCT was observed in only two and one patients, respectively. The numbers of CD4+ and CD8+ T-cells and T-cell receptor rearrangement excision circles remained low within 1 year after HSCT. These findings suggest that the use of alemtuzumab at this dose in a conditioning regimen enables safe allogeneic HSCT even from a 2- or 3-antigen-mismatched donor. However, the use of a lower dose of alemtuzumab should be explored in future studies to accelerate immune recovery after HSCT.
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