Reduced Toxicity Conditioning for Nonmalignant Hematopoietic Cell Transplants.

Allogeneic hematopoietic cell transplantation (HCT) for children with nonmalignant disorders is challenged by potential drug-related toxicities and poor engraftment. This retrospective analysis expands on our single pediatric medical center experience with targeted busulfan, fludarabine, and intravenous (IV) alemtuzumab as a low-toxicity regimen to achieve sustained donor engraftment. Sixty-two patients received this regimen for their first HCT for a nonmalignant disorder between 2004 and 2018. Donors were matched sibling in 27%, 8/8 HLA allele-matched unrelated in 50%, and 7/8 HLA allele-mismatched in 23% (some of whom received additional immunoablation with thiotepa or clofarabine). Five patients experienced graft failure for a cumulative incidence of 8.4% (95% CI, 1 to 16%). In engrafted patients, the median donor chimerism in whole blood and CD3, CD14/15, and CD19 subsets at 1-year were 96%, 90%, 99%, and 99%, respectively. Only one patient received donor lymphocyte infusions (DLIs) for poor chimerism. Two patients died following disease progression despite 100% donor chimerism. The 3-year cumulative incidence of treatment-related mortality was 10% (95% CI, 2 to 17%). Overall survival and event-free-survival at 3-years were 87% (95% CI, 78 to 95%) and 80% (95% CI, 70 to 90%), respectively. The 6-month cumulative incidence of grade II to IV acute graft-versus-host disease (GVHD) was 7% (95% CI, 3 to 13%), while the 3-year cumulative incidence of chronic GVHD was 5% (95% CI, 0 to 11%). These results suggest that use of targeted busulfan, fludarabine and IV alemtuzumab offers a well-tolerated option for children with nonmalignant disorders to achieve sustained engraftment with a low incidence of GVHD.