Haploidentical hematopoietic stem cell transplantation using reduced‐intensity conditioning for pediatric patients with familial hemophagocytic lymphohistiocytosis

IMPORTANCE: Allogeneic hematopoietic stem cell transplantation (HSCT) is considered to be the only curative treatment for familial hemophagocytic lymphohistiocytosis (FHLH). Treatment of pediatric FHLH with reduced‐intensity conditioning (RIC)‐based haploidentical donor (HID) HSCT has been rarely reported. OBJECTIVE: To investigate outcomes and adverse events in patients with FHLH who received HID‐HSCT. METHODS: We conducted a retrospective study of five patients, including three with mutations in PRF1 and two with XIAP deficiency. Four of the five donors were heterozygous for these mutations. The conditioning regimen included fludarabine, cyclophosphamide, and antithymocyte globulin, with or without low‐dose irradiation. Unmanipulated mobilized bone marrow and peripheral blood stem cells were used as the grafts. RESULTS: All five patients were successfully engrafted. Four patients survived, and one patient died. All exhibited complete response (CR) after HSCT. All of the patients who survived exhibited CR to FHLH without severe regimen‐related complications at a median of 29.5 months (range: 23–34 months) after HSCT. Four of the five patients had mixed donor chimerism. Three patients had 17% to 87% mixed donor chimerism but remained free of disease. Four patients received donor lymphocyte infusion (DLI), which improved the level of mixed donor chimerism. One patient experienced a decrease in donor chimerism to 1% and relapsed; Four patients developed acute graft‐versus‐host disease (GvHD) (grade I or II), and one patient developed grade IV GvHD. INTERPRETATION: HID‐HSCT with RIC can be considered for treatment for patients with FHLH, but the conditions and DLI regimens need to be optimized for long‐term use, and more prospective studies should be conducted.