Treosulfan-Based Conditioning in Matched Family, Unrelated and Haploidentical Hematopoietic Stem Cell Transplantation for Genetic Hemophagocytic Lymphohistiocytosis: Experience and Outcomes over 10 Years from India.

We aimed to analyze data in children with primary hemophagocytic lymphohistiocytosis (HLH) who underwent hematopoietic stem cell transplantation (HSCT). We performed a retrospective study where children up to 18 years, with primary HLH and who underwent HSCT from January 2011 to December 2019, were included. Twenty-five children with genetic HLH underwent HSCT, including variants (Griscelli syndrome (GS2) 7, Chediak-Higashi syndrome (CHS) 2, XIAP mutation 2). Donors were matched family 8 (32%), umbilical cord blood unit 3 (12%), matched unrelated 2 (8%), haploidentical HSCT 12 (48%), (TCR alpha/beta depletion 2 and post-transplant cyclophosphamide 10). With treosulfan-based conditioning, engraftment was achieved in 23/25 (92%) transplants (100% in haplo-HSCT), with sustained complete chimerism in 87%. Disease-free survival was noted in 2/3 children with stable mixed chimerism. Graft-versus-host disease (GVHD) of grade I/II was noted in 6 (24%), grade III in 3 (13%); chronic limited skin GVHD in 2 (12%) children. Overall survival was 72% (87.5% in matched donor, 66.7% in the haplo-HSCT), 71% in GS2, 50% in CHS, 100% in XIAP. HSCT is curative in primary HLH with acceptable disease-free survival with mixed chimerism. Haplo-HSCT is a viable option for those without matched family or unrelated donors.