Successful Unmanipulated Haploidentical Hematopoietic Stem Cell Transplant With Post-transplant Cyclophosphamide in a Child With Down Syndrome and Myelodysplastic Syndrome.

Allogeneic hematopoietic stem cell transplant (HSCT) in children with Down syndrome and hematologic malignancies is challenging and is reserved for those who develop relapsed/refractory disease due to concerns regarding transplant-related mortality. Haploidentical HSCT, although performed in limited cases using graft manipulation methods to prevent graft-versus-host disease (GVHD), often results in dismal outcomes. Herein, we report a case of a 12-year-old boy with Down syndrome and myelodysplastic syndrome who underwent unmanipulated haploidentical HSCT using a reduced toxicity treosulfan-based conditioning and in vivo T-cell depletion with post-transplant cyclophosphamide. At the 1-year follow-up, he is alive with complete donor chimerism and no chronic GVHD.