Successful Salvage Haploidentical Alpha-Beta T Cell–Depleted Stem Cell Transplantation After Busulfan-Based Myeloablation in a Patient With IPEX Syndrome: A Case Report

X-linked immunodysregulation syndrome with polyendocrinopathy and enteropathy (IPEX) is caused by FOXP3 gene mutations that block the generation of regulatory T lymphocytes. We report an 18-month-old boy with classic IPEX who underwent 2 hematopoietic stem cell transplantations (HSCTs). The first HSCT from an unrelated 8/10 HLA-matched umbilical cord blood donor (UCB) was performed after a conditioning regimen consisting of treosulfan, fludarabine, thiotepa, and thymoglobulin. Due to complete rejection of the UCB transplant, a second transplantation from a 6/10 HLA-matched mother was performed after alpha-beta T-cell depletion. The second conditioning regimen consisted of busulfan, fludarabine, a single dose of cyclophosphamide 1 g/m2, and Grafalon (Neovii Pharmaceuticals, Rapperswil, Switzerland). The T-cell depletion product contained 15.06 x 106 CD34+ cells per kilogram body weight (BW) and 4.19 x 105 alpha-beta T lymphocytes per kilogram BW. Due to acute graft rejection, the boy was treated with thymoglobulin, and full donor chimerism in both T lymphocytes and mononuclear cells was achieved. The immunosuppressive therapy was stopped 1 year after transplantation. To date, the patient remains free from graft-vs-host disease (GVHD) and immunosuppression. HSCT after busulfan-based reduced-toxicity conditioning in patients with IPEX syndrome is feasible and well tolerated and can result in full donor engraftment. Monitoring of chimerism and aggressive therapy in cases of graft rejection are warranted due to the high reactivity of residual autologous T lymphocytes. T-cell depletion reduces the risk of GVHD and the need for steroid therapy, which is especially challenging in patients with diabetes. •Haploidentical T cell–depleted transplantation in X-linked immunodysregulation syndrome with polyendocrinopathy and enteropathy (IPEX) is feasible.•Busulfan-based reduced toxicity conditioning can result in full donor engraftment.•Autologous T lymphocytes in IPEX have a high potential for acute graft rejection.