The aim of the current study is to evaluate the safety and efficacy of low dose treosulfan based conditioning regimen in HSCT with post-transplant cyclophosphamide in Nijmegen breakage syndrome

Nijmegen breakage syndrome (NBS) is a DNA repair disorder. The only curative option for combine immunodeficiency in NBS is allogeneic hematopoietic stem cell transplantation (HSCT). Standard myeloablative conditioning regimens in DNA repair disorders lead to increased morbidity and mortality after HSCT. Low doses of alkylators are used to reduce toxicity rates, which, however, increase the risks of mixed chimerism and graft failure. The data of treosulfan usage in NBS are sparse. To evaluate the safety and efficacy of low dose treosulfan based conditioning regimen in NBS, treosulfan 21g/m2 in combination with fludarabine 150mg/mg, thymoglobulin (Genzyme) 5mg/kg and rituximab 100mg/m2 will be used from day -6 to -1 day, followed by stem cell infusion and post-transplant cyclophosphamide 25mg/kg/day (+3,+4 day) for GVHD prophylaxis. The primary endpoint is event-free survival, where graft failure, death, and malignancies are considered as events.

Inclusion Criteria:

1. Patients aged ≥ 3 months and < 21 years
2. Patients diagnosed with NBS eligible for an allogeneic HSCT
3. Signed written informed consent signed by a parent or legal guardian