Treosulfan-Based Reduced Toxicity Regimen Prior to Allogeneic Hematopoietic Cell Transplantation in Non-Malignant Disorders.

Graft rejection is a major cause of failure after alloHCT in non-malignant hematopoietic disorders including severe aplastic anemia (SAA) and paroxysmal nocturnal hemaoglobinuria (PNH). For patients with high risk of this complication we introduced a novel conditioning regimens, based on treosulfan - an alkylating agent possesing both immuno- and myeloablative properties. Between 2003–2006, eleven patients (age: 23(14–35) years) with SAA (n=6) or PNH (n=5) were treated in a single institution with alloHSCT from either HLA-identical sibling (n=3) or an unrelated volunteer (n=8). For patients with SAA conditioning regimen consisted of treosulfan 10 g/m2/d on days -7, -6, cyclophosphamide 40 mg/kg/d on d. -5, -4, -3, -2, and anti-thymocyte globulin (ATG) 2 mg/kg/d on d. -3, -2, -1. PNH patients received treosulfan 14 g/m2/d on days -6, -5, -4, fludarabine 30 g/m2 on d. -6, -5, -4, -3, -2, and (ATG) 2 mg/kg/d on d. -3, -2, -1. Bone marrow was used as a source of stem cells in 5 patients and peripheral blood - in 6 cases. Graft-vs.-host disease (GVHD) prophylaxis consisted of Cyclosporin A and short-course Methotrexate.

All patients engrafted with the median time to neutrophil >0.5×10e9/L and platelet >50×10e9/L recovery of 16 (14–22) days and 21.5 (12–29) days, respectively. Complete donor chimerism was achieved on day +30 in all cases. None of the patients developed grade III-IV acute GVHD, two patients experienced grade II acute GVHD. At one year the cumulative incidence of extensive chronic GVHD equaled 22%. No severe organ toxicity was observed. With the median follow-up of 19 months, the disease-free survival at 2.5 years was 91%. A single PNH patient died of haemorrhagic cystitis.

We conclude that treosulfan-based preparative regimens are well-tolerated and allow stable engraftment in SAA and PNH patients. The use of treosulfan allows intensification of the conditioning without providing an additional non-hematological toxicity.