Conditioning with Treosulfan and Cyclophosphamide without Application of Antibodies in MHC Mismatch Transplantations in Mice

BACKGROUND: Treosulfan is increasingly used in clinical conditioning regimens because of its myeloablative and immunosuppressive effects and the low hepatotoxicity compared to busulfane. The myeloablative and immunosuppressive characteristics of treosulfane was investigated in a murine MHC mismatch transplantation model. METHODS: C57BL/10 (H-2Db) female mice were treated with treosulfan (2000 mg/kg) on day -3 to -1 and increasing doses of cyclophosphamide (without, 100 or 200mg/kg) at day -1, or 3000 mg/kg treosulfan with and without 200 mg/kg cyclophosphamide at day -1. Some mice were not transplanted to examine the myeloablative effect of the regimens, the rest of mice were transplanted with 10 × 10^6 marrow cells from Balb/c mice (H-2Dd) donors and monitored for donor-type chimerism determined by flow cytometry. RESULTS: Mice treated with treosulfan and cyclophosphamid without transplantation died, indicating the myeloablative effect of the regimens. Ca. 50% of mice treated with 3000 mg/kg treosulfan and 200 mg/kg cyclophosphamide at day -1 died. Analysis of bone marrow cells in the remaining mice showed a complete rejection at day 55. Approximately 90% of the recipients of three daily doses of treosulfan and increasing doses of cyclophosphamide survived until the end of experiment (day +100). All hosts engrafted when 200 mg/kg cyclophosphamide was applied. 85% of mice engrafted after 100mg/kg cyclophosphamide. 100% of grafts were rejected in the group with treosulfan alone (2000 mg/kg). CONCLUSION: A chemotherapeutic regimen for achieving a long term survival in a MHC-mismatch situation without additional need of antibodies was established in mice. While investigated for the practicability in an animal model as alternative to TBI, the high rate of engraftments in a MHC mismatch situation makes the chemotherapeutic regimen suitable for clinical situations.