Busulfan-conditioned bone marrow transplantation results in high-level allogeneic chimerism in mice made tolerant by in utero hematopoietic cell transplantation

Objective. In utero hematopoietic cell transplantation (IUHCT) is a nonablative approach that achieves mixed allogeneic chimerism and donor-specific tolerance. However, clinical application of IUHCT has been limited by minimal engraftment. We have previously demonstrated in the murine model that low-level allogeneic chimerism achieved by IUHCT can be enhanced to near-complete donor chimerism by postnatal minimally myeloablative total body irradiation (TBI) followed by same-donor bone marrow transplantation. Because of concerns of toxicity related to even low-dose TBI in early life, we wondered if a potentially less toxic strategy utilizing a single myelosuppressive agent, Busulfan (BU), would provide similar enhancement of engraftment. Methods. In this study, mixed chimerism was created by IUHCT in a fully allogeneic strain combination. After birth, chimeric mice were conditioned with BU followed by transplantation of bone marrow cells congenic to the prenatal donor. Results. We demonstrate that: 1) low-level chimerism after IUHCT can be converted to high-level chimerism by this protocol; 2) enhancement of chimerism is BU dose-dependent; and 3) BU reduces the proliferative potential of hematopoietic progenitor cells thus conferring a competitive advantage to the non-BU-treated postnatal donor cells. Conclusion. This study confirms the potential of IUHCT for facilitation of minimally toxic postnatal regimens to achieve therapeutic levels of allogeneic engraftment. (c) 2006 International Society for Experimental Hematology. Published by Elsevier Inc.