Conditioning regimens using growth factors prior to low dose tbi enhance engraftment of murine stem cells after bone marrow transplantations

Low toxic regimens to prepare recipients of autologous and allogeneic bone marrow transplantations (BMT) are currently being explored extensively for an expanding variety of clinical applications. We have developed a novel conditioning protocol with the aim to enhance donor cell engraftment after low dose total body irradiation (TBI). Autologous BMT was performed in mice pretreated with early acting growth factors (GF) prior to irradiation to increase the radiosensitivity of host bone marrow cells, which should lead to their selective depletion. Mice (C57BL/6, Ly5.2) were treated 1, 3, or 7 days with SCF (2.5 μg/day) and IL-11 (2.0 μg/day) before sublethal (4Gy) TBI. Survival of radioresistant subsets of host stem cells was assessed using the CAFC assay. We analyzed % donor chimerism post-transplantation after infusion of 3×106 Ly5.1 BM cells by FACS analysis. The CAFC data accurately predicted both short- and long-term development of donor cell engraftment. One-day pretreated mice showed a 2-fold increase in remaining host CAFC subsets after TBI compared to untreated, irradiated mice. The elevated host CAFC subsets were associated with low donor leukocyte chimerism (<10%). In sharp contrast, 7-day GF pretreatment of recipients prior to TBI resulted in a 2 log increase in stem cell kill. Consequently, high levels of donor cell contribution were observed in these recipient mice. Untreated and 3-7 day pretreated mice showed a more or less stable donor chimerism from 2 months after transplantation onwards. We conclude that engraftment of autologous donor bone marrow cells can be strongly enhanced by administration of early acting GF to recipients prior to low dose TBI. We are currently testing this approach in allogeneic settings (experimental minitransplants), as well as assessing the potential of alternative GF combinations.