Improved hematopoietic stem cell engraftment following ex vivo expansion of murine marrow cells with SCF and Flt3L

BackgroundIn vitro incubation of murine BM cells with IL-3, IL-6, IL-11 and SCF induces expansion of HPC but fails to preserve ‘engraftability’ in comparison with normal untreated marrow cells. We studied how culturing marrow cells for 48 and 72 h with a combination of the cytokines SCF and Flt3L influences cell expansion and engraftability.MethodsCompetitive repopulation of lethally irradiated C57BL/6 mice was used to examine engraftability of ex vivo cytokine-expanded Ptprc chimeric BM. A methylcellulose in vitro assay was used to determine the expansion of substitute progenitors.ResultsBoth cytokine combinations successfully expanded progenitor populations when assayed in methylcellulose culture in vitro. After 72 h, the colony numbers of the expansion cultures increased 61% with IL-3, IL-6, IL-11 and SCF stimulation and 96% with SCF and Flt3L stimulation. Engraftment of competitively transplanted cells, cultured with IL-3, IL-6, IL-11 and SCF, consistently dropped to levels below 16%. However, 48 h culture with SCF and Flt3L resulted in 53.5 ± 1.6% engraftment at 17 days and 64 ± 3.7% engraftment at 19 weeks post-transplantation. Extending the cytokine exposure to 72 h resulted in 70 ± 4.4% short-term engraftment at 17 days, and 64 ± 2.4% engraftment at 19 weeks post-transplantation.DiscussionThe data demonstrate the ability of SCF and Flt3L cytokine-stimulated BM cells to maintain short- and long-term engraftability. We conclude that these cytokines play a crucial role in maintaining engraftment of hematopoietic progenitors.