Modulation of hematopoietic stem/progenitor cell engraftment by transforming growth factor β

Objective: To investigate if cell cycle progression plays a role in modulating the engraftment potential of mouse hemtopoietic stem and progenitor cells (HSPC), Materials and Methods. HSPC were isolated from adult mouse hone marrow, cultured in vitro under conditions promoting cell cycle arrest, and subsequently were evaluated for cell cycle status, clonogenic activity, and transplant potential. Results. In the presence of steel factor (STL) as a survival cytokine, transforming growth factor beta (TGF-beta) increased the G(0)/G(1) fraction of cycling progenitor cells (R-high) after a 20-hour culture, Clonogenic activity of quiescent long-term repopulating (Rh-low) HSPC was unaffected by this culture, whereas clonogenic potential of Rh-high tells decreased by about 30%. In competitive repopulation assays, Rh-low cells cultured in STL + TGF-beta engrafted better than cells cultured in STL alone. However, culture in STL + TGF-beta did not overcome the failure of Rh-high cells to engraft after transplant. We also utilized a two-stage culture system to first induce proliferation of Rh-low HSPC by a 48-hour culture in STL + interleukin 6 + Fit-3 ligand, follow ed by shifting the culture to STL + TGF-beta for 24 hours to induce cycle arrest. A competitive repopulation assay demonstrated a relative decrease in repopulating potential in cultures that were cycle arrested compared to those that were trot. Conclusion. Cell cycle progression by itself cannot account for the decrease in repopulating potential that is observed after ex vivo espansion, Other determinants of engraftment must be identified to facilitate the transplantation of cultured HSPC, (C) 2000 International Society for Experimental Hematology. Published by Elsevier Science Inc.