Mobilization of Hematopoietic Stem and Progenitor Cell Subpopulations From the Marrow to the Blood of Mice Following Cyclophosphamide and/or Granulocyte Colony-Stimulating Factor

Committed progenitor cells and primitive stem cells mediate early and sustained engraftment, respectively, after lethal irradiation and stem cell transplantation. Peripheral blood stem cells (PBSC) from unstimulated mice are deficient in both cell types. To study techniques to mobilize both progenitor cells and primitive stem cells from the marrow to the blood, we collected peripheral blood from C57BL/6 mice 6 to 7 days after a single dose of cyclophosphamide (CY; 200 mg/kg intraperitoneally), after recombinant human granulocyte colony-stimulating factor (rhG-CSF) (250 pg/ kg/d twice per day subcutaneously for 4 days), or after CY followed by G-CSF. Significant increases in white blood cell counts (1.6to 2.7-fold) and circulating day 8 colony-forming unit spleen (CFU-S) (1 1 to 36-fold) were seen with all three mobilization methods compared with unstimulated control mice. Transplantation of mobilized blood stem cells into lethally irradiated hosts decreased the time to erythroid engraftment. Blood stem cells were analyzed for primitive stem cell content by Rs, an assay for CFU-S self-renewal, and competitive repopulation index (CRI), an assay of longterm repopulating ability. The primitive stem cell content