CHARACTERIZATION OF PERIPHERAL-BLOOD STEM-CELLS IN MICE

Peripheral blood stem cells (PBSCs) were mobilized in mice by treatmen t with cytosine-arabinoside on day 0, followed by the administration b y injection of granulocyte colony-stimulating factor for 4 days. There were remarkable increases in the numbers of cells with lineage-negati ve (Lin(-)) c-kit(+) markers, cells with colony-forming unit-cell (CFU -C) and colony-forming unit-spleen (CFU-S) activities, and cells with marrow-repopulating ability (MRA) in the extramedullary sites (the spl een, peripheral blood, and liver) on day 5, whereas the number of thes e immature hematopoietic cells decreased in the bone marrow (PM) on da y 5, This finding suggests the mobilization of immature hematopoietic cells from the BM to the extramedullary sites, Three-color flow cytome tric analyses showed that CD4 antigen was not expressed on the Lin(-)S ca-1(+) cells in the mobilized PB cells (PBCs), although CD4(lo) cells were found in those of normal BM cells, Lin(-)c-kit(+) cells in the m obilized PBCs contained more cells with immature phenotypes (Sca-1(+) Thy1.2(lo), CD71(-), and Rh123(dull)) than in normal BMCs, indicating an alteration of the hierarchical composition of the Lin(-)c-kit(+) ce lls, The Lin(-)c-kit(+)Sca-1(+) cells in the mobilized PBCs had simila r CFU-C and CFU-S activities to those in normal BMCs, Electron microsc opic studies of these cells in the mobilized PBCs showed that only 10% to 20% of these cells had a thin rim of cytoplasm with poorly develop ed organelles. Allogeneic transplantation [B6-->C3H] of PBSCs showed l ong-term reconstituting activity across the major histocompatibility c omplex barrier 24 weeks after transplantation, although longer observa tion is necessary. (C) 1996 by The American Society of Hematology.