Isolation of small, primitive XXXX hematopoietic stem cells: distribution of cell surface cytokine receptors and growth in @entity466 -Hu @entity19 .

@entity1 @entity852 @entity650 @entity6826 @entity1261 @entity1075 @entity19 @entity8116 @entity3053 @entity466 @entity1192 @entity2772 @entity2280 @entity2841 @entity10557 @entity1116
@entity1 @entity2280 + cells were subfractionated into three size classes using counterflow centrifugal elutriation followed by immunoadsorption to @entity852 cell separation devices. The three @entity2280 + cell fractions (Fr), Fr 25/29, Fr 33/37, and Fr RO, had mean sizes of 8.5, 9.3 and 13.5 microns, respectively. The majority of cells in the large Fr RO @entity2280 + cell population expressed the committed stage antigens @entity1116 , @entity1075 , @entity3053 , or HLA-DR and contained the majority of granulocyte-macrophage colony-forming units ( @entity8116 ), burst-forming units-erythroid (BFU-E), and CFU-mixed lineage (GEMM). In contrast, the small Fr 25/29 @entity2280 + cells were devoid of committed cell surface antigens and lacked colony-forming activity. When seeded to allogeneic stroma, Fr RO @entity2280 + cells produced few @entity8116 at week 5, whereas cells from the Fr 25/29 @entity2280 + cell population showed a 30- to 55-fold expansion of myeloid progenitors at this same time point. Furthermore, @entity2280 + cells from each size fraction supported ontogeny of T cells in @entity1 thymus/liver grafts in @entity466 ( @entity466 ) @entity19 . Upon cell cycle analyses, greater than 97% of the Fr 25/29 @entity2280 + cells were in G0/G1 phase, whereas greater proportions of the two larger @entity2280 + cell fractions were in active cell cycle. Binding of the cytokines @entity1192 , @entity2772 , @entity650 , @entity6826 ( @entity6826 ), @entity10557 , @entity1261 ( @entity1261 ), and @entity2841 to these @entity2280 + cell populations was also analyzed by flow cytometry. As compared with the larger @entity2280 + cell fractions, cells in the small Fr 25/29 @entity2280 + cell population possessed the highest numbers of receptors for @entity6826 , @entity10557 , and @entity1192 . Collectively, these results indicate that the Fr 25/29 @entity2280 + cell is a very primitive, quiescent progenitor cell population possessing a high number of receptors for @entity6826 and @entity10557 and capable of yielding both myeloid and lymphoid lineages when placed in appropriate in vitro or in vivo culture conditions.
