Bone marrow stromal cells induce myeloid and lymphoid development of the sorted hematopoietic stem cells in vitro.

Regulation of development of hematopoietic stem cells was examined by culturing Lin- c-Kit+ Sca1+ stem cells sorted from bone marrow (BM) cells by fluorescence-activated cell sorting on a layer of TBR59, a BM stromal cell line established from simian virus 40 T-antigen gene transgenic mice. The sorted stem cells did not show self-renewal, but two waves (at 7 and 13 days) of a cobblestone formation were induced by the stromal cell layer. The cobblestones were formed by finite cell division (eight divisions on average) of sorted Lin- c-Kit+ Sca1+ stem cells, and divided cells were still immature. The c-Kithigh stem cell population was induced to form the first wave of cobblestone formation committed to myeloid lineage, whereas c-Kitlow population was induced to form the second wave of this formation committed to lymphoid lineage. Both cobblestone formations require c-Kit function, but very late activation antigen-4-vascular cell adhesion molecule-1 interaction plays different parts in the two lineages.