Immortalized hemopoietic cells with stem cell properties.

We have established a hemopoietic cell line, BL3, that possesses a rearranged retroviral genome, which we used as a genetic tag for their engraftment into lethally irradiated mice. Analysis of recipients up to 7 months after engraftment indicates that the marker was present in differentiated cells of various hemopoietic organs, in colony-forming cells, pre-CFU-S-forming cells, and in organs of secondary recipients from bone marrow cells of primary recipients. BL3 cells are Thy-1+, Sca-1+, B220-, Mac-1-, and Gr-1-. They express GATA-1 and are able to develop "cobblestones" with stromal cells. They do not express and respond to several hemopoietic growth factors known to facilitate marrow recovery. However, they are negatively regulated by TGF beta and can be stimulated by mitogen-stimulated spleen cell-conditioned medium. We conclude that BL3 cells possess properties of hemopoietic stem cells, including their capability to contribute to long-term repopulation.