Cytokine-dependent long-term culture of highly enriched precursors of hematopoietic progenitor cells from human bone marrow

Human marrow cells positive for the CD34 antigen but not expressing HLA-DR, CD15, or CD71 antigens were isolated. In a liquid culture system supplemented with 48-hourly additions of recombinant interleukins IL-1α, IL-3, IL-6, or granulocyte/macrophage colony-stimulating factor (GM-CSF), these cells were capable of sustaining in vitro hematopoiesis for up to eight weeks. The establishment of an adherent cell layer was never observed. Cultures containing no exogenous cytokine produced clonogenic cells for only 1 wk. IL-1α and IL-6 were alone able to support hematopoiesis for 2 or 3 wk. Cells maintained with GM-CSF proliferated and contained assayable colony-forming cells for 3 or 4 wk, while maximal cellular expansion and generation of assayable progenitor cells occurred in the presence of IL-3 for 4-5 wk. When IL-3 was combined with IL-1α or IL-6, hematopoiesis was sustained for 8 wks. Basophil numbers were markedly increased in the presence of IL-3. These studies indicate that marrow subpopulations can sustain hematopoiesis in vitro in the presence of repeated additions of cytokines. We conclude that a major function of marrow adherent cells in long-term cultures is that of providing cytokines which promote the proliferation and differentiation of primitive hematopoietic cells.