Effect of interleukin-3, stem cell factor and granulocyte-macrophage colony-stimulating factor on committed stem cells, long-term culture initiating cells and bone marrow stroma in a one-step long-term bone marrow culture.

Long-term bone marrow culture (LTBMC) supports both differentiation and conservation of hematopoietic progenitor cells. During the culture period, the frequency and proliferative potential of early repopulating stem cells that give rise to progenitors detectable after 5 weeks in LTBMC--so-called long-term culture-initiating cells (LTC-IC)--can be investigated. The adherent stroma cell layer was modified by interleukin-3 (IL-3) + granulocyte-macrophage colony-stimulating factor (GM-CSF)+ stem-cell factor (SCF) with an increased cellularity and higher percentage of differentiated myeloid cells and a reduced percentage of stroma cells. We have studied the effects of stimulative cytokines, such as GM-CSF, SCF, and IL-3, on proliferation of committed colony-forming unit cells (CFU-C), LTC-IC, and stroma cell formation in LTBMC of unseparated bone-marrow cells. IL-3, GM-CSF, and SCF significantly stimulated the cumulative proliferation of nucleated cells and committed CFU-C. Weekly stimulation of LTBMC during the culture period did not exhaust the proliferative capacity of stem cells as seen in maintenance of LTC-IC after 5 weeks in LTBMC. In contrast, no LTC-IC were seen in limiting dilution analyses from LTBMC cultured 5 weeks without cytokine supplementation. Our data indicate that an increased proliferation of committed stem cells can be achieved by the addition of stimulatory growth factors, and maintenance of LTC-IC is possible over a period of 5 weeks. A net expansion of LTC-IC if compared with the starting bone-marrow suspension could not be obtained after a 5-week LTBMC period.