Clone formation and progenitor expansion from single cell cultures of CD34⁺CD38⁻ adult human bone marrow cells.

CD34⁺CD38⁻ cells were isolated and cultured as single cells in serum-free medium in the presence of 300 ng/mL stem cell factor, Flt-3 ligand, and 60 ng/mL IL-3 (High) or 30 ng/mL stem cell factor, Flt-3 ligand, and 6 ng/mL IL-3 (Low) for 10 days before analysis. Analysis consisted of determining the number of clones produced under each condition and then performing LTC-IC and CFC assays on a pool of each set of clones generated under the same condition. These studies showed that although the same number of clones and CFC were generated in the High versus the Low cytokine concentrations, the net generation of LTC-IC was dramatically affected by changes in cytokine concentration. Taken together these results suggested that self-renewal versus differentiation, not self-renewal versus survival, was being modulated. Results are from reference 8.