Proliferative response of single CD34⁺CD38⁺ (A) or CD34⁺CD38⁻ cells (B) cultured in serum-free pre-CFU media stimulated with either 4 HGF or 4 HGF + FLT3L (shown as the solid columns). The number of viable cells present after 14 days of culture was determined for each single cell that divided. The results are from one of the experiments performed to generate data shown in Fig 4.