Inhibition of CD34⁺ cell differentiation by IL-6 and M-CSF. CD34⁺ cells were cultured with GM-CSF+TNF alone (control) or in the presence of 10% CLB-VER CM, IL-6 (20 ng/mL), M-CSF (20 ng/mL), or VEGF (25 ng/mL) from day 6 to 12. Neutralizing antibodies ([▪] control antibodies), (░) anti–IL-6+IL-6R, () anti–M-CSF, or (▨) the combination of anti–IL-6+IL-6R and anti–M-CSF were added at 10 μg/mL in the culture. At day 12, cells were harvested and processed for a double staining with CD14-PE and CD1a-FITC. Results are expressed as the percentage of CD14⁺ and CD1a⁺ cells. For all conditions, the SD ranged from 1% to 2%.