Dose-response analysis of PD98059 effect on the presence of CD34⁺, CD41⁺, and CD41⁺CD34⁺ cells in MGDF-induced cultures. CD34⁺ cells were grown with rhuMGDF in the presence of the indicated concentrations of PD98059 diluted in DMSO or the equivalent volumes of DMSO alone. After 7 days, cells were labeled with FITC-anti-CD41 and R-PE-anti-CD34 antibodies either separately or simultaneously. Results are expressed as a percent of the frequency of positives cells for each marker obtained with control cells.