The percentage of MKs equal to or greater than 8N in PB and CB cultures differed depending on media source and rTpo concentration. PB- and CB-CD34⁺ cells were cultured for 14 days in UCM (A) and CM (B), with varying rTpo concentrations. PB-derived MKs (solid lines) cultured in UCM (A) exhibited a rTpo dose-dependent increase in ploidy levels, an effect inhibited by the presence of CM (B). CB-derived MKs (dashed lines) reached highest ploidy levels when cultured in CM with no rTpo, an effect that was reversed by rTpo concentrations of 1 ng/mL or more (B). Data shown represent the means and standard error of the mean (SEM) of 4 separate experiments.