Effects of culture conditions on MK growth (A), proplatelet formation (B), and platelet production (C). CD34⁺ cells from marrow (n = 3, ▧) or blood (n = 3, ▧) were grown during 14 days in the presence of PEG-rHuMGDF (10 ng/mL) in serum-free conditions, in serum derived from PPP, or normal serum in the absence or presence of heparin (H) or an anti–TGF-β antibody. MKs and platelet bearing MKs were enumerated using an inverted microscope and hemocytometer. The results represent the mean ± SD of three independent experiments, and are expressed per 1 × 10³ plated CD34⁺ cells. Asterisks denote a significative difference (P < .05) in comparison with culture in serum-free conditions.