Platelet production from healthy donor (HD) plus CD34⁺ cell cultures in the presence of increasing concentrations of native VWF. Relative number of platelets at day 7 of treatment with TPO or TPO and VWF at the indicated doses. The number of platelets was calculated by flow cytometry on a CD41⁺/calcein am⁺-labeled population analyzed in combination with a known number of calibration beads. Data are from 2 independent experiments. All the samples were analyzed with Bonferroni test against TPO treatment (means ± SD; *P < .05 vs TPO treatment).