Characterization of platelets from hESCs. (A) Surface markers of hESC-derived platelets were examined by flow cytometry using the same forward- and side-scatter gates used for human plasma-derived adult platelets. Most small particles positive for CD41a (x-axis) were also positive for CD42b (y-axis; lower panel). (B) Transmission electron micrographs of fresh plasma-derived platelets or of hESC-derived platelets on day 23. Bar represents 1μm. (C) Numbers of platelets released into the culture supernatant from day 20 to day 32. The graph shows the relative number when the total number on day 20 per initial 105 hESCs was assigned a value of 1.0. Platelets were collected every other day from culture days 20 to 32, and the cells were counted by flow cytometry using True Count Beads. Data are means (± SD) from 3 independent experiments. (D) Numbers of CD41a+ platelets counted in the absence or presence of TPO (100 ng/mL) alone and in combination with SCF (25 or 50 ng/mL), IL-6 (50 mg/mL), IL-11 (50 mg/mL), and/or heparin (25 U/mL). The graph shows the relative platelet number when the total number of platelets yielded without cytokine was assigned a value of 1.0. Data are means (± SD) from more than 3 independent experiments.
