Dose effect of TPO on the expansion of HPCs in FLT3-L culture. Purified CD34⁺ HPCs from peripheral blood of G-CSF–mobilized donors were cultured in medium supplemented with FLT3-L with or without the indicated doses of TPO. Kinetics of HPC expansion under different TPO dosages were monitored by counting cells on days 5, 10, 15, 20, 25, and 30. Data shown are aggregate results of TPO dose effect on HPC expansion in FLT3-L culture with HPCs from 3 different donors and are presented as mean ± SD.