Dose response of rhTPO to the growth of CD41⁺PI⁺ cells from liquid culture of umbilical cord blood MNCs. Cells were cultured for 8 days in the presence of various concentrations of rhTPO and 10% control plasma. The yields of CD41⁺PI⁺cells in cultures were determined by means of the 2-color flow cytometric technique (means ± SDs; n was at least 2 for each dose).