Effects of 5 individual cytokines on the proliferative potential of human fetal BM CD34⁺ thy-1⁺cells in vitro. Data are presented as the total number of hematopoietic cells per well (average of 15 wells) in each culture condition at each weekly time point. The standard deviation for the 15 wells in the LIF-treated cultures at each weekly time point is less than 8% of the mean value. (□), Control; (◊), IL-3; (○), IL-6; (▵), GM-CSF; (⊞), SCF; (▨), LIF.