Requirement for IL-7 during early lymphoid development from Lin^−/loSca1⁺c-kit⁺progenitors. A total of 500 Lin^−/loSca1⁺c-kit⁺ cells/mL was cultured in the presence of FL from initiation of culture. IL-7 was added to the cultures at the indicated time points, whereas KL was added to all groups 64 hours after initiation of culture. Total cell expansion was evaluated 12 days after initiation of culture. Each data point represents the mean (+SEM) of 3 individual experiments with duplicate wells in each experiment.