Density-dependent effect of Delta1^ext-IgG on generation of T-cell progenitors. LSK cells were cultured for 28 days with Delta1^ext-IgG plated at increasing concentrations and were analyzed by FACS to determine the percentage of cells expressing CD44 and CD25. Numbers in right upper corner represent the percent of CD44⁺CD25⁺ cells plus or minus the standard error of the mean (SEM) of 5 separate experiments.