Proportion of nonviable cells per G418R erythroid colony. CD34⁺ cells were retrovirally infected with LNL6 (▨) or LNC(SCL) (▪) and placed into agar cultures stimulated for erythroid colonies for 7, 10, and 14 days. For each experiment, 40 G418R colonies were pooled in 150 μL PBS and analyzed as outlined below. The results were divided by the number of colonies pooled. (A) The percentage of dying cells was determined by comparing the number of cells that stained with eosin to the total number of cells present. Data points represent the mean ± SD percentage of nonviable cells per erythroid colony at days 7 (n = 3 experiments), 10 (n = 6 experiments), and 14 (n = 6 experiments). (B) The number of dying cells was determined by staining with PI. Fluorescently stained nonviable cells were quantitated using UV microscopy and compared with the total number of cells observed under phase contrast to determine the percentage of nonviable cells per G418R erythroid colony at day 10 (n = 5 experiments).