Proliferation-induced decline of CML primitive progenitors in response to SB216763 alone or in combination with IM. CFSE-labeling assays were used to measure the effects of IM (1μM), SB216763 (5μM), or the combination on cell division of CML and normal CD34⁺CD38⁻ primitive and CD34⁺CD38⁺ committed progenitors after 96 hours of culture for each treatment. (A) Representative CFSE plots for CML CD34⁺CD38⁻ primitive and CD34⁺CD38⁺ committed progenitors treated as indicated. The calculated proliferation index for each dot plot is indicated. (B) Compiled data for proliferation (expressed relative to proliferation of untreated cells) of inhibitor-treated CML (n = 5) and normal (n = 3) CD34⁺ cell subsets, respectively. The mean ± SD values of replicate experiments are shown (n = 3, CML primitive progenitors; n = 5, CML committed progenitors; n = 3, normal primitive and committed progenitors). (C) The percentage of viable, nondividing CML primitive progenitors retaining maximal CFSE fluorescence after 96 hours of culture for each indicated treatment.