Activation by CD154 and induction of p73 enhances the sensitivity of p53-deficient CLL cells to F-Ara-A. (A) CLL cells with nonfunctional p53 were exposed to HeLa cells (control) or CD154-HeLa cells (CD154) with (+) or without (-) 10 μM imatinib and then cultured alone with (+) or without (-) 3 μM F-ara-A, as indicated at the bottom of the panel. The cells were stained with DiOC₆ (x-axis) and PI (y-axis) and then examined via flow cytometry. The numbers in each quadrant represent the relative proportion of cells found within each gated compartment. (B) CLL samples (n = 2) with nonfunctional p53 were exposed to HeLa (control, ▪) or CD154-HeLa (CD154, □) with various concentrations of imatinib, as indicated at the bottom of the panel in μM. The cells were then isolated and cultured without (-) or with (+)3 μM F-ara-A, as indicated at the bottom of the panel. Each bar represents the mean proportion of apoptotic CLL cells, as indicated on the y-axis, plus or minus standard deviation. Bars with asterisks indicate that the difference in the relative levels of apoptosis observed for control-treated cells (▪) or CD154-treated cells (□) is statistically significant (P < .05). (C) CLL cells with nonfunctional (p53-, top panel; n = 2) or functional p53 (p53+, bottom panel; n = 2) were transduced with Ad-TAp73α or Ad-LacZ or remained untransduced (control), as indicated at the bottom of panel. Twenty-four hours later the CLL cells were washed extensively and cultured for another 48 hours in media (▪) or in the presence of 3 μM F-ara-A (□). At the end of this incubation period the proportion of apoptotic cells was assessed via flow cytometry after staining the cells with DiOC₆ and PI. Each bar represents the mean relative proportion of apoptotic CLL cells, as indicated on the y-axis, plus or minus the standard deviation. Bars with asterisks indicate that the difference in the relative levels of apoptosis observed for control-treated CLL cells (▪) versus F-ara-A-treated CLL cells (□) is statistically significant (P < .05).