Expression of death receptors after CD40 ligation on CLL B cells in vitro and in vivo. Surface expression of death receptors on CD19⁺ CLL cells was monitored by flow cytometry. (A) CLL B cells were cocultured for 24 hours with HeLa cells (control) or HeLa cells expressing CD154 (CD40 ligation). Representative shaded histograms show the expression of DR4 (left column), DR5 (middle column), or CD95 (right column) on CLL cells 24 hours after coculture with HeLa cells (top row) or HeLa cells that express CD154 (bottom row). The open histograms represent the fluorescence of the cells stained with a fluorochrome-conjugated isotype control mAbs of irrelevant specificity. (B) CLL B cells were isolated from gene therapy patients before treatment and 24 hours after infusion of Ad-CD154–transduced CLL cells (after treatment). Representative shaded histograms show the expression of DR5 (left column) or CD95 (right column). The open histograms represent the fluorescence of the cells stained with isotype-matched control mAbs of irrelevant specificity.