Phosphorylation of H2AX in CLL cells after treatment with bendamustine, fludarabine, or their combination. CLL cells were either cultured in suspension (A,C) or cocultured with bone marrow stroma cells (B,D). Panels A and B show samples from 1 patient that were either untreated (control) or incubated with 30 µM bendamustine, 10 µM fludarabine, their simultaneous combination, or their sequential combination (bendamustine followed by fludarabine or fludarabine followed by bendamustine) for the indicated times. Phosphorylation of H2AX was measured using flow cytometry. Panels C and D show results from 10 patient samples, and cells were either untreated (speckled bars) or treated with bendamustine alone (white bar), fludarabine alone (gray bar), or the simultaneous combination of fludarabine and bendamustine (black bar). Phosphorylation of H2AX was measured using flow cytometry, and data are mean ± SD. 8H, 8 hours; B, bendamustine; F, fludarabine.