Effect of bone marrow stroma coculturing on the induction of apoptosis in CLL cells by bendamustine, fludarabine, or their combination. CLL cells were either cultured in suspension (A,C) or cocultured with bone marrow stroma cells (B,D) and incubated with 30 µM bendamustine (white bars), 10 µM fludarabine (gray bars), their simultaneous combination (black bars), or their sequential combination (bendamustine followed by fludarabine, line bar; or fludarabine flowed by bendamustine, check bar) for 24 (A-B) or 48 (C-D) hours. Cell death was measured using a DiOC6 assay as described in “Materials and methods.” Data are from individual patient samples, and results are corrected to a time-matched control (untreated sample) for each patient sample. B, bendamustine; F, fludarabine; FB, fludarabine followed by bendamustine; F+B, fludarabine plus bendamustine.