Mcl-1 and PARP expression in CLL cells cocultured with MSCs. CLL cells were cultured with the MSC lines displayed on the top horizontal axes or in suspension (“Control”) for 48 hours with or without 10 μM F-ara-A (labeled “Ctr” or “+F,” respectively). Then, cleaved and uncleaved Mcl-1 and PARP were analyzed by Western blotting, and the respective immunobands are indicated on the left-hand side. Cell viability for each condition was measured by flow cytometry, and the percentage of viable cells is displayed below each of the blots. In most cases, MSCs coculture up-regulated Mcl-1 and PARP expression compared with CLL cells in suspension (control at 48 hours vs the “Ctr” bands in the presence of MSCs). Suspension culture of CLL cells results in spontaneous apoptosis, with associated Mcl-1 and PARP cleavage (panels A-B 2nd lane from the left), which was paralleled by a decrease in CLL cell viability from 99% to 47% in panel A and from 96% to 81% in panel B. Treatment with fludarabine resulted in cleavage of the majority of Mcl-1 and PARP in the absence of MSCs (panels A-B 5th lane from the left). This was largely inhibited, sometimes almost abrogated (eg, panel A lanes 6-7) by the presence of MSCs. Displayed are Western blots of CLL B-cell lysates from 2 representative patients (A-B).