Coculture with MSCs protects CLL cells from dexamethasone-induced apoptosis. (A) Bar diagram depicts the mean (± SEM) relative viabilities of CLL cells treated with dexamethasone in the presence or absence of murine (KUSA H) or human (StromaNKTert) MSCs at the time points displayed on the horizontal axis from 5 different patients with CLL. *Significant protection from dexamethasone-induced cytotoxicity compared with control sample (P < .05). (B) Contour plots from a representative CLL sample depict viability of CLL cells, as determined by staining with DiOC₆ and PI, after 48 hours of incubation with 10 μM dexamethasone in absence or presence of MSCs, as indicated above each of the plots. The percentage of viable cells is displayed above each of the gates that define viable cells (DiOC₆^bright PI^exclusion).