Mcl-1 down-regulation induces rapid apoptosis in primary CLL B cells. (A) Time course experiments comparing the viability of CLL cells nucleofected with control, Mcl-1, Bcl-xL, and XIAP siRNA. Untransfected samples (untransf.) and samples transfected without RNA (no RNA) were used to evaluate apoptosis induced by the nucleofection procedure. Viability was determined by Annexin V/PI staining at 3, 24, and 48 hours after nucleofection. (B) Purified CLL B cells from 11 patients were transfected with the indicated siRNAs. Cell viability was evaluated after 24 and 48 hours. ○ represents the percentage of viable cells in individual cases. Mean values are indicated by ●, error bars indicate standard deviation.