Proapoptotic effect of IL-21 and CpG ODN on B-CLL cells is direct. PBMCs from 3 patients with B-CLL were isolated and divided into 2 fractions. One fraction was purified to a percentage of more than 99% CD5⁺, CD19⁺ B-CLL cells. Both fractions were incubated for 3 days with IL-21, CpG ODN, or both agents, and apoptosis was determined flow cytometrically. Data are from 1 representative experiment of 3. Dot plots demonstrate the purity of B-cell populations based on CD19 expression. Numbers in the gates represent percentages of displayed events. Bar graphs illustrate the mean B-CLL cell-survival rates in response to treatment. Error bars indicate SEM from experimental replicates.