IL-21 plus CpG ODN induces apoptosis of B-CLL cells. PBMCs from 9 patients with B-CLL were cultured for 4 days in the presence of CpG ODN (2.5 μg/mL) and IL-21 (100 ng/mL) or IL-2 (100 U/mL). Cell survival of B-CLL cells was determined using annexin V and PI staining and counterstaining with antibodies to CD19. (A) Shown are annexin V/PI dot plots from 1 representative experiment. Gated are CD19⁺ B-CLL cells. Numbers in the gates represent percentages of displayed events. (B) The mean B-CLL cell-survival rates from 9 independent experiments are plotted. Error bars indicate SEM.