Biologic effects of IL-21 on CD19⁺CD138⁺ cells obtained from patients with WM (n = 5, WM14, WM15, WM25-WM27). (A) Proliferative effects of IL-21 (25 ng/mL or 100 ng/mL) on CD19⁺CD138⁺ cells cultured for 72 hours. Proliferation was assessed by [³H]-thymidine incorporation. Each patient sample was run in quadruplicate, with data presented as the mean ± SD. (B) IgM secretion by CD19⁺CD138⁺ cells cultured in the presence or absence of IL-21 (25 ng/mL or 100 ng/mL). After 72 hours, cell-free supernatants were harvested, and IgM levels were determined by ELISA. Samples were run in triplicate, and data are presented as the mean ± SD. The 100-ng/mL well from WM25 became infected and was therefore not usable for this experiment. (C) Viability of CD19⁺CD138⁺ cells cultured in the presence or absence of IL-21 (25 ng/mL or 100 ng/mL) for 72 hours. All values are adjusted relative to the viability of the control, which was set at 100%. The 100-ng/mL well from WM25 became infected and was therefore not usable for this experiment. Experiments were performed once for each patient sample. *Statistically significant at P < .05.