IL-21 alters the antiapoptotic profile induced by CD40L by downregulating Bcl-XL and induces proliferation through Jak-STAT3. (A) Gene expression analysis of sorted CD19⁺ CD5⁺ CLL cells, cultured with CD40L-expressing fibroblasts in the absence or presence of IL-21 for 16 hours. Heatmap of 51 differentially expressed genes (ANOVA P < .01; fold change >3; minimum present calls >3; minimum highest expression >200), depicting results for paired samples from 4 patients (samples 2, 5B, 11, 30). (B) The RNA samples from panel A were analyzed for expression of different apoptotic mediators by MLPA. Results are shown for relevant genes as relative expression to HK genes (mean ± SD; n = 4). (C-D) CLL cells cultured as in panel A were analyzed after 72 hours by western blot for the indicated BCl-2 family members. Tubulin and β-actin were used as loading controls. (E) CFSE-stained CLL cells were cultured with CD40L-expressing fibroblasts alone, together with IL-21 (25 ng/mL) or IL-21 plus an inhibitor of Jak kinases (Ruxolitinib, 1 μg/mL) for 5 days. Representative histograms from sample 23 are shown. (F) CLL cells were cultured as in panel E. The percentage of divided cells is depicted as mean ± SD, for samples 16B, 23, and 29C.