In vivo IL-21 inhibits tumor growth and prolongs survival of MCL-bearing mice. (A-B) C57BL/6 mice (n = 5 per group) were SC injected with FC-muMCL1 cells and treated with IL-21 or PBS as described in “Materials and methods.” (A) Depicts tumor volume of lymphoma-bearing mice and (B) illustrates Kaplan–Meier survival curves. (C) FC-muMCL1 cells were treated with 100 ng/mL IL-21 for 72 hours, and cell death was measured by YO-PRO and PI staining followed by flow cytometry. (D) FC-muMCL1 cells were stimulated with 100 ng/mL IL-21 in vitro for 15 minutes or 24 hours followed by immunoblotting for phosphorylated STAT3 and cMyc, respectively. For panels A-D, data are representative of 2 independent experiments. Error bars represent standard error of the mean.