In situ injections of IL-21 induce tumor remission and prolong survival of mice bearing DLBCL xenograft tumors. Mice bearing subcutaneous RC-K8 or MC116 xenograft tumors were treated with 10 μL in situ injections of either PBS (3 mice per experiment) or IL-21 (1 mg/mL; 5 mice per experiment). (A-B) Tumor size (area) in IL-21–treated and PBS-treated mice bearing RC-K8 (A) or MC116 (B) tumors. Dashed lines represent tumor size in individual PBS-treated mice, whereas solid lines represent individual IL-21–treated mice. (C-D) Overall survival of mice bearing RC-K8 (C) or MC116 (D) tumors treated with PBS (dashed line; n = 3) or IL-21 (solid line; n = 5). Similar results to those shown in panels A-D were observed in an additional independent experiment performed with each cell line.