Increase of the overall survival rate by IL-2 therapy given after tumor challenge in vivo. (A) Mice were intravenously injected on day 0 with EL4-huCD20 cells (n = 24) and divided into 3 groups. The first group (□, n = 8) was used as a control group and left untreated. Mice from the second group (■, n = 16) received the CAT-13 mAb therapy. Mice from the third group (gray pentagons, n = 8) received the CAT-13 mAb therapy associated with 2 intraperitoneal injections of IL-2 on days 1 and 4 (log-rank analysis, *P < .001; **P < .001). (B) Surviving CAT-13–treated mice (n = 10) were challenged intravenously with EL4-huCD20 cells on day 70 and divided into 2 groups. The first group was left untreated (■, n = 5). The second group was subsequently intraperitoneally injected with IL-2 on days 71 and 74 (gray pentagons, n = 5). Naive mice injected with EL4-huCD20 cells (□, n = 5) were used as controls (log-rank analysis, †P = .002; ††P = .002). Black arrows indicate CAT-13 mAb injections; and gray arrows, IL-2 injections.