Antitumor activity of 4-1BB mAb therapy against CT26 colon carcinoma. a) The administration of a double dose of 4-1BB mAb (1 mg/kg) induced reproducible CT26 tumor regressions (n = 12 mice per group; 3.8 ± 0.4 4-1BB mAb group vs 9.2 ± 0.3 control, on day 14 post-tumor implant; p < 0.0001 by two-way Anova). b) Kaplan-Meier plot of improved survival in mice (n = 12 mice per group; p = 0.0001 for tumor diameters by two-way Anova and p = 0.0001 for survival by log rank test). c and d) Different 4-1BB mAb doses were also tested showing a significant tumor growth inhibition by day 21 in animals receiving 0.1 or 1 mg/kg 4-1BB mAb (ns = not significant * P < 0.05, ** P < 0.01, *** P < 0.001 by t-test). e) Re-challenge of surviving tumor-free mice 55 days after complete tumor shrinkage showed a total CT26 tumor rejection by the animals. 4 T1 cells were used as positive control.