OX40-induced protection is through T reg cell inhibition. Effect of OX86 mAb in the absence of T reg cells. 1 mg anti-CD25 mAb or anti-OX40 mAb was administered i.p. to BALB/c naive mice before injection of 5 × 104 CT26 cells. As mock treatment, rat IgG was injected. OX86 mAb was given to mice pretreated or not with PC61 mAb, and rat IgG was given as mock treatment. All mice were challenged with 5 × 104 CT26 tumor cells at day 0. (A) PC61 was injected 14 d before tumor challenge. (B) 7 d later, half of the PC61-treated mice received OX86 or rat IgG injection. (C) A mice cohort received OX86 only 7 d before tumor challenge. Tumor growth was monitored twice per week. One representative out of two independent experiments is shown. (D) Effective T reg cell depletion was monitored by Foxp3 staining in lymph nodes 7 and 14 d after PC61 or OX86 injection. Each symbol corresponds to a single lymph node from each mouse analyzed among the experimental groups. The solid line represents the median value. Representative plots of CD4 versus Foxp3 expression (percentages) are shown for the day 7 observation.
