CD137 stimulation prevents the induction of anergy on OT-1 cells in vivo. (A) B6 mice were given OT-1 cells prior to the intravenous administration of PBS or OVA peptide. On the day of peptide administration and again 3 days later, mice were given 100 μg of either control rat IgG or anti-CD137 (2A). Mice were killed at the time points indicated, and the total number of OT-1 cells present in each mouse was calculated following tetramer analysis. The data shown are the mean (± SD) of 3 mice in each group. (B-C) Ten days following the administration of PBS or OVA, spleens were harvested and restimulated in triplicate in the absence or presence of OVA peptide (1 ng/mL) in 96-well plates. At the time of restimulation, the frequency of OVA-specific T cells was determined by tetramer analysis. OVA-specific proliferation and IL-2 production were determined 72 and 48 hours later, respectively. Thymidine incorporation and IL-2 production were determined on a per cell basis as described in “Materials and methods.” Data shown are representative of at least 3 independently performed experiments.