Combined treatment with IL-7 and agonistic anti–4-1BB increases the number of functional CD8 T cells and decreases viral load in a TRAF1-dependent manner. Mice were infected with LCMV clone 13 for 21 d and treated with either IL-7 alone, agonistic anti–4-1BB (3H3) alone, or in combination as indicated, using the following treatment regimen: 10 µg/mouse of IL-7 on day 21, 23, and 25, and 100 µg/mouse of 3H3 on day 25. Mice were sacrificed on d30 (a and b) or day 37 (c). (a) The number of tetramer⁺ CD8 T cells specific for LCMV epitopes was examined for each treatment group, with each data point representing a single mouse. (b) Splenocytes from mice in each group were subjected to LCMV peptide restimulation with brefeldin A, monensin, and anti-CD107a or isotype control for 6 h. Cells were then harvested for surface and intracellular staining and FACS analysis. (c) Organs were harvested at day 37, and viral titers were measured. Data in a–c are representative of three similar experiments for tetramer analysis and viral clearance, the latter presented as the median of seven or eight individual mice. The dotted line indicates the limit of detection of the assay. (d) WT and TRAF1^−/− mice were treated with IL-7/anti–4-1BB or left untreated as described in a. At day 37 (12 d after treatment), the number of gp33-specific CD8 T cells were enumerated in the spleen (left). Viral titers were evaluated in spleen and liver (right). Data in d are pooled from two independent experiments with 7 TRAF1^−/− and 10 WT mice per group.