Enhanced expansion of Ag-reactive CD8⁺ T cells by blockade of B7-H1/CD80 interaction. B6 mice were transferred intravenously with OTA-specific CD8 (OT-I) T cells and injected intravenously with 0.5 mg of OVA_257-264 peptide. On day of peptide injection and 3 days later, the mice were treated intraperitoneally with 200 μg of 43H12 or control rat IgG. (A) PBMCs were harvested at the indicated time points, and a percentage of OT-I T cells in total CD8-positive cells was assessed in the 43H12-treated (●) or control IgG-treated (○) mice by flow cytometry. The data are shown as mean ± SEM. (B) Mice were given 100 μg of BrdU intraperitoneally on day 2 (top panels) or day 4 (bottom panels) after OVA peptide injection. Twenty-four hours after BrdU injection, spleen cells were harvested and BrdU incorporation in CD8/OVA-tetramer double-positive OT-I T cells was analyzed by flow cytometry (black histogram). As background level, OT-I T cells in the mice without BrdU administration were stained similarly (gray histogram). (C) Spleen cells were harvested 4 days after OVA peptide injection and annexin V staining in CD8/OVA-tetramer double-positive OT-I T cells was analyzed by flow cytometry (black histogram). Background level without annexin V staining is also shown (gray histogram). All experiments were independently repeated at least 3 times, and the representative data are shown. The numbers in the histogram indicate the percentage of positively stained cells.