B7-H3^−/− T cells have increased activation and proliferation and decreased apoptosis. (A) MLR was performed by coculturing B6-WT or B7-H3^−/−-purified T cells that were CFSE labeled with irradiated BALB/c DC stimulators (10:1). Cells were analyzed by flow cytometry on day 5. Cells were gated on H2K^b-positive, viability dye–negative CD4 or CD8 positive events and were analyzed for dilution of CFSE (n = 5). One of 2 representative experiments is shown. (B) BALB/c mice were lethally irradiated and infused with 10⁷ B6 NTCD BM and 1 × 10⁶ B6-WT or B7-H3^−/−-purified T cells. Mice were euthanized on day 7, and splenocytes were analyzed for total cell numbers (n = 4). One experiment was performed. (C) Splenocytes were analyzed for Ki-67, IFN-γ, IL-2, and annexin V α₄β₇ expression (n = 4). One experiment was performed. *P < .05; **P < .01; ***P < .001.