CD8⁺ memory T cells are inactivated by cognate antigen-expressing DC. CD45.1⁺ OT-I effector/memory cells were transferred intravenously to 11c.OVA or nontransgenic (non-tg) controls. Mice were left unchallenged or challenged with OVA/QuilA s.c. at 21 or 35 days after transfer. (A) The frequency of OT-I T cells in spleens secreting IFN-γ in response to OVA_257–264 was determined by ELISpot assay 7 days after OVA/QuilA challenge. (B) The total number of OT-I (CD45.1⁺/CD8⁺/Vα2⁺) T cells in spleens of recipient mice was determined 7 days after OVA/QuilA challenge. Data are pooled from 2 independent experiments with 2 mice per group. (C) CD45.1⁺ OT-I effector/memory cells were transferred i.v. to 11c.OVA or non-tg controls. Recipients were treated with anti-CD40 (FGK-45) or PBS on days 0, 5, 10, 15, and 20 after transfer and challenged or not with OVA/QuilA s.c. 21 days after transfer. The total number of OT-I (CD45.1⁺/CD8⁺/Vα2⁺) cells and the total number of IFN-γ–producing OT-I cells per spleen was determined by ICS and bead-based counting assays. Data are pooled from 2 independent experiments with 2 mice per group. The horizontal bars represent mean values.