Memory formation and secondary responsiveness after DC transfer. Experimental set-up as described for Figure 2 with CD27^−/− recipients of OT-I T cells and DCs. (A) Representative flow cytometric profiles of blood cells at 10 weeks after DC transfer. Numbers indicate percentages of H-2K^b/OVA_257-264 tetramer-positive cells within the CD8⁺ T-cell population as marked by the oval. (B) Quantification of the steady state memory T-cell pool in blood at 10 weeks after adoptive transfer of WT or CD27^−/− OT-I T cells and CD27^−/− (control) or CD70tg;CD27^−/− (CD70tg) OVA_257-264 peptide-loaded DCs. (C) At 10 weeks after primary challenge, recipients were injected intravenously with OVA_257-264 peptide in combination with LPS and percentages of H-2K^b/OVA_257-264 tetramer-positive cells among CD8⁺ T cells in blood were determined on successive days. Data in panels B and C represent mean values (+SEM) for 4 mice per group and are representative of 2 independent experiments. Asterisks indicate statistical significance between the groups that received control or CD70tg peptide-loaded DCs and WT T cells according to Student t test for *P < .05, **P < .01, and ***P < .001.