Cell-cycle state of antigen-specific memory CD8 T cells in CD27^−/− mice. WT or CD27^−/− mice were infected intravenously with VSV. (A) After 7 days, BM and lung VSV-N tetramer-positive CD8 T cells were analyzed for RNA/DNA content, and the number of cells not in G₀ is shown. The results represent the mean ± SEM of 3 mice per group. (B) After 35 to 65 days, BM and lung VSV-N tetramer–positive CD8 memory T cells were analyzed for RNA/DNA content. The data are the combined results of 2 independent experiments, showing the mean ± SEM of 8 mice total per group. The number of cells in S plus G₂/M was less than 1%.