Vector persistence drives proliferation of antigen-specific T cells. C57Bl/6 Thy1.1 mice were immunized with 10¹⁰ vp of either AdC68NPOVA green fluorescent protein or AdC68rab.gp vector (3 mice per group). After 4 months, 3 × 10⁷ CFSE-labeled splenocytes isolated from OT1 mice were transferred into each of the immunized mice. One week after transfer the mice were killed and lymphocytes were isolated from the indicated tissues, stained with anti-CD8 and anti-Thy1.2 to identify donor cells, and the amount of CFSE in those cells was determined by flow cytometry. The numbers within the graphs show the percent of cells with low CFSE staining as indicated by the gates.