FIG. 4.

Premature suppression of transgene expression attenuates the magnitude of the primary responses and impairs memory maintenance. (A to C) Mice (eight per group) were immunized with 10⁹ PFU of Ad-tTA-SIINFEKL-Luc on day zero and were separated into four groups. Groups 1, 2, and 3 were started on DOX 3 days (DOX d+3) (open squares), 7 days (DOX d+7) (open circles), and 13 days (DOX d+13) (open diamonds) after immunization, respectively, while group 4 received no DOX (filled squares). At the time points indicated, mice were sacrificed, and SIINFEKL-specific CD8⁺ T cells in the spleen (A), lung (B), and blood (C) were enumerated. Each data point represents the mean ± standard error of the mean. (D to F) Mice (five per group) were immunized with 10⁹ PFU of Ad-tTA-SIINFEKL-Luc on day zero and were treated with DOX 7 days, 13 days, 20 days, or 30 days later. The control group received no DOX (−). Ninety days after immunization, mice were sacrificed, and SIINFEKL-specific CD8⁺ T cells were enumerated in the spleen (D), lung (E), and blood (F). Each bar represents the mean ± standard error of the mean. *, significantly different from the group receiving no DOX (P < 0.05); **, significantly different from the groups receiving DOX on days 13 to 30 (P < 0.05).