LLO91-99–specific CD8 CTLs confer a high degree of protective immunity to wild-type L. monocytogenes (Lm) infection 30 minutes or 48 hours after T cell infusion (a). T cell recipients are not protected from a challenge with LLOSer92L. monocytogenes 30 minutes after CTL infusion, demonstrating in vivo antigen specificity (b). CFUs per organ are shown on the y axis in log scale. Time interval between CTL transfer and infection is indicated. Control animals received PBS, while experimental animals received 6 × 106 LLO91-99–specific CD8 CTLs. *Lower limit of detection. Data are the mean and SD of two to three animals per group and are representative of two independent experiments.