FIG. 2.

Prime-boost vaccination with live Y. pestis generates protective T cells. CD4 and CD8 T cells were copurified from prime-boost-vaccinated mice, as well as naïve control mice, as described for Fig. 1. The residual non-T cells were also collected from each purification. Both the T-cell and non-T-cell populations (5 × 10⁶) were individually transferred intravenously to naïve mice. On the following day, all recipient mice were challenged intranasally with a lethal dose of KIM5 (2 × 10⁵ CFU) and then monitored for 20 days. (A) T cells isolated from mice that were prime-boost vaccinated with KIM5 provided significant protection compared with non-T cells isolated from the same mice (P < 0.002; n = 5 mice/group; ratio of CD4/CD8 = 1.7). (B) T cells isolated from mice that were prime-boost vaccinated with KIM6 provided protection that did not achieve statistical significance in this experiment (P = 0.1; n = 5 mice/group; ratio of CD4/CD8 = 1.6). (C) T cells isolated from naïve mice did not provide any measurable protection (n = 5 mice/group; ratio of CD4/CD8 = 1.6).