Fig. 4.

In vivo CTL assay. To analyze SARS-CoV-specific cytotoxicity in vivo, a 1:1 mixture of 10⁷ cells of each target cell population was injected i.v. into naïve BALB/c mice 7 days after the second injection with the DNA vaccine. After 4 h, the mice were killed and the splenocytes were analyzed for the presence of CFSE^high and CFSE^low target cell populations. The percentage of specific lysis was then determined as described in Materials and methods. (A) Representative histogram plot of lymph node cells obtained from the mice injected with SARS-CoV DNA vaccines 4 h after transfer of CFSE-labeled target cells. (B–E) The SARS-CoV-specific cytotoxic responses in the lymph nodes are shown from mice previously injected by the pcD3d vector control, pcD3d/E, pcD3d/M, and pcD3d/N constructs, respectively. Each datum has been repeated twice.