Immunogenicity of SARS-S–derived peptide SSp-1 in HLA-A2.1/K^b transgenic mice. IFN-γ release by bulk CTLs from immunized mice was detected by ELISPOT assay (A) and lytic activity was tested using a standard 4-hour chromium release assay (B). (A) Bulk CTLs from SSp-1–immunized mice released IFN-γ in response to T2 cells pulsed with SSp-1 (T2/SSp-1) in a dose-dependent manner, but not those with irrelevant peptide CAP-1 (T2/CAP-1) or T2 cells alone. (B) Bulk CTLs from SSp-1–immunized mice lysed T2 cells loaded with SSp-1, but not T2 cells pulsed with the irrelevant peptide CAP-1 or T2 cells alone. Data represent means ± SD.