Identification of SSp-1 as a naturally processed and presented HLA-A2.1–restricted epitope. DC-induced human CTLs against SSp-1 were tested for specific lytic activity (A) and IFN-γ release (B) in response to genetically modified cell lines. (A) CTLs lysed pAd-SARS/S–transduced HLA-A2.1⁺ SW480 cells (SW480/SARS/S) but did not lyse pAd-SARS/S–transduced HLA-A2.1^– HT29 cells (HT29/SARS/S) or pAd-LacZ–transduced SW480 (SW480/LacZ) and HT29 cells (HT29/LacZ). (B) CTLs elicited strong IFN-γ production in response to pAd-SARS/S–transduced SW480 cells, but only very low levels were elicited by pAd-SARS/S–transduced HT29 cells or pAd-LacZ–transduced cell lines. Results are representative of 3 independent experiments. Data represent means ± SD.