Characterization of ST-specific CD8+ T cells using splenocytes stimulated with ST peptide aa 19-27. (A) Outline of the vaccination schedule. C57BL/6 mice (5 per group) were immunized with pcDNA3-MCC/ST intradermally with DNA-coated particles using a helium-driven gene gun 3 times at 4-day intervals. Pooled splenocytes from vaccinated mice were collected and cultured in vitro with overlapping ST peptide overnight, and stained for intracellular IFN-γ and CD8+ cell surface marker. (B) Intracellular cytokine staining followed by flow cytometry analysis to characterize ST-specific CD8+ T cell epitope using a single ST peptide (aa 19-27) from splenocytes harvested from mice vaccinated with pcDNA3-MCC/ST or pcDNA3. (C) Bar graph of representative flow cytometry data showing the number of ST-specific CD8+ T cells among 3 × 105 splenocytes. Note that peptide 19-27 activated the highest number of ST-specific CD8+ T cells.