CD8+ T cells cytolytic activity in the immunized mice as demonstrated by IFN-γ intracellular staining. Two weeks after the last HCV vaccine immunization, cultured splenocytes were unstimulated (A), stimulated with CE1E2 protein (B), core peptide (C), or vaccinia HCV poly (D). Cells were cultured for 18 hrs in the presence of brefeldin A then stained intracellularly with anti-IFN-γ antibody and surface stained with anti-CD3+ and anti-CD8+ antibodies to be analyzed by flow cytometry. Percentages in the upper right quadrant represent the frequency of CD3+8+ T lymphocytes expressing IFN-γ. The P value for significant differences was < 0.05.