CTL activity of splenocytes from vaccinated mice 2 weeks after the last immunization. Splenocyte samples (10 mice per group) isolated from the vaccinated mice were stimulated with the MEAP. After 6 days the CTL activities were detected using a cytotoxicity assay kit by measurement of the LDH released. All the measurements were made in triplicate, with the mean ± standard error (SE) shown. P < 0.05 compared with groups immunized with PBS or inactivated vaccine.