Results are expressed as the means ± standard errors of the means (SEM). Statistical comparisons were performed by one-way ANOVA test, followed by a Bonferroni post test using the Prism 4.0, GraphPad Software. A p-value of <0.05 was considered to be statistically significant. 293 T-cells were transiently transfected with expression plasmids (previously verified by sequencing) to characterize expression levels. Since antibodies recognizing the HA of the novel H1N1 were not available, both plasmids were designed to express an ollas-tag [19] at the intracellular selleck chemicals C-terminus. While the protein expressed from the wildtype sequence was only barely detected by Western blot using an antibody

to the tag, the expression was readily detectable after transfection of the codon-optimized plasmid (Fig. 1). The protein was expressed as an uncleaved HA precursor on the cell surface and was released into the cell culture supernatant. The secreted HA could be pelleted by ultracentrifugation through a 20% sucrose cushion indicating its incorporation into exosome-like vesicles (data not shown). This is of interest, because these exosomes might be involved in learn more the immune response elicited by the DNA vaccination. Since the expression levels differ strongly

between the two plasmids, we evaluated the influence of codon-optimization on the immunogenicity. In our vaccination schedule, 6–8-week-old Balb/c mice were immunized twice by DNA electroporation in a 3-week interval. The CD4 response was characterized by an intracellular cytokine staining of splenocytes 2 weeks after the second vaccination. Vaccination with either the wildtype or the codon-optimized sequence containing plasmids leads to the induction of substantial antigen-specific CD4+ T-cell responses. Interestingly, the levels of cytokine-producing CD4+ T-cells after an in vitro restimulation with the immunodominant peptide were similar. There were no statistically significant many differences between the frequencies of CD4+ T-cells producing one of the inflammatory cytokines TNF-α, IFN-γ or IL-2 in animals receiving either the wildtype or codon-optimized

plasmid ( Fig. 1). This response was very consistent and was observed in all vaccinated animals. Furthermore polyfunctional CD4+ T-cells described by the expression of all three cytokines are detected at high frequencies in both groups as this subpopulation of cells represented approximately 75% of all IFN-γ producing cells. This suggests that electroporation based DNA vaccine delivery may be well suited for promoting polyfunctional CD4+ T-cell responses In contrast to the CD4+ T-cell response, the magnitude of the antigen-specific CD8+ T-cell response depended on the plasmids delivered by electroporation. Specifically, the immune response is significantly higher in the animals, which were immunized by the codon-optimized expression plasmid.