Protective effect of a polyvalent influenza DNA vaccine in pigs.

Background: Influenza A virus in swine herds represents a major problem for the swine industry and poses a constant threat for the emergence of novel pandemic viruses and the development of more effective influenza vaccines for pigs is desired. By optimizing the vector backbone and using a needle-free delivery method, we have recently demonstrated a polyvalent influenza DNA vaccine that induces a broad immune response, including both humoral and cellular immunity. Objectives: To investigate the protection of our polyvalent influenza DNA vaccine approach in a pig challenge study. Methods: By intradermal needle-free delivery to the skin, we immunized pigs with two different doses (500 mu g and 800 mu g) of an influenza DNA vaccine based on six genes of pandemic origin, including internally expressed matrix and nucleoprotein and externally expressed hemagglutinin and neuraminidase as previously demonstrated. Two weeks following immunization, the pigs were challenged with the 2009 pandemic H1N1 virus. Results: When challenged with 2009 pandemic H1N1, 0/5 vaccinated pigs (800 mu g DNA) became infected whereas 5/5 unvaccinated control pigs were infected. The pigs vaccinated with the low dose (500 mu g DNA) were only partially protected. The DNA vaccine elicited binding-, hemagglutination inhibitory (HI) - as well as cross reactive neutralizing antibody activity and neuraminidase inhibiting antibodies in the immunized pigs, in a dose dependent manner. Conclusion: The present data, together with the previously demonstrated immunogenicity of our influenza DNA vaccine, indicate that naked DNA vaccine technology provides a strong approach for the development of improved pig vaccines, applying realistic low doses of DNA and a convenient delivery method for mass vaccination.