Particle-mediated DNA vaccines against seasonal and pandemic influenza viruses elicit strong mucosal antibody and T cell responses in the lung

The recent outbreaks of H5N1 avian and H1N1 swine-origin influenza viruses highlight the urgent need for vaccine strategies able to confer broad host immunity against both seasonal and pandemic strains of influenza. As the lung mucosa is the first barrier against pulmonary influenza infection, an effective influenza vaccine strategy should elicit anti-viral immune responses in the respiratory tract where they may afford better protection. As a safe alternative to live attenuated vaccines, we evaluated the immunogenicity of gene gun-based immunization using a tetravalent DNA vaccine encoding the HA genes from three seasonal flu strains (H1, H3, and B) and a H5N1 pandemic strain. Vaccinated mice were found to exhibit high titers of serum antibodies specific for each of the encoded HA antigens, as well as cross-reactivity to drifted strains of virus. Importantly, significant levels of HA-specific mucosal antibodies were also detected in the lung airways of vaccinated mice. Consistent with the belief that immune responses against conserved regions of the virus may provide cross-protection against divergent strains of influenza, we also evaluated the immunogenicity of particle-mediated DNA vaccines encoding the highly conserved viral nucleoprotein (NP). Mice immunized with a DNA vaccine encoding a consensus NP sequence derived from circulating strains of virus exhibited robust NP-specific CD8 T cell responses in both spleen and lung tissue. Together, these results demonstrate the ability of skindelivered particle-mediated DNA vaccines to elicit strong systemic and mucosal immune responses against both variable and conserved influenza antigens and support the concept that particle-mediated DNA vaccines may offer an effective strategy to improve protection against seasonal and pandemic influenza.