Mucosal co-administration of cholera toxin and influenza virus hemagglutinin-DNA in ponies generates a local IgA response.

We have previously demonstrated that equine influenza virus hemagglutinin (HA) DNA vaccination protects ponies from challenge infection, and induces protective IgGa and IgGb responses. However, this approach does not induce a nasal IgA response. The objective of this study was to examine the value of cholera toxin (CT) administration as an adjuvant for intranasal HA DNA vaccination, and to measure protection 3 months after DNA vaccination. After an immunogenic dose of CT was determined, ponies were immunized on two occasions by intranasal administration of HA DNA and cholera toxin, or HA DNA alone. Ponies in both groups received two additional HA DNA particle mediated vaccinations at skin and mucosal sites. Antibody responses, and protection from challenge infection 3 months after the last vaccination were studied and compared to an influenza virus naive control group. Ponies in both vaccination groups produced virus-specific IgG antibodies in serum following vaccination and showed clinical protection from challenge infection 3 months after the last vaccination. Co-administration of CT plus HA DNA vaccination induced a nasal IgA response. In addition, analysis of antibody titers in nasal secretions indicated local production of nasal IgGb, which was amplified by CT administration.