Protection against influenza virus infection in mice immunized by administration of hemagglutinin-expressing DNAs with electroporation.

Electroporation for the transfer of plasmid DNA encoding influenza virus hemagglutinin (HA) into muscle or nasal mucosa was tried in BALB/c mice to examine the efficacy of this method for inducing anti-HA immune responses and providing protection against homologous A/PR/8/34 (PR8) virus infection. Mice were immunized by two injections, 3 weeks apart, of HA-DNA with electroporation into the muscle wherein a pair of electrode needles was inserted to deliver the electric pulses. One or 3 weeks after the immunization, the mice were infected with a lethal dose of the PR8 virus. Ten micrograms or more of HA-DNA/dose induced strong serum anti-HA IgG antibody (Ab) responses, in which both IgG1 and IgG2a were predominant, and weak cytotoxic T lymphocyte responses. These immune responses were sufficient to provide efficient protection against the lethal infection. In addition, mice were immunized by dropping HA-DNA (12 microg) three times, 2 weeks between each dose into nostrils where each of two electrode needles was placed on the right nostril or the palate. One week after the immunization, the mice were infected with a sublethal dose of the PR8 virus. The DNA immunization by electroporation provided reduced nasal virus titers, in parallel with a relatively high levels of serum anti-HA IgG Ab and a slight nasal anti-HA IgA Ab production. The intranasal administration of cholera toxin before HA-DNA immunization by electroporation enhanced the nasal IgA Ab production together with enhancement of the efficiency of protection. These results suggest that electroporation can be used as one of the efficient gene delivery systems for the transfer of influenza DNA-vaccine into muscle or nasal mucosa to provide protection against influenza virus infection.