Protection against influenza virus challenge by topical application of influenza DNA vaccine

We studied the use of a DNA vaccine expressing the matrix (M) gene of the influenza virus A/PR/8/34. Mice were immunized by painting the DNA vaccine three times on the skin after removal of its keratinocytic layers. Immunization by this method produced M-specific antibodies and cytotoxic T lymphocyte (CTL) response, and acquired resistance against influenza virus challenge. This protection was abrogated by the in vivo injection of anti-CD8 or anti-CD4 monoclonal antibody. We further found that simultaneous topical application (t.a.) of GM-CSF expression plasmid (pGM-CSF) or liposomes plus mannan produced stronger immune response competence and enhanced the protective effect against influenza virus challenge. The present study revealed that administering DNA vaccine by topical application can elicit both humoral and cell-mediated immunity (CMI).