Plasmid Encoding CD40 Ligand Enhances Immune Response to Influenza DNA Vaccine*

CD40L gene can act as a genetic adjuvant. The objective of this study was to test the effectiveness of CD40L-expressing plasmid on the immune response to influenza A/PR/8 virus hemagglutinin (HA) DNA vaccine. To achieve this, we constructed plasmid DNA encoding murine CD40L and coimmunnized the plasmid with HA DNA to the BALB/c mice muscle by electroporation. Each DNA at a dose of 30 μg was administered twice at a 3-week interval. One week after the second vaccination, the mice were challenged with a lethal dose of influenza A/PR/8 virus. We found that, after lethal influenza virus challenge, CD40L and HA DNA-coimmunized mice exhibited higher induction of specific IgG (in particular IgG2a) against HA as well as lower body weight loss than those of HA DNA immunized alone. We concluded that CD40L gene had adjuvant effects on influenza DNA vaccine.