Protection Against Influenza Virus Infection In Mice Immunized With DNA Vaccine By Intramuscular Electrical Transfer

This article consists of two parts .I. Influenza A (H5N1) viruses could cause a severe worldwide epidemic, with high attack rates, large number of deaths and wide distr-uption. Effective vaccines against these viruses in human are urgently needed. The use of DNA vaccine seems to be a promising approach to the development of effective vaccines against influenza. In this study, an avian influenza H5N1 virus strain (A/Chicken/Henan/12/2004), isolated in Henan Province, China, was used to infect BALB/c mice for adaptation. After seven lung-to-lung passages, the virus was stably proliferated in a large quantity in the murine lung and caused the deaths of mice. In addition, we explored the ability of plasmid DNA encoding hemagglutini-n (HA) or neuraminidase (NA) from avian influenza virus A/Chicken/ Henan/12/2004 (H5N1) for protecting BALB/c mice against viral infection. Female BALB/c mice aged 6-8 weeks were immunized twice at a 3-week interval with HA-DNA and NA-DNA by electro- poration at a dose of 30 microgramme. The mice were challenged with a lethal dose (5 or 40×LD₅₀) of influenza H5N1 virus one week after the second immunization. The protections of DNA vaccines were evaluated by the serum antibody titers, residual lung virus titers, and survival rates of the mice. The result showed that immunization with 30μg HA-DNA orNA-DNA provided effective protection against a lethal dose of influenza H5N1 virus infection.II. In order to efficiently deliver multiple antigens with use of DNA vaccine technology, new antigen delivery systems must be assessed. This study utilized a bicistronic vector construct, containing an internal ribosome entry site (IRES), expressing a combination of neuraminidase (NA) from influenza virus A/PR/8/34 (H1N1) and A/Guizhou-X (H3N2). Female BALB/c mice aged 6-8 weeks were immunized twice with 60ug pNl-IRES-N2 or pN2-IRES-Nl at a 3-week interval by electroporation. The mice were challenged with a lethal dose of influenza H1N1 or H3N2 virus one week after the second immunization. The protections of DNA vaccines were evaluated by the serum antibody titers, residual lung virus titers, and survival rates of the mice. The result shows that pNl-IRES-N2 provided complete protection against H1N1 influenza virus challenge, but only provided partial protecion against H3N2 influenza virus infectio-n. Mice immunized with pN2-IRES-Nl survived 100% after H3N2 influenza virus challenge, but only 60% after H1N1 influenza virus infection. These results suggested that IRES vectors can produce polycistronic mRNAs to produce two foreign proteins.