Comparing the ability of a series of viral protein-expressing plasmid DNAs to protect against H5N1 influenza virus

Avian influenza has been regarded as a human health threat. A major measure to prevent its outbreak is vaccination. In this study, a series of expression plasmids carrying the hemagglutinin (HA), neuraminidase (NA), nucleoprotein (NP), matrix protein 1 (M1), and matrix protein 2 (M2) genes, respectively, of the avian influenza virus (AIV) A/Chicken/Henan/12/2004(H5N1) strain were constructed. These plasmids were administered to mice by electroporation (50 mu g for each per administration, 1-5 times, at an interval of 2 weeks), and the mice were challenged with the homologous virus later. The mice immunized with HA plasmid once and the NA plasmid twice survived 100%, and those with NP plasmid showed 60-80% survival rate with at least three immunizations. The mice immunized with M1 plasmid survived 25% with five immunizations, while M2 plasmid had no protection even with five immunizations. The mixture of M1 and NP plasmids protected 95% of the mice against the homologous virus, and 80% of the mice against a challenge with heterologous H1N1 (PR8) virus. Moreover, the homologous protection lasted at least 6 months. Our data provided a basis for selecting multiple-component AIV vaccines.