Biological and immunological characterization of influenza virus haemagglutinin expressed from the haemagglutinin locus of vaccinia virus

Plasmid vectors were constructed to facilitate the insertion and expression of a foreign gene in the haemagglutinin (HA) gene locus of vaccinia virus. Five unique cloning sites adjacent to the P7.5 promoter of vaccinia virus permit the rapid insertion of a foreign sequence coding for a protein into these plasmids. This vector system provides a simple procedure to select recombinant viruses because they can be readily identified on the basis of their HA-defective phenotype. Recombinant vaccinia viruses expressing influenza virus HA were constructed to characterize the possible use of this system. The recombinant viruses did express the influenza HA through the authentic pathway of biosynthesis. In addition to having immunological characteristics similar to the authentic influenza HA, the expressed HA was found to possess haemagglutinating, haemadsorption and acid-inducible fusion activities. These findings demonstrate the usefulness of this eukaryotic vector system.