Submitted to: Virology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/19/2002
Publication Date: 1/1/2003
Citation: Subbarao, K., Chen, H., Swayne, D.E., Mingay, L., Fodor, E., Brownlee, G., Xu, X., Lu, X., Katz, J., Cox, N. 2003. Evaluation Of A Genetically Modified Reassortant H5N1 Influenza A Virus Vaccine Candidate Generated By Plasmid-Based Reverse Genetics. Virology 305:192-200. Interpretive Summary: Avian influenza viruses of the H5N1 subtype caused human infections in Hong Kong during 1997. The current inactivated human influenza vaccine does not contain an H5 vaccine virus and thus the human population does not have any protection from the H5N1 influenza. This study developed a new H5 vaccine virus strain through molecular biotechnology that can potentially be used as an inactivated human vaccine virus should the H5 influenza subtype emerge in the human population.
Technical Abstract: Reports that avian influenza A H5N1 viruses that are similar to those that infected humans in HK in 1997 continue to circulate in waterfowl and have reemerged in poultry in the region raise concerns that these viruses could reappear in humans. The currently licensed trivalent inactivated influenza vaccines contain influenza A antigens prepared from seed viruses containing hemagglutinin (HA) and neuraminidase genes from epidemic strains in a background of internal genes derived from the vaccine donor strain, A/Puerto Rico/8/34 (PR8). Such reassortant candidate vaccine viruses are currently not available for the prevention of human infections by H5N1 influenza viruses. A transfectant H5N1/PR8 virus was generated by co-transfecting 293-T cells with 8 plasmids encoding the virion RNA segments and 4 plasmids expressing the ribonucleoproteins. The H5 HA gene was modified by replacement of the multibasic cleavage site associated with high pathogenicity in chickens with the sequence seen in nonpathogenic avian viruses. The antigenicity of the H5 HA was preserved in the H5N1/PR8 transfectant virus. Unlike the H5N1 parent virus, the H5N1/PR8 transfectant virus replicated poorly in chickens following intravenous inoculation and was not highly pathogenic for chickens. In mice, this virus replicated in the lungs but, unlike the H5N1 parent virus, failed to replicate in extrapulmonary tissues following intranasal inoculation and was not lethal for BALB/c mice. Thus, the removal of the multibasic amino acid motif in the HA gene and the new genotype of the H5N1/PR8 transfectant virus attenuated the virus for chickens and mice without altering the antigenicity of the HA. A formalin-inactivated vaccine prepared from this virus was immunogenic and protected mice from subsequent wild-type H5N1 virus challenge. The H5N1/PR8 transfectant virus demonstrates properties that are desirable in a vaccine and make it a promising candidate for further evaluation in humans.