title: The development and characterization of H5 influenza virus vaccines derived from a 2003 human isolate.
abstract: The pandemic threat posed by highly pathogenic H5N1 influenza A viruses has created an urgent need for vaccines to protect against H5 virus infection. Because pathogenic viruses grow poorly in chicken eggs and their virulence poses a biohazard to vaccine producers, avirulent viruses produced by reverse genetics have become the preferred basis for vaccine production. Here, we investigated two key characteristics of potential H5 vaccine candidates: the hemaggutinin (HA) cleavage site sequence and its modification to attenuate virulence and the choice of background virus to provide a high-growth rate. We produced recombinant (6:2 reassortant) viruses that possessed a series of modified avirulent-type HA and neuraminidase genes, both of which were derived from an H5N1 human isolate. The other genes of these recombinant viruses were derived from donor virus strains known to grow well in eggs: the human strain A/Puerto Rico/8/34 (PR8) or an avian strain. All of the recombinant viruses grew well in eggs, were avirulent in chicks, and protected animals against infection with a wild-type virus. However, one of the recombinant viruses with an avian virus background acquired a mutation in the HA cleavage site sequence that conferred virulence potential to this virus. Moreover, vaccine candidates with the avian virus background were more virulent than those with the human virus background. We conclude that 6:2 recombinant viruses with a PR8 background are more suitable than those with an avian virus background for vaccine development and that the HA cleavage site sequence must be modified to minimize the potential for a vaccine virus to convert to a virulent form.
authors.affiliation: Division of Virology, Department of Microbiology and Immunology, Institute of Medical Science, University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan. horimoto@ims.u-tokyo.ac.jp
authors.forename: Taisuke
authors.initials: T
authors.lastname: Horimoto
authors.forename: Ayato
authors.initials: A
authors.lastname: Takada
authors.forename: Ken
authors.initials: K
authors.lastname: Fujii
authors.forename: Hideo
authors.initials: H
authors.lastname: Goto
authors.forename: Masato
authors.initials: M
authors.lastname: Hatta
authors.forename: Shinji
authors.initials: S
authors.lastname: Watanabe
authors.forename: Kiyoko
authors.initials: K
authors.lastname: Iwatsuki-Horimoto
authors.forename: Mutsumi
authors.initials: M
authors.lastname: Ito
authors.forename: Yuko
authors.initials: Y
authors.lastname: Tagawa-Sakai
authors.forename: Shinya
authors.initials: S
authors.lastname: Yamada
authors.forename: Hirotoshi
authors.initials: H
authors.lastname: Ito
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Ito
authors.forename: Masaki
authors.initials: M
authors.lastname: Imai
authors.forename: Shigeyuki
authors.initials: S
authors.lastname: Itamura
authors.forename: Takato
authors.initials: T
authors.lastname: Odagiri
authors.forename: Masato
authors.initials: M
authors.lastname: Tashiro
authors.forename: Wilina
authors.initials: W
authors.lastname: Lim
authors.forename: Yi
authors.initials: Y
authors.lastname: Guan
authors.forename: Malik
authors.initials: M
authors.lastname: Peiris
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Kawaoka
mesh_terms: D000818:Animals; D002460:Cell Line; D002642:Chick Embryo; D005260:Female; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000235:genetics / Q000276:immunology*; D006801:Humans; D053124:Influenza A Virus, H5N1 Subtype / Q000254:growth & development / Q000276:immunology* / Q000472:pathogenicity; D007252:Influenza Vaccines / Q000276:immunology*; D051379:Mice; D008807:Mice, Inbred BALB C; D009439:Neuraminidase / Q000235:genetics / Q000276:immunology*; D016865:Reassortant Viruses / Q000276:immunology; D014614:Vaccines, Synthetic / Q000276:immunology*; D014774:Virulence
chemical_list: D019267:Hemagglutinin Glycoproteins, Influenza Virus; D007252:Influenza Vaccines; D014614:Vaccines, Synthetic; D009439:Neuraminidase