Rescue of infectious influenza B virus from cloned cDNA for the development of novel vaccines

Influenza viruses are enveloped RNA viruses belonging to the family Orthomyxoviridae (Lamb & Krug, 1996). Influenza virions contain eight ribonucleoproteins (vRNPs), which are negative-sense viral RNA (vRNA) segments associated with nucleoproteins (NP) and complexed with polymerase proteins PB 1, PB2 and PA (Hsu et al., 1987). In this project, it is planned to establish a plasmidbased system for the rescue of influenza B viruses, which will not require helper virus infection. Thus, no selection system is needed to obtain the recombinant virus from a vast background of wild-type virus. This system has already been successfully established for influenza A virus (Neumann et al., 1999; Fodor et al., 1999). Briefly, eight negative-sense RNA transcripts are synthesized in vivo by RNA pol I. Cotransfection of eight pol I-plasmids together with plasmids encoding the viral polymerase complex genes into cells results in the production of 8 vRNPs, and initiation of a virus transcription-replication cycle results in the formation of infectious influenza virus. Construction of the polI plasmids as well as of the expression plasmids is already completed. In the future, the plasmid-based transfection system for the rescue of influenza B entirely from cloned cDNAs will be established. With the aid of this system recombinant viruses carrying the segments for the hemagglutinin (HA) and neuraminidase (NA) of the currently circulating strains can readily be generated every year. Thus, this system can be used to rapidly and safely generate influenza B virus for use in formalininactivated or live attenuated vaccine preparations.