[Research and development of reverse genetics for influenza viruses]

Influenza viruses have long been refractory to reconstitution from cloned cDNAs, likely because of the properties of their genome : segmented and negative-stranded RNA, infectious only if in association with the nucleoprotein and polymerase complex. In the late 90s, by relying on an RNA polymerase I dependent transcription system and by cotransfecting 12 or 8 plasmids, reconstitution of the eight ribonucleoproteins of an influenza A virus in a cell was achieved, and production of recombinant viruses was finally obtained. Plasmidbased reverse genetics systems are now widely used to study the molecular mechanisms of virus replication and pathogenicity. They are also proving very useful in the field of vaccinology, as they allow the conception of pandemic vaccines as well as new types of attenuated live vaccines. They could also lead to the use of recombinant influenza viruses as gene delivery vehicles, for prophylactic or therapeutic purposes.