Properties and in vivo mechanism(s) of action of cloned influenza virus interfering RNA - a new type of antiviral agent

Influenza represents a continuing threat to human health. It has long been known that viruses containing genomes which have been significantly deleted can interfere with the replication of fully infectious virus. We have generated a specific interfering virus using molecular cloning techniques. Studies in mice have shown that exposure to this interfering virus does not generate disease but confers protection against a range of different influenza viruses. We intend to characterise the nature of the interfering virus genome and investigate the mechanism by which the interfering virus works. We will also study some fundamental characteristics of the interfering virus to determine the optimal method of production and stability. The interfering virus is a new approach to generating antiinfluenza drugs and, if successful, this would offer protection against a wide range of different strains, potentially including avian influenza virus.

Deleted forms of influenza A virus genome RNA segments which retain replication and packaging signals are packaged into virions when present in cells together with fully infectious virus. The deleted RNA interferes with the production of fully infectious virus in vitro and in vivo by an unknown mechanism and is termed interfering RNA (iRNA), and the particles which contain it are called interfering virus. In vivo, iRNA prophylactically protects mice and ferrets from clinical influenza. This protection is active against several different influenza subtypes, and is thus independent of the antigenicity of their surface proteins. We have cloned three iRNAs derived from influenza virus genome segment 1 and can make large amounts of cloned interfering virus in embryonated hen?s eggs. The different cloned interfering viruses protect mice from a lethal influenza challenge to different degrees. Using the cloned iRNA we intend to determine how influenza iRNAs effect protection. Possible mechanisms include iRNA-vRNA competition for a limiting essential replication factor; induction of alpha/beta interferon by iRNA; and, least likely, the creation of siRNAs from iRNA. None of these mechanisms is exclusive, and it may be that different iRNAs differ quantitatively or even qualitatively in their action. Data gained in this study will inform the potential of iRNAs for combating influenza in humans, birds and other animals, and open the way to human clinical trials.