[Show abstract][Hide abstract] ABSTRACT: Influenza A viruses are a major cause of morbidity and mortality in the human population, causing epidemics in the winter, and occasional worldwide pandemics. In addition there are periodic outbreaks in domestic poultry, horses, pigs, dogs, and cats. Infections of domestic birds can be fatal for the birds and their human contacts. Control in man operates through vaccines and antivirals, but both have their limitations. In the search for an alternative treatment we have focussed on defective interfering (DI) influenza A virus. Such a DI virus is superficially indistinguishable from a normal virus but has a large deletion in one of the eight RNAs that make up the viral genome. Antiviral activity resides in the deleted RNA. We have cloned one such highly active DI RNA derived from segment 1 (244 DI virus) and shown earlier that intranasal administration protects mice from lethal disease caused by a number of different influenza A viruses. A more cogent model of human influenza is the ferret. Here we found that intranasal treatment with a single dose of 2 or 0.2 µg 244 RNA delivered as A/PR/8/34 virus particles protected ferrets from disease caused by pandemic virus A/California/04/09 (A/Cal; H1N1). Specifically, 244 DI virus significantly reduced fever, weight loss, respiratory symptoms, and infectious load. 244 DI RNA, the active principle, was amplified in nasal washes following infection with A/Cal, consistent with its amelioration of clinical disease. Animals that were treated with 244 DI RNA cleared infectious and DI viruses without delay. Despite the attenuation of infection and disease by DI virus, ferrets formed high levels of A/Cal-specific serum haemagglutination-inhibiting antibodies and were solidly immune to rechallenge with A/Cal. Together with earlier data from mouse studies, we conclude that 244 DI virus is a highly effective antiviral with activity potentially against all influenza A subtypes.
[Show abstract][Hide abstract] ABSTRACT: The main antivirals employed to combat seasonal and pandemic influenza are oseltamivir and zanamivir which act by inhibiting the virus-encoded neuraminidase. These have to be deployed close to the time of infection and antiviral resistance to the more widely used oseltamivir has arisen relatively rapidly. Defective interfering (DI) influenza virus is a natural antiviral that works in a different way to oseltamivir and zanamivir, and a cloned version (segment 1 244 DI RNA in a cloned A/PR/8/34 virus; 244/PR8) has proved effective in preclinical studies in mice. The active principle is the DI RNA, and this is thought to interact with all influenza A viruses by inhibiting RNA virus synthesis and packaging of the cognate virion RNA into nascent DI virus particles. We have compared the ability of DI virus and oseltamivir to protect ferrets from intranasal 2009 pandemic influenza virus A/California/04/09 (A/Cal, H1N1). Ferrets were treated with a single 2μg intranasal dose of 244 DI RNA delivered as 244/PR8 virus, or a total of 25mg/kg body weight of oseltamivir given as 10 oral doses over 5days. Both DI virus and oseltamivir reduced day 2 infectivity and the influx of cells into nasal fluids, and permitted the development of adaptive immunity. However DI virus, but not oseltamivir, significantly reduced weight loss, facilitated better weight gain, reduced respiratory disease, and reduced infectivity on days 4 and 6. 244 DI RNA was amplified by A/Cal by >25,000-fold, consistent with the amelioration of clinical disease. Treatment with DI virus did not delay clearance or cause persistence of infectious virus or DI RNA. Thus in this system DI virus was overall more effective than oseltamivir in combatting pandemic A/California/04/09.
Full-text · Article · Oct 2012 · Antiviral research
[Show abstract][Hide abstract] ABSTRACT: We have shown earlier that a single dose of cloned defective interfering (DI) influenza A virus strongly protects mice from disease following a lethal challenge with different subtypes of influenza A virus. These animals suffered no clinical disease but experienced a subclinical infection which rendered them immune to reinfection with the same challenge virus. However, little is known about how DI virus achieves such protection. Here we investigated the role of adaptive immunity in DI virus-mediated protection using severe-combined immunodeficient (SCID) mice, which lack competence in both B- and T-cell compartments but retain NK cell activity. SCID mice which were treated with DI virus and infected with influenza virus initially remained completely well, while infected litter mates that received UV-inactivated DI virus became seriously ill and died. However, after 10 days of good health, the DI virus-protected SCID mice developed a clinical disease that was similar, but not completely identical, to the acute influenza disease. Disease was delayed longer by a higher dose of DI virus. We excluded the possibilities that the DI virus load in the lungs had declined, that the DI RNA sequence had changed so that it no longer interfered with the infectious genome, or that infectious virus had become resistant to the DI virus. These data show that while DI virus provides full protection from the acute disease in the absence of adaptive immunity, that same immunity is essential for clearing the infection. This indicates that the conventional view that DI virus-induced protection is mediated solely by competition for replication with the challenge virus is incorrect for influenza virus.
[Show abstract][Hide abstract] ABSTRACT: Influenza A and B viruses are major human respiratory pathogens that contribute to the burden of seasonal influenza. They are both members of the family Orthomyxoviridae but do not interact genetically and are classified in different genera. Defective interfering (DI) influenza viruses have a major deletion of one or more of their eight genome segments, which renders them both non-infectious and able to interfere in cell culture with the production of infectious progeny by a genetically compatible, homologous virus. It has been shown previously that intranasal administration of a cloned DI influenza A virus, 244/PR8, protects mice from various homologous influenza A virus subtypes and that it also protects mice from respiratory disease caused by a heterologous virus belonging to the family Paramyxoviridae. The mechanisms of action in vivo differ, with homologous and heterologous protection being mediated by probable genome competition and type I interferon (IFN), respectively. In the current study, it was shown that 244/PR8 also protects against disease caused by a heterologous influenza B virus (B/Lee/40). Protection from B/Lee/40 challenge was partially eliminated in mice that did not express a functional type I IFN receptor, suggesting that innate immunity, and type I IFN in particular, are important in mediating protection against this virus. It was concluded that 244/PR8 has the ability to protect in vivo against heterologous IFN-sensitive respiratory viruses, in addition to homologous influenza A viruses, and that it acts by fundamentally different mechanisms.
Full-text · Article · Jun 2011 · Journal of General Virology
[Show abstract][Hide abstract] ABSTRACT: We have identified and characterised a defective-interfering (DI) influenza A virus particles containing a highly deleted segment 1 RNA that has broad-spectrum antiviral activity. In young adult mice it exerts protection against several different subtypes of influenza A virus (defined here as homologous or genetically compatible protection) and against a paramyxovirus and an influenza B virus (heterologous or genetically unrelated protection). Homologous protection is mediated by replication competition between the deleted and full-length genomes, and heterologous protection occurs through stimulation of innate immunity, especially interferon type I.
A single dose of the protective DI virus was administered intranasally to elderly mice at -7, -1 and +1 days relative to intranasal challenge with influenza A virus.
A single dose of the DI virus given 1 or 7 days protected elderly mice, reducing a severe, sometimes fatal disease to a subclinical or mild infection. In contrast, all members of control groups treated with inactivated DI virus before challenge became extremely ill and most died. Despite the subclinical/mild nature of their infection, protected mice developed solid immunity to a second infectious challenge.
The defective interfering virus is effective in preventing severe influenza A in elderly mice and may offer a new approach to protection of the human population.
[Show abstract][Hide abstract] ABSTRACT: Respiratory viruses represent a major clinical burden. Few vaccines and antivirals are available, and the rapid appearance of resistant viruses is a cause for concern. We have developed a novel approach which exploits defective viruses (defective interfering (DI) or protecting viruses). These are naturally occurring deletion mutants which are replication-deficient and multiply only when coinfection with a genetically compatible infectious virus provides missing function(s) in trans. Interference/protection is believed to result primarily from genome competition and is therefore usually confined to the virus from which the DI genome originated. Using intranasally administered protecting influenza A virus we have successfully protected mice from lethal in vivo infection with influenza A viruses from several different subtypes . Here we report, contrary to expectation, that protecting influenza A virus also protects in vivo against a genetically unrelated respiratory virus, pneumonia virus of mice, a pneumovirus from the family Paramyxoviridae. A single dose that contains 1μg of protecting virus protected against lethal infection. This protection is achieved by stimulating type I interferon and possibly other elements of innate immunity. Protecting virus thus has the potential to protect against all interferon-sensitive respiratory viruses and all influenza A viruses.
[Show abstract][Hide abstract] ABSTRACT: The cell surface receptor used by an influenza virus to infect that cell is an N-acetyl neuraminic acid (NANA) residue terminally linked by an alpha2,3 or alpha2,6 bond to a carbohydrate moiety of a glycoprotein or glycolipid. Our aim was to determine a quick and technically simple method to determine cell receptor usage by whole influenza A virus particles.
We employed surface plasmon resonance to detect the binding of viruses to fetuin, a naturally occurring glycoprotein that has both alpha2,3- and alpha2,6-linked NANA, and free 3'-sialyllactose or 6'-sialyllactose to compete virus binding. All virus stocks were produced in embryonated chicken's eggs.
The influenza viruses tested bound preferentially to NANAalpha2,3Gal or to NANAalpha2,6Gal, or showed no preference. Two PR8 viruses had different binding preferences. Binding preferences of viruses correlated well with their known biological properties.
Our data suggest that it is not easy to predict receptor usage by influenza viruses. However, direct experimental determination as described here can inform experiments concerned with viral pathogenesis, biology and structure. In principle, the methodology can be used for any virus that binds to a terminal NANA residue.
Full-text · Article · May 2010 · Influenza and Other Respiratory Viruses