Production of genetically modified chickens resistant to important avian respiratory diseases.

Our ultimate objective is to improve the resistance of livestock species to viral diseases. . This has important implications for animal health and welfare but avian species and pigs can also act as bridging hosts that enable novel strains of influenza virus to cause infection in humans. Currently we are focusing on chickens as a test-bed for identifying the most effective ways to achieve this objective. Producing AI resistant chickens would reduce the threat of a new pandemic influenza virus emerging in humans, contribute to global food security and decrease the economic consequences of controlling the infection in poultry. Our approach is to introduce novel genes into the chicken genome that become activated by influenza infection and produce molecules that specifically and potently suppress virus replication. These molecules are intrinsically harmless to the chicken, safe for consumption and in the absence of virus infection are produced at very low levels. Influenza virus infection results in the increased production of these inhibitory molecules which then either interfere directly with the virus replication machinery or trigger the production of normal cellular proteins with antiviral properties.

The project involves the construction and testing of a series of different inhibitory genes firstly in cell culture and then introducing the most effective ones into chickens using genetic modification techniques. These transgenic birds are then tested to determine whether they are resistant to AI infection. The project is described as a pipeline because the various inhibitory transgenes have reached different stages of development. Some have already been shown to be effective in GM chickens, some in cell culture and others are still at the conceptual phase. Most of the work is aimed at influenza virus. However, some preliminary work is proposed to determine whether similar approaches can be developed against other important avian virus infections.

Our objective is to use genetically modified chickens to improve our understanding of resistance to infection by avian influenza (AI) virus and other livestock viral diseases. We have previously generated transgenic chickens that express a small RNA decoy molecule (Decoy 5) that inhibited transmission of AIV from infected transgenic birds to other birds cohoused with them. We will extend this study by analysing the AIV shed by these birds to determine the basis of the block to transmission. We will generate homozygous Decoy 5 birds to test if a doubling of the transgene expression enhances protection. We have produced a new version of the decoy molecule that is more effective in in vitro assays. This will be used to generate transgenic chickens by lentivector injection into chick embryos that will be hatched and screened to identify germline transgenic birds. Transgenic offspring will be challenged with H5N1 virus to determine the effectiveness of the transgene in vivo.
Previous BBSRC funding enabled the development of an RNA replicon-based influenza-contingent gene expression system that can be used transgenically to produce inhibitory effector proteins in response to influenza virus infection. Flu-contingent expression of chicken tBID and interferon alpha caused potent inhibition of gene expression in cell culture. They await introduction into chickens and testing by in vivo challenge studies. We shall extend this strategy to induce expression of a strong CTL target protein from another avian virus routinely controlled by vaccination. Induction of this target protein by AI infection should result in cell lysis by CTLs generated by the normal vaccination schedule of chickens. We also intend to introduce a functional Mx gene under the control of the chMx promoter that might combine synergistically with the chIFN replicon described above.

We will also explore the potential of developing decoy and RNA replicon based strategies for Infectious bronchitis, Infectious bursal disease and Newcastle disease virus

The work described in this programme has the potential to have a very wide impact. It may benefit the industrial partner directly but also the vaccine, poultry breeding and production industries. The prior research has already been noted by policy makers e.g. the applicants have been asked to POST notes by the Parliamentary office of science and technology, and this programme is likely to increase the interest of policy makers internationally. The wider public are interested in the programme and could be beneficiaries as consumers.
How will they benefit:
Industrial partner: the industrial partner will be in a position to evaluate the potential for improving disease resistance by alternative vaccination technologies, conventional genetic methods or GM technologies.
Producers: the elimination of avian influenza from the commercial poultry sector would have a major impact on the economic, food security, public health and animal welfare consequences of this disease. Currently in the UK AI is controlled by biosecurity measures. It is unlikely that this development would significantly reduce these costs because the measures are necessary to control other pathogens. However, stringent biosecurity measures are largely incompatible with free-range production, which is an expanding sector of the industry. Resistant chickens would reduce the vulnerability of this sector to production losses due to influenza infection.
In other parts of the world, vaccination is used as an adjunct or even as an alternative to biosecurity. This is also costly and unless rigorously maintained may become ineffective. The potential for production losses has been amply demonstrated by the consequences of the H5N1 epizootic in SE Asia and in parts of Africa. Influenza resistant chickens would eliminate the requirement for vaccination and the associated costs of updating vaccines against avian influenza virus.
Consumers: resistant chickens would reduce the threat of a severe epidemic causing shortages of this increasingly important source of the world's universally acceptable source of protein.
Scientists: The research will help evaluate alternative approaches to improving disease resistance of domestic livestock. The development of influenza virus resistant chickens would provide a highly persuasive example of the potential benefits of GM technologies for reducing the zoonotic threat posed by avian influenza virus and improving animal health, productivity and welfare. This could help to change public attitude to genetic modification to a more favourable view. Such a development would encourage other scientists in the UK and elsewhere to re-engage with GM research, particularly where it relates to zoonotic threats and food security.
The public at large: the public health threat of avian influenza is ever present and unlikely to be managed by vaccination against avian influenza.