Development of novel multivalent vaccines

The objective of this project is to use reverse genetics to develop better ways of making vaccines that protect against more than one disease (multivalent vaccines). This technology allows us to mutate RNA virus genomes through DNA copies (cDNA) of the RNA genome. The new genome cDNA can then be used to obtain the mutated form of the virus. In these studies we will use an existing vaccine for peste des petits ruminants virus (PPRV), as a vector to deliver antigens from other economically important viruses. PPRV causes a devastating plague in small ruminants and has a severe impact on animal welfare and the economies of many countries in Africa and Asia. In previous studies using this technology with a related virus, rinderpest virus (RPV), we were able to express foreign proteins efficiently in infected cells and to produce effective marker vaccines for RPV as well as identify some of the molecular factors which determine differences in virulence between virus strains. Recently it has been shown that the genome of measles virus (MV), a closely related virus, can be artificially segmented and that cDNAs of these segments can be used in a similar way to the full-length nonsegmented cDNA to rescue viable virus. The segmentation and rescue of PPRV will provide a new way to deliver immunogens from other small ruminant viral pathogens. Work with other nonsegmented negative strand (NNS) viruses has shown that there is a limit to the amount of extra genetic material that can be added to NNS virus genomes before a reduction in virus viability is seen. Segmentation of NNS genome can effectively overcome this limit, as evidenced by the ability of the segmented MV to encode at up to six foreign proteins efficiently. If this is applicable to related viruses then it would increase their coding capacity and enable us to produce multivalent vaccines to simultaneously protect against several economically important diseases of ruminants and increase their cost-effectiveness. Whilst RPV has been virtually eliminated from the globe as a result of a concerted vaccination campaign over the past 20 years, PPRV is a disease emerging in new regions of the world and is now causing great economic losses across much of the developing world as well as on the borders of the European Union. The current live-attenuated vaccines developed for PPRV are safe and highly effective and are, therefore, ideal candidates for use as vaccine vectors that can be tagged to allow differentiation between infected and vaccinated animals. We wish to explore the segmented approach using PPRV as a vector delivery system for multiple antigens from other economically significant viruses such as bluetongue virus (BTV) and Rift Valley Fever virus (RVFV), insect borne pathogens which can infect cattle and sheep, the latter also being able to infect humans. BTV and RVFV were once considered exotic diseases although recently BTV has entered the European Union, having a devastating effect on agriculture. RVFV has the potential to also enter Europe as insect vectors that carry BTV may also competent for RVFV infection. Current use of the PPRV vaccine generates a sterilising immunity that gives lifelong protection against the virus and, for RVFV, a similar response is thought to be generated post vaccination. However, for BTV a number of distinct genetic variants exist which, although diverse, cluster across distinct geographical regions. We wish to develop vaccines that target viruses circulating within a specific areas. Both RVFV and BTV are endemic across much of Asia and Africa and effective vaccination strategies are integral to their control. The three viral diseases targeted in this proposal are in line with the BBSRC's combating diseases of the developing world strategy as well as DFID's long term commitment to improving the sustainability of agriculture in developing countries.

The objective of the proposed work is to explore ways of producing novel multivalent vaccine delivery systems using reverse genetics technology. Reverse genetics provides a means to manipulate the genomes of non-segmented, negative strand RNA (NNS) viruses through DNA copies of their genomes. Virus can be 'rescued' from the cDNAs and the effects of any changes introduced into the viral sequence can be studied both in vitro and in vivo. For this work we will use peste des petits ruminants virus (PPRV), a morbillivirus which is closely related to human measles virus (MV) that causes a devastating plagues in sheep and goats and in some wild ruminants. Recently it has been shown that the MV genome can be artificially segmented and that these segments can also be used to rescue viable virus. This is a very promising avenue to explore for the production of multivalent vaccines that also enable serological differentiation between infected and vaccinated animals within the herd post vaccination, so called DIVA vaccines. We wish to use segmented versions of PPRV as a vaccine vector to express immunogens from other viral disease of small ruminants such as Rift Valley Fever virus (RVFV) and Bluetongue virus (BTV). This approach would be highly cost-effective as available vaccination strategies for these viruses are problematic. Current use of the PPRV vaccine generates a sterilising immunity that gives lifelong protection against the virus and, for RVFV, a similar response is thought to be generated post vaccination. However, for BTV a number of different serotypes exist which, although diverse, cluster phylogenetically allowing the possibility of neutralisation both within and between different serotypes. This approach will allow the rapid development of effective vaccines to protect against all BTV serotypes circulating within distinct locations by creating a bank of recombinants representing each serotype.

Should the aim of this project be realised the impact on agricultural practises within the developing world will be profound. All three of these viruses targeted in this proposal affect farm animals, especially small ruminants that are the mainstay of rural economies in the developing world. The application of PPRV as a live attenuated vaccine vector expressing immunogens from BTV and RVFV will potentially reduced the administration of vaccine to a one dose schedule to cover all three viruses, greatly aiding the current situation for protecting small ruminants against these diseases. This factor is of great importance across the developing world where the economic infrastructure is often unable to support mass vaccination campaigns, especially where multiple dose schedules are required. The development of such multivalent vaccines against these agents will reduce the burden of disease and in turn through improving the sustainability of agricultural practises, help alleviate poverty. These areas will benefit from enhanced animal health and animal production resulting from the availability of safe multivalent vaccines for disease control and eradication programmes. The impact of PPRV, RVFV and BTV across the developing world is of great importance to sustainable agriculture in these areas. These diseases are of particular concern to subsistence farmers in remote areas where vaccination of domestic animals is difficult to achieve. The development of multivalent vaccines, which protect against several pathogens of sheep and goats with one vaccination, increases the financial viability of vaccination programmes through their cost-effectiveness. Furthermore, developing vaccines and novel diagnostic assays that allow differentiation between naturally infected and vaccinated animals is of paramount importance in combating these infectious agents. The technology detailed in this proposal will be used to add both positive and negative serologically detectable genetic markers that will allow serological differentiation of vaccinated animals from those naturally infected. This factor, using both current and novel serological assays, will enhance serosurveillance of vaccinated animals and identify pockets of animals that have come into contact with circulating virus strains. In developing research that aims to generate vaccines to combat such diseases this proposal strongly supports the BBSRCs Animal Science strategy and highlights the research council's dedication to fighting disease on a global scale. In addition a report sponsored by DFID highlighted PPR as a transboundary disease which threatens the economic health of many developing countries. Within the scientific community the potential impacts of this research will be realised through several pathways: through presentations of the results of this research at national and international scientific conferences; through contacts with international bodies (FAO / OIE) dealing with transboundary diseases; through public presentation of the data through media contacts and by direct contact with the commercial sector since the project involves a vaccine manufacturer, Indian Immunologicals Limited (IIL). IIL is a subsidiary of the Indian National Dairy Development Board. As a non-profit making organisation they have a mandate to provide cheap and effective vaccines and other health products for farm animals in India. In Africa this contact will be made through the National Institute for Communicable Diseases (NICD) in Johannesburg which deals with relevant transboundary diseases for Southern Africa. The resources for these impact activities will firstly be through the established contacts of the participating laboratories with regional and national laboratories in developing countries which are ongoing and the funding which will be provided by the project for research, training and travel to international conferences where further networking opportunities will arise.