Antigen specificity of T cells mediating suppression of immunity to porcine reproductive and respiratory syndrome virus infection and vaccination.

Vaccines are the most cost effective method for controlling many infectious diseases. Using vaccines also reduces the use of antibiotics and that results in less antimicrobial resistance to drugs used to treat infection.

Many pathogens affect livestock species and, in the pork industry, porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most economically important infections today. This viral disease has spread world-wide and pig farmers struggle to control the disease. There are vaccines available in the market, but the performance of these formulations is limited. Specifically, these vaccines only provide good protection against similar strains of the virus and there are two major types and many subtypes. So, protection is fairly narrow when the farmers need the vaccine to have very broad protection.

We will develop tools that will allow for the design of next generation vaccines to control spread of infection even when the circulating virus is very different from the virus used to make the vaccine. We propose to develop technologies for pig research that are already available to human vaccine researchers and that allow a more accurate and informative assessment of the immune response to vaccination. Using these modern, more informative technologies will provide new and clear results to be used in the design and testing of more affordable vaccines for PRRSV. These efforts will give farmers an important tool to control a disease that causes significant economic loss and serious pain and suffering in their animals.

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most widespread and economically devastating viral diseases. Vaccines for PRRSV only have effective protection profiles against closely related strains of the virus. This RNA virus mutates rapidly and vaccine matching to outbreak strains is difficult. Further, PRRSV infection results in the development of an immunosuppressive state in the pig where CD 4 T regulatory (Treg) cells play a role.

To more accurately assess immune responses to PRRSV, and other pathogens of pigs, we will develop new tools for the analysis of T cells. Major histocompatilbility complex (MHC) tetramer technology has been used for decades in humans and mouse models to analyse immune responses of T cells, and the technology is readily transferred to livestock species. Since T cell epitopes recognised by the antigen-specific receptor on T cells (the TcR) are in fact MHC I and II proteins that have bound peptides from the infecting pathogen (e.g. viral peptides), MHC tetramers allow the researcher to focus on antigen specific T cells. Our experience with MHC I and II tetramers for cattle will be applied in this project to develop MHC II tetramers for swine.

First, we will express four swine leukocyte antigen (SLA) II proteins and analyse peptides derived from PRRSV encoded proteins for SLA II protein binding. Once the PRRSV peptide binding profile is established, we will use these proteins to construct SLA II/PRRSV tetramers for use in the study of CD4 expressing T cells in pigs infected with PRRSV. We will compare those results to the analysis of pigs vaccinated against PRRSV with two different, commercially available vaccines. The data from these studies will provide the basis for Zoetis to redesign PRRSV vaccines eliminating immunosuppression mediated by Tregs. The resulting, next generation PRRSV vaccines will give farmers better tools to control of PRRSV and improve the economic performance of their herds.

PRRSV is a problem worldwide and swine are critical to small holder farmers, being inexpensive to buy and raise. A new, more efficacious catalogue of vaccines mitigating this disease will have large impacts on Low to Middle Income Countries (LMICs). Our major collaborators on this application from Chulalongkorn University, Faculty of Veterinary Science will immediately bring these technologies to a LMIC as well as be a resource to other LMIC based veterinary and human vaccine researchers in the region.

Critical to this application, Moredun has added the next generation flow cytometry technology to our resources by purchasing a (SONY SA3800) spectral analyser. This new technology for flow is critical in that the overlapping spectra of fluorophores is no longer an issue as the spectral pattern of each fluorophore is measured independently. For veterinary immunologists who have very limited flow cytometry reagents available, this is a major advance. This will be available to scientists on the Easter Bush campus and will provide vaccine scientists worldwide the example of another tool to more accurately measure immune responses. They can apply these novel vaccine assessment technologies to considerable benefit in other vaccine programs. To facilitate this, we will regularly participate in meetings and conferences attracting the vaccine design and delivery communities. Publication of high quality manuscripts in appropriate peer-reviewed international journals will make these approaches and technologies readily available, particularly by targeting open-access journals to allow maximum impact.

Key stakeholders in this proposal are the Foreign and Commonwealth Offices through their commitment to addressing challenges relevant to the health and prosperity of LMIC countries, and the International Veterinary Vaccine Network, a BBSRC funded network to promote coordination and collaboration in the development of vaccines for food animals. Moredun is represented by one of the co-PIs of the IVVN, Alisdair Nisbet, in this network.

Moredun scientists, including the PI, regularly attend and present talks at farmer and animal health meetings throughout the UK and attend most major UK agricultural events. Moredun and Zoetis scientists also have close working relationships with industry bodies such as Quality Meat Scotland (QMS), and the National Pig Association (a subgroup of the National Farmers Union (NFU) and NFU Scotland (NFUS)). Chulalongkorn University has ongoing interactions and collaborations with the Thai Swine Veterinary Practitioner Association and various partners in the Thai swine industry including Charoen Pokphand (CP), and Betagro Groups, the major swine producers in the Southeast Asia region. These pre-existing relationships will allow the group to actively engage with and directly communicate the impact of this project rapidly to these stakeholders in an appropriate format through regular face-to-face interactions, newsletters and Chulalongkorn Univ. and Moredun website content (https://www.chula.ac.th/en/academic/faculty-of-veterinary-science, https://www.moredun.org.uk).

The present PRRSV vaccines available from Zoetis and others are effective but have performance characteristics that can be improved. We anticipate that data from these studies will allow us to work with Zoetis to inform design of next generation PRRSV vaccines that will serve pork producers worldwide in the extensive efforts to control this disease.