Development of next generation vaccine technology inducing rapid and strong immunity through targeted delivery of antigens to chicken immune cells

Safe and disease-free poultry production systems are crucial for maintaining food supplies to feed the increasing human population and to improve the livelihoods of farming communities. However, the biggest threat in the sustainable growth of farmed animal production is the emergence, re-emergence and continual prevalence of a multitude of infectious animal pathogens, such as avian influenza. Primarily, the control against these pathogens is achieved through vaccination. However, the effectiveness of most of the current vaccines is suboptimal, where they may only reduce manifestation of clinical disease and mortality, but infected animals continue to shed viruses resulting in a continual chain of infections to susceptible naïve and vaccinated animals. For example, despite the large-scale deployment of multiple doses of influenza vaccine to an individual bird, manifestation of disease continues in the form of endemic prevalence and farmers continue to bear debilitating losses with up to 100 percent flock mortality or loss of egg production along with the threat of zoonotic infections. Therefore, improvement of the current vaccines are required that produce stronger immunity and full protection against disease, together with a reduction in shedding of infectious virus from infected animals, preventing the endemic prevalence of these viruses in farmed animals.

In this proposal, we plan to develop robust and effective vaccines that elicit strong and durable humoral and cellular immune responses against viral pathogens which cause severe economic losses in poultry industries. As a proof-of-principle, we have demonstrated that targeted delivery of antigens to chicken immune cells potentiate the antigen-specific immune responses in vaccinated chickens compared to the untargeted counterpart or the conventional killed virus vaccines. The targeted vaccines demonstrated a significantly faster and a significantly higher immune response. These studies therefore provided strong data to take this new vaccine technology from laboratory to the farm. To achieve this goal, we have established partnership with a commercial poultry vaccine producer "MSD Animal Health". Through this collaboration, we will investigate how our developed targeted antigen delivery vaccine (TADV) formulation can further be optimised to i) induce even more rapid immunity and provide more potent and broader immune responses against antigenic AIV variants infecting poultry in different geographic regions; ii) enhance the production and delivery methods in chickens using our well-established insect cell cultures and recombinant viral vector (herpesvirus of turkey) system. The result obtained from this proposed research would provide a novel next generation improved AIV vaccine and a platform for improvement of vaccine technology against other important livestock and human pathogens. Availability of these novel highly protective and cost-effective disease control tools and strategies should minimise the impact of infectious diseases on farm animals, and offer substantial indirect economic, public health, environmental and social benefits to the UK and rest of the world.

This project will exploit novel "targeted antigen delivery vaccine" (TADV) technology, utilising specificity of antibodies that bind to chicken antigen-presenting cells (APCs). This will allow antigens fused to APCs-specific antibody fragments be delivered to immune cells for processing, presentation and induction of immune responses. To demonstrate the effectiveness of this TADV approach, we have developed a model vaccine for avian influenza virus (AIV) in which virus haemagglutinin (HA) antigen was fused with a single-chain fragment variable (scFv) region of APCs-specific antibody. This influenza TADV induced rapid and stronger immune responses compared to the untargeted counterpart or conventional inactivated virus vaccine. To take this TADV approach further, we will investigate the ability of different APCs-specific antibodies in enhancing the immunogenicity and protective efficacy of influenza vaccine. Several recombinant protein expression cassettes will be generated consisting of HA antigen fused with different scFv targeting chicken APCs. We will use our established insect cell expression system for vaccine production and generate recombinant herpesvirus of turkey (HVT)-based viral vector vaccines for in situ delivery of antigens to APCs. The level of protection and the mechanism of the induction of the improved immune response will be studied in chickens. Broader protection against antigenic variants will be achieved by formulating bivalent vaccines containing two antigenically divergent HA antigens fused with two distinct APCs-targeting scFv. Resulting vaccines are expected to deliver antigens directly to the APCs without being taken up by other non-immune cells. This will increase the amount of antigens reaching the APCs inducing rapid and stronger immune response with an added advantage of dose sparing. Availability of these novel highly protective and cost-effective vaccines should minimise the impact of infectious diseases on farmed animals and humans.

The project will develop new vaccine technology to improve vaccine effectiveness to reduce devastating economic losses pertaining to farmed animal production due to infectious viral diseases. Consequences and repercussions of these infectious animal diseases on trade, food security, public health and livelihood of millions of farming and associated communities around the world is increasingly evident from the continued global prevalence and spread of many farmed animal pathogens including avian influenza viruses. This can be exemplified from a recent global spread of avian influenza viruses which led to the culling of over a billion domestic poultry and estimated over ten million wild birds in 30 European countries as well as across Asia, North America and Africa. In the UK, a handful of localised poultry outbreaks with high pathogenicity H5N8 (between October 2016 and January 2017) led to the significant culling of over one million high-value chicken, duck and turkey flocks. Furthermore, a 10-kilometre restriction zone was implemented around the infected premises to prevent the movement of domestic poultry and livestock, resulting in further economic losses to neighbouring farms. Considering these events, further spread of AIV would incur severe losses to the UK poultry industry (an industry that contributes approximately £8 billion to the UK economy and supports over 80,000 jobs). A similar kind of devastation to poultry production is being exerted by a large number of other avian pathogens. Therefore, new improved vaccination technologies are required that can control and eradicate these pathogens from farmed animals.

This innovative research, which proposes to deliver protective antigens selectively to immune cells for enhancing the protective efficacy of vaccines, will serve as a foundation for next generation of vaccines. The development of model recombinant herpesvirus of turkey (HVT)-based avian influenza vaccines will demonstrate the feasibility, that a single dose of vaccine delivered to either one-day-old chick or in eggs (in ovo) to 18-day-old embryos could provide robust and life-long immunity against two or more important poultry diseases; avian influenza and Marek's disease. Furthermore, enhancement of broader cross protection by expressing multiple antigens in a single vaccine construct will afford protection from antigenically diverse co-infecting viruses in the field.

The project will generate knowledge that will directly impact on poultry disease control systems globally. We will undertake integrated and innovative approaches which will increase our fundamental understanding of critical requirements for improving farm animal vaccines by efficient delivery of antigens to immune cells. The developed approaches and reagents can be an expediting improvement in human vaccines. The research will also enhance research capacity and training of the next generation of scientists for multi-disciplinary research that addresses priority concerns of infectious diseases on global health and food security.

Major beneficiaries of research will be the poultry industry, vaccine developers, academic researchers and farmers whose livelihood depends on selling poultry products. To fully realise the impacts of this project we will communicate the outcomes to these stakeholders via multiple mechanisms including publication of the outcomes on publicly available open access information sharing systems. Information will be shared promptly via peer-reviewed open access journals, presentations at conferences and workshops. Proactive engagements with potential stakeholders with interest in improving farmed animal disease control and prevention strategies including funding bodies and policy makers (BBSRC, MRC, Defra, OIE, WHO, FAO) will allow making informed decisions and developing effective strategies to combat the increasing number of farm animal diseases.