A One Health approach to pan-valent morbillivirus vaccines

Paramyxoviruses are a family of viruses that pose a significant threat to humans and animals alike. For example, Hendra virus outbreaks in Australia have targeted both racehorses and their trainers, while Nipah virus outbreaks in Malaysia spread through pig farms, resulting in 105 human fatalities and the culling of approximately 1.1 million pigs. While such cross-species transmission events may occur relatively infrequently, when they do occur, the consequences can be devastating for humans and animals alike. The Paramyxovirus family also includes the morbillivirus genus of viruses, possibly the most notable of which are measles virus in humans and rinderpest virus in cattle. Morbilliviruses of animals have a very high potential for cross-species transmission, or "zoonosis". Although originally described as a pathogen of dogs, canine distemper virus (CDV) has jumped species into critically endangered lion, tiger, seal and giant panda populations. A closely related morbillivirus of sheep and goats, peste des petits ruminants virus (PPRV) has caused severe disease outbreaks in saiga antelope in Mongolia, buffalo in India and camels in Ethiopia and Sudan. If we are to combat the future spread of such zoonotic morbilliviruses, we need to develop a better understanding of the process of cross-species transmission and how this can be prevented by vaccination.

Vaccination against one species of morbillivirus can provide immunity to infection with morbilliviruses from other species; a rinderpest vaccine can protect cattle from rinderpest, a goat from PPRV and a dog from CDV. Vaccination triggers the production of neutralising antibodies (nAbs) targeting the surface glycoproteins of the virus, hence, some of these antibodies must recognize determinants that are conserved across diverse morbilliviruses. In this project, we set out to identify the determinants on the viral surface glycoproteins that are recognised by neutralising antibodies. If these binding sites can be identified, we will be able to design better pan-morbilliviral vaccines, vaccines that will protect against cross-species infection with emerging morbilliviruses.

To achieve this goal, we have designed in vitro systems with which we can recreate the cellular environment of the susceptible host species. Morbilliviruses attach to target cells by binding to either of two protein molecules expressed on the cell surface, CD150 or nectin-4. Variations in the amino acid sequences of these molecules are key determinants of which species the viruses target, hence CDV is able to bind to CD150 from many species and thus has a very broad species tropism. Neither CDV nor PPRV bind human CD150 well and hence infect human cells very inefficiently. However, with a small adaptation to the amino acid sequence of the viral glycoproteins, binding is enhanced greatly and the viruses display an enhanced ability to infect human cells. We have developed assays with which we can study the propensity for morbilliviruses to develop such mutations. Moreover, we can assess how efficient antibodies generated in the host by vaccination are at preventing infection with such viruses. In effect, we have developed systems with which we can determine the likelihood of zoonotic transmission occurring and how to prevent it by vaccination.

This project will guide the design of the next generation of pan-morbilliviral vaccines and will develop assays systems with which their likely efficacy in preventing zoonoses can be assessed in vitro. By defining the viral targets for neutralising antibodies and by assessing their function against potentially zoonotic viruses, this project offers a unique opportunity to protect both humans and animals alike against the emerging threat posed by novel morbilliviruses.

Paramyxoviruses pose a significant emerging threat to humans and animals alike, exemplified by the devastating consequences of Hendra and Nipah virus outbreaks in Australia and Malaysia respectively. The very high potential for zoonotic transmission is further illustrated by the morbillivirus canine distemper virus (CDV). Ostensibly a virus of dogs, CDV has jumped species into critically endangered lion, tiger, seal and giant panda populations. Further, CDV can also infect macaques, suggesting that barriers to zoonotic transmission to humans may be fragile.

Vaccination against one species of morbillivirus can provide immunity to infection with other species, hence a rinderpest vaccine can protect cattle from rinderpest (RPV), a goat from peste des petits ruminants (PPRV) and a dog from CDV, while measles vaccination provides partial protection of non-human primates from infection with CDV. We have found that vaccinated and convalescent sera from animals and humans alike, often contain antibodies that cross-neutralise both homologous and heterologous species of virus and hence must recognise determinants that are conserved across diverse morbilliviruses. In this project, we will identify the epitopes recognised by such antibodies, informing the design of the next generation of pan-morbilliviral vaccines, vaccines that will protect against cross-species infection with emerging morbilliviruses.

To achieve this aim, we have developed in vitro systems with which we can assay neutralising activity against primary morbilliviral strains using target cells bearing both cognate and heterologous viral receptors. Moreover, we have developed in vitro assays with which we can investigate the likelihood of potentially zoonotic viruses emerging, characterise the mutations conferring enhanced transmission and assess the sensitivity of the viruses to cross-neutralising antibodies.

Informing the design of the next generation of morbilliviral vaccines: Live attenuated morbilliviral vaccines have proven efficacy in preventing, controlling and eradicating morbilliviral diseases. Some of these vaccines induce potent cross-neutralising antibodies. The significance of these observations cannot be overstated, if we can identify the molecular determinants targeted by these antibodies, we can engineer the next generation of "pan-morbilliviral" vaccines that will prevent the emergence of novel morbilliviruses. Researchers may choose to pursue diverse vaccine platforms, from classical live attenuated viruses, to engineered chimp adenoviruses bearing surface glycoproteins or adjuvanted recombinant proteins. Irrespective of the platform technology, the data generated in this project will facilitate enhancement and optimisation of antigenicity, inducing a more potent and cross-protective immune response.

Platform technologies for vaccine efficacy testing: This project will deliver high-throughput quantitative assays that facilitate a rapid assessment of neutralising activity in sera from vaccinates and convalescent individuals against biologically relevant field strains of virus. Moreover, we will deliver target cells that recreate the cellular environment of the host species for which efficacy is being assessed. The novel approach we present to predicting likely emergent strains and evaluating their sensitivity to cross-protective neutralising antibodies presents a unique opportunity for vaccine researchers and manufacturers to optimise vaccine formulations to protect animals and humans against not only "known" pathogens, but also against likely "emerging" pathogens, a novel approach to contingency planning in vaccine development.

Tools, resources and reagents for application in the field: As we build up a map of cross neutralising epitopes on the morbilliviral haemagglutinin proteins, we will develop an antigenic map of the major morbillivirus neutralising epitopes targeted by field sera. Hence, when novel field strains of virus emerge that appear to evade immunity induced by existing vaccines, it should be possible to predict which epitopes confer resistance upon the escape mutants. By building structure predictions based on the solved structures of measles virus haemagglutinin, it will be possible to make informed decisions regarding future vaccine compositions. Ultimately, it should be possible to generate a database of morbillivirus mutations that can be used for epidemiological monitoring of inter-species and zoonotic morbillivirus emergence.

Advancement of scientific knowledge within both the academic community and general public: The academic community will benefit directly from this research through an advancement of our understanding of morbillivirus pathogenesis and immunity, the nature of the virus-receptor interaction and the mechanisms of virus neutralisation, stimulating the emergence of new areas of research. At present, the field of paramyxovirus research is relatively small in the UK. This project will build capacity for animal and human morbilliviral research, establishing a strong collaboration between two of the UK's major centres for virology, the Centre for Virus Research and The Pirbright Institute.

Development and showcasing of novel technologies and assay platforms: We have developed a number of novel strategies for integrating high throughout fusion and budding assays with immune-surveillance (particularly neutralising antibodies) and the prediction of zoonotic transmission events. By publishing and presenting these approaches we will foster their application in academia, industry and one-health care. Our close links with clinicians in human and animal health will enable us to expand the outlook of researchers in both human and animal diseases, providing an informed perspective on zoonoses, their animal origins and how to prevent them happening.