BBSRC EASTBIO DTP - A novel approach to passive vaccination against livestock disease

Infections and diseases are caused by micro-organisms (pathogens) such as viruses, bacteria and parasites. In both humans and animals, the prevalence of many deadly diseases are controlled by vaccination. Typically, this process involves administering a form of the pathogen that is either less harmful than the actual pathogen - an attenuated strain - or an inactivated form of the pathogen that is no longer able to replicate in the host species. In this form of vaccination, protection relies on an active immune response being mounted by the vaccinated individual, so that when infection with the real pathogen occurs the body recognizes it has seen it before and can fight it off readily using antibodies previously generated against the vaccine. However, this approach is not always successful and an alternative is to protect individuals by administering pre-formed antibodies - this is termed passive vaccination. However, the antibodies are difficult and costly to produce in the laboratory in quantities sufficient for large-scale vaccinations, and they are rapidly cleared from the body, leading to only short-term protection. This is a particular issue for livestock diseases, as the economics of production demand simple, low cost vaccination strategies.

In this project, the objective is to develop a novel passive vaccination method for livestock, using the sheep disease scrapie for initial proof-of-principle. Scrapie is one of a family of neurodegenerative diseases, known as transmissible spongiform encephalopathies (TSEs), or prion diseases. Other prion diseases include Creutzfeld-Jakob disease (CJD) in humans and bovine spongiform encephalopathy (BSE) in cattle, which caused a major epidemic with substantial negative impacts on the UK agricultural industry during the 1980s and 1990s. BSE also transmitted to humans in the form of variant CJD, resulting in >200 fatalities worldwide to date. Current threats to animal health/food security include atypical forms of scrapie and BSE, which do not appear amenable to existing disease control strategies, and chronic wasting disease (CWD), a devastating disease that is at epidemic proportions throughout North America, and was recently identified in Europe. Novel approaches are urgently needed to improve prospects for eradication of these diseases, and reduce the risk of future spread to the human population.

In prion diseases, neurodegenerative changes leading to disease are associated with the misfolding and aggregation of a normal host protein, the prion protein (PrPC). The misfolded, disease-associated protein (PrPSc) is also believed to be the infectious agent responsible for transmission of disease. As such, PrPSc is a potential target for vaccination, but this presents problems because as a “self” protein, it is not recognized as foreign by the host immune system. Nevertheless, some conventional immunization methods have been able to confer at least partial protection to prion infection, and passive administration of antibodies starting at around the time of infection has been shown to delay or prevent onset of disease.

The main aim of the project is to develop a novel passive vaccination technique for prions, using a gene therapy approach, in which DNA encoding anti-PrP antibodies will be administered to individuals, allowing them to produce the antibodies using their own cellular machinery. This will allow the antibody to be produced persistently over a long period, circumventing the need for large-scale laboratory production and repeated administration of preformed antibodies. We have already generated a panel of 28 monoclonal anti-PrP antibodies, and initial work will screen and select which of these antibodies are most effective in clearing prions from persistently infected cell cultures. The antigen-binding domains of the selected antibodies will be genetically engineered to allow them to be expressed as single chain variable fragments (scFv), which retain the specificity of the original antibody, but lack the constant regions responsible for triggering adverse cytotoxic reactions to passive immunotherapies. The scFv DNA will be inserted into the genome of non-harmful viral vectors that will drive production of the antibody fragment within the animal. To test the ability of these vaccines to protect against prion infection in vivo, they will be administered intranasally to mice before and after experimental infection with scrapie.

The project will provide training and enable the student to gain expertise in a wide range of research techniques, comprising molecular biology, protein biochemistry, cell culture, immunology, as well as work with experimental animal models of infection. The student will benefit from interactions with supervisors and collaborators who are recognized internationally as experts in prion diseases, immunology, and the use of animal models in development of gene therapies.