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Defining the immune mechanisms by a live attenuated CSFV vaccine - SE0796

Description
Classical swine fever (CSF) is a devastating disease that poses one of the greatest risks to the swine industry worldwide. Existing live classical swine fever virus (CSFV) vaccines, such as the C-strain viruses, provide a rapid onset of complete protection against the disease and viral transmission but pose problems in discriminating infected amongst vaccinated animals (DIVA), which is critical for eradicating a disease and for the resumption of international trade following a disease outbreak. DIVA vaccines, based on the E2 protein of CSFV have been licensed but the time required for this vaccine to protect animals means it is of questionable value under emergency outbreak conditions. As a result, there are considerable efforts being placed in laboratories around the world, to develop DIVA vaccines that can provide similar efficacy to the C-strain vaccine. Multiple strategies are being deployed including the generation of chimeric viruses, whereby CSFV genes encoding vaccine targets are incorporated into the related cattle virus, BVDV, and by genetically modifying CSFV by deleting genes implicated in disease or evasion of the immune system.

The development of next-generation DIVA vaccines with an ability to provide rapid protection would benefit greatly from an understanding of the immunological mechanisms underlying the remarkable efficacy of the C-strain vaccine. This project will utilise a C-strain vaccine to understand (1) the early immune events triggered by the virus in the tonsil, which is the natural primary site of infection by CSFV, (2) the protective effector mechanisms, induced by vaccination, which are responsible for dealing so effectively with CSFV infection even after only a few days, and (3) the viral components that trigger these responses, since it is critical that they be considered in any future vaccine.

The project will involve a broad range of methods from molecular biology and immunology to animal experiments that will attempt to dissect the processes involved in the induction of protective immune responses by live attenuated CSFV. Study of tonsils from vaccinated and challenged animals will inform experiments in the laboratory that will investigate the cellular interactions and their functional consequences.

Micro-arrays, a technology that allows the simultaneous comparison of the expression of thousands of genes, will be applied to tonsils from vaccinated and infected animals to provide data that will underpin the quest for protective mechanisms. Cutting edge laser dissection and microscopy techniques will be used to examine the cellular interactions and responses in the tonsil in the days following vaccination and infection. These data will then inform experiments in the lab with defined cell populations that will aim to test hypotheses relating to the induction of the immune response by C-strain CSFV.

The immunological effector mechanisms that actually confer rapid protection afforded by C-strain vaccines will next be investigated. Previous studies have implicated a role for killer T cells and T cells secreting an effector molecule, interferon-gamma (IFN-ã), but it is unclear which or both are required for protection. Using a C-strain vaccination and challenge regime we will determine the kinetics of virus-specific IFN-ã and killer responses, and determine how each response relates to the timing of clearance of the challenge virus. Studies will be conducted to determine the effects of IFN-ã on CSFV, either directly by inhibiting its growth or by activating killer cells. Direct evidence for the role of T cell populations including killer cells will be obtained through experiments that will attempt to deplete these cell populations from animals and to determine whether they still remain protected against CSFV.

The final component of the project, aims to determine the viral proteins or peptides that are the targets of the protective T cell response. Knowledge of this is necessary to ensure that genetically attenuated or sub-unit DIVA vaccines include these regions. T cells from immune pigs will be used in an IFN-ã based screen of a peptide library spanning all CSFV proteins to rapidly define the relevant sequences. Computer analyses will subsequently be performed on the identified sequences to determine how conserved they are across CSFV isolates, since this is critical if a vaccine is to protect in the field.

The results of this project will contribute to the development of improved DIVA vaccines and would improve strategies to control the spread of CSF and reduce the need for mass slaughter of infected and suspected contact pigs in future outbreaks. The knowledge gained will ultimately reduce suffering of animals, ensuring high standards of animal health and welfare. A reduction in disease losses and barriers to trade caused by CSF will contribute to securing the chain of food production for both the UK consumer and the pig industry
Objective
1. To characterise the early immune events post-vaccination with live attenuated CSF vaccine and challenge with CSFV

2. To define the cell-mediated effector mechanisms induced by components of a live attenuated CSF vaccine

3. To define the protective cell populations critical to the rapid protection induced by a live attenuated CSF vaccine
Time-Scale and Cost
From: 2010

To: 2016

Cost: £1,117,542
Contractor / Funded Organisations
Veterinary Laboratories Agency
Keywords
Animal Diseases              
Animal Health              
Classical Swine Fever              
Plants and Animals              
Vaccines              
Fields of Study
Animal Health