A reverse vaccinology approach to a bTB vaccine

Bovine tuberculosis, bTB, is the result of the infection of cattle by the bacterium Mycobacterium bovis. The bacterium is distributed widely in nature as it also infects many other wildlife species and as a result of this, wildlife infection acts as a reservoir for the bacterium which periodically get across into domestic cattle. The consequence of this is twofold. First, cattle that are bTB positive must be culled with a knock-on effect on the farmer and his ability to maintain a herd. Second, bTB is a threat for human infection, primarily via the consumption of contaminated milk. Today bTB infection of individuals is extremely rare, but the threat remains and for these reasons bTB infection is unwelcome and needs to be controlled or, preferably, eradicated. Since a historical review in the mid-1990s, the badger has been identified as one of the major routes of transmission of bTB to domestic cattle and this, in turn, has led to attempts to break this transmission route via badger culling. These have met with only limited success and immense public concern leaving the physical breaking of the transmission route mostly unaltered. An alternative approach is to accept that bTB circulates widely in the environment but to prevent cattle infection by previous vaccination. At the present time however an effective vaccine for bTB in cattle is not available and new methods to develop such a vaccine are urgently needed. It is generally accepted that vaccines function by generating an antibody response in the target animal which prevents the bacterium from establishing the initial infection. These antibodies, which are a normal product of the immune system of all mammals, generally bind to the outside of the bacterium and so prevent it from binding to cattle cells, usually the epithelial cells of the lung. It follows that the protective components of bTB, that is, the components that will generate the antibody response that is protective, are to be found on the outside of the bacterium surface. Bacteria have many components on their surface and any, or perhaps a combination of many, of these components, proteins encoded by the bacterium genome, could be essential for the development of effective immunity. However exactly which are required is currently unknown. In this research, we propose to produce all of the surface components of bTB and to test them in batches for their ability to induce an effective immune response. We propose to do this work in cattle so that the response measured to our test vaccines is typical of what will be found if an eventual vaccine is used in typical herds. Our work breaks down into three related components. Firstly, we will identify all of those proteins from the M. bovis bacterium that are to be found on the surface of the organism and produce each of them in a safe and efficient manner. Our initial calculations suggest that several hundred such proteins may be required in order to find the few that are necessary for effective immunity. Secondly, we will use our surface proteins as test vaccines in cattle and to make this process efficient we will carry out this work with mixes of proteins so that the least number of cattle has to be used. Following the immunizations we will take blood samples from the cattle and test them for the ability to prevent M. bovis infection. Finally, we will examine the mechanism of protection and how the individual components so we have identified work together to provide the cattle with an effective barrier of immunity. Our approach is exhaustive but it has the potential to draw a line under the vaccine discovery program for bTB and to identify the best mix of candidates for eventual effective vaccine production.