A DNA vaccine encoding MPB 83 from Mycobacterium bovis reduces M bovis dissemination to the kidneys of mice and is expressed in primary cell cultures of the European badger (Meles meles)

SUMMARY Nucleic acid (DNA) vaccination against tuberculosis in the European badger (Meles meles) is one approach to addressing the escalating problem of bovine tuberculosis in Great Britain. The aim of vaccination is to reduce the burden of tuberculosis within the badger population and the shedding of Mycobacterium bovis to levels that would break the transmission of infection to cattle. To this end, the vaccine would be required to limit the amount of disseminated tuberculosis in the badger, especially dissemination to the kidney from where M bovis can be shed in the urine. A promising candidate DNA vaccine encoding a 26 kDa major antigen (MPB83) of M bovis was evaluated in a mouse model of disseminated M bovis infection. Using the DNA vaccine, protection against infection of the kidney was found to be greater than that achieved with the current live vaccine, Bacille Calmette-Guerin( BCG). Kidney tissue and skeletal muscle from the badger was used to derive primary cell cultures in which to examine the expression of MPB83 following transfection with the DNA vaccine. Kidney cortex gave rise to a monotypic culture of epithelial cells whilst the muscle gave rise to a mixed culture of fibroblasts and myoblasts. During culture the myoblasts differentiated into multinucleated myotubes, verified by immunofluorescent detection of mammalian desmin. Successful expression of MPB83 by transfected epithelial and myotube cells was confirmed by immunofluorescence using a monoclonal antibody specific to the protein. These observations fulfil the early requirements for the development of a DNA vaccine for badger tuberculosis. NATIONAL bovine tuberculosis programmes based on regular tuberculin testing and removal of infected ani- mals have had a profound influence on reducing the incidence of bovine tuberculosis in cattle and farmed deer herds. However, in a number of countries, the pre- valence of bovine tuberculosis in certain geographical areas has remained stubbornly high. Since the 1970s, accumulating evidence suggests that the European badger (Meles meles) acts as a maintenance host for M bovis infection and as an important source of infec- tion for cattle in the UK (Gallagher et al 1976, Little et al 1982). Lesions in the kidney resulting from haematogenous spread of M bovis, have been described as characteristic of badger tuberculosis (Gallagher and Clifton-Hadley 2000) and large numbers of bacilli can be shed in the urine of affected badgers (Gallagher and Clifton-Hadley 2000, MAFF 1979). However, the precise route of transmission and the factors that influence it, have not been established. The intention of vaccinating badgers against infection with M bovis would be to reduce the burden of infection within the badger popul- ation and reduce the level of shedding of the organism to levels that would break the potential transmission of infection to cattle. To this end, the vaccine would be required to limit the amount of disseminated disease in the badger but not necessarily to prevent primary infection.