Germination of the spore in the gastrointestinal tract provides a novel route for heterologous antigen delivery.

We have evaluated the potential of endospores of the Gram-positive bacterium Bacillus subtilis as an oral vaccine delivery system. The key features of the B. subtilis spore as a vaccine are, non-pathogenicity, advanced cloning tools, extreme robustness, long-term storage properties and its current use as a probiotic for both humans and animals. We have shown previously that the spore germinates in the small intestine of the mouse and have exploited this attribute for heterologous antigen delivery in this work. The first part of this study was to evaluate the fate of spores in vivo as well as under simulated gut conditions. This showed that spores were extremely robust with most being excreted in the faeces. Using a recombinant gene expressing high levels of beta-galactosidase specifically in the germinated spore (vegetative cell) we showed that spores administered orally could elicit beta-galactosidase-specific local and systemic immune responses. This demonstrated proof of principle that the germinating spore might be effective in the safe delivery of antigens across the stomach barrier. Interestingly, analysis of IgG subclasses suggested a potential bias towards a Th1 response and the involvement of cellular immunity.