Live attenuated Salmonella: a paradigm of mucosal vaccines

Two key steps control immune responses in mucosal tissues: the sampling and transepkhelial transport of antigens, and their targeting into professional antigen‐presenting cells in mucosa‐associated lymphoid tissue. Live Salmonella bacteria use strategies that allow them to cross the epithelial barrier of the gut, to survive in antigen‐presenting cells where bacterial antigens are processed and presented to the immune cells, and to express adjuvant activity that prevents induction of oral tolerance. Two Salmonella serovars have been used as vaccines or vectors, S. typhimurium in mice and S. lyph'i in humans. S. lyphimurium causes gasiroenieritis in a broad host range, including humans, while S. typhi infection is restricted to humans. Attenuated S. typhitnurium has been used successfully in mice to induce systemic and mucosal responses against more than 60 heterolo‐gous antigens. Tbis review aims to revisit S. typhimurium‐based vaccination, as an alternative to S. typhi, with special emphasis on the molecttlar pathogenesis of S. typhimurium and the host response. We then discuss how such knowledge constitutes the basis for the rational design of novel live mucosal vaccines.