Live Salmonella as vaccines and carriers of foreign antigenic determinants.

Salmonella species can be rationally attenuated by introducing non-reverting defined mutations into the genome to produce live vaccine strains. Several genes have been identified which when mutated, will attenuate Salmonellae. In particular, salmonella strains harbouring mutations in genes involved in the pre-chorismate biosynthetic pathway make excellent oral vaccines evoking strong humoral, local and cellular immune responses in the host. Because of the spectrum of immune responses induced by live vaccine strains they have the potential to be used for delivery of heterologous antigens to the mammalian immune system. A number of antigens from other bacteria, viruses and parasites have been expressed in live salmonella vaccine strains. Such hybrid strains have the potential to be used as multivalent vaccines against a number of infectious diseases.