Expression of heterologous antigens inSalmonellaTyphimurium vaccine vectors using the in vivo-inducible, SPI-2 promoter,ssaG

DNA derived from regions upstream of theSalmonella entericaserovar TyphimuriumssaGgene were used to drive expression of different reporter genes in putativeSalmonellavaccine strains. Expression fromssaGwas shown to be significantly upregulated onceSalmonellahad entered murine or human macrophages, and levels of expression were dependent on the length of thessaG5' sequence incorporated.S.Typhimurium derivatives harbouring theEscherichia coliheat labile toxin B subunit (LT-B) fused to various lengths of thessaGpromoter region were also constructed as single copy chromosomal integrations. Expression of LT-B by theseSalmonelladerivatives was detected at significant levels after intra-macrophage survival and mice immunised with these derivatives mounted marked anti-LT-B humoral antibody responses.