VACCINE EFFICACY OF SALMONELLA STRAINS EXPRESSING GLYCOPROTEIN-63 WITH DIFFERENT PROMOTERS

The development of Salmonella vaccine vectors has been hindered by bot h the requirement for multiple doses to induce immune responses and a lack of plasmid stability, Direct comparisons of different promoter sy stems with the same antigen are necessary to address these important i ssues, We have previously described an AroA(-) AroD(-) deletion mutant of Salmonella typhimurium (GID101) which expresses the gene encoding the Leishmania major promastigote surface glycoprotein gp63 (GID101). While this construct provided significant protection against L, major challenge to highly susceptible BALB/c mice, this required at least tw o oral doses. We report here the use of two different inducible promot ers, the nir B and osmC promoters, to improve vaccine efficacy. These constructs (termed GID105 and GID106, respectively) expressed gp63 in vitro under inducible conditions and colonized BALB/c mice after oral administration, GID105 demonstrated greater plasmid stability in vitro and in vivo than did either GID106 or GID101, which expresses gp63 co nstitutively. Spleen and lymph node cells from mice immunized with a s ingle oral dose of GID105 proliferated in vitro in response to L. majo r and secreted gamma interferon, whereas cells from mice given the oth er constructs did not. Mice immunized with a single oral dose of GID10 5 or GID106 developed significantly smaller lesions upon challenge wit h L. major, whereas mice administered GID101 did not. Mice administere d GID105 also showed considerable resistance to Leishmania donovani in fection, These data provide re direct comparison of promoter systems a nd demonstrate that the use of inducible promoters such as the nirB pr omoter allows a considerable improvement over the previous vaccine con struct in terms of protection against infection.