A MURINE MODEL OF INTRANASAL IMMUNIZATION TO ASSESS THE IMMUNOGENICITY OF ATTENUATED SALMONELLA-TYPHI LIVE VECTOR VACCINES IN STIMULATING SERUM ANTIBODY-RESPONSES TO EXPRESSED FOREIGN ANTIGENS

The lack of a practical small animal model to study the immunogenicity of Salmonella typhi-based five vector vaccines expressing foreign ant igens has seriously impeded the vaccine development process. For some foreign antigens, stimulation of serum IgG antibody is the desired pro tective immune response. We administered to mice, by orogastric or int ranasal (i.n.) routes, attenuated Delta aroC Delta aroD S. typhi CVD 9 08 carrying a plasmid encoding fragment C (fragC) of tetanus toxin fus ed to the eukaryotic cell receptor binding domain of diphtheria toxin (fragC-bDt), and monitored serum antibody. White orogastric inoculatio n of three doses was not immunogenic, in. immunization elicited high t iters of serum IgG tetanus antitoxin, generating peak ELISA geometric mean titers (GMT) of 27024 and 35658 with 10(8) and 10(9) c.f.u. dosag es, respectively; 10(9) c.f.u. i.n. of an Delta aroA S. typhimurium li ve vector stimulated apeak antitoxin GMT of 376 405. Mice immunized wi th the S. typhi live vector were 100% protected against challenge with 100 50% lethal doses of tetanus toxin that rapidly killed all control mice. Intranasal immunization with two doses of S. typhi expressing u nfused fragment C under control of art anaerobically-activated promote r derived from nirB stimulated significantly higher titers of serum ne utralizing antitoxin than fused fragC-bDt controlled by the same promo ter (GMT 0.10 AU ml(-1) vs 0.01 AU ml(-1), P=0.0095). Two i.n. doses o f S typhi encoding fragC under control of powerful constitutive promot er Ipp led to significantly higher peak serum neutralizing antitoxin t iters than the otherwise identical construct utilizing the nirB promot er (peak GMT 0.72 AU ml(-1) vs 0.10 AU ml(-1), P=0.022). The in. route of inoculation of mice may constitute a practical breakthrough that c ould expedite the development of some S. typhi-based live vector vacci nes by allowing, for the first time, quantitative measurement of serum antibody responses to candidate constructs following Ln, mucosal immu nization. (C) 1997 Elsevier Science Ltd.