In vivo characterization of the murine intranasal model for assessing the immunogenicity of attenuated Salmonella enterica serovar typhi strains as live mucosal vaccines and as live vectors

Attenuated Salmonella enterica serovar Typhi live vector vaccine strains ar e highly immunogenic in mice following intranasal but not orogastric inocul ation. To elucidate the relationship between organs within which vaccine or ganisms are found and the induction of specific serum immunoglobulin G (IgG ) antibodies, we examined the in vivo distribution of serovar Typhi vaccine strain CVD 908-htrA following intranasal administration. Vaccine organisms were cultured from the nasal lymphoid tissue (NALT), lungs, and Peyer's pa tches 2 min after intranasal inoculation. Vaccine organisms persisted longe r in NALT than in other organs. By decreasing the volume of intranasal inoc ulum containing 10(9) CFU (from a single 30- or 10-mu l dose to four 2.5-mu l doses given over the course of 1 h), we were able to significantly reduc e the number of vaccine organisms isolated from the lungs (P < 0.05) withou t reducing the number of vaccine organisms in NALT, Reducing the number of vaccine organisms in the lungs resulted in a significant decrease in the se rum tetanus antitoxin response elicited by CVD 908-htrA expressing tetanus toxin fragment C under the control of the redox-responsive nir15 promoter, In contrast, a similar construct expressing tetanus toxin fragment C under control of the constitutive Ipp promoter stimulated a strong serum IgG teta nus antitoxin response with both inoculation regimens. The data suggest tha t following intranasal inoculation, NALT is a sufficient inductive site for elicitation of an immune response against both the live vector and heterol ogous antigen and, as occurs following oral inoculation of humans, attenuat ed serovar Typhi vaccine organisms elicit serum IgG responses.