Enhanced immune responses to viral epitopes by combining macrophage-inducible expression with multimeric display on a Salmonella vector

Abstract

In this study, the immunogenicity of chimeric 987P fimbriae on a Salmonella vaccine strain was improved by optimizing fimbrial expression. The constitutive tetA promoter and the in vivo activated nirB and pagC promoters were evaluated for their use to express two epitopes of the transmissible gastroenteritis virus (TGEV) spike protein carried by fimbriae which were displayed on a Salmonella vaccine strain. Constructs with the pagC promoter were shown to drive increased expression of chimeric 987P fimbriae in macrophages as well as in Mg(2+)-poor media, mimicking a major environmental signal found in Salmonella-containing endocytic vacuoles of macrophages. Mice immunized orally with a Salmonella vaccine strain which expressed chimeric fimbriae from the pagC promoter elicited significantly higher mucosal and systemic immune responses to both the 987P fimbriae and the TGEV epitopes than mice immunized with the same strain hosting a tetA or nirB promoter-driven expression plasmid. Moreover, only the Salmonella vaccine strains harboring a plasmid with the pagC promoter, with or without an additional tetA promoter in tandem, elicited neutralizing antibodies to TGEV. This indicated that the pagC promoter can be used successfully to improve epitope-display by chimeric fimbriae on Salmonella vaccine strains for the induction of a desired immune response.

Comparison of a Regulated Delayed Antigen Synthesis System withIn Vivo-Inducible Promoters for Antigen Delivery by Live AttenuatedSalmonellaVaccines

“…Inserting the IVIP into the bacterial chromosome, as has been done with P ssaG driving eltB (41,82), may be a better choice to ensure proper regulation. Previous work that directly compares different IVIPs showed that the most effective promoter to achieve the desired immune response varied for different antigens (9,14,22,29,63,77); in some cases, a constitutive promoter may be optimal (30,45,83). In addition, for IVIPs, measures of in vitro expression may have limited correlation with their performance in vivo (95).…”

“…P pagC has been shown to function in different species (88). While P nirB has been used to express a number of different antigen genes in live attenuated Salmonella vaccines and other species (15,28,43,57,63,90,94), P pagC has emerged as a favorable choice in several studies, including studies that directly compare the two promoters (9,10,14,22,39,79). In studies comparing a number of promoters, P pagC was found to have the greatest activity in murine tissues (11,22).…”

Regulated Antigen Expression in Live RecombinantSalmonella entericaSerovar Typhimurium Strongly Affects Colonization Capabilities and Specific CD4+-T-Cell Responses

“…strains that express foreign antigens are promising oral vaccines (6,30,41). Among the many parameters that have been shown to influence their efficacy, regulated antigen expression appears to have particularly strong effects (3,4,9,10,19,26,32,34,35,37,39,43). In vivo-inducible (IVI) instead of constitutive antigen expression allows the culture and administration of recombinant Salmonella cells expressing low levels of antigen that minimally interfere with bacterial viability.…”

Comparison of a fimbrial versus an autotransporter display system for viral epitopes on an attenuated Salmonella vaccine vector

“…Expression from plasmid pCS263 was as efficient as that from plasmid pCS265, which carried the asd gene for plasmid stabilization by the balanced-lethal system ( Fig. 2A), an alternative plasmid maintenance system that we had used previously [8,16,19]. However, TGEVCA-MisL expression from pCS263 was reduced by approximately one-half when the Salmonella vector contained also pCS173 for simultaneous expression of the TGEVAC from surface exposed fimbriae [1].…”