title: Salmonella vaccine vectors displaying delayed antigen synthesis in vivo to enhance immunogenicity.
abstract: We have developed a regulated delayed antigen synthesis (RDAS) system for use in recombinant attenuated Salmonella vaccine (RASV) strains to enhance immune responses by reducing the adverse effects of high-level antigen synthesis. This system includes a chromosomal repressor gene, lacI, expressed from the arabinose-regulated araC PBAD promoter. LacI serves to regulate expression from a plasmid promoter, Ptrc, that directs antigen synthesis. In the presence of arabinose LacI is produced, which binds to Ptrc, blocking antigen synthesis. In vivo, an arabinose-poor environment, the concentration of LacI decreases with each cell division, allowing increased antigen synthesis. To optimize the system and for comparison, we altered the lacI ribosome-binding site, start codon, and/or codon content to construct RDAS strains chi9095, chi9959, and chi9241, synthesizing from low to high levels of LacI, respectively, and non-RDAS strain chi9555 as a control. We evaluated this system with two test antigens, the green fluorescent protein for initial in vitro assessment and the Streptococcus pneumoniae PspA protein for validation of our system in mice. All RASV strains expressing PspA generated high antilipopolysaccharide antibody titers, indicating that expression of lacI did not interfere with the capacity to induce an immune response. Strain chi9241 induced significantly higher anti-PspA IgG and IgA antibody titers than strain chi9555, which expressed PspA constitutively. Anti-PspA antibody titers were inversely correlated to the level of LacI synthesis. Strain chi9241 also induced significantly greater protective efficacy against challenge with virulent S. pneumoniae. These results suggest that regulated delayed antigen synthesis is useful for improving immunogenicity of RASV strains.
authors.affiliation: The Biodesign Institute, Center for Infectious Diseases and Vaccinology. Arizona State University, P.O. Box 875401, 1001 S. McAllister Avenue, Tempe, AZ 85287-5401, USA.
authors.forename: Shifeng
authors.initials: S
authors.lastname: Wang
authors.forename: Yuhua
authors.initials: Y
authors.lastname: Li
authors.forename: Giorgio
authors.initials: G
authors.lastname: Scarpellini
authors.forename: Wei
authors.initials: W
authors.lastname: Kong
authors.forename: HuoYing
authors.initials: H
authors.lastname: Shi
authors.forename: Chang-Ho
authors.initials: CH
authors.lastname: Baek
authors.forename: Bronwyn
authors.initials: B
authors.lastname: Gunn
authors.forename: Soo-Young
authors.initials: SY
authors.lastname: Wanda
authors.forename: Kenneth L
authors.initials: KL
authors.lastname: Roland
authors.forename: Xin
authors.initials: X
authors.lastname: Zhang
authors.forename: Patti
authors.initials: P
authors.lastname: Senechal-Willis
authors.forename: Roy
authors.initials: R
authors.lastname: Curtiss
mesh_terms: D000818:Animals; D000942:Antigens, Bacterial / Q000096:biosynthesis*; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000276:immunology; D005260:Female; D005822:Genetic Vectors; D049452:Green Fluorescent Proteins / Q000096:biosynthesis; D056968:Lac Repressors / Q000235:genetics; D051379:Mice; D008807:Mice, Inbred BALB C; D010957:Plasmids; D011401:Promoter Regions, Genetic; D012475:Salmonella / Q000235:genetics* / Q000254:growth & development / Q000472:pathogenicity; D014613:Vaccines, Attenuated / Q000276:immunology; D014614:Vaccines, Synthetic / Q000276:immunology*; D014774:Virulence
chemical_list: D000942:Antigens, Bacterial; D001426:Bacterial Proteins; D056968:Lac Repressors; D014613:Vaccines, Attenuated; D014614:Vaccines, Synthetic; C051592:pneumococcal surface protein A; D049452:Green Fluorescent Proteins