Elsevier

Vaccine

Volume 12, Issue 11, 1994, Pages 1004-1011
Vaccine

Paper
Construction and evaluation of an expression vector allowing the stable expression of foreign antigens in a Salmonella typhimurium vaccine strain

https://doi.org/10.1016/0264-410X(94)90336-0Get rights and content

Abstract

Salmonella strains have great potential as live carriers of heterologous antigens to induce immunity against a variety of infectious diseases. However, the amount of heterologous antigen required to induce an adequate immune response may be toxic for the bacterium and result in cell death, overattenuation or loss of expression of the heterologous antigen. To solve this problem an expression vector was developed with a strong promoter located on a DNA fragment which is inverted at random. Antigen is only expressed in one particular orientation of the promoter. Thus a bacterial population harbouring the plasmid will consist of a subpopulation which does not produce heterologous antigen, and is therefore not affected in growth, persistence and dissemination within the host. Further, this non-producing population will continuously segregate antigen-producing bacteria. To evaluate the system, CtxB was used as a model antigen. Analysis of the plasmid DNA isolated from Salmonella revealed a selection against the promoter orientation that directs transcription of the ctxB gene. In spite of this, the vector was stably maintained in vivo and induced CtxB-specific IgA and IgG in mice. These results indicate that this kind of expression vector may offer a solution to the problem of unstable expression of foreign antigens in live bacterial vaccine strains.

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    Present address: Department of Pathology, Free University Hospital, de Boelelaan 1117, 1081 HV Amsterdam, The Netherlands.

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