The ability of live attenuated Salmonella enterica serovar typhimurium (S. typhimurium) as a carrier of DNA vaccine was evaluated using model plasmid encoding beta-galactosidase (β-Gal) and BALB/c mice. We constructed pBRCMVβ, β-Gal expression apparatus having a replication origin from low copy pBR322. Comparison of the plasmid stability showed that pBRCMVβ remained stable in Salmonella even after oral administration, while pUC-based pCMVβ tended to be lost quickly. However, titers for β-Gal

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... cific IgG in sera did not significantly increase in mice orally administered S. typhimurium harboring pBRCMVβ. These data suggest that the stability of plasmid in S. typhimurium is associated with its replication origin. Further studies are required to scientifically establish this methodology. The use of live attenuated intracellular bacteria as vehicles to deliver plasmid DNA vaccine is a novel and attractive approach of inducing effective immunity [2] . After the release of the plasmid DNA from the bacteria, the plasmid-encoded antigens can be expressed directly by the host cell. These bacteria infect antigen (presenting cells (APCs) such as macrophages and dendritic cells, so that the plasmid DNA vaccine is delivered effectively into APCs. These bacteria also act as a natural adjuvant and activate immune responses. S. typhimurium is a typical intracellular bacteria, and was first used to show that bacterial DNA vaccine de-