An attenuated strain of S. typhimurium has been used as a vehicle for oral genetic immunization. Eukaryotic expression vectors containing truncated genes of ActA and listeriolysin—two virulence factors of Listeria monocytogenes—have been used to transform S. typhimurium aroA. Multiple or even single oral immunizations with such transformants induced excellent cellular and humoral responses. In addition, protective immunity was induced with listeriolysin transformants. The quality of the responses suggested a transfer of plasmid DNA from the bacterial carrier to the host. Such transfer was unequivocally shown in vitro with primary peritoneal macrophages. We describe a highly versatile system for antigen delivery, identification of protective antigens for vaccination, and efficient generation of antibodies against the product of open reading frames present on virtually any DNA segment.
