PROTECTIVE IMMUNIZATION WITH PLASMID DNA CONTAINING THE OUTER SURFACELIPOPROTEIN-A GENE OF BORRELIA-BURGDORFERI IS INDEPENDENT OF AN EUKARYOTIC PROMOTER

Plasmid DNA encoding the outer surface lipoprotein A (OspA) of Borreli a burgdorferi under the control of either strong eukaryotic/viral or i ts own bacterial promoter was injected intramuscularly (m. tibialis an terior) or intradermally into BALB/c and AKR/N mice. OspA-specific ant ibodies and OspA-reactive T helper 1 cells (Th1) were induced only wit h those plasmids containing the ospA structural gene including its own regulatory control region immediately upstream. In the absence of the ospA promoter, no or only marginal immune responses to OspA were obta ined, even when strong eukaryotic promoter/enhancer elements were pres ent. Together with the finding that the ospA promoter is active in a m ouse B-lymphoma line, the data suggest that spirochetes are able to ex press at least part of their genes in the mammalian environment. Mice previously vaccinated with the relevant ospA plasmid DNA were protecte d against subsequent experimental challenge with a virulent strain of B. burgdorferi, as measured by the appearance of antibodies to a promi nent protective epitope (LA-2) and the failure to re-isolate spirochet es from ear biopsies. In addition, C.B-17 severe-combined immunodefici ent mice could be protected against infection by passive transfer of i mmune sera from ospA plasmid DNA-inoculated normal mice. Protective LA -2-related antibody titers obtained after repeated immunization persis ted for 200 days and longer. This simple procedure of immunization usi ng plasmid DNA consisting of a prokaryotic gene under the control of i ts own promoter holds great promise for the development of alternative subunit vaccines against bacterial infections, including Lyme disease . In addition, the availability of this novel prokaryotic promoter ele ment now allows the study of the basis for the differential expression of bacterial genes in prokaryotic and eukaryotic environments.