Regulation of transgene expression in genetic immunization

The use of mammalian gene expression vectors has become increasingly important for genetic immunization and gene therapy as well as basic research. Essential for the success of these vectors in genetic immunization is the proper choice of a promoter linked to the antigen of interest. Many genetic immunization vectors use promoter elements from pathogenic viruses including SV40 and CMV. Lymphokines produced by the immune response to proteins expressed by these vectors could inhibit further transcription initiation by viral promoters. Our objective was to determine the effect of IFN-g on transgene expression driven by viral SV40 or CMV promoter/enhancer and the mammalian promoter/enhancer for the major histocompatibility complex class I (MHC I) gene. We transfected the luciferase gene driven by these three promoters into 14 cell lines of many tissues and several species. Luciferase assays of transfected cells untreated or treated with IFN-g indicated that although the viral promoters could drive luciferase production in all cell lines tested to higher or lower levels than the MHC I promoter, treatment with IFN-g inhibited transgene expression in most of the cell lines and amplification of the MHC I promoter-driven transgene expression in all cell lines. These data indicate that the SV40 and CMV promoter/enhancers may not be a suitable choice for gene delivery especially for genetic immunization or cancer cytokine gene therapy. The MHC I promoter/enhancer, on the other hand, may be an ideal transgene promoter for applications involving the immune system

The role of T cell subsets and cytokines in the regulation of intracellular bacterial infection

Cellular immune responses are a critical part of the host's defense against intracellular bacterial infections. Immunity to Brucella abortus crucially depends on antigen-specific T cell-mediated activation of macrophages, which are the major effectors of cell-mediated killing of this organism. T lymphocytes that proliferate in response to B. abortus were characterized for phenotype and cytokine activity. Human, murine, and bovine T lymphocytes exhibited a type 1 cytokine profile, suggesting an analogous immune response in these different hosts. In vivo protection afforded by a particular cell type is dependent on the antigen presented and the mechanism of antigen presentation. Studies using MHC class I and class II knockout mice infected with B. abortus have demonstrated that protective immunity to brucellosis is especially dependent on CD8+ T cells. To target MHC class I presentation we transfected ex vivo a murine macrophage cell line with B. abortus genes and adoptively transferred them to BALB/c mice. These transgenic macrophage clones induced partial protection in mice against experimental brucellosis. Knowing the cells required for protection, vaccines can be designed to activate the protective T cell subset. Lastly, as a new strategy for priming a specific class I-restricted T cell response in vivo, we used genetic immunization by particle bombardment-mediated gene transfer.