Both humoral and cellular immune responses can be induced by inoculating naked plasmid DNA encoding a foreign antigen (Ag). This technology, genetic vaccination, has been used to induce immune responses against infectious pathogens, including HIV-1. In those experiments CMV promoter was used as a transcription regulatory unit, thus, leading to the expression of the gene products (i.e., Ag) in virtually all cell types. We now propose to develop a new class of vaccines against HIV-1, by directing the expression of gp120 gene to Langerhans cells (LC), which possess all phenotypic and functional properties required for presenting foreign Ag to immunologically naive T cells. In fact, LC are known to play a critical role in initiating immune responses against a wide variety of Ag, including infectious pathogens. Thus, we hypothesize that the efficacy of anti-HIV-1 vaccines can be improved significantly by targeting gene expression to LC. We hypothesize further that such a vaccine will activate predominantly the MHC class I-dependent arm of immunity (e.g., CD8+ T cell-mediated cytotoxicity), because the Ag is produced endogenously within LC. We have also isolated a unique promoter, termed dectin-2 promoter and validated its capacity to direct gene expression to LC in animal levels. We have also observed that an in vitro transfected LC line, when injected s.c. in mice, induces a wide array of immune responses (including cytotoxicity). Thus, we are now in a unique position to determine whether this new vaccine strategy is potentially applicable to the development of a safe and effective vaccine for HIV-1.
Our specific aims are: 1) To study the expression of gp120 mRNA and protein after inoculation of LC-targeted genetic vaccine. We will deliver, by gene gun, the pDec2-gp120 plasmid (containing the coding sequence of gp120 under the control of dectin-2 promoter) into abdominal skin of BALB/c mice and determine the amount, cellular and tissue distributions, and time-course of gp120 mRNA and protein expression. 2) To characterize gp120-specific immune responses that are induced by LC-targeted genetic vaccine. Mice vaccinated with pDec2-gp120 will be examined for the generation of humoral and T cell-mediated immune responses and for potential adverse effects. 3) To establish strategies to improve the efficacy of LC-targeted genetic vaccine. The strategies to be tested include: a) to combine with keratinocyte-targeted genetic vaccine. in which the tPA-gp120 gene (encoding a soluble form of gp120) is expressed under the control of keratin-14 promoter, for activating the class II-dependent arm, b) to increase the transcriptional activity of dectin-2 promoter, c) to co-deliver IL-12 or IL-4 gene in an LC-targeted manner for selective activation of Th1 or Th2 subset, and d) to deliver GM-CSF gene in a keratinocyte-targeted manner to assist the maturation of LC. The proposed experiments will, ultimately, lead to the establishment of unique vaccine strategies to induce maximal protection against HIV-1 infection, by controlling the magnitude, the class (MHC class I versus class II), and the type (Th1 versus Th2) of immune responses.
