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AAV-Based Plasmacytoid Dendritic Cell Cancer Vaccine

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The objective is to develop a vaccine approach targeting carcinoembryonic antigen (CEA), an oncofetal antigen expressed by many common cancers. Although CEA vaccines have demonstrated promise in clinical trials, the induction of cellular immune responses has been inconsistent, and there has been little evidence of antitumor activity. Dendritic cells (DC) are considered the most potent antigen-presenting cells for initiating cellular immunity. There is experimental evidence suggesting that the plasmacytoid DC subpopulation (pDC) plays an important role in regulating the T-helper (Th) polarization of the immune response. The central hypothesis is that failure of CEA vaccine strategies to elicit therapeutic antitumor immunity is the result of suboptimal activation of pDC to promote Th1/cytolytic T lymphocyte responses. High levels of antigen promote pDC Th1 polarization. The vaccine approach will exploit the natural and physical properties of recombinant adeno-associated virus (rAAV) vectors to stably express high levels of CEA in the absence of competing viral vector antigens. Signaling through specific Toll-like receptors (TLR) is involved in pDC activation. The vaccine approach will also exploit potentially synergistic interactions between synthetic TLR agonists in promoting pDC Th1 polarization. Preclinical studies of this AAV-CEA immunogen-TLR agonist adjuvant approach in mouse tumor models are proposed. The specific aims are to: 1) correlate the dynamics of tumor antigen expression by rAAV-CEA vectors with pDC activation and anti-tumor immunity;2) characterize the dynamics of pDC Th1 polarization by TLR agonists;and 3) determine the role of pDC activation in anti-tumor immunity elicited by effective rAAV-CEA and TLR agonist combination vaccines. The ability of this vaccine approach to elicit CEA-specific, antitumor, cellular immunity and the mechanisms involved will be evaluated. Studies will include novel rAAV-CEA constructs and novel quantitative, real-time polymerase chain reaction assessment of the effects of rAAV-CEA and TRL agonists on pDC activation at the vaccine administration site, in regional lymph nodes, and systemically. Studies will also include the use of transgenic mice that express CEA. The results of this project may lead to an effective vaccine for the many cancers that express CEA, establish a vaccine approach that can be applied to other tumor-associated antigens, and help improve the understanding of the role of pDC in vaccine responses.

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