Advances in our understanding of human dendritic cells have resolved many important unknowns about the onset of innate and adaptive immunity and how dendritic cells could control these responses against cancer. Tumor antigens are poor immunogens by themselves, because they are either self or altered-self antigens. Hence the bar to overcoming tolerance toward cancer-self antigens, while attainable, is quite high. Dendritic cells can circumvent many of these barriers by presenting tumor antigens in association with all the other requisite molecules that elicit immune reactivity. Countervailing suppressor mechanisms involving indoleamine 2,3-dioxygenase (IDO) and mediated by regulatory lymphocytes must also be addressed, however. Genetic strategies offer advantages in coupling tumor antigens to dendritic cells. Multiple epitopes can be expressed, tailored to a variety of MHC alleles. Antigen-presentation is sustained over time, cytokines and other costimulatory molecules can be manipulated, and immune suppressor mechanisms can be altered. We will address these areas in a series of testable hypotheses using human Langerhans-type dendritic cells, genetically modified by retroviral or plasmid vectors to express melanoma antigens and other proteins of interest. We will introduce IL-12p70 by genetic alteration of Langerhans cells to stimulate and harness the adjuvant properties of natural killer (NK) cells. Novel approaches will also be tested for the sustained activation of Langerhans cells and improved cross-presentation of opsonized tumor antigen through transduced expression of the activating Fc-gamma Rll, CD32a. This will be tested in combination with gene-based IL-12p70-Fc fusion constructs to assess increased cytokine adjuvanticity. Genetic methods that interfere with suppressor mechanisms involving IDO and mediated by regulatory lymphocytes will be studied. The results of these studies should lead to improved, coordinate stimulation of innate and adaptive immunity against cancer by a single, genetically optimized dendritic cell. (Relevance to public health/Lay summary: Genetic alterations of specialized Langerhans-type dendritic cells will be tested and improved to increase immunity against cancer, using melanoma as the model. These approaches should find their greatest application in treating minimal residual disease after primary therapy.)
