Polarized Dendritic Cells for Tumor Immunotherapy

An elusive objective for tumor immunologists has been the development of an effective tumor vaccine capable of inducing potent immune responses to eliminate established tumors and induce long-term protective antitumor immunity. Dendritic cells (DCs) are potent inducers of immunity and represent a promising tool for the purpose of immune-based tumor therapies. However, DC-based vaccines have enjoyed only limited success in clinical trials, probably due to the use of immature/intermediate mature DCs that maintain tolerance during the steady state, or to the use of non-polarized DCs which lack the proper cytokine production that favors cellular immune responses needed to eliminate established tumors. The failure of past tumor vaccines demonstrates a need to examine and enhance immunization strategies on multiple levels. The underlying hypothesis for these studies was that combining a DC1 polarization signal with an effective antigen-loading strategy will result in enhanced tumor immunotherapy. Our first aim was to compare cytosolic and membrane-bound antigen presentation of tumor-derived proteins by DCs following three different antigen-loading strategies; coculture of DCs and tumor cells, feeding DCs with tumor lysate, and fusion of DCs and tumor cells. We demonstrated that both DC-tumor coculture and fusion result in a higher level of tumor-derived peptide presentation compared to feeding DCs with tumor lysate. Our second aim was to develop a murine DC1 polarization model to evaluate DC1-based tumor immunotherapy. Herein, we described the synergistic affect of TLR3 and TLR9 ligation on IL-12p70 production by murine DCs, characterizing the timing and exhaustion of IL-12p70 production. Furthermore, we examined the ability of polarized DCs to stimulate T cell proliferation and cytokine secretion in response to a model antigen in vitro. For our third aim we examined the capacity of DC1s to stimulate immune responses to a model antigen as well as native tumor antigens in vivo and tested the therapeutic effect of tumor-loaded DC1 vaccines. These studies demonstrate the ability of antigen-loaded polarized DCs to induce strong Th1-mediated anti-tumor immunity characterized by tumor infiltrating CD4+ T cells and macrophages, but not CD8+ T cells, resulting in tumor growth inhibition