Strategies to improve dendritic cell-based immunotherapy against cancer.

Dendritic cells (DCs) play a pivotal role in T cell-mediated immunity and have been shown to induce strong antitumor immune responses in vitro and in vivo. Various approaches utilizing different vaccine cell formats, cell numbers, vaccination schedule, site of vaccination and maturation stages of DCs were investigated worldwide. While clinical trials have demonstrated the safety of such strategies, the clinical outcome was less than expected in most cases. This is due to in part host immunodeficiency imposed by tumors and immunoediting of tumor cells. To overcome these obstacles, new approaches to improve DC-mediated immunotherapeutic strategies are under investigation. First, functional enhancement of monocyte-derived DCs can be generated with using flt3-ligand (FL). Second, diverse antigenic determinants from heat shock-treated tumor cells may improve the immunogenicity of DC-based vaccines. Third, inclusion of ex vivo expanded NK/NKT cells in DC-based vaccines could be beneficial since the bidirectional interaction of these two cell types are known to enhance NK cell effector function and to induce DC maturation. Application of these approaches may induce a broadened antitumor immune response and thereby promote the elimination of tumor antigen-negative variant clones that had escaped immunosurveillance or undergone immunoediting. We are currently examining the feasibility of these immunotherapeutic approaches using a murine pancreatic cancer model system.