Tumor vaccines: from gene therapy to dendritic cells--the emerging frontier.

Gene-modified tumor cells have been employed in a vaccination setting to trigger therapeutic antitumor immunity against metastatic renal cell carcinoma. Recent studies suggest that dendritic cells may be even more potent, because these cells can efficiently present tumor antigens to effector T cells, thereby circumventing the poor antigen-presenting properties of tumor cells. Proof of concept studies using antigen-loaded dendritic cells have been performed, establishing clear evidence of vaccine safety and bioactivity by stimulating immunologic and even clinical responses in cancer patients. Nevertheless, key aspects of such vaccination remain undefined. The critical challenge remains to understand fully the mechanisms of action and to further optimize dendritic cell vaccines to produce effective, durable, and, ultimately, therapeutic antitumor responses