Dendritic cells in cancer immunotherapy

Antigen presentation is a critical regulatory element for the induction of cellular immune responses. Thus, one of the principal current goals of tumor immunotherapy is to control and enhance tumor antigen presentation. In this respect, dendritic cells (DC) are now being widely investigated as immunotherapeutic agents for the treatment of disseminated malignancies. At present, numerous ways to employ DCs for tumor immunotherapy are being tested, ranging from direct in situ expansion and activation of DCs to adoptive transfer of ex vivo generated DCs, and numerous techniques have been designed to optimize DC activation, tumor antigen delivery to DCs, and induction of tumor-specific, as well as helper immune responses, in vivo. However, the results of recent preclinical studies and the diversity of the clinical phase I trials that are currently underway indicate that little is still known about the exact mechanisms by which DCs modulate tumor immunity and pose the concern that premature clinical trials might not yield the desired results and might be harmful to, rather than promote, the concept of DC-based tumor immunotherapy. This review summarizes some of the current approaches to induce tumor immunity by DC-based vaccination and discusses their advantages and concerns.