Increasing the efficacy of tumor cell vaccines by enhancing cross priming

Cancer immunotherapy has been attempted for more than a century, and investment has intensified in the last 20 years. The complexity of the immune system is exemplified by the myriad of immunotherapeutic approaches under investigation. While anti-tumor immunity has been achieved experimentally with multiple effector cells and molecules, particular promise is shown for harnessing the CD8 T cell response. Tumor cell-based vaccines have been employed in hundreds of clinical trials to date and offer several advantages over subunit and peptide vaccines. However, tumor cell-based vaccines, often aimed at cross priming tumor-reactive CD8 T cells, have shown modest success in clinical trials. Here we review the mechanisms of cross priming and discuss strategies to increase the efficacy of tumor cell-based vaccines. A synthesis of recent findings on tissue culture conditions, cell death, and dendritic cell activation reveals promising new avenues for clinical investigation.