Targeted Tumor Immunotherapy: Are Vaccines the Future of Cancer Treatment?

Recent advances in cancer immunotherapy have significantly improved patient life expectancy, either prophylactically or by active treatment of existing malignancies. Effective immune response by host innate and adaptive immune systems can be generated by targeting critical elements of these immune systems which include antigenpresenting cells (APC), toll-like receptors (TLR), and natural killer (NK) cells, as well as specific tumor sites which display tumor specific tumor-associated antigens. One of the major hurdles in the development of therapeutic cancer vaccines arises from the various immunosuppressive mechanisms powered by tumor cells including down-regulation of immunoresponsive antigens and cytokines. Significant strides have been made in the last decade in the identification of specific tumor receptors and tumor-specific tissue-associated antigens. Gaining a deeper level of understanding of the mechanisms by which various effectors meditate immune response and the interplay between various components of innate and adaptive immune systems has spurred research in this field. This review will discuss the innovative approaches for design and active targeted delivery of vaccines to cancers and solid tumors. Delivery systems investigated for this purpose predominantly fall into two main categories; namely biological and physical systems. Biological vaccine delivery systems include bacterial ghosts, plasmid DNA, modified dendritic cells (DCs), whole cells and tumor cell lysates, and modified viral vectors etc. Physical delivery systems include nanoparticulate and nanocolloidal systems as liposomes, polymerosomes, dendrimers, etc. The efficiency of targeting by both types of systems can be further improved by surface modification by antibodies and ligands to effectively target the appropriate tumor target.