Viral vectors in cancer immunotherapy: Which vector for which strategy?

Gene therapy involves the transfer of genetic information to a target cell to facilitate the production of therapeutic proteins and is now a realistic prospect as a cancer treatment. Gene transfer may be achieved through the use of both viral and non-viral delivery methods and the role of this method in the gene therapy of cancer has been demonstrated. Viruses represent an attractive vehicle for cancer gene therapy due to their high efficiency of gene delivery. Many viruses can mediate long term gene expression, while some are also capable of infecting both dividing and non-dividing cells. Given the broadly differing capabilities of various viral vectors, it is imperative that the functionality of the virus meets the requirements of the specific treatment. A number of immunogene therapy strategies have been undertaken, utilising a range of viral vectors, and studies carried out in animal models and patients have demonstrated the therapeutic potential of viral vectors to carry genes to cancer cells and induce anti-tumour immune responses. This review critically discusses the advances in the viral vector mediated delivery of immunostimulatory molecules directly to tumour cells, the use of viral vectors to modify tumour cells, the creation of whole cell vaccines and the direct delivery of tumour antigens in animal models-and clinical trials, specifically in the context of the suitability of vector types for specific strategies.