For many patients standard chemo- and/or radio-therapy treatments for cancer are not curative and are associated with significant side-effects. Using viruses to treat cancer is an example of the newer biological therapies being developed. Viruses can be modified to multiply in cancer cells at much higher rates than in healthy cells, producing a wave of infection that spreads through solid tumour deposits and destroys them (a process called oncolysis). To date there have been around 30 clinical trials using oncolytic adenoviruses in patients with cancer. While the side effects even with large doses of virus are fairly mild, the success rates have been variable. One of the limitations to viral therapy is the patient‘s immune system that quickly recognises the virus as foreign and starts to remove it from the tumour before it has had a chance to cause significant tumour-cell death. The project that I propose to undertake is to investigate the interactions between the host immune system and the oncolytic adenovirus. The ultimate aim is to develop a way of modifying the patient‘s immune response to minimise its detrimental effect on the virus thus enhancing the virus anti-tumour potency.