The hypothesis at the root of this study is that a healthy immune system will recognise a cell when it becomes malignant and destroy it thus preventing the growth and spread of cancer. Therefore cancer can only occur when this process goes wrong. If we could find out how the immune system interacts with cancer cells and what abnormalities are occurring in this interaction we may then be able to develop strategies to improve the immune response to cancer. This would represent a potentially novel form of treatment and would be expected to improve the response to vaccination therapies that are already undergoing clinical trials in some cancers. This study will look at T cell function in blood samples from patients with leukaemia and lymphoma and then go on to look at mechanisms of improving that function in a mouse model. Finally, attempts will be made to generate a patient tumour-specific T cell response in vitro using the information gained in the earlier parts of the study. This research will be carried out by a clinical research fellow in the Institute of Cancer, Charterhouse Square, London.