Principles of cancer treatment by immunotherapy

The concept of immunotherapy as a modality to treat cancer was recognized more than a hundred years ago. High dose interleukin-2 was one of the first agents to demonstrate that the host's immune system can be harnessed to treat even advanced malignancy as was shown in a subset of patients with renal cancer and melanoma. Many tumours are immunogenic and provoke a host immune response, but this is normally not sufficient to overcome host tolerance. Further it is the lymphocyte that has a central role in the cellular response that results in transplant and tumour rejection and the direct lytic action on tumour cells that are referred to most often in discussions about immunotherapy. For decades now, researchers have tried various methods to enhance host immunological responses such as the use of non-specific immunotherapeutic cytokines, tumour vaccines, adoptive immunotherapy and the use of monoclonal antibodies against a wide variety of molecules such as check point blockade molecules that target cytotoxic lymphocyte antigen 4-CTLA4 and against those involved in signal transduction, angiogenesis and immune surveillance. This article concentrates on the applications of immunotherapy in solid tumours, though it has immense value in haematological cancers.