The role of immunological factors in the treatment of cancer.

Evidence has accumulated in the last 15 years that many experimentally-induced tumours in animals carry a tumour-specific transplantation-type antigen (TSTA) in their plasma membrane and that the tumour-bearing host responds to the TSTAs with the production of antibodies and cytotoxic mononuclear cells. In man the situation is not yet clear but there are indications that a similar situation may apply in many human malignancies. These findings have led to a resurgence in interest in the role of immunotherapy in the treatment of malignant disease, but as yet there is no clear evidence from properly controlled clinical trials that immunotherapy is the treatment of choice for any tumour. At present clinical immunotherapy constitutes a field for careful investigation but it cannot be considered a proven modality of treatment. At present its use must be confined to controlled studies in which benefit or possible harm can be determined. When giving immunotherapy it is necessary to monitor carefully the specific immune reaction of the host against the tumour. Further progress in immunotherapy requires a better understanding of why tumour cells succeed in vivo to escape destruction by the immune responses of the host. This review summarizes the current state of knowledge concerning the nature of TSTAs, the effect of the immune response to TSTAs on metastatic spread and the mechanisms of escape with special reference to the role which circulating soluble TSTA plays in 'neutralizing' the action of cytotoxic cells and antibodies. It is stressed that there is no support for the hypothesis of a 'blocking antibody'. Finally the different types of immunotherapy which have been developed in animal systems are described and possible clinical applications are discussed.