Host factors important in immune surveillance against tumours.

The nonspecific and specific arms of the immune response are described. The nonspecific components consist of three cell types - macrophages, natural killer and killer cells - and the specific components are antibody produced by B lymphocytes and regulatory and effector T lymphocytes. The evidence suggests that a surveillance system does operate, since at least some tumours are contained. Malignant lesions are more common in unselected autopsies and surgical biopsies of noncancer patients compared with the observed rate of clinical cases; and spontaneous cures of cancer do occur. There is general agreement that surveillance of all types of tumours by the specific components of the immune response does not occur; but there is direct evidence from some model systems and correlations from the incidence and class of tumours which arise in germ-free athymic mice, in immunosuppressed patients with transplants and in immunodeficient patients that the specific immune response, particularly by effector T cells, may control the expression of some tumours of lymphoreticular cells. Such surveillance may be superimposed on a more general system which is mediated by the nonspecific elements. One possible way of increasing the efficiency of the system would be to provide some of the soluble mediators of activated effector cells such as macrophages and T cells. Thus, administration of interferon has had some success, and there is a case for further purification of these and other lymphokines and monokines for administration to patients.