Immunologically-mediated restraint of latent tumour metastases

Abstract

DIFFERENT grafted sarcomas, all originally from chemically-induced autochthonous tumours, vary widely in their capacity to form metastases, as determined by the incidence of secondaries which appear in the lung and lymph nodes in the months following surgical removal of the ‘primary’ transplant from syngeneic rats¹. Tumours which do not form metastases readily in normal animals can be induced to do so by grafting into syngeneic rats depleted of T lymphocytes by procedures which do not compromise the bone marrow¹. We concluded that specific immune processes requiring the participation of T lymphocytes contributed to the control of metastatic spread—possibly by reducing the number of tumour cells released because there is an inverse relationship between the number of macrophages within the tumour and metastasis^1,2. In addition, circulating tumour cells may be destroyed immunologically and an immunologically-specific factor that acted against intravenously-injected sarcoma cells was demonstrated in the serum and lymph of tumour-bearing rats^3,4.