Significance of tumour associated antigens on human colonic carcinomata.

A microcytotoxicity assay was used to detect cell mediated immunity against colon and rectum carcinoma cells in vitro. Lymphocytes from 62% of colon carcinoma patients were cytotoxic for the cells, but no cross reactions between colon carcinomata and tumours of other types were observed. The effect of papain solubilized tumour membrane extracts was evaluated by testing lymphocytes for reactivity following preincubation with the extracts. Soluble preparations of pooled colon carcinomata inhibited cytotoxicity by sensitized lymphocytes, but similar extracts of normal colon or melanoma had no inhibitory effect. The results suggest that soluble tumour antigen may play a role in abolishing lymphocyte reactivity, and this supports the concept that cellular immunity against tumours in may be inhibited by circulating antigen.