The in vitro cytotoxic action of patients' lymphocytes against colon carcinoma cells was evaluated following incubation of the lymphocytes with papain‐solubilized tumour‐membrane preparations. Soluble extracts of pooled colon carcinomas 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 is interpreted as supporting the concept that cellular immunity against tumours in vivo may be inhibited by circulating antigen.

Soluble tumor antigens can inhibit lymphocyte reactivity, potentially impairing cellular immunity against tumors in vivo.

Inhibition of lymphocyte cytotoxicity for human colon carcinoma by treatment with solubilized tumour membrane fractions

Key Takeaway: Soluble tumor antigens can inhibit lymphocyte reactivity, potentially impairing cellular immunity against tumors in vivo.