Inhibition of cell-mediated cytotoxicity to chemically induced rat tumours by soluble tumour and embryo cell extracts.

When lymph-node and spleen cells from rats bearing or immunized against aminoazo dye-induced rat hepatomas or 3-methylcholanthrene-induced rat sarcomas were pretreated with 3 M KCl extracts of these tumors, their cytotoxicity for cultured cells from the corresponding tumour was specificially inhibited. In cross-test combinations of target tumour and tumour-bearer effector-cell donor, tumour extracts only inhibited cytotoxic responses when they were derived from the tumour homologous to the target-cell and not when the extract was from the tumour borne by the effector-cell donor. One component of the tumour-bearer cytotoxic response was shown to be directed against tumour-associated embryonic antigens since soluble extracts of embryos or tumour extracts containing embryonic antigens inhibited tumour-bearer cell-mediated cytotoxicity in both specific and cross-test combinations of target tumour and effector cells. These findings are discussed in relation to tumour antigen expression and the immune responses that these tumour-associated antigens may evoke in tumour-bearing rats.