Antitumour antibodies induced by rat embryo cells and spontaneous mammary carcinoma cells treated with 3-methylcholanthrene.

It has previously been shown that rat embryo cells treated in vitro with 3-methylcholanthrene (MCA) elicit antibodies in syngeneic rats which react specifically against established MCA-induced sarcomas. To examine the possibility that clonal amplification of one or a few antigenic, preneoplastic clones is responsible for the previously observed specific antibody responses, MCA-treated rat embryo cells have been subjected to 150 Gy of gamma-irradiation before injection into host animals. The resulting antisera were screened for reactivity against a panel of established syngeneic tumours by membrane immunofluorescence and an isotopic antiglobulin test. A positive reaction was observed between an antiserum pool raised against gamma-irradiated MCA-treated cells and the cells of an immunogenic spontaneous mammary carcinoma. Antiserum to gamma-irradiated control (acetone-treated) cells was negative. Thus gamma-irradiation of carcinogen-treated cells before injection failed to abolish specific antibody responses in immunized rats. To investigate further the relationships between cell-carcinogen interaction, neoantigen induction and malignancy, the cells of a non-immunogenic, spontaneous mammary carcinoma were treated with MCA in vitro, and antisera against treated and untreated cells were tested against a panel of established tumours. A positive membrane-immunofluorescence reaction was obtained with an antiserum to MCA-treated cells, but not to untreated cells against an aminoazodye-induced hepatoma, indicating that the previously non-immunogenic mammary carcinoma cells had acquired new antigenic specificities as a consequence of carcinogen treatment.