Studies on the Nature of Oncofetal Antigen Expressed on MCA-Induced Sarcoma Cells of Rats

Oncofetal antigen(s) was found to be expressed on the surface of MCA-induced sarcoma cells. The nature, especially the immunogenicity was investigated and the following results were obtained. (1) Anti-embryo sera (AES) which were cross-reactive between tumor and fetal cells were obtained by immunizing rats with syngeneic fetal cells of mid gestation. (2) Immunofluorescence studies and complement dependent cytotoxicity test revealed that AES reacted with MCA-induced tumor cells (KMT-17, KMT-50) and fetal cells of the 16th day, but did not react with fetal cells of the 10th day and normal adult thymus cells. By the absorption test, it was demonstrated that KMT-17 and KMT-50 cells had the same absorptive capability against AES. (3) The same studies with multiparous sera (MPS) also revealed that MPS reacted with tumor cells and its reactivity tended to increase according to the frequencies of pregnancy. The activity of absorption against MPS was high with fetus of the 16th day but weak with the 13th and the 14th day. No activity was seen with placenta of the 14th and the 16th day. (4) Some normal sera of adult rats were cytotoxic against syngeneic tumor cells but no positive finding was obtained by indirect immunofluorescence using FITC-conjugated anti IgG serum. (5) Induction of tumor transplantation resistance failed in rats immunized with syngeneic fetal tissues. From these results, it is confirmed that oncofetal antigen(s) is expressed in most of chemicaly induced tumors and that immunization with syngeneic fetus is able to induce humoral antibody which cross-reacts with tumors and fetus, but no strong resistance against tumor, such as rejection of tumor, is induced