Effect of Embryonic Tissue Immunization on Chemically Induced Gastrointestinal Tumors in Rats. I. Can Embryonic Antigens Act as Rejection Antigens? 1,2

ABSTRACT-Inbred WF rats were inoculated with crude suspen-sions prepared from liver and gut tissue of 12- to 15-day fetuses of the same strain. Rats previously unsensitized to syngeneic embry-onic tissue were inoculated with fetal material sc three times dur-ing exposure to l,2-dimethylhydrazine dihydrochloride (OM H), a gastrointestinal (GI) carcinogen in rodents. Properly timed immu-nization inhibited the development, growth, and metastasis of pri-mary GI tumors. This effect was observed in both sexes; however, it was more pronounced in male rats. Nine WF rats with OMH-in-duced carcinoma of the GI tract were inoculated sc with synge-neic fetal tissue. Of 9 rats, 7 rejected the embryonal tissue implants, which thus demonstrated the presence of a concomitant immune response to embryonic antigen(s). Two rats in which fetal tissue grew out to palpable nodules had multiple GI tumors with metastasis and extra-GI tumors, i.e., a massive tumor load. Te