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Summary.-An apparently unique circulating common oncofoetal protein has been identified in rat small-bowel, colonic and pancreatic adenocarcinomas. The tumours were induced by ionizing radiation (small bowel), an alkyl hydrocarbon, 1,2-dimethylhydrazine (colon) and a polyaromatic hydrocarbon, 7,12-dimethylbenz[a]anthracene (pancreas). The oncofoetal protein was identified by the use of specific xenogenic antitumour rabbit sera generated to the X-ray-induced neoplasm. In addition, the foetal protein was also found always to occur in the liver and lungs of those animals bearing the chemically induced tumours as well as in their serum. These results suggest the existence of a close relationship at the molecular level in the tumorigenic processes, even though induction is by apparently different mechanisms, for cancers arising in tissue or common embryonic origin,

Cell-mediated immunity (CMI) directed towards rat fetal cells was evaluated in Fischer F344 young inbred male rats having asbestos-induced peritoneal mesothelioma. The tumors were induced by exposure to Canadian chrysotile B fibers and the CMI delineated by the injury and destruction brought about to 6- to 10-day-old primary fetal cell cultures by the so-called educated peripheral blood lymphoid-cells (PBLC) obtained from the cancer-bearing rats. A significant cytotoxicity was found to be expressed by the PBLCs, suggesting that during the development of mesothelioma, a cellular retrodifferentiation occurs, thereby educating the effectors to recognize a common determinant existing in both the tumor and fetal cells. Educated PBLCs were produced from rats having endodermal tissue cancers (adenocarcinomas of the small bowel, colon and pancreas) and were found to also be cytotoxic to the fetal cultures, yet no injury was apparently inflicted upon cultured mesothelioma target cells by these effectors. These results suggested that the tumor education was specific and that probably a unique and different fetal component was being recognized by the effector cells obtained from the rats with lesions arising either in the mesodermal or endodermal tissue. Further support for this concept was the failure of an antibody, specific to an oncofetal protein existing in endodermal lesions, to apparently recognize any common oncogenic proteins in the mesothelioma. Preliminary studies have also been accomplished which suggests the existence of natural killing immune responses existing to the mesothelioma target cells.(ABSTRACT TRUNCATED AT 250 WORDS)

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