Hypertonic salt extracts (3 M KCl) of x-irradiation-induced Holtzman rat small bowel adenocarcinomas blocked the in vitro destruction of allogeneic cultured cells of this malignancy by sensitized lymphoid cells obtained from tumor-bearing animals. The protective effects were mediated by a blocking action at both the effector and the target cell level. The extracts were separated into 50% ammonium sulfate soluble and insoluble fractions with the soluble fraction being more effective in blocking the cytotoxic responses through interaction with the lymphoid cells whereas the insoluble one had a greater effect upon tumor target cells. Associated with both fractions was the oncofetal glycoprotein previously identified with the cellular membrane of this x-ray-induced malignancy. Immunoglobulins were identified with the insoluble fraction; some were able to bind the oncofetal protein, thus classifying it as a fetal antigen. The protective effects of the soluble fraction and this neoantigen were found to be citric acid labile, whereas the effects due to the insoluble fraction were unchanged.
This work was supported in part by Contract NOI-CB-43891, awarded by the National Cancer Institute, Department of Health, Education and Welfare, by Grant IN-122, awarded by the American Cancer Society, through the University of Iowa, College of Medicine.