Nonimmunogenic sarcomas induced by 3-methylcholanthrene treatment of murine fibroblasts in diffusion chambers.

A 30-mug dose of 3-methylcholanthrene (MCA) was applied for 1 week to normal BALB/c fibroblasts in cell-impermeable diffusion chambers (DC) in the peritoneal cavities of BALB/c micemtwo groups of DC cultures, in which the carcinogen was given during weeks 1 and 5 of cultivation, respectively, were compared for the frequency of malignant transformation and for the immunogenicity of the resulting neoplasms. The cells from each DC were transplanted sc into immunodepressed semisyngeneic mice for assay of their tumorigenicity. Although tumor yield was similar in the 2 groups (25 and 22%, respectively), there was clear difference in immunogenicity; 10 of 16 sarcomas from fibroblasts treated during week 1 of culture were nonimmunogenic, whereas 8 of 9 tumors from the older cultures were immunogenic (P less than 0.02). A kinetic study of normal fibroblasts in DC revealed that cells proliferated rapidly, with a peak at day 4 after seeding, then grew progressively more slowly and ceased to replicate between 14 and 28 days of culture. Thus there was a notable difference at the moment of MCA application in the growth phase of the target cell population of the first as compared with the fifth week of culture, possible related to the different expression of tumor-associated transplantation antigens in the resulting neoplasms.