Expression of the gene coding for a human mucin in mouse mammary tumor cells can affect their tumorigenicity

The human epithelial mucin which is the product of the MUC1 gene is expressed by many carcinomas, including those of breast, ovary, colon, and lung. The core protein is aberrantly glycosylated in the tumors resulting in the exposure or appearance of novel epitopes. To examine the possibility of using the MUC1 gene and its products in active immunization against breast and other carcinomas, we have developed a syngeneic mouse model, by transfecting the gene into the mouse mammary epithelial tumor cell 410.4. An 8.3-kilobase EcoRI fragment of the gene was transfected using the expression vector pEMSV scribe alpha 2. Transcripts of the correct size, initiating from the transcriptional start site seen in human cells, were observed in the transfectants. The mucin was expressed in the cytoplasm and in the membrane, and the glycosylation pattern appeared to be similar to that seen in human tumor cells, since the core protein epitopes recognized by antibodies HMFG-1, HMFG-2, and SM-3 were exposed. The 410.4 transfectants expressing the human mucin showed a reduction in tumor incidence at low inocula and a delay in tumor growth at higher inocula. Pretreatment with 10(4) transfected cells could inhibit the development of tumors from a subsequent inoculum of 10(6) transfectants, but had no effect on the tumor development of the untransfected 410.4 cells. Our results suggest that the human mucin expressed by the 410.4 cells may mobilize an immune response which inhibits tumor development. They also indicate that the mouse model will be useful for evaluation of efficacy of immunogens based on the MUC1 gene and its product.