A retrovirus-producing transformed mouse cell line derived from a human breast adenocarcinoma transplanted in a nude mouse.

A transplantable tumor was established in NIH/Swiss/Nu mice from tissue derived from a human breast adenocarcinoma metastatic to the brain. Cultivation of dispersed cells from the third transplant generation of the tumor produced a rapidly growing, high-density culture of fibroblastlike cells. Chromosome and isozyme assays showed these cells to be of mouse origin. The cells behaved as an established line from initial culture. Cells of the tissue culture line, designated NM-1, produced rapidly growing fibrohistiocytomas in nude mice. Electron microscopy revealed that the cells produced large numbers of type C virus particles. Serological, biochemical, and infectivity assays indicated that the retrovirus produced by NM-1 cells is an ecotropic, infective, murine retrovirus antigenically related to, but distinguishable from, Gross and Moloney viruses. The virus did not transform mouse fibroblasts. The data support the conclusion that mouse stromal cells within the transplanted human tumor had undergone malignant transformation and induction to virus replication. The role of the virus in the malignant transformation remains to be clarified.