Properties of mouse mammary epithelial cell lines characterized by in vivo transplantation and in vitro immunocytochemical methods

Immunocytochemical and in vivo transplantation methods were used to study the characteristics of a series of newly developed mammary epithelial cell lines. These mouse mammary cell lines were derived from mid-pregnant primiparous BALB/c female mice and were routinely grown in Dulbecco's modified Eagle medium supplemented with 1% fetal bovine serum, insulin, transferrin, epidermal growth factor, and selenite. Of the 6 cell lines, 1 cell line, COMMA-D, produced normal and preneoplastic mammary outgrowths when it was transplanted into mammary fat pads of syngeneic mice. One cell line, MOD, produced only mammary adenocarcinomas. The other 4 cell lines, COMMA-F, COMMA-T, MOMA-1, and MOMA-2, produced neither normal nor neoplastic outgrowths. Immunocytochemical staining with polyclonal antibodies to keratin and vimentin intermediate filament proteins revealed that 5 of the 6 cell lines were epithelial. The sixth cell line, MOMA-2, was apparently of fibroblastic origin. The COMMA-D cell line was unique compared to the other cell lines with respect to several characteristics. The cell line was morphologically heterogeneous as determined by phase-contrast microscopy, cytologically heterogeneous as determined by immunocytochemical staining, and heterogeneous with respect to DNA content. Finally, the full morphogenic potential of COMMA-D included not only normal mammary ductal and preneoplastic mammary alveolar outgrowthS but also adenocarcinomas and fibrosarcomas. The expression of this morphogenic potential upon transplantation in vivo was drastically diminished after passage 14. The significance of the cellular heterogeneity with respect to expression of mammary-specific morphogenesis is not understood at this time; however, conceivably, the observed heterogeneity reflects an essential requirement for morphogenesis in vivo. The transplantation and immunocytochemical characteristics provide the descriptive basis for further studies on these cell lines to determine the cell lineages involved in morphogenesis and preneoplastic transformation in vivo.