In vitro phenotypic and functional characterization of epithelial progenitors present in the normal adult human breast

The developmental relationships between the different epithelial cell lineages in the normal human mammary gland are not well defined. To characterize the progenitor activity of freshly isolated human breast epithelial cells (HBEC), 2- and 3-dimensional culture systems were developed that optimized their clonal growth, and fluorescence-activated cell sorting was used to characterize the progenitors of the different types of colonies obtained. These studies identified one type of progenitor cell that generates colonies of varying sizes with an alveolar-like morphology and generally contains cells expressing markers of luminal cells; i.e.: the apical glycoprotein MUC1 and epithelial cell adhesion molecule. They also express relatively high levels of erbB-2, retain rhodamine 123, express variable levels of the epidermal growth factor receptor and CD44v6 and express low levels of the ct6 integrin, the histo-blood group antigen type 2 and the common acute lymphoblastic leukemia antigen. A second type of progenitor identified is one that generates colonies composed of cells that express myoepithelial lineage markers and variable numbers of cells that express luminal cell markers. These progenitors generate colonies in collagen gels that have a branching duct-like morphology. These bipotent progenitors express the epidermal growth factor receptor, erbB-2, epithelial cell adhesion molecule, the α6 integrin, the common acute lymphoblastic leukemia antigen, variable levels of MUC1, and retain low levels of rhodamine 123. Single cell cultures verified the clonal origin of both types of colonies. Epidermal growth factor at 10 ng/ml within the breast epithelial colony assay promoted the survival of cells enriched for luminal cell progenitors, as well as the migration of keratin 14 expressing cells in a manner that could be interpreted as ductal elongation. Serial passaging of highly enriched populations of bipotent progenitors indicated that some cells produced in the mixed and pure myoepithelial marker+ colonies can generate colonies composed only of cells expressing myoepithelial characteristics, but not luminal characteristics. These latter results suggest that the culture conditions used compromise both the self-renewal of human breast epithelial stem cells and their differentiation into the luminal lineage.Medicine, Faculty ofGraduat