Quantification of regenerative potential in primary human mammary epithelial cells

We present an organoid regeneration assay in which freshly dissociated human mammary epithelial cells from healthy donors are grown in adherent/rigid or floating/compliant collagen I gels. In both conditions, luminal progenitors (CD49f+EpCAM+) form spheres, whereas basal cells (CD49fhiEpCAM-) generate branched ductal structures. However, in compliant but not rigid collagen gels, branching ducts form alveoli at their tips, express basal and luminal markers at correct positions and display contractility, which is required for alveologenesis. Thereby, branched structures generated in compliant collagen gels resemble terminal ductal-lobular units (TDLUs), the functional units of the mammary gland. Moreover, the membrane metallo-endopeptidase CD10 as an additional surface marker enriches for TDLU-formation and reveals the presence of stromal cells within the CD49fhiEpCAM- population. In summary, we describe a defined in vitro assay system to quantify cells with regenerative potential and systematically investigate their interaction with the physical environment at distinct steps of morphogenesis. Comparison of three cell populations derived from FACS-sorted primary human mammary epithelial cells: luminal progenitors, CD10+ basal cells and CD10- basal cells.