Enrichment for breast cancer cells with stem/progenitor properties by differential adhesion

Cancer stem cells are commonly isolated by cell sorting for surface antigens that typify stem cells. This technique is very expensive, requiring advanced, high-speed sorters and high-quality antibodies, and yields are often low. Some stem cells can be isolated based on ability to exclude dyes, conferred by expression of membrane transporters, but this property is not universal. Mammary stem cells are known to down-regulate cell-cell junctions and exhibit mesenchymal behaviors in vitro. We predicted that such cells should be readily detachable from tissue-culture plastic and that this might serve as a basis for their isolation from differentiated cells. We found that immortalized or transformed mammary epithelial cells can indeed be resolved into trypsin-sensitive and trypsin-resistant populations. The former are mesenchymal in morphology and expression profile and are enriched in stem cell properties such as mammosphere-forming ability, drug resistance, and CD44 stem cell antigen relative to the trypsin-resistant population. The latter, in contrast, are cobblestone in morphology, epithelial in expression profile, and deficient in mammosphere formation. After several rounds of differential trypsinization, the trypsin-sensitive pool had 80-fold higher mammosphere-forming ability than the trypsin-resistant population and 20-fold higher than the starting population. This resolution compares favorably with other enrichment methods. Thus, for relatively differentiated epithelial cell types, differential adhesion may serve as an enrichment strategy to increase the stem cell pool for subsequent manipulations.