Amnion-derived mesenchymal stromal cells show a mesenchymal-epithelial phenotype in culture

The amnionic membrane is a rich source of multipotent mesenchymal stromal cells (hAMSC), which are readily available and show a potential use in regenerative medicine and tissue engineering. Before these cells can be applied clinically, careful characterization is necessary, especially as primary cells are known to change their phenotype in culture. We analyzed the mesenchymal phenotype of hAMSC at different stages after isolation using immunohistochemistry. Shortly after isolation (1 day), 92 % (± 7 %) of the hAMSC expressed the mesenchymal marker vimentin, 2 % (± 1 %) stained for the epithelial marker cytokeratin-7 and 5 % (± 4 %) co-expressed these markers. After 5 days, the double positive cells slightly increased to 7 % (± 3 %), while exclusive expression of cytokeratin-7 or vimentin remained unchanged (1 % ± 2 % and 92 % ± 1 %, respectively). After the first passage, all attached cells were vimentin-positive, while 54 % (± 9 %) co-expressed cytokeratin-7 and vimentin. Thus, we conclude that under culture, hAMSC adopt a hybrid mesenchymal-epithelial phenotype. It is also essential to perform microscopical examination during the first days after isolation to detect contaminations with human amnion-derived epithelial cells in cultures of hAMSC.