Identification of stem cell marker-positive cells by immunofluorescence in term human amnion

The placenta contains different populations of stem/progenitor cells such as mesenchymal, hematopoietic, trophoblastic and pluripotent stem cells. Although some tissue-specific stem cells are restricted to particular parts of the placenta, the localization of embryonic stem cell-like cells in term human placenta has not been determined. We have used immunofluorescence staining techniques with antibodies to pluripotent stem cell antigens, SSEA-3, SSEA-4, TRA 1-60 and TRA 1-81, and confocal microscopic analysis to identify and localize stem cells within the placenta. Stem cell marker-positive cells were found in amnion but not in choriodecidua, tissues known to contain hematopoietic and trophoblastic stem cells. Amniotic mesenchymal cells did not react with these pluripotent stem cell markers, while all amniotic epithelial cells reacted with at least one antibody. The TRA 1-60 and TRA 1-81 positive cells were solitary and present throughout the surface of amniotic membrane without a specific pattern of distribution, whereas SSEA-3 was negative and SSEA-4 was weakly positive on all amniotic epithelial cells. These data suggest that the human amnion contains stem cell-like cells at different states of differentiation. Human term amnion may be useful source of pluripotent stem cells for regenerative medicine.