Amnion-derived stem cells: in quest of clinical applications

The emerging field of regenerative medicine requires a reliable cell source in addition to biomaterial scaffolds and cytokine/growth factors. The 'cell' is a particularly critical element for cell replacement therapies in order to provide a safe and sufficient cell supply for clinical applications. Efforts to search for an adequate cell type and cell source have been conducted and have continued along with the discussions for their use in clinical application.There are many potential cell sources for regenerative medicine, including bone marrow-derived mesenchymal stem cells, tissue-specific progenitor cells, embryonic stem (ES) cells, and induced pluripotent stem (iPS) cells. Although their biological potentials have been demonstrated, none of these cells is widely accepted as a definitive cell source for clinical applications. Each cell type possesses different advantages as well as limitations for their use, such as safety or availability. It will be helpful to search for a potential stem cell source from the perspective of its potential for clinical application. What is the sine qua non of the cells for clinically applicable regenerative medicine? At the end of this review, this question will be discussed further.There is increasing evidence that the human placenta contains pluripotent or multipotent stem cells or both. Various multipotent stem cells have been isolated from different parts of the human placenta, such as the amnion, chorion, umbilical cord, and fetal blood. As placenta-derived cells, these stem cells have common advantages (Figure 1). Specific types of placenta-derived stem cells, such as trophoblastic, hematopoietic, and mesenchymal stroma cells, have been discussed elsewhere [1-3]. Here, we will review stem cells derived from the amnion of human placentae, specifically amniotic epithelial (AE) cells. First, we will summarize previous studies that have demonstrated the unique stem cell characteristics of AE cells. On the basis of these findings,