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Placental tissues as sources of stem cells—Review

Recently the fetal membranes are regarded to be abundant, ethically acceptable and easily accessible sources of mesenchymal stem cells, which cause only minor immunogenic troubles. In addition, these membranes have been studied as an alternative to adult and embryonic stem cells. The chorion develops firstly as a layer of simple avascular epithelium (trophoblast). The amnion, as the chorion is also an avascular membrane. It is derived from the ectoderm, and forms a very thin membrane which surrounded the embryo in development. The hypoblast and exocoelomic membrane together originates the yolk sac which late will give rise to the allantois. The study of the origin and development of these tissues is of vital importance for obtaining stem cells. Different cell lineages can be obtained from the fetal placental tissues: the hematopoietic lineage is found in the chorion, allantois and, yolk sac, and the mesenchymal lineage is found in the chorion and amnion. The properties and potential for differentiation of fetal stem cells isolated from placental tissues must be characterized in order for them to be used in the treatment of several diseases. The chorion, yolk sac, allantois, and amnion contain heterogeneous cell populations. However, few studies have focused on characterizing these alternative stem cells sources. The amnion has a significant advantage over the other fetal membranes, mainly due to its easily accessibility for collection in humans and rodents and also because it contains populations of pluripotent and multipotent cells. In some other species (dogs, ruminants, horses, cats, and swine) the allantoic fluid is more easily accessible, but there is little information regarding the characterization of the cell population. This review will address advances in the isolation of stem cells from fetal placental tissues and describe their characterization and possible use in cell therapy, as well as their origin and development.