Sheep Placenta Cotyledons: A Noninvasive Source of Ovine Mesenchymal Stem Cells

Sheep are one of the most frequently used large animal models in stem cell research. However, minimal invasive or noninvasive sources of mesenchymal stem cells (MSCs) in sheep are scarce. In the light of the principles of the 3Rs (reduce, refine, replace), it would therefore be desirable to identify a minimally invasive or noninvasive ovine MSC source. In humans, the chorionic villi of the placenta, which can be noninvasively harvested as part of the afterbirth, have been identified as a rich source of MSCs. Therefore, in the present study, ovine placenta cotyledons, which have similar function and structure to human chorionic villi, were tested for their potential use as a noninvasive source of ovine MSCs. Through mincing of the placental cotyledons, collagenase digestion, and Ficoll density gradient centrifugation, combined with plastic adherence selection, MSCs were successfully isolated. Their morphological, immunophenotypical, and cellular growth characteristics, as well as their proliferation, differentiation, and migration potential, were evaluated and compared to the currently best-researched MSC source, bone marrow-derived stem cells. Ovine cotyledons were shown to be a reliable, abundant source for the noninvasive, pain- and risk-free harvest of MSCs. The collection procedure does not interfere with partum or the initial bonding phase between ewes and lambs and is therefore exempt from ethical debate. Ovine placenta cotyledon-derived MSCs exhibit multipotential characteristics and can be cryopreserved for later use.