An ex vivo human placental vessel perfusion method to study mesenchymal stem/stromal cell migration

To initiate tissue repair, mesenchymal stem/stromal cells (MSCs) must enter the blood stream, migrate to the targeted area, cross the endothelial barrier and home to the damaged tissue. This process is not yet fully understood in humans and thus, the aim of this study was to develop an ex vivo placental vessel perfusion method to examine human MSC movement from a blood vessel into human tissue. This will provide a better understanding of MSC migration, movement through the endothelial barrier and engraftment into target tissue, in a setting that more closely represents the in vivo state, compared with conventional in vitro human cell culture models. Moreover, important similarities and differences to animal experimental model systems may be revealed by this method.

Human placental hTERT transformed MSC lines were labelled with live-cell fluorescence dyes, and then perfused into term human placental blood vessel. After labelled MSCs were perfused into the vessel, the vessel was dissected from the placenta and incubated at cell growth conditions. Following incubation, the vessel was washed thoroughly to remove unattached, labelled MSCs and then snap frozen for sectioning. After sectioning, immunofluorescence staining of the endothelium was carried out to detect if labelled MSCs crossed the endothelial barrier.

Twelve placental vessel perfusions were successfully completed. In eight of the twelve perfused vessels, qualitative assessment of immunofluorescence in sections (n=20, 5 µm sections/vessel) revealed labelled MSCs had crossed the endothelial barrier.

The human placental ex vivo vessel perfusion method could be used to assess human MSC migration into human tissue. Cells of the MSC lines were able to adhere and transmigrate through the endothelial barrier in a manner similar to that of leukocytes. Notably, cells that transmigrated remained in close proximity to the endothelium, which is consistent with the reported MSC vascular niche in placental blood vessels.