Size-sieved subpopulations of mesenchymal stem cells from intervascular and perivascular equine umbilical cord matrix.

Objectives: Umbilical cord matrix (UCM) has been recently proposed as an alternative source of mesenchymal stem cells (MSCs). The aim of this study was to isolate and characterize presumptive stem cells from intervascular and perivascular equine UCM and to obtain homogeneous subpopulations from both sites. Materials and methods: Umbilical cords were processed for retrieval of MSCs. Unsieved cells from intervascular and perivascular portions were evaluated for cell cycle analysis and for immunophenotyping by flow cytometry. Cells from each site were separated into larger and smaller sieved populations using multi-dishes with 8-μm pore transwell inserts. Each cell population was characterized in terms of renewal capability, specific marker expression and differentiation potential. Cryopreservation was performed on sieved cells only. Results: Cells from both areas expressed MSC and pluripotential specific markers and were able to differentiate into mesodermic and ectodermic lineages. The sieving procedure yielded two relatively homogeneous subpopulations with comparable characteristics. Surprisingly, after sieving, large intervascular and small perivascular cells were the most rapidly replicating cells [20.53 and 19.49 cell population doublings (PD) after 31days respectively] and also showed higher fibroblast colony forming unit frequency. Unsieved cell populations were used as controls, and showed PD of 9.42(intervascular cells) and 8.54 (perivascular cells) after 31days. Conclusions: Here, cells from UCM represented an intermediate stage between pluripotent embryonic and adult stem cells. Size-sieving can be used to isolate more rapidly proliferating cell populations.