Prospective purification of a subpopulation of human synovial mesenchymal stem cells with enhanced chondro-osteogenic potency.

We previously reported the coexistence, within cultured mesenchymal stem cells (MSCs) from human synovial membrane, of single-cell-derived clonal cell populations with distinct differentiation potency. The aim of this study was to investigate marker sets for prospective purification of functionally distinct MSC subsets. Cells were enzymatically released from human synovium and culture expanded. Phenotype analysis was performed by flow cytometry using combinations of MSC markers. Sorting was carried out using the FACS DiVA cell sorter. Sorted cell populations were assessed for clonogenicity, kinetics of growth, cell senescence and chondro-osteogenic potency. During culture expansion, the co-localization of CD39 within the CD73(+) cell population identified a small cell subset that was maintained from passage 1 (P1) up to at least P12 in all donors tested. The CD73(+)CD39(+) cell subset displayed higher expression levels of Sox9 and Runx2 and a significantly greater chondro-osteogenic potency than the CD73(+)CD39(-) cell subset. In contrast, it was less clonogenic and proliferative. There was no difference in cell senescence between the sorted MSC subsets and the parental MSCs. Notably, there were no detectable differences in chondro-osteogenic potency between the CD73(+)CD39(-) and CD73(+)CD39(+) cell subsets purified from fresh synovial cell populations. Our findings indicate that the combination of CD73 and CD39 allows the prospective purification from culture-expanded heterogeneous synovial MSC populations of a distinct MSC subset with greater chondro-osteogenic potency. We anticipate that such an approach will enhance the consistency of cell-based therapeutic protocols for the repair of osteochondral defects.