Identification, quantification and isolation of mesenchymal progenitor cells from osteoarthritic synovium by fluorescence automated cell sorting

Objective: Identification, quantification and isolation of subpopulations with characteristics of mesenchymal progenitor cells (MPC) from the synovial membrane (SM) from patients with osteoarthritis (OA). Method: Cells from the SM of patients with end stage OA who underwent total knee joint replacement were enzymatically isolated. One aliquot was directly analyzed by fluorescence automated cell sorting (FAGS) using various combinations of surface markers of bone marrow MPC (CD9, CD44, CD54, CD90, and CD166). Remaining cells were cultivated on plastic, expanded over several passages, analyzed by FAGS again and tested for their osteo- and chondrogenic potential. The differentiation was analyzed by immuno-/histochemistry and by RT-PCR for the expression of lineage related marker genes. Results: Using FAGS analysis we could show that the relative proportion of subpopulations expressing triplicate combinations of CD9, CD44, CD54, CD90 and CD166 in the SM from OA patients varies between 3 and 10%. Upon cultivation their relative amount markedly increased to values between 24 and 48%. Within the heterogeneous cell populations it was possible to induce osteogenic and chondrogenic differentiation. Initial sorting for CD9/CD90/CD166 triplicate positive cells proved that this subpopulation contains cells with multipotency for mesenchymal differentiation and thus characteristics of MPC. Conclusion: Our results show that SM from OA patients contains cells that express typical combinations of MPC surface markers and have the potency of osteogenic and chondrogenic differentiation. Their relative enrichment during in vitro cultivation and the possibility of cell sorting to get more homogenous populations offer interesting perspectives for possible future therapeutic applications. (C) 2003 OsteoArthritis Research Society International. Published by Elsevier Ltd. All rights reserved.