Abstract
Human culture-expanded mesenchymal stromal cells (MSC) are being considered for multiple therapeutic applications because of their regenerative and anti-inflammatory properties. Although a large number of MSC can be propagated from a small initial sample, several lines of evidence indicate that MSC lose their immunosuppressive and regenerative potency aftaer multiple passages. In this report, we use the FACSCAP Lyoplate proteomic analysis system to detect changes in cell surface protein expression of CD45- /CD31- /CD34- /CD73+ /CD105+ stromal cells in unpassaged bone marrow (BM) and through 10 serial culture passages. We provide for the first time a detailed characterization of native unpassaged BM MSC (0.08% of BM mononuclear cells) as well as the changes that occur during the initial expansion. Adipogenic and osteogenic differentiative potential was determined though the serial passages and correlated with immunophenotypic changes and senescence. Among the most prominent were striking decreases in Fas ligand, CD98, CD205, and CD106, accompanied by a gain in the expression of CD49c, CD63, CD98, and class 1 and class 2 major histocompatibility complex (MHC) molecules. Other molecules that are down-modulated with later passage include CD24, CD54, CD59, CD243/P-glycoprotein, and CD273/PD-L2. Early senescence, as defined by the loss of replicative capacity occurring with the loss of differentiative capacity, increase in CDKN2A p16, and increased time to confluence, was accompanied by loss of the motility-associated metalloproteinase CD10 and the proliferation-associated transferrin receptor CD71. Among the strongest statistical associations were loss of MAC-inhibitory protein/CD59, loss of ICAM-1/CD54, and increase in CDKN2A as a function of increasing passage, as well as increased CD10 expression with adipogenic and osteogenic capacities. The data provide a clear set of markers that can be used to assess MSC quality. We suggest that clinically relevant numbers of highly functional low passage MSC can be manufactured starting with large quantities of BM, which are readily available from cadaveric organ donors.