Long-term culture in vitro impairs the immunosuppressive activity of mesenchymal stem cells on T cells.

Improved knowledge of the immunological properties of mesenchymal stem cells (MSCs) creates a potential cell-mediated immunotherapeutic approach for arthritic diseases. The low frequency of MSCs necessitates their in vitro expansion prior to clinical use. As sequential passage has been used as the most popular strategy for expansion of MSCs, the effect of long-term culture on the immunological properties of MSCs is not clear. In this study, we observed that the morphology of MSCs showed the typical characteristics of the Hayflick model of cellular aging during sequential expansion. The growth kinetics of MSCs decreased while the number of MSCs staining positive for SA ß-gal (senescence marker) increased in long-term culture. Although long-term culture exerts less of an effect on the immunophenotype of MSCs, the immunosuppressive effects of MSCs on the allogeneic T-cell proliferation, activation-antigen expression (CD69 and CD25) and cytokine production (IFN-γ, TNF-α, IL-10) were significantly impaired following stimulation with phytohemagglutinin (PHA).