Prostaglandin E2: a putative potency indicator of the immunosuppressive activity of human mesenchymal stem cells

Mesenchymal stem cells (MSCs) are non-hematopoietic, pluripotent cells that give rise to stromal cells in the marrow. MSCs have been shown to be immunosuppressive and have become an attractive therapeutic option for the modulation of undesired immune responses. Currently, ex vivo expanded human (h)MSCs are being utilized in clinical trials both in the USA and in Europe to treat a variety of immune disorders. hMSCs need to be harvested, isolated and expanded in culture. This necessary expansion may also result in decrease or loss of the immunomodulatory potential of hMSCs. Ideally, the intrinsic immunomodulatory activity (potency) of an hMSC preparation should be assessed prior to its administration. The goal of the experiments described here was to develop a simple potency assay for the immunomodulatory properties of hMSCs. The immunosuppressive activity of hMSCs conditioned media was tested in enzyme-linked immunosorbent spot assays (ELISpot) and the immunosuppressive activity of the conditioned media was correlated with the concentration of several cytokines present in these conditioned media. The concentration of prostaglandin E(2) in the media correlated with their immunosuppressive activity. The concentration of the other cytokines measured did not correlate with the immunosuppressive activity of the media. The dose-response effect could be replicated by adding PGE(2) to ELISpot assays. Furthermore, the immunosuppressive activity of the conditioned media was inhibitable by a neutralizing anti-PGE(2) antibody. These data suggest that measurement of PGE(2) in media conditioned by hMSCs exposed to inflammatory stimuli could be used as a surrogate measure of their immunosuppressive capacity. These findings need to be confirmed in vitro using different assays of immune function and validated in vivo to determine the level of correlation of these data with efficacy in pre-clinical models of immune disorders.