[Immunosuppression and mesenchymal stem cells: back to the future]

Since their efficiency to treat graft versus host disease has been proven, mesenchymal stem cells (MSC) represent a promising cell therapy approach for the treatment of immune disorders. In this context, much attention has focused on their mechanisms of action, in particular once the fact that their immune properties are also crucial for their efficiency in regenerative medicine was demonstrated. By their production of various and redundant soluble factors, MSC exert powerful anti-inflammatory and immunosuppressive effects targeting the main immune cell subsets. These immunoregulatory properties are essentially inducible by inflammatory mediators. In addition, it is now clear that allogeneic MSC are not immunoprivileged in immunocompetent recipient in agreement with their low persistence in vivo. They should thus display an early "touch-and-go" effect involving both direct interactions with recruited immune effectors and further amplification of this immunosuppression process through activation or conditioning of other regulatory immune cells. A better understanding of immunological properties of MSC will clearly improve their use in clinical settings.