Mesenchymal stem cells and innate tolerance: biology and clinical applications.

The properties of mesenchymal stem cells (MSC) have been widely investigated during the last decade, from their differentiation capacity to their immunosuppressive effect on any type of immune cell. These properties have been successfully harnessed for the treatment of inflammatory diseases such as graft versus host disease (GvHD). Different mechanisms have been proposed for their immunosuppressive properties, although it seems likely that they are used in concert. The inflammatory environment to which MSC are exposed plays a pivotal role in activating their functions. Conversely, the interplay of MSC with the immunoregulatory networks recruited during inflammation is fundamental to the delivery of immunosuppression. Since other types of terminally differentiated stromal cells share these properties, it is plausible that stemness is not a required feature. Therefore these functions may be involved in the physiological control of acute inflammation in various tissues. These notions highlight the importance of investigating the role of stromal cells as modulators of immune responses.