Mesenchymal stromal cells and immune tolerance: towards clinical applications?

Multipotent mesenchymal stromal cells, or mesenchymal stem cells (MSC), are isolated mainly from bone marrow and adipose tissue but are identified in other tissues such as synovium, periosteum or placenta. They are characterized by their property to adhere to plastic, their phenotype and their ability to differentiate into three lineages (chondrocytes, osteoblasts and adipocytes). More recently, these cells were shown to escape immune recognition and inhibit immune responses. MSC may modulate the function of the major immune cell populations, including antigen-presenting cells, T cells, B cells and natural killer cells. The aim of this review is to focus on the molecular mechanisms, still poorly understood, which are responsible of the immunosuppressive effects mediated by the MSC. Finally, the data obtained from in vivo experimentation in various animal models as well as potential therapeutic applications will be presented.