Mesenchymal stem cells in rheumatology: a regenerative approach to joint repair.

The advent of biologics in rheumatology has considerably changed the evolution and prognosis of chronic inflammatory arthritis. The success of these new treatments has contributed to steering more attention to research focussed on repair and remodelling of joint tissues. Indeed, when the tissue damage is established, treatment options are very limited and the risk of progression towards joint destruction and failure remains high. Increasing evidence indicates that mesenchymal stem cells persist postnatally within joint tissues. It is postulated that they would function to safeguard joint homoeostasis and guarantee tissue remodelling and repair throughout life. Alterations in mesenchymal stem cell biology in arthritis have indeed been reported but a causal relationship has not been demonstrated, mainly because our current knowledge of mesenchymal stem cell niches and functions within the joint in health and disease is very limited. Nonetheless, mesenchymal stem cell technologies have attracted the attention of the biomedical research community as very promising tools to achieve the repair of joint tissues such as articular cartilage, subchondral bone, menisci and tendons. This review will outline stem-cell-mediated strategies for the repair of joint tissues, spanning from the use of expanded mesenchymal stem cell populations to therapeutic targeting of endogenous stem cells, resident in their native tissues, and related reparative signals in traumatic, degenerative and inflammatory joint disorders.