Mesenchymal stem cell therapy in skin: why and what for?

In recent years, few stem cells have gained as much clinical notoriety as mesenchymal stem cells. Indeed, MSCs are already in use for a range of systemic inflammatory and autoimmune conditions that also affect the skin, such as acute and chronic graft versus host disease or lupus erythematosus. Most interestingly, these cells are able to improve skin wound healing in multiple preclinical models and few patient series. An additional potential of these cells is the delivery of missing structural elements in skin inherited disorders. However, we here contend that MSCs are not appropriate for cell replacement therapies in the context of wound healing. Indeed, engraftment of cells in the dermis is poor in the absence of irradiation and the observed effects seem mainly due to paracrine factors. In this viewpoint, we favour the hypothesis of a replete niche and competition with resident mesenchymal populations in the dermis not allowing the engraftment of newly delivered MSCs. Consequently, we propose that the benefit of MSCs may be at least in part reproduced by the growth factors or immunomodulatory molecules that they produce. In any case, the rapid progress in this field has allowed the emergence of important questions in skin biology that need to be addressed in parallel with the predictable future use of MSCs in the clinic.