Journal of Blood & Lymph

Mesenchymal stem/stromal cells (MSCs) have been widely studied for regeneration therapy in various organs/diseases and are currently being developed for clinical practice. Despite the hope brought by MSC therapy, the characteristics of MSCs remain ambiguous, where cells have distinct features depending on their sources and species. With regard to cartilage therapy, MSCs from the bone marrow and synovium have been clinically examined based on their differentiation into chondrocytes in animal studies. However, recent studies have outlined other reparative mechanisms of MSCs, such as paracrine effects. Thus, the regeneration mechanisms are still elusive, and the key features of MSCs that determine their reparative activity have not been established. In this review, we summarize the current literature and discuss the importance of the assays to evaluate “human” MSCs considering the in vivo environment and reparative mechanisms.