The W8B2 antibody reacts with an antigen, TNAP (Tissue non-specific alkaline phosphatase), that is selectively expressed on bone marrow mesenchymal stem cells, but not on placenta-derived mesenchymal stem cells. It was previously reported that the antibody recognized MSCA-1, mesenchymal stem cell antigen-1. Mesenchymal stem cells or MSCs were originally named as bone marrow stromal cells. They are a population of adult stem cells with a large capacity for self-renewal and multipotency for differentiation into a variety of cell types including osteoblasts, chondrocytes, myocytes, adipocytes, beta-pancreatic islets cells and certain neuronal cells. MSCs reside in many tissues, such as bone marrow, placenta, adipose tissue, adult peripheral blood, fetal blood, skin, as well as liver and lung. Besides their plasticity for tissue repair, MSCs also exhibit a powerful immunosuppressive activity and play important role in supporting hematopoiesis.