The W4A5 antibody was generated by immunization with Weri-RB-1 cells. It reacts with a subpopulation of mesenchymal stem cells and neural progenitor cells (NPCs). Mesenchymal stem cells or MSCs are originally name 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. NPCs can give rise to astrocytes, neurons, and oligodendrocytes