Background
nonunion, fracture, fractures
A considerable proportion (5–10%) of fractures fail to heal, resulting in delayed union or nonunion [Current clinical investigations have focused on cell-based therapies for bone formation as a category of regenerative medicine. CD34 + adult human peripheral blood (PB) cells are candidates for cell-based regenerative therapy, as they contain abundant endothelial progenitor cells (EPCs) and hematopoietic stem cells [We conducted a series of preclinical studies to demonstrate the therapeutic effects of CD34 + cells in fracture healing. First, we showed that the systemic infusion of circulating CD34 + cells from humans into immunodeficient rats with nonhealing fractures contributed to fracture healing by enhancing vasculogenesis and osteogenesis [