Circulating osteogenic cells: implications for injury, repair, and regeneration.

The aim of this review is to provide a critical reading of recent literature pertaining to the presence of circulating, fluid-phase osteoblastic cells and their possible contribution to bone formation. We have termed this group of cells collectively as circulating osteogenic precursor (COP) cells. We present evidence for their existence, methods used for their isolation and identification, possible physiological and pathophysiological roles, cellular origins, and possible mechanisms for their migration to target tissues.