Bone from Blood (IMAGE) University of Pennsylvania School of Medicine Caption Circulating osteogenic precursor cells form bone in vivo. COP cells were transplanted into nude mice with histological sections revealing hard tissue containing osteoctyes and bone-lining cells (boxed area) eight weeks later. Credit Robert Pignolo, MD, PhD, University of Pennsylvania School of Medicine Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.