In vivo bone formation by prospectively isolated human MSCs. Tissue sections from a representative transplant, stained as indicated, are shown. HA indicates hydroxyapatite scaffold. For each panel, black arrows indicate new bone formation; white arrows, fibrous tissue. The lower 3 panels show immunohistochemistry for human osteocalcin (OC) in red and nuclear staining with DAPI in blue. Original magnification: 10×/0.3 NA Ph1 (top 2 panels), 20×/0.4 NA Ph1 (lower panels).