VEGF enhances healing of critical-sized calvarial defects elicited by MDSCs expressing BMP4. (a–c) Radiography shows complete bone healing of the defects in both the BMP4 and the BMP4+VEGF groups and no bone healing in the LacZ+VEGF group at 3 weeks PI. Arrows mark the edge of defects or newly formed bone. (d and e) Quantitative analysis shows a significant enhancement of bone regeneration in the BMP4+VEGF groups relative to the BMP4 group (*P < 0.05, n = 4). (f–h) von Kossa staining reveals coarser mineralized bone trabeculae in the BMP4+VEGF group than in the BMP4 group. No mineralized bone formed in the defect of the LacZ+VEGF group. Magnification: f–h, ×40.