Histopathological examinations.

<p>Histopathological examinations were performed to validate imaging results. (A) Cy5.5 and anti-rat endothelial progenitor cell antibody positive cells (<i>arrow</i>) were observed in the connective tissue or at the tumor margin at day 3. Scale bar = 50 µm. In contrast, no Alex Fluo 488 signal was observed in the control group. (B) Sections collected at day 7 showed significant double positive cells (<i>arrow</i>) inside the tumor. Scale bar = 50 µm. (C) The numbers of Cy5.5 positive cells increased in tumors (30.75±6.24 cells/field of view at day 3 vs. 43.13±9.17 cells/field of view at day 7, <i>p</i><0.05, <i>n</i> = 15), but remained the same afterwards. (D) CD31 and Cy5.5 double positive cells (<i>arrow</i>) were observed at the vessel walls inside the tumor at the day 14 (<i>asterisk</i> represent the lumen). Scale bar = 30 µm. (E) CD31 positive microvessels were counted in MVD quantification at 7, 14 and 21 days after cell transplantation. Compared to the control, no significant differences were found between the groups (<i>p</i>>0.05, <i>n</i> = 15).