Suppression of tumor angiogenesis in PC3 tumor mass by anti–c-Kit mAb. The anti–c-Kit mAb, ACK2, was injected for 4 days (1 mg/d per mouse) into nude mice as described in the legend to Figure 3. (A) Photographs of mice taken 14 days after inoculation with PC3 cells. Arrows indicate the tumor mass in mice that had been treated with ACK2 (anti–c-Kit) or anti-B220 mAb (control). (B) Tumor volume on day 14 in mice that had been treated with ACK2 (anti–c-Kit) or anti-B220 mAb (control). The tumor volumes measured on day 14 were 486 ± 53 mm³ (ACK2: n = 8), and 1927 ± 258 mm³ (B220: n = 8). Results are expressed as the mean volume of 8 experiments (± SEM). (C-D) Tissue sections of the tumors from the mice observed in panel A, stained with anti–PECAM-1 mAb and counterstained with fast red. Tissue sections of the tumors from mice that had been injected with anti-B220 mAb (C) or ACK2 (D) are shown. The dotted line shows the border between the fibrous cap surrounding the tumor mass and the tumor mass. The area above the dotted line is the tumor mass. Arrow indicates a capillary that migrated into the tumor. The arrowheads show a vascular bed observed in the fibrous cap surrounding the tumor mass. Bar indicates 150 μm in panels C,D.