Suppression of tumor angiogenesis in colon26 tumor mass by leukocytopenia. (A-F) Whole mount staining of colon26 tumor mass with anti–PECAM-1 mAb (dark blue) (A,B,D,E) or anti–PECAM-1 (dark blue) and anti-CD45 (red) mAbs (C,F). The tumor mass along with skin was dissected 3 days after inoculation of colon26 tumor cells from mice after treatment with the anti–c-Kit mAb, ACK2 (D-F), or anti-B220 mAb as a control (A-C). The dotted line shows the mass of inoculated tumor cells (A,D). (B,E) High-power view of the location indicated by the arrow in panels A,D, respectively. (G,H) Gross appearance of tumor mass. The photographs of the dissected tumors were taken 5 days after inoculation of colon26 tumor cells from ACK2-treated mice (H) or anti-B220–treated mice (G). (I) Number of white blood cells (WBCs) in the peripheral blood after treatment with ACK2 (blue line) or anti-B220 mAb (red line; control [CTL]) for 4 days from day –4 to day –1. Results are expressed as the mean number of WBCs in 3 experiments (± SEM). (J) Tumor volume in mice that had been treated with ACK2 (blue line) or anti-B220 mAb (red line; CTL). Day 0 in this graph corresponds to the day 0 indicated in panel I. The tumor volumes measured on day 5, day 7, and day 14 were as follows: ACK2 (c-Kit): 52 ± 13 mm³ at day 5, 65 ± 15 mm³ at day 7, and 1020 ± 358 mm³ at day 14; B220 (CTL): 86 ± 15 mm³ at day 5, 890 ± 211 mm³ at day 7, and 1856 ± 325 mm³ at day 14. Results are expressed as the mean volume of 6 experiments (± SEM).