Immunohistochemical analyses. Tumors that developed 20 days after subcutaneous injection into nude mice of CHO cells stably transfected with empty vector (Ctl), vector containing wild-type or mutant proVEGF-C cDNA were analyzed for angiogenesis and lymphangiogenesis using an anti-mouse CD-31 monoclonal antibody and an anti–VEG-FR-C polyclonal antibody, respectively. The sections were observed at a magnification of ×200. Arrows indicate vessels. The number of intratumoral vascular and lymphatic vessels was counted in ten different fields for each tumor. Data are presented as mean ± SD.