Viral tumor infection activates the tumor vasculature. Athymic nude mice bearing human GI-101A tumors were injected with 5 × 106 pfu of GLV-1h68 and tumors were harvested 42 days p.i.. (a-c) GLV-1h68-colonized GI-101A tumors showed increased CD31 fluorescence intensity compared to GI-101A control tumors. The tumor vasculature was labelled with anti-CD31 antibody (red) and the fluorescence signals in 9 images (x50 magnification) were measured using ImageJ. Shown are the mean values +/- standard deviations. (e) GLV-1h68-infected and control GI-101A tumors showed the same level of vascularization. Vascular density was measured in CD31-labelled tumor cross-sections (nine per group). Shown are the mean values +/- standard deviations. (d) Gene expression profile of both, VACV infected and uninfected GI-101A xenografts 21 and 42 days p.i.. Genes were selected based on pathway analysis as described in material and methods and clustered using uncentered correlation algorithm. Genes that passed the filtering criteria (at least 2fold change in one experiment and 60% presence call across the experimental set) are displayed. The asterisk (a) indicate a significant difference between experimental groups (*** P < 0.001; Student's t test). All images are representative examples. Scale bars represent 500 μm (a, b).