HLX reduces vessel formation in an endothelial spheroid xenografting assay in vivo. HUVEC were infected with HLX-encoding adenoviruses and control viruses with an MOI of 20. The infected cells were used to generate endothelial cell spheroids consisting of approximately 100 cells/spheroid. Spheroids were suspended in a Matrigel/fibrinogen mixture containing 500 ng/mL VEGF and bFGF. After addition of thrombin the spheroid suspension was injected subcutaneously into SCID mice (2 plugs/mouse, 8 mice/experimental group). Plugs were harvested after 14 days, fixed, and analyzed by immunohistochemistry using CD31 or CD34 or antibodies. (A) Representative images of sections of plugs containing HUVECs infected with Ad.HLX or Ad.con and stained with anti-human CD34 antibodies or anti-human CD31 antibodies plus hematoxylin. (B) Evaluation of vessel formation was performed by measuring the vessel areas stained for CD34 on 16 images of 8 sections. The MVD per mm² ± SEM is depicted for plugs containing vessels with Ad.HLX (■) and Ad.con (□) infected HUVEC. *P < .05, t test.