Fig. 4. Human KS lesions express VEGF, and human skin graft promotes the development of KS-like lesions with vascular lumens expressing vß3 integrin. A, representative section of human KS tumor from an HIV-1-infected individual; the tumor was stained with antibody-targeting VEGF and developed with alkaline phosphatase anti-phosphatase/Fast Red system. The section also demonstrates vascular structures of KS tissues and cells expressing VEGF (red indicator). Approximately 1030% of cells in human KS lesions express VEGF protein. B and C, high power images of KS lesion stained with anti-VEGF antibody. D, representative section stain with human-specific anti-PECAM antibody of skin graft on SCID mouse showing fusion of mouse (M) and human (H) skin tissue. Tumor induced by inoculation of KS SLK cells grew under human skin graft (T; see also Fig. 3 ). Antihuman PECAM-1 staining selectively localized to cells in tumor (arrow) and was absent in mouse tissue (M). Morphology and distribution of PECAM-1-staining cells were consistent with those EC of tumor tissue. E, representative section of tumor induced by KS SLK under human skin stained with anti-vitronectin antibody highlight cells in vessel-like structure (vß3 integrin +, PECAM-1 -). Shown is one (arrow) of many vessel-like structures in tumor tissue having apparent lumens and cells heavily stained with the antivitronectin receptor vß3. F, a tumor induced by SLK cells under a human skin graft stained with anti-PECAM-1 antibody. Arrow, PECAM-1 staining of cells in tumor vessels. The KS SLK tumor cells lack PECAM-1 staining.