ROBO4 and neoplasm: As such, we created our final Ad vector, RGD.H5/3.ROBO4 that uniquely incorporates three crucial facets of: enhanced tumor EC adhesion (fiber/knob RGD display), augmented extrahepatic gene payload delivery (capsid hexon serotype swap), and tumor microenvironment-induced transcriptional upregulation (EC-specific ROBO4 enhancer/promoter) (Figure 8A).