Model epitopes incorporated in HVRs are accessible in the context of an intact virion. In the assay, varying amounts of purified viruses were immobilized in the wells of ELISA plates and incubated with anti-His6 tag antibody. The binding was detected with an AP-conjugated secondary antibody. These results suggested that the model antigens (tagged with His6 epitopes) and the His6 epitopes (controls) incorporated into HVR2 or HVR5 were accessible to anti-His6 tag antibody at the virion level, indicating that the epitopes were exposed on the virion surface. All of the Ad vectors except Ad5 present His6or RGD-His6within the hexon. The His6 antigenic peptide is presented by Ad5/HVR5-His6and Ad5/HVR5-His6.