The foregoing studies validated our ability to derive stable vectors that incorporate MPER within hexon HVR2. Having established the technical feasibilities that allowed us to place large epitopes within hexon's HVR2, we next sought to explore the functional utilities of these modified vectors. To this end, we performed an ELISA assay to verify that the HIV MPER motif in the HVR2 was accessible on the virion surface ( Figure 3A ). In this assay, varying amounts of purified viruses were immobilized in the wells of an ELISA plate and incubated with anti-gp41 antibody. The results showed significant binding of the anti-gp41 antibody to the Ad5/HVR2-MPER-L15(Gag) and Ad5/HVR2-MPER-L15DE1, whereas no binding was seen in response to AdCMVGag control. These results indicate that the reactive MPER epitope was properly exposed on the virion surfaces when incorporated within HVR2.