Despite the many potential advantages of Ad vectors for vaccine application, full utility of current Ad vaccines may be limited by the host anti-vector immune response. Specifically, the anti-Ad humoral immunity abrogates the effectiveness of subsequent administrations of the Ad vector, confounding expression of the encoded transgene, and thus practically restricting the gains that might be accrued via booster effect. In order to exploit the inherent antigenicity of the Ad vector we have developed a vaccination approach based on incorporation of the immunizing antigen epitope directly into the Ad capsid. This novel paradigm is based upon Ad presenting the antigen as a component of the capsid rather than an encoded transgene. Incorporation of immunogenic peptides into the Ad capsid offers potential advantages. Most noteworthy, the processing of the capsid incorporated antigen via the exogenous pathway should result in a strong humoral response akin to the response provoked by native Ad capsid proteins. In addition, since anti-Ad capsid responses are augmented by repeated vector administration, immune responses against antigenic epitopes that are part of the Ad capsid should be augmented by repeated administration as well, thus allowing boosting. These considerations suggest that this novel capsid-incorporated antigen approach may offer exciting potentials to realize Ad-based vaccine strategies that circumvent the major limitations associated with Ad vectors. Critical to the realization of this approach is to define the optimal configuration of antigen in the adenoviral capsid context. To this end, we have established several key technologies that will enable us to reach our goal. In particular, we have developed the means to incorporate heterologous peptide epitopes within the surface-exposed domains of the major Ad capsid protein hexon. We have begun to determine the size and structural factors that predicate functional utility of these domains in the hexon. In addition, we have developed the means to apply cryoelectron microscopy (cryoEM) single particle reconstruction methods to allow us to explore the capsid-incorporated peptide localization with unprecedented, subnanometer resolution. Based on these technologies, we will be able to establish the critical correlates between antigen locale/accessibility within the capsid context and vaccine efficacy. On the basis of these established feasibilities, we hypothesize that Ad vectors can be created with novel capsid-incorporated antigens that can serve as vaccine agents against HIV in animal models. CryoEM-guided capsid design will be applied to develop an optimized vector with optimal anti-HIV immunization. We envision that our proposed structural studies will provide complementary information to in vitro assays and biological readouts and thereby will enable us to understand the functional determinants of incorporated HIV epitopes. This project will design new and innovative methodologies to create HIV vaccines, in hopes of preventing the spread of HIV disease.
