Strategies for the design of epitope targeting vaccines

There is need for vaccines that target production of antibodies (Ab) to conserved sites on highly-variable pathogens, such as HIV-1. Strategies targeting Ab production to such sites are called “epitope-targeting vaccines”, and this dissertation explores this theme by: i) using filamentous phage-based carriers for focusing Ab responses to peptides, and ii) developing a protein-prime, peptide-boost immunization strategy for targeting Ab production to a specific epitope on a protein. In Chapter 2, phage are compared as a carrier for a synthetic peptide to the classical carrier protein, ovalbumin (OVA). Both immunogens elicited strong anti-peptide Ab titers, with those elicited by OVA-peptide conjugate exceeding those produced by phage-peptide conjugate. Comparison of the anti-peptide and anti-carrier Ab responses showed that phage-peptide conjugate elicited a more focused anti-peptide Ab response than OVA-peptide conjugate. In Chapter 3, the dominant epitopes on phage are removed or altered. Engineered phage are tested as immunogens to determine if reduction of B-cell epitopes on the virion could further focus an Ab response against a peptide. One engineered phage variant (Δ3) produced lower Ab titers than wild type (WT) phage. A recombinant peptide displayed on the surface of the Δ3 phage immunogen produced a poor anti-peptide Ab responses compared to WT. In contrast, the Δ3 phage did focus an Ab response against a chemically-conjugated synthetic peptide compared to WT. These differences may be due to variation in copy number or inherent peptide immunogenicity. Chapter 4 tests if an Ab-specific peptide can selectively amplify an oligoclonal population of memory B-cells that were primed by an immunization with the polyclonal antigen hen egg lysozyme (HEL). This approach is enhanced by adding a T-cell epitope from OVA to the priming and boosting immunogens. A prime with HEL followed by a boost with phage bearing a HEL-specific peptide, produced a moderate increase in Abs that cross-react with HEL. However, this came at the expense of producing a de novo Ab response to non-targeted epitopes on the boosting immunogen. Taken together, these results suggest that, in some situations, moderate epitope targeting is possible; however, more studies are required to optimize this approach.