Abstract
A major hurdle in vaccine development is the difficulty in identifying relevant target epitopes and then presenting them to the immune system in a context that mimics their native conformation. We have engineered novel virus-like-particle (VLP) technology that is able to display complex libraries of random peptide sequences on a surface-exposed loop in the coat protein without disruption of protein folding or VLP assembly. This technology allows us to use the same VLP particle for both affinity selection and immunization, integrating the power of epitope discovery and epitope mimicry of traditional phage display with the high immunogenicity of VLPs. Previously, we showed that using affinity selection with our VLP platform identifies linear epitopes of monoclonal antibodies and subsequent immunization generates the proper antibody response. To test if our technology could identify immunologic mimotopes, we used affinity selection on a monoclonal antibody (AP4-24H11) that recognizes the Staphylococcus aureus autoinducing peptide 4 (AIP4). AIP4 is a secreted eight amino acid, cyclized peptide produced from the S. aureus accessory gene regulator (agrIV) quorum-sensing operon. The agr system coordinates density dependent changes in gene expression, leading to the upregulation of a host of virulence factors, and passive transfer of AP4-24H11 protects against S. aureus agrIV-dependent pathogenicity. In this report, we identified a set of peptides displayed on VLPs that bound with high specificity to AP4-24H11. Importantly, similar to passive transfer with AP4-24H11, immunization with a subset of these VLPs protected against pathogenicity in a mouse model of S. aureus dermonecrosis. These data are proof of principle that by performing affinity selection on neutralizing antibodies, our VLP technology can identify peptide mimics of non-linear epitopes and that these mimotope based VLP vaccines provide protection against pathogens in relevant animal models.
Highlights
The small particulate nature and multivalent structure of viruslike particles cause them to provoke strong immune responses and make them effective scaffolds for displaying heterologous antigens in a highly immunogenic format
We recently showed the utility of this VLP technology to identify linear epitopes and to elicit the proper antibody response by performing affinity selection using a set of well-characterized monoclonal antibodies (mAbs) [10]
In order to identify mimotopes of the autoinducing peptide 4 (AIP4) mAb AP4-24H11 epitope, we performed affinity selection on AP4-24H11 using our random sequence peptide libraries displayed on MS2 VLPs
Summary
The small particulate nature and multivalent structure of viruslike particles cause them to provoke strong immune responses and make them effective scaffolds for displaying heterologous antigens in a highly immunogenic format. The most widely used method for epitope identification is through affinity selection using peptide libraries displayed on a filamentous phage This technology has identified the epitopes of many monoclonal antibodies (mAbs), and is a powerful technique for mapping linear epitopes and discovering peptide mimics of conformational and non-peptide epitopes. Epitopes identified by phage display must be produced synthetically, linked to a carrier, and displayed in a structural context unrelated to the selected phage. Often, in this new conformation the peptides have vastly decreased affinity for the selecting molecule and frequently lose the ability to induce antibodies that mimic the selecting antibody
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