New Approaches to the Development of Peptoid Vaccines

Abstract

The ideal prophylactic vaccine against a toxin or pathogen should elicit the production of broadly protective antibodies against conserved epitopes. However, the epitopes that elicit these antibodies are often not immunodominant and even when they are, characterizing and synthesizing them can be difficult, particularly if they are conformational. The long-term goal of this work was to develop prophylactic vaccines that elicit such antibodies without epitope characterization. To develop such a vaccine platform, it was hypothesized that screening large one-bead-one-compound libraries of synthetic compounds with monoclonal antibodies that have already been shown to be broadly protective against a toxin or pathogen would allow the identification of mimetic B cell epitopes. For this platform, peptoids were chosen to construct one-bead-one-compound libraries. Peptoids are N-oligosubstituted glycines that resemble peptides but bear their side groups on backbone nitrogens instead of carbons. This renders them protease resistant and enormously diverse, since they are not restricted to the twenty standard amino acids. Furthermore, previous work had demonstrated that a monoclonal antibody could be used to screen libraries of peptoids. Moreover, while peptoids themselves were not immunogenic, the attachment of peptoids to carrier proteins using a linker elicited antibodies against the peptoid/linker. Such T-cell dependent antigens elicited high-affinity, class-switched antibodies. The goal of this dissertation research was to continue optimizing the magnetic and color-based assays by which peptoid vaccine candidates could be identified and to screen libraries with neutralizing monoclonal antibodies against West Nile virus and murine norovirus type 1. In addition, the immunogenicity of peptoids was further examined by designing a peptoid-carrier, using it to immunize rabbits, and demonstrating that anti-peptoid antibodies could be affinity-purified from the resulting antisera. This antibody was then used in further optimization of the magnetic screening assay to ensure that future screens will efficiently and specifically identify the best vaccine candidates.