Exploiting a Hepatitis B Core Protein VLP Vaccine Scaffold for Affimer-Based Antigen Capture

Abstract

Generating a fast and easily transferable system to develop highly immunogenic vaccines, providing long-lasting protection against future disease outbreaks, is highly desirable. The hepatitis core antigen (HBc) forms VLPs that are well-characterised and therefore could be modified to serve as a universal scaffold system. The work described in this thesis aimed to further modify this platform system and to evaluate the immunogenicity of antigen-bound VLPs. The immunogenicity experiments employed VLPs with an Affimer which bound to a SUMO tag at the N-terminus (N-VelcroVax VLP) scaffold system in murine models. A soluble RSV-G glycoprotein fragment was fused to a SUMO tag and used to decorate the VLPs. Enhanced levels of RSV- G antibodies were detected when the antigen was displayed on the VLP. In addition, VLPs with a C-terminal truncation of the nucleic acid binding region of HBc were compared. It appeared that encapsulated nucleic acids within N-VelcroVax VLPs most likely acted as an adjuvant and generated higher antibody titres than the VLPs generated from the truncated HBc proteins. This work also aimed to utilise a trimerisation motif to present an antigen in its trimeric form via Affimer technology. Two motifs were used. Foldon, a common trimerisation domain used in vaccine research, was used as the first target for Affimer selection. Human cartilage matrix protein (hCMP) forms a stable trimer via disulphide bonds to a fused antigen and was a successful target for Affimer selection. Five Affimer clones were selected for further study. To find the best binding sequence, ELISA and direct competition assay by native mass spectrometry were used. Affimers were introduced into the N-terminus of HBc to generate hCMP-Affimer HBc VLPs. ELISA was used to evaluate the interaction between the VLPs and a tagged antigen. Overall, the work presented here demonstrates the utility of the HBc system as an antigen-presentation platform.