Development of flexible hepatitis B virus core protein virus-like particles as a universal vaccine scaffold using a range of antigen-capturing systems

Abstract

The development of safe and flexible vaccines is an essential tool to fight emerging and re-emerging pathogens. Virus-like particles (VLPs) offer promising and adaptable options in vaccine development due to their safety and high immunogenicity. VLPs are non-infectious viral structures mimicking native viruses and can stimulate cellular and humoral immune responses. Additionally, VLPs can be modified as generic vaccine platforms to present various antigens.

In this project, hepatitis B core antigen (HBcAg) VLPs were investigated as a presentation platform based on a fused dimer of two monomeric subunits. HBcAg VLPs were modified to incorporate antigen-capturing systems (ACSs) to create a new platform. The ACSs used here are small artificial non-antibody binding proteins that recognise and bind specific protein targets. The ACSs selected were an Affimer against small ubiquitin-like modifier (SUMO) tag, as well as the SpyTag/SpyCatcher systems. In model one, VLPs presented a single ACS: Affimer, SpyTag, or SpyCatcher at the N-terminus or the major immunodominant region (MIR) of HBcAg. In model two, dual antigen-capturing systems (dACSs) were used: Affimer was engineered into the MIR and SpyTag into the N-terminus. The dACS VLPs allow the decoration with dual antigens to enhance immunogenicity against a specific pathogen. These VLPs were successfully produced in a yeast expression system (Pichia pastoris, which is also known as Komagataella phaffii).

In addition to the production of different VLPs, a fragment of glycoprotein G from respiratory syncytial virus (RSV-G) was also generated. The RSV-G protein was tagged with either SUMO tag or SpyCatcher to allow interaction with the corresponding VLP. RSV-G proteins were then successfully expressed in mammalian expression systems.

The VLPs described above were decorated with a range of proteins, including glycoprotein 1 (GP1) of the Junín virus and glycoprotein G of the RSV-G. One of the VLPs was tested in an immunisation study in mice (with Junín virus GP1 as an antigen). The results showed superior responses for the decorated VLPs compared to the noncomplexed GP1. The results described in this thesis have demonstrated the development of a novel vaccine platform that could be employed with a number of different antigens in the future.