Structural presentation of influenza epitopes on modular virus-like particles

Abstract

Vaccine development has increasingly developed toward subunit vaccine approach which uses highly-purified and well characterised components, such as antigenic peptides, to elicit an immune response. An antigenic peptide requires a protein carrier or platform e.g. virus-like particle (VLP), to improve its poor immunogenicity. Based on this approach, murine polyomavirus (MuPyV) VLP and its subunit (capsomere) have been employed as vaccine platforms to present heterogeneous epitopes or antigenic elements from targeted pathogens. The design rule for epitope presentation on VLPs still remains unclear. A tandem repeat display strategy, in which antigenic element was repetitively arrayed, led to the induction of a significant antibody titer against its native structure, compared with the use of flanking sequence. Tandem repeat display strategy might retain the epitope conformation that is close to its native structure. This work further investigates the structural presentation of Helix 190 (H190) and Helix A (HA2A), from influenza hemagglutinin, using tandem repeat strategy. Different tools are exploited to characterise the structures of presented epitopes. The major outcomes of this research are: (i) demonstrating the limitation of phage antibody panning as a tool to inform the structural presentation of epitope on modular VLPs; (ii) developing a simple tool for rapid screening of presented epitope conformation using circular dichroism spectroscopy coupled with singular value decomposition algorithms (CD-SVD); (iii) demonstrating the capability of tandem repeat strategy in promoting the helicity of the helical structure; (iv) establishing initial steps in determining atomic structure of presented epitope using X-ray crystallography. This work introduces, to the best of our knowledge, a CD-SVD method, a simple and rapid tool to characterise epitope conformation, particularly helical structure, on modular capsomeres. Due to the simplicity and speed, it enables the CD-SVD method to be employed as a screening tool for the structural presentation of antigenic modules. It allows the rapid identification of potential vaccine constructs in the early stage of vaccine development and therefore, reduces the further cost of pre-clinical and clinical trials. This work also demonstrates the structural presentation of HA2A using tandem repeat display strategy led to induce antibody titer against full-length hemagglutinin in the chicken trial. The finding reveals that a tandem repeat strategy promotes the helicity of inserts derived from native helical regions; this approach deserves further research into its potential as a generic design for the presentation of the helical antigenic elements on modular VLPs.