Immunogenicity and Vaccine Efficacy Boosted by Engineering Human Heavy Chain Ferritin and Chimeric Hepatitis B Virus Core Nanoparticles

Human heavy-chain ferritin (HFn) and hepatitis B virus core (HBc) are both nanoparticle proteins presenting a well-oriented architecture with constant size and shape, which can be engineered to carry epitopes on the surface of the nanoparticle protein cage, enabling vaccine design. This study aims to investigate the immunogenicity differences between engineered HFn and chimeric HBc bearing the same epitope. As a proof of concept, the model epitope Epstein-Barr nuclear antigen 1 (EBNA1) is inserted at the N-terminus of the HFn and HBc subunit to produce two vaccine candidates named EBNA1-HFn (E1F1) and EBNA1-HBc (E1H1), respectively. From in vivo immunogenicity studies, E1H1 demonstrates the capability to prompt significant humoral and cell-mediated immune responses in adjuvant-free formulation. When formulated with the aluminum hydroxide adjuvant, E1H1 produces approximately 5× higher titer and 2× stronger proliferation index (PI) than E1F1. These results confirm that the HBc carrier induces a stronger humoral immune response than HFn. On the other hand, from lymphocyte activation experiments, E1F1 induces a stronger cell-mediated immune response indicated by 5× more CD8+T cells and 2× more effector memory T cells in the E1F1 group versus the E1H1 group. Through this study, HFn and HBc are shown to be potentially effective vaccine carrier nanoparticles having subtly different immunological responses.