Flavivirus-based bivalent nanoparticle vaccines induce neutralizing antibodies and Th1 responses against flavivirus and coupling antigens.

Effective vaccines against flaviviruses, including Japanese encephalitis virus (JEV), are widely used. We developed antigen-loaded nanoparticle vaccines, using JEV virus-like particles (JEV-VLPs) as carriers. The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike receptor-binding domain (S-RBD) was covalently coupled to specific peptide insertion sites on the JEV envelope protein. Mice immunized with these coupled particles (JEprME-S-RBD) produced high levels of neutralizing antibodies against both JEV and SARS-CoV-2, with broad activity against multiple SARS-CoV-2 variants. These mice also had a larger number of interferon (IFN)-γ-producing cells with higher levels of anti-S-RBD IgG2a production than mice receiving the JEV-VLP and S-RBD without coupling. These results suggested the induction of T helper (Th) 1 immune responses. We also constructed JEV nanoparticles coupled with human parvovirus B19 RBD, which efficiently induced neutralizing antibodies against both JEV and parvovirus. Therefore, flaviviral nanoparticles can serve as versatile multivalent vaccine platforms by incorporating neutralizing epitopes from different pathogens.