Adenovirus Nanoparticles Displaying RBD Induce a Protective Immune Response Against BA.5 in Mice.

INTRODUCTION: Adenovirus (Ad) vectors demonstrated significant efficacy as vaccine vectors during the COVID-19 pandemic. Hexon is the major capsid protein, and multiple hypervariable regions (HVRs) have been used for displaying exogenous antigens and inducing a strong antibody responses. METHODS: We utilized SpyCatcher/SpyTag technology to incorporate SpyTag into HVR2, 4, and 7 of the hexon of the bivalent vaccine strain rAd3/7, respectively, to construct recombinant Ad, rAd3/7-SpyTag. The receptor-binding domain (RBD) of the SARS-CoV-2 BA5.2 strain fused with SpyCatcher was expressed as SpyCatcher-RBD, Spycatcher-RBD and rAd3/7-SpyTag were incubated in vitro to prepare a novel nanoparticle vaccine candidate, rAd3/7-SpyRBD, against SARS-CoV-2. Characterize rAd3/7-SpyRBD using Western blot, ELISA, transmission electron microscopy (TEM), and particle size measurement, and verify its immunogenicity through mouse immunization. RESULTS: We have successfully established a universal nanoparticle vaccine platform, rAd3/7-SpyTag, and the RBD protein was successfully displayed on the surface of rAd3/7-SpyTag. Compared with SpyCatcher-RBD, rAd3/7-SpyRBD can rapidly induce the production of antibodies and stronger immune responses. Both Spycatcher-RBD and rAd3/7-SpyRBD provide a protective immune response against BA.5 in mouse model mice and can be used as candidates for SARS-CoV-2 vaccine. We also found that rAd3/7-SpyRBD induced the production of neutralizing antibodies against Ad3 and Ad7, suggested that it could serve as an Ads vaccine candidate. CONCLUSION: We developed a universal nanoparticle vaccine platform and obtained a trivalent vaccine candidate rAd3/7-SpyRBD, against SARS-CoV-2, Ad3, and Ad7, and this is the first time to use SpyCatcher/SpyTag technology in a bivalent rAd3/7 vector for trivalent immunity.