ABSTRACT
Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has caused a pandemic and multiple vaccines have been developed and authorized for human use. While these vaccines reduce disease severity, they do not prevent infection allowing SARS-CoV-2 to continue to spread and evolve. To confer protection against infection and limit transmission, vaccines must be developed that induce mucosal immunity in the respiratory tract. Therefore, we performed proof-of-principle pre-clinical vaccine and challenge studies with a virus-particle mimicking intranasal vaccine against SARS-CoV-2. The vaccine candidate consisted of the self-assembling 60-subunit I3-01 protein scaffold covalently decorated with the SARS-CoV-2 receptor binding domain (RBD) using the SpyCatcher-SpyTag system. We verified the intended antigen display features by reconstructing the I3-01 scaffold to 3.4A using cryo-EM, and established RBD decoration through both SDS-PAGE and negative stain TEM. Using this RBD grafted SpyCage scaffold (RBD+SpyCage), we performed two vaccination studies in Syrian hamsters using an intranasal prime and boost vaccine regiment followed by SARS-CoV-2 challenge. The initial study focused on assessing the immunogenicity of RBD+SpyCage, which indicated that vaccination of hamsters induced a non-neutralizing antibody response that enhanced viral clearance but did not prevent infection. In an expanded study, we demonstrated that covalent bonding of RBD to the scaffold was required to induce an antibody response. Consistent with the initial study, animals vaccinated with RBD+SpyCage more rapidly cleared SARS-CoV-2 from both the upper and lower respiratory tract, whereas admixtures of SpyCage and RBD, or either component alone did not. These findings demonstrate the intranasal SpyCage vaccine platform can induce protection against SARS-CoV-2 and, with additional modifications to improve immunogenicity, is a versatile and adaptable system for the development of intranasal vaccines targeting respiratory pathogens.