SARS-CoV-2 vaccines based on RBDs with engineered glycosylation sites

We are developing vaccine antigens for SARS-CoV-2 that focus the antibody response onto neutralizing epitopes in the receptor binding domain (RBD) of the viral Spike (S) protein. Booster antigens derived from variants of SARS-CoV-2 would especially benefit from being limited to the RBD, due to the preponderance of conserved but non-neutralizing epitopes in the full-length S protein. However, RBD-only vaccines face the technical limitations of aggregation and poor expression, due to hydrophobic patches on the RBD that form the inter-subunit interfaces in the native S protein. We have overcome these limitations by engineering N- linked glycosylation sites into the RBD. These glycans also help to focus the immune response away from off-target faces of the RBD, and onto the targets for potent neutralizing antibody responses. We will extend this strategy further, to focus the antibody response onto neutralizing epitopes in the RBD that are conserved among variants of SARS-CoV-2. The RBD antigens will be tested as lipid nanoparticle (LNP)-mRNA vaccines. In Phase I of this project, we will enhance the intrinsic immunogenicity of RBD antigens delivered as LNP-mRNA vaccines. In Phase II, we will build upon this platform to compare boosters based on variant- derived RBD versus variant-derived full-length S, and to optimize RBD antigens for focusing antibody responses onto neutralizing epitopes that are conserved among variants of SARS-CoV-2. The antigens generated by this project will exploit four levels of immunofocusing to elicit or boost antibody responses that recognize conserved epitopes in the RBD and neutralize antigenically-distinct variants of SARS-CoV-2.