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

ABSTRACT 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. Efficient expression of the RBD in technically-demanding formats, e.g., on a self-assembling multimer scaffold, was achieved by engineering N-linked glycosylation sites into the RBD. The engineered N-linked glycosylation sites occlude hydrophobic patches that form inter-subunit interfaces in the native S protein, but that interfere with expression of the RBD in other contexts. The 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 the potential for this strategy to focus the neutralizing antibody response further, onto conserved epitopes in the RBD. This overall strategy maximizes the focusing of neutralizing antibody responses onto epitopes that are conserved among variants of SARS-CoV-2. In addition, we will compare, and possibly combine, immunofocusing with approaches designed to elicit variant-specific neutralizing antibodies. We will develop and utilize two distinct platforms for expressing these RBD antigens: mRNA delivered by lipid nanoparticles (LNPs), and a novel scaffold for efficiently displaying multimers of RBD antigens as recombinant protein. LNP-mRNA vaccines have the advantage of being a validated approach for vaccinating against SARS-CoV-2, whereas the novel multimer scaffold has the advantage of being heat stable after lyophilization. The antigens generated by this project exploit three layers of immunofocusing to elicit or boost antibody responses that neutralize diverse variants of SARS-CoV-2.