Single-dose immunisation with a multimerised SARS-CoV-2 receptor binding domain (RBD) induces an enhanced and protective response in mice

The COVID-19 pandemic, caused by the SARS-CoV-2 coronavirus, has triggered a worldwide health emergency. So far, several different types of vaccines have shown strong efficacy. However, both the emergence of new SARS-CoV-2 variants and the need to vaccinate a large fraction of the worlds population necessitate the development of alternative vaccines, especially those that are simple and easy to store, transport and administer. Here, we showed that ferritin-like Dps protein from hyperthermophilic Sulfolobus islandicus can be covalently coupled with different SARS-CoV-2 antigens via the SpyCatcher system, to form extremely stable and defined multivalent dodecameric vaccine nanoparticles that remain intact even after lyophilisation. Immunisation experiments in mice demonstrated that the SARS-CoV-2 receptor binding domain (RBD) coupled to Dps (RBD-S-Dps) shows particular promise as it elicited a higher antibody titre and an enhanced neutralising antibody response compared to the monomeric RBD. Furthermore, we showed that a single immunisation with the multivalent RBD-S-Dps completely protected hACE2-expressing mice from serious illness and led to efficient viral clearance from the lungs upon SARS-CoV-2 infection. Our data highlight that multimerised SARS-CoV-2 subunit vaccines are a highly efficacious modality, particularly when combined with an ultra-stable scaffold.