A bispecific monomeric nanobody induces SARS-COV-2 spike trimer dimers (preprint)

Antibodies binding to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike have therapeutic promise, but emerging variants show the potential for virus escape. Thus, there is a need for therapeutic molecules with distinct and novel neutralization mechanisms. Here we isolated a nanobody that potently neutralizes SARS-CoV-2, including the B.1.351 variant, and cross-neutralizes SARS-CoV. We demonstrate the therapeutic potential of the nanobody in a human ACE2 transgenic mouse model. Using biochemistry and electron cryomicroscopy we show that this nanobody simultaneously interacts with two RBDs from different spike trimers, rapidly inducing the formation of spike trimer-dimers. This naturally elicited bispecific monomeric nanobody establishes a novel strategy for potent immobilization of viral antigens.

Adjuvanted SARS-CoV-2 Spike Protein Elicits Neutralizing Antibodies and CD4 T Cell Responses after a Single Immunization in Mice (preprint)

Background: SARS-CoV-2 has caused a global pandemic, infecting millions of people. A safe, effective vaccine is urgently needed and remains a global health priority. Subunit vaccines are used successfully against other viruses when administered in the presence of an effective adjuvant. Methods: We evaluated three different clinically tested adjuvant systems in combination with the SARS-CoV-2 pre-fusion stabilized (S-2P) spike protein using a one-dose regimen in mice.Findings: Whilst spike protein alone was only weakly immunogenic, the addition of either Aluminum hydroxide, a squalene based oil-in-water emulsion system (SE) or a cationic liposome-based adjuvant significantly enhanced antibody responses against the spike receptor binding domain (RBD). Kinetics of antibody responses differed, with SE providing the most rapid response. Neutralizing antibodies developed after a single immunization in all adjuvanted groups with ID 50 titers ranging from 86 - 4063. Spike-specific CD4 T helper responses were also elicited, comprising mainly of IFN-g and IL-17 producing cells in the cationic liposome adjuvanted group, and more IL-5- and IL-10-secreting cells in the AH group.Interpretation: These results demonstrate that adjuvanted spike protein subunit vaccine is a viable strategy for rapidly eliciting SARS-CoV-2 neutralizing antibodies and CD4 T cell responses of various qualities depending on the adjuvant used, which can be explored in further vaccine development against COVID-19.Funding: This work was supported by the European Union Horizon 2020 research and innovation program under grant agreement no. 101003653.Declaration of Interests: D.C. is co-inventor on patents on the cationic adjuvant formulations (CAF). All rights have been turned over to Statens Serum Institut, which is a non-profit government research facility. The rest of the authors declare that there are no competing interests.Ethics Approval Statement: Mouse studies were conducted in accordance with the regulations set forth by the National Committee for the Protection of Animals used for Scientific Purposes and in accordance with European Community Directive 86/609. The experiments have been approved by the governmental Animal Experiments Inspectorate under license 2017-15- 0201-01363.