A SARS-CoV-2 neutralizing antibody selected from COVID-19 patients by phage display is binding to the ACE2-RBD interface and is tolerant to most known recently emerging RBD mutations

The novel betacoranavirus SARS-CoV-2 causes a form of severe pneumonia disease, termed COVID-19 (coronavirus disease 2019). Recombinant human antibodies are proven potent neutralizers of viruses and can block the interaction of viral surface proteins with their host receptors. To develop neutralizing anti-SARS-CoV-2 antibodies, antibody gene libraries from convalescent COVID-19 patients were constructed and recombinant antibody fragments (scFv) against the receptor binding domain (RBD) of the S1 subunit of the viral spike (S) protein were selected by phage display. The selected antibodies were produced in the scFv-Fc format and 30 showed more than 80% inhibition of spike (S1-S2) binding to cells expressing ACE2, assessed by flow cytometry screening assay. The majority of these inhibiting antibodies are derived from the VH3-66 V-gene. The antibody STE90-C11 showed a sub nM IC50 in a plaque-based live SARS-CoV-2 neutralization assay. The in vivo efficacy of the antibody was demonstrated in the Syrian hamster and in the hACE2 mice model using a silenced human IgG1 Fc part. The crystal structure of STE90-C11 Fab in complex with SARS-CoV-2-RBD was solved at 2.0 Å resolution showing that the antibody binds at the same region as ACE2 to RBD. The binding and inhibtion of STE90-C11 is not blocked by many known RBD mutations including N439K, L452R, E484K or L452R+E484Q (emerging B.1.617). STE90-C11 derived human IgG1 with FcγR silenced Fc (COR-101) is currently undergoing Phase Ib/II clinical trials for the treatment of moderate to severe COVID-19. In Brief Human antibodies were selected from convalescent COVID-19 patients using antibody phage display. The antibody STE90-C11 is neutralizing authentic SARS-CoV-2 virus in vitro and in vivo and the crystal structure of STE90-C11 in complex with SARS-CoV-2-RBD revealed that this antibody is binding in the RBD-ACE2 interface. S1 binding of STE90-C11 and inhibition of ACE2 binding is not blocked by many known RBD mutations. ### Competing Interest Statement The authors declare a conflict of interest. F.B., D.M., N.L., S.S., P.A.H., R.B., M.R., K.T.S., K.D.R.R., S.Z.-E., M.B., V.F., S.T., M.S. and M.H. are inventors on a patent application on blocking antibodies against SARS-CoV-2. A.H., A.F. and T.S. are officers of CORAT Therapeutics GmbH, a company founded by YUMAB GmbH for the clinical and regulatory development of STE90-C11 (development name COR-101) (ClinicalTrials.gov ID: [NCT04674566][1] for safety and efficacy of COR-101 in hospitalized patients with moderate to severe COVID-19). A.H. is shareholder of CORAT Therapeutics GmbH. S.D. and M.H. are advisors of Corat Therapeutics GmbH. A.F., T.S., S.D. and M.H. are shareholders of YUMAB GmbH. [1]: /lookup/external-ref?link_type=CLINTRIALGOV&access_num=NCT04674566&atom=%2Fbiorxiv%2Fearly%2F2021%2F05%2F21%2F2020.12.03.409318.atom