SARS-CoV-2 neutralizing human recombinant antibodies selected from pre-pandemic healthy donors binding at RBD-ACE2 interface

COVID-19 is a severe acute respiratory disease caused by SARS-CoV-2, a novel betacoronavirus discovered in December 2019 and closely related to the SARS coronavirus (CoV). Both viruses use the human ACE2 receptor for cell entry, recognizing it with the Receptor Binding Domain (RBD) of the S1 subunit of the viral spike (S) protein. The S2 domain mediates viral fusion with the host cell membrane. Experience with SARS and MERS coronavirus has shown that potent monoclonal neutralizing antibodies against the RBD can inhibit the interaction with the virus cellular receptor (ACE2 for SARS) and block the virus cell entry. Assuming that a similar strategy would be successful against SARS-CoV-2, we used phage display to select from the human naive universal antibody gene libraries HAL9/10 anti SARS2 spike antibodies capable of inhibiting interaction with ACE2. 309 unique fully human antibodies against S1 were identified. 17 showed more than 75% inhibition of spike binding to cells expressing ACE2, assessed by flow cytometry and several antibodies showed even an 50% inhibition at a molar ratio of the antibody to spike protein or RBD of 1:1. Furthermore, these antibodies neutralized active SARS-Cov-2 virus infection of VeroE6 cells. All 17 were all able to bind the isolated RBD, four of them with sub-nanomolar EC50. Epitope analysis of the antibodies revealed that six bind at the RBD-ACE2 interface and two on the opposite side of the domain. Universal libraries from healthy donors offer the advantage that antibodies can be generated quickly and independent from the availability of material from recovered patients in a pandemic situation.