Efficient therapeutic options are needed to control the spread of SARS-CoV-2 that has caused more than 922,000 fatalities as of September 13th, 2020. We report the isolation and characterization of two ultrapotent SARS-CoV-2 human neutralizing antibodies (S2E12 and S2M11) that protect hamsters against SARS-CoV-2 challenge. Cryo-electron microscopy structures show that S2E12 and S2M11 competitively block ACE2 attachment and that S2M11 also locks the spike in a closed conformation by recognition of a quaternary epitope spanning two adjacent receptor-binding domains. Cocktails including S2M11, S2E12 or the previously identified S309 antibody broadly neutralize a panel of circulating SARS-CoV-2 isolates and activate effector functions. Our results pave the way to implement antibody cocktails for prophylaxis or therapy, circumventing or limiting the emergence of viral escape mutants.

Highlights d The receptor-binding motif (RBM) is a highly variable region of SARS-CoV-2 spike d RBM mutation N439K has emerged independently in multiple lineages d N439K increases spike affinity for hACE2; viral fitness and disease are unchanged d N439K confers resistance to several mAbs and escapes some polyclonal responses

An ideal anti-SARS-CoV-2 antibody would resist viral escape [1][2][3] , have activity against diverse SARS-related coronaviruses (sarbecoviruses) [4][5][6][7] , and be highly protective through viral neutralization [8][9][10][11] and effector functions 12,13 . Understanding how these properties relate to each other and vary across epitopes would aid development of antibody therapeutics and guide vaccine design. Here, we comprehensively characterize escape, breadth, and potency across a panel of SARS-CoV-2 antibodies targeting the receptor-binding domain (RBD). Despite a tradeoff between in vitro neutralization potency and breadth of sarbecovirus binding, we identify neutralizing antibodies with exceptional sarbecovirus breadth and a corresponding resistance to SARS-CoV-2 escape. One of these antibodies, S2H97, binds with high affinity across all sarbecovirus clades to a previously undescribed cryptic epitope and prophylactically protects hamsters from viral challenge. Antibodies targeting the ACE2 receptor binding motif (RBM) typically have poor breadth and are readily escaped by mutations despite high neutralization potency. Nevertheless, we characterize one potent RBM antibody (S2E12 8 ) with breadth across sarbecoviruses related to SARS-CoV-2 and a high barrier to viral escape. These data highlight principles underlying variation in escape, breadth, and potency among antibodies targeting the RBD, and identify epitopes and features to prioritize for therapeutic development against the current and potential future pandemics.The most potently neutralizing antibodies to SARS-CoV-2-including those in clinical use 14 and dominant in polyclonal sera 15,16 -target the spike receptor-binding domain (RBD). Mutations in the RBD that reduce binding by antibodies have emerged among SARS-CoV-2 variants [17][18][19][20][21] , highlighting the need for antibodies and vaccines that are robust to viral escape. We have previously described an antibody, S309 4 , that exhibits potent effector functions and neutralizes all current SARS-CoV-2 variants 22,23 and the divergent sarbecovirus SARS-CoV-1. S309 forms the basis for an antibody therapy (VIR-7831, recently renamed sotrovimab) that has received Emergency Use Authorization from the FDA for treatment of COVID-19 24 . Longer term, antibodies with broad activity across SARS-related coronaviruses (sarbecoviruses) would be useful to combat potential future spillovers 6 . These efforts would be aided by a systematic understanding of the relationships among antibody epitope,

VIR-7831 and VIR-7832 are dual action monoclonal antibodies (mAbs) targeting the spike glycoprotein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). VIR-7831 and VIR-7832 were derived from a parent antibody (S309) isolated from memory B cells of a 2003 severe acute respiratory syndrome coronavirus (SARS-CoV) survivor. Both mAbs contain an LS mutation in the Fc region to prolong serum half-life and potentially enhance distribution to the respiratory mucosa. In addition, VIR-7832 encodes an Fc GAALIE mutation that has been shown previously to evoke CD8+ T-cells in the context of an in vivo viral respiratory infection. VIR-7831 and VIR-7832 potently neutralize live wild-type SARS-CoV-2 in vitro as well as pseudotyped viruses encoding spike protein from the B.1.1.7, B.1.351 and P.1 variants. In addition, they retain activity against monoclonal antibody resistance mutations that confer reduced susceptibility to currently authorized mAbs. The VIR-7831/VIR-7832 epitope does not overlap with mutational sites in the current variants of concern and continues to be highly conserved among circulating sequences consistent with the high barrier to resistance observed in vitro. Furthermore, both mAbs can recruit effector mechanisms in vitro that may contribute to clinical efficacy via elimination of infected host cells. In vitro studies with these mAbs demonstrated no enhancement of infection. In a Syrian Golden hamster proof-of concept concept wildtype SARS-CoV-2 infection model, animals treated with VIR-7831 had less weight loss, and significantly decreased total viral load and infectious virus levels in the lung compared to a control mAb. Taken together, these data indicate that VIR-7831 and VIR-7832 are promising new agents in the fight against COVID-19.