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Understanding broadly neutralizing sarbecovirus antibody responses is key to developing countermeasures against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants and future zoonotic sarbecoviruses. We describe the isolation and characterization of a human monoclonal antibody, designated S2K146, that broadly neutralizes viruses belonging to SARS-CoV– and SARS-CoV-2–related sarbecovirus clades, which use angiotensin-converting enzyme 2 (ACE2) as an entry receptor. Structural and functional studies show that most of the virus residues that directly bind S2K146 are also involved in binding to ACE2. This allows the antibody to potently inhibit receptor attachment. S2K146 protects against SARS-CoV-2 Beta variant challenge in hamsters, and viral passaging experiments reveal a high barrier for emergence of escape mutants, making it a good candidate for clinical development. The conserved ACE2-binding residues present a site of vulnerability that might be leveraged for developing vaccines eliciting broad sarbecovirus immunity.

The recent emergence of SARS-CoV-2 variants of concern1-10 and the recurrent spillovers of coronaviruses11,12 into the human population highlight the need for broadly neutralizing antibodies that are not affected by the ongoing antigenic drift and that can prevent or treat future zoonotic infections. Here we describe a human monoclonal antibody designated S2X259, which recognizes a highly conserved cryptic epitope of the receptor-binding domain and cross-reacts with spikes from all clades of sarbecovirus. S2X259 broadly neutralizes spike-mediated cell entry of SARS-CoV-2, including variants of concern (B.1.1.7, B.1.351, P.1, and B.1.427/B.1.429), as well as a wide spectrum of human and potentially zoonotic sarbecoviruses through inhibition of angiotensin-converting enzyme 2 (ACE2) binding to the receptor-binding domain. Furthermore, deep-mutational scanning and in vitro escape selection experiments demonstrate that S2X259 possesses an escape profile that is limited to a single substitution, G504D. We show that prophylactic and therapeutic administration of S2X259 protects Syrian hamsters (Mesocricetus auratus) against challenge with the prototypic SARS-CoV-2 and the B.1.351 variant of concern, which suggests that this monoclonal antibody is a promising candidate for the prevention and treatment of emergent variants and zoonotic infections. Our data reveal a key antigenic site that is targeted by broadly neutralizing antibodies and will guide the design of vaccines that are effective against all sarbecoviruses.

The SARS-CoV-2 spike (S) glycoprotein contains an immunodominant receptor-binding domain (RBD) targeted by most neutralizing antibodies (Abs) in COVID-19 patient plasma. Little is known about neutralizing Abs binding to epitopes outside the RBD and their contribution to protection. Here, we describe 41 human monoclonal Abs (mAbs) derived from memory B cells, which recognize the SARS-CoV-2 S N-terminal domain (NTD) and show that a subset of them neutralize SARS-CoV-2 ultrapotently. We define an antigenic map of the SARS-CoV-2 NTD and identify a supersite (designated site i) recognized by all known NTD-specific neutralizing mAbs. These mAbs inhibit cell-to-cell fusion, activate effector functions, and protect Syrian hamsters from SARS-CoV-2 challenge, albeit selecting escape mutants in some animals. Indeed, several SARS-CoV-2 variants, including the B.1.1.7, B.1.351 and P1 lineages, harbor frequent mutations within the NTD supersite suggesting ongoing selective pressure and the importance of NTD-specific neutralizing mAbs for protective immunity and vaccine design., McCallum et al. identify a supersite in the N-terminal domain of SARS-CoV-2 spike protein that is targeted by neutralizing antibodies and exhibits mutation in response to selective pressure.

A strong cocktail against SARS-CoV-2 Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is initiated by the trimeric spike protein that decorates the virus and binds the ACE2 receptor. Antibodies against the spike that neutralize viral infection have potential as therapeutics. Tortorici et al. describe two very potent antibodies, S2E12 and S2M11. Electron microscopy structures characterized the binding and showed that S2E12 traps the spike in a conformation that cannot bind ACE2. Both antibodies protected hamsters against SARS-CoV-2 challenge and may be useful in antibody cocktails to combat the virus and prevent the development of resistance. Science, this issue p. 950, A potent antibody cocktail blocks attachment of SARS-CoV-2 to the host receptor and activates a protective immune response., Efficient therapeutic options are needed to control the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that has caused more than 922,000 fatalities as of 13 September 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 angiotensin-converting enzyme 2 (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. Antibody cocktails that include 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.

In this study, a series of 10 quinoline analogues was evaluated for their in vitro antiviral activity against a panel of alpha- and beta-coronaviruses, including the severe acute respiratory syndrome coronaviruses 1 and 2 (SARS-CoV-1 and SARS-CoV-2), as well as the human coronaviruses (HCoV) 229E and OC43. Chloroquine and hydroxychloroquine were the most potent with antiviral EC50 values in the range of 0.12–12 μM. Chloroquine displayed the most favorable selectivity index (i.e. ratio cytotoxic versus antiviral concentration), being 165 for HCoV-OC43 in HEL cells. Potent anti-coronavirus activity was also observed with amodiaquine, ferroquine and mefloquine, although this was associated with substantial cytotoxicity for mefloquine. Primaquine, quinidine, quinine and tafenoquine only blocked coronavirus replication at higher concentrations, while piperaquine completely lacked antiviral and cytotoxic effects. A time-of-addition experiment in HCoV-229E-infected HEL cells revealed that chloroquine interferes with viral entry at a post-attachment stage. Using confocal microscopy, no viral RNA synthesis could be detected upon treatment of SARS-CoV-2-infected cells with chloroquine. The inhibition of SARS-CoV-2 replication by chloroquine and hydroxychloroquine coincided with an inhibitory effect on the autophagy pathway as visualized by a dose-dependent increase in LC3-positive puncta. The latter effect was less pronounced or even absent with the other quinolines. In summary, we showed that several quinoline analogues, including chloroquine, hydroxychloroquine, amodiaquine, ferroquine and mefloquine, exhibit broad anti-coronavirus activity in vitro.