Neutralizing antibodies are associated with protection in animal models of coronavirus infection and vaccination.

Prior to the emergence of severe acute respiratory syndrome coronavirus (SARS-CoV) in 2002, human coronaviruses were primarily thought to cause relatively mild, respiratory disease. The emergence of Middle East respiratory syndrome coronavirus (MERS-CoV) in 2012 marked the introduction of a second highly pathogenic respiratory coronavirus, which continues to cause sporadic cases in Saudi Arabia. Dromedary camels are currently the only known animal reservoir for MERS-CoV and contact with camels is thought to be the source of over half of all primary human cases. Currently, several efforts are being made to develop a vaccine for camels as an intervention strategy to stop transmission from camels into humans. To date, there have been limited studies regarding the immune response from natural infection or vaccination in camels against MERS-CoV. Given the limitations in accessing and working with dromedary camels, an alpaca model which accurately recapitulates MERS-CoV infection in camels was established and subsequently, the neutralizing antibody response to infection and vaccination was characterized. The induction of neutralizing IgG1 and IgG3 isotypes following experimental MERS-CoV infection protected alpacas from subsequent re-infection. Similarly, a S1-based subunit vaccine delivered intramuscularly induced a similar IgG1 and IgG3 neutralizing antibody response, resulting in nearly complete protection following MERS-CoV challenge in alpacas. Moreover, the antibodies induced following infection as well vaccination were able to neutralize currently circulating MERS-CoV isolates from Saudi Arabian dromedary camels, despite of the presence of amino acid changes in the spike protein, the major target for neutralizing antibodies. This data suggests that the neutralizing antibody response may be useful for predicting protection following infection and vaccination. The recently emerged severe acute respiratory syndrome coronavirus- 2 (SARS-CoV-2), the causative agent of one of the worst pandemics, continues to circulate in humans. Since the isolation of the first strain of SARS-CoV-2, various variants of concern (VOC) have emerged with increased transmissibility and potential for immune escape. Using a hamster model, the neutralizing and cross-neutralizing activity for the B.1.1.7 and B.1.351 VOCs of SARS-CoV-2 were evaluated. The neutralizing activity varied depending on the VOC used for the challenge, with B.1.351 infection in hamsters inducing overall lower levels of neutralizing antibodies. These findings were consistent with differential neutralizing activity against VOCs induced by two different S1 based subunit vaccines. In the vaccine study, reduced neutralizing activity against B.1.351 resulted in reduced protection in hamsters. Finally, to demonstrate that neutralizing antibodies alone can provide protection from infection, two monoclonal antibodies; Ab1 and Ab8 targeting spike protein of SARS-CoV-2 were administered prophylactically and therapeutically in a hamster model of SARS-CoV-2 infection. Both monoclonal antibodies reduced SARS-CoV-2 viral titers as well as lung pathology in dose-dependent manner. Interestingly, higher concentrations of Ab8 were found in hamster lungs compared to Ab1 despite of being administered at comparable doses. The ability of monoclonal antibodies to reduce levels of virus and virus-induced pathology provides further supporting evidence that neutralizing antibodies likely play a critical role in protection from infection with respiratory CoV. These findings have major implications to design better vaccine and therapeutic strategies against the coronaviruses to provide a protection against severe disease

High Potency of a Bivalent Human VH Domain in SARS-CoV-2 Animal Models

Novel COVID-19 therapeutics are urgently needed. We generated a phage-displayed human antibody VH domain library from which we identified a high-affinity VH binder ab8. Bivalent VH, VH-Fc ab8, bound with high avidity to membrane-associated S glycoprotein and to mutants found in patients. It potently neutralized mouse-adapted SARS-CoV-2 in wild-type mice at a dose as low as 2 mg/kg and exhibited high prophylactic and therapeutic efficacy in a hamster model of SARS-CoV-2 infection, possibly enhanced by its relatively small size. Electron microscopy combined with scanning mutagenesis identified ab8 interactions with all three S protomers and showed how ab8 neutralized the virus by directly interfering with ACE2 binding. VHFc ab8 did not aggregate and did not bind to 5,300 human membrane-associated proteins. The potent neutralization activity of VH-Fc ab8 combined with good developability properties and cross-reactivity to SARS-CoV-2 mutants provide a strong rationale for its evaluation as a COVID-19 therapeutic

Rapid identification of a human antibody with high prophylactic and therapeutic efficacy in three animal models of SARS-CoV-2 infection

Effective therapies are urgently needed for the SARS-CoV-2/COVID-19 pandemic. We identified panels of fully human monoclonal antibodies (mAbs) from large phage-displayed Fab, scFv, and VH libraries by panning against the receptor binding domain (RBD) of the SARS-CoV-2 spike (S) glycoprotein. A high-affinity Fab was selected from one of the libraries and converted to a full-size antibody, IgG1 ab1, which competed with human ACE2 for binding to RBD. It potently neutralized replication-competent SARS-CoV-2 but not SARS-CoV, as measured by two different tissue culture assays, as well as a replication-competent mouse ACE2-adapted SARS-CoV-2 in BALB/c mice and native virus in hACE2-expressing transgenic mice showing activity at the lowest tested dose of 2 mg/kg. IgG1 ab1 also exhibited high prophylactic and therapeutic efficacy in a hamster model of SARS-CoV-2 infection. The mechanism of neutralization is by competition with ACE2 but could involve antibody-dependent cellular cytotoxicity (ADCC) as IgG1 ab1 had ADCC activity in vitro. The ab1 sequence has a relatively low number of somatic mutations, indicating that ab1-like antibodies could be quickly elicited during natural SARS-CoV-2 infection or by RBD-based vaccines. IgG1 ab1 did not aggregate, did not exhibit other developability liabilities, and did not bind to any of the 5,300 human membrane-associated proteins tested. These results suggest that IgG1 ab1 has potential for therapy and prophylaxis of SARS-CoV-2 infections. The rapid identification (within 6 d of availability of antigen for panning) of potent mAbs shows the value of large antibody libraries for response to public health threats from emerging microbes

High Potency of a Bivalent Human V H Domain in SARS-CoV-2 Animal Models

Novel COVID-19 therapeutics are urgently needed. We generated a phage-displayed human antibody V domain library from which we identified a high-affinity V binder ab8. Bivalent V , V -Fc ab8, bound with high avidity to membrane-associated S glycoprotein and to mutants found in patients. It potently neutralized mouse-adapted SARS-CoV-2 in wild-type mice at a dose as low as 2 mg/kg and exhibited high prophylactic and therapeutic efficacy in a hamster model of SARS-CoV-2 infection, possibly enhanced by its relatively small size. Electron microscopy combined with scanning mutagenesis identified ab8 interactions with all three S protomers and showed how ab8 neutralized the virus by directly interfering with ACE2 binding. V -Fc ab8 did not aggregate and did not bind to 5,300 human membrane-associated proteins. The potent neutralization activity of V -Fc ab8 combined with good developability properties and cross-reactivity to SARS-CoV-2 mutants provide a strong rationale for its evaluation as a COVID-19 therapeutic