With the emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants with increased transmissibility and potential resistance, antibodies and vaccines with broadly inhibitory ...activity are needed. Here, we developed a panel of neutralizing anti-SARS-CoV-2 monoclonal antibodies (mAbs) that bound the receptor binding domain of the spike protein at distinct epitopes and blocked virus attachment to its host receptor, human angiotensin converting enzyme-2 (hACE2). Although several potently neutralizing mAbs protected K18-hACE2 transgenic mice against infection caused by ancestral SARS-CoV-2 strains, others induced escape variants in vivo or lost neutralizing activity against emerging strains. One mAb, SARS2-38, potently neutralized all tested SARS-CoV-2 variants of concern and protected mice against challenge by multiple SARS-CoV-2 strains. Structural analysis showed that SARS2-38 engaged a conserved epitope proximal to the receptor binding motif. Thus, treatment with or induction of neutralizing antibodies that bind conserved spike epitopes may limit the loss of potency of therapies or vaccines against emerging SARS-CoV-2 variants.
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•SARS-CoV-2 mAbs recognizing the RBD block viral attachment and/or entry•SARS2-38 mAb efficiently inhibits infection of a broad panel of SARS-CoV-2 variants•Cryo-EM shows SARS2-38 binds a highly conserved region of the spike protein•SARS2-38 controls infection in vivo in K18-hACE2 transgenic mice and hamsters
VanBlargan et al. describe a potently neutralizing mAb, SARS2-38, that recognizes a panel of SARS-CoV-2 variants and confers therapeutic protection in vivo. Structure analysis of SARS2-38 bound to the viral spike protein reveals the basis of its broadly neutralizing activity, highlighting an epitope target for antibody therapeutics and vaccine design.
Omicron variant strains encode large numbers of changes in the spike protein compared to historical SARS-CoV-2 isolates. Although in vitro studies have suggested that several monoclonal antibody ...therapies lose neutralizing activity against Omicron variants, the effects in vivo remain largely unknown. Here, we report on the protective efficacy against three SARS-CoV-2 Omicron lineage strains (BA.1, BA.1.1, and BA.2) of two monoclonal antibody therapeutics (S309 Vir Biotechnology monotherapy and AZD7442 AstraZeneca combination), which correspond to ones used to treat or prevent SARS-CoV-2 infections in humans. Despite losses in neutralization potency in cell culture, S309 or AZD7442 treatments reduced BA.1, BA.1.1, and BA.2 lung infection in susceptible mice that express human ACE2 (K18-hACE2) in prophylactic and therapeutic settings. Correlation analyses between in vitro neutralizing activity and reductions in viral burden in K18-hACE2 or human FcγR transgenic mice suggest that S309 and AZD7442 have different mechanisms of protection against Omicron variants, with S309 utilizing Fc effector function interactions and AZD7442 acting principally by direct neutralization. Our data in mice demonstrate the resilience of S309 and AZD7442 mAbs against emerging SARS-CoV-2 variant strains and provide insight into the relationship between loss of antibody neutralization potency and retained protection in vivo.
Although mRNA vaccines encoding the spike protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) prevent COVID-19, the emergence of new viral variants jeopardizes their efficacy. ...Here, we assessed the immunogenicity and protective activity of historical (mRNA-1273, designed for Wuhan-1 spike protein) or modified (mRNA-1273.351, designed for B.1.351 spike protein) Moderna mRNA vaccines in 129S2 and K18-hACE2 mice. Mice were immunized with either high-dose or low-dose formulations of the mRNA vaccines, where low-dose vaccination modeled suboptimal immune responses. Immunization with formulations at either dose induced neutralizing antibodies in serum against ancestral SARS-CoV-2 WA1/2020 and several virus variants, although serum titers were lower against the B.1.617.2 (Delta) virus. Protection against weight loss and lung pathology was observed with all high-dose vaccines against all viruses. However, low-dose formulations of the vaccines, which produced lower magnitude antibody and T cell responses, showed breakthrough lung infections with B.1.617.2 and development of pneumonia in K18-hACE2 mice. Thus, in individuals with reduced immunity after mRNA vaccination, breakthrough infection and disease may occur with some SARS-CoV-2 variants.
Emerging severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants with antigenic changes in the spike protein are neutralized less efficiently by serum antibodies elicited by legacy ...vaccines against the ancestral Wuhan-1 virus. Nonetheless, these vaccines, including mRNA-1273 and BNT162b2, retained their ability to protect against severe disease and death, suggesting that other aspects of immunity control infection in the lung. Vaccine-elicited antibodies can bind Fc gamma receptors (FcγRs) and mediate effector functions against SARS-CoV-2 variants, and this property correlates with improved clinical coronavirus disease 2019 outcome. However, a causal relationship between Fc effector functions and vaccine-mediated protection against infection has not been established. Here, using passive and active immunization approaches in wild-type and FcγR-knockout mice, we determined the requirement for Fc effector functions to control SARS-CoV-2 infection. The antiviral activity of passively transferred immune serum was lost against multiple SARS-CoV-2 strains in mice lacking expression of activating FcγRs, especially murine FcγR III (CD16), or depleted of alveolar macrophages. After immunization with the pre-clinical mRNA-1273 vaccine, control of Omicron BA.5 infection in the respiratory tract also was lost in mice lacking FcγR III. Our passive and active immunization studies in mice suggest that Fc-FcγR engagement and alveolar macrophages are required for vaccine-induced antibody-mediated protection against infection by antigenically changed SARS-CoV-2 variants, including Omicron strains.
MXRA8 is a receptor for chikungunya (CHIKV) and other arthritogenic alphaviruses with mammalian hosts. However, mammalian MXRA8 does not bind to alphaviruses that infect humans and have avian ...reservoirs. Here, we show that avian, but not mammalian, MXRA8 can act as a receptor for Sindbis, western equine encephalitis (WEEV), and related alphaviruses with avian reservoirs. Structural analysis of duck MXRA8 complexed with WEEV reveals an inverted binding mode compared with mammalian MXRA8 bound to CHIKV. Whereas both domains of mammalian MXRA8 bind CHIKV E1 and E2, only domain 1 of avian MXRA8 engages WEEV E1, and no appreciable contacts are made with WEEV E2. Using these results, we generated a chimeric avian-mammalian MXRA8 decoy-receptor that neutralizes infection of multiple alphaviruses from distinct antigenic groups in vitro and in vivo. Thus, different alphaviruses can bind MXRA8 encoded by different vertebrate classes with distinct engagement modes, which enables development of broad-spectrum inhibitors.
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•Avian but not mammalian MXRA8 is an entry receptor for WEE complex alphaviruses•Mammalian but not avian MXRA8 binds to Semliki Forest complex alphaviruses•Avian and mammalian MXRA8 bind different alphaviruses in flipped orientations•A chimeric duck-mouse MXRA8 inhibits alphaviruses from multiple antigenic groups
Avian MXRA8 is an entry receptor for alphaviruses belonging to the Western equine encephalitis complex that have bird reservoirs but not for those in the Semliki Forest complex, which instead utilize mammalian MXRA8. Avian MXRA8 and mammalian MXRA8 engage different alphaviruses using inverted binding modes and distinct regions. A duck domain 1-mouse domain 2 chimeric MXRA8 serves as a decoy-receptor and inhibits infection of multiple alphaviruses from distinct antigenic complexes in vitro and in vivo.
Cleavage of the flavivirus premembrane (prM) structural protein during maturation can be inefficient. The contribution of partially mature flavivirus virions that retain uncleaved prM to pathogenesis ...during primary infection is unknown. To investigate this question, we characterized the functional properties of newly-generated dengue virus (DENV) prM-reactive monoclonal antibodies (mAbs) in vitro and using a mouse model of DENV disease. Anti-prM mAbs neutralized DENV infection in a virion maturation state-dependent manner. Alanine scanning mutagenesis and cryoelectron microscopy of anti-prM mAbs in complex with immature DENV defined two modes of attachment to a single antigenic site. In vivo, passive transfer of intact anti-prM mAbs resulted in an antibody-dependent enhancement of disease. However, protection against DENV-induced lethality was observed when the transferred mAbs were genetically modified to inhibit their ability to interact with Fcγ receptors. These data establish that in addition to mature forms of the virus, partially mature infectious prM
virions can also contribute to pathogenesis during primary DENV infections.
Most neutralizing anti-SARS-CoV-2 monoclonal antibodies (mAbs) target the receptor binding domain (RBD) of the spike (S) protein. Here, we characterize a panel of mAbs targeting the N-terminal domain ...(NTD) or other non-RBD epitopes of S. A subset of NTD mAbs inhibits SARS-CoV-2 entry at a post-attachment step and avidly binds the surface of infected cells. One neutralizing NTD mAb, SARS2-57, protects K18-hACE2 mice against SARS-CoV-2 infection in an Fc-dependent manner. Structural analysis demonstrates that SARS2-57 engages an antigenic supersite that is remodeled by deletions common to emerging variants. In neutralization escape studies with SARS2-57, this NTD site accumulates mutations, including a similar deletion, but the addition of an anti-RBD mAb prevents such escape. Thus, our study highlights a common strategy of immune evasion by SARS-CoV-2 variants and how targeting spatially distinct epitopes, including those in the NTD, may limit such escape.
The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants in the Omicron lineage has resulted in diminished Coronavirus Disease 2019 (COVID-19) vaccine efficacy and ...persistent transmission. In this study, we evaluated the immunogenicity and protective efficacy of two, recently authorized, bivalent COVID-19 vaccines that contain two mRNAs encoding Wuhan-1 and either BA.1 (mRNA-1273.214) or BA.4/5 (mRNA-1273.222) spike proteins. As a primary two-dose immunization series in mice, both bivalent vaccines induced greater neutralizing antibody responses against Omicron variants than the parental, monovalent mRNA-1273 vaccine. When administered to mice as a booster at 7 months after the primary vaccination series with mRNA-1273, the bivalent vaccines induced broadly neutralizing antibody responses. Whereas most anti-Omicron receptor binding domain antibodies in serum induced by mRNA-1273, mRNA-1273.214 and mRNA-1273.222 boosters cross-reacted with the antecedent Wuhan-1 spike antigen, the mRNA-1273.214 and mRNA-1273.222 bivalent vaccine boosters also induced unique BA.1-specific and BA.4/5-specific responses, respectively. Although boosting with parental or bivalent mRNA vaccines substantially improved protection against BA.5 compared to mice receiving two vaccine doses, the levels of infection, inflammation and pathology in the lung were lowest in animals administered the bivalent mRNA vaccines. Thus, boosting with bivalent Omicron-based mRNA-1273.214 or mRNA-1273.222 vaccines enhances immunogenicity and confers protection in mice against a currently circulating SARS-CoV-2 strain.
The large number of spike substitutions in Omicron lineage variants (BA.1, BA.1.1., and BA.2) could jeopardize the efficacy of SARS-CoV-2 vaccines. We evaluated in mice the protective efficacy of the ...Moderna mRNA-1273 vaccine against BA.1 before or after boosting. Whereas two doses of mRNA-1273 vaccine induced high levels of neutralizing antibodies against historical WA1/2020 strains, lower levels against BA.1 were associated with breakthrough infection and inflammation in the lungs. A primary vaccination series with mRNA-1273.529, an Omicron-matched vaccine, potently neutralized BA.1 but inhibited historical or other SARS-CoV-2 variants less effectively. However, boosting with either mRNA-1273 or mRNA-1273.529 vaccines increased neutralizing titers and protection against BA.1 and BA.2 infection. Nonetheless, the neutralizing antibody titers were higher, and lung viral burden and cytokines were slightly lower in mice boosted with mRNA-1273.529 and challenged with BA.1. Thus, boosting with mRNA-1273 or mRNA-1273.529 enhances protection against Omicron infection with limited differences in efficacy measured.
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•Primary immunization series with mRNA-1273 results in BA.1 breakthrough infection•Primary immunization with BA.1-matched vaccine neutralizes BA.1 but not Wuhan-1•Both mRNA-1273 and BA.1-matched boosters protect against BA.1 challenge•A BA.1-matched booster induces greater neutralizing antibody responses against BA.1
A comparison of the immunogenicity and efficacy of Omicron BA.1-matched and historical mRNA vaccines as boosters shows that although boosting with either vaccine increased neutralizing titers against Omicron BA.1 and BA.2, slightly greater protection against BA.1 challenge was observed in mice boosted with the BA.1-matched vaccine.
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