No abstract

The COVID-19 pandemic is a major threat to global health for which there are only 50 limited medical countermeasures, and we lack a thorough understanding of mechanisms of 51 humoral immunity 1,2 . From a panel of monoclonal antibodies (mAbs) targeting the spike 52 (S) glycoprotein isolated from the B cells of infected subjects, we identified several mAbs 53 that exhibited potent neutralizing activity with IC50 values as low as 0.9 or 15 ng/mL in 54 pseudovirus or wild-type (wt) SARS-CoV-2 neutralization tests, respectively. The most 55 potent mAbs fully block the receptor-binding domain of S (SRBD) from interacting with 56 human ACE2. Competition-binding, structural, and functional studies allowed clustering 57 of the mAbs into defined classes recognizing distinct epitopes within major antigenic sites 58 on the SRBD. Electron microscopy studies revealed that these mAbs recognize distinct 59 conformational states of trimeric S protein. Potent neutralizing mAbs recognizing unique 60 sites, COV2-2196 and COV2-2130, bound simultaneously to S and synergistically 61 neutralized authentic SARS-CoV-2 virus. In two murine models of SARS-CoV-2 infection, 62 passive transfer of either COV2-2916 or COV2-2130 alone or a combination of both mAbs 63 protected mice from severe weight loss and reduced viral burden and inflammation in the 64 lung. These results identify protective epitopes on the SRBD and provide a structure-based 65 framework for rational vaccine design and the selection of robust immunotherapeutic 66 cocktails. 67 68 The S protein of SARS-CoV-2 is the molecular determinant of viral attachment, fusion, and 69 entry into host cells 3 . The cryo-EM structure of a prefusion-stabilized trimeric S protein 70 ectodomain (S2Pecto) for SARS-CoV-2 reveals similar features to that of the SARS-CoV S 71 protein 4 . This type I integral membrane protein and class I fusion protein possesses an N-72

Eastern equine encephalitis virus (EEEV) is a mosquito-transmitted alphavirus with a high case mortality rate in humans. EEEV is a biodefense concern because of its potential for aerosol spread and the lack of existing countermeasures. In this study, we identified a panel of 18 neutralizing murine monoclonal antibodies (mAbs) against the EEEV E2 protein, several of which had “elite” activity with 50% and 99% inhibitory concentrations (EC 50 and EC 99 ) of less than 10 and 100 ng/ml, respectively. Alanine-scanning mutagenesis and neutralization escape mapping analysis revealed epitopes for these mAbs in domains A or B of the E2 glycoprotein. A majority of the neutralizing mAbs blocked at a post-attachment stage, with several inhibiting viral membrane fusion. Administration of one dose of anti-EEEV mAbs protected mice from lethal subcutaneous or aerosol challenge. These experiments define the mechanistic basis for neutralization by protective anti-EEEV mAbs and suggest a path forward for treatment and vaccine design.

No abstract

No abstract