Human IgG Neutralizing Monoclonal Antibodies Block SARS-CoV-2 Infection

The coronavirus induced disease 19 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has become a worldwide threat to human lives, and neutralizing antibodies present a great therapeutic potential in curing affected patients. We purified more than one thousand memory B cells specific to SARS-CoV-2 S1 or RBD (receptor binding domain) antigens from 11 convalescent COVID-19 patients, and a total of 729 naturally paired heavy and light chain fragments were obtained by single B cell cloning technology. Among these, 178 recombinant monoclonal antibodies were tested positive for antigen binding, and the top 13 binders with Kd below 0.5 nM are all RBD binders. Interestingly, among these 13 antibodies and found 10 unique CDR3H sequences, while 505-3, 505-5 and 515-1 shared identical CDR3H. Importantly, all these 13 antibodies could block pseudoviral entry into HEK293T cells overexpressing ACE2, with the best ones showing IC50s around 2-3 nM. We further identified 8 neutralizing antibodies against authentic virus with IC50s within 10 nM. Among these, 414-1 blocked authentic viral entry at IC50 of 1.75 nM and in combination with 105-38 could achieve IC50 as low as 0.45 nM. Meanwhile, we also found that 3 antibodies could cross-react with the SARS-CoV spike protein. Altogether, our study provided a panel of potent human neutralizing antibodies for COVID19 as therapeutics candidates for further development. Funding: This work was supported by Zhejiang University special scientific research fund for COVID-19 prevention and control (2020XGZX023), National Key Research and Development program of China (2016YFA0101800 and 2018YFA0108700), the national Natural Science Foundation of China (31925010) and Shanghai Municipal Science and Technology Major Project (2017SHZDZX01). Conflict of Interest: Fei Lan is a scientific advisor of Active Motif China Inc. All other authors declare no conflicts of interest. Ethical Approval: The experiments involving authentic COVID-19 virus were performed in Fudan University biosafety level 3 (BSL-3) facility. The overall study was reviewed and approved by the SHAPHC Ethics Committee (approval no. 2020-Y008-01).