Hyung J. Kwon¹, Jun Zhang^2,3, Matina Kosikova¹, Weichun Tang¹, Uriel Ortega‐Rodriguez¹, Hanqin Peng^2,3, Clement A. Meseda⁴, Cyntia L. Pedro⁴, Falko Schmeisser⁴, Jianming Lu^5,6, Insung Kang¹, Bin Zhou⁷, Charles T. Davis⁷, David E. Wentworth⁷, Wilbur H. Chen⁸, Mallory C. Shriver⁸, Robin S. Barnes⁸, Marcela F. Pasetti⁸, Jerry P. Weir⁴, Bing Chen^2,3, Hang Xie¹

¹Laboratory of Pediatric and Respiratory Viral Diseases, Division of Viral Products, Center for Biologics Evaluation and Research, Office of Vaccines Research andReview, United States Food and Drug Administration, Silver Spring, Maryland, USA
²Division of Molecular Medicine, Boston Children's Hospital, Boston, Massachusetts, USA
³Department of Pediatrics, Harvard Medical School, Boston, Massachusetts, USA
⁴Laboratory of DNA viruses, Division of Viral Products, Center for Biologics Evaluation and Research, Office of Vaccines Research and Review, UnitedStates Foodand Drug Administration, Silver Spring, Maryland, USA
⁵Codex BioSolutions, Inc., Rockville, Maryland, USA
⁶Department of Biochemistry and Molecular and Cellular Biology, Georgetown University School of Medicine, Washington, District of Columbia, USA
⁷CDC COVID‐19 Response, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
⁸Center for Vaccine Development and Global Health, University of Maryland School of Medicine, Baltimore, Maryland, USA

Hyung J. Kwon and Jun Zhang contributed equally to this work.
Correspondence : Hang Xie, Bing Chen, Jerry P. Weir

Broadly neutralizing antibodies against SARS-CoV-2 variants are sought to curb COVID-19 infections. Here we produced and characterized a set of mouse monoclonal antibodies (mAbs) specific for the ancestral SARS-CoV-2 receptor binding domain (RBD). Two of them, 17A7 and 17B10, were highly potent in microneutralization assay with 50% inhibitory concentration (IC₅₀ ) ≤ 135 ng/ml against infectious SARS-CoV-2 variants, including G614, Alpha, Beta, Gamma, Delta, Epsilon, Zeta, Kappa, Lambda, B.1.1.298, B.1.222, B.1.5 and R.1. Both mAbs (especially 17A7) also exhibited strong in vivo efficacy in protecting K18-hACE2 transgenic mice from the lethal infection with G614, Alpha, Beta, Gamma and Delta viruses. Structural analysis indicated that 17A7 and 17B10 target the tip of the receptor binding motif (RBM) in the RBD-up conformation. A third RBD-reactive mAb (3A6) although escaped by Beta and Gamma, was highly effective in cross-neutralizing Delta and Omicron BA.1 variants in vitro and in vivo. In competition experiments, antibodies targeting epitopes similar to these 3 mAbs were rarely enriched in human COVID-19 convalescent sera or post-vaccination sera. These results are helpful to inform new antibody/vaccine design and these mAbs can be useful tools for characterizing SARS-CoV-2 variants and elicited antibody responses. This article is protected by copyright. All rights reserved.