Rapid characterization of spike variants via mammalian cell surface display

Kamyab Javanmardi, Chia-Wei Chou, Cynthia Terrace, Ankur Annapareddy, Tamer S. Kaoud, Qingqing Guo, Josh Lutgens, Hayley Zorkic, Andrew P. Horton, Elizabeth C. Gardner, Giaochau Nguyen, Daniel R. Boutz, Jule Goike, Will N. Voss, Hung-Che Kuo, Kevin N. Dalby, Jimmy D. Gollihar & Ilya J. Finkelstein, BioRxiv (2021).
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The SARS-CoV-2 spike (S) protein is a critical component of subunit vaccines and a target for neutralizing antibodies. Spike is also undergoing immunogenic selection with clinical variants that increase infectivity and partially escape convalescent plasma. Here, we describe spike display, a high-throughput platform to rapidly characterize glycosylated spike ectodomains across multiple coronavirus-family proteins. We assayed ~200 variant SARS-CoV-2 spikes for their expression, ACE2 binding, and recognition by thirteen neutralizing antibodies (nAbs). An alanine scan of the N-terminal domain (NTD) highlights a public class of epitopes in the N3 and N5 loops that are recognized by most of the NTD-binding nAbs assayed in this study. Some clinical NTD substitutions abrogate binding to these epitopes but are circulating at low frequencies around the globe. NTD mutations in variants of concern B.1.1.7 (United Kingdom), B.1.351 (South Africa), B.1.1.248 (Brazil), and B.1.427/B.1.429 (California) impact spike expression and escape most NTD-targeting nAbs. However, two classes of NTD nAbs still bind B.1.1.7 spikes and neutralize in pseudoviral assays. B.1.1351 and B.1.1.248 include compensatory mutations that either increase spike expression or increase ACE2 binding affinity. Finally, B.1.351 and B.1.1.248 completely escape a potent ACE2 peptide mimic. We anticipate that spike display will be useful for rapid antigen design, deep scanning mutagenesis, and epitope mapping of antibody interactions for SARS-CoV-2 and other emerging viral threats.