Abstract
The ongoing Coronavirus Disease 2019 (COVID-19) pandemic caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) threatens global public health and economy unprecedentedly, requiring accelerating development of prophylactic and therapeutic interventions. Molecular understanding of neutralizing antibodies (NAbs) would greatly help advance the development of monoclonal antibody (mAb) therapy, as well as the design of next generation recombinant vaccines. Here, we applied H2L2 transgenic mice encoding the human immunoglobulin variable regions, together with a state-of-the-art antibody discovery platform to immunize and isolate NAbs. From a large panel of isolated antibodies, 25 antibodies showed potent neutralizing activities at sub-nanomolar levels by engaging the spike receptor-binding domain (RBD). Importantly, one human NAb, termed PR1077, from the H2L2 platform and 2 humanized NAb, including PR953 and PR961, were further characterized and subjected for subsequent structural analysis. High-resolution X-ray crystallography structures unveiled novel epitopes on the receptor-binding motif (RBM) for PR1077 and PR953, which directly compete with human angiotensin-converting enzyme 2 (hACE2) for binding, and a novel non-blocking epitope on the neighboring site near RBM for PR961. Moreover, we further tested the antiviral efficiency of PR1077 in the Ad5-hACE2 transduction mouse model of COVID-19. A single injection provided potent protection against SARS-CoV-2 infection in either prophylactic or treatment groups. Taken together, these results shed light on the development of mAb-related therapeutic interventions for COVID-19.
Highlights
As of March 22, 2021, the Coronavirus Disease 2019 (COVID-19) has already infected over 124 million individuals and resulted in over 2.7 million deaths worldwide, requiring urgent prophylactic and therapeutic interventions
Sera were collected before and after each vaccination, and serum binding to receptor-binding domain (RBD) was determined by enzyme-linked immunosorbent assay (ELISA)
Plasma B cells were loaded onto the Berkeley Lights Beacon Optofluidic system mounted with the OptoSelect chip, and assays were run to select single plasma B cells secreting SARS-CoV-2 RBD protein-specific antibodies [9,10] (Fig 1A, S1 Fig, S1 Table)
Summary
As of March 22, 2021, the Coronavirus Disease 2019 (COVID-19) has already infected over 124 million individuals and resulted in over 2.7 million deaths worldwide, requiring urgent prophylactic and therapeutic interventions. The etiological agent of COVID-19 is Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) [1]. This emerging coronavirus shares high primary sequence identity with other lineage B coronaviruses and has been categorized into the Betacoronavirus genus. SARS-CoV-2 is an enveloped virus with corona-like spike protein protruding from the viral particles. Tomography image indicated that more than half of the spike trimers adopt the “all close” state on SARS-CoV-2 particles [4]; interaction with cellular receptor hACE2 requires and locks the RBD into the “up” conformation, inducing virus–host cell membrane fusion engaged by the S2 subunit. The SARS-CoV-2 spike protein, especially the RBD region, serves as the primary target for interfering with the virus entry process [5]
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