Generation of Neutralizing Monoclonal Antibodies Against SARS-CoV-2 for Prevention and Therapy in Patients with COVID-19

National Institute Of Allergy And Infectious Diseases

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Abstract

Screening of more than 120 convalescent patients from COVID-19, recruited at the NIH Blood Bank, identified 15 sera with high titers of neutralizing antibodies against SARS-CoV-2. Whole blood from these 15 donors was processed (isolation of PBMCs, B-cell purification, extraction of mRNA, cDNA synthesis, and PCR amplification of VH, VK and VL genes) and 4 antibody phage-display libraries were constructed from isolated B-cell RNA. All 4 libraries were panned against the recombinant trimeric S protein of SARS-CoV-2, which has led so far to the identification of 612 positive clones that specifically bind to the S protein. Sequence analysis identified 18 distinct clones. The selected monoclonal antibodies have been functionally characterized by ELISA and affinity measurement by using surface plasmon resonance (SPR), followed by expression of Fabs as full-length IgG. Determination of the neutralizing activity against SARS-CoV2 was initially performed using a pseudovirus-based assay system and then a neutralization assay with the entire virus. Binding affinity of the 18 Fabs by SPR showed that their affinity was extremely high in all, with most of them in the picomolar range. Full-length IgG were used for testing their neutralizing activity. We found that several antibodies potently neutralized the wild-type variant (WA1-2020), as well as the South African variant (B.1.351), the UK variant (B.1.1.7) and the delta variant (B.1.1.7). The neutralizing activity of our monoclonal antibodies was also confirmed using live virus against the wild-type variant, the South African variant, and the UK variant. Studies in the animal model using golden Syrian hamsters are in progress to determine the prophylactic and therapeutic activity of our monoclonal antibodies.