Equine immunoglobulin fragment F(ab')₂ displays high neutralizing capability against multiple SARS-CoV-2 variants

Neutralizing antibody-based passive immunotherapy could be an important therapeutic option against COVID-19. Herein, we demonstrate that equines hyper-immunized with chemically inactivated SARS-CoV-2 elicited high antibody titers with a strong virus-neutralizing potential, and F(ab')₂ fragments purified from them displayed strong neutralization potential against five different SARS-CoV-2 variants. F(ab')₂ fragments purified from the plasma of hyperimmunized horses showed high antigen-specific affinity. Experiments in rabbits suggested that the F(ab')₂ displays a linear pharmacokinetics with approximate plasma half-life of 47 h. In vitro microneutralization assays using the purified F(ab')₂ displayed high neutralization titers against five different variants of SARS-CoV-2 including the Delta variant, demonstrating its potential efficacy against the emerging viral variants. In conclusion, this study demonstrates that F(ab')₂ generated against SARS-CoV-2 in equines have high neutralization titers and have broad target-range against the evolving variants, making passive immunotherapy a potential regimen against the existing and evolving SARS-CoV-2 variants in combating COVID-19.