An Engineered IgG-VHH Bispecific Antibody against SARS-CoV-2 and Its Variants

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) neutralizing antibodies are shown to be effective therapeutics for providing coronavirus disease 2019 (COVID-19) protection. However, recurrent variants arise and facilitate significant escape from current antibody therapeutics. Bispecific antibodies (bsAbs) represent a unique platform to increase antibody breadth and to reduce neutralization escape. Herein, a novel immunoglobulin G-variable domains of heavy-chain-only antibody (IgG-VHH) format bsAb derived from a potent human antibody R15-F7 and a humanized nanobody P14-F8-35 are rationally engineered. The resulting bsAb SYZJ001 efficiently neutralizes wild-type SARS-CoV-2 as well as the alpha, beta, gamma, and delta variants, with superior efficacy to its parental antibodies. Cryo-electron microscopy structural analysis reveals that R15-F7 and P14-F8-35 bind to nonoverlapping epitopes within the RBD and sterically hindered ACE2 receptor binding. Most importantly, SYZJ001 shows potent prophylactic and therapeutic efficacy against SARS-CoV-2 in three established mouse models. Collectively, the current results demonstrate that the novel bsAb format is feasible and effective, suggesting great potential as an inspiring antiviral strategy.