Humanized single domain antibodies neutralize SARS-CoV-2 by targeting the spike receptor binding domain
Xiaojing Chi, Xiuying Liu, Conghui Wang, Xinhui Zhang, Xiang Li, Jianhua Hou, Lili Ren, Qi Jin, Jianwei Wang, Wei Yang
Abstract
Abstract Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spreads worldwide and leads to an unprecedented medical burden and lives lost. Neutralizing antibodies provide efficient blockade for viral infection and are a promising category of biological therapies. Here, using SARS-CoV-2 spike receptor-binding domain (RBD) as a bait, we generate a panel of humanized single domain antibodies (sdAbs) from a synthetic library. These sdAbs reveal binding kinetics with the equilibrium dissociation constant ( K D ) of 0.99–35.5 nM. The monomeric sdAbs show half maximal neutralization concentration (EC 50 ) of 0.0009–0.07 µg/mL and 0.13–0.51 µg/mL against SARS-CoV-2 pseudotypes, and authentic SARS-CoV-2, respectively. Competitive ligand-binding experiments suggest that the sdAbs either completely block or significantly inhibit the association between SARS-CoV-2 RBD and viral entry receptor ACE2. Fusion of the human IgG1 Fc to sdAbs improve their neutralization activity by up to ten times. These results support neutralizing sdAbs as a potential alternative for antiviral therapies.