Camel Nanobodies Neutralize Sars-Cov-2 Variants

Abstract

Background and Significance With the emergence of SARS-CoV-2 variants during the global pandemic from 2020 to 2023, there is need for broadly neutralizing antibodies. Due to their small size and unique conformations, nanobodies can recognize protein cavities that are not accessible to conventional antibodies. Methods and Results Here, we used phage display libraries built from dromedary camels to isolate two VHH nanobodies (7A3 and 8A2), which have high affinity for the receptor-binding domain (RBD) of the SARS-CoV-2 spike. Cryo-EM complex structures revealed that 8A2 binds the RBD in its up mode and 7A3 targets a conserved and deeply buried site in the spike regardless of the conformational state of the RBD. At a dose of ≥5 mg/kg, nanobody 7A3 efficiently protected K18-hACE2 transgenic mice from the lethal challenge of SARS-CoV-2 variants B.1.351 or B.1.617. With the addition of omicron variant, a new VHH nanobody (J1B4) was isolated to target the S2 subunit of the SARS-CoV-2 spike that can bind across many variants including omicron. Trispecific nanobodies were made using 7A3, 8A2, and J1B4 which had increased binding signals compared to the nanobodies alone. Using this method, we hope to create a therapeutic that is able to broadly neutralize not only all pre-existing variants of SARS-CoV-2, but also be effective towards future SARS-CoV related variants. Conclusions and Future Directions By combining nanobodies targeting the RBD of the S1 subunit (7A3+8A2) with a nanobody targeting the S2 subunit (J1B4), we can increase the chance of protection against all SARS-CoV-2 infections. Due to the increased protein binding of the trispecific compared to individual nanobodies alone, it shows great promise that the trispecific may be able to enhance its activity across all variants. Nanobody-based therapeutics may be developed as a nasal spray which can be self-administered and inhaled directly to the lungs to treat the infection at its source.