BioProject

Since the start of the coronavirus disease-2019 (COVID-19) pandemic, severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has caused more than 2 million deaths worldwide. More...

Since the start of the coronavirus disease-2019 (COVID-19) pandemic, severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has caused more than 2 million deaths worldwide. Many vaccines have been deployed to date; however, the continual evolution of the viral receptor binding domain (RBD) has recently challenged their efficacy. In particular, SARS-CoV-2 variants originating in South Africa (B.1.351) and the U.K. (B.1.1.7) have reduced plasma neutralization activity and crippled antibody cocktails that received emergency use authorization1-3. Whereas vaccines can be updated periodically to account for emerging variants, complementary strategies are urgently needed to overcome viral escape. One potential alternative are camelid VHHs (also known as nanobodies), which can access conserved epitopes often hidden to conventional antibodies4-6. We here isolate anti-RBD nanobodies from llamas and mice engineered to produce VHHs from alpacas, dromedaries and camels. Through neutralization assays and cryo-electron microscopy we identify two “nanomouse” VHHs that circumvent RBD antigenic drift by recognizing a domain conserved in coronaviruses, away from the ACE2 binding motif. Conversely, llama nanobodies recognize the RBD-ACE2 interphase and as monomers they are ineffective against E484K or N501Y substitutions. Notably, as homotrimers those same VHHs neutralize RBD variants with ultrahigh (pM) affinity, rivaling the most potent antibodies produced to date against SARS-CoV-2. We conclude that multivalent nanobodies can avert SARS-CoV-2 escape mutants and thus they represent promising tools to prevent COVID-19 mortality when vaccines are compromised. Overall design: VHH gene sequence from llamas and camelid mice Less...