Single domain antibodies derived from ancient animals as broadly neutralizing agents for SARS-CoV-2 and other coronaviruses

Abstract

With severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) as an emergent human virus since December 2019, the world population is susceptible to coronavirus disease 2019 (COVID-19). SARS-CoV-2 has higher transmissibility than the previous coronaviruses, associated by the ribonucleic acid (RNA) virus nature with high mutation rate, caused SARS-CoV-2 variants to arise while circulating worldwide. Neutralizing antibodies are identified as immediate and direct-acting therapeutic against COVID-19. Single-domain antibodies (sdAbs), as small biomolecules with non-complex structure and intrinsic stability, can acquire antigen-binding capabilities comparable to conventional antibodies, which serve as an attractive neutralizing solution. SARS-CoV-2 spike protein attaches to human angiotensin-converting enzyme 2 (ACE2) receptor on lung epithelial cells to initiate viral infection, serves as potential therapeutic target. sdAbs have shown broad neutralization towards SARS-CoV-2 with various mutations, effectively stop and prevent infection while efficiently block mutational escape. In addition, sdAbs can be developed into multivalent antibodies or inhaled biotherapeutics against COVID-19.

Keywords: γ , Gamma; δ , Delta; ACE2, Angiotensin-converting enzyme 2; ADCC, Antibody-dependent cell-mediated cytotoxicity; ADCP, Antibody-dependent cellular phagocytosis; ADE, Antibody-dependent enhancement; Alb, Albumin; Bat-SL-CoV, Bat SARS-like coronavirus; Broad neutralization; CDC, Complement-dependent cytotoxicity; CDR, Complementarity-determining region; CH, Constant domain of antibody heavy chain; CHO, Chinese hamster ovary; CL, Constant domain of antibody light chain; CNAR, Constant domain of immunoglobulin new antigen receptor; COVID-19; COVID-19, Coronavirus disease 2019; Cryo-EM, Cryogenic electron microscopy; Cu, Copper; DNA, Deoxyribonucleic acid; DPP4, Dipeptidyl peptidase 4; E, Envelope; EC50, Half-maximal effective concentration; FDA, The United States Food and Drug Administration; Fab, Antigen-binding fragment; Fc, Crystallisable fragment; FcR, Crystallisable fragment receptor; Fig., Figure; HCoV, Human coronavirus; HIV, Human immunodeficiency virus; HR, Heptad repeat; HRP, Horseradish peroxidase; HV, Hypervariable region; IC50, Half-maximal inhibitory concentration; Ig, Immunoglobulin; IgNAR, Immunoglobulin new antigen receptor; KD, Equilibrium dissociation constant; L, Litre; LRT, Lower respiratory tract; M, Membrane; MERS, Middle East respiratory syndrome; MERS-CoV, Middle East respiratory syndrome coronavirus; N, Nucleocapsid; ND50, 50% neutralizing dose; NTD, N-terminal domain; Nb, Nanobody; PCR, Polymerase chain reaction; PEG, Polyethylene glycol; RBD, Receptor-binding domain; RBM, Receptor-binding motif; RNA, Ribonucleic acid; S, Spike; SARS, Severe acute respiratory syndrome; SARS-CoV, Severe acute respiratory syndrome coronavirus; SARS-CoV-2 mutation; SARS-CoV-2, Severe acute respiratory syndrome coronavirus 2; SPAAC, Strain-promoted azide-alkyne cycloaddition; Single-domain antibody; Spike protein; TMPRSS2, Transmembrane serine protease 2; Therapeutic; URT, Upper respiratory tract; VH, Variable domain of antibody heavy chain; VHH, Variable domain of camelid heavy-chain only antibody; VL, Variable domain of antibody light chain; VNAR, Variable domain of immunoglobulin new antigen receptor; WHO, World Health Organization; cDNA, Complementary deoxyribonucleic acid; dpi, Days' post infection; g, Gram; kDa, Kilodalton; koff, Dissociation rate constant; mAb, Monoclonal antibody; mRNA, Messenger ribonucleic acid; nM, Nanomolar; pM, Picomolar; scFv, Single-chain variable fragment; sdAb, Single-domain antibody; ß, Beta; α, Alpha.