Exceptionally Potent Neutralization of Middle East Respiratory Syndrome Coronavirus by Human Monoclonal Antibodies

Abstract

The recently discovered Middle East respiratory syndrome coronavirus (MERS-CoV) continues to infect humans, with high mortality. Specific, highly effective therapeutics and vaccines against the MERS-CoV are urgently needed to save human lives and address the pandemic concerns. We identified three human monoclonal antibodies (MAbs), m336, m337, and m338, targeting the receptor (CD26/DPP4) binding domain (RBD) of the MERS-CoV spike glycoprotein from a very large naïve-antibody library (containing ϳ10 11 antibodies). They bound with high affinity: equilibrium dissociation constants for the three MAbs were equal to 4.2, 9.3, and 15 nM, respectively, as measured by Biacore for Fabs binding to RBD. The avidity for IgG1 m336, m337, and m338 was even higher: 99, 820, and 560 pM, respectively. The antibodies bound to overlapping epitopes that overlap the receptor binding site on the RBD as suggested by competition experiments and further supported by site-directed mutagenesis of the RBD and a docking model of the m336-RBD complex. The highest-affinity MAb, m336, neutralized both pseudotyped and live MERS-CoV with exceptional potency, 50% neutralization at 0.005 and 0.07 g/ml, respectively, likely by competing with DPP4 for binding to the S glycoprotein. The exceptionally high neutralization activity of these antibodies and especially m336 suggests that they have great potential for prophylaxis and therapy of MERS-CoV infection in humans and as a tool for development of vaccine immunogens. The rapid identification (within several weeks) of potent MAbs suggests a possibility to use the new large antibody library and related methodology for a quick response to the public threat resulting from emerging coronaviruses. IMPORTANCEA novel human coronavirus, the Middle East respiratory syndrome coronavirus (MERS-CoV), was found to infect humans with a high mortality rate in 2012, just 1 decade after the appearance of the first highly pathogenic coronavirus, severe acute respiratory syndrome coronavirus (SARS-CoV). There are no effective therapeutics available. It is highly desirable to find an approach for rapidly developing potent therapeutics against MERS-CoV, which not only can be implemented for MERS treatment but also can help to develop a platform strategy to combat future emerging coronaviruses. We report here the identification of human monoclonal antibodies (MAbs) from a large nonimmune antibody library that target MERS-CoV. One of the antibodies, m336, neutralized the virus with exceptional potency. It therefore may have great potential as a candidate therapeutic and as a reagent to facilitate the development of vaccines against MERS-CoV.

MERS – A cautionary tale

“…As further demonstrated by Jiang's group, combining HR2P-M2 peptide with m336, an RBD-specific human neutralizing monoclonal antibody (mAb) having potent neutralizing activity against MERS-CoV infection in vitro and in vivo, resulted in a strong synergistic effect against MERS-CoV infection [14,15]. They therefore proposed that combinatorial use of the HR2P-M2 peptide intranasally and the m336 mAb intravenously could be used to treat MERS patients [15].…”

Phage and Yeast Display

“…Despite the presence of the full-length protein during selections, this campaign resulted in S1 domain-specific mAbs, which neutralized MERS-CoV pseudotyped virus-like particles by blocking the DPP4 binding site on the viral glycoprotein (72). Similarly, Fab-pIII library selections against truncated DPP4 receptor binding domain-only antigen yielded mAbs capable of neutralizing both pseudotyped and live MERS-CoV (73). These studies provide examples of the ongoing relevance of phage display technology in current, emerging infectious diseases.…”

Middle East respiratory syndrome coronavirus: current knowledge and future considerations

“…It targets viral MERS-CoV 3C protease (79) and the interface between the MERS-CoV receptor-binding domain (RBD) and the receptor by inhibiting the enzymatic function of dipeptidyl peptidase 4 (DPP4) (100). An experimental recombinant nanoparticle vaccine candidate has been produced (101) based on MERS-CoV S monoclonal antibodies directed towards the S protein, and this holds promise for use as a therapeutic and prophylactic agent (102)(103)(104). A further vaccine candidate has been shown to elicit antibodies in mice (105,106), and another is a conserved peptide that may provide the basis for an epitopedirected universal vaccine (107).…”