Identification of human neutralizing antibodies against MERS-CoV and their role in virus adaptive evolution

Abstract

The newly emerging Middle East Respiratory Syndrome coronavirus (MERS-CoV) causes a Severe Acute Respiratory Syndrome-like disease with ∼43% mortality. Given the recent detection of virus in dromedary camels, zoonotic transfer of MERS-CoV to humans is suspected. In addition, little is known about the role of human neutralizing Ab (nAb) pressure as a driving force in MERS-CoV adaptive evolution. Here, we used a well-characterized nonimmune human Ab-phage library and a panning strategy with proteoliposomes and cells to identify seven human nAbs against the receptor-binding domain (RBD) of the MERS-CoV Spike protein. These nAbs bind to three different epitopes in the RBD and human dipeptidyl peptidase 4 (hDPP4) interface with subnanomolar/nanomolar binding affinities and block the binding of MERS-CoV Spike protein with its hDPP4 receptor. Escape mutant assays identified five amino acid residues that are critical for neutralization escape. Despite the close proximity of the three epitopes on the RBD interface, escape from one epitope did not have a major impact on neutralization with Abs directed to a different epitope. Importantly, the majority of escape mutations had negative impacts on hDPP4 receptor binding and viral fitness. To our knowledge, these results provide the first report on human nAbs against MERS-CoV that may contribute to MERS-CoV clearance and evolution. Moreover, in the absence of a licensed vaccine or antiviral for MERS, this panel of nAbs offers the possibility of developing human mAbbased immunotherapy, especially for health-care workers.IGHV1-69 | biodefense | emerging pathogen | zoonosis | humoral immunity

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“…Human monoclonal neutralising antibodies and convalescent sera from recovered patients might be useful for treatment if delivered in a timely fashion 91,101,102 , an exploratory post-hoc meta-analysis of studies of SARS and severe influenza showed a significant reduction of mortality following antibody treatment compared with placebo or no treatment 103 . Systemic corticosteroids have been used empirically in some patients to dampen immune pathological host responses, although no survival benefit has been reported 95 .…”

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).…”

Phage and Yeast Display

“…Selections against full-length MERS-CoV S protein using scFv-pIII display libraries yielded neutralizing antibodies localizing to the receptor binding domain. 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).…”

“…The majority of the mAbs characterized in this study localized to domain III (DIII) of the viral E antigen. In addition, yeast surface display mapped a panel of E-selected neutralizing mAbs from a phage library to specific domains of the viral glycoprotein (72). These phage library-derived scFvs selectively bound DI/DII, with no interaction with DIII.…”