Human Neutralizing Monoclonal Antibody Inhibition of Middle East Respiratory Syndrome Coronavirus Replication in the Common Marmoset

Abstract

Middle East respiratory syndrome coronavirus (MERS-CoV) infection in humans is highly lethal, with a fatality rate of 35%. New prophylactic and therapeutic strategies to combat human infections are urgently needed. We isolated a fully human neutralizing antibody, MCA1, from a human survivor. The antibody recognizes the receptor-binding domain of MERS-CoV S glycoprotein and interferes with the interaction between viral S and the human cellular receptor human dipeptidyl peptidase 4 (DPP4). To our knowledge, this study is the first to report a human neutralizing monoclonal antibody that completely inhibits MERS-CoV replication in common marmosets. Monotherapy with MCA1 represents a potential alternative treatment for human infections with MERS-CoV worthy of evaluation in clinical settings.

Keywords: MERS-CoV; common marmoset; human monoclonal antibody.

Figure 1.

MCA1 neutralized Middle East respiratory syndrome coronavirus (MERS-CoV) in vitro. The neutralizing activities of MCA1 against MERS-CoV were examined using Vero E6 cells. An irrelevant human immunoglobulin G (IgG) was used as a control.

Figure 2.

Prophylactic efficacy of MCA1 in common marmosets, which were intravenously inoculated with the antibody at doses of 5 mg/kg (designated G1) and 20 mg/kg (G2) and then challenged with Middle East respiratory syndrome coronavirus (MERS-CoV) 24 hours later. A control group was simultaneously infected and set up as a model (M) group. All groups were monitored twice daily for 3 days. A, Clinical scores (n = 3 per group). B, Temperature changes (n = 3 per group). C, Mean body weight changes (n = 3 per group). Results are presented as means with standard deviations. *P < .05 (t test).

Figure 3.

Therapeutic treatment using MCA1 in common marmosets, which were initially intratracheally infected with Middle East respiratory syndrome coronavirus (MERS-CoV), followed by intravenous inoculation with MCA1 at 2 (G3) or 12 (G4) hours, at 20 mg/kg. A control group was simultaneously infected and set up as a model (M) group. A, Clinical scores (n = 3 per group). B, Temperature changes (n = 3 per group). C, Mean body weight changes (n = 3 per group). Results are presented as means with standard deviations. *P < .05; ^†P < .01 (t test).

Figure 4.

Histopathology and viral titer detection. The common marmosets, were intravenously inoculated with MCA1 at doses of 5 mg/kg (G1) and 20 mg/kg (G2) and then challenged with Middle East respiratory syndrome coronavirus (MERS-CoV) 24 hours later, or were initially intratracheally infected with MERS-CoV, followed by intravenous inoculation with MCA1 at 2 (G3) or 12 (G4) hours, at 20 mg/kg. A control group was simultaneously infected and set up as a model (M) group. A, Histopathological appearance of pulmonary tissue from MERS-CoV–infected marmosets. Lungs of marmosets in the model group (M) showed acute bronchointerstitial pneumonia; the pulmonary alveoli were infiltrated by a large amount of inflammatory cells (arrowhead), with fibrin exudation (asterisk). The alveolar interstitium were thickened and pulmonary alveoli were filtrated by inflammatory cells (arrows) in the G1, G2, G3, and G4 groups. Scale bar, 100 μm. B, Viral titers from lung and trachea were determined 3 days after infection.

Figure 5.

Crystal structures of MCA1 fragment of antigen binding (Fab) in complex with Middle East respiratory syndrome coronavirus (MERS-CoV) receptor-binding domain (RBD). A, Crystal structure of MCA1/MERS-CoV RBD complex in graphic representation. The receptor-binding site (RBS) and core subdomain of MERS-CoV RBD are colored light pink and magenta, respectively; the heavy chain is green, and the light chain cyan. The ethylene glycol between the heavy and light chains and the N-linked glycans in the RBD are represented as magentas sticks. B, Closer view of the interaction between MCA1 Fab and the RBS. The RBS is depicted in surface representation. Three complementarity-determining regions (CDRs) of the heavy and light chains are colored orange. C, Detailed interactions between MCA1 and the RBS. Key residues are shown as sticks. D, Superimposed structures of MERS-CoV RBD binding to MCA1 and dipeptidyl peptidase (DPP4). The heavy and light chains of MCA1 are depicted in surface representation, and DPP4 is shown in red.