Neutralizing Monoclonal Antibodies Block Chikungunya Virus Entry and Release by Targeting an Epitope Critical to Viral Pathogenesis

Abstract

Summary We evaluated the mechanism by which neutralizing human monoclonal antibodies inhibit chikungunya virus (CHIKV) infection. Potently neutralizing antibodies (NAbs) blocked infection at multiple steps of the virus life cycle, including entry and release. Cryo-electron microscopy structures of Fab fragments of two human NAbs and chikungunya virus-like particles showed a binding footprint that spanned independent domains on neighboring E2 subunits within one viral spike, suggesting a mechanism for inhibiting low pH-dependent membrane fusion. Detailed epitope mapping identified residue E2-W64 as a critical interaction residue. An escape mutation (E2-W64G) at this residue rendered CHIKV attenuated in mice. Consistent with this data, CHIKV-E2-W64G failed to emerge in vivo under the selection pressure of one of the NAbs, IM-CKV063. As our study suggests that antibodies engaging the residue E2-W64 can potently inhibit CHIKV at multiple stages of infection, antibody-based therapies or immunogens that target this region might have protective value.

Mxra8 is a receptor for multiple arthritogenic alphaviruses

“…Binding of Mxra8-Fc to each mutant expressed in HEK-293T cells was determined by immunofluorescence detected with a high-throughput flow cytometer (Intellicyt), as described previously 35 . Residues of domains A or B were identified as contributing to the binding site if their mutation eliminated Mxra8-Fc binding, but supported binding of CHIKV mAbs that bind to the appropriate domain (control mAbs were CHV-84, CHKV-88, IM-CHKV063, IM-CKV065, and C9 5,35,36 ).…”

Chikungunya virus: epidemiology, replication, disease mechanisms, and prospective intervention strategies

“…An IgG response can be detected approximately 7-10 days after onset of illness, often after viremia has been cleared (37,(154)(155)(156). Many mouse and human IgM and IgG antibodies broadly and potently neutralize CHIKV (157)(158)(159)(160)(161)(162). The most potently neutralizing antibodies target domains A and B of the E2 glycoprotein, with those targeting domain B often displaying broad neutralization against multiple strains of CHIKV and other related alphaviruses (157,(159)(160)(161).…”

Immune-Mediated Protection and Pathogenesis of Chikungunya Virus

“…Indeed, passive transfer of purified monoclonal or polyclonal anti-CHIKV antibodies can protect immunocompromised mice from lethal disease when administered prior to or shortly after infection (24, 67–72). …”

“…Many mouse and human anti-CHIKV MAbs neutralize CHIKV in vitro and protect in vivo against acute or chronic musculoskeletal disease in mice and non-human primates (72–75). Neutralizing antibodies target the envelope glycoproteins, which are displayed on the virion surface as trimers of E2/E1 heterodimers (76).…”

“…Most strongly neutralizing antibodies target the A and B domains on the E2 protein, and antibodies against the B domain of CHIKV broadly inhibit infection against several arthritogenic alphaviruses (74). Neutralizing anti-CHIKV antibodies can inhibit at multiple steps of the virus lifecycle including blockade of virus attachment, entry, pH-dependent fusion in the endosome, new virion assembly, release of the virion from the plasma membrane, and cell-to-cell spread (24, 68,72, 74, 77–79). Apart from this, antibodies may protect against CHIKV infection through their effector functions including antibody mediated cellular cytotoxicity (ADCC), complement activation, and virus opsinization.…”