Structures of respiratory syncytial virus G antigen bound to broadly neutralizing antibodies

Respiratory syncytial virus (RSV) is a top cause of severe lower respiratory tract disease and mortality in young children and the elderly. The viral envelope G glycoprotein contributes to pathogenesis through its roles in host cell attachment and modulation of host immunity. Although the G glycoprotein is a target of protective RSV-neutralizing antibodies, its development as a vaccine antigen has been hindered by its heterogeneous glycosylation and sequence variability outside a conserved central domain (CCD). We describe the cocrystal structures of two high-affinity broadly neutralizing human monoclonal antibodies bound to the RSV G CCD. The antibodies bind to neighboring conformational epitopes, which we named antigenic sites gamma 1 and gamma 2, that span a highly conserved surface, illuminating an important region of vulnerability. We further show that isolated RSV G CCD activates the chemokine receptor CX3CR1 and that antibodies block this activity. These studies provide a template for rational vaccine design targeting this key contributor to RSV disease.