Flexible RSV Prefusogenic Fusion Glycoprotein Exposes Multiple Neutralizing Epitopes that May Collectively Contribute to Protective Immunity
Open Access
- 14 October 2020
- Vol. 8 (4), 607
- https://doi.org/10.3390/vaccines8040607
Abstract
Human respiratory syncytial virus (RSV) is a cause of lower respiratory tract infection in infants, young children, and older adults. There is no licensed vaccine and prophylactic treatment options are limited. The RSV fusion (F) glycoprotein is a target of host immunity and thus a focus for vaccine development. F-trimers are metastable and undergo significant rearrangements from the prefusion to a stable postfusion structure with neutralizing epitopes on intermediate structures. We hypothesize that vaccine strategies that recapitulate the breathable F quaternary structure, and provide accessibility of B-cells to epitopes on intermediate conformations, may collectively contribute to protective immunity, while rigid prefusion F structures restrict access to key protective epitopes. To test this hypothesis, we used the near full-length prefusogenic F as a backbone to construct three prefusion F variants with substitutions in the hydrophobic head cavity: (1) disulfide bond mutant (DS), (2) space filling hydrophobic amino acid substitutions (Cav1), and (3) DS, Cav1 double mutant (DS-Cav1). In this study, we compared the immunogenicity of prefusogenic F to prefusion F variants in two animal models. Native prefusogenic F was significantly more immunogenic, producing high titer antibodies to prefusogenic, prefusion, and postfusion F structures, while animals immunized with DS or DS-Cav1 produced antibodies to prefusion F. Importantly, prefusogenic F elicited antibodies that target neutralizing epitopes including prefusion-specific site zero (Ø) and V and conformation-independent neutralizing sites II and IV. Immunization with DS or DS-Cav1 elicited antibodies primarily to prefusion-specific sites Ø and V with little or no antibodies to other key neutralizing sites. Animals immunized with prefusogenic F also had significantly higher levels of antibodies that cross-neutralized RSV A and B subtypes, while immunization with DS or DS-Cav1 produced antibodies primarily to the A subtype. We conclude that breathable trimeric vaccines that closely mimic the native F-structure, and incorporate strategies for B-cell accessibility to protective epitopes, are important considerations for vaccine design. F structures locked in a single conformation restrict access to neutralizing epitopes that may collectively contribute to destabilizing F-trimers important for broad protection. These results also have implications for vaccine strategies targeting other type 1 integral membrane proteins.This publication has 48 references indexed in Scilit:
- Cross-neutralization of four paramyxoviruses by a human monoclonal antibodyNature, 2013
- Respiratory Syncytial Virus Fusion Glycoprotein Expressed in Insect Cells Form Protein Nanoparticles That Induce Protective Immunity in Cotton RatsPLOS ONE, 2012
- Structure of Respiratory Syncytial Virus Fusion Glycoprotein in the Postfusion Conformation Reveals Preservation of Neutralizing EpitopesJournal of Virology, 2011
- Structural basis for immunization with postfusion respiratory syncytial virus fusion F glycoprotein (RSV F) to elicit high neutralizing antibody titersProceedings of the National Academy of Sciences of the United States of America, 2011
- Elevated temperature triggers human respiratory syncytial virus F protein six-helix bundle formationVirology, 2010
- Respiratory Syncytial Virus (RSV) Fusion Protein Subunit F2, Not Attachment Protein G, Determines the Specificity of RSV InfectionJournal of Virology, 2003
- Effect of Proteolytic Processing at Two Distinct Sites on Shape and Aggregation of an Anchorless Fusion Protein of Human Respiratory Syncytial Virus and Fate of the Intervening SegmentVirology, 2002
- Electron Microscopy of the Human Respiratory Syncytial Virus Fusion Protein and Complexes That It Forms with Monoclonal AntibodiesVirology, 2000
- Palivizumab, a Humanized Respiratory Syncytial Virus Monoclonal Antibody, Reduces Hospitalization From Respiratory Syncytial Virus Infection in High-risk InfantsPEDIATRICS, 1998
- Two disulfide-linked polypeptide chains constitute the active F protein of paramyxovirusesVirology, 1977