title: Influence of Respiratory Syncytial Virus F Glycoprotein Conformation on Induction of Protective Immune Responses.
abstract: Human respiratory syncytial virus (hRSV) vaccine development has received new impetus from structure-based studies of its main protective antigen, the fusion (F) glycoprotein. Three soluble forms of F have been described: monomeric, trimeric prefusion, and trimeric postfusion. Most human neutralizing antibodies recognize epitopes found exclusively in prefusion F. Although prefusion F induces higher levels of neutralizing antibodies than does postfusion F, postfusion F can also induce protection against virus challenge in animals. However, the immunogenicity and protective efficacy of the three forms of F have not hitherto been directly compared. Hence, BALB/c mice were immunized with a single dose of the three proteins adjuvanted with CpG and challenged 4 weeks later with virus. Serum antibodies, lung virus titers, weight loss, and pulmonary pathology were evaluated after challenge. Whereas small amounts of postfusion F were sufficient to protect mice, larger amounts of monomeric and prefusion F proteins were required for protection. However, postfusion and monomeric F proteins were associated with more pathology after challenge than was prefusion F. Antibodies induced by all doses of prefusion F, in contrast to other F protein forms, reacted predominantly with the prefusion F conformation. At high doses, prefusion F also induced the highest titers of neutralizing antibodies, and all mice were protected, yet at low doses of the immunogen, these antibodies neutralized virus poorly, and mice were not protected. These findings should be considered when developing new hRSV vaccine candidates.
  
  
  
  Protection against hRSV infection is afforded mainly by neutralizing antibodies, which recognize mostly epitopes found exclusively in the viral fusion (F) glycoprotein trimer, folded in its prefusion conformation, i.e., before activation for membrane fusion. Although prefusion F is able to induce high levels of neutralizing antibodies, highly stable postfusion F (found after membrane fusion) is also able to induce neutralizing antibodies and protect against infection. In addition, a monomeric form of hRSV F that shares epitopes with prefusion F was recently reported. Since each of the indicated forms of hRSV F may have advantages and disadvantages for the development of safe and efficacious subunit vaccines, a direct comparison of the immunogenic properties and protective efficacies of the different forms of hRSV F was made in a mouse model. The results obtained show important differences between the noted immunogens that should be borne in mind when considering the development of hRSV vaccines.
authors.affiliation: Unidad de Biología Viral, Centro Nacional de Microbiología, and CIBER de Enfermedades Respiratorias, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain.
authors.forename: Concepción
authors.initials: C
authors.lastname: Palomo
authors.affiliation: Unidad de Biología Viral, Centro Nacional de Microbiología, and CIBER de Enfermedades Respiratorias, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain.
authors.forename: Vicente
authors.initials: V
authors.lastname: Mas
authors.affiliation: The Pirbright Institute, Ash Road, Pirbright, Woking, Surrey, United Kingdom.
authors.forename: Michelle
authors.initials: M
authors.lastname: Thom
authors.affiliation: Unidad de Biología Viral, Centro Nacional de Microbiología, and CIBER de Enfermedades Respiratorias, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain.
authors.forename: Mónica
authors.initials: M
authors.lastname: Vázquez
authors.affiliation: Unidad de Biología Viral, Centro Nacional de Microbiología, and CIBER de Enfermedades Respiratorias, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain.
authors.forename: Olga
authors.initials: O
authors.lastname: Cano
authors.affiliation: Unidad de Microscopía Electrónica y Confocal, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain.
authors.forename: María C
authors.initials: MC
authors.lastname: Terrón
authors.affiliation: Unidad de Microscopía Electrónica y Confocal, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain.
authors.forename: Daniel
authors.initials: D
authors.lastname: Luque
authors.affiliation: The Pirbright Institute, Ash Road, Pirbright, Woking, Surrey, United Kingdom geraldine.taylor@pirbright.ac.uk jmelero@isciii.es.
authors.forename: Geraldine
authors.initials: G
authors.lastname: Taylor
authors.affiliation: Unidad de Biología Viral, Centro Nacional de Microbiología, and CIBER de Enfermedades Respiratorias, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain geraldine.taylor@pirbright.ac.uk jmelero@isciii.es.
authors.forename: José A
authors.initials: JA
authors.lastname: Melero
mesh_terms: D000276:Adjuvants, Immunologic; D000818:Animals; D057134:Antibodies, Neutralizing / Q000097:blood / Q000276:immunology*; D000914:Antibodies, Viral / Q000097:blood / Q000276:immunology*; D004306:Dose-Response Relationship, Immunologic; D000939:Epitopes / Q000276:immunology; D005260:Female; D006801:Humans; D007114:Immunization; D000071497:Immunogenicity, Vaccine; D008168:Lung / Q000473:pathology / Q000821:virology; D051379:Mice; D008807:Mice, Inbred BALB C; D009838:Oligodeoxyribonucleotides / Q000276:immunology; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000008:administration & dosage / Q000737:chemistry / Q000276:immunology; D018357:Respiratory Syncytial Virus Infections / Q000276:immunology / Q000517:prevention & control*; D012136:Respiratory Syncytial Viruses / Q000737:chemistry* / Q000235:genetics / Q000276:immunology* / Q000302:isolation & purification; D014760:Viral Fusion Proteins / Q000008:administration & dosage / Q000737:chemistry* / Q000276:immunology*
chemical_list: D000276:Adjuvants, Immunologic; D057134:Antibodies, Neutralizing; D000914:Antibodies, Viral; C408982:CPG-oligonucleotide; D000939:Epitopes; C526850:F protein, human respiratory syncytial virus; D009838:Oligodeoxyribonucleotides; D011994:Recombinant Proteins; D014760:Viral Fusion Proteins