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Liu Y, Pan H, Wang H, Yuan Y, Cao F, Song W, Wang Z. Mutations in the NDV fusion protein HR4 region decreased fusogenic activity due to failed protein expression. Microb Pathog 2024; 192:106713. [PMID: 38810765 DOI: 10.1016/j.micpath.2024.106713] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2024] [Revised: 04/28/2024] [Accepted: 05/24/2024] [Indexed: 05/31/2024]
Abstract
Newcastle disease virus (NDV) is the pathogen of a zoonosis that is primarily transmitted by poultry and has severe infectivity and a high fatality rate. Many studies have focused on the role of the NDV fusion (F) protein in the cell-cell membrane fusion process. However, little attention has been given to the heptad repeat region, HR4, which is located in the NDV F2 subunit. Here, site-directed mutants were constructed to study the function of the NDV F protein HR4 region and identify the key amino acids in this region. Nine conserved amino acids were substituted with alanine or the corresponding amino acid of other aligned paramyxoviruses. The desired mutants were examined for changes in fusogenic activity through three kinds of membrane fusion assays and expression and proteolysis through IFA, FACS and WB. The results showed that when conserved amino acids (L81, Y84, L88, L91, L92, P94, L95 and I99) were replaced with alanine, the fusogenic activity of the F protein was abolished, possibly because of failed protein expression not only on the cell surface but also inside cells. These data indicated that the conserved amino acids above in NDV F HR4 are critical for normal protein synthesis and expression, possibly for the stability of the F protein monomer, formation of trimer and conformational changes.
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Affiliation(s)
- Yaqing Liu
- Department of Clinical Laboratory, The Affiliated Hospital of Qingdao University, Qingdao, 266000, China; Department of Virology, School of Public Health, Cheeloo College of Medicine, Shandong University, Jinan, 250014, China
| | - Huazheng Pan
- Department of Clinical Laboratory, The Affiliated Hospital of Qingdao University, Qingdao, 266000, China
| | - Hongwei Wang
- Department of Clinical Laboratory, The Affiliated Hospital of Qingdao University, Qingdao, 266000, China
| | - Yuan Yuan
- Department of Clinical Laboratory, The Affiliated Hospital of Qingdao University, Qingdao, 266000, China
| | - Fangfang Cao
- Department of Clinical Laboratory, The Affiliated Hospital of Qingdao University, Qingdao, 266000, China
| | - Wei Song
- Department of Clinical Laboratory, The Affiliated Hospital of Qingdao University, Qingdao, 266000, China
| | - Zhiyu Wang
- Department of Virology, School of Public Health, Cheeloo College of Medicine, Shandong University, Jinan, 250014, China.
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Reverse genetics systems for contemporary isolates of respiratory syncytial virus enable rapid evaluation of antibody escape mutants. Proc Natl Acad Sci U S A 2021; 118:2026558118. [PMID: 33811145 DOI: 10.1073/pnas.2026558118] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Human respiratory syncytial virus (RSV) is the leading cause of acute lower respiratory infection in children under 5 y of age. In the absence of a safe and effective vaccine and with limited options for therapeutic interventions, uncontrolled epidemics of RSV occur annually worldwide. Existing RSV reverse genetics systems have been predominantly based on older laboratory-adapted strains such as A2 or Long. These strains are not representative of currently circulating genotypes and have a convoluted passage history, complicating their use in studies on molecular determinants of viral pathogenesis and intervention strategies. In this study, we have generated reverse genetics systems for clinical isolates of RSV-A (ON1, 0594 strain) and RSV-B (BA9, 9671 strain) in which the full-length complementary DNA (cDNA) copy of the viral antigenome is cloned into a bacterial artificial chromosome (BAC). Additional recombinant (r) RSVs were rescued expressing enhanced green fluorescent protein (EGFP), mScarlet, or NanoLuc luciferase from an additional transcription unit inserted between the P and M genes. Mutations in antigenic site II of the F protein conferring escape from palivizumab neutralization (K272E, K272Q, S275L) were investigated using quantitative cell-fusion assays and rRSVs via the use of BAC recombineering protocols. These mutations enabled RSV-A and -B to escape palivizumab neutralization but had differential impacts on cell-to-cell fusion, as the S275L mutation resulted in an almost-complete ablation of syncytium formation. These reverse genetics systems will facilitate future cross-validation efficacy studies of novel RSV therapeutic intervention strategies and investigations into viral and host factors necessary for virus entry and cell-to-cell spread.
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McFarland EJ, Karron RA, Muresan P, Cunningham CK, Perlowski C, Libous J, Oliva J, Jean-Philippe P, Moye J, Schappell E, Barr E, Rexroad V, Fearn L, Cielo M, Wiznia A, Deville JG, Yang L, Luongo C, Collins PL, Buchholz UJ. Live-Attenuated Respiratory Syncytial Virus Vaccine With M2-2 Deletion and With Small Hydrophobic Noncoding Region Is Highly Immunogenic in Children. J Infect Dis 2021; 221:2050-2059. [PMID: 32006006 DOI: 10.1093/infdis/jiaa049] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2019] [Accepted: 01/30/2020] [Indexed: 11/13/2022] Open
Abstract
BACKGROUND Respiratory syncytial virus (RSV) is the leading viral cause of severe pediatric respiratory illness, and vaccines are needed. Live RSV vaccine D46/NS2/N/ΔM2-2-HindIII, attenuated by deletion of the RSV RNA regulatory protein M2-2, is based on previous candidate LID/ΔM2-2 but incorporates prominent differences from MEDI/ΔM2-2, which was more restricted in replication in phase 1. METHODS RSV-seronegative children aged 6-24 months received 1 intranasal dose (105 plaque-forming units [PFUs] of D46/NS2/N/ΔM2-2-HindIII [n = 21] or placebo [n = 11]) and were monitored for vaccine shedding, reactogenicity, RSV-antibody responses and RSV-associated medically attended acute respiratory illness (RSV-MAARI) and antibody responses during the following RSV season. RESULTS All 21 vaccinees were infected with vaccine; 20 (95%) shed vaccine (median peak titer, 3.5 log10 PFUs/mL with immunoplaque assay and 6.1 log10 copies/mL with polymerase chain reaction). Serum RSV-neutralizing antibodies and anti-RSV fusion immunoglobulin G increased ≥4-fold in 95% and 100% of vaccines, respectively. Mild upper respiratory tract symptoms and/or fever occurred in vaccinees (76%) and placebo recipients (18%). Over the RSV season, RSV-MAARI occurred in 2 vaccinees and 4 placebo recipients. Three vaccinees had ≥4-fold increases in serum RSV-neutralizing antibody titers after the RSV season without RSV-MAARI. CONCLUSIONS D46/NS2/N/ΔM2-2-HindIII had excellent infectivity and immunogenicity and primed vaccine recipients for anamnestic responses, encouraging further evaluation of this attenuation strategy. CLINICAL TRIALS REGISTRATION NCT03102034 and NCT03099291.
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Affiliation(s)
- Elizabeth J McFarland
- Department of Pediatrics, University of Colorado Anschutz Medical Campus and Children's Hospital Colorado, Aurora, Colorado, USA
| | - Ruth A Karron
- Center for Immunization Research, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, USA
| | - Petronella Muresan
- Center for Biostatistics in AIDS Research, Harvard T.H. Chan School of Public Health/Frontier Science Foundation, Boston, Massachusetts, USA
| | - Coleen K Cunningham
- Department of Pediatrics, Duke University Medical Center, Durham, North Carolina, USA
| | | | | | - Jennifer Oliva
- Center for Immunization Research, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, USA
| | - Patrick Jean-Philippe
- Maternal, Adolescent and Pediatric Research Branch, Division of AIDS, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA
| | - Jack Moye
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, USA
| | - Elizabeth Schappell
- Center for Immunization Research, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, USA
| | - Emily Barr
- Department of Pediatrics, University of Colorado Anschutz Medical Campus and Children's Hospital Colorado, Aurora, Colorado, USA
| | - Vivian Rexroad
- Investigational Drug Service Pharmacy, Johns Hopkins Hospital, Baltimore, Maryland, USA
| | - Laura Fearn
- Department of Pediatrics, Northwestern University Medical School and Ann & Robert H. Lurie Children's Hospital of Chicago, Chicago, Illinois, USA
| | - Mikhaela Cielo
- Division of Infectious Diseases, Maternal Child & Adolescent Center, University of Southern California Keck School of Medicine, Los Angeles, California, USA
| | - Andrew Wiznia
- Department of Pediatrics, Albert Einstein College of Medicine and Jacobi Medical Center, Bronx, New York, USA
| | - Jaime G Deville
- David Geffen School of Medicine at University of California Los Angeles, California, USA
| | - Lijuan Yang
- Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA
| | - Cindy Luongo
- Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA
| | - Peter L Collins
- Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA
| | - Ursula J Buchholz
- Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA
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4
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Wang LN, Peng XL, Xu M, Zheng YB, Jiao YY, Yu JM, Fu YH, Zheng YP, Zhu WY, Dong ZJ, He JS. Evaluation of the Safety and Immune Efficacy of Recombinant Human Respiratory Syncytial Virus Strain Long Live Attenuated Vaccine Candidates. Virol Sin 2021; 36:706-720. [PMID: 33559831 PMCID: PMC8379332 DOI: 10.1007/s12250-021-00345-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2020] [Accepted: 09/18/2020] [Indexed: 11/30/2022] Open
Abstract
Human respiratory syncytial virus (RSV) infection is the leading cause of lower respiratory tract illness (LRTI), and no vaccine against LRTI has proven to be safe and effective in infants. Our study assessed attenuated recombinant RSVs as vaccine candidates to prevent RSV infection in mice. The constructed recombinant plasmids harbored (5′ to 3′) a T7 promoter, hammerhead ribozyme, RSV Long strain antigenomic cDNA with cold-passaged (cp) mutations or cp combined with temperature-sensitive attenuated mutations from the A2 strain (A2cpts) or further combined with SH gene deletion (A2cptsΔSH), HDV ribozyme (δ), and a T7 terminator. These vectors were subsequently co-transfected with four helper plasmids encoding N, P, L, and M2-1 viral proteins into BHK/T7-9 cells, and the recovered viruses were then passaged in Vero cells. The rescued recombinant RSVs (rRSVs) were named rRSV-Long/A2cp, rRSV-Long/A2cpts, and rRSV-Long/A2cptsΔSH, respectively, and stably passaged in vitro, without reversion to wild type (wt) at sites containing introduced mutations or deletion. Although rRSV-Long/A2cpts and rRSV-Long/A2cptsΔSH displayed temperature-sensitive (ts) phenotype in vitro and in vivo, all rRSVs were significantly attenuated in vivo. Furthermore, BALB/c mice immunized with rRSVs produced Th1-biased immune response, resisted wtRSV infection, and were free from enhanced respiratory disease. We showed that the combination of ΔSH with attenuation (att) mutations of cpts contributed to improving att phenotype, efficacy, and gene stability of rRSV. By successfully introducing att mutations and SH gene deletion into the RSV Long parent and producing three rRSV strains, we have laid an important foundation for the development of RSV live attenuated vaccines.
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Affiliation(s)
- Li-Nan Wang
- College of Life Sciences and Bioengineering, School of Science, Beijing Jiaotong University, Beijing, 100044, China
| | - Xiang-Lei Peng
- College of Life Sciences and Bioengineering, School of Science, Beijing Jiaotong University, Beijing, 100044, China
| | - Min Xu
- College of Life Sciences and Bioengineering, School of Science, Beijing Jiaotong University, Beijing, 100044, China
| | - Yuan-Bo Zheng
- College of Life Sciences and Bioengineering, School of Science, Beijing Jiaotong University, Beijing, 100044, China
| | - Yue-Ying Jiao
- College of Life Sciences and Bioengineering, School of Science, Beijing Jiaotong University, Beijing, 100044, China
| | - Jie-Mei Yu
- College of Life Sciences and Bioengineering, School of Science, Beijing Jiaotong University, Beijing, 100044, China
| | - Yuan-Hui Fu
- College of Life Sciences and Bioengineering, School of Science, Beijing Jiaotong University, Beijing, 100044, China
| | - Yan-Peng Zheng
- College of Life Sciences and Bioengineering, School of Science, Beijing Jiaotong University, Beijing, 100044, China
| | - Wu-Yang Zhu
- National Institute for Viral Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Beijing, 102206, China
| | - Zhong-Jun Dong
- School of Medicine and Institute for Immunology, Beijing Key Lab for Immunological Research on Chronic Diseases, Tsinghua University, Beijing, 100084, China
| | - Jin-Sheng He
- College of Life Sciences and Bioengineering, School of Science, Beijing Jiaotong University, Beijing, 100044, China.
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5
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Patel N, Tian JH, Flores R, Jacobson K, Walker M, Portnoff A, Gueber-Xabier M, Massare MJ, Glenn G, Ellingsworth L, Smith G. Flexible RSV Prefusogenic Fusion Glycoprotein Exposes Multiple Neutralizing Epitopes that May Collectively Contribute to Protective Immunity. Vaccines (Basel) 2020; 8:E607. [PMID: 33066540 PMCID: PMC7711572 DOI: 10.3390/vaccines8040607] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2020] [Revised: 10/01/2020] [Accepted: 10/06/2020] [Indexed: 01/08/2023] Open
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.
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Affiliation(s)
| | | | | | | | | | | | | | | | | | | | - Gale Smith
- Novavax, Inc. 21 Firstfield Road, Gaithersburg, MD 20878, USA; (N.P.); (J.-H.T.); (R.F.); (K.J.); (M.W.); (A.P.); (M.G.-X.); (M.J.M.); (G.G.); (L.E.)
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6
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Gilman MSA, Furmanova-Hollenstein P, Pascual G, B van 't Wout A, Langedijk JPM, McLellan JS. Transient opening of trimeric prefusion RSV F proteins. Nat Commun 2019; 10:2105. [PMID: 31068578 PMCID: PMC6506550 DOI: 10.1038/s41467-019-09807-5] [Citation(s) in RCA: 62] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2018] [Accepted: 04/02/2019] [Indexed: 01/19/2023] Open
Abstract
The respiratory syncytial virus (RSV) F glycoprotein is a class I fusion protein that mediates viral entry and is a major target of neutralizing antibodies. Structures of prefusion forms of RSV F, as well as other class I fusion proteins, have revealed compact trimeric arrangements, yet whether these trimeric forms can transiently open remains unknown. Here, we perform structural and biochemical studies on a recently isolated antibody, CR9501, and demonstrate that it enhances the opening of prefusion-stabilized RSV F trimers. The 3.3 Å crystal structure of monomeric RSV F bound to CR9501, combined with analysis of over 25 previously determined RSV F structures, reveals a breathing motion of the prefusion conformation. We also demonstrate that full-length RSV F trimers transiently open and dissociate on the cell surface. Collectively, these findings have implications for the function of class I fusion proteins, as well as antibody prophylaxis and vaccine development for RSV.
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MESH Headings
- Animals
- Antibodies, Neutralizing/chemistry
- Antibodies, Neutralizing/immunology
- Antibodies, Neutralizing/metabolism
- Antibodies, Viral/chemistry
- Antibodies, Viral/immunology
- Antibodies, Viral/metabolism
- B-Lymphocytes/virology
- Chlorocebus aethiops
- Computer Simulation
- Crystallography, X-Ray
- Drug Development
- HEK293 Cells
- HeLa Cells
- Humans
- Models, Molecular
- Protein Multimerization/physiology
- Respiratory Syncytial Virus Infections/immunology
- Respiratory Syncytial Virus Infections/prevention & control
- Respiratory Syncytial Virus Infections/virology
- Respiratory Syncytial Virus Vaccines/immunology
- Respiratory Syncytial Virus, Human/isolation & purification
- Respiratory Syncytial Virus, Human/physiology
- Vero Cells
- Viral Fusion Proteins/chemistry
- Viral Fusion Proteins/immunology
- Viral Fusion Proteins/metabolism
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Affiliation(s)
- Morgan S A Gilman
- Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, NH, 03755, USA
- Department of Molecular Biosciences, University of Texas at Austin, Austin, TX, 78712, USA
| | | | - Gabriel Pascual
- Janssen Immunosciences, World Without Disease Accelerator, San Diego, CA, 92121, USA
| | - Angélique B van 't Wout
- Janssen Prevention Center, Janssen Vaccines & Prevention B.V, Leiden, CN, 2333, The Netherlands
- AlphaBiomics, London, SW4 0PA, United Kingdom
| | | | - Jason S McLellan
- Department of Molecular Biosciences, University of Texas at Austin, Austin, TX, 78712, USA.
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7
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Malekshahi SS, Razaghipour S, Samieipoor Y, Hashemi FB, Manesh AAR, Izadi A, Faghihloo E, Ghavami N, Mokhtari-Azad T, Salimi V. Molecular characterization of the glycoprotein and fusion protein in human respiratory syncytial virus subgroup A: Emergence of ON-1 genotype in Iran. INFECTION GENETICS AND EVOLUTION 2019; 71:166-178. [PMID: 30946992 DOI: 10.1016/j.meegid.2019.03.026] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/27/2018] [Revised: 03/05/2019] [Accepted: 03/29/2019] [Indexed: 12/20/2022]
Abstract
HRSV is a principle cause of infant hospitalization, childhood wheezing and a common pathogen in the elderly. Limited information exists regarding HRSV genotypes in Iran. In order to better understand HRSV strain diversity, we performed an in-depth evaluation of the genetic variability of the HRSV F protein detected in children under two years of age that, presented with acute respiratory symptoms during 2015-2016 in Tehran. A total of 180 nasopharyngeal swabs were evaluated. The HRSV positive samples were genotyped for G and F gene sequences using RT-PCR and sequencing methods. Phylogenetic analysis was performed using the neighbor-joining and maximum likelihood methods. Genetic and antigenic characteristics of the F gene, nucleotide and amino acids in significant positions and immune system binding regions, as well as the p-distance, positive/negative selection site, linear epitopes and glycosylation sites were investigated in all selected sequences. Among the 83 HRSV positive samples, the Fifty-five cases were successfully sequenced. All of them were classified as subgroup A and belonged to the ON-1 genotype, which possessed 72-nt duplication in the G gene. This study is the first report on the emergence of ON-1 in Iran. ON-1 Iranian sequences clustered in three lineages according to virus fusion (F) gene variations. F gene sequence analysis showed that all genetic changes in the isolates from Iran were base substitutions and no deletion/insertions were identified. The low dN/dS ratio and lack of positively selected sites showed that the fusion genes found in the strains from Iran are not under host selective pressure. Continuing and long-term molecular epidemiological surveys for early detection of circulating and newly emerging genotypes are necessary to gain a better understanding of their epidemic potential.
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Affiliation(s)
| | - Shaghayegh Razaghipour
- Department of Microbiology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran
| | - Yazdan Samieipoor
- Virology Department, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran
| | - Farhad B Hashemi
- Department of Microbiology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran
| | | | - Anahita Izadi
- Bahrami Children Hospital, Tehran University of Medical Sciences, Tehran, Iran
| | - Ebrahim Faghihloo
- Department of Microbiology, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran
| | - Nastaran Ghavami
- Virology Department, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran
| | - Talat Mokhtari-Azad
- Virology Department, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran
| | - Vahid Salimi
- Virology Department, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran.
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8
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Hicks SN, Chaiwatpongsakorn S, Costello HM, McLellan JS, Ray W, Peeples ME. Five Residues in the Apical Loop of the Respiratory Syncytial Virus Fusion Protein F 2 Subunit Are Critical for Its Fusion Activity. J Virol 2018; 92:e00621-18. [PMID: 29743373 PMCID: PMC6052300 DOI: 10.1128/jvi.00621-18] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2018] [Accepted: 05/07/2018] [Indexed: 11/20/2022] Open
Abstract
The respiratory syncytial virus (RSV) fusion (F) protein is a trimeric, membrane-anchored glycoprotein capable of mediating both virus-target cell membrane fusion to initiate infection and cell-cell fusion, even in the absence of the attachment glycoprotein. The F protein is initially expressed in a precursor form, whose functional capabilities are activated by proteolysis at two sites between the F1 and F2 subunits. This cleavage results in expression of the metastable and high-energy prefusion conformation. To mediate fusion, the F protein is triggered by an unknown stimulus, causing the F1 subunit to refold dramatically while F2 changes minimally. Hypothesizing that the most likely site for interaction with a target cell component would be the top, or apex, of the protein, we determined the importance of the residues in the apical loop of F2 by alanine scanning mutagenesis analysis. Five residues were not important, two were of intermediate importance, and all four lysines and one isoleucine were essential. Alanine replacement did not result in the loss of the pre-F conformation for any of these mutants. Each of the four lysines required its specific charge for fusion function. Alanine replacement of the three essential lysines on the ascent to the apex hindered fusion following a forced fusion event, suggesting that these residues are involved in refolding. Alanine mutations at Ile64, also on the ascent to the apex, and Lys75 did not prevent fusion following forced triggering, suggesting that these residues are not involved in refolding and may instead be involved in the natural triggering of the F protein.IMPORTANCE RSV infects virtually every child by the age of 3 years, causing nearly 33 million acute lower respiratory tract infections (ALRI) worldwide each year in children younger than 5 years of age (H. Nair et al., Lancet 375:1545-1555, 2010). RSV is also the second leading cause of respiratory system-related death in the elderly (A. R. Falsey and E. E. Walsh, Drugs Aging 22:577-587, 2005; A. R. Falsey, P. A. Hennessey, M. A. Formica, C. Cox, and E. E. Walsh, N Engl J Med 352:1749-1759, 2005). The monoclonal antibody palivizumab is approved for prophylactic use in some at-risk infants, but healthy infants remain unprotected. Furthermore, its expense limits its use primarily to developed countries. No vaccine or effective small-molecule drug is approved for preventing disease or treating infection (H. M. Costello, W. Ray, S. Chaiwatpongsakorn, and M. E. Peeples, Infect Disord Drug Targets, 12:110-128, 2012). The essential residues identified in the apical domain of F2 are adjacent to the apical portion of F1, which, upon triggering, refolds into a long heptad repeat A (HRA) structure with the fusion peptide at its N terminus. These essential residues in F2 are likely involved in triggering and/or refolding of the F protein and, as such, may be ideal targets for antiviral drug development.
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Affiliation(s)
- Stephanie N Hicks
- The Ohio State Biochemistry Program, The Ohio State University, Columbus, Ohio, USA
- Center for Vaccines and Immunity, The Research Institute at Nationwide Children's Hospital, Columbus, Ohio, USA
| | - Supranee Chaiwatpongsakorn
- Center for Vaccines and Immunity, The Research Institute at Nationwide Children's Hospital, Columbus, Ohio, USA
| | - Heather M Costello
- Center for Vaccines and Immunity, The Research Institute at Nationwide Children's Hospital, Columbus, Ohio, USA
| | - Jason S McLellan
- Department of Molecular Biosciences, The University of Texas at Austin, Austin, Texas, USA
| | - William Ray
- Department of Pediatrics, The Ohio State University College of Medicine, Columbus, Ohio, USA
- Battelle Center for Mathematical Medicine, The Research Institute at Nationwide Children's Hospital, Columbus, Ohio, USA
| | - Mark E Peeples
- The Ohio State Biochemistry Program, The Ohio State University, Columbus, Ohio, USA
- Center for Vaccines and Immunity, The Research Institute at Nationwide Children's Hospital, Columbus, Ohio, USA
- Department of Pediatrics, The Ohio State University College of Medicine, Columbus, Ohio, USA
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9
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McFarland EJ, Karron RA, Muresan P, Cunningham CK, Valentine ME, Perlowski C, Thumar B, Gnanashanmugam D, Siberry GK, Schappell E, Barr E, Rexroad V, Yogev R, Spector SA, Aziz M, Patel N, Cielo M, Luongo C, Collins PL, Buchholz UJ. Live-Attenuated Respiratory Syncytial Virus Vaccine Candidate With Deletion of RNA Synthesis Regulatory Protein M2-2 is Highly Immunogenic in Children. J Infect Dis 2018; 217:1347-1355. [PMID: 29509911 PMCID: PMC5894092 DOI: 10.1093/infdis/jiy040] [Citation(s) in RCA: 44] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2017] [Accepted: 01/25/2018] [Indexed: 11/13/2022] Open
Abstract
Background Live respiratory syncytial virus (RSV) candidate vaccine LIDΔM2-2 is attenuated by deletion of the RSV RNA regulatory protein M2-2, resulting in upregulated viral gene transcription and antigen expression but reduced RNA replication. Methods RSV-seronegative children ages 6-24 months received a single intranasal dose of 105 plaque forming units (PFU) of LIDΔM2-2 (n = 20) or placebo (n = 9) (NCT02237209, NCT02040831). RSV serum antibodies, vaccine infectivity, and reactogenicity were assessed. During the following RSV season, participants were monitored for respiratory illness and pre- and post-RSV season serum antibodies. Results Vaccine virus was shed by 95% of vaccinees (median peak titers of 3.8 log10 PFU/mL by quantitative culture and 6.3 log10 copies/mL by PCR); 90% had ≥4-fold rise in serum neutralizing antibodies. Respiratory symptoms and fever were common in vaccine (95%) and placebo (78%). One vaccinee had grade 2 rhonchi concurrent with vaccine shedding, rhinovirus, and enterovirus. Eight of 19 vaccinees versus 2 of 9 placebo recipients had substantially increased RSV antibody titers after the RSV season without medically attended RSV disease, indicating anamnestic vaccine responses to wild-type RSV without significant illness. Conclusion LIDΔM2-2 had excellent infectivity and immunogenicity, encouraging further study of vaccine candidates attenuated by M2-2 deletion. Clinical Trials Registration NCT02237209, NCT02040831.
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Affiliation(s)
- Elizabeth J McFarland
- Department of Pediatrics, University of Colorado Anschutz Medical Campus and Children’s Hospital Colorado, Aurora
| | - Ruth A Karron
- Center for Immunization Research, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland
| | - Petronella Muresan
- Statistical and Data Analysis Center, Harvard School of Public Health, Boston, Massachusetts
| | | | | | | | - Bhagvanji Thumar
- Center for Immunization Research, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland
| | - Devasena Gnanashanmugam
- Maternal, Adolescent and Pediatric Research Branch, Division of AIDS, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda
| | - George K Siberry
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda
| | - Elizabeth Schappell
- Center for Immunization Research, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland
| | - Emily Barr
- Department of Pediatrics, University of Colorado Anschutz Medical Campus and Children’s Hospital Colorado, Aurora
| | - Vivian Rexroad
- Investigational Drug Service Pharmacy, Johns Hopkins Hospital, Baltimore, Maryland
| | - Ram Yogev
- Department of Pediatrics, Northwestern University Medical School and Ann and Robert H. Lurie Children’s Hospital of Chicago, Illinois
| | - Stephen A Spector
- Department of Pediatrics, University of California San Diego, La Jolla
| | - Mariam Aziz
- Section of Infectious Disease, Rush University Medical Center, Chicago, Illinois
| | - Nehali Patel
- Department of Pediatrics, St. Jude Children’s Research Hospital, Memphis, Tennessee
| | - Mikhaela Cielo
- Division of Infectious Diseases, Maternal Child and Adolescent Center, University of Southern California Keck School of Medicine, Los Angeles
| | - Cindy Luongo
- Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryl
| | - Peter L Collins
- Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryl
| | - Ursula J Buchholz
- Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryl
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10
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Gonzàlez-Parra G, De Ridder F, Huntjens D, Roymans D, Ispas G, Dobrovolny HM. A comparison of RSV and influenza in vitro kinetic parameters reveals differences in infecting time. PLoS One 2018; 13:e0192645. [PMID: 29420667 PMCID: PMC5805318 DOI: 10.1371/journal.pone.0192645] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2017] [Accepted: 01/26/2018] [Indexed: 11/19/2022] Open
Abstract
Influenza and respiratory syncytial virus (RSV) cause acute infections of the respiratory tract. Since the viruses both cause illnesses with similar symptoms, researchers often try to apply knowledge gleaned from study of one virus to the other virus. This can be an effective and efficient strategy for understanding viral dynamics or developing treatment strategies, but only if we have a full understanding of the similarities and differences between the two viruses. This study used mathematical modeling to quantitatively compare the viral kinetics of in vitro RSV and influenza virus infections. Specifically, we determined the viral kinetics parameters for RSV A2 and three strains of influenza virus, A/WSN/33 (H1N1), A/Puerto Rico/8/1934 (H1N1), and pandemic H1N1 influenza virus. We found that RSV viral titer increases at a slower rate and reaches its peak value later than influenza virus. Our analysis indicated that the slower increase of RSV viral titer is caused by slower spreading of the virus from one cell to another. These results provide estimates of dynamical differences between influenza virus and RSV and help provide insight into the virus-host interactions that cause observed differences in the time courses of the two illnesses in patients.
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Affiliation(s)
- Gilberto Gonzàlez-Parra
- Department of Physics and Astronomy, Texas Christian University, Fort Worth, TX, United States of America
- Department of Mathematics, New Mexico Tech, Socorro, NM, United States of America
| | | | | | | | | | - Hana M. Dobrovolny
- Department of Physics and Astronomy, Texas Christian University, Fort Worth, TX, United States of America
- * E-mail:
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11
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The Heptad Repeat C Domain of the Respiratory Syncytial Virus Fusion Protein Plays a Key Role in Membrane Fusion. J Virol 2018; 92:JVI.01323-17. [PMID: 29212939 DOI: 10.1128/jvi.01323-17] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2017] [Accepted: 11/28/2017] [Indexed: 11/20/2022] Open
Abstract
Respiratory syncytial virus (RSV) mediates host cell entry through the fusion (F) protein, which undergoes a conformational change to facilitate the merger of viral and host lipid membrane envelopes. The RSV F protein comprises a trimer of disulfide-bonded F1 and F2 subunits that is present on the virion surface in a metastable prefusion state. This prefusion form is readily triggered to undergo refolding to bring two heptad repeats (heptad repeat A [HRA] and HRB) into close proximity to form a six-helix bundle that stabilizes the postfusion form and provides the free energy required for membrane fusion. This process can be triggered independently of other proteins. Here, we have performed a comprehensive analysis of a third heptad repeat region, HRC (amino acids 75 to 97), an amphipathic α-helix that lies at the interface of the prefusion F trimer and is a major structural feature of the F2 subunit. We performed alanine scanning mutagenesis from Lys-75 to Met-97 and assessed all mutations in transient cell culture for expression, proteolytic processing, cell surface localization, protein conformation, and membrane fusion. Functional characterization revealed a striking distribution of activity in which fusion-increasing mutations localized to one side of the helical face, while fusion-decreasing mutations clustered on the opposing face. Here, we propose a model in which HRC plays a stabilizing role within the globular head for the prefusion F trimer and is potentially involved in the early events of triggering, prompting fusion peptide release and transition into the postfusion state.IMPORTANCE RSV is recognized as the most important viral pathogen among pediatric populations worldwide, yet no vaccine or widely available therapeutic treatment is available. The F protein is critical for the viral replication process and is the major target for neutralizing antibodies. Recent years have seen the development of prefusion stabilized F protein-based approaches to vaccine design. A detailed understanding of the specific domains and residues that contribute to protein stability and fusion function is fundamental to such efforts. Here, we present a comprehensive mutagenesis-based study of a region of the RSV F2 subunit (amino acids 75 to 97), referred to as HRC, and propose a role for this helical region in maintaining the delicate stability of the prefusion form.
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12
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Dubois J, Cavanagh MH, Terrier O, Hamelin MÈ, Lina B, Shi R, Rosa-Calatrava M, Boivin G. Mutations in the fusion protein heptad repeat domains of human metapneumovirus impact on the formation of syncytia. J Gen Virol 2017; 98:1174-1180. [PMID: 28613142 DOI: 10.1099/jgv.0.000796] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Human metapneumovirus (HMPV) is an important cause of respiratory tract infections. The mechanism by which its fusion (F) protein is responsible for variable cytopathic effects in vitro remains unknown. We aligned the F sequences of the poorly fusogenic B2/CAN98-75 strain and the hyperfusogenic A1/C-85473 strain and identified divergent residues located in the two functional heptad repeats domains (HRA and HRB). We generated recombinant viruses by inserting the mutations N135T-G139N-T143K-K166E-E167D in HRA and/or K479R-N482S in HRB, corresponding to swapped sequences from C-85473, into CAN98-75 background and investigated their impact on in vitro phenotype and fusogenicity. We demonstrated that the five HRA mutations enhanced the fusogenicity of the recombinant rCAN98-75 virus, almost restoring the phenotype of the wild-type rC-85473 strain, whereas HRB substitutions alone had no significant effect on cell-cell fusion. Altogether, our results support the importance of the HRA domain for an HMPV-triggered fusion mechanism and identify key residues that modulate syncytium formation.
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Affiliation(s)
- Julia Dubois
- Centre de Recherche en Infectiologie of the Centre Hospitalier Universitaire de Québec and Université Laval, Québec, Canada.,Laboratoire de Virologie et Pathologie Humaine - VirPath Team, Centre International de Recherche en Infectiologie CIRI, Inserm U1111, CNRS UMR5308, ENS Lyon, Université Claude Bernard Lyon 1, Lyon, France
| | - Marie-Hélène Cavanagh
- Centre de Recherche en Infectiologie of the Centre Hospitalier Universitaire de Québec and Université Laval, Québec, Canada
| | - Olivier Terrier
- Laboratoire de Virologie et Pathologie Humaine - VirPath Team, Centre International de Recherche en Infectiologie CIRI, Inserm U1111, CNRS UMR5308, ENS Lyon, Université Claude Bernard Lyon 1, Lyon, France
| | - Marie-Ève Hamelin
- Centre de Recherche en Infectiologie of the Centre Hospitalier Universitaire de Québec and Université Laval, Québec, Canada
| | - Bruno Lina
- Laboratoire de Virologie et Pathologie Humaine - VirPath Team, Centre International de Recherche en Infectiologie CIRI, Inserm U1111, CNRS UMR5308, ENS Lyon, Université Claude Bernard Lyon 1, Lyon, France.,Hospices Civils de Lyon, Centre National de Référence Virus Influenzae France Sud, Laboratoire de Virologie, Groupement Hospitalier Nord, F-69317, Lyon, France
| | - Rong Shi
- Institut de Biologie Intégrative et des Systèmes (IBIS), Université Laval, Pavillon Charles-Eugene-Marchand, Québec, Canada.,Département de Biochimie, de Microbiologie et de Bio-informatique, PROTEO, Université Laval, Québec, Canada
| | - Manuel Rosa-Calatrava
- Laboratoire de Virologie et Pathologie Humaine - VirPath Team, Centre International de Recherche en Infectiologie CIRI, Inserm U1111, CNRS UMR5308, ENS Lyon, Université Claude Bernard Lyon 1, Lyon, France
| | - Guy Boivin
- Centre de Recherche en Infectiologie of the Centre Hospitalier Universitaire de Québec and Université Laval, Québec, Canada
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13
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Yasui Y, Yamaji Y, Sawada A, Ito T, Nakayama T. Cell fusion assay by expression of respiratory syncytial virus (RSV) fusion protein to analyze the mutation of palivizumab-resistant strains. J Virol Methods 2016; 231:48-55. [PMID: 26794681 DOI: 10.1016/j.jviromet.2016.01.003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2015] [Revised: 12/11/2015] [Accepted: 01/09/2016] [Indexed: 11/18/2022]
Abstract
Respiratory syncytial virus (RSV) consists of fusion (F), glyco (G), and small hydrophobic (SH) proteins as envelope proteins, and infects through cell fusion. F protein is expressed on the surface of infected cells, and induces cell fusion. In the present report, expression plasmids of the F, G and SH proteins were constructed and cell fusion activity was investigated under T7 RNA polymerase. F protein alone induced cell fusion at a lower concentration than previously reported, and co-expression of F and SH proteins induced cell fusion more efficiently than F protein alone. Palivizumab is the only prophylactic agent against RSV infection. Palivizumab-resistant strains having mutations of the F protein of K272E and S275F were reported. These mutations were introduced into an F-expression plasmid, and exhibited no inhibition of cell fusion with palivizumab. Among the RSV F protein mutants, N276S has been reported to have partial resistance against palivizumab, but the F expression plasmid with the N276S mutation showed a reduction in cell fusion in the presence of palivizumab, showing no resistance to palivizumab. The present expression system was useful for investigating the mechanisms of RSV cell fusion.
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Affiliation(s)
- Yosuke Yasui
- Keio University, Health Center, 4-1-1 Hiyoshi, Kouhoku, Yokohama, Kanagawa, Japan; Laboratory of Viral Infection I, Kitasato Institute for Life Sciences, Kitasato University, 5-9-1 Shirokane, Minato-ku, Tokyo, Japan.
| | - Yoshiaki Yamaji
- Laboratory of Viral Infection I, Kitasato Institute for Life Sciences, Kitasato University, 5-9-1 Shirokane, Minato-ku, Tokyo, Japan.
| | - Akihito Sawada
- Laboratory of Viral Infection I, Kitasato Institute for Life Sciences, Kitasato University, 5-9-1 Shirokane, Minato-ku, Tokyo, Japan.
| | - Takashi Ito
- Laboratory of Viral Infection I, Kitasato Institute for Life Sciences, Kitasato University, 5-9-1 Shirokane, Minato-ku, Tokyo, Japan.
| | - Tetsuo Nakayama
- Laboratory of Viral Infection I, Kitasato Institute for Life Sciences, Kitasato University, 5-9-1 Shirokane, Minato-ku, Tokyo, Japan.
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14
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Enhanced Neutralizing Antibody Response Induced by Respiratory Syncytial Virus Prefusion F Protein Expressed by a Vaccine Candidate. J Virol 2015; 89:9499-510. [PMID: 26157122 DOI: 10.1128/jvi.01373-15] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2015] [Accepted: 07/01/2015] [Indexed: 11/20/2022] Open
Abstract
UNLABELLED Respiratory syncytial virus (RSV) and human parainfluenza virus type 3 (HPIV3) are the first and second leading viral agents of severe respiratory tract disease in infants and young children worldwide. Vaccines are not available, and an RSV vaccine is particularly needed. A live attenuated chimeric recombinant bovine/human PIV3 (rB/HPIV3) vector expressing the RSV fusion (F) glycoprotein from an added gene has been under development as a bivalent vaccine against RSV and HPIV3. Previous clinical evaluation of this vaccine candidate suggested that increased genetic stability and immunogenicity of the RSV F insert were needed. This was investigated in the present study. RSV F expression was enhanced 5-fold by codon optimization and by modifying the amino acid sequence to be identical to that of an early passage of the original clinical isolate. This conferred a hypofusogenic phenotype that presumably reflects the original isolate. We then compared vectors expressing stabilized prefusion and postfusion versions of RSV F. In a hamster model, prefusion F induced increased quantity and quality of RSV-neutralizing serum antibodies and increased protection against wild-type (wt) RSV challenge. In contrast, a vector expressing the postfusion F was less immunogenic and protective. The genetic stability of the RSV F insert was high and was not affected by enhanced expression or the prefusion or postfusion conformation of RSV F. These studies provide an improved version of the previously well-tolerated rB/HPIV3-RSV F vaccine candidate that induces a superior RSV-neutralizing serum antibody response. IMPORTANCE Respiratory syncytial virus (RSV) and human parainfluenza virus type 3 (HPIV3) are two major causes of pediatric pneumonia and bronchiolitis. The rB/HPIV3 vector expressing RSV F protein is a candidate bivalent live vaccine against HPIV3 and RSV. Previous clinical evaluation indicated the need to increase the immunogenicity and genetic stability of the RSV F insert. Here, we increased RSV F expression by codon optimization and by modifying the RSV F amino acid sequence to conform to that of an early passage of the original isolate. This resulted in a hypofusogenic phenotype, which likely represents the original phenotype before adaptation to cell culture. We also included stabilized versions of prefusion and postfusion RSV F protein. Prefusion RSV F induced a larger quantity and higher quality of RSV-neutralizing serum antibodies and was highly protective. This provides an improved candidate for further clinical evaluation.
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15
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Identification of residues in the human respiratory syncytial virus fusion protein that modulate fusion activity and pathogenesis. J Virol 2014; 89:512-22. [PMID: 25339762 DOI: 10.1128/jvi.02472-14] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
UNLABELLED Human respiratory syncytial virus (RSV) lower respiratory tract infection can result in inflammation and mucus plugging of airways. RSV strain A2-line19F induces relatively high viral load and mucus in mice. The line 19 fusion (F) protein harbors five unique residues compared to the non-mucus-inducing strains A2 and Long, at positions 79, 191, 357, 371, and 557. We hypothesized that differential fusion activity is a determinant of pathogenesis. In a cell-cell fusion assay, line 19 F was more fusogenic than Long F. We changed the residues unique to line 19 F to the corresponding residues in Long F and identified residues 79 and 191 together as responsible for high fusion activity. Surprisingly, mutation of residues 357 or 357 with 371 resulted in gain of fusion activity. Thus, we generated RSV F mutants with a range of defined fusion activity and engineered these into recombinant viruses. We found a clear, positive correlation between fusion activity and early viral load in mice; however, we did not detect a correlation between viral loads and levels of airway mucin expression. The F mutant with the highest fusion activity, A2-line19F-K357T/Y371N, induced high viral loads, severe lung histopathology, and weight loss but did not induce high levels of airway mucin expression. We defined residues 79/191 as critical for line 19 F fusion activity and 357/371 as playing a role in A2-line19F mucus induction. Defining the molecular basis of the role of RSV F in pathogenesis may aid vaccine and therapeutic strategies aimed at this protein. IMPORTANCE Human respiratory syncytial virus (RSV) is the most important lower respiratory tract pathogen of infants for which there is no vaccine. Elucidating mechanisms of RSV pathogenesis is important for rational vaccine and drug design. We defined specific amino acids in the fusion (F) protein of RSV strain line 19 critical for fusion activity and elucidated a correlation between fusion activity and viral load in mice. Further, we identified two distinct amino acids in F as contributing to the mucogenic phenotype of the A2-line19F virus. Taken together, these results illustrate a role for RSV F in virulence.
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