title: Development of influenza A(H7N9) candidate vaccine viruses with improved hemagglutinin antigen yield in eggs.
abstract: BACKGROUND
  The emergence of avian influenza A(H7N9) virus in poultry causing zoonotic human infections was reported on March 31, 2013. Development of A(H7N9) candidate vaccine viruses (CVV) for pandemic preparedness purposes was initiated without delay. Candidate vaccine viruses were derived by reverse genetics using the internal genes of A/Puerto/Rico/8/34 (PR8). The resulting A(H7N9) CVVs needed improvement because they had titers and antigen yields that were suboptimal for vaccine manufacturing in eggs, especially in a pandemic situation.
  
  
  METHODS
  Two CVVs derived by reverse genetics were serially passaged in embryonated eggs to improve the hemagglutinin (HA) antigen yield. The total viral protein and HA antigen yields of six egg-passaged CVVs were determined by the BCA assay and isotope dilution mass spectrometry (IDMS) analysis, respectively. CVVs were antigenically characterized by hemagglutination inhibition (HI) assays with ferret antisera.
  
  
  RESULTS
  Improvement of total viral protein yield was observed for the six egg-passaged CVVs; HA quantification by IDMS indicated approximately a twofold increase in yield of several egg-passaged viruses as compared to that of the parental CVV. Several different amino acid substitutions were identified in the HA of all viruses after serial passage. However, HI tests indicated that the antigenic properties of two CVVs remained unchanged.
  
  
  CONCLUSIONS
  If influenza A(H7N9) viruses were to acquire sustained human-to-human transmissibility, the improved HA yield of the egg-passaged CVVs generated in this study could expedite vaccine manufacturing for pandemic mitigation.
authors.affiliation: Influenza Division, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, GA, USA.
authors.forename: Callie
authors.initials: C
authors.lastname: Ridenour
authors.affiliation: Influenza Division, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, GA, USA.
authors.forename: Adam
authors.initials: A
authors.lastname: Johnson
authors.affiliation: Division of Laboratory Sciences, National Center for Environmental Health, Centers for Disease Control and Prevention, Atlanta, GA, USA.|Battelle Memorial Institute, Atlanta, Georgia, USA.
authors.forename: Emily
authors.initials: E
authors.lastname: Winne
authors.affiliation: Influenza Division, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, GA, USA.
authors.forename: Jaber
authors.initials: J
authors.lastname: Hossain
authors.affiliation: Influenza Division, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, GA, USA.
authors.forename: Guaniri
authors.initials: G
authors.lastname: Mateu-Petit
authors.affiliation: Influenza Division, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, GA, USA.
authors.forename: Amanda
authors.initials: A
authors.lastname: Balish
authors.affiliation: Division of Laboratory Sciences, National Center for Environmental Health, Centers for Disease Control and Prevention, Atlanta, GA, USA.
authors.forename: Wanda
authors.initials: W
authors.lastname: Santana
authors.affiliation: Influenza Division, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, GA, USA.
authors.forename: Taejoong
authors.initials: T
authors.lastname: Kim
authors.affiliation: Influenza Division, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, GA, USA.
authors.forename: Charles
authors.initials: C
authors.lastname: Davis
authors.affiliation: Influenza Division, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, GA, USA.
authors.forename: Nancy J
authors.initials: NJ
authors.lastname: Cox
authors.affiliation: Division of Laboratory Sciences, National Center for Environmental Health, Centers for Disease Control and Prevention, Atlanta, GA, USA.
authors.forename: John R
authors.initials: JR
authors.lastname: Barr
authors.affiliation: Influenza Division, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, GA, USA.
authors.forename: Ruben O
authors.initials: RO
authors.lastname: Donis
authors.affiliation: Influenza Division, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, GA, USA.
authors.forename: Julie
authors.initials: J
authors.lastname: Villanueva
authors.affiliation: Division of Laboratory Sciences, National Center for Environmental Health, Centers for Disease Control and Prevention, Atlanta, GA, USA.
authors.forename: Tracie L
authors.initials: TL
authors.lastname: Williams
authors.affiliation: Influenza Division, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, GA, USA.
authors.forename: Li-Mei
authors.initials: LM
authors.lastname: Chen
mesh_terms: D000818:Animals; D002642:Chick Embryo; D004531:Eggs / Q000821:virology*; D005289:Ferrets; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000235:genetics / Q000276:immunology*; D006801:Humans; D064766:Influenza A Virus, H7N9 Subtype / Q000235:genetics / Q000276:immunology*; D007252:Influenza Vaccines / Q000235:genetics / Q000276:immunology*; D007251:Influenza, Human / Q000517:prevention & control* / Q000821:virology; D059386:Reverse Genetics; D012692:Serial Passage; D014776:Virus Cultivation
chemical_list: D019267:Hemagglutinin Glycoproteins, Influenza Virus; D007252:Influenza Vaccines
keywords: Antigen yield; H7N9; hemagglutinin; influenza; serial passage; vaccine