title: Recombinant influenza A virus hemagglutinin HA2 subunit protects mice against influenza A(H7N9) virus infection.
abstract: A novel avian influenza A(H7N9) virus has emerged to infect humans in eastern China since 2013. An effective vaccine is needed because of the high mortality despite antiviral treatment and intensive care. We sought to develop an effective vaccine for A(H7N9) virus. The HA2 subunit was chosen as the vaccine antigen because it is highly conserved among the human A(H7N9) virus strains. Moreover, in silico analysis predicted two immunogenic regions within the HA2 subunit that may contain potential human B-cell epitopes. The HA2 fragment was readily expressed in Escherichia coli. In BALB/c mice, intraperitoneal immunization with two doses of HA2 with imiquimod (2-dose-imiquimod) elicited the highest geometric mean titer (GMT) of anti-HA2 IgG (12699), which was greater than that of two doses of HA2 without imiquimod (2-dose-no-adjuvant) (6350), one dose of HA2 with imiquimod (1-dose-imiquimod) (2000) and one dose of HA2 without imiquimod (1-dose-no-adjuvant) (794). The titer of anti-HA2 IgG was significantly higher in the 1-dose-imiquimod group than the 1-dose-no-adjuvant group. Although both hemagglutination inhibition titers and microneutralization titers were below 10, serum from immunized mice showed neutralizing activity in a fluorescent focus microneutralization assay. In a viral challenge experiment, the 2-dose-imiquimod group had the best survival rate (100 %), followed by the 2-dose-no-adjuvant group (90 %), the 1-dose-imiquimod group (70 %) and the 1-dose-no-adjuvant group (40 %). The 2-dose-imiquimod group also had significantly lower mean pulmonary viral loads than the 1-dose-imiquimod, 1-dose-no-adjuvant and non-immunized groups. This recombinant A(H7N9)-HA2 vaccine should be investigated as a complement to egg- or cell-based live attenuated or subunit influenza vaccines.
authors.affiliation: State Key Laboratory of Emerging Infectious Diseases, The University of Hong Kong, Hong Kong, China.
authors.forename: Kelvin K W
authors.initials: KK
authors.lastname: To
authors.forename: Anna J X
authors.initials: AJ
authors.lastname: Zhang
authors.forename: Andy S F
authors.initials: AS
authors.lastname: Chan
authors.forename: Can
authors.initials: C
authors.lastname: Li
authors.forename: Jian-Piao
authors.initials: JP
authors.lastname: Cai
authors.forename: Candy C Y
authors.initials: CC
authors.lastname: Lau
authors.forename: Chuan-Gen
authors.initials: CG
authors.lastname: Li
authors.forename: Akhee S
authors.initials: AS
authors.lastname: Jahan
authors.forename: Wai-Lan
authors.initials: WL
authors.lastname: Wu
authors.forename: Lanjuan
authors.initials: L
authors.lastname: Li
authors.forename: Alan Ka-Lun
authors.initials: AK
authors.lastname: Tsang
authors.forename: Kwok-Hung
authors.initials: KH
authors.lastname: Chan
authors.forename: Honglin
authors.initials: H
authors.lastname: Chen
authors.forename: Kwok-Yung
authors.initials: KY
authors.lastname: Yuen
mesh_terms: D000276:Adjuvants, Immunologic / Q000008:administration & dosage; D000634:Aminoquinolines / Q000008:administration & dosage; D000818:Animals; D057134:Antibodies, Neutralizing / Q000097:blood; D000914:Antibodies, Viral / Q000097:blood; D004195:Disease Models, Animal; D004926:Escherichia coli / Q000235:genetics; D015870:Gene Expression; D006385:Hemagglutination Inhibition Tests; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000235:genetics / Q000276:immunology*; D000077271:Imiquimod; D007074:Immunoglobulin G / Q000097:blood; D064766:Influenza A Virus, H7N9 Subtype / Q000276:immunology*; D007252:Influenza Vaccines / Q000008:administration & dosage / Q000235:genetics / Q000276:immunology*; D007274:Injections, Intraperitoneal; D008807:Mice, Inbred BALB C; D009500:Neutralization Tests; D009976:Orthomyxoviridae Infections / Q000517:prevention & control*; D021122:Protein Subunits / Q000235:genetics / Q000276:immunology; D011994:Recombinant Proteins / Q000235:genetics / Q000276:immunology; D016019:Survival Analysis; D014611:Vaccination / Q000379:methods; D022223:Vaccines, Subunit / Q000008:administration & dosage / Q000235:genetics / Q000276:immunology; D014614:Vaccines, Synthetic / Q000008:administration & dosage / Q000235:genetics / Q000276:immunology
chemical_list: D000276:Adjuvants, Immunologic; D000634:Aminoquinolines; D057134:Antibodies, Neutralizing; D000914:Antibodies, Viral; D019267:Hemagglutinin Glycoproteins, Influenza Virus; D007074:Immunoglobulin G; D007252:Influenza Vaccines; D021122:Protein Subunits; D011994:Recombinant Proteins; D022223:Vaccines, Subunit; D014614:Vaccines, Synthetic; D000077271:Imiquimod