Cross-Clade Protective Immune Responses to Influenza Viruses with H5N1 HA and NA Elicited by an Influenza Virus-Like Particle

Abstract

BackgroundVaccination is a cost-effective counter-measure to the threat of seasonal or pandemic outbreaks of influenza. To address the need for improved influenza vaccines and alternatives to egg-based manufacturing, we have engineered an influenza virus-like particle (VLP) as a new generation of non-egg or non-mammalian cell culture-based candidate vaccine.Methodology/Principal FindingsWe generated from a baculovirus expression system using insect cells, a non-infectious recombinant VLP vaccine from both influenza A H5N1 clade 1 and clade 2 isolates with pandemic potential. VLPs were administered to mice in either a one-dose or two-dose regimen and the immune responses were compared to those induced by recombinant hemagglutinin (rHA). Both humoral and cellular responses were analyzed. Mice vaccinated with VLPs were protected against challenge with lethal reassortant viruses expressing the H5N1 HA and NA, regardless if the H5N1 clade was homologous or heterologous to the vaccine. However, rHA-vaccinated mice showed considerable weight loss and death following challenge with the heterovariant clade virus. Protection against death induced by VLPs was independent of the pre-challenge HAI titer or cell-mediated responses to HA or M1 since vaccinated mice, with low to undetectable cross-clade HAI antibodies or cellular responses to influenza antigens, were still protected from a lethal viral challenge. However, an apparent association rate of antibody binding to HA correlated with protection and was enhanced using VLPs, particularly when delivered intranasally, compared to rHA vaccines.Conclusion/SignificanceThis is the first report describing the use of an H5N1 VLP vaccine created from a clade 2 isolate. The results show that a non-replicating virus-like particle is effective at eliciting a broadened, cross-clade protective immune response to proteins from emerging H5N1 influenza isolates giving rise to a potential pandemic influenza vaccine candidate for humans that can be stockpiled for use in the event of an outbreak of H5N1 influenza.

H5N1 Virus-Like Particle Vaccine Elicits Cross-Reactive Neutralizing Antibodies That Preferentially Bind to the Oligomeric Form of Influenza Virus Hemagglutinin in Humans

“…Furthermore, VLPs present the key antigenic targets of influenza virus, HA and NA, in a native-like conformation similar to the intact virion. Studies in animal models also provided evidence for generation of cross-clade protective antibodies following H5N1 VLP (but not rHA) immunization (4,5,30,38).…”

“…In previous studies, these VLPs were shown to be immunogenic in mice and ferrets and to provide protection against respira-tory challenge with homologous and heterologous influenza virus strains (4,5,37).…”

Achievement of avian influenza virus-like particles that could be used as a subunit vaccine against low-pathogenic avian influenza strains in ducks

“…All these results make feasible the reliable use of AI VLPs as subunit vaccines in ducks, notably as a boost immunization by either the parenteral or mucosal route, after a prime immunization with a recombinant vaccine. In addition, very recently Bright et al (2008) confirmed the potential of such a VLP vaccine as an effective immunogen and delivery system for influenza antigens to protect mice against lethal human H5N1 influenza isolates.…”

New technologies for influenza vaccines

“…46,47 Formulation in a lipid bilayer may help maintain HA and NA stability and conformation in more sensitive strains, and the mounting of HA on a particle probably enhances its immunogenicity. 48 An advantage of VLPs is that the virus used to express the proteins that assemble into particles is not an influenza virus but rather a recombinant vector, such as the baculovirus used to infect insect cells in the vaccine candidates produced by Novavax or the Agrobacterium tumefaciens bacterial vector used to infect tobacco leaves in the candidates produced by Medicago. 46,47 These recombinant vectors do not depend on the function of the expressed influenza HA and NA for their replication.…”