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United States Department of Agriculture

Agricultural Research Service

Research Project: IMMUNE FACTORS IN VACCINE-ENHANCED PANDEMIC H1N1 INFLUENZA DISEASE
2013 Annual Report


1a.Objectives (from AD-416):
1. Determine if antibodies elicited by an inactivated vaccine predispose pigs for enhanced disease when infected with the heterologous panH1N1 virus. The working hypothesis of this aim is that vaccination elicits IgG antibodies that do not neutralize the challenge virus but trigger greater inflammation of the infected lungs. 2. Determine if mismatch between viral surface antigens of vaccine and challenge strains is sufficient to cause enhanced disease following challenge. The working hypothesis is that disease enhancement primed by the heterologous vaccine stems from antigenic differences in the highly variable HA and/or NA envelope proteins.


1b.Approach (from AD-416):
We will determine if antibodies induced by heterologous H1 virus vaccination are sufficient to predispose pigs for enhanced disease after panH1N1 infection. We will test our working hypothesis using an experimental approach of passively immunizing pigs followed by heterologous panH1N1 inoculation. The rationale for this aim is that completing it will reveal whether a systemic antibody response creates susceptibility to enhanced disease. The additional experimental approach is to generate two virus-like particle (VLP) vaccines that bear HA, NA, and M1 proteins of either MN08 or CA09. Adjuvanted vaccines will be formulated from the two VLP’s, with HA activity calibrated to match the corresponding inactivated whole-virus vaccines. We will analyze the cross-reactivity of antibodies and T cells induced by each VLP and whole-virus vaccine, and test the protective or enhancing effects on CA09 challenge. The rationale for this aim is that it will reveal whether viral envelope proteins in an inactivated H1 vaccine trigger the pathogenic immune response to heterologous panH1N1 infection. Findings from this work will aid future efforts to identify specific epitopes and immune mechanisms pivotal to the problem. Outcomes will provide insight into the safety and efficacy of VLP and other subunit forms of IAV vaccine, when vaccinates encounter antigenically divergent zoonotic strains.

Animal studies will be conducted at the NADC; blood and tissue samples will be processed to access humoral and cell mediated immune response to vaccine. Post-challenge, samples will be processed at NADC for bacteriologic, virologic, and histologic studies to assess virus replication and pathology in various porcine tissues. Blood samples will also be given to our collaborators to perform the cell mediated immune assays.


3.Progress Report:

For objective 1, sows were separated into 3 groups: one group received inactivated H1N1pdm09 virus vaccine, while the second group received live-attenuated H1N1pdm09 virus, and the third group were non-immunized controls. Antibodies from the vaccinated sows were passed to piglets in their respective litters, supplying the piglets with circulating antibody titers. We then tested the hypothesis by experimentally challenging the passively immunized piglets with heterologous H1N2 virus. If antibodies are necessary and sufficient to trigger vaccine associated enhanced respiratory disease (VAERD) then we expect to observe VAERD in the piglets of whole inactivated virus (WIV)-vaccinated sows. Data analysis and manuscript preparation are in progress.

For objective 2, we expressed the surface hemagglutinin (HA) and neuraminidase (NA) of MN08 H1N2 and CA09 H1N1pdm09 as virus-like particle (VLP) antigens using a Baculovirus system, and showed the VLP's were produced with functional and antigenic properties very similar to whole influenza virus. Supernatants of recombinant Baculovirus-infected cells have hemagglutination activity, evidence of proper HA protein expression. The supernatants also contain functional neuraminidase activity, evidence of proper NA protein expression. Swine antisera induced by MN08 and CA09 influenza viral antigens have strain-specific hemagglutination inhibition (HI) activity against the respective VLP supernatants. In a pilot study, pigs immunized with MN08 and CA09 VLP's seroconverted in a strain-specific manner (i.e. they develop HI titers that can be titrated against whole influenza virus antigens). This result shows convincingly that the VLP's formed from recombinant proteins should serve our intended purpose in the experimental design. Production of VLP was scaled up to make vaccine batches sufficient for the experimental design and the final animal study is in progress.


Last Modified: 11/25/2014
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