CategorySwine Health - General Disease
Date Full Report Received08/06/2011
Date Abstract Report Received08/06/2011
Funded ByIowa Pork Producers Association
Swine influenza is a growing problem in the U.S. swine industry although the disease and etiology have been known for a long time. Historically, swine influenza in the U.S. had been only due to classical H1N1 (i.e., clade) swine influenza virus (SIV) and can be relatively well controlled through vaccination using inactivated viruses. However, after introduction of H3N2 SIV, emergence of numerous reassortants between H1N1 and H3N2 and increased antigenic changes within each subtype have become a nightmare for swine veterinarians and producers from a disease control standpoint and have raised the need for better vaccination strategies. In order to develop an effective vaccine, better understanding of the immune ontogeny of pigs to SIV infection was necessary as natural exposure induces a strong and protective immune response. The proposed study was intended to combine findings on the role of each SIV protein in immunity with an advanced vector technology to formulate a novel way for delivering specific viral antigens to pigs in a targeted manner so that enhanced yet balanced immune response to SIV can be obtained in the animals.
The main objective of the study was to generate an immunization vector capable of providing the source of both immunogenic endogenous and exogenous antigens for the balanced stimulation of the immune system (i.e., both virus-specific antibody and cell-mediated immunity). Baculovirus was chosen as antigen exchange vector to prove the concept of surface display-endogenous expression of targeted antigens for better immunization against SIV. The target antigens were hemagglutinin (HA) for surface display and matrix (M) protein for endogenous expression. The resulting recombinant baculovirus was then used as immunogen (i.e., vaccine) and evaluated in animal trials measuring parameters associated with humoral and cell-mediated immune responses. A viable recombinant baculovirus displaying immunologically recognizable HA protein on the surface and harboring functional M gene was successfully constructed. After immunized with the recombinant baculovirus twice, pigs developed antibodies against the HA protein which were measurable by HI, ELISA and SN tests. The kinetic of antibody response was comparable with that in pigs infected with the donor SIV. However, antigen-specific CMI response was much weaker in immunized pigs as compared to that in challenged pigs, suggesting that replication of the recombinant baculovirus in pigs was not optimal or matrix protein did not contain T-cell epitopes.
Although optimal CMI response could not be obtained in pigs and further work remains to address this issue, the proposed work was a new approach combining the capability of surface display, mammalian cell transduction and the sequential endogenous antigen expression in the same baculovirus vector construct, mimicking the natural infection pathway of the virus on host cells. Therefore, it should provide a new tool for safe antigen delivery, which in turn enhances protective immunity by inducing the balanced immune responses against the target pathogen. A similar platform would allow biologic firms to rapidly formulate a vaccine using contemporary SIV strains once a cloning cassette is formulated.