Protective antiviral immune responses to pseudorabies virus induced by DNA vaccination using dimethyldioctadecylammonium bromide as an adjuvant.

To enhance the efficacy of a DNA vaccine against pseudorabies virus (PRV), we evaluated the adjuvant properties of plasmids coding for gamma interferon or interleukin-12, of CpG immunostimulatory motifs, and of the conventional adjuvants dimethyldioctadecylammonium bromide in water (DDA) and sulfolipo-cyclodextrin in squalene in water. We demonstrate that a DNA vaccine combined with DDA, but not with the other adjuvants, induced significantly stronger immune responses than plasmid vaccination alone. Moreover, pigs vaccinated in the presence of DDA were protected against clinical disease and shed significantly less PRV after challenge infection. This is the first study to demonstrate that DDA, a conventional adjuvant, enhances DNA vaccine-induced antiviral immunity.

Vaccination of pigs with a DNA construct expressing an influenza virus M2-nucleoprotein fusion protein exacerbates disease after challenge with influenza A virus.

In mice, vaccines inducing antibodies to the extracellular domain of the M2 protein (M2e) can confer protection to influenza A virus infection. Unlike the surface glycoproteins, haemagglutinin and neuraminidase, this domain of M2 is highly conserved and is therefore a potential broad-spectrum immunogen. In this study, the protection conferred by vaccines inducing antibodies to M2e was evaluated in a challenge model for swine influenza in pigs. A protein resulting from the fusion between M2e and the hepatitis B virus core protein (M2eHBc), with or without adjuvant, was evaluated. In addition, a DNA construct expressing a fusion protein between M2e and influenza virus nucleoprotein (M2eNP) was evaluated to see if the broad-spectrum protection conferred by antibodies could be further enhanced by T helper cells and cytotoxic T cells. All vaccines induced an antibody response against M2e, and the M2eNP DNA vaccine additionally induced an influenza virus-specific lymphoproliferation response. However, after challenge with a swine influenza virus (H1N1), no protection was observed in the vaccinated groups compared with the non-vaccinated control group. On the contrary, vaccinated pigs showed more severe clinical signs than the control pigs. The M2eNP DNA-vaccinated pigs showed the most severe clinical signs and three out of six pigs died on days 1 and 2 post-challenge. These results indicate that antibodies to M2e, especially in combination with cell-mediated immune responses, exacerbate disease. Thus, clinical signs after infection should be observed closely in further studies using M2e as an immunogen and caution should be exercised in using M2e in humans.

Respiratory and systemic humoral and cellular immune responses of pigs to a heterosubtypic influenza A virus infection.

The level of heterosubtypic immunity (Het-I) and the immune mechanisms stimulated by a heterosubtypic influenza virus infection were investigated in pigs. Pigs are natural hosts for influenza virus and, like humans, they host both subtypes H1N1 and H3N2. Marked Het-I was observed when pigs were infected with H1N1 and subsequently challenged with H3N2. After challenge with H3N2, pigs infected earlier with H1N1 did not develop fever and showed reduced virus excretion compared with non-immune control pigs. In addition, virus transmission to unchallenged group-mates could be shown by virus isolation in the non-immune control group but not in the group infected previously with H1N1. Pigs infected previously with homologous H3N2 virus were protected completely. After challenge with H3N2, pigs infected previously with H1N1 showed a considerable increase in serum IgG titre to the conserved extracellular domain of M2 but not to the conserved nucleoprotein. These results suggest that antibodies against external conserved epitopes can have an important role in broad-spectrum immunity. After primary infection with both H1N1 and H3N2, a long-lived increase was observed in the percentage of CD8(+) T cells in the lungs and in the lymphoproliferation response in the blood. Upon challenge with H3N2, pigs infected previously with H1N1 again showed an increase in the percentage of CD8(+) T cells in the lungs, whereas pigs infected previously with H3N2 did not, suggesting that CD8(+) T cells also have a role in Het-I. To confer broad-spectrum immunity, future vaccines should induce antibodies and CD8(+) T cells against conserved antigens.