Comparative evaluation of human and porcine adenovirus vectors for vaccine application agianst avian influenza (H5N1)

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Patel, Ami
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First in 1997, and later re-emerging in 2003, highly pathogenic avian influenza A virus, subtype H5N1, has spread from wild bird reservoirs to domestic bird flocks. As a result, cross-transmission has been confirmed in people living or working in close contact with infected birds. H5N1 virus infection is associated with a high mortality rate (>60%) in humans and the rapid evolution of the virus suggests that it could potentially develop into a new, and possibly severe, pandemic influenza virus. To-date, conventional inactivated and live-attenuated vaccine strategies offers the best protection against influenza virus infection; however, poor immunogenicity and weaker efficacy have been observed against H5N1 viruses. It was hypothesized that experimental adenovirus-based vaccines based on human adenovirus serotype 5 (AdHu5) or porcine adenovirus serotype 3 (PAV3) can offer protection against a broad range of avian influenza, subtype H5N1, viruses. Ad vaccine vectors are highly immunogenic and have demonstrated protective efficacy against several disease models. However, natural immunity against AdHu5 can interfere with vector efficacy. The nonhuman PAV3 was not neutralized by pooled human serum from 10,000-60,000 individuals and offers a promising alternative to AdHu5-based vectors. Systematic antigen screening using DNA vaccines identified the hemagglutinin (HA) glycoprotein as the most immunogenic H5N1 antigen. HA was then inserted directly into PAV3 or AdHu5. Comparable immune responses were observed between both vectors but, interestingly, the PAV3-based vaccine generated stronger T-cell responses and better rapid protection 8 days following immunization. Additionally, better long-term protection 1 year following vaccination was observed with the PAV3-HA vaccine. The co-administration of multiple H5N1 antigens was also screened to improve protection against divergent H5N1 challenge. Combinations of DNA vaccines expressing (HA+NA) and (HA+NP) offered the best promise for enhancing protection against homologous and heterologous H5N1 challenges, respectively. However, addition of three or more antigens reduced overall protection possibly by antigen dilution, competition, or interference. Co-administration of PAV3 or AdHu5 vectors expressing both the HA and NP antigens reduced protection against homologous and heterologous H5N1 virus challenges. For all combination vaccines, T-cell responses were strong against HA but significantly decreased against additional antigens in each combination vaccine. Overall, the experimental porcine-based Ad-based vaccine offered better protection than the H5N1 conventional vaccine against a broad range of different H5N1 viruses. Understanding of the relationship between immune parameters and protection will be critical in future improvement of adenovirus-based and other vaccines against avian influenza H5N1.
Vaccine, Infectious disease, Virology
Patel, A., Tikoo, S., Kobinger, G., 2010, A porcine adenovirus with low human seroprevalence is a promising alternative vaccine vector to human adenovirus 5 in an H5N1 virus disease model. PLoS One 5, e15301.
Patel, A., Tran, K., Gray, M., Li, Y., Ao, Z., Yao, X., Kobasa, D., Kobinger, G.P., 2009, Evaluation of conserved and variable influenza antigens for immunization against different isolates of H5N1 viruses. Vaccine 27, 3083-3089.