Employing XIAP to Enhance the Duration of Antigen Expression and Immunity Against an Avian Influenza H5 DNA Vaccine

Abstract

DNA vaccine represents a powerful approach for prevention of avian H5N1 influenza infection. Yet, DNA vaccine-induced immune responses might be limited by the short duration of antigen expression. As a strategy to enhance adaptive immune responses elicited by a hemagglutinin 5 (H5) DNA vaccine, we explored the effect of co-administration of a DNA encoding X-linked inhibitor of apoptosis protein (XIAP) as a modulator of apoptosis and a stimulator of inflammatory signaling. In cultured cells as early as 24 hours (h), we found that the DNA vaccine encoded H5 antigen was a potent stimulator of apoptosis, and the H5 pro-apoptotic activity was significantly suppressed by the co-expression of full-length XIAP or mutant XIAP (ΔRING). However, full-length XIAP showed a higher potency than mutant XIAP (ΔRING) in the inhibition of H5-induced apoptosis. We also compared the immunizing ability of transmembrane and secretory forms of H5. Mice vaccinated (twice with 3-week intervals) with the secretory form of H5 showed higher hemagglutination inhibition (HI) antibody titers than mice vaccinated with the transmembrane form of H5. Furthermore, co-administration of XIAP with the secretory form of H5 resulted into a stronger antibody response than the transmembrane form of H5. Our findings suggest that in the design of DNA vaccines for a given pro-apoptotic antigen, using an anti-apoptotic molecular adjuvant and the secretory form of antigen may be a greater stimulus to induce immune responses.

• Apoptosis
• avian H5N1 influenza
• DNA vaccine
• XIAP

ACKNOWLEDGEMENTS

We thank M. Kohanghadr and A. Mahouti at the Faculty of Veterinary Medicine, Ferdowsi University of Mashhad for the technical assistance; Dr. H. A. Seifi at the Faculty of Veterinary Medicine, Ferdowsi University of Mashhad for statistical analysis; the Imaging Facility of the Faculty of Sciences, Ferdowsi University of Mashhad; and the Imaging Facility of the Buali Research Institute, Mashhad University of Medical Sciences.

The authors would like to thank Robert G. Korneluk at Apoptosis Research Centre, Children's Hospital of Eastern Ontario Research Institute, Ottawa, Ontario, Canada for the generous gift of 6Myc-XIAP encoding plasmid. This work was supported by a grant (No. 56896) from Institute of Biotechnology, Ferdowsi University of Mashhad and Iran's Headquarters for Development of Biotechnology to H.D.

DECLARATION OF INTEREST

The authors declare that they have no conflict of interest. The authors alone are responsible for the content and writing of the paper.