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Open Access Research

L1R, A27L, A33R and B5R vaccinia virus genes expressed by fowlpox recombinants as putative novel orthopoxvirus vaccines

Sole Maria Pacchioni1, Massimiliano Bissa1, Carlo Zanotto1, Carlo De Giuli Morghen12, Elena Illiano3 and Antonia Radaelli234*

Author Affiliations

1 Department of Medical Biotechnologies and Translational Medicine, University of Milan, via Vanvitelli 32, 20129 Milan, Italy

2 Cellular and Molecular Pharmacology Section, CNR Institute of Neurosciences, University of Milan, via Vanvitelli 32, 20129 Milan, Italy

3 Department of Medical Biotechnologies and Translational Medicine, University of Milan, via Vanvitelli, 32, 20129 Milan, Italy

4 Laboratory of Molecular Virology and Recombinant Vaccine Development, Department of Medical Biotechnologies and Translational Medicine, University of Milan, Via Vanvitelli 32, 20129 Milan, Italy

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Journal of Translational Medicine 2013, 11:95  doi:10.1186/1479-5876-11-95

Published: 11 April 2013

Abstract

Background

The traditional smallpox vaccine, administered by scarification, was discontinued in the general population from 1980, because of the absence of new smallpox cases. However, the development of an effective prophylactic vaccine against smallpox is still necessary, to protect from the threat of deliberate release of the variola virus for bioterrorism and from new zoonotic infections, and to improve the safety of the traditional vaccine. Preventive vaccination still remains the most effective control and new vectors have been developed to generate recombinant vaccines against smallpox that induce the same immunogenicity as the traditional one. As protective antibodies are mainly directed against the surface proteins of the two infectious forms of vaccinia, the intracellular mature virions and the extracellular virions, combined proteins from these viral forms can be used to better elicit a complete and protective immunity.

Methods

Four novel viral recombinants were constructed based on the fowlpox genetic background, which independently express the vaccinia virus L1 and A27 proteins present on the mature virions, and the A33 and B5 proteins present on the extracellular virions. The correct expression of the transgenes was determined by RT-PCR, Western blotting, and immunofluorescence.

Results and conclusions

Using immunoprecipitation and Western blotting, the ability of the proteins expressed by the four novel FPL1R, FPA27L, FPA33R and FPB5R recombinants to be recognized by VV-specific hyperimmune mouse sera was demonstrated. By neutralisation assays, recombinant virus particles released by infected chick embryo fibroblasts were shown not be recognised by hyperimmune sera. This thus demonstrates that the L1R, A27L, A33R and B5R gene products are not inserted into the new viral progeny. Fowlpox virus replicates only in avian species, but it is permissive for entry and transgene expression in mammalian cells, while being immunologically non–cross-reactive with vaccinia virus. These recombinants might therefore represent safer and more promising immunogens that can circumvent neutralisation by vector-generated immunity in smallpox-vaccine-experienced humans.

Keywords:
Smallpox vaccine; Orthopoxvirus infections; Fowlpox recombinants; Transgene expression