Genomic Expression Libraries for the Identification of Cross-Reactive Orthopoxvirus Antigens

Daniel Stern,Marco Richter,Andreas Nitsche,Stephen Mark Tompkins,Lilija Miller,Christoph Hapke

doi:10.1371/journal.pone.0021950

Abstract

Increasing numbers of human cowpox virus infections that are being observed and that particularly affect young non-vaccinated persons have renewed interest in this zoonotic disease. Usually causing a self-limiting local infection, human cowpox can in fact be fatal for immunocompromised individuals. Conventional smallpox vaccination presumably protects an individual from infections with other Orthopoxviruses, including cowpox virus. However, available live vaccines are causing severe adverse reactions especially in individuals with impaired immunity. Because of a decrease in protective immunity against Orthopoxviruses and a coincident increase in the proportion of immunodeficient individuals in today's population, safer vaccines need to be developed. Recombinant subunit vaccines containing cross-reactive antigens are promising candidates, which avoid the application of infectious virus. However, subunit vaccines should contain carefully selected antigens to confer a solid cross-protection against different Orthopoxvirus species. Little is known about the cross-reactivity of antibodies elicited to cowpox virus proteins. Here, we first identified 21 immunogenic proteins of cowpox and vaccinia virus by serological screenings of genomic Orthopoxvirus expression libraries. Screenings were performed using sera from vaccinated humans and animals as well as clinical sera from patients and animals with a naturally acquired cowpox virus infection. We further analyzed the cross-reactivity of the identified immunogenic proteins. Out of 21 identified proteins 16 were found to be cross-reactive between cowpox and vaccinia virus. The presented findings provide important indications for the design of new-generation recombinant subunit vaccines.

Highlights

The genus Orthopoxvirus (OPV) from the family Poxviridae contains complex viruses which replicate entirely in the cytoplasm of the infected cell [1,2]
Other human-pathogenic OPV members include monkeypox virus and cowpox virus (CPXV) [1], the latter having the largest genome of all OPVs [11]
By analyzing the whole set of antigens, we found 16 out of 21 proteins to be cross-reactive between CPXV and vaccinia virus (VACV)

Summary

Introduction

The genus Orthopoxvirus (OPV) from the family Poxviridae contains complex viruses which replicate entirely in the cytoplasm of the infected cell [1,2] Their linear double-stranded DNA genome of up to 220 kbp [1] contains no introns and encodes more than 200 open reading frames (ORFs) [3]. VACV was used to eradicate VARV, the causative agent of smallpox, through a worldwide vaccination campaign [4,5]. This was possible due to an antigenic relationship between members of OPVs. An earlier infection with one of these members provides some protection against subsequent infections with the others [6]. Other human-pathogenic OPV members include monkeypox virus and cowpox virus (CPXV) [1], the latter having the largest genome of all OPVs [11]

Methods

Results

Conclusion