Replication and expression of a swinepox virus vector delivering feline leukemia virus Gag and Env to cell lines of swine and feline origin.

The host range of swinepox virus (SPV) is restricted to swine, although SPV has been shown to infect mammalian, non-swine cells, without recovery of infectious virus. SPV is a reasonable candidate for development as a non-productively replicating viral vector for use in non-swine, mammalian species, such as the cat. A novel SPV gene deletion (SPV 043) was created and found to be non-attenuating. This deletion was utilized to generate a stable recombinant virus expressing the Gag-Pro and Env proteins of feline leukemia virus (FeLV). Expression and replication of this vector was studied in embryonic swine kidney cells (ESK-4), and two feline cell lines, Crandell feline kidney cells (CRFK) and feline skin fibroblasts (FSF). Our results showed that feline cells were susceptible to infection by SPV and supported expression of foreign genes driven by synthetic poxvirus promoters, however, SPV viral DNA was not replicated in feline cells and infectious virus was not recovered. In addition, FeLV Gag virus-like particles were produced from both ESK-4 and CRFK cells and foreign antigens were incorporated into infectious SPV intracellular mature virions (IMV). These results suggest that SPV may have potential as a safe vaccine delivery vector for cats.

The genome of swinepox virus.

Swinepox virus (SWPV), the sole member of the Suipoxvirus genus of the Poxviridae, is the etiologic agent of a worldwide disease specific for swine. Here we report the genomic sequence of SWPV. The 146-kbp SWPV genome consists of a central coding region bounded by identical 3.7-kbp inverted terminal repeats and contains 150 putative genes. Comparison of SWPV with chordopoxviruses reveals 146 conserved genes encoding proteins involved in basic replicative functions, viral virulence, host range, and immune evasion. Notably, these include genes with similarity to genes for gamma interferon (IFN-gamma) receptor, IFN resistance protein, interleukin-18 binding protein, IFN-alpha/beta binding protein, extracellular enveloped virus host range protein, dUTPase, hydroxysteroid dehydrogenase, superoxide dismutase, serpin, herpesvirus major histocompatibility complex inhibitor, ectromelia virus macrophage host range protein, myxoma virus M011L, variola virus B22R, four ankyrin repeat proteins, three kelch-like proteins, five vaccinia virus (VV) A52R-like family proteins, and two G protein-coupled receptors. The most conserved genomic region is centrally located and corresponds to the VV region located between genes F9L and A38L. Within the terminal 13 kbp, colinearity is disrupted and multiple poxvirus gene homologues are absent or share a lower percentage of amino acid identity. Most of these differences involve genes and gene families with likely functions involving viral virulence and host range. Three open reading frames (SPV018, SPV019. and SPV020) are unique for SWPV. Phylogenetic analysis, genome organization, and amino acid identity indicate that SWPV is most closely related to the capripoxvirus lumpy skin disease virus, followed by the yatapoxvirus yaba-like disease virus and the leporipoxviruses. The gene complement of SWPV better defines Suipoxvirus within the Chordopoxvirinae subfamily and provides a basis for future genetic comparisons.

Recombinant swinepox virus expressing beta-galactosidase: investigation of viral host range and gene expression levels in cell culture.

Swinepox virus (SPV) has been proposed as a potential vector for generating recombinant vaccines for swine. However, little is known about important aspects of SPV biology, such as the functionality of SPV promoters or the host range of SPV. Using a transient expression assay, well-characterized vaccinia virus promoters were shown to be active in cells infected with SPV. A recombinant SPV expressing beta-galactosidase (beta-gal) was constructed and characterized. The E. coli LacZ gene was placed under the control of a strong vaccinia synthetic early/late promoter and was inserted by homologous recombination in a noncoding region of the SPV genome. The recombinant SPV expressing beta-gal was used to characterize the host range of the virus by measuring protein expression and virus production in different cell lines. In general, SPV expressed more protein and grew more efficiently than vaccinia virus in porcine cell lines. Surprisingly, the recombinant SPV was able to infect and replicate in several cell lines of nonswine origin. The virus directed regulated early and late gene expression of beta-gal in those cells and formed blue plaques in cell monolayers in the presence of X-gal. Upon infection with the recombinant SPV, there was a significant level of viral replication, and the virus can be serially passaged in some nonswine cell lines. The data presented suggest that despite the strict host tropism of SPV, the virus exhibits a relatively broad host range in cell culture.