Identification and cloning of the fowlpox virus thymidine kinase gene using vaccinia virus

Osteosarcoma

Osteosarcoma is the most common primary malignant tumour of the bone. Osteosarcoma incidence is bimodal, peaking at 18 and 60 years of age, and is slightly more common in males. The key pathophysiological mechanism involves several possible genetic drivers of disease linked to bone formation, causing malignant progression and metastasis. While there have been significant improvements in the outcome of patients with localized disease, with event-free survival outcomes exceeding 60%, in patients with metastatic disease, event-free survival outcomes remain poor at less than 30%. The suspicion of osteosarcoma based on radiographs still requires pathological evaluation of a bone biopsy specimen for definitive diagnosis and CT imaging of the chest should be performed to identify lung nodules. So far, population-based screening and surveillance strategies have not been implemented due to the rarity of osteosarcoma and the lack of reliable markers. Current screening focuses only on groups at high risk such as patients with genetic cancer predisposition syndromes. Management of osteosarcoma requires a multidisciplinary team of paediatric and medical oncologists, orthopaedic and general surgeons, pathologists, radiologists and specialist nurses. Survivors of osteosarcoma require specialized medical follow-up, as curative treatment consisting of chemotherapy and surgery has long-term adverse effects, which also affect the quality of life of patients. The development of osteosarcoma model systems and related research as well as the evaluation of new treatment approaches are ongoing to improve disease outcomes, especially for patients with metastases.

Canine and murine models of osteosarcoma

Osteosarcoma (OS) is the most common malignant bone tumor in children. Despite efforts to develop and implement new therapies, patient outcomes have not measurably improved since the 1980s. Metastasis continues to be the main source of patient mortality, with 30% of cases developing metastatic disease within 5 years of diagnosis. Research models are critical in the advancement of cancer research and include a variety of species. For example, xenograft and patient-derived xenograft (PDX) mouse models provide opportunities to study human tumor cells in vivo while transgenic models have offered significant insight into the molecular mechanisms underlying OS development. A growing recognition of naturally occurring cancers in companion species has led to new insights into how veterinary patients can contribute to studies of cancer biology and drug development. The study of canine cases, including the use of diagnostic tissue archives and clinical trials, offers a potential mechanism to further canine and human cancer research. Advancement in the field of OS research requires continued development and appropriate use of animal models. In this review, animal models of OS are described with a focus on the mouse and tumor-bearing pet dog as parallel and complementary models of human OS.

Vaccination of cats with an attenuated recombinant myxoma virus expressing feline calicivirus capsid protein

Myxoma virus, a member of the Poxviridae family (genus Leporipoxvirus) is the agent responsible for myxomatosis in the European rabbit. Recombinant myxoma viruses expressing the capsid gene of an F9 strain of feline calicivirus (FCV) were constructed from an apathogenic, laboratory attenuated, isolate of myxoma virus. The FCV capsid genes were recombined into the myxoma growth factor (MGF) locus of the myxoma genome and expressed from synthetic poxvirus promoters. Myxoma virus is unable to replicate productively in feline cells in vitro, however, cells infected with recombinant viruses do express the heterologous antigens from both late and early/late synthetic promoters. Cats immunised with myxoma-FCV recombinant virus generated high levels of serum neutralising antibody and were protected from disease on subsequent challenge with virulent FCV. Furthermore, there was no evidence of transmission of myxoma-FCV recombinant virus from vaccinated to non-vaccinated cats. These results demonstrate the potential of myxoma virus as a safe vaccine vector for use in non-lepori species and in particular the cat.

Construction and characterization of recombinant vaccinia viruses co-expressing a respiratory syncytial virus protein and a cytokine

Recombinant vaccinia viruses are well-characterized tools that can be used to define novel approaches to vaccine formulation and delivery. While vector co-expression of immune mediators has enormous potential for optimizing the composition of vaccine-induced immune responses, the impact on antigen expression and vector antigenicity must also be considered. Co-expression of IL-4 increased vaccinia virus vector titres, while IFN-gamma co-expression reduced vaccinia virus replication in BALB/c mice and in C57BL/6 mice infected with some recombinant viruses. Protection against respiratory syncytial virus (RSV) challenge was similar in mice immunized with vaccinia virus expressing RSV G glycoprotein and IFN-gamma, even though the replication efficiency of the vector was diminished. These data demonstrate the ability of vector-expressed cytokine to influence the virulence of the vector and to direct the development of selected immune responses. This suggests that the co-expression of cytokines and other immunomodulators has the potential to improve the safety of vaccine vectors while improving the immunogenicity of vaccine antigens.

Sequence and analysis of a swinepox virus homologue of the vaccinia virus major envelope protein P37 (F13L)

P37 (F13L gene product), the most abundant protein in the envelope of the extracellular virus form of the prototype poxvirus, vaccinia virus (VV), is a crucial player in the process leading to acquisition of the envelope, virus egress and transmission. We have cloned and sequenced a swinepox virus (SPV) gene homologous to VV F13L. The SPV gene product, termed P42, was 54% identical to P37, the VV F13L gene product, and, among the poxviruses, was most similar (73% identity) to the myxoma virus homologue. The SPV P42 gene contained late transcription signals and was expressed only at late times during infection. The protein was palmitylated, and showed an intracellular distribution similar to that of VV P37, both by immunofluorescence and by subcellular fractionation. As with VV P37, SPV P42 was incorporated in extracellular enveloped SPV particles, but was absent from the intracellular mature virus form. To check the ability of SPV P42 to function in the context of VV infection, we inserted the SPV gene into a VV deficient in P37, which is severely blocked in virus envelopment and cell-to-cell transmission. Despite correct expression of SPV P42, the resulting recombinant VV showed no rescue of extracellular virus formation or cell-to-cell virus spread. The lack of function of SPV P42 in the VV genetic background suggests that specific interactions between SPV P42 or VV P37 and other viral proteins is required to drive the envelopment process.

Identification of the canarypox virus thymidine kinase gene and insertion of foreign genes

We mapped the canarypox virus (CaPV) thymidine kinase (TK) gene within a 5.8-kbp XbaI fragment of the genome by Southern blotting using the fowlpox virus (FPV) TK gene as a probe. Nucleotide sequence analysis of the fragment revealed seven open reading frames (ORFs) showing gene organization similar to that of FPV. The TK gene contained in this region had an ORF of 179 amino acids encoding a polypeptide with a putative molecular mass of 20.0 kDa. An A/T-rich region and a transcription termination signal, TTTTTAT, were found upstream and at the end of the ORF, which is consistent with poxvirus early gene regulation. The consensus sequence of the late promoter TAAAT also overlapped with the initiation codon of the ORF. The amino acid sequence similarity between the TK genes of CaPV and FPV, avipoxviruses, was 64.2%, which was lower than the similarities between vaccinia and variola orthopoxviruses (97.2%) and between Shope fibroma and myxoma leporipoxviruses (82.6%). However, the monophyly of avian clades of CaPV and FPV was supported by phylogenetic analysis. We then inserted the genes encoding lacZ, luciferase (luci), and envelope of human T-lymphotropic virus type 1 (HTLV-1 env) into the TK gene of CaPV to evaluate its suitability as an expression vector. The recombinant viruses obtained were unstable, although the foreign genes were expressed efficiently in the mammalian cells infected with the viruses.

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.

A synthetic vaccinia virus promoter with enhanced early and late activity

A synthetic vaccinia virus promoter (Psel) was constructed based upon sequences which increase activity of the P7.5 early/late promoter. Comparison of luciferase activity in lysates from cells infected with recombinant vaccinia viruses expressing the luciferase gene either under the control of the P7.5 promoter or Psel, demonstrated significantly enhanced activity mediated by Psel at both early and late times post infection. This promoter may be of considerable benefit in the construction of recombinant poxviruses where early foreign gene expression is important for generating a protective immune response in vaccinated animals, or in reporter/target gene expression in vitro.

A novel strategy for determining protective antigens of the parapoxvirus, orf virus

We investigated the feasibility of using vaccinia virus (VAC) recombinants containing large multigene fragments of orf virus DNA to identify protective antigens of orf virus (OV). Sixteen OV strain NZ2 DNA fragments with an average size of 11.4 kb were recombined into VAC strain Lister. Each fragment was mapped relative to OV restriction endonuclease maps but was otherwise uncharacterized. Together the recombinants represent 95% of the OV genome in an overlapping manner. Immunofluorescence showed all 16 constructs expressed products recognized by OV antiserum and radioimmune precipitation with the same antiserum allowed the localization of the major antigens of OV to specific recombinants. These data indicated the approximate genomic locations of the genes encoding the OV major antigens and showed that their expression was authentic rather than resulting from read through from VAC sequences adjacent to the site of recombination. Vaccination of OV-naive sheep with the recombinant library provided protection against a subsequent challenge with virulent OV. These data confirm the feasibility of the proposed strategy.

Interleukin-7 enhances cell-mediated immune responses in vivo in an interleukin-2-dependent manner

We have engineered recombinant vaccinia virus vectors expressing murine interleukin-7 (IL-7) in order to study the activity of this factor during virus infection. Virus-encoded IL-7 dramatically increased splenic cellularity in infected mice and enhanced the proliferative activity of T cells and their capacity to secrete IL-2 and IL-6, but not IFN-gamma, TNF-alpha or IL-4. Numbers of splenic CD4+ and CD8+ T lymphocytes were elevated two- to threefold. IL-7 also mediated a marked enhancement of both antigen-specific and nonspecific cellular immune activity. Total splenic antiviral cytotoxic T cells (CTL), natural killer (NK), and lymphokine-activated killer cells (LAK) responses were augmented significantly in mice given VV-HA-IL-7 compared with those given control virus, with accelerated clearance of the former. The enhanced antiviral cellular immune activity mediated by IL-7 was critically dependent on IL-2 produced by the host, but occurred independently of IFN-gamma. The ability of IL-7 to induce cellular immune responses in vivo may have applications in antiviral immunotherapy, particularly in cases of immunodeficiency.

A recombinant vaccinia virus encoding inducible nitric oxide synthase is attenuated in vivo

To investigate the role of nitric oxide during vaccinia virus (VV) infection of mice, a recombinant VV encoding the inducible nitric oxide synthase (iNOS) gene (VV-HA-iNOS) was constructed. Following infection of immunocompromised or immunocompetent mice, the virus was highly attenuated compared with a control recombinant VV. Athymic and sublethally irradiated mice survived infection with 10(7) PFU of VV-HA-iNOS, a dose that resulted in uniform mortality in mice infected with the control recombinant VV. Attenuated virus growth was evident as early as 24 h following infection, suggesting that NO had direct antiviral activity. We have previously shown that treatment of mice with the inhibitor of NO production N(G)-methyl-L-arginine did not influence the course of VV infection in mice. The present study has indicated that NO can potentially exert an antiviral effect during murine VV infection. We propose that during VV infection, nitric oxide production contributes to the control of virus growth, but that in its absence, other antiviral mechanisms are sufficient to mediate fully effective virus clearance.

Assembly, intracellular localization, and nucleotide binding properties of the human peptide transporters TAP1 and TAP2 expressed by recombinant vaccinia viruses

The transporter associated with antigen processing (TAP) transports short peptides from the cytosol to the endoplasmic reticulum, where peptides assemble with class I molecules of the major histocompatibility complex. TAP is comprised of two subunits, termed TAP1 and TAP2. We produced recombinant vaccinia viruses that direct synthesis of the TAP subunits, either individually or together. Virus-encoded TAP is rapidly and efficiently assembled (t1/2 of 5 min or less) by cells and does not spontaneously assemble in detergent extracts. By confocal immunofluorescence microscopy, TAP1 when expressed alone or with TAP2 is largely, if not exclusively, localized to the endoplasmic reticulum. Metabolic labeling with [2-3H]mannose demonstrates that TAP1 (but not TAP2) possesses Asn-linked oligosaccharides, but the lack of binding of [35S]methionine-labeled TAP to concanavalin A-agarose suggests that the glycosylated form represents a minor population of TAP1. The two subunits of the assembled complex present in detergent extracts photolabeled equally with 8-azido-[alpha-32P]ATP. Photolabeling of the two subunits was inhibited in parallel by various di- and trinucleotides, suggesting that their nucleotide binding sites function in a highly similar manner. Incubation of detergent extracts at 37 degrees C results in the rapid loss of TAP1 immunoreactivity, indicating either an unusual sensitivity to proteases or an irreversible conformation alteration.

Studies of fowlpox virus recombination in the generation of recombinant vaccines

A p7.5/beta-galactosidase (7.5 lacZ) gene construct, cloned adjacent to the fowlpox virus (FPV) thymidine kinase (tk) gene was used as a marker to identify the products of recombination as 'blue' FPV plaques. The rFPVs were detected as early as 4 h after the introduction of plasmid DNAs and by 72 h post-infection (p.i.) for one transfer vector comprised 0.48% of the viral population. The proportion of rFPV increased linearly from 0.073% to 0.62% as the cumulative length of homologous sequences in the transfer vector increased from 0.73 to 4.5 kb. Two approaches using a second reporter gene, the Newcastle disease virus haemagglutinin-neuraminidase (NDV HN) gene were tested to differentiate between single and double cross-over events. In one, the HN gene was cloned into the FPV tk gene and the 7.5 lacZ cloned outside of the homologous region. Progeny of a single cross-over with FPV DNA generated an unstable plaque containing the HN gene and subsequent intramolecular recombination resulted in excision of the 7.5 lacZ and the generation of a stable 'white' plaque. For virus grown in CEF cells (tk+) in the presence of 5-bromo-deoxyuridine, only those viruses which contained a tk gene disrupted by the HN gene formed plaques. This approach allowed us to easily identify rFPV containing the HN gene but lacking 7.5 lacZ or other bacterial sequences. In a second approach, a double cross-over between rFPV DNA containing a stably expressed beta-galactosidase gene cloned into the tk gene (blue plaque) and plasmid DNA containing the HN gene flanked by tk sequences would allow transplacement of the 7.5 lacZ gene with the HN gene, and generating a white plaque. We were unable to generate recombinant viruses with the HN gene and which generated a white plaque, indicating that double cross-over events do not occur at a sufficiently high frequency in FPV.

The adenovirus E3 14.7-kilodalton protein which inhibits cytolysis by tumor necrosis factor increases the virulence of vaccinia virus in a murine pneumonia model

The 14.7-kilodalton protein (14.7K protein) encoded by the adenovirus (Ad) E3 region inhibits tumor necrosis factor alpha (TNF-alpha)-mediated lysis of cells in tissue culture experiments, but the relevance of this effect in vivo is incompletely understood. To examine the effect of the ability of the Ad 14.7K protein to block TNF lysis upon viral pathogenesis in a murine model, we cloned the 14.7K protein-encoding gene into vaccinia virus (VV), permitting its study in isolation from other Ad E3 immunomodulatory proteins. The gene for murine TNF-alpha was inserted into the same VV containing the 14.7K gene to ensure that each cell infected with the VV recombinant would express both the agonist (TNF) and its antagonist (14.7K). VV was utilized as the vector because it accommodates large and multiple inserts of foreign DNA with faithful, high-level expression of the protein products. In addition, infection of mice with VV induces disease with quantifiable morbidity, mortality, and virus replication. The results of intranasal infections of BALB/c mice with these VV recombinants indicate that the Ad 14.7K protein increases the virulence of VV carrying the TNF-alpha gene by reversing the attenuating effect of TNF-alpha on VV pathogenicity. This was demonstrated by increased mortality, pulmonary pathology, and viral titers in lung tissue following infection with VV coexpressing the 14.7K protein and TNF-alpha, compared with the control virus expressing TNF-alpha alone. These results suggest that the 14.7K protein, which is nonessential for Ad replication in tissue culture, is an immunoregulatory protein which functions in vivo to help counteract the antiviral effects of TNF-alpha.

In vivo recognition of orf virus early transcriptional promoters in a vaccinia virus recombinant

The 4.4-kb BamHI-E fragment of the orf virus (OV) genome contains three discrete open reading frames designated ORF-pp, ORF-1, and ORF-3, all of which are flanked by vaccinia virus-like early transcriptional control sequences. To determine whether the vaccinia transcriptional machinery would recognize these promoters and faithfully transcribe OV genes in vivo the BamHI-E fragment was inserted into the thymidine kinase (TK) locus of vaccinia virus and the recombinant used in transcription studies. Northern blotting analysis of early RNA isolated from 143B-TK- cells infected with the recombinant virus showed that OV genes were transcribed and that the three transcripts of 0.70-(ORF-pp), 0.48- (ORF1), and 0.75-kb (ORF-3) were the same size as their counterparts in OV-infected cells. Analysis of the 5' end of transcripts by S1 nuclease and primer extension showed that the transcriptional start points (tsp) of ORF-pp, ORF-1, and ORF-3 in the recombinant were identical or within four nucleotides of the tsps of the same ORFs in OV. However, there were quantitative differences. ORF-1 was transcribed more efficiently in recombinant virus-infected cells than in those infected with OV and analysis of the putative promoter, 5'-AAAATTGTAAATGTA, showed that it was similar to the 7.5-kDa early promoter of vaccinia virus. This demonstrates that the transcriptional control sequences of OV genes are recognized by vaccinia virus transcriptional factors but that quantitative differences exist suggesting that the generically different transcriptional factors have different promoter sequence requirements for maximal transcription.

Isolation and molecular characterization of the swinepox virus thymidine kinase gene

Swinepox virus (SPV), the only member of the Suipoxvirus genus, shows little antigenic relatedness or DNA homology to members of the other poxvirus genera. A SPV thymidine kinase (TK) gene was detected and mapped to the left end of the HindIII G fragment using degenerate oligonucleotide probes. Cloning and sequencing of a 1.8-kb HindIII-BamHI fragment containing the SPV TK gene revealed an open reading frame (ORF) of 181 amino acids yielding a predicted polypeptide of Mr 20.6 kDa with significant homology to both poxvirus and vertebrate thymidine kinases. Comparison with other TK protein sequences showed that the SPV thymidine kinase was closely related to the TK genes of avipoxviruses (52.0%) and vertebrates (57.1-59.7%). The TK gene from African swine fever virus (ASF) showed little homology (30.5%) to the SPV TK gene suggesting that these two viruses are not closely related though they share many biochemical features and infect a single, common mammalian host (swine). The SPV TK gene, like that of other poxviruses, is transcribed early, and when cloned into a TK- strain of vaccinia converted the virus to a TK+ phenotype. BUdRR mutants of SPV contained frameshift, deletion, and missense mutations in the TK ORF.

Vaccinia virus-mediated expression of African swine fever virus genes

Bacteriophage lambda and plasmid clones containing African swine fever virus (ASFV) DNA inserts, which together covered more than 90% of the genome of a Malawi ASFV isolate (LIL 20/1), were transfected into vaccinia virus (VV)-infected cells. Expression of ASFV-encoded proteins was assayed at late times after VV infection by immunoprecipitation of [35S]methionine-labeled proteins with hyperimmune serum from ASFV-infected pigs, separation of immunoprecipitated proteins by denaturing polyacrylamide gel electrophoresis, and detection by autoradiography. Synthesis of eight additional proteins not observed in control experiments was detected. Seven VV recombinants were constructed, each containing an ASFV DNA insert from a separate bacteriophage lambda clone ranging in size from 9 to 15 kb. BSC40 cells were infected with recombinant viruses and expression of ASFV-encoded proteins assayed at early and late times postinfection. Synthesis of additional proteins, not observed in control experiments, was detected by immunoprecipitation with ASFV antiserum both early and late postinfection with two of these recombinants. In these experiments VV promoters were not included upstream of individual ASFV genes.

Identification and nucleotide sequence of the thymidine kinase gene of swinepox virus

Using degenerative oligonucleotide probes, representing two different conserved regions of poxvirus and mammalian thymidine kinase (TK) genes, the swinepox virus (SPV) TK gene was mapped to a 1.7-kb BamHI-HindIII fragment of the viral genome. Nucleotide sequencing of this DNA piece revealed that the SPV TK gene was encoded by an open reading frame (ORF) of 177 codons. Immediately downstream of the TK gene was a second ORF with homologues at the same location in both capripoxvirus and leporipoxvirus genomes. A similar gene had translocated to near the left hand terminus of the vaccinia virus (orthopoxvirus) genome. Flanking the two SPV genes were ORFs whose counterparts in other poxvirus genera are located at the same relative positions. SPV appeared to be most closely related to capripoxvirus, based on the organization of the four genes and on the percentage of identical amino acid residues of the respective encoded proteins.

Construction of a pigeonpox virus recombinant: expression of the Newcastle disease virus (NDV) fusion glycoprotein and protection of chickens against NDV challenge

A pigeonpox transfer plasmid was constructed by cloning a 2.5 kb DNA fragment containing the viral thymidine kinase (TK) gene in the psp65 plasmid. The vaccinia virus P11K promoter followed by the NDV fusion (F) gene was inserted in the TK gene. The F gene was transferred to the viral genome by homologous recombination in pigeonpox virus infected CEF cells, transfected with the recombinant plasmid. Recombinant viruses were selected with BUdR and screened for their ability to induce fusion between adjacent cells. Because of the unexpected growth advantage of the TK+ WT over the TK- recombinants, viral purification was needed to obtain stable recombinants expressing a glycosylated and cleaved F protein. Vaccination of chickens by the follicular method induced high anti-F antibody titers and good protection against challenge with the virulent Italian NDV strain. Half of the oculonasal vaccinated chickens showed anti F antibodies and also half of them were protected. Although protection seems to be correlated with antibody titers, no neutralizing antibodies were found.

An improved dot-blot method for virus detection in chicken embryo fibroblast cultures

A simplified dot-blot procedure is described for the detection of fowlpox virus (FPV) in infected monolayers of chicken embryo fibroblasts (CEF) cultured in 96-well microtiter plates. The relative resistance of DNA to hot NaOH, which hydrolyzes other macromolecules including RNA and protein, was exploited to solubilize virus infected cells and denature intracellular DNA in a simple, quick manner. Moreover, there was no need to purify virus or isolate viral DNA from cellular DNA prior to dot blotting. After incubation of CEF with FPV, the extracellular fluid from infected cells was collected for storage in 96-well microtiter plates. The remaining cell monolayers in each well were then solubilized with hot NaOH. The solubilized and denatured DNA was transferred to a nylon membrane using a dot-blot vacuum filtration manifold. Hybridization was carried out with a 32P-labeled FPV DNA probe. With this methodology it was possible to detect specific viral DNA sequences following the infection of cell monolayers with as little as 1 infectious unit per well. The ability to detect specific viral DNA sequences in infected cells, without the need to isolate pure viral DNA, made it possible to analyze large numbers of samples in a single experiment. Moreover, sufficient fowlpox virus was present in the extracellular media from each well for further amplification and analysis of selected samples.

Restriction endonuclease mapping of the fowlpox virus genome

The genome of fowlpox virus (Webster's mild vaccine strain) is composed of a single, double-stranded DNA molecule with covalently linked terminal hairpins and approximately 300 kb in length. Sites for cleavage by restriction endonucleases Pstl, Sal/l, Smal, and Notl have been identified with partial maps for EcoRI and BamHI. Differences in Pstl restriction fragment profiles for two separately prepared viruses (FPV-M and FPV-M3), both derived from the vaccine strain, indicate the presence of a nonessential region and potential insertion site for foreign DNA, toward one end of the viral genome. The size of the fowlpox virus genome, which is more than 100 kb larger than the orthopoxvirus vaccinia, indicates that the avipox viruses have the potential to code for more proteins than other groups of poxviruses.

Recombinant fowlpox viruses inducing protective immunity against Newcastle disease and fowlpox viruses

The haemagglutinin-neuraminidase gene of Newcastle disease virus was inserted into a non-essential region of the fowlpox virus genome and expressed under control of the vaccinia virus 7.5 kDa polypeptide gene promoter. Immunization with the recombinant fowlpox virus elicited protective immunity in chickens against both virulent Newcastle disease and fowlpox virus infection.

Activity of a fowlpox virus late gene promoter in vaccinia and fowlpox virus recombinants

Characterization of a late promoter of fowlpox virus (FPV) and a study of its activity in FPV and vaccinia virus (VV) was carried out. The 5'-mRNA start site of the FPV late gene mapped to a TAAAT sequence near the translation start site (ATG). A cloned DNA fragment of FPV genome (PFL1) comprising of the 5'-end of the late gene was used to express the LacZ gene of E. coli in FPV and VV recombinants. A comparative analysis of beta-galactosidase (BG) expression from the LacZ gene under the control of the FPV promoter and a VV late promoter (PL11) was performed. Like FPV-PL11-LacZ and VV-PL11-LacZ constructs, FPV-PFL1-LacZ and VV-PFL1-LacZ virus recombinants expressed BG indicating that essential features of transcription were conserved in the two viruses. Furthermore, the LacZ transcripts originating from PFL1 in FPV and VV recombinants mapped to the expected TAAAT sequence. Time course analysis of BG expressed by VV and FPV recombinants suggested that although the transcription machinery in the two viruses was essentially conserved, subtle differences in the efficiency of transcription or translation may exist.

Comparative analysis of vaccinia virus promoter activity in fowlpox and vaccinia virus recombinants

A quantitative and qualitative comparison of vaccinia virus (VV) promoter activity in fowlpox virus (FPV) and VV recombinants was performed. The VV PL11 late promoter was used to express beta-galactosidase from the E. coli LacZ gene in FPV (FPV-LacZ) and VV (VV-LacZ) recombinants. Time courses of FPV-LacZ beta-galactosidase expression in chicken embryo skin (CES) cells demonstrated temporal regulation of the PL11 promoter with maximum enzyme activity nine- and four-fold lower than those obtained in VV-LacZ infected 143B and CES cells, respectively. The level of beta-galactosidase activity per LacZ DNA gene copy was determined for each recombinant and found to be greater for VV-LacZ than FPV-LacZ. The VV P7.5 early/late promoter was used to express the E. coli xanthine-guanine phosphoribosyl transferase (Ecogpt) gene in FPV and VV recombinants. Northern blot analysis showed early Ecogpt RNA transcripts to be of defined lengths. Transcript size estimations mapped the termination sites to regions containing sequences associated with VV early transcript termination, providing supportive evidence for a common poxvirus early transcript termination signal. Late LacZ and Ecogpt transcripts were heterogeneous in length. S1 nuclease mapping of the 5'-ends of early and late Ecogpt RNA transcripts produced by FPV and VV recombinants showed transcription initiation occurred at the same sites in both poxviruses and corresponded to the regions previously identified as the early and late start sites of the P7.5 promoter. These results would indicate a high level of conservation in the expression and regulation of genes by poxviruses.

Transient expression assay for qualitative assessment of gene expression by fowlpox virus

A transient expression assay for fowlpox virus (FPV) was developed to assess the feasibility of using heterologous promoters in FPV and to qualitatively determine relative promoter strength. A transient expression system for FPV has not been reported, and various methods used for transient expression in vaccinia-virus-infected cells produced negative results when used with FPV. Here a successful method for transient expression of E. coli beta-galactosidase in FPV-infected chick embryo fibroblasts is reported. This transient expression assay has been developed to qualitatively assess promoter recognition and gene expression by FPV. It should also prove useful in the identification of promoters from the FPV genomic library and in testing the accuracy of chimeric promoter-gene constructs.

Mapping of a major early/late gene of fowlpox virus

Identification, cloning and mapping of a major gene expressed during the early and late stages of infection with fowlpox virus is described. The gene is located within a 17.3 kb PstI fragment of the fowlpox virus genome and has an open reading frame of 501 bp. Analysis of the 5'-ends of mRNA transcribed from this gene showed that the start sites of both early and late transcripts map to the sequence TAAAT near the translation start site (ATG). This is the first poxvirus early/late gene described in which both early and late transcription start sites map to same DNA sequence. From northern hybridization analysis it was shown that the early function of this gene gives rise to the most abundant early mRNA coded by 17% of the fowlpox virus genome. The strong early function of this gene promoter will be useful in the construction of recombinant fowlpox viruses.

A poxvirus-derived vector that directs high levels of expression of cloned genes in mammalian cells

High levels of expression of cloned genes have been obtained in mammalian cells by using poxvirus-derived insertion/expression vectors. These vectors employ the cis-acting element (CAE I) that directs the transcription of one of the most strongly expressed genes of cowpox virus. This gene (the 160K gene) encodes the 160-kDa protein that is the major component of the A-type cytoplasmic inclusions. Its counterpart in vaccinia virus (VV) is the 94K gene contained in the HindIII A fragment of the viral DNA. Two insertion vectors have been constructed; each is designed to allow cloned genes to be placed immediately downstream of a modified version of CAE I within a poxvirus genome. One vector, p1200, enables the CAE I-cloned-gene constructs to be inserted into the thymidine kinase gene of VV. This vector was used to create a VV recombinant that directed expression of the chloramphenicol acetyltransferase (CAT) gene. The other vector, p2101, enables the CAE I-cloned-gene constructs to be inserted into the VV 94K gene. The prototype of this vector was used to create a VV recombinant that directed expression of a hybrid CAT-lacZ gene. Infection of cultured human cells with these recombinants led to high levels of synthesis of either the CAT gene product or the CAT-lacZ gene product. Each of these proteins was produced in quantities that were easily detected by Coomassie blue staining of total cell proteins resolved by polyacrylamide gel electrophoresis. We estimate that these vectors are capable of directing the synthesis of milligram amounts of gene product per 10(9) mammalian cells.

A general method for the construction of recombinant vaccinia viruses expressing multiple foreign genes

Plasmid vectors with multiple cloning sites adjacent to a vaccinia virus (VV) promoter were constructed and used to insert a protein coding sequence and a dominant selectable marker into a non-essential region of the VV genome. Recombinant viruses, selected on the basis of expression of the herpes simplex virus (HSV) thymidine kinase gene (tk), were shown to express in infected cells the model gene product, murine major histocompatibility complex (MHC) antigen H-2Kd, by cell-surface binding of antibody and by MHC-restricted recognition by cytotoxic T lymphocytes. Double recombinant VVs with insertions at two sites (in the VV tk gene and in the VV HindIII-F region) were constructed and shown to express influenza A/PR/8/34 haemagglutinin and H-2Kd antigen in addition to the HSV tk gene. The plasmids described allow the construction of recombinant VV expressing two genes of interest under the control of the same VV promoter. Such recombinant VVs can be used to study the interaction of immunologically important antigens simultaneously expressed.

A rapid method for identifying the thymidine kinase genes of avipoxviruses

The thymidine kinase (TK) genes of poxviruses can be rapidly located without using TK- mutants or having to restriction map and clone the viral genomes. Identification of the TK gene is based on in situ gel hybridization with an end-labelled degenerate oligonucleotide probe, representing a consensus sequence near the 3' end of the gene. Restriction fragments of the viral DNAs are electrophoresed in agarose gels and annealed with the probe. Using this method, the TK genes of fowl pox (FPV) and quail pox (QPV) viruses were initially localized to HindIII fragments of approximately 3.8 and 6.7 kb, respectively. After inserting these fragments into pUC 19, recombinant plasmids containing the TK genes were screened by a modified in situ gel annealing procedure. Restriction mapping of the two cloned fragments and subsequent hybridization analysis more precisely placed at least the 3' portion of the FPV and QPV TK genes within a 1.4 kb ClaI-XbaI and 1.7 kb ClaI-PstI fragment, respectively. The site of the FPV TK gene was verified by comparison to the mapped position of the similar gene in an Australian FPV. The location of the QPV TK gene was confirmed by hybridization with the FPV TK gene, despite the apparent divergency of these two genes.

Construction of recombinant fowlpox viruses as vectors for poultry vaccines

Plasmid vectors have been constructed which allow the construction of infectious fowlpox virus (FPV) recombinants expressing foreign genes. The foreign genes were inserted within the thymidine kinase (TK) gene of FPV contained in these vectors. To facilitate the selection of recombinants the Escherichia coli xanthine guanine phosphoribosyl transferase (Ecogpt) gene was developed as a dominant selectable marker. This marker operates in a wide variety of cell types and obviates the need for TK- cell lines for selection of TK- recombinants when foreign genes have been inserted within the TK gene of FPV. The general approach adopted was to construct plasmid vectors in which the FPV TK was interrupted by the Ecogpt gene under the control of a poxvirus promoter in tandem with a gene of interest under the control of another poxvirus promoter. Selection of viruses expressing the Ecogpt gene simultaneously selects for recombinants carrying both the Ecogpt gene and the gene of interest. Using this approach a series of plasmid vectors was constructed in which the FPV TK gene was interrupted by the Ecogpt gene under the control of the P7.5 vaccinia virus promoter in tandem with the A/PR/8/34 haemagglutinin gene under the control of the PL11 vaccinia virus promoter. A recombinant FPV constructed using these plasmids had the expected genome arrangement, expressed influenza haemagglutinin, and induced haemagglutination-inhibiting antibodies when inoculated into chickens. These techniques should allow the construction of a variety of recombinant FPVs expressing poultry vaccine antigens. Such recombinants should be a very cost-effective means of delivering vaccines to poultry.

Identification, mapping and cloning of the thymidine kinase gene of fish lymphocystis disease virus

The thymidine kinase (TK) gene of fish lymphocystis disease virus (FLDV) was identified by biochemical transformation of 3T3 TK negative (TK-) to 3T3 TK positive (TK+) cells using specific viral DNA sequences. DNA fragments of the viral genome used in this study were obtained from a defined gene library of FLDV genome containing the complete viral DNA sequences. The selection of the converted cells was carried out under the condition of the HAT selection procedure. The results of these experiments revealed that the EcoRI FLDV DNA fragment C (11.2 kbp; 0.611 to 0.718 map units) is able to transform 3T3 TK- to 3T3 TK+ cells. Additional experiments using the subclones of EcoRI DNA fragment C revealed that DNA sequences of 4.1 kbp size between the coordinates 0.669 to 0.718 of the FLDV genome possessed the ability for biochemical transformation, indicating that the TK gene locus is located in this particular region.

Similar genetic organization between a region of fowlpox virus DNA and the vaccinia virus HindIII J fragment despite divergent location of the thymidine kinase gene

DNA from Fowlpox virus, a member of the Avipoxvirus genus, has been found to hybridize to DNA from vaccinia virus, a member of the Orthopoxvirus genus. The greatest homology detected was around the region containing the vaccinia virus thymidine kinase locus. A 3.1-kbp fowlpox virus fragment that hybridizes to the vaccinia virus HindIII J fragment has been cloned and its sequence determined. Comparison of the nucleotide and deduced amino acid sequence to the cross hybridizing vaccinia fragment revealed extensive conservation of six open reading frames as well as a similar organization along the genome. Nevertheless a fowlpox virus gene corresponding to the vaccinia virus thymidine kinase gene was apparently lacking within the region studied and is probably located elsewhere in the genome. Despite this intriguing divergence, our results indicate that the Avipoxviruses are more closely related to the Orthopoxviruses than previously suspected.

Fowlpox virus polypeptides: sequential appearance and virion associated polypeptides

The polypeptides associated with fowlpox virus (FPV) infection of chicken embryo skin (CES) cells were examined by metabolic labelling with [35S]-methionine and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Polypeptide synthesis was followed over the first 48 hours post infection, as this was shown to be the period of viable virus production in CES cells. In contrast to infection with vaccinia virus (VV), which leads to a rapid total inhibition of host polypeptide synthesis in a number of cell lines, FPV infection of CES cells failed to cause a complete shut down of host polypeptide synthesis, with only a small number of host polypeptides being inhibited. A total of 21 FPV coded or induced polypeptides were resolved by metabolic labelling. As with VV, these polypeptides can be divided into two groups, the pre-replicative polypeptides containing a single member of 70,000 daltons, synthesised before viral DNA replication, and the post-replicative polypeptides, synthesised only after viral DNA replication has commenced. FPV DNA replication was shown to commence between 12 and 16 hours post-infection and to continue up to 48 hours post-infection. As also observed with VV, two temporally distinct classes of post-replicative polypeptides were identified based on their time of synthesis post-infection. The examination of purified FPV and VV by SDS-PAGE and coomassie blue staining allowed the resolution of 57 FPV particle associated polypeptides and 27 VV associated polypeptides.

Fowlpox virus thymidine kinase: nucleotide sequence and relationships to other thymidine kinases

The thymidine kinase (TK) gene of fowlpox virus (FPV) is located in a 2.2-kb HindIII-ClaI fragment derived from a 5.5-kb EcoR1 fragment of the FPV genome. The TK gene was mapped to the region of a 700-bp XbaI fragment contained within this HindIII-ClaI fragment. Nucleotide sequence analysis of this region revealed an open reading frame of 183 codons. Identification of this region as the FPV TK gene was confirmed by its homology with the vaccinia virus TK at both the nucleotide and amino acid levels. The derived FPV TK polypeptide has a calculated molecular weight of 20,380 and is six amino acids larger than the vaccinia virus TK gene product. We have reported previously that the FPV TK gene operates in vaccinia virus without the requirement for a vaccinia virus promoter. The sequence homologies between the two TK promoters substantiated this observation. Northern blot analysis of RNAs from cells infected with a vaccinia virus recombinant expressing the FPV TK gene showed major (700 nucleotide) and minor (1000 nucleotide) transcripts from the FPV TK gene. The deduced amino acid sequence of the FPV TK has significant homology with the TKs from chicken, man, and three other poxviruses, but shows no homology with herpes simplex virus TK. Comparisons of the homologous sequences indicated that the "core" of the enzyme has probably evolved in poxviruses four times as quickly as in vertebrates. Characterization of the FPV TK gene may facilitate the construction of recombinant FPVs as vehicles for the delivery of vaccine antigens to poultry and other avian species.