Novel recombinant parapoxvirus vectors induce protective humoral and cellular immunity against lethal herpesvirus challenge infection in mice

Efficient and scalable clarification of Orf virus from HEK suspension for vaccine development

The Orf virus (ORFV) is a promising vector platform for the generation of vaccines against infectious diseases and cancer, highlighted by its progression to clinical testing phases. One of the critical steps during GMP manufacturing is the clarification of crude harvest because of the enveloped nature and large size of ORFV. This study presents the first description of ORFV clarification process from a HEK suspension batch process. We examined various filter materials, membrane pore sizes, harvest timings, and nuclease treatments. Employing the Ambr® crossflow system for high-throughput, small-volume experiments, we identified polypropylene-based Sartopure® PP3 filters as ideal. These filters, used in two consecutive stages with reducing pore sizes, significantly enhanced ORFV recovery and addressed scalability challenges. Moreover, we demonstrated that the time of harvest and the use of a nuclease play a decisive role to increase ORFV yields. With these findings, we were able to establish an efficient and scalable clarification process of ORFV derived from a suspension production process, essential for advancing ORFV vaccine manufacturing.

Immunogenicity of chimeric hemagglutinins delivered by an orf virus vector platform against swine influenza virus

Orf virus (ORFV) is a large DNA virus that can harbor and efficiently deliver viral antigens in swine. Here we used ORFV as a vector platform to deliver chimeric hemagglutinins (HA) of Influenza A virus of swine (IAV-S). Vaccine development against IAV-S faces limitations posed by strain-specific immunity and the antigenic diversity of the IAV-S strains circulating in the field. A promising alternative aiming at re-directing immune responses on conserved epitopes of the stalk segment of the hemagglutinin (HA2) has recently emerged. Sequential immunization with chimeric HAs comprising the same stalk but distinct exotic head domains can potentially induce cross-reactive immune responses against conserved epitopes of the HA2 while breaking the immunodominance of the head domain (HA1). Here, we generated two recombinant ORFVs expressing chimeric HAs encoding the stalk region of a contemporary H1N1 IAV-S strain and exotic heads derived from either H6 or H8 subtypes, ORFVΔ121cH6/1 and ORFVΔ121cH8/1, respectively. The resulting recombinant viruses were able to express the heterologous protein in vitro. Further, the immunogenicity and cross-protection of these vaccine candidates were assessed in swine after sequential intramuscular immunization with OV-cH6/1 and OV-cH8/1, and subsequent challenge with divergent IAV-S strains. Humoral responses showed that vaccinated piglets presented increasing IgG responses in sera. Additionally, cross-reactive IgG and IgA antibody responses elicited by immunization were detected in sera and bronchoalveolar lavage (BAL), respectively, by ELISA against different viral clades and a diverse range of contemporary H1N1 IAV-S strains, indicating induction of humoral and mucosal immunity in vaccinated animals. Importantly, viral shedding was reduced in nasal swabs from vaccinated piglets after intranasal challenge with either Oh07 (gamma clade) or Ca09 (npdm clade) IAV-S strains. These results demonstrated the efficiency of ORFV-based vectors in delivering chimeric IAV-S HA-based vaccine candidates and underline the potential use of chimeric-HAs for prevention and control of influenza in swine.

An investigation of excipients for a stable Orf viral vector formulation

The Orf virus (ORFV) is a promising candidate for vector vaccines as well as for immunomodulatory and oncolytic therapies. However, few publications are available on its infectivity degradation or on suitable additives for prolonging its viral stability. In this study, the non-supplemented ORFV itself showed a very high stability at storage temperatures up to 28 °C, with a linear titer loss of 0.10 log infectious particles per day at 4 °C over a period of five weeks. To prolong this inherent stability, thirty additives, i.e., detergents, sugars, proteins, salts, and buffers as well as amino acids, were tested for their time- and temperature-dependent influence on the ORFV infectivity. A stabilizing effect on the infectivity was identified for the addition of all tested proteins, i.e., gelatine, bovine serum albumin, and recombinant human serum albumin (rHSA), of several sugars, i.e., mannitol, galactose, sucrose, and trehalose, of amino acids, i.e., arginine and proline, of the detergent Pluronic F68, and of the salt Na2SO4. The infectivity preservation was especially pronounced for proteins in liquid and frozen formulations, sugars in frozen state, and arginine und Pluronic in liquid formulations at high storage temperatures (37 °C). The addition of 1% rHSA with and without 5% sucrose was evaluated as a very stable formulation with a high safety profile and economic validity at storage temperatures up to 28 °C. At increased temperatures, the supplementation with 200 mM arginine performed better than with rHSA. In summary, this comprehensive data provides different options for a stable ORFV formulation, considering temperature, storage time, economic aspects, and downstream processing integrity.

Stability studies for the identification of critical process parameters for a pharmaceutical production of the Orf virus

A promising new vaccine platform is based on the Orf virus, a viral vector of the genus Parapoxvirus, which is currently being tested in phase I clinical trials. The application as a vaccine platform mandates a well-characterised, robust, and efficient production process. To identify critical process parameters in the production process affecting the virus' infectivity, the Orf virus was subjected to forced degradation studies, including thermal, pH, chemical, and mechanical stress conditions. The tests indicated a robust virus infectivity within a pH range of 5-7.4 and in the presence of the tested buffering substances (TRIS, HEPES, PBS). The ionic strength up to 0.5 M had no influence on the Orf virus' infectivity stability for NaCl and MgCl₂, while NH₄Cl destabilized significantly. Furthermore, short-term thermal stress of 2d up to 37 °C and repeated freeze-thaw cycles (20cycles) did not affect the virus' infectivity. The addition of recombinant human serum albumin was found to reduce virus inactivation. Last, the Orf virus showed a low shear sensitivity induced by peristaltic pumps and mixing, but was sensitive to ultrasonication. The isoelectric point of the applied Orf virus genotype D1707-V was determined at pH3.5. The broad picture of the Orf virus' infectivity stability against environmental parameters is an important contribution for the identification of critical process parameters for the production process, and supports the development of a stable pharmaceutical formulation. The work is specifically relevant for enveloped (large DNA) viruses, like the Orf virus and like most vectored vaccine approaches.

An Orf-Virus (ORFV)-Based Vector Expressing a Consensus H1 Hemagglutinin Provides Protection against Diverse Swine Influenza Viruses

Influenza A viruses (IAV-S) belonging to the H1 subtype are endemic in swine worldwide. Antigenic drift and antigenic shift lead to a substantial antigenic diversity in circulating IAV-S strains. As a result, the most commonly used vaccines based on whole inactivated viruses (WIVs) provide low protection against divergent H1 strains due to the mismatch between the vaccine virus strain and the circulating one. Here, a consensus coding sequence of the full-length of HA from H1 subtype was generated in silico after alignment of the sequences from IAV-S isolates obtained from public databases and was delivered to pigs using the Orf virus (ORFV) vector platform. The immunogenicity and protective efficacy of the resulting ORFVΔ121conH1 recombinant virus were evaluated against divergent IAV-S strains in piglets. Virus shedding after intranasal/intratracheal challenge with two IAV-S strains was assessed by real-time RT-PCR and virus titration. Viral genome copies and infectious virus load were reduced in nasal secretions of immunized animals. Flow cytometry analysis showed that the frequency of T helper/memory cells, as well as cytotoxic T lymphocytes (CTLs), were significantly higher in the peripheral blood mononuclear cells (PBMCs) of the vaccinated groups compared to unvaccinated animals when they were challenged with a pandemic strain of IAV H1N1 (CA/09). Interestingly, the percentage of T cells was higher in the bronchoalveolar lavage of vaccinated animals in relation to unvaccinated animals in the groups challenged with a H1N1 from the gamma clade (OH/07). In summary, delivery of the consensus HA from the H1 IAV-S subtype by the parapoxvirus ORFV vector decreased shedding of infectious virus and viral load of IAV-S in nasal secretions and induced cellular protective immunity against divergent influenza viruses in swine.

ORFV can carry TRAP gene expression via intracellular CRISPR/Cas9 gene editing technology

Orf is an acute and highly contracted human and animal infection caused by orf virus (ORFV), which mainly affects sheep, goats, and other species. Clinically, opportunistic or conditional pathogens such as Staphylococcus aureus (S. aureus) are often detected in cases of orf, which greatly increases the risk of disease progression and clinical death. It has been reported that TRAP gene products of S. aureus can broadly influence bacterial life and pathogenicity in vivo, and introduction of exogenous TRAP genes may help to inhibit the proliferation of bacteria. In order to achieve the combined control of ORFV and S. aureus, a novel approach to design a S. aureus TRAP gene vaccine using a live attenuated ORFV vector is proposed. In this study, CRISPR/Cas9 gene editing technology was used to disable vascular endothelial growth factor E of ORFV (VEGF-v) and introduced TRAP gene into this position. TRAP gene expression was detected in keratinocytes infected with recombinant virus. The construction and experimental verification of recombinant ORFV (ORFV-v/TRAP) will provide a reference for in-depth studies on the prevention and control of mixed infectious disease.

Deletion of gene OV132 attenuates Orf virus more effectively than gene OV112

Orf virus (ORFV), a Parapoxvirus in Poxviridae, infects sheep and goats resulting in contagious pustular dermatitis. ORFV is regarded as a promising viral vector candidate for vaccine development and oncolytic virotherapy. Owing to their potential clinical application, safety concerns have become increasingly important. Deletion of either the OV132 (encoding vascular endothelial growth factor, VEGF) or OV112 (encoding the chemokine binding protein, CBP) genes reduced ORFV infectivity, which has been independently demonstrated in the NZ2 and NZ7 strains, respectively. This study revealed that the VEGF and CBP gene sequences of the local strain (TW/Hoping) shared a similarity of 47.01% with NZ2 and 90.56% with NZ7. Due to the high sequence divergence of these two immunoregulatory genes among orf viral strains, their contribution to the pathogenicity of Taiwanese ORFV isolates was comparatively characterized. Initially, two ORFV recombinants were generated, in which either the VEGF or CBP gene was deleted and replaced with the reporter gene EGFP. In vitro assays indicated that both the VEGF-deletion mutant ORFV-VEGFΔ-EGFP and the CBP deletion mutant ORFV-CBPΔ-EGFP were attenuated in cells. In particular, ORFV-VEGFΔ-EGFP significantly reduced plaque size and virus yield compared to ORFV-CBPΔ-EGFP and the wild-type control. Similarly, in vivo analysis revealed no virus yield in the goat skin biopsy infected by ORFV-VEGFΔ-EGFP, and significantly reduced the virus yield of ORFV-CBPΔ-EGFP relative to the wild-type control. These results confirmed the loss of virulence of both deletion mutants in the Hoping strain, whereas the VEGF-deletion mutant was more attenuated than the CBP deletion strain in both cell and goat models. KEY POINTS: • VEGF and CBP genes are crucial in ORFV pathogenesis in the TW/Hoping strain • The VEGF-deletion mutant virus was severely attenuated in both cell culture and animal models • Deletion mutant viruses are advantageous vectors for the development of vaccines and therapeutic regimens.

Production and purification of high-titer OrfV for preclinical studies in vaccinology and cancer therapy

Poxviruses have been used extensively as vaccine vectors for human and veterinary medicine and have recently entered the clinical realm as immunotherapies for cancer. We present a comprehensive method for producing high-quality lots of the poxvirus Parapoxvirus ovis (OrfV) for use in preclinical models of vaccinology and cancer therapy. OrfV is produced using a permissive sheep skin-derived cell line and is released from infected cells by repeated freeze-thaw combined with sonication. We present two methods for isolation and purification of bulk virus. Isolated virus is concentrated to high titer using polyethylene glycol to produce the final in vivo-grade product. We also describe methods for quantifying OrfV infectious virions and determining genomic copy number to evaluate virus stocks. The methods herein will provide researchers with the ability to produce high-quality, high-titer OrfV for use in preclinical studies, and support the translation of OrfV-derived technologies into the clinic.

A Novel Orf Virus D1701-VrV-Based Dengue Virus (DENV) Vaccine Candidate Expressing HLA-Specific T Cell Epitopes: A Proof-of-Concept Study

Although dengue virus (DENV) affects almost half of the world’s population there are neither preventive treatments nor any long-lasting and protective vaccines available at this time. The complexity of the protective immune response to DENV is still not fully understood. The most advanced vaccine candidates focus specifically on humoral immune responses and the production of virus-neutralizing antibodies. However, results from several recent studies have revealed the protective role of T cells in the immune response to DENV. Hence, in this study, we generated a novel and potent DENV vaccine candidate based on an Orf virus (ORFV, genus Parapoxvirus) vector platform engineered to encode five highly conserved or cross-reactive DENV human leukocyte antigen (HLA)-A*02- or HLA-B*07-restricted epitopes as minigenes (ORFV-DENV). We showed that ORFV-DENV facilitates the in vitro priming of CD8⁺ T cells from healthy blood donors based on responses to each of the encoded immunogenic peptides. Moreover, we demonstrated that peripheral blood mononuclear cells isolated from clinically confirmed DENV-positive donors stimulated with ORFV-DENV generate cytotoxic T cell responses to at least three of the expressed DENV peptides. Finally, we showed that ORFV-DENV could activate CD8⁺ T cells isolated from donors who had recovered from Zika virus (ZIKV) infection. ZIKV belongs to the same virus family (Flaviviridae) and has epitope sequences that are homologous to those of DENV. We found that highly conserved HLA-B*07-restricted ZIKV and DENV epitopes induced functional CD8⁺ T cell responses in PBMCs isolated from confirmed ZIKV-positive donors. In summary, this proof-of-concept study characterizes a promising new ORFV D1701-VrV-based DENV vaccine candidate that induces broad and functional epitope-specific CD8⁺ T cell responses.

Protective Efficacy of an Orf Virus-Vector Encoding the Hemagglutinin and the Nucleoprotein of Influenza A Virus in Swine

Swine influenza is a highly contagious respiratory disease of pigs caused by influenza A viruses (IAV-S). IAV-S causes significant economic losses to the swine industry and poses challenges to public health given its zoonotic potential. Thus effective IAV-S vaccines are needed and highly desirable and would benefit both animal and human health. Here, we developed two recombinant orf viruses, expressing the hemagglutinin (HA) gene (OV-HA) or the HA and the nucleoprotein (NP) genes of IAV-S (OV-HA-NP). The immunogenicity and protective efficacy of these two recombinant viruses were evaluated in pigs. Both OV-HA and OV-HA-NP recombinants elicited robust virus neutralizing antibody response in pigs, with higher levels of neutralizing antibodies (NA) being detected in OV-HA-NP-immunized animals pre-challenge infection. Although both recombinant viruses elicited IAV-S-specific T-cell responses, the frequency of IAV-S-specific proliferating CD8+ T cells upon re-stimulation was higher in OV-HA-NP-immunized animals than in the OV-HA group. Importantly, IgG1/IgG2 isotype ELISAs revealed that immunization with OV-HA induced Th2-biased immune responses, whereas immunization with OV-HA-NP virus resulted in a Th1-biased immune response. While pigs immunized with either OV-HA or OV-HA-NP were protected when compared to non-immunized controls, immunization with OV-HA-NP resulted in incremental protection against challenge infection as evidenced by a reduced secondary antibody response (NA and HI antibodies) following IAV-S challenge and reduced virus shedding in nasal secretions (lower viral RNA loads and frequency of animals shedding viral RNA and infectious virus), when compared to animals in the OV-HA group. Interestingly, broader cross neutralization activity was also observed in serum of OV-HA-NP-immunized animals against a panel of contemporary IAV-S isolates representing the major genetic clades circulating in swine. This study demonstrates the potential of ORFV-based vector for control of swine influenza virus in swine.

Orf virus ORFV112, ORFV117 and ORFV127 contribute to ORFV IA82 virulence in sheep

The parapoxvirus orf virus (ORFV) encodes several immunomodulatory proteins (IMPs) that modulate host innate and pro-inflammatory responses to infection. Using the ORFV IA82 strain as the parental virus, recombinant viruses with individual deletions in the genes encoding the IMPs chemokine binding protein (CBP; ORFV112), inhibitor of granulocyte-monocyte colony-stimulating factor and IL-2 (GIF, ORFV117) and interleukin 10 homologue (vIL-10; ORFV127) were generated and characterized in vitro and in vivo. The replication properties of the individual gene deletion viruses in cell culture was not affected comparing with the parental virus. To investigate the effect of the individual gene deletions in ORFV infection and pathogenesis, groups of four lambs were inoculated with each virus and were monitored thereafter. Lambs inoculated with either recombinant or with the parental ORFV developed characteristic lesions of contagious ecthyma. The onset, nature and severity of the lesions in the oral commissure were similar in all inoculated groups from the onset (3 days post-inoculation [pi]) to the peak of clinical lesions (days 11-13 pi). Nonetheless, from days 11-13 pi onwards, the oral lesions in lambs inoculated with the recombinant viruses regressed faster than the lesions produced by the parental virus. Similarly, the amount of virus shed in the lesions were equivalent among lambs of all groups up to day 15 pi, yet they were significantly higher in the parental virus group from day 16-21 pi. In conclusion, individual deletion of these IMP genes from the ORFV genome resulted in slight reduction in virulence in vivo, as evidenced by a reduction in the duration of the clinical disease and virus shedding.

NF-κB as an Important Factor in Optimizing Poxvirus-Based Vaccines against Viral Infections

Poxviruses are large dsDNA viruses that are regarded as good candidates for vaccine vectors. Because the members of the Poxviridae family encode numerous immunomodulatory proteins in their genomes, it is necessary to carry out certain modifications in poxviral candidates for vaccine vectors to improve the vaccine. Currently, several poxvirus-based vaccines targeted at viral infections are under development. One of the important aspects of the influence of poxviruses on the immune system is that they encode a large array of inhibitors of the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), which is the key element of both innate and adaptive immunity. Importantly, the NF-κB transcription factor induces the mechanisms associated with adaptive immunological memory involving the activation of effector and memory T cells upon vaccination. Since poxviruses encode various NF-κB inhibitor proteins, before the use of poxviral vaccine vectors, modifications that influence NF-κB activation and consequently affect the immunogenicity of the vaccine should be carried out. This review focuses on NF-κB as an essential factor in the optimization of poxviral vaccines against viral infections.

Orf Virus-Based Therapeutic Vaccine for Treatment of Papillomavirus-Induced Tumors

Orf virus (ORFV) represents a suitable vector for the generation of efficient, prophylactic antiviral vaccines against different pathogens. The present study investigated for the first time the therapeutic application of ORFV vector-based vaccines against tumors induced by cottontail rabbit papillomavirus (CRPV). ORFV-CRPV recombinants were constructed expressing the early CRPV gene E1, E2, E7, or LE6. In two independent experiments we used in total 23 rabbits which were immunized with a mixture of the four ORFV-CRPV recombinants or empty ORFV vector as a control 5 weeks after the appearance of skin tumors. For the determination of the therapeutic efficacy, the subsequent growth of the tumors was recorded. In the first experiment, we could demonstrate that three immunizations of rabbits with high tumor burden with the combined four ORFV-CRPV recombinants resulted in significant growth retardation of the tumors compared to the control. A second experiment was performed to test the therapeutic effect of 5 doses of the combined vaccine in rabbits with a lower tumor burden than in nonimmunized rabbits. Tumor growth was significantly reduced after immunization, and one vaccinated rabbit even displayed complete tumor regression until the end of the observation period at 26 weeks. Results of delayed-type hypersensitivity (DTH) skin tests suggest the induction of a cellular immune response mediated by the ORFV-CRPV vaccine. The data presented show for the first time a therapeutic potential of the ORFV vector platform and encourage further studies for the development of a therapeutic vaccine against virus-induced tumors.IMPORTANCE Viral vectors are widely used for the development of therapeutic vaccines for the treatment of tumors. In our study we have used Orf virus (ORFV) strain D1701-V for the generation of recombinant vaccines expressing cottontail rabbit papillomavirus (CRPV) early proteins E1, E2, LE6, and E7. The therapeutic efficacy of the ORFV-CRPV vaccines was evaluated in two independent experiments using the outbred CRPV rabbit model. In both experiments the immunization achieved significant suppression of tumor growth. In total, 84.6% of all outbred animals benefited from the ORFV-CRPV vaccination, showing reduction in tumor size and significant tumor growth inhibition, including one animal with complete tumor regression without recurrence.

Orf Virus-Based Vaccine Vector D1701-V Induces Strong CD8+ T Cell Response against the Transgene but Not against ORFV-Derived Epitopes

The potency of viral vector-based vaccines depends on their ability to induce strong transgene-specific immune response without triggering anti-vector immunity. Previously, Orf virus (ORFV, Parapoxvirus) strain D1701-V was reported as a novel vector mediating protection against viral infections. The short-lived ORFV-specific immune response and the absence of virus neutralizing antibodies enables repeated immunizations and enhancement of humoral immune responses against the inserted antigens. However, only limited information exists about the D1701-V induced cellular immunity. In this study we employed major histocompatibility complex (MHC) ligandomics and immunogenicity analysis to identify ORFV-specific epitopes. Using liquid chromatography-tandem mass spectrometry we detected 36 ORFV-derived MHC I peptides, originating from various proteins. Stimulated splenocytes from ORFV-immunized mice did not exhibit specific CD8+ T cell responses against the tested peptides. In contrast, immunization with ovalbumin-expressing ORFV recombinant elicited strong SIINFEKL-specific CD8+ T lymphocyte response. In conclusion, our data indicate that cellular immunity to the ORFV vector is negligible, while strong CD8+ T cell response is induced against the inserted transgene. These results further emphasize the ORFV strain D1701-V as an attractive vector for vaccine development. Moreover, the presented experiments describe prerequisites for the selection of T cell epitopes exploitable for generation of ORFV-based vaccines by reverse genetics.

Lentivirus expressing shRNAs inhibit the replication of contagious ecthyma virus by targeting DNA polymerase gene

BACKGROUND

Contagious ecthyma or Orf is known as a zoonotic disease remains prevalently worldwide despite the application of some control strategies against it. RNAi particularly shRNA provides us with the chance to tackle this obstacle by an encouraging new approach. The current study indicates the design and experiment of third-generation lentivirus packaging systems delivering shRNAs to inhibit Orf virus (ORFV) replication and infection. Given the importance of DNA-pol gene in virus replication, in this study, three shRNAs against this gene were designed and cloned into lentiviral vectors to stabilize the expression of shRNAs. After producing lentivectors expressing ORFV-DNA- pol in HEK293T cells, the synthesized shRNAs were applied to downregulate viral replication and gene expression. The reduction in viral titer and RNA was evaluated by TCID50 test as well as real-time RT-PCR. The results were then analyzed in comparison with the control group.

RESULTS

Designed shRNAs significantly reduced virus yield approximately 90 to 97% and 96.8 to 99.4%, respectively compared to the control groups (cells infected with ORFV and infected with ORFV and scrambled vector) by TCID50 test. Real-time RT-PCR revealed a dramatic reduction in the expression of viral RNA approximately 99% compared to cells infected with ORFV and from 92.6 to 99%, respectively compared to cells infected with ORFV and scrambled vector.

CONCLUSIONS

Therefore, it can be stated that RNAi is capable of being used as a potent therapeutically option against viruses like ORFV.

Recombinant Modified Vaccinia Virus Ankara (MVA) Vaccines Efficiently Protect Cockatiels Against Parrot Bornavirus Infection and Proventricular Dilatation Disease

Parrot bornaviruses (PaBVs) are the causative agents of proventricular dilatation disease (PDD), a chronic and often fatal neurologic disorder in Psittaciformes. The disease is widely distributed in private parrot collections and threatens breeding populations of endangered species. Thus, immunoprophylaxis strategies are urgently needed. In previous studies we demonstrated a prime-boost vaccination regime using modified vaccinia virus Ankara (MVA) and Newcastle disease virus (NDV) constructs expressing the nucleoprotein and phosphoprotein of PaBV-4 (MVA/PaBV-4 and NDV/PaBV-4, respectively) to protect cockatiels (Nymphicus hollandicus) against experimental challenge infection. Here we investigated the protective effect provided by repeated immunization with either MVA/PaBV-4, NDV/PaBV-4 or Orf virus constructs (ORFV/PaBV-4) individually. While MVA/PaBV-4-vaccinated cockatiels were completely protected against subsequent PaBV-2 challenge infection and PDD-associated lesions, the course of the challenge infection in NDV/PaBV-4- or ORFV/PaBV-4-vaccinated birds did not differ from the unvaccinated control group. We further investigated the effect of vaccination on persistently PaBV-4-infected cockatiels. Remarkably, subsequent immunization with MVA/PaBV-4 and NDV/PaBV-4 neither induced obvious immunopathogenesis exacerbating the disease nor reduced viral loads in the infected birds. In summary, we demonstrated that vaccination with MVA/PaBV-4 alone is sufficient to efficiently prevent PaBV-2 challenge infection in cockatiels, providing a suitable vaccine candidate against avian bornavirus infection and bornavirus-induced PDD.

Genomic Characterization of Orf Virus Strain D1701-V (Parapoxvirus) and Development of Novel Sites for Multiple Transgene Expression

The Orf virus (ORFV; Parapoxvirus) strain D1701 with an attenuated phenotype and excellent immunogenic capacity is successfully used for the generation of recombinant vaccines against different viral infections. Adaption for growth in Vero cells was accompanied by additional major genomic changes resulting in ORFV strain variant D1701-V. In this study, restriction enzyme mapping, blot hybridization and DNA sequencing of the deleted region s (A, AT and D) in comparison to the predecessor strain D1701-B revealed the loss of 7 open reading frames (ORF008, ORF101, ORF102, ORF114, ORF115, ORF116, ORF117). The suitability of deletion site D for expression of foreign genes is demonstrated using novel synthetic early promoter eP1 and eP2. Comparison of promoter strength showed that the original vegf-e promoter Pv as well as promoter eP2 display an up to 11-fold stronger expression than promoter eP1, irrespective of the insertion site. Successful integration and expression of the fluorescent marker genes is demonstrated by gene- and insertion-site specific PCR assays, fluorescence microscopy and flow cytometry. For the first time ORFV recombinants are generated simultaneously expressing transgenes in two different insertion loci. That allows production of polyvalent vaccines containing several antigens against one or different pathogens in a single vectored ORFV vaccine.

Orf virus: A promising new therapeutic agent

The orf virus (ORFV) is a zoonotic, epitheliotropic, DNA parapoxvirus that infects principally sheep and goats. Exposure of animals to the virus or immunization by an ORFV preparation can accentuate the severity of disease, which has provoked an interest in the underlying cellular, virological, and molecular mechanisms. The identified ORFV virulence genes and the fact that the virus can repeatedly infect a host, owing to its evasive mechanisms, contribute to the development of potent immune modulators in various animal species. ORFV has been developed as a vaccine in veterinary medicine. The unique host immune-evasion ability of ORFV has made it an important candidate for vaccine vectors and biological agents (as an oncolytic virus). Genetic modifications using ORFV to obtain safe and efficient preparations and mechanistic studies are improvements to the currently available methods for disease treatment.

Vaccines against pseudorabies virus (PrV)

Aujeszkýs disease (AD, pseudorabies) is a notifiable herpesvirus infection of pigs causing substantial economic losses to swine producers. AD in pigs is controlled by the use of vaccination with inactivated and attenuated live vaccines. Starting with classically attenuated live vaccines derived from low virulent field isolates, AD vaccination has pioneered novel strategies in animal disease control by the first use of genetically engineered live virus vaccines lacking virulence-determining genes, and the concept of DIVA, i.e. the serological differentiation of vaccinated from field-virus infected animals by the use of marker vaccines and respective companion diagnostic tests. The basis for this concept has been the molecular characterization of PrV and the identification of so-called nonessential envelope glycoproteins, e.g. glycoprotein E, which could be eliminated from the virus without harming viral replication or immunogenicity. Eradication of AD using the strategy of vaccination-DIVA testing has successfully been performed in several countries including Germany and the United States. Furthermore, by targeted genetic modification PrV has been developed into a powerful vector system for expression of foreign genes to vaccinate against several infectious diseases of swine, while heterologous vector systems have been used for expression of major immunogens of PrV. This small concise review summarizes the state-of-the-art information on PrV vaccines and provides an outlook for the future.

Rabies Control and Treatment: From Prophylaxis to Strategies with Curative Potential

Rabies is an acute, fatal, neurological disease that affects almost all kinds of mammals. Vaccination (using an inactivated rabies vaccine), combined with administration of rabies immune globulin, is the only approved, effective method for post-exposure prophylaxis against rabies in humans. In the search for novel rabies control and treatment strategies, live-attenuated viruses have recently emerged as a practical and promising approach for immunizing and controlling rabies. Unlike the conventional, inactivated rabies vaccine, live-attenuated viruses are genetically modified viruses that are able to replicate in an inoculated recipient without causing adverse effects, while still eliciting robust and effective immune responses against rabies virus infection. A number of viruses with an intrinsic capacity that could be used as putative candidates for live-attenuated rabies vaccine have been intensively evaluated for therapeutic purposes. Additional novel strategies, such as a monoclonal antibody-based approach, nucleic acid-based vaccines, or small interfering RNAs (siRNAs) interfering with virus replication, could further add to the arena of strategies to combat rabies. In this review, we highlight current advances in rabies therapy and discuss the role that they might have in the future of rabies treatment. Given the pronounced and complex impact of rabies on a patient, a combination of these novel modalities has the potential to achieve maximal anti-rabies efficacy, or may even have promising curative effects in the future. However, several hurdles regarding clinical safety considerations and public awareness should be overcome before these approaches can ultimately become clinically relevant therapies.

Immunogenicity of a recombinant parapoxvirus expressing the spike protein of Porcine epidemic diarrhea virus

The parapoxvirus Orf virus (ORFV), has long been recognized for its immunomodulatory properties in permissive and non-permissive animal species. Here, a new recombinant ORFV expressing the full-length spike (S) protein of Porcine epidemic diarrhea virus (PEDV) was generated and its immunogenicity and protective efficacy were evaluated in pigs. The PEDV S was inserted into the ORFV121 gene locus, an immunomodulatory gene that inhibits activation of the NF-κB signalling pathway and contributes to ORFV virulence in the natural host. The recombinant ORFV-PEDV-S virus efficiently and stably expressed the PEDV S protein in cell culture in vitro. Three intramuscular (IM) immunizations with the recombinant ORFV-PEDV-S in 3-week-old pigs elicited robust serum IgG, IgA and neutralizing antibody responses against PEDV. Additionally, IM immunization with the recombinant ORFV-PEDV-S virus protected pigs from clinical signs of porcine epidemic diarrhoea (PED) and reduced virus shedding in faeces upon challenge infection. These results demonstrate the suitability of ORFV121 gene locus as an insertion site for heterologous gene expression and delivery by ORFV-based viral vectors. Additionally, the results provide evidence of the potential of ORFV as a vaccine delivery vector for enteric viral diseases of swine. This study may have important implications for future development of ORFV-vectored vaccines for swine.

Generation and Selection of Orf Virus (ORFV) Recombinants

Orf virus (ORFV) is an epitheliotropic poxvirus, which belongs to the genus Parapoxvirus. Among them the highly attenuated, apathogenic strain D1701-V is regarded as a promising candidate for novel virus vector vaccines. Our recent work demonstrated that those ORFV-based recombinants were able to induce protective, long-lasting immunity in various hosts that are non-permissive for ORFV. In this chapter we describe procedures for the generation, selection, propagation, and titration of ORFV recombinants as well as transgene detection by PCR or immunohistochemical staining.

Identification of Toll-like receptor 9 as parapoxvirus ovis-sensing receptor in plasmacytoid dendritic cells

Parapoxvirus ovis (PPVO) is known for its immunostimulatory capacities and has been successfully used to generate vector vaccines effective especially in non-permissive host species. Murine conventional and plasmacytoid dendritic cells (cDC and pDC) are able to recognize PPVO. The PPVO-sensing receptor on pDC is hitherto unknown. In this study we aimed to define the pattern recognition receptor responsible for the activation of murine pDC by inactivated and replication-competent PPVO. We show that PPVO-induced expression of type I and type III interferons, pro-inflammatory cytokines, and co-stimulatory CD86 by bone marrow-derived pDC but not cDC is blocked by chloroquine, an inhibitor of endosomal maturation. The activation of pDC is independent of viral replication and depends mainly on TLR9. Moreover, the use of phosphatidylinositol 3-kinase inhibitor wortmannin or C-Jun-N-terminal kinase inhibitor SP600125 results in significant reduction of PPVO-induced pDC activation. Taken together, our data identify endosomal TLR9 as PPVO-sensing receptor in pDC.

Orf virus (ORFV) ANK-1 protein mitochondrial localization is mediated by ankyrin repeat motifs

Orf virus (ORFV) strain D1701-V, a Parapoxvirus belonging to the family Poxviridae, became attractive as a novel virus vector system that we successfully used for the generation of recombinant vaccines. Therefore, the identification of viral genes involved in host tropisms or immune modulation is of great interest, as for instance the ORFV-encoded ankyrin-repeat (AR) containing proteins. The present study shows for the first time that the ANK-1 designated gene product of ORFV126 is targeted to mitochondria of ORFV-infected and in ANK-1 transiently expressing cells. Taking advantage of ANK-1 EGFP fusion proteins and confocal fluorescence microscopy mutational and deletion analyses indicated the importance of AR8 and AR9, which may contain a novel class of mitochondria-targeting sequence (MTS) in the central to C-terminal part of this AR-containing protein. The fluorescent findings were corroborated by cell fractionation and Western blotting experiments. The presented results open the avenue for more detailed investigations on cellular binding partners and the function of ANK-1 in viral replication or virulence.

New Orf virus (Parapoxvirus) recombinant expressing H5 hemagglutinin protects mice against H5N1 and H1N1 influenza A virus

Previously we demonstrated the versatile utility of the Parapoxvirus Orf virus (ORFV) as a vector platform for the development of potent recombinant vaccines. In this study we present the generation of new ORFV recombinants expressing the hemagglutinin (HA) or nucleoprotein (NP) of the highly pathogenic avian influenza virus (HPAIV) H5N1. Correct foreign gene expression was examined in vitro by immunofluorescence, Western blotting and flow cytometry. The protective potential of both recombinants was evaluated in the mouse challenge model. Despite adequate expression of NP, the recombinant D1701-V-NPh5 completely failed to protect mice from lethal challenge. However, the H5 HA-expressing recombinant D1701-V-HAh5n mediated solid protection in a dose-dependent manner. Two intramuscular (i.m.) injections of the HA-expressing recombinant protected all animals from lethal HPAIV infection without loss of body weight. Notably, the immunized mice resisted cross-clade H5N1 and heterologous H1N1 (strain PR8) influenza virus challenge. In vivo antibody-mediated depletion of CD4-positive and/or CD8-posititve T-cell subpopulations during immunization and/or challenge infection implicated the relevance of CD4-positive T-cells for induction of protective immunity by D1701-V-HAh5n, whereas the absence of CD8-positive T-cells did not significantly influence protection. In summary, this study validates the potential of the ORFV vectored vaccines also to combat HPAIV.

Animal poxvirus vaccines: a comprehensive review

The family Poxviridae includes several viruses of medical and veterinary importance. Global concerted efforts combined with an intensive mass-vaccination campaign with highly efficaceious live vaccine of vaccinia virus have led to eradication of smallpox. However, orthopoxviruses affecting domestic animals continue to cause outbreaks in several endemic countries. Different kinds of vaccines starting from conventional inactivated/attenuated to recombinant protein-based vaccines have been used for control of poxvirus infections. Live virus homologous vaccines are currently in use for diseases including capripox, parapox, camelpox and fowlpox, and these vaccines are highly effective in eliciting (with the exception of parapoxviruses) long-lasting immunity. Attenuated strains of poxviruses have been exploited as vectored vaccines to deliver heterologous immunogens, many of them being licensed for use in animals. Worthy of note are vaccinia virus, fowlpox virus, capripoxvirus, parapoxvirus and canary pox, which have been successfully used for developing new-generation vaccines targeting many important pathogens. Remarkable features of these vaccines are thermostability and their ability to engender both cellular and humoral immune responses to the target pathogens. This article updates the important vaccines available for poxviruses of livestock and identifies some of the research gaps in the present context of poxvirus research.

A new rabies vaccine based on a recombinant ORF virus (parapoxvirus) expressing the rabies virus glycoprotein

The present study describes the generation of a new Orf virus (ORFV) recombinant, D1701-V-RabG, expressing the rabies virus (RABV) glycoprotein that is correctly presented on the surface of infected cells without the need of replication or production of infectious recombinant virus. One single immunization with recombinant ORFV can stimulate high RABV-specific virus-neutralizing antibody (VNA) titers in mice, cats, and dogs, representing all nonpermissive hosts for the ORFV vector. The protective immune response against severe lethal challenge infection was analyzed in detail in mice using different dosages, numbers, and routes for immunization with the ORFV recombinant. Long-term levels of VNA could be elicited that remained greater than 0.5 IU per ml serum, indicative for the protective status. Single applications of higher doses (10(7) PFU) can be sufficient to confer complete protection against intracranial (i.c.) challenge, whereas booster immunization was needed for protection by the application of lower dosages. Anamnestic immune responses were achieved by each of the seven tested routes of inoculation, including oral application. Finally, in vivo antibody-mediated depletion of CD4-positive and/or CD8-posititve T cell subpopulations during immunization and/or challenge infection attested the importance of CD4 T cells for the induction of protective immunity by D1701-V-RabG. This report demonstrates another example of the potential of the ORFV vector and also indicates the capability of the new recombinant for vaccination of animals.

Orf virus interferes with MHC class I surface expression by targeting vesicular transport and Golgi

BACKGROUND

The Orf virus (ORFV), a zoonotic Parapoxvirus, causes pustular skin lesions in small ruminants (goat and sheep). Intriguingly, ORFV can repeatedly infect its host, despite the induction of a specific immunity. These immune modulating and immune evading properties are still unexplained.

RESULTS

Here, we describe that ORFV infection of permissive cells impairs the intracellular transport of MHC class I molecules (MHC I) as a result of structural disruption and fragmentation of the Golgi apparatus. Depending on the duration of infection, we observed a pronounced co-localization of MHC I and COP-I vesicular structures as well as a reduction of MHC I surface expression of up to 50%. These subversion processes are associated with early ORFV gene expression and are accompanied by disturbed carbohydrate trimming of post-ER MHC I. The MHC I population remaining on the cell surface shows an extended half-life, an effect that might be partially controlled also by late ORFV genes.

CONCLUSIONS

The presented data demonstrate that ORFV down-regulates MHC I surface expression in infected cells by targeting the late vesicular export machinery and the structure and function of the Golgi apparatus, which might aid to escape cellular immune recognition.

C7L family of poxvirus host range genes inhibits antiviral activities induced by type I interferons and interferon regulatory factor 1

Vaccinia virus (VACV) K1L and C7L function equivalently in many mammalian cells to support VACV replication and antagonize antiviral activities induced by type I interferons (IFNs). While K1L is limited to orthopoxviruses, genes that are homologous to C7L are found in diverse mammalian poxviruses. In this study, we showed that the C7L homologues from sheeppox virus and swinepox virus could rescue the replication defect of a VACV mutant deleted of both K1L and C7L (vK1L(-)C7L(-)). Interestingly, the sheeppox virus C7L homologue could rescue the replication of vK1L(-)C7L(-) in human HeLa cells but not in murine 3T3 and LA-4 cells, in contrast to all other C7L homologues. Replacing amino acids 134 and 135 of the sheeppox virus C7L homologue, however, made it functional in the two murine cell lines, suggesting that these two residues are critical for antagonizing a putative host restriction factor which has some subtle sequence variation in human and murine cells. Furthermore, the C7L family of host range genes from diverse mammalian poxviruses were all capable of antagonizing type I IFN-induced antiviral activities against VACV. Screening of a library of more than 350 IFN-stimulated genes (ISGs) identified interferon-regulated factor 1 (IRF1) as an inhibitor of vK1L(-)C7L(-) but not wild-type VACV. Expression of either K1L or C7L, however, rendered vK1L(-)C7L(-) resistant to IRF1-induced antiviral activities. Altogether, our data show that K1L and C7L antagonize IRF1-induced antiviral activities and that the host modulation function of C7L is evolutionally conserved in all poxviruses that can readily replicate in tissue-cultured mammalian cells.

Detection of anatid herpesvirus 1 gC gene by TaqMan fluorescent quantitative real-time PCR with specific primers and probe

BACKGROUND

Anatid herpesvirus 1 (AHV-1) is known for the difficulty of monitoring and controlling, because it has a long period of asymptomatic carrier state in waterfowls. Furthermore, as a significant essential agent for viral attachment, release, stability and virulence, gC (UL44) gene and its protein product (glycoprotein C) may play a key role in the epidemiological screening. The objectives of this study were to rapidly, sensitively, quantitatively detect gC gene of AHV-1 and provide the underlying basis for further investigating pcDNA3.1-gC DNA vaccine in infected ducks by TaqMan fluorescent quantitative real-time PCR assay (FQ-PCR) with pcDNA3.1-gC plasmid.

RESULTS

The repeatable and reproducible quantitative assay was established by the standard curve with a wide dynamic range (eight logarithmic units of concentration) and very good correlation values (1.000). This protocol was able to detect as little as 1.0 x 101 DNA copies per reaction and it was highly specific to AHV-1. The TaqMan FQ-PCR assay successfully detected the gC gene in tissue samples from pcDNA3.1-gC and AHV-1 attenuated vaccine (AHV-1 Cha) strain inoculated ducks respectively.

CONCLUSIONS

The assay offers an attractive method for the detection of AHV-1, the investigation of distribution pattern of AHV-1 in vivo and molecular epidemiological screening. Meanwhile, this method could expedite related AHV-1 and gC DNA vaccine research.

Comparison of different prime-boost regimes with DNA and recombinant Orf virus based vaccines expressing glycoprotein D of pseudorabies virus in pigs

Both DNA and Orf virus (ORFV; Parapox virus) based vaccines have shown promise as alternatives for conventional vaccines in pigs against pseudorabies virus (PRV) infection causing Aujeszky's disease. In the present study we evaluated the efficacy of different prime-boost regimes in pigs in terms of immunogenicity and protection against challenge infection with PRV. The different prime-boost regimes consisted of the homologous prime-boost regimes (DNA followed by DNA or ORFV followed by ORFV) and the heterologous prime-boost regimes (DNA followed by ORFV and ORFV followed by DNA), all based on glycoprotein D (gD) of PRV. Moreover, we compared the efficacy of the different prime-boost regimes with the efficacy of a conventional modified live vaccine (MLV). The different prime-boost regimes resulted in different levels of immunity and protection against challenge infection. Most effective was the regime of priming with DNA vaccine followed by boosting with the ORFV based vaccine. This regime resulted in strong antibody responses, comparable to the antibody responses obtained after prime-boost vaccination with a conventional MLV vaccine. Also with regard to protection, the prime DNA-boost ORFV regime performed better than the other prime-boost regimes. This study demonstrates the potential of a heterologous prime-boost vaccination strategy against PRV based on a single antigen, and that in the natural host, the pig.

New baculovirus recombinants expressing Pseudorabies virus (PRV) glycoproteins protect mice against lethal challenge infection

The present study demonstrates the protective potential of novel baculovirus recombinants, which express the glycoproteins gB, gC, or gD of Pseudorabies virus (PRV; Alphaherpesvirus of swine) and additionally contain the glycoprotein G of Vesicular Stomatitis Virus (VSV-G) in the virion (Bac-G-PRV). To evaluate the protective capacity, mixtures of equal amounts of the PRV gB-, gC-, and gD-expressing baculoviruses were used for immunization. Three intramuscular immunizations with that Bac-G-PRV mixture could protect mice against a lethal PRV challenge infection. To achieve complete protection high titers of Bac-G-PRV and three immunizations were necessary. This immunization with Bac-G-PRV resulted in the induction of high titers of PRV-specific serum antibodies of the IgG2a subclass and of interferon (IFN)-gamma, indicating a Th1-type immune response. Moreover, splenocytes of immunized mice exhibited natural killer cell activity accompanied by the production of IFN-alpha and IFN-gamma. Collectively, the presented data demonstrate for the first time that co-expression of VSV-G in baculovirus recombinant vaccines can improve the induction of a protective immune response against foreign antigens.

Antigen delivery systems for veterinary vaccine development. Viral-vector based delivery systems

The recent advances in molecular genetics, pathogenesis and immunology have provided an optimal framework for developing novel approaches in the rational design of vaccines effective against viral epizootic diseases. This paper reviews most of the viral-vector based antigen delivery systems (ADSs) recently developed for vaccine testing in veterinary species, including attenuated virus and DNA and RNA viral vectors. Besides their usefulness in vaccinology, these ADSs constitute invaluable tools to researchers for understanding the nature of protective responses in different species, opening the possibility of modulating or potentiating relevant immune mechanisms involved in protection.

Targeting the porcine immune system--particulate vaccines in the 21st century

During the last decade, the propagation of immunological knowledge describing the critical role of dendritic cells (DC) in the induction of efficacious immune responses has promoted research and development of vaccines systematically targeting DC. Based on the promise for the rational design of vaccine platforms, the current review will provide an update on particle-based vaccines of both viral and synthetic origin, giving examples of recombinant virus carriers such as adenoviruses and biodegradable particulate carriers. The viral carriers carry pathogen-associated molecular patterns (PAMP), used by the original virus for targeting DC, and are particularly efficient and versatile gene delivery vectors. Efforts in the field of synthetic vaccine carriers are focussing on decorating the particle surface with ligands for DC receptors such as heparan sulphate glycosaminoglycan structures, integrins, Siglecs, galectins, C-type lectins and toll-like receptors. The emphasis of this review will be placed on targeting the porcine immune system, but reference will be made to advances with murine and human vaccine delivery systems where information on DC targeting is available.

Preparation of monoclonal antibodies against pseudorabies virus glycoprotein gC by adenovirus immunization alone or as a boost following DNA priming

The objective of the present study was to demonstrate the usefulness of recombinant adenoviral vector in the generation of monoclonal antibodies (MAb) against natural epitopes of proteins using the glycoprotein gC of pseudorabies virus (PRV) as the target antigen. The recombinant adenovirus expressing the glycoprotein gC (Ad-gC) was constructed according to the AdMax method. Three immunization protocols consisting of various combinations of intramuscular injection of Ad-gC and a plasmid DNA expressing gC (pcDNA-gC) were conducted in BALB/c mice at 2-week intervals. The two groups with the highest antibody levels (Ad-gC/Ad-gC and pcDNA-gC/pcDNA-gC/Ad-gC) were selected for fusion following a final protein boost. Nine MAbs against the glycoprotein gC of PRV were subsequently developed and characterized to be isotypes of IgG1, IgG2a, and IgG2b with ascitic titers ranging from 1:2 x 10(5) to 1:5 x 10(6). Immunofluorescence assay (IFA) and Western blotting analysis confirmed that these MAbs could recognize linear epitopes on the glycoprotein gC of PRV. Our results provide a new strategy for preparation of specific MAb against viral protein.

Identification from diverse mammalian poxviruses of host-range regulatory genes functioning equivalently to vaccinia virus C7L

Vaccinia virus (VACV) C7L is a host-range gene that regulates cellular tropism of VACV. Distantly related C7L homologues are encoded by nearly all mammalian poxviruses, but whether they are host-range genes functioning similar to VACV C7L has not been determined. Here, we used VACV as a model system to analyze five different C7L homologues from diverse mammalian poxviruses for their abilities to regulate poxvirus cellular tropism. Three C7L homologues (myxoma virus M63R, M64R and cowpox virus 020), when expressed with an epitope tag and from a VACV mutant lacking the host-range genes K1L and C7L (vK1L-C7L-), failed to support productive viral replication in human and murine cells. In nonpermissive cells, these viruses did not synthesize viral late proteins, expressed a reduced level of the early protein E3L, and were defective at suppressing cellular PKR activation. In contrast, two other C7L homologues, myxoma virus (MYXV) M62R and yaba-like disease virus (YLDV) 67R, when expressed with an epitope tag and from vK1L(-)C7L(-), supported normal viral replication in human and murine cells and restored the ability of the virus to suppress PKR activation. Furthermore, M62R rescued the defect of vK1L(-)C7L(-) at replicating and disseminating in mice following intranasal inoculation. These results show that MYXV M62R and YLDV 67R function equivalently to C7L at supporting VACV replication in mammalian hosts and suggest that a C7L-like host-range gene is essential for the replication of many mammalian poxviruses in mammalian hosts.

Efficient priming against classical swine fever with a safe glycoprotein E2 expressing Orf virus recombinant (ORFV VrV-E2)

An increasing demand in livestock animal husbandry for intervention or emergency vaccination strategies requires a rapid onset of protection linked to prevention of infectious agent spread. Using the new recombinant parapoxvirus (PPV) Orf virus (ORFV) as a vaccine expressing the CSFV E2 glycoprotein we demonstrate that a single intra-muscular application confers solid protection. In the prime only concept, multi-site application of the vector vaccine turned out to be superior to single-site application as no pyrexia occurred after virulent CSFV challenge and CSFV neutralizing serum antibodies regularly were detectable before challenge. Vector virus vaccinated swine were able to cope with the lymphocyte and in particular B-cell depression in peripheral blood after challenge showing no clinical signs and no viremia. Early after challenge CSFV-specific IFN gamma production (IFN-gamma) and high neutralizing serum antibody titers clearly differentiated naïve from vaccinated and protected animals. After CSFV challenge neutralizing serum antibodies titers in vector vaccinated swine were significantly higher than those in sera from live attenuated vaccine primed animals. Horizontal challenge virus transmission was prevented under strict sentinel isolation before mingling but not in next-door stables separated by a wooden barrier at the day of challenge. The presence of CSFV-specific pre-challenge serum antibodies although in low titers is a good prognostic parameter for solid protection after ORFV vector vaccination even when a significant CSFV-specific IFN-gamma production was not detectable before challenge. A heterologous prime-boost regimen as a combination of prime with baculovirus-expressed glycoprotein E2 followed by boost with the parapoxvirus vector turned out to be a better immune stimulant than a homologous prime/boost with the modified live CSFV vaccine. A similar beneficial effect became evident when the challenge infection mimicked the booster vaccination after a single PPV vector prime.

Genus Parapoxvirus

Highly contagious pustular skin infections of sheep, goats and cattle that were unwittingly transmitted to humans from close contact with infected animals, have been the scourge of shepherds, herdsmen and dairy farmers for centuries. In more recent times we recognise that these proliferative pustular lesions are likely to be caused by a group of zoonotic viruses that are classified as parapoxviruses. In addition to infecting the above ungulates, parapoxviruses have more recently been isolated from seals, camels, red deer and reindeer and most have been shown to infect man. The parapoxviruses have one of the smallest genomes of the poxvirus family (140 kb) yet share over 70% of their genes with the most virulent members. Like other poxviruses, the central core of the genomes encode factors for virus transcription and replication, and structural proteins, whereas the terminal regions encode accessory factors that give the parapoxvirus group many of its unique features. Several genes of parapoxviruses are unique to this genus and encode factors that target inflammation, the innate immune responses and the development of acquired immunity. These factors include a homologue of mammalian interleukin (IL)-10, a chemokine binding protein and a granulocyte-macrophage colony stimulating factor /IL-2 binding protein. The ability of this group to reinfect their hosts, even though a cell-mediated memory response is induced during primary infection, may be related to their epitheliotropic niche and the immunomodulators they produce. In this highly localised environment, the secreted immunomodulators only interfere with the local immune response and thus do not compromise the host’s immune system. The discovery of a vascular endothelial growth factor-like gene may explain the highly vascular nature of parapoxvirus lesions. There are many genes of parapoxviruses which do not encode polypeptides with significant matches with protein sequences in public databases, separating this genus from most other mammalian poxviruses. These genes appear to be involved in inhibiting apoptosis, manipulating cell cycle progression and degradation of cellular proteins that may be involved in the stress response, thus allowing the virus to subvert intracellular antiviral mechanisms and enhance the availability of cellular molecules required for replication. Parapoxviruses in common with Molluscum contagiosum virus lack a number of genes that are highly conserved in other poxviruses, including factors for nucleotide metabolism, serine protease inhibitors and kelch-like proteins. It is apparent that parapoxviruses have evolved a unique repertoire of genes that have allowed adaptation to the highly specialised environment of the epidermis.

Orf virus infection and host immunity

PURPOSE OF REVIEW

A summary of recent advances in our knowledge of the biology of orf virus is presented to illustrate the interaction of a zoonotic pathogen with host skin. This is providing novel and interesting data on the viral mechanism of skin infection and the host response.

RECENT FINDINGS

The full genome sequences of two parapoxviruses (orf virus and bovine papular stomatitis virus) have recently been published, defining the parapoxvirus genus at the molecular genetic level. This, along with more detailed characterization of viral immuno-modulatory proteins, is providing an insight into the acquisition of host genes and the mechanism of pathogenesis. A new chemokine-binding protein has been discovered with unique features. Structure-function analysis of the viral granulocyte/macrophage colony-stimulating factor inhibitory factor has revealed a similarity to type 1 cytokine receptors. The viral vascular endothelial growth factor-E stimulates angiogenesis in the skin without the side effects seen with cellular vascular endothelial growth factor-A, and may have therapeutic potential. Finally, orf virus is proving useful both as an immuno-modulator and as a vector for the expression of foreign antigens in non-permissive species.

SUMMARY

Orf virus infection provokes a vigorous skin immune response. However, the virus has acquired a range of immuno-modulatory/pathogenesis-related genes that function to limit (at least transiently) the effectiveness of host immunity. With the advent of the orf virus genome sequence, the study of this dynamic process will provide important insights into virus pathogenesis and the host skin immune response to infection.

Viral vectors for use in the development of biodefense vaccines

The heightened concerns about bioterrorism and the use of biowarfare agents have prompted substantial increased efforts towards the development of vaccines against a wide range of organisms, toxins, and viruses. An increasing variety of platforms and strategies have been analyzed for their potential as vaccines against these agents. DNA vectors, live-attenuated viruses and bacteria, recombinant proteins combined with adjuvant, and viral- or bacterial-vectored vaccines have been developed as countermeasures against many potential agents of bioterrorism or biowarfare. The use of viruses, for example adenovirus, vaccinia virus, and Venezuelan equine encephalitis virus, as vaccine vectors has enabled researchers to develop effective means for countering the threat of bioterrorism and biowarfare. An overview of the different viral vectors and the threats they counter will be discussed.

Vaccine-induced protection against Borna disease in wild-type and perforin-deficient mice

Borna disease virus (BDV) can persistently infect the central nervous system and induce CD8+ T-cell-mediated neurological disease in MRL mice. To determine whether specific immune priming would prevent disease, a prime-boost immunization protocol was established in which intramuscular injection of a recombinant parapoxvirus expressing BDV nucleoprotein (BDV-N) was followed by intraperitoneal infection with vaccinia virus expressing BDV-N. Immunized wild-type and perforin-deficient mice remained healthy after intracerebral infection with BDV and contained almost no virus in the brain at 5 weeks post-challenge. Immunization failed to induce resistance against BDV in mice lacking mature CD8+ T cells. Immunization of perforin-deficient mice with a poxvirus vector expressing mutant BDV-N lacking the known CD8+ T-cell epitope did not efficiently block multiplication of BDV in the brain and did not prevent neurological disease, indicating that vaccine-induced immunity to BDV in wild-type and perforin-deficient mice resulted from the action of CD8+ T cells.

Prevention of virus persistence and protection against immunopathology after Borna disease virus infection of the brain by a novel Orf virus recombinant

The Parapoxvirus Orf virus represents a promising candidate for novel vector vaccines due to its immune modulating properties even in nonpermissive hosts such as mouse or rat. The highly attenuated Orf virus strain D1701 was used to generate a recombinant virus (D1701-VrVp40) expressing nucleoprotein p40 of Borna disease virus, which represents a major antigen for the induction of a Borna disease virus-specific humoral and cellular immune response. Infection with Borna disease virus leads to distinct neurological symptoms mediated by the invasion of activated specific CD8+ T cells into the infected brain. Usually, Borna disease virus is not cleared from the brain but rather persists in neural cells. In the present study we show for the first time that intramuscular application of the D1701-VrVp40 recombinant protected rats against Borna disease, and importantly, virus clearance from the infected brain was demonstrated in immunized animals. Even 4 and 8 months after the last immunization, all immunized animals were still protected against the disease. Initial characterization of the immune cells attracted to the infected brain areas suggested that D1701-VrVp40 mediated induction of B cells and antibody-producing plasma cells as well as T cells. These findings suggest the induction of various defense mechanisms against Borna disease virus. First studies on the role of antiviral cytokines indicated that D1701-VrVp40 immunization did not lead to an enhanced early response of gamma or alpha interferon or tumor necrosis factor alpha. Collectively, this study describes the potential of the Orf virus vector system in mediating long-lasting, protective antiviral immunity and eliminating this persistent virus infection without provoking massive neuronal damage.

Appearance of the bona fide spiral tubule of ORF virus is dependent on an intact 10-kilodalton viral protein

Parapoxviruses can be morphologically distinguished from other poxviruses in conventional negative staining electron microscopy (EM) by their ovoid appearance and the spiral tubule surrounding the virion's surface. However, this technique may introduce artifacts. We have examined Orf virus (ORFV; the prototype species of the Parapoxvirus genus) by cryoelectron microscopy (cryo-EM) and cryo-negative staining EM. From these studies we suggest that the shape and unique spiral tubule are authentic features of the parapoxviruses. We also constructed an ORFV mutant deleted of a gene encoding a 10-kDa protein, which is an orthologue of the vaccinia virus (VACV) 14-kDa fusion protein, and investigated its ultrastructure. This mutant virus multiplied slowly in permissive cells and produced infectious but morphologically aberrant particles. Mutant virions lacked the spiral tubule but displayed short disorganized tubules similar to those observed on the surface of VACV. In addition, thin extensions or loop-like structures were appended to the ORFV mutant particles. We suggest that these appended structures arise from a failure of the mutant virus particles to properly seal and that the sealing activity is dependent on the 10-kDa protein.

Lung-specific expression of active Raf kinase results in increased mortality of influenza A virus-infected mice

Alterations in signalling via the Raf/MEK/ERK pathway interfere with influenza A virus replication in cell culture. While virus yields are reduced in cells expressing dominant-negative Raf or ERK, virus propagation is enhanced upon expression of constitutively active Raf or MEK. To study the impact of active Raf on influenza virus propagation in vivo, we investigated transgenic mice expressing an activated mutant of c-Raf (Raf-BxB) in the main target tissue of influenza virus, the lung. Raf-BxB expression results in multicentric alveolar adenomas. Influenza virus A infection of Raf-BxB mice results in increased disease symptoms and higher mortality rates. The immune response against viral pathogens in transgenic animals did not differ from wild-type mice as determined by the use of a Pseudorabies virus (PRV) as a model for a viral infection not affecting the lung. No significant differences of influenza virus titers in the lung of Raf-BxB and wild-type mice were observed. However, immunohistology revealed increased numbers of influenza NP-positive cells in the alveolar linings of Raf-BxB mice, demonstrating the strong tropism of influenza virus for cells expressing active Raf. These findings disclose the possibility to use modified influenza virus for the therapy of tumors with an activated Ras/Raf signalling pathway.