Development of bovine herpesvirus 4 as an expression vector using bacterial artificial chromosome cloning

Impact of equine herpesvirus-1 ORF15 (EUL45) on viral replication and neurovirulence

Equine herpesvirus 1 (EHV-1) causes respiratory illness, fetal loss, perinatal mortality, and myeloencephalopathy. This study investigated ORF15's impact on virus infectivity and neurovirulence. The Ab4p neurovirulent strain of EHV1 was used as a backbone to create Ab4p attB, Ab4p∆ORF15, and Ab4p∆ORF15R chimeras via BAC DNA transfection into RK-13 cells. Viral growth kinetics, plaque size, transcription, and growth were assessed in MDBK cells, mouse neurons, and fetal equine brain cells. Neurovirulence was evaluated post-intranasal inoculation into male CBA/N1 SPF mice, measuring signs, virus titers, and histopathological changes. Deletion of EUL45 (Ab4p-∆EUL45) reduced viral replication efficiency, resulting in decreased release and smaller plaques. EUL45 deletion also upregulated neighbouring genes (EUL46 and EUL44). Ab4p-∆EUL45 exhibited reduced virulence and poor growth in neural cells compared to wild-type viruses. This study sheds light on EUL45's role in EHV-1, viral replication, and regulation of EUL46 and EUL44 expression, suggesting potential as a vaccine candidate.

An attenuated herpesvirus vectored vaccine candidate induces T-cell responses against highly conserved porcine reproductive and respiratory syndrome virus M and NSP5 proteins that are unable to control infection

Porcine reproductive and respiratory syndrome virus (PRRSV) remains a leading cause of economic loss in pig farming worldwide. Existing commercial vaccines, all based on modified live or inactivated PRRSV, fail to provide effective immunity against the highly diverse circulating strains of both PRRSV-1 and PRRSV-2. Therefore, there is an urgent need to develop more effective and broadly active PRRSV vaccines. In the absence of neutralizing antibodies, T cells are thought to play a central role in controlling PRRSV infection. Herpesvirus-based vectors are novel vaccine platforms capable of inducing high levels of T cells against encoded heterologous antigens. Therefore, the aim of this study was to assess the immunogenicity and efficacy of an attenuated herpesvirus-based vector (bovine herpesvirus-4; BoHV-4) expressing a fusion protein comprising two well-characterized PRRSV-1 T-cell antigens (M and NSP5). Prime-boost immunization of pigs with BoHV-4 expressing the M and NSP5 fusion protein (vector designated BoHV-4-M-NSP5) induced strong IFN-γ responses, as assessed by ELISpot assays of peripheral blood mononuclear cells (PBMC) stimulated with a pool of peptides representing PRRSV-1 M and NSP5. The responses were closely mirrored by spontaneous IFN-γ release from unstimulated cells, albeit at lower levels. A lower frequency of M and NSP5 specific IFN-γ responding cells was induced following a single dose of BoHV-4-M-NSP5 vector. Restimulation using M and NSP5 peptides from PRRSV-2 demonstrated a high level of cross-reactivity. Vaccination with BoHV-4-M-NSP5 did not affect viral loads in either the blood or lungs following challenge with the two heterologous PRRSV-1 strains. However, the BoHV-4-M-NSP5 prime-boost vaccination showed a marked trend toward reduced lung pathology following PRRSV-1 challenge. The limited effect of T cells on PRRSV-1 viral load was further examined by analyzing local and circulating T-cell responses using intracellular cytokine staining and proliferation assays. The results from this study suggest that vaccine-primed T-cell responses may have helped in the control of PRRSV-1 associated tissue damage, but had a minimal, if any, effect on controlling PRRSV-1 viral loads. Together, these results indicate that future efforts to develop effective PRRSV vaccines should focus on achieving a balanced T-cell and antibody response.

Bovine Herpesvirus-4 Based Vaccine Provides Protective Immunity against Streptococcus suis Disease in a Rabbit Model

Streptococcus suis (S. suis) is a bacterial pathogen of pigs that has a major animal health and economic impact on the pig industry. Bovine herpesvirus-4 (BoHV-4) is a new virus-based vaccine vector that has been used for the immunogenic delivery of antigens from a variety of pathogens. In the present study, two recombinant BoHV-4-based vectors were evaluated for their ability to induce immunity and protection against S. suis in a rabbit model. The GMD protein is a fusion protein consisting of multiple dominant B-cell epitopes ((B-cell dominant epitopes of GAPDH, MRP, and DLDH antigens) (BoHV-4/GMD)) and the second suilysin (SLY) (BoHV-4/SLY) from S. suis serotype 2 (SS2). Both GMD and SLY delivered by the BoHV-4 vectors were recognized by sera from SS2-infected rabbits. The vaccination of rabbits with the BoHV-4 vectors induced antibodies against SS2, as well as against additional S. suis serotypes, SS7 and SS9. However, sera from BoHV-4/GMD-vaccinated animals promoted a significant level of phagocytic activity by pulmonary alveolar macrophages (PAMs) against SS2, SS7, and SS9. In contrast, sera from rabbits immunized with BoHV-4/SLY induced PAM phagocytic activity against only SS2. In addition, BoHV-4 vaccines differed in the associated level of protection against lethal SS2 challenge, which ranged from high (71.4%) to low (12.5%) for BoHV-4/GMD and BoHV-4/SLY, respectively. These data suggest BoHV-4/GMD as a promising vaccine candidate against S. suis disease.

Assessment of replication of bovine herpesvirus type 4 in human glioblastoma and breast cancer cells as a potential oncolytic virus

Oncolytic viruses have been extensively used in cancer treatment due to their tropism, selective replication only in tumor cells, and possible synergic interaction with other therapeutics. Different researchers have demonstrated that bovine herpesvirus 4 (BoHV-4), a member of the gammaherpesviridae family, has oncolytic potential in some human-origin cancer cell lines like glioma through the selective replication strategy. Using four apoptosis detection methods, namely MTT, LDH, TUNEL, and Annexin V assays, we evaluated the apoptotic effect of BoHV-4 Movar33/63 reference strain along with a recombinant BoHV-4 expressing EGFP in U87 MG cells (human glioblastoma cell line), MDA MB-231 (human breast cancer cell line), and MCF10a (non-tumorigenic human mammary epithelial cell line). Our findings indicate that this virus can replicate and induce apoptosis in these cell lines and hinder in vitro proliferation in a dose-dependent manner. In conclusion, BoHV-4 has in vitro potential as a novel oncolytic virus in human cancer therapy. However, its replication potential in the MCF10a cells as a non-tumorigenic human mammary epithelial cell line is a concern in using this virus in cancer therapy, at least against human mammary tumors. Further studies must therefore be conducted to examine the specific apoptotic pathways induced by this virus to move on to further experiments.

Bovine Herpesvirus Type 4 (BoHV-4) Vector Delivering Nucleocapsid Protein of Crimean-Congo Hemorrhagic Fever Virus Induces Comparable Protective Immunity against Lethal Challenge in IFNα/β/γR-/- Mice Models

Crimean-Congo hemorrhagic fever virus (CCHFV) is the causative agent of a tick-borne infection with a significant mortality rate of up to 40% in endemic areas, with evidence of geographical expansion. Due to a lack of effective therapeutics and control measures, the development of a protective CCHFV vaccine remains a crucial public health task. This paper describes, for the first time, a Bovine herpesvirus type 4 (BoHV-4)-based viral vector (BoHV4-∆TK-CCHFV-N) and its immunogenicity in BALB/c and protection potential in IFNα/β/γR−/− mice models in comparison with two routinely used vaccine platforms, namely, Adenovirus type 5 and a DNA vector (pCDNA3.1 myc/His A), expressing the same antigen. All vaccine constructs successfully elicited significantly elevated cytokine levels and specific antibody responses in immunized BALB/c and IFNα/β/γR−/− mice. However, despite highly specific antibody responses in both animal models, the antibodies produced were unable to neutralize the virus in vitro. In the challenge experiment, only the BoHV4-∆TK-CCHFV-N and Ad5-N constructs produced 100% protection against lethal doses of the CCHFV Ank-2 strain in IFNα/β/γR−/− mice. The delivery platforms could not be compared due to similar protection rates in IFNα/β/γR−/− mice. However, during the challenge experiment in the T cell and passive antibody transfer assay, BoHV4-∆TK-CCHFV-N was dominant, with a protection rate of 75% compared to others. In conclusion, vector-based CCHFV N protein expression constitutes an effective approach for vaccine development and BoHV-4 emerged as a strong alternative to previously used viral vectors.

Primary replication and invasion of the bovine gammaherpesvirus BoHV-4 in the genital mucosae

Bovine herpesvirus 4 (BoHV-4) is a gammaherpesvirus that is widespread in cattle. Ex vivo models with bovine genital tract mucosa explants were set up to study molecular/cellular BoHV-4-host interactions. Bovine posterior vagina, cervix and uterus body were collected from cows at two stages of the reproductive cycle for making mucosa explants. The BoHV-4 replication kinetics and characteristics within the three different mucosae of animals in the follicular and luteal phase were assessed by virus titration. The number of plaques, plaque latitude and number of infected cells were determined by immunofluorescence. BoHV-4 replicated in a productive way in all genital mucosal tissues. It infected single individual cells in both epithelium and lamina propria of the genital mucosae at 24 hours post-inoculation (hpi). Later, small BoHV-4 epithelial plaques were formed that did not spread through the basement membrane. 50% of the number of BoHV-4 infected cells were identified as cytokeratin⁺ and CD172a⁺ cells in the three parts of the genital tract at 24 hpi. Upon a direct injection of genital explants with BoHV-4, fibrocytes became infected, indicating that the unidentified 50% of the infected cells are most probably fibrocytes. In this study, in vivo-related in vitro genital tract models were successfully established and the early stage of the pathogenesis of a genital infection was clarified: BoHV-4 starts with a productive infection of epithelial cells in the reproductive tract, forming small foci followed by a non-productive infection of surveilling monocytic cells which help BoHV-4 to invade into deeper tissues.

Replacement of Glycoprotein B in Alcelaphine Herpesvirus 1 by Its Ovine Herpesvirus 2 Homolog : Implications in Vaccine Development for Sheep-Associated Malignant Catarrhal Fever

Vaccine development is a top priority in malignant catarrhal fever (MCF) research. In the case of sheep-associated MCF (SA-MCF) caused by ovine herpesvirus 2 (OvHV-2), progress toward this objective has been hindered by the absence of methods to attenuate or modify the virus, since it cannot be propagated in vitro. As an alternative for vaccine development, in this study, we tested the hypothesis that one of the SA-MCF vaccine candidate targets, OvHV-2 glycoprotein B (gB), could be expressed by a nonpathogenic alcelaphine herpesvirus 1 (AlHV-1) and then evaluated the potential of the AlHV-1/OvHV-2 chimera to be used as a vaccine and a diagnostic tool. The construction and characterization of an AlHV-1/OvHV-2 chimeric virus that is nonpathogenic and expresses an OvHV-2 vaccine target are significant steps toward the development of an SA-MCF vaccine and also provide a valuable means to study OvHV-2 biology.

Bovine Herpesvirus 4 Modulates Its β-1,6-N-Acetylglucosaminyltransferase Activity through Alternative Splicing

Carbohydrates play major roles in host-virus interactions. It is therefore not surprising that, during coevolution with their hosts, viruses have developed sophisticated mechanisms to hijack for their profit different pathways of glycan synthesis. Thus, the Bo17 gene of Bovine herpesvirus 4 (BoHV-4) encodes a homologue of the cellular core 2 protein β-1,6-N-acetylglucosaminyltransferase-mucin type (C2GnT-M), which is a key player for the synthesis of complex O-glycans. Surprisingly, we show in this study that, as opposed to what is observed for the cellular enzyme, two different mRNAs are encoded by the Bo17 gene of all available BoHV-4 strains. While the first one corresponds to the entire coding sequence of the Bo17 gene, the second results from the splicing of a 138-bp intron encoding critical residues of the enzyme. Antibodies generated against the Bo17 C terminus showed that the two forms of Bo17 are expressed in BoHV-4 infected cells, but enzymatic assays revealed that the spliced form is not active. In order to reveal the function of these two forms, we then generated recombinant strains expressing only the long or the short form of Bo17. Although we did not highlight replication differences between these strains, glycomic analyses and lectin neutralization assays confirmed that the splicing of the Bo17 gene gives the potential to BoHV-4 to fine-tune the global level of core 2 branching activity in the infected cell. Altogether, these results suggest the existence of new mechanisms to regulate the activity of glycosyltransferases from the Golgi apparatus.

IMPORTANCE

Viruses are masters of adaptation that hijack cellular pathways to allow their growth. Glycans play a central role in many biological processes, and several studies have highlighted mechanisms by which viruses can affect glycosylation. Glycan synthesis is a nontemplate process regulated by the availability of key glycosyltransferases. Interestingly, bovine herpesvirus 4 encodes one such enzyme which is a key enzyme for the synthesis of complex O-glycans. In this study, we show that, in contrast to cellular homologues, this virus has evolved to alternatively express two proteins from this gene. While the first one is enzymatically active, the second results from the alternative splicing of the region encoding the catalytic site of the enzyme. We postulate that this regulatory mechanism could allow the virus to modulate the synthesis of some particular glycans for function at the location and/or the moment of infection.

Viral semaphorin inhibits dendritic cell phagocytosis and migration but is not essential for gammaherpesvirus-induced lymphoproliferation in malignant catarrhal fever

Viral semaphorins are semaphorin 7A (sema7A) mimics found in pox- and herpesviruses. Among herpesviruses, semaphorins are encoded by gammaherpesviruses of the Macavirus genus only. Alcelaphine herpesvirus 1 (AlHV-1) is a macavirus that persistently infects wildebeest asymptomatically but induces malignant catarrhal fever (MCF) when transmitted to several species of susceptible ruminants and the rabbit model. MCF is caused by the activation/proliferation of latently infected T lymphocytes. Viral semaphorins have been suggested to mediate immune evasion mechanisms and/or directly alter host T cell function. We studied AlHV-sema, the viral semaphorin encoded by the A3 gene of AlHV-1. Phylogenetic analyses revealed independent acquisition of pox- and herpesvirus semaphorins, suggesting that these proteins might have distinct functions. AlHV-sema showed a predicted three-dimensional structure very similar to sema7A and conserved key residues in sema7A-plexinC1 interaction. Expression analyses revealed that AlHV-sema is a secreted 93-kDa glycoprotein expressed during the early phase of virus replication. Purified AlHV-sema was able to bind to fibroblasts and dendritic cells and induce F-actin condensation and cell retraction through a plexinC1 and Rho/cofilin-dependent mechanism. Cytoskeleton rearrangement was further associated with inhibition of phagocytosis by dendritic cells and migration to the draining lymph node. Next, we generated recombinant viruses and demonstrated that the lack of A3 did not significantly affect virus growth in vitro and did not impair MCF induction and associated lymphoproliferative lesions. In conclusion, AlHV-sema has immune evasion functions through mechanisms similar to poxvirus semaphorin but is not directly involved in host T cell activation during MCF.

IMPORTANCE

Whereas most poxviruses encode viral semaphorins, semaphorin-like genes have only been identified in few gammaherpesviruses belonging to the Macavirus genus. Alcelaphine herpesvirus 1 (AlHV-1) is a macavirus carried asymptomatically by wildebeest but induces a latency-associated lymphoproliferative disease of T lymphocytes in various ruminant species, namely, malignant catarrhal fever (MCF). Viral semaphorins have been hypothesized to have immune evasion functions and/or be involved in activating latently infected T cells. We present evidence that the viral semaphorin AlHV-sema inhibits dendritic cell phagocytosis and migration to the draining lymph node, both being indispensable mechanisms for protective antiviral responses. Next, we engineered recombinant viruses unable to express AlHV-sema and demonstrated that this protein is dispensable for the induction of MCF. In conclusion, this study suggests that herpesvirus and poxvirus semaphorins have independently evolved similar functions to thwart the immune system of the host while AlHV-sema is not directly involved in MCF-associated T-cell activation.

Herpesvirus mutagenesis facilitated by infectious bacterial artificial chromosomes (iBACs)

A critical factor in the study of herpesviruses, their genes and gene functions is the capacity to derive mutants that harbor deletions, truncations, or insertions within the genetic elements of interest. Once constructed the impact of the introduced mutation on the phenotypic properties of the rescued virus can be determined in either in vitro or in vivo systems. However, the construction of such mutants by traditional virological mutagenesis techniques can be a difficult and laborious undertaking. The maintenance of a viral genome as an infectious bacterial artificial chromosome (iBAC), however, endows the capacity to manipulate the viral genome for mutagenesis studies with relative ease. Here, the construction and characterization of two gene deletion mutants of an alphaherpesvirus maintained as iBAC in combination with an inducible homologous recombination system in Escherichia coli is detailed. The methodology is generally applicable to any iBAC and is demonstrated to be a highly efficient and informative approach for mutant virus construction.

A gammaherpesvirus uses alternative splicing to regulate its tropism and its sensitivity to neutralization

Human gammaherpesviruses are associated with the development of lymphomas and epithelial malignancies. The heterogeneity of these tumors reflects the ability of these viruses to route infection to different cell types at various stages of their lifecycle. While the Epstein Barr virus uses gp42 – human leukocyte antigen class II interaction as a switch of cell tropism, the molecular mechanism that orientates tropism of rhadinoviruses is still poorly defined. Here, we used bovine herpesvirus 4 (BoHV-4) to further elucidate how rhadinoviruses regulate their infectivity. In the absence of any gp42 homolog, BoHV-4 exploits the alternative splicing of its Bo10 gene to produce distinct viral populations that behave differently based on the originating cell. While epithelial cells produce virions with high levels of the accessory envelope protein gp180, encoded by a Bo10 spliced product, myeloid cells express reduced levels of gp180. As a consequence, virions grown in epithelial cells are hardly infectious for CD14+ circulating cells, but are relatively resistant to antibody neutralization due to the shielding property of gp180 for vulnerable entry epitopes. In contrast, myeloid virions readily infect CD14+ circulating cells but are easily neutralized. This molecular switch could therefore allow BoHV-4 to promote either, on the one hand, its dissemination into the organism, or, on the other hand, its transmission between hosts.

Gammaherpesviruses are highly prevalent human and animal pathogens. These viruses display sophisticated entry mechanisms, allowing them to infect different cell types inside a host but also to transmit between hosts in the presence of neutralizing antibodies. Here, we used bovine herpesvirus 4 (BoHV-4) to decipher how some gammaherpesviruses manage to do this. We found that, as function of the originating cell types, BoHV-4 is able to modify its tropism as well as its sensitivity to antibody neutralization just by controlling the alternative splicing of one of its genes. This virus therefore exploits post-transcriptional events to generate viral populations with distinct phenotypes.

Bovine herpesvirus 4 glycoprotein B is indispensable for lytic replication and irreplaceable by VSVg

BACKGROUND

Bovine herpesvirus 4 (BoHV-4) is a gammaherpesvirus, belonging to Rhadinovirus genus, with no clear association with disease. However, there is increasing evidence of its secondary pathogenic role in cases of post-partum metritis in cattle. BoHV-4 Open Reading Frame 8 (ORF8) codifies for glycoprotein B (gB) that shows a heterodimeric structure, composed of two subunits and covalently linked by disulfide bonds and responsible for host cell adhesion through binding to heparan sulfates associated with cellular proteoglycans. Here we describe the generation of several tagged soluble forms of gB ectodomain, in order to test their ability to neutralize BoHV-4 infection.

RESULTS

The results show, however, that none of these soluble forms are able to block viral infectivity. To better understand the role of gB during BoHV-4 lytic replication, a recombinant BoHV-4 was generated by homologous recombination from a BoHV-4 cloned as a Bacterial artificial chromosome (BAC) (pBAC-BoHV-4-A), in which most of the BoHV-4 gB ORF was substituted by the insertion of a DNA stuffer selectable cassette. The resulting recombinant BoHV-4 genome (pBAC-BoHV-4-AΔgB-KanaGalK) was completely unable to reconstitute infectious replicating viral particles (Infectious Replicating Viral Particles, IRVPs) and to replicate when transfected in permissive cell lines in comparison to its revertant clone (pBAC-BoHV-4-ΔgB-Rev) or pBAC-BoHV-4-A parental clone.

CONCLUSION

This demonstrates that the BoHV-4 replicating cycle is dependent on gB. Moreover, when gB was deleted from a recombinant BoHV-4 genome delivering an heterologous glycoprotein, Vesicular Stomatitis Virus Glycoprotein (VSVg), VSVg was unable to complement gB. This study provides direct evidence that gB is necessary for BoHV-4 lytic replication.

Proteomic characterization of bovine herpesvirus 4 extracellular virions

Gammaherpesviruses are important pathogens in human and animal populations. During early events of infection, these viruses manipulate preexisting host cell signaling pathways to allow successful infection. The different proteins that compose viral particles are therefore likely to have critical functions not only in viral structures and in entry into target cell but also in evasion of the host's antiviral response. In this study, we analyzed the protein composition of bovine herpesvirus 4 (BoHV-4), a close relative of the human Kaposi's sarcoma-associated herpesvirus. Using mass spectrometry-based approaches, we identified 37 viral proteins associated with extracellular virions, among which 24 were resistant to proteinase K treatment of intact virions. Analysis of proteins associated with purified capsid-tegument preparations allowed us to define protein localization. In parallel, in order to identify some previously undefined open reading frames, we mapped peptides detected in whole virion lysates onto the six frames of the BoHV-4 genome to generate a proteogenomic map of BoHV-4 virions. Furthermore, we detected important glycosylation of three envelope proteins: gB, gH, and gp180. Finally, we identified 38 host proteins associated with BoHV-4 virions; 15 of these proteins were resistant to proteinase K treatment of intact virions. Many of these have important functions in different cellular pathways involved in virus infection. This study extends our knowledge of gammaherpesvirus virions composition and provides new insights for understanding the life cycle of these viruses.

Viral bacterial artificial chromosomes: generation, mutagenesis, and removal of mini-F sequences

Maintenance and manipulation of large DNA and RNA virus genomes had presented an obstacle for virological research. BAC vectors provided a solution to both problems as they can harbor large DNA sequences and can efficiently be modified using well-established mutagenesis techniques in Escherichia coli. Numerous DNA virus genomes of herpesvirus and pox virus were cloned into mini-F vectors. In addition, several reverse genetic systems for RNA viruses such as members of Coronaviridae and Flaviviridae could be established based on BAC constructs. Transfection into susceptible eukaryotic cells of virus DNA cloned as a BAC allows reconstitution of recombinant viruses. In this paper, we provide an overview on the strategies that can be used for the generation of virus BAC vectors and also on systems that are currently available for various virus species. Furthermore, we address common mutagenesis techniques that allow modification of BACs from single-nucleotide substitutions to deletion of viral genes or insertion of foreign sequences. Finally, we review the reconstitution of viruses from BAC vectors and the removal of the bacterial sequences from the virus genome during this process.

Back to BAC: the use of infectious clone technologies for viral mutagenesis

Bacterial artificial chromosome (BAC) vectors were first developed to facilitate the propagation and manipulation of large DNA fragments in molecular biology studies for uses such as genome sequencing projects and genetic disease models. To facilitate these studies, methodologies have been developed to introduce specific mutations that can be directly applied to the mutagenesis of infectious clones (icBAC) using BAC technologies. This has resulted in rapid identification of gene function and expression at unprecedented rates. Here we review the major developments in BAC mutagenesis in vitro. This review summarises the technologies used to construct and introduce mutations into herpesvirus icBAC. It also explores developing technologies likely to provide the next leap in understanding these important viruses.

Bovine herpesvirus type 4 glycoprotein L is nonessential for infectivity but triggers virion endocytosis during entry

The core entry machinery of mammalian herpesviruses comprises glycoprotein B (gB), gH, and gL. gH and gL form a heterodimer with a central role in viral membrane fusion. When archetypal alpha- or betaherpesviruses lack gL, gH misfolds and progeny virions are noninfectious. However, the gL of the rhadinovirus murid herpesvirus 4 (MuHV-4) is nonessential for infection. In order to define more generally what role gL plays in rhadinovirus infections, we disrupted its coding sequence in bovine herpesvirus 4 (BoHV-4). BoHV-4 lacking gL showed altered gH glycosylation and incorporated somewhat less gH into virions but remained infectious. However, gL(-) virions showed poor growth associated with an entry deficit. Moreover, a major part of their entry defect appeared to reflect impaired endocytosis, which occurs upstream of membrane fusion itself. Thus, the rhadinovirus gL may be more important for driving virion endocytosis than for incorporating gH into virions, and it is nonessential for membrane fusion.

Antibody evasion by a gammaherpesvirus O-glycan shield

All gammaherpesviruses encode a major glycoprotein homologous to the Epstein-Barr virus gp350. These glycoproteins are often involved in cell binding, and some provide neutralization targets. However, the capacity of gammaherpesviruses for long-term transmission from immune hosts implies that in vivo neutralization is incomplete. In this study, we used Bovine Herpesvirus 4 (BoHV-4) to determine how its gp350 homolog--gp180--contributes to virus replication and neutralization. A lack of gp180 had no impact on the establishment and maintenance of BoHV-4 latency, but markedly sensitized virions to neutralization by immune sera. Antibody had greater access to gB, gH and gL on gp180-deficient virions, including neutralization epitopes. Gp180 appears to be highly O-glycosylated, and removing O-linked glycans from virions also sensitized them to neutralization. It therefore appeared that gp180 provides part of a glycan shield for otherwise vulnerable viral epitopes. Interestingly, this O-glycan shield could be exploited for neutralization by lectins and carbohydrate-specific antibody. The conservation of O-glycosylation sites in all gp350 homologs suggests that this is a general evasion mechanism that may also provide a therapeutic target.

Sequencing of bovine herpesvirus 4 v.test strain reveals important genome features

Background

Bovine herpesvirus 4 (BoHV-4) is a useful model for the human pathogenic gammaherpesviruses Epstein-Barr virus and Kaposi's Sarcoma-associated Herpesvirus. Although genome manipulations of this virus have been greatly facilitated by the cloning of the BoHV-4 V.test strain as a Bacterial Artificial Chromosome (BAC), the lack of a complete genome sequence for this strain limits its experimental use.

Methods

In this study, we have determined the complete sequence of BoHV-4 V.test strain by a pyrosequencing approach.

Results

The long unique coding region (LUR) consists of 108,241 bp encoding at least 79 open reading frames and is flanked by several polyrepetitive DNA units (prDNA). As previously suggested, we showed that the prDNA unit located at the left prDNA-LUR junction (prDNA-G) differs from the other prDNA units (prDNA-inner). Namely, the prDNA-G unit lacks the conserved pac-2 cleavage and packaging signal in its right terminal region. Based on the mechanisms of cleavage and packaging of herpesvirus genomes, this feature implies that only genomes bearing left and right end prDNA units are encapsulated into virions.

Conclusions

In this study, we have determined the complete genome sequence of the BAC-cloned BoHV-4 V.test strain and identified genome organization features that could be important in other herpesviruses.

Ex vivo bioluminescence detection of alcelaphine herpesvirus 1 infection during malignant catarrhal fever

Alcelaphine herpesvirus 1 (AlHV-1), carried by wildebeest asymptomatically, causes malignant catarrhal fever (WD-MCF) when cross-species transmitted to a variety of susceptible species of the Artiodactyla order. Experimentally, WD-MCF can be reproduced in rabbits. WD-MCF is described as a combination of lymphoproliferation and degenerative lesions in virtually all organs and is caused by unknown mechanisms. Recently, we demonstrated that WD-MCF is associated with the proliferation of CD8(+) cells supporting a latent type of infection in lymphoid tissues. Here, we investigated the macroscopic distribution of AlHV-1 infection using ex vivo bioluminescence imaging in rabbit to determine whether it correlates with the distribution of lesions in lymphoid and nonlymphoid organs. To reach that goal, a recombinant AlHV-1 strain was produced by insertion of a luciferase expression cassette (luc) in an intergenic region. In vitro, the reconstituted AlHV-1 luc(+) strain replicated comparably to the parental strain, and luciferase activity was detected by bioluminescence imaging. In vivo, rabbits infected with the AlHV-1 luc(+) strain developed WD-MCF comparably to rabbits infected with the parental wild-type strain, with hyperthermia and increases of both CD8(+) T cell frequencies and viral genomic charge over time in peripheral blood mononuclear cells and in lymph nodes at time of euthanasia. Bioluminescent imaging revealed that AlHV-1 infection could be detected ex vivo in lymphoid organs but also in lung, liver, and kidney during WD-MCF, demonstrating that AlHV-1 infection is prevalent in tissue lesions. Finally, we show that the infiltrating mononuclear leukocytes in nonlymphoid organs are mainly CD8(+) T cells and that latency is predominant during WD-MCF.

Swine adipose stromal cells loaded with recombinant bovine herpesvirus 4 virions expressing a foreign antigen induce potent humoral immune responses in pigs

Increasingly effective vaccination strategies are needed to counteract the high incidence of contagious diseases associated with intensive swine breeding. Recombinant viral vaccines are a promising new avenue in this direction. Key features of viral vectors suitable for immunoprophylaxis are safety, ease of manipulation and the ability to replicate in a variety of hosts. Most of the above requirements are met by bovine herpesvirus 4 (BoHV-4), a non-pathogenic dsDNA virus capable of infecting a broad range of cell types in vitro. Here we report the results of an exploratory study using an engineered BoHV-4 virus (eBoHV-4) expressing two unrelated glycoprotein antigens from bovine viral diarrhea virus (BVDV) and bovine herpesvirus 1 (BoHV-1), to assess the potential of recombinant BoHV-4 as a self-adjuvanted immunogen in pigs. Free eBoHV-4 virions and virions preloaded into homologous swine adipose-derived stromal cells (SADSC) were tested. Neither virus formulation elicited neutralizing anti-BoHV-4 antibodies, nor any disease symptom, yet both induced specific immune responses against the heterologous antigens. However, a much earlier (18 vs 28 days post-infection) and more robust neutralizing response against BVDV and BoHV-1 viruses was elicited by eBoHV-4-preinfected SADSCs compared to free virions. The data validate BoHV-4 as a safe and effective heterologous antigen carrier/producer and identify SADSCs as helpful tools for the formulation of increasingly efficacious recombinant immunogens for pig vaccination.

The bovine herpesvirus 4 Bo10 gene encodes a nonessential viral envelope protein that regulates viral tropism through both positive and negative effects

All gammaherpesviruses encode a glycoprotein positionally homologous to the Epstein-Barr virus gp350 and the Kaposi's sarcoma-associated herpesvirus (KSHV) K8.1. In this study, we characterized the positional homologous glycoprotein of bovine herpesvirus 4 (BoHV-4), encoded by the Bo10 gene. We identified a 180-kDa gene product, gp180, that was incorporated into the virion envelope. A Bo10 deletion virus was viable but showed a growth deficit associated with reduced binding to epithelial cells. This seemed to reflect an interaction of gp180 with glycosaminoglycans (GAGs), since compared to the wild-type virus, the Bo10 mutant virus was both less infectious for GAG-positive (GAG(+)) cells and more infectious for GAG-negative (GAG(-)) cells. However, we could not identify a direct interaction between gp180 and GAGs, implying that any direct interaction must be of low affinity. This function of gp180 was very similar to that previously identified for the murid herpesvirus 4 gp150 and also to that of the Epstein-Barr virus gp350 that promotes CD21(+) cell infection and inhibits CD21(-) cell infection. We propose that such proteins generally regulate virion attachment both by binding to cells and by covering another receptor-binding protein until they are displaced. Thus, they regulate viral tropism both positively and negatively depending upon the presence or absence of their receptor.

Cloning of Bovine herpesvirus type 1 and type 5 as infectious bacterial artifical chromosomes

Background

Bovine herpesviruses type 1 (BoHV1) and type 5 (BoHV5) are two closely related pathogens of cattle. The identity of the two viruses on the amino acid level averages 82%. Despite their high antigenetic similarities the two pathogens induce distinctive clinical signs. BoHV1 causes respiratory and genital tract infections while BoHV5 leads to severe encephalitis in calves.

Findings

The viral genomes of BoHV1 and BoHV5 were cloned as infectious bacterial artificial chromosomes (BACs). First, recombinant viruses carrying the genetic elements for propagation in bacteria were generated. Second, DNA from these recombinant viruses were transferred into prokaryotic cells. Third, DNA from these bacteria were transferred into eukaryotic cells. Progeny viruses from BAC transfections showed similar kinetics as their corresponding wild types.

Conclusion

The two viral genomes of BoHV1 and BoHV5 cloned as BACs are accessible to the tools of bacterial genetics. The ability to easily manipulate the viral genomes on a molecular level in future experiments will lead to a better understanding of the difference in pathogenesis induced by these two closely related bovine herpesviruses.

Anchoring tick salivary anti-complement proteins IRAC I and IRAC II to membrane increases their immunogenicity

Tick salivary proteins are promising targets for the development of anti-tick vaccines. Recently, we described two paralogous anti-complement proteins, called Ixodes ricinus anti-complement (IRAC) proteins I and II, that are co-expressed in tick I. ricinus salivary glands. However, our previous attempts to immunize rabbits against IRAC via infection with recombinant Bovine herpesvirus 4 (BoHV-4) vectors invariably failed although both recombinants expressed high levels of functional IRAC proteins in vitro. As IRAC are soluble monovalent antigens, one of the possible explanations is that monovalent ligation of the B-cell receptor induces receptor activation but fails to promote antigen presentation, a phenomenon that is thought to induce a state of B-cell tolerance. In the present study, we tried to increase IRAC immunogenicity by expressing them as oligovalent antigens. To this end, IRAC were fused to membrane anchors and BoHV-4 vectors expressing these recombinant forms were produced. The immunization potentials of recombinant viruses expressing either secreted or transmembrane IRAC proteins were then compared. While the former did not induce a detectable immune response against IRAC, the latter led to high titres of anti-IRAC antibodies that only marginally affected tick blood feeding. All together, the data presented in this study demonstrate that the immunogenicity of a soluble antigen can be greatly improved by anchoring it in membrane.

The major portal of entry of koi herpesvirus in Cyprinus carpio is the skin

Koi herpesvirus (KHV), recently designated Cyprinid herpesvirus 3, is the causative agent of a lethal disease in koi and common carp. In the present study, we investigated the portal of entry of KHV in carp by using bioluminescence imaging. Taking advantage of the recent cloning of the KHV genome as a bacterial artificial chromosome (BAC), we produced a recombinant plasmid encoding a firefly luciferase (LUC) expression cassette inserted in the intergenic region between open reading frame (ORF) 136 and ORF 137. Two viral strains were then reconstituted from the modified plasmid, the FL BAC 136 LUC excised strain and the FL BAC 136 LUC TK revertant strain, including a disrupted and a wild-type thymidine kinase (TK) locus, respectively. In vitro, the two recombinant strains replicated comparably to the parental FL strain. The FL BAC 136 LUC TK revertant strain was shown in vitro to induce a bioluminescent signal allowing the detection of single positive cells as early as 24 h postinfection, while in vivo, it induced KHV infection in carp that was indistinguishable from that induced by the parental FL strain. To identify the KHV portal of entry, carp were analyzed by bioluminescence imaging at different times postinfection with the FL BAC 136 LUC TK revertant strain. These analyses demonstrated that the skin of the fish covering the fins and also the body is the major portal of entry for KHV in carp. Finally, to further demonstrate the role of the skin as the KHV portal of entry, we constructed an original system, nicknamed "U-tube," to perform percutaneous infection restricted to the posterior part of the fish. All the data obtained in the present study demonstrate that the skin, and not the gills, is the major portal of entry for KHV in carp.

Cloning of the koi herpesvirus genome as an infectious bacterial artificial chromosome demonstrates that disruption of the thymidine kinase locus induces partial attenuation in Cyprinus carpio koi

Koi herpesvirus (KHV) is the causative agent of a lethal disease in koi and common carp. In the present study, we describe the cloning of the KHV genome as a stable and infectious bacterial artificial chromosome (BAC) clone that can be used to produce KHV recombinant strains. This goal was achieved by the insertion of a loxP-flanked BAC cassette into the thymidine kinase (TK) locus. This insertion led to a BAC plasmid that was stably maintained in bacteria and was able to regenerate virions when permissive cells were transfected with the plasmid. Reconstituted virions free of the BAC cassette but carrying a disrupted TK locus (the FL BAC-excised strain) were produced by the transfection of Cre recombinase-expressing cells with the BAC. Similarly, virions with a wild-type revertant TK sequence (the FL BAC revertant strain) were produced by the cotransfection of cells with the BAC and a DNA fragment encoding the wild-type TK sequence. Reconstituted recombinant viruses were compared to the wild-type parental virus in vitro and in vivo. The FL BAC revertant strain and the FL BAC-excised strain replicated comparably to the parental FL strain. The FL BAC revertant strain induced KHV infection in koi carp that was indistinguishable from that induced by the parental strain, while the FL BAC-excised strain exhibited a partially attenuated phenotype. Finally, the usefulness of the KHV BAC for recombination studies was demonstrated by the production of an ORF16-deleted strain by using prokaryotic recombination technology. The availability of the KHV BAC is an important advance that will allow the study of viral genes involved in KHV pathogenesis, as well as the production of attenuated recombinant candidate vaccines.

The A5 gene of alcelaphine herpesvirus 1 encodes a constitutively active G-protein-coupled receptor that is non-essential for the induction of malignant catarrhal fever in rabbits

Many gammaherpesviruses encode G-protein-coupled receptors (GPCRs). Several in vivo studies have revealed that gammaherpesvirus GPCRs are important for viral replication and for virus-induced pathogenesis. The gammaherpesvirus alcelaphine herpesvirus 1 (AlHV-1) is carried asymptomatically by wildebeest, but causes malignant catarrhal fever (MCF) following cross-species transmission to a variety of susceptible species. The A5 ORF of the AlHV-1 genome encodes a putative GPCR. In the present study, we investigated whether A5 encodes a functional GPCR and addressed its role in viral replication and in the pathogenesis of MCF. In silico analysis supported the hypothesis that A5 could encode a functional GPCR as its expression product contained several hallmark features of GPCRs. Expression of A5 as tagged proteins in various cell lines revealed that A5 localizes in cell membranes, including the plasma membrane. Using [35S]GTPgammaS and reporter gene assays, we found that A5 is able to constitutively couple to alpha i-type G-proteins in transfected cells, and that this interaction is able to inhibit forskolin-triggered cAMP response element-binding protein (CREB) activation. Finally, using an AlHV-1 BAC clone, we produced a strain deleted for A5 and a revertant strain. Interestingly, the strain deleted for A5 replicated comparably to the wild-type parental strain and induced MCF in rabbits that was indistinguishable from that of the parental strain. The present study is the first to investigate the role of an individual gene of AlHV-1 in MCF pathogenesis.

Establishment of a bovine herpesvirus 4 based vector expressing a secreted form of the bovine viral diarrhoea virus structural glycoprotein E2 for immunization purposes

Background

The biological characteristics of BoHV-4 make it a good candidate as a gene delivery vector for vaccination purposes. These characteristics include little or no pathogenicity, unlikely oncogenicity, the capability to accommodate large amounts of foreign genetic material, the ability to infect several cell types from different animal species, and the ability to maintain transgene expression in both undifferentiated and differentiated cells.

Results

A recombinant bovine herpesvirus 4 (BoHV-4CMV-IgKE2-14ΔTK) expressing an enhanced secreted form of the bovine viral diarrhea virus (BVDV) structural glycoprotein E2 (gE2-14), obtained by the removal of the putative transmembrane domain and addition of a 14 amino acids peptide at its carboxyl terminal and an immunoglobulin K signal peptide to the amino terminal, was successfully constructed using a Recombineering (recombination -mediated genetic engineering) approach on BoHV-4 cloned as bacterial artificial chromosome. The galactokinase – based recombineering system was modified by the introduction of a kanamycin expression cassette and a kanamycin selection step that allowed a significant reduction of the untargeted background clones. BoHV-4CMV-IgKE2-14ΔTK infected cell lines highly expressed gE2-14, which maintained native antigenic properties in a serum neutralization inhibition test. When rabbits and sheep were immunized with BoHV-4CMV-IgKE2-14ΔTK, high levels of serum neutralized antibodies against BVDV were generated.

Conclusion

This work highlights the engineerization of BoHV-4 genome as a vector for vaccine purposes and may provide the basis for BVDV vaccination exploiting the BoHV-4- based vector that delivers an improved secreted version of the BVDV structural glycoprotein E2.

Early inflammation in the airways of a cystic fibrosis foetus

In cystic fibrosis patients, inflammation is often considered to be secondary to chronic infections. In the present study, we show increased levels of pro-inflammatory proteins in the lungs of a cystic fibrosis foetus compared to the lungs of two normal foetuses. Our findings suggest therefore the existence of an early intrinsic pro-inflammatory state in cystic fibrosis airways.

Incorporation of a lambda phage recombination system and EGFP detection to simplify mutagenesis of Herpes simplex virus bacterial artificial chromosomes

Background

Targeted mutagenesis of the herpesvirus genomes has been facilitated by the use of bacterial artificial chromosome (BAC) technology. Such modified genomes have potential uses in understanding viral pathogenesis, gene identification and characterization, and the development of new viral vectors and vaccines. We have previously described the construction of a herpes simplex virus 2 (HSV-2) BAC and the use of an allele replacement strategy to construct HSV-2 recombinants. While the BAC mutagenesis procedure is a powerful method to generate HSV-2 recombinants, particularly in the absence of selective marker in eukaryotic culture, the mutagenesis procedure is still difficult and cumbersome.

Results

Here we describe the incorporation of a phage lambda recombination system into an allele replacement vector. This strategy enables any DNA fragment containing the phage attL recombination sites to be efficiently inserted into the attR sites of the allele replacement vector using phage lambda clonase. We also describe how the incorporation of EGFP into the allele replacement vector can facilitate the selection of the desired cross-over recombinant BACs when the allele replacement reaction is a viral gene deletion. Finally, we incorporate the lambda phage recombination sites directly into an HSV-2 BAC vector for direct recombination of gene cassettes using the phage lambda clonase-driven recombination reaction.

Conclusion

Together, these improvements to the techniques of HSV BAC mutagenesis will facilitate the construction of recombinant herpes simplex viruses and viral vectors.

Cloning of full length genome of varicella-zoster virus vaccine strain into a bacterial artificial chromosome and reconstitution of infectious virus

The complete genome of the varicella-zoster virus (VZV) Oka vaccine strain (vOka) has been cloned into a bacterial artificial chromosome (BAC), and several BAC clones with the vOka genome have been obtained. Infectious viruses were reconstituted in MRC-5 cells transfected with the vOka-BAC DNA clones. The clones were distributed into two groups based on differences in amino acids found in ORF 62/71 region among the vOka-BAC clones. The recombinant vOka (rvOka) grew slower than recombinant Oka parental virus (rpOka), pOka and vOka. This is the first report that the vOka genome was cloned into BAC vector. The rvOka-BAC system would be useful as a vector for construction of recombinant live vaccines.

Ixodes ticks belonging to the Ixodes ricinus complex encode a family of anticomplement proteins

The alternative pathway of complement is an important innate defence against pathogens including ticks. This component of the immune system has selected for pathogens that have evolved countermeasures. Recently, a salivary protein able to inhibit the alternative pathway was cloned from the American tick Ixodes scapularis (Valenzuela et al., 2000; J. Biol. Chem. 275, 18717-18723). Here, we isolated two different sequences, similar to Isac, from the transcriptome of I. ricinus salivary glands. Expression of these sequences revealed that they both encode secreted proteins able to inhibit the complement alternative pathway. These proteins, called I. ricinus anticomplement (IRAC) protein I and II, are coexpressed constitutively in I. ricinus salivary glands and are upregulated during blood feeding. Also, we demonstrated that they are the products of different genes and not of alleles of the same locus. Finally, phylogenetic analyses demonstrate that ticks belonging to the Ixodes ricinus complex encode a family of relatively small anticomplement molecules undergoing diversification by positive Darwinian selection.

The paralogous salivary anti-complement proteins IRAC I and IRAC II encoded by Ixodes ricinus ticks have broad and complementary inhibitory activities against the complement of different host species

Several observations suggest that inhibition of the host complement alternative pathway by Ixodes tick saliva is crucial to achieve blood feeding. We recently described two paralogous anti-complement proteins called Ixodes ricinus anti-complement (IRAC) proteins I and II co-expressed in I. ricinus salivary glands. Phylogenetic analyses suggested that these sequences were diversifying by a process of positive Darwinian selection, possibly leading to molecules with different biological properties. In the present study, we tested the hypothesis that each paralogue may have different inhibitory activities against the complement of different natural host species, thereby contributing to broaden the host range of I. ricinus ticks. IRAC I and IRAC II were tested against the complement of eight I. ricinus natural host species (six mammals and two birds). The results demonstrate that IRAC I and IRAC II have broad and complementary inhibition activities against the complement of different host species. This report is the first description of paralogous anti-complement molecules encoded by a pathogen with broad and complementary inhibitory activities against the complement of different host species.

Generation of a transposon insertion mutant library for bovine herpesvirus 4 cloned as a bacterial artificial chromosome by in vitro MuA based DNA transposition system

Bovine herpesvirus 4 (BoHV-4) is a gammaherpesvirus with no clear disease association. Although the BoHV-4 genome has been sequenced, the function of the majority of putative genes is elusive. Several features make BoHV-4 attractive as a backbone for use as a viral expression vector and/or as a model to study gamma herpesvirus biology and determining which genes are essential for its replication is a very important task. Starting from BoHV-4 genome cloned as infectious bacterial artificial chromosome (BAC-BoHV-4) in Escherichia coli. A random insertion mutant library for BoHV4 was generated by the use of MuA transposase-catalyzed in vitro transposition reaction. Viral mutant transfection and direct sequencing allow the rapid determination of which BoHV-4 genes are essential for viral growth in a permissive eukaryotic cell line. BoHV-4 functional analysis information is fundamental when the BoHV-4 genome is modified for vector purposes.

Felid herpesvirus 1 glycoprotein G is a structural protein that mediates the binding of chemokines on the viral envelope

Glycoprotein G (gG) orthologues have been described in several alphaherpesviruses. gG is expressed both as a membrane-anchored form on infected cells and as a secreted form. Recently, we reported that both forms of gG encoded by alphaherpesviruses infecting large herbivores and by Felid herpesvirus 1 (FeHV-1) bind with high affinity to a broad range of CXC, CC and C-chemokines. Based on the viral species, gG has been reported either as a structural or a non-structural protein. To date, the incorporation of FeHV-1 gG into virions has never been tested, nor the property of alphaherpesvirus structural gG to bind chemokines on the virion surface. In the present study, to address these questions, various FeHV-1 gG recombinant strains were produced using an original technique based on an infectious FeHV-1 BAC clone and restriction endonuclease mediated recombination. Using the recombinants produced, we were able to determine that FeHV-1 gG is a structural protein that acts as a chemokine-binding protein on the virion surface. In the light of these results, putative roles of gG in alphaherpesvirus infections are discussed, and an evolutionary scenario is proposed to explain the structural versus non-structural property of gG amongst alphaherpesviruses.

Recombinant bovine herpesvirus 4 (BoHV-4) expressing glycoprotein D of BoHV-1 is immunogenic and elicits serum-neutralizing antibodies against BoHV-1 in a rabbit model

Several biological characteristics of bovine herpesvirus 4 (BoHV-4) make it a good candidate as a gene delivery vector for vaccination purposes. These characteristics include little or no pathogenicity, unlikely oncogenicity, the capability to accommodate large amounts of foreign genetic material, the ability to infect several cell types coming from different animal species, and the ability to maintain transgene expression in both undifferentiated and differentiated cells. Starting from BoHV-4 cloned as a bacterial artificial chromosome (BAC), we used MuA transposase-mediated in vitro transposition to generate recombinant BoHV-4 expressing the immunodominant glycoprotein D (gD) of BoHV-1, one of the most important pathogens of cattle. Although a cis-acting element from woodchuck hepatitis virus (the woodchuck hepatitis virus posttranscriptional regulatory element [WPRE]) in the 3' end of the gD expression cassette was required for maximal gD expression from plasmids in transient transfection assays, this element was not necessary for efficient expression of gD from recombinant BoHV-4 genomes. BoHV-4 recombinants containing gD expression cassettes with or without the WPRE expressed gD at similarly high levels. Several cell lines originating from different animal species expressed gD when infected with BoHV-4 recombinants. When rabbits were immunized with one of the recombinants, high levels of serum neutralizing antibodies against BoHV-1 were generated. This work is one of the first demonstrations of the use BoHV-4 as a vector for vaccine purposes and may provide the basis for BoHV-1 vaccination of cattle with recombinant BoHV-4.

Bovine herpesvirus 4 based vector interaction with liver cells in vitro and in vivo

Gene transfer into hepatocytes is highly desirable for the long-term goal of replacing deficient proteins and correcting metabolic disorders. Bovine herpesvirus 4 (BoHV-4) based vector capability to transduce rat liver cells in vitro and in vivo was assessed. For the in vitro study, a buffalo rat liver cell line was successfully transduced by BoHV-4 and although did not show toxicity, the immediate early two viral gene was transcribed and cells harboring the intact viral genome could be pharmacologically selected, but no viral replication took place. For the in vivo study, adult male rats were inoculated intraportally and intraparenchimally with a BoHV-4 expressing enhanced green fluorescent protein and liver sections were analyzed through fluorescent microscopy. Although the liver parenchyma could not be transduced, the endothelial layer of the liver vasculature showed a robust transgene expression without toxicity. Successful BoHV-4 based vector transduction of primary cultures of rat hepatocytes suggests that extrinsic factors, and not hepatocytes per se, are the cause of such lack of transducibility. The present study serves as a starting point for study of the use of BoHV-4 based vectors to target gene delivery to vascular endothelial cells.

Cloning of the genome of Alcelaphine herpesvirus 1 as an infectious and pathogenic bacterial artificial chromosome

Alcelaphine herpesvirus 1 (AlHV-1), carried asymptomatically by wildebeest, causes malignant catarrhal fever (MCF) following cross-species transmission to a variety of susceptible species of the order Artiodactyla. The study of MCF pathogenesis has been impeded by an inability to produce recombinant virus, mainly due to the fact that AlHV-1 becomes attenuated during passage in culture. In this study, these difficulties were overcome by cloning the entire AlHV-1 genome as a stable, infectious and pathogenic bacterial artificial chromosome (BAC). A modified loxP-flanked BAC cassette was inserted in one of the two large non-coding regions of the AlHV-1 genome. This insertion allowed the production of an AlHV-1 BAC clone stably maintained in bacteria and able to regenerate virions when transfected into permissive cells. The loxP-flanked BAC cassette was excised from the genome of reconstituted virions by growing them in permissive cells stably expressing Cre recombinase. Importantly, BAC-derived AlHV-1 virions replicated comparably to the virulent (low-passage) AlHV-1 parental strain and induced MCF in rabbits that was indistinguishable from that of the virulent parental strain. The availability of the AlHV-1 BAC is an important advance for the study of MCF that will allow the identification of viral genes involved in MCF pathogenesis, as well as the production of attenuated recombinant candidate vaccines.

Construction of an infectious clone of canine herpesvirus genome as a bacterial artificial chromosome

Canine herpesvirus (CHV) is an attractive candidate not only for use as a recombinant vaccine to protect dogs from a variety of canine pathogens but also as a viral vector for gene therapy in domestic animals. However, developments in this area have been impeded by the complicated techniques used for eukaryotic homologous recombination. To overcome these problems, we used bacterial artificial chromosomes (BACs) to generate infectious BACs. Our findings may be summarized as follows: (i) the CHV genome (pCHV/BAC), in which a BAC flanked by loxP sites was inserted into the thymidine kinase gene, was maintained in Escherichia coli; (ii) transfection of pCHV/BAC into A-72 cells resulted in the production of infectious virus; (iii) the BAC vector sequence was almost perfectly excisable from the genome of the reconstituted virus CHV/BAC by co-infection with CHV/BAC and a recombinant adenovirus that expressed the Cre recombinase; and (iv) a recombinant virus in which the glycoprotein C gene was deleted was generated by lambda recombination followed by Flp recombination, which resulted in a reduction in viral titer compared with that of the wild-type virus. The infectious clone pCHV/BAC is useful for the modification of the CHV genome using bacterial genetics, and CHV/BAC should have multiple applications in the rapid generation of genetically engineered CHV recombinants and the development of CHV vectors for vaccination and gene therapy in domestic animals.

Bovine herpesvirus 4 induces apoptosis of human carcinoma cell lines in vitro and in vivo

The idea of using oncolytic viruses for the treatment of cancers was proposed a century ago. During the last two decades, viruses able to replicate specifically in cancer cells and to induce their lysis were identified and were genetically modified to improve their viro-oncolytic properties. More recently, a new approach consisting of inducing selective apoptosis in cancer cells through viral infection has been proposed; this approach has been called viro-oncoapoptosis. In the present study, we report the property of bovine herpesvirus-4 (BoHV-4) to induce, in vitro and in vivo, apoptosis of some human carcinomas. This conclusion relies on the following observations: (a) In vitro, BoHV-4 infection induced apoptosis of A549 and OVCAR carcinoma cell lines in a time- and dose-dependent manner. (b) Apoptosis was induced by the expression of an immediate-early or an early BoHV-4 gene, but did not require viral replication. (c) Cell treatment with caspase inhibitors showed that apoptosis induced by BoHV-4 relied mainly on caspase-10 activation. (d) Infection of cocultures of A549 or OVCAR cells mixed with human 293 cells (in which BoHV-4 does not induce apoptosis) showed that BoHV-4 specifically eradicated A549 or OVCAR cancer cells from the cocultures. (e) Finally, in vivo experiments done with nude mice showed that BoHV-4 intratumoral injections reduced drastically the growth of preestablished A549 xenografts. Taken together, these results suggest that BoHV-4 may have potential as a viro-oncoapoptotic agent for the treatment of some human carcinomas. Moreover, further identification of BoHV-4 proapoptotic gene(s) and the cellular pathways targeted by this or these gene(s) could lead to the design of new cancer therapeutic strategies.