Expression of bovine viral diarrhoea virus glycoprotein E2 by bovine herpesvirus-1 from a synthetic ORF and incorporation of E2 into recombinant virions

Recombinant Bovine Herpesvirus Type I Expressing the Bovine Viral Diarrhea Virus E2 Protein Could Effectively Prevent Infection by Two Viruses

Bovine respiratory disease complex (BRDC) is a comprehensive disease in cattle caused by various viral and bacterial infections. Among them, bovine herpesvirus type I (BoHV−1) and bovine viral diarrhea virus (BVDV) play important roles and have caused huge financial losses for the cattle industry worldwide. At present, vaccines against BRDC include trivalent attenuated BoHV−1, BVDV−1, and BVDV−2 live vaccines, BoHV−1 live attenuated vaccines, and BoHV−1/BVDV bivalent live attenuated vaccines, which have limitations in terms of their safety and efficacy. To solve these problems, we optimized the codon of the BVDV−1 E2 gene, added the signal peptide sequence of the BoHV−1 gD gene, expressed double BVDV−1 E2 glycoproteins in tandem at the BoHV−1 gE gene site, and constructed a BoHV−1 genetics-engineered vectored vaccine with gE gene deletion, named BoHV−1 gE/E2−Linker−E2⁺ and BoHV−1 ΔgE. This study compared the protective effects in BoHV−1, BoHV−1 ΔgE, BoHV−1 gE/E2−Linker−E2⁺, and BVDV−1 inactivated antigen immunized guinea pigs and calves. The results showed that BoHV−1 gE/E2−Linker−E2⁺ could successfully induce guinea pigs and calves to produce specific neutralizing antibodies against BVDV−1. In addition, after BoHV−1 and BVDV−1 challenges, BoHV−1 gE/E2−Linker−E2⁺ can produce a specific neutralizing antibody response against BoHV−1 and BVDV−1 infections. Calves immunized with this type of virus can be distinguished as either vaccinated animals (gE^-) or naturally infected animals (gE⁺). In summary, our data suggest that BoHV−1 gE/E2−Linker−E2⁺ and BoHV−1 ΔgE have great potential to prevent BVDV−1 or BoHV−1 infection.

BoHV-1-Vectored BVDV-2 Subunit Vaccine Induces BVDV Cross-Reactive Cellular Immune Responses and Protects against BVDV-2 Challenge

The bovine respiratory disease complex (BRDC) remains a major problem for both beef and dairy cattle industries worldwide. BRDC frequently involves an initial viral respiratory infection resulting in immunosuppression, which creates a favorable condition for fatal secondary bacterial infection. Current polyvalent modified live vaccines against bovine herpesvirus type 1(BoHV-1) and bovine viral diarrhea virus (BVDV) have limitations concerning their safety and efficacy. To address these shortcomings and safety issues, we have constructed a quadruple gene mutated BoHV-1 vaccine vector (BoHV-1 QMV), which expresses BVDV type 2, chimeric E2 and Flag-tagged Erns-fused with bovine granulocyte monocyte colony-stimulating factor (GM-CSF) designated here as QMV-BVD2*. Here we compared the safety, immunogenicity, and protective efficacy of QMV-BVD2* vaccination in calves against BVDV-2 with Zoetis Bovi-shield Gold 3 trivalent (BoHV-1, BVDV types 1 and 2) vaccine. The QMV-BVD2* prototype subunit vaccine induced the BoHV-1 and BVDV-2 neutralizing antibody responses along with BVDV-1 and -2 cross-reactive cellular immune responses. Moreover, after a virulent BVDV-2 challenge, the QMV-BVD2* prototype subunit vaccine conferred a more rapid recall BVDV-2-specific neutralizing antibody response and considerably better recall BVDV types 1 and 2-cross protective cellular immune responses than that of the Zoetis Bovi-shield Gold 3.

Utilization of herpesviridae as recombinant viral vectors in vaccine development against animal pathogens

Throughout the past few decades, numerous viral species have been generated as vaccine vectors. Every viral vector has its own distinct characteristics. For example, the family herpesviridae encompasses several viruses that have medical and veterinary importance. Attenuated herpesviruses are developed as vectors to convey heterologous immunogens targeting several serious and crucial pathogens. Some of these vectors have already been licensed for use in the veterinary field. One of their prominent features is their capability to accommodate large amount of foreign DNA, and to stimulate both cell-mediated and humoral immune responses. A better understanding of vector-host interaction builds up a robust foundation for the future development of herpesviruses-based vectors. At the time, many molecular tools are applied to enable the generation of herpesvirus-based recombinant vaccine vectors such as BAC technology, homologous and two-step en passant mutagenesis, codon optimization, and the CRISPR/Cas9 system. This review article highlights the most important techniques applied in constructing recombinant herpesviruses vectors, advantages and disadvantages of each recombinant herpesvirus vector, and the most recent research regarding their use to control major animal diseases.

Polycistronic Herpesvirus Amplicon Vectors for Veterinary Vaccine Development

Heterologous virus-vectored vaccines, particularly those based on canarypox virus vectors, have established a firm place in preventive veterinary medicine. However, herpesvirus-based vaccines have paved the way for DIVA vaccines (discrimination of infected against vaccinated animals), which are particularly desirable for highly contagious livestock diseases that are otherwise combatted by culling of infected animals.In this chapter, we describe the design, the preparation, and the testing of a polycistronic herpesvirus amplicon vaccine against rotaviruses with a particular emphasis on generating heterologous virus-like particles for immunization. After the design, the procedure consists of three steps, first, transient expression of the construct in cell cultures, second, expression and antibody response in a mouse model, and third, application of the system to the desired host species. As a whole, the present information will facilitate the design of novel vaccines of veterinary interest from the designing process until pre-licensing.

Effect of foot-and-mouth disease virus capsid precursor protein and 3C protease expression on bovine herpesvirus 1 replication

Several reports have previously shown that expression of the foot-and-mouth disease virus (FMDV) capsid precursor protein encoding region P1-2A together with the 3C protease (P1-2A/3C) results in correct processing of the capsid precursor into VP0, VP1 and VP3 and formation of FMDV capsid structures that are able to induce a protective immune response against FMDV challenge after immunization using naked DNA constructs or recombinant viruses. To elucidate whether bovine herpesvirus 1 (BHV-1) might also be suitable as a viral vector for empty capsid generation, we aimed to integrate a P1-2A/3C expression cassette into the BHV-1 genome, which, however, failed repeatedly. In contrast, BHV-1 recombinants that expressed an inactive 3C protease or the P1-2A polyprotein alone could be easily generated, although the recombinant that expressed P1-2A exhibited a defect in direct cell-cell spread and release of infectious particles. These results suggested that expression of the original, active FMDV 3C protease is not compatible with BHV-1 replication. This conclusion is supported by the isolation of recombinant BHV-1/3C*, which contained mutations within the 3C ORF (3C* ORF)--probably introduced spontaneously during generation of BHV-1/3C*--instead of the authentic 3C ORF contained in the transfer plasmids. Within the 3C* ORF, the codons for glycine 38 and phenylalanine 48 were both substituted by codons for serine. The resulting 3C* protease exhibits a highly reduced activity for proteolytic processing of the P1-2A polyprotein and thus might be a good candidate for the generation of live attenuated FMDV variants.

Characterisation of a new infectious full-length cDNA clone of BVDV genotype 2 and generation of virus mutants

Based on their genomic sequences, two genotypes of Bovine viral diarrhea virus (BVDV) can be differentiated, BVDV type 1 (BVDV-1) and BVDV type 2 (BVDV-2). The complete genomic sequence of the highly virulent BVDV-2 strain 890 was cloned as cDNA to establish the infectious cDNA clone p890FL. In vitro-synthesised full-length RNA of p890FL was transfected into bovine cells and infectious virus could be recovered (v890FL). In vitro, recombinant v890FL showed similar growth characteristics as wild type virus v890WT. However, infection experiments in calves revealed an attenuation of recombinant v890FL in comparison to the parental isolate. Both leukocytopenia and fever were less pronounced in v890FL-infected calves. Nevertheless, viremia and virus shedding were comparable between recombinant and parental BVDV 890. Furthermore, mutants with partial deletions of the genomic region encoding for the autoprotease N(pro) (p890DeltaN(pro)) or the capsid protein (p890DeltaC) were constructed and characterised. In order to generate pseudovirions, replicon p890DeltaC was efficiently trans-complemented on a helper cell line. In summary, the newly developed construct p890FL represents the first infectious full-length cDNA clone for the BVDV-2 strain 890 and offers a useful tool for further studies on the pathogenesis of BVDV-2 and the development of novel recombinant BVDV-2 specific vaccine candidates.

Modified bovine herpesvirus 1 for protein secretion

The traditional way to utilize bovine herpesvirus 1 (BHV-1) and many other herpesviruses as vectors for synthesis of heterologous proteins like reporter proteins, antigens, or immunomodulatory active molecules was (and still is) the expression of the protein of interest from an entire gene consisting of promoter, 5'- and 3'-noncoding regions, the open reading frame (ORF), and a signal sequence for polyadenylation. This approach is doubtlessly appropriate especially in cases when expression of large proteins or of proteins that do not enter the secretory pathway is envisaged. My laboratory has developed an alternative expression strategy for secreted proteins and peptides that uses the essential BHV-1 glycoprotein B (gB) as transporter for a cargo protein that is embedded in gB as a furin-excisable polypeptide that is released from the gB precursor molecule in the trans-Golgi network by the ubiquitously present endoprotease furin. The general applicability of this novel expression strategy is demonstrated by using GFP as reporter protein to monitor secretion. We hypothesize that also other secreted or membrane-bound (glyco)proteins can be engineered to function as transporters for oligopeptides and also more complex larger proteins.

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.

Immunoprophylaxis against important virus disease of horses, farm animals and birds

Since the refinement of tissue culture techniques for virus isolation and propagation from the mid 1960s onwards, veterinary virology has received much academic and industrial interest, and has now become a major global industry largely centred on vaccine development against economically important virus diseases of food animals. Bio-tech approaches have been widely used for improved vaccines development. While many viral diseases are controlled through vaccination, many still lack safe and efficacious vaccines. Additional challenges faced by academia, industry and governments are likely to come from viruses jumping species and also from the emergence of virulent variants of established viruses due to natural mutations. Also viral ecology is changing as the respective vectors adapt to new habitats as has been shown in the recent incursion by bluetongue virus into Europe. In this paper the current vaccines for livestock, horses and birds are described in a species by species order. The new promising bio-tech approaches using reverse genetics, non-replicating viral vectors, alpha virus vectors and genetic vaccines in conjunction with better adjuvants and better ways of vaccine delivery are discussed as well

Sequence-optimised E2 constructs from BVDV-1b and BVDV-2 for DNA immunisation in cattle

We report DNA immunisation experiments in cattle using plasmid constructs that encoded glycoprotein E2 from bovine viral diarrhoea virus (BVDV)-1 (E2.1) and BVDV-2 (E2.2). The coding sequences were optimised for efficient expression in mammalian cells. A modified leader peptide sequence from protein gD of BoHV1 was inserted upstream of the E2 coding sequences for efficient membrane export of the proteins. Recombinant E2 were efficiently expressed in COS7 cells and they presented the native viral epitopes as judged by differential recognition by antisera from cattle infected with BVDV-1 or BVDV-2. Inoculation of pooled plasmid DNA in young cattle elicited antibodies capable of neutralising viral strains representing the major circulating BVDV genotypes.

Nonstructural proteins NS2-3 and NS4A of classical swine fever virus: essential features for infectious particle formation

The nonstructural protein NS2-3 of pestiviruses undergoes tightly regulated processing. For bovine viral diarrhea virus it was shown that uncleaved NS2-3 is required for infectious particle formation while cleaved NS3 is essential for genome replication. To further investigate the functions of NS2-3 and NS4A in the pestivirus life cycle, we established T7 RNA polymerase-dependent trans-complementation for p7-NS2-3-4A of classical swine fever virus (CSFV). Expression of NS2-3 and NS4A in trans restored the production of infectious particles from genomes lacking NS2-3 expression. Co-expression of cleaved NS4A was essential. None of the enzymatic activities harbored by NS2-3 were required for infectious particle formation. Importantly, expression of uncleavable NS2-3 together with NS4A rescued infectious particles from a genome lacking NS2, demonstrating that cleaved NS2 per se has no additional essential function. These data indicate that NS2-3 and NS3, each in association with NS4A, have independent functions in the CSFV life cycle.

High-level expression of biologically active bovine alpha interferon by Bovine herpesvirus 1 interferes only marginally with recombinant virus replication in vitro

An artificial open reading frame (ORF) for bovine alpha interferon (boIFN-α) with the codon preference of Bovine herpesvirus 1 (BHV-1) glycoprotein B was constructed to assess the effect of expression of boIFN-α by BHV-1 from an expression cassette. Transient expression of the ORF revealed that transfected cells secreted substantial amounts of biologically active boIFN-α, which moderately inhibited replication of BHV-1 after stimulation of bovine cells with 104 U ml−1. The boIFN-α-encoding expression cassette was recombined into the glycoprotein E locus of the glycoprotein E-negative BHV-1 vaccine strain GKD. Cells infected with the resulting recombinant BHV-1/boIFN-α secreted up to 107 U boIFN-α per ml cell culture supernatant, which is about 40- to more than 100-fold the activity reached with other virus expression systems. Bioassays demonstrated that the BHV-1-expressed interferon induced a rapid and sustained antiviral state in stimulated bovine cells. Analysis of the in vitro growth properties of the recombinant revealed, depending on the cell line used, no or only slight inhibition in direct spreading from cell to cell and a modest delay in virus egress from infected cells. Final titres, however, were comparable to those reached by the parent strain. Penetration into cells was not affected. The results from this study demonstrate that BHV-1/boIFN-α expresses high levels of boIFN-α, grows to high titres in cell culture and thus represents a potential alternative means to deliver endogenously produced boIFN-α in situ for a period of time.

Expression of the genomic form of the bovine viral diarrhea virus E2 ORF in a bovine herpesvirus-1 vector

Bovine viral diarrhea virus (BVDV) is a ubiquitous pathogen of cattle with a world-wide distribution. Recently, the possibility of using recombinant virus vectors to immunize cattle against selected BVDV genes has gained widespread interest. Among the virus vectors tested, bovine herpesvirus-1 (BHV1) provides many unique advantages. However, results of recent studies have raised the possibility that the codon usage pattern required for optimal expression in a BHV1-infected cell may be incompatible with the codon usage pattern of BVDV. If true, use of BHV1 to express BVDV proteins would require construction of synthetic BVDV genes that have been modified to resemble the codon pattern of BHV1. To explore this possibility, we constructed a BHV1 recombinant containing the genomic form of the BVDV (NADL) E2 ORF and compared expression of the E2 protein with that of the endogenous BHV1 gD protein. We observed that E2 was expressed at a significant rate compared to that of the gD protein. We conclude that codon usage problems are unlikely to constitute a serious problem for expression of BVDV proteins in BHV1 vectors.

A hepadnavirus regulatory element enhances expression of a type 2 bovine viral diarrhea virus E2 protein from a bovine herpesvirus 1 vector

Recently, the possibility of using virus vectors to immunize cattle against selected bovine viral diarrhea virus (BVDV) genes has gained widespread interest. However, when we attempted to express the E2 protein from type 2 (890 strain) BVDV in a bovine herpesvirus 1 (BHV1) vector, we observed that expression was poor. This often happens when genes from a cytoplasmic virus are expressed in the cell nucleus. To counter this effect, we attempted to enhance expression by a strategy employed by viruses. RNAs of retroviruses and hepadnaviruses contain cis-acting elements that facilitate expression of RNAs that otherwise are degraded or retained within the nucleus. In Mason-Pfizer monkey virus, the required RNA sequence element is known as a constitutive transport element (CTE). A related element from woodchuck hepatitis virus is known as the woodchuck posttranscriptional regulatory element (WPRE). We tested the ability of the CTE, the WPRE, and introns to enhance expression of E2. All three elements stimulated expression of E2 from plasmids. The combination of the WPRE and an intron yielded the highest level of E2 expression in plasmids. However, when E2 was expressed from a BHV1 vector, the presence of an intron was inhibitory. In contrast, the WPRE was very efficient at stimulating E2 expression from a BHV1 vector. This result represents the first expression of a type 2 BVDV E2 protein from a mammalian virus vector and raises the possibility that the WPRE may provide a general method of enhancing foreign gene expression from BHV1 and other herpesvirus vectors.

Trans-complementation of autonomously replicating Bovine viral diarrhea virus replicons with deletions in the E2 coding region

Autonomously replicating Bovine viral diarrhea virus (BVDV) genomes (replicons) were constructed from the full-length BVDV cDNA clone pA/BVDV/Ins- (G. Meyers et al., J. Virol. 70, 8606-8613, 1996). The sequences coding for envelope protein E2, for E2 without the C-terminal transmembrane region, or for E2 and nonstructural protein p7 were deleted, and the resulting mutants were tested for their ability to replicate after transfection. All deletion mutants were able to replicate and to express the inserted green fluorescent protein but did not produce infectious progeny virus in bovine kidney PT cells. The replicons were also tested for their ability to be trans-complemented in the bovine cell line PT_805, which constitutively expresses BVDV structural proteins. E2-negative BVDV mutants were complemented and >10(6) infectious units were obtained at 24 h after transfection. Complementing PT_805 cells could only inefficiently be infected using trans-complemented virions, however, and low levels of virus production were observed when complemented BVDV was passaged using PT_805 cells. Similarly, infection of PT_805 cells with BVDV was highly inefficient, but transfection of full-length BVDV NCP7 RNA into PT_805 resulted in 10,000-fold higher virus titers when compared to those obtained 24 h after transfection of parental PT cells. We concluded that self-replicating E2-deleted BVDV RNAs can be efficiently trans-complemented by constitutively expressed E2, and that expression of BVDV structural proteins markedly influences susceptibility of cells to BVDV infection as well as BVDV titers after transfection of full-length BVDV RNA.

Rapid and efficient construction of recombinant bovine herpesvirus 1 genomes

Bovine herpesvirus 1 (BoHV-1) is an important pathogen of cattle. Recombinant bovine herpesvirus 1 viruses (rBoHV) have been studied extensively as potential vaccines for BoHV-1 associated diseases. A method is described which advances protocols used currently for constructing rBoHV by producing recombinant viruses free of parent virus. The method, restriction endonuclease mediated recombination (REMR), utilises a unique NsiI site in the BoHV-1 genome. Following NsiI digestion the two genomic fragments are prevented from recombining by dephosphorylation. However, when the genomic fragments are co-transfected into a susceptible cell-line with a third DNA fragment (DNA bridge), which encodes DNA homologous to the digested viral termini, the three DNA molecules are able to undergo homologous recombination and produce infectious BoHV-1. During the recombination process foreign DNA within the DNA bridge is incorporated into the BoHV-1 genome, producing rBoHV. In the absence of the DNA bridge virus reconstitution does not occur thus eliminating contamination by the nonrecombinant parent virus. As REMR used an NsiI site occurring naturally in the BoHV-1 genome it can be used for the insertion of foreign DNA into the genome without any prior modifications. REMR could also be applied to any herpesvirus for which the genome sequence is known.

Construction and manipulation of an infectious clone of the bovine herpesvirus 1 genome maintained as a bacterial artificial chromosome

The complete genome of bovine herpesvirus 1 (BoHV-1) strain V155 has been cloned as a bacterial artificial chromosome (BAC). Following electroporation into Escherichia coli strain DH10B, the BoHV-1 BAC was stably propagated over multiple generations of its host. BAC DNA recovered from DH10B cells and transfected into bovine cells produced a cytopathic effect which was indistinguishable from that of the parent virus. Analysis of the replication kinetics of the viral progeny indicated that insertion of the BAC vector into the thymidine kinase gene did not affect viral replication. Specific manipulation of the BAC was demonstrated by deleting the gene encoding glycoprotein E by homologous recombination in DH10B cells facilitated by GET recombination. These studies illustrate that the propagation and manipulation of herpesviruses in bacterial systems will allow for rapid and accurate characterization of BoHV-1 genes. In turn, this will allow for the full utilization of BoHV-1 as a vaccine vector.

Glycoprotein M of bovine herpesvirus 1 (BHV-1) is nonessential for replication in cell culture and is involved in inhibition of bovine respiratory syncytial virus F protein induced syncytium formation in recombinant BHV-1 infected cells

Cell cultures infected with BHV-1/F(syn), a recombinant bovine herpesvirus 1 (BHV-1) which expresses a synthetic open reading frame encoding the fusion (F) protein of the bovine respiratory syncytial virus (BRSV), showed a cytopathic effect (CPE) indistinguishable from that induced by wildtype BHV-1 although transient transfection experiments demonstrated that expression of the F protein leads to formation of large syncytia. Since it has been shown that glycoprotein M (gM) of pseudorabies virus inhibits BRSV F-induced syncytium formation in transient plasmid transfection experiments [Pseudorbies virus glycoprotein M inhibits membrane fusion. J. Virol. 74 (2000) 6760], the gM ORF of wtBHV-1 and BHV-1/F(syn) was interrupted. Infection of cell cultures with the resulting gM(-) mutant of BHV-1/F(syn) led to formation of syncytia, whereas the CPE in gM(-)BHV-1 infected cells was comparable to the CPE in wtBHV-1 infected cultures. Our results demonstrate that gM is not essential for BHV-1 replication in cell culture and that gM is involved in inhibition of the cell fusion activity of the BHV-1 expressed BRSV F protein.

Cytokine adjuvancy of BVDV DNA vaccine enhances both humoral and cellular immune responses in mice

The effect of cytokine adjuvancy on a bovine viral diarrhoea virus (BVDV) DNA vaccine expressing the major glycoprotein E2 was investigated in mice. Murine interleukin-2 (IL-2) and granulocyte-macrophage colony-stimulating factor (GM-CSF) were chosen for their potential ability to enhance the humoral and cellular immune responses involved in protection against BVDV. Both cytokines, co-administered as separate plasmid constructs, had a marked effect on ELISA and neutralising antibody titres, improving the spectrum of neutralisation induced by the E2 DNA vaccine, as demonstrated in heterologous neutralisation assays. The predominance of IgG2a isotypes, in sera from all DNA injected groups, indicated a Th1 biased immune response. Antigen specific proliferation of murine splenocytes from immunised mice was enhanced by cytokine co-administration, with the highest stimulation indexes observed in the group co-injected with the GM-CSF construct. These results obtained in the mouse (Balb/c; H2-kd) animal model demonstrate the value of the two cytokines as adjuvants for the E2 DNA vaccine. The need for an adjuvant in this system was emphasised by the MHC restriction observed when C57BL/6 mice (H2-kb) were immunised with the E2 DNA construct. Antibody levels were dramatically lower in this mouse strain.

Recombinant bovine adenovirus type 3 expressing bovine viral diarrhea virus glycoprotein E2 induces an immune response in cotton rats

Recombinant bovine adenovirus is being developed as a live vector for animal vaccination and for human gene therapy. In this study, two replication-competent bovine adenovirus 3 (BAV-3) recombinants (BAV331 and BAV338) expressing bovine viral diarrhea virus (BVDV) glycoprotein E2 in the early region 3 (E3) of BAV-3 were constructed. Recombinant BAV331 contains chemically synthesized E2 gene (nucleotides modified to remove internal cryptic splice sites) under the control of BAV-3 E3/major late promoter (MLP), while recombinant BAV338 contains original E2 gene under the control of human cytomegalovirus immediate early promoter. Since E2, a class I membrane glycoprotein, does not contain its own signal peptide sequence at the 5' end, the bovine herpesvirus 1 (BHV-1) glycoprotein D signal sequence was fused in frame to the E2 open reading frame (ORF) for proper processing of the E2 glycoprotein in both the recombinant viruses. Recombinant E2 protein expressed by BAV331 and BAV338 recombinant viruses was recognized by E2-specific monoclonal antibodies as a 53-kDa protein, which also formed dimer with an apparent molecular weight of 94 kDa. Insertion of an E2-expression cassette in the E3 region did not effect the replication of recombinant BAV-3s. Intranasal immunization of cotton rats with these recombinant viruses generated E2-specific IgA and IgG responses at the mucosal surfaces and in the serum. In summary, these results show that the pestivirus glycoprotein can be expressed efficiently by BAV-3. In addition, mucosal immunization with replication-competent recombinant bovine adenovirus 3 can induce a specific immune response against the expressed antigen.

Fusion of the green fluorescent protein to amino acids 1 to 71 of bovine respiratory syncytial virus glycoprotein G directs the hybrid polypeptide as a class II membrane protein into the envelope of recombinant bovine herpesvirus-1

It was recently shown that the class II membrane glycoprotein G of bovine respiratory syncytial virus (BRSV) is integrated into the envelope of recombinant bovine herpesvirus-1 (BHV-1) virions in the correct orientation. To verify the hypothesis that the membrane anchor of BRSV G might be suitable to target heterologous polypeptides into the membrane of recombinant BHV-1 particles, an open reading frame encoding a fusion protein between amino acids 1 to 71 of the BRSV G glycoprotein and the green fluorescent protein (TMIIGFP) was recombined into the genome of BHV-1. The resulting recombinant BHV-1/eTMIIGFP had growth properties similar to those of wild-type BHV-1. Live-cell analysis of cells infected with BHV-1/eTMIIGFP indicated that the fusion protein localized to the cell surface. Immunoprecipitations and virus neutralization assays using a GFP-specific antiserum proved that TMIIGFP was incorporated as a class II membrane protein into virions.