A prime-boost vaccination strategy using naked DNA followed by recombinant porcine adenovirus protects pigs from classical swine fever

Weaned pigs (6-week-old) and 7-day-old pre-weaned piglets were vaccinated with naked plasmid DNA expressing the gp55/E2 gene from classical swine fever virus (CSFV). Both groups of pigs were then given a booster dose of recombinant porcine adenovirus expressing the gp55 gene (rPAV-gp55). Following challenge with CSFV, 100% of weaned pigs and 75% pre-weaned piglets were protected from disease. Weaned pigs given a single dose of rPAV-gp55 were also protected, but showed a slight increase in temperature immediately post-challenge. However, weaned animals given a DNA prime before rPAV-gp55 showed no fluctuation in body temperature following challenge and no pathology in spleen or lymph nodes upon post-mortem. In addition, no CSFV could be re-isolated from the rPAV vaccinated group and from only one pig in the prime-boost group following challenge, suggesting that both vaccination regimes have the potential to reduce or prevent virus shedding following experimental challenge.

Comparative studies of piscine and amphibian iridoviruses

A total of 30 iridoviruses collected from Australia, South-East Asia, North America, South America and Europe were characterised. With the exception of the South-East Asian iridoviruses all viruses were found to belong to the genus Ranavirus. All viruses, except those originating from South-East Asia, cross-reacted with antisera against epizootic haematopoietic necrosis virus (EHNV). Viruses or virus-infected cells were examined using electron microscopy, SDS PAGE, restriction endonuclease (RE) digestion, DNA hybridisation, and DNA sequencing. Data from RE digestion of genomic DNA, and from the sequencing of PCR products indicated that the viruses generally grouped according to their geographic and taxonomic (i.e. amphibian or fish) origin. The one exception to this was the viruses from the United Kingdom that grouped with the North American ranaviruses. The differences between specified genomic regions were small. To assess the validity of the differences in sequence homology, similar studies were performed with different isolates from two viruses (EHNV and Guatopo virus (GV), collected from different animals at different locations and time). The sequence data showed complete homology for the isolates for any one virus over the 200 and 586 bp regions examined. Collectively, the data showed that the coding region for the major coat protein (MCP) is stable for any one species (e.g. EHNV).

Rapid dissemination of intramuscularly inoculated DNA vaccines

Deoxyribonucleic acid (DNA) vaccination offers the prospect of novel, safe vaccines that can stimulate cell-mediated immunity as well as antibody. An understanding of how and where transfection occurs in vivo will assist strategies to enhance their efficacy. Plasmid DNA encoding for the expression of firefly luciferase was injected intramuscularly into sheep. The DNA was rapidly disseminated and could be detected in efferent lymph within 5 min. At the earliest time that cells were tested separately from lymph plasma (1 h), DNA was found to be present in both the lymph plasma and within lymph cells. Although plasmid DNA could be detected intracellularly in lymph and in muscle tissue at the site of inoculation, no luciferase gene expression could be detected. The results suggest that, in addition to the internalization of plasmid DNA, other factors may limit gene expression, possibly the rate of DNA migration into the nucleus.

The immune response to a polyoma virus replicon-based DNA vaccine

DNA vaccination has proven to be effective against a number of tumours and microbial diseases. As DNA vaccines are unable to replicate, plasmid copy number per cell is dependent on in vivo transfection efficiency, which is usually quite low. Consequently, immune responses generated are likely to be sub-optimal due to low antigen expression levels in transfected cells. During this study, replicating DNA vaccines delivered intra-epidermally by gene gun, were assessed for their ability to more efficiently generate immune responses in mice. The data demonstrate that, using a polyoma virus-based system of replication, 10-fold less DNA expressing the haemagglutinin gene of influenza virus, was required to stimulate a humoral immune response, compared to an equivalent non-replicating vaccine. This observation suggests that the use of replicating DNA vaccines in some delivery systems may enhance the effectiveness of immune responses.

Protection of pigs against classical swine fever with DNA-delivered gp55

Classical swine fever virus causes significant mortality and morbidity in commercial piggeries in many countries in Europe and Asia. The protective antigen, gp55, is highly conformation-dependent and thus killed virus or bacterially produced proteins are not protective. This report demonstrates that DNA vaccination with the gene encoding gp55 can provide protective immunity with inoculation of two doses of 25 microg DNA or a single shot of 200 microg. Furthermore, the DNA can be delivered intramuscularly or by a simple spring-loaded needleless inoculator. In addition it is shown that inoculation of the DNA at a single site conveys the same level of immunity as division of the dose between two sites.

Insertion sites for recombinant vaccinia virus construction: effects on expression of a foreign protein

The expression of antigens or other molecules from recombinant vaccinia viruses requires the insertion of coding sequence at specific sites in the viral genome. Here we investigate the influence of two different sites on the level of protein expressed during a viral infection. The level of immune response in mice to vaccinia virus-expressed murine interleukin 2 (IL-2) or IL-4 varied depending on whether the coding sequence was inserted into the vaccinia virus thymidine kinase (tk) gene or into the HindIII F fragment of the viral genome where herpes simplex virus (HSV) tk was used as a selectable marker. In each case the intensity of the response was greater when the relevant gene was expressed from the HindIII F insertion site. In order to quantify these differences a series of recombinant viruses expressing luciferase was constructed. Luciferase activity from coding sequence inserted into the HindIII F fragment was significantly higher than that from the tk gene insertion, provided HSV tk(+) constructs were compared. Insertion of a marker gene (HSV tk) into the HindIII F site with disruption of the F7L open reading frame led to a reduced level of luciferase expressed from the tk insert, despite more than 45 kb of intervening sequence. In mice, luciferase expression was higher from the HindIII F inserted gene than from the tk insert in both lungs and ovaries.

The ovine cytotoxic T lymphocyte responses to bluetongue virus

This study uses recombinant vaccinia viruses expressing truncated or entire bluetongue virus (BTV) proteins to map the location of epitopes recognized by cytotoxic T lymphocytes (CTL) from Australian merino sheep. The non-structural protein, NS1, was recognised by CTL from all sheep, while VP2, VP3, VP5 and VP7 were recognised by CTL from only some sheep. The remaining proteins (except for VP1, which was not tested) did not contain CTL epitopes. When truncated genes were used to map the location of CTL epitopes, it was found that sheep often have CTL that recognise more than one epitope in NS1 or VP2. Overall there was considerable diversity in the CTL recognition patterns in the sheep tested.

Expression of the potyvirus coat protein mediated by recombinant vaccinia virus and assembly of potyvirus-like particles in mammalian cells

The coat protein of the potyvirus, Johnsongrass mosaic virus (JGMV), was expressed using a recombinant vaccinia virus (VV) system. Ultra-thin section electron microscopy demonstrated that the coat protein assembled into potyvirus-like particles (PVLPs) in recombinant VV infected cells. Infection of cells with two additional VV recombinants expressing coat protein plus N-terminal and N- and C-terminal extensions also resulted in the formation of PVLPs. These results suggest that the ability of VV to express the potyvirus coat protein at sufficient levels to allow PVLP formation in vitro, could make VV a suitable vector for the delivery of PVLPs displaying vaccine antigens in vivo without the need for particle purification and/or inclusion of adjuvant. Use of such a vaccine strategy would also benefit from the proven advantages of poxviruses as vaccines such as stability in a freeze dried form, resistance to environmental factors and the potential for oral administration.

Targeting a polyepitope protein incorporating multiple class II-restricted viral epitopes to the secretory/endocytic pathway facilitates immune recognition by CD4+ cytotoxic T lymphocytes: a novel approach to vaccine design

The role of CD4+ and CD8+ cells in the generation of an effective immune response against viral infections is well established. Moreover, there is an increasing realization that subunit vaccines which include both CD4+- and CD8+-T-cell epitopes are highly effective in controlling viral infections, as opposed to those which are designed to activate a CD8+- or CD4+-T-cell response alone. One of the major limitations of epitope-based vaccines designed to stimulate virus-specific CD4+ T cells is that endogenously expressed class II-restricted minimal cytotoxic-T-lymphocyte (CTL) epitopes are poorly recognized by CD4+ CTLs. In the present study we attempted to enhance the efficiency of class II-restricted endogenous presentation of minimal class II-restricted CTL epitopes by specifically targeting a polyepitope protein to class II processing compartments through the endosomal and/or lysosomal pathway. A significantly enhanced stimulation of virus-specific CD4+-T-cell clones by antigen-presenting cells (APC) expressing the recombinant polyepitope protein targeted to the endocytic/secretory pathway was readily demonstrated in cytotoxicity assays. In addition, in vitro activation of Epstein-Barr virus- and influenza virus-specific CD4+ memory CTLs by the recombinant constructs encoding the polyepitope protein, specifically targeted to the lysosomal compartment, was also demonstrated. The enhanced stimulatory capacity of APC expressing a lysosome-targeted polyepitope protein has important implications for vaccine design.

Antibody responses and protective immunity to recombinant vaccinia virus-expressed bluetongue virus antigens

The role of individual viral proteins in the immune response to bluetongue virus (BTV) is not clearly understood. To investigate the contributions of the outer capsid proteins, VP2 and VP5, and possible interactions between them, these proteins were expressed from recombinant vaccinia viruses either as individual proteins or together in double recombinants, or with the core protein VP7 in a triple recombinant. Comparison of the immunogenicity of the vaccinia expressed proteins with BTV expressed proteins was carried out by inoculation of rabbits and sheep. Each of the recombinants was capable of stimulating an anti-BTV antibody response, although there was a wide range in the level of response between animals and species. Vaccinia-expressed VP2 was poorly immunogenic, particularly in rabbits. VP5, on the whole, stimulated higher ELISA titers in rabbits and sheep and in some animals in both species was able to stimulate virus neutralizing antibodies. When the protective efficacy of VP2 and VP5 was tested in sheep, vaccinia-expressed VP2, VP5 and VP2 + VP5 were protective, with the most consistent protection being in groups immunized with both proteins.

Field and vaccine strains of fowlpox virus carry integrated sequences from the avian retrovirus, reticuloendotheliosis virus

For baculoviruses and herpesviruses, integration of transposons or retroviruses into the virus genome has been documented. We report here that field and vaccine strains of fowlpox virus (FPV) carry integrated sequences from the avian retrovirus, reticuloendotheliosis virus (REV). Using PCR and hybridization analysis we observed that vaccine and field strains of FPV carry REV sequences integrated into a previously uncharacterized region of the right 1/3 of the FPV genome. Long-range PCR, hybridization, and nucleotide sequence determination demonstrated that one vaccine strain (FPV S) and recently isolated field strains carry a near-full-length REV provirus. For another vaccine strain (FPV M) a rearranged remnant of the LTR was found at the same insertion site. By Western blotting and reverse transcriptase assays we were unable to demonstrate free REV in supernatants of FPV S cultures. The near-full-length REV provirus integrated into the FPV genome is infectious since FPV S DNA gave rise to REV upon transfection into chicken embryo fibroblasts. Upon infection of chickens with FPV S, all chickens developed high-titered antibodies to REV, and REV was isolated from the blood of half of the inoculated chickens. Our observations add to the list of targets for retrovirus integration into DNA virus genomes. The integration of a near-full-length, and apparently infectious, REV provirus into FPV provides additional transmission routes for the retrovirus by way of the infectious cycle of FPV, including the possibility of mechanical transmission by biting insects since FPV is believed to be transmitted by this route. For large DNA viruses, including the poxviruses, retrovirus integration with attendant possibilities of gene transduction may be an important mechanism for virus evolution, including the acquisition of cellular genes with the potential to modify virus virulence and pathogenicity.

A synthetic vaccinia virus promoter with enhanced early and late activity

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

Comparison of field and vaccine strains of Australian fowlpox viruses

The mild fowlpox vaccine, FPV M, widely used in Australia is composed of two predominant genotypes based upon differences identifiable in restriction enzyme analyses of plaque purified derivatives of this vaccine. The differences, where identifiable, were in the end fragments of the genomes. Five field isolates of FPV from chickens in New South Wales showed restriction enzyme profiles closely related to the more virulent (standard) vaccine strain, FPV S. The FPV S strain differs from FPV M in both terminal genome fragments and in the presence of a PstI fragment of approximately 10kb (this fragment was also present in PstI digests of all of the field isolates). Plaque purified derivatives of FPV M showed similar lesion development upon inoculation into the wing web of chickens. The field isolates showed significantly higher virulence in day-old and three-week-old chickens in comparison with FPV M. One field isolate was similar to the FPV S vaccine. Two isolates had slowly developing wing web lesions, caused significant secondary lesions in three-week-old chickens and generalised poxvirus infection when inoculated into day-old chickens. For two isolates, the primary wing web lesion took even longer to develop and resolve although these isolates did not cause generalised poxvirus infection. It was possible to identify four virulence/pathogenicity types amongst these vaccine and field isolates of FPV. These strains may allow the characterisation of FPV encoded virulence factors. The field strains with higher virulence may be suitable as parent strains for the construction of FPV recombinants with enhanced immune responses to co-expressed vaccine antigens when compared with current FPV M strain based recombinants.

Recombinant polyepitope vaccines for the delivery of multiple CD8 cytotoxic T cell epitopes

Development of epitope-based CD8 alpha beta CTL vaccines requires effective strategies for codelivery of large numbers of individual epitopes. We have designed an artificial "polyepitope" protein containing 10 contiguous minimal CTL epitopes, which were restricted by five MHC alleles and derived from five viruses, a parasite, and a tumor model. A recombinant vaccinia virus coding for this protein was capable of inducing MHC-restricted primary CTL responses to all 10 epitopes. Mice immunized with this recombinant vaccinia showed protection against murine cytomegalovirus, Sendai virus, and a tumor model. This simple generic approach to multiepitope delivery should find application in CTL-based vaccine design.

Recombinant polyepitope vaccines for the delivery of multiple CD8 cytotoxic T cell epitopes

Development of epitope-based CD8 alpha beta CTL vaccines requires effective strategies for codelivery of large numbers of individual epitopes. We have designed an artificial "polyepitope" protein containing 10 contiguous minimal CTL epitopes, which were restricted by five MHC alleles and derived from five viruses, a parasite, and a tumor model. A recombinant vaccinia virus coding for this protein was capable of inducing MHC-restricted primary CTL responses to all 10 epitopes. Mice immunized with this recombinant vaccinia showed protection against murine cytomegalovirus, Sendai virus, and a tumor model. This simple generic approach to multiepitope delivery should find application in CTL-based vaccine design.

Production and characterisation of ovine GM-CSF expressed in mammalian and bacterial cells

A cDNA encoding ovine granulocyte-macrophage colony-stimulating factor (GM-CSF) was isolated and two forms of recombinant ovine GM-CSF were produced. A glycosylated form was produced in mammalian cells infected with a recombinant vaccinia virus encoding ovine GM-CSF. Recombinant ovine GM-CSF was also produced in Escherichia coli and purified by affinity chromatography. Both forms of the protein were detected by ovine GM-CSF-specific monoclonal antibodies, and exhibited activity on ovine bone marrow haemopoetic progenitor cells.

Induction of rotavirus-specific cytotoxic T lymphocytes by vaccinia virus recombinants expressing individual rotavirus genes

We determined the capacity of vaccinia virus recombinants expressing individual rotavirus genes to induce virus-specific cytotoxic T lymphocytes (CTLs) in mice. Mice were orally inoculated with vaccinia virus recombinants containing genes which encode rotavirus outer capsid proteins vp4 or vp7, single-shelled virus proteins vp1, vp2, or vp6, or rotavirus nonstructural proteins NS53, NS35, NS28, or NS26/NS12. We found that (i) the greatest frequencies of virus-specific CTLs were induced by vaccinia virus recombinants expressing vp7, (ii) transport of vp7 beyond the endoplasmic reticulum was not necessary for induction of CTLs, (iii) recombinants expressing vp7 induced CTLs which reacted with different rotavirus serotypes, and (iv) CTLs were induced among both intestinal and nonintestinal lymphocytes after oral inoculation. These findings may be relevant to vaccine strategies which utilize vectors expressing individual rotavirus genes.

Rotavirus VP6 modified for expression on the plasma membrane forms arrays and exhibits enhanced immunogenicity

The major inner capsid protein of rotavirus is VP6, a 42-kDa polypeptide that forms the icosahedral surface of the rotavirus single-shelled particle. A chimeric form of VP6 (VP6sc) was constructed containing an upstream leader sequence derived from the influenza virus hemagglutinin and a downstream membrane-spanning (anchor) domain from a mouse immunoglobulin gene. When VP6sc was expressed in cells using a recombinant vaccinia virus, the protein was transported, glycosylated, and anchored in the plasma membrane as a trimer with the major domains of the protein orientated externally. Immunofluorescence and immunolabeling with colloidal gold indicated that VP6sc also localized in patches on the cell surface; electron microscopy revealed that the protein assembled into two-dimensional arrays which exhibited the same periodicity as the paracrystalline arrays formed by purified (viral) VP6. Mice inoculated with a recombinant vaccinia virus that expressed VP6sc produced rotavirus-specific antibodies at a titer 10 times higher than that achieved when wild-type, intracellular VP6 was delivered in the same way. Presentation at the cell surface therefore may represent a general method for enhancing the immunogenicity of rotavirus proteins.

Biological effects of recombinant vaccinia virus-expressed interleukin 4

Recombinant vaccinia viruses expressing murine interleukin 4 (IL-4), either alone or together with interleukin 2 (IL-2) or gamma interferon (gamma-IFN), were constructed. Unlike IL-2, IL-4 expressing viruses were not cleared from immunodeficient mice and the mice died. As they died more rapidly than immunodeficient mice inoculated with a control virus, it appeared that IL-4 contributed to their death and the IL-4 mediated toxicity was confirmed in normal immunocompetent mice. The toxicity was reversed by co-expression of either IL-2 or gamma-IFN, probably due to virus clearance and therefore lower levels of circulating IL-4. Vaccinia virus-expressed IL-4 did not increase antibody or natural killer cell levels and caused a slight decrease in cytotoxic T lymphocyte levels.

Relocation of antigens to the cell surface membrane can enhance immune stimulation and protection

The major outer capsid glycoprotein of rotaviruses, VP7, is normally synthesized and directed to the ER, where it is required for virus assembly. By substituting a foreign signal sequence for the VP7 signal peptide, a secreted form of VP7 with an authentic amino terminus was produced. Secreted VP7 was further modified by the addition of a transmembrane anchor and cytoplasmic domain to its C-terminus. When the novel chimeric protein was expressed in transfected cells it became anchored in the cell surface membrane. The antigenicity of the chimeric protein was compared with that of the intracellular form of VP7 using recombinant vaccinia viruses to deliver the antigens in vivo. The novel antigen produced enhanced stimulation of both B and T lymphocytes of the immune system, and in mice it was able to induce protection against rotavirus-induced diarrhoeal disease. Other secreted and intracellular antigens show a similar improved level of antigenicity as a result of their relocation to the cell surface. Surface localization may therefore have general utility in the development of recombinant subunit vaccines.

Vaccinia-rotavirus VP7 recombinants protect mice against rotavirus-induced diarrhoea

Recombinant vaccinia viruses expressing wild type intracellular VP7 (VP7wt) from rotavirus SA11 or VP7sc, a cell surface-anchored variant, boosted antibody titres in SA11-immune mice. Pups born to these mice were protected from diarrhoea following challenge with SA11. In rotavirus-naive mice, two immunizations with recombinant vaccinia virus expressing VP7sc stimulated protective immunity that could be transferred to pups, whereas viruses expressing VP7wt did not stimulate protective immunity. Recombinant vaccinia viruses expressing intracellular or cell surface-anchored VP6, the rotavirus group-reactive antigen from the inner capsid, did not stimulate protective immunity. These experiments demonstrate that a live viral vector expressing cell surface anchored VP7 may represent a strategy for the development of safe, effective vaccines against rotavirus-induced diarrhoea.

Effects of vaccinia virus-expressed interleukin 2 on the immune system of sublethally irradiated mice

Vaccinia virus that expressed interleukin 2 (IL 2) was cleared from immunodeficient irradiated mice more efficiently than virus that did not express interleukin 2. These results extend the previously observed protection from nude mice to another model of immunodeficiency. No antibody or cytotoxic T lymphocyte response could be detected in sublethally irradiated mice that had been inoculated with IL 2-expressing vaccinia virus, but levels of splenic natural killer cell activity were elevated. Sublethally irradiated mice that had recovered from IL 2-plus hemagglutinin-expressing vaccinia virus were partially protected against both influenza virus and vaccinia virus. These results indicate that vaccinia virus-expressed IL 2 mediates clearance of primary viral infection via a mechanism that does not involve antibody or cytotoxic T lymphocytes. They also indicate that inclusion of lymphokine genes in live recombinant viral vaccine vectors may increase vaccine safety.

A bluetongue serogroup-reactive epitope in the amino terminal half of the major core protein VP7 is accessible on the surface of bluetongue virus particles

Immunoelectron microscopy has been used to confirm that the core protein VP7 is accessible on the surface of bluetongue virus (BTV) particles. Monospecific antibodies generated to vaccinia virus-expressed VP7 and an anti-VP7 monoclonal antibody (MAb 20E9) bound to native virus particles and were localized by protein A-gold. In contrast, MAb 20E9 labeled directly with gold failed to gain access and bind, suggesting that VP7 is neither adventitiously adsorbed to the virion surface nor exposed in a manner such as protrusion through the outer capsid. Thus the surface layer of BTV may be considered as a net which only partially obscures the underlying core particle. Sequencing of VP7 revealed it to be an extremely hydrophobic protein, 350 amino acids in length with cysteine residues at positions 15, 65, and 154. Examination of VP7 in the cytosol of cells infected with either BTV or a vaccinia virus recombinant expressing VP7 indicated that the protein may exist as an oligomer, whose constituent monomers are not linked by intermolecular disulfide bonds. The cysteine residues in sodium dodecyl sulfate (SDS)-denatured, dithiothreitol (DTT)-treated VP7 were labeled with the fluorescent iodoacetamide AEDANS and the protein was cleaved by V8 protease. The size of the labeled peptides and knowledge of the location of potential V8 cleavage sites suggested that the enzyme cleaved VP7 at three locations (glutamic acid residues at positions 61, 104 (or 108), and 132 (or 134 or 135). Analysis of the fluorescent peptides generated by V8 protease cleavage of VP7 labeled with AEDANS in the absence of DTT (i.e., with any putative intramolecular disulfide bonds intact) suggested that the cysteine at position 154 was the only one accessible to AEDANS. The cysteines at positions 15 and 65 may therefore be linked via a disulfide bond. Denaturation of VP7 with SDS did not eliminate the capacity of the protein to bind MAb 20E9. However, the sensitivity of the epitope to reduction and acetylation and its resistance to either of these processes alone suggest that it may be located near a disulfide bond linking cysteines at positions 15 and 65. Confirmation that the epitope lay in the amino-terminal half of the VP7 came from immunoelectron microscopy experiments in which thin sections of bacteria expressing the complete VP7 and the amino-terminal half were probed with MAb 20E9 and protein A-gold.

Restriction endonuclease mapping of the fowlpox virus genome

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

Vaccinia virus expression and sequence of an avian influenza nucleoprotein gene: potential use in diagnosis

The nucleoprotein (NP) gene from avian influenza strain A/Shearwater/Aust/1/72 (H6N5) was cloned, sequenced, and expressed in vaccinia virus for the production of potent sera in immunised rabbits. The NP gene is 1565 bp and shares greater than 95% amino acid sequence identity with other NPs of the avian subtype. The recombinant NP expressed by vaccinia virus comigrated with endogenous A/Shearwater/Aust/1/72 NP by Western blot analysis. Polyclonal rabbit sera raised against recombinant NP was evaluated in an antigen capture ELISA system as a potential diagnostic tool for the detection of avian influenza. All type A strains, comprising several HA and NA subtypes, but not type B nor other avian viruses, were detected.

Elevated natural killer cell responses in mice infected with recombinant vaccinia virus encoding murine IL-2

The role of cytotoxic T cells and NK cells in the recovery of immunodeficient, athymic, nude mice infected with a recombinant vaccinia virus (VV) encoding murine IL-2 was investigated. Kinetic studies with the IL-2-encoding recombinant (VV-HA-IL2) and control (VV-HA-TK) viruses excluded a role for cytotoxic T cells but suggested the possible involvement of NK cells. In athymic nude mice given VV-HA-IL2, NK activity was at least threefold higher than mice infected with VV-HA-TK and this activity persisted for at least 6 days after infection. The effectors mediating the NK-like activity were asialo-GM1+ (as-GM1+), Thy1.2+/-, CD4- and CD8-, the phenotype of conventional NK cells. Elevated NK activity coincided with the rapid clearance of VV-HA-IL2 from ovaries of infected normal CBA/H mice but not from ovaries of CBA beige mice which had no detectable NK activity in spleens or ovaries. The expression of IL-2 in recombinant VV infection probably induces a cascade of immunologic effects of which elevated NK activity is one. We speculate that the chemoattractant and NK activity augmenting effects of IL-2 may contribute to recovery from VV-infection.

Elevated natural killer cell responses in mice infected with recombinant vaccinia virus encoding murine IL-2

The role of cytotoxic T cells and NK cells in the recovery of immunodeficient, athymic, nude mice infected with a recombinant vaccinia virus (VV) encoding murine IL-2 was investigated. Kinetic studies with the IL-2-encoding recombinant (VV-HA-IL2) and control (VV-HA-TK) viruses excluded a role for cytotoxic T cells but suggested the possible involvement of NK cells. In athymic nude mice given VV-HA-IL2, NK activity was at least threefold higher than mice infected with VV-HA-TK and this activity persisted for at least 6 days after infection. The effectors mediating the NK-like activity were asialo-GM1+ (as-GM1+), Thy1.2+/-, CD4- and CD8-, the phenotype of conventional NK cells. Elevated NK activity coincided with the rapid clearance of VV-HA-IL2 from ovaries of infected normal CBA/H mice but not from ovaries of CBA beige mice which had no detectable NK activity in spleens or ovaries. The expression of IL-2 in recombinant VV infection probably induces a cascade of immunologic effects of which elevated NK activity is one. We speculate that the chemoattractant and NK activity augmenting effects of IL-2 may contribute to recovery from VV-infection.

Humoral and cell-mediated immune responses to recombinant vaccinia viruses in mice

Intravenous (i.v.) immunization of mice with recombinant vaccinia viruses stimulated the highest antibody and cytotoxic T lymphocyte (CTL) responses when i.v., intraperitoneal (i.p.), intranasal (i.n.), footpad (f.p.) and tail scarification (t.s.) routes were compared. Intraperitoneal immunization of mice resulted in high CTL activity, but low antibody responses. Antibody levels after i.n., f.p., and t.s. immunization were slightly lower than following i.v. immunization. Although very low levels of CTL primary activity were stimulated by i.n. or f.p. inoculation of recombinant vaccinia virus, levels of secondary CTL activity after in vitro restimulation of splenocytes were as high as those seen from i.v. immunized splenocytes. The effect of the thymidine kinase (TK) phenotype of the virus also was examined. Wildtype (TK positive) viruses replicated to a higher titre in vivo and stimulated higher antibody and CTL responses than a TK negative recombinant virus. A recombinant virus that expressed the TK gene from herpes simplex virus at a low level was intermediate between wildtype and TK negative virus, both in virus replication in vivo and in immunogenicity.

Vaccinia-interleukin 2 recombinant virus or exogenous interleukin 2 does not alter the magnitude or immune response gene defects of the cytotoxic T-cell response to vaccinia virus in vivo

We investigated the role of interleukin 2 (IL-2), a T cell-derived lymphokine, in the generation of in vivo cytotoxic T-cell responses to vaccinia virus. We made use of a recombinant vaccinia virus encoding and expressing the murine IL-2 gene and recombinant IL-2 to test the role of IL-2 in the expression of major histocompatibility complex (MHC) class I determined immune response (Ir) gene defects in the response to vaccinia virus. IL-2 expressed either by the vaccinia virus vector or exogenous IL-2 does not alter Ir gene defects nor does IL-2 under such conditions elevate the cytotoxic T-cell response in general.

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

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

Efficacy of influenza haemagglutinin and nucleoprotein as protective antigens against influenza virus infection in mice

Influenza nucleoprotein (NP)-specific cytotoxic T lymphocytes (CTL) stimulated by immunization of mice with VV-PR8-NP6, a recombinant vaccinia virus expressing A/PR/8/34 NP, did not protect mice against challenge with A/PR/8/34 4 days later. Neither were secondary NP-specific CTL stimulated by reimmunization able to protect mice. These results contrast with the ability of transferred, in vitro-cultured and stimulated, NP-specific CTL to protect recipient mice from challenge with A/PR/8/34. Immunization of mice with a recombinant vaccinia virus expressing A/PR/8/34 HA protected mice challenged 4 days later, either via the small amount of antibody already present, or via HA-specific CTL that would have to be more efficient than NP-specific CTL in either trafficking to the infected lung or in effector function.

Construction of recombinant fowlpox viruses as vectors for poultry vaccines

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

A dominant selectable marker for the construction of recombinant poxviruses

Mycophenolic acid has been shown to be a potent inhibitor of vaccinia virus growth. By inserting the Escherichia coli xanthine-guanine phosphoribosyl transferase gene (gpt) into the vaccinia virus genome under control of the P-7.5 promoter this inhibition was overcome. When coupled in tandem with another gene of interest, recombinant vaccinia viruses can be positively selected carrying both genes. Since the gpt gene operates as a selectable marker in most mammalian cells it will be useful as a dominant selectable marker for the construction of recombinant viruses based on other host-specific poxviruses.

Recovery of immunodeficient mice from a vaccinia virus/IL-2 recombinant infection

Vaccinia virus recombinants that express cloned genes encoding antigens of unrelated infectious agents, such as hepatitis B virus and human immunodeficiency virus (HIV), provide a new approach to the development of live vaccines. Although there is evidence that genetically engineered vaccinia viruses have reduced pathogenicity a major obstacle to their use as vaccines is that severe complications can occur after vaccination, especially in immunodeficient individuals. We describe here a recombinant vaccinia virus expressing murine interleukin-2 (IL-2) and show that athymic nude mice infected with the recombinant virus resolve the virus infection rapidly whereas mice infected with control virus develop a progressive vaccinal disease. By incorporating the gene for IL-2 in live virus vaccines it may be possible to prevent the severe complications that arise in recipients with an impaired immune system.

Recognition by major histocompatibility complex class I-restricted cytolytic T lymphocytes of cells expressing vaccinia-encoded viral and class I proteins

Target cells expressing influenza virus hemagglutinin (HA) could be recognized by cytotoxic T lymphocytes (CTL) in conjunction with the murine major histocompatibility complex class I antigen, H-2Kd, when both antigens were encoded by recombinant vaccinia virus. This recognition occurred if HA and H-2Kd were encoded by separate vaccinia viruses following dual infection of target cells or if HA and H-2Kd were encoded by a single recombinant virus. In contrast, target cells expressing nucleoprotein (NP) were only recognized by H-2Kd-restricted CTL if both NP and H-2Kd were encoded by the same vaccinia virus. These results show that the requirements for association of H-2Kd with different viral antigens derived from HA or NP can vary. Possible factors contributing to this difference are discussed.

Effect of in vitro mutations in a vaccinia virus early promoter region monitored by herpes simplex virus thymidine kinase expression in recombinant vaccinia virus

The location of a promoter (PF) in the HindIII F region of the vaccinia virus genome was mapped by introducing deletions into this region of the DNA. Modified promoters were fused to the herpes simplex virus (HSV) thymidine kinase (TK) gene in plasmids facilitating the construction of recombinant vaccinia viruses, and promoter function was monitored by the ability of such plasmids to rescue TK+ vaccinia viruses from cells infected with TK- virus. Deletions from the 3' end of the promoter region produced mutants for which function was either not inhibited or abolished, allowing the 3' promoter boundary to be defined to within 13 nucleotides. As indicated by the presence of the PF transcript in early RNA and the kinetics of HSV TK expression in recombinant vaccinia viruses, transcription from PF occurred primarily at early times during infection. The major transcript was initiated at a site within 20 nucleotides of the 3' end of the promoter and nine bases upstream of the probable translation initiation codon. In one mutant for which a small but reproducible increase in promoter function was detected, the transcription start site was deleted. Nevertheless, transcription still appeared to begin at the equivalent position with respect to the promoter, despite the altered nucleotide sequence. The location of the start site for the PF transcript indicated that the HSV TK gene, inserted at the BamHI site following the promoter, was preceded by an initiation codon which could potentially attenuate expression of the inserted gene. Conversion of this ATG codon to TAG did not significantly improve HSV TK expression.

Vaccinia virus recombinants expressing the SA11 rotavirus VP7 glycoprotein gene induce serotype-specific neutralizing antibodies

A cDNA copy of the gene coding for the major outer neutralizing protein (VP7) of simian 11 rotavirus was incorporated into the vaccinia virus genome under the control of the vaccinia promoter (molecular weight, 7,500). A deletion mutant of this gene which codes for a secreted form of VP7 when expressed under the control of the simian virus 40 late promoter (M. S. Poruschynsky, C. Tyndall, G. W. Both, F. Sato, A. R. Bellamy, and P. H. Atkinson, J. Cell Biol. 101:2199-2209, 1985) was also inserted. Each recombinant vaccinia virus directed the synthesis of a rotavirus protein in infected cells, and the product encoded by the mutated gene was secreted. Rabbits immunized with the two types of recombinant vaccinia virus generated antibodies that were able both to recognize simian 11 rotavirus in an enzyme-linked immunosorbent assay and to neutralize the virus in a plaque-reduction test. Antibodies induced by the recombinant vaccinia viruses expressing either form of VP7 were serotype specific.

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

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

The roles of influenza virus haemagglutinin and nucleoprotein in protection: analysis using vaccinia virus recombinants

Vaccinia virus recombinants expressing haemagglutinin (HA) or nucleoprotein (NP) from influenza virus A/PR/8/34 were used to investigate protective immunity in mice, with two protocols. Protection was assessed by mortality and morbidity rates and by lung virus titres after infection intranasally with A/PR/8/34. In the first protocol, mice immunized with vaccinia-HA recombinant virus and infected intranasally with A/PR/8/34 were almost totally protected, but mice immunized with vaccinia-NP virus were very poorly protected. In the second protocol, the recombinant viruses were used to stimulate in vitro T cells that are specific for HA and NP; both populations of T cells, when transferred to A/PR/8/34-infected mice, afforded good protection. The results indicate that an immune response specific for just HA provided protection that was almost indistinguishable from that provided by whole A/PR/8/34. On the other hand, immunization with vaccinia-NP provided poor protective immunity, despite the fact that transferred NP-specific T cells were very effective and vaccinia-NP immunization has previously been shown to stimulate cytotoxic T cells. These results demonstrate that a single viral antigen, delivered by live vaccinia virus, can provide effective protection, but that immunization for cross-protection against heterologous influenza virus remains elusive.

Temporal regulation of influenza hemagglutinin expression in vaccinia virus recombinants and effects on the immune response

Regulation of the expression of influenza A/PR/8/34 hemagglutinin (HA) by the vaccinia virus promoters PF (early), P7.5 (early and late) and PL11 (late) has been demonstrated using HA-vaccinia recombinant viruses VV-PR8-HA3, VV-PR8-HA6 and VV-PR8-HA, respectively. Levels of HA on the surface of VV-PR8-HA3 (PF)-infected cells were lower than with either VV-PR8-HA6 (P7.5) or VV-PR8-HA8 (PL11). Expression of HA under the control of the late promoter PL11 was inhibited in the absence of DNA replication. All three recombinant viruses stimulated a specific antibody response in mice which was dependent on the presence of infectious virus. Recognition of HA by cytotoxic T lymphocytes (CTL) was assessed by the ability of the viruses to stimulate naive precursors in vivo, to restimulate primed CTL in vitro and by target cell recognition. HA expressed under the control of either of the promoters with early function (PF or P7.5) was recognized by CTL when VV-PR8-HA3 or VV-PR8-HA6 were used to prime or restimulate splenocytes or to infect target cells. On the other hand, HA expressed by VV-PR8-HA8 (PL11) failed to prime for a CTL response in naive CBA/H mice, was ineffective at restimulation of primed splenocytes and failed to produce target cells for recognition by specific CTL. However, in BALB/c mice VV-PR8-HA8 did prime for a specific CTL response. These studies show that HA synthesized early in infection was recognized by both B and T cells while HA expressed after DNA replication was not generally recognized by T cells. The implications of the observations with the late promoter with respect to the use of late promoters in potential vaccinia virus-based vaccines are considered.

Cell-mediated immune responses to influenza virus antigens expressed by vaccinia virus recombinants

Recombinant vaccinia viruses enable studies of immune recognition of antigens expressed from single viral genes. We have constructed recombinants expressing the haemagglutinin (HA) and nucleoprotein (NP) genes of the influenza virus A/PR/8/34 (H1N1). These recombinant viruses together with a recombinant expressing the HA from influenza virus A/JAP/305/57 (H2N2) have been used to examine the cytotoxic T lymphocyte (CTL) response to these influenza virus antigens. Both antigens are recognised by murine CTL and recognition of HA is influenza virus subtype-specific, whereas recognition of NP is crossreactive. In limiting dilution studies approximately 10% of the influenza CTL response is HA-specific, while approximately 30% of the response is NP-specific. Despite the ability of NP to stimulate a significant CTL response, mice immunised with the NP-vaccinia recombinant are not as well protected from subsequent lethal challenge with influenza virus, as mice immunised with the HA vaccinia recombinant. These studies demonstrate that viral antigens expressed from vaccine recombinants can provide protective immunity and that the influenza-poxvirus recombinants can provide data on protective immunity generated by individual viral proteins.

Immune responses to H-2Kd antigen expressed by recombinant vaccinia virus

A recombinant vaccinia virus (VV-H2Kd-6) containing the coding sequence for the murine major histocompatibility complex class I antigen H-2Kd has been constructed and used to express H-2Kd on the surface of infected cells. Vaccinia expressed H-2Kd has been shown to generate an H-2Kd-specific primary cytotoxic T-cell response in mice infected with the recombinant virus and to stimulate an H-2Kd-specific cytotoxic T-cell response in vitro. Cells infected with the recombinant virus acted as targets for specific lysis by appropriate alloreactive cytotoxic T cells, albeit relatively inefficiently when compared with alloreactive recognition and specific lysis of H-2Kd-containing P815 cells. However, H-2Kd expressed by the recombinant virus was recognized efficiently as a restricting element in association with vaccinia virus antigens, while lysis of VV-H2Kd-6-infected L929 (H-2k) cells by CBA/H (H-2k) anti-C3H.OH (H-2KdDk) cytotoxic T cells was comparatively weak. These data suggest that there are quantitative or qualitative differences, or both, between H-2Kd expressed by vaccinia virus and cells of the H-2d haplotype. Qualitative differences have not been demonstrated but cannot be excluded.

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

Using vaccinia virus as a selection and cloning vehicle, a thymidine kinase (TK) gene of fowlpox virus (FPV) has been identified. A plasmid, pF130, containing part of the HindIII-F region of vaccinia virus was used to shotgun clone EcoRI fragments of FPV DNA into TK- vaccinia virus and select for TK+ recombinants. The TK+ recombinant vaccinia virus contained a 5.5 kb EcoRI fragment of FPV. This FPV fragment was cloned into pUC9 and the presence of the TK gene in this fragment was confirmed by its ability to rescue TK+ vaccinia virus from TK- virus, when inserted into pF130. A recombinant vaccinia virus containing this FPV fragment induced TK enzyme activity in the cytoplasm of infected cells. The vaccinia virus RNA polymerase appeared able to recognize the FPV promoter sequences of the FPV TK gene since the fragment operated in the marker rescue, irrespective of its orientation to the vaccinia virus promoter in pF130. Using restriction enzyme analysis, insertion of subfragments of the 5.5 kb FPV fragment into pF130 and marker rescue, we were able to map the position of the TK gene in the 5.5 kb EcoRI fragment. This approach may facilitate identification and cloning of TK genes from other poxviruses.

Responses of cattle, sheep and poultry to a recombinant vaccinia virus expressing a swine influenza haemagglutinin

Groups of cattle, sheep and poultry were inoculated with a recombinant vaccinia virus expressing the haemagglutinin of the swine influenza virus A/NJ/11/76. No adverse clinical responses were recorded and none of the animals developed a viraemia when inoculated with the recombinant or wild-type vaccinia virus. Recombinant virus reisolated from lesions in cattle was stable, maintaining its thymidine kinase negative phenotype and ability to express the swine influenza haemagglutinin. Antibodies to the influenza haemagglutinin were detected in cattle, sheep and poultry inoculated with the recombinant virus. While no animals inoculated with wild-type virus developed these antibodies, there was no detectable spread of either recombinant or wild-type virus from the inoculation sites or to in-contact uninoculated animals. The results indicate that recombinant vaccinia viruses can induce immune responses in cattle, sheep and poultry demonstrating their potential as vaccine vectors in a variety of important veterinary species.

Multiple-cloning-site plasmids for the rapid construction of recombinant poxviruses

Plasmid vectors containing multiple cloning sites suitable for the rapid insertion of protein-coding sequences into poxviruses have been constructed. They are based on pUC plasmids and carry the thymidine kinase (TK) gene of vaccinia virus interrupted by a vaccinia virus promoter. Six unique restriction enzyme sites (BamHI, SalI/HincII, PstI, HindIII, EcoRI), located within 40 bp of vaccinia virus promoters transposed from the HindIII-F or HindIII-C fragment of the vaccinia virus genome, allow rapid insertion of foreign-protein-coding sequences into these plasmids. Such plasmids can be used to construct recombinant poxviruses expressing foreign proteins using marker-rescue recombination techniques and selection for TK negative viruses. Vaccinia viruses expressing the haemagglutinin (HA) gene of swine influenza virus, A/NJ/11/76 (H1N1), have been constructed.