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

Oncolytic tanapoxvirus expressing FliC causes regression of human colorectal cancer xenografts in nude mice

Colorectal cancers are significant causes of morbidity and mortality and existing therapies often perform poorly for individuals afflicted with advanced disease. Oncolytic virotherapy is an emerging therapeutic modality with great promise for addressing this medical need. Herein we describe the in vivo testing of recombinant variants of the tanapoxvirus (TPV). Recombinant viruses were made ablated for either the 66R gene (encoding a thymidine kinase), the 2L gene (encoding a TNF-binding protein), or both. Some of the recombinants were armed to express mouse chemotactic protein 1 (mCCL2/mMCP-1), mouse granulocyte-monocyte colony stimulating factor (mGM-CSF), or bacterial flagellin (FliC). Tumors were induced in athymic nude mice by implantation of HCT 116 cells and subsequently treated by a single intratumoral injection of one of the recombinant TPVs. Histological examination showed a common neoplastic cell type and a range of immune cell infiltration, necrosis, and tumor cell organization. Significant regression was seen in tumors treated with virus TPV/Δ2L/Δ66R/fliC, and to a lesser extent the recombinants TPV/Δ2L and TPV/Δ66R. Our results suggest that oncolytic recombinants of the TPV armed with activators of the innate immune response may be effective virotherapeutic agents for colorectal cancers in humans and should be explored further to fully realize their potential.

MBT/Pas mouse: a relevant model for the evaluation of Rift Valley fever vaccines

Currently, there are no worldwide licensed vaccines for Rift Valley fever (RVF) that are both safe and effective. Development and evaluation of vaccines, diagnostics and treatments depend on the availability of appropriate animal models. Animal models are also necessary to understand the basic pathobiology of infection. Here, we report the use of an inbred MBT/Pas mouse model that consistently reproduces RVF disease and serves our purpose for testing the efficacy of vaccine candidates; an attenuated Rift Valley fever virus (RVFV) and a recombinant RVFV–capripoxvirus. We show that this model is relevant for vaccine testing.

A comparative analysis of HIV-specific mucosal/systemic T cell immunity and avidity following rDNA/rFPV and poxvirus-poxvirus prime boost immunisations

In this study we have firstly compared a range of recombinant DNA poxvirus prime-boost immunisation strategies and shown that combined intramuscular (i.m.) 2× DNA-HIV/intranasal (i.n.) 2× FPV-HIV prime-boost immunisation can generate high-level of HIV-specific systemic (spleen) and mucosal (genito-rectal nodes, vaginal tissues and lung tissues) T cell responses and HIV-1 p24 Gag-specific serum IgG1, IgG2a and mucosal IgG, SIgA responses in vaginal secretions in BALB/c mice. Data indicate that following rDNA priming, two rFPV booster immunisations were necessary to generate good antibody and mucosal T cell immunity. This data also revealed that mucosal uptake of recombinant fowl pox (rFPV) was far superior to plasmid DNA. To further evaluate CD8+ T cell immunity, i.m. 2× DNA-HIV/i.n. 1× FPV-HIV immunisation strategy was directly compared with single shot poxvirus/poxvirus, i.n. FPV-HIV/i.m. VV-HIV immunisation. Results indicate that the latter strategy was able to generate strong sustained HIV-specific CD8+ T cells with higher avidity, broader cytokine/chemokine profiles and better protection following influenza-K(d)Gag(197-205) challenge compared to rDNA poxvirus prime-boost strategy. Our findings further substantiate the importance of vector selection/combination, order and route of delivery when designing effective vaccines for HIV-1.

Evaluating vaccinia virus cytokine co-expression in TLR GKO mice

Using Toll-like receptor (TLR) and MyD88 gene knock-out (GKO) mice the effect of TLRs and MyD88 on virus replication, interferon (IFN)-β production, natural killer (NK) cell and CD8T cell responses were assessed following ectromelia virus (ECTV) and recombinant vaccinia virus (rVV) infection. The capacity for rVVs encoding cytokines to restore immune function in MyD88(-/-) mice was clearly demonstrated. Results showed that TLR2(-/-), TLR4(-/-)and TLR7(-/-) mice survived ECTV infection whereas MyD88(-/-) and TLR9(-/-)mice, in contrast, were highly susceptible. Next, following infection with rVV, MyD88(-/-) mice elicited reduced serum IFN-β, NK cell and CD8T cell responses compared with wild-type mice, whereas TLR9(-/-) mice showed elevated CD8T cell responses. When MyD88(-/-)mice were infected with rVV co-expressing IFN-β these mice were able to restore IFN-β levels and CD8T cell responses but not NK cell activation. Interestingly, even though rVV co-expressing interleukin (IL)-2 enhanced NK cell activation in MyD88(-/-) mice, this was not associated with an antiviral effect, as observed in normal mice. Surprisingly, co-infection with rVV IL-2/rVV IL-12, but not rVV IL-2/rVV IFN-β, restored the attenuated phenotype of rVV IL-2 in MyD88(-/-) mice indicating that the IL-2/IL-12 combination promotes antiviral responses. Our results clearly show that the CD8T cell defect observed in MyD88(-/-) mice to vaccinia virus infection can be restored by rVV-encoding IFN-β demonstrating the critical role of this cytokine in T cell mediated immunity and illustrates that the model can provide an effective platform for the elucidation of cytokine immunobiology.

Differential effects of the type I interferons alpha4, beta, and epsilon on antiviral activity and vaccine efficacy

The type I IFNs exert a range of activities that include antiviral, antiproliferative, and immunomodulatory effects. To study this further, we have constructed recombinant vaccinia viruses expressing HIV or hemagglutinin (HA) Ags along with murine type I IFNs, IFN-alpha(4) (HA-VV-IFN-alpha(4)), IFN-beta (HA-VV-IFN-beta), or IFN-epsilon (HIV-VV-IFN-epsilon), a recently discovered member of this family. Our aims were to characterize IFN-epsilon functionality as a type I IFN and also to study the biological properties of these factors toward the development of safer and more effective vector-based vaccines. HIV-VV-IFN-epsilon and HA-VV-IFN-beta grew to lower titers than did their parental controls in murine cell lines. In vivo, however, HIV-VV-IFN-epsilon growth was not attenuated, while IFN-beta demonstrated potent local antiviral activity with no replication of HA-VV-IFN-beta detected. Flow cytofluorometric analysis of B lymphocytes incubated with virally encoded IFN-epsilon showed up-regulation of activation markers CD69 and CD86, while RT-PCR of IFN-epsilon-treated cells revealed that gene expression levels of antiviral proteins were elevated, indicating the induction of an antiviral state. The use of these constructs in a poxvirus prime-boost immunization regime led to robust humoral and cellular immune responses against the encoded Ags, despite the lack of replication in the case of HA-VV-IFN-beta. Thus, coexpression of these factors may be beneficial in the design of safer vector-based vaccines. Our data also indicate that while IFN-epsilon exhibits certain biological traits similar to other type I IFNs, it may also have a specific role in mucosal immune regulation that is quite distinct.

Recombinant capripoxviruses expressing proteins of bluetongue virus: evaluation of immune responses and protection in small ruminants

The development of recombinant capripoxviruses for protective immunization of ruminants against bluetongue virus (BTV) infection is described. Sheep (n=11) and goats (n=4) were immunized with BTV recombinant capripoxviruses (BTV-Cpox) individually expressing four different genes encoding two capsid proteins (VP2 and VP7) and two non-structural proteins (NS1, NS3) of BTV serotype 2 (BTV-2). Seroconversion was observed against NS3, VP7 and VP2 in both species and a lymphoproliferation specific to BTV antigens was also demonstrated in goats. Finally, partial protection of sheep challenged 3 weeks after BTV-Cpox administration with a virulent strain of BTV-2, was observed.

Mucosal HIV-1 Pox Virus Prime-Boost Immunization Induces High-Avidity CD8+ T Cells with Regime-Dependent Cytokine/Granzyme B Profiles

The quality of virus-specific CD8(+) CTL immune responses generated by mucosal and systemic poxvirus prime-boost vaccines were evaluated in terms of T cell avidity and single-cell analysis of effector gene expression. Intranasal (I.N.) immunization regimes generated higher avidity CTL responses specific for HIV K(d)Gag(197-205) (amino acid sequence AMQMLKETI; H-2K(d) binding) compared with i.m. immunization regime. Single-cell RT-PCR of K(d)Gag(197-205)-specific mucosal and systemic CTL revealed that the cytokine and granzyme B expression profiles were dependent on both the route and time after immunization. The I.N./i.m.-immunized group elicited elevated number of CTL-expressing granzyme B mRNA from the genitomucosal sites compared with the i.m./i.m. regime. Interestingly, CTL generated after both I.N. or i.m. immunization demonstrated expression of Th2 cytokine IL-4 mRNA that was constitutively expressed over time, although lower numbers were observed after I.N./I.N. immunization. Results suggest that after immunization, Ag-specific CTL expression of IL-4 may be an inherent property of the highly evolved poxvirus vectors. Current observations indicate that the quality of CTL immunity generated after immunization can be influenced by the inherent property of vaccine vectors and route of vaccine delivery. A greater understanding of these factors will be crucial for the development of effective vaccines in the future.

4-1BBL coexpression enhances HIV-specific CD8 T cell memory in a poxvirus prime-boost vaccine

We have constructed a recombinant fowlpox virus expressing HIV antigens and the costimulatory molecule 4-1BBL. When included in the boost, but not the prime of a poxvirus prime-boost strategy, 4-1BBL significantly enhanced the anti-HIV T cell response generated to this vaccination in BALB/c mice, as detected by ex vivo IFNgamma ELISPOT responses, intracellular cytokine staining to HIV Gag antigens, and enumeration of Gag-reactive CD8 T cells. 4-1BBL however, is not capable of modulating the CD4 T cell response, nor the antibody response to this vaccination strategy. Enhancement of the T cell response by 4-1BBL continues into the memory phase, as detected 2 months post vaccination. This data is the first to show modulation of the immune response to a viral vaccine by coexpression of 4-1BBL and supports this strategy as an exciting approach for enhancement of T cell memory in prime-boost vaccines.

Evaluation of fowlpox–vaccinia virus prime-boost vaccine strategies for high-level mucosal and systemic immunity against HIV-1

We have tested the efficacy of recombinant fowl pox (rFPV) and recombinant vaccinia virus (rVV) encoding antigens of AE clade HIV-1 in a prime-boost strategy, using both systemic and mucosal delivery routes. Of the various vaccine routes tested, intranasal/intramuscular (i.n./i.m.) AE FPV/AE VV prime-boosting generated the highest mucosal and systemic T cell responses. Peak mucosal T cell responses occurred as early as 3 days post-boost vaccination. In contrast only low systemic responses were observed at this time with the peak response occurring at day 7. Current data also revealed that, due to better uptake of the rFPV, intranasal viral priming was much more effective than intranasal rDNA priming tested previously. The i.m./i.m. prime-boost delivery also generated strong systemic but poor mucosal responses to Gag peptides. Interestingly, the oral administration of AE FPV followed by i.m. AE VV delivery elicited strong systemic responses to sub-dominant Pol 1 peptides that were absent in mice that received vaccine by other routes. Moreover, priming with AE FPV co-expressing cytokine IL-12 significantly enhanced the T cell responses to target antigens, whilst co-expression of IFNgamma decreased these responses. The results also indicated that the route of inoculation and the vaccine vector combination could radically influence not only the magnitude but also the antigen specificity of the immune response generated. Further, in contrast to the generally protracted HIV rDNA/rFPV multiple delivery prime-boosting, this single rFPV prime and rVV boost approach was more flexible and generated excellent mucosal and systemic immune responses to HIV vaccine antigens.

A recombinant vaccinia virus encoding the interferon-inducible T-cell alpha chemoattractant is attenuated in vivo

Murine interferon-inducible T-cell alpha chemoattractant (I-TAC) is a potent non-ELR CXC chemokine that predominantly attracts activated T lymphocytes, binds to the receptor CXCR3 and is induced by interferon-gamma (IFN-gamma). We analysed I-TAC expression by reverse transcriptase-polymerase chain reaction during three different virus-infection models in mice, respiratory syncytial virus (RSV), influenza A and vaccinia virus western reserve (VV-WR). In the lungs from mice infected with RSV or influenza A viruses, peak expression of I-TAC coincided with peak viraemia. Surprisingly, there was no expression in the lungs of mice infected with vaccinia, unlike the elevated expression shown previously for other interferon-regulated chemokines, such as Crg2 and Mig. To further investigate the importance of this difference during vaccinia infection in mice, a recombinant virus encoding I-TAC (rVV I-TAC) was generated. Studies in C57BL/6 and Swiss nude mice showed that I-TAC expression caused increased mononuclear cell infiltration and significantly attenuated the VV. Infection of the footpads of naïve or already immune (with VV-WR) mice with either rVV I-TAC or VV-WR demonstrated that I-TAC expression reduced overall inflammation during infection and that this reduction was more pronounced in already immune mice. The data presented here show that I-TAC can have an important role during virus infections and that vaccinia has evolved ways to avoid inducing I-TAC expression.

Amino acids 1-20 of the hepatitis C virus (HCV) core protein specifically inhibit HCV IRES-dependent translation in HepG2 cells, and inhibit both HCV IRES- and cap-dependent translation in HuH7 and CV-1 cells

A self-modulating mechanism by the hepatitis C virus (HCV) core protein has been suggested to influence the level of HCV replication, but current data on this subject are contradictory. We examined the effect of wild-type and mutated core protein on HCV IRES- and cap-dependent translation. The wild-type core protein was shown to inhibit both IRES- and cap-dependent translation in an in vitro system. This effect was duplicated in a dose-dependent manner with a synthetic peptide representing amino acids 1-20 of the HCV core protein. This peptide was able to bind to the HCV IRES as shown by a mobility shift assay. In contrast, a peptide derived from the hepatitis B virus (HBV) core protein that contained a similar proportion of basic residues was unable to inhibit translation or bind the HCV IRES. A recombinant vaccinia-HCV core virus was used to examine the effect of the HCV core protein on HCV IRES-dependent translation in cells and this was compared with the effects of an HBV core-recombinant vaccinia virus. In CV-1 and HuH7 cells, the HCV core protein inhibited translation directed by the IRES elements of HCV, encephalomyocarditis virus and classical swine fever virus as well as cap-dependent translation, whereas in HepG2 cells, only HCV IRES-dependent translation was affected. Thus, the ability of the HCV core protein to selectively inhibit HCV IRES-dependent translation is cell-specific. N-terminal truncated (aa 1-20) HCV core protein that was expressed from a novel recombinant vaccinia virus in cells abrogated the inhibitory phenotype of the core protein in vivo, consistent with the above in vitro data.

IL-4 diminishes perforin-mediated and increases Fas ligand-mediated cytotoxicity In vivo

CTL have evolved two major mechanisms for target cell killing: one mediated by perforin/granzyme secretion and the other by Fas/Fas ligand (L) interaction. Although cytokines are integral to the development of naive CTL into cytolytic effectors, the role of cytokines on mechanisms of CTL killing is just emerging. In this study, we evaluate the effects of IL-4 in Fas(CD95)/FasL(CD95L)-mediated killing of Fas-overexpressing target cells. Recombinant vaccinia viruses (vv) were constructed to express respiratory syncytial virus M2 Ag alone (vvM2) or coexpress M2 and IL-4 (vvM2/IL-4). MHC-matched Fas-overexpressing target cells (L1210Fas+) were used to measure both perforin- and FasL-mediated killing pathways. In contrast to Fas-deficient (L1210Fas-) target cells, effectors from vvM2/IL-4-immunized mice were able to lyse L1210Fas+ target cells with similar magnitude as vvM2-infected mice. Addition of EGTA/Mg2+ revealed that effectors from vvM2/IL-4-infected mice primarily lyse targets by a Ca2+-independent Fas/FasL pathway. Analysis of FasL expression by flow cytometry showed that IL-4 increased cell surface FasL expression on CD4+ and CD8+ splenocytes, with peak expression on day 4 after infection. These data demonstrate that IL-4 increases FasL expression on T cells, resulting in a shift of the mechanism of CTL killing from a dominant perforin-mediated cytolytic pathway to a dominant FasL-mediated cytolytic pathway.

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.

Interleukin-4 diminishes CD8(+) respiratory syncytial virus-specific cytotoxic T-lymphocyte activity in vivo

Although interleukin-4 (IL-4) has been implicated in respiratory syncytial virus (RSV)-enhanced disease, the mechanism by which it modulates immune responses to primary RSV infection remains unclear. We have developed a system to investigate the effect of IL-4 on RSV epitope-specific cytotoxic T-lymphocyte (CTL) effector function in vivo, using an H-2K(d)-restricted RSV M2 epitope. BALB/c mice were infected with recombinant vaccinia virus (rVV) constructed to express RSV M2 protein (vvM2) alone or coexpress M2 and IL-4 (vvM2/IL-4). Splenocytes were assessed for M2-specific CTL activity in a direct (51)Cr release assay and intracellular gamma interferon (IFN-gamma) production by fluorescence-activated cell sorting analysis. Mice infected with vvM2/IL-4 had less M2-specific primary CTL activity than those infected with vvM2. M2-specific CTL frequency, as measured by M2 peptide-induced intracellular IFN-gamma production, was diminished in the vvM2/IL-4 group, partially accounting for the reduction of CTL activity. Mice immunized with either construct were challenged intravenously with RSV 4 weeks postimmunization, and direct CTL were measured. These results demonstrate that local expression of IL-4, at the time of antigen presentation, diminishes the cytolytic activity of primary and memory CD8(+) RSV-specific CTL responses in vivo.

The serine proteinase inhibitor (serpin) plasminogen activation inhibitor type 2 protects against viral cytopathic effects by constitutive interferon alpha/beta priming

The serine proteinase inhibitor (serpin) plasminogen activator inhibitor type 2 (PAI-2) is well characterized as an inhibitor of extracellular urokinase-type plasminogen activator. Here we show that intracellular, but not extracellular, PAI-2 protected cells from the rapid cytopathic effects of alphavirus infection. This protection did not appear to be related to an effect on apoptosis but was associated with a PAI-2-mediated induction of constitutive low-level interferon (IFN)-alpha/beta production and IFN-stimulated gene factor 3 (ISGF3) activation, which primed the cells for rapid induction of antiviral genes. This primed phenotype was associated with a rapid development of resistance to infection by the PAI-2 transfected cells and the establishment of a persistent productive infection. PAI-2 was also induced in macrophages in response to viral RNA suggesting that PAI-2 is a virus response gene. These observations, together with the recently demonstrated PAI-2-mediated inhibition of tumor necrosis factor-alpha induced apoptosis, (a) illustrate that PAI-2 has an additional and distinct function as an intracellular regulator of signal transduction pathway(s) and (b) demonstrate a novel activity for a eukaryotic serpin.

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.

Constitutive transduction of peptide transporter and HLA genes restores antigen processing function and cytotoxic T cell-mediated immune recognition of human melanoma cells

Potentiation of immunogenicity of malignant cells by gene transduction provides a unique opportunity for immune targeting of human cancers in vivo. This approach is undoubtedly influenced by the ability of the malignant cells to process and present endogenously target epitopes on their cell surface for immune recognition by cytotoxic T lymphocytes (CTLs). In the present study, we have investigated potential immune-resistance pathways in human malignant melanoma by analyzing the major histocompatibility complex (MHC) gene expression and function in a panel of tumour cell lines. Our analysis showed that a large proportion of these cell lines consistently display a functional defect in the endogenous processing of CTL epitopes and are recognised poorly by specific T cells in spite of high levels of target antigen expression in the tumour cells. Molecular characterisation of this defect revealed that tumour cells under-expressed peptide transporters and surface-assembled MHC class I molecules, which constitute essential components of the class I processing pathway. Induction of peptide transporter and surface class I following treatment of these tumour cells with interferon gamma (IFN-gamma) suggested a transcriptional defect in the expression of antigen-processing genes. Endogenous processing function in these tumour cells was restored completely following simultaneous transduction of cells with peptide transporter and HLA class I genes. Our findings provide a rationale for focussing on strategies designed to improve antigen-processing function in tumour cells and, thus, may strongly influence future strategies for melanoma-specific immunotherapy.

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.

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.

Immunogenicity and protection studies with recombinant mycobacteria and vaccinia vectors coexpressing the 18-kilodalton protein of Mycobacterium leprae

The activation of antigen-specific T lymphocytes is essential for the control of leprosy infection in humans and experimental animals. T cells recognize a variety of protein antigens from Mycobacterium leprae, including the 18-kDa protein, which is limited in distribution among mycobacteria and which is absent from Mycobacterium tuberculosis and the vaccine strain, Mycobacterium bovis BCG. Adjuvant preparations of mycobacterial protein antigens have had limited protective efficacy for experimental infections in animals. Since recombinant vectors may elicit more effective T-cell responses than adjuvant preparations, recombinant vaccinia virus (VV18) and M. bovis BCG (BCG18) vectors expressing the 18-kDa protein of M. leprae were prepared. Both VV18 and BCG18 stimulated anti-18-kDa protein antibody and lymphocyte proliferative responses. Sequential immunization with VV18 followed by BCG18 induced higher levels of specific immunoglobulin G2a antibodies than immunoglobulin G1 antibodies, in contrast to immunization with VV18 or BCG18 alone. The protective efficacy of immunization with VV18 from a challenge with BCG18 was examined in two murine models of mycobacterial infection. After intravenous challenge, mice immunized with recombinant vaccinia virus exhibited lower initial levels of replication and earlier clearance of BCG18 from their spleens than mice immunized with vaccinia virus expressing an unrelated protein. After footpad infection in a dissemination model, there was earlier clearance of BCG18 from specifically immunized mice. However, immunization of mice with VV18 did not prevent a productive mycobacterial infection.

Topography and immunogenicity of bluetongue virus VP7 epitopes

The core of bluetongue virus (BTV) consists of ten dsRNA viral genome segments and five proteins, including two major (VP7 and VP3) and three minor (VP1, VP4 and VP6) components. The major core protein VP7 is believed to be an important structural constituent because it interacts, not only with the underlying core protein VP3, but also with two outer capsid proteins (VP2 and VP5). In this communication we summarise data on the mapping of at least six different epitopes of VP7 distributed along the molecule. Two of the six epitopes have not been mapped previously. The accessibility of these epitopes in intact virions and core particles was analysed using immunoelectron microscopy. The epitope located near the N-terminus of VP7 was accessible at the surface of intact virions and core particles. Epitopes in other parts of the VP7 molecule were detected weakly in core particles but not in intact virions. These results support the proposal that VP7 molecules are orientated with their N-terminus accessible on the surface of either the particle or at least one of the three different channels observed by cryoelectron microscopy in the outer capsid layer. Analysis of the immune response to BTV-infected or -immunised sheep and rabbits to three selected epitopes, which are located in different regions of the VP7 molecule, demonstrated that all of them were recognised by the animals tested. These results provided further molecular evidence suggesting that VP7 is indeed a major immunogenic antigen ideal for BTV antibody detection.

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.

Antigen specificity of the ovine cytotoxic T lymphocyte response to bluetongue virus

Bluetongue virus (BTV), an arbovirus transmitted by midges, can cause serious disease in sheep. Both virus neutralizing antibody and cytotoxic T lymphocytes (CTL) have been shown to have a role in protective immunity. In this study, the antigen specificity of CTL from BTV-immune sheep has been determined using recombinant vaccinia viruses expressing individual BTV antigens. The results show that, in the sheep studied thus far, the serotype-specific outer coat protein, VP2, and the non-structural protein, NS1 are major immunogens for CTL, with VP5 (an outer coat protein) and NS3 being minor immunogens. No VP7 (a major group-reactive inner coat protein) specific CTL were detected. The CTL from sheep immunized with serotype 1 were cross-reactive and able to recognize target cells infected with other BTV serotypes. Further work demonstrated that the cross-reactive CTL recognized NS1, but not VP2.

Minimal epitopes expressed in a recombinant polyepitope protein are processed and presented to CD8+ cytotoxic T cells: implications for vaccine design

The epitopes recognized by CD8+ cytotoxic T lymphocytes (CTL) are generated from cytosolic proteins by proteolytic processing. The nature of the influences exerted by the sequences flanking CTL epitopes on these processing events remains controversial. Here we show that each epitope within an artificial polyepitope protein containing nine minimal CD8+ CTL epitopes in sequence was processed and presented to appropriate CTL clones. Natural flanking sequences were thus not required to direct class I proteolytic processing. In addition, unnatural flanking sequences containing other CTL epitopes did not interfere with processing. The ability of every CTL epitope to be effectively processed from a protein containing only CTL epitopes is likely to find application in the construction of recombinant polyepitope CTL vaccines.

High-titer immune responses elicited by recombinant vaccinia virus priming and particle boosting are ineffective in preventing virulent SIV infection

Eighteen rhesus monkeys were vaccinated with recombinant vaccinia viruses expressing SIVmac antigens in 3 separate rounds of experiments. Twelve of the monkeys were primed with a trivalent vaccinia virus recombinant expressing Gag, Pol, and Env polypeptides that can assemble into SIV pseudovirion particles and boosted with SIV particles in adjuvant. Four of the monkeys were primed with different vaccinia virus recombinants expressing env or gag+env followed by SIV particle boosts; two received vaccinia virus recombinants alone (env or env+gag). Despite the induction of vigorous immune responses, 17 of 18 rhesus monkeys became infected on challenge with a low dose of virulent SIVmac. The single protected animal was one of three challenged with homologous cloned SIV exactly matched to the clone used for construction of trivalent vaccinia virus recombinant and particles. Vaccination may have diminished SIV burdens and rates of CD4+ cell declines in some of the animals, but vaccinated/challenge/infected animals eventually developed fatal disease similar to control animals. These results highlight the extreme difficulty in achieving vaccine protection against virulent SIVmac infection even under idealized laboratory conditions.

The role of interleukin-6 in mucosal IgA antibody responses in vivo

In mice with targeted disruption of the gene that encodes interleukin-6 (IL-6), greatly reduced numbers of immunoglobulin A (IgA)-producing cells were observed at mucosae and grossly deficient local antibody responses were recorded after mucosal challenge with either ovalbumin or vaccinia virus. The IgA response in the lungs was completely restored after intranasal infection with recombinant vaccinia viruses engineered to express IL-6. These findings demonstrate a critical role for IL-6 in vivo in the development of local IgA antibody responses and illustrate the effectiveness of vector-directed cytokine gene therapy.

Interleukin-5 expressed by a recombinant virus vector enhances specific mucosal IgA responses in vivo

Several in vitro studies have shown that murine interleukin-5 (mIL-5) enhances IgA production by activated mucosal B cells. To date, however, there is no evidence that this factor significantly up-regulates mucosal IgA responses in vivo. Here, we show that expression of the gene for mIL-5 in a recombinant vaccinia virus vector markedly increases IgA responses to co-expressed heterologous antigen in the lungs of mice given intranasal inocula of the virus. The elevated local IgA responses to vectors expressing mIL-5 peaked at a fourfold higher level than those elicited by control virus at 14 days after infection and were sustained for at least 4 weeks. Increased IgA responses were abrogated in mice treated with monoclonal antibody against mIL-5 and were not detected in systemic lymphoid tissue. No enhancement of specific IgG levels was found either locally or systemically. Our results indicate that mIL-5 selectively enhances the development of mucosal IgA responses in vivo and suggest that expression of this factor in mucosal vaccine vectors may stimulate local immune reactivity.

Recombinant viral vaccines for enzootic bovine leucosis

Recently published studies on the development and use of recombinant vaccinia virus (VV) vaccines incorporating either the complete envelope (env) gene or only a fragment of the env gene consisting of the coding sequence for the env glycoprotein 51 (gp51) and part of gp30 of the bovine leukaemia virus (BLV) are described. It has been reported that vaccination of sheep with recombinant VV vaccines containing the complete env gene appears to protect sheep against challenge infection with BLV. The evidence for this protection is based on the lack of persistence of high titres of anti-gp51 antibodies compared with unvaccinated BLV infected controls, on the enhanced CD4 proliferative responses to specific BLV gp51 synthetic peptides in the vaccinated sheep, and on the inability to detect BLV pro-virus by polymerase chain reaction in the vaccinated sheep after 4 months following challenge infection compared with continual detection in unvaccinated sheep over a 16 month trial period. It has been suggested that cell-mediated immune responses may be an important aspect of protective immunity against BLV infection and it has been reported that large tracts of amino acid sequences within the env and pol genes are highly conserved in different isolates from different countries which is of importance in designing peptide derived vaccines.

Flavivirus premembrane protein cleavage and spike heterodimer secretion require the function of the viral proteinase NS3

Flavivirus protein biosynthesis involves the proteolytic processing of a single polyprotein precursor by host- and virus-encoded proteinases. In this study, the requirement for the proteolytic function of the viral proteinase NS3 for correct processing of a polyprotein segment encompassing the Murray Valley encephalitis virus structural proteins is shown. The NS3-mediated cleavage in the structural polyprotein region presumably releases the capsid protein from its membrane anchor and triggers the appearance of the premembrane (prM) protein. This suggests that cleavage of prM by signal peptidase in the lumen of the endoplasmic reticulum is under control of a cytoplasmic cleavage catalyzed by a viral proteinase. The function of the viral proteinase is also essential for secretion of flaviviral spike proteins when expressed from cDNA via vaccinia virus recombinants or in COS cell transfections. This has important implications for the design of flavivirus subunit vaccines.

Protection of sheep against bovine leukemia virus (BLV) infection by vaccination with recombinant vaccinia viruses expressing BLV envelope glycoproteins: correlation of protection with CD4 T-cell response to gp51 peptide 51-70

We have previously constructed vaccinia virus (VV) recombinants containing a complete or truncated envelope (env) gene of bovine leukemia virus (BLV). Only recombinants carrying the complete env gene (VV-BLV2 and VV-BLV3) expressed env glycoprotein on the surface of virus-infected cells and produced an antibody response in rabbits. In the present study, these VV recombinants were used to immunize sheep prior to challenge with BLV-infected peripheral blood mononuclear cells. Both humoral and cell-mediated immunity were monitored in infected animals. Sheep inoculated with recombinants containing the complete env gene showed a CD4 response to a defined epitope of gp51, but this response was absent 4 months postchallenge. Anti-gp51 antibodies appeared in animals inoculated with complete env 2 weeks after challenge, reached a peak at 4 weeks, and subsequently declined over 16 months. No CD4 response was recorded in animals inoculated with recombinants containing truncated env gene (VV-BLV1). BLV-infected control animals and those animals receiving VV-BLV1 were slower to develop antibodies postchallenge, and the titers of anti-gp51 antibodies continued to increase over 16 months. Proviral DNA was detected by the polymerase chain reaction in the four groups at 6 weeks after challenge. However, it could not be detected 4 months postinfection in the VV groups inoculated with complete env. Provirus was present in the VV-BLV1 and control groups over the 16-month trial period. These results demonstrate that vaccination with VV recombinants containing the complete env gene of BLV protects sheep against infection and that protection correlated with a CD4 T-cell response to a defined epitope.

Vaccination with two different vaccinia recombinant viruses: long-term inhibition of secondary vaccination

The effects of immunity to vaccinia virus on the efficiency of vaccination with a vaccinia recombinant virus were studied. In mice the efficiency and duration of the B-cell response to the recombinant gene product of a second vaccinia recombinant virus were suppressed for more than 9 months, i.e. practically lifelong. Antibody titres against the recombinant gene product were not only lower but also lasted for a shorter time. Thus, immunity to vaccinia virus may influence both the titre and duration of the antibody response induced by a second distinct vaccinia recombinant vaccine.

Stable expression of the human immunodeficiency virus type 1 envelope glycoprotein in transfected L cells

An SV40-based expression vector was used to generate CD4-negative murine L cell lines which stably expressed the human immunodeficiency virus envelope glycoprotein (env). Despite the presence of abundant intracellular envelope glycoprotein, the expression of env gp120/41 was not detected on the cell surface. Pulse-chase studies showed that the majority of the gp120 detected at the end of a 20-h chase was in the culture medium. Therefore gp120 was shed and/or secreted from these cells. Transfected L cells (H-2k) served as targets for specific lysis by CTL raised against vaccinia virus-encoded env gp160. The discrepancy in relative levels of intracellular versus surface expression of env was probably due to the highly inefficient processing of newly synthesized gp160, as well as the apparent instability of the gp120/41 complex in the transfected cell lines. Digestion of immunoprecipitated gp120 and gp160 with endoglycosidase H and peptide N-glycosidase F revealed that the envelope glycoprotein in transfected L cells possessed both high mannose and complex N-glycans, analogous to the posttranslational modification of the mature envelope glycoprotein in infected T cells. These studies indicate that the relatively inefficient processing of env gp160 occurs in the absence of CD4, and that the stable surface expression of envelope gp120/41 complex may require additional factors not present in transfected cells.

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.

Quantitative assessment of poxvirus promoters in fowlpox and vaccinia virus recombinants

A comparison was undertaken of poxvirus promoters in vaccinia and fowlpox virus (FPV) recombinants using the level of beta-galactosidase expressed from the LacZ gene as a measure of promoter function. In this study a comparison was made of the vaccinia virus promoters, P 7.5 and P L11, the major late promoter of cowpox virus, P CPX (expressing the abundant inclusion body protein), and the FPV promoters, P E/L and P L. In vaccinia virus recombinants the FPV P E/L promoter expressed one-third to one-half the level of beta-galactosidase expressed by the P L11 promoter. In comparison with the P 7.5 promoter, the FPV P E/L promoter expressed four to five times the level of beta-galactosidase. In FPV recombinants beta-galactosidase activity expressed was equal for the P E/L and P CPX promoters. Levels expressed by P L11 and P L were one-half and one-fifth that level, respectively. The temporal regulation of the promoters was maintained in both vaccinia virus and FPV recombinants. The P E/L promoter of FPV has the TAAATG sequence characteristic of late poxvirus promoters at the transcription initiation site. In an attempt to enhance the utility of this promoter for the expression of foreign genes in FPV and vaccinia virus recombinants, the effect upon promoter function of changing the G of the ATG to A, T, or C was determined using transient expression assays with vaccinia virus. Substitution of A, T, or C for the G abolished promoter function. Because of its early/late function, the level of expression and the presence of the oppositely oriented late P L promoter, the FPV P E/L promoter will be valuable for the expression of foreign genes in poxvirus recombinants.

Processing of dengue virus type 2 structural proteins containing deletions in hydrophobic domains

The 5' end of the genome of the dengue virus type 2 encoding the structural proteins was expressed using recombinant vaccinia virus. Three additional recombinants derived by deletion of selected dengue sequences within the parental construct were also expressed. They were designed to assess the role of hydrophobic domains in the processing of the viral polyprotein in intact cells. The first construct contained a deletion of nucleotides encoding most of the C protein; nucleotides encoding the hydrophobic domain at the carboxy terminus were retained. The second and third constructs contained smaller deletions of 72 bp and 129 bp encoding hydrophobic domains at the carboxy termini of C and prM respectively. Indirect immunofluorescence and radioimmunoprecipitation were used to detect prM and E in cells infected with recombinant viruses. The results showed that deletion of 90% of C had no apparent effect on the processing of prM and E, and that the signal sequence for E at the carboxy terminus of prM was active in the absence of the upstream signal sequence for prM at the carboxy terminus of C. Deletion of the hydrophobic sequences preceding the amino terminus of E prevented cleavage at the prM-E junction. These results obtained using infected cells were consistent with the published findings for the translation of flavivirus RNA in vitro, and indicated the importance of membrane association in the cleavage of structural proteins from the flavivirus polyprotein. In addition, cells infected with the recombinant virus containing the large deletion in the C coding region released the E glycoprotein into the culture medium.

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.

Expression of the NS1 gene of dengue virus type 2 using vaccinia virus. Dimerisation of the NS1 glycoprotein

A part of the genome of dengue virus type 2 spanning the coding region from the carboxy terminus of the envelope protein E to the beginning of the NS3 protein was expressed using recombinant vaccinia virus. Additional constructs which contained open reading frames terminating within the NS1 or NS2A genes were also expressed. NS1 dimers were formed by extended NS1 molecules containing 61 amino acids of NS2A. No dimers were detected when NS1 was shortened by 79 amino acids at its carboxy terminus.

The immunobiology of murine interleukin-1 alpha encoded by recombinant vaccinia virus

Recombinant vaccinia viruses were constructed which encoded murine interleukin-1 alpha (IL-1 alpha) (VV-IL1). One virus also encoded the hemagglutinin (HA) gene of influenza virus (VV-HA-IL1). Mice were infected with these viruses and the effects of co-expressed IL-1 on various immune parameters were assessed. The growth of VV-IL1 in vivo was less than that of the control virus, and this was reflected in the reduced virus-induced cell-mediated immune responses. However, specific antibody responses generated after challenge with vaccinia or influenza viruses were significantly higher when VV-HA-IL1 was used to prime mice, compared to the control virus (VV-HA-TK). This study demonstrates that co-expressed cytokines may be useful for selective alteration of immune reactivity.

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.

A poxvirus bidirectional promoter element with early/late and late functions

A novel bidirectional promoter element of fowlpox virus (FPV) was characterized by transcription analysis, transient expression assays, and recombinant virus construction. This promoter element contained an early/late and a late function in opposite orientation, all within 42 bp of the DNA sequence. The 42-bp sequence was sufficient to express two reporter genes simultaneously in a temporally regulated manner. Both early and late mRNA from the early/late promoter originated at the same TAAAT motif and lacked a long 5'poly(A) leader sequence. Late mRNA, initiated from a TAAAT motif of the oppositely oriented late promoter strand, had a leader sequence of approximately 26 bases. Sequence alignment of two strands of the bidirectional element showed that 28 of 42 bases matched. Because of its small and defined size as well as unique structure, this bidirectional promoter should prove to be an important tool in defining the sequences required for the temporal regulation of poxvirus genes.

Expression of bovine leukaemia virus envelope gene by recombinant vaccinia viruses

Recombinant vaccinia viruses (VV) containing the envelope gene of bovine leukaemia virus (BLV) were constructed. Three virus constructs were designed: VV-BLV1 which contained the open reading frame for envelope glycoprotein gp51 alone, under control of VVP7.5 promoter; VV-BLV2 and VV-BLV3 contained the entire gene (gp51 + gp30) coding sequence downstream of VP7.5 and the fowlpox virus early/late promoter (PFE/L) respectively. All three VV recombinants expressed envelope glycoproteins as determined by the agar gel diffusion assay. By immunofluorescence techniques it was shown that while VV-BLV2 and VV-BLV3 expressed envelope glycoprotein on the surface of virus-infected cells, VV-BLV1 failed to do so. Rabbits inoculated with VV-BLV1 failed to show an anti envelope glycoprotein antibody response, however, significant levels of antibodies against envelope glycoprotein were detected in sera from rabbits inoculated with VV-BLV2 and VV-BLV3.

Vaccinia virus-mediated damage of murine ovaries and protection by virus-expressed interleukin-2

Vaccinia virus was shown to replicate in the ovaries of normal inbred mice and cause sufficient damage to ovarian follicles to decrease fertility of the mice. The mouse-adapted strain, VV-WR, had a greater affinity for growth in ovaries than the vaccine strains, VV-Elstree, VV-NYBH or VV-Copenhagen. Virus reached the ovaries after intravenous or intraperitoneal inoculation, but not after subcutaneous inoculation in the foot pad. Interleukin-2 (IL-2), when expressed by a recombinant vaccinia virus was able to decrease the titre of virus in the ovaries and prevent infertility. Both non-specific (natural killer cells) and antigen-specific mechanisms were active within the ovaries and may play a role in the IL-2-mediated clearance of vaccinia virus.

The immunogenicity of VP7, a rotavirus antigen resident in the endoplasmic reticulum, is enhanced by cell surface expression

The glycoprotein VP7, the major serotype antigen of rotaviruses, is localized to the endoplasmic reticulum (ER) of the cell, where it is retained as a membrane-associated protein before assembly into mature virus particles. Wild-type VP7 expressed by a recombinant vaccinia virus was also located internally and was poorly antigenic. Using recombinant techniques, a correctly processed, secreted form of VP7 (S.C. Stirzaker and G.W. Both, Cell 56:741-747, 1989) was modified by addition to its C terminus of the membrane anchor and cytoplasmic domains from the influenza virus hemagglutinin. The hybrid protein was directed to the surface of cells, where it was anchored in the plasma membrane. When expressed in mice and rabbits by a recombinant vaccinia virus, the surface-anchored antigen stimulated a level of rotavirus-specific antibodies that was greater than 100-fold above the level induced by wild-type VP7. T-cell responses to the novel antigen were also elevated in comparison with the wild-type, intracellular protein. Cell surface anchoring may provide a strategy to increase the immunogenicity of intracellular antigens from other parasites and viruses.

Sequences in rotavirus glycoprotein VP7 that mediate delayed translocation and retention of the protein in the endoplasmic reticulum

Glycosylation and translocation of the simian rotavirus protein VP7, a resident ER protein, does not occur co-translationally in vivo. In pulse-chase experiments in COS cells, nonglycosylated VP7 was still detectable after a 25-min chase period, although the single glycosylation site was only 18 residues beyond the signal peptide cleavage site. After labeling, glycosylated and nonglycosylated VP7 was recovered in microsomes but the latter was sensitive to trypsin (i.e., the nascent protein became membrane associated) but most of it entered the ER posttranslationally because of a rate-limiting step early in translocation. In contrast with the simian protein, bovine VP7 was glycosylated and translocated rapidly. Thus, delayed translocation per se was not required for retention of VP7 in the ER. By constructing hybrid proteins, it was further shown that the signal peptide together with residues 64-111 of the simian protein caused delayed translocation. The same sequences were also necessary and sufficient for retention of simian VP7 in the ER. The data are consistent with the idea that certain proteins are inserted into the ER membrane in a loop configuration.

The vaccinia virus HindIII F fragment: nucleotide sequence of the left 6.2 kb

The nucleotide sequence of the left 6.2 kb of the 13.2-kb HindIII F fragment of vaccinia virus was determined. Translation of the sequence revealed nine closely spaced, tandemly oriented open reading frames (ORFs), all reading leftward. The transcriptional organization of this region was determined by Northern blot and S1 nuclease mapping. The analysis suggested that ORFs 1, 2, 4, 5, 6, 7, and 8 are transcribed early in infection, whereas ORFs 3 and 9 are probably late genes. Two of these ORFs have been reported previously. ORF F4L encodes the small subunit of ribonucleotide reductase and ORF F2L is homologous to a retroviral protease-like gene.

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

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