Barbara E.H. Coupar

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.

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.

The Roles of Influenza Virus Haemagglutinin and Nueleoprotein in Protection: Analysis Using Vaccinia Virus Recombinants

Vaccinia virus recombinants expressing haemagglutinin (HA) or nucleoprotein (NP) from influenza virus A/PR/8/4 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 recombinaant 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 almsot 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.

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.

Efficacy of DNA and fowlpox virus priming/boosting vaccines for simian/human immunodeficiency virus

ABSTRACT Further advances are required in understanding protection from AIDS by T-cell immunity. We analyzed a set of multigenic simian/human immunodeficiency virus (SHIV) DNA and fowlpox virus priming and boosting vaccines for immunogenicity and protective efficacy in outbred pigtail macaques. The number of vaccinations required, the effect of DNA vaccination alone, and the effect of cytokine (gamma interferon) coexpression by the fowlpox virus boost was also studied. A coordinated induction of high levels of broadly reactive CD4 and CD8 T-cell immune responses was induced by sequential DNA and fowlpox virus vaccination. The immunogenicity of regimens utilizing fowlpox virus coexpressing gamma interferon, a single DNA priming vaccination, or DNA vaccines alone was inferior. Significant control of a virulent SHIV challenge was observed despite a loss of SHIV-specific proliferating T cells. The outcome of challenge with virulent SHIVmn229 correlated with vaccine immunogenicity except that DNA vaccination alone primed for protection almost as effectively as the DNA/fowlpox virus regimen despite negligible immunogenicity by standard assays. These studies suggest that priming of immunity with DNA and fowlpox virus vaccines could delay AIDS in humans.

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.

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.

Localization of the non-structural protein NS3 in bluetongue virus-infected cells

The localization of the blue tongue virus (BTV) non-structural proteins NS3 and NS3a has been identified using immunoelectron microscopical techniques. NS3 and NS3a have been observed in the plasma membrane of BTV- and recombinant vaccinia virus (expressing NS3)-infected cells. The NS3 protein was associated with areas of membrane perturbation. There was a good correlation between the presence of NS3 and NS3a and BTV release. The NS3 protein was associated with membrane fragments and the inability to detect it on the extracellular aspect of intact cells suggested that the protein was not exposed extracellularly. Electron microscopical and biochemical evidence suggested that fragments of plasma membrane containing NS3 and NS3a were released from infected cells. Collectively, the data indicate that NS3 and NS3a may be involved in the final stages of BTV morphogenesis, i.e. the release of BTV from infected cells.

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.

Comparative Efficacy of Subtype AE Simian-Human Immunodeficiency Virus Priming and Boosting Vaccines in Pigtail Macaques

ABSTRACT Vaccination against AIDS is hampered by great diversity between human immunodeficiency virus (HIV) strains. Heterologous B-subtype-based simian-human immunodeficiency virus (SHIV) DNA prime and poxvirus boost vaccine regimens can induce partial, T-cell-mediated, protective immunity in macaques. We analyzed a set of DNA, recombinant fowlpox viruses (FPV), and vaccinia viruses (VV) expressing subtype AE HIV type 1 (HIV-1) Tat, Rev, and Env proteins and SIV Gag/Pol in 30 pigtail macaques. SIV Gag-specific CD4 and CD8 T-cell responses were induced by sequential DNA/FPV vaccination, although lower FPV doses, VV/FPV vaccination, and DNA vaccines alone were not as consistently immunogenic. The SHIV AE DNA prime, FPV boost regimens were significantly less immunogenic than comparable B-subtype SHIV vaccination. Peak viral load was modestly (0.4 log10 copies/ml) lower among the AE subtype SHIV-immunized animals compared to controls following the virulent B subtype SHIV challenge. Protection from persistent high levels of viremia and CD4 T-cell depletion was less in AE subtype compared to B subtype SHIV-vaccinated macaques. Gag was highly immunodominant over the other AE subtype SHIV vaccine proteins after vaccination, and this immunodominance was exacerbated after challenge. Interestingly, the lower level of priming of immune responses did not blunt postchallenge Gag-specific recall responses, despite more modest protection. These studies suggest priming of T-cell immunity to prevent AIDS in humans is possible, but differences in the immunogenicity of various subtype vaccines and broad cross-subtype protection are substantial hurdles.