Promoter activity in the 5' flanking regions of the Bohle iridovirus ICP 18, ICP 46 and major capsid protein genes

Bohle iridovirus (BIV) belongs to the genus Ranavirus, of which Frog virus 3 (FV-3) is the type species. We are developing BIV as a recombinant viral delivery vector, and as a first step we located specific BIV promoter sequences to drive foreign gene expression in the recombinant virus. By comparison with FV-3 sequences, the genes encoding ICP 18 and ICP 46 in BIV were identified and sequenced. Putative promoter regions of these two early genes and of the major capsid protein (MCP) gene were identified, cloned into pSFM21, and luciferase production was then used to assess the promoter activity of these regions.

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.

Identification of type B-specific and cross-reactive cytotoxic T-lymphocyte responses to Epstein-Barr virus

Persistent Epstein-Barr virus (EBV) infection is primarily controlled by HLA class I-restricted memory cytotoxic T-cell (CTL) responses which can be reactivated in vitro by stimulation of peripheral blood lymphocytes with autologous lymphoblastoid cell lines. During an investigation of a donor infected by both type A and type B EBV, CTL specific for type B EBV were isolated. The CTL were found to recognize an epitope encoded by the EBNA-6B gene. The minimal epitope sequence was identified as QNGALAINTF, corresponding to residues 213 to 222 in the EBNA-6B protein, and presentation of this epitope was shown to be via HLA B62 (B15). This is the first report of the characterization of an epitope that is EBV type B specific. CTL recognizing sequences common to type A and type B EBV were identified as well. A cross-reactive epitope recognized by these CTL was encoded within the EBNA-6 gene of both type A and type B. This minimal sequence for this epitope was LLDFVRFMGV (residues 284 to 293 in both types), and the epitope was restricted through HLA A*0201. This second epitope sequence overlaps with a published EBV B44-restricted epitope (EENLLDFVRF). The implications of these findings are discussed with respect to the design and efficacy of epitope-based vaccines.

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.

Recombinant vaccinia viruses expressing interleukin-5 stimulate an earlier appearance of antibody-secreting cells in the lung

Interleukin-5 (IL-5) is a cytokine that participates in the regulation of antibody secretion, in particular promoting the secretion of IgA at mucosal sites. In this report, recombinant vaccinia viruses expressing IL-5 have been inoculated into mice and the appearance of antibody-secreting cells in the spleen and lungs investigated. Although vaccinia virus-expressed IL-5 did not increase the level of IgA in serum, antibody-secreting cells, measured in an enzyme-linked immunosorbent spot assay, appeared earlier in lungs when the immunizing virus expressed IL-5. These early B cells secreted either IgM or IgG1.

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.

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.

Defective presentation to class I-restricted cytotoxic T lymphocytes in vaccinia-infected cells is overcome by enhanced degradation of antigen

Vaccinia infection interferes with the presentation of influenza Haemagglutinin (HA) and Nucleoprotein (NP) to class I-restricted CTL. The inhibitory effect is selective for certain epitopes, and is more profound during the late phase of infection. For influenza A/NT/60/68 NP, the block is present during both early and late phases of infection, and is selective for the COOH-terminal epitope defined by peptide 366-379, having no detectable effect on the presentation of the NH2-terminal epitope 50-63. The presentation of HA is inhibited only during the late phase of vaccinia infection. For both proteins, presentation is partially (NP) or completely (HA) restored by expression of rapidly degraded protein fragments in the vaccinia infected target cell. For HA, deletion of the NH2-terminal signal sequence completely overcomes the block. For NP, either a large NH2-terminal deletion or the construction of a rapidly degraded ubiquitin-NP fusion protein partially restores presentation. These results illustrate the relationship between degradation of viral proteins in the cytoplasm of an infected cell and recognition of epitopes at the cell surface by class I-restricted T cells.