A recombinant vaccinia virus expressing herpes simplex virus type 1 glycoprotein B induces cytotoxic T lymphocytes in mice

Use of Reporter Genes in the Generation of Vaccinia Virus-Derived Vectors

Vaccinia virus (VACV) is one of the most extensively-studied viruses of the Poxviridae family. It is easy to genetically modify, so it has become a key tool for many applications. In this context, reporter genes facilitate the study of the role of foreign genes introduced into the genome of VACV. In this review, we describe the type of reporter genes that have been used to generate reporter-expressing VACV and the applications of the recombinant viruses obtained. Reporter-expressing VACV are currently employed in basic and immunology research, in the development of vaccines and cancer treatment.

Developments in herpes simplex virus vaccines: old problems and new challenges

Vaccination has remained the best method for preventing virus spread. The herpes simplex virus (HSV) candidate vaccines tested till now were mostly purified subunit vaccines and/or recombinant envelope glycoproteins (such as gB and gD). In many experiments performed in mice, guinea pigs and rabbits, clear-cut protection against acute virus challenge was demonstrated along with the reduction of the extent of latency, when established in the immunized host. The immunotherapeutic effect of herpes vaccines seems less convincing. However, introduction of new adjuvants, which shift the cytokine production of helper T-cells toward stimulation of cytotoxic T-cells (TH1 type cytokine response), reveals a promising development. Mathematical analysis proved that overall prophylactic vaccination of seronegative women, even when eliciting 40-60 % antibody response only, would reduce the frequency of genital herpes within the vaccinated population. Even when partially effective, immunotherapeutic vaccination might represent a suitable alternative of chronic chemotherapy in recurrent labial and genital herpes.

A soluble divalent class I MHC/IgG1 fusion protein activates CD8+ T cells in vivo

CD8+ T lymphocytes recognize tumor and viral antigens bound to class I major histocompatibility complexes (MHC). Tumors and viruses may evade detection by preventing antigen presentation. The present study was designed to determine whether a soluble divalent fusion protein, containing the extracellular domains of a class I MHC molecule fused to beta2-microglobulin and the constant domains of IgG1, could induce an immune response in vivo. Administration to mice of the fusion protein loaded with a tumor peptide induced peptide-specific T cell activation and retarded tumor growth. Administration of the fusion protein loaded with a glycoprotein B (gB) peptide derived from herpes simplex virus type 1 (HSV-1) induced gB-specific cytotoxic T lymphocytes and protected mice from a lethal HSV-1 challenge. These data suggest that antigen-loaded MHC/IgG fusion proteins may enhance T cell immunity in conditions where antigen presentation is altered.

Development of HSV-specific CD4+ Th1 responses and CD8+ cytotoxic T lymphocytes with antiviral activity by vaccination with the HSV-2 mutant ICP10DeltaPK

A growth compromised herpes simplex virus type 2 (HSV-2) mutant which is deleted in the PK domain of the large subunit of ribonucleotide reductase (ICP10DeltaPK) protects from HSV-2 challenge in the mouse and guinea pig cutaneous and vaginal models and reduces the incidence and frequency of recurrent disease (Vaccine (17) (1999) 1951; Vaccine (19) (2001) 1879). The present studies were designed to identify the immune responses induced by ICP10DeltaPK and define the component responsible for protective activity. We found that ICP10DeltaPK elicits a predominant HSV-specific T helper type 1 (Th1) response, as evidenced by: (1) higher levels of HSV-specific IgG2a (Th1) than IgG1 (Th2) isotypes and (2) higher numbers of CD4+ IFN-gamma than IL-10 secreting T cells in popliteal lymph nodes. This Th1 response pattern was associated with a significant increase in the levels of IL-12 produced by dendritic cells from ICP10DeltaPK than HSV-2 immunized animals. Lymph node cells (LNCs) from ICP10DeltaPK immunized mice had significantly higher levels of HSV-2 specific cytolytic activity than LNCs from mice immunized with HSV-2 and it was mediated by CD8+ T cells. CD8+ CTL were not seen in LNCs from HSV-2 immunized mice. In adoptive transfer experiments, CD8+ T cells and, to a lower extent, CD4+ T cells from ICP10DeltaPK immunized mice inhibited HSV-2 replication, suggesting that they are involved in the protective immunity induced by ICP10DeltaPK vaccination.

Herpes simplex virus type 1-specific cytotoxic T-lymphocyte arming occurs within lymph nodes draining the site of cutaneous infection

Various studies have shown that major histocompatibility complex class I-restricted cytotoxic T lymphocytes (CTL) can be isolated from lymph nodes draining sites of cutaneous infection with herpes simplex virus type 1 (HSV-1). Invariably, detection of this cytolytic activity appeared to require some level of in vitro culture of the isolated lymph node cells, usually for 3 days, in the absence of exogenous viral antigen. This in vitro "resting" period was thought to represent the phase during which committed CD8(+) T cells become "armed" killers after leaving the lymph nodes and prior to their entry into infected tissue as effector CTL. In this study we reexamined the issue of CTL appearance in the HSV-1 immune response and found that cytolytic activity can be isolated directly from draining lymph nodes, although at levels considerably below those found after in vitro culture. By using T-cell receptor elements that represent effective markers for class I-restricted T cells specific for an immunodominant glycoprotein B (gB) determinant from HSV-1, we show that the increase in cytotoxicity apparent after in vitro culture closely mirrors the expansion of gB-specific CTL during the same period. Taken together, our results suggest that HSV-1-specific CTL priming does not appear to require any level of cytolytic machinery arming outside the lymph node compartment despite the absence of any detectable infection within that site.

The cytotoxic T-cell response to herpes simplex virus type 1 infection of C57BL/6 mice is almost entirely directed against a single immunodominant determinant

Many virus infections give rise to surprisingly limited T-cell responses directed to very few immunodominant determinants. We have been examining the cytotoxic T-lymphocyte (CTL) response to herpes simplex virus type 1 (HSV-1) infection. Previous studies have identified the glycoprotein B-derived peptide from residues 498 to 505 (gB(498-505)) as one of at least three determinants recognized by HSV-1-specific CTLs isolated from C57BL/6 mice. We had previously found that in vitro-derived CTLs directed to gB(498-505) show a characteristic pattern of T-cell receptor (TCR) usage, with 60% of gB(498-505)-specific CD8(+) T cells expressing BV10(+) TCR beta chains and a further 20% expressing BV8S1. In this report, we confirm that this TCR V-region bias is also reflected in the ex vivo response to HSV-1 infection. A high proportion of activated CD8(+) draining lymph node cells were found to express these dominant V regions, suggesting that a substantial number of in vivo responding T cells were directed to this one viral determinant. The use of an HSV-1 deletion mutant lacking the gB(498-505) determinant in combination with accurate intracellular gamma interferon staining allowed us to quantify the extent of gB-specific T-cell dominance. Together, these results suggested that between 70 and 90% of all CD8(+) HSV-1-specific T cells target gB(498-505). While deletion of this determinant resulted in an attenuated CD8(+) T-cell response, it also permitted the emergence of one or more previously unidentified cryptic specificities. Overall, HSV-1 infection of C57BL/6 mice results in an extremely focused pattern of CD8(+) T-cell selection in terms of target specificity and TCR expression.

Immunization with a replication-deficient mutant of herpes simplex virus type 1 (HSV-1) induces a CD8+ cytotoxic T-lymphocyte response and confers a level of protection comparable to that of wild-type HSV-1

Replication-deficient viruses provide an attractive alternative to conventional approaches used in the induction of antiviral immunity. We have quantitatively evaluated both the primary and memory cytotoxic T-lymphocyte (CTL) responses elicited by immunization with a replication-deficient mutant of herpes simplex virus type 1 (HSV-1). In addition, we have examined the potential role of these CTL in protection against HSV infection. Using bulk culture analysis and limiting-dilution analysis, we have shown that a replication-deficient virus, d301, generates a strong primary CTL response that is comparable to the response induced by the wild type-strain, KOS1.1. Furthermore, the CTL induced by d301 immunization recognized the immunodominant, H-2Kb-restricted, CTL recognition epitope gB498-505 to a level similar to that for CTL from KOS1.1-immunized mice. The memory CTL response evoked by d301 was strong and persistent, even though the frequencies of CTL were slightly lower than the frequencies of CTL induced by KOS1.1. Adoptive transfer studies indicated that both the CD8+ and the CD4+ T-cell responses generated by immunization with d301 and KOS1.1 were able to limit the extent of a cutaneous HSV infection to comparable levels. Overall, these results indicate that viral replication is not necessary to elicit a potent and durable HSV-specific immune response and suggest that replication-deficient viruses may be effective in eliciting protection against viral pathogens.

Deletion of the carboxy-terminus of herpes simplex virus type 1 (HSV-1) glycoprotein B does not affect oligomerization, heparin-binding activity, or its ability to protect against HSV challenge

A recombinant vaccinia virus designated VgBt which expresses a truncated secreted herpes simplex virus gB (gBt) was constructed and compared to V11gB, a vaccinia recombinant previously studied which expresses gB exclusively on the surface of infected cells. Indirect immunofluorescence assay (IFA) revealed that gBt was strongly associated with the surface of infected cells despite being released slowly into the cell culture medium. Both gB and gBt existed as oligomers, and both membrane bound and secreted forms of gBt exhibited heparin-binding activity. In protection studies VgBt and V11gB conferred equivalent protection against both homologous (HSV-1) and heterologous (HSV-2) challenge with HSV.

Characterization of diverse primary herpes simplex virus type 1 gB-specific cytotoxic T-cell response showing a preferential V beta bias

The glycoprotein B (gB) from herpes simplex virus type I is a major target of cytotoxic T lymphocytes (CTL) in C57BL/6 mice. The majority of these T cells are directed to a single Kb-restricted determinant, gB498-505. We have analyzed the T-cell receptor (TCR) usage in gB-specific CTL lines derived shortly after virus infection. The CTL populations preferentially used two V beta regions, a dominant V beta 10 element and a subdominant V beta 8 element. Detailed sequence analysis revealed considerable TCR beta-chain heterogeneity despite a striking level of predicted amino acid conservation at the V beta-D beta junction. This junction forms part of the third hypervariable loop of the TCR thought to directly contact the major histocompatibility complex-bound antigenic peptide. The results reveal considerable diversity within the primary T cells responding to a single viral determinant while still maintaining a high degree of TCR V beta bias and sequence conservation at the V-D-J junction.

Vaccine potential of a herpes simplex virus type 1 mutant with an essential glycoprotein deleted

Several approaches to the production of vaccines to human herpesviruses have been proposed. Subunit vaccines, subunits delivered by live vectors, and rationally attenuated vaccines have all been shown to be efficacious in animal models but suffer from uncertainties as to the roles of individual genes involved in pathogenesis and the most relevant components of the immune response required for protection in humans and the target antigens involved. With these problems in mind, we examined the vaccine potential of a fully disabled herpes simplex virus type 1 mutant that is capable of only a single round of replication, since a virus of this type should induce the full spectrum of immune responses but has no pathogenic potential. A virus has been described which lacks essential glycoprotein H (gH) and can be propagated in a cell line which supplies gH in trans (A. Forrester, H. Farrell, G. Wilkinson, J. Kaye, N. Davis-Poynter, and T. Minson, J. Virol. 66:341-348, 1992). Infection of normal cells with this mutant is indistinguishable from a wild-type infection, except that the resulting progeny are gH negative and noninfectious: the virus is self-limiting. Infection of mice by the ear pinna route was similarly self-limiting in that input infectivity decreased rapidly at the inoculation site and no infectivity was detected in sensory ganglia. Animals given a wide range of doses of the gH-negative mutant produced both humoral and T-cell responses to herpes simplex virus type 1 and proved solidly resistant to challenge with a high dose of wild-type virus. The gH-negative mutant is presumably capable of establishing a latent infection, but since no infectious virus was detected in numerous attempts to reactivate the mutant, the risk of a pathogenic outcome is minimal.

Recombinant vaccinia viruses expressing GP46/M-2 protect against Leishmania infection

Leishmania is a genus of parasitic protozoa capable of causing a spectrum of human diseases. The GP46/M-2 membrane glycoprotein has been demonstrated in a murine model system to elicit a protective immune response against infection with Leishmania amazonensis; in highly susceptible BALB/c mice, immunization leads to significant protection against infection. In the present study, for induction of long-term immunological effects, two recombinant vaccinia viruses, derived from the wild type and attenuated variant 48-7 and expressing the GP46/M-2 protein, were constructed; to ensure safety, we used the attenuated vaccinia virus mutant (48-7) as a live vector. Susceptible BALB/c mice immunized with either GP46/M-2-recombinant vaccinia virus were significantly protected against infection with L. amazonensis; 45 to 76% of the animals were completely protected (sterile) against a challenge inoculum of 10(3) infective organisms. The protectively immunized animals demonstrated T- and B-cell-dependent immunological responses; both lymphokine responses as well as antibody responses and long-term memory are indicative of T-cell activation. This first report of the use of a recombinant vaccinia virus to induce protection against a Leishmania infection indicates that recombinant vaccinia viruses should be of value in the design of a safe and effective vaccine against this parasitic disease.

Replication-defective mutants of herpes simplex virus (HSV) induce cellular immunity and protect against lethal HSV infection

Live viruses and live virus vaccines induce cellular immunity more readily than do inactivated viruses or purified proteins, but the mechanism by which this process occurs is unknown. A trivial explanation would relate to the ability of live viruses to spread and infect more cells than can inactivated virus. We have used live but replication-defective mutants to investigate this question. Our studies indicate that the immune responses of mice to live virus differ greatly from the responses to inactivated virus even when the virus does not complete a replicative cycle. Further, these studies indicate that herpes simplex virus-specific T-cell responses can be generated by infection with replication-defective mutant viruses. These data indicate that the magnitude of the cellular immunity to herpes simplex virus may be proportional to the number or quantity of different viral gene products expressed by an immunizing virus.

Human CD8+ herpes simplex virus-specific cytotoxic T-lymphocyte clones recognize diverse virion protein antigens

The role of the HLA class I-restricted, CD8+, herpes simplex virus (HSV)-specific cytotoxic T lymphocytes (CTL) in the control of human HSV infections is controversial because previous reports suggest that a substantial portion of the antigen-specific lytic response is mediated by CD4+ cells. To address this question directly, we isolated HSV-specific CD8+ CTL clones from a patient with recurrent genital herpes. These CTL were cloned by coculturing responder peripheral blood mononuclear cells (PBMC) with phytohemagglutinin-stimulated PBMC that had been infected with live HSV-2 and then irradiated prior to the addition of responder cells. After 1 week, CTL were cloned by limiting dilution using phytohemagglutinin stimulation and allogeneic feeder PBMC. Seven clones were isolated; all seven clones were CD8+ CD4- CD3+ DRbright, six lysed only HSV-2-infected targets, and one lysed both HSV-1- and HSV-2-infected targets. Antigen presentation was restricted by two to three different HLA class I loci. To determine the antigens recognized by these HSV-specific CTL, target cells were infected with HSV in the presence of acyclovir, 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole, or cycloheximide in a series of drug block/release protocols to limit the repertoire of viral gene expression to select transcriptional classes. Five of the clones exhibited a different pattern of cytotoxicity, suggesting that each recognized a distinct HSV antigen. One of the clones appears to be directed against an immediate-early antigen; six of the clones recognize virion proteins. Five of these clones recognized internal virion proteins that could be introduced into target cells by HSV infection in the absence of virus gene expression. Antigen specificity was further tested by using vaccinia virus vectors that express glycoproteins gD2 and gB2 or the tegument protein VP16. One clone lysed vaccinia virus/gD2-infected target cells; the remaining clones did not recognize any of these gene products. The diversity of the CD8+ response from a single individual indicated that several different antigens are recognized when presented in the context of a variety of class I HLA alleles, a pattern that markedly differs from that described for another human herpesvirus, cytomegalovirus.

Herpes simplex virus type 1-specific cytotoxic T lymphocytes recognize immediate-early protein ICP27

The identity of herpes simplex virus type 1 (HSV-1) antigens that serve as targets for cytotoxic T lymphocytes (CTL) and their ability to induce protective immunity remain uncertain. In this article, we report the identification of the immediate-early protein ICP27 as a CTL antigen in H-2d mice but not in H-2k or H-2b mice. Calculation of the frequencies of H-2d-restricted virus-specific CTL demonstrated that approximately one-fourth of the total HSV-1-specific response was directed against ICP27. To define the location of this CTL epitope, four truncated derivatives of the ICP27 gene which place the epitope in a 217-amino-acid region (amino acids 189 to 406) near the central portion of the protein were constructed. Mice immunized with ICP27 were able both to induce HSV-1-specific CTL and to survive a lethal intraperitoneal challenge with virulent HSV-1. However, neither appreciable antibody nor delayed-type hypersensitivity responses were induced in immunized mice, and they were also unable to clear a local epithelial virus challenge. It appears that ICP27, although capable of inducing several aspects of the immune response, is by itself unable to provide complete immunity.

Recombinant virus vaccine-induced SIV-specific CD8+ cytotoxic T lymphocytes

Evidence indicates that cytotoxic T lymphocytes (CTLs) may be important in containing the spread of the human immunodeficiency virus (HIV) in the infected host. Although the use of recombinant viruses has been proposed as an approach to elicit protective immunity against HIV, the ability of recombinant viral constructs to elicit CD8+ CTL responses in higher primates has never been demonstrated. A live recombinant virus, vaccinia-simian immunodeficiency virus of macaques (SIVmac), was used to determine whether such a genetically restricted, T lymphocyte-mediated antiviral response could be generated in a primate. Vaccinia-SIVmac vaccination elicited an SIVmac Gag-specific, CD8+ CTL response in rhesus monkeys. These CTLs recognized a peptide fragment that spans residues 171 to 195 of the Gag protein. The rhesus monkey major histocompatibility complex (MHC) class I gene product restricting this CTL response was defined. Both the vaccinated and SIVmac-infected monkeys that shared this MHC class I gene product developed CTLs with the same Gag epitope specificity. These findings support the use of recombinant virus vaccines for the prevention of HIV infections in humans.

The simian herpesvirus SA8 homologue of the herpes simplex virus gB gene: mapping, sequencing, and comparison to the HSV gB

The genomic location and DNA sequence of the simian herpesvirus SA8 gene encoding a homologue of the HSV1 gB glycoprotein was determined. Using a cloned gB gene of herpes simplex virus type 1 (HSV1) as probe in Southern blot hybridizations, the SA8 gB gene was localized to a 10-kbp KpnI fragment mapping in the unique long part of the genome. A 2.8 kbp, 68.4% GC segment of this fragment was sequenced. It contained a 2649 nucleotide ORF possibly encoding a 98.4 kDa polypeptide. The predicted amino acid sequence of the SA8 gB polypeptide is 78.4% and 78.9% identical to the sequence of the HSV1 and HSV2 gBs, respectively, and was 88.4% similar or identical to both HSV gB sequences. Structural characteristics predicted for the SA8 gB polypeptide were very similar to those of HSV1 gB. These included a hydrophobic signal sequence of 29 amino acids, conservation of all 10 cysteine residues and 5 of 6 potential N-linked glycosylation sites present in the HSV1 gB, a triple hydrophobic transmembrane domain, and a highly charged cytoplasmic tail region. Both hierarchical cluster analysis and phylogenetic analysis of sequences for gB polypeptides of 12 different herpesviruses demonstrated that the gB glycoprotein of SA8 is most closely related to the HSV gB glycoproteins. Comparison of these closely related gB sequences identified four regions in which non-conservative amino acid substitutions were clustered. Localized regions of the gB polypeptide were identified which are likely to be associated with the conserved structure/function of the polypeptide.

Identification of an immunodominant cytotoxic T-lymphocyte recognition site in glycoprotein B of herpes simplex virus by using recombinant adenovirus vectors and synthetic peptides

Cytotoxic T-lymphocyte (CTL) responses to herpes simplex virus (HSV) polypeptides play an important role in recovery from infection and in preventing latency. We have previously shown that glycoprotein B (gB) is a major target recognized by HSV-specific CTLs in C57BL/6 (H-2b) and BALB/c (H-2d) mice but not in CBA/J (H-2k) mice (L. A. Witmer, K. L. Rosenthal, F. L. Graham, H. M. Friedman, A. Yee, and D. C. Johnson, J. Gen. Virol. 71:387-396, 1990). In this report, we utilize adenovirus vectors expressing gB with various deletions to localize an immunodominant site in gB, recognized by H-2b-restricted anti-HSV CTLs, to a region between residues 462 and 594. Overlapping peptides spanning this region were synthesized and used to further localize the immunodominant site to residues 489 to 515, a region highly conserved in HSV type 1 (HSV-1) and HSV-2 strains. The 11-amino-acid peptide was apparently associated exclusively with the Kb major histocompatibility complex gene product and not the Db gene product. In contrast, H-2d-restricted CTLs recognized an immunodominant site between residues 233 and 379.

Immunogenicity of herpes simplex virus type 1 glycoproteins expressed in vaccinia virus recombinants

Vaccinia virus recombinants expressing glycoproteins B (vgB11), D (VgD52), E (gE/7.5 and gE/4B), G (gG-vac), H (gH-vac), and I (gI-vac) of HSV-1 were used to compare the protective response to these individual glycoproteins in the mouse. Glycoprotein D induced the best neutralizing antibody titers and the most increased rates of HSV clearance from the ear as well as good protection from the establishment of latent HSV infections in the sensory ganglia. Glycoprotein B also induced good neutralizing antibody titers and as great a protection from the establishment of latency as gD although the rate of virus clearance from the ear was not as great as after immunization with gD. Glycoprotein E induced weak neutralizing antibody but gG, gH, and gI did not show a neutralizing antibody response. At higher challenge doses of virus (10(6) PFU HSV-1 in the ear), gE induced a protective response by increasing the rate of virus clearance and reducing the acute infection of ganglia as compared to negative control immunized mice. However there was no protection from the establishment of latent infections after immunization with gE. No protective response was seen to gG, gH, or gl.

Comparative studies of HSV-1 antigens solubilised from infected cells by using non-ionic or zwitterionic detergents

HSV-1 antigen preparations solubilised from Vero cells by using either the non-ionic detergent Nonidet P40 or the zwitterionic detergent Empigen BB, and purified on sucrose density gradients or over a sucrose cushion, were tested by ELISA with anti-HSV-1 glycoprotein monoclonal antibodies and by radioimmunoprecipitation (RIP) with polyclonal HSV-1 antiserum. Amongst several proteins detected in these preparations, the four major HSV-1 glycoproteins, gB, gC, gD, and gE, were found to be present. Differences between NP40 or Empigen-solubilised HSV-1 antigen preparations with respect to two of these glycoproteins, gB and gE, were detected by using a small panel of monoclonal antibodies. Comparative studies in mice showed the Empigen-solubilised HSV-1 antigen preparations elicited greater antibody responses and greater protection against lethal HSV-1 challenge infection than the NP40-solubilised preparation.

Vaccinia virus vectors: new strategies for producing recombinant vaccines

The development and continued refinement of techniques for the efficient insertion and expression of heterologous DNA sequences from within the genomic context of infectious vaccinia virus recombinants are among the most promising current approaches towards effective immunoprophylaxis against a variety of protozoan, viral, and bacterial human pathogens. Because of its medical relevance, this area is the subject of intense research interest and has evolved rapidly during the past several years. This review (i) provides an updated overview of the technology that exists for assembling recombinant vaccinia virus strains, (ii) discusses the advantages and disadvantages of these approaches, (iii) outlines the areas of outgoing research directed towards overcoming the limitations of current techniques, and (iv) provides some insight (i.e., speculation) about probable future refinements in the use of vaccinia virus as a vector.

Protection of mice against lethal challenge with herpes simplex virus by vaccination with an adenovirus vector expressing HSV glycoprotein B

Increasing attention has been focused on the use of recombinant mammalian viruses as potential vaccines. Recombinant human adenoviruses are one of the more promising vaccine vectors because they can be easily constructed and because live adenovirus vaccines have been administered orally to large numbers of military recruits without adverse reactions. In order to examine the efficacy of human adenoviruses as vaccines we have studied the immunity induced by a recombinant adenovirus vector, AdgB2, which induces high level expression of herpes simplex virus (HSV) glycoprotein B (gB) in human and murine cells. Mice inoculated with AdgB2 produced antibodies specific for gB which neutralized HSV in the presence of complement. Although mice inoculated with AdgB2 showed no ill-effects after AdgB2 inoculation and we were unable to detect replication of human adenoviruses in mice, the mice were protected from a lethal challenge with HSV after a single inoculation with AdgB2.