Immunization with replication-defective mutants of herpes simplex virus type 1: sites of immune intervention in pathogenesis of challenge virus infection

Vaccine-induced serum immunoglobin contributes to protection from herpes simplex virus type 2 genital infection in the presence of immune T cells

Herpes simplex type virus 2 (HSV-2) is a sexually transmitted pathogen that causes genital lesions and spreads to the nervous system to establish acute and latent infections. Systemic but not mucosal cellular and humoral immune responses are elicited by immunization of mice with a replication-defective mutant of HSV-2, yet the mice are protected against disease caused by subsequent challenge of the genital mucosa with virulent HSV-2. In this study, we investigated the role of immune serum antibody generated by immunization with a replication-defective HSV-2 vaccine prototype strain in protection of the genital mucosa and the nervous system from HSV-2 infection. Passive transfer of replication-defective virus-immune serum at physiologic concentrations to SCID or B-cell-deficient mice had no effect on replication of challenge virus in the genital mucosa but did significantly reduce the incidence and severity of genital and neurologic disease. In contrast, B-cell-deficient mice immunized with replication-defective HSV-2 were able to control replication of challenge virus in the genital mucosa, but not until 3 days postchallenge, and were not completely protected against genital and neurologic disease. Passive transfer of physiologic amounts of immune serum to immunized, B-cell-deficient mice completely restored their capacity to limit replication of challenge virus in the genital mucosa and prevented signs of genital and systemic disease. In addition, the numbers of viral genomes in the lumbosacral dorsal root ganglia of immunized, B-cell-deficient mice were dramatically reduced by transfer of immune serum prior to challenge. These results suggest that there is an apparent synergism between immune serum antibody and immune T cells in achieving protection and that serum antibody induced by vaccination with replication-defective virus aids in reducing establishment of latent infection after genital infection with HSV-2.

Effects of preexisting immunity on the response to herpes simplex-based oncolytic viral therapy

Herpes simplex viruses (HSV) type 1 are the basis of a number of anticancer strategies that have proven efficacious in animal models. They are natural human pathogens and the majority of adults have anti-HSV immunity. The current study examined the effect of preexisting immunity on the response to herpes-based oncolytic viral treatment of hepatic metastatic cancer in a murine model designed to simulate a clinical approach likely to be utilized for nonneurological tumors. Specifically, the anticancer effects of NV1020 or G207, two multimutated HSV-1 oncolytic viruses, were tested in immunocompetent mice previously immunized with a wild-type herpes simplex type 1 virus. Mice were documented to have humoral as well as cell-mediated immunity to HSV-1. Tumor response to oncolytic therapy was not measurably abrogated by immunity to HSV at the doses tested. The influence of route of viral administration was also tested in models of regional hepatic arterial and intravenous therapy. Route of viral administration influenced efficacy, as virus delivered intravenously produced some detectable attenuation while hepatic arterial therapy remained unaffected. These results demonstrate that when given at appropriate doses and in reasonable proximity to tumor targets, HSV-based oncolytic therapy can still be expected to be effective treatment for patients with hepatic malignancies.

Biological properties of herpes simplex virus 2 replication-defective mutant strains in a murine nasal infection model

We used a mouse nasal model of herpes simplex virus 2 (HSV-2) infection to examine the biological properties of HSV-2 wild-type (wt), TK-negative, and replication-defective strains in vivo. Nasal septa tissue is the major site of wt viral replication post intranasal (i.n.) inoculation. The HSV-2 strain 186 syn(+)-1 wt virus caused lethal encephalitis at doses of 10(4) PFU and above per nostril, and at lower doses no neurons in the trigeminal ganglia were positive for the latency-associated transcript, indicating a lack of latent infection. The 186DeltaKpn TK-negative mutant virus replicated in nasal septa tissue but showed low-level replication in trigeminal ganglia at only one timepoint. In situ hybridization of trigeminal ganglia showed that the number of LAT-positive neurons was proportional to the inoculum dose from 10(3) to 10(6) PFU per nare. The replication-defective mutant virus 5BlacZ showed no replication in nasal septa tissue and no persistence of viral DNA at the inoculation site or the trigeminal ganglia. Nevertheless, inoculation of 5BlacZ or the double-mutant dl5-29 at distal sites reduced acute replication and latent infection of 186DeltaKpn following intranasal challenge. This infection model provides a biological system to test the properties of HSV-2 strains and shows that replication-defective mutant strains do not persist at sites of inoculation or in sensory ganglia but can induce immune protection that reduces the latent viral load of a challenge virus.

Disruption of virion host shutoff activity improves the immunogenicity and protective capacity of a replication-incompetent herpes simplex virus type 1 vaccine strain

The virion host shutoff (vhs) protein encoded by herpes simplex virus type 1 (HSV-1) destabilizes both viral and host mRNAs. An HSV-1 strain with a mutation in vhs is attenuated in virulence and induces immune responses in mice that are protective against corneal infection with virulent HSV-1, but it has the capacity to establish latency. Similarly, a replication-incompetent HSV-1 strain with a mutation in ICP8 elicits an immune response protective against corneal challenge, but it may be limited in viral antigen production. We hypothesized therefore that inactivation of vhs in an ICP8(-) virus would yield a replication-incompetent mutant with enhanced immunogenicity and protective capacity. In this study, a vhs(-)/ICP8(-) HSV-1 mutant was engineered. BALB/c mice were immunized with incremental doses of the vhs(-)/ICP8(-) double mutant or vhs(-) or ICP8(-) single mutants, or the mice were mock immunized, and protective immunity against corneal challenge with virulent HSV-1 was assessed. Mice immunized with the vhs(-)/ICP8(-) mutant showed prechallenge serum immunoglobulin G titers comparable to those immunized with replication-competent vhs(-) virus and exceed those of mice immunized with the ICP8(-) single mutant. Following corneal challenge, the degrees of protection against ocular disease, weight loss, encephalitis, and establishment of latency were similar for vhs(-)/ICP8(-) and vhs(-) virus-vaccinated mice. Moreover, the double deleted vhs(-)/ICP8(-) virus protected mice better in all respects than the single deleted ICP8(-) mutant virus. The data indicate that inactivation of vhs in a replication-incompetent virus significantly enhances its protective efficacy while retaining its safety for potential human vaccination. Possible mechanisms of enhanced immunogenicity are discussed.

Vaccine protection against simian immunodeficiency virus by recombinant strains of herpes simplex virus

An effective vaccine for AIDS may require development of novel vectors capable of eliciting long-lasting immune responses. Here we report the development and use of replication-competent and replication-defective strains of recombinant herpes simplex virus (HSV) that express envelope and Nef antigens of simian immunodeficiency virus (SIV). The HSV recombinants induced antienvelope antibody responses that persisted at relatively stable levels for months after the last administration. Two of seven rhesus monkeys vaccinated with recombinant HSV were solidly protected, and another showed a sustained reduction in viral load following rectal challenge with pathogenic SIVmac239 at 22 weeks following the last vaccine administration. HSV vectors thus show great promise for being able to elicit persistent immune responses and to provide durable protection against AIDS.

Construction, phenotypic analysis, and immunogenicity of a UL5/UL29 double deletion mutant of herpes simplex virus 2

A number of studies have shown that replication-defective mutant strains of herpes simplex virus (HSV) can induce protective immunity in animal systems against wild-type HSV challenge. However, all of those studies used viruses with single mutations. Because multiple, stable mutations provide optimal levels of safety for live vaccines, we felt that additional mutations needed to be engineered into a candidate vaccine strain for HSV-2 and genital herpes. We therefore isolated an HSV-2 strain with deletion mutations in two viral DNA replication protein genes, UL5 and UL29. The resulting double deletion mutant virus strain, dl5-29, fails to form plaques or to give any detectable single cycle yields in normal monkey or human cells. Nevertheless, dl5-29 expresses nearly the same pattern of gene products as the wild-type virus or the single mutant viruses and induces antibody titers in mice that are equivalent to those induced by single deletion mutant viruses. Therefore, it is feasible to isolate a mutant HSV strain with two mutations in essential genes and with an increased level of safety but which is still highly immunogenic.

Twenty-five-year panorama of corneal immunology: emerging concepts in the immunopathogenesis of microbial keratitis, peripheral ulcerative keratitis, and corneal transplant rejection

PURPOSE

To describe the most recent advances in our understanding of the cellular and molecular mechanisms involved in the immunopathogenesis of corneal immunoinflammatory disorders including microbial keratitis, peripheral ulcerative keratitis. and allograft rejection.

METHODS

Review of the published peer-reviewed literature that has contributed significantly to our modern understanding of corneal immunology. In addition, the authors have summarized the information in conceptual diagrams that highlight the critical cellular and molecular pathways that lead to corneal immune responses in the two most thoroughly studied corneal immune disorders, herpes simplex keratitis (HSK) and transplant rejection.

RESULTS

In spite of the wide array of molecular and cellular factors that mediate corneal immunity, critical mechanistic facets are shared by the various corneal immunoinflammatory disorders. These include activation and migration of local antigen-presenting cells (APCs), including Langerhans cells (LCs), upregulation in pleiotropic proinflammatory cytokines such as interleukin-1 (IL-1) and tumor necrosis factor-alfa (TNF-alpha) that can mediate a wide array of immune functions in addition to up-regulating protease expression. and chemokines that play a critical role on the one hand in attracting nonantigen-specific inflammatory cells such as neutrophils and on the other in attracting CD4+ T helper type 1 (Th1) cells that mediate most of the destruction in the cornea.

CONCLUSIONS

In the last 25 years, we have seen our field develop from a descriptive stage into a new phase where the fundamental processes that mediate and effect corneal immunity are being accurately deciphered. It is anticipated that this new knowledge will allow development of specific molecular and genetic therapeutic strategies that could target critical steps in the immunopathogenesis of disease without the untoward side-effects of nonspecific generalized immune suppression that still remains the standard of care today.

Herpes simplex virus virion host shutoff (vhs) activity alters periocular disease in mice

During lytic infection, the virion host shutoff (vhs) protein of herpes simplex virus (HSV) mediates the rapid degradation of RNA and shutoff of host protein synthesis. In mice, HSV type 1 (HSV-1) mutants lacking vhs activity are profoundly attenuated. HSV-2 has significantly higher vhs activity than HSV-1, eliciting a faster and more complete shutoff. To examine further the role of vhs activity in pathogenesis, we generated an intertypic recombinant virus (KOSV2) in which the vhs open reading frame of HSV-1 strain KOS was replaced with that of HSV-2 strain 333. KOSV2 and a marker-rescued virus, KOSV2R, were characterized in cell culture and tested in an in vivo mouse eye model of latency and pathogenesis. The RNA degradation kinetics of KOSV2 was identical to that of HSV-2 333, and both showed vhs activity significantly higher than that of KOS. This demonstrated that the fast vhs-mediated degradation phenotype of 333 had been conferred upon KOS. The growth of KOSV2 was comparable to that of KOS, 333, and KOSV2R in cell culture, murine corneas, and trigeminal ganglia and had a reactivation frequency similar to those of KOS and KOSV2R from explanted latently infected trigeminal ganglia. There was, however, significantly reduced blepharitis and viral replication within the periocular skin of KOSV2-infected mice compared to mice infected with either KOS or KOSV2R. Taken together, these data demonstrate that heightened vhs activity, in the context of HSV-1 infection, leads to increased viral clearance from the skin of mice and that the replication of virus in the skin is a determining factor for blepharitis. These data also suggest a role for vhs in modulating host responses to HSV infection.

Prospects for control of herpes simplex virus disease through immunization

Herpes simplex viruses (HSVs) can cause a variety of infections, including genital herpes. Despite effective antiviral therapy, HSV infections remain a significant worldwide public health problem. Vaccines offer the best hope for controlling spread and limiting HSV disease. This article discusses the pathogenesis and immunobiology of mucocutaneous HSV infections, summarizes the spectrum of diseases caused by HSV, and provides a review of the field of HSV vaccine research. This article also discusses what might be realistically expected of a vaccine intended for control of genital herpes and explores the question of whether a vaccine that is effective in controlling genital HSV disease might also be effective in controlling nongenital HSV disease. The efficacy of such vaccines for the full spectrum of HSV disease will eventually determine the timing and targeting of immunization, ranging from selective immunization in preadolescence to universal childhood immunization as part of the routine childhood regimen.

BAC-VAC, a novel generation of (DNA) vaccines: A bacterial artificial chromosome (BAC) containing a replication-competent, packaging-defective virus genome induces protective immunity against herpes simplex virus 1

This study aimed to exploit bacterial artificial chromosomes (BAC) as large antigen-capacity DNA vaccines (BAC-VAC) against complex pathogens, such as herpes simplex virus 1 (HSV-1). The 152-kbp HSV-1 genome recently has been cloned as an F-plasmid-based BAC in Escherichia coli (fHSV), which can efficiently produce infectious virus progeny upon transfection into mammalian cells. A safe modification of fHSV, fHSVDeltapac, does not give rise to progeny virus because the signals necessary to package DNA into virions have been excluded. However, in mammalian cells fHSVDeltapac DNA can still replicate, express the HSV-1 genes, cause cytotoxic effects, and produce virus-like particles. Because these functions mimic the lytic cycle of the HSV-1 infection, fHSVDeltapac was expected to stimulate the immune system as efficiently as a modified live virus vaccine. To test this hypothesis, mice were immunized with fHSVDeltapac DNA applied intradermally by gold-particle bombardment, and the immune responses were compared with those induced by infection with disabled infectious single cycle HSV-1. Immunization with either fHSVDeltapac or disabled infectious single cycle HSV-1 induced the priming of HSV-1-specific cytotoxic T cells and the production of virus-specific antibodies and conferred protection against intracerebral injection of wild-type HSV-1 at a dose of 200 LD(50). Protection probably was cell-mediated, as transfer of serum from immunized mice did not protect naive animals. We conclude that BAC-VACs per se, or in combination with genetic elements that support replicative amplification of the DNA in the cell nucleus, represent a useful new generation of DNA-based vaccination strategies for many viral and nonviral antigens.

Effect of prior exposure to herpes simplex virus 1 on viral vector-mediated tumor therapy in immunocompetent mice

Replication-competent, attenuated mutants of herpes simplex virus type 1 (HSV-1) have been shown to be efficacious for tumor therapy. However, these studies did not address the consequences of prior exposure to HSV, as will be the case with many patients likely to receive this therapy. Two strains of mice, A/J and BALB/c, were infected with wild-type HSV-1 by intraperitoneal injection and the immune response was determined by plaque reduction assay for neutralizing antibody and ELISA for IgG and IgM. Syngeneic tumors, N18 neuroblastoma and CT26 colon carcinoma, were implanted subcutaneously in HSV-1 seropositive and naive A/J and BALB/c mice, respectively. Established tumors were subsequently treated intratumorally with a multi-mutated HSV-1, G207. G207 inhibited tumor growth to a similar extent whether the mice were seropositive or not. We next examined the effect of multiple intratumoral inoculations of a 10-fold lower dose of G207 on tumor growth. In the multiple treatment group (biweekly for 3 weeks), 75% of tumors were cured, whereas no cures were seen in the single treatment group. We conclude that HSV seropositivity should not deleteriously affect the efficacy of G207 tumor therapy, and multiple inoculations of virus should be considered for clinical evaluation.

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.

A novel anti-herpes simplex virus type 1-specific herpes simplex virus type 1 recombinant

A recombinant herpes simplex virus (HSV) capable of inhibiting its own replication as well as the replication of wild-type virus would have greatly increased safety as a general purpose vector for in vivo gene transfer, antitumor therapy, and viral vaccine against HSV infection. By using a tetracycline repressor (tetR)-mediated HSV-1 viral replication switch [Yao and Eriksson (1999). Hum. Gene Ther. 10, 419-427], we have generated a novel anti-HSV-1-specific HSV-1 recombinant (CJ83193) that expresses a trans-dominant negative HSV-1 UL9 origin-binding protein, UL9-C535C. The de novo synthesis of CJ83193 can be suppressed by UL9-C535C by at least 1 x 10(6)-fold in non-tetR-expressing cells, and is subject to tetracycline regulation over a range of four to five orders of magnitude in a tetR-expressing osteosarcoma line. In particular, the UL9-C535C peptides expressed from the CJ83193 genome can inhibit the replication of wild-type HSV-1 by 100- to 200-fold in single-step growth assays. The construction of CJ83193 creates a new general strategy for developing recombinant viral vectors able to function as an intracellular therapy against wild-type viral infections.

Immunization against genital herpes with a vaccine virus that has defects in productive and latent infection

An effective vaccine for genital herpes has been difficult to achieve because of the limited efficacy of subunit vaccines and the safety concerns about live viruses. As an alternative approach, mutant herpes simplex virus strains that are replication-defective can induce protective immunity. To increase the level of safety and to prove that replication was not needed for immunization, we constructed a mutant herpes simplex virus 2 strain containing two deletion mutations, each of which eliminated viral replication. The double-mutant virus induces protective immunity that can reduce acute viral shedding and latent infection in a mouse genital model, but importantly, the double-mutant virus shows a phenotypic defect in latent infection. This herpes vaccine strain, which is immunogenic but has defects in both productive and latent infection, provides a paradigm for the design of vaccines and vaccine vectors for other sexually transmitted diseases, such as AIDS.

Immunogenicity of herpes simplex virus type 1 mutants containing deletions in one or more alpha-genes: ICP4, ICP27, ICP22, and ICP0

Replication defective mutants of HSV have been proposed both as vaccine candidates and as vehicles for gene therapy because of their inability to produce infectious progeny. The immunogenicity of these HSV replication mutants, at both qualitative and quantitative levels, will directly determine their effectiveness for either of these applications. We have previously reported (Brehm et al., J. Virol., 71, 3534, 1997) that a replication defective mutant of HSV-1, which expresses a substantial level of viral genes without producing virus particles, is as efficient as wild-type HSV-1 in eliciting an HSV-specific cytotoxic T-lymphocyte (CTL) response. In this report, we have further evaluated the immunogenic potential of HSV-1-derived replication defective mutants by examining the generation of HSV-specific CTL following immunization with viruses that are severely restricted in viral gene expression due to mutations in one or more HSV alpha genes (ICP4, ICP27, ICP22, and ICP0). To measure the CTL responses induced by the HSV alpha-mutants, we have targeted two H-2Kb-restricted CTL epitopes: an epitope in a virion protein, gB (498-505), and an epitope in a nonvirion protein, ribonucleotide reductase (RR1 822-829). The HSV mutants used in this study are impaired in their ability to express gB while a majority of them still express RR1. Our findings demonstrate that a single immunization with these mutants is able to generate a strong CTL response not only to RR1 822-829, but also to gB498-505 despite their inability to express wild-type levels of gB. Furthermore, a single immunization with any individual mutant can also provide immune protection against HSV challenge. These results suggest that mutants which are restricted in gene expression may be used as effective immunogens in vivo.

Herpes simplex virus vaccines

Herpes simplex virus (HSV) infections are common and produce not only a primary infection, but also latent and recurrent infections. Therefore, the goals of a HSV vaccine are different from other vaccines. In this review, the goals of both prophylactic and therapeutic HSV vaccines are discussed and related to the immunobiology of acute and recurrent HSV infections. Next, the vaccine strategies that have been and are being evaluated for control of HSV disease are described. Current approaches take advantage of many of the modern methodologies for vaccine development. Thus, as we await final evaluations of subunit HSV glycoprotein vaccines, early phase I trails are evaluating newer vaccine approaches including DNA-based vaccines and replication-impaired viruses. The definitive HSV vaccine may await increased knowledge of the optimal viral antigen(s) and routes to induce genital tract immunity.

Immunization with a single major histocompatibility complex class I-restricted cytotoxic T-lymphocyte recognition epitope of herpes simplex virus type 2 confers protective immunity

We have evaluated the potential of conferring protective immunity to herpes simplex virus type 2 (HSV-2) by selectively inducing an HSV-specific CD8(+) cytotoxic T-lymphocyte (CTL) response directed against a single major histocompatibility complex class I-restricted CTL recognition epitope. We generated a recombinant vaccinia virus (rVV-ES-gB498-505) which expresses the H-2Kb-restricted, HSV-1/2-cross-reactive CTL recognition epitope, HSV glycoprotein B residues 498 to 505 (SSIEFARL) (gB498-505), fused to the adenovirus type 5 E3/19K endoplasmic reticulum insertion sequence (ES). Mucosal immunization of C57BL/6 mice with this recombinant vaccinia virus induced both a primary CTL response in the draining lymph nodes and a splenic memory CTL response directed against HSV gB498-505. To determine the ability of the gB498-505-specific memory CTL response to provide protection from HSV infection, immunized mice were challenged with a lethal dose of HSV-2 strain 186 by the intranasal (i.n.) route. Development of the gB498-505-specific CTL response conferred resistance in 60 to 75% of mice challenged with a lethal dose of HSV-2 and significantly reduced the levels of infectious virus in the brains and trigeminal ganglia of challenged mice. Finally, i.n. immunization of C57BL/6 mice with either a recombinant influenza virus or a recombinant vaccinia virus expressing HSV gB498-505 without the ES was also demonstrated to induce an HSV-specific CTL response and provide protection from HSV infection. This finding confirms that the induction of an HSV-specific CTL response directed against a single epitope is sufficient for conferring protective immunity to HSV. Our findings support the role of CD8(+) T cells in the control of HSV infection of the central nervous system and suggest the potential importance of eliciting HSV-specific mucosal CD8(+) CTL in HSV vaccine design.

Control of STDs--the role of prophylactic vaccines against herpes simplex virus

OBJECTIVES

To summarise the current status of genital herpes simplex virus (HSV) vaccine development and provide a discussion of the potential benefits and limitations of genital herpes vaccines.

METHODS

Literature review.

RESULTS

Genital herpes simplex virus infection has a complex pathogenesis that has contributed to it becoming a serious worldwide problem. In an attempt to control the problem five different types of genital herpes vaccines have been developed. These include inactivated virion derived vaccines, adjuvanted subunit vaccines, vectored vaccines, replication limited live viral vaccines, genetically attenuated live viral vaccines, and nucleic acid vaccines. While available commercially in some parts of the world, inactivated virion derived vaccines have not been proved effective. Of the others, adjuvanted subunit vaccines, replication limited live viral vaccines, and nucleic acid vaccines are currently in clinical trials and vectored vaccines and genetically attenuated live viral vaccines are in preclinical development.

CONCLUSION

With regard to HSV vaccines in general, it is reasonable to expect that the newer vaccines may protect the individual from developing symptomatic genital herpes but may not protect against asymptomatic viral infection. With widespread use HSV vaccines might help to prevent the spread of genital herpes.

Herpes simplex virus replication-induced expression of chemokines and proinflammatory cytokines in the eye: implications in herpetic stromal keratitis

On infection of the cornea with herpes simplex virus (HSV), an immunopathologic response termed herpetic stromal keratitis (HSK) ensues. This response is mediated primarily by CD4+ T cells and only occurs if mice are infected with replication-competent virus, although replication-defective mutants induce cellular immune responses following infection. To determine the consequences of HSV replication in the cornea, which is crucial for HSK manifestation, corneas infected with productive virus and replication-defective mutants were analyzed for chemokines and proinflammatory cytokine mRNA expression by RT-PCR at various times. While productive infection resulted in rapid upregulation and sustained expression of such chemokines as N51/KC, macrophage inflammatory protein-1beta (MIP-1beta), MIP-2, and monocyte chemotactic protein-1 (MCP-1) and such cytokines as interleukin-1 (IL-1), IL-6, IL-12, and tumor necrosis factor-alpha (TNF-alpha), expression of such inflammatory mediators was minimal and transient after unproductive infection. Expression of MIP-1alpha and lymphotactin along with a biphasic expression of IL-6 and MIP-2 were seen only with productive infection. Initial PMN recruitment into the cornea was approximately 50-fold greater with productive infection than with unproductive infection. These data suggest that a replication-induced proinflammatory milieu in the cornea is crucial for the subsequent progression of HSK possibly because of enhancement of the expression of corneal agonists that drive HSK manifestation.

A gamma34.5 mutant of herpes simplex 1 causes severe inflammation in the brain

A number of viral vectors are currently being evaluated as potential gene therapy vectors for gene delivery to the brain. As well as evaluating their ability to express a transgene for extended periods of time it is also essential to examine any cytotoxic immune response to such vectors as this may not only limit transgene expression but also cause irreparable harm. This work describes the effect of inoculating a gamma34.5 mutant of herpes simplex type 1 (1716lacZ) into the brain of different strains of rats and mice. Animals were monitored for weight loss and signs of illness, and their brains were evaluated for inflammation, beta-galactosidase expression and recoverable infectious virus. We report that there is (i) a powerful immune response consisting of an early non-specific phase and a later presumably T-cell-mediated phase; (ii) significant weight loss in some animals strains accompanied by severe signs of clinical illness and (iii) transient reporter gene expression in all animal strains examined. To be useful for gene therapy we suggest this virus requires further modification, it should be tested in several animal strains and the dose of virus used may be critical in order to limit damage.

Expression of the human immunodeficiency virus gag gene products by a replication-incompetent herpes simplex virus vector

A recombinant replication-incompetent herpes simplex virus vector (vd120/Gag) that expressed the human immunodeficiency virus 1 gag gene and part of the pol gene that encodes the HIV-1 protease was constructed. Examination of cells infected with vd120/Gag revealed the presence of the Gag polyprotein Pr55gag by 12 h post-infection, as well as abundant levels of the proteolytically processed 24-kDa capsid protein. Analysis of vector-infected cells and culture supernatant indicated that the majority of the 24-kDa protein remained cell-associated. Although the HIV-1 Gag polyprotein was produced in vd120/Gag-infected cells, there was no evidence of HIV virus-like particle production upon examination of vector-infected cells by transmission electron microscopy.

Immunization with HSV-1 antigen rapidly protects against HSV-1-induced encephalitis and is IFN-gamma independent

Herpes simplex virus type 1 (HSV-1) infection of mice frequently culminates in fatal encephalitis. Intraperitoneal administration of heat-inactivated HSV-1 0-5 days before infection (active immunization) protected mice from encephalitis. In addition, active immunization 2-5 days before ocular infection with HSV-1 reduced the frequency of establishment of latent HSV-1 infection in the trigeminal ganglion (TG). However, intraperitoneal administration of heat-inactivated HSV-1 did not induce interferon (IFN) production in the peritoneum or serum, as determined by bioassay and ELISA. Intraperitoneal administration of heat-attenuated HSV-1 elicited IFN-gamma but not type I IFN production in the peritoneum. The production of IFN-gamma correlated with the infiltration of CD4 and CD8 cells in the peritoneum as determined by RT-PCR. In addition, there was a significant increase in interleukin (IL)-12 p40, IL-12p35, IL-6, IL-10, and IFN-gamma mRNA in peritoneal cells, as determined by RT-PCR following immunization with heat-attenuated HSV-1, which was not observed using heat-inactivated HSV-1. The results suggest that resistance to HSV-1 is induced rapidly following immunization with viral antigen but that protection against encephalitis is independent of the cytokines that are generated in the peritoneum.

Modulation of mucosal and systemic immunity by enteric administration of nonreplicating herpes simplex virus expressing cytokines

In this report the ability of enteric immunization with recombinant replication deficient (ICP4-/-) HSV expressing IFN gamma to generate protection and modulate mucosal and systemic immunity was evaluated. ICP4-/-HSV, ICP4-/-HSV expressing IL4, live replicating, and uv HSV were used as controls. Following enteric administration of live HSV, a Th1 cytokine response was induced in the spleen, while both Th1 and notable Th2 cytokine production were detected at mucosal sites. Modulation of mucosal and systemic immune response was achieved when nonreplicating recombinant HSV viruses expressing cytokines were used. Compared to the control replication defective viruses, decreased frequency of Th2 cytokine producing cells in Peyer's patches was observed following enteric administration of nonreplicating HSV expressing IFN gamma. When IFN gamma expressing virus was given enterically, modulation was observed at the systemic level, measured by ELISPOT for cytokine producing cells, ELISA from the in vitro restimulated splenic cell cultures, and by the increase of the IgG2a/IgG1 ratio in the serum. This report provides evidence that replication defective viruses expressing cytokine genes in contrast to uv HSV, are immunogenic when administered enterically and can generate significant immunomodulatory effects at the mucosal and systemic levels.

Mucosal and parenteral vaccination against acute and latent murine cytomegalovirus (MCMV) infection by using an attenuated MCMV mutant

We used a live attenuated murine cytomegalovirus (MCMV) mutant to analyze mechanisms of vaccination against acute and latent CMV infection. We selected MCMV mutant RV7 as a vaccine candidate since this virus grows well in tissue culture but is profoundly attenuated for growth in normal and severe combined immunodeficient (SCID) mice (V. J. Cavanaugh et al., J. Virol. 70:1365-1374, 1996). BALB/c mice were immunized twice (0 and 14 days) subcutaneously (s.c.) with tissue culture-passaged RV7 and then challenged with salivary gland-passaged wild-type MCMV (sgMCMV) intraperitoneally (i.p.) on day 28. RV7 vaccination protected mice against challenge with 10(5) PFU of sgMCMV, a dose that killed 100% of mock-vaccinated mice. RV7 vaccination reduced MCMV replication 100- to 500-fold in the spleen between 1 and 8 days after challenge. We used the capacity to control replication of MCMV in the spleen 4 days after challenge as a surrogate for protection. Protection was antigen specific and required both live RV7 and antigen-specific lymphocytes. Interestingly, RV7 was effective when administered s.c., i.p., perorally, intranasally, and intragastrically, demonstrating that attenuated CMV applied to mucosal surfaces can elicit protection against parenteral virus challenge. B cells and immunoglobulin G were not essential for RV7-induced immunity since B-cell-deficient mice were effectively vaccinated by RV7. CD8 T cells, but not CD4 T cells, were critical for RV7-induced protection. Depletion of CD8 T cells by passive transfer of monoclonal anti-CD8 (but not anti-CD4) antibody abrogated RV7-mediated protection, and RV7 vaccination was less efficient in CD8 T-cell-deficient mice with a targeted mutation in the beta2-microglobulin gene. Although gamma interferon is important for innate resistance to MCMV, it was not essential for RV7 vaccination since gamma interferon receptor-deficient mice were protected by RV7 vaccination. Establishment of and/or reactivation from latency by sgMCMV was decreased by RV7 vaccination, as measured by diminished reactivation of MCMV from splenic explants. We found no evidence for establishment of splenic latency by RV7 after s.c. vaccination. We conclude that RV7 administered through both systemic and mucosal routes is an effective vaccine against MCMV infection. It may be possible to design human CMV vaccines with similar properties.

Contributions of antibody and T cell subsets to protection elicited by immunization with a replication-defective mutant of herpes simplex virus type 1

Replication-defective mutants of herpes simplex virus 1 (HSV-1) elicit immune responses in mice that reduce acute and latent infection after corneal challenge and are protective against development of disease. To understand the basis for the protective immunity induced by this new form of immunization, we investigated the contribution of various components of the immune response to protection against corneal infection and disease. Passive transfer of sera from mice immunized with the replication-defective mutant virus, d301, its parental HSV-1 strain, or uninfected cell lysate was used to examine the role of antibody. Despite posttransfer neutralizing antibody titers equivalent to those in control mice directly immunized with mutant virus, recipients of immune serum showed no reductions in primary replication in the eye, keratitis, or latent infection of the nervous system. However, immune serum protected mice from encephalitis and death. To examine the contribution of T cell subsets to protection, mice were immunized once with mutant virus and then were depleted in vivo of CD4+ or CD8+ T cells prior to corneal challenge. CD4 depletion resulted in higher titers of challenge virus in the eye at 3 to 4 days after challenge compared to control mice. Latent infection of the nervous system was increased by depletion of CD4+ T cells but not by depletion of CD8+ T cells keratitis developed only in a portion of the CD8+ T cell-depleted mice, suggesting that an immunopathologic potential of CD4+ T cells is held in check when immune CD8+ T cells are also present. Taken together, these data support a role for antibody induced by immunization with a replication-defective virus principally in protecting the central nervous system from disease, roles for CD4+ T cells in reducing primary replication in the eye and protecting against latent infection of the nervous system, and a role for CD8+ T cells in regulating the immunopathologic activity of CD4+ T cells.

Equine herpesvirus 1 mutants devoid of glycoprotein B or M are apathogenic for mice but induce protection against challenge infection

Equine herpesvirus 1 (EHV-1) mutants devoid of the open reading frames (ORFs) of either glycoprotein (g) B or M were constructed and tested for their immunogenic potential in a murine model of EHV-1 infection. The mutant viruses were engineered using the virulent EHV-1 strain RacL11 or the modified live vaccine strain RacH by inserting the Escherichia coli LacZ gene into the viral ORFs. RacL11-infected mice showed signs typical of an EHV-1 infection, whereas mice infected with the EHV-1 gB- or gM-negative mutants or with RacH did not develop disease. No difference in the pathogenic potential of RacL11 gB- and gM-negative viruses was observed after application of either phenotypically completed or negative viruses. However, revertant RacL11 viruses in which the gB or gM gene had been restored caused EHV-1-related symptoms that were indistinguishable from those induced by RacL11. Mice that had been immunized with phenotypically negative gB- and gM-deficient EHV-1 were challenged with the RacL11 virus 25 days after immunization. Mock-immunized mice developed EHV-1 disease and high virus loads in their lungs were observed. In contrast, mice developed not exhibit EHV-1-caused disease. It was concluded (i) that deletion of either gB or gM abolished the virulence of strain RacL11 and (ii) that immunization with gB- or gM-negative EHV-1 elicited a protective immunity that was reflected by both virus-neutralizing antibodies and EHV-1-specific T-cells in spleens of immunized mice.

Innate and acquired immunity to herpes simplex virus type 1

Immunization with heat-inactivated herpes simplex virus type 1 (HSV-1) 2-5 days before ocular infection reduced the frequency of establishment of latent HSV-1 infection in the trigeminal ganglion (TG); this induction of resistance coincided with reduced expression of IFN-gamma mRNA in the TG. Immunization with unrelated antigens was not protective. In part, this resistance to nervous system invasion correlated with the appearance of serum antibody to HSV-1. Immunization reduced viral replication in the eye and trigeminal ganglion, and prevented HSV-1 spread to the cerebellum. IFN-gamma was detected in immunized mice 4 days postocular infection as determined by plaque reduction using neutralizing Ab to IFN-alpha/beta and IFN-gamma. Injection of antibody (Ab) to IFN-alpha/beta and IFN-gamma administered at the time of immunization did not affect survival. Anti-IFN-gamma-treated mice had significantly reduced levels of IFN in their serum. Treatment with anti-IFN-alpha/beta Ab resulted in an elevation in viral replication as determined by the expression of latency associated transcripts in the TG of mice. Likewise, there was a significant increase in the CD8, IL-12 (p40), and TNF-alpha mRNA levels in the TG of the anti-IFN-alpha/beta-treated mice TG explant cultures demonstrated that viral load was significantly increased in the TG of anti-IFN-alpha/beta-treated mice relative to TG of control mice 7 days after infection. The results suggest that exposure to viral antigens 2-5 days before infection is an important determinant of the extent of HSV-1 spread to the nervous system. Moreover, the data suggest that both an antibody response and IFN-alpha/beta play a role in limiting the progress of infection from the peripheral tissues to the central nervous system.

Construction and characterization of a replication-defective herpes simplex virus 2 ICP8 mutant strain and its use in immunization studies in a guinea pig model of genital disease

A replication-defective mutant of herpes simplex virus 2 (HSV-2) was engineered by replacing the ICP8 gene of HSV-2 strain 186 with an ICP8-lacZ fusion gene from the herpes simplex virus 1 (HSV-1) HD-2 mutant strain. The resulting virus, HSV-2 5BlacZ, is defective for growth in Vero cells but is capable of growth in a cell line that expresses HSV-1 ICP8. In Vero cells, the mutant virus is defective for DNA synthesis but is able to express many viral proteins at levels similar to those of wild-type virus, including several of the late kinetic class. SDS-PAGE and Western blot analysis demonstrated the expression of glycoproteins B and D by 5BlacZ in Vero cells. Initial studies have shown that immunization with 5BlacZ protects guinea pigs from intravaginal HSV-2 challenge. Immunized animals had less severe genital skin disease and reduced replication of the challenge virus in the genital tract during primary infection and reduced episodes of recurrent disease. Thus, HSV-2 ICP8 shows gene regulatory properties similar to those of HSV-1 ICP8, and this HSV-2 ICP8 mutant virus shows a phenotype similar to those of HSV-1 ICP8 mutant strains. Replication-defective mutants of HSV-2 offer a potential vaccine approach for immune intervention against HSV-2 genital disease and latent infection.

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.

Protease-deficient herpes simplex virus protects mice from lethal herpesvirus infection

Null mutants and attenuated mutants of herpes simplex virus (HSV) have been shown to induce immunity against challenge from wild-type virus. Null viruses with a defect in late gene products would be expected to express more viral genes than viruses with defects in essential early gene products and thus induce a better immune response. Herpesviruses encode a late gene product (serine protease) that is autocatalytic and cleaves the capsid assembly protein during viral replication. To determine whether a virus with a mutation in this gene could induce immunity, we constructed a recombinant virus containing the gusA reporter gene in the protease domain of the HSV type 1 UL26 open reading frame (ORF). Consistent with previous results (M. Gao, L. Matusick-Kumar, W. Hurlburt, S. F. DiTusa, W. W. Newcomb, J. C. Brown, P. J. McCann, I. Deckman, and R. J. Colonno, J. Virol. 68:3702-3712, 1994), recombinant virus could be isolated only from helper cell lines expressing the product of the UL26 ORF. Mice inoculated with the recombinant virus were unaffected by doses of virus that were lethal to mice infected with wild-type virus. Mice which were previously inoculated with the recombinant virus were also protected by a subsequent challenge with wild-type virus in a dose-dependent manner. These results indicate that recombinant viruses lacking the protease gene are avirulent but render protection from subsequent challenge.

Human herpes viruses latent infection in the nervous system

The neurotropic herpes viruses, HSV-1, HSV-2 and VZV, colonize and establish latent infection in human peripheral sensory ganglia. Recurrent diseases due to reactivation of these viral pathogens can take place despite an effective immune response. Molecular, cellular, physiological and immune mechanisms work in concert to enable the establishment of latency, the maintenance of the latent state for the entire life of the host, and the reactivation infection. Although all three viruses belong to the same family and establish latent infection in the same tissue, the clinical pattern of their reactivation is quite different. This review covers current knowledge of the basis of these infections, and offers a theory explaining the basis of HSV-1 latent infection and the differences of the disorders caused by HSV-1 and VZV reactivation in humans.

Viral replication is required for induction of ocular immunopathology by herpes simplex virus

Corneal infection of BALB/c mice with herpes simplex virus type 1 results in a chronic inflammatory response in the stroma termed herpetic stromal keratitis (HSK). This disease is considered to be immunopathological and mediated primarily by CD4+ T cells of the type 1 cytokine profile. However, the nature of the antigens, virus or host derived, which drive the inflammatory response remains in doubt. In this study, the relevance of infection with replicating virus for the subsequent development of HSK was evaluated with immunocompetent mice as well as with SCID mice reconstituted with herpes simplex virus-immune CD4+ T cells. In the corneas of immunocompetent mice, infectious virus, viral antigen, and mRNA expression were detectable for only a brief period of time (< or = 7 days postinfection), and all were undetectable by the time clinical lesions were evident (10 to 15 days). Viral replication, however, was necessary for the development of HSK in both models, since infection with UV-inactivated virus or with mutant viruses which were incapable of multiple rounds of replication in vivo failed to induce HSK. The inactivated and mutant viral preparations did, however, stimulate T-cell immune responses in immunocompetent mice. The results are discussed in terms of possible involvement of host antigens exposed in response to transient progeny virion replication in the immune-privileged cornea.

Herpes simplex virus vaccines as immunotherapeutic agents

As persistent viruses can escape immune surveillance, chronic or recurrent disease can be a major problem. Only after nearly 60 years of work have recent reproducible data, using herpes simplex virus infection as a model for persistent viral disease, established that vaccine immunotherapy is effective in the treatment of such viral infections.