Therapeutic vaccination with vhs(-) herpes simplex virus reduces the severity of recurrent herpetic stromal keratitis in mice

Prior Corneal Scarification and Injection of Immune Serum are Not Required Before Ocular HSV-1 Infection for UV-B-Induced Virus Reactivation and Recurrent Herpetic Corneal Disease in Latently Infected Mice

PURPOSE

Blinding ocular herpetic disease in humans is due to spontaneous reactivation of herpes simplex virus type 1 (HSV-1) from latency, rather than to primary acute infection. Mice latently infected with HSV-1 undergo little or no in vivo spontaneous reactivation with accompanying virus shedding in tears. HSV-1 reactivation can be induced in latently infected mice by several in vivo procedures, with UV-B-induced reactivation being one commonly used method. In the UV-B model, corneas are scarified (lightly scratched) just prior to ocular infection to increase efficiency of the primary infection and immune serum containing HSV-1 neutralizing antibodies is injected intraperitoneally (i.p.) to increase survival and decrease acute corneal damage. Since scarification can significantly alter host gene transcription in the cornea and in the trigeminal ganglia (TG; the site of HSV-1 latency) and since injection of immune serum likely modulates innate and adaptive herpes immunity, we investigated eliminating both treatments.

MATERIAL AND METHODS

Mice were infected with HSV-1 with or without corneal scarification and immune serum. HSV-1 reactivation and recurrent disease were induced by UV-B irradiation.

RESULTS

When corneal scarification and immune serum were both eliminated, UV-B irradiation still induced both HSV-1 reactivation, as measured by shedding of reactivated virus in tears and herpetic eye disease, albeit at reduced levels compared to the original procedure.

CONCLUSION

Despite the reduced reactivation and disease, avoidance of both corneal scarification and immune serum should improve the clinical relevance of the UV-B mouse model.

Decreased reactivation of a herpes simplex virus type 1 (HSV-1) latency-associated transcript (LAT) mutant using the in vivo mouse UV-B model of induced reactivation

Blinding ocular herpetic disease in humans is due to herpes simplex virus type 1 (HSV-1) reactivations from latency, rather than to primary acute infection. The cellular and molecular immune mechanisms that control the HSV-1 latency-reactivation cycle remain to be fully elucidated. The aim of this study was to determine if reactivation of the HSV-1 latency-associated transcript (LAT) deletion mutant (dLAT2903) was impaired in this model, as it is in the rabbit model of induced and spontaneous reactivation and in the trigeminal ganglia (TG) explant-induced reactivation model in mice. The eyes of mice latently infected with wild-type HSV-1 strain McKrae (LAT((+)) virus) or dLAT2903 (LAT((-)) virus) were irradiated with UV-B, and reactivation was determined. We found that compared to LAT((-)) virus, LAT((+)) virus reactivated at a higher rate as determined by shedding of virus in tears on days 3 to 7 after UV-B treatment. Thus, the UV-B-induced reactivation mouse model of HSV-1 appears to be a useful small animal model for studying the mechanisms involved in how LAT enhances the HSV-1 reactivation phenotype. The utility of the model for investigating the immune evasion mechanisms regulating the HSV-1 latency/reactivation cycle and for testing the protective efficacy of candidate therapeutic vaccines and drugs is discussed.

Proinflammatory cytokines and chemokines - but not interferon-β - produced in response to HSV-2 in primary human genital epithelial cells are associated with viral replication and the presence of the virion host shutoff protein

PROBLEM

It is unknown whether viral replication or viral components that subvert innate responses in other cells, specifically the virion host shutoff (VHS) protein, play a role in determining primary genital epithelial cell (GEC) innate antiviral responses.

METHOD OF STUDY

Cultures of primary female GECs were exposed to wildtype (WT), VHS-deleted (vhsB), or UV-inactivated HSV-2. Antiviral pathway induction was evaluated by measuring nuclear factor-κB (NFκB) translocation by immunofluorescent microscopy. Proinflammatory cytokines, chemokines, and interferon (IFN) were measured by Luminex or ELISA. Biological activity of IFN-β was evaluated via VSV-GFP bioassay, by blocking secreted IFN-β with neutralizing antibodies and by measuring interferon-stimulated genes by RT-PCR.

RESULTS

Proinflammatory cytokines and chemokines were upregulated in primary GECs in response to replication-competent HSV-2, but suppressed in the presence of the VHS protein. In contrast, upregulation of IFN-β depended on viral replication, but was not affected by VHS. However, the IFN-β produced was biologically active and reduced the viral burden.

CONCLUSION

Viral factors such as replication and the presence of the VHS protein play important roles in regulating innate antiviral responses against HSV-2 from primary GECs.

Recurrent herpetic stromal keratitis in mice, a model for studying human HSK

Herpetic eye disease, termed herpetic stromal keratitis (HSK), is a potentially blinding infection of the cornea that results in over 300,000 clinical visits each year for treatment. Between 1 and 2 percent of those patients with clinical disease will experience loss of vision of the infected cornea. The vast majority of these cases are the result of reactivation of a latent infection by herpes simplex type I virus and not due to acute disease. Interestingly, the acute infection is the model most often used to study this disease. However, it was felt that a recurrent model of HSK would be more reflective of what occurs during clinical disease. The recurrent animal models for HSK have employed both rabbits and mice. The advantage of rabbits is that they experience reactivation from latency absent any known stimulus. That said, it is difficult to explore the role that many immunological factors play in recurrent HSK because the rabbit model does not have the immunological and genetic resources that the mouse has. We chose to use the mouse model for recurrent HSK because it has the advantage of there being many resources available and also we know when reactivation will occur because reactivation is induced by exposure to UV-B light. Thus far, this model has allowed those laboratories using it to define several immunological factors that are important to this disease. It has also allowed us to test both therapeutic and vaccine efficacy.

mRNA decay during herpes simplex virus (HSV) infections: mutations that affect translation of an mRNA influence the sites at which it is cleaved by the HSV virion host shutoff (Vhs) protein

During lytic infections, the herpes simplex virus (HSV) virion host shutoff (Vhs) endoribonuclease degrades many host and viral mRNAs. Within infected cells it cuts mRNAs at preferred sites, including some in regions of translation initiation. Vhs binds the translation initiation factors eIF4H, eIF4AI, and eIF4AII, suggesting that its mRNA degradative function is somehow linked to translation. To explore how Vhs is targeted to preferred sites, we examined the in vitro degradation of a target mRNA in rabbit reticulocyte lysates containing in vitro-translated Vhs. Vhs caused rapid degradation of mRNAs beginning with cleavages at sites in the first 250 nucleotides, including a number near the start codon and in the 5' untranslated region. Ligation of the ends to form a circular mRNA inhibited Vhs cleavage at the same sites at which it cuts capped linear molecules. This was not due to an inability to cut any circular RNA, since Vhs cuts circular mRNAs containing an encephalomyocarditis virus (EMCV) internal ribosome entry site (IRES) at the same sites as linear molecules with the IRES. Cutting linear mRNAs at preferred sites was augmented by the presence of a 5' cap. Moreover, mutations that altered the 5' proximal AUG abolished Vhs cleavage at nearby sites, while mutations that changed sequences surrounding the AUG to improve their match to the Kozak consensus sequence enhanced Vhs cutting near the start codon. The results indicate that mutations in an mRNA that affect its translation affect the sites at which it is cut by Vhs and suggest that Vhs is directed to its preferred cut sites during translation initiation.

Herpes keratitis

Herpes simplex virus-1 (HSV-1) infects the majority of the world's population. These infections are often asymptomatic, but ocular HSV-1 infections cause multiple pathologies with perhaps the most destructive being herpes stromal keratitis (HSK). HSK lesions, which are immunoinflammatory in nature, can recur throughout life and often cause progressive corneal scaring resulting in visual impairment. Current treatment involves broad local immunosuppression with topical steroids along with antiviral coverage. Unfortunately, the immunopathologic mechanisms defined in animal models of HSK have not yet translated into improved therapy. Herein, we review the clinical epidemiology and pathology of the disease and summarize the large amount of basic research regarding the immunopathology of HSK. We examine the role of the innate and adaptive immune system in the clearance of virus and the destruction of the normal corneal architecture that is typical of HSK. Our goal is to define current knowledge of the pathogenic mechanisms and recurrent nature of HSK and identify areas that require further study.

Recurrent herpetic stromal keratitis in mice: a model for studying human HSK

Herpes simplex virus 1 (HSV-1) infection of the cornea leads to a potentially blinding disease, termed herpetic stromal keratitis (HSK) that is characterized by lesions of an immunoinflammatory nature. In spite of the fact that HSK typically presents as a recurrent disease due to reactivation of virus which latently infects the trigeminal ganglia, most murine studies of HSK have employed a primary and not recurrent model of the disease. This report documents the several recurrent models of HSK that have been developed and how data generated from these models differs in some important aspects from data generated following primary infection of the cornea. Chief among these differences is the fact that recurrent HSK takes place in the context of an animal that has a preexisting anti-HSV immune response, while primary HSK occurs in an animal that is developing such a response. We will document both differences and similarities that derive from this fundamental difference in these models with an eye towards possible vaccines and therapies that demonstrate promise in treating HSK.

The ongoing pursuit of a prophylactic HSV vaccine

HSV is among the most common human pathogens in the world. It is known to cause painful, persistent skin lesions, while also being the most common cause of fatal non-epidemic encephalitis as well as the leading cause of corneal blindness. The development of prophylactic vaccines could substantially reduce global health problems associated with HSV. So far, HSV vaccine strategies have shown noticeable efficacy in early development during preclinical phases but remained unsuccessful or unproven in human trials. New understanding of how the immune system mounts a defence against HSV offers practical strategies for vaccine development. A number of promising vaccine candidates are currently awaiting clinical development or already undergoing clinical testing. Therefore, this is a suitable time to assess the progress of HSV vaccine development and consider existing challenges and future improvements needed to achieve an effective prophylactic HSV vaccine.

The virion host shutoff protein of herpes simplex virus 1 blocks the replication-independent activation of NF-κB in dendritic cells in the absence of type I interferon signaling

Immune evasion is a defining feature of the virus-host relationship. During infection, herpes simplex virus type 1 (HSV-1) utilizes multiple proteins to manipulate the host immune response. In the present study, we investigated the mechanism by which the virion host shutoff (vhs) protein blocks the activation of dendritic cells (DCs). Previously, we found that coinfection of wild-type HSV-1 with a panel of RNA viruses resulted in a block to DC activation that was attributable to vhs. These observations led us to hypothesize that the vhs-mediated inhibition was dependent on signaling through the RIG-I-like receptor (RLR) signaling pathway. By examining DCs generated from MAVS (IPS-1) knockout (KO) mice, we determined that RLR/MAVS signaling is not essential for the DC response to HSV-1. We also evaluated the requirement for the type I interferon (IFN) signaling pathway in DC activation following infection with HSV-1 and found that stimulation of DCs with wild-type HSV-1 required intact type I IFN signaling for the production of cytokines, whereas the vhs deletion (vhs(-)) mutant virus activated DCs without the need for exogenous IFN signaling. Comparisons of transcription factor activation in DCs infected with wild-type HSV and the vhs(-) mutant virus revealed that NF-κB activation was inhibited by vhs in the early phase of the infection. In contrast, IRF3 activation was not influenced by vhs. In these studies, measurement of proinflammatory cytokines and type I IFN release from the infected DCs reflected the activation status of these transcription factors. Taken together, the work presented here (i) describes a novel role for the vhs protein as an inhibitor of the early activation of NF-κB during HSV-1 infection of DCs and (ii) offers a mechanistic explanation of how this protein interferes with DC activation.

Host responses to wild-type and attenuated herpes simplex virus infection in the absence of Stat1

Humans and mice lacking the interferon signaling molecule Stat1 are sensitive to a variety of pathogens due to their presumed inability to mount a strong innate immune response. The herpes simplex virus type 1 (HSV-1) virion host shutoff (vhs) protein is a multifunctional immunomodulator that counteracts the innate immune response and viruses lacking vhs are attenuated and effective live vaccines in animal models. To investigate the interplay of viruses with an immunocompromised host, we performed functional genomics analyses on control and Stat1(-/-) mouse corneas infected with wild-type or vhs-null viruses. In control mice, correlative with viral growth, both viruses induced a transient increase in immunomodulators, followed by viral clearance. In contrast, infection of the Stat1(-/-) mice induced a heightened and prolonged induction of inflammatory modulators for both viruses, manifesting as a significant immune cell infiltrate and ocular disease. Moreover, while wild-type virus infection of Stat1(-/-) was always lethal, vhs-null infection was rarely lethal. There was a significant increase in Stat3- and interleukin-6 (IL-6)-dependent transcription in Stat1(-/-) mice, implicating the Stat3 and IL-6 pathways in the observed ocular pathology. Further, infected Stat1(-/-) mice showed phosphorylated Stat3 in the corneal epithelium. Our data show a role for vhs in evading innate host responses and a role for Stat1 in limiting virus infection and for facilitating an appropriate nonpathological inflammatory response.

Ocular HSV-1 latency, reactivation and recurrent disease

Ocular infection with HSV-1 continues to be a serious clinical problem despite the availability of effective antivirals. Primary infection with HSV-1 can involve ocular and adenaxial sites and can manifest as blepharitis, conjunctivitis, or corneal epithelial keratitis. After initial ocular infection, HSV-1 can establish latent infection in the trigeminal ganglia for the lifetime of the host. During latency, the viral genome is retained in the neuron without producing viral proteins. However, abundant transcription occurs at the region encoding the latency-associated transcript, which may play significant roles in the maintenance of latency as well as neuronal reactivation. Many host and viral factors are involved in HSV-1 reactivation from latency. HSV-1 DNA is shed into tears and saliva of most adults, but in most cases this does not result in lesions. Recurrent disease occurs as HSV-1 is carried by anterograde transport to the original site of infection, or any other site innervated by the latently infected ganglia, and can reinfect the ocular tissues. Recurrent corneal disease can lead to corneal scarring, thinning, stromal opacity and neovascularization and, eventually, blindness. In spite of intensive antiviral and anti-inflammatory therapy, a significant percentage of patients do not respond to chemotherapy for herpetic necrotizing stromal keratitis. Therefore, the development of therapies that would reduce asymptomatic viral shedding and lower the risks of recurrent disease and transmission of the virus is key to decreasing the morbidity of ocular herpetic disease. This review will highlight basic HSV-1 virology, and will compare the animal models of latency, reactivation, and recurrent ocular disease to the current clinical data.

Small interfering RNAs that deplete the cellular translation factor eIF4H impede mRNA degradation by the virion host shutoff protein of herpes simplex virus

The herpes simplex virus (HSV) virion host shutoff (Vhs) protein is an endoribonuclease that accelerates decay of many host and viral mRNAs. Purified Vhs does not distinguish mRNAs from nonmessenger RNAs and cuts target RNAs at many sites, yet within infected cells it is targeted to mRNAs and cleaves those mRNAs at preferred sites including, for some, regions of translation initiation. This targeting may result in part from Vhs binding to the translation initiation factor eIF4H; in particular, several mutations in Vhs that abrogate its binding to eIF4H also abolish its mRNA-degradative activity, even though the mutant proteins retain endonuclease activity. To further investigate the role of eIF4H in Vhs activity, HeLa cells were depleted of eIF4H or other proteins by transfection with small interfering RNAs (siRNAs) 48 h prior to infection or mock infection in the presence of actinomycin D. Cellular mRNA levels were then assayed 5 h after infection. In cells transfected with an siRNA for the housekeeping enzyme glyceraldehyde-3-phosphate dehydrogenase, wild-type HSV infection reduced beta-actin mRNA levels to between 20 and 30% of those in mock-infected cells, indicative of a normal Vhs activity. In contrast, in cells transfected with any of three eIF4H siRNAs, beta-actin mRNA levels were indistinguishable in infected and mock-infected cells, suggesting that eIF4H depletion impeded Vhs-mediated degradation. Depletion of the related factor eIF4B did not affect Vhs activity. The data suggest that eIF4H binding is required for Vhs-induced degradation of many mRNAs, perhaps by targeting Vhs to mRNAs and to preferred sites within mRNAs.

Enhanced pathogenesis of an attenuated herpes simplex virus for mice lacking Stat1

Mice lacking the Stat1 interferon signaling gene were infected with herpes simplex virus type 1 (HSV-1) or an attenuated recombinant lacking virion host shutoff (Delta vhs). Delta vhs virus-infected Stat1(-/-) mice showed levels of replication equivalent to that of the wild-type virus-infected control mice but reduced relative to wild-type virus-infected Stat1(-/-) mice. Stat1 deficiency relieves the immunomodulatory deficiency of Delta vhs virus, but not its inherent growth defect. Also Vhs is dispensable for reactivation.

Herpes simplex virus virion host shutoff attenuates establishment of the antiviral state

Herpes simplex virus mutants lacking the vhs protein are severely attenuated in animal models of pathogenesis and exhibit reduced growth in primary cell culture. As a result of these properties, viruses with vhs deleted have been proposed as live-attenuated vaccines. Despite these findings and their implications for vaccines, the mechanisms by which vhs promotes infection in cell culture and in vivo are not understood. In this study we demonstrate that vhs-deficient viruses replicate to reduced levels in interferon (IFN)-primed cells and that this deficit has both IFN-dependent and IFN-independent components. Furthermore, vhs-defective viruses induce increased and physiologically active levels of IFN, increased amounts of IFN-stimulated transcripts, and more phosphorylated eIF2alpha. In addition, we demonstrate greater accumulation of viral RNAs following infection with a vhs-deficient virus. This leads to the hypothesis that attenuation of viruses lacking vhs may be attributed to increased levels of double-stranded RNA, a potent pathogen-associated molecular pattern. Together these data show that vhs likely functions to reduce innate immune responses and thereby acts as a critical determinant of viral pathogenesis.

Glycoprotein D adjuvant herpes simplex virus vaccine

Herpes simplex virus (HSV) Type-1 and -2 are common infections that can cause primary and recurrent herpes labialis and genitalis, as well as gingivostomatitis, keratoconjunctivitis, encephalitis, disseminated infections in immunocompromised persons and neonatal infections. Despite several decades of HSV vaccine development, no effective vaccine has been developed until recently. The following review of the genital HSV-2 glycoprotein D (gD2t, t is for truncated) subunit vaccine formulated with a new adjuvant (AS04) containing alum and 3-O deacylated monophosphoryl lipid A (MPL) provides a background in which to evaluate the vaccine as well as a brief review of other approaches to herpes vaccines. The gD2t-AS04 vaccine has been demonstrated to be safe in several large clinical trials. In two trials, the vaccine reduced genital herpes disease by 73 and 74%, but only in females with no previous HSV infection. A large ongoing trial in HSV seronegative females will provide additional data on protection from HSV disease and infection.

[Herpes simplex virus vaccines: perspectives]

PURPOSE

Despite effective antiviral therapy, infection with herpes simplex virus (HSV) is a critical public health issue, particularly genital herpes by its social and psychological burden and its contribution to the neonatal herpes and possibly to the HIV/AIDS pandemic.

CURRENT KNOWLEDGE

Many prophylactic and therapeutic vaccination approaches have been explored but no effective vaccine is presently available. In fact, as members of the Herpesviridae family, both HSV-1 and 2 types have genes involved in immune evasion.

FUTURE PROSPECTS

Further research is needed to define determinants of immunity in order to design more effective vaccines.

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.

Ocular herpes simplex: changing epidemiology, emerging disease patterns, and the potential of vaccine prevention and therapy

PURPOSE

To review the changing epidemiology of herpes simplex virus infection, emerging patterns of herpetic ocular disease, and the challenges and promise of herpes simplex virus vaccine therapy.

DESIGN

Perspective.

METHODS

Literature review.

RESULTS

An epidemic increase in genital herpes simplex type 2 infection is reflected in a 30% increase in HSV-2 antibodies in the United States since 1976. Approximately one in four people in the United States over age 30 is infected with HSV-2. Primary acquisition of herpes simplex type 1 is becoming progressively delayed in many industrialized countries, in contrast to developing nations where the virus is acquired early in life and is ubiquitous. Changes in sexual behavior among young adults have been associated with a recent increase in genital HSV-1 infection, resulting from oral-genital rather than genital-genital contact. Clinical trials of HSV vaccines using selected herpes simplex virus type 2 proteins mixed in adjuvant have shown limited efficacy in seronegative women, but not in men.

CONCLUSIONS

The recent epidemic of genital herpes simplex type 2 infection is likely to result in an increase in neonatal ocular herpes and in delayed cases of acute retinal necrosis syndrome. The increase in genital HSV-1 may lead to industry production of vaccines that contain components of both HSV-1 and HSV-2 targeted toward limiting genital disease and transmission. As newer herpes simplex vaccines become available, ophthalmologists must be vigilant that a boost in immunity against HSV does not have a paradoxical effect in exacerbating break-through cases that develop immune-mediated herpes simplex stromal keratitis.

mRNA decay during herpes simplex virus (HSV) infections: protein-protein interactions involving the HSV virion host shutoff protein and translation factors eIF4H and eIF4A

During lytic infections, the virion host shutoff (Vhs) protein of herpes simplex virus accelerates the degradation of both host and viral mRNAs. In so doing, it helps redirect the cell from host to viral protein synthesis and facilitates the sequential expression of different viral genes. Vhs interacts with the cellular translation initiation factor eIF4H, and several point mutations that abolish its mRNA degradative activity also abrogate its ability to bind eIF4H. In addition, a complex containing bacterially expressed Vhs and a glutathione S-transferase (GST)-eIF4H fusion protein has RNase activity. eIF4H shares a region of sequence homology with eIF4B, and it appears to be functionally similar in that both stimulate the RNA helicase activity of eIF4A, a component of the mRNA cap-binding complex eIF4F. We show that eIF4H interacts physically with eIF4A in the yeast two-hybrid system and in GST pull-down assays and that the two proteins can be coimmunoprecipitated from mammalian cells. Vhs also interacts with eIF4A in GST pull-down and coimmunoprecipitation assays. Site-directed mutagenesis of Vhs and eIF4H revealed residues of each that are important for their mutual interaction, but not for their interaction with eIF4A. Thus, Vhs, eIF4H, and eIF4A comprise a group of proteins, each of which is able to interact directly with the other two. Whether they interact simultaneously as a tripartite complex or sequentially is unclear. The data suggest a mechanism for linking the degradation of an mRNA to its translation and for targeting Vhs to mRNAs and to regions of translation initiation.

Low CD8 T-cell proliferative potential and high viral load limit the effectiveness of therapeutic vaccination

Therapeutic vaccination has the potential to boost immune responses and enhance viral control during chronic infections. However, many therapeutic vaccination approaches have fallen short of expectations, and effective boosting of antiviral T-cell responses is not always observed. To examine these issues, we studied the impact of therapeutic vaccination, using a murine model of chronic infection with lymphocytic choriomeningitis virus (LCMV). Our results demonstrate that therapeutic vaccination using a recombinant vaccinia virus expressing the LCMV GP33 CD8 T-cell epitope can be effective at accelerating viral control. However, mice with lower viral loads at the time of vaccination responded better to therapeutic vaccination than did those with high viral loads. Also, the proliferative potential of GP33-specific CD8 T cells from chronically infected mice was substantially lower than that of GP33-specific memory CD8 T cells from mice with immunity to LCMV, suggesting that poor T-cell expansion may be an important reason for suboptimal responses to therapeutic vaccination. Thus, our results highlight the potential positive effects of therapeutic vaccination on viral control during chronic infection but also provide evidence that a high viral load at the time of vaccination and the low proliferative potential of responding T cells are likely to limit the effectiveness of therapeutic vaccination.

Herpes simplex virus type 2 vaccines: new ground for optimism?

The development of effective prophylactic and therapeutic vaccines against genital herpes has proven problematic. Difficulties are associated with the complexity of the virus life cycle (latency) and our relatively poor understanding of the mechanism of immune control of primary and recurrent disease. The types of effector cells and the mechanisms responsible for their activation and regulation are particularly important. Studies from my and other laboratories have shown that recurrent disease is prevented by virus-specific T helper 1 (Th1) cytokines (viz., gamma interferon) and activated innate immunity. Th2 cytokines (viz., interleukin-10 [IL-10]) and regulatory (suppressor) T cells downregulate this immune profile, thereby allowing unimpeded replication of reactivated virus and recurrent disease. Accordingly, an effective therapeutic vaccine must induce Th1 immunity and be defective in Th2 cytokine production, at least IL-10. These concepts are consistent with the findings of the most recent clinical trials, which indicate that (i) a herpes simplex virus type 2 (HSV-2) glycoprotein D (gD-2) vaccine formulated with a Th1-inducing adjuvant has prophylactic activity in HSV-2- and HSV-1-seronegative females, an activity attributed to the adjuvant function, and (ii) a growth-defective HSV-2 mutant (ICP10DeltaPK), which is deleted in the Th2-polarizing gene ICP10PK, induces Th1 immunity and has therapeutic activity in both genders. The ICP10DeltaPK vaccine prevents recurrent disease in 44% of treated subjects and reduces the frequency and severity of recurrences in the subjects that are not fully protected. Additional studies to evaluate these vaccines are warranted.

Inhibition of TAP by pseudorabies virus is independent of its vhs activity

Previously we have shown that pseudorabies virus (PrV) down-regulates the expression of porcine MHC class I molecules by interfering with the transporter associated with antigen processing (TAP). During lytic PrV infection, the half-lives of both host and viral mRNA are regulated by the product of virion host shut-off (vhs) gene, UL41. PrV vhs protein induces degradation of cellular mRNA including those encoding class I and TAP. Therefore, further elucidation of specific mechanisms of down-regulation of class I molecules by PrV necessitates construction of a vhs deletion mutant. Two such mutants (vhsDelta1 and vhsDelta2) were generated by homologous recombination between the wild type (wt) PrV Indiana-F strain, and plasmids containing truncated UL41 gene of PrV into which the enhanced green fluorescent protein (EGFP) cassette was inserted. Compared with the wt virus, both the vhs mutants exhibited slower in vitro growth kinetics. The mutants, like the wt virus, inhibited the peptide transport activity of TAP and down-regulated cell surface expression of class I molecules. These findings suggest that, inhibition of TAP activity in PrV-infected cells is due to mechanism(s) specifically directed at class I pathway and not due to the non-specific vhs activity of the virus.