In vivo enhancement of herpes simplex virus thymidine kinase/ganciclovir cancer gene therapy with polyamine biosynthesis inhibition

We have earlier demonstrated that inhibition of polyamine biosynthesis with difluoromethylornithine (DFMO) can be used to enhance the cytotoxicity of herpes simplex virus thymidine kinase/ganciclovir (HSV-TK/GCV) gene therapy in different tumor cell lines. Here, the utility of this treatment combination was tested in vivo in a nude mouse tumor model. First, the effect of DFMO was verified by treating mice bearing subcutaneous 9L rat glioma tumors with 2% DFMO in drinking water. The drug treatment induced almost complete suppression of ornithine decarboxylase activity, and as a result, a strong decrease in intratumoral putrescine and spermidine concentrations, which were normalized 4 days after drug removal. Consequently, the tumors displayed a significant reduction in the proliferation activity that was increased to 20% higher than the normal level at day 4 and returned to normal level 7 days after DFMO removal. Next, 9L tumors with 30% of TK-GFP fusion gene positive cells were induced and the animals were given DFMO and GCV in 2 treatment schemes, with the drug administration periods overlapping either 5 or 2 days. The analysis of tumor size at the end of the treatment revealed that DFMO can enhance HSV-TK/GCV cytotoxicity when the overlap between DFMO and GCV was 5 days, but the result was not significant. However, the 2-day overlap scheme yielded a significantly (p < 0.05, ANOVA) enhanced antitumor effect. In conclusion, the data here confirms that a novel combination of 2 clinically relevant treatment modalities, polyamine deprivation and HSV-TK/GCV suicide gene therapy, can be used synergistically in vivo.

Herpes simplex virus US3 protein kinase regulates virus-induced apoptosis in olfactory and vomeronasal chemosensory neurons in vivo

A role for the US3 protein kinase of herpes simplex virus (HSV) in regulating virus-induced neuronal apoptosis was investigated in an experimental mouse system, in which wild-type HSV invades the central nervous system (CNS) via the olfactory and vomeronasal systems upon intranasal infection. Wild-type HSV-2 strain 186 infected a fraction of olfactory and vomeronasal chemosensory neurons without inducing apoptosis and was transmitted to the CNS, precipitating lethal encephalitis. In sharp contrast, an US3-disrupted mutant, L1BR1, induced neuronal apoptosis in these peripheral conduits upon infection, blocking viral transmission to the CNS and causing no signs of disease. An US3-repaired mutant, L1B(-)11, behaved similarly to the wild-type virus. Only 5 p.f.u. of L1BR1 was sufficient to compromise mice when the mutant virus was introduced directly into the olfactory bulb, a viral entry site of the CNS. These results suggest that the US3 protein kinase of HSV regulates virus-induced neuronal apoptosis in peripheral conduits and determines the neuroinvasive phenotype of HSV. Furthermore, virus-induced neuronal apoptosis of peripheral nervous system cells may be a protective host response that blocks viral transmission to the CNS.

Keratin, a dual role in herpes simplex virus pathogenesis

Keratin is a strong, fibrous protein that coats the skin, male genitalia and some tissues in the mouth and female genitalia. Keratin protects the host by providing a barrier against primary herpes simplex virus infection. We postulate that keratin may also hinder the host by protecting the virus from effective immune responses such as those present on mucosal surfaces, enabling recurrent lesions to preferentially develop within keratinized tissues at mucocutaneous junctions. The natural history of infection supports the importance of preventing infection in keratinized tissues for developing an effective herpes simplex virus vaccine, since potent immunity on mucosal surfaces may be inadequate to protect keratinized tissues.

Genetically engineered herpes simplex viruses that express IL-12 or GM-CSF as vaccine candidates

We are using genetically modified, conditionally replicating herpes simplex virus (HSV) that express either interleukin (IL)-12 or granulocyte macrophage-colony stimulating factor (GM-CSF) as live, attenuated vaccine candidates for protection against HSV infection and/or disease. We report the following: (1) animals previously vaccinated with these candidate vaccines exhibited dose-dependent protection after intranasal, intraperitoneal or intracranial challenge with the highly virulent E377-MB wild-type HSV-1; (2) the IL-12 expressing virus (M002) consistently conferred protection at lower immunization doses than GM-CSF expressing virus (M004); (3) between 80 and 100% protection from E377-MB challenge was conferred after intramuscular immunization of mice with any of the three Deltagamma1 34.5 HSV, as opposed to 50% protection elicited after immunization with wild-type HSV-1 (F); and (4) latent virus was not detected at a higher rate in animals immunized and subsequently challenged with E377-MB than in immunized animals alone. These data suggest that conditionally replicating, cytokine-expressing HSV are able to elicit protective immune responses while retaining safety in an experimental murine model.

Neuropathogenesis of herpesvirus papio 2 in mice parallels infection with Cercopithecine herpesvirus 1 (B virus) in humans

Cercopithecine herpesvirus 1 (monkey B virus; BV) produces extremely severe and usually fatal infections when transmitted from macaque monkeys to humans. Cercopithecine herpesvirus 16 (herpesvirus papio 2; HVP2) is very closely related to BV, yet cases of human HVP2 infection are unknown. However, following intramuscular inoculation of mice, HVP2 rapidly invades the peripheral nervous system and ascends the central nervous system (CNS) resulting in death, very much like human BV infections. In this study, the neurovirulence of HVP2 in mice was further evaluated as a potential model system for human BV infections. HVP2 was consistently neurovirulent when administered by epidermal scarification, intracranial inoculation and an eye splash. Quantitative real-time PCR, histopathology and immunohistochemistry were used to follow the temporal spread of virus following skin scarification and to compare the pathogenesis of neurovirulent and apathogenic isolates of HVP2. Apathogenic isolates were found to be capable of reaching the CNS but were extremely inefficient at replicating within the CNS. It is concluded that neurovirulent strains of HVP2 exhibit a pathogenesis in mice that parallels that observed in human BV infections and that this model system may prove useful in dissecting the viral determinants underlying the extreme severity of zoonotic BV infections.

A naturally occurring fatal case of Herpesvirus papio 2 pneumonia in an infant baboon (Papio hamadryas anubis)

Here we describe the unusual finding of herpesvirus pneumonia in a 7-d-old infant baboon (Papio hamadryas anubis). This animal had been separated from its dam the morning of its birth and was being hand-reared for inclusion in a specific pathogen-free colony. The baboon was presented for anorexia and depression of 2 d duration. Physical examination revealed a slightly decreased body temperature, lethargy, and dyspnea. The baboon was placed on a warm-water blanket and was given amoxicillin-clavulanate orally and fluids subcutaneously. The animal's clinical condition continued to deteriorate despite tube feeding, subcutaneous fluid administration, and antibiotic therapy, and it died 2 d later. Gross necropsy revealed a thin carcass and severe bilateral diffuse pulmonary consolidation. Histopathology of the lung revealed severe diffuse necrotizing pneumonia. Numerous epithelial and endothelial cells contained prominent intranuclear herpetic inclusion bodies. Virus isolated from lung tissue in cell culture was suspected to be Herpesvirus papio 2 (HVP2) in light of the viral cytopathic effect. Real-time polymerase chain reaction (PCR) analysis and DNA sequencing of PCR products both confirmed that the virus was HVP2. This case is interesting because the age at onset suggests perinatal transmission at or immediately after birth, and the disease course suggests inoculation of the virus into the respiratory tract.

Immunotherapeutic potential of DISC-HSV and OX40L in cancer

Several vectors, viral and bacterial, have been developed over the past few years for means of generating an effective antitumor immune response. We have developed and studied a "model for immunotherapy" using a viral vector disabled infectious single cycle-herpes simplex virus (DISC-HSV), which efficiently transduces various tumor cell lines and offers a useful vehicle for the further development of cell-based vaccines. The immunotherapeutic potential of DISC-HSV encoding granulocyte macrophage colony stimulating factor (GM-CSF) was demonstrated in a number of murine carcinoma models, leading to complete regression of well-established tumors in up to 70% of the mice. Moreover, the therapeutic potential of DISC-HSV-GM-CSF was significantly enhanced when used in combination therapy with either OX40L or dendritic cells (DC), even in a poorly immunogenic tumor model. The ability of this vector to accept large gene inserts, its good safety profile, its ability to undergo only a single round of infection, the inherent viral immunostimulatory properties and its ability to infect various tumor cell lines efficiently, make DISC-HSV an ideal candidate vector for immunotherapy. The DISC- CT-26 tumor model was used to investigate the mechanisms associated with immunotherapy induced tumor rejection. Although CTL induction, was positively correlated with regression, MHC class I down regulation and accumulation of immature Gr1+ myeloid cells were shown to be the main immuno-suppressor mechanisms operating against regression and associated with progressive tumor growth. The CTL response was associated with the immuno-dominant AH-1 peptide of the retroviral glycoprotein gp70. This model of immunotherapy has provided an opportunity to dissect further the immunological events associated with tumor-rejection and escape. Since other antigens may be important in initiating tumor rejection, we have investigated the expression of MTA-1, an antigen that appears to be expressed widely in human and murine tumors. The immunogenicity of MTA-1 was studied and its potential as a tumor rejection antigen is under investigation.

Herpes simplex virus and toll-like receptors

The earliest interactions between viruses and host cells are critical to determining the outcome of infections. The interactions between a virus and its host cells that lead to the production of inflammatory cytokines are essential to the development of T cells and antibodies that provide long-term defense against the invaders. At the same time, however, these same cytokines (or sometimes other mediators or chemokines) stimulate inflammation, which may lead to localized tissue damage and/or systemic circulatory collapse and death. This review focuses on the interaction between Toll-like receptors, a critical component of the innate immune system of mammals, and their role in herpes simplex pathogenesis and immunity.

Alanine substitution of conserved residues in the cytoplasmic tail of herpes simplex virus gB can enhance or abolish cell fusion activity and viral entry

Herpes simplex virus (HSV) glycoprotein B (gB) is one of the four viral glycoproteins required for viral entry and cell fusion and is highly conserved among herpesviruses. Mutants of HSV type 2 gB were generated by substituting conserved residues in the cytoplasmic tail with alanine or by deleting 41 amino acids from the C-terminus. Some of the mutations abolished cell fusion activity and also prevented transport of gB to the cell surface, identifying residues in the gB cytoplasmic tail that are critical for intracellular transport of this glycoprotein. These mutations also prevented production of infectious virus, possibly because the mutant forms of gB were not transported to the site of envelopment. Other mutations, particularly the deletion, significantly enhanced cell fusion activity. These mutations, as well as others described previously, identify regions of the gB cytoplasmic domain that modulate cell fusion activity.

Phosphorylation of the VP16 transcriptional activator protein during herpes simplex virus infection and mutational analysis of putative phosphorylation sites

VP16 is a virion phosphoprotein of herpes simplex virus and a transcriptional activator of the viral immediate-early (IE) genes. We identified four novel VP16 phosphorylation sites (Ser18, Ser353, Ser411, and Ser452) at late times in infection but found no evidence of phosphorylation of Ser375, a residue reportedly phosphorylated when VP16 is expressed from a transfected plasmid. A virus carrying a Ser375Ala mutation of VP16 was viable in cell culture but with a slow growth rate. The association of the mutant VP16 protein with IE gene promoters and subsequent IE gene expression was markedly reduced during infection, consistent with prior transfection and in vitro results. Surprisingly, the association of Oct-1 with IE promoters was also diminished during infection by the mutant strain. We propose that Ser375 is important for the interaction of VP16 with Oct-1, and that the interaction is required to enable both proteins to bind to IE promoters.

Structure of unliganded HSV gD reveals a mechanism for receptor-mediated activation of virus entry

Herpes simplex virus (HSV) entry into cells requires binding of the envelope glycoprotein D (gD) to one of several cell surface receptors. The 50 C-terminal residues of the gD ectodomain are essential for virus entry, but not for receptor binding. We have determined the structure of an unliganded gD molecule that includes these C-terminal residues. The structure reveals that the C-terminus is anchored near the N-terminal region and masks receptor-binding sites. Locking the C-terminus in the position observed in the crystals by an intramolecular disulfide bond abolished receptor binding and virus entry, demonstrating that this region of gD moves upon receptor binding. Similarly, a point mutant that would destabilize the C-terminus structure was nonfunctional for entry, despite increased affinity for receptors. We propose that a controlled displacement of the gD C-terminus upon receptor binding is an essential feature of HSV entry, ensuring the timely activation of membrane fusion.

Herpes simplex virus type 1 glycoprotein e is required for axonal localization of capsid, tegument, and membrane glycoproteins

Herpes simplex virus type 1 (HSV-1) glycoprotein E (gE) promotes cell-to-cell spread at basolateral surfaces of epithelial cells, but its activity in neurons is less clear. We used the mouse retina infection model and neuronal cell cultures to define the spread phenotype of gE mutant viruses. Wild-type (WT) and gE-null (NS-gEnull) viruses both infected retina ganglion cell neurons; however, NS-gEnull viral antigens failed to reach the optic nerve, which indicates a defect in axonal localization. We evaluated two Fc receptor-negative gE mutant viruses containing four amino acid inserts in the gE ectodomain. One mutant virus failed to spread from the retina into the optic nerve, while the other spread normally. Therefore, the gE ectodomain is involved in axonal localization, and the Fc receptor and neuronal spread are mediated by overlapping but distinct gE domains. In the retina infection model, virus can travel to the brain via the optic nerve from presynaptic to postsynaptic neurons (anterograde direction) or via nerves that innervate the iris and ciliary body from postsynaptic to presynaptic neurons (retrograde direction). WT virus infected the brain by anterograde and retrograde routes, whereas NS-gEnull virus failed to travel by either pathway. The site of the defect in retrograde spread remains to be determined; however, infection of rat superior cervical ganglia neurons in vitro indicates that gE is required to target virion components to the axon initial segment. The requirement for gE in axonal targeting and retrograde spread highlights intriguing similarities and differences between HSV-1 and pseudorabies virus gE.

Temporal progression of viral replication and gross and histological lesions in Balb/c mice inoculated epidermally with Saimiriine herpesvirus 1 (SaHV-1)

Saimiriine herpesvirus 1 (SaHV-1), an alphaherpesvirus enzootic in squirrel monkeys, is genetically related to monkey B virus and human herpes simplex virus (HSV). To study the temporal progression of viral spread and associated lesions, Balb/c mice were inoculated epidermally by scarification with a green fluorescent protein (GFP)-expressing recombinant strain of SaHV-1 and killed sequentially. Pinpoint ulcerative lesions in the inoculated epidermis progressed over a few days to unilateral or bilateral hindlimb paresis or paralysis, urinary and faecal incontinence, abdominal distension, hunched posture and eventual depression warranting euthanasia. Viral replication was present within epidermal keratinocytes, neurons of the dorsal root ganglia and thoracolumbar spinal cord, regional autonomic ganglia, lower urinary tract epithelium and colonic myenteric plexuses, as indicated by histological lesions and GFP expression. Almost all mice inoculated with 10(5) or 10(6) plaque-forming units (PFU) of SaHV-1 developed rapidly progressive disease. Two of eight mice given 10(4)PFU developed disease, but no mice receiving less than 10(4)PFU gave evidence of infection. Mice that showed no clinical signs also failed to develop an antiviral IgG response, indicating absence of active viral infection. For SaHV-1 inoculated epidermally, the ID(50), CNSD(50) and LD(50) values were identical (10(4.38)), indicating that successful infection by this route invariably resulted in lethal CNS (central nervous system) disease. Consistently severe disease in all infected animals, with regionally extensive distribution of viral replication, constituted a marked difference from the disease produced by intramuscular inoculation.

Experimental infection of baboons (Papio cynocephalus anubis) with apathogenic and neurovirulent subtypes of herpesvirus papio 2

Cercopithecine herpesvirus 16 (Herpesvirus papio 2; HVP2) is an alpha-herpesvirus of baboons (Papio spp.) that generally causes minimal to inapparent disease in the natural host species. HVP2 is very closely related genetically and antigenically to Cercopithecine herpesvirus 1 (monkey B virus; BV) of macaques, which is well known for its extreme lethality in nonmacaque species including humans. Preliminary evidence suggests that a mouse model of HVP2 would be an excellent tool for studying zoonotic BV infections. Although the pathogenicity of different BV isolates in mice spans the full range of severity from apathogenic to extremely neurovirulent, testing of multiple HVP2 isolates revealed only two distinct phenotypes in mice regardless of route of inoculation: apathogenic (HVP2ap) and highly neurovirulent (HVP2nv). For the HVP2nv mouse model to truly reflect BV infection in both its natural host and the differential pathogenicity of BV in aberrant host species, HVP2nv should not produce severe disease in its natural host. To test this, juvenile baboons were inoculated with doses of 10(6) or 10(4) plaque-forming units of HVP2ap or HVP2nv by using an oral subdermal inoculation route. Parameters followed included the appearance of lesions, shedding of infectious virus, general health, and the immune response to the infection. Regardless of the inoculum dose used, no differences were noted between the two HVP2 subtypes in baboons in any of the parameters measured. These findings further support the use of the HVP2nv mouse system as a model to elucidate and study the viral determinants associated with cross-species BV neurovirulence.

Les hépatites herpétiques néonatales

Herpes simplex virus (HSV) infection can affect various organs-systems in the neonatal period. Herpetic hepatitis was seldom reported in the literature. We report on 2 cases. Firstly, a 16 day-old newborn infant was admitted because of haemorrhagic syndrome and shock. Biological assessment showed a severe hepatic insufficiency. Antibiotic and aciclovir therapy was started as HSV infection was suspected. Five days later, the herpetic attack was confirmed by polymerase chain reaction (PCR) in blood and cerebrospinal fluid (CSF). The genotye of the virus in the CSF was HSV1. Treatment included aciclovir for 21 days intravenously and 2 months orally. At 10 months, the clinical and biological examinations were normal. Secondly, a 4 day-old newborn was hospitalised because of fever and polypnea. Pulmonary X rays showed heterogeneous opacities of the right base. Serum C reactive protein was 30 mg/l. Antibiotic therapy was started. Two days later, the fever persisted while a severe hepatic insufficiency developed. The diagnosis of herpetic hepatitis was evoked and the child was given aciclovir. Forty-eight hours later, the PCR confirmed a HSV in blood, while viral culture of a mouth swab found HSV 2. Evolution was favourable after 21 days of specific and symptomatic treatment. Aciclovir treatment was continued orally for six months. Herpetic hepatitis is rare in the neonatal period. Diagnosis must be evoked early when facing severe neonatal hepatic insufficiency. Provided specific treatment, prognosis is good.

Olfactory transmission of neurotropic viruses

Olfactory receptor neurons are unique in their anatomical structure and function. Each neuron is directly exposed to the external environment at the site of its dendritic nerve terminals where it is exposed to macromolecules. These molecules can be incorporated into by olfactory receptor neurons and transported transsynaptically to the central nervous system. Certain neurotropic pathogens such as herpes simplex virus and Borna disease virus make use of this physiological mechanism to invade the brain. Here the authors review the olfactory transmission of infectious agents and the resulting hazards to human and animal health.

Number IV Erythema multiforme

Erythema multiforme (EM) is an acute mucocutaneous hypersensitivity reaction characterised by a skin eruption, with or without oral or other mucous membrane lesions. Occasionally EM may involve the mouth alone. EM has been classified into a number of different variants based on the degree of mucosal involvement and the nature and distribution of the skin lesions. EM minor typically affects no more than one mucosa, is the most common form and may be associated with symmetrical target lesions on the extremities. EM major is more severe, typically involving two or more mucous membranes with more variable skin involvement - which is used to distinguish it from Stevens-Johnson syndrome (SJS), where there is extensive skin involvement and significant morbidity and a mortality rate of 5-15%. Both EM major and SJS can involve internal organs and typically are associated with systemic symptoms. Toxic epidermal necrolysis (TEN) may be a severe manifestation of EM, but some experts regard it as a discrete disease. EM can be triggered by a number of factors, but the best documented is preceding infection with herpes simplex virus (HSV), the lesions resulting from a cell mediated immune reaction triggered by HSV-DNA. SJS and TEN are usually initiated by drugs, and the tissue damage is mediated by soluble factors including Fas and FasL.

Towards an understanding of the molecular basis of herpes simplex virus latency

The survival strategy of herpes simplex virus centres on the establishment of latency in sensory neurons innervating the site of primary infection followed by periodic reactivation to facilitate transmission. This is a highly evolved and efficient survival mechanism, which despite being the subject of intense research, has proven remarkably difficult to dissect at a molecular level. This review will focus on data, emerging from both in vitro and in vivo model systems, which provide a framework for a mechanistic understanding of latency and the existence and possible significance of non-uniform latent states.

Viral encephalitis

Acute viral encephalitis may be caused by a wide range of viruses but the most important is herpes simplex encephalitis (HSE) because of its severity, especially if untreated, and its good response to specific treatment with acyclovir. The outcome of any CNS viral infection is dependent on both the immune status of the host and the virulence of the infecting virus. In evaluating a patient with suspected viral encephalitis there are 3 essential steps, namely the identification of a true parenchymal virus infection of the brain rather than a non-infective encephalopathy, the distinction of an infectious viral encephalitis from an acute disseminated encephalomyelitis (ADEM), and then the determination, where possible, of the specific virus involved. In practice, the precise viral cause of the encephalitis may never be established. Analysis of the CSF for herpes simplex virus (HSV) DNA using the Polymerase Chain Reaction (PCR) has been a significant advance in the diagnosis of HSE as this test has a very high sensitivity and specificity especially with appropriate sample timing. It is essential to commence early treatment with intravenous acyclovir in patients suspected of having HSE because of the remarkable safety and efficacy of this drug and the dangers of delaying potentially effective treatment of life threatening disease. This review outlines the general management approach in patients suspected of having viral encephalitis.