Molecular and biological characterization of a herpes simplex virus type 1 (HSV-1) neuroinvasiveness gene

Pathogenetic studies of herpes simplex virus type 1 (HSV-1) strains ANG and its mouse brain-passaged descendant ANG path revealed no difference in neurovirulence but a significant difference in neuroinvasiveness. Thus, both viruses induced a fatal encephalitis in mice after direct injection into the brain, but only ANG path induced lethal neurologic disease after inoculation on rear footpads. The difference in neuroinvasiveness is not related to the capacity to replicate in mouse neural tissues or mouse cells in general, but is specifically related to virus entry into the peripheral nervous system in the footpad. Marker rescue experiments in which ANG path genes were used to confer neuroinvasiveness on ANG indicated that the gene that codes for glycoprotein D (gD) is responsible for the phenotypic difference. Analyses of the gD genes by dideoxy-sequencing techniques identified a base difference in the coding sequences and predicted that the ANG gD gene codes for alanine (GCC codon) at amino acid position 84 in the open reading frame and the ANG path gD gene codes for glycine (GGC codon) at this site. Using these data, an oligonucleotide probe predicted to be specific for the ANG path gD gene was prepared, and in Southern blot analyses, this probe revealed that neuroinvasiveness-rescued agents had incorporated the base change seen in the ANG path gD gene. We conclude that HSV-1 glycoprotein D functions to effect neuroinvasiveness and we discuss potential mechanisms that may be involved.     

Multiplicity dependence and sensitivity of herpes simplex virus isolates to antiviral compounds

An immunoassay that enables one to assess both viral multiplicity and sensitivity to antiviral drugs, was used to determine the sensitivity of untreated patients' virus isolates. The upper border levels for judging clinical isolates sensitive to Ara-A, ACV, PFA or IDU were calculated from a total of 48 primary herpes simplex isolates. Although five isolates were considered less sensitive to one drug and one isolate to two drugs, all were sensitive at a lower virus multiplicity. Analysis of these isolates showed that no isolate was genetically resistant, but that multiplicity dependence of drugs was high with ACV and Ara-A, lower with PFA. In view of the multiplicity dependence of HSV sensitivity to different drugs, it is recommended that isolates from treatment failures or isolates considered resistant should be assayed in detail.     

A novel protein tag from herpes simplex virus type 1 DNA polymerase.

An epitope (HPOL) derived from the so-called thumb region of the herpes simplex virus type 1 DNA polymerase in combination with a monoclonal antibody (MAb 1051c) was tested for protein tagging. Using a conventional expression vector, a DNA cassette encoding the HPOL epitope was fused to the C-terminus of the dihydrofolate reductase (DHFR) gene such that the recombinant DHFR contained both a N-terminal HIS-tag and a C-terminal HPOL tag. Expression of recombinant DHFR in Escherichia coli cells was compared by Western blot analysis using either mouse RGS.HIS antibody or MAb 1051c. Immunostaining revealed that both antibodies reacted specifically with DHFR, but the detection sensitivity achieved with MAb 1051c was about 15-fold greater using a standard staining protocol. An HPOL antibody column was successfully applied for affinity purification of DHFR, demonstrating the usefulness of the HPOL epitope/MAb 1051c system for protein tagging, expression monitoring and purification of HPOL-tagged recombinant proteins.     

Susceptibilities of several drug-resistant herpes simplex virus type 1 strains to alternative antiviral compounds.

Resistant herpes simplex virus type 1 strains were obtained under the selective pressure of acyclovir, ganciclovir, bromovinyldeoxyuridine, foscarnet, 2-phosphonylmethoxyehtyl (PME) derivatives of adenine and 2,6-diaminopurine, 3-hydroxy-2-phosphonylmethoxypropyl derivatives of adenine and cytosine, and 2-amino-7-(1,3-dihydroxy-2-propoxymethyl)purine (S2242). The drug susceptibility profiles of resistant strains point to differences in the modes of action of PME and 3-hydroxy-2-phosphonylmethoxypropyl derivatives and common mechanisms of action of foscarnet, S2242, and PME derivatives against herpes simplex virus type 1 replication.     

Prolonged detection of herpes simplex virus type 2 (HSV-2) DNA in cerebrospinal fluid despite antiviral therapy in a patient with HSV-2-associated radiculitis

Herpes simplex virus type 2 (HSV-2) can cause radiculo-myelitis as a neurological manifestation. We report a case of ongoing HSV-2 DNA positivity in the cerebrospinal fluid (CSF) of at least eight weeks under antiviral therapy with acyclovir in a highly immunocompromised hemato-oncologic patient with HSV-2-associated radiculitis. Upon admission, the patient presented with pain, leg paresis, and urinary incontinence, as well as pleocytosis in the CSF. Quantitative real-time PCR of the CSF at day 3 after admission revealed HSV-2 with a concentration of 2.0×10(5) copies/ml and treatment with acyclovir intravenously and prednisolone by mouth was started. Clinical symptoms resolved almost completely after approximately 3 weeks of antiviral therapy. However, CSF samples of day 12, 19, 26, 33, 39, 48 and 54 after admission showed a slow decline of HSV-2 DNA concentrations. HSV-2 DNA was still detectable (1.6×10(4) copies/ml) at day 54 after admission. Genotypic resistance testing showed, as far as available, no mutations indicative for acyclovir resistance. Since an increasing specific antibody index for HSV was observed, we speculate that the prolonged detectability of HSV-2 DNA in the CSF might not necessarily indicate ongoing viral replication but neutralized virus. Other hypotheses and the consequences on treatment are discussed. To our knowledge this is the first report about the long-term viral load kinetics of HSV-2 in the CSF of a patient with radiculitis under antiviral therapy, highlighting the need for further studies on HSV DNA kinetics in the CSF and their significance for an appropriate antiviral treatment.     

Mode of antiviral action of penciclovir in MRC-5 cells infected with herpes simplex virus type 1 (HSV-1), HSV-2, and varicella-zoster virus.

The metabolism and mode of action of penciclovir [9-(4-hydroxy-3-hydroxymethylbut-1-yl)guanine; BRL 39123] were studied and compared with those of acyclovir. In uninfected MRC-5 cells, low concentrations of the triphosphates of penciclovir and acyclovir were occasionally just detectable, the limit of detection being about 1 pmol/10(6) cells. In contrast, in cells infected with either herpes simplex virus type 2 (HSV-2) or varicella-zoster virus (VZV), penciclovir was phosphorylated quickly to give high concentrations of the triphosphate ester. Following the removal of penciclovir from the culture medium, penciclovir-triphosphate remained trapped within the cells for a long time (half-lives, 20 and 7 h in HSV-2- and VZV-infected cells, respectively). In HSV-2-infected cells, acyclovir was phosphorylated to a lesser extent and the half-life of the triphosphate ester was only 1 h. We were unable to detect any phosphates of acyclovir in VZV-infected cells. (S)-Penciclovir-triphosphate inhibited HSV-1 and HSV-2 DNA polymerase competitively with dGTP, the Ki values being 8.5 and 5.8 microM, respectively, whereas for acyclovir-triphosphate, the Ki value was 0.07 microM for the two enzymes. Both compounds had relatively low levels of activity against the cellular DNA polymerase alpha, with Ki values of 175 and 3.8 microM, respectively. (S)-Penciclovir-triphosphate did inhibit DNA synthesis by HSV-2 DNA polymerase with a defined template-primer, although it was not an obligate chain terminator like acyclovir-triphosphate. These results provide a biochemical rationale for the highly selective and effective inhibition of HSV-2 and VZV DNA synthesis by penciclovir and for the greater activity of penciclovir than that of acyclovir when HSV-2-infected cells were treated for a short time.     

In vivo gene transfer to the rat retina using herpes simplex virus type 1 (HSV-1)-based amplicon vectors

The purpose of our study was to evaluate the transduction profiles of herpes simplex virus type 1 (HSV-1)-based amplicon vectors following subretinal injection in the rat. Two amplicon vectors were tested, pHy-CMVGFP and pHy-RPEGFP, both carrying the green fluorescent protein (GFP) under the control of the cytomegalovirus (CMV) ubiquitous promoter or the RPE65-specific promoter, respectively. For the two amplicon vectors, the GFP reporter gene was efficiently expressed in retinal pigment epithelial (RPE) cells but not in the adjacent photoreceptors. GFP expression was maximum as early as 2 days post-administration but decreased over time to become almost undetectable at 6 weeks postinjection. Super-transduction with a second amplicon vector, pHSVlac, reactivated expression of GFP in approximately 10% of the cells initially transduced at 2 days postinjection of pHy-CMVGFP or pHy-RPEGFP. Reactivation of transgene expression was transient, no GFP signal was detected 8 days after pHSVlac injection. In conclusion, HSV-1 amplicon vectors allow rapid and efficient, but transient, gene transfer in RPE cells following subretinal injection.     

Replicating DNA of herpes simplex virus type 1.

Newly synthesized herpes simplex virus type 1 DNA yielded a heterogeneous sedimentation profile in neutral sucrose gradients, with the main peak occurring at approximately 40S. Components sedimenting slower than virion DNA and a rapidly sedimenting intracellular HSV DNA were also observed. Both the low-molecular weight and the rapidly sedimenting components seemed to be precursors of virion DNA: they almost completely disappeared after a 60-min chase of a 3-min pulse of 3H-thymidine, and were converted into DNA which cosedimented with virion 32P-labeled DNA. However, sedimentation analysis in alkaline sucrose gradients showed that a 60-min period was insufficient for completing the maturation of HSV DNA. Cleavage of parental DNA molecules was observed in neutral sucrose gradients after infection with 3H-thymidine-labeled virions. No evidence for the formation of covalently closed circles during the replication process was obtained. The presence of single-stranded regions in the replicative form of HSV DNA was revealed. Some of the short-pulse (30 sec) labeled HSV DNA (26.1%) was eluted from hydroxylapatite columns with the properties of single-stranded DNA, and 22% of its trichloroacetic acid precipitability was susceptible to single-strand specific S1 nuclease treatment. Pulse-chase experiments indicated that the life-time of this single-stranded component in nascent DNA was probably not longer than 3 min. A small proportion of single-stranded regions, however, survived for longer periods. Almost all of the newly synthesized short-pulse-labeled HSV DNA exhibited an affinity for nitrocellulose filters. This affinity, which was S1 nuclease-sensitive, gradually decreased with prolongation of the time of the chase. After chasing the pulse for 1 h, the attachment of newly synthesized DNA was comparable with virion DNA.     

CD8(+) T cells can block herpes simplex virus type 1 (HSV-1) reactivation from latency in sensory neurons

Recurrent herpes simplex virus type 1 (HSV-1) disease usually results from reactivation of latent virus in sensory neurons and transmission to peripheral sites. Therefore, defining the mechanisms that maintain HSV-1 in a latent state in sensory neurons may provide new approaches to reducing susceptibility to recurrent herpetic disease. After primary HSV-1 corneal infection, CD8(+) T cells infiltrate the trigeminal ganglia (TGs) of mice, and are retained in latently infected ganglia. Here we demonstrate that CD8(+) T cells that are present in the TGs at the time of excision can maintain HSV-1 in a latent state in sensory neurons in ex vivo TG cultures. Latently infected neurons expressed viral genome and some expressed HSV-1 immediate early and early proteins, but did not produce HSV-1 late proteins or infectious virions. Addition of anti-CD8alpha monoclonal antibody 5 d after culture initiation induced HSV-1 reactivation, as demonstrated by production of viral late proteins and infectious virions. Thus, CD8(+) T cells can prevent HSV-1 reactivation without destroying the infected neurons. We propose that when the intrinsic capacity of neurons to inhibit HSV-1 reactivation from latency is compromised, production of HSV-1 immediate early and early proteins might activate CD8(+) T cells aborting virion production.     

Herpes simplex virus type 1 that exhibits herpes simplex virus type 2 sensitivity to (E)-5-(2-bromovinyl)-2'-deoxyuridine.

A clinical isolate, designated 145, of herpes simplex virus (HSV) had type 1 characteristics as determined by monoclonal antibody immunofluorescence, heat stability of viral thymidine kinase (TK), BamHI restriction endonuclease pattern, and absence of the HSV-2-specific 38-kD protein. However, instead of being sensitive to E-5-(2-bromovinyl)-2'-deoxyuridine (BVDU) like HSV-1, isolate 145 displayed a resistance pattern like HSV-2 to the drug as determined by viral replication and viral DNA synthesis. Because BVDU is activated by viral TK phosphorylation, we cloned the TK-containing DNA region from isolate 145 and compared it by restriction mapping using several endonucleases to similar regions of HSV-1 and HSV-2. In each instance, the patterns for HSV-1 and isolate 145 were identical to each other, but distinct from the patterns for the corresponding region of HSV-2, suggesting that the genome TK region of isolate 145 was HSV-1-like.     

Antiviral activity of antilipidemic compounds on herpes simplex virus type 1

Two antilipidemic compounds, clofibrate and procetofene, inhibited the replication of herpes simplex virus type 1 (HSV-1) in African green monkey kidney cells. Clofibrate, at a concentration of 400 mumol/liter caused a 63% reduction (P < 0.001) in HSV-1 yield and at 100 mumol/liter caused a 62% reduction (P < 0.001) in plaque formation. Two stereoisomeric analogs of clofibric acid, (-)- and (+)-desmethyl clofibric acid, also caused a significant inhibition of HSV-1 replication. Procetofene at 5 mumol/liter caused a 56% reduction (P < 0.001) in HSV-1 plaques and at 10 mumol/liter caused a significant reduction (P < 0.001) in both viral yield (42 to 54%) and plaque formation (65%). Procetofene also inhibited the development of HSV-1 plaques. A concentration of 5 mumol/liter resulted in a 26% reduction (P < 0.001) in plaque diameter. Because of their nonspecific inhibitory effect on the uptake of cellular macromolecular precursors for nucleic acid and protein biosynthesis, these antilipidemic compounds may exert their antiviral activity by affecting one or more key metabolic host cell pathways.     

Antiviral activity of CTC-8 against herpes simplex virus (HSV-1) in cell culture: evidence for a selective antiviral effect via a cellular mechanism

A synthetic programme produced a series of compounds related to natural prostaglandins, which are known to affect the growth of a number of viruses. Several of the compounds showed potent biological activity including antiviral effects. The compound CTC-8 [(S)-4-tert-butyldimethylsilyloxy-2-cyclopenten-1-one] contains the cyclopentenone ring of prostaglandin A1, but the extended side chains common to the prostaglandin family are truncated. The present study demonstrates that CTC-8 inhibits HSV-1 replication in cell culture at sub-toxic concentrations. The antiviral effect was evidenced by reduction in infectious virus yield, although the compound was not effective in the standard plaque-reduction assay. Time-of-addition studies and other experiments provide a possible explanation for these results by suggesting that the antiviral activity is confined to a single cycle. Under the standard conditions of high-multiplicity infection in BHK cells it was notable that CTC-8 is most effective when added for a short period 6-8 h post-infection. Furthermore, multiple passage of HSV-1 in the presence of CTC-8 did not result in the selection of resistant mutants. The results of these and other experiments are consistent with the hypothesis that the mechanism by which CTC-8 inhibits virus replication involves a cellular target. These results encourage further research into the therapeutic potential of this series of compounds.     

Mice genetic immunization with plasmid DNA encoding a secreted form of HSV-1 gB induces a protective immune response against herpes simplex virus type 1 infection

Intramuscularly (i.m.) delivered plasmid DNA encoding a secreted form of glycoprotein B of herpes simplex virus type 1 (HSV-1 gB1s) was evaluated for the ability to elicit a protective immune response in Balb/c mice. Animals received three i.m. injections of a gB1s expression plasmid (pRP-RSV-gB1s) or of a wild-type transmembrane gB1 coding plasmid (pRP-RSV-gB1), while control mice were injected with the vector alone (pRP-RSV). A specific antibody response was observed in almost all immunized animals, and in most cases antibodies were also detected after 1 month in the absence of further vaccine boosts. Serum antibodies mostly displayed neutralizing activity against HSV-1. Glycoprotein B1s DNA immunization was also effective in protecting animals against the primary infection induced by a subsequent HSV-1 challenge and limited HSV-1 infection of sensitive ganglia.     

Incorporation of 1-beta-D-arabinofuranosylcytosine into DNA and mutagenesis of herpes simplex virus type 1.

To investigate the association between incorporation of 1-beta-D-arabinofuranosylcytosine (ara-C) into herpes simplex virus type 1 (HSV-1) DNA and mutagenesis at selected genetic loci, we grew virus in the presence or absence of ara-C and compared the mutation frequencies. Both the forward mutation frequency of HSV-1 (KOS) to the tk- phenotype and the reversion frequency of a temperature-sensitive mutant to the non-temperature-sensitive (ts+) phenotype were significantly increased following growth in ara-C. When the same viruses were grown in an inhibitor of the HSV-1 DNA polymerase that is not incorporated into DNA, no significant increase in the frequency of tk- or ts+ particles was observed. Furthermore, HSV-1 araAr, a mutant resistant to ara-C on the basis of reduced incorporation of the analog into viral DNA, did not demonstrate an increase in the number of tk- particles following growth in ara-C. These results suggest that mutagenesis of HSV-1 following growth in ara-C correlates with incorporation of the nucleoside analog into viral DNA.     

Effect of antiviral agents on replication of herpes simplex virus type 1 in brain cultures.

An in vitro tissue culture system consisting of reaggregated embryonic brain cells was used to evaluate the inhibition of herpes simplex type 1 (HSV-1) by several antiviral compounds. The efficacy of acyclovir, vidarabine, bromovinyldeoxyuridine, and 9-(1,3-dihydroxy-2-propoxymethyl) guanine in HSV-1-infected Vero cell monolayer cultures was compared with that seen with brain cell aggregates. At a mean 50% inhibitory dose with Vero cells, acyclovir showed a 99% reduction of virus titer in brain cell aggregates. Vidarabine and 9-(1,3-dihydroxy-2-propoxymethyl) guanine gave a dose-dependent reduction in virus titer with Vero cells; however, in aggregate cultures treated with the same drugs a dose-dependent decrease at 24 h was followed by an increase to a point of no inhibition at 72 h postinfection. Pretreatment of brain cell aggregates with a hybrid human leukocyte interferon (Le IF-AD) reduced virus titers at 48 h postinfection but did not maintain this reduction at 72 h. In contrast, infected Vero cell monolayer cultures demonstrated a dose-dependent reduction in virus titers with Le IF-AD. Postinfection treatment with Le IF-AD did not reduce plaque formation in Vero cells but was effective in reducing virus titer in HSV-1-infected brain cell aggregates at 48 h postinfection. Antiviral concentrations of up to 200 micrograms or 200,000 IU/ml for interferon did not appear morphologically toxic to brain cells. Antiviral therapy of HSV-1-infected brain cell aggregates may more closely mimic in vivo responses than monolayer cultures.     

Detection of herpes simplex virus type 1 in addition to Epstein-Bar virus in tonsils using a new multiplex polymerase chain reaction assay

HSV-1, HSV-2, CMV, EBV, which are the members of the herpes virus family colonize and establish latent infection in human. Although EBV is a well known virus most involved in recurrent bouts of acute tonsillitis, the role and possibility of HSV-1, HSV-2, and CMV for establishing infection in tonsils are not clear. The purpose of this study is to verify whether the tonsils might harbor the HSV-1, HSV-2, and CMV, in addition to EBV, in chronically hyperplastic nasopharyngeal lymphoid tissue. To accomplish the purpose, we developed a new Multiplex Polymerase Chain Reaction (M-PCR) assay using a single consensus forward primer and virus specific reverse primers for DNA polymerase gene of HSV-1, and 2, EBV, and CMV, and investigated its efficiency for detecting HSV1, HSV2, CMV, and EBV. The sample of 52 patients underwent tonsillectomy or adenectomy because of chronic lymphoid hyperplasia without any evidence of acute infections and were investigated for presence of HSV-1, HSV-2, CMV, and EBV. Of the 54 samples, 11 (20.4%) of them were positive for EBV, 4 of them (7.4%) were positive for HSV-1, and none of the samples were positive for HSV-2 and CMV. To the best of our knowledge, this is the first report that tonsils may be the reservoir for HSV-1 in addition to EBV, and HSV-1 may have a role in recurrent tonsillitis and systemic diseases. The MC-PCR assay presented in this study can provide a rapid, sensitive, and economical method for detection of HSV-1, HSV-2, EBV, and CMV in a single PCR tube.