Synthetic analogues of bovine bactenecin dodecapeptide reduce herpes simplex virus type 2 infectivity in mice

We have evaluated the potential of four synthetic peptides (denoted HH-2, 1002, 1006, 1018) with a distant relationship to the host defense peptide bovine bactenecin dodecapeptide for their ability to prevent genital infections with herpes simplex virus type 2 (HSV-2) in mice. All four peptides showed antiviral properties in vitro and reduced HSV-2 infection of Vero cells in a dose-dependent manner. Detailed analysis showed that the peptides were able to interfere with both viral attachment and entry, but not with replication post-entry, and were effective antivirals also when HSV-2 was introduced in human semen. Two of the peptides proved especially effective in reducing HSV-2 infection also in vivo. When admixed with virus prior to inoculation, both HH-2 and 1018 reduced viral replication and disease development in a genital model of HSV-2 infection in mice, and also when using very high infectious doses of HSV-2. These data show that peptides HH-2 and 1018 have antiviral properties and can be used to prevent genital herpes infection in mice.

Role of IFN-alpha/beta signaling in the prevention of genital herpes virus type 2 infection

This study has shown that IFN-alpha/beta signaling is crucial for combating primary herpes simplex virus type 2 (HSV-2) infection and for responding to immunotherapy using ligands to TLR3, 7 and 9, but not for vaccine-induced immunity. Both genital viral replication and the disease progression were enhanced in HSV-2-infected mice lacking the IFN-alpha/beta receptor (IFN-alpha/betaR-/-). IFN-alpha/betaR-/- mice were, however, able to mount a normal HSV-2-specific Th1 response and acquired sterilizing immunity following vaccination. Anti-viral treatments using agonists to TLR3, 7 and 9 by administration of synthetic dsRNA, imiquimod and oligonucleotides containing unmethylated CpG motifs, respectively, were strongly dependent on IFN-alpha/beta receptor signaling for their efficacy. Even though all treatments had a weak impact on local vaginal viral replication in infected IFN-alpha/betaR-/- animals, they did not affect disease progression or mortality in these animals as opposed to wild type controls where all three treatments reduced viral replication as well as disease severity and mortality. Lack of IFN-alpha/betaR signaling also blocked production of IFN-gamma and TNF-alpha in response to TLR9 activation. These studies have shown that IFN-alpha/beta receptor signaling is important for multiple events in the anti-viral defense.

Neurokinin 1 receptor signaling affects the local innate immune defense against genital herpes virus infection

We show that genital infection with neurotropic HSV type 2 (HSV-2) induced a significant increase of the neuropeptide substance P (SP) within the genital tract of mice. SP was shown to weakly interfere with the HSV-2 replication. Furthermore, lack of SP signaling through the use of mice deficient in the SP receptor, neurokinin 1 receptor (NK1R), revealed an important role for SP in the innate defense against HSV-2. NK1R-deficient mice had significantly enhanced levels of HSV-2 in the genital tract and in the CNS following infection and a significantly accelerated disease progression, which was associated with an impaired NK cell activity locally in the vagina. Lack of NK1R signaling did, however, not impair the animals' ability to mount a protective immune response to HSV-2 following vaccination with an attenuated virus. Both NK1R+/+ and NK1R-/- mice developed strong HSV-2-specific Th1 T cell responses following vaccination. No genital viral replication was observed in either vaccinated NK1R-deficient or NK1R+/+ control animals following a genital HSV-2 challenge, and all of these animals survived without any symptoms of disease. In conclusion, the present results indicate that SP and NK1R signaling contributes to the innate resistance against HSV-2 infection in mice.

CD8+ T-Cells Suppress Antigen-Specific and Allogeneic CD4+ T-Cell Responses to Herpes Simplex Virus Type 2–Infected Human Dendritic Cells

In this study we show that human dendritic cells (DC), productively infected with herpes simplex virus type 2 (HSV-2), activate CD8+ T cells that suppress antigen-specific and alloreactive CD4+ T cell expansion. Addition of CD8+ T cells to cultures of DC and CD4+ T cells blocked CD4+ T-cell proliferation in response to HSV-2-infected but not to uninfected DC. The effect was independent of prior HSV exposure or cognate MHC class I-restricted CD8-DC recognition as it was induced in CD8+ T cells from HSV-2-seronegative individuals and in mixed lymphocyte reactions using allogeneic DC. Both CD8+ CD25+ and CD8+ CD25- cells were shown to have suppressive capacities. The blood-derived CD25+ CD8+ T cells did not express Foxp3 mRNA but had a bona fide antiproliferative capacity in response to both uninfected and HSV-2-infected DC, whereas the CD25-CD8+ T cells were selectively activated to become antiproliferative by HSV-2-infected DC. These data imply that HSV infection of DC could modulate the immune response by activating CD8+ T cells.

Protective immunity to genital herpes simplex [correction of simpex] virus type 2 infection is mediated by T-bet

We show, for the first time, that the transcription factor T-bet, which is implicated in IFN-gamma production, is required for the induction of vaccine-induced antiviral immune protection. T-bet was found to be important in both the innate and acquired immune protection against genital HSV-2 infection. T-bet(-/-) and T-bet(+/+) mice were infected vaginally with HSV-2 and examined daily for disease and mortality. T-bet(-/-) mice had significantly higher virus titers than T-bet(+/+) mice following a primary HSV-2 infection, and succumbed significantly earlier to the infection. This result was associated with an impaired NK cell cytotoxic capacity and NK cell-mediated IFN-gamma production in the T-bet(-/-) mice. To assess the induction of acquired antiviral immune protection, mice were vaccinated with an attenuated virus before infection. Vaccinated T-bet(-/-) mice could not control viral replication following an HSV-2 challenge and had significantly higher virus titers and mortality rates than vaccinated T-bet(+/+) mice that remained healthy. The impaired acquired immune protection in T-bet(-/-) mice was associated with a significantly decreased HSV-2-specific delayed-type hypersensitivity response and a significantly reduced HSV-2-specific IFN-gamma production from CD4(+) T cells. However, T-bet deficiency did not impair either the IFN-gamma production or the cytotoxic capacity of HSV-2-specific CD8(+) T cells. We conclude that T-bet plays a crucial role in both the innate defense and the generation of vaccine-induced immunity against genital HSV-2 infection in mice.

In vitro selection of drug-resistant varicella-zoster virus (VZV) mutants (OKA strain): differences between acyclovir and penciclovir?

Varicella-zoster virus (VZV) mutants were isolated under the pressure of different classes of antiviral compounds: (i) drugs that depend on the viral thymidine kinase (TK) for their activation, i.e. acyclovir (ACV), brivudin (BVDU), penciclovir (PCV) and sorivudine (BVaraU); (ii) drugs that are independent of the viral TK for their activation, i.e. 2-phosphonylmethoxyethyl (PME) derivatives of adenine (PMEA, adefovir) and 2,6-diaminopurine (PMEDAP); and (iii) drugs that do not require any metabolism to inhibit the viral DNA polymerase, i.e. foscarnet (PFA). Drug-resistant virus strains were obtained by serial passage of the OKA strain in human embryonic lung (HEL) fibroblasts and the different drug-resistant mutants were subsequently evaluated for their in vitro susceptibility to a broad range of antiviral drugs. Virus strains emerging under the pressure of ACV, BVDU and BVaraU were cross-resistant to all drugs that depend on the viral TK for activation, but remained susceptible to the acyclic nucleoside phosphonates (i.e. PMEA, PMEDAP and the 3-hydroxy-2-phosphonylmethoxypropyl derivatives of adenine (HPMPA) and cytosine (HPMPC, cidofovir)) and PFA. In contrast, the virus strains selected under pressure of PCV were resistant to PCV, ACV, PMEA and PFA; but not BVDU, BVaraU, GCV, HPMPC or HPMPA. Similar patterns of drug susceptibility were noted for the virus strains selected under the pressure of PMEA or PFA, pointing to an alteration in the viral DNA polymerase as basis for the resistant phenotype selected by PCV, as well as PMEA and PFA. In contrast, the resistant phenotype selected by ACV as well as BVDU and BVaraU may be attributed primarily to mutations in the viral TK gene. Our data thus indicate that ACV and PCV select in vitro for different drug-resistant VZV phenotypes; whether this is also the situation in vivo remains to be investigated.

Drug resistance patterns of recombinant herpes simplex virus DNA polymerase mutants generated with a set of overlapping cosmids and plasmids

Herpes simplex virus (HSV) DNA polymerase (Pol) mutations can confer resistance to all currently available antiherpetic drugs. However, discrimination between mutations responsible for drug resistance and those that are part of viral polymorphism can be difficult with current methodologies. A new system is reported for rapid generation of recombinant HSV type 1 (HSV-1) DNA Pol mutants based on transfection of a set of overlapping viral cosmids and plasmids. With this approach, twenty HSV-1 recombinants with single or dual mutations within the DNA pol gene were successfully generated and subsequently evaluated for their susceptibilities to acyclovir (ACV), foscarnet (FOS), cidofovir (CDV), and adefovir (ADV). Mutations within DNA Pol conserved regions II (A719T and S724N), VI (L778M, D780N, and L782I), and I (F891C) were shown to induce cross-resistance to ACV, FOS, and ADV, with two of these mutations (S724N and L778M) also conferring significant reduction in CDV susceptibility. Mutant F891C was associated with the highest levels of resistance towards ACV and FOS and was strongly impaired in its replication capacity. One mutation (D907V) lying outside of the conserved regions was also associated with this ACV-, FOS-, and ADV-resistant phenotype. Some mutations (K522E and Y577H) within the delta-region C were lethal, whereas others (P561S and V573M) induced no resistance to any of the drugs tested. Recombinants harboring mutations within conserved regions V (N961K) and VII (Y941H) were resistant to ACV but susceptible to FOS. Finally, mutations within conserved region III were associated with various susceptibility profiles. This new system allows a rapid and accurate evaluation of the functional role of various DNA Pol mutations, which should translate into improved management of drug-resistant HSV infections.

Herpes simplex virus isolates with reduced adefovir susceptibility selected in vivo by foscarnet therapy

Sequential herpes simplex virus (HSV) isolates from AIDS patients receiving foscarnet therapy were evaluated for susceptibility to adefovir. Foscarnet-resistant isolates with DNA polymerase mutations in regions II, VI, and between I and VII were also associated with an important decrease in susceptibility to adefovir (mean IC50 increase: 4.6-fold compared to pre-foscarnet or wild-type isolates) suggesting that adefovir-resistant HSV could be selected in vivo by foscarnet therapy.

Characterization of wild-type and cidofovir-resistant strains of camelpox, cowpox, monkeypox, and vaccinia viruses

Cidofovir ([(S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine] [HPMPC])-resistant forms of camelpox, cowpox, monkeypox, and vaccinia viruses were developed by prolonged passage in Vero 76 cells in the presence of drug. Eight- to 27-fold-higher concentrations of cidofovir were required to inhibit the resistant viruses than were needed to inhibit the wild-type (WT) viruses. Resistant viruses were characterized by determining their cross-resistance to other antiviral compounds, examining their different replication abilities in two cell lines, studying the biochemical basis of their drug resistance, and assessing the degrees of their virulence in mice. These viruses were cross resistant to cyclic HPMPC and, with the exception of vaccinia virus, to (S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)adenine. Three of the four resistant cowpox and monkeypox viruses exhibited reduced abilities to infect and replicate in 3T3 cells compared to their abilities in Vero 76 cells. Compared to the WT virus polymers the resistant cowpox virus DNA polymerase was 8.5-fold less sensitive to inhibition by cidofovir diphosphate, the active form of the drug. Intracellular phosphorylation of [3H]cidofovir was not stimulated or inhibited by infection with resistant cowpox virus. In intranasally infected BALB/c mice, WT cowpox virus was 80-fold more virulent than the resistant virus. Cidofovir treatment (100 mg/kg of body weight, given one time only as early as 5 min after virus challenge) of a resistant cowpox virus infection could not protect mice from mortality. However, the drug prevented mortality in 80 to 100% of the mice treated with a single 100-mg/kg dose at 1, 2, 3, or 4 days after WT virus challenge. By application of these results to human orthopoxvirus infections, it is anticipated that resistant viruses may be untreatable with cidofovir but their virulence may be attenuated. Studies will need to be conducted with cidofovir-resistant monkeypox virus in monkeys to further support these hypotheses.

6-[2-(Phosphonomethoxy)alkoxy]pyrimidines with antiviral activity

6-Hydroxypyrimidines substituted at positions 2 and 4 by hydrogen, methyl, amino, cyclopropylamino, dimethylamino, methylsulfanyl, or hydroxyl group afford by the reaction with diisopropyl 2-(chloroethoxy)methylphosphonate in the presence of NaH, Cs(2)CO(3), or DBU a mixture of N(1)- and O(6)-[2-(diisopropylphosphorylmethoxy)ethyl] isomers which were converted to the free phosphonic acids by treatment with bromotrimethylsilane followed by hydrolysis. Analogously, 2,4-diamino-6-hydroxypyrimidine gave on reaction with [(R)- and (S)-2-(diisopropylphosphorylmethoxy)propyl] tosylate, followed by deprotection, the enantiomeric 6-[2-(phosphonomethoxy)propoxy]pyrimidines. 2,4-Diamino-6-sulfanylpyrimidine gave, on treatment with diisopropyl 2-(chloroethoxy)methylphosphonate in the presence of NaH and subsequent deprotection, 2,4-diamino-6-[[2-(phosphonomethoxy)ethyl]sulfanyl]pyrimidine. 2-Amino-4-hydroxy-6-[2-(phosphonomethoxy)ethyl]pyrimidine was obtained from the appropriate 2-amino-4-chloropyrimidine derivative by alkaline hydrolysis and ester cleavage. Direct alkylation of 2-amino-4,6-dihydroxypyrimidine afforded a mixture of 2-amino-4,6-bis[2-(phosphonomethoxy)ethyl]- and 2-amino-1,4-bis[2-(phosphonomethoxy)ethyl]pyrimidine. None of the N(1)-[2-(phosphonomethoxy)ethyl] isomers exhibited any antiviral activity against DNA viruses or RNA viruses tested in vitro. On the contrary, the O(6)-isomers, namely the compounds derived from 2,4-diamino-, 2-amino-4-hydroxy-, or 2-amino-4-[2-(phosphonomethoxy)ethoxy]-6-hydroxypyrimidine, inhibited the replication of herpes viruses [herpes simplex type 1 (HSV-1) and type 2 (HSV-2), varicella-zoster virus (VZV), and cytomegalovirus (CMV)] and retroviruses [Moloney sarcoma virus (MSV) and human immunodeficiency virus type 1 (HIV-1) and type 2 (HIV-2)], their activity being most pronounced against the latter. The antiviral activity was lower if the oxygen at the position 6 was replaced by a sulfur atom, as in 2,4-diamino-6-[2-(phosphonomethoxy)ethylsulfanyl]pyrimidine. In analogy to N(9)-[2-(phosphonomethoxy)propyl]-2,6-diaminopurine (PMPDAP), solely the (R)-2,4-diamino-6-[2-(phosphonomethoxy)propoxy]pyrimidine exerted antiviral activity, whereas its (S)-enantiomer was essentially inactive.

Resistance of herpesviruses to antiviral drugs: clinical impacts and molecular mechanisms

Nucleoside analogues such as acyclovir and ganciclovir have been the mainstay of therapy for alphaherpesviruses (herpes simplex virus (HSV) and varicella-zoster virus (VZV)) and cytomegalovirus (CMV) infections, respectively. Drug-resistant herpesviruses are found relatively frequently in the clinic, almost exclusively among severely immunocompromised patients receiving prolonged antiviral therapy. For instance, close to 10% of patients with AIDS receiving intravenous ganciclovir for 3 months excrete a drug-resistant CMV isolate in their blood or urine and this percentage increases with cumulative drug exposure. Many studies have reported that at least some of the drug-resistant herpesviruses retain their pathogenicity and can be associated with progressive or relapsing disease. Viral mutations conferring resistance to nucleoside analogues have been found in either the drug activating/phosphorylating genes (HSV or VZV thymidine kinase, CMV UL97 kinase) and/or in conserved regions of the viral DNA polymerase. Currently available second line agents for the treatment of herpesvirus infections--the pyrophosphate analogue foscarnet and the acyclic nucleoside phosphonate derivative cidofovir--also inhibit the viral DNA polymerase but are not dependent on prior viral-specific activation. Hence, viral DNA polymerase mutations may lead to a variety of drug resistance patterns which are not totally predictable at the moment due to insufficient information on specific drug binding sites on the polymerase. Although some CMV and HSV DNA polymerase mutants have been found to replicate less efficiently in cell cultures, further research is needed to correlate viral fitness and clinical outcome.

Interleukin-12 (IL-12) and IL-18 are important in innate defense against genital herpes simplex virus type 2 infection in mice but are not required for the development of acquired gamma interferon-mediated protective immunity

Using a combination of gene-targeted mice and neutralizing antibodies, we showed that interleukin-12 (IL-12) and IL-18 are important in the innate control of genital herpes simplex virus type 2 infection but were not found to be critical, either singly or in combination, for the development of a protective gamma interferon-mediated immune response.

Highly reliable heterologous system for evaluating resistance of clinical herpes simplex virus isolates to nucleoside analogues

Clinical resistance of herpes simplex virus (HSV) types 1 and 2 to acyclovir (ACV) is usually caused by the presence of point mutations within the coding region of the viral thymidine kinase (TK) gene. The distinction between viral TK mutations involved in ACV resistance or part of viral polymorphism can be difficult to evaluate with current methodologies based on transfection and homologous recombination. We have developed and validated a new heterologous system based on the expression of the viral TK gene by the protozoan parasite Leishmania, normally devoid of TK activity. The viral TK genes from 5 ACV-susceptible and 13 ACV-resistant clinical HSV isolates and from the reference strains MS2 (type 2) and KOS (type 1) were transfected as part of an episomal expression vector in Leishmania. The susceptibility of TK-recombinant parasites to ganciclovir (GCV), a closely related nucleoside analogue, was evaluated by a simple measurement of the absorbance of Leishmania cultures grown in the presence of the drug. Expression of the TK gene from ACV-susceptible clinical isolates resulted in Leishmania susceptibility to GCV, whereas expression of a TK gene with frameshift mutations or nucleotide substitutions from ACV-resistant isolates gave rise to parasites with high levels of GCV resistance. The expression of the HSV TK gene in Leishmania provides an easy, reliable, and sensitive assay for evaluating HSV susceptibility to nucleoside analogues and for assessing the role of specific viral TK mutations.

Differential roles of B cells and IFN-gamma-secreting CD4(+) T cells in innate and adaptive immune control of genital herpes simplex virus type 2 infection in mice

The role of B, CD4(+) T and CD8(+) T cells in both primary genital infection with attenuated herpes simplex virus type 2 (HSV-2) and development of protective immunity to a later challenge with virulent HSV-2 using lymphocyte-deficient mice has been elucidated. Following primary inoculation with attenuated thymidine kinase-deficient (TK(-)) HSV-2, B cell-deficient (microMT) mice developed a local viraemia and transient genital inflammation, suggesting a role for B cells in the innate control of local infection and inflammation. Natural antibodies are implicated in this process, as passive transfer of normal serum into microMT mice significantly reduced HSV-2 TK(-) shedding in the vaginal lumen, although it did not affect subsequent inflammation. Protection against lethal HSV-2 challenge was noted in HSV-2-vaccinated wild-type, CD8(+) T cell-deficient and microMT mice and was characterized by strong virus-specific IFN-gamma responses in vitro and delayed type hypersensitivity (DTH) responses in vivo. In contrast, CD4(+) T cell-deficient (CD4(-/-)) mice had impaired HSV-2-specific IFN-gamma production and DTH responses and succumbed rapidly to genital HSV-2 challenge. However, protective responses to HSV-2 could be induced in HSV-2-vaccinated CD4(-/-) mice by treatment with recombinant IFN-gamma. Taken together, these results suggest that CD4(+) T cells secreting IFN-gamma are critical for immune protection against lethal genital HSV-2 re-infection, whereas B cells/natural antibodies have anti-viral and -inflammatory effects in the innate control of a primary infection.

Acyclic/carbocyclic guanosine analogues as anti-herpesvirus agents

Several guanosine analogues, i.e. acyclovir (and its oral prodrug valaciclovir), penciclovir (in its oral prodrug form, famciclovir) and ganciclovir, are widely used for the treatment of herpesvirus [i.e. herpes simplex virus type 1 (HSV-1), and type 2 (HSV-2), varicella-zoster virus (VZV) and/or human cytomegalovirus (HCMV)] infections. In recent years, several new guanosine analogues have been developed, including the 3-membered cyclopropylmethyl and -methenyl derivatives (A-5021 and synguanol) and the 6-membered D- and L-cyclohexenyl derivatives. The activity of the acyclic/carbocyclic guanosine analogues has been determined against a wide spectrum of viruses, including the HSV-1, HSV-2, VZV, HCMV, and also human herpesviruses type 6 (HHV-6), type 7 (HHV-7) and type 8 (HHV-8), and hepatitis B virus (HBV). The new guanosine analogues (i.e. A-5021 and D- and L-cyclohexenyl G) were found to be particularly active against those viruses (HSV-1, HSV-2, VZV) that encode for a specific thymidine kinase (TK), suggesting that their antiviral activity (at least partially) depends on phosphorylation by the virus-induced TK. Marked antiviral activity was also noted with A-5021 against HHV-6 and with D- and L-cyclohexenyl G against HCMV and HBV. The antiviral activity of the acyclic/carbocyclic nucleoside analogues could be markedly potentiated by mycophenolic acid, a potent inhibitor of inosine 5'-monophosphate (IMP) dehydrogenase. The new carbocyclic guanosine analogues (i.e. A-5021 and D- and L-cyclohexenyl G) hold great promise, not only as antiviral agents for the treatment of herpesvirus infections, but also an antitumor agents for the combined gene therapy/chemotherapy of cancer, provided that (part of) the tumor cells have been transduced by the viral (HSV-1, VZV) TK gene.