Acyclovir-resistant Varicella Zoster Virus Research Articles

Utility of ultra-deep sequencing for detection of varicella-zoster virus antiviral resistance mutations

We report the first application of ultra-deep sequencing (UDS) to varicella-zoster virus (VZV) genotypic antiviral testing in a case of acyclovir-resistant VZV infection initially detected by Sanger sequencing within a deeply immunocompromised heart transplant recipient. As added-value compared to Sanger analysis, UDS revealed complex dynamics of viral population under antiviral pressure.Varicella-zoster virus (VZV) is a ubiquitous human herpesvirus affecting populations worldwide. VZV is commonly acquired in youth whose primary infection usually manifests as benign varicella (chickenpox). After the initial infection, the virus establishes lifelong latency in sensory ganglia leading to a risk of subsequent reactivation. Reactivation usually results in the development of localized herpes zoster (HZ) lesions, a painful skin rash commonly known as shingles (Cohen, 2013). The incidence and severity of HZ increase with impaired specific cell-mediated immunity mainly as a result of increasing age, malignancy, immunodeficiency, organ transplantation, or immunosuppressive drug therapy (Cohen, 2013; Koo et al., 2014; Pavlopoulou et al., 2015). In particular, HZ remains a significant cause of morbidity among solid organ transplant (SOT) recipients, especially in patients undergoing heart transplantation (HT) compared with liver, kidney, or lung transplant recipients (Carby et al., 2007; Koo et al., 2014; Pavlopoulou et al., 2015). These particular individuals are at increased risk of primary infection, reactivation followed by dissemination with visceral involvement and associated with bacterial superinfection, and chronic recurrences (Cohen, 2013). VZV infections may also engender debilitating neuralgia among highly immunocompromised patients (Sampathkumar et al., 2009). HT is also associated with the risk of reactivation of other latent viruses belonging to the Herpesviridae family as herpes simplex virus (HSV). Currently licensed drugs to prevent or to cure HSV- or VZV-associated diseases target the viral DNA polymerase (Pol). Acyclovir (ACV) and its prodrug valacyclovir (VACV) are considered as the first-line therapy, whereas foscarnet (FOS) or cidofovir (CDV) constitute alternative options. After primophosphorylation by the viral thymidine kinase (TK), ACV targets the viral DNA polymerase and inhibits the viral genome replication by a chain termination mechanism. According to this mechanism of action, viral mutations conferring resistance to ACV have been mapped both in TK and Pol encoding genes. Viral mutations conferring resistance to FOS and CDV are only detected in Pol gene. VZV ACV-resistance is mostly mediated by TK alterations, consisting in either translational frameshifts, sometimes associated with premature stop codon, or amino acid substitutions. In the remaining cases, amino acid substitutions are detected within Pol (De et al., 2015; Piret and Boivin, 2014). Classically, Sanger sequencing has been recognized as the gold standard for the detection of drug resistance mutations (DRMs) within VZV TK and Pol genes (Perrier et al., 2016; Piret and Boivin, 2014). However, this approach cannot detect minor variants present at a frequency below 20%. Ultra-deep sequencing (UDS) has an enhanced sensitivity compared to Sanger method and allows quantitative evaluation of the viral mutants (Chin et al., 2013). We report here a case of VZV resistant infection in an HT recipient. Our retrospective study aimed at showing the utility of UDS for DRM detection as a complement of Sanger method.

Role of the JNK Pathway in Varicella-Zoster Virus Lytic Infection and Reactivation.

Mechanisms of neuronal infection by varicella-zoster virus (VZV) have been challenging to study due to the relatively strict human tropism of the virus and the paucity of tractable experimental models. Cellular mitogen-activated protein kinases (MAPKs) have been shown to play a role in VZV infection of nonneuronal cells, with distinct consequences for infectivity in different cell types. Here, we utilize several human neuronal culture systems to investigate the role of one such MAPK, the c-Jun N-terminal kinase (JNK), in VZV lytic infection and reactivation. We find that the JNK pathway is specifically activated following infection of human embryonic stem cell-derived neurons and that this activation of JNK is essential for efficient viral protein expression and replication. Inhibition of the JNK pathway blocked viral replication in a manner distinct from that of acyclovir, and an acyclovir-resistant VZV isolate was as sensitive to the effects of JNK inhibition as an acyclovir-sensitive VZV isolate in neurons. Moreover, in a microfluidic-based human neuronal model of viral latency and reactivation, we found that inhibition of the JNK pathway resulted in a marked reduction in reactivation of VZV. Finally, we utilized a novel technique to efficiently generate cells expressing markers of human sensory neurons from neural crest cells and established a critical role for the JNK pathway in infection of these cells. In summary, the JNK pathway plays an important role in lytic infection and reactivation of VZV in physiologically relevant cell types and may provide an alternative target for antiviral therapy.IMPORTANCE Varicella-zoster virus (VZV) has infected over 90% of people worldwide. While primary infection leads to the typically self-limiting condition of chickenpox, the virus can remain dormant in the nervous system and may reactivate later in life, leading to shingles or inflammatory diseases of the nervous system and eye with potentially severe consequences. Here, we take advantage of newer stem cell-based technologies to study the mechanisms by which VZV infects human neurons. We find that the c-Jun N-terminal kinase (JNK) pathway is activated by VZV infection and that blockade of this pathway limits lytic replication (as occurs during primary infection). In addition, JNK inhibition limits viral reactivation, exhibiting parallels with herpes simplex virus reactivation. The identification of the role of the JNK pathway in VZV infection of neurons reveals potential avenues for the development of alternate antiviral drugs.

Compartmentalization of Acyclovir-Resistant Varicella Zoster Virus: Implications for Sampling in Molecular Diagnostics

Acyclovir resistance of varicella zoster virus (VZV) may arise in stem cell transplant (SCT) recipients with VZV disease and is usually a result of mutations in VZV thymidine kinase (TK), which is the target protein of acyclovir. Early detection of such mutations is necessary to enable timely therapy adaptation, for example, to foscarnet. We aimed to investigate whether TK mutations arise over time, and what sample types might be the most useful for this method. Spatially and temporally distinct samples from 3 SCT recipients with VZV disease unresponsive to acyclovir treatment were retrospectively investigated for the presence of TK mutations by polymerase chain reaction and sequence analysis. In all 3 patients, a mutation in the VZV TK coding region was found resulting in an amino acid substitution. TK mutations were not only temporally but also spatially compartmentalized. In particular, plasma samples frequently showed wild-type TK sequences, whereas cerebrospinal fluid or skin vesicle fluid acquired on the same day contained mutant sequences. This study shows the importance of careful sampling for molecular diagnostics of acyclovir resistance in VZV disease. All affected body sites should be sampled and plasma samples may not be representative for the viral mutation status.

Foscarnet Salvage Therapy for Acyclovir-Resistant Varicella Zoster

The authors describe an acyclovir-resistant varicella zoster virus infection in a pediatric patient after hematopoietic stem cell transplant, the use of foscarnet as salvage therapy, and review the literature to clarify the pediatric experience with foscarnet in this setting. A novel thymidine kinase mutation is described, along with a new phenotypic assay for characterizing acyclovir resistance in varicella zoster virus.

The hepatologist in the haematologists' camp.

The hepatologist in the haematologists' camp.

Pharmacology and clinical use of foscarnet

Foscarnet, licenced by Astra pharmaceutical products, is a pyrophosphate analogue that selectively inhibits replication of viruses in infected cells. It inhibits in vitro the replication of all herpes viruses, including human cytomegalovirus (HCMV) at concentrations of 100 to 300 μmol/l and has a dose-related inhibitory effect on HIV-1 virus, influenza virus and hepatitis B virus. It does not require intra-cellular phosphorylation for antiviral activity. Oral bioavailability of foscarnet is low (12–22%), and foscarnet must be administered intravenously. It is mainly eliminated unchanged by the kidneys. Mean half-life in plasma ranges from 3.4 to 5 h. For acute therapy, the currently recommended regimen is 60 mg/kg t.i.d. or 90–100 mg/kg b.i.d. In AIDS patients, foscarnet is an effective treatment of HCMV retinitis. Healing or stabilisation of lesions is obtained in 85–95% of patients after 2 weeks or 3 weeks therapy. For HCMV gastrointestinal disease, complete or partial response rates of 57–95% have been reported with foscarnet. The optimal maintenance dosage of foscarnet necessary in CMV infections in AIDS patients remains to be clearly established. Data from small samples size studies have shown that foscarnet decreased significantly circulating levels of HIV antigen in AIDS patients with HCMV disease. Foscarnet is an effective treatment for acyclovir-resistant herpes simplex virus and for acyclovir-resistant varicella-zoster virus (40 mg/kg every 8 h). In patients with immunosuppression not HIV-related HCMV infections, particularly interstitial pneumonia in transplant recipients, experience with foscarnet is limited. The major adverse effect of foscarnet is reversible renal dysfunction, due to acute tubular toxicity. In may be partially prevented by hyperhydratation during the treatment. Fluctuations in serum calcium and phosphore levels, with both increase and decrease are also frequent adverse reactions. Most clinical symptoms are related to decrease in ionized calcium levels. Hyperphosphatemia, a clinically benign phenomenom, reflects the incorporation of foscarnet in bone. Penile ulcerations have been described and may result from mococutaneous direct toxicity of foscarnet eliminated in urine. Although relapses frequently occur after a few months of maintenance therapy, foscarnet that shows a marked activity against HCMV in vitro, has allowed important progress in therapy of HCMV infections in AIDS patients.

Inhibitory action of acyclovir (ACV) and penciclovir (PCV) on plaque formation and partial cross-resistance of ACV-resistant varicella-zoster virus to PCV

Penciclovir has potent antiviral activity against varicella-zoster virus (VZV). We have characterized the inhibitory effects of penciclovir and acyclovir on the plaque formation of cell-free VZV and cross-resistance of acyclovir-resistant VZV to penciclovir. The apparent effective concentration for 50% plaque reduction (EC 50) of penciclovir determined on the third day was significantly lower than that determined on the fourth or fifth day. The size of plaques was smaller in the presence of penciclovir than in the presence of acyclovir. The effective concentrations for 50% reduction of the number of infected cells per plaque were 1.40 and 5.00 μg/ml for penciclovir and acyclovir, respectively. Thus penciclovir suppressed spread of infection within developing plaques more efficiently than acyclovir. Five acyclovir-resistant VZV strains with altered DNA polymerase selected by acyclovir were examined for cross-resistance to penciclovir. They were 11- to 18-fold more resistant to ACV than the parent strain, but only 4- to 5-fold more resistant to PCV. Penciclovir-triphosphate carrying the 3′-hydroxyl group of 2′-deoxyribose might have better affinity to the altered viral DNA polymerase than acyclovir-triphosphate without the 3′-hydroxyl group.

Phenotypic and genotypic characterization of acyclovir-resistant varicella-zoster viruses isolated from persons with AIDS.

Phenotypic and genotypic analyses were done on 17 varicella-zoster virus (VZV) isolates recovered from 10 persons with AIDS (mean CD4 cell count, 16.4/mm3) who had chronic VZV lesions. Eleven acyclovir-resistant isolates were recovered from 10 patients after a mean of 20.1 weeks of therapy. Six susceptible isolates were recovered before acyclovir treatment (n = 1), early during therapy (n = 4; mean time, 4.2 weeks), or after discontinuation of acyclovir (n = 1). Acyclovir-resistant VZV isolates were deficient in thymidine kinase (TK) or induced a TK with altered substrate specificity; all isolates were susceptible to foscarnet. Ten of 11 acyclovir-resistant mutants contained tk gene mutations, including single nucleotide substitutions in highly conserved binding sites (n = 2) as well as nucleotide deletions (n = 4) and insertions (n = 4). These findings suggest that multiple, nonuniform mutations within the tk gene are associated with acyclovir-resistant VZV phenotypes.

Acyclovir-Resistant Varicella Zoster Responsive to Foscarnet

<h3>To the Editor.—</h3> Acyclovir-resistant herpes simplex virus (HSV) in human immunodeficiency virus (HIV)-infected patients has been reported, often after long-term therapy with acyclovir.¹In some cases the lesions responded to foscarnet (trisodium phosphonoformate) therapy.¹Acyclovir-resistant varicella zoster virus (VZV) has also been reported with increasing frequency in HIV-infected patients, and is commonly associated with chronic localized verrucous skin lesions.^2,3Although in vitro sensitivity to foscarnet has been reported, we believe that this is the first report in which chronic lesions due to acyclovir-resistant varicella zoster virus have resolved after treatment with foscarnet. <h3>Report of a Case.—</h3> A 24-year-old white man with acquired HIV infection (Walter Reed Stage VI) presented with a history of herpes-zoster occurring in the left C7-8 dermatome in July 1989. The cutaneous lesions were typical vesicular lesions of VZV. The patient was treated with high-dose oral acyclovir (4 g/d for 10 days) with apparent

Foscarnet therapy in five patients with AIDS and acyclovir-resistant varicella-zoster virus infection.

To determine whether foscarnet has potential efficacy in the treatment of acyclovir-resistant mucocutaneous varicella-zoster infection in patients with the acquired immunodeficiency syndrome (AIDS). Open-label study. Three university medical centers. Five patients with AIDS who were infected with thymidine-kinase-deficient or -altered strains of varicella-zoster virus. Foscarnet, 40 mg/kg body weight every 8 hours in 1-hour infusions for 10 or more days. Four patients had healing in response to foscarnet therapy, and each of four tested patients became culture negative for virus during foscarnet therapy. Results of fluorescent antigen testing remained positive during therapy in two patients; one of these patients had concomitant clinical failure but the other patient healed fully. One patient had complete healing despite the emergence of resistance to foscarnet in serial specimens obtained during foscarnet therapy. Foscarnet is a potentially effective and tolerable antiviral agent for patients with acyclovir-resistant, varicella-zoster virus infection; however, the optimal dosage and duration of therapy require further study, as does the relation between clinical findings and in-vitro susceptibility results.

Novel Sensitivity of Acyclovir-Resistant Varicella–Zoster Virus to Anti-Herpetic Drugs

Acyclovir-resistant varicella–zoster virus (VZV) selected in the presence of acyclovir was 3–20 times more sensitive to nucleoside analogues with arabinosyl configuration than the parent virus. Their sensitivity in comparison with a thymidine kinase-deficient mutant to anti-herpetic drugs and sensitivity to phosphonoacetic acid suggested that recognition by altered mutants' DNA polymerase might result in their novel sensitivity to nucleoside analogues. Information on the unique sensitivity of these acyclovir-resistant mutants may be useful in designing chemotherapeutic agents against VZV.

Acyclovir-resistant varicella zoster virus infection after chronic oral acyclovir therapy in patients with the acquired immunodeficiency syndrome (AIDS)

Four patients with human immunodeficiency virus (HIV) infection who received chronic oral acyclovir therapy for suppression of recurrent varicella zoster or herpes simplex virus infection developed persistent disseminated hyperkeratotic papules that failed to heal with intravenous or high-dose oral acyclovir therapy. Varicella zoster virus, resistant to acyclovir in vitro, was isolated from skin lesions of all four patients. Three patients were adults in whom the acquired immunodeficiency syndrome (AIDS) had been diagnosed 12 to 20 months before isolation of acyclovir-resistant varicella zoster virus. The fourth patient was a perinatally HIV-infected child who developed primary varicella infection at age 7 years when profoundly immunosuppressed (absolute CD4+ lymphocyte count less than 50 cells/microL). Mean antiviral susceptibilities (ED50 values) of the four clinical isolates compared with the ED50 values of the reference strain Oka were 85 compared with 3.3 mumol/L for acyclovir, 1.4 compared with 0.8 mumol/L for vidarabine, and 123 compared with 117 mumol/L for foscarnet. When assayed by [125I]-dC plaque autoradiography, 90% to 100% of the viral isolate populations had altered or no measurable thymidine kinase function. Acyclovir-resistant varicella zoster virus infection may complicate long-term oral acyclovir administration in patients with AIDS and may be associated with the appearance of atypical hyperkeratotic papules.

Prolonged Cutaneous Herpes Zoster in Acquired Immunodeficiency Syndrome

We described the development of prolonged disseminated cutaneous herpes zoster in two patients with acquired immunodeficiency syndrome. Both patients developed hyperkeratotic, verrucous lesions that progressed despite acyclovir therapy. The biopsy specimens were typical of herpes infection. The development of acyclovir-resistant varicella-zoster virus during therapy was suspected clinically in the first patient and documented in vitro in the second patient. The inability to mount an effective cell-mediated immune response contributed to the prolonged course of cutaneous zoster in our patients. The hyperkeratotic nature of the skin lesions may reflect their chronic nature. Treatment with inadequate doses of acyclovir, allowing viral persistence and the selection of resistant strains of virus, may also be implicated. We recommend prolonged high-dose intravenous acyclovir therapy in the initial management of herpes zoster in patients with acquired immunodeficiency syndrome.

Acyclovir-Resistant Varicella Zoster Virus Infection after Chronic Oral Acyclovir Therapy in Patients with the Acquired Immunodeficiency Syndrome (AIDS)

Four patients with human immunodeficiency virus (HIV) infection who received chronic oral acyclovir therapy for suppression of recurrent varicella zoster or herpes simplex virus infection developed persistent disseminated hyperkeratotic papules that failed to heal with intravenous or high-dose oral acyclovir therapy. Varicella zoster virus, resistant to acyclovir in vitro, was isolated from skin lesions of all four patients. Three patients were adults in whom the acquired immunodeficiency syndrome (AIDS) had been diagnosed 12 to 20 months before isolation of acyclovir-resistant varicella zoster virus. The fourth patient was a perinatally HIV-infected child who developed primary varicella infection at age 7 years when profoundly immunosuppressed (absolute CD4+ lymphocyte count less than 50 cells/microL). Mean antiviral susceptibilities (ED50 values) of the four clinical isolates compared with the ED50 values of the reference strain Oka were 85 compared with 3.3 mumol/L for acyclovir, 1.4 compared with 0.8 mumol/L for vidarabine, and 123 compared with 117 mumol/L for foscarnet. When assayed by [125I]-dC plaque autoradiography, 90% to 100% of the viral isolate populations had altered or no measurable thymidine kinase function. Acyclovir-resistant varicella zoster virus infection may complicate long-term oral acyclovir administration in patients with AIDS and may be associated with the appearance of atypical hyperkeratotic papules.

Molecular analysis of the pyrimidine deoxyribonucleoside kinase gene of wild-type and acyclovir-resistant strains of varicella-zoster virus.

The pyrimidine deoxyribonucleoside kinase (dPK) genes from five wild-type and four acyclovir-resistant varicella-zoster virus (VZV) strains were studied. One of the acyclovir-resistant strains was isolated from a patient receiving chronic acyclovir therapy. Acyclovir-resistant strains expressed the 1.8 kb VZV dPK transcript but lacked dPK activity. To determine the basis for the lack of enzyme activity the dPK gene from each strain was cloned and its DNA sequence determined. The VZV dPK gene was found to be highly conserved among strains, with greater than 99% nucleotide and amino acid homology. Each acyclovir-resistant VZV strain differed from its wild-type parent in only a single amino acid. The dPK genes from the acyclovir-resistant strains contained either point mutations near the putative thymidine-binding site of the enzyme or ones that resulted in the premature termination of protein synthesis. Single point mutations were sufficient to render these strains dPK-negative and highly resistant to acyclovir. The molecular basis for acyclovir resistance at the dPK locus of VZV is similar to that previously noted to render herpes simplex viruses resistant to acyclovir.