Analysis of the UL97 phosphotransferase coding sequence in clinical cytomegalovirus isolates and identification of mutations conferring ganciclovir resistance

Diagnosis of Human Cytomegalovirus Drug Resistance Mutations in Solid Organ Transplant Recipients-A Review

Human cytomegalovirus (HCMV) infection may be asymptomatic in healthy individuals but can cause severe complications in immunocompromised patients, including transplant recipients. Breakthrough and drug-resistant HCMV infections in such patients are major concerns. Clinicians are first challenged to accurately diagnose HCMV infection and then to identify the most effective antiviral drug and determine when to initiate therapy, alter drug dosage, or switch medication. This review critically examines HCMV diagnostics approaches, particularly for immunocompromised patients, and the development of genotypic techniques to rapidly diagnose drug resistance mutations. The current standard method to identify prevalent and well-known resistance mutations involves polymerase chain reaction amplification of UL97, UL54, and UL56 gene regions, followed by Sanger sequencing. This method can confirm clinical suspicion of drug resistance as well as determine the level of drug resistance and range of cross-resistance with other drugs. Despite the effectiveness of this approach, there remains an urgent need for more rapid and point-of-care HCMV diagnosis, allowing for timely lifesaving intervention.

Global estimate of phenotypic and genotypic ganciclovir resistance in cytomegalovirus infections among HIV and organ transplant patients; A systematic review and meta-analysis

Human cytomegalovirus (CMV), an opportunistic pathogen belonging to Herpesviridae family, is considered as one of the major causes of morbidity and mortality among wide variety of patients, particularly in transplant recipients and HIV positive patients. As this virus can be resistant to treatment, frequency of CMV in patients who receive organ transplantation and people suffering from AIDS was studied between 1980 and 2019. Medline (via PubMed), Embase, Web of Science, and the Iranian Database were reviewed, and Comprehensive Meta-Analysis (V2.0, Biostat) software analyzed all data. Finally, we used Cochran's Q-statistic to encounter heterogeneity between different studies. Meta-analyses indicated, GCV resistance was 14.1% (95% CI 11.2-17.7); however, in patients suffering from AIDS and organ transplantation were 19.5% (95% CI 14.7-25.4) and 11.4% (95% CI 8.1-15.8), respectively. There were increasing rates in the prevalence of GCV resistance in CMV among transplant recipients, and HIV positive patients. Therefore, evaluation of these refractory infections is beneficial.

Advances in the genotypic diagnosis of cytomegalovirus antiviral drug resistance

Cytomegalovirus (CMV) drug resistance mutation maps are updated with recent information for polymerase inhibitors, the terminase inhibitor letermovir and the UL97 kinase inhibitor maribavir. Newly mapped mutations and their phenotypes provide more detail on cross-resistance properties and suggest the need to expand the CMV gene regions covered in diagnostic testing. Next-generation deep sequencing technology offers a more sensitive, higher resolution view of emerging antiviral resistance and is recommended for use in clinical trials. Issues of standardization and diagnostic utility in comparison with traditional Sanger sequencing remain unresolved. Quality control is important for the accurate and reproducible detection of mutant viral populations in clinical specimens.

Clinical evaluation of Roche COBAS® AmpliPrep/COBAS® TaqMan® CMV test using nonplasma samples

Cytomegalovirus (CMV) infection is a leading cause of loss of hearing, vision, and mental retardation in congenitally infected children. It is also associated with complications of organ transplant and opportunistic HIV coinfection. The Roche COBAS^® AmpliPrep/COBAS^® TaqMan^® CMV test is an FDA-approved test that measures CMV DNA viral load in plasma for the diagnosis and management of patients at risk of CMV-associated diseases. Besides plasma, CMV is often found in bronchoalveolar lavage (BAL), cerebrospinal fluid (CSF), and urine. Thus, monitoring of CMV for critical care of patients in these nonplasma samples becomes necessary. The objective of this study was to conduct an analytic and clinical feasibility study of the Roche CMV test in BAL, CSF, and urine. The lower limit of detection, analytic measurement range, assay sensitivity, specificity, and precision were determined. Results of this study showed that the lower limit of detections were 50, 100, and 300 IU/mL for BAL, CSF, or urine, respectively. The analytic measurement ranges were from log₁₀ 2.48 to log₁₀ 5.48. The assay specificity was 94.4% for BAL and 100% for CSF and urine. The assay precision was all within the acceptable range. The performance of Roche test was further compared with 2 comparators including the RealTime CMV assay (Abbott Molecular) and a CMV Quantitative Polymerase Chain Reaction test (Vela Diagnostics). There was a general positive correlation between the Roche method and the Abbott or the Vela method. Overall, this study suggests that the Roche CMV test is suitable for the quantification of CMV viral load DNA in the described nonplasma samples.

HCMV UL97 phosphotransferase gene mutations may be associated with antiviral resistance in immunocompromised patients in Belém, PA, Northern Brazil

INTRODUCTION

Human cytomegalovirus is one of the causes of opportunist infections in immunocompromised patients, and is triggered by factors such as state of viral latency, weakened immune responses, and development of antiviral resistance to ganciclovir, the only drug offered by the public health system in Brazil to treat the infection. The goal of this study was to identify mutations that may be associated with antiviral resistance in immunocompromised patients.

METHODS

Molecular analysis was performed in 82 blood samples and subjected to genomic DNA extraction by a silica-based method. Three sequences of the HCMV UL97 gene, which encodes a phosphotransferase protein required for activation of ganciclovir, were amplified by polymerase chain reaction. Pyrosequencing methods were applied to one external 2096-bp segment DNA and two internal sequences between nucleotides 1087 to 1828 to detect mutations in this gene.

RESULTS

Approximately 10% of sequences contained mutations between nucleotides 377 and 594, in conserved regions of the UL97 gene, leading to amino acid changes. Eleven coding mutations were identified, including changes leading to amino acid substitutions, E596K and S604F, which were observed in 100% of samples and are described for the first time in Brazil. In addition, one mutation (A594V) that is associated with ganciclovir resistance was detected in a kidney transplant patient.

CONCLUSIONS

Further studies to detect mutations associated with HCMV resistance to antiviral drugs are required to demonstrate the need to increase the variety and availability of drugs used to treat viral infections in the public health care system in Brazil.

Differentiated Levels of Ganciclovir Resistance Conferred by Mutations at Codons 591 to 603 of the Cytomegalovirus UL97 Kinase Gene

Diagnostic mutations in the cytomegalovirus UL97 kinase gene are used to assess the level of associated ganciclovir resistance and therapeutic options. The best-known mutations at codons 460, 520, or 591 to 607 individually confer 5- to 10-fold-decreased ganciclovir susceptibility, except that a 3-fold decrease occurs in the case of the amino acid substitution C592G. Less common point and in-frame deletion mutations at codons 591 to 603 remain incompletely characterized. The ganciclovir susceptibilities of 17 mutants in this codon range were evaluated by use of the same recombinant phenotyping system and extensive assay replicates in two types of cell cultures. Amino acid substitutions K599E and T601M conferred no ganciclovir resistance, while A591V conferred 3.8-fold-decreased susceptibility. In-frame deletions of three or more codons conferred at least 8-fold-increased ganciclovir resistance, while the level of resistance conferred by one- or two-codon deletions varied from 4- to 10-fold, depending on their location. Measured levels of ganciclovir resistance were closely comparable when assays were performed in either fibroblasts or modified retinal epithelial cells. The significant revision of a few previously published resistance phenotypes and the new data strengthen the interpretation of genotypic testing for cytomegalovirus drug resistance.

Successful treatment with foscarnet for ganciclovir-resistant cytomegalovirus infection in a kidney transplant recipient: A case report

Cytomegalovirus (CMV) infection is the most common infectious complication following solid organ transplantation. Ganciclovir (GCV)-resistant CMV infection may be fatal, and is difficult to treat while avoiding allograft rejection. A 31-year-old woman received a second ABO-incompatible kidney transplant, from her father. Induction therapy consisted of basiliximab and rituximab followed by maintenance immunosuppression with tacrolimus, mycophenolate mofetil, and methylprednisolone. Her CMV serostatus was D(+) /R(-) at second transplant and she received prophylactic low-dose valganciclovir (VGCV). BK polyoma virus nephropathy (BKVN) developed 7 months after transplant concurrent with CMV hepatitis and retinitis. VGCV was increased to a therapeutic dose combined with reduced immunosuppression with minimal methylprednisolone (2 mg/day) and everolimus (0.5 mg/day). However, pp65 antigenaemia continued to increase for 6 weeks. Her CMV was defined as ganciclovir (GCV)-resistant. Foscarnet was therefore administered and her CMV disease resolved within 2 weeks. Kidney allograft dysfunction developed 9 months after transplant, and graft biopsy showed tubulointerstitial injury with crystal deposition suggesting foscarnet nephrotoxicity, with no findings of BKVN or rejection. Kidney function recovered after cessation of foscarnet and the patient had good graft function 18 months after transplant. This case demonstrates the successful use of foscarnet to treat GCV-resistant CMV infection after ABO-incompatible kidney transplant complicated with BKVN, without acute allograft rejection. This case further highlights the need to establish appropriate management for CMV D(+) /R(-) patients to avoid the acquisition of GCV-resistant gene mutations.

How I treat resistant cytomegalovirus infection in hematopoietic cell transplantation recipients

Cytomegalovirus (CMV) infection is a significant complication in hematopoietic cell transplantation (HCT) recipients. Four antiviral drugs are used for preventing or treating CMV: ganciclovir, valganciclovir, foscarnet, and cidofovir. With prolonged and repeated use of these drugs, CMV can become resistant to standard therapy, resulting in increased morbidity and mortality, especially in HCT recipients. Antiviral drug resistance should be suspected when CMV viremia (DNAemia or antigenemia) fails to improve or continue to increase after 2 weeks of appropriately dosed and delivered antiviral therapy. CMV resistance is diagnosed by detecting specific genetic mutations. UL97 mutations confer resistance to ganciclovir and valganciclovir, and a UL54 mutation confers multidrug resistance. Risk factors for resistance include prolonged or previous anti-CMV drug exposure or inadequate dosing, absorption, or bioavailability. Host risk factors include type of HCT and degree of immunosuppression. Depending on the genotyping results, multiple strategies can be adopted to treat resistant CMV infections, albeit no randomized clinical trials exist so far, after reducing immunosuppression (if possible): ganciclovir dose escalation, ganciclovir and foscarnet combination, and adjunct therapy such as CMV-specific cytotoxic T-lymphocyte infusions. Novel therapies such as maribavir, brincidofovir, and letermovir should be further studied for treatment of resistant CMV.

The D-form of a novel heparan binding peptide decreases cytomegalovirus infection in vivo and in vitro

Human cytomegalovirus (HCMV) infection in utero can lead to congenital sensory neural hearing loss and mental retardation. Reactivation or primary infection can increase the morbidity and mortality in immune suppressed transplant recipients and AIDS patients. The current standard of care for HCMV disease is nucleoside analogs, which can be nephrotoxic. In addition resistance to current treatments is becoming increasingly common. In an effort to develop novel CMV treatments, we tested the effectiveness of the D-form of a novel heparan sulfate binding peptide, p5R_D, at reducing infection of ganciclovir (GCV) resistant HCMVs in vitro and MCMV in vivo. HCMV infection was reduced by greater than 90% when cells were pretreated with p5R_D. Because p5R_D acts by a mechanism unrelated to those used by current antivirals, it was effective at reducing GCV resistant HCMVs by 85%. We show that p5R_D is resistant to common proteases and serum inactivation, which likely contributed to its ability to significantly reduced infection of peritoneal exudate cells and viral loads in the spleen and the lungs in vivo. The ability of p5R_D to reduce HCMV infectivity in vitro including GCV resistant HCMVs and MCMV infection in vivo suggests that this peptide could be a novel anti-CMV therapeutic.

Cidofovir, a New Agent with Potent Anti-Herpesvirus Activity

Cidofovir is a potent, broad spectrum antiviral agent with activity in vitro and in vivo against cytomegalovirus and other members of the herpesvirus family, as well as certain other DNA viruses. After uptake into cells it is converted enzymatically to cidofovir diphosphate, a structural analogue of deoxycytidine triphosphate, which selectively inhibits viral DNA polymerases relative to host cell polymerases. Cross-resistance to cidofovir is not usually seen with human cytomegalovirus isolates that are foscarnet-resistant, or isolates that are ganciclovir-resistant due to a deficiency in ganciclovir phosphorylation. Cross-resistance is seen, however, with isolates that are ganciclovir resistant due to polymerase mutations. A prolonged elimination phase seen in vivo, correlates with a long intracellular half-life seen in vitro and allows for efficacy in animal models of virus infection with infrequent dosing or prophylaxis. Clinical studies of intravenous cidofovir in cytomegalovirus retinitis in patients with AIDS are claimed to show delay of retinitis progression with maintenance doses given once every 2 weeks.

Detection of Two Drug-Resistance Mutants of the Cytomegalovirus by High-Resolution Melting Analysis

BACKGROUND

Human cytomegalovirus (CMV) is an opportunistic pathogen that can be treated with ganciclovir. Mutations in the UL97 gene of CMV render the virus ganciclovir resistance. These include H520Q and C603W mutations, against which we developed a novel genotyping assay for their identification.

METHODS

PCR reactions were performed to amplify fragments of the UL97 gene containing H520Q or C603W mutations. High resolution melting analysis (HRMA) coupled with unlabeled DNA probes was employed to identify the shift in melting temperature of the probe-template complex, which reflexes the presence of point mutations.

RESULTS

Melting point analysis performed on the dimeric DNA of PCR products of UL97 gene could not identify mutations in the gene. When coupled to unlabeled probes, point mutations in UL97 can be identified by analyzing the melting curve of probe-template complex. When WT and mutant UL97 DNAs were mixed together to mimic heterogeneous viral population in clinical samples, the genotyping assay is sensitive enough to detect H520Q and C603W mutants that constitute 10% of total DNA input.

CONCLUSION

Probe-based HRMA is effective in detecting H520Q and C603W mutations in the UL97 gene of CMV.

Antiviral Drug- and Multidrug Resistance in Cytomegalovirus Infected SCT Patients

In pediatric and adult patients after stem cell transplantation (SCT) disseminated infections caused by human cytomegalovirus (HCMV) can cause life threatening diseases. For treatment, the three antivirals ganciclovir (GCV), foscarnet (PFA) and cidofovir (CDV) are approved and most frequently used. Resistance to all of these antiviral drugs may induce a severe problem in this patient cohort. Responsible for resistance phenomena are mutations in the HCMV phosphotransferase-gene (UL97) and the polymerase-gene (UL54). Most frequently mutations in the UL97-gene are associated with resistance to GCV. Resistance against all three drugs is associated to mutations in the UL54-gene. Monitoring of drug resistance by genotyping is mostly done by PCR-based Sanger sequencing. For phenotyping with cell culture the isolation of HCMV is a prerequisite. The development of multidrug resistance with mutation in both genes is rare, but it is often associated with a fatal outcome. The manifestation of multidrug resistance is mostly associated with combined UL97/UL54-mutations. Normally, mutations in the UL97 gene occur initially followed by UL54 mutation after therapy switch. The appearance of UL54-mutation alone without any detection of UL97-mutation is rare. Interestingly, in a number of patients the UL97 mutation could be detected in specific compartments exclusively and not in blood.

Resolution of Mild Ganciclovir-Resistant Cytomegalovirus Disease with Reduced-Dose Cidofovir and CMV-Hyperimmune Globulin

Ganciclovir-resistant cytomegalovirus (CMV) is associated with significant morbidity in solid organ transplant recipients. Management of ganciclovir-resistant CMV may be complicated by nephrotoxicity which is commonly observed with recommended therapies and/or rejection induced by “indirect” viral effects or reduction of immunosuppression. Herein, we report a series of four high serologic risk (donor CMV positive/recipient CMV negative) kidney transplant patients diagnosed with ganciclovir-resistant CMV disease. All patients initially developed “breakthrough” viremia while still receiving valganciclovir prophylaxis after transplant and were later confirmed to exhibit UL97 mutations after failing to eradicate virus on adequate dosages of valganciclovir. The patients were subsequently and successfully treated with reduced-dose (1-2 mg/kg) cidofovir and CMV-hyperimmune globulin, given in 2-week intervals. In addition, all patients exhibited stable renal function after completion of therapy, and none experienced acute rejection. The combination of reduced-dose cidofovir and CMV-hyperimmune globulin appeared to be a safe and effective regimen in patients with mild disease due to ganciclovir-resistant CMV.

Differential properties of cytomegalovirus pUL97 kinase isoforms affect viral replication and maribavir susceptibility

The human cytomegalovirus (HCMV)-encoded kinase pUL97 is required for efficient viral replication. Previous studies described two isoforms of pUL97, the full-length isoform (M1) and a smaller isoform likely resulting from translation initiation at codon 74 (M74). Here, we report the detection of a third pUL97 isoform during viral infection resulting from translation initiation at codon 157 (isoform M157). The consistent expression of isoform M157 as a minor component of pUL97 during infection with clinical and laboratory-adapted HCMV strains was suppressed when codon 157 was mutagenized. Viral mutants expressing specific isoforms were generated to compare their growth and drug susceptibility phenotypes, as well as pUL97 intracellular localization patterns and kinase activities. The exclusive expression of isoform M157 resulted in substantially reduced viral growth and resistance to the pUL97 inhibitor maribavir while retaining susceptibility to ganciclovir. Confocal imaging demonstrated reduced nuclear import of amino-terminal deletion isoforms compared to isoform M1. Isoform M157 showed reduced efficiency of various substrate protein interactions and autophosphorylation, whereas Rb phosphorylation was preserved. These results reveal differential properties of pUL97 isoforms that affect viral replication, with implications for the antiviral efficacy of maribavir.

IMPORTANCE

The HCMV UL97 kinase performs important functions in viral replication that are targeted by the antiviral drug maribavir. Here, we describe a naturally occurring short isoform of the kinase that when expressed by itself in a recombinant virus results in altered intracellular localization, impaired growth, and high-level resistance to maribavir compared to those of the predominant full-length counterpart. This is another factor to consider in explaining why maribavir appears to have variable antiviral activity in cell culture and in vivo.

Laboratory diagnosis of viral infection

Since the last Handbook of Clinical Neurology volume on this topic, viral diagnosis has made tremendous strides, moving from the margin to the mainstream of clinical care. For many years, conventional virus isolation was the mainstay of viral diagnosis since it was sensitive and “open-minded.” However, growth in conventional cell culture entails an inherent delay that limits its clinical impact. Although rapid culture and viral antigen methods detect fewer pathogens and are less sensitive than conventional culture, both require less expertise and have greatly reduced time to result. Polymerase chain reaction has ushered in a new era in virology, especially in the diagnosis of neurologic diseases. Molecular amplification methods are rapid, highly sensitive, can be automated, quantitative, and detect viruses not amenable to routine culture. User-friendly, walk-away tests with results in an hour, as well as multiplex tests that can detect 20 viruses in a single reaction, are now a reality. As the variety of test methods and commercial products proliferate, the challenges for clinicians and laboratories are selecting which tests to utilize in which clinical scenarios, and understanding how to interpret the results. The advantages and limitations of each method are discussed in this chapter, with special attention to neurologic disease.

Successful ganciclovir treatment of primary cytomegalovirus infection containing the UL97 mutation N510S in an intestinal graft recipient

In solid organ transplantation, human cytomegalovirus (HCMV) is considered to be the most important viral pathogen. We report a case of a CMV R-/D+ small intestine transplant recipient with a primary CMV infection on valganciclovir prophylaxis. Sequencing of the HCMV DNA for drug resistance-associated mutations revealed the UL97 mutation N510S. This mutation has been initially reported to confer ganciclovir resistance. Based on in vitro recombinant phenotyping, this assumption has recently been questioned. Switching the antiviral treatment to an intravenous regimen of ganciclovir eliminated HCMV DNAemia, showing the in vivo efficacy of ganciclovir for the UL97 mutation N510S. Hence, knowledge of drug efficacy is crucial for an adequate choice of antiviral medication, carefully balancing antiviral potency versus the risk of harmful side effects.

The genetic basis of human cytomegalovirus resistance and current trends in antiviral resistance analysis

Infections due to resistant human cytomegalovirus (CMV) are an emerging problem, particularly in immunocompromised hosts. When managing such patients, clinicians should be aware of the possibility of developing CMV antiviral resistance, especially while on prolonged therapy or if severe immunosuppression is present. CMV resistance to current antiviral agents is mediated by alterations in either the UL97 kinase or DNA polymerase, encoded by the UL97 and UL54 genes, respectively. UL97 mutations are capable of conferring resistance to ganciclovir, while UL54 mutations can impart resistance to ganciclovir, cidofovir, and foscarnet. If treatment failure is suspected to be due to antiviral resistance, CMV resistance analysis should be obtained. Phenotypic resistance assays performed on clinical isolates measure antiviral susceptibilities directly, but are laborious and time-consuming. Therefore, genotypic resistance analysis has become the more common means of diagnosing CMV resistance. Mutations in UL97 or UL54 may be clinically associated with resistance, but their effect on antiviral susceptibility must be confirmed by marker transfer techniques such as recombinant phenotyping.

Recurrent and persistent cytomegalovirus infection in a kidney recipient caused by the L595S mutation in UL97 phosphotransferase gene

Ganciclovir (GCV) is the first therapeutic choice for prevention and treatment of active cytomegalovirus (CMV) infection in solid organ transplant recipients in Bahia state, Brazil. Prolonged and repeated GCV therapy may result in drug-resistant virus, associated with progressive and disseminated disease. We present a case report of a young male kidney recipient, who was CMV-seronegative with a CMV-seropositive donor (D(+)/R(-)), and who developed clinical GCV resistance, confirmed by mutation in viral UL97 phosphotransferase responsible for GCV activation. Under prophylactic therapy with intravenous GCV for 6 weeks post-transplantation, he developed severe anaemia and hepatic enzyme increases, probably due to drug side effects. At this moment, the drug was discontinued and he started to be monitored by pp65 antigen test. At week 10 post-transplantation, he presented fever, myalgia, thrombocytopenia and neutropaenia, with a positive CMV antigen test. During treatment with intravenous GCV, antigenaemia assay demonstrated a higher number of positive cells, requiring GCV at higher doses. Pre-emptive therapy lasted for 31 days and he started the maintenance therapy with oral GCV. However, antigenaemia assay demonstrated an extremely high number of positive cells, and he was rehospitalized and prescribed intravenous GCV. Severe leukopaenia led to GCV interruption, but immunosuppressive dose reduction helped to control the active CMV infection. GCV-resistant CMV infection resulted in increased morbidity, rehospitalization episodes and increased costs; therefore, implementation of resistance diagnostic tests in the transplantation routine is of great importance. We documented the first case of GCV-resistant CMV infection due to the L595S mutation in UL97 phosphotransferase gene in a kidney recipient from Bahia state, Brazil.

Genotyping cytomegalovirus UL97 mutations by high-resolution melting analysis with unlabeled probe

Human cytomegalovirus (CMV) is an opportunistic pathogen, and infections with this virus can be treated with ganciclovir (GCV). Most GCV-resistant clinical CMV isolates contain a mutation in the UL97 gene. Genotypic assays for diagnostic screening of GCV-resistant CMV have been developed. High-resolution melting analysis (HRMA) with unlabeled probe is considered a perfect tool for this purpose. In this study, we have developed an HRMA-based genotypic test for the detection of UL97 mutations. Wild type and M460V/I mutants of UL97 were constructed. HRMA with unlabeled probe was used as a genotyping method for the detection of M460V/I mutations. The melting peaks obtained directly from PCR products did not enable us to distinguish the wild type from M460 mutants. The sensitivity and accuracy of HRMA were dramatically improved by using unlabeled probe. HRMA with unlabeled probe successfully distinguished M460V from M460I and served well for the detection of M460V/I mutations in clinical samples. HRMA with unlabeled probe proves to be a sensitive and cost-effective genotyping method for the detection of M460 mutations.

Genotypic characterization of human cytomegalovirus UL97 phosphotransferase natural polymorphism in the era of ganciclovir and maribavir

The molecular mechanisms of human cytomegalovirus (CMV) resistance to both ganciclovir and maribavir reported so far rely predominantly on the presence of mutations within UL97 phosphotransferase. The accurate interpretation of genotypic antiviral resistance assay results requires the clear distinction between resistance mutations and natural interstrain sequence variations. The objective of this work was to extend the catalog of CMV UL97 phosphotransferase natural polymorphisms. The full-length UL97 gene sequence analysis from 4 laboratory strains and 35 clinical samples from patients who had not received any previous anti-CMV treatment was performed. At the nucleotide level, the interstrain identity was >98%. At the amino acid level, ten natural polymorphisms never previously described were identified. Together with all previous results reported in the literature, a new map of UL97 phosphotransferase natural polymorphism could be settled in the era of ganciclovir and maribavir.

Does Cytomegalovirus Develop Resistance following Antiviral Prophylaxis and Treatment in Renal Transplant Patients in Kuwait?

The resistance of cytomegalovirus (CMV) to ganciclovir or valganciclovir is a factor in therapeutic failure and disease progression. CMV strains resistant to ganciclovir or valganciclovir have been associated with specific mutations in the UL97 and UL54 genes. Sequencing of both CMV UL97 and UL54 genes was performed to detect the presence of CMV antiviral resistance in six patients who received ganciclovir (and/or valganciclovir) and had prolonged detectable CMV DNA in their blood during antiviral treatment. Sequencing results showed no specific mutations in either UL97 or UL54 gene of CMV and therefore the CMV strains in kidney transplant patients who received ganciclovir either prophylactically or therapeutically were from the wild type. Our results suggest that CMV management and immunosuppression protocols for kidney transplant patients followed in the Organ Transplant Centre, Kuwait, is very effective in reducing the opportunity of developing CMV antiviral resistance.

The role of cytomegalovirus infection and disease in pediatric bone marrow transplant recipients in Mexico City in the context of viral drug resistance

We aimed to identify those pediatric patients undergoing ABMT with CMV EOD who developed GCV resistance. Forty-seven patients were analyzed following ABMT. Prospective post-transplant CMV monitoring was performed weekly for the detection of viral leukocyte DNAaemia, viral plasma DNAaemia, and viral DNAuria by PCR. Plasma DNAaemia was confirmed from whole blood by the detection of CMV pp67 late mRNA using NASBA technology. In the cases of persistence of viral DNA in plasma, and positive viral RNA detection in blood, CMV drug resistance screening by comprehensive PCR-based RFLP and sequencing of the viral UL97 gene were performed retrospectively. Thirty of the 47 (63.82%) patients showed active CMV infection with 27/30 (74.4%) patients belonging to the D+R+ group and 25/30 with proven viral replication. In total, 2/30 (6.6%) children developed CMV pneumonia proven by immunohistochemistry. Screening of the viral UL97 gene revealed in one of these two cases (1/30, 3.3%) the simultaneous presence of two point mutations in codon 460 (M460V, M460I) conferring GCV resistance. The CMV seroprevalence (81%) and the incidence of active infection (63.8%) in Mexican children undergoing ABMT are very high.

Antiviral drug resistance of human cytomegalovirus

The study of human cytomegalovirus (HCMV) antiviral drug resistance has enhanced knowledge of the virological targets and the mechanisms of antiviral activity. The currently approved drugs, ganciclovir (GCV), foscarnet (FOS), and cidofovir (CDV), target the viral DNA polymerase. GCV anabolism also requires phosphorylation by the virus-encoded UL97 kinase. GCV resistance mutations have been identified in both genes, while FOS and CDV mutations occur only in the DNA polymerase gene. Confirmation of resistance mutations requires phenotypic analysis; however, phenotypic assays are too time-consuming for diagnostic purposes. Genotypic assays based on sequencing provide more rapid results but are dependent on prior validation by phenotypic methods. Reports from many laboratories have produced an evolving list of confirmed resistance mutations, although differences in interpretation have led to some confusion. Recombinant phenotyping methods performed in a few research laboratories have resolved some of the conflicting results. Treatment options for drug-resistant HCMV infections are complex and have not been subjected to controlled clinical trials, although consensus guidelines have been proposed. This review summarizes the virological and clinical data pertaining to HCMV antiviral drug resistance.

The effects of maribavir on the autophosphorylation of ganciclovir resistant mutants of the cytomegalovirus UL97 protein

Background

The UL97 protein kinase of human cytomegalovirus phosphorylates the antiviral drug ganciclovir and is the target of maribavir action. A detailed enzyme kinetic analysis of maribavir on the various enzymatic functions of wild type and ganciclovir resistant forms of UL97 is required.

Methods

Wild type and site directed mutant forms of the human cytomegalovirus UL97 gene product were expressed using recombinant baculoviruses and the purified products used to assess the effects of maribavir on the ganciclovir (GCV) kinase and protein kinase (PK) activities.

Results

Maribavir was a potent inhibitor of the autophosporylation of the wild type and all the major GCV resistant UL97 mutants analysed (M460I, H520Q, A594V and L595F) with a mean IC₅₀ of 35 nM. The M460I mutation resulted in hypersensitivity to maribavir with an IC₅₀ of 4.8 nM. A maribavir resistant mutant of UL97 (L397R) was functionally compromised as both a GCV kinase and a protein kinase (~ 10% of wild type levels). Enzyme kinetic experiments demonstrated that maribavir was a competitive inhibitor of ATP with a Ki of 10 nM.

Discussion

Maribavir is a potent competitive inhibitor of the UL97 protein kinase function and shows increased activity against the M460I GCV-resistant mutant which may impact on the management of GCV drug resistance in patients.

Recombinant phenotyping of cytomegalovirus UL97 kinase sequence variants for ganciclovir resistance

A strain of human cytomegalovirus, T2211, modified from standard laboratory strain AD169 to contain a secreted alkaline phosphatase reporter gene for rapid viral quantitation, was cloned as a bacterial artificial chromosome, BA1, and then mutagenized to create recombinant viruses containing viral UL97 kinase sequence variants found in clinical specimens after ganciclovir treatment, but with no phenotypic data to determine their role in drug resistance. Seven control strains and 14 other recombinant strains were phenotyped for ganciclovir resistance and compared with similar strains created using prior technology to show a good concordance of findings. Sequence changes V466M, H469Y, A478V, N510S, A588V, K599R, L600I, G623S, T659I, and V665I were found to confer no significant ganciclovir resistance, while mutations L405P, M460T, A594E, and C603R conferred 3- to 9-fold increases in ganciclovir 50% inhibitory concentrations. Different mutations at codons 594 (A594V, A594E) and 603 (C603W, C603S) conferred varied amounts of ganciclovir resistance. Advances in recombinant phenotyping make it easier to show that many uncharacterized UL97 sequence variants do not confer ganciclovir resistance, but some are newly confirmed as resistance associated, including one (L405P) which is outside the codon range where such mutations are usually found. This information should improve the interpretation of genotypic data generated by diagnostic laboratories.

Testing the susceptibility of human herpesviruses to antivirals

Herpesviruses cause chronic lifelong infections in humans and may cause life-threatening diseases in immunosuppressed patients. Antiviral drugs targeted to viral DNA polymerase, such as acyclovir, penciclovir, ganciclovir, foscarnet and cidofovir, are currently available and have been proven to be efficient against clinical symptoms of herpesvirus infections. The resistance of herpesviruses to these drugs is associated with specific mutations of viral genes encoding either DNA polymerase or enzymes phosphorylating nucleoside analogs. Resistance is detected and characterized by means of specific susceptibility assays, which can be classified as phenotypic, genetic and functional. These tests are used both to investigate novel antiviral compounds and look for the emergence of resistant viruses in treated patients in case of clinical failure. Although susceptibility assays are often time consuming and present some limitations regarding the interpretation of their results, their use in the monitoring of antiherpetic treatments should be promoted and improved, in parallel to the development of novel efficient drugs.

Cytomegalovirus encephalitis/retinitis in allogeneic haematopoietic stem cell transplant recipient treated successfully with combination of cidofovir and foscarnet

We report an 18-yr-old female patient with repeated CMV reactivations after HSCT treated by several pre-emptive courses of virostatic therapy. Seven months after HSCT, she developed CMV encephalitis/retinitis. Initial therapy with GCV and hyperimmune globulin failed, and later on GCV-resistant strain was detected. Continual increase of CMV DNA in peripheral blood led us to combined therapy with CDV and FCV, which was successful and free of severe renal toxicity. To our best knowledge, this is the first reported case of successful CMV treatment with a combination of CDV and FCV.

Single and multiple mutations in the human cytomegalovirus UL97 gene and their relationship to the enzymatic activity of UL97 kinase for ganciclovir phosphorylation

In this study we determined that the double mutant M460V/D605E in the UL97 gene of an HCMV isolate from an immunocompromised patient (MMT isolate) is related to resistance to ganciclovir (GCV) therapy. Our results suggest that the aspartic acid-to-glutamic acid substitution at codon 605 may be associated with a natural polymorphism of the UL97 gene, and not with positive selection pressure exerted by the antiviral drug. We also determined that GCV resistance due to the M460V mutation in the HCMV UL97 gene is not offset by a second mutation (D605E) at codon 605. Furthermore, we showed that when the two mutations related to GCV resistance were simultaneously detected in the same HCMV construct, virus-drug resistance might be enhanced in comparison to that of the single mutants studied separately. To our knowledge for the first time, seven of 12 amino acid changes (F102L, D118V, M330T, T400A, R507P and C511R and I533V) in the UL97 gene of an isolate are herein reported.

Antiviral treatment of cytomegalovirus infection and resistant strains

This review discusses the management of resistant cytomegalovirus and prevention strategies for fatal therapy failures. Five drugs, ganciclovir/valganciclovir, cidofovir, foscarnet and fomivirsen, have been approved so far for the treatment of human cytomegalovirus (HCMV) diseases. Except for fomivirsen, all of the approved drugs share the same target molecule, the viral DNA polymerase. The emergence of drug-resistant HCMV has also been reported for all of them. For optimal care of patients, the clinical virologist has to provide the most meaningful assays for monitoring of therapy and early detection of emerging drug-resistant HCMV. Additionally, a quantitative drug monitoring would be helpful. New antiviral agents are urgently needed with less adverse effects, good oral bioavailability and possibly novel targets or mechanisms of action to avoid cross-resistance and to improve the ability to suppress the selection of resistant virus strains by combination therapy. Compounds like maribavir, leflunomide and artesunate, which exhibit anti-HCMV activity in vitro and in patients need to be evaluated in clinical studies. Besides these, new therapy approaches like immunotherapy or new diagnostic techniques like pyrosequencing have to be considered in the future.

HHV-6 DNA throughout the tissues of two stem cell transplant patients with chromosomally integrated HHV-6 and fatal CMV pneumonitis

Two patients with the characteristic high human herpesvirus 6 (HHV-6) DNA loads in peripheral blood caused by chromosomally integrated (CI) virus received a haematopoietic stem cell transplant (HSCT) from a donor without CI HHV-6. Both patients died in consequence of cytomegalovirus (CMV) pneumonitis. At autopsy, high amounts of CMV DNA were detected in lungs but at much lower levels in other organs. In contrast HHV-6 DNA was detected at high levels throughout the organs with the exception of donor-derived haematopoietic tissue. In individuals with chromosomal integration, HHV-6 DNA is found in every tissue of recipient origin indicating inheritance through the germ line.

Valganciclovir as pre-emptive therapy for cytomegalovirus infection post-allogenic stem cell transplantation: implications for the emergence of drug-resistant cytomegalovirus

OBJECTIVES

Valganciclovir is a well established drug for the management of cytomegalovirus (CMV) infection in haematopoietic stem cell transplantation (HSCT). Data concerning its safety regarding the development of drug resistance are required. The aim of the present study was to retrospectively investigate CMV drug resistance in a group of HSCT patients experiencing relapses of CMV infection after a first-line pre-emptive antiviral therapy.

METHODS

Thirteen adult HSCT patients out of 26 with asymptomatic CMV infection, experiencing relapsing infections 45-155 days after either intravenous (iv) ganciclovir (2 patients) or valganciclovir (11 patients), were studied. Genotypic assays for mutations in the viral phosphotransferase (UL97) and DNA-polymerase (UL54) genes were directly applied on patient specimens. Baseline CMV sequences were compared with those at the time of relapses to identify drug-resistant strains.

RESULTS

UL97 mutations A594V and M460V known to confer drug resistance developed in one relapsing patient who received iv ganciclovir as first-line therapy, corresponding to a rate of 7.7% of relapses due to drug-resistant strains and an overall 3.8% rate of infections due to CMV drug-resistant strains. UL54 drug resistance mutations were absent. No evidence of drug resistance was found in patients on valganciclovir either as first-line therapy or as treatment for relapses.

CONCLUSIONS

The safety profile of valganciclovir as anti-CMV pre-emptive therapy was confirmed, as well as that monitoring CMV drug resistance with genotypic tests on sequential isolates over the time-course of therapy offers guidance to tailor antiviral treatment in a clinically relevant time frame.

Case report: persistent cytomegalovirus (CMV) infection after haploidentical hematopoietic stem cell transplantation using in vivo alemtuzumab: emergence of resistant CMV due to mutations in the UL97 and UL54 genes

Addition of in vivo alemtuzumab to the conditioning regimen enabled 2- or 3-locus-mismatched hematopoietic stem cell transplantation with an acceptable incidence of graft-versus-host-disease. However, the procedure was associated with a high incidence of cytomegalovirus (CMV) reactivation. Although preemptive therapy with ganciclovir prevented successfully severe CMV diseases and CMV-related mortality, a patient developed persistent positive CMV antigenemia for more than 1 year after transplantation and CMV disease, despite the use of ganciclovir and foscarnet. The in vitro susceptibility assay showed that the clinical isolate was resistant to foscarnet, moderately resistant to ganciclovir, but sensitive to cidofovir. Therefore, cidofovir was administered. CMV antigenemia became negative within 2 weeks and never developed again. Nucleotide sequence of the UL54 and UL97 of the clinical isolate showed 4 amino acid substitutions (V11L, Q578H, S655L, and G874R) in UL54 and 2 mutations (A140V and A594V) in UL97 compared with the Towne and AD169 strains. Ganciclovir resistance was suspected to be caused by both A594V of UL97 and Q578H of UL54, whereas foscarnet resistance was due mainly to Q578H of UL54. In conclusion, the in vitro susceptibility assay as well as nucleotide sequence of clinical isolate is important to choose appropriate antiviral agents for patients who have persistent CMV reactivation after stem cell transplantation.

Cytomegalovirus UL97 mutations in the era of ganciclovir and maribavir

Mutations in the human CMV UL97 kinase gene are a major mechanism of viral resistance to two anti-CMV drugs, ganciclovir (GCV) and maribavir (MBV). GCV, the most widely used and established therapy for CMV, is a substrate for the UL97 kinase. Well-characterised GCV-resistance mutations at UL97 codons 460, 520 and 590-607 impair the phosphorylation of GCV that is necessary for its antiviral activity, presumably by altering substrate recognition. In contrast, MBV is an inhibitor of the UL97 kinase and is the first new CMV therapy to reach later stage clinical trials in many years. No MBV-resistant CMV isolates have yet been detected in clinical trials, but after culture propagation under drug, UL97 mutations that confer moderate to high-level MBV resistance have been identified at codons 353, 397, 409 and 411. These mutations are located upstream of the GCV-resistance mutations and are close to the ATP-binding and catalytic domains common to all kinases, consistent with MBV acting as a small molecule ATP-competitive kinase inhibitor. So far, no UL97 mutations are known to confer resistance to both GCV and MBV.

Rapid Semiquantitative Real-Time PCR for the Detection of Human Cytomegalovirus UL97 Mutations Conferring Ganciclovir Resistance

Background

The development of infections with ganci-clovir (GCV)-resistant human cytomegalovirus (HCMV) remains a serious problem in recipients of stem cell or organ transplants. Nearly all GCV-resistant clinical isolates have mutations in the viral UL97 gene. The rapid detection of GCV-resistant HCMV infections is necessary and the relative proportions of wild-type and mutant strains are predictive for the efficiency of antiviral therapy. To date, genotypical resistance screening has been limited to restriction fragment length polymorphism (RFLP) and sequencing analyses. Here, we present a comprehensive real-time PCR approach for the detection of most frequent mutations in the UL97 gene associated with GCV resistance.

Methods

The laboratory strains AD169 and Towne, different wild-type isolates and plasmids constructed by site-directed mutagenesis and overlap extension with specific point-mutations in the UL97 gene were analysed by LightCycler PCR and compared with UL97 RFLP and sequencing analyses.

Results

A new and comprehensive set of LightCycler PCRs was created using specific hybridization probes with melting-point analysis for the relevant codons 594, 595, 603 and 607. Different wild-type isolates and plasmids containing specific UL97 mutations conferring GCV resistance were investigated in the real-time PCR assay. Total processing time was 80 min per assay, whereas combinations of RFLP and sequencing needed at least 3–4 days. Proportions of co-existing wild-type and mutant strains in mixed viral populations can be obtained.

Conclusions

We established a rapid real-time PCR approach for the detection of most frequent HCMV UL97 mutations associated with GCV resistance. Moreover, the method allows semiquantitative differentiation of the proportions of co-existing wild-type and mutant strains. This approach represents a new alternative for laborious RFLP analysis.

Maribavir prophylaxis for prevention of cytomegalovirus infection in allogeneic stem cell transplant recipients: a multicenter, randomized, double-blind, placebo-controlled, dose-ranging study

The anti-cytomegalovirus (CMV) activity and safety of oral maribavir in CMV-seropositive allogeneic stem-cell transplant recipients were evaluated in a randomized, double-blind, placebo-controlled, dose-ranging study. After engraftment, 111 patients were randomized to receive CMV prophylaxis with maribavir (100 mg twice daily, 400 mg once daily, or 400 mg twice daily) or placebo. Within the first 100 days after transplantation, the incidence of CMV infection based on CMV pp65 antigenemia was lower in each of the respective maribavir groups (15%, P = .046; 19%, P = .116; 15%, P = .053) compared with placebo (39%). Similarly, the incidence of CMV infection based on plasma CMV DNA was lower in each of the respective maribavir groups (7%, P = .001; 11%, P = .007; 19%, P = .038) compared with placebo (46%). Anti-CMV therapy was also used less often in patients receiving each respective dose of maribavir (15%, P = .001; 30%, P = .051; 15%, P = .002) compared with placebo (57%). There were 3 cases of CMV disease in placebo patients but none in the maribavir patients. Adverse events, mostly taste disturbance, nausea, and vomiting, were more frequent with maribavir. Maribavir had no adverse effect on neutrophil or platelet counts. These results show that maribavir can reduce the incidence of CMV infection and, unlike ganciclovir, does not cause myelosuppression.

Development of SYBR Green I-based real-time PCR assay for detection of drug resistance mutations in cytomegalovirus

Ganciclovir (GCV) is an antiviral drug that is used to treat cytomegalovirus (CMV) infection. However, long-term monotherapy does not commonly result in complete suppression of viral replication and is associated with the emergence of resistant mutants. In this study, a method for detecting CMV resistance mutations was carried out by real-time amplification refractory mutation system PCR (real-time ARMS PCR) using SYBR Green I fluorescent dye. Three recombinant plasmids were constructed by overlapping extension PCR to be used as standard mutation or wild-type models. Four pairs of primers were used to amplify the approximately 150 bp of the UL97 gene spanning codon 460, where mutations associated with resistance to GCV invariably occur. As little as 20% mutants DNA in 10(7)copies/ml mixture DNA were detected. Though this approach was not more sensitive than PCR-restriction fragment length polymorphism (RFLP) for the detection of the presence of mixtures, it was a high-throughput and automation method, and the specific mutation type can be deduced by the real-time ARMS PCR data. Overall, this study has demonstrated an approach that could be a sensitive and rapid method for the detection of GCV resistance-associated mutation in CMV.

Resistance to combined ganciclovir and foscarnet therapy in a liver transplant recipient with possible dual-strain cytomegalovirus coinfection

We present a case report of a cytomegalovirus (CMV)-seronegative, 58-year-old male who received a CMV-seropositive donor liver transplant without CMV prophylaxis. On postoperative day 30, the patient developed primary CMV disease that responded to ganciclovir. On postoperative day 114, however, he was diagnosed with recurrent CMV infection. Despite aggressive, combined antiviral treatment with ganciclovir and foscarnet and reduction of immunosuppression, viral clearance was never achieved. Serum samples were collected throughout the infectious process for viral DNA analysis. Portions of the UL97 and UL54 genes were amplified and compared to the AD169 wild-type strain. Sequencing studies revealed the presence of mutations in viral isolates obtained after clinical resistance was observed. These mutations were not present in samples obtained during the primary CMV infection. Our findings suggest the presence of coinfection with at least 2 different strains of CMV rather than induction of mutations after ganciclovir therapy.

The use of sirolimus in ganciclovir-resistant cytomegalovirus infections in renal transplant recipients

BACKGROUND

The widespread use of prophylactic ganciclovir and anti-lymphocyte/thymocyte therapies are associated with increased induction of ganciclovir-resistant cytomegalovirus (CMV) strains. The use of sirolimus has been associated with a lower incidence of CMV infection in transplant recipients. We questioned whether it could also be effective as a therapeutic treatment of resistant CMV infection.

METHODS

Patients with ganciclovir-resistant CMV infections determined clinically and by DNA sequencing analysis were enrolled. Antigenaemia and DNA sequencing were used to diagnosis and follow the mutations.

RESULTS

Nine transplant patients were given sirolimus plus mycophenolate mofetil (n = 4) or a calcineurin inhibitor (n = 5). Seven out of nine recipients were CMV IgG negative before transplantation. We observed a rapid decrease in antigenaemia levels, reaching zero in eight out of nine (88.9%) patients within a median of 20.3 +/- 10.1 d. Graft function remained stable and no patient presented acute rejection or recurrence of the CMV infection.

CONCLUSIONS

This suggests that the use of sirolimus plus ganciclovir therapy could be useful in ganciclovir-resistant CMV infections.

The interplay between host and viral factors in shaping the outcome of cytomegalovirus infection

Cytomegalovirus (CMV) remains a major human pathogen causing significant morbidity and mortality in immunosuppressed or immunoimmature individuals. Although significant advances have been made in dissecting out certain features of the host response to human CMV (HCMV) infection, the strict species specificity of CMVs means that most aspects of antiviral immunity are best assessed in animal models. The mouse model of murine CMV (MCMV) infection is an important tool for analysis of in vivo features of host-virus interactions and responses to antiviral drugs that are difficult to assess in humans. Important studies of the contribution of host resistance genes to infection outcome, interplays between innate and adaptive host immune responses, the contribution of virus immune evasion genes and genetic variation in these genes to the establishment of persistence and in vivo studies of resistance to antiviral drugs have benefited from the well-developed MCMV model. In this review, we discuss recent advances in the immunobiology of host-CMV interactions that provide intriguing insights into the complex interplay between host and virus that ultimately facilitates viral persistence. We also discuss recent studies of genetic responses to antiviral therapy, particularly changes in DNA polymerase and protein kinase genes of MCMV and HCMV.