A simplified assay for screening of drug resistance of cell-associated cytomegalovirus strains

Peptide Derivatives of Platelet-Derived Growth Factor Receptor Alpha Inhibit Cell-Associated Spread of Human Cytomegalovirus

Cell-free human cytomegalovirus (HCMV) can be inhibited by a soluble form of the cellular HCMV-receptor PDGFRα, resembling neutralization by antibodies. The cell-associated growth of recent HCMV isolates, however, is resistant against antibodies. We investigated whether PDGFRα-derivatives can inhibit this transmission mode. A protein containing the extracellular PDGFRα-domain and 40-mer peptides derived therefrom were tested regarding the inhibition of the cell-associated HCMV strain Merlin-pAL1502, hits were validated with recent isolates, and the most effective peptide was modified to increase its potency. The modified peptide was further analyzed regarding its mode of action on the virion level. While full-length PDGFRα failed to inhibit HCMV isolates, three peptides significantly reduced virus growth. A 30-mer version of the lead peptide (GD30) proved even more effective against the cell-free virus, and this effect was HCMV-specific and depended on the viral glycoprotein O. In cell-associated spread, GD30 reduced both the number of transferred particles and their penetration. This effect was reversible after peptide removal, which allowed the synchronized analysis of particle transfer, showing that two virions per hour were transferred to neighboring cells and one virion was sufficient for infection. In conclusion, PDGFRα-derived peptides are novel inhibitors of the cell-associated spread of HCMV and facilitate the investigation of this transmission mode.

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.

Assessment of the Human Cytomegalovirus UL97 Gene for Identification of Resistance to Ganciclovir in Iranian Immunosuppressed Patients

Background

Human cytomegalovirus (HCMV) infections are a major cause of morbidity and mortality among immunocompromised patients. Prolonged antiviral therapy is a cause of mutation and drug resistance in the HCMV genome.

Objectives

The aim of this study was to identify resistance to ganciclovir (GCV) in Iranian immunosuppressed patients at two different stages of the disease: early (before GCV is initiated) and late (after six months of GCV therapy).

Patients and Methods

In this study, 87 specimens from Iranian patients were amplified using nested PCR amplification of the UL97 gene. Sequence analyses of products were performed for identifying the mutated codons.

Results

The present study show that the most frequent GCV-resistant mutations occurred in codons A594V (26.43%), H520Q (18.39%), and M460V (13.79%), consequently occurring at a low frequency in the L595S (2.29%), E596G (1.14%), and Del 594 (1.14%) codons, and with intermediate frequency in the C592G (10.34%), M460I (9.19%), and C603W (6.89%) codons. We describe for the first time a new GCV-resistance mutation, the deletion of codon 594, in the UL97 gene of Iranian HCMV patients after GCV therapy, following renal transplantation.

Conclusions

The findings of the present study can be utilized to detect GCV resistance patterns among Iranian immunocompromised patients and to treat HCMV infections accordingly.

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.

DSTP-27 prevents entry of human cytomegalovirus

Human cytomegalovirus (HCMV) can cause life-threatening diseases in neonates and immunocompromised patients. Due to multiple problems caused by the current available drugs, development of new antiviral compounds is urgently needed. In this study, we characterize the anti-HCMV spectrum and mechanism of action of the N-N'-(bis-5 nitropyrimidyl)dispirotripiperazine derivate 27 (DSTP-27). DSTP-27 exhibited strong antiviral activity against two laboratory HCMV strains with different cell tropism as well as ganciclovir (GCV)-sensitive and GCV-resistant clinical isolates in plaque reduction assays and viral growth kinetics experiments. Interestingly, neither infectious nor noninfectious viral particles were observed by electron microscopy. Pretreatment of cell-free virus with DSTP-27 prevented virus infection. The results from time of addition assays, in which DTSP-27 was added to cells (i) before infection, (ii) during virus adsorption, or (iii) after adsorption, demonstrated an inhibitory effect on early steps of the HCMV replication cycle. This observation was confirmed by immunofluorescence as well as Western blot analysis, whereby reduced levels of the immediate early protein IE1, the processivity factor pUL44, and the tegument protein pp28 were detected. Results from attachment and penetration analyses of prechilled human embryonic lung fibroblasts revealed that virus attachment is not blocked. In addition, DSTP-27 inactivated HCMV by stable binding. Taken together, these results demonstrate that DSTP-27 (i) blocks viral penetration by interacting with the host cell and (ii) inactivates HCMV by interacting with the virus.

Recent developments in human cytomegalovirus diagnosis

Since the early 1990s, great efforts have been made in the field of human cytomegalovirus (HCMV) diagnosis. Besides HCMV diagnosis in immunosuppressed patients (solid organ transplant recipients, hematopoietic stem cell transplant patients and AIDS patients), diagnosis in connection with congenital HCMV infection is of great interest. This review focuses on the development and clinical utility of serological assays, as well as on virological tests (molecular and nonmolecular assays). Interpretation of these tests is strongly dependent on the patient group (solid organ transplant recipients and hematopoietic stem cell transplant patients) and whether the tests are used for screening, risk stratification or diagnosis. Furthermore, a better understanding of HCMV infection has led to new approaches in HCMV diagnosis and monitoring. Thus, assays for viral resistance testing and assays for monitoring the HCMV-specific cellular immune response are increasingly important for the guidance of antiviral therapy.

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.

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.

Fluorescence-based assay for phenotypic characterization of human cytomegalovirus polymerase mutations regarding drug susceptibility and viral replicative fitness

One essential prerequisite for genotypic drug susceptibility testing of human cytomegalovirus (HCMV) is the phenotypic characterization of mutations identified in the viral protein kinase gene UL97 and the viral DNA polymerase gene UL54 regarding their quantitative impact on drug susceptibility. We developed a new method for phenotypic characterization of UL54 mutations with regard to polymerase activity, viral replication, and drug susceptibility. To determine the most suitable viral indicator gene, enhanced green fluorescence protein was C-terminally fused to the HCMV early-late protein UL83 (pp65) or the late proteins UL32 (pp150) and UL99 (pp28), resulting in reporter viruses vTB65g, vTB150g, and vTB28g. vTB65g proved to be superior to the other constructs due to its favorable signal-to-noise ratio and was therefore used to establish the optimum conditions for our assay. The UL54 E756K and D413E mutations were introduced into vTB65g by markerless bacterial artificial chromosome mutagenesis, resulting in virus strains vE756Kg and vD413Eg. The drug susceptibility phenotypes of vE756Kg and vD413Eg were comparable to those previously reported. Furthermore, we found a reduced replicative fitness of vE756Kg by measuring fluorescence intensity as well as by conventional virus growth kinetics. Decreased fluorescence signals of vE756Kg- and vD413Eg-infected cells at late times of infection suggested a reduced polymerase activity, which was confirmed by real-time PCR quantification of the newly synthesized viral DNAs. This new fluorescence-based assay is a highly reproducible method for the phenotypic characterization of mutations potentially influencing drug susceptibility, viral replicative fitness, and polymerase activity of HCMV after marker transfer.

Dynamics of the emergence of a human cytomegalovirus UL97 mutant strain conferring ganciclovir resistance in a pediatric stem-cell transplant recipient

Stem-cell transplant recipients are at risk of developing ganciclovir-resistant human cytomegalovirus (HCMV) infection caused by mutations in the viral UL97 gene. Knowledge of the relative proportions of coexisting HCMV wild-type and mutant strains may contribute to a better understanding of the dynamics of in vivo mutant strain selection under ganciclovir. Currently, genotype resistance screening for UL97 is routinely performed by restriction fragment length polymorphism detection and sequencing. We present here the longitudinal course of a pediatric recipient of an allogeneic stem-cell transplant infected with a ganciclovir-resistant HCMV strain. EDTA-treated blood samples were analyzed longitudinally. The patient acquired a primary HCMV infection shortly before transplantation and reactivated the virus following allogeneic hematopoietic stem cell transplantation, thus receiving an intensive antiviral treatment schedule. Three different methods for UL97 mutation analysis, restriction fragment length polymorphism detection, sequencing, and a new, real-time PCR approach were performed. In conclusion, for our pediatric patient, during peak viral load, the UL97 wild-type strain predominates, while during clinical deterioration with low viral load, the predominant mutant strain persists.

Rapid determination of antiviral drug susceptibility of human cytomegalovirus by real-time PCR

A quantitative real-time PCR-based assay was developed for determination of cytomegalovirus (HCMV) susceptibility to antiviral drugs. After HCMV isolate-growth for 4 days, antiviral drug susceptibility was determined by measuring the reduction of intracellular HCMV DNA in the presence of increasing concentrations of either ganciclovir, or foscarnet or cidofovir. The 50% inhibitory concentration (IC(50)) was the drug concentration that reduced the number of HCMV genome copies by 50%. The IC(50) values were measured for seven HCMV reference strains sensitive or resistant to one or more antiviral drugs. The antiviral susceptibility of 21 HCMV isolates was then tested and the results were consistent with prior determination of their phenotype and/or genotype by plaque reduction assay and sequencing. The real-time PCR susceptibility assay reported here was found to be highly reproducible, simpler to perform than the plaque reduction assay, and amenable to use in the routine diagnostic virology laboratory.

Synthesis and in vitro activities of a new antiviral duplex drug linking Zidovudine (AZT) and Foscarnet (PFA) via an octadecylglycerol residue

To prepare a new antiviral duplex drug linking Zidovudine (AZT) and Foscarnet (PFA) via a lipophilic octadecylglycerol residue we condensed 1-O-4-monomethoxytrityl-3-O-octadecyl-sn-glycerol-2-hydrogenphosphonate obtained from 3-O-octadecyl-sn-glycerol with AZT by the phosphonate method. The purified condensation product was de-tritylated resulting in 3'-azido-3'-deoxythymidylyl-(5'-->2-O)-3-O-octadecyl-sn-glycerol, followed by treatment with (ethoxycarbonyl)phosphoric dichloride. The resulting 3'-azido-3'-deoxy-thymidylyl-(5'-->2)-3-O-octadecyl-sn-glycerol-1-O-(ethoxycarbonyl)phosphonate was purified by preparative RP-18 column chromatography. The antiviral duplex drug 3'-azido-3'-deoxythymidylyl-(5'-->2-O)-3-O-octadecyl-sn-glycerol-1-O-phosphonoformate trisodium salt (AZT-lipid-PFA) was obtained after alkaline cleavage of the phosphonoformate ethylester residue. The overall yield of the five step synthesis performed at gram scale was about 30%. According to a supposed pathway AZT-lipid-PFA could be cleaved to yield a mixture of different antiviral compounds such as AZT, AZT-5'-monophosphate, octadecylglycerol-AZT, PFA and octadecylglycerol-PFA, possibly producing additive and/or synergistic antiviral effects. In vitro studies showed that the duplex drug exhibits antiviral activities against HIV and especially against drug-resistant strains and clinical isolates of HSV and HCMV. The E(50) values of AZT-lipid-PFA against HIV ranged between 170 and 200 nM. The half-maximal inhibitory doses (IC(50)) against highly acyclovir (ACV)-resistant HSV isolates determined by a plaque reduction assay ranged between 1.87 and 4.59 microM. Using ganciclovir (GCV)-sensitive, GCV resistant and drug cross-resistant HCMV strains the IC(50)-values of AZT-lipid-PFA were between 2.78 and 1.18 microM. With regard to PFA, the IC(50)-value of AZT-lipid-PFA determined on a multi-drug-resistant HCMV strain was about 90-fold lower than that of PFA, demonstrating the superior antiviral effect of the duplex-drug.

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.

Novel real-time monitoring system for human cytomegalovirus-infected cells in vitro that uses a green fluorescent protein-PML-expressing cell line

Promyelocytic leukemia (PML) bodies are discrete nuclear foci that are intimately associated with many DNA viruses. In human cytomegalovirus (HCMV) infection, the IE1 (for "immediate-early 1") protein has a marked effect on PML bodies via de-SUMOylation of PML protein. Here, we report a novel real-time monitoring system for HCMV-infected cells using a newly established cell line (SE/15) that stably expresses green fluorescent protein (GFP)-PML protein. In SE/15 cells, HCMV infection causes specific and efficient dispersion of GFP-PML bodies in an IE1-dependent manner, allowing the infected cells to be monitored by fluorescence microscopy without immunostaining. Since a specific change in the detergent solubility of GFP-PML occurs upon infection, the infected cells can be quantified by GFP fluorescence measurement after extraction. With this assay, the inhibitory effects of heparin and neutralizing antibodies were determined in small-scale cultures, indicating its usefulness for screening inhibitory reagents for laboratory virus strains. Furthermore, we established a sensitive imaging assay by counting the number of nuclei containing dispersed GFP-PML, which is applicable for titration of slow-growing clinical isolates. In all strains tested, the virus titers estimated by the GFP-PML imaging assay were well correlated with the plaque-forming cell numbers determined in human embryonic lung cells. Coculture of SE/15 cells and HCMV-infected fibroblasts permitted a rapid and reliable method for estimating the 50% inhibitory concentration values of drugs for clinical isolates in susceptibility testing. Taken together, these results demonstrate the development of a rapid, sensitive, quantitative, and specific detection system for HCMV-infected cells involving a simple procedure that can be used for titration of low-titer clinical isolates.

Use of time-saving flow cytometry for rapid determination of resistance of human cytomegalovirus to ganciclovir

There are two ways to assess the susceptibility of human cytomegalovirus (HCMV) to ganciclovir (GCV): one is a genotypic test that detects resistance-related mutations and the other is a phenotypic test that actually assesses susceptibility. The advantages of genotyping the UL 97 gene are its rapidity and accuracy. However, to detect novel mutations or mutations affecting the UL 54 DNA polymerase, a phenotypic test such as the plaque reduction assay (PRA) is also required. To avoid the shortcomings of PRA such as its time-consuming nature and labor-intensiveness, we developed a time-saving fluorescence-activated cell sorting (TS-FACS) technique. We obtained a GCV 50% inhibitory concentration (IC(50)) from five clinical isolates and an HCMV laboratory strain (AD169) and compared the results with those from the PRA. The laboratory strain and three clinical isolates were sensitive to GCV. Although there was a minor discrepancy in the case of one of the three isolates, the GCV IC(50) values obtained by TS-FACS analysis correlated well with the results of the PRA. The remaining two isolates were resistant to GCV; one was GCV resistant due to the mutation M 460 V, and the GCV IC(50) results obtained by TS-FACS analysis and by PRA were also comparable. The advantages of TS-FACS analysis are the shorter time required, the possibility of automation, and its comparability to PRA, considered the gold standard. Thus, TS-FACS analysis may be useful as an alternative to PRA in the clinic.

The influence of mixed HCMV UL97 wildtype and mutant strains on ganciclovir susceptibility in a cell associated plaque reduction assay

BACKGROUND

Ganciclovir (GCV) resistance is an emerging problem following organ transplantation. A restriction fragment length polymorphism (RFLP) assay is a convenient and rapid method to discover known resistance mutations within the UL97 (phosphotransferase) gene for the determination of GCV resistance. Phenotypic resistance testing remains important for the identification of human cytomegalovirus (HCMV) strains possibly harboring novel mutations and also for the determination of foscarnet and cidofovir resistance.

OBJECTIVE

The aim of this work was to evaluate the reliability of a cell-associated plaque reduction assay with respect to an expanded UL97 RFLP assay for use on codons 460, 520, 591, 592, 594, 595 and 603. Furthermore, the influence of mixed viral populations with coexistent wildtype and mutant UL97 sequences on GCV IC(50) values was investigated.

STUDY DESIGN

Twenty-eight clinical HCMV isolates were obtained from six adult patients under clinical and virological suspicion for development of GCV resistance following peripheral blood stem cell transplantation (PBSCT), and from one adult and three pediatric patients with confirmed GCV resistance following PBSCT. All isolates were tested for drug susceptibility and screened for UL97 resistance mutations.

RESULTS

The plaque reduction assay exceeded the GCV cut-off for resistance even when only a small number (5-10%) of the viral population was resistant. The proportion of UL97 mutant and wildtype strains influenced GCV IC(50) values. Genotypically detected GCV resistance always preceded phenotypically detected resistance. Long-term follow-up UL97 resistance screening revealed evidence for transient and compartment-specific UL97 mutations.

CONCLUSION

The stringent and longitudinal use of an expanded HCMV UL97 RFLP assay of specimens from different sites contributes to the rapid and reliable diagnosis of GCV resistance. The influence of the proportion of UL97 mutant and wildtype strains on GCV IC(50) values along with the strong correlation between phenotype and genotype suggests that the cell associated plaque reduction assay is highly reliable.

Rapid development of ganciclovir-resistant cytomegalovirus infection in children after allogeneic stem cell transplantation in the early phase of immune cell recovery

As recently reported, children having T cell-depleted peripheral blood stem cell transplantation (PBSCT) might be at increased risk for the development of drug resistance. To investigate if delayed immune recovery was a potential risk factor, the recovery of the CD3(+), CD4(+), CD8(+) and CD19(+) cells was related retrospectively to genotypic detected resistance development in three pediatric patients with ganciclovir (GCV)-resistant human cytomegalovirus (HCMV)-infection out of 79 receiving allogeneic PBSCT. Selected control groups consisted of HCMV-seronegative patients without any infection (A, n = 8), asymptomatic infected patients with viral leuko- and plasmaDNAemia (B, n = 4) and patients with HCMV-disease (pneumonia) (C, n = 3). Patient No. 1 with very early resistance development exhibited a rapid immune recovery with higher T cell counts than in group A. Immune recovery of patient No. 2 was delayed, as also observed in groups B and C. Patient No. 3 showed an immune recovery comparable to group A. Resistance developed before (No. 2) or during (Nos 1 and 3) the recovery of the relevant CD3(+), CD4(+), CD8(+) lymphocytes. GCV-resistance development did not necessarily coincide with delayed immune recovery, but appeared in all three cases in the early phase of immune recovery (range: day +44 to day +95). Therefore, children seem to be at special risk for resistance development in the early phase after transplantation before immune cells have recovered. These results suggest that GCV treatment of an HCMV infection in the early posttransplant phase of children after T cell-depleted PBSCT/BMT should promote more stringent resistance screening.

Susceptibility testing. Viral pathogens

The control of the global expansion and proliferation of the AIDS pandemic has been complicated by the emergence of resistant strains of HIV-1 to the many new antiviral drugs directed to the genes coding for reverse transcriptase and protease enzymes of the virus. Similarly, new drug regimens for the management of chronic hepatitis B and C infections have been complicated by the lack of sustained clinical responses recently associated with either nucleotide mutation (HBV) or specific genotype of the virus (HCV). Commercial systems for performing and interpreting genotypic analysis will facilitate the recognition of informative mutations, standardize results between laboratories, and produce informative and interpretative result formats for optimal treatment of patients. Drug-resistant strains of herpesviruses (HSV, VZV, CMV) are generally associated with prolonged treatment of these infections in immunocompromised patients. Ultimate relevance of genotypic assays for routine clinical practice will require correlation with phenotypic results and the outcomes of long-term studies associating clinical improvement with antiviral drugs with specific mutation patterns of these viruses.

Drug-resistant human cytomegalovirus infection in children after allogeneic stem cell transplantation may have different clinical outcomes

Three seropositive pediatric recipients of allogeneic stem cell transplantation out of a group of 42 patients receiving T-cell–depleted, unrelated transplants and 37 patients receiving T-cell–depleted, haploidentical transplants were monitored longitudinally for human cytomegalovirus (HCMV) infection and the emergence of antiviral drug resistance. Early in the posttransplant course, all 3 patients developed HCMV mutations conferring drug resistance to ganciclovir. One child additionally developed multidrug resistance to foscarnet and cidofovir, with mutations in the viral phosphotransferase gene (UL97) and the DNA-polymerase gene (UL54) being found. These data show that resistant HCMV infection does not necessarily correlate with a severe clinical outcome. The early detection of genotypic resistance up to 129 days before the emergence of phenotypic resistance and the dissociation of resistance patterns among different body sites emphasize the importance of genotypic analyses of different DNA specimens for an efficient antiviral therapy. T-cell–depleted children having transplantation might be at an increased risk for the development of drug resistance.

Drug-resistant human cytomegalovirus infection in children after allogeneic stem cell transplantation may have different clinical outcomes

Three seropositive pediatric recipients of allogeneic stem cell transplantation out of a group of 42 patients receiving T-cell–depleted, unrelated transplants and 37 patients receiving T-cell–depleted, haploidentical transplants were monitored longitudinally for human cytomegalovirus (HCMV) infection and the emergence of antiviral drug resistance. Early in the posttransplant course, all 3 patients developed HCMV mutations conferring drug resistance to ganciclovir. One child additionally developed multidrug resistance to foscarnet and cidofovir, with mutations in the viral phosphotransferase gene (UL97) and the DNA-polymerase gene (UL54) being found. These data show that resistant HCMV infection does not necessarily correlate with a severe clinical outcome. The early detection of genotypic resistance up to 129 days before the emergence of phenotypic resistance and the dissociation of resistance patterns among different body sites emphasize the importance of genotypic analyses of different DNA specimens for an efficient antiviral therapy. T-cell–depleted children having transplantation might be at an increased risk for the development of drug resistance.

Recombinant green fluorescent protein-expressing human cytomegalovirus as a tool for screening antiviral agents

A recombinant human cytomegalovirus (AD169-GFP) expressing green fluorescent protein was generated by homologous recombination. Infection of human fibroblast cultures with AD169-GFP virus produced stable and readily detectable amounts of GFP signals which were quantitated by automated fluorometry. Hereby, high levels of sensitivity and reproducibility could be achieved, compared to those with the conventional plaque reduction assay. Antiviral activities were determined for four reference compounds as well as a set of putative novel cytomegalovirus inhibitors. The results obtained were exactly in line with the known characteristics of reference compounds and furthermore revealed distinct antiviral activities of novel in vitro inhibitors. The fluorometric data could be confirmed by GFP-based flow cytometry and fluorescence microscopy. In addition, laboratory virus variants derived from the recombinant AD169-GFP virus provided further possibilities for study of the characteristics of drug resistance. The GFP-based antiviral assay appeared to be very reliable for measuring virus-inhibitory effects in concentration- and time-dependent fashions and might also be adaptable for high-throughput screenings of cytomegalovirus-specific antiviral agents.

New strategies for prevention and therapy of cytomegalovirus infection and disease in solid-organ transplant recipients

In the past three decades since the inception of human organ transplantation, cytomegalovirus (CMV) has gained increasing clinical import because it is a common pathogen in the immunocompromised transplant recipient. Patients may suffer from severe manifestations of this infection along with the threat of potential fatality. Additionally, the dynamic evolution of immunosuppressive and antiviral agents has brought forth changes in the natural history of CMV infection and disease. Transplant physicians now face the daunting task of recognizing and managing the changing spectrum of CMV infection and its consequences in the organ recipient. For the microbiology laboratory, the emphasis has been geared toward the development of more sophisticated detection assays, including methods to detect emerging antiviral resistance. The discovery of novel antiviral chemotherapy is an important theme of clinical research. Investigations have also focused on preventative measures for CMV disease in the solid-organ transplant population. In all, while much has been achieved in the overall management of CMV infection, the current understanding of CMV pathogenesis and therapy still leaves much to be learned before success can be claimed.

Human cytomegalovirus: challenges, opportunities and new drug development

In the age of highly active antiretroviral therapy, the incidence of human cytomegalovirus (HCMV) retinitis in AIDS patients has decreased substantially. However, this change does not indicate that HCMV disease in AIDS patients and other immunocompromised patients has abated and is no longer a concern. On the contrary, HCMV disease in graft recipients, newborns, and even in AIDS patients still accounts for considerable morbidity, and drug resistance to the anti-HCMV compounds is a major problem. Furthermore, HCMV may have a role in metabolic diseases, such as atherosclerosis. Fortunately there are novel and potentially very effective new compounds undergoing pre-clinical and clinical evaluation. These developments point the way toward new therapies and also to a clearer understanding of the biology of HCMV replication, infection and disease.