Double resistance to ganciclovir and foscarnet of four human cytomegalovirus strains recovered from AIDS patients

Isolation of human monoclonal antibodies that potently neutralize human cytomegalovirus infection by targeting different epitopes on the gH/gL/UL128-131A complex

Human cytomegalovirus (HCMV) is a widely circulating pathogen that causes severe disease in immunocompromised patients and infected fetuses. By immortalizing memory B cells from HCMV-immune donors, we isolated a panel of human monoclonal antibodies that neutralized at extremely low concentrations (90% inhibitory concentration [IC(90)] values ranging from 5 to 200 pM) HCMV infection of endothelial, epithelial, and myeloid cells. With the single exception of an antibody that bound to a conserved epitope in the UL128 gene product, all other antibodies bound to conformational epitopes that required expression of two or more proteins of the gH/gL/UL128-131A complex. Antibodies against gB, gH, or gM/gN were also isolated and, albeit less potent, were able to neutralize infection of both endothelial-epithelial cells and fibroblasts. This study describes unusually potent neutralizing antibodies against HCMV that might be used for passive immunotherapy and identifies, through the use of such antibodies, novel antigenic targets in HCMV for the design of immunogens capable of eliciting previously unknown neutralizing antibody responses.

Anticytomegaloviral activity of esterified milk proteins and L-polylysines

MRC-5 fibroblasts infected with human cytomegalovirus (HCMV) reference strain AD 169 were treated with different concentrations of methylated alpha-lactalbumin (Met-ALA) or methylated beta-lactoglobulin (Met-BLG), as well as with their peptic hydrolysates, and with the highly basic polypeptides such as are L-polylysines (4-15 kDa). The antiviral activity was calculated by comparing the number of infected cells in the presence and absence of the tested substances. Both Met-ALA and Met-BLG, as well as their peptic hydrolysates, decreased the infectious activity of cytomegalovirus in fibroblast cells. As expected, L-polylysines showed the highest antiviral activity. However, the tested basic proteins and polypeptides despite their lower antiviral activities might be potentially quite useful in fight of arising drug resistance activities and the persistence capacities of this virus.

Prevalence of human cytomegalovirus UL97 D605E mutation in transplant recipients in China

Human cytomegalovirus (CMV) resistance to gancyclovir (GCV) occurs via mutation in the UL97 gene, ethylene diamine tetraacetic acid blood samples were obtained from 23 transplant recipients who received a GCV implant. A nested polymerase chain reaction amplifying UL97 codons 450 to 672 was performed. Nested amplifications were sequenced directly. No known UL97 GCV resistance mutations were found. Eighteen of 23 patients (78%) had revealed mutations at codon 605 (D to E). Mutant D605E may reverse to wild-type during the follow-up treatment. We conclude that human CMV UL97 D605E mutation occurred in Chinese transplant recipients. This mutation may be regarded as a natural sequence variant.

How evolution of mutations conferring drug resistance affects viral dynamics and clinical outcomes of cytomegalovirus-infected hematopoietic cell transplant recipients

Infection with cytomegalovirus (CMV) remains a significant cause of morbidity and mortality among hematopoietic cell transplant (HCT) recipients. We describe two pediatric HCT recipients who developed persistent and severe drug-resistant CMV infections. CMV resistance to foscarnet and ganciclovir was detected after only 6 and 11 weeks of therapy, respectively. Viral pol mutations associated with drug resistance in these patients included T838A (a novel mutation) and D588N, which were shown by marker transfer to confer foscarnet and multidrug resistance, respectively. Each of these mutations significantly reduced in vitro replication of CMV, suggesting that they may decrease viral fitness. This finding was further supported by the disappearance of mutations upon withdrawal of antiviral pressure in one patient. Novel antivirals or combination therapy may be required for the treatment of drug-resistant CMV in HCT recipients and perhaps in other severely immunocompromised patients.

Rhesus cytomegalovirus is similar to human cytomegalovirus in susceptibility to benzimidazole nucleosides

Rhesus and human cytomegalovirus (RhCMV and HCMV, respectively) exhibit comparable inhibition by benzimidazole nucleosides, including 2,5,6-trichloro-(1-beta-d-ribofuranosyl)benzimidazole (TCRB), and pyrrolo[2,3-d]pyrimidines. The two HCMV protein targets of TCRB, UL89 and UL56, are highly conserved with their RhCMV homologues. These data indicate that infection of rhesus macaques with RhCMV represents a useful model to test novel anti-HCMV drugs.

Synthesis and antiviral activities of 3-aralkylthiomethylimidazo[1,2-b]pyridazine derivatives

The synthesis of novel substituted 3-aralkylthiomethylimidazo[1,2-b]pyridazines is reported. All of the synthesized compounds are devoid of antiviral activity against the replication of human immunodeficiency virus. However, compounds 6-chloro-8-methyl-3-phenethylthioimidazo[1,2-b]pyridazine and 6-chloro-2-methyl-3-phenethylthioimidazo[1,2-b]pyridazine are potent inhibitors of the replication of human cytomegalovirus in vitro, while compounds 6-chloro-2-methyl-3-benzylthiomethylimidazo[1,2-b]pyridazine and 6-chloro-2-methyl-3-phenethyl-thioimidazo[1,2-b]pyridazineare inhibitors of the replication of varicella-zoster virus. The results presented here suggest that compound 10 should be considered as a new lead in the development of antiviral agents.

Clinical and biologic aspects of human cytomegalovirus resistance to antiviral drugs

The emergence of human cytomegalovirus (HCMV) drug resistant strains is a life-threatening condition in immunocompromised individuals with active HCMV infection. HCMV drug resistance represented a major problem in patients with acquired immunodeficiency syndrome until the recent introduction of highly active antiretroviral combination therapy, which dramatically decreased the incidence in this clinical setting. However, HCMV resistance to antiviral drugs is now an emerging problem in the transplantation setting. The molecular mechanisms of HCMV drug resistance have been elucidated and rely on the selection during treatment of HCMV strains harboring mutations in two key viral genes: UL97 coding for a viral phosphotransferase and UL54 coding for the viral DNA polymerase.

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

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

Longitudinal observations on mutations conferring ganciclovir resistance in patients with acquired immunodeficiency syndrome and cytomegalovirus retinitis: The Cytomegalovirus and Viral Resistance Study Group Report Number 8

PURPOSE

Cytomegalovirus retinitis is the most common intraocular infection in patients with acquired immunodeficiency syndrome (AIDS). With prolonged suppressive anticytomegalovirus maintenance therapy, resistance occurs in over 25% of patients. We evaluated longitudinal changes in the cytomegalovirus genotype in patients with cytomegalovirus retinitis who developed ganciclovir resistance that was demonstrated in either the blood or urine.

METHODS

Patients with AIDS and previously untreated cytomegalovirus retinitis were followed prospectively for the occurrence of resistance while on treatment. Blood and urine specimens were obtained periodically for cytomegalovirus culture according to a predetermined schedule. Positive isolates were tested for phenotypic susceptibility and for mutations in the UL97 and UL54 genes.

RESULTS

A mutation conferring resistance to ganciclovir in either the UL97 or UL54 gene was detected in 18 patients. In general, patients with a genotypically resistant virus developed increasing phenotypic resistance over time. There was a suggestion that unless therapy was changed, UL97 mutations tended to persist. In seven of eight patients, the mutations identified in isolates from the blood and urine were identical. In selected patients, there was a suggestion that a mixed population of cytomegalovirus might be present. Progression of the retinitis in an involved eye (15 of 18), contralateral eye retinitis (10 of 11), and extraocular cytomegalovirus disease (5 of 18) occurred commonly among patients with resistant virus.

CONCLUSION

Resistance-conferring mutations in the cytomegalovirus genome emerge and may persist when the selective pressure for resistance is maintained. Some patients appear to harbor complex subpopulations of virus with different mutations and different levels of phenotypic resistance. Changes in therapy may result in a shift in virus population and changes in the cytomegalovirus genotype identified.

A novel nonnucleoside inhibitor specifically targets cytomegalovirus DNA maturation via the UL89 and UL56 gene products

3-Hydroxy-2,2-dimethyl-N-[4([[5-(dimethylamino)-1-naphthyl]sulfonyl]amino)-phenyl]propanamide (BAY 38-4766) is a novel selective nonnucleoside inhibitor of cytomegalovirus (CMV) replication with an excellent safety profile. This compound and structural analogues inhibit neither viral DNA synthesis nor viral transcription and translation. Accumulation of dense bodies and noninfectious enveloped particles coincides with inhibition of both concatemer processing and functional cleavage at intergenomic transitions, pointing to interference with viral DNA maturation and packaging of monomeric genome lengths. Resistant virus populations, including a murine CMV (MCMV) isolate with 566-fold-decreased drug sensitivity, were selected in vitro. Sequencing of the six open reading frames (ORFs) known to be essentially involved in viral DNA cleavage and packaging identified mutations in ORFs UL56, UL89, and UL104. Construction of MCMV recombinants expressing different combinations of murine homologues of mutant UL56, UL89, and UL104 and analysis of drug susceptibilities clearly demonstrated that mutant ORFs UL89 exon II (M360I) and M56 (P202A I208N) individually confer resistance to BAY 38-4766. A combination of both mutant proteins exhibited a strong synergistic effect on resistance, reconstituting the high-resistance phenotype of the in vitro mutant. These findings are consistent with genetic mapping of resistance to TCRB (2,5,6-trichloro-1-beta-D-ribofuranosyl benzimidazole) (P. M. Krosky et al., J. Virol. 72:4721-4728, 1998) and provide further indirect evidence that proteins encoded by UL89 and UL56 function as two subunits of the CMV terminase. While these studies also suggest that the molecular mechanism of BAY 38-4766 is distinct from that of benzimidazole ribonucleosides, they also offer an explanation for the excellent specificity and tolerability of BAY 38-4766, since mammalian DNA does not undergo comparable maturation steps.

Inhibition of murine cytomegalovirus and human cytomegalovirus by a novel non-nucleosidic compound in vivo

Novel non-nucleosidic compounds have recently been identified as potent inhibitors of the human cytomegalovirus (HCMV) and murine cytomegalovirus (MCMV) in vitro. We have now investigated the antiviral activity of these compounds in MCMV-infected NOD/LtSz-scid/j mice that lack functional T, B and, in contrast to C.B-17/Icr scid/scid mice, natural killer cells, and represent a novel model for cytomegalovirus infection in immunocompromised hosts. BAY 38-4766 (3-hydroxy-2,2-dimethyl-N-[4(([5-(dimethylamino)-1-naphthyl]sulfonyl)amino)- phenyl]propanamide) was identified as the most potent representative of this class of antiviral compounds. Per os administration of BAY 38-4766 at dosages > or = 10 mg/kg body weight led to antiviral effects that were comparable to ganciclovir 9-(1,3-dihydroxy-2-propoxymethyl)-guanine (Cymevene) as measured by survival and levels of viral DNA in organs of infected mice. In order to assess the anti-HCMV activity of BAY 38-4766 in vivo, we used a model, in which HCMV-infected human cells were entrapped in hollow fibers and subsequently transplanted into immunodeficient mice. Using this model, we demonstrated antiviral activity of BAY 38-4766 similar to that of ganciclovir. We conclude that BAY 38-4766 shows potential as an anti-HCMV drug.

Antiviral properties of a series of 1,6-naphthyridine and 7, 8-dihydroisoquinoline derivatives exhibiting potent activity against human cytomegalovirus

A series of 1,6-naphthyridine (L. Chan, H. Jin, T. Stefanac, J. F. Lavallee, G. Falardeau, W. Wang, J. Bedard, S. May, and L. Yuen, J. Med. Chem. 42:3023-3025, 1999) and isoquinoline (L. Chan, H. Jin, T. Stefanac, W. Wang, J. F. Lavallee, J. Bedard, and S. May, Bioorg. Med. Chem. Lett. 9:2583-2586, 1999) analogues exhibiting a high level of anti-human cytomegalovirus (HCMV) activity were investigated in a series of studies aimed at better understanding the mechanism of action of some representatives of this class of compounds. In vitro antiviral profiling revealed that these compounds were active against a narrow spectrum of viruses, essentially the human herpesviruses and type 2 rhinovirus. In HCMV assays, a 39- to 223-fold lower 50% inhibitory concentration was obtained for compound A1 than for ganciclovir against strains AD 169 and Towne. In addition, ganciclovir, foscarnet, cidofovir, and BDCRB (2-bromo-5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole)-resistant HCMV strains remained susceptible to 1,6-naphthyridines and 7, 8-dihydroisoquinolines tested in this study, supporting the view that a novel mechanism of action could be involved. Drug combination studies showed a small but significant synergistic antiviral effect between compound B2 and ganciclovir. Cytotoxicity profiling of representative compounds under various cell growth conditions indicated a generally similar cytotoxic effect, relative to ganciclovir, in log-phase growing cells. However, in stationary cells, a relatively higher level of toxicity was observed than that for control compound. Effect of time of drug addition showed that the anti-HCMV activity of compound A1, ganciclovir, and cidofovir was lost at approximately the same time (72 h postinfection), indicating that the compound was affecting events at the early and late stage of virus replication. This interpretation is also supported by reduction of de novo synthesis of pp65 tegument protein and lack of any effect of the compound on viral adsorption. A reduction of the HCMV enhancer-promoter-directed luciferase expression was also observed in a stably transfected cell line when compound A1 was present at relatively high concentrations.

Effect of desferrioxamine (DFO) and calcium trinatrium diethylenetriaminepentaacetic acid (DTPA) on rat cytomegalovirus replication in vitro and in vivo

Cytomegalovirus (CMV) infection is a major problem in the immunosuppressed patient. It is thought that besides direct CMV induced cell lysis, immunological damage is part of CMV pathogenesis. New antiviral drugs, which combine immunomodulating and antiviral qualities, could be beneficial. Recently, it has been described that desferrioxamine (DFO) and calcium trinatrium diethylenetriaminepentaacetic acid (DTPA) exhibit both properties. In this report the antiviral effects of both compounds against rat CMV (RCMV) are described in vitro and in vivo using a generalised and local infection model. In vitro, both compounds exhibited a significant antiviral effect, DTPA being more potent than DFO. However, in the generalised infection model no effect was seen on mortality, morbidity or presence of virus in internal organs. In rats infected subcutaneously in the hind paw, no effect was seen locally on paw thickness, presence of viral antigens and inflammatory response. In addition, these rats suffered from a generalised infection of low magnitude at 15 days post infection, although both DFO and DTPA were able to lower the level of viral replication. In conclusion, our data indicate that despite in vitro activity, in vivo usage of DFO or DTPA for acute CMV infection is not warranted.

Comparative study of the anti-human cytomegalovirus activities and toxicities of a tetrahydrofuran phosphonate analogue of guanosine and cidofovir

Cidofovir is the first nucleoside monophosphate analogue currently being used for the treatment of human cytomegalovirus (HCMV) retinitis in individuals with AIDS. Unfortunately, the period of therapy with the use of this compound may be limited due to the possible emergence of serious irreversible nephrotoxic effects. New drugs with improved toxicity profiles are needed. The goal of this study was to investigate the anticytomegaloviral properties and drug-induced toxicity of a novel phosphonate analogue, namely, (-)-2-(R)-dihydroxyphosphinoyl-5-(S)-(guanin-9'-yl-methyl) tetrahydrofuran (compound 1), in comparison with those of cidofovir. The inhibitory activities of both compounds on HCMV propagation in vitro were similar against the AD 169 and Towne strains, with 50% inhibitory concentrations ranging from 0.02 to 0.17 microgram/ml for cidofovir and < 0.05 to 0.09 microgram/ml for compound 1. A clinical HCMV isolate that was resistant to ganciclovir and that had a known mutation within the UL54 DNA polymerase gene and a cidofovir-resistant laboratory strain derived from strain AD 169 remained sensitive to compound 1, whereas their susceptibilities to ganciclovir and cidofovir were reduced by 33- and 10-fold, respectively. Both compound 1 and cidofovir exhibited equal potencies in an experimentally induced murine cytomegalovirus (MCMV) infection in mice, with a prevention or prolongation of mean day to death at dosages of 1.0, 3.2, and 10.0 mg/kg of body weight/day. In cytotoxicity experiments, compound 1 was found to be generally more toxic than cidofovir in cell lines Hs68, HFF, and 3T3-L1 (which are permissive for HCMV or MCMV replication) but less toxic than cidofovir in MRC-5 cells (which are permissive for HCMV replication). Drug-induced toxic side effects were noticed for both compounds in rats and guinea pigs in a 5-day repeated-dose study. In guinea pigs, a greater weight loss was noticed with cidofovir than with compound 1 at dosages of 3.0 and 10.0 mg/kg/day. An opposite effect was detected in rats, which were treated with the compounds at relatively high dosages (up to 100 mg/kg/day). Compound 1 and cidofovir were nephrotoxic in both rats and guinea pigs, with the epithelium lining the proximal convoluted tubules in the renal cortex being the primary target site. The incidence and the severity of the lesions were found to be dose dependent. The lesions observed were characterized by cytoplasm degeneration and nuclear modifications such as karyomegaly, the presence of pseudoinclusions, apoptosis, and degenerative changes. In the guinea pig model, a greater incidence and severity of lesions were observed for cidofovir than for compound 1 (P < 0.001) with a drug regimen of 10 mg/kg/day.

Summary of the II International Symposium on Cytomegalovirus

Human cytomegalovirus (HCMV) is a highly species-specific DNA virus belonging to the Betaherpesvirinae subfamily of the herpesviridae family. Like other herpesviruses, primary infection with HCMV is followed by persistence of the virus in a latent form. The sites of latency are still largely undefined, but they probably include bone marrow progenitor cells and peripheral blood monocytes. From these sites, the virus can reactivate, resulting in renewed shedding of the virus, or, in immunocompromized persons, development of disease. Humans are the only reservoir of HCMV and transmission occurs by person-to-person contact. Infection with HCMV is common. In most developed countries, HCMV seroprevalence steadily increases after infancy and 10-20% of children are infected before puberty. In adults, the prevalence of antibodies ranges from 40 to 100%. Although HCMV has a world-wide distribution, infection with HCMV is more common in the developing countries and in areas of low socioeconomic conditions, which is predominantly related to the closeness of contacts within these populations. Except for a mononucleosis-like illness in some persons, infection with HCMV rarely causes disease in immunocompetent individuals. However, HCMV can cause severe morbidity and mortality in congenitally infected newborns and immunocompromized patients, most notably transplant-recipients and HIV-infected persons. This article provides a review of the information presented at the Second International Symposium on Cytomegalovirus organized and convened by The Macrae Group (New York City, NY) in Acapulco, Mexico on 24-28 April 1998. During this symposium, the state-of-the-art knowledge on diagnosis, treatment and prophylaxis of HCMV infections were discussed, and, based on this information, attempts to highlight the future directions in basic and clinical research areas that need to be stimulated to facilitate advancement in prevention and treatment of CMV disease.

Ganciclovir resistance as a result of oral ganciclovir in a heart transplant recipient with multiple human cytomegalovirus strains in blood

BACKGROUND

The emergence of a ganciclovir (GCV)-resistant human cytomegalovirus (HCMV) strain in a heart transplant recipient (HTR) coinfected by multiple HCMV strains was investigated.

METHODS

A HTR with primary HCMV infection was treated with three induction courses of intravenous GCV followed by a 2-month maintenance treatment with oral GCV. HCMV antigenemia, viremia, and leukoDNAemia levels were monitored. GCV susceptibility was analyzed by an immediate-early antigen plaque reduction assay and by a rapid screening assay performed using peripheral blood leukocytes (PBL) as viral inoculum. The viral population in blood was investigated by restriction analysis of multiple genome regions. UL97 and UL54 genes were sequenced in parallel in both HCMV isolates and the relevant PBL samples. A rapid molecular assay for detection and quantitation of the GCV-resistant mutant was developed.

RESULTS

The emergence of a GCV-resistant UL97 mutant (Cys-607 --> Tyr) was responsible for treatment failure during oral GCV therapy. The genetic analysis of the HCMV population showed the sequential appearance in blood of two unrelated strains (referred to as A and B). Strain A most likely derived from the transplanted organ and strain B from a subsequent blood transfusion. The resistant variant (Br) emerged from strain B and became predominant "in vivo" under the GCV pressure. However, after foscarnet administration, the resistant mutant disappeared in viral isolates, whereas it was still present as a minor proportion in PBL samples.

CONCLUSION

(a) Oral GCV may select resistant strains in transplanted patients; (b) results of the rapid screening assay were clinically useful for shifting to an alternative treatment, thus avoiding the appearance of HCMV disease; (c) virus isolation may not be the most reliable approach to detection of HCMV drug-resistant strains; (d) a novel molecular assay for rapid detection of UL97 Cys-607 --> Tyr mutation directly in clinical specimens was developed, allowing earlier "in vivo" detection of the resistant mutant.

Use of the human cytomegalovirus (HCMV) antigenemia assay for diagnosis and monitoring of HCMV infections and detection of antiviral drug resistance in the immunocompromised

BACKGROUND

Quantification of viral load in blood has proven to be helpful in the follow-up of disseminated HCMV infections in immunocompromised patients.

OBJECTIVES

(i) To describe the antigenemia assay and its optimization and (ii) to analyze the use of the antigenemia assay for the diagnosis and monitoring of HCMV infections and for the detection of treatment failures.

STUDY DESIGN

This article is intended to give an overview of our experience in the use of the antigenemia assay.

RESULTS AND CONCLUSIONS

In solid organ transplant recipients and patients with AIDS, HCMV symptomatic infections mostly appear when antigenemia values are > 300 pp65-positive PBL/2 x 10(5) examined. To avoid the appearance of overt HCMV disease antiviral treatment could be administered when antigenemia levels are > 100 pp65-positive PBL/2 x 10(5) examined. Bone marrow transplant recipients show symptomatic HCMV infections when antigenemia values are > 100 pp65-positive PBL/2 x 10(5) examined. This group of patients should be treated when antigenemia levels are < 10 pp65-positive PBL/2 x 10(5) examined due to the higher mortality rate associated with HCMV complications. A decrease in antigenemia levels during therapy indicates a good response to antiviral drug, while stable or increasing values document a treatment failure and the emergence of drug-resistant HCMV strains.

Characterization of drug resistance-associated mutations in the human cytomegalovirus DNA polymerase gene by using recombinant mutant viruses generated from overlapping DNA fragments

A number of specific point mutations in the human cytomegalovirus (HCMV) DNA polymerase (UL54) gene have been tentatively associated with decreased susceptibility to antiviral agents and consequently with clinical failure. To precisely determine the roles of UL54 mutations in HCMV drug resistance, recombinant UL54 mutant viruses were generated by using cotransfection of nine overlapping HCMV DNA fragments into permissive fibroblasts, and their drug susceptibility profiles were determined. Amino acid substitutions located in UL54 conserved region IV (N408D, F412C, and F412V), region V (A987G), and delta-region C (L501I, K513E, P522S, and L545S) conferred various levels of resistance to cidofovir and ganciclovir. Mutations in region II (T700A and V715M) and region VI (V781I) were associated with resistance to foscarnet and adefovir. The region II mutations also conferred moderate resistance to lobucavir. In contrast to mutations in other UL54 conserved regions, those residing specifically in region III (L802M, K805Q, and T821I) were associated with various drug susceptibility profiles. Mutations located outside the known UL54 conserved regions (S676G and V759M) did not confer any significant changes in HCMV drug susceptibility. Predominantly an additive effect of multiple UL54 mutations with respect to the final drug resistance phenotype was demonstrated. Finally, the influence of selected UL54 mutations on the susceptibility of viral DNA replication to antiviral drugs was characterized by using a transient-transfection-plus-infection assay. Results of this work exemplify specific roles of the UL54 conserved regions in the development of HCMV drug resistance and may help guide optimization of HCMV therapy.

Rising levels of human cytomegalovirus (HCMV) antigenemia during initial antiviral treatment of solid-organ transplant recipients with primary HCMV infection

In 7 of 18 solid-organ transplant recipients with primary human cytomegalovirus (HCMV) infection, HCMV antigenemia levels were unexpectedly found to rise significantly (P = 0.018) during a mean time of 7.3 +/- 3.2 days after initiation of specific antiviral treatment, whereas corresponding levels of viremia dropped significantly (P = 0.043). Thus, shifting to an alternative antiviral drug based solely on increasing antigenemia levels is not justified in this group of patients.

The Cys607-->Tyr change in the UL97 phosphotransferase confers ganciclovir resistance to two human cytomegalovirus strains recovered from two immunocompromised patients

Two ganciclovir (GCV)-resistant human cytomegalovirus (HCMV) strains recovered from an AIDS patient (strain VR4990) and a heart transplant recipient (strain VR5474) showed a Cys607-->Tyr change in the UL97-encoded phosphotransferase. No amino acid substitutions were observed in the viral DNA polymerase. Marker transfer experiments showed marked reduction in GCV phosphorylation and drug susceptibility of the recombinant HCMV strain VR4990rec2-1-1. These results further extend the region of the carboxy-terminal domain of the UL97 phosphotransferase involved in GCV substrate recognition.

What clinicians need to know about antiviral drugs and viral resistance

The development of safe and effective antiviral therapies for the management of a variety of viral infections has expanded tremendously in recent years. Treatment is now possible for serious and potentially life-threatening infections with herpesviruses, respiratory viruses such as influenza A and respiratory syncytial virus, and the human immunodeficiency virus. The increased availability and use of antiviral drugs, however, has led to the emergence of drug-resistant viruses, especially in immunocompromised hosts. With this review, the major antiviral agents are presented with a description of the mechanisms of action, the evolution of drug resistance, and the need for in vitro antiviral susceptibility testing.

Antiviral susceptibility testing-flow cytometric analysis (AST-FCA) for the detection of cytomegalovirus drug resistance

Antiviral susceptibility testing-flow cytometric analysis (AST-FCA), an application of flow cytometry in conjunction with cell culture, was developed to identify susceptibility of cytomegalovirus (CMV) isolates to the antiviral drugs ganciclovir (GCV) and foscarnet (PFA). The viral isolates used in this study were obtained from peripheral blood of AIDS patients. Among GCV-susceptible strains, the mean 50% inhibitory concentration (IC50) using AST-FCA was 18 microns (SI50 = 1.4). Among GCV resistant strains, the mean IC50 was 47 microns (SI50 = 3.6). For PFA, the mean IC50 was 80 microns (SI50 = 1.0) for susceptible strains. IC50s for strains resistant to PFA, showed no significant reduction of infectivity at the highest drug concentration (i.e., 200 microns PFA) tested. Additional analyses confirmed the accuracy of AST-FCA by parallel testing using plaque reduction assay. AST-FCA is a novel, nonisotopic, and relatively simple to perform laboratory procedure for the identification of CMV drug-resistant strains.

Quantitative systemic and local evaluation of the antiviral effect of ganciclovir and foscarnet induction treatment on human cytomegalovirus gastrointestinal disease of patients with AIDS. Italian Foscarnet GID Study Group

In a group of 29 AIDS patients with biopsy-proven human cytomegalovirus (HCMV) gastrointestinal disease (GID), HCMV GID was shown to correlate mostly with systemic HCMV infection. The antiviral induction treatment (IT) with either ganciclovir (GCV) or foscarnet (PFA) caused a significant reduction in the level of HCMV antigenemia, viremia and leukoDNAemia, and a complete virus clearance or a sharp drop of viral load in the blood of 13/13 patients and in the gastrointestinal (GI) mucosa of 12/13 (92%) patients in the GCV arm, and in the blood of 13/14 (93%) patients and in the GI mucosa of 10/12 (83%) patients in the PFA arm of the study, respectively. Similarly, the clinical response was good in 13/15 (87%) patients in the GCV arm and in 13/14 (93%) patients in the PFA arm. In addition, the finding that 2/6 patients positive for HCMV isolated from both GI mucosa and blood prior to IT were still positive in the GI tract after IT, suggested that IT could be prolonged to clear the virus from GI tract. In conclusion, both GCV and PFA showed a remarkable systemic and local antiviral effect in the treatment of HCMV GID in AIDS patients.

Summary of the International Consensus Symposium on Advances in the Diagnosis, Treatment and Prophylaxis and Cytomegalovirus Infection

CMV infection and CMV disease can be difficult to differentiate and the diagnosis is usually based on a compatible clinical picture and the results of a diagnostic test for CMV. The only exception to this rule is in HIV-infected patients where fundoscopy is sufficient to diagnose CMV retinitis. Of the current diagnostic tests, qualitative and quantitative PCR, branched DNA and Hybrid Capture, are the most promising. The pp65 antigenemia assay has the disadvantage of being more labor-intensive than the DNA based tests. Preliminary data show that a positive qualitative PCR in a HIV-infected patient has a predictive value for the development of CMV retinitis. However, of the patients positive by qualitative PCR, those with high viral loads in quantitative PCR were at the greatest risk of CMV disease. This might make it possible to identify with great certainty the patients who will go on to develop CMV retinitis, thereby decreasing the number of patients eligible for preemptive or prophylactic therapy and increasing the cost-benefit of this therapeutic measure. Quantitative test might also be useful in monitoring response to therapy, but randomized trials comparing the test are needed. Prophylactic antiviral agents should not be used in seronegative transplant recipients receiving organs from seronegative donors. In high-risk transplant recipients, ganciclovir should be used. CMV vaccines are useful for the protection of babies from CMV seronegative mothers against congenital CMV disease. It also may be useful in seronegative transplant recipients receiving a seropositive donor organ, although the benefit of chemo prophylaxis may surpass that of vaccine. HIV-infected patients with CMV retinitis who relapse under either ganciclovir or foscarnet benefit from subsequent combination therapy, rather than switching to the other drug. However, the cost is high in terms of quality of life. Intravitreal therapy for CMV retinitis is very efficacious, suggesting that drug delivery is a problem in systemic therapy. However, intravitreal therapy does not protect against the development of CMV retinitis in the contralateral eye or from CMV disease elsewhere. Therefore, systemic therapy should be added. CMV disease of the CNS should be diagnosed early and treated agressively, possible with combination therapy. A diagnosis of CMV disease should be based on a compatible clinical picture and the demonstration of CMV in CSF by DNA or antigen assays which are more sensitive than culture.

Single amino acid changes in the DNA polymerase confer foscarnet resistance and slow-growth phenotype, while mutations in the UL97-encoded phosphotransferase confer ganciclovir resistance in three double-resistant human cytomegalovirus strains recovered from patients with AIDS

Three human cytomegalovirus (HCMV) strains (VR4760, VR4955, and VR5120) showing double resistance to ganciclovir (GCV) and foscarnet (PFA) were isolated from three patients with AIDS who underwent multiple sequential courses of therapy with GCV and PFA (A. Sarasini, F. Baldanti, M. Furione, E. Percivalle, R. Brerra, M. Barbi, and G. Gerna, J. Med. Virol., 47:237-244, 1995). We previously demonstrated that the three strains were genetically unrelated and that each of them was present as a single viral population in vivo. Thus, in each of the three cases, a single viral strain was resistant to both GCV and PFA. In the present paper, we report the characterization of the molecular bases of the double resistance and demonstrate that the PFA resistance is associated with a slower replication of HCMV strains in cell cultures. Sequencing of the UL97 and UL54 genes, GCV anabolism assays, and marker transfer experiments showed that GCV resistance was due to single amino acid changes in the UL97 gene product (VR4760, Met-460 --> Ile; VR4955, Ala-594 --> Val; VR5120, Leu595 --> Ser), while single amino acid changes in domain II of the DNA polymerase (VR4760 and VR5120, Val-715 --> Met; VR4955, Thr-700 --> Ala) were responsible for both the PFA resistance and the slow-growth phenotype. Thus, in these three cases, double resistance to GCV and PFA was not due to a single mutation conferring cross-resistance or to the presence of a mixture of strains with different drug susceptibilities. The HCMV DNA polymerase recombinant strains carrying the mutations conferring PFA resistance were sensitive to GCV and (S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine (HPMPC). In addition, the same UL54 mutations were responsible for the slow growth of the clinical isolates, since the recombinant strains showed a marked delay in immediate-early antigen plaque formation and a reduction of infectious virus yield compared with AD169, from which they were derived. These results may have some important implications for the successful isolation, propagation, and characterization of PFA-resistant strains from clinical samples containing mixed viral populations.