Clinical impact of ganciclovir-resistant cytomegalovirus infections in solid organ transplant patients

Efficacy of antimicrobials in preventing resistance in solid organ transplant recipients: A systematic review of clinical trials

BACKGROUND

In the absence of effective antimicrobials, transplant surgery is not viable, and antirejection immunosuppressants cannot be administered, as resistant infections compromise the life-saving goal of organ transplantation.

AIM

To evaluate the efficacy of antimicrobials in preventing resistance in solid organ transplant recipients.

METHODS

A systematic review was conducted using a search methodology consistent with the preferred reporting items for systematic reviews and meta-analyses. This review included randomized clinical trials that evaluated the efficacy of antimicrobial agents (prophylactic or therapeutic) aimed at preventing antimicrobial resistance. The search strategy involved analyzing multiple databases, including PubMed/MEDLINE, Web of Science, Embase, Scopus, and SciELO, as well as examining gray literature sources on Google Scholar. A comprehensive electronic database search was conducted from the databases’ inception until May 2024, with no language restrictions.

RESULTS

After the final phase of the eligibility assessment, this systematic review ultimately included 7 articles. A total of 2318 patients were studied. The most studied microorganisms were cytomegalovirus, although vancomycin-resistant enterococci, Clostridioides difficile, and multidrug-resistant Enterobacterales were also analyzed. The antimicrobials used in the interventions were mainly maribavir, valganciclovir, ganciclovir, and colistin-neomycin. Of concern, all clinical trials showed significant proportions of resistant microorganisms after the interventions, with no statistically significant differences between the groups (mean resistance 13.47% vs 14.39%), except for two studies that demonstrated greater efficacy of maribavir and valganciclovir (mean resistance 22.2% vs 41.1% in the control group; P < 0.05). The total reported deaths in three clinical trials were 75, and there were 24 graft rejections in two studies.

CONCLUSION

All clinical trials reported significant proportions of antimicrobial-resistant microorganisms following interventions. More high-quality randomized clinical trials are needed to corroborate these results.

Nuclear Egress Complexes of HCMV and Other Herpesviruses: Solving the Puzzle of Sequence Coevolution, Conserved Structures and Subfamily-Spanning Binding Properties

Herpesviruses uniquely express two essential nuclear egress-regulating proteins forming a heterodimeric nuclear egress complex (core NEC). These core NECs serve as hexameric lattice-structured platforms for capsid docking and recruit viral and cellular NEC-associated factors that jointly exert nuclear lamina as well as membrane-rearranging functions (multicomponent NEC). The regulation of nuclear egress has been profoundly analyzed for murine and human cytomegaloviruses (CMVs) on a mechanistic basis, followed by the description of core NEC crystal structures, first for HCMV, then HSV-1, PRV and EBV. Interestingly, the highly conserved structural domains of these proteins stand in contrast to a very limited sequence conservation of the key amino acids within core NEC-binding interfaces. Even more surprising, although a high functional consistency was found when regarding the basic role of NECs in nuclear egress, a clear specification was identified regarding the limited, subfamily-spanning binding properties of core NEC pairs and NEC multicomponent proteins. This review summarizes the evolving picture of the relationship between sequence coevolution, structural conservation and properties of NEC interaction, comparing HCMV to α-, β- and γ-herpesviruses. Since NECs represent substantially important elements of herpesviral replication that are considered as drug-accessible targets, their putative translational use for antiviral strategies is discussed.

The Cytomegalovirus Protein Kinase pUL97:Host Interactions, Regulatory Mechanisms and Antiviral Drug Targeting

Human cytomegalovirus (HCMV) expresses a variety of viral regulatory proteins that undergo close interaction with host factors including viral-cellular multiprotein complexes. The HCMV protein kinase pUL97 represents a viral cyclin-dependent kinase ortholog (vCDK) that determines the efficiency of HCMV replication via phosphorylation of viral and cellular substrates. A hierarchy of functional importance of individual pUL97-mediated phosphorylation events has been discussed; however, the most pronounced pUL97-dependent phenotype could be assigned to viral nuclear egress, as illustrated by deletion of the UL97 gene or pharmacological pUL97 inhibition. Despite earlier data pointing to a cyclin-independent functionality, experimental evidence increasingly emphasized the role of pUL97-cyclin complexes. Consequently, the knowledge about pUL97 involvement in host interaction, viral nuclear egress and additional replicative steps led to the postulation of pUL97 as an antiviral target. Indeed, validation experiments in vitro and in vivo confirmed the sustainability of this approach. Consequently, current investigations of pUL97 in antiviral treatment go beyond the known pUL97-mediated ganciclovir prodrug activation and henceforward include pUL97-specific kinase inhibitors. Among a number of interesting small molecules analyzed in experimental and preclinical stages, maribavir is presently investigated in clinical studies and, in the near future, might represent a first kinase inhibitor applied in the field of antiviral therapy.

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.

Low-dose valganciclovir prohylaxis is efficacious and safe in cytomegalovirus seropositive heart transplant recipients with anti-thymocyte globulin

BACKGROUND

Cytomegalovirus (CMV) remains an important pathogen in solid organ transplant patients.

OBJECTIVE

We executed a hybrid prophylactic and pre-emptive valganciclovir (VGCV) prophylaxis to prevent CMV infection in heart transplant patients with anti-thymocyte globulin (ATG) induction and retrospectively evaluated the efficacy and safety of this regimen.

METHODS

Hundred adult heart transplant patients between 2004 and 2010 were included. Recipients with CMV serostatus D+/R- received VGCV 900 mg OD for 6 months and 94.2% (81/86) of R+ recipients received a low-dose 450 mg OD for 3 months. Blood CMV was monitored until 3 months after cessation of the prophylaxis.

RESULTS

All patients accomplished the prophylaxis. The overall incidence of CMV disease was 4% (4/100) and it was more frequent in D+/R- patients (P = .001). Three of eighty-six (3.5%) of R+ patients had CMV infection (one CMV disease) while on prophylaxis, 2/3 were still on the original significantly reduced renal dose though. There was one late CMV disease in both D+/R- and R+ groups. Ganciclovir/VGCV treatment was successful in all patients.

CONCLUSIONS

The hybrid strategy with low-dose VGCV in R+ patients with ATG was efficient and safe. The good treatment results indicate that the regimen did not lead to a clinically relevant resistance. Optimal renal dosage is essential throughout prophylaxis.

Tolerability of up to 200 days of prophylaxis with valganciclovir oral solution and/or film-coated tablets in pediatric kidney transplant recipients at risk of cytomegalovirus disease

This multicenter, open-label study evaluated the tolerability of extended prophylaxis with valganciclovir in pediatric kidney transplant recipients at risk of CMV disease. Fifty-six patients aged 4 months to 16 years received once-daily valganciclovir oral solution and/or tablets, dosed by BSA and renal function, for up to 200 days. The most common AEs on treatment were upper respiratory tract infection (33.9%), urinary tract infection (33.9%), diarrhea (32.1%), leukopenia (25.0%), neutropenia (23.2%), and headache (21.4%). There were fewer AEs during days 101-228 vs days 1-100. Twenty-seven patients (48.2%) had treatment-related AEs during valganciclovir treatment, most commonly leukopenia (21.4%), neutropenia (19.6%), anemia (7.1%), and tremor (5.4%). Treatment-related serious AEs were reported for nine patients (16.1%) and six withdrew due to AEs. Viremia was centrally confirmed in 10 patients; there was no confirmed CMV disease. One patient tested positive for a resistance mutation (UL97 L595F). Biopsy-proven acute rejection occurred in six patients (10.7%), but no graft loss or deaths occurred. In conclusion, up to 200 days of valganciclovir prophylaxis in pediatric kidney allograft recipients showed a safety profile consistent with that established in adult transplant patients.

Evaluation of ganciclovir resistance in cytomegalovirus infection of renal transplant recipients in Tehran

BACKGROUND

Human cytomegalovirus (CMV) infection is a major issue in solid organ transplant recipients. Although development of prophylaxis and preemptive procedures have presented significantly improved consequences in CMV infection, increasing incidence of antiviral resistance has raised virologists' concern.

METHODS

The present study focused on kidney transplant recipients with high quantities of CMV load after antiviral therapy. We collected 5 mL blood from each of 58 patients. DNA extraction was performed with the use of the QIAamp DNA Mini kit (Qiagen), in accordance with the manufacturer's instructions.

RESULTS

Our population study was 38% female and 62% male. CMV DNA was observed in 50 specimens (86%) with the range of 1.9 × 10(3) to 11 × 10(7) copies/mL serum. All of these patients had received ganciclovir for >3 months. Sequencing showed 18 mutations in 10 patients. Among these, 16 mutations were associated with Ul97 and the rest with Ul54 gene. Forty CMV-positive patients did not show any mutations.

CONCLUSIONS

The consequences of long-term ganciclovir resistance could not be determined.

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.

Clinical utility of viral load in management of cytomegalovirus infection after solid organ transplantation

The negative impact of cytomegalovirus (CMV) infection on transplant outcomes warrants efforts toward improving its prevention, diagnosis, and treatment. During the last 2 decades, significant breakthroughs in diagnostic virology have facilitated remarkable improvements in CMV disease management. During this period, CMV nucleic acid amplification testing (NAT) evolved to become one of the most commonly performed tests in clinical virology laboratories. NAT provides a means for rapid and sensitive diagnosis of CMV infection in transplant recipients. Viral quantification also introduced several principles of CMV disease management. Specifically, viral load has been utilized (i) for prognostication of CMV disease, (ii) to guide preemptive therapy, (iii) to assess the efficacy of antiviral treatment, (iv) to guide the duration of treatment, and (v) to indicate the risk of clinical relapse or antiviral drug resistance. However, there remain important limitations that require further optimization, including the interassay variability in viral load reporting, which has limited the generation of standardized viral load thresholds for various clinical indications. The recent introduction of an international reference standard should advance the major goal of uniform viral load reporting and interpretation. However, it has also become apparent that other aspects of NAT should be standardized, including sample selection, nucleic acid extraction, amplification, detection, and calibration, among others. This review article synthesizes the vast amount of information on CMV NAT and provides a timely review of the clinical utility of viral load testing in the management of CMV in solid organ transplant recipients. Current limitations are highlighted, and avenues for further research are suggested to optimize the clinical application of NAT in the management of CMV after transplantation.

Strategies for the prevention of infection after solid organ transplantation

Infection is a frequent complication of organ transplantation and is associated with significant morbidity and mortality. Preventative antimicrobial strategies are a key component of the care received by transplant patients. This review summarizes the evidence supporting anti-infective prophylaxis in this setting. Specific recommendations for the prevention of bacterial, fungal, viral and parasitic infection after transplant are made, with a focus on recent developments in the field of transplant infectious diseases.

Prevention and management of cytomegalovirus infection in solid-organ transplantation

Cytomegalovirus (CMV) is the most common opportunistic viral infection to occur following solid-organ transplantation. This review will discuss the current strategies of management of CMV in solid-organ transplantation and their challenges. There are two principal approaches for preventing CMV disease in recipients of solid-organ transplants: prophylactic and pre-emptive. Ganciclovir is the most studied and used antiviral for both treatment and prevention, and is the first-line treatment for CMV infection and CMV disease in transplant recipients. There is no consensus regarding the most appropriate prevention method and the approach to CMV disease prevention differs among transplantation centers owing to the paucity of data comparing the two strategies head-to-head. Currently, the recommended treatment for CMV disease is intravenous ganciclovir.

Phenotypic evaluation of previously uncharacterized cytomegalovirus DNA polymerase sequence variants detected in a valganciclovir treatment trial

BACKGROUND

In a large randomized trial comparing oral valganciclovir and intravenous ganciclovir for treatment of cytomegalovirus disease in solid organ transplantation, confirmed genotypic drug resistance was uncommon (<5%), but definitive interpretation was limited by the detection of 110 uncharacterized UL54 viral DNA polymerase sequence variants.

METHODS

Based on treatment history and genetic locus of the sequence changes, 39 of the sequence variants were prioritized for recombinant phenotyping by construction of cloned viral mutants and drug susceptibility testing in cell culture.

RESULTS

Four amino acid substitutions were newly confirmed to alter ganciclovir susceptibility: A505V and I726T conferred a borderline decrease in ganciclovir and cidofovir susceptibility, while Q578L and G841S conferred slightly decreased ganciclovir and foscarnet susceptibility. A nonviable phenotype was found for 8 mutations distributed among amino terminal, exonuclease and catalytic domains. Retesting of stored study specimens could not confirm the original detection of >20 sequence variants, including the nonviable mutations and several resistance mutations.

CONCLUSIONS

Newly phenotyped UL54 sequence variants did not significantly change the reported incidence of drug resistance in the clinical trial. Unrecognized sequence variants in diagnostic genotyping reports should be confirmed by additional testing in order to improve clinical decision making.

High rate of cytomegalovirus drug resistance among patients receiving preemptive antiviral treatment after haploidentical stem cell transplantation

We examined the rate, clinical impact, and risk factors of cytomegalovirus (CMV) drug resistance in 561 patients who underwent 616 hematopoietic stem cell transplantations (HSCTs) over 5 years. Drug resistance was exclusively identified in haploidentical (haplo)-HSCT recipients receiving preemptive therapy, among whom the rate was 14.5%. Resistance appeared after prolonged treatment (median, 70 days), was associated with higher preceding viral load (P < .001), and was the strongest predictor for disease by multivariate analysis. The high rate of drug resistance as interlinked with severe disease in haplo-HSCT recipients suggests the potential advantage of prophylactic over preemptive treatment in high-risk patients and highlights the need for better-tolerable anti-CMV drugs.

Use of high-dose ganciclovir for the treatment of cytomegalovirus replication in solid organ transplant patients with ganciclovir resistance-inducing mutations

BACKGROUND

Experience with high-dose ganciclovir for the management of resistant cytomegalovirus (CMV) replication in transplant patients is limited despite its adoption as an effective therapy by some consensus documents.

METHODS

We studied six cases of CMV replication in solid organ transplant patients whose genotypic testing showed mutations associated with different levels of resistance to ganciclovir. All were treated with high-dose intravenous ganciclovir (7.5-10 mg/kg/12 hr) or oral valganciclovir (1350-1800 mg/12 hr) corrected according to creatinine clearance. The virologic response was considered positive if the CMV plasma viral load was undetectable. Safety was evaluated by clinical assessment, including the review of vital signs and laboratory tests.

RESULTS

All patients had asymptomatic replication, except one who had digestive disease. Four patients received universal prophylaxis with valganciclovir. Two patients received preemptive therapy with valganciclovir for individual episodes of replication. Two of the six patients received steroid boluses before the episode of replication by resistant CMV. All patients responded to treatment, including those with mutations associated with a high level of ganciclovir resistance. Four patients had neutropenia (<1.5 × 10/L), but only one received treatment.

CONCLUSIONS

High-dose ganciclovir/valganciclovir can be an option in the treatment of resistant CMV replication and could be considered an alternative treatment in nonsevere patients for whom the use of foscarnet should be avoided. The toxicity of this regimen does not appear to limit its use.

Rapid detection and quantitation of ganciclovir resistance in cytomegalovirus quasispecies

Human cytomegalovirus (HCMV) may cause severe or fatal disease among immunocompromised patients. The first line prophylaxis and systemic HCMV disease therapy is ganciclovir (GCV). The presence of GCV-resistant virus has been linked to fatal HCMV disease. The implementation of rapid and sensitive techniques for the early detection and monitoring of GCV-resistance may be helpful to support antiviral therapy management. A pyrosequencing assay for the detection and quantitation of the most frequent mutations conferring moderate- and high-grade GCV resistance was implemented. The pyrosequencing achieved an analytical sensitivity for adequate interpretation of ≥10(3)  copies/ml. The assay was validated with 18 whole blood samples taken over a 6-month period from an umbilical cord blood recipient infected persistently with HCMV and allowed the detection and monitoring of the M460I and A594V GCV-resistant mutations. The percentage of resistant quasispecies ranged from 7.9% to 55.2% for the M460I mutation and from 19.8% to 43% for the A594V mutation. Clearance of the M460I mutation occurred in parallel with a decrease in the HCMV viremia, while the A594V mutation persisted. The pyrosequencing method for detection of GCV is sensitive enough to be used directly on clinical samples for the early identification of resistance mutations and allows the quantitation of resistant and wild type virus quasispecies within hours. The quantitation of minor resistant variants is an important issue to understand their relationship with viral load modification, and potentially anticipate treatment adjustment.

The time course of development and impact from viral resistance against ganciclovir in cytomegalovirus infection

(Val)ganciclovir is used to treat cytomegalovirus (CMV) infection following solid organ (SOT) or hematopoietic stem cell (HSCT) transplantation. Treatment failures occur, but the contribution from 39 known ganciclovir-related mutations (GRMs) in the CMV-UL97 gene remains controversial. We propose a categorization of these GRMs potentially useful when interpreting sequence analyses in clinical settings. The UL97 gene was sequenced from first/recurrent CMV infections among consecutive SOT or HSCT recipients during 2004-2009. GRMs were categorized as: Signature GRM (sGRM) if in vitro ganciclovir IC(50) ratio for mutated versus wild-type virus >2 (n = 24); polymorphic GRM (pGRM) if ratio <2 (n = 15). (Val)ganciclovir treatment failure was defined as persistent viremia for 30 days or switch to foscarnet within this period. Of 99 (49 HSCT and 50 SOT) recipients with one CMV infection episode, 15 (13 HSCT and 2 SOT) experienced a total of 19 recurrent infection episodes. The prevalence of sGRM was 0% at start of first episode, whereas at start of recurrent episodes, prevalence was 37%. Only one sGRM was present at a time in individual patients. Patients with CMV containing an sGRM (vs. wild type)-but not with a pGRM-were at excess risk of treatment failure (odds ratio = 70.6 [95% CI:8.2-609.6]; p < 0.001). sGRMs emerged only following longer termed use of antiherpetic drugs and usually in recurrent CMV infection episodes. Risk of ganciclovir treatment failure was raised if an sGRM was detected.

CMV: Prevention, Diagnosis and Therapy

Cytomegalovirus (CMV) is the most common infection after organ transplantation and has a major impact on morbidity, mortality and graft survival. Optimal prevention, diagnosis and treatment of active CMV infection enhance transplant outcomes, and are the focus of this section. Methods to prevent CMV include universal prophylaxis and preemptive therapy; each has its merits, and will be compared and contrasted. Diagnostics have improved substantially in recent years, both in type and quality, allowing for more accurate and savvy treatment; advances in diagnostics include the development of an international standard, which should allow comparison of results across different methodologies, and assays for cellular immune function against CMV. Therapy primarily involves ganciclovir, now rendered more versatile by data suggesting oral therapy with valganciclovir is not inferior to intravenous therapy with ganciclovir. Treatment of resistant virus remains problematic, but is enhanced by the availability of multiple novel therapeutic agents.

Letermovir Treatment of Human Cytomegalovirus Infection Antiinfective Agent

Novel therapies are urgently needed for the management of cytomegalovirus (CMV) disease in high-risk patients. Currently licensed agents target the viral DNA polymerase, and although they are effective, they are fraught with toxicities to patients. Moreover, emergence of antiviral resistance is an increasing problem, particularly for patients on long-term suppressive therapy. A new agent, letermovir (AIC246), shows great promise for the management of CMV infection. Advantages include its good oral bioavailability, its lack of toxicity, and the apparent absence of drug-drug interactions. Letermovir has a novel mechanism of action, exerting its antiviral effect by interfering with the viral pUL56 gene product and in the process disrupting the viral terminase complex. This agent demonstrates substantial promise as an alternative to more toxic antivirals in patients at high risk for CMV disease, particularly in the transplantation setting.

Herpesvirus infections of the central nervous system in immunocompromised patients

Human herpesviruses may cause infections of the central nervous system during primary infection or following reactivation from a latent state. Especially in immunosuppressed patients the infection can take a life-threatening course, and therefore early diagnosis of herpesvirus-associated neurological diseases should have high priority. Clinical presentation in these patients is usually without typical features, making diagnosis even more challenging. Therefore general broad testing for different herpesviruses in cerebrospinal fluid samples is highly recommended. In addition, determination of the virus DNA level in the cerebrospinal fluid by quantitative assays seems to be of high importance to determine prognosis. Moreover, it might help to differentiate between specific virus-associated disease and unspecific presence of virus in the cerebrospinal fluid, especially in immunocompromised patients. Polymerase chain reaction analysis of cerebrospinal fluid has revolutionized the diagnosis of nervous system viral infections, particularly those caused by human herpesviruses. This review summarizes the role human herpesviruses play in central nervous system infections in immunocompromised patients, with a focus on the clinical manifestation of encephalitis.

Effects on maribavir susceptibility of cytomegalovirus UL97 kinase ATP binding region mutations detected after drug exposure in vitro and in vivo

Resistance to the experimental human cytomegalovirus (CMV) UL97 kinase inhibitor maribavir has been mapped to UL97 mutations at codons 353, 397, 409 and 411, in the kinase ATP-binding region, and to mutations in the UL27 gene. We studied the maribavir susceptibility phenotypes of additional UL97 mutations observed in vitro and in clinical trials, and the effect of simultaneous mutation in both UL97 and UL27. In vitro selection under maribavir identified a new locus of UL97 mutation within the conserved kinase p-loop (L337M), which conferred low grade maribavir resistance (3.5-fold increased EC50) without ganciclovir cross-resistance. During maribavir Phase III CMV prevention clinical trials, three previously unknown UL97 sequence variants were detected in plasma samples after 27-98 days of drug exposure (I324V, S334G and S386L). These variants did not confer any drug resistance despite proximity to mutations that confer maribavir resistance. The UL27 resistance mutation R233S, when added to strains containing UL97 mutations L337M or V353A, doubled their maribavir EC50s. These results expand the range of UL97 maribavir-resistance mutations into another part of the kinase ATP-binding region, but offer no genotypic evidence that development of drug resistance affected the outcomes of Phase III maribavir clinical trials after drug exposure of up to 14 weeks. There is a potential for increased maribavir resistance in UL27-UL97 double mutants.

[Prevention of cytomegalovirus disease in lung transplantation]

Lung transplant recipients, more than other organ transplant recipients, are at particular risk for cytomegalovirus (CMV) infection and disease. CMV prevention avoids the indirect effects of this virus, such as opportunistic fungal infections and obliterative bronchiolitis, the latter being the major limiting factor in the long-term success of lung-transplantation. CMV prevention strategies have significantly reduced CMV disease and CMV-related mortality. Two major strategies are commonly used for CMV prevention: universal prophylaxis and preemptive therapy. In lung transplant recipients, the efficacy and safety of preemptive treatment have not been studied and therefore, cannot be recommended. Universal prophylaxis is the best strategy for preventing CMV disease in lung transplant recipients. There is no consensus on the optimal duration of prophylaxis, but the recently published GESITRA-SEIMC/REIPI 2011 Guidelines for the management of CMV infection in solid-organ transplant patients recommend 6 months posttransplantation. In D+/R- recipients, this period can be prolonged to 12 months if there are difficulties in monitoring at 6 months posttransplantation. The future of prevention will probably depend on immunoguided strategies.

[Treatment of cytomegalovirus disease]

For years, intravenous ganciclovir has been the recommended treatment for cytomegalovirus (CMV) in transplant recipients. Recently, oral valganciclovir has been shown to induce a response to CMV similar to that produced by intravenous ganciclovir and could consequently be an alternative to ganciclovir in patients with non-severe disease. Sequential therapy with ganciclovir followed by valganciclovir, after the onset of clinical improvement, reduces costs and avoids prolonged hospital stays, thus benefitting patients. Optimal treatment duration is guided by clinical response and virological monitoring (polymerase chain reaction or antigenemia) and is maintained until the results are negative. Some groups use secondary prophylaxis in patients with risk factors for recurrence of CMV disease. Reducing the intensity of immunosuppression or complementing antiviral therapy with immunoglobulins can be considered in patients with severe disease or immunodepression. There are no conclusive data on the most effective treatment in ganciclovir-resistant CMV. Therapeutic decisions should be based on genotypic resistance studies, the patient's immune status and disease severity. Treatment consists of foscarnet alone or in combination with ganciclovir in the most severe forms and in high-resistance mutations, or in increasing the dose of ganciclovir in clinical forms or in mild resistance. There are no conclusive data on alternative antiviral drugs or complementary therapy with mTOR inhibitors. Several CMV vaccines are under development and the preclinical results are encouraging.

Valganciclovir to prevent or treat cytomegalovirus disease in organ transplantation

Cytomegalovirus (CMV) is generally considered the most significant pathogen to infect patients following organ transplantation. Significant improvements have been achieved in the management of CMV disease over recent years, especially since the introduction of oral drugs such as oral ganciclovir followed by valganciclovir (VGC), a prodrug of ganciclovir with enhanced bioavailability. Several randomized controlled trials have shown that VGC is an efficacious and convenient oral drug to prevent or treat CMV disease in solid-organ transplant recipients. In this article, we discuss the clinical and pharmacological experience with the use of VGC for the management of CMV in solid-organ transplant recipients. Finally, novel strategies to further reduce the incidence of CMV disease after transplantation are also reviewed.

Recombinant phenotyping of cytomegalovirus UL54 mutations that emerged during cell passages in the presence of either ganciclovir or foscarnet

Selection of human cytomegalovirus variants in the presence of ganciclovir or foscarnet led to 18 DNA polymerase mutations, 14 of which had not been previously studied. Using bacterial artificial chromosome technology, each of these mutations was individually transferred into the genome of a reference strain. Following reconstitution of infectious viral stocks, each mutant was assessed for its drug susceptibility and growth kinetics in cell culture. Computer-assisted three-dimensional (3D) modeling of the polymerase was also used to position each of the mutations in one of four proposed structural domains and to predict their influence on structural stability of the protein. Among the 10 DNA polymerase mutations selected with ganciclovir, 7 (P488R, C539R, L545S, V787L, V812L, P829S, and L862F) were associated with ganciclovir resistance, whereas 2 (F595I and V946L) conferred only foscarnet resistance. Among the eight mutations selected with foscarnet, only two (T552N and S585A) conferred foscarnet resistance, whereas four (N408D, K500N, L802V, and L957F) had an impact on ganciclovir susceptibility. Surprisingly, the combination of mutations, some of which were not associated with resistance for a specific antiviral, resulted in increasing resistance effects. 3D modeling suggested that none of the mutated residues were directly involved in the polymerase catalytic site but rather had an influence on drug susceptibility by modifying the structural flexibility of the protein. Our study significantly adds to the number of DNA polymerase mutations conferring in vitro drug resistance and emphasizes the point that evaluation of individual mutations may not accurately reflect the phenotype conferred by multiple mutations.

First report of successful treatment of multidrug-resistant cytomegalovirus disease with the novel anti-CMV compound AIC246

We report the first case of cytomegalovirus (CMV) disease treated with AIC246, a novel anti-CMV compound which targets the viral terminase complex and remains active against virus resistant to DNA polymerase inhibitors. A lung transplant recipient developed refractory multidrug-resistant CMV disease involving the lungs, gastrointestinal tract and retina. His disease progressed despite treatment with all DNA polymerase inhibitors; multiple agents reported to have activity against CMV in case series, and reduction in his immunosuppressive medications. AIC246 which is in clinical development was obtained for emergency use, and combined with additional reduction in immunosuppression resulted in rapid clinical, virological and radiological resolution of disease. The patient has remained free of CMV disease or viremia off treatment for greater than 3 months. In summary AIC246, while still in development, may be a promising alternative to current therapies.

Recombinant phenotyping of cytomegalovirus sequence variants detected after 200 or 100 days of valganciclovir prophylaxis

BACKGROUND

In a phase III controlled trial IMproved Protection Against Cytomegalovirus in Transplantation (IMPACT) comparing 200 with 100 days of valganciclovir prophylaxis in 318 cytomegalovirus D+/R- kidney transplant recipients, an equal number of patients (n=3 per arm) had known ganciclovir resistance mutations detected during viral breakthrough. In addition, many other viral sequence variants were observed that were of unknown significance for ganciclovir resistance. Recombinant phenotyping was performed to determine whether the previously uncharacterized genotypic changes affected ganciclovir susceptibility, especially in those receiving the longer duration of prophylaxis.

METHODS

Sequences encoding individual amino acid substitutions in the UL97 kinase or UL54 DNA polymerase gene were transferred by recombination into a cloned cytomegalovirus laboratory strain, followed by reporter-based yield reduction phenotypic assay of the resulting virus for ganciclovir susceptibility.

RESULTS

Twenty-six uncharacterized amino acid substitutions were detected, 2 in UL97 and 24 in UL54. All 10 substitutions in the 200-day arm and 9 of 17 substitutions in the 100-day arm (prioritized based on location and conservation) were selected for phenotyping; one substitution was detected in both subsets. Results were generated for nine of ten 200-day and eight of nine 100-day substitutions, with no substitution demonstrating a significant reduction in ganciclovir susceptibility. The two remaining amino acid substitutions, both in UL54, were not evaluated because of poor viral viability.

CONCLUSION

Phenotypic evaluation of previously uncharacterized viral genotypes in the 200-day valganciclovir prophylaxis group showed no evidence of an increased incidence of genotypic ganciclovir resistance when compared with those in the 100-day prophylaxis group.

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.

Antiviral drug resistance: mechanisms and clinical implications

Antiviral drug resistance is an increasing concern in immunocompromised patient populations, where ongoing viral replication and prolonged drug exposure lead to the selection of resistant strains. Rapid diagnosis of resistance can be made by associating characteristic viral mutations with resistance to various drugs as determined by phenotypic assays. Management of drug resistance includes optimization of host factors and drug delivery, selection of alternative therapies based on knowledge of mechanisms of resistance, and the development of new antivirals. This article discusses drug resistance in herpesviruses and hepatitis B.

Strategies for managing cytomegalovirus in transplant recipients

IMPORTANCE OF THE FIELD

Cytomegalovirus (CMV) is the most important pathogen that affects transplant recipients, by directly causing clinical disease and by indirectly reducing patient and allograft survival.

AREAS COVERED IN THIS REVIEW

This review provides a brief overview of the direct and indirect effects of CMV disease and the traditional and newly described factors that increase the risk of disease after transplantation. Newly acquired data in the diagnostics, prevention and treatment of CMV infection are discussed, with emphasis on guidelines for management as recently endorsed by the American Society of Transplantation and the Transplantation Society.

WHAT THE READER WILL GAIN

The reader will gain up-to-date insights into the contemporary management of CMV after solid organ transplantation. Practical aspects of its diagnosis, prevention and treatment are discussed. Emerging concerns of late-onset CMV disease and antiviral resistance are also highlighted to emphasize the need to optimize CMV-prevention strategies.

TAKE HOME MESSAGE

Prevention of CMV disease is an important goal in the management of solid organ transplant recipients. The efficacy of CMV prevention should be measured not only by the significant reduction in CMV incidence but, as importantly, by the improvement in long-term allograft and patient survival.

[Cytomegalovirus effects in solid organ transplantation and the role of antiviral prophylaxis]

Cytomegalovirus (CMV) belongs to β-Herpesviridae family. Morbidity related to this infectious agent remains a serious concern in the context of immunosuppression. Occurence of CMV infection within the first 3 months post-renal transplantation without any antiviral prophylaxis is about 70% of patients. Direct and indirect effects of CMV infection in the setting of organ transplantation are described in this review. A 3 to 6 months course of prophylaxis with valganciclovir is advised concerning high-risk transplant recipients (D+/R-) but recommendation regarding intermediate-risk transplant recipients (CMV-seropositive patients) is still unclear. Recent studies highlight a benefit of long time prophylaxis (until 6 months) in terms of CMV disease occurence among D+/R- patients. News assays that measures IFNγ responses to a variety of CMV epitopes (Quantiferon(®) and Elispot IFNγ) are developped to predict CMV disease onset after discontinuation of antiviral prophylaxis. These assays could contribute to adapt prophylaxis to each recipient.

Antiviral drug resistance: mechanisms and clinical implications

Antiviral drug resistance is an increasing concern in immunocompromised patient populations, where ongoing viral replication and prolonged drug exposure lead to the selection of resistant strains. Rapid diagnosis of resistance can be made by associating characteristic viral mutations with resistance to various drugs as determined by phenotypic assays. Management of drug resistance includes optimization of host factors and drug delivery, selection of alternative therapies based on knowledge of mechanisms of resistance, and the development of new antivirals. This article discusses drug resistance in herpesviruses and hepatitis B.

International consensus guidelines on the management of cytomegalovirus in solid organ transplantation

Cytomegalovirus (CMV) remains one of the most common infections after solid organ transplantation, resulting in significant morbidity, graft loss, and occasional mortality. Management of CMV varies considerably among transplant centers. A panel of experts on CMV and solid organ transplant was convened by The Infectious Diseases Section of The Transplantation Society to develop evidence and expert opinion-based consensus guidelines on CMV management including diagnostics, immunology, prevention, treatment, drug resistance, and pediatric issues.

Amphipathic DNA polymers exhibit antiviral activity against systemic murine Cytomegalovirus infection

Background

Phosphorothioated oligonucleotides (PS-ONs) have a sequence-independent, broad spectrum antiviral activity as amphipathic polymers (APs) and exhibit potent in vitro antiviral activity against a broad spectrum of herpesviruses: HSV-1, HSV-2, HCMV, VZV, EBV, and HHV-6A/B, and in vivo activity in a murine microbiocide model of genital HSV-2 infection. The activity of these agents against animal cytomegalovirus (CMV) infections in vitro and in vivo was therefore investigated.

Results

In vitro, a 40 mer degenerate AP (REP 9) inhibited both murine CMV (MCMV) and guinea pig CMV (GPCMV) with an IC₅₀ of 0.045 μM and 0.16 μM, respectively, and a 40 mer poly C AP (REP 9C) inhibited MCMV with an IC₅₀ of 0.05 μM. Addition of REP 9 to plaque assays during the first two hours of infection inhibited 78% of plaque formation whereas addition of REP 9 after 10 hours of infection did not significantly reduce the number of plaques, indicating that REP 9 antiviral activity against MCMV occurs at early times after infection. In a murine model of CMV infection, systemic treatment for 5 days significantly reduced virus replication in the spleens and livers of infected mice compared to saline-treated control mice. REP 9 and REP 9C were administered intraperitoneally for 5 consecutive days at 10 mg/kg, starting 2 days prior to MCMV infection. Splenomegaly was observed in infected mice treated with REP 9 but not in control mice or in REP 9 treated, uninfected mice, consistent with mild CpG-like activity. When REP 9C (which lacks CpG motifs) was compared to REP 9, it exhibited comparable antiviral activity as REP 9 but was not associated with splenomegaly. This suggests that the direct antiviral activity of APs is the predominant therapeutic mechanism in vivo. Moreover, REP 9C, which is acid stable, was effective when administered orally in combination with known permeation enhancers.

Conclusion

These studies indicate that APs exhibit potent, well tolerated antiviral activity against CMV infection in vivo and represent a new class of broad spectrum anti-herpetic agents.

Kinetics of host immune responses and cytomegalovirus resistance in a liver transplant patient

Among solid organ transplant (SOT) recipients, donor-seropositive/recipient-seronegative (D+/R-) cytomegalovirus (CMV) status is associated with the highest risk of ganciclovir-resistant CMV disease, which has been reported for patients receiving oral ganciclovir but not valganciclovir prophylaxis. We report a case of CMV breakthrough infection in a D+/R- liver transplant patient while he was receiving oral valganciclovir. Forty samples collected over 6 months were analyzed for the CMV viral load, lymphocyte counts, cytokine levels, and lymphocyte differentiation status. Genotypic resistance testing of the viral UL97 gene was performed when the patient failed to respond. CMV viremia occurred on day 50 post-transplant, and 5 samples taken between days 50 and 85 showed the wild-type UL97 genotype. The appearance of deletion 594-595 was observed from day 114 post-transplant. Viral loads declined when foscarnet was commenced and remained below 10,000 copies/mL when the lymphocyte count was greater than 1000/microL (P = 0.02). T cell responses revealed significant expansion of CD8+ terminal effector memory cells. CD4+ cells were largely populations of naïve and central memory cells. Circulating interleukin 10 (IL-10) levels correlated with the viral load (P < 0.0001). Seroconversion occurred on day 230. The CMV viral load in combination with lymphocyte counts and IL-10 may be a predictive marker for the risk of development of resistant CMV disease in D+/R- SOT patients.

Cytomegalovirus resistance in solid organ transplant recipients treated with intravenous ganciclovir or oral valganciclovir

Background

The rate of cytomegalovirus (CMV) mutations conferring ganciclovir resistance was assessed in a trial comparing intravenous ganciclovir and oral valganciclovir for treatment of CMV disease in solid organ transplant (SOT) recipients.

Methods

Viral genes ( UL97 and UL54) conferring ganciclovir resistance were amplified and sequenced from blood samples collected at days 0 (before therapy), 21 (end of induction) and 49 (end of maintenance).

Results

The overall risk of developing a confirmed or probable ganciclovir resistance mutation during treatment was similar for patients treated with ganciclovir (2.3%) and valganciclovir (3.6%; P=0.51). A persistent viral load at day 21 was associated with a significant risk of ganciclovir resistance by day 49 (odds ratio 11.83; P=0.022). In multivariate analyses, presence of a confirmed ganciclovir resistance mutation was independently associated with virological failure (viral load ≥600 copies/ml) at days 21 and 49. One-third (3/9) of patients with confirmed CMV resistance mutations had recurrent CMV disease. The plasma half-life of confirmed ganciclovir-resistant UL97 mutants was significantly longer than that of wild-type strains, polymorphic variants and strains with mutations of unknown significance ( P=0.045). Multiple UL54 mutations of unknown significance were found in clinical strains. Viral kinetic analysis of these latter strains revealed no effect (negative or positive) on in vivo viral fitness.

Conclusions

Treatment with oral valganciclovir or intravenous ganciclovir results in similar and low rates of resistance mutations in SOT recipients. Patients with drug-resistant CMV strains often have virological failure and might have unfavourable clinical outcomes.

Immunocompromised hosts: perspectives in the treatment and prophylaxis of cytomegalovirus disease in solid-organ transplant recipients

Cytomegalovirus (CMV) infection is an important complication of solid-organ transplantation. The availability of potent antiviral therapies has decreased the incidence of CMV disease among solid-organ transplant recipients but has also led to challenges, including ganciclovir resistance, late-onset CMV disease, and uncertainty about the optimal duration of prophylaxis or therapy for CMV disease. Specific therapies and management of CMV resistance will be addressed here. The best approach for CMV disease in solid-organ transplant recipients is prevention, but which strategy--prophylaxis or preemptive therapy--is optimal remains debatable. Ganciclovir and valganciclovir remain the best options for prevention and treatment of CMV disease in solid-organ transplant recipients, but they are costly and associated with toxicity. Foscarnet and cidofovir, indicated for the treatment of patients who fail to respond to ganciclovir, are less attractive alternatives because of renal toxicity. Therefore, new therapeutic agents for CMV and an immunogenic, safe CMV vaccine are critically needed.

Gastrointestinal cytomegalovirus disease in the immunocompromised patient

Cytomegalovirus (CMV) has emerged as a significant opportunistic pathogen in the era of immunosuppression. CMV was a common cause of gastrointestinal disease in AIDS patients, but the introduction of highly active antiretroviral therapy has led to a dramatic decline in AIDS-related disease. Among patients with solid organ transplants, CMV has become an increasingly important cause of gastrointestinal disease as more routine use of early CMV prophylaxis has increased delayed-onset disease, which is often tissue invasive at presentation. The role of CMV in inflammatory bowel disease is controversial; treatment may be indicated in selected cases of steroid-refractory disease with evidence of CMV. Diagnosis of gastrointestinal CMV disease generally requires endoscopic biopsy with histologic confirmation. CMV culture of biopsy material may be falsely positive because of contamination from latently infected cells. The standard induction treatment of gastrointestinal CMV disease uses intravenous ganciclovir, though the use of oral valganciclovir is increasing, especially for long-term maintenance or suppression therapy.