Oral maribavir for treatment of refractory or resistant cytomegalovirus infections in transplant recipients

Cytomegalovirus Treatment in Solid Organ Transplantation: An Update on Current Approaches

OBJECTIVE

The article reviews the safety and efficacy of treatments for cytomegalovirus (CMV) in solid organ transplantation.

DATA SOURCES

A literature review was conducted in PubMed, MEDLINE, and Clinicaltrials.gov from database inception through January 2024, using terms CMV, therapy, and solid organ transplantation.

STUDY SELECTION AND DATA EXTRACTION

Clinical trials, meta-analyses, cohort studies, case reports, and guidelines were included. Letters to the editor, reviews, and commentaries were excluded.

DATA SYNTHESIS

After abstract screening and full-text review of 728 citations for eligibility, 53 were included. Valganciclovir and intravenous ganciclovir are drugs of choice for CMV management and, until recently, the availability of alternative options has been restricted due to toxicity. For instance, foscarnet and cidofovir serve as second-line agents due to potential bone marrow and renal toxicity. In patients with refractory or resistant CMV, maribavir, a novel oral agent, has proven efficacy and a lower adverse effect profile. However, in refractory or resistant CMV, foscarnet and cidofovir are preferred in invasive disease (CMV gastritis, CMV retinitis, and CMV encephalitis), high viral loads, and inability to tolerate oral preparations.

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

Consensus guidelines have not been revised since approval of novel antivirals in solid organ transplantation. Valganciclovir and ganciclovir remain drugs of choice for initial CMV therapy. Foscarnet, cidofovir, and maribavir are treatments for refractory or resistant-CMV.

CONCLUSIONS

Selection of CMV antiviral treatment should be determined by patient-specific factors, including severity of illness, resistant or refractory disease, dose-limiting adverse effects, and the preferred route of administration.

The emergence of letermovir and maribavir drug-resistant mutations: from clinical trials to real-world studies

PURPOSE OF REVIEW

Cytomegalovirus (CMV) infection is associated with severe clinical disease and high morbidity in immunocompromised hosts. Letermovir and maribavir, are two recently developed antiviral drugs used in the prevention and treatment of resistant and refractory CMV. Following the publication of landmark randomized trials and increased use, both clinical trial data and real-world experience has reported the development of antiviral drug resistance. The aim of this review was to comprehensively review the published literature on letermovir and maribavir drug resistance and to describe the clinical scenarios in which they may emerge.

RECENT FINDINGS

For letermovir, the most frequently detected resistance mutations occur in the UL56 gene (C325Y/W/F) and confer total resistance. Maribavir resistance mutations most often occur in the UL97 gene and resistance-associated variants (RAVs) T409M, H411Y, C480F have all been detected. The clinical context in which letermovir and maribavir resistance occurs include high viral loads at initiation, intensified immunosuppression, subtherapeutic drug exposure because of poor adherence, drug interactions, and inadequate central nervous system (CNS) penetration. Emergence of resistance mutations generally occurs within the first 3 months of initiation.

SUMMARY

The detection of letermovir and maribavir resistance mutations highlights an ongoing clinical challenge in the management of CMV.

Advances in pharmacotherapies for cytomegalovirus infection: what is the current state of play?

INTRODUCTION

Cytomegalovirus (CMV) remains a serious opportunistic infection in hematopoietic cell transplant (HCT) and solid-organ transplant (SOT) recipients. Traditional anti-CMV drugs are limited by toxicities and the development of resistance. Letermovir and maribavir are newly approved antivirals for the prevention and treatment of CMV.

AREAS COVERED

Prior reviews have discussed use of letermovir for prevention of CMV after HCT and maribavir for resistant or refractory (R/R) CMV post HCT or SOT. Subsequent data have expanded their use including letermovir for primary CMV prophylaxis in high-risk renal transplant recipients and new recommendations for extending prophylaxis through day + 200 in certain HCT patients. Data on the use of maribavir for first asymptomatic CMV infection post-HCT has also been published. This review compares the pharmacology of anti-CMV agents and discusses the updated literature of these new drugs in the prevention and treatment of CMV.

EXPERT OPINION

Letermovir and maribavir are much needed tools that spare toxicities of ganciclovir, foscarnet, and cidofovir. High cost is a challenge preventing their integration into clinical practice in resource-limited countries. Transplant centers need to exercise restraint in overuse to avoid resistance, particularly in the setting of high viral loads.

New Treatment Options for Refractory/Resistant CMV Infection

Despite advances in monitoring and treatment, cytomegalovirus (CMV) infections remain one of the most common complications after solid organ transplantation (SOT). CMV infection may fail to respond to standard first- and second-line antiviral therapies with or without the presence of antiviral resistance to these therapies. This failure to respond after 14 days of appropriate treatment is referred to as "resistant/refractory CMV." Limited data on refractory CMV without antiviral resistance are available. Reported rates of resistant CMV are up to 18% in SOT recipients treated for CMV. Therapeutic options for treating these infections are limited due to the toxicity of the agent used or transplant-related complications. This is often the challenge with conventional agents such as ganciclovir, foscarnet and cidofovir. Recent introduction of new CMV agents including maribavir and letermovir as well as the use of adoptive T cell therapy may improve the outcome of these difficult-to-treat infections in SOT recipients. In this expert review, we focus on new treatment options for resistant/refractory CMV infection and disease in SOT recipients, with an emphasis on maribavir, letermovir, and adoptive T cell therapy.

Oral antiviral drugs for treatment of cytomegalovirus in transplant recipients

BACKGROUND

Cytomegalovirus (CMV) is an opportunistic pathogen responsible for substantial morbidity after solid organ transplantation and haematopoietic stem cell transplantation. Treatment of CMV disease involves a two-pronged approach with antiviral drug treatment coupled with strategies to minimize the intensity of immune suppression.

OBJECTIVES

This narrative review examines the evidence for the current treatment of CMV disease in transplant recipients, including the use of oral antiviral drugs.

SOURCES

Literature search was performed on PubMed with keywords cytomegalovirus, transplantation, ganciclovir, valganciclovir, maribavir, letermovir, cidofovir, and foscarnet.

CONTENT

Intravenous and oral valganciclovir are the standard first-line treatment of cytomegalovirus disease after transplantation. Oral maribavir has demonstrated superior efficacy and safety over CMV DNA polymerase inhibitors for the treatment of refractory or resistant CMV infection. Transplant patients with severe and life-threatening CMV disease, those with very high viral load, and patients with impaired gastrointestinal absorption should still be treated initially with intravenous antiviral drugs, including ganciclovir and foscarnet. Criteria for the safe transition from intravenous therapies to oral antiviral drugs include achieving clinical improvement and satisfactory decline in viral load. Recurrence of CMV viremia and disease is common, particularly among transplant patients who are lymphopenic and have impaired CMV-specific immunity.

IMPLICATIONS

Oral antiviral drugs for the treatment of CMV infection and disease in transplant recipients have improved the CMV landscape, because they reduce the cost and mitigate the inconvenience and risks related to prolonged hospitalization and the need for long-term intravascular access. However, their antiviral efficacy should be complemented by an intentional strategy of reducing the degree of immune suppression to allow for immunologic recovery that ensures durable control of CMV infection.

Maribavir

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Cytomegalovirus in children undergoing haematopoietic stem cell transplantation: a diagnostic and therapeutic approach to antiviral resistance

Cytomegalovirus (CMV) is a ubiquitous virus which causes a mild illness in healthy individuals. In immunocompromised individuals, such as children receiving haematopoietic stem cell transplantation, CMV can reactivate, causing serious disease and increasing the risk of death. CMV can be effectively treated with antiviral drugs, but antiviral resistance is an increasingly common complication. Available therapies are associated with adverse effects such as bone marrow suppression and renal impairment, making the choice of appropriate treatment challenging. New agents are emerging and require evaluation in children to establish their role. This review will discuss established and emerging diagnostic tools and treatment options for CMV, including antiviral resistant CMV, in children undergoing haematopoietic stem cell transplant.

N-substitution Reactions of 2-Aminobenzimidazoles to Access Pharmacophores

Benzimidazole (BI) and its derivatives are interesting molecules in medicinal chemistry because several of these compounds have a diversity of biological activities and some of them are even used in clinical applications. In view of the importance of these compounds, synthetic chemists are still interested in finding new procedures for the synthesis of these classes of compounds. Astemizole (antihistaminic), Omeprazole (antiulcerative), and Rabendazole (fungicide) are important examples of compounds used in medicinal chemistry containing BI nuclei. It is interesting to observe that several of these compounds contain 2-aminobenzimidazole (2ABI) as the base nucleus. The structures of 2ABI derivatives are interesting because they have a planar delocalized structure with a cyclic guanidine group, which have three nitrogen atoms with free lone pairs and labile hydrogen atoms. The 10-π electron system of the aromatic BI ring conjugated with the nitrogen lone pair of the hexocyclic amino group, making these heterocycles to have an amphoteric character. Synthetic chemists have used 2ABI as a building block to produce BI derivatives as medicinally important molecules. In view of the importance of the BIs, and because no review was found in the literature about this topic, we reviewed and summarized the procedures related to the recent methodologies used in the N-substitution reactions of 2ABIs by using aliphatic and aromatic halogenides, dihalogenides, acid chlorides, alkylsulfonic chlorides, carboxylic acids, esters, ethyl chloroformates, anhydrides, SMe-isothioureas, alcohols, alkyl cyanates, thiocyanates, carbon disulfide and aldehydes or ketones to form Schiff bases. The use of diazotized 2ABI as intermediate to obtain 2-diazoBIs was included to produce Nsubstituted 2ABIs of pharmacological interest. Some commentaries about their biological activity were included.

New Perspectives on Antimicrobial Agents: Maribavir

Maribavir was approved by the U.S. Food and Drug Administration in November 2021 for the treatment of adult and pediatric patients with post-transplant cytomegalovirus (CMV) infection/disease that is refractory to treatment (with or without genotypic resistance) with ganciclovir, valganciclovir, cidofovir, or foscarnet. Maribavir is an oral benzimidazole riboside with potent and selective multimodal anti-CMV activity. It utilizes a novel mechanism of action which confers activity against CMV strains that are resistant to traditional anti-CMV agents, and also offers a more favorable safety profile relative to the dose-limiting side effects of previously available therapies. Maribavir was initially studied as an agent for CMV prophylaxis in solid organ and hematopoietic stem cell recipients, but initial phase III trials failed to meet clinical efficacy endpoints. It has been more recently studied as a therapeutic agent at higher doses for refractory-resistant (R-R) CMV infections with favorable outcomes. After an overview of maribavir's chemistry and clinical pharmacology, this review will summarize clinical efficacy, safety, tolerability, and resistance data associated with maribavir therapy.

Maribavir for the Management of Cytomegalovirus in Adult Transplant Recipients: A Review of the Literature and Practical Considerations

OBJECTIVE

To review the efficacy and safety of maribavir for management of cytomegalovirus (CMV) in solid organ transplant recipients.

DATA SOURCES

A literature search of PubMed and the Cochrane Controlled Trials Register (1960 to early July 2022) was performed using the following search terms: maribavir, 1263W94, and cytomegalovirus.

STUDY SELECTION AND DATA EXTRACTION

All relevant English-language studies were reviewed and considered, with a focus on phase 3 trials.

DATA SYNTHESIS

Maribavir, an orally available benzimidazole riboside with minimal adverse effects, was originally studied for universal prophylaxis in phase 3 trials but failed to demonstrate noninferiority over placebo and oral ganciclovir. It was effective for preemptive treatment in a dose-finding Phase 2 study. Maribavir is FDA approved for treatment of refractory/resistant CMV infection based on improved response rate at 8 weeks compared with investigator-assigned therapy (IAT) when initiated at median viral loads less than approximately 10 000 IU/mL (55.7% vs 23.9%, P < 0.001). Recurrence after 8-week treatment for refractory/resistant CMV was high (maribavir 50% vs IAT 39%). Significant drug interactions exist and must be managed by a pharmacotherapy expert to prevent harm.

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

The addition of maribavir to the antiviral armamentarium should improve the management of refractory/resistant CMV, allowing early transition from toxic, high-cost, intravenous agents such as foscarnet and outpatient management. Optimal timing of initiation, duration, and potential alternative uses are unclear.

CONCLUSION

Future studies are needed to fully elucidate the role of maribavir in the management of CMV after transplant.

Evaluating the Safety of Maribavir for the Treatment of Cytomegalovirus

Purpose of Review

Cytomegalovirus (CMV) infections are a common complication in solid organ (SOT) and hematopoietic stem cell transplant (HSCT) recipients, leading to increased morbidity and mortality. Currently available treatment options have reduced the burden of infection, but utilization of these agents can be limited by toxicities such as nephrotoxicity and/or myelosuppression as well as emergence of resistance. The expansion of our current armamentarium towards CMV infection is crucial. Here, we review an emerging therapy, maribavir, and the safety and efficacy of this potential new agent for the prophylaxis and treatment of CMV infections including resistant/refractory disease.

Recent Findings

Maribavir is a novel agent with CMV activity approved by Federal Food and Drug Administration (FDA) in December 2021 for resistant/refractory disease. Compared to currently available treatment for CMV infection, maribavir has a unique mechanism of action, retains activity against most (val)ganciclovir resistant strains, provides a more predictable pharmacokinetic profile, and fewer severe toxicities. Maribavir has been studied in phase 2 and 3 studies with ongoing phase 3 studies. While maribavir failed to meet the primary endpoints in the initial phase 3 study for prophylaxis therapy in allogeneic-HSCT and liver transplant recipients, results from the phase 2 study when used for pre-emptive therapy after HSCT show similar efficacy to valganciclovir, and results from the phase 3 study examining resistant/refractory disease demonstrate superiority to investigator-initiated therapy of (val)ganciclovir, foscarnet, or cidofovir.

Summary

Maribavir provides a new agent for the management of resistant/refractory CMV infection. Results of the recently published phase 3 study provide further insight into the role of this novel therapy.

Viral Enteritis in Solid-Organ Transplantation

Solid organ transplant recipients are at increased risk for infections due to chronic immunosuppression. Diarrhea is a commonly encountered problem post transplantation, with infectious causes of diarrhea being a frequent complication. Viral infections/enteritides in solid organ transplant recipients often result from frequently encountered pathogens in this population such as cytomegalovirus, adenovirus, and norovirus. However, several emerging viral pathogens are increasingly being recognized as more sensitive diagnostic techniques become available. Treatment is often limited to supportive care and reduction in immunosuppression, though antiviral therapies mayplay a role in the treatment in certain diseases. Viral enteritis is an important entity that contributes to morbidity and mortality in transplant recipients.

Human cytomegalovirus infection: A considerable issue following allogeneic hematopoietic stem cell transplantation

Cytomegalovirus (CMV) is an opportunistic virus, whereby recipients are most susceptible following allogeneic hematopoietic stem cell transplantation (allo-HSCT). With the development of novel immunosuppressive agents and antiviral drugs, accompanied with the widespread application of prophylaxis and preemptive treatment, significant developments have been made in transplant recipients with human (H)CMV infection. However, HCMV remains an important cause of short- and long-term morbidity and mortality in transplant recipients. The present review summarizes the molecular mechanism and risk factors of HCMV reactivation following allo-HSCT, the diagnosis of CMV infection following allo-HSCT, prophylaxis and treatment of HCMV infection, and future perspectives. All relevant literature were retrieved from PubMed and have been reviewed.

Resistant or refractory cytomegalovirus infections after hematopoietic cell transplantation: diagnosis and management

PURPOSE OF REVIEW

Refractory or resistant cytomegalovirus (CMV) infections are challenging complications after hematopoietic cell transplantation (HCT). Most refractory or resistant CMV infections are associated with poor outcomes and increased mortality. Prompt recognition of resistant or refractory CMV infections, understanding the resistance pathways, and the treatment options in HCT recipients are imperative.

RECENT FINDINGS

New definitions for refractory and resistant CMV infections in HCT recipients have been introduced for future clinical trials. Interestingly, refractory CMV infections are more commonly encountered in HCT recipients when compared with resistant CMV infections. CMV terminase complex mutations in UL56, UL89, and UL51 could be associated with letermovir resistance; specific mutations in UL56 are the most commonly encountered in clinical practice. Finally, brincidofovir, maribavir, letermovir, and CMV-specific cytotoxic T-cell therapy expanded our treatment options for refractory or resistant CMV infections.

SUMMARY

Many advances have been made to optimize future clinical trials for management of refractory or resistant CMV infections, and to better understand new resistance mechanisms to novel drugs. New drugs or strategies with limited toxicities are needed to improve outcomes of difficult to treat CMV infections in HCT recipients.

Maribavir for Refractory or Resistant Cytomegalovirus Infections in Hematopoietic-cell or Solid-organ Transplant Recipients: A Randomized, Dose-ranging, Double-blind, Phase 2 Study

Background

Cytomegalovirus (CMV) infections that are refractory or resistant (RR) to available antivirals ([val]ganciclovir, foscarnet, cidofovir) are associated with higher mortality in transplant patients. Maribavir is active against RR CMV strains.

Methods

Hematopoietic-cell or solid-organ transplant recipients ≥12 years old with RR CMV infections and plasma CMV deoxyribonucleic acid (DNA) ≥1000 copies/mL were randomized (1:1:1) to twice-daily dose-blinded maribavir 400, 800, or 1200 mg for up to 24 weeks. The primary efficacy endpoint was the proportion of patients with confirmed undetectable plasma CMV DNA within 6 weeks of treatment. Safety analyses included the frequency and severity of treatment-emergent adverse events (TEAEs).

Results

From July 2012 to December 2014, 120 patients were randomized and treated (40 per dose group): 80/120 (67%) patients achieved undetectable CMV DNA within 6 weeks of treatment (95% confidence interval, 57–75%), with rates of 70%, 63%, and 68%, respectively, for maribavir 400, 800, and 1200 mg twice daily. Recurrent on-treatment CMV infections occurred in 25 patients; 13 developed mutations conferring maribavir resistance. Maribavir was discontinued due to adverse events in 41/120 (34%) patients, and 17/41 discontinued due to CMV infections. During the study, 32 (27%) patients died, 4 due to CMV disease. Dysgeusia was the most common TEAE (78/120; 65%) and led to maribavir discontinuation in 1 patient. Absolute neutrophil counts <1000/µL were noted in 12/106 (11%) evaluable patients, with rates similar across doses.

Conclusions

Maribavir ≥400 mg twice daily was active against RR CMV infections in transplant recipients; no new safety signals were identified.

Clinical Trials Registration

NCT01611974.

Moving Past Ganciclovir and Foscarnet: Advances in CMV Therapy

PURPOSE OF REVIEW

CMV DNA polymerase inhibitors such as ganciclovir and foscarnet have dramatically reduced the burden of CMV infection in the HCT recipient. However, their use is often limited by toxicities and resistance. Agents with novel mechanisms and favorable toxicity profiles are critically needed. We review recent developments in CMV antivirals and immune-based approaches to mitigating CMV infection.

RECENT FINDINGS

Letermovir, an inhibitor of the CMV terminase complex, was approved in 2017 for primary CMV prophylaxis in adult seropositive allogeneic HCT recipients. Maribavir, an inhibitor of the CMV UL97 kinase, is currently in two phase 3 treatment studies. Adoptive immunotherapy using third-party T cells has proven safe and effective in preliminary studies. Vaccine development continues, with several promising candidates currently under study. No longer limited to DNA polymerase inhibitors, the prevention and treatment of CMV infections in the HCT recipient is a rapidly evolving field which should translate into improvements in CMV-related outcomes.

Antiviral combination therapy for cytomegalovirus infection in high-risk infants

BACKGROUND

Cytomegalovirus (CMV) infection is a major risk factor for mortality in infants with severe combined immunodeficiency (SCID) and other profound immune defects. Specific antiviral therapy must be initiated early and aggressively because of the potential for antiviral resistance, rapid dissemination and poor transplant outcomes. Combination antiviral therapy is routinely administered for some viral infections, but the value of this approach for the treatment of CMV is unclear. Here we explore a strategy of initial combination therapy for high-risk infants with CMV infection.

METHODS

We reviewed medical records of infants ≤6 months of age hospitalized between 2007-2015 who received ganciclovir (GCV) or foscarnet (FOS) monotherapy or initial combination GCV + FOS for CMV disease. The combination therapy group consisted of severely immunocompromised infants being considered for haematopoietic cell transplantation (HCT).

RESULTS

Four patients received initial combination antiviral therapy and 26 patients received initial monotherapy during the study period. Combination antiviral recipients demonstrated initial improvement in viraemia and two of three who continued with this therapy survived the infection. Clinically significant resistance mutations did not emerge. Toxicity was common; neutropenia, thrombocytopenia and electrolyte abnormalities were the most frequent adverse events in both groups. Creatinine elevation was uncommon in both groups.

CONCLUSIONS

Combination GCV + FOS therapy may be a safe alternative to monotherapy in high-risk infants, especially those who are pre-transplant with primary immune deficiency syndromes and high viral loads.

Maribavir for Preemptive Treatment of Cytomegalovirus Reactivation

BACKGROUND

Maribavir is a benzimidazole riboside with activity against cytomegalovirus (CMV). The safety and efficacy of maribavir for preemptive treatment of CMV infection in transplant recipients is not known.

METHODS

In a phase 2, open-label, maribavir dose-blinded trial, recipients of hematopoietic-cell or solid-organ transplants (≥18 years of age, with CMV reactivation [1000 to 100,000 DNA copies per milliliter]) were randomly assigned to receive maribavir at a dose of 400, 800, or 1200 mg twice daily or the standard dose of valganciclovir for no more than 12 weeks. The primary efficacy end point was the percentage of patients with a response to treatment, defined as confirmed undetectable CMV DNA in plasma, within 3 weeks and 6 weeks after the start of treatment. The primary safety end point was the incidence of adverse events that occurred or worsened during treatment.

RESULTS

Of the 161 patients who underwent randomization, 159 received treatment, and 156 had postbaseline data available - 117 in the maribavir group and 39 in the valganciclovir group. The percentage of patients with postbaseline data available who had a response to treatment within 3 weeks was 62% among those who received maribavir and 56% among those who received valganciclovir. Within 6 weeks, 79% and 67% of patients, respectively, had a response (risk ratio, 1.20; 95% confidence interval, 0.95 to 1.51). The percentages of patients with a response to treatment were similar among the maribavir dose groups. Two patients who had a response to treatment had a recurrence of CMV infection within 6 weeks after starting maribavir at a dose of 800 mg twice daily; T409M resistance mutations in CMV UL97 protein kinase developed in both patients. The incidence of serious adverse events that occurred or worsened during treatment was higher in the maribavir group than in the valganciclovir group (52 of 119 patients [44%] vs. 13 of 40 [32%]). A greater percentage of patients in the maribavir group discontinued the trial medication because of an adverse event (27 of 119 [23%] vs. 5 of 40 [12%]). A higher incidence of gastrointestinal adverse events was reported with maribavir, and a higher incidence of neutropenia was reported with valganciclovir.

CONCLUSIONS

Maribavir at a dose of at least 400 mg twice daily had efficacy similar to that of valganciclovir for clearing CMV viremia among recipients of hematopoietic-cell or solid-organ transplants. A higher incidence of gastrointestinal adverse events - notably dysgeusia - and a lower incidence of neutropenia were found in the maribavir group. (Funded by ViroPharma/Shire Development; EudraCT number, 2010-024247-32.).

Safety considerations with current and emerging antiviral therapies for cytomegalovirus infection in transplantation

Introduction: Human cytomegalovirus (HCMV) is a major contributor of morbidity and mortality, and its management is essential for the successful outcome of solid organ and hematopoietic stem cell transplantation. Areas covered: This review discusses the safety profiles of currently available and emerging antiviral drugs and the other strategies for HCMV prevention and treatment after transplantation. Expert opinion: Strategies for management of HCMV rely largely on the use of antiviral agents that inhibit viral DNA polymerase (ganciclovir/valganciclovir, foscarnet, and cidofovir/brincidofovir) and viral terminase complex (letermovir), with different types and degrees of adverse effects. An investigational agent, maribavir, exerts its anti-CMV effect through UL97 inhibition, and its safety profile is under clinical evaluation. In choosing the antiviral medication to use, it is important to consider these safety profiles in addition to overall efficacy. In addition to antiviral drugs, reduction of immunosuppression is often generally needed in the management of HCMV infection, but with a potential risk of allograft rejection or graft-versus-host disease. The use of HCMV-specific or non-specific intravenous immunoglobulins remains debated, while adoptive HCMV-specific T cell therapy remains investigational, and associated with unique set of adverse effects.

New Developments in the Management of Cytomegalovirus Infection After Transplantation

Cytomegalovirus (CMV) continues to be one of the most important pathogens that universally affect solid organ and allogeneic hematopoietic stem cell transplant recipients. Lack of effective CMV-specific immunity is the common factor that predisposes to the risk of CMV reactivation and clinical disease after transplantation. Antiviral drugs are the cornerstone for prevention and treatment of CMV infection and disease. Over the years, the CMV DNA polymerase inhibitor, ganciclovir (and valganciclovir), have served as the backbone for management, while foscarnet and cidofovir are reserved for the management of CMV infection that is refractory or resistant to ganciclovir treatment. In this review, we highlight the role of the newly approved drug, letermovir, a viral terminase inhibitor, for CMV prevention after allogeneic hematopoietic stem cell transplantation. Advances in immunologic monitoring may allow for an individualized approach to management of CMV after transplantation. Specifically, the potential role of CMV-specific T-cell measurements in guiding the need for the treatment of asymptomatic CMV infection and the duration of treatment of CMV disease is discussed. The role of adoptive immunotherapy, using ex vivo-generated CMV-specific T cells, is highlighted. This article provides a review of novel drugs, tests, and strategies in optimizing our current approaches to prevention and treatment of CMV in transplant recipients.

Cytomegalovirus in solid organ transplant recipients-Guidelines of the American Society of Transplantation Infectious Diseases Community of Practice

Cytomegalovirus (CMV) is one of the most common opportunistic infections that affect the outcome of solid organ transplantation. This updated guideline from the American Society of Transplantation Infectious Diseases Community of Practice provides evidence-based and expert recommendations for screening, diagnosis, prevention, and treatment of CMV in solid organ transplant recipients. CMV serology to detect immunoglobulin G remains as the standard method for pretransplant screening of donors and transplant candidates. Antiviral prophylaxis and preemptive therapy are the mainstays of CMV prevention. The lack of a widely applicable viral load threshold for diagnosis and preemptive therapy is highlighted, as a result of variability of CMV nucleic acid testing, even in the contemporary era when calibrators are standardized. Valganciclovir and intravenous ganciclovir remain as drugs of choice for CMV management. Strategies for managing drug-resistant CMV infection are presented. There is an increasing use of CMV-specific cell-mediated immune assays to stratify the risk of CMV infection after solid organ transplantation, but their role in optimizing CMV prevention and treatment efforts has yet to be demonstrated. Specific issues related to pediatric transplant recipients are discussed.

Overview of Infections Complicating Pediatric Hematopoietic Cell Transplantation

Hematopoietic cell transplantations (HCT) are increasingly being performed in children for the treatment of malignant and nonmalignant diseases. Infections remain an important cause of morbidity and mortality after HCT, where the type and timing of infection is influenced by host, transplant, and pathogen-related factors. Herein, an overview of the epidemiology of infections is presented and organized by timing before and after HCT, understanding that infection may occur at any time point until there is successful immune reconstitution.

The Third International Consensus Guidelines on the Management of Cytomegalovirus in Solid-organ Transplantation

Despite recent advances, cytomegalovirus (CMV) infections remain one of the most common complications affecting solid organ transplant recipients, conveying higher risks of complications, graft loss, morbidity, and mortality. Research in the field and development of prior consensus guidelines supported by The Transplantation Society has allowed a more standardized approach to CMV management. An international multidisciplinary panel of experts was convened to expand and revise evidence and expert opinion-based consensus guidelines on CMV management including prevention, treatment, diagnostics, immunology, drug resistance, and pediatric issues. Highlights include advances in molecular and immunologic diagnostics, improved understanding of diagnostic thresholds, optimized methods of prevention, advances in the use of novel antiviral therapies and certain immunosuppressive agents, and more savvy approaches to treatment resistant/refractory disease. The following report summarizes the updated recommendations.

Clinical development of letermovir and maribavir: Overview of human cytomegalovirus drug resistance

The prevention and treatment of human cytomegalovirus (HCMV) infections is based on the use of antiviral agents that currently target the viral DNA polymerase and that may cause serious side effects. The search for novel inhibitors against HCMV infection led to the discovery of new molecular targets, the viral terminase complex and the viral pUL97 kinase. The most advanced compounds consist of letermovir (LMV) and maribavir (MBV). LMV inhibits the cleavage of viral DNA and its packaging into capsids by targeting the HCMV terminase complex. LMV is safe and well tolerated and exhibits pharmacokinetic properties that allow once daily dosing. LMV showed efficacy in a phase III prophylaxis study in hematopoietic stem cell transplant (HSCT) recipients seropositive for HCMV. LMV was recently approved under the trade name Prevymis^™ for prophylaxis of HCMV infection in adult seropositive recipients of an allogeneic HSCT. Amino acid substitutions conferring resistance to LMV selected in vitro map primarily to the pUL56 and rarely to the pUL89 and pUL51 subunits of the HCMV terminase complex. MBV is an inhibitor of the viral pUL97 kinase activity and interferes with the morphogenesis and nuclear egress of nascent viral particles. MBV is safe and well tolerated and has an excellent oral bioavailability. MBV was effective for the treatment of HCMV infections (including those that are refractory or drug-resistant) in transplant recipients in two phase II studies and is further evaluated in two phase III trials. Mutations conferring resistance to MBV map to the UL97 gene and can cause cross-resistance to ganciclovir. MBV-resistant mutations also emerged in the UL27 gene in vitro and could compensate for the inhibition of pUL97 kinase activity by MBV. Thus, LMV and probably MBV will broaden the armamentarium of antiviral drugs available for the prevention and treatment of HCMV infections.

Infection in Kidney Transplant Recipients

In organ transplant recipients, impaired inflammatory responses suppress the clinical and radiologic findings of infection. The possible etiologies of infection are diverse, ranging from common bacterial and viral pathogens that affect the entire community to opportunistic pathogens that cause invasive disease only in immunocompromised hosts. Antimicrobial therapies required to treat established infection are often complex, with accompanying risks for drug toxicities and drug interactions with the immunosuppressive agents used to maintain graft function. Rapid and specific diagnosis is essential for successful therapy. The risk of serious infections in the organ transplant patient is largely determined by the interaction between two factors: the patient’s epidemiologic exposures and the patient’s net state of immunosuppression. The epidemiology of infection includes environmental exposures and nosocomial infections, organisms derived from donor tissues, and latent infections from the recipient activated with immunosuppression. The net state of immune suppression is a conceptual framework that measures those factors contributing to risk for infection: the dose, duration, and temporal sequence of immunosuppressive drugs; the presence of foreign bodies or injuries to mucocutaneous barriers; neutropenia; metabolic abnormalities including diabetes; devitalized tissues, hematomas, or effusions postsurgery; and infection with immunomodulating viruses. Multiple factors are present in each host. A timeline exists to aid in the development of a differential diagnosis for infection. The timeline for each patient is altered by changes in prophylaxis and immunosuppressive drugs. For common infections, new microbiologic assays, often nucleic acid based, are useful in the diagnosis and management of opportunistic infections.

Treatment and Prevention of CMV Disease in Transplant Recipients: Current Knowledge and Future Perspectives

This review summarizes the significant impact of cytomegalovirus (CMV) infection on solid organ and hematopoietic stem cell transplant recipients. A discussion of the various CMV prevention and treatment strategies is provided, including a detailed description of each of the available CMV antiviral drugs.

Pediatric transplantation case conference: Update on cytomegalovirus

The prevention and management of cytomegalovirus (CMV) remain challenging in children who have undergone solid organ transplantation, despite the availability of effective antiviral medications and sensitive diagnostic assays. The primary objective of this invited commentary is to provide an updated and multidisciplinary approach to persistently challenging CMV cases that commonly occur in pediatric transplantation candidates and recipients, including cases for which published data are frequently lacking.

Antiviral activity of maribavir in combination with other drugs active against human cytomegalovirus

The human cytomegalovirus (CMV) UL97 kinase inhibitor maribavir is in Phase III clinical trials as antiviral therapy, including use for infections refractory or resistant to standard therapy. To assess its activity in combination with approved and experimental CMV antivirals, and with the mTor inhibitor rapamycin (sirolimus), drug effects were tested by in vitro checkerboard assays and the data were analyzed using a three dimensional model based on an independent effects definition of additive interactions. Baseline virus and representative drug-resistant mutants were tested. According to the volume of synergy at 95% confidence, maribavir showed additive interactions with foscarnet, cidofovir, letermovir and GW275175X when tested against wild type and mutant viruses, strong antagonism with ganciclovir, and strong synergy with rapamycin, the latter suggesting a potentially useful therapeutic combination.

In vitro evaluation of current and novel antivirals in combination against human cytomegalovirus

Human cytomegalovirus (HCMV) can cause severe disease in patients with compromised or immature immune systems. Currently approved pharmacotherapies for the treatment of systemic HCMV infections [ganciclovir (GCV), cidofovir (CDV), foscarnet] are limited by a high incidence of adverse effects and/or the development of drug resistance. Given that many of these drugs have the same viral target (HCMV-encoded DNA polymerase), cross-resistance is relatively common. The primary means to combat drug resistance is combination pharmacotherapy using therapeutics with different molecular mechanisms of action with the expectation that those combinations result in an additive or synergistic enhancement of effect; combinations that result in antagonism can, in many cases, be detrimental to the outcome of the patient. We therefore tested select combinations of approved (GCV, CDV, letermovir (LMV)) and experimental (brincidofovir (BCV), cyclopropavir (CPV), maribavir (MBV), BDCRB) drugs with the hypothesis that combinations of drugs with different and distinct molecular mechanisms of action will produce an additive and/or synergistic enhancement of antiviral effect against HCMV in vitro. Using MacSynergy II (a statistical package that measures enhancement or lessening of effect relative to zero/additive), select drug combination studies demonstrated combination indices ranging from 160 to 372 with 95% confidence intervals greater than zero indicating that these combinations elicit a synergistic enhancement of effect against HCMV in vitro. These data suggest that administration of a viral DNA polymerase inhibitor, MBV, and/or a viral terminase inhibitor in combination has the potential to address the resistance/cross-resistance problems associated with currently available therapeutics.

Recent advances in understanding and managing infectious diseases in solid organ transplant recipients

Background: Undergoing solid organ transplantation (SOT) exposes the recipient to various infectious risks, including possible transmission of pathogen by the transplanted organ, post-surgical infections, reactivation of latent pathogens, or novel infections. Recent advances: In the last few years, the emergence of Zika virus has raised concerns in the transplant community. Few cases have been described in SOT patients, and these were associated mainly with moderate disease and favorable outcome; the notable exception is a recent case of fatal meningo-encephalopathy in a heart transplant recipient. Because of the advances in treating hepatitis C, several teams recently started to use organs from hepatitis C-positive donors. The worldwide increasing incidence of multidrug-resistant pathogens, as well as the increasing incidence of Clostridioidesdifficile infection, is of particular concern in SOT patients. In the field of mycology, the main recent therapeutic advance is the availability of isavuconazole for the treatment of invasive aspergillosis and mucormycosis. This drug has the advantage of minimal interaction with calcineurin inhibitors. Regarding the viral reactivations occurring after transplant, cytomegalovirus (CMV) infection is still a significant issue in SOT patients. The management of resistant CMV remains particularly difficult. The approval of letermovir, albeit in bone marrow transplantation, and the therapeutic trial of maribavir bring a ray of hope. Another advancement in management of post-transplant infections is the development of in vitro tests evaluating pathogen-specific immune response, such as immunodiagnostics for CMV and, more recently, tests for monitoring immunity against BK virus. Conclusion: The increasing number of organ transplantations, the use of newer immunosuppressive drugs, and high-risk donors continue to define the landscape of transplant infectious diseases in the current era.

Ganciclovir-Resistant Cytomegalovirus Infection in Abdominal Solid Organ Transplant Recipients: Case Series and Review of the Literature

Ganciclovir-resistant cytomegalovirus (GR-CMV) is emerging as a significant infection in the abdominal transplant population. GR-CMV is difficult to manage, and treatment options are limited. We report a descriptive case series of 15 patients who had documented GR-CMV at our center and review the literature on treatment of GR-CMV. The first case in this series was detected in 2012; the majority of cases occurred after January 1, 2014, with approximately 50% occurring in 2015. UL97 and UL54 viral genome mutations were present in 100% and 40% of CMV-infected patients, respectively. GR-CMV infection occurred ≤ 1 year posttransplantation in 11 patients (73%). All patients experienced dose reduction of valganciclovir (the oral prodrug of ganciclovir) before the development of GR-CMV. Initial treatment for GR-CMV included a variety of regimens, all including reduction in maintenance immunosuppression. Of the 6 patients with detectable GR-CMV by polymerase chain reaction (PCR) who were discharged without GR-CMV treatment and had a length of stay (LOS) less than 14 days, 83% were subsequently readmitted for treatment of GR-CMV within 2 months (60% in < 20 days); none received leflunomide. Of six patients with a LOS ≥ 14 days, 80% had CMV PCR below quantification on hospital discharge, and only one patient was readmitted in less than 20 days; 83% received leflunomide. Following GR-CMV, there was a 50% rejection incidence, 27% graft loss, and 20% mortality. For patients with more than three admissions for GR-CMV treatment, 100% had a major complication: 60% rejection, 20% graft loss, and 40% mortality. Common clinical characteristics of patients with GR-CMV included high-risk serostatus, lymphocyte depletion, and history of valganciclovir dose reduction. Overall, outcomes were poor. It appears that hospital readmission rate was reduced when CMV was treated to negativity with an initial treatment regimen of reduced immunosuppression, foscarnet, intravenous immunoglobulins, and leflunomide.

Emerging concepts in cytomegalovirus infection following hematopoietic stem cell transplantation

Despite the refinements in molecular methods for the detection of cytomegalovirus (CMV) and the advent of highly effective preemptive strategies, CMV remains a leading cause of morbidity and mortality in hematopoietic cell transplant (HCT) recipients. CMV can cause tissue-invasive disease including pneumonia, hepatitis, colitis, retinitis, and encephalitis. Mortality in HCT recipients with CMV disease can be as high as 60%. CMV infection has been associated with increased risk of secondary bacterial and fungal infections, increased risk of graft-versus-host disease, and high rates of non-relapse mortality following HCT. The risk of CMV is highly dependent on the donor (D) and the recipient (R) serostatus (D^-/R⁺>D⁺/R⁺>D⁺/R^->D^-/R^-). Among allogeneic HCT recipients, high-dose corticosteroids, T-cell depletion, graft-versus-host disease, and mismatched or unrelated donors constitute the main predisposing factors. However, not all seropositive individuals with these risk factors develop CMV, which strongly suggests that host factors, such as those regulating CMV-specific T-cell responses, play a major role in predisposition to CMV in HCT recipients. Here, we discuss emerging concepts in CMV infection in HCT with emphasis on immunological factors that govern CMV reactivation and the applicability of immune monitoring to understand correlates of pathogenesis and its potential to guide clinical decision making.

Cytomegalovirus infection in lung transplant recipients

INTRODUCTION

Cytomegalovirus (CMV) infection is a major cause of morbidity and mortality in solid organ transplant (SOT) patients. Lung transplant recipients are particularly at risk given the intense immunosuppression required. Areas covered: The Detailed review of the literature related to CMV infection, its direct and indirect effect on lung allograft function, as well as diagnosis, immune monitoring, treatment options and prevention strategies. Expert commentary: In lung transplant recipients, CMV infection is associated with pro-inflammatory and immune inhibitory effects that increase the risk of graft dysfunction and loss. Diagnosis of CMV infection remains challenging. Treatment options remain relatively limited.

Treatment of alpha and beta herpesvirus infections in solid organ transplant recipients

INTRODUCTION

Human herpesviruses frequently cause infections in solid organ transplant (SOT) recipients. Areas covered: We provide an overview of the clinical impact of alpha and beta herpesviruses and highlight the mechanisms of action, pharmacokinetics, clinical indications, and adverse effects of antiviral drugs for the management of herpes simplex virus, varicella zoster virus and cytomegalovirus. We comprehensively evaluated key clinical trials that led to drug approval, and served as the foundation for management guidelines. We further provide an update on investigational antiviral agents for alpha and beta herpesvirus infections after SOT. Expert commentary: The therapeutic armamentarium for herpes infections is limited by the emergence of drug resistance. There have been major efforts for discovery of new drugs against these viruses, but the results of early-phase clinical trials have been less than encouraging. We believe, however, that more antiviral drug options are needed given the adverse side effects associated with current antiviral agents, and the emergence of drug-resistant virus populations in SOT recipients. Likewise, optimized use and strategies are needed for existing and novel antiviral drugs against alpha and beta-herpesviruses in SOT recipients.

How I treat resistant cytomegalovirus infection in hematopoietic cell transplantation recipients

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

Outcomes in Transplant Recipients Treated With Foscarnet for Ganciclovir-Resistant or Refractory Cytomegalovirus Infection

BACKGROUND

Antiviral-resistant or refractory cytomegalovirus (CMV) infection is challenging, and salvage therapies, foscarnet, and cidofovir, have significant toxicities. Several investigational anti-CMV agents are under development, but more information is needed on outcomes of current treatments to facilitate clinical trial design for new drugs.

METHODS

Records of solid organ transplant (SOT) and hematopoietic cell transplant (HCT) recipients at a single center over a 10-year period were reviewed retrospectively to characterize those who had received foscarnet treatment for ganciclovir-resistant or refractory CMV infection. Data were collected on virologic responses, mortality, and nephrotoxicity.

RESULTS

Of 39 patients (22 SOT, 17 HCT), 15 had documented ganciclovir resistance mutations and 11 (28%) of 39 had tissue-invasive CMV. Median duration of foscarnet was 32 days. Virologic failure occurred in 13 (33%) of 39 and relapses of viremia occurred in 31%. Mortality was 12 (31%) of 39 and was higher in HCT than SOT (P = 0.001), although ganciclovir resistance was more common in SOT (P = 0.003). Doses of ganciclovir or valganciclovir were low in 10 (26%) of 39 at some time before switching to foscarnet. Renal dysfunction occurred in 20 (51%) of 39 by end of treatment and in 7 (28%) of 25 after 6 months.

CONCLUSIONS

Outcomes of existing treatment for ganciclovir-resistant or refractory CMV are suboptimal, in terms of virologic clearance, renal dysfunction, and mortality. These data should provide background information for future clinical trials of newer antiviral agents.

Adjuvant and salvage therapy with leflunomide for recalcitrant cytomegalovirus infections in hematopoietic cell transplantation recipients: A case series

Cytomegalovirus (CMV) reactivation is a clinically significant complication in hematopoietic stem cell transplant (HCT) recipients. Alternative therapy for multidrug-resistant CMV is limited and often fails. Leflunomide has been used to treat resistant CMV infections, however, data on efficacy, safety, and guidance for therapeutic drug level monitoring are lacking. In this report, we describe 3 HCT recipients with multi-drug resistant CMV infections who received leflunomide as adjuvant and salvage therapy. The therapeutic effect of leflunomide as an anti-CMV agent based on virologic responses and therapeutic drug monitoring were evaluated.

Infectious diseases in allogeneic haematopoietic stem cell transplantation: prevention and prophylaxis strategy guidelines 2016

Infectious complications after allogeneic haematopoietic stem cell transplantation (allo-HCT) remain a clinical challenge. This is a guideline provided by the AGIHO (Infectious Diseases Working Group) of the DGHO (German Society for Hematology and Medical Oncology). A core group of experts prepared a preliminary guideline, which was discussed, reviewed, and approved by the entire working group. The guideline provides clinical recommendations for the preventive management including prophylactic treatment of viral, bacterial, parasitic, and fungal diseases. The guideline focuses on antimicrobial agents but includes recommendations on the use of vaccinations. This is the updated version of the AGHIO guideline in the field of allogeneic haematopoietic stem cell transplantation utilizing methods according to evidence-based medicine criteria.

CMV in Hematopoietic Stem Cell Transplantation

Due to its negative impact on the outcome of stem cell transplant (SCT) and solid organ transplant patients (SOT) CMV has been called “the troll of transplantation”. One of the greatest advances in the management of SCT has been the introduction of the preemptive strategy. Since its introduction, the incidence of the viremia, as expected, remains unchanged but there has been a marked decline in the incidence of early CMV disease. However, in spite of the advances in prevention of CMV disease, CMV is still today an important cause of morbidity and mortality. Late CMV disease is still occurring in a significant proportion of patients and the so-called indirect effects of CMV are causing significant morbidity and mortality. Fortunately there have been several advances in the development of new antivirals, adoptive immunotherapy and DNA-CMV vaccines that might transform the management of CMV in the near future.

In vitro studies of the impact of maribavir on CMV-specific cellular immune responses

BACKGROUND

Ganciclovir has demonstrated immunosuppressive effects in vitro which may lead to delayed cytomegalovirus (CMV)-specific immune reconstitution when the drug is given prophylactically. Maribavir is a new and more potent anti-CMV drug that is under evaluation for therapeutic use in transplant recipients.

OBJECTIVES

The objective of this study was to evaluate the potential effect of maribavir on CMV-specific T cell function in comparison to ganciclovir.

STUDY DESIGN

In ten immunocompetent CMV seropositive donors, maribavir and ganciclovir were compared over a broad range of concentrations (0.2-500μM) regarding their effects on lymphoproliferation, CMV-specific CD4+ and CD8+ cytokine expression, T cell multifunctionality, degranulation and apoptosis.

RESULTS

Maribavir inhibited lymphocyte proliferation at concentrations of 50μM and above, however, cytokine expression, cellular degranulation and multifunctionality of CD4+ and CD8+ T cells in response to CMV lysate and pp65 peptide mix were not impaired except at the highest concentration of 500μM. Ganciclovir inhibited lymphoproliferative responses starting at 10μM. As with maribavir, other cellular responses following stimulation with CMV lysate and pp65 peptide mix were only impaired at the highest concentration of 500μM of ganciclovir. Neither maribavir nor ganciclovir showed induction of lymphocyte apoptosis.

CONCLUSIONS

Maribavir exhibits a low potential to suppress CMV-specific T cell function. This finding supports the use of higher doses in the prophylactic setting than originally proposed.

Resistant cytomegalovirus infection in renal transplant recipients

Resistant cytomegalovirus infection is a significant problem in the transplant population including renal transplant recipients. A combination of factors including receipt of potent immunosuppression, high viral loads and suboptimal levels of anti-cytomegalovirus antivirals leads to emergence of resistant strains. Reports of associated poor graft survival and mortality demonstrate the potential pathogenic nature of such strains. Genotypic and phenotypic resistance testing are available for laboratory diagnosis of resistant cytomegalovirus infection and may help guide therapy. Various agents, including novel and newly minted antivirals and treatment approaches have been employed, with variable success. Thus, in spite of major advances in both diagnostics and therapeutics, management of resistant cytomegalovirus infection in renal transplant recipients remains a challenging prospect.