Emergence and Persistence of Letermovir-Resistant Cytomegalovirus in a Patient With Primary Immunodeficiency

Letermovir for cytomegalovirus infection in allogeneic hematopoietic stem-cell transplantation: tips and notes for effective use in clinical practice

INTRODUCTION

Cytomegalovirus (CMV) infection remains a major complication after allogeneic hematopoietic stem cell transplantation (allo-HSCT). While conventional antiviral agents such as ganciclovir can be used for CMV prophylaxis, toxicities such as myelosuppression are a major concern.

AREA COVERED

This work aimed to summarize the latest information and practical issues regarding a new anti-CMV agent, letermovir (LET).

EXPERT OPINION

LET inhibits CMV replication by binding to components of the DNA terminase complex. A phase 3 trial in allo-HSCT recipients showed a reduced incidence of clinically significant CMV infection in the LET group. In 2017, this agent was first approved for CMV prophylaxis in adult CMV-seropositive allo-HSCT recipients in the United States, and is now used worldwide. While LET has an excellent toxicity profile, there are issues to be aware of, such as interactions with other drug classes (e.g. immunosuppressants and antifungals) and reactivation of CMV infection following LET cessation. While LET is the current standard of care for CMV prophylaxis, there are no established protocols for preemptive treatment of asymptomatic CMV viremia or for treatment of developed CMV disease. Further research is needed to maximize the benefits of LET, including the discovery of biomarkers.

Development and validation of a next-generation sequencing assay with open-access analysis software for detecting resistance-associated mutations in CMV

Cytomegalovirus (CMV) resistance testing by targeted next-generation sequencing (NGS) allows for the simultaneous analysis of multiple genes. We developed and validated an amplicon-based Ion Torrent NGS assay to detect CMV resistance mutations in UL27, UL54, UL56, and UL97 and compared the results to standard Sanger sequencing. NGS primers were designed to generate 83 overlapping amplicons of four CMV genes (~10 kb encompassing 138 mutation sites). An open-access software plugin was developed to perform read alignment, call variants, and interpret drug resistance. Plasmids were tested to determine NGS error rate and minor variant limit of detection. NGS limit of detection was determined using the CMV WHO International Standard and quantified clinical specimens. Reproducibility was also assessed. After establishing quality control metrics, 185 patient specimens previously tested using Sanger were reanalyzed by NGS. The NGS assay had a low error rate (<0.05%) and high accuracy (95%) for detecting CMV-associated resistance mutations present at ≥5% in contrived mixed populations. Mutation sites were reproducibly sequenced with 40× coverage when plasma viral loads were ≥2.6 log IU/mL. NGS detected the same resistance-associated mutations identified by Sanger in 68/69 (98.6%) specimens. In 16 specimens, NGS detected 18 resistance mutations that Sanger failed to detect; 14 were low-frequency variants (<20%), and six would have changed the drug resistance interpretation. The NGS assay showed excellent agreement with Sanger and generated high-quality sequence from low viral load specimens. Additionally, the higher resolution and analytic sensitivity of NGS potentially enables earlier detection of antiviral resistance.

Current Perspectives on the Management of Herpesvirus Infections in Solid Organ Transplant Recipients

Solid organ transplant recipients (SOTRs) are at high risk of human herpesvirus (HHV)-related morbidity and mortality due to the use of immunosuppressive therapy. We aim to increase awareness and understanding of HHV disease burden in SOTRs by providing an overview of current prevention and management strategies as described in the literature and guidelines. We discuss challenges in both prevention and treatment as well as future perspectives.

Identification of Small Molecule Inhibitors of Human Cytomegalovirus pUL89 Endonuclease Using Integrated Computational Approaches

Replication of Human Cytomegalovirus (HCMV) requires the presence of a metal-dependent endonuclease at the C-terminus of pUL89, in order to properly pack and cleave the viral genome. Therefore, pUL89 is an attractive target to design anti-CMV intervention. Herein, we used integrated structure-based and ligand-based virtual screening approaches in combination with MD simulation for the identification of potential metal binding small molecule antagonist of pUL89. In this regard, the essential chemical features needed for the inhibition of pUL89 endonuclease domain were defined and used as a 3D query to search chemical compounds from ZINC and ChEMBL database. Thereafter, the molecular docking and ligand-based shape screening were used to narrow down the compounds based on previously identified pUL89 antagonists. The selected virtual hits were further subjected to MD simulation to determine the intrinsic and ligand-induced flexibility of pUL89. The predicted binding modes showed that the compounds reside well in the binding site of endonuclease domain by chelating with the metal ions and crucial residues. Taken in concert, the in silico investigation led to the identification of potential pUL89 antagonists. This study provided promising starting point for further in vitro and in vivo studies.

Cytomegalovirus and other herpesviruses after hematopoietic cell and solid organ transplantation: From antiviral drugs to virus-specific T cells

Herpesviruses can either cause primary infection or may get reactivated after both hematopoietic cell and solid organ transplantations. In general, viral infections increase post-transplant morbidity and mortality. Prophylactic, preemptive, or therapeutically administered antiviral drugs may be associated with serious side effects and may induce viral resistance. Virus-specific T cells represent a valuable addition to antiviral treatment, with high rates of response and minimal side effects. Even low numbers of virus-specific T cells manufactured by direct selection methods can reconstitute virus-specific immunity after transplantation and control viral replication. Virus-specific T cells belong to the advanced therapy medicinal products, and their production is regulated by appropriate legislation; also, strict safety regulations are required to minimize their side effects.

Cytomegalovirus in primary immunodeficiency

PURPOSE OF REVIEW

Cytomegalovirus (CMV) infection and disease are well described in the setting of secondary immunodeficiency. Less is known about CMV in the context of primary immunodeficiencies (PIDs), where inborn errors in one or more arms of the immune system result in variable degrees of CMV susceptibility.

RECENT FINDINGS

PID presents unique challenges in the diagnosis and management of CMV disease. The clinical presentation of CMV in PID is often severe, accelerated by underlying immune dysregulation and iatrogenic immunosuppression. Here we describe the clinical significance of CMV infection in PID, the key components of immune defence against CMV and how these are affected in specific PIDs. CMV disease is under-recognized as a complication of common variable immunodeficiency (CVID). High rates of CMV end-organ disease, mortality, development of CMV resistance and prolonged antiviral use have been observed in individuals with CVID.

SUMMARY

We recommend that clinicians tailor their approach to the individual based on their underlying immune deficit and maintain a high index of suspicion and low threshold for treatment. More research is required to improve stratification of CMV risk in PID, develop new diagnostic tools and manage end-organ disease in this cohort.

Combined Therapy with Intravenous Immunoglobulins, Letermovir and (Val-)Ganciclovir in Complicated Courses of CMV-Infection in Transplant Recipients

The treatment options for cytomegalovirus (CMV) infections in immunosuppressed patients are limited, mainly consisting of (val-)ganciclovir (VGC/GCV) as the first-line treatment. We report on three transplant recipients, one stem cell transplant (allo-HSCT) patient and two kidney transplant (KTx) recipients, with prolonged CMV viremia treated with a combined therapy based on letermovir (LMV), CMV-specific intravenous immunoglobulins (IVIg), and VGC/GCV, which led to the sustained control of CMV viremia in all patients.

Successful Treatment of UL97 Mutation Ganciclovir-Resistant Cytomegalovirus Viremia in a Renal Transplant Recipient With Letermovir and Adjunct Hyperimmune Cytomegalovirus Immunoglobulin: A Case Report

Letermovir is an antiviral agent indicated for primary prophylaxis of cytomegalovirus (CMV) infection and disease in adult allogeneic hematopoietic stem cell transplant recipients. In this case, UL97 mutation that conferred resistance to ganciclovir was seen in a patient 8 months after renal transplant. We report the off-label use of letermovir with adjunct hyperimmune CMV immunoglobulin in the successful treatment of CMV disease. This report is the first to use this combination for treatment of CMV infection with a high viral load. It contributes to the limited available literature supporting the use of letermovir in the treatment of resistant CMV, where current therapeutic options can be suboptimal due to adverse effects and the risk of cross-resistance.

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.

Antiviral Drugs Against Herpesviruses

The discovery of the nucleoside analogue, acyclovir, represented a milestone in the management of infections caused by herpes simplex virus and varicella-zoster virus. Ganciclovir, another nucleoside analogue, was then used for the management of systemic and organ-specific human cytomegalovirus diseases. The pyrophosphate analogue, foscarnet, and the nucleotide analogue, cidofovir, have been approved subsequently and constitute the second-line antiviral drugs. However, the viral DNA polymerase is the ultimate target of all these antiviral agents with a possible emergence of cross-resistance between these drugs. Recently, letermovir that targets the viral terminase complex was approved for the prophylaxis of human cytomegalovirus infections in hematopoietic stem cell transplant recipients. Other viral targets such as the protein kinase and the helicase-primase complex are also evaluated for the development of novel potent inhibitors against herpesviruses.

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.

Summary

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.

Regulation of the MIE Locus During HCMV Latency and Reactivation

Human cytomegalovirus (HCMV) is a ubiquitous herpesviral pathogen that results in life-long infection. HCMV maintains a latent or quiescent infection in hematopoietic cells, which is broadly defined by transcriptional silencing and the absence of de novo virion production. However, upon cell differentiation coupled with immune dysfunction, the virus can reactivate, which leads to lytic replication in a variety of cell and tissue types. One of the mechanisms controlling the balance between latency and reactivation/lytic replication is the regulation of the major immediate-early (MIE) locus. This enhancer/promoter region is complex, and it is regulated by chromatinization and associated factors, as well as a variety of transcription factors. Herein, we discuss these factors and how they influence the MIE locus, which ultimately impacts the phase of HCMV infection.

Bromodomain Inhibitors as Therapeutics for Herpesvirus-Related Disease: All BETs Are Off?

Although the ubiquitous human herpesviruses (HHVs) are rarely associated with serious disease of the healthy host, primary infection and reactivation in immunocompromised individuals can lead to significant morbidity and, in some cases, mortality. Effective drugs are available for clinical treatment, however resistance is on the rise such that new anti-viral targets, as well as novel clinical treatment strategies, are required. A promising area of development and pre-clinical research is that of inhibitors of epigenetic modifying proteins that control both cellular functions and the viral life cycle. Here, we briefly outline the interaction of the host bromo- and extra-terminal domain (BET) proteins during different stages of the HHVs' life cycles while giving a full overview of the published work using BET bromodomain inhibitors (BRDis) during HHV infections. Furthermore, we provide evidence that small molecule inhibitors targeting the host BET proteins, and BRD4 in particular, have the potential for therapeutic intervention of HHV-associated disease.

Potential Therapeutic Approaches Against Brain Diseases Associated with Cytomegalovirus Infections

Cytomegalovirus (CMV) is one of the major human health threats worldwide, especially for immunologically comprised patients. CMV may cause opportunistic infections, congenital infections, and brain diseases (e.g., mental retardation and glioblastoma). The etiology of brain diseases associated with human CMV (HCMV) infections is usually complex and it is particularly difficult to treat because HCMV has a life-long infection in its hosts, high mutation rate, and latent infections. Moreover, it is almost impossible to eradicate latent viruses in humans. Although there has been progress in drug discovery recently, current drugs used for treating active CMV infections are still limited in efficacy due to side effects, toxicity, and viral resistance. Fortunately, letermovir which targets the HCMV terminase complex rather than DNA polymerase with fewer adverse reactions has been approved to treat CMV infections in humans. The researchers are focusing on developing approaches against both productive and latent infections of CMV. The gene or RNA targeting approaches including the external guide sequences (EGSs)-RNase, the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) system and transcription activator-like effector nucleases (TALENs) are being investigated to remove acute and/or latent CMV infections. For the treatment of glioblastoma, vaccine therapy through targeting specific CMV antigens has improved patients’ survival outcomes significantly and immunotherapy has also emerged as an alternative modality. The advanced research for developing anti-CMV agents and approaches is promising to obtain significant outcomes and expecting to have a great impact on the therapy of brain diseases associated with CMV infections.

Advances in the genotypic diagnosis of cytomegalovirus antiviral drug resistance

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

Antiviral Agents as Therapeutic Strategies Against Cytomegalovirus Infections

Cytomegalovirus (CMV) is a threat to human health in the world, particularly for immunologically weak patients. CMV may cause opportunistic infections, congenital infections and central nervous system infections. CMV infections are difficult to treat due to their specific life cycles, mutation, and latency characteristic. Despite recent advances, current drugs used for treating active CMV infections are limited in their efficacy, and the eradication of latent infections is impossible. Current antiviral agents which target the UL54 DNA polymerase are restricted because of nephrotoxicity and viral resistance. CMV also cannot be prevented or eliminated with a vaccine. Fortunately, letermovir which targets the human CMV (HCMV) terminase complex has been recently approved to treat CMV infections in humans. The growing point is developing antiviral agents against both lytically and latently infected cells. The nucleic acid-based therapeutic approaches including the external guide sequences (EGSs)-RNase, the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) system and transcription activator-like effector nucleases (TALENs) are being explored to remove acute and/or latent CMV infections. HCMV vaccine is being developed for prophylaxis. Additionally, adoptive T cell therapy (ACT) has been experimentally used to combate drug-resistant and recurrent CMV in patients after cell and/or organ transplantation. Developing antiviral agents is promising in this area to obtain fruitful outcomes and to have a great impact on humans for the therapy of CMV infections.