Possible reactivation of chromosomally integrated human herpesvirus 6 after treatment with histone deacetylase inhibitor

Persistent viremia in an immunocompetent patient with inherited chromosomally integrated HHV-6B

Human herpesvirus-6 (HHV-6), the virus which causes roseola, has traditionally been associated with benign and self-limited childhood illness. However, HHV-6 establishes lifelong latency and can reactivate in immunocompromised adult patients. In about 1% of cases, it integrates into the human genome as inherited chromosomally integrated HHV-6 (iciHHV-6). We report the case of a 70-year-old man presenting with altered mental status and agitation. His infectious workup revealed a cerebrospinal fluid sample positive for HHV-6 with virus detectable in the blood as well. He was subsequently treated with ganciclovir. HHV-6 viremia (DNAemia) persisted, and the antiviral medications were switched to foscarnet under the assumption of treatment failure due to drug resistance. After several admissions to the hospital for the same complaint, and after noticing that DNAemia persisted despite adequate treatment for HHV-6, infectious disease specialists ordered testing for chromosomally integrated virus. Test results confirmed the presence of iciHHV-6, explaining his consistently elevated serum viral load. Primary HHV-6 infection in adults causes a transient increase in viral load with resolution and clearance after a few weeks while iciHHV-6 is characterized by persistent detection of viral DNA at a high copy number. Individuals with iciHHV-6 can develop HHV-6 disease and are at increased risk for active viral replication when treated with immunosuppressive medications, but only mRNA testing, which is not widely available can differentiate between latent and active infection. This makes the decision to treat challenging in this patient population. When faced with a positive HHV-6 DNA result in the setting of equivocal symptoms, clinicians should consider the possibility of chromosomally integrated virus rather than drug-resistant virus in order to reduce exposure to potentially toxic antiviral medications.

Elevation of HHV-6 viral load mimicking HHV-6 reactivation after second umbilical cord blood transplantation in chromosomally integrated human herpesvirus-6

Human herpesvirus-6 (HHV-6) reactivation is an important complication in patients receiving umbilical cord blood transplantation (CBT). Chromosomally integrated human herpesvirus-6 (ciHHV-6) is a condition in which the complete HHV-6 genome is integrated into the host germline genome and is transmitted in a Mendelian manner. The influence of ciHHV-6 in recipients or donors in cases of CBT is unknown. We report the first case with ciHHV-6 that received CBT twice for acute lymphoblastic T-cell leukemia. HHV-6 DNA in peripheral blood leukocytes (PBLs) was examined over time through two CBTs. After the first CBT, the HHV-6 viral load was significantly reduced by conversion to PBLs derived from the first donor. During the second CBT, an increase in HHV-6 DNA in PBLs and plasma were observed. However, HHV-6 mRNA was not detected in either the sample before 2nd CBT or at the time of HHV-6 DNA elevation. It is considered that the HHV-6 DNA detected in PBLs and plasma samples might be the HHV-6 genome released due to tissue damage. This case suggests that physicians should be aware of HHV-6 DNA variability during allogeneic hematopoietic stem cell transplantation in ciHHV-6 patients.

Post-allogeneic hematopoietic stem cell transplantation viral reactivations and viremias: a focused review on human herpesvirus-6, BK virus and adenovirus

Human cytomegalovirus and Epstein-Barr virus have been recognized as potential drivers of morbidity and mortality of patients undergoing allogeneic stem cell transplantation for years. Specific protocols for monitoring, prophylaxis and pre-emptive therapy are in place in many transplant settings. In this review, we focus on the next three most frequent viruses, human herpesvirus-6, BK virus and adenovirus, causing reactivation and/or viremia after allogeneic transplant, which are increasingly detected in patients in the post-transplant period owing to emerging techniques of molecular biology, recipients' characteristics, treatment modalities used for conditioning and factors related donors or stem cell source. Given the less frequent detection of an illness related to these viruses, there are often no specific protocols in place for the management of affected patients. While some patients develop significant morbidity (generally older), others may not need therapy at all (generally younger or children). Furthermore, some of the antiviral therapies used are potentially toxic. With the addition of increased risk of secondary infections, risk of graft failure or increased risk of graft-versus-host disease as well as the relationship with other post-transplant complications, the outcomes of patients with these viremias remain unsatisfactory and even long-term survivors experience increased morbidity.

The U94 Gene of Human Herpesvirus 6: A Narrative Review of Its Role and Potential Functions

Human herpesvirus 6 (HHV-6) is a β-herpesvirus that is highly prevalent in the human population. HHV-6 comprises two recognized species (HHV-6A and HHV-6B). Despite different cell tropism and disease association, HHV-6A/B show high genome homology and harbor the conserved U94 gene, which is limited to HHV-6 and absent in all the other human herpesviruses. U94 has key functions in the virus life cycle and associated diseases, having demonstrated or putative roles in virus replication, integration, and reactivation. During natural infection, U94 elicits an immune response, and the prevalence and extent of the anti-U94 response are associated with specific diseases. Notably, U94 can entirely reproduce some virus effects at the cell level, including inhibition of cell migration, induction of cytokines and HLA-G expression, and angiogenesis inhibition, supporting a direct U94 role in the development of HHV-6-associated diseases. Moreover, specific U94 properties, such as the ability to modulate angiogenesis pathways, have been exploited to counteract cancer development. Here, we review the information available on this key HHV-6 gene, highlighting its potential uses.

Human herpesvirus 6 in transplant recipients: an update on diagnostic and treatment strategies

PURPOSE OF REVIEW

The current review article focuses on recent advances in the approach to the diagnosis and treatment of human herpesvirus 6B (HHV-6B) in hematopoietic cell and solid organ transplant recipients.

RECENT FINDINGS

Over the past few years, key studies have broadened our understanding of best practices for the prevention and treatment of HHV-6B encephalitis after transplantation. Moreover, important data have been reported that support a potential role of HHV-6B reactivation in the development of acute graft-versus-host disease and lower respiratory tract disease in transplant recipients. Finally, increasing recognition of inherited chromosomally integrated HHV-6 (iciHHV-6) and an expanding array of diagnostic tools have increased our understanding of the potential for complications related to viral reactivation originating from iciHHV-6 in donors or recipients.

SUMMARY

Recent advances in diagnostic tools, disease associations, and potential treatments for HHV-6B present abundant opportunities for improving our understanding and management of this complex virus in transplant recipients.

The Promyelocytic Leukemia Protein facilitates human herpesvirus 6B chromosomal integration, immediate-early 1 protein multiSUMOylation and its localization at telomeres

Human herpesvirus 6B (HHV-6B) is a betaherpesvirus capable of integrating its genome into the telomeres of host chromosomes. Until now, the cellular and/or viral proteins facilitating HHV-6B integration have remained elusive. Here we show that a cellular protein, the promyelocytic leukemia protein (PML) that forms nuclear bodies (PML-NBs), associates with the HHV-6B immediate early 1 (IE1) protein at telomeres. We report enhanced levels of SUMOylated IE1 in the presence of PML and have identified a putative SUMO Interacting Motif (SIM) within IE1, essential for its nuclear distribution, overall SUMOylation and association with PML to nuclear bodies. Furthermore, using PML knockout cell lines we made the original observation that PML is required for efficient HHV-6B integration into host chromosomes. Taken together, we could demonstrate that PML-NBs are important for IE1 multiSUMOylation and that PML plays an important role in HHV-6B integration into chromosomes, a strategy developed by this virus to maintain its genome in its host over long periods of time.

Human herpesvirus 6B (HHV-6B) is a ubiquitous virus that can be life threatening in immunocompromised patients. HHV-6B is among a few other herpesviruses that integrate their genome in host chromosomes as a mean to establish dormancy. Integration of HHV-6B occurs in host telomeres, a region that protects our genome from deterioration and controls the cellular lifespan. To date, the mechanisms leading to HHV-6B integration remain elusive. Our laboratory has identified that the IE1 protein of HHV-6B associates with PML, a cellular protein that is responsible for the regulation of important cellular mechanisms including DNA recombination and repair. With the objective of understanding how IE1 is brought to PML, we discovered that PML aids the SUMOylation of IE1. This finding led us to identify a putative SUMO interaction motif on IE1 that is essentials for both its SUMOylation and IE1 oligomerization with PML-NBs. We next studied the role of PML on HHV-6B integration and identified that cells that are deficient for PML were less susceptible to HHV-6B integration. These results correlate with the fact that PML influences IE1 localization at telomeres, the site of HHV-6B integration. Our study further contributes to our understanding of the mechanisms leading to HHV-6B chromosomal integration.

Guidelines from the 2017 European Conference on Infections in Leukaemia for management of HHV-6 infection in patients with hematologic malignancies and after hematopoietic stem cell transplantation

Of the two human herpesvirus 6 (HHV-6) species, human herpesvirus 6B (HHV-6B) encephalitis is an important cause of morbidity and mortality after allogeneic hematopoietic stem cell transplant. Guidelines for the management of HHV-6 infections in patients with hematologic malignancies or post-transplant were prepared a decade ago but there have been no other guidelines since then despite significant advances in the understanding of HHV-6 encephalitis, its therapy, and other aspects of HHV-6 disease in this patient population. Revised guidelines prepared at the 2017 European Conference on Infections in Leukaemia covering diagnosis, preventative strategies and management of HHV-6 disease are now presented.

Chromatin Profiles of Chromosomally Integrated Human Herpesvirus-6A

Human herpesvirus-6A (HHV-6A) and 6B (HHV-6B) are two closely related betaherpesviruses that are associated with various diseases including seizures and encephalitis. The HHV-6A/B genomes have been shown to be present in an integrated state in the telomeres of latently infected cells. In addition, integration of HHV-6A/B in germ cells has resulted in individuals harboring this inherited chromosomally integrated HHV-6A/B (iciHHV-6) in every cell of their body. Until now, the viral transcriptome and the epigenetic modifications that contribute to the silencing of the integrated virus genome remain elusive. In the current study, we used a patient-derived iciHHV-6A cell line to assess the global viral gene expression profile by RNA-seq, and the chromatin profiles by MNase-seq and ChIP-seq analyses. In addition, we investigated an in vitro generated cell line (293-HHV-6A) that expresses GFP upon the addition of agents commonly used to induce herpesvirus reactivation such as TPA. No viral gene expression including miRNAs was detected from the HHV-6A genomes, indicating that the integrated virus is transcriptionally silent. Intriguingly, upon stimulation of the 293-HHV-6A cell line with TPA, only foreign promoters in the virus genome were activated, while all HHV-6A promoters remained completely silenced. The transcriptional silencing of latent HHV-6A was further supported by MNase-seq results, which demonstrate that the latent viral genome resides in a highly condensed nucleosome-associated state. We further explored the enrichment profiles of histone modifications via ChIP-seq analysis. Our results indicated that the HHV-6 genome is modestly enriched with the repressive histone marks H3K9me3/H3K27me3 and does not possess the active histone modifications H3K27ac/H3K4me3. Overall, these results indicate that HHV-6 genomes reside in a condensed chromatin state, providing insight into the epigenetic mechanisms associated with the silencing of the integrated HHV-6A genome.

Human Herpesvirus 6 and Malignancy: A Review

In order to determine the role of human herpesvirus 6 (HHV-6) in human disease, several confounding factors, including methods of detection, types of controls, and the ubiquitous nature of the virus, must be considered. This is particularly problematic in the case of cancer, in which rates of detection vary greatly among studies. To determine what part, if any, HHV-6 plays in oncogenesis, a review of the literature was performed. There is evidence that HHV-6 is present in certain types of cancer; however, detection of the virus within tumor cells is insufficient for assigning a direct role of HHV-6 in tumorigenesis. Findings supportive of a causal role for a virus in cancer include presence of the virus in a large proportion of cases, presence of the virus in most tumor cells, and virus-induced in-vitro cell transformation. HHV-6, if not directly oncogenic, may act as a contributory factor that indirectly enhances tumor cell growth, in some cases by cooperation with other viruses. Another possibility is that HHV-6 may merely be an opportunistic virus that thrives in the immunodeficient tumor microenvironment. Although many studies have been carried out, it is still premature to definitively implicate HHV-6 in several human cancers. In some instances, evidence suggests that HHV-6 may cooperate with other viruses, including EBV, HPV, and HHV-8, in the development of cancer, and HHV-6 may have a role in such conditions as nodular sclerosis Hodgkin lymphoma, gastrointestinal cancer, glial tumors, and oral cancers. However, further studies will be required to determine the exact contributions of HHV-6 to tumorigenesis.