Primary human herpes virus 6 infection transmitted from donor to recipient through bone marrow infusion

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.

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.

Host and Graft Factors Impacting Infection Risk in Hematopoietic Cell Transplantation

Infection contributes significantly to morbidity and mortality in hematopoietic cell transplantation. A complex interplay of host, graft, and technical factors contributes to infectious risk in the recipient. Host factors such as age, underlying disease, and comorbidities; central venous access; and the preparative regimen contribute to mucosal disruption, organ dysfunction, and immunodeficiency before hematopoietic cell transplantation. Graft factors, including donor histocompatibility, cell source, and graft components, along with immunosuppression and graft-versus-host disease, contribute to the speed of immune reconstitution. Evaluation of these factors, plus previous and posttransplant exposure to pathogens, is necessary to best assess an individual recipient's infection risk.

Management of herpesvirus infections

Management of human herpesviruses remains a considerable clinical challenge, in part due to their ability to cause both lytic and latent disease. Infection with the Herpesviridae results in lifelong infection, which can reactivate at any time. Control of herpesviruses is by the innate and adaptive immune systems. Herpesviruses must evade the host innate immune system to establish infection. Once infected, the adaptive immune response, primarily CD8(+) T-cells, is crucial in establishing and maintaining latency. Latent herpesviruses are characterised by the presence of viral DNA in infected cells and limited or no viral replication. These characteristics provide a challenge to clinicians and those developing antiviral agents. The scope of this review is two-fold. First, to provide an overview of all antivirals used against herpesviruses, including their mechanism of action, pharmacokinetics, side effects, resistance and clinical uses. And second, to address the management of each of the eight herpesviruses both in the immunocompetent and immunocompromised host, providing evidence for clinical management and therapeutic options, which is important to the clinician engaged in the management of these infections.

[Human herpesvirus-6 and human herpesvirus-7 (HHV-6, HHV-7)]

human herpesvirus 6 (HHV-6) is the major causative agent of exanthem subitum which is one of popular diseases in infant, and establishes latent infections in adults of more than 90%. Recently, the encephalitis caused by reactivated- HHV-6 has been shown in patients after transplantation. In addition, the relationship HHV-6 and drug-induced hypersensitivity syndrome has also been reported. human herpesvirus 7 (HHV-7) was isolated from the stimulated-peripheral blood lymphocytes of a healthy individual, and also causes exanthema subitum. Both viruses are related viruses which belong to betaherpesvirus subfamily, and replicate and produce progeny viruses in T cells.

Herpes viruses in transplant recipients: HSV, VZV, human herpes viruses, and EBV

The herpes viruses are responsible for a wide range of diseases in patients following transplant, resulting from direct viral effects and indirect effects, including tumor promotion. Effective treatments and prophylaxis exist for the neurotropic herpes viruses HSV-1, HSV-2, varicella zoster virus, and possibly HHV-6. Antivirals seem to be less effective at prevention of the tumor-promoting effects of Epstein-Barr virus and HHV-8. Reduction in immunosuppression is the cornerstone to treatment of many diseases associated with herpes virus infections.

Fatal human herpesvirus-6 infection after renal transplantation

INTRODUCTION

Human herpesvirus (HHV)-6 infection is common after organ transplantation; however, most cases are associated with a mild clinical course. Donor-derived infection is rare, and there are no reports of HHV-6 infection in more than one recipient from a common donor.

METHODS

We describe two patients who developed severe, and in one case fatal, HHV-6 variant A infection after renal transplantation.

RESULTS

Both patients presented with severe colitis followed by the development of liver dysfunction and cytopenia. Multiple specimens from both recipients were positive for HHV-6 polymerase chain reaction variant A. Serum and white cells from the donor were positive for HHV-6 DNA, suggesting a donor-derived infection in these patients.

CONCLUSIONS

We report two cases of donor-derived HHV-6 infection from the same deceased donor, resulting in a fatal outcome in one patient. Treatment with valganciclovir was successfully instigated in one patient with a full recovery from the infection.

Human herpesvirus-6 infection in solid organ and stem cell transplant recipients

HHV-6 has in recent years become recognized as a potential significant pathogen in both solid organ and stem cell transplant recipients. HHV-6 infections are common after transplantation regardless of the utilized diagnostic technique. Several different clinical manifestations have been described including fever, bone marrow suppression, encephalitis, skin rash, and hepatitis. The most important end-organ disease is encephalitis in stem cell transplant recipients that has been reported to have a mortality of at least 40%. HHV-6 is also considered an immunomodulatory and immunosuppressive virus that may facilitate super-infections with other opportunistic pathogens such as CMV and fungal infections and thereby contribute to overall mortality. No established therapy exists but both ganciclovir and foscarnet have been reported to have in vitro and in vivo efficacy against HHV-6.

Fever, Human Herpesvirus-6 (HHV-6) Seroconversion, and Acute Rejection Episodes as a Function of the Initial Seroprevalence for HHV-6 in Renal Transplant Recipients

Human herpesvirus-6 (HHV-6) is an opportunistic viral pathogen of emerging clinical significance in immunocompromised patients. We performed a seroepidemiological survey to test the relation between seroprevalence among donors and recipients for HHV-6 at three endpoints. Before transplantation sera obtained from cadaveric donors and from potential recipients were tested for IgG antibodies against HHV-6 using an enzyme-linked immunoassay. The group of recipient sera, including samples obtained before as well as 2, 4, 12, and 48 weeks after transplantation, were tested for anti-HHV-6 IgM antibodies using an indirect immunofluorescence assay. The statistical analysis was performed with the Cox proportional hazards models. The HHV-6 seronegative group (n = 11) compared with the HHV-6 seropositive group (n = 109) showed twice the risk of HHV-6 IgM seroconversion (RR = 2.24; P < .04), with a greater risk of fever, namely 3.8, which was on the verge of statistical significance. The opposite trend toward an association with acute rejection episodes was observed among HHV-6 seronegative patients (RR = 1.81). The presence of IgG antibody in the sera of donors to IgG seropositive recipients had no association with the occurrence of IgM seroconversion. In contrast, IgM antibodies to HHV-6 appeared in four of five seronegative patients who received allografts from IgG seropositive donors. These preliminary data suggest that the effects seem to be the consequence of HHV-6 transmission through a renal allograft.

The natural history and laboratory diagnosis of human herpesviruses-6 and -7 infections in the immunocompetent

BACKGROUND

Human herpesviruses-6 and -7 (HHV-6/7) are widespread in all populations. In some individuals HHV-6 is found integrated into human chromosomes, which results in a high viral load in blood. HHV-6 variant B (HHV-6B) and HHV-7 primary infections, although usually silent, not infrequently cause the childhood exanthem roseola infantum and are sometimes accompanied by neurological illness. HHV-6 variant A (HHV-6A) is not associated with any disease.

OBJECTIVES

The present review focuses on the immunocompetent individual and considers the epidemiology of the two viruses and their role as human pathogens. It discusses the importance of satisfactory diagnostic tests to distinguish them, compares those currently available, and recommends how best to differentiate primary from persistent infection in each case.

RESULTS

It is explained that at the present time antibody avidity immunofluorescence tests are the most reliable discriminators of the two types of infection. In primary infection these tests can be supplemented by PCR for viral DNA in blood but careful interpretation is required for HHV-6 in view of the high persistent viral DNA load seen with chromosomal integration. Since the contribution of primary HHV-6 and -7 infections to the burden of severe neurological illness in young children is only now emerging as significant, the need to test for these viruses in such cases is stressed.

CONCLUSIONS

1. Primary HHV-6/7 infections must be distinguished from persistent infections. 2. Chromosomal integration of HHV-6 requires urgent study. 3. HHV-6A/B must be distinguished in clinical situations. 4. Where serious neurological disease/encephalitis is temporally related to immunisation it is particularly important to test for HHV-6/7 primary infection since otherwise the condition might wrongly be diagnosed as a vaccine reaction. 5. Because less is currently known about HHV-7 and HHV-6A than HHV-6B, future studies should concentrate on the former two. 6. Improvements in diagnostic tests are required for each virus.

Update on human herpesvirus 6 biology, clinical features, and therapy

Human herpesvirus 6 (HHV-6) is a betaherpesvirus that is closely related to human cytomegalovirus. It was discovered in 1986, and HHV-6 literature has expanded considerably in the past 10 years. We here present an up-to-date and complete overview of the recent developments concerning HHV-6 biological features, clinical associations, and therapeutic approaches. HHV-6 gene expression regulation and gene products have been systematically characterized, and the multiple interactions between HHV-6 and the host immune system have been explored. Moreover, the discovery of the cellular receptor for HHV-6, CD46, has shed a new light on HHV-6 cell tropism. Furthermore, the in vitro interactions between HHV-6 and other viruses, particularly human immunodeficiency virus, and their relevance for the in vivo situation are discussed, as well as the transactivating capacities of several HHV-6 proteins. The insight into the clinical spectrum of HHV-6 is still evolving and, apart from being recognized as a major pathogen in transplant recipients (as exemplified by the rising number of prospective clinical studies), its role in central nervous system disease has become increasingly apparent. Finally, we present an overview of therapeutic options for HHV-6 therapy (including modes of action and resistance mechanisms).

Human herpesvirus 6 (HHV6) infection

Human herpes virus-6 was first reported in 1986 and is the sixth member of the herpes virus family. HHV-6 consists of two closely related variants HHV-6A and HHV-6B. The majority of infections occur in healthy infants with most infections caused by HHV-6B. The virus preferentially infects CD4+T-lymphocytes and the surface marker CD46 acts as a co-receptor. Infection is followed by persistence and latency in different cells and organs including monocytes/macrophages, salivary glands, the brain and the kidneys. In this article we will discuss the clinical manifestations of HHV-6 infection in healthy children and the syndromes associated with HHV-6 reactivation in immunocompromised patients. Evidence of association between HHV-6 infection and different clinical entities such as multiple sclerosis, malignancy, infectious momononucleosis, drug hypersensitivity syndromes and skin eruptions is discussed. Published data on the use and efficacy of antiviral agents in complicated infections and infections in immunocompromised patients is presented.

Human Herpesvirus-6: A Short Review of Its Biological Behavior

HHV-6 shows a widespread distribution with life-long persistence. The virus is frequently reactivated, yet remains clinically inapparent unless the patient is immunodeficient in some way. Even then, HHV-6 reactivation may simply enhance the pathogenicity of other viruses or existing autoimmune disorders rather than becoming a pathogen itself. Future clinical studies need to focus on such indirect viral influences mediated through molecular mimicry and interference with cell receptor expression, and cytokine and chemokine network regulation. Nevertheless, such disturbances may afford therapeutic intervention to disrupt herpesvirus interference and improve certain disease processes. There are only a few diseases for which an immediate causal relationship to HHV-6 infection has been suggested.

Human herpesvirus 6: molecular biology and clinical features

Human herpesvirus 6 (HHV-6) exists as distinct variants HHV-6A and HHV-6B. The complete genomes of HHV-6A and HHV-6B have been sequenced. HHV-6B contains 97 unique genes. CD46 is the cell receptor for HHV-6, explaining its broad tissue tropism but its restricted host-species range. HHV-6 utilizes a number of strategies to down-regulate the host immune response, including molecular mimicry by production of a functional chemokine and chemokine receptors. Immunosuppression is enhanced by depletion of CD4 T lymphocytes via direct infection of intra-thymic progenitors and by apoptosis induction. Infection is widespread in infants between 6 months and 2 years of age. A minority of infants develop roseola infantum, but undifferentiated febrile illness is more common. Reactivation from latency occurs in immunocompromised hosts. Organ-specific clinical syndromes occasionally result, but indirect effects including interactions with other viruses such as human immunodeficiency virus type 1 and human cytomegalovirus or graft dysfunction in transplant recipients may be more significant complications in this population. Recent advances in quantitative PCR are providing additional insights into the natural history of infection in paediatric populations and immunocompromised hosts.

Human herpesvirus 6 and human herpesvirus 7: emerging pathogens in transplant patients

Human herpesvirus 6 (HHV-6) and HHV-7 are two recently identified beta-herpesviruses, genetically related to human cytomegalovirus (CMV). Infection with both viruses is common worldwide with rates of seropositivity in adults over 90%. Infection with both viruses usually occurs in early childhood. In this age group HHV-6 is a cause of febrile illness including exanthem subitum, and likewise, primary HHV-7 infection has been associated with febrile illness. Similar to the other human herpesviruses, in particular CMV, the viruses have the potential for enhanced pathogenicity in the immunocompromised host. Active infection with both viruses is common following bone marrow or solid organ transplantation, most likely through reactivation of recipient's virus or re-infection considering their high prevalence in the population. Both viruses can be detected by PCR in the peripheral blood of healthy individuals and although the significance of blood-borne transmission is not clear, a preliminary study suggested that it was not significant for HHV-6. However, there is growing evidence that these viruses may be medically important in the post-transplant period. In bone marrow transplant patients HHV-6 has been associated with a range of clinical disease including encephalitis, interstitial pneumonitis, early and late graft failure and bone marrow suppression. There is also growing evidence for potential interactions among the beta-herpesviruses in liver and renal transplant patients. HHV-6 infection has been associated with an increased risk of developing CMV disease and opportunistic infections and HHV-7 infection has also been linked to an increased risk of CMV disease.

Successful mismatched sibling cord blood transplant in Hb Bart's disease

A 20-month-old girl with Hb Bart's disease, who had survived neonatal complications, underwent HLA-DR antigen mismatched sibling cord blood transplantation successfully. Immune thrombocytopenia, which occurred around 2.5 months after transplant, responded to intravenous gamma-globulin. The fetal hemoglobin level rose to a peak of 52.3% on day +69 post transplant and declined gradually during the following year. Ten percent of hemoglobin Bart's was detected 2 months after transplant and this reflects the alpha-thalassemia trait of the donor.

Primary human herpesvirus 6 infection in liver transplant recipients

We detected primary human herpesvirus 6 (HHV-6) infection in 5 infants who received living related liver transplantation from their HHV-6 seropositive mothers. Primary HHV-6 infection was confirmed by demonstrating the seroconversion of HHV-6 antibodies with an immunofluorescence assay, by the isolation of the virus, or both. Seroconversion of HHV-6 immunoglobulin G antibody was demonstrated in all 5 recipients. HHV-6 was isolated from 3 of the 5 recipients between 2 and 3 weeks after transplantation. Moreover, the virus genome was detected in plasma by polymerase chain reaction in 4 of the 5 recipients during the same period. Although the 5 recipients had pyrexia at the time of primary HHV-6 infection, none of the recipients had a skin rash after defervescence. Clinical symptoms disappeared without specific antiviral treatment in all but 1 of the recipients.

Human herpesvirus 6: its impact and influence on infectious diseases and their management

Human herpesvirus (HHV)-6 was discovered 15 years ago and was then grouped as a member of the family human herpesviridae. Its first clinical manifestation was identified 2 years later as the agent responsible for exanthem subitum. With the advent of newer molecular techniques, its diagnosis is easier and prospective studies have shown that it is the most common pathogen responsible for febrile illness in infants. In some infants, it is associated with febrile convulsions. Two subtypes, A and B, have been identified, B subtype commonly being responsible for primary infection in infants. Primary infection in healthy adults is rare. Most of the clinical manifestations are mild, self-limiting and rarely fatal. Reactivation of HHV-6 is frequently found in bone marrow as well as solid organ transplant recipients. HHV-6 has been shown to be an independent risk factor responsible for recurrence of cytomegalovirus infection, especially in solid organ transplants. In bone marrow transplant recipients, HHV-6 has been associated with various manifestations like marrow suppression and graft versus host disease, although most infections present as usually mild febrile illness with or without rash. It has been reported to cause encephalitis in transplant recipients. Although HHV-6 has been shown to be responsible for upregulation of HIV in vitro studies, its exact role in AIDS is yet to be defined. In addition to its neurotropic manifestation of febrile convulsion in infancy, it has been found in plaques in the brain of multiple sclerosis and progressive multifocal leukoencephalopathy. Further studies are needed before its role in the pathogenesis of these neurological illnesses can be established. Its lymphotropic feature was responsible for its discovery and now it has only been detected in some lesions of primary ocular mucosa associated lymphoid tissue lymphoma. As HHV-6 is found to be responsible for more and more illnesses, especially causing serious illnesses in the immunocompromised, it is becoming necessary to find effective treatment. Some agents, like cidofovir and phosphonoformic acid, are effective in in vitro studies and some have shown effectiveness in a clinical setting. Further studies are needed to identify its role in the pathogenesis of various neurological and malignant lesions and AIDS. Various treatment regimens should be tested in clinical scenario and especially in immunocompromised transplant recipients.

Human herpesvirus-6 and -7 in transplantation

Infections with the beta-herpesviruses human herpesvirus-6 (HHV-6) and human herpesvirus-7 (HHV-7) are ubiquitous in childhood. The immunosuppression secondary to organ or bone marrow transplantation together with posttransplantation management may favour viral replication and reactivation. HHV-6 and -7 induce immunosuppression by targeting lymphocytes, natural killer cells and monocytes. HHV-6 is commonly detected posttransplantation but variability in definitions of clinical syndromes related to this virus and detection methods have complicated understanding of the clinical relevance of HHV-6 posttransplantation. Clinical symptoms associated with HHV-6 include febrile illness, pneumonitis, hepatitis, encephalitis and bone marrow suppression. However, the majority of HHV-6 infections are asymptomatic. The incidence of HHV-7 infection and its clinical manifestations posttransplantation are even less well characterised. In addition, HHV-6 and HHV-7 are related to CMV disease or acute graft-versus-host disease and, indirectly, to increases in resource utilisation. Based on the potential relevance of these two beta-herpesviruses in transplant recipients, further studies are required to establish their real impact in transplantation. For this, sensitive and specific molecular diagnostic techniques allowing for the rapid detection and quantitation of virus and for the analysis of susceptibility to current antiviral agents are required.

The spectrum of human herpesvirus 6 infection: from roseola infantum to adult disease

Human herpesvirus 6 is the causative agent of roseola infantum, a generally benign rash illness of infants. Most persons acquire HHV-6 infection by age 2 years, and HHV-6 infection is a common cause of fever and febrile seizures in infants. In adults, primary infection with HHV-6 can produce a mononucleosis-like illness and, more rarely, severe disease, including encephalitis. In addition to primary infections, HHV-6 can cause clinical illness during reactivation, particularly in immunocompromised persons.

Human herpesvirus-6 and -7 infections in children: agents of roseola and other syndromes

Human herpesvirus-6 (HHV-6) and -7 (HHV-7) infections typically are silent or manifested as mild febrile illnesses including classic roseola. In addition, case reports and epidemiologic data support the rare occurrence of HHV-6 encephalitis in immunocompromised as well as immunocompetent subjects. Although many other diseases have been putatively associated with HHV-6 or HHV-7, these associations are not well documented due to small numbers, use of tests incapable of distinguishing latent from replicating virus, potential virus cross-reactivity, or contradictory results. Further careful studies are needed to confirm these disease associations. Laboratory tests for diagnosing active HHV-6 and HHV-7 infections include virus culture, antigen detection, and polymerase chain reaction of cell-free biologic fluid. Although HHV-6 and HHV-7 are inhibited by several antiviral drugs in the laboratory, including ganciclovir and foscarnet, no clinical trials have assessed their benefit. Nevertheless, treatment may be considered for patients with serious HHV-6- or HHV-7-associated disease confirmed with accurate virologic tests.

Human herpesvirus-6 and human herpesvirus-7 in the bone marrow from healthy subjects

BACKGROUND

Human herpesviruses (HHVs) 6 and 7 are recently discovered betaherpesviruses. Although HHV-6 has been associated with disordered hematopoiesis in bone marrow transplant recipients, little information is available on the presence of both viruses in the bone marrow from healthy subjects.

METHODS

We detected HHV-6 and HHV-7 DNA by means of polymerase chain reaction in bone marrow and peripheral blood samples from 18 healthy subjects who underwent total hip arthroplasty.

RESULTS

Genomic HHV-6 and HHV-7 DNA were detected in 11% and 67% of the blood samples, respectively, and in 28% and 50% of the bone marrow samples, respectively.

CONCLUSIONS

Both viruses may be present in the bone marrow without hematopoiesis disorder and can be transmitted through bone marrow infusion. Therefore, the causative role of these two viruses in some bone marrow diseases cannot be inferred simply from the detection of their genome in bone marrow by means of polymerase chain reaction.

Unusual infections and novel therapy in the immunocompromised host

Many of the reports of infection in immunocompromised patients over the past year have been caused by unusual bacterial pathogens or fungi, which are often multiresistant and difficult to treat. Although many difficulties still remain some progress has been made over the past year in the development of new antimicrobial agents and alternative therapies.

The epidemiology and pathogenesis of infections caused by the high numbered human herpesviruses in children: HHV-6, HHV-7 and HHV-8

Human herpesvirus 6 may be transmitted from saliva to infants, but other routes of transmission, such as organ and bone marrow transplantation, have also been reported. Intrauterine infection has also been suggested. Although the clinical symptoms during the primary infection in children are mild, human herpesvirus 6 may have neurotropic properties and be involved in the pathogenesis of febrile seizures in infants. The clinical symptoms caused by human herpesvirus 7 are not yet clear, but reports have described neurological symptoms. Human herpesvirus 8 has been identified from Kaposi's sarcoma tissue using molecular procedures. Serological study shows that human herpesvirus 8 is not so common in society and the mode of transmission is still unclear. Several routes of infection have, however, been considered, including sexual transmission.