Human herpesvirus 6 reactivation and encephalitis in allogeneic bone marrow transplant recipients

Herpesvirus infections of the nervous system

There are eight human herpesviruses (HHVs). Primary infection by any of the eight viruses, usually occurring in childhood, is either asymptomatic or produces fever and rash of skin or mucous membranes; other organs might be involved on rare occasions. After primary infection, the virus becomes latent in ganglia or lymphoid tissue. With the exception of HHV-8, which causes Kaposi's sarcoma in patients with AIDS, reactivation of HHVs can produce one or more of the following complications: meningitis, encephalitis, myelitis, vasculopathy, ganglioneuritis, retinal necrosis and optic neuritis. Disease can be monophasic, recurrent or chronic. Infection with each herpesvirus produces distinctive clinical features and imaging abnormalities. This Review highlights the patterns of neurological symptoms and signs, along with the typical imaging abnormalities, produced by each of the HHVs. Optimal virological studies of blood, cerebrospinal fluid and affected tissue for confirmation of diagnosis are discussed; this is particularly important because some HHV infections of the nervous system can be treated successfully with antiviral agents.

Effectiveness of ganciclovir against human herpesvirus-6 excreted in saliva in stem cell transplant recipients

The aim of this study was to evaluate the effect of ganciclovir on human herpesvirus-6 (HHV)-6. Forty allogeneic stem cell transplant recipients were prospectively studied by repeated sampling of the saliva. The saliva samples were assayed for HHV-6 by quantitative polymerase chain reaction. HHV-6 was detected in 33 patients. Ganciclovir was given as preemptive therapy for cytomegalovirus infection during 15 episodes that were compared to 18 episodes without any concomitant antiviral therapy. The mean HHV-6 load decreased 0.49 (s.e. 0.31) log(10)/week in patients receiving ganciclovir whereas it increased 0.15 (s.e. 0.17) log(10)/week in episodes without antiviral therapy (P=0.04). We conclude that ganciclovir can decrease the HHV-6 viral load in saliva.

Human Herpesvirus-6 and -7 After Lung and Heart–Lung Transplantation

BACKGROUND

The impact of herpesvirus-6 and -7 (HHV-6, HHV-7) activation in lung transplant recipients is still poorly understood. We report the appearance of HHV-6 and HHV-7 antigenemia after lung transplantation and evaluate the efficacy of anti-viral drugs against these viruses.

METHODS

Twenty-two lung or heart-lung recipients were monitored for HHV-6, HHV-7 and cytomegalovirus (CMV) during 12 post-operative months. HHV-6- and HHV-7-specific antigens and CMV pp65 antigens were analyzed in blood leukocytes and bronchoalveolar lavage fluid cells by monoclonal antibodies. Ganciclovir or valganciclovir prophylaxis for a minimum of 3 months was given to 19 recipients at risk for CMV infection.

RESULTS

HHV-6, HHV-7 and CMV antigenemia was detected in 20 (91%), 11 (50%) and 12 (55%) recipients (median 16, 31 and 165 days) after transplantation, respectively. HHV-6 antigenemia occurred in 15 (79%), HHV-7 antigenemia in 7 (37%) and CMV antigenemia in 1 (7%) of these patients during anti-viral prophylaxis. HHV-6 or HHV-7 antigenemia was frequently associated with CMV antigenemia, which was detected 3 to 12 months after transplantation. Ganciclovir or valganciclovir treatment of CMV infection was effective against the concomitant HHV-6 and HHV-7 antigenemia in 9 of 12 (75%) and 5 of 6 (83%) cases, respectively. One case of pneumonitis and 1 of encephalitis were temporally associated with HHV-6. No other clinical manifestations could be linked solely to HHV-6 or -7.

CONCLUSIONS

HHV-6 and -7 antigenemia was common and appeared early after lung transplantation. CMV prophylaxis was not able to prevent the appearance of HHV-6 and -7 antigenemia.

Surveillance of active human herpesvirus 6 infection in chinese patients after hematopoietic stem cell transplantation with 3 different methods

Human herpesvirus 6 (HHV-6) reactivation was studied in 72 consecutive allogeneic hematopoietic stem cell transplant (HSCT) recipients and 53 "healthy" donors. The feasibilities of real-time quantitative polymerase chain reaction (RQ-PCR), nested-PCR, and antigenemia assays in the assessment of HHV-6 reactivation were also evaluated. HHV-6 DNA was detected in 62.5% and 48.6% of post-HSCT patients with the nested-PCR assay and RQ-PCR analysis, respectively, and HHV-6B was identified as the predominant variant. The incidence of HHV-6 infection peaked from the second to the seventh week, whereas the HHV-6B DNA loads peaked from the second to the third week. Compared with RQ-PCR analysis, the sensitivity and specificity of the nested-PCR assay were 100% and 88%, respectively, with positive and negative predictive values of 60% and 99%, respectively. For the HHV-6 antigenemia assay, the sensitivity and specificity were 89% and 97%, respectively, and the positive and negative predictive values were both 94%. Conditioning with antithymocyte globulin in HLA-mismatched or unrelated HSCT increased the possibility of HHV-6B reactivation after HSCT (hazard ratio, 5.92; 95% confidence interval, 1.99-17.59; P = .001). In conclusion, HHV-6B reactivation is commonly encountered after HSCT. Of the 3 methods we adopted for HHV-6 detection, both RQ-PCR analysis and the antigenemia assay could be seen as essential tests for predicting HHV-6 reactivation.

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.

Emerging viral infections in transplantation

Viral infections are an important complication of transplantation. The introduction of more potent immunosuppressive agents over the past decade correlates with an increase in the rate of hospitalizations of transplant patients with infections. Specifically, viral infections have emerged as a major source of morbidity and mortality in transplantation. There are several potential intervention strategies in the face of emerging infections and it is likely that the approach will differ depending on the virus in question. These include viral surveillance and pre-emptive therapy, intervention of the transplant community, and policy change at the level of government, blood bank and organ procurement organizations. This review focuses on the emergence of the herpesviruses; HHV-6 and HHV-7. In addition, the issue of virus transmission through organ transplant is addressed with a discussion of West Nile virus and the rabies virus.

The Impact of Human Herpesvirus 6B Reactivation on Early Complications following Allogeneic Hematopoietic Stem Cell Transplantation

Although human herpesvirus 6 (HHV-6) has been considered an important opportunistic and potentially fatal pathogen for allogeneic hematopoietic stem cell transplantation (HSCT), the clinical significance of HHV-6 reactivation remains controversial. In this study, we monitored HHV-6 DNAemia in 72 consecutive allogeneic HSCT recipients by real-time quantitative polymerase chain reaction. A total of 680 peripheral blood specimens were collected from the recipients before HSCT or at weekly intervals after HSCT. As the predominant variant, HHV-6B was detectable at least once in 47.2% (34/72) of HSCT recipients on the median day 21 (range, 7-84 days); HHV-6A reactivation occurred in only 1 recipient (1.4%). Detectable HHV-6B reactivation was associated with increased probability of skin rash by day 30 after HSCT (hazard ratio [HR], 3.68; 95% confidence interval [CI], 1.24-10.92; P = .019), cytomegalovirus (CMV) antigenemia (HR, 2.35; 95%CI, 1.32-4.19; P = .004), and hemorrhagic cystitis (HC) (HR, 2.59; 95%CI, 0.96-6.98; P = .061) by day 100 after HSCT. Neutrophil and platelet engraftment, mortality for 100 days after HSCT were not affected by HHV-6B reactivation. In conclusion, HHV-6 reactivation is a common event, and this study demonstrates a correlation between HHV-6B infection and CMV reactivation, early rash, and possibly increased incidence of HC after transplantation.

Evaluation of pulmonary infiltrates in patients after stem cell transplantation

Hematopoietic stem cell transplantation is potentially curative therapy that has become the standard of care for many hematologic malignancies. Pulmonary complications occur in about 50% of stem cell transplant recipients and no other organ dysfunction has a higher mortality. Unfortunately the diagnosis of these infiltrates is hampered by the poor yield from routine studies and this patient population is rarely able to tolerate more risky procedures that will obtain tissue for microscopy and culture. A bronchoalveolar lavage (BAL) is usually insufficient to make a diagnosis of invasive fungal, significant bacterial, or pathogenic viral infections in patients that will still benefit from a change in therapy. In this review we discuss the infectious etiologies of pulmonary infiltrates post hematopoietic stem cell transplant, the non-infectious causes of infiltrates such as diffuse alveolar hemorrhage, engraftment syndrome, and idiopathic pneumonia syndrome, and the yield of newer diagnostic procedures ranging from peripheral blood galactomannan to cytomegalovirus antigenemia, and report on new technologies that promise more accurate and timely diagnoses of these infiltrates.

Central nervous system infections in transplantation

Central nervous system (CNS) infections are a rare but serious complication of transplantation. An appropriate diagnostic workup should be streamlined with stratification of infection risk by length and degree of immune suppression, lesion localization, and timing. Polymerase chain reaction has high sensitivity and specificity for rapid identification of viral infections and should be used when available. Early diagnosis is imperative, and biopsy should be pursued if a diagnosis is not readily obtained with noninvasive testing. Treatment is pathogen specific. Combination antifungal therapy should be considered for cerebral aspergillosis. Zygomycetes and related invasive fungi require surgical resection and high-dose antifungal therapy. Viral meningoencephalitis therapy should be continued until resolution of clinical signs and symptoms, and viral clearance is verified with repeat cerebrospinal fluid analysis. Cytomegalovirus encephalitis requires ongoing maintenance therapy until clearance of viremia or antigenemia. Bacterial meningitis is uncommon in transplantation and should be treated with 21 days of antibiotics. CNS bacterial abscesses, including nocardiosis, should be surgically drained if feasible and treated until resolution of clinical and radiographic evidence of infection.

Emerging viral infections after hematopoietic cell transplantation

This overview summarizes recent data on emerging viruses after hematopoietic cell transplantation (HCT), including adenovirus, BK virus, human metapneumovirus (hMPV), and human herpesvirus (HHV) 6. The increased recognition of these infections is due to improved molecular detection methods, increased surveillance and more profound immunosuppression in the host. Adenovirus can cause serious disease especially in T-cell depleted transplant recipients. Adenovirus viremia is an important risk factor for disease in this setting. BK virus has been associated with hemorrhagic cystitis in HCT recipients. BK viremia is significantly associated with hemorrhagic cystitis. hMPV shows a seasonal distribution and can cause fatal pneumonia in HCT recipients. hMPV may be the etiology of some cases previously categorized as idiopathic pneumonia syndrome. HHV-6 commonly leads to viremia in HCT recipients. HHV-6 has been strongly associated with encephalitis and delayed platelet engraftment. Prospective studies are needed to further examine epidemiology, disease associations, and management strategies for these viruses.

Differential tropism of human herpesvirus 6 (HHV-6) variants and induction of latency by HHV-6A in oligodendrocytes

Human herpesvirus 6 (HHV-6) is a ubiquitous β-herpesvirus associated with a number of clinical disorders. Two closely but biologically distinct variants have been described. HHV-6 variant B causes the common childhood disease exhanthem subitum, and although the pathologic characteristics for HHV-6 variant A are less well defined, HHV-6A has been suggested to be more neurotropic. We studied the effect of both HHV-6 variants in an oligodendrocyte cell line (MO3.13). Infection of M03.13 was monitored by cytopathic effect (CPE), quantitative TaqMan PCR for viral DNA in cells and supernatant, reverse transcriptase-polymerase chain reaction (RT-PCR) to detect viral RNA, and indirect immunofluorescence (IFA) to detect viral protein expression. HHV-6A infection induced significantly more CPE than infection with HHV-6B. HHV-6B induced an abortive infection associated with a decrease of the initial viral DNA load over time, early RNA expression, and no expression of viral antigen. In contrast, infection with HHV-6A DNA persisted in cells for at least 62 days. During the acute phase of infection with HHV-6A, intracellular and extracellular viral load increased and cells expressed the viral protein IE-2 and gp116/54/64. No HHV-6A RNA or protein was expressed after 30 days post infection, suggesting that HHV-6A formed a latent infection. These studies provide in vitro support to the hypothesis that HHV-6 can actively infect oligodendrocytes. Our results suggest that HHV-6A and HHV-6B have different tropism in MO3.13 cells and that an initially active HHV-6A infection can develop latency. Differences between HHV-6A and -6B infection in different neural cell types may be associated with different neurological diseases.

The human herpesvirus 6 G protein-coupled receptor homolog U51 positively regulates virus replication and enhances cell-cell fusion in vitro

Human herpesvirus 6 (HHV-6) is a ubiquitous T-lymphotropic betaherpesvirus that encodes two G protein-coupled receptor homologs, U12 and U51. HHV-6A U51 has been reported to bind to CC chemokines including RANTES, but the biological function of U51 remains uncertain. In this report, we stably expressed short interfering RNAs (siRNAs) specific for U51 in human T cells and then infected these cells with HHV-6. Viral DNA replication was reduced 50-fold by the U51 siRNA, and virally induced cytopathic effects were also inhibited. In contrast, viral replication and syncytium formation were unaltered in cells that expressed a scrambled derivative of the siRNA or an irrelevant siRNA and were restored to normal when a human codon-optimized derivative of U51 was introduced into cells containing the U51 siRNA. To examine the mechanism whereby U51 might contribute to viral replication, we explored the signaling characteristics of U51. None of the chemokines and opioids tested was able to induce G protein coupling by U51, and no evidence for opioid ligand binding by U51 was obtained. The effect of U51 on cell-cell fusion was also evaluated; these studies showed that U51 enhanced cell fusion mediated by the G protein of vesicular stomatitis virus. However, a U51-specific antiserum had no virus-neutralizing activity, suggesting that U51 may not be involved in the initial interaction between the virus particle and host cell. Overall, these studies suggest that HHV-6 U51 is a positive regulator of virus replication in vitro, perhaps because it may promote membrane fusion and facilitates cell-cell spread of this highly cell-associated virus.

Risk of transmission of herpesviruses through cord blood transplantation

Cord blood (CB) progenitor cells are increasingly used for transplantation in children because of the lower risk of graft-versus-host disease compared with unrelated bone marrow and comparable rates of disease-free survival. There is concern that CB might carry a higher risk of opportunistic infections. Human herpesviruses (HHV) are common pathogens in transplant recipients. CB donors are routinely tested for the presence of anti-cytomegalovirus (CMV) immunoglobulin M to reduce the risk of collecting CMV-infected CB. To assess the incidence of beta and gamma HHV infection of CB collected under standard procedures, we tested 362 CB samples for the presence of CMV; HHV-6, -7, and -8; and Epstein-Barr virus DNA by polymerase chain reaction. HHV-6 DNA was found in 2 samples, yielding an incidence of 0.55% (95% confidence interval, 0.1%-2%). None of the other viral DNAs was found, resulting in a 95% confidence interval of 0% to 1% for the incidence of CMV, Epstein-Barr virus, HHV-7, and HHV-8. Because the seroprevalence of HHV-8 among the CB donors in this study was only 4%, these findings cannot be extended to HHV-8-endemic areas. Our data show that screening prospective CB donors with anti-CMV immunoglobulin M practically eliminates the risk of CB CMV transmission, but HHV-6 warrants CB testing by polymerase chain reaction.

Clinical Outcomes of Human Herpesvirus 6 Reactivation after Hematopoietic Stem Cell Transplantation

BACKGROUND

Although human herpesvirus 6 (HHV-6) is known to reactivate during hematopoietic stem cell transplantation (HSCT), the clinical significance of this finding is controversial.

METHODS

We used a quantitative PCR test for HHV-6 to assay plasma samples prospectively collected from a cohort of 110 allogeneic HSCT recipients to evaluate the clinical effects of HHV-6 infection. A retrospective review of medical records was performed to determine clinical end points.

RESULTS

HHV-6 reactivation occurred in 52 (47%) of the 110 subjects. Factors that increased the risk of subsequent HHV-6 reactivation were hematologic malignancy that occurred at a time other than the first remission (adjusted P = .002), a mismatch in the sexes of donor and recipient (adjusted P=.05), younger age (adjusted P = .01), and the receipt of glucocorticoids (adjusted P = .06). HHV-6 reactivation was associated with subsequent all-cause mortality (adjusted hazard ration [HR], 2.9; 95% confidence interval [CI], 1.1-7.5), grade 3-4 graft-versus-host disease (GVHD) (adjusted HR, 4.9; 95% CI, 1.5-16), a lower probability of monocyte engraftment (adjusted HR, 0.42; 95% CI; 0.22-0.80), a lower probability of platelet engraftment (adjusted HR, 0.47; 95% CI, 0.21-1.1; P = .05) and a higher platelet transfusion requirement (adjusted P = .02). A higher level of HHV-6 DNA was associated with subsequent central nervous system (CNS) dysfunction (HR, 21; 95% CI, 1.8-249).

CONCLUSIONS

HHV-6 reactivation is common after allogeneic HSCT and is associated with subsequent delayed monocyte and platelet engraftment, increased platelet transfusion requirements, all-cause mortality, grade 3-4 GVHD, and CNS dysfunction.

Encephalopathy in pediatric patients after allogeneic hematopoietic stem cell transplantation is associated with a poor prognosis

Encephalopathy is a poorly characterized complication of hematopoietic stem cell transplantation (HSCT). No comprehensive report of encephalopathy exists for children, and the literature contains only a few for adults. We analyzed a large cohort of 405 pediatric patients who underwent allogeneic HSCT during a 10-year period and identified 26 patients (6.4%) who experienced encephalopathy. Identifiable causes of encephalopathy included infection (n=5), single or multiorgan failure (n=4), medication-related complications (n=3), nonconvulsive seizures (n=4), acute disseminated encephalomyelitis (n=2), thrombotic thrombocytopenic purpura (n=2), and stroke (n=1). We were unable to identify the etiology of encephalopathy in five (19%) patients. The prognosis for pediatric patients with encephalopathy was poor: only four (15%) experienced complete neurologic recovery, and 10 (38%) patients experienced partial recovery with residual neurologic deficits. Nine (35%) patients with complete or partial recovery survive long term. A total of 17 patients died; one died of progressive encephalopathy, and 16 died of either relapse of primary disease or toxicity. MRI, CSF analysis including molecular testing for infectious pathogens, and brain biopsy were helpful in obtaining a diagnosis in most of our patients. However, a standardized approach to accurate and timely diagnosis and treatment is needed to improve outcome in these patients.

A population-based study of primary human herpesvirus 6 infection

BACKGROUND

Serologic studies indicate that human herpesvirus 6 (HHV-6) infects 90 percent of children by two years of age. Little is known about the acquisition, virologic course, and clinical manifestations of HHV-6 infection.

METHODS

We prospectively studied a cohort of 277 children from birth through the first two years of life to define the pattern of acquisition of HHV-6. The children's saliva was tested weekly for HHV-6 DNA with the use of the polymerase chain reaction. Parents maintained a daily log of signs and symptoms of illness in their children.

RESULTS

Primary HHV-6 infection occurred in 130 children, with cumulative percentages of 40 percent by the age of 12 months and 77 percent by the age of 24 months. The peak age of acquisition was between 9 and 21 months. The acquisition of HHV-6 was associated with female sex (adjusted hazard ratio, 1.7; 95 percent confidence interval, 1.2 to 2.4) and having older siblings (adjusted hazard ratio, 2.1; 95 percent confidence interval, 1.4 to 2.9). Among 81 children with a well-defined time of acquisition of HHV-6, 93 percent had symptoms, and 38 percent were seen by a physician. None had seizures. As compared with children who had other illnesses, those with primary HHV-6 infection were more likely to have fever (P=0.003), fussiness (P=0.02), diarrhea (P=0.03), rash (P=0.003), and roseola (P=0.002) and were more likely to visit a physician (P=0.003).

CONCLUSIONS

The acquisition of HHV-6 in infancy is usually symptomatic and often results in medical evaluation. Roseola occurs in a minority of patients, and febrile seizures are infrequently associated with primary HHV-6 infection. Older siblings appear to serve as a source of HHV-6 transmission.

Interactions between viruses in transplant recipients

Viral coinfections may modulate disease expression, enhance pathogenicity, and lead to greater cumulative immunosuppression in the host. The pathophysiological basis of these may be direct virus-virus interactions, effect of cohabitating viruses on host cell function, or impaired host immune responses. The interrelationship between viral pathogens has become increasingly more relevant and its scope wider as new or previously unrecognized viruses continue to emerge as pathogens in transplant recipients. The pathways and mediators that modulate biological activity represent potential targets for immunomodulatory interventions as adjunctive therapies for transplant recipients.

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).

Combating infections in hematopoietic stem cell transplant recipients

Infections with a diverse group of microorganisms remain the leading causes of morbidity and mortality after hematopoietic stem cell transplantation. Importantly, the epidemiology of infectious complications has shifted substantially with changes in antimicrobial prophylaxis, conditioning regimens and graft manipulation, such that invasive mould infections and late viral infections are now the over-riding concerns. New antivirals and antifungals have entered clinical practice and hold considerable promise for improved outcomes.

Human herpesvirus 6 antigenaemia in allogeneic stem cell transplant recipients: impact on clinical course and association with other beta-herpesviruses

Human herpesvirus 6 (HHV-6) antigenaemia was prospectively studied in 58 adult allogeneic stem cell transplant (SCT) recipients. Altogether 42 of 58 recipients (72%) demonstrated HHV-6 specific antigens in peripheral blood mononuclear cells after SCT, 22 of 36 (61%) when the donor was a sibling and 20 of 22 (91%) when the donor was unrelated. The cumulative incidence of HHV-6A, HHV-6B, HHV-7, and cytomegalovirus antigenaemia during the first 6 months after SCT was 33%, 62%, 44% and 63% respectively. The median day of the onset of each antigenaemia was +24, +4, +59, and +46 after SCT respectively. There were no clinical findings related to HHV-6A and HHV-7 antigenaemias. A rash was diagnosed in 10 of 38 (26%) HHV-6B antigenaemia positive patients during the first month after SCT compared with one of 20 (5%) HHV-6B negative patients. Of the HHV-6B antigenaemia cases, six of 10 rashes were treated as acute graft-versus-host disease (GVHD) and four of 10 were considered to be of a viral origin. Fifteen patients had acute GVHD diagnosed. Acute GVHD manifested statistically significantly (P = 0.034) earlier in the nine patients with HHV-6B antigenaemia compared with the six patients who were HHV-6B negative.

Encephalitis owing to human herpesvirus-6 after cardiac transplant

Human herpesvirus-6 (HHV-6), a beta herpesvirus closely related to cytomegalovirus (CMV), infects the majority of the population in childhood. Human herpesvirus-6 can be reactivated in the immunosuppressed patient. After bone marrow and orthotopic liver transplant, it has been linked to various clinical syndromes, including undifferentiated febrile illness, encephalitis, pneumonitis and bone marrow suppression. To date its infectious role after orthotopic heart transplant has not been well documented. We present the case of a 32-year-old cardiac transplant recipient who initially presented 8 weeks after his transplant with high fever and headache. He developed increasing confusion, pulmonary infiltrates and neutropenia. Cytomegalovirus viral loads were negative. Polymerase chain reaction (PCR) of blood and cerebrospinal fluid detected HHV-6 DNA, consistent with HHV-6-related encephalitis, pneumonitis and bone marrow suppression. He was treated with foscarnet with gradual improvement in clinical status. We review the literature on the significance of this virus post cardiac transplant.

Human herpesvirus 6 infection of the central nervous system

Human herpesvirus (HHV) 6 infects all children, usually during the first year of life. High fever is the hallmark of primary infection, with febrile seizures the most common complication. After primary infection, HHV-6 remains latent or persistent at multiple sites, with intermittent reactivation. Many disorders of the central nervous system (CNS) have been linked to HHV-6 reactivation, including chronic seizure disorders, encephalitis, and demyelinating disorders including multiple sclerosis. Although multiple studies have pieced together an understanding of the molecular organization, viral characteristics, immunology, and epidemiology of HHV-6, the true role of this virus in diseases of the CNS is still unfolding.

Management of infectious complications in the hematopoietic stem cell transplant recipient

Despite impressive accomplishments in supportive care over the past decade, infections with a diverse group of microorganisms remain leading causes of morbidity and mortality after hematopoietic stem cell transplantation. The epidemiology of infectious complications has shifted substantially in the past decade with changes in antimicrobial prophylaxis, conditioning regimens, and graft manipulation, such that invasive mould infections and late viral infections are now the overriding concerns. Individual patient risk for infections is predicated on multiple disease-specific, patient-specific, and transplant-related factors but often tracks with the cumulative level of immunosuppression (such as dose of corticosteroids used for the treatment of graft vs host disease [GVHD]). New antivirals and antifungals have entered clinical practice and hold considerable promise for improved outcomes.

Significance of human herpesviruses to transplant recipients

PURPOSE OF REVIEW

Despite recent great advances in transplantation techniques, herpesvirus infections remain a major cause of morbidity and mortality in transplant recipients. While improvement in immunosuppressive drug regimens have decreased the risk of graft-versus-host disease and rejection in bone marrow transplant recipients and solid organ transplant recipients, all such drugs carry with them an increased risk of herpesvirus reactivation. The following review consolidates recent findings in this field, covering reports published from January 2002 to August 2003.

RECENT FINDINGS

Real-time polymerase chain reaction has improved the ability to distinguish between latent and active herpesvirus infection, which had been a major difficulty in the diagnosis of such conditions. It has been suggested that evaluation of virus-specific cytotoxic T lymphocyte activity is important for prediction of viral diseases. Development of new antiviral drugs has provided other therapeutic options. However, neither prophylactic nor preemptive administration of antiviral drugs can completely abolish the risk of herpesvirus infection. Transfusion of virus-specific cytotoxic T lymphocytes has been suggested to be a useful treatment for recipients with continuous viral replication due to severe immunosuppression.

SUMMARY

Recent progress has been made in learning more about the role of virus-specific cytotoxic T lymphocytes, and developing better diagnostic procedures and therapeutic protocols that are efficient and have reduced adverse side effects. Reliable monitoring methods for viral load, in combination with evaluation of virus-specific cytotoxic T cells, has made possible the prediction of viral diseases and furthered understanding of the role of these cells in controlling viral infections. Furthermore, adoptive immunotherapy has been improved by analyzing host immune responses.

Differentiation and quantitation of human herpesviruses 6A, 6B and 7 by real-time PCR

The beta-herpesviruses cause considerable morbidity in immunocompromised individuals, such as transplant patients. Most notably within this group is human cytomegalovirus, although HHV-6 and -7 are a growing concern. Identifying HHV-6 and -7 as the cause of post-transplant illness can be challenging due to high seroprevalence and latency properties associated with these human herpesviruses. We have developed a sensitive and specific real-time PCR assay, which can differentiate reliably and quantify HHV-6A, -6B and -7. Using two sets of hybridization probes specific for HHV-6A or -6B and HHV-7, the assay reliably differentiates the three viruses using melting curve analysis. The lower limit of detection for all three viruses was determined to be ten viral genomes. This real-time PCR assay will be useful for differentiation and quantitation of HHV-6A, -6B and -7, especially for monitoring transplant patients.

Human herpesvirus-6 and -7 infections in transplantation

Human herpesvirus-6 (HHV-6) and human herpesvirus-7 (HHV-7) are ubiquitous in the human population and cause exanthem subitum, a benign disease seen in infancy. The viruses remain latent in the body after primary infection, and reactivate in immunocompromised patients. HHV-6 infection occurs in nearly 50% of all bone marrow and in 20-30% of solid-organ transplant recipients, 2-3 weeks following the procedure. It has been suggested that the viral infection and activation result in clinical symptoms, including fever, skin rash, pneumonia, bone marrow suppression, encephalitis, and rejection. In order to understand the viral infection in greater detail, several studies investigating the route of viral transmission and diagnostic procedures have been carried out. In contrast to studies of HHV-6 infection in organ-transplant recipients, the number of studies examining HHV-7 infection in these patients is limited. According to several recent studies, HHV-7 may act as a cofactor for cytomegalovirus disease in organ-transplant recipients.

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.

Characterisation of a human herpesvirus 6 variant A 'amplicon' and replication modulation by U94-Rep 'latency gene'

The human herpesvirus 6 (HHV-6) variant A genome has conserved sequences which are signals for initiating lytic replication (origin, 'ori-lyt') and DNA packaging into the virion (pac2/1). Here these are functionally characterised and used to construct a gene-expression amplifiable-vector, an 'amplicon', with applications for gene delivery to lymphoid-myeloid cells or their progenitor stem cells. A minimal efficient ori-lyt for replication was identified which was enhanced in the presence of the imperfect direct repeated DNA domain (IDR). In A variant strains these are arranged as three adjacent repeats with the most divergence in IDR3. Addition of the pac2/1 sequences also enhanced detection of ori-lyt replication and conferred DNA packaging properties, thus, the amplicon could be packaged with 'helper' virus. An HHV-6 specific factor, which inhibits amplicon replication was identified by trans replication assays. This is the U94-Rep 'latency' gene product, which can modulate efficiency of such amplifiable vectors, based on the lytic origin. It could also affect maintenance of viral genomes or vectors during latency.

Ganciclovir-resistant cytomegalovirus encephalitis in a bone marrow transplant recipient

A 20-year-old patient, who received a bone marrow transplant in order to treat metachromatic leukodystrophy (MLD), succumbed to cytomegalovirus (CMV) encephalitis. After CMV viremia developed, the patient received ganciclovir, but he was switched to foscarnet when ganciclovir resistance was suspected. Foscarnet was discontinued because of concern about its potential central nervous system toxicity. Autopsy samples of brain and cerebrospinal fluid contained CMV DNA with a UL97 mutation (M460V) known to confer ganciclovir resistance. No foscarnet resistance mutations were found.

Cytokines, viruses, and graft-versus-host disease

Proinflammatory cytokines released by host tissues during conditioning treatment and interferon gamma released from donor T cells play a major role in acute graft-versus-host disease (GVHD). In the past year the interaction of cytokines has been elucidated further. Host antigen-presenting cells play a key role in the induction of allogeneic recognition. Their activity is modulated by cytokines such as flt3-ligand, viruses, and donor T cells. Expansion of donor T cells is crucial for the pathogenesis of acute GVHD. Cytokines of the T helper 1 response-IFN-gamma, IL-12, and IL-18-regulate the expansion of donor and host cells via the induction of Fas and FasL and subsequent apoptosis. However TNF-alpha, FasL, and IL-1 also cause damage to target cells. Cytokine and receptor gene polymorphism has an impact on the activity of both host and donor cell activation. Genetic factors, conditioning treatment, lipopolysaccharides (LPS) from gram-negative microorganisms, viral infections, and donor T cells determine the activity level of host antigen-presenting cells and macrophages, which have an impact on acute GVHD and other complications of allogeneic stem cell transplantation.

Beta-herpesvirus challenges in the transplant recipient

Cytomegalovirus (CMV) has major consequences after allogeneic stem cell and solid organ transplantation. CMV may cause significant morbidity and mortality, and monitoring to detect reactivation to reduce disease or management of end organ disease is associated with increased resource utilization. Two other members of the beta-herpesvirus family, human herpesvirus (HHV) type 6 and HHV-7, are increasingly recognized as important pathogens in transplant recipients, either by direct infection (e.g., encephalitis, hepatitis, or pneumonitis) or via interaction with CMV. In addition to direct effects of CMV infection, such indirect effects as an increased risk for bacterial and fungal infections or impaired graft acceptance and function are important research topics. Diagnosis and treatment of CMV infection is currently more advanced than for HHV-6 and HHV-7.

[Herpetic meningo-encephalitis]

Herpes simplex encephalitis is characterized by a very poor prognosis. HSV1 and HSV2 are the two viruses responsible for this neurological infection. The gold standard assay for the diagnosis is PCR on CSF. However, one should not wait for the result of this assay to initiate an antiviral treatment, using i.v. aciclovir.

Markers of viral infection in monozygotic twins discordant for chronic fatigue syndrome

To estimate the prevalence of viruses associated with chronic fatigue syndrome (CFS) and to control for genetic and environmental factors, we conducted a co-twin control study of 22 monozygotic twin pairs, of which one twin met criteria for CFS and the other twin was healthy. Levels of antibodies to human herpesvirus (HHV)-8, cytomegalovirus, herpes simplex virus 1 and 2, and hepatitis C virus were measured. Polymerase chain reaction (PCR) assays for viral DNA were performed on peripheral blood mononuclear cell specimens to detect infection with HHV-6, HHV-7, HHV-8, cytomegalovirus, Epstein-Barr virus, herpes simplex virus, varicella zoster virus, JC virus, BK virus, and parvovirus B19. To detect lytic infection, plasma was tested by PCR for HHV-6, HHV-8, cytomegalovirus, and Epstein-Barr virus DNA, and saliva was examined for HHV-8 DNA. For all assays, results did not differ between the group of twins with CFS and the healthy twins.

Human herpesvirus 6 meningoencephalitis successfully treated with ganciclovir in a patient who underwent allogeneic bone marrow transplantation from an HLA-identical sibling

Human herpesvirus 6 (HHV-6) has recently been recognized as an important pathogen in immunocompromised hosts, such as patients who have undergone allogeneic bone marrow transplantation (allo-BMT). Here we report a case of HHV-6 meningoencephalitis in a patient who underwent allo-BMT from an HLA-identical sibling. The patient suffered from headache, high fever, tremor, and disorientation on day 35 after allo-BMT. Findings at magnetic resonance imaging, electroencephalography, and routine cerebrospinal fluid (CSF) examination suggested the presence of viral meningoencephalitis. We diagnosed HHV-6 meningoencephalitis by means of polymerase chain reaction (PCR) analysis of a CSF specimen. Successful treatment was achieved with ganciclovir. Because HHV-6 encephalitis has a potentially fatal and fulminant course, it is necessary that HHV-6 encephalitis be recognized as one of the central nervous system complications that can follow allo-BMT. PCR analysis for HHV-6 in the CSF specimen is necessary for appropriate diagnosis and treatment.

A humanized non-FcR-binding anti-CD3 antibody, visilizumab, for treatment of steroid-refractory acute graft-versus-host disease

Visilizumab is a humanized anti-CD3 monoclonal antibody characterized by a mutated IgG2 isotype, lack of binding to Fcgamma-receptors, and ability to induce apoptosis selectively in activated T cells. To test pharmacokinetics, safety, and immunosuppressive activity of visilizumab, 17 patients with glucocorticoid-refractory acute graft-versus-host disease (GVHD) were enrolled in a phase 1 study. Six patients were given 7 doses of visilizumab (0.25 or 1.0 mg/m(2)) on days 1, 3, 5, 7, 9, 11, and 13. Because multiple doses of 1 mg/m(2) caused delayed visilizumab accumulation and prolonged lymphopenia, the next 11 patients received a single dose of 3.0 mg/m(2) on day 1. GVHD improved in all patients; 15 were evaluable through day 42. Multiple dosing resulted in 1 of 6 complete responses (CRs) and 5 partial responses (PRs), but all 6 patients died at a median of 87 days after starting visilizumab therapy. Single dosing resulted in 6 of 9 CRs, 3 PRs, and 7 of 11 patients surviving after 260 to 490 days (median, 359 days; P =.03). There were no allergic reactions and 3 grade 1 acute infusional toxicities. Plasma Epstein-Barr virus (EBV) DNA titers more than 1000 copies/mL and posttransplant lymphoproliferative disease (PTLD) developed in 2 of the first 7 patients. Based on rising EBV DNA titers, 5 of the next 10 patients were given the B cell-specific monoclonal antibody, rituximab. EBV DNA became undetectable and no overt PTLD developed. Visilizumab is well tolerated and has activity in advanced GVHD. A phase 2 study incorporating preemptive therapy for PTLD is warranted to determine the efficacy of visilizumab in GVHD.

Case report: primary human herpesvirus-6 associated with an afebrile seizure in a 3-week-old infant

We describe a 3-week-old male infant with an afebrile seizure in whom serologic and polymerase chain reaction (PCR) findings support concomitant primary human herpesvirus 6 (HHV-6) infection. Although HHV-6 infection has been associated with first-time febrile seizures and encephalitis in both immunocompetent and immunocompromised hosts, it has not been associated previously with afebrile seizures in healthy infants. This report provides additional evidence of the neuropathogenic potential of HHV-6.

Effect of antivirals on human herpesvirus 6 replication in hematopoietic stem cell transplant recipients

Human herpesvirus 6 (HHV-6) appears to cause central nervous system (CNS) syndromes, especially in hematopoietic stem cell transplant (HSCT) recipients. We reviewed our experience with HHV-6-associated CNS disease to evaluate both the clinical and virological presentation and response to antiviral therapy. A search of our virology database from January 1998 through June 2000 identified 11 HSCT recipients who had HHV-6 DNA detected by polymerase chain reaction in cerebrospinal fluid (CSF); 8 of whom had CNS dysfunction without another clear etiology identified. HHV-6 levels in serum and CSF were evaluated before and after ganciclovir and/or foscarnet therapy. Median log HHV-6 CSF levels appeared to decrease over time concurrent with antiviral therapy (serum level, 2.0 vs. 0 copies/mL [P=.38]; CSF level, 4.4 vs. 2.0 copies/mL [P=.13], sign test). Our data suggests that HHV-6 may cause moderate to severe CNS disease after HSC transplantation. Prospective studies are needed to define the spectrum of HHV-6-associated disease and to determine whether antiviral therapy offers clinical benefit.