Identification of integrated human herpesvirus 6 DNA in early pre-B cell acute lymphoblastic leukemia

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.

Associations between human herpesvirus-6, human papillomavirus and cervical cancer

Cervical cancer (CxCa) is the second most common cancer among women globally. Human papillomavirus (HPV) infection is thought to be a necessary, but not sufficient, causal factor in CxCa development. Why some women are able to clear HPV infection with no adverse effects, whereas others develop cancer, remains unclear. HHV-6 has demonstrated transformative abilities and has been shown to be present in the genital tract. However, based on the current evidence, we cannot conclude that HHV-6 is a co-factor in HPV-associated carcinogenesis. Nonetheless, future research is warranted because of several crucial gaps in the literature.

Anal cancer incidence and survival: comparing the greater San-Francisco bay area to other SEER cancer registries

The incidence of squamous cell carcinoma of the anus, anal canal, and anorectum (SCCA) has increased over time. However, there are still no national guidelines on screening for SCCA among high-risk populations. Providers at University of California, San Francisco have been at the forefront of providing anal dysplasia screening. To determine whether such a screening program allows for earlier detection of abnormalities and consequently, improves patient survival, we conducted an ecological study using data from the Surveillance, Epidemiology, and End Results (SEER) program to compare the San Francisco-Oakland catchment area (SF-O) to other SEER sites where routine screening has not been as accessible. Cox regression models were utilized to assess the impact of residing in the SF-O region, versus other SEER sites, on cause-specific mortality hazard. Logistic regression was used to determine if site was associated with the probability of having an in situ versus invasive tumor among SCCA cases. All analyses were stratified on calendar time (1985-1995 and 1996-2008) to compare differences pre- and post- highly active anti-retroviral therapy. Among SCCA cases, being reported by the SF-O registry was associated with a four fold higher probability of having an in situ tumor (rather than an invasive tumor) [95% CI: 3.48-4.61], compared to sites outside of California, between 1996 and 2008. Cases reported from the SF-O region between 1996 and 2008 had a 39% lower mortality risk than those reported from registries outside California (95% CI: 0.51-0.72). However, there was no decrease in the rate of invasive SCCA over this period. This is the first ecological study to evaluate whether access to anal cancer screening programs may help improve patient survival by allowing for earlier detection of lesions. Our results imply that routine screening programs may help detect SCCA at an earlier stage and thus, potentially impact patient survival.

Chromosomally-integrated human herpesvirus 6 in familial glioma etiology

Human herpesvirus 6 (HHV-6) is a highly neurotropic beta-herpesvirus with demonstrated transformative properties. HHV-6 infection has been implicated in the etiologies of cancers, including lymphoma and leukemia; conditions with brain involvement, including epilepsy and encephalitis; and other disorders. HHV-6 is also the only human herpesvirus that has been proven to integrate into the chromosomes of a proportion (1-12%) of infected individuals. Because several traditional genetic association studies have failed to identify a variant that can account for the established relationship between family history and glioma risk, the possibility that chromosomally-integrated HHV-6 (CI-HHV-6), as a heritable factor, may explain a proportion of familial glioma cases warrants evaluation. To test this hypothesis, the prevalence of CI-HHV-6 in familial glioma cases and related and unrelated cancer-free control groups should be compared. Among glioma-affected families, the inheritance pattern of CI-HHV-6 could be evaluated by constructing pedigrees. If CI-HHV-6 is found to be associated with familial glioma risk, this knowledge could potentially lead to the future development of novel therapeutic and preventive approaches, including vaccines and immunotherapies targeted at the HHV-6 sequences.

Impact of human herpes virus 6 in liver transplantation

Human herpes virus 6 (HHV-6) infects > 95% of humans. Primary infection which occurs mostly during the first 2 years of life in the form of roseola infantum, non-specific febrile illness, or an asymptomatic illness, results in latency. Reactivation of latent HHV-6 is common after liver transplantation. Since the majority of human beings harbor the latent virus, HHV-6 infections after liver transplantation are most probably caused by endogenous reactivation or superinfection. In a minority of cases, primary HHV-6 infection may occur when an HHV-6-seronegative individual receives a liver allograft from an HHV-6-seropositive donor. The vast majority of HHV-6 infections after liver transplantation are asymptomatic. Only in a minority of cases, when HHV-6 causes a febrile illness associated with rash and myelosuppression, hepatitis, gastroenteritis, pneumonitis, and encephalitis after liver transplantation. In addition, HHV-6 has been implicated in a variety of indirect effects, such as allograft rejection and increased predisposition to and severity of other infections, including cytomegalovirus, hepatitis C virus, and opportunistic fungi. Because of the uncommon nature of the clinical illnesses directly attributed to HHV-6, there is currently no recommended HHV-6-specific approach prevention after liver transplantation. Asymptomatic HHV-6 infection does not require antiviral treatment, while treatment of established HHV-6 disease is treated with intravenous ganciclovir, foscarnet, or cidofovir and this should be complemented by a reduction in immunosuppression.

Herpesviruses and chromosomal integration

Herpesviruses are members of a diverse family of viruses that colonize all vertebrates from fish to mammals. Although more than one hundred herpesviruses exist, all are nearly identical architecturally, with a genome consisting of a linear double-stranded DNA molecule (100 to 225 kbp) protected by an icosahedral capsid made up of 162 hollow-centered capsomeres, a tegument surrounding the nucleocapsid, and a viral envelope derived from host membranes. Upon infection, the linear viral DNA is delivered to the nucleus, where it circularizes to form the viral episome. Depending on several factors, the viral cycle can proceed either to a productive infection or to a state of latency. In either case, the viral genetic information is maintained as extrachromosomal circular DNA. Interestingly, however, certain oncogenic herpesviruses such as Marek's disease virus and Epstein-Barr virus can be found integrated at low frequencies in the host's chromosomes. These findings have mostly been viewed as anecdotal and considered exceptions rather than properties of herpesviruses. In recent years, the consistent and rather frequent detection (in approximately 1% of the human population) of human herpesvirus 6 (HHV-6) viral DNA integrated into human chromosomes has spurred renewed interest in our understanding of how these viruses infect, replicate, and propagate themselves. In this review, we provide a historical perspective on chromosomal integration by herpesviruses and present the current state of knowledge on integration by HHV-6 with the possible clinical implications associated with viral integration.

Human herpesvirus 6 infections after liver transplantation

Human herpesvirus 6 (HHV-6) infections occur in > 95% of humans. Primary infection, which occurs in early childhood as an asymptomatic illness or manifested clinically as roseola infantum, leads to a state of subclinical viral persistence and latency. Reactivation of latent HHV-6 is common after liver transplantation, possibly induced and facilitated by allograft rejection and immunosuppressive therapy. Since the vast majority of humans harbor the virus in a latent state, HHV-6 infections after liver transplantation are believed to be mostly due to endogenous reactivation or superinfection (reactivation in the transplanted organ). In a minority of cases, however, primary HHV-6 infection may occur when an HHV-6 negative individual receives a liver allograft from an HHV-6 positive donor. The vast majority of documented HHV-6 infections after liver transplantation are asymptomatic. In a minority of cases, HHV-6 has been implicated as a cause of febrile illness with rash and myelosuppression, hepatitis, pneumonitis, and encephalitis after liver transplantation. In addition, HHV-6 has been associated with a variety of indirect effects such as allograft rejection, and increased predisposition and severity of other infections including cytomegalovirus (CMV), hepatitis C virus, and opportunistic fungi. Because of the uncommon nature of the clinical illnesses directly attributed to HHV-6, there is currently no recommended HHV-6-specific approach to prevention. However, ganciclovir and valganciclovir, which are primarily intended for the prevention of CMV disease, are also active against HHV-6 and may prevent its reactivation after transplantation. The treatment of established HHV-6 disease is usually with intravenous ganciclovir, cidofovir, or foscarnet, complemented by reduction in the degree of immunosuppression. This article reviews the current advances in the pathogenesis, clinical diagnosis, and therapeutic modalities against HHV6 in the setting of liver transplantation.

The prevalence of chromosomally integrated human herpesvirus 6 genomes in the blood of UK blood donors

A lesser-recognized form of human herpesvirus 6 (HHV-6) persistence is integration of the viral genome in a host chromosome and high viral copy numbers in blood or sera are characteristic of this phenomenon. A cross-sectional study was performed to determine the frequency of high HHV-6 viral loads in whole blood (>6 log(10) copies/ml) in a population of blood donors in London, UK. Blood samples from 500 anonymized blood donors were collected from one donation center, DNA extracted, and quantitative realtime PCR used to measure viral load. Four samples (0.8%) were found to have high viral copy numbers of HHV-6 (median 6.7 log(10) copies/ml; range 6.5- 6.9 log(10) copies/ml). Cellular DNA was also quantitated using qRT-PCR for beta-globin. By comparing these two results, we calculated that there were between two and five copies of HHV-6 present per cell in these four donors. The median viral load detected in plasma from the four individuals was 3.8 log(10) copies/ml (range 3.5-4.0 log(10) copies/ml). All samples were HHV-6 variant B. In addition, a retrospective analysis of all diagnostic blood samples performed for HHV-6 in our center showed a prevalence of 2.9% of high viral loads characteristic of integration. In conclusion, high viral copy numbers of HHV-6, representing a population of viral integration, is detected in 0.8% of UK blood donors. The presence of high HHV-6 viral loads in healthy normal individuals reiterates the need to consider the confounding effect of HHV-6 viral integration in any laboratory diagnosis of HHV-6 infection.

Hematologic Malignancies in Pregnancy

Hematologic malignancies complicating pregnancy are uncommon, but a delay in diagnosis or treatment can mean the difference between life and death. It is the responsibility of the obstetrician, nurse-midwife, or nurse practitioner to maintain a high index of suspicion when patients present with unexplained lymphadenopathy or protracted constitutional symptoms. Management of these patients requires a multifaceted team from the oncology, pediatrics, and obstetrics services. With most hematologic cancers now requiring multiagent chemotherapy for optimal survival, the patient, her family, and her physicians are often faced with what seems to be a Faustian dilemma. Most infants exposed in utero to multiagent chemotherapy, however, seem to suffer no long-term detrimental consequences.

Unexpected occasional persistence of high levels of HHV-6 DNA in sera: Detection of variants A and B

Previously it was thought that in the immunocompetent human herpesvirus-6 [HHV-6] DNA was present transiently in serum during early primary infection but not thereafter. In this study, HHV-6 serum IgG avidity was detected by immunofluorescence and HHV-6 variants A/B [HHV-6A/B] serum DNA by semi-quantitative PCR [titre-log(10) copies/ml] in: (a) young children <3 years old from an encephalitis Survey, and a control Anonymised Serum Bank and (b) children/adults referred for diagnosis. The results showed that 11 out of 15 children [all <2 years] with primary infection proven by seroconversion had transient low levels of serum HHV-6B DNA [mean titre 2.6]. However, 3.3% (6/184) of Survey Children had significantly higher levels [mean titre 5.3; 2 HHV-6A; 4 HHV-6B; P < 0.001]. Similarly high level serum DNA [mean titre 4.0; 4 HHV-6A; 6 HHV-6B] was found in 1.5% (10/653) of the Serum Bank Children. Moreover, seven young children <3 years old [four Survey Children and three referred for diagnosis] had high titre serum HHV-6 DNA [mean 4.8] persisting i.e., in all available samples [median 186 days]. Three older children >3 years old and 4 adults [3 of whom were the mothers of 3 of the young children with persisting HHV-6] also had persisting high titre viral DNA [mean 4.2; median 108 days]. Thus in contrast to acute primary infection, where only HHV-6B DNA is found transiently, both HHV-6A and B DNA persist in serum at high titre in occasional individuals of all ages. The significance of this newly described phenomenon in relation to diagnosis, clinical consequences and congenital infection are discussed.

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).

An infectious aetiology for childhood acute leukaemia: a review of the evidence

There are three current hypotheses concerning infectious mechanisms in the aetiology of childhood leukaemia: exposure in utero or around the time of birth, delayed exposure beyond the first year of life to common infections and unusual population mixing. No specific virus has been definitively linked with childhood leukaemia and there is no evidence to date of viral genomic inclusions within leukaemic cells. The case-control and cohort studies have revealed equivocal results. Maternal infection during pregnancy has been linked with increased risk whilst breast feeding and day care attendance in the first year of life appear to be protective. There is inconclusive evidence from studies on early childhood infectious exposures, vaccination and social mixing. Some supportive evidence for an infectious aetiology is provided by the findings of space-time clustering and seasonal variation. Spatial clustering suggests that higher incidence is confined to specific areas with increased levels of population mixing, particularly in previously isolated populations. Ecological studies have also shown excess incidence with higher population mixing. The marked childhood peak in resource-rich countries and an increased incidence of the childhood peak in acute lymphoblastic leukaemia (ALL) (occurring at ages 2-6 years predominantly with precursor B-cell ALL) is supportive of the concept that reduced early infection may play a role. Genetically determined individual response to infection may be critical in the proliferation of preleukaemic clones as evidenced by the human leucocyte antigen class II polymorphic variant association with precursor B-cell and T-cell ALL.

Congenital infections with human herpesvirus 6 (HHV6) and human herpesvirus 7 (HHV7)

OBJECTIVE

To examine whether: (1) congenital human herpesvirus 6 (HHV6) and human herpesvirus 7 (HHV7) infections occur; whether (2) their manifestations differ from postnatal infections; and whether (3) HHV6 and HHV7 infections differ despite their close relatedness.

STUDY DESIGN

HHV6 and HHV7 infections acquired congenitally and postnatally in normal children were compared using viral isolation, serology, reverse-transcription polymerase chain reaction (RT-PCR) and nested DNA-PCR for HHV6 variant A (HHV6A), HHV6 variant B (HHV6B), and HHV7.

RESULTS

HHV6 DNA was detected in 57 (1%) of 5638 cord bloods. HHV7 DNA, however, was not detected in 2129 cord bloods. Congenital HHV6 infections differed from postnatal infections, which were acute febrile illnesses. Congenital infections were asymptomatic, 10% demonstrated reactivation at birth, and HHV6 DNA persistence in follow-up blood samples was significantly more frequent. One-third of congenital infections were HHV6A, whereas all postnatal infections were HHV6B.

CONCLUSIONS

Congenital HHV6 infections occurred in 1% of births, similar to the rate for cytomegalovirus infection. Congenital infections were clinically and virologically distinct from postnatal infections. Congenital HHV7 infections, however, were not detected, suggesting considerable differences in transmission and pathogenesis in these closely related beta-herpesviruses.

Human herpesvirus-6 rep/U94 gene product has single-stranded DNA-binding activity

The characterization is reported of the human herpesvirus-6B (HHV-6B) rep/U94 gene, which is a homologue of the adeno-associated virus type 2 rep. In this study, a monoclonal antibody was produced against HHV-6B REP (anti-REP mAb). Immunofluorescence staining using the anti-REP mAb showed that REP was localized to the nucleus in HHV-6-infected MT4 cells. It was first detected at 24 h post-infection (p.i.) and accumulated to higher levels by 72 h p.i. REP may be expressed only at very low levels in HHV-6-infected cells: even when the late protein glycoprotein H was detected in nearly 90% of HHV-6-infected cells, REP was detected in only a small percentage of them. Western blot analysis showed that the anti-REP mAb recognized a 56-kDa polypeptide in HHV-6B-infected MT4 cells. Furthermore, the REP protein was shown to bind single-stranded DNA.

Antibody status to HHV-6 in children with leukaemia

Forty children with acute lymphoblastic (33) or myeloid leukaemia (seven) were studied for IgG and IgM antibodies and IgG avidity against human herpesvirus 6 (HHV-6) at the time of diagnosis, and compared with age-, sex- and season-matched children with various neurological diseases of suspected viral origin. Of the children with leukaemia, 97.5% had IgG antibodies and 40% IgM antibodies to HHV-6 compared with 92.3% and 7.7% of reference subjects (P = 0.005). A seronegative child with leukaemia seroconverted 3 weeks after the diagnosis. The avidity of IgG antibodies (based on the resistance to urea treatment) was high in all children with leukaemia. One reference child had HHV-6-specific IgG antibodies with low avidity, which together with his positive IgM indicated an acute infection. The presence of specific IgM antibodies in 40% of children with leukaemia and the high avidity of IgG suggest a reactivation or an inaproppriate primary response to HHV-6 infection. The results support the conclusion of the role of the HHV-6 infection at the onset of childhood leukaemia.

Human herpesvirus 6 infection mimicking juvenile myelomonocytic leukemia in an infant

In vitro cell culture studies of bone marrow and peripheral blood progenitor cells from patients with juvenile myclomonocytic leukemia (JMML) consistently show spontaneous proliferation and selective hypersensitivity to granulocyte-macrophage colony-stimulating factor (GM-CSF). This GM-CSF hypersensitivity dose-response assay has become a component of the international diagnostic criteria for JMML. The authors report a 2-week-old boy with perinatal human herpesvirus 6 (HHV-6) infection in whom in vitro bone marrow culture studies suggested the diagnosis of JMML by showing increased spontaneous proliferation, inhibition of this growth by anti-GM-CSF antibodies, and hypersensitivity to GM-CSF. Polymerase chain reaction viral studies from whole blood DNA and the shell vial viral culture assay were both positive for HHV-6. The patient's condition improved with expectant treatment, with an eventual return to normal blood counts and resolution of hepatosplenomegaly. This case of perinatal HHV-6 infection shows that viruses can initially mimic the in vitro culture results found in patients with JMML. It also illustrates that patients suspected of having JMML should be observed if there are no signs of progressive disease and concurrent features suggestive of viral infection.

Virally encoded 7TM receptors

A number of herpes- and poxviruses encode 7TM G-protein coupled receptors most of which clearly are derived from their host chemokine system as well as induce high expression of certain 7TM receptors in the infected cells. The receptors appear to be exploited by the virus for either immune evasion, cellular reprogramming, tissue targeting or for cell entry. Through their efficient evolutionary machinery and through in vivo selection performed directly on the human cellular and molecular targets, virus have been able to optimize the encoded receptors for distinct pharmacological profiles to help in various parts of the viral life cyclus. Most of the receptors encoded by human pathogenic virus are still orphan receptors, i.e. the endogenous ligand is unknown. In the few cases where it has been possible to characterize these receptors pharmacologically, they have been found to bind a broad spectrum of either CC chemokines, US28 from human cytomegalovirus, or CXC chemokines, ORF74 from human herpesvirus 8. Nevertheless, US28 has been specifically optimized for recognition of the membrane bound chemokine, fractalkine, conceivably involved in cell-cell transfer of virus; whereas ORF74 among the endogenous CXC chemokines has selected angiogenic chemokines as agonists and angiostatic/modulatory chemokines as inverse agonists. ORF74 possess substantial cell-transforming properties and signals with high constitutive activity through the phospholipase C and MAP kinase pathways. Interestingly, transgenic expression of this single gene in certain lymphocyte cell lineages leads to the development of lesions which are remarkably similar to Kaposi's sarcoma, a human herpesvirus 8 associated disease. Thus, this and other virally encoded 7TM receptors appear to be attractive future drug targets.

Screening for herpesvirus genomes in common acute lymphoblastic leukemia

There is epidemiological evidence that infection may play a role in the etiology of childhood leukemia in particular common B cell precursor acute lymphoblastic leukemia. A panel of 20 leukemic samples (panel 1) was examined for the presence of four lymphotropic herpesviruses using conventional molecular techniques. A second independent panel of 27 leukemic samples (panel 2), along with 28 control peripheral blood samples from children with other forms of cancer, was tested for the presence of the same four viruses using sensitive real-time quantitative PCR. While herpesvirus genomes were detected, they were present at very low levels; detection rates and levels were similar in the leukemic and control panels. In addition we surveyed 18 leukemic samples (five from panel 1, six from panel 2 and a further seven samples not previously analyzed) using a degenerate PCR assay capable of detecting the genomes of known herpesviruses plus putative new members of the family. No novel herpesvirus genomes were detected suggesting that a herpesvirus is unlikely to be etiologically involved as a transforming agent in common acute lymphoblastic leukemia.

Inheritance of Chromosomally Integrated Human Herpesvirus 6 DNA

Human herpesvirus 6 (HHV-6) genome has been detected in several human lymphoproliferative disorders with no signs of active viral infection, and found to be integrated into chromosomes in some cases. We previously reported a woman with HHV-6–infected Burkitt’s lymphoma. Fluorescence in situ hybridization showed that the viral genome was integrated into the long arm of chromosome 22 (22q13). The patient’s asymptomatic husband also carried HHV-6 DNA integrated at chromosome locus 1q44. To assess the possibility of chromosomal transmission of HHV-6 DNA, we looked for HHV-6 DNA in the peripheral blood of their daughter. She had HHV-6 DNA on both chromosomes 22q13 and 1q44, identical to the site of viral integration of her mother and father, respectively. The findings suggested that her viral genomes were inherited chromosomally from both parents. The 3 family members were all seropositive for HHV-6, but showed no serological signs of active infection. To confirm the presence of HHV-6 DNA sequences, we performed polymerase chain reaction (PCR) with 7 distinct primer pairs that target different regions of HHV-6. The viral sequences were consistently detected by single-step PCR in all 3 family members. We propose a novel latent form for HHV-6, in which integrated viral genome can be chromosomally transmitted. The possible role of the chromosomally integrated HHV-6 in the pathogenesis of lymphoproliferative diseases remains to be explained.

Inheritance of Chromosomally Integrated Human Herpesvirus 6 DNA

Human herpesvirus 6 (HHV-6) genome has been detected in several human lymphoproliferative disorders with no signs of active viral infection, and found to be integrated into chromosomes in some cases. We previously reported a woman with HHV-6–infected Burkitt’s lymphoma. Fluorescence in situ hybridization showed that the viral genome was integrated into the long arm of chromosome 22 (22q13). The patient’s asymptomatic husband also carried HHV-6 DNA integrated at chromosome locus 1q44. To assess the possibility of chromosomal transmission of HHV-6 DNA, we looked for HHV-6 DNA in the peripheral blood of their daughter. She had HHV-6 DNA on both chromosomes 22q13 and 1q44, identical to the site of viral integration of her mother and father, respectively. The findings suggested that her viral genomes were inherited chromosomally from both parents. The 3 family members were all seropositive for HHV-6, but showed no serological signs of active infection. To confirm the presence of HHV-6 DNA sequences, we performed polymerase chain reaction (PCR) with 7 distinct primer pairs that target different regions of HHV-6. The viral sequences were consistently detected by single-step PCR in all 3 family members. We propose a novel latent form for HHV-6, in which integrated viral genome can be chromosomally transmitted. The possible role of the chromosomally integrated HHV-6 in the pathogenesis of lymphoproliferative diseases remains to be explained.

Quantification of human herpesvirus 6 in healthy volunteers and patients with lymphoproliferative disorders by PCR-ELISA

To determine whether actual numbers of human herpesvirus 6 (HHV-6) genome in hematologic neoplasias are associated with disease condition, we developed a quantitative PCR-ELISA for detection of HHV-6. The amount of viral DNA was determined using externally amplified known amounts of the plasmid DNA containing the viral target sequences. First, we determined a viral burden in peripheral blood leukocytes obtained from 23 healthy volunteers and four specimens of lymph nodes with reactive hyperplasia. Using 1 microg of DNA, the prevalence of HHV-6 was 43.4% (10/23), ranging from 0 to 100 HHV-6 genomes in blood obtained from healthy volunteers. The amounts of HHV-6 genomes were < 10 in four non-neoplastic lymph node specimens. We next examined the amount of viral DNA in 21 blood specimens and 19 lymph node specimens obtained from patients with lymphoproliferative diseases (LPD) at the time of diagnosis. The number of HHV-6 genomes in most of the B-cell lymphoma was < 5 in both blood and lymph node specimens, however, two lymph node specimens obtained from immunoblastic lymphadenopathy (IBL) and T-cell lymphoma had very high levels of HHV-6 viral DNA (3705 and 810, respectively). We also found that HHV-6 genomes in peripheral blood were more than 1000 in two patients with chronic lymphocytic leukemia. For all LPD patients combined, there were significantly higher levels of viral DNA (200.6 +/- 654.8 HHV-6 genomes per 1 microg purified DNA) compared to those in healthy volunteers (10.0 +/- 21.0 HHV-6 genomes per 1 microg purified DNA) (P < 0.05). This study demonstrates that a high level of HHV-6 viral DNA is occasionally associated with LPD patients. Although it is still uncertain whether HHV-6 is related to the pathogenesis in LPD or not, our results suggest that measurement of HHV-6 genomes using PCR-ELISA may be useful not only to understand the mechanism of HHV-6 infection in hemopoietic neoplasia but also to manage the care of immnocompromised patients such as bone marrow transplant patients.

Fine mapping of an apparently targeted latent human herpesvirus type 6 integration site in chromosome band 17p13.3

An unusually high level of latent HHV-6 infection has been documented in the peripheral blood and/or bone marrow cells of a small group of patients with predominantly malignant lymphoid disorders, and in at least one healthy individual. We have shown previously in peripheral blood mononuclear cells (PBMCs) of three patients, two with a history of lymphoma and one with multiple sclerosis, a specific target site for latent integration of the full-length HHV-6 viral genome on the distal short arm of chromosome 17, in band p13.3. Fluorescence in situ hybridization (FISH) procedures were used to map more precisely the location of the viral integration site in one of those patients, relative to two known oncogenes mapped previously, namely CRK, and the more telomeric ABR oncogene. It is shown that the HHV-6 integration site is located at least 1,000 kb telomeric of ABR, and is very likely to map close to or within the telomeric sequences of 17p. This finding is significant given that human telomeric-like repeats flank the terminal ends of the HHV-6 genome. Cytogenetic studies showed evidence of karyotype instability in the peripheral blood cells infected latently.

The kinetics of cancer cells and of HIV1: the problems of cell and virus rebounds and of latency

The kinetics of non treated and especially of treated HIV1 is compared to that of non treated and of treated cancer cells. Contrary to Skipper's scheme, based on constancy of cancer cell proliferation or post-chemotherapy decrease slope, the same chemotherapy successive cycles decrease in fact less and less the proportion of cell number reduction, and the hope of killing the "last cell" is a utopian concept. Hence, the very poor global benefit in cancer medicine registered in the last 50 years. The only cures are seen in child tumors and young adults testis cancer: the immunity reaction being stronger before 40 years of age than after 40 may explain this difference with age. The a priori systematic opposition to active immunotherapy of cancer from some authorities has been a grave fault. Such fault should not be committed for the treatment of HIV1-AIDS complex. The continuous HIV1 so called intensive virostatic chemotherapy is complicated by severe toxicities, and resistances of relapses and virus re-activation when it must be discontinued. The widely accepted triple therapy only affects two virus targets (retro-transcriptase and virus protease), which is insufficient, as we have shown. We have also observed that the constant and most rapid VL decrease to < 200 or < 20 RNA copies/mL is obtained when four virus targets are affected, including some concerning DNA provirus (which is the case of acriflavine and methylhydroxy-ellipticine). As in acute lymphoid leukemia, two treatment phases can be distinguished: a) the VL reduction to 20 copies; b) the maintenance of the residual < 20 copies of viruses. Excellent results as far as VL decrease and maintenance at < 20 copies have been obtained with a follow-up between 1 1/2 and 6 years, without any toxicity nor global resistance, with combinations of four drugs affecting four viral targets, applied in short (3 week) sequences, different from each others owing to drug rotation. This can be compared with the 65% remission rate obtained with alternative different cycles of cancer chemotherapy in tumors resistant to conventional modalities. The possibility of repeating for ten patients the evaluation of viral load and of immunologic parameters has allowed us to discover that some VL decrease curves are fractal. As well, maintenance 20 copies are not rarely interrupted by short and reversible HIV1 rebounds as those we had described in "cured" acute lymphoid leukemia patients. Of utmost importance, all HIV1 rebounds were associated with the presence of one cofactor: chimerism, chronic hepatitis, CMV, herpes 8, herpes 6, and influenza are those we observed. The problem today is not to "kill the last tumor cell in cancer" or "the last HIV1 particle" in HIV1-AIDS complex. It is to keep the residual cells or virus in latency. Active immunotherapy and other biologic interventions, such as hypermethylation, should be studied in this aim, as they are also able to do so.

Human herpesvirus 6: An emerging pathogen

Infections with human herpesvirus 6 (HHV-6), a beta-herpesvirus of which two variant groups (A and B) are recognized, is very common, approaching 100% in seroprevalence. Primary infection with HHV-6B causes roseola infantum or exanthem subitum, a common childhood disease that resolves spontaneously. After primary infection, the virus replicates in the salivary glands and is shed in saliva, the recognized route of transmission for variant B strains; it remains latent in lymphocytes and monocytes and persists at low levels in cells and tissues. Not usually associated with disease in the immunocompetent, HHV-6 infection is a major cause of opportunistic viral infections in the immunosuppressed, typically AIDS patients and transplant recipients, in whom HHV-6 infection/reactivation may culminate in rejection of transplanted organs and death. Other opportunistic viruses, human cytomegalovirus and HHV-7, also infect or reactivate in persons at risk. Another disease whose pathogenesis may be correlated with HHV-6 is multiple sclerosis. Data in favor of and against the correlation are discussed.

Integration of human herpesvirus 6 in a Burkitt's lymphoma cell line

Human herpesvirus 6 (HHV-6) genome has been found in several human lymphoid malignancies, but configuration of the HHV-6 genome has not been well delineated. We established the HHV-6-positive, Epstein-Barr virus-negative Burkitt's lymphoma cell line Katata. In this study we investigated the status of the HHV-6 genome in Katata cells. Neither linear nor circular HHV-6 DNA was detected by Gardella gel analysis. The fluorescence in situ hybridization technique enabled us to directly visualize the integrated HHV-6 DNA at the single-cell level. Only one integrated site of viral DNA was detected in metaphase chromosomes and it was preferentially located at the long arm of chromosome 22 (22q13). Treatment of the cells with 12-O-tetradecanoyl-phorbol-13-acetate (TPA) or with calcium ionophore A23187 led to induction of the HHV-6 immediate-early gene as well as the late gene. Sodium n-butyrate also gave rise to expression of the HHV-6 genes. The TPA inducibility was synergistically enhanced when combined with A23187 or n-butyrate. Our study provides, for the first time, an in vitro model system of latent HHV-6 infection whose genome is integrated into host DNA of lymphoma cells.