Prediction of Human Herpesvirus 6 Infection After Allogeneic Bone Marrow Transplantation

Impact of Specific Antibody Level on Human Herpesvirus 6 Reactivation after Allogeneic Stem Cell Transplantation

The majority of adults are seropositive for human herpesvirus 6 (HHV-6). HHV-6 reactivation can occur after allogeneic hematopoietic stem cell transplantation (HSCT) and lead to life-threatening central nervous system disorders. In this prospective study, we evaluated the relationship between HHV-6 reactivation and anti-HHV-6 IgG antibody levels in recipients of allogeneic HSCT. The HHV-6 viral load in the plasma was quantitatively measured weekly after allogeneic HSCT by real-time polymerase chain reaction. The level of anti-HHV-6 IgG antibody was measured by enzyme-linked immunosorbent assay before and serially after transplantation. In 28 of the 56 evaluated patients (50%), HHV-6 reactivation was detected after transplantation. In a multivariate analysis, cord blood as the stem cell source was the only significant factor associated with HHV-6 reactivation (odds ratio, 8.6; 95% confidence interval, 2.3 to 32.6; P < .01). When evaluated in the recipients of cord blood transplantation (CBT), the anti-HHV-6 antibody level before transplantation was significantly lower in the patients with HHV-6 reactivation compared with those without (sample positivity index: median, 2.04 [range, 0.95 to 5.98] versus 4.15 [range, 3.93 to 5.65]; P < .05). The anti-HHV-6 antibody level was significantly decreased at 3 months post-transplantation compared with before transplantation (P < .01). Such differences were not observed in other stem cell sources. Our results demonstrate that the low anti-HHV-6 antibody level before transplantation was associated with the reactivation of HHV-6 after CBT, and that the anti-HHV-6 antibody level was significantly decreased specifically after CBT. These results suggest that HHV-6-specific humoral immunity plays a role in HHV-6 reactivation after CBT.

Diagnostic Clues to Human Herpesvirus 6 Encephalitis and Wernicke Encephalopathy After Pediatric Hematopoietic Cell Transplantation

Human herpesvirus 6 (HHV6) encephalitis and Wernicke encephalopathy are treatable yet frequently undiagnosed causes of encephalopathy in pediatric recipients of allogeneic and autologous hematopoietic cell transplantation. Here we review representative cases of both conditions to highlight specific and relevant neurologic features that prompted effective diagnosis and treatment. Two patients with confusion accompanied by seizures, memory changes, or specific visual hallucinations and HHV6 detectable by polymerase chain reaction (PCR) in cerebrospinal fluid had improvement in viral load with ganciclovir or foscarnet treatment. Two patients had confusion, ataxia, or ocular changes and low serum thiamine levels, which resolved with parenteral thiamine. In all cases, definitive diagnosis and treatment were facilitated by a high index of suspicion and search for specific pathognomonic neurologic deficits accompanying the confusional state. It is critical to clinically differentiate these 2 conditions from other common neurologic syndromes occurring after transplant, allowing potentially improved patient outcomes by prompt diagnosis and effective treatment.

Frequent human herpesvirus-6 viremia but low incidence of encephalitis in double-unit cord blood recipients transplanted without antithymocyte globulin

Cord blood transplantation (CBT) is a known risk factor for human herpesvirus-6 (HHV-6) infection. We analyzed the nature of HHV-6 infections in 125 double-unit CBT recipients (median age, 42 years) transplanted for hematologic malignancies with calcineurin inhibitor/mycophenolate mofetil prophylaxis and no antithymocyte globulin. One hundred seventeen patients (94%) reactivated HHV-6 by quantitative plasma PCR (median peak, 7600 copies/mL; range, 100 to 160,000) at a median of 20 days (range, 10 to 59) after transplantation. HHV-6 encephalitis occurred in 2 patients (1.6%), of whom 1 died and 1 recovered with therapy. No association was found between high-level HHV-6 viremia (≥10,000 or ≥25,000 copies/mL) and age, diagnosis, conditioning intensity, or dominant unit characteristics or between high-level viremia and transplant outcomes (engraftment, cytomegalovirus reactivation, day 100 grades II to IV acute graft-versus-host disease, day 100 transplant-related mortality, or 1-year disease-free survival). HHV-6 therapy delayed the onset of cytomegalovirus reactivation. Interestingly, HHV-6 resolution was observed in untreated patients, and resolution of viremia correlated with absolute lymphocyte count recovery. We observed a low incidence of encephalitis and no association with CBT outcomes. Our data suggest therapy in uncomplicated viremia may not be warranted. However, further investigation of the risk-to-benefit of HHV-6 viremia treatment and standardization of PCR testing is required.

Human parvovirus B19, varicella zoster virus, and human herpesvirus-6 in mesenchymal stem cells of patients with osteoarthritis: analysis with quantitative real-time polymerase chain reaction

OBJECTIVE

To investigate whether there is a possible viral transmission using mesenchymal stem cells (MSCs) in autologous or allogeneic transplantation in the context of osteoarthritis (OA) patients. The presence of parvovirus B19 (B19), varicella zoster virus (VZV), and human herpesvirus-6 (HHV-6) was studied in MSCs from bone marrow of patients with OA and healthy controls.

METHODS

MSCs were prepared from bone marrow aspirates obtained from 18 patients undergoing joint replacement as a result of OA and from 10 healthy controls. DNA was extracted from primary MSCs' culture established from these cells and quantitative real-time polymerase chain reaction was performed to analyse the prevalence and viral load of B19, VZV and HHV-6.

RESULTS

The prevalence of total viral DNA among patients with OA was 16.7% (3/18), with a mean viral load of 29.7 copies/microg of DNA. One out of 18 was positive for B19 (viral load, 61.2 copies/microg of DNA), two for VZV (mean viral load, 14.4 copies/microg of DNA), and none for HHV-6. The prevalence of total viral DNA in the control group was 20% (2/10), with a mean viral load of 13.4 copies/microg of DNA. Both positive results were of B19 parvoviruses. There were no statistically significant differences among patients and controls.

CONCLUSIONS

This first approach to the viral prevalence in MSCs of bone marrow in OA patients and healthy controls seems to show a very low risk of viral transmission or reactivation in a possible MSCs' transplantation.

Risk factors for developing human herpesvirus 6 (HHV-6) reactivation after allogeneic hematopoietic stem cell transplantation and its association with central nervous system disorders

We prospectively evaluated the incidence of human herpesvirus 6 (HHV-6) DNAemia after allogeneic hematopoietic stem cell transplantation (HSCT) using quantitative plasma real-time polymerase chain reaction. Of 46 recipients of bone marrow or peripheral blood stem cell transplantation (BMT/PBSCT) from related (n = 11) or unrelated donors (n = 22), and cord blood transplantation (CBT) from unrelated donors (n = 13), 22 (47.8%) developed HHV-6 DNAemia. HHV-6 DNA levels ranged from 200 to 200,000 copies/mL of plasma, and HHV-6 DNAemia was observed significantly more frequently after CBT than after BMT/PBSCT (92.3% vs 30.3%; P < .001). Multivariate analyses identified CBT (vs BMT/PBSCT), HLA mismatches between recipient and donor, and low anti-HHV-6 IgG titer before transplantation as the only risk factors for developing HHV-6 DNAemia. Three patients developed central nervous system (CNS) disorders with detectable HHV-6 DNA in the cerebrospinal fluid; all of these patients simultaneously developed HHV-6 DNAemia. These results suggest that HHV-6 DNAemia is frequently observed after allogeneic HSCT, especially in patients with the aforementioned risk factors. Thus, together with the assessment of risk factors, monitoring of HHV-6 DNAemia could be a useful asset in diagnosing HHV-6-associated CNS disorders.

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.

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.

Monitoring of active HHV-6 infection in bone marrow transplant recipients by real time PCR; comparison to detection of viral DNA in plasma by qualitative PCR

Twelve (46%) of the 26 patients had human herpesvirus 6 (HHV-6) viremia after bone marrow transplant (BMT). All isolates were recovered from the samples obtained at 2 weeks after BMT. The sensitivity and the specificity of detection of viral DNA in plasma by qualitative polymerase chain reaction (PCR) for monitoring active virus replication were 92% and 97% respectively. Moreover, the positive (85%) and negative (99%) predictive values were also high. The patients with HHV-6 viremia showed a clear peak in HHV-6 DNA in peripheral blood mononuclear cells (PBMCs) at 2 weeks after BMT, which was measured by real time PCR. The virus DNA level in PBMCs between the two groups (patients with viremia and patients without viremia) was statistically different at 2 weeks after BMT (P = 0.033). In patients with HHV-6 viremia, mean HHV-6 DNA copy number was higher in the samples collected at 2 weeks after BMT than the samples collected at any other time period.

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.

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.

Emerging viral infections

The past decade has witnessed the emergence of several significant viral pathogens and the further evolution of additional viral pathogens. Transmitted by a variety of differing routes, these organisms have presented substantial intellectual challenges to medicine of the 20th and 21st centuries. As perhaps the benchmark pathogen of the past decade, HIV has provided medicine and society with a most formidable opponent, and one that has yet to be fully conquered. Nonetheless, a variety of additional viral pathogens have also perplexed medicine over the past 10-15 years.

Monitoring four herpesviruses in unrelated cord blood transplantation

Cord blood transplantation, which has lower risk of graft-versus-host disease than bone marrow transplantation, might have higher risk of infections. A system to quantify four herpesviruses, CMV, human herpesvirus 6 (HHV6), EBV, varicella-zoster virus using the real-time PCR assay was established and applied for prospective viral load monitoring in three recipients undergoing cord blood transplantation. CMV and HHV6 were detected in peripheral blood from all three recipients, while EBV was detected in two. Varicella-zoster virus was not detected at all. At the peak of HHV6 or CMV, each patient showed virus-related symptoms. During the pre-transplant period, CMV DNA was detected in two recipients who later developed CMV-related diseases. These observations indicate that our system is not only useful for managing herpesviruses infections in transplant recipients, but also a powerful method for clarifying the relationships between the viral load and clinical symptoms.

Human herpesvirus 6 infection after autologous or allogeneic stem cell transplantation: a single-center prospective longitudinal study of 92 patients

To determine the incidence and clinical relevance of active human herpesvirus 6 (HHV-6) infection, 92 consecutive unselected recipients of autologous or allogeneic stem cell grafts were investigated in a prospective longitudinal study. Active infection was assessed by the presence of viral deoxyribonucleic acid (DNA) in 846 peripheral blood mononuclear cell specimens and 115 plasma specimens, by means of a specially developed polymerase chain reaction designed to avoid detection of latent genome. The incidence of HHV-6 infection observed was 42.5%, irrespective of the type or source of graft, and infection was significantly associated with partial (P=.002) or total myelosuppression (P=.01) and fever (P<. 000001). Infusion of bone marrow as the source of graft, reactivation occurring before platelet or neutrophil engraftment, and presence of HHV-6 DNA in plasma were identified as risk factors for symptomatic HHV-6 infection (P<.002).