Impact of Human Herpesvirus-6 Reactivation on Outcomes of Allogeneic Hematopoietic Stem Cell Transplantation

A systematic review and meta-analysis of HHV-6 and mortality after hematopoietic cell transplant

Human herpesvirus-6B (HHV-6B) reactivation has been associated with non-relapse mortality (NRM) and overall mortality (OM) following allogeneic hematopoietic stem cell transplant (HCT). We performed a systematic review and meta-analysis to better quantify the association. Studies were included if they systematically tested a cohort of HCT recipients for HHV-6 infection or reactivation and described mortality for patients with and without HHV-6B. Random effects models were used to assess the pooled effect of HHV-6B positivity on each outcome of interest. Bayesian aggregation was additionally performed if models included 10 or fewer studies. Eight studies were included in the NRM analysis, which demonstrated a significant association between HHV-6 detection and NRM (pooled effect: 1.84; 95% CI: 1.29-2.62) without significant heterogeneity (I2 = 0.0%, p = 0.55). A Bayesian aggregation of the raw data used to construct the NRM random effects model supported these findings (95% credible interval: 0.15-1.13). Twenty-five studies were included in OM analysis, which showed a significant positive association (pooled effect: 1.37; 95% CI: 1.07-1.76), though considerable heterogeneity was observed (I2 = 36.7%, p < 0.05). HHV-6 detection is associated with NRM and OM following HCT. Randomized trials are warranted to evaluate if preventing or treating HHV-6B reactivation improves outcomes.

Risk factors and long-term outcomes for human herpesvirus 6 encephalitis in the early period after allogeneic stem cell transplantation

Human herpesvirus 6 (HHV6) encephalitis is a rare but life-threatening complication for patients undergoing allogeneic hematopoietic stem cell transplantation (allo-HSCT). However, reports on susceptibility factors and clinical outcomes are limited. We enrolled HHV6 encephalitis patients following allo-HSCT between 2018 and 2022, then conducted a 1:4 nested case-control cohort study to evaluate risk factors and long-term outcomes. Among 1350 patients, 20 (1.48%) developed HHV6 encephalitis, with a median onset time of 25.5 days after HSCT. Patient age<30 (odds ratio [OR], 3.24, P = 0.016) and NK cell count<115/ul at 21 days (OR, 6.07, P = 0.018) were identified as independent risk factors in multivariate analysis. Moreover, the HHV6 encephalitis group was significantly associated with higher incidence of grade II-IV graft-versus-host disease (aGVHD) (hazard ratio [HR], 5.52, P < 0.001) and transplant-associated microangiopathy (HR,9.86, P < 0.001), and demonstrated a significantly higher non-relapse mortality (NRM) (HR, 5.28, P = 0.004) and a lower overall survival (HR, 4.34, P = 0.001) or progression-free survival (HR, 3.94, P = 0.001) compared to control group. In conclusion, patients <30 years old or with delayed NK cell recovery are more susceptible to HHV6 encephalitis after allo-HSCT, and patients with HHV6 encephalitis after transplantation have poorer clinical outcomes.

AMPK restricts HHV-6A replication by inhibiting glycolysis and mTOR signaling

AMP-activated protein kinase (AMPK) is a cellular energy sensor regulating metabolic homeostasis. In this study, we investigated the role of AMPK in response to human herpesvirus 6A (HHV-6A) infection. We show that HHV-6A infection significantly downregulates the active phosphorylated state of AMPK in infected T cells. Pharmacological activation of AMPK highly attenuated HHV-6A propagation. Mechanistically, we found that the activation of AMPK by AICAR blocked HHV-6-induced glycolysis by inhibiting glucose metabolism and lactate secretion, as well as decreasing expressions of key glucose transporters and glycolytic enzymes. In addition, mTOR signaling has been inactivated in HHV-6A infected T cells by AICAR treatment. We also showed that HHV-6A infection of human umbilical cord blood mononuclear cells (CBMCs) reduced AMPK activity whereas the activation of AMPK by metformin drastically reduced HHV-6A DNA replication and virions production. Taken together, this study demonstrates that AMPK is a promising antiviral therapeutic target against HHV-6A infection.

Human herpesvirus type 6 reactivation after haploidentical hematopoietic cell transplantation with post-transplant cyclophosphamide and antithymocyte globulin: risk factors and clinical impact

Human herpesvirus type 6 (HHV6) reactivation after haploidentical hematopoietic cell transplantation (HCT) with post-transplant cyclophosphamide (PT-Cy) has been scarcely studied, especially when antithymocyte globulin (ATG) is added to the graft-versus-host disease (GvHD) prophylaxis. We conducted a retrospective cohort study in 100 consecutive patients receiving haploidentical HCT with PT-Cy. We systematically monitored HHV6 DNA loads in blood samples on a weekly basis using quantitative PCR until day +100. The 100-day cumulative incidence of HHV6 reactivation was 54%. Clinically significant HHV6 infections were rare (7%), associated with higher HHV6 DNA loads, and had favorable outcomes after antiviral therapy. The main risk factor for HHV6 reactivation was a low absolute lymphocyte count (ALC) \< 290/µL on day +30 (68% versus 40%, p = 0.003). Adding ATG to PT-Cy did not increase the incidence of HHV6 reactivation (52% with ATG versus 79% without ATG, p = 0.12). Patients experiencing HHV6 reactivation demonstrated delayed platelet recovery (HR 1.81, 95% CI 1.07-3.05, p = 0.026), higher risk of acute grade II-IV GvHD (39% versus 9%, p \< 0.001) but similar overall survival and non-relapse mortality to the other patients. In conclusion, our findings endorse the safety of combining ATG and PT-Cy in terms of the risk of HHV6 reactivation and infection in patients undergoing haploidentical HCT. Patients with a low ALC on day +30 face a higher risk of HHV6 reactivation and may require careful monitoring.

Oral shedding of herpesviruses and clinical outcomes in hematopoietic stem cell transplant patients

OBJECTIVES

To characterize the oral shedding of herpes viruses in patients who underwent allogeneic hematopoietic stem cell transplantation (alloHSCT) and investigate its relationship with clinical outcomes.

MATERIALS AND METHODS

Polymerase chain reaction and enzymatic digestion were performed to identify the oral shedding of the members of the Herpesviridae family in 31 patients. The samples were collected from the oral cavity at five timestamps.

RESULTS

The presence of each herpesvirus in the oral cavity was observed in 3.2%, 12.9%, 19.3%, 32.2%, 54.8% and 93.5% patients for human herpesvirus (HHV)-6A, herpes simplex virus-1, HHV-6B, cytomegalovirus (CMV), Epstein-Barr virus (EBV) and HHV-7, respectively. Oral shedding of herpes virus was not uncommon after alloHSCT. There was a statistically significant association between the EBV and CMV oral shedding at C1 and the cumulative incidence of acute graft-versus-host disease (aGVHD). The results suggested that the presence of HSV-1 at C2 was related to a relapse. The HHV-7 oral shedding at C2 suggests a possible link between relapse, progression-free survival and overall survival of the patients.

CONCLUSIONS

Patients who developed aGVHD showed higher CMV and EBV shedding in the oral cavity at aplasia, suggesting modifications to the pattern of immune cell response and inflammatory microenvironment.

Human herpesvirus-6 in hematopoietic stem cell transplant recipients: a prospective cohort study in Egypt

BACKGROUND

Immunocompromised patients face reactivation of latent viruses that increase the risk of morbidity.

AIM

The study aimed to detect human herpes virus 6 (HHV-6) reactivation among allogeneic (allo) and autologous (auto) hematopoietic stem cell transplant (HSCT) recipients and to correlate potentially attributed clinical manifestations to HHV-6 DNA plasma level.

METHODS

A prospective study included all (forty) patients undergoing allo and auto-HSCT from Jan 2020 till June 2022. Plasma samples were collected for HHV-6 serology, and for HHV-6 quantitative PCR at post-transplantation weeks 2, 4, 6. Demographic and clinical data were recorded.

RESULTS

Out of 40 peripheral blood stem cell transplant (PBSCT) recipients, 34 (85%) were HHV-6 IgG positive pre-HSCT. Of which, fourteen patients (14/34, 41.2%) showed positive HHV-6 DNaemia. HHV-6 DNAemia (15/40, 37.5%) was significantly higher among allo (8/12, 66.7%) versus auto (7/28, 25%) HSCT recipients (p = 0.030). Patients with HHV-6 DNAemia developed fever, delayed engraftment and bone marrow suppression in 6/15, 40%, thrombocytopenia (5/15, 33.3%), rash and pneumonitis (2/15, 13.3%), acute GVHD (aGVHD) (1/15, 6.7%). HHV-6 DNAemia ranged from 101 to 102,000 copies/mL. Univariate analysis identified conditioning with busulfan-cyclophosphamide as a significant risk (p = 0.043), while receiving BEAM protocol was a protective factor (p = 0.045). In multivariate analysis, receiving BEAM protocol retained significance (p = 0.040).

CONCLUSION

Frequent HHV-6 reactivation was detected after HSCT, especially in allo-HSCT recipients with clinical manifestations which could not be otherwise explained. To our best knowledge this is the first study of HHV6 reactivation in HSCT recipients from Egypt. Raising awareness for HHV-6 reactivation manifestations and screening in HSCT recipients could be lifesaving.

HHV-6 Encephalitis After Chimeric Antigen Receptor T-cell Therapy (CAR-T): 2 Case Reports and a Brief Review of the Literature

Human herpesvirus 6 (HHV-6) reactivation can occur in patients who are highly immunosuppressed, including those who have undergone hematopoietic stem cell transplantation (HSCT). HHV-6 encephalitis is a severe manifestation that is well described in the HSCT population. Chimeric antigen receptor T-cell (CAR-T) therapy is a novel cancer-directed immunotherapy that results in severe immunosuppression. Patients undergoing CAR-T therapy may be at risk for HHV-6 encephalitis, which can be difficult to distinguish from a common adverse effect of CAR-T therapy, neurotoxicity. Herein, we describe 2 patients diagnosed with HHV-6 encephalitis after CAR-T therapy and discuss the diagnostic approach and differential diagnosis for altered mental status after CAR-T therapy. Diagnosing HHV-6 encephalitis can be difficult in this patient population as altered mental status is common after CAR-T therapy and may be attributed to CAR-T-associated neurotoxicity.

Human herpes virus 6 DNAemia is associated with worse survival after ex vivo T-cell depleted hematopoietic cell transplant

BACKGROUND

We examined the correlation between persistent HHV-6 DNAemia (p-HHV-6) and absolute lymphocyte counts (ALC), platelet counts (PLT) and all-cause mortality the 1-year after ex vivo T-cell depleted (TCD) hematopoietic cell transplant (HCT).

METHODS

We analyzed a cohort of adult TCD HCT recipients 2012-2016 prospectively monitored for plasma HHV-6 by qPCR from day +14 post-HCT (D+14) through D+100. P-HHV-6 was defined as ≥2 consecutive values of ≥500 copies/mL by D+100. PLT and ALC were compared between patients with and without p-HHV-6 using mixed model analysis of variance. Multivariable Cox proportional hazard models were used to identify the impact of p-HHV-6 on 1-year mortality.

RESULTS

Of 312 patients, 83 (27%) had p-HHV-6 by D+100. P-HHV-6 was associated with lower ALC and PLT in the first year post-HCT. In multivariable models, p-HHV-6 was associated with higher mortality by 1-year post-HCT (adjusted hazard ratio 2.97, 95% confidence intervals: 1.62-5.47, P=0.0005), after adjusting for age, antiviral treatment, and ALC at D+100.

CONCLUSIONS

P-HHV-6 was associated with lower ALC and PLT in the first year post-HCT. P-HHV-6 was an independent predictor of mortality in the first year after TCD HCT.

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

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

Viral Infections in HSCT: Detection, Monitoring, Clinical Management, and Immunologic Implications

In spite of an increasing array of investigations, the relationships between viral infections and allogeneic hematopoietic stem cell transplantation (HSCT) are still controversial, and almost exclusively regard DNA viruses. Viral infections per se account for a considerable risk of morbidity and mortality among HSCT recipients, and available antiviral agents have proven to be of limited effectiveness. Therefore, an optimal management of viral infection represents a key point in HSCT strategies. On the other hand, viruses bear the potential of shaping immunologic recovery after HSCT, possibly interfering with control of the underlying disease and graft-versus-host disease (GvHD), and eventually with HSCT outcome. Moreover, preliminary data are available about the possible role of some virome components as markers of immunologic recovery after HSCT. Lastly, HSCT may exert an immunotherapeutic effect against some viral infections, notably HIV and HTLV-1, and has been considered as an eradicating approach in these indications.

Human herpesvirus 6 reactivation in unmanipulated haploidentical hematopoietic stem cell transplantation predicts the occurrence of grade II to IV acute graft-versus-host disease

BACKGROUND

Human herpesvirus 6 (HHV-6) reactivation is relatively common after allogeneic hematopoietic stem cell transplantation (allo-HSCT). However, the incidence of HHV-6 reactivation and the clinical outcomes following unmanipulated haploidentical HSCT (haplo-HSCT) remain unknown.

METHOD

We prospectively monitored blood HHV-6 DNA using real-time quantitative polymerase chain reaction weekly until day 100 post unmanipulated haplo-HSCT in patients with hematological malignancies.

RESULTS

From November 2016 to March 2017, 102 patients (58 male and 44 female, median age 25(2-58) years old) were enrolled. Within 100 days post-transplantation, 27 patients (27/136, 19.9%) developed HHV-6 viremia with a median onset time of 14 (7-98) days. The cumulative incidence of HHV-6 reactivation on day 100 post-HSCT was 25.5 ± 4.3% in haplo-HSCT. The median HHV-6 copy number was 1.45 × 10³ (5.48 × 10² -2.00 × 10⁴ ) copies/ml. The HHV-6 viremia duration time was 7 days in 23 patients, 14 days in one patient and 21 days in one patient. In multivariate analysis, prior HHV-6 reactivation was an independent risk factor for grade 2-4 graft-versus-host disease (GVHD). But it did not influence the overall survival (OS)(HR 1.624, 95%CI 0.768-3.432, P = .204), disease-free survival (DFS) (HR 1.640, 95%CI 0.799-3.367, P = .177) and non-relapse mortality (NRM) (HR 1.644, 95%CI 0.670-4.038, P = .278).

CONCLUSION

The reactivation of HHV-6 after unmanipulated haploidentical transplantation predicts the occurrence of grade 2-4 a-GVHD, but it may not influence the overall survival (OS), disease-free survival (DFS) and non-relapse mortality (NRM).

Reactivation of human herpesvirus 6 in pediatric allogeneic hematopoietic stem cell transplant recipients

BACKGROUND

Reactivation of human herpesvirus 6 (HHV-6) occurs in 30%-50% of patients (pts) who receive allogeneic (allo) hematopoietic stem cell transplant (HCT). However, the recommendation for post-transplant HHV-6 monitoring and treatment in pediatric pts is not well established.

METHODS

HHV-6 incidence rates and the clinical outcomes were reported for 139 pediatric pts (≤18 years) undergoing first allo-HCT at City of Hope from July 2011 to July 2017, for whom HHV-6 was monitored weekly throughout HCT hospitalization. For 57 pediatric pts, who underwent first HCT from January 2009 to July 2011, HHV-6 was tested as clinically indicated and only rates of HHV-6 viremia were collected.

RESULTS

From July 2011 to July 2017, HHV-6 was detected in 88/139 pts (63%). The frequency of HHV-6 viremia was associated with malignant diagnoses, myeloablative conditioning, and cord blood HCT. Treatment with antiviral agents was offered to symptomatic pts with a higher viral load (VL), for whom the time to VL clearance was longer and the frequency of subsequent recurrences was higher. Pts with a lower VL cleared HHV-6 without treatment. HHV-6 viremia was associated with a higher frequency of grade II-IV acute graft-versus-host disease (GVHD) (P = .022), but did not affect overall survival (OS), disease-free survival (DFS), non-relapsed mortality (NRM), myeloid, or platelet (Plt) engraftment.

CONCLUSIONS

HHV-6 weekly screening is not necessary for all HCT pts but may be considered for high-risk pts with malignant diagnoses undergoing cord blood HCT; otherwise, HHV-6 should be tested as clinically indicated. Only symptomatic pts (especially with a high VL > 25 000) could benefit from treatment. HHV-6 viremia at the time of initiation and administration of the conditioning regimen cleared promptly without the need to augment the transplant process.

Presence of Parvovirus B19 but Not Herpesvirus Genome in Acute Skin Rash after Allogeneic Stem Cell Transplantation Correlates with Outcome

INTRODUCTION

Skin rash is a first symptom of acute graft-versus-host disease (GvHD) after allogeneic stem cell transplantation (ASCT) but can also be caused by viruses. The relevance of virus DNA analyses in skin rash for diagnosis and clinical outcome is unknown.

OBJECTIVES

To record the frequencies of detection of herpes and parvovirus B19 (ParvoB19) DNA in skin rash within 100 days after ASCT and to analyze their relevance for diagnosis, clinical course, and non-relapse mortality (NRM).

METHODS

We retrospectively identified 55 patients with virus DNA analysis for CMV, EBV, HHV6, HHV8, HSV, VZV, or ParvoB19. We assessed the rate of virus DNA detection and studied associations with histological diagnosis, virus DNA from concomitantly analyzed blood, clinical presentation, exanthema treatment, and NRM.

RESULTS

CMV, EBV, HHV6, HHV8, HSV, VZV and ParvoB19 DNA were detected in 12.5, 11.8, 10, 0, 0, 2.9, and 26.7% of exanthemas. Histopathological diagnosis was not associated with virus polymerase chain reaction (PCR) results. Detection of CMV, EBV, or HHV6 DNA but not ParvoB19 in skin and blood was associated with PCR results (p = 0.016; p < 0.001; p = 0.067; p = n.a.). Detection of CMV, EBV, HHV6, or ParvoB19 DNA in the skin was not significantly associated with patient, ASCT, or GvHD characteristics. Detection of ParvoB19 but not herpes virus DNA was associated with less immunosuppressive treatment (p = 0.015) and lower NRM (p = 0.041). In multivariate analyses, detection of ParvoB19 was associated with a lower NRM.

CONCLUSIONS

Detection of ParvoB19 DNA in exanthema after ASCT might be associated with lower NRM.

Human herpesvirus 6A promotes glycolysis in infected T cells by activation of mTOR signaling

Human herpesvirus 6 (HHV-6) is an important immunosuppressive and immunomodulatory virus worldwide. However, whether and how HHV-6 infection influences the metabolic machinery of the host cell to provide the energy and biosynthetic resources for virus propagation remains unknown. In this study, we identified that HHV-6A infection promotes glucose metabolism in infected T cells, resulting in elevated glycolytic activity with an increase of glucose uptake, glucose consumption and lactate secretion. Furthermore, we explored the mechanisms involved in HHV-6A-mediated glycolytic activation in the infected T cells. We found increased expressions of the key glucose transporters and glycolytic enzymes in HHV-6A-infected T cells. In addition, HHV-6A infection dramatically activated AKT-mTORC1 signaling in the infected T cells and pharmacological inhibition of mTORC1 blocked HHV-6A-mediated glycolytic activation. We also found that direct inhibition of glycolysis by 2-Deoxy-D-glucose (2-DG) or inhibition of mTORC1 activity in HHV-6A-infected T cells effectively reduced HHV-6 DNA replication, protein synthesis and virion production. These results not only reveal the mechanism of how HHV-6 infection affects host cell metabolism, but also suggest that targeting the metabolic pathway could be a new avenue for HHV-6 therapy.

Viral reactivations following hematopoietic stem cell transplantation in pediatric patients - A single center 11-year analysis

Viral reactivation occurs frequently in the context of immunodeficiency and immunosuppression after allogeneic hematopoietic stem cell transplantation (allo-HSCT) and can cause severe complications. The aim of this single-center retrospective analysis was to characterize viral infections in the first year after HSCT, to investigate risk factors and to study the impact of viral infections on transplantation outcome. This will facilitate the identification of at-risk patients and the development of new preventive strategies. 107 pediatric allo-HSCT from January 2005 through December 2015 were analyzed for infections with Epstein-Barr virus (EBV), cytomegalovirus (CMV), human herpesvirus 6 (HHV-6), adenovirus (ADV), herpes simplex virus (HSV) and varicella zoster virus (VZV). Viral infections were detected after 68.2% of transplantations. The viruses most commonly encountered were HHV-6 (36/107) and EBV (30/107). Severe viral disease was rare (7/107) and none of the patients died as result of viral reactivation. Important risk factors for viral infections were higher age at HSCT, donor type and occurrence of acute graft-versus-host disease (aGvHD). Especially for EBV, transplant from an unrelated donor and in-vivo T-cell depletion (TCD) had a significant effect on infection rates, whereas for CMV the strongest effect was seen by donor and recipient serostatus with recipient seropositivity most predictive for reactivation. The occurrence of severe aGvHD was associated with EBV and ADV infections. For HSV, the recipient serostatus was identified as prognostic factor for HSV infections, while we found higher age at time of HSCT as risk factor for VZV infections. The overall survival of patients with or without viral infections did not differ significantly. Interestingly, when looking at the 85 patients in our cohort who had received an HSCT for a malignant disease, a tendency towards lower relapse rates was seen in patients affected by viral infections (HR 0.51, 95% CI 0.25 - 1.06, p = 0.072). Viral reactivations are common after pediatric allo-HSCT, though severe complications were rare in our collective. Determining risk factors for viral reactivations may help to identify patients in need of intensified monitoring and to individualize preventive strategies.

First-Onset Herpesviral Infection and Lung Injury in Allogeneic Hematopoietic Cell Transplantation

Rationale: "Noninfectious" pulmonary complications are significant causes of morbidity and mortality after allogeneic hematopoietic cell transplant. Early-onset viral reactivations or infections are common after transplant. Whether the first-onset viral infection causes noninfectious pulmonary complications is unknown. Objectives: To determine whether the first-onset viral infection within 100 days after transplant predisposes to development of noninfectious pulmonary complications. Methods: We performed a retrospective review of 738 allogeneic hematopoietic cell transplant patients enrolled from 2005 to 2011. We also established a novel bone marrow transplantation mouse model to test whether herpesviral reactivation after transplant causes organ injury. Measurements and Main Results: First-onset viral infections with human herpesvirus 6 or Epstein-Barr virus within 100 days after transplant increase the risk of developing idiopathic pneumonia syndrome (adjusted hazard ratio [aHR], 5.52; 95% confidence interval [CI], 1.61-18.96; P = 0.007; and aHR, 9.21; 95% CI, 2.63-32.18; P = 0.001, respectively). First infection with human cytomegalovirus increases risk of bronchiolitis obliterans syndrome (aHR, 2.88; 95% CI, 1.50-5.55; P = 0.002) and grade II-IV acute graft-versus-host disease (aHR, 1.59; 95% CI, 1.06-2.39; P = 0.02). Murine roseolovirus, a homolog of human herpesvirus 6, can also be reactivated in the lung and other organs after bone marrow transplantation. Reactivation of murine roseolovirus induced an idiopathic pneumonia syndrome-like phenotype and aggravated acute graft-versus-host disease. Conclusions: First-onset herpesviral infection within 100 days after allogeneic hematopoietic cell transplant increases risk of pulmonary complications. Experimentally reactivating murine roseolovirus causes organ injury similar to phenotypes seen in human transplant recipients.

Chromosomal Integration by Human Herpesviruses 6A and 6B

Upon infection and depending on the infected cell type, human herpesvirus 6A (HHV-6A) and 6B (HHV-6B) can replicate or enter a state of latency. HHV-6A and HHV-6B can integrate their genomes into host chromosomes as one way to establish latency. Viral integration takes place near the subtelomeric/telomeric junction of chromosomes. When HHV-6 infection and integration occur in gametes, the virus can be genetically transmitted. Inherited chromosomally integrated HHV-6 (iciHHV-6)-positive individuals carry one integrated HHV-6 copy per somatic cell. The prevalence of iciHHV-6⁺ individuals varies between 0.6% and 2%, depending on the geographical region sampled. In this chapter, the mechanisms leading to viral integration and reactivation from latency, as well as some of the biological and medical consequences associated with iciHHV-6, were discussed.

Lymphocyte Area Under the Curve as a Predictive Factor for Viral Infection after Allogenic Hematopoietic Stem Cell Transplantation

Viral infection is a serious complication that can greatly affect patient mortality and morbidity after allogenic hematopoietic stem cell transplantation (allo-HSCT). For the early identification of patients at high risk for viral infection, we evaluated the impact of lymphocyte area under the curve (AUC) value as a new predictive factor for early immune reconstitution after allo-HSCT against viral infection. This study included 286 patients who underwent their first allo-HSCT at Kyoto University Hospital between 2005 and 2017. Lymphocyte AUC from day 0 to day +15 was calculated in the analysis of human herpesvirus 6 (HHV-6), and lymphocyte AUC from day 0 to day +30 was calculated in the analysis of other viruses (cytomegalovirus [CMV], adenovirus, BK virus, JC virus, and varicella zoster virus). The risk factors for each viral reactivation/infection were assessed by multivariate analysis. The median age at transplantation was 51years (range, 17 to 68 years). The median lymphocyte AUC was 63/μL (range, 0 to 5620/μL) at day +15 and 3880 (range, 0 to 118,260/μL) at day +30. An increase in lymphocyte AUC was significantly associated with a high frequency of HHV-6 reactivation (P = .033) and a low frequency of CMV antigenemia (P = .014). No apparent association was found between lymphocyte AUC and reactivation/infection of other viruses. Aplastic anemia as a primary disease (hazard ratio [HR], 5.34; P < .001) and cord blood as a donor source (HR, 3.05; P = .006) were other risk factors for HHV-6 reactivation. Other risk factors for CMV antigenemia included the occurrence of acute graft-versus-host disease (HR 2.21; P < .001) and recipient age (HR 1.55; P = .017). Higher lymphocyte AUC at day +30 was significantly associated with low treatment-related mortality (HR, .47; P = .045). Lymphocyte AUC may be a good predictive factor for immune reconstitution against CMV reactivation. It also provides valuable information for predicting HHV-6 reactivation and treatment-related mortality.

Late-phase human herpesvirus 6B reactivation in hematopoietic stem cell transplant recipients

BACKGROUND

We sought to determine whether late-phase human herpesvirus 6B (HHV-6B) infection in hematopoietic stem cell transplant (HSCT) recipients was associated with serious outcomes and mortality.

METHODS

The occurrence and course of HHV-6B infection was monitored for at least 60 days after transplant using virus isolation and real-time polymerase chain reaction. Risk factors for late-phase HHV-6B infection were examined, and the propensity score was calculated with significant risk factors. The inverse probability-weighted multivariable logistic regression analysis was performed to estimate odds ratios (ORs) and the 95% confidence intervals (95% CI) for mortality.

RESULTS

Late-phase HHV-6B infection was observed in 12/89 (13.5%) of the HSCT recipients. Older age (OR: 10.3, 95% CI: 2.1/72.9, P = .0027), hematologic malignancy (OR: 10.3, 95% CI: 1.8/97.1, P = .0063), unrelated donor transplantation (OR: 5.3, 95% CI: 1.1/36.0, P = .0345), and sex-mismatched donor transplantation (OR: 6.3, 95% CI: 1.4/39.5, P = .0149) were identified as risk factors for late-phase HHV-6B infection. Fifteen subjects died (17%). Inverse probability-weighted multivariable logistic model analysis revealed that late-phase HHV-6B infection was an independent risk factor for mortality (OR: 4.2, 95% CI: 1.7/11.0, P = .0012). Among 5 of the fatal cases of late-phase HHV-6B infection, viral infection might be associated with severe clinical manifestations.

CONCLUSION

Late-phase HHV-6B infection in HSCT recipients was associated with worse outcomes. The full spectrum of clinical features of the infection has not been fully elucidated, and therefore, recipients with high-risk factors for late-phase HHV-6B infection should be carefully monitored.

HHV-6B infection, T-cell reconstitution, and graft-vs-host disease after hematopoietic stem cell transplantation

Successful and sustained CD4⁺ T-cell reconstitution is associated with increased survival after hematopoietic cell transplantation (HCT), but opportunistic infections may adversely affect the time and extent of immune reconstitution. Human herpesvirus 6B (HHV-6B) efficiently infects CD4⁺ T cells and utilizes as a receptor CD134 (OX40), a member of the TNF superfamily that antagonizes regulatory T-cell (T_reg) activity. Reactivation of HHV-6B has been associated with aberrant immune reconstitution and acute graft-versus-host disease (aGVHD) after HCT. Given that T_reg counts are negatively correlated with aGVHD severity, we postulate that one mechanism for the poor CD4⁺ T-cell reconstitution observed shortly after transplant may be HHV-6B infection and depletion of peripheral (extra-thymic) CD4⁺ T cells, including a subpopulation of T_reg cells. In turn, this may trigger a series of adverse events resulting in poor clinical outcomes such as severe aGVHD. In addition, recent evidence has linked HHV-6B reactivation with aberrant CD4⁺ T-cell reconstitution late after transplantation, which may be mediated by a different mechanism, possibly related to central (thymic) suppression of T-cell reconstitution. These observations suggest that aggressive management of HHV-6B reactivation in transplant patients may facilitate CD4⁺ T-cell reconstitution and improve the quality of life and survival of HCT patients.

Absence of early HHV-6 reactivation after cord blood allograft predicts powerful graft-versus-tumor effect

Approximately 75% of cord blood transplant (CBT) recipients experience human herpes virus-6 (HHV-6) reactivation. Considering the immunomodulatory effects of HHV-6, we hypothesized that early HHV-6 reactivation may influence the risk of relapse of the underlying hematologic malignancy. In 152 CBT recipients with hematological malignancies, we determined the association between HHV-6 reactivation by day +28 and 2-year cumulative incidence of relapse. In univariate analysis, the absence of HHV-6 reactivation (n = 32) was associated with less relapse (26 [18-35]% vs. 7 [0-17]% in groups with vs. without HHV-6 reactivation, respectively; P = .03). This difference was due to a remarkably low relapse incidence among patients without HHV-6 reactivation. In multivariable analysis, the absence of HHV-6 reactivation was associated with less relapse (hazard ratio [95% confidence interval]: 0.2 [0.05-0.9], P = .03). This association was independent of patient-, disease-, and transplant-related characteristics known to influence the risk of relapse. Natural killer cell and T-cell reconstitution at day +28 were similar between patients with vs. without HHV-6 reactivation. Our results suggest that CB allografts not complicated by HHV-6 reactivation by day +28 have a powerful graft-versus-tumor effect. Knowledge about early HHV-6 reactivation may stratify patients at day +28 into low vs. high relapse risk groups.

Human Herpesvirus-6B Reactivation Is a Risk Factor for Grades II to IV Acute Graft-versus-Host Disease after Hematopoietic Stem Cell Transplantation: A Systematic Review and Meta-Analysis

Graft-versus-host disease (GVHD) is an important cause of morbidity and mortality after allogeneic hematopoietic cell transplantation (HCT). Many studies have suggested that human herpesvirus-6B (HHV-6B) plays a role in acute GVHD (aGVHD) after HCT. Our objective was to systematically summarize and analyze evidence regarding HHV-6B reactivation and development of aGVHD. PubMed and EMBASE databases were searched using terms for HHV-6, HCT, and aGVHD, yielding 865 unique results. Case reports, reviews, articles focusing on inherited chromosomally integrated HHV-6, poster presentations, and articles not published in English were excluded. The remaining 467 articles were reviewed for the following requirements: a statistical analysis of HHV-6B reactivation and a GVHD was described, HHV-6B reactivation was defined by PCR, and blood (plasma, serum, or peripheral blood mononuclear cells) was used for HHV-6B PCR. Data were abstracted from publications that met these criteria (n = 33). Publications were assigned to 1 of 3 groups: (1) HHV-6B reactivation was analyzed as a time-dependent risk factor for subsequent aGVHD (n = 14), (2) aGVHD was analyzed as a time-dependent risk factor for subsequent HHV-6B reactivation (n = 1), and (3) analysis without temporal specification (n = 18). A statistically significant association (P < .05) between HHV-6B reactivation and aGVHD was observed in 10 of 14 studies (71%) in group 1, 0 of 1 study (0%) in Group 2, and 8 of 18 studies (44.4%) in Group 3. Of the 14 studies that analyzed HHV-6B as a risk factor for subsequent aGVHD, 11 performed a multivariate analysis and reported a hazard ratio, which reached statistical significance in 9 of these s tudies. Meta-analysis of these 11 studies demonstrated a statistically significant association between HHV-6B and subsequent grades II to IV aGVHD (hazard ratio, 2.65; 95% confidence interval, 1.89 to 3.72; P < .001).HHV-6B reactivation is associated with aGVHD, and when studies have a temporal component to their design, HHV-6B reactivation is associated with subsequent aGVHD. Further research is needed to investigate whether antiviral prophylaxis reduces incidence or severity of aGVHD.

Effects of Prophylactic Foscarnet on Human Herpesvirus-6 Reactivation and Encephalitis in Cord Blood Transplant Recipients: A Prospective Multicenter Trial with an Historical Control Group

Cord blood transplantation (CBT) is a distinct risk factor for human herpesvirus-6 (HHV-6) reactivation and HHV-6 encephalitis. In a prospective multicenter trial we investigated the effects of prophylactic foscarnet (90 mg/kg i.v. infusion from days 7 to 27 after CBT) on the occurrence of HHV-6 reactivation, HHV-6 encephalitis, and acute graft-versus-host disease (aGVHD) in CBT recipients. Between 2014 and 2016, 57 patients were included in a foscarnet-prophylaxis group. Outcomes were compared with an historical control group who received CBT between 2010 and 2014 (standard-treatment group, n = 63). The cumulative incidence of high-level HHV-6 reactivation, defined as plasma HHV-6 DNA ≥ 10⁴ copies/mL, at 60 days after CBT was significantly lower in the foscarnet-prophylaxis group than in the standard-treatment group (18.3% versus 57.3%, P < .001). Multivariate analysis revealed that myeloablative preconditioning and standard treatment were significant risk factors for high-level HHV-6 reactivation. The cumulative incidence of HHV-6 encephalitis at 60 days after CBT was not different between the groups (foscarnet-prophylaxis group, 12.4%; standard-treatment group, 4.9%; P = .14). The cumulative incidences of grades II to IV and grades III to IV aGVHD at 60 days after CBT were not different between the groups (grades II to IV aGVHD: foscarnet-prophylaxis group, 42.0%; standard-treatment group, 40.5%; P = .96; grades III to IV aGVHD: foscarnet-prophylaxis group, 14.5%; standard-treatment group, 14.5%; P = 1.00). In the setting of this study foscarnet significantly suppressed systemic HHV-6 reactivation in CBT recipients but failed to prevent the development of HHV-6 encephalitis. Suppression of HHV-6 reactivation by foscarnet did not show any effects against the incidence of aGVHD.

Betaherpesvirus Complications and Management During Hematopoietic Stem Cell Transplantation

Two of the four betaherpesviruses, Cytomegalovirus (CMV) and human herpesvirus 6B (HHV-6B), play an important role in opportunistic infections in hematopoietic stem cell transplant (HSCT) recipients. These viruses are ubiquitous in humans and can latently infect mononuclear lymphocytes, complicating the diagnosis of the diseases they cause. Although the detection of viral DNA in a patient's peripheral blood by real-time PCR is widely used for monitoring viral infection, it is insufficient for the diagnosis of virus-associated disease. Theoretically, end-organ disease should be confirmed by detecting either viral antigen or significant amounts of viral DNA in a tissue sample obtained from the involved organ; however, this is often difficult to perform in clinical practice. The frequency of CMV-associated diseases has decreased gradually as a result of the introduction of preemptive or prophylactic treatments; however, CMV and HHV-6B infections remain a major problem in HSCT recipients. Measurement of viral DNA load in peripheral blood or plasma using real-time PCR is commonly used for monitoring these infections. Additionally, recent data suggest that an assessment of host immune response, particularly cytotoxic T-cell response, may be a reliable tool for predicting these viral infections. The antiviral drugs ganciclovir and foscarnet are used as first-line treatments; however, it is well known that these drugs have side effects, such as bone marrow suppression and nephrotoxicity. Further research is required to develop less-toxic antiviral drugs.

Divergent tropism of HHV-6AGS and HHV-6BPL1 in T cells expressing different CD46 isoform patterns

CD46 is a receptor for HHV-6A, but its role as a receptor for HHV-6B is controversial. The significance of CD46 isoforms for HHV-6A and HHV-6B tropism is unknown. HHV-6A_GS was able to initiate transcription of the viral genes U7 and U23 in the CD46⁺CD134^- T-cell lines Peer, Jurkat, Molt3, and SupT1, whereas HHV-6B_PL1 was only able to do so in Molt3 and SupT1, which expressed a CD46 isoform pattern different from Peer and Jurkat. The HHV-6B_PL1-susceptible T-cell lines were characterized by low expression of the CD46 isoform BC2 and domination of isoforms containing the cytoplasmic tail, CYT-1. A HHV-6B_PL1 susceptible cell line, Be13, changed over time its CD46 isoform pattern to resemble Peer and Jurkat and concomitantly lost its susceptibility to HHV-6B_PL1 but not HHV-6A_GS infection. We propose that isoforms of CD46 impact on HHV-6B infection and thereby in part explain the distinct tropism of HHV-6A_GS and HHV-6B_PL1.

Human Herpesvirus 6 replication predicts Cytomegalovirus reactivation after allogeneic stem cell transplantation from haploidentical donor

BACKGROUND AND OBJECTIVES

Since HHV-6 reactivation after transplant has been reported to increase the risk of CMV infection, we tested this hypothesis in the HLA-haploidentical hematopoietic stem cell transplantation setting.

STUDY DESIGN

From February 2011 to October 2015, 75 patients received hematopoietic stem cell transplantation using a T-cell replete graft from a HLA-haploidentical donor at our Institution.

RESULTS

Interestingly, 87% of HHV-6 reactivations were followed by a CMV reactivation, at a median of 15days between the two viruses. Incidence of CMV reactivation was 14.5-fold higher in those patients with prior HHV-6 reactivation vs. those without it (p-value<0.001).

CONCLUSION

The present results suggest that HHV-6 can be considered as a predicting indicator of cellular immunosuppression preceding the onset of CMV infection.

Laboratory Diagnosis of Infections in Cancer Patients: Challenges and Opportunities

Infections remain a significant cause of morbidity and mortality in cancer patients. The differential diagnosis for these patients is often wide, and the timely selection of the right clinical tests can have a significant impact on their survival. However, laboratory findings with current methodologies are often negative, challenging clinicians and laboratorians to continue the search for the responsible pathogen. Novel methodologies are providing increased sensitivity and rapid turnaround time to results but also challenging our interpretation of what is a clinically significant pathogen in cancer patients. This minireview provides an overview of the most common infections in cancer patients and discusses some of the challenges and opportunities for the clinical microbiologist supporting the care of cancer patients.

A Simple Proteomics-Based Approach to Identification of Immunodominant Antigens from a Complex Pathogen: Application to the CD4 T Cell Response against Human Herpesvirus 6B

Most of humanity is chronically infected with human herpesvirus 6 (HHV-6), with viral replication controlled at least in part by a poorly characterized CD4 T cell response. Identification of viral epitopes recognized by CD4 T cells is complicated by the large size of the herpesvirus genome and a low frequency of circulating T cells responding to the virus. Here, we present an alternative to classical epitope mapping approaches used to identify major targets of the T cell response to a complex pathogen like HHV-6B. In the approach presented here, extracellular virus preparations or virus-infected cells are fractionated by SDS-PAGE, and eluted fractions are used as source of antigens to study cytokine responses in direct ex vivo T cell activation studies. Fractions inducing significant cytokine responses are analyzed by mass spectrometry to identify viral proteins, and a subset of peptides from these proteins corresponding to predicted HLA-DR binders is tested for IFN-γ production in seropositive donors with diverse HLA haplotypes. Ten HHV-6B viral proteins were identified as immunodominant antigens. The epitope-specific response to HHV-6B virus was complex and variable between individuals. We identified 107 peptides, each recognized by at least one donor, with each donor having a distinctive footprint. Fourteen peptides showed responses in the majority of donors. Responses to these epitopes were validated using in vitro expanded cells and naturally expressed viral proteins. Predicted peptide binding affinities for the eight HLA-DRB1 alleles investigated here correlated only modestly with the observed CD4 T cell responses. Overall, the response to the virus was dominated by peptides from the major capsid protein U57 and major antigenic protein U11, but responses to other proteins including glycoprotein H (U48) and tegument proteins U54 and U14 also were observed. These results provide a means to follow and potentially modulate the CD4 T-cell immune response to HHV-6B.