High human herpesvirus 6 viral load in pediatric allogeneic hematopoietic stem cell transplant patients is associated with detection in end organs and high mortality

Viral load: We need a new look at an old problem?

The concept of viral load was introduced in the 1980s to measure the amount of viral genetic material in a person's blood, primarily for human immunodeficiency virus (HIV). It has since become crucial for monitoring HIV infection progression and assessing the efficacy of antiretroviral therapy. However, during the coronavirus disease 2019 pandemic, the term "viral load" became widely popularized, not only for the scientific community but for the general population. Viral load plays a critical role in both clinical patient management and research, providing valuable insights for antiviral treatment strategies, vaccination efforts, and epidemiological control measures. As measuring viral load is so important, why don't researchers discuss the best way to do it? Is it simply acceptable to use raw Ct values? Relying solely on Ct values for viral load estimation can be problematic due to several reasons. First, Ct values can vary between different quantitative polymerase chain reaction assays, platforms, and laboratories, making it difficult to compare data across studies. Second, Ct values do not directly measure the quantity of viral particles in a sample and they can be influenced by various factors such as initial viral load, sample quality, and assay sensitivity. Moreover, variations in viral RNA extraction and reverse-transcription steps can further impact the accuracy of viral load estimation, emphasizing the need for careful interpretation of Ct values in viral load assessment. Interestingly, we did not observe scientific articles addressing different strategies to quantify viral load. The absence of standardized and validated methods impedes the implementation of viral load monitoring in clinical management. The variability in cell quantities within samples and the variation in viral particle numbers within infected cells further challenge accurate viral load measurement and interpretation. To advance the field and improve patient outcomes, there is an urgent need for the development and validation of tailored, standardized methods for precise viral load quantification.

Reduced impact of viral load of HHV-6 in liquor on severity of AESD due to exanthema subitum: A case report and literature review

BACKGROUND

The most common causative pathogen of acute encephalopathy with biphasic seizures and late reduced diffusion (AESD) was reported as HHV-6. Although excitotoxic injury with delayed neuronal death is considered to be a possible pathogenesis of AESD, the detailed pathophysiology remains unclear.

CASE PRESENTATION

We present a twelve-month-old girl with AESD due to HHV-6 primary infection. She was successfully treated for AESD including targeted temperature management and the administration of vitamin B1, B6, and L-carnitine. Although the viral load of HHV-6 in her liquor was high (12,000 copies/mL), she fully recovered without antiviral agent use.

DISCUSSION

There has been no study focusing on the HHV-6 viral load in patients with AESD, and only a few case reports have been published. We reviewed the clinical features and viral load in the liquor of our case and four reported infants with AESD due to HHV-6 primary infection who had real-time PCR tests results. Viral loads in the three patients with a poor prognosis were 31.5, negative, and 3,390 copies/mL, respectively. On the other hand, the copy numbers of HHV-6 DNA in the two patients with no sequelae were 12,000 and 106 copies/mL, respectively, and our case had the highest viral load among the five summarized patients.

The role of early natural killer cell adoptive infusion before engraftment in protecting against human herpesvirus-6B encephalitis after naïve T-cell-depleted allogeneic stem cell transplantation

BACKGROUND

Naïve T-cell-depleted grafts have been employed as an ex vivo T-cell depletion (TCD) platform to prevent graft-versus-host disease (GvHD) and improve immune reconstitution by providing rapid donor memory T-cell reconstitution after allogenic hematopoietic stem cell transplantation (allo-HSCT). CD45RA^- memory T cells confer protection against viruses such as cytomegalovirus, Epstein-Barr virus, and adenovirus; however, reports have shown an unexpectedly high incidence of human herpesvirus (HHV)-6B encephalitis among pediatric allo-HSCT patients.

METHODS

We report the first 18 consecutive allo-HSCT, 16 haplo-HSCT, and two human leukocyte antigen-matched related donors implanted with naïve TCD grafts. All donors were administered three cell products: first, a CD34⁺ stem cell product; second, a CD45RA⁺ TCD graft, followed by an adoptive natural killer (NK) cell infusion within 10 days after HSCT. The study's primary endpoint was the incidence of HHV-6B encephalitis.

RESULTS

Engraftment was achieved in 94.5% of cases; 2-year overall survival, event-free survival, and GvHD/relapse-free survival were 87.2% (95% CI 78.6-95.8), 67.3% (95% CI 53.1-81.5), and 64% (95% CI 50.5-78.1), respectively. HHV-6B reactivation occurred in 7 of the haplo-HSCT patients, six of who received a cell infusion with an NK/CD4 ratio <2. None of the patients developed encephalitis.

CONCLUSIONS

In this clinical study, we show that early adoptive NK cell infusion after a 45RA⁺ TCD allo-HSCT graft is safe and can prevent HHV-6B encephalitis. We recommend infusing adoptive NK cells after allo-HSCT using CD45RA⁺ TCD grafts.

Epidemiology and outcome for viremia in children undergoing bone marrow transplant: A retrospective cohort study

INTRODUCTION

Viral infections pose a serious risk for children undergoing hematopoietic stem cell transplant (HSCT). There are few published case series of prevalence, risk factors, and outcomes examining multiple viruses simultaneously, and no pediatric Australasian data published to date. We describe the real-life experience of viremia in pediatric HSCT in a single tertiary center.

METHODS

All episodes of viremia in children undergoing HSCT between 2000 and 2018 were identified by matching HSCT patients' unique identification numbers with positive blood polymerase chain reaction (PCR) results for human adenovirus (HAdV), cytomegalovirus (CMV), Epstein-Barr virus (EBV), and human herpes virus 6 (HHV-6). Paper or electronic charts and electronic pathology results were used to extract the study variables.

RESULTS

Viremia was detected in 177/445 (39.8%) HSCT episodes, of which 46% were allogeneic and 19% autologous transplants. Viremia was disseminated in 96 (21.6%) episodes, with 80 (18%) having more than one virus. HAdV was detected in 108 (24.3% of total episodes) and frequently in autologous transplants, CMV in 71 (16.0%), EBV in 60 (13.5%), and HHV-6 in 38 (8.5%). Of 174 children, 19 (10.9%) died of a viral-associated cause, with viral mortality highest in CMV (18.3%), lowest in HHV-6 (2.6%) with HAdV and EBV similar (6.6% and 6.7%). Adenoviral (but not other virus) dissemination was significantly associated with lower lymphocyte count at time of first detection. CMV dissemination and death were significantly associated with initial and highest CMV viral loads (copies/mL).

CONCLUSION

This study presents the first pediatric-specific Australasian data for viremia in HSCT. Findings may help guide clinicians in prophylaxis and treatment decisions.

Advances in the understanding of poor graft function following allogeneic hematopoietic stem-cell transplantation

Poor graft function (PGF) following allogeneic hematopoietic stem-cell transplantation (allo-HSCT) is a life-threatening complication and is characterized by bilineage or trilineage blood cell deficiency and hypoplastic marrow with full chimerism. With the rapid development of allo-HSCT, especially haploidentical-HSCT, PGF has become a growing concern. The most common risk factors illustrated by recent studies include low dose of infused CD34+ cells, donor-specific antibody, cytomegalovirus infection, graft versus host disease (GVHD), iron overload and splenomegaly, among others. Because of the poor prognosis of PGF, it is crucial to uncover the underlying mechanism, which remains elusive. Recent studies have suggested that the bone marrow microenvironment may play an important role in the pathogenesis of PGF. Deficiency and dysfunction of endothelial cells and mesenchymal stem cells, elevated reactive oxygen species (ROS) levels, and immune abnormalities are believed to contribute to PGF. In this review, we also discuss recent clinical trials that evaluate the safety and efficacy of new strategies in patients with PGF. CD34+-selected stem-cell boost (SCB) is effective with an acceptable incidence of GVHD, despite the need for a second donation. Alternative strategies including the applications of mesenchymal stem cells, N-acetyl-l-cysteine (NAC), and eltrombopag have shown favorable outcomes, but further large-scale studies are needed due to the small sample sizes of the recent clinical trials.

HHV-6-Associated Neurological Disease in Children: Epidemiologic, Clinical, Diagnostic, and Treatment Considerations

Human herpesviruses 6A and 6B, often referred to collectively as human herpesvirus 6, are a pair of beta-herpesviruses known to cause a variety of clinical syndromes in both immunocompetent and immunocompromised individuals. Most humans are infected with human herpesvirus 6B, and many with human herpesvirus 6A. Primary infection typically occurs in early childhood, although large-scale reviews on the topic are limited. Herein, the authors explore the clinical manifestations of human herpesvirus 6-associated disease in both immunocompetent and immunocompromised pediatric patients, the risk factors for development of human herpesvirus 6-associated neurological disease, the risk of autoimmunity associated with development of active or latent infection, the relevance of human herpesvirus 6-specific diagnostic tests, and the medications used to treat human herpesvirus 6. The goal of this review is to improve the current understanding of human herpesvirus 6 in pediatric populations and to examine the most effective diagnostic and therapeutic interventions in this disease state.

Human herpesvirus-6B infection in pediatric allogenic hematopoietic stem cell transplant patients: Risk factors and encephalitis

BACKGROUND

Human herpesvirus-6B (HHV-6B) infection after allogenic hematopoietic stem cell transplantation (allo-HSCT) is known to be associated with post-transplant limbic encephalitis in adults. Meanwhile, the association between HHV-6B infection and central nervous system complications remains unclear in pediatric allo-HSCT patients.

METHODS

In this study, HHV-6B infection was monitored for more than 50 days after HSCT using virus isolation and real-time PCR. Clinical information such as patient background and encephalitis status was collected retrospectively from medical records. Risk factors for HHV-6B infection were determined by the Cox proportional hazards model, and the clinical features of HHV-6B encephalitis in pediatric allo-HSCT patients were elucidated.

RESULTS

Human herpesvirus-6B infection was observed in 74 (33.8%) of 219 patients at 3-47 days (median 18, interquartile range 13-20). Risk factors identified in multivariable analysis were hematological malignancy (hazards ratio [HR], 5.0; 95% confidence interval [CI], 2.3/12.5; P < .0001), solid tumor (HR, 4.8; CI, 1.5/16.3; P = .0104), unrelated donor (HR, 2.1; CI, 1.0/4.6; P = .0378), and sex-mismatched donor (HR 1.8; CI, 1.1/3.0; P = .0257). HHV-6B encephalitis occurred in only one of the 219 patients (0.46%); this patient demonstrated the typical clinical course of posterior reversible encephalopathy syndrome.

CONCLUSION

Hematological malignancy, solid tumor, unrelated donor, and sex-mismatched donor were significant risk factors for HHV-6B infection after pediatric allo-HSCT. In pediatric allo-HSCT patients, the incidence of HHV-6B encephalitis was low and the clinical features differed from those in adult patients.

Chromatin Profiles of Chromosomally Integrated Human Herpesvirus-6A

Human herpesvirus-6A (HHV-6A) and 6B (HHV-6B) are two closely related betaherpesviruses that are associated with various diseases including seizures and encephalitis. The HHV-6A/B genomes have been shown to be present in an integrated state in the telomeres of latently infected cells. In addition, integration of HHV-6A/B in germ cells has resulted in individuals harboring this inherited chromosomally integrated HHV-6A/B (iciHHV-6) in every cell of their body. Until now, the viral transcriptome and the epigenetic modifications that contribute to the silencing of the integrated virus genome remain elusive. In the current study, we used a patient-derived iciHHV-6A cell line to assess the global viral gene expression profile by RNA-seq, and the chromatin profiles by MNase-seq and ChIP-seq analyses. In addition, we investigated an in vitro generated cell line (293-HHV-6A) that expresses GFP upon the addition of agents commonly used to induce herpesvirus reactivation such as TPA. No viral gene expression including miRNAs was detected from the HHV-6A genomes, indicating that the integrated virus is transcriptionally silent. Intriguingly, upon stimulation of the 293-HHV-6A cell line with TPA, only foreign promoters in the virus genome were activated, while all HHV-6A promoters remained completely silenced. The transcriptional silencing of latent HHV-6A was further supported by MNase-seq results, which demonstrate that the latent viral genome resides in a highly condensed nucleosome-associated state. We further explored the enrichment profiles of histone modifications via ChIP-seq analysis. Our results indicated that the HHV-6 genome is modestly enriched with the repressive histone marks H3K9me3/H3K27me3 and does not possess the active histone modifications H3K27ac/H3K4me3. Overall, these results indicate that HHV-6 genomes reside in a condensed chromatin state, providing insight into the epigenetic mechanisms associated with the silencing of the integrated HHV-6A genome.