Human Herpesvirus 6B and Lower Respiratory Tract Disease After Hematopoietic Cell Transplantation

Pulmonary Immunocompromise in Stem Cell Transplantation and Cellular Therapy

Hematopoietic cell transplantation (HCT) and cellular therapies, such as chimeric-antigen receptor T-cell (CAR-T) treatments, are potentially curative treatments for certain hematologic malignancies and some nonmalignant disorders. However, pulmonary complications, both infectious and noninfectious, remain a significant cause of morbidity and mortality in patients who receive cellular therapies. This review article provides an overview of pulmonary complications encountered in the context of HCT and CAR-T. The authors discuss mechanisms of underlying immunocompromise that lead to a rise in infections. Additionally, they highlight key noninfectious complications of HCT that can mimic acute infections and suggest diagnostic approaches and preventive strategies to distinguish these entities promptly.

Evaluation of Inborn Errors of Immunity Among Patients with Opportunistic Pulmonary Infection

This review of immunocompromised host pneumonia as the result of inborn errors of immunity (IEI) is organized by opportunistic pulmonary pathogen. The authors identify patients who warrant an evaluation for an IEI based on their clinical presentation. Their recommendations are guided by the immune defect(s) associated with each opportunistic pulmonary infection. Physicians without expertise in immunology may begin an evaluation for IEI using the guidance provided here. Comprehensive evaluation by an immunologist may also be warranted in many instances.

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.

Diffuse Alveolar Hemorrhage in Hematopoietic Cell Transplantation

Diffuse alveolar hemorrhage (DAH) is a morbid syndrome that occurs after autologous and allogeneic hematopoietic cell transplantation in children and adults. DAH manifests most often in the first few weeks following transplantation. It presents with pneumonia-like symptoms and acute respiratory failure, often requiring high levels of oxygen supplementation or mechanical ventilatory support. Hemoptysis is variably present. Chest radiographs typically feature widespread alveolar filling, sometimes with peripheral sparing and pleural effusions. The diagnosis is suspected when serial bronchoalveolar lavages return increasingly bloody fluid. DAH is differentiated from infectious causes of alveolar hemorrhage when extensive microbiological testing reveals no pulmonary pathogens. The cause is poorly understood, though preclinical and clinical studies implicate pretransplant conditioning regimens, particularly those using high doses of total-body-irradiation, acute graft-versus-host disease (GVHD), medications used to prevent GVHD, and other factors. Treatment consists of supportive care, systemic corticosteroids, platelet transfusions, and sometimes includes antifibrinolytic drugs and topical procoagulant factors. Therapeutic blockade of tumor necrosis factor-α showed promise in observational studies, but its benefit for DAH remains uncertain after small clinical trials. Even with these treatments, mortality from progression and relapse is high. Future investigational therapies could target the vascular endothelial cell biology theorized to contribute to alveolar bleeding and pathways that contribute to susceptibility, inflammation, cellular resilience, and tissue repair. This review will help clinicians navigate through the limited evidence to diagnose and treat DAH, counsel patients and families, and plan for future research.

Human herpesvirus-6, HHV-8 and parvovirus B19 after allogeneic hematopoietic cell transplant: the lesser-known viral complications

PURPOSE OF REVIEW

Viral infections continue to burden allogeneic hematopoietic cell transplant (HCT) recipients. We review the epidemiology, diagnosis, and management of human herpesvirus (HHV)-6, HHV-8 and parvovirus B19 following HCT.

RECENT FINDINGS

Advances in HCT practices significantly improved outcomes but impact viral epidemiology: post-transplant cyclophosphamide for graft-versus-host disease prevention increases HHV-6 reactivation risk while the impact of letermovir for CMV prophylaxis - and resulting decrease in broad-spectrum antivirals - is more complex. Beyond the well established HHV-6 encephalitis, recent evidence implicates HHV-6 in pneumonitis. Novel less toxic therapeutic approaches (brincidofovir, virus-specific T-cells) may enable preventive strategies in the future. HHV-8 is the causal agent of Kaposi's sarcoma, which is only sporadically reported after HCT, but other manifestations are possible and not well elucidated. Parvovirus B19 can cause severe disease post-HCT, frequently manifesting with anemia, but can also be easily overlooked due to lack of routine screening and ambiguity of manifestations.

SUMMARY

Studies should establish the contemporary epidemiology of HHV-6, and other more insidious viruses, such as HHV-8 and parvovirus B19 following HCT and should encompass novel cellular therapies. Standardized and readily available diagnostic methods are key to elucidate epidemiology and optimize preventive and therapeutic strategies to mitigate the burden of infection.

Human Herpes Virus-6 (HHV-6) Reactivation after Hematopoietic Cell Transplant and Chimeric Antigen Receptor (CAR)- T Cell Therapy: A Shifting Landscape

HHV-6B reactivation affects approximately half of all allogeneic hematopoietic cell transplant (HCT) recipients. HHV-6B is the most frequent infectious cause of encephalitis following HCT and is associated with pleiotropic manifestations in this setting, including graft-versus-host disease, myelosuppression, pneumonitis, and CMV reactivation, although the causal link is not always clear. When the virus inserts its genome in chromosomes of germ cells, the chromosomally integrated form (ciHHV6) is inherited by offspring. The condition of ciHHV6 is characterized by the persistent detection of HHV-6 DNA, often confounding diagnosis of reactivation and disease-this has also been associated with adverse outcomes. Recent changes in clinical practice in the field of cellular therapies, including a wider use of post-HCT cyclophosphamide, the advent of letermovir for CMV prophylaxis, and the rapid expansion of novel cellular therapies require contemporary epidemiological studies to determine the pathogenic role and spectrum of disease of HHV-6B in the current era. Research into the epidemiology and clinical significance of HHV-6B in chimeric antigen receptor T cell (CAR-T cell) therapy recipients is in its infancy. No controlled trials have determined the optimal treatment for HHV-6B. Treatment is reserved for end-organ disease, and the choice of antiviral agent is influenced by expected toxicities. Virus-specific T cells may provide a novel, less toxic therapeutic modality but is more logistically challenging. Preventive strategies are hindered by the high toxicity of current antivirals. Ongoing study is needed to keep up with the evolving epidemiology and impact of HHV-6 in diverse and expanding immunocompromised patient populations.

HHV-6B detection and host gene expression implicate HHV-6B as pulmonary pathogen after hematopoietic cell transplant

Limited understanding of the immunopathogenesis of human herpesvirus 6B (HHV-6B) has prevented its acceptance as a pulmonary pathogen after hematopoietic cell transplant (HCT). In this prospective multicenter study of patients undergoing bronchoalveolar lavage (BAL) for pneumonia after allogeneic HCT, we test blood and BAL fluid (BALF) for HHV-6B DNA and mRNA transcripts associated with lytic infection and perform RNA-seq on paired blood. Among 116 participants, HHV-6B DNA is detected in 37% of BALs, 49% of which also have HHV-6B mRNA detection. We establish HHV-6B DNA viral load thresholds in BALF that are highly predictive of HHV-6B mRNA detection and associated with increased risk for overall mortality and death from respiratory failure. Participants with HHV-6B DNA in BALF exhibit distinct host gene expression signatures, notable for enriched interferon signaling pathways in participants clinically diagnosed with idiopathic pneumonia. These data implicate HHV-6B as a pulmonary pathogen after allogeneic HCT.

Human herpesvirus-6 reactivation and disease after allogeneic haematopoietic cell transplantation in the era of letermovir for cytomegalovirus prophylaxis

OBJECTIVES

Letermovir for cytomegalovirus (CMV) prophylaxis in allogeneic haematopoietic cell transplant (HCT) recipients has decreased anti-CMV therapy use. Contrary to letermovir, anti-CMV antivirals are also active against human herpesvirus-6 (HHV-6). We assessed changes in HHV-6 epidemiology in the post-letermovir era.

METHODS

We conducted a retrospective cohort study of CMV-seropositive allogeneic HCT recipients comparing time periods before and after routine use of prophylactic letermovir. HHV-6 testing was at the discretion of clinicians. We computed the cumulative incidence of broad-spectrum antiviral initiation (foscarnet, (val)ganciclovir, and/or cidofovir), HHV-6 testing, and HHV-6 detection in blood and cerebrospinal fluid within 100 days after HCT. We used Cox proportional-hazards models with stabilized inverse probability of treatment weights to compare outcomes between cohorts balanced for baseline factors.

RESULTS

We analysed 738 patients, 376 in the pre-letermovir and 362 in the post-letermovir cohort. Broad-spectrum antiviral initiation incidence decreased from 65% (95% CI, 60-70%) pre-letermovir to 21% (95% CI, 17-25%) post-letermovir. The cumulative incidence of HHV-6 testing (17% [95% CI, 13-21%] pre-letermovir versus 13% [95% CI, 10-16%] post-letermovir), detection (3% [95% CI, 1-5%] in both cohorts), and HHV-6 encephalitis (0.5% [95% CI, 0.1-1.8%] pre-letermovir and 0.6% [95% CI, 0.1-1.9%] post-letermovir) were similar between cohorts. First HHV-6 detection occurred at a median of 37 days (interquartile range, 18-58) in the pre-letermovir cohort and 27 (interquartile range, 25-34) in the post-letermovir cohort. In a weighted model, there was no association between the pre-versus post-letermovir cohort and HHV-6 detection (adjusted hazard ratio, 1.08; 95% CI, 0.44-2.62).

DISCUSSION

Despite a large decrease in broad-spectrum antivirals after the introduction of letermovir prophylaxis in CMV-seropositive allogeneic HCT recipients, there was no evidence for increased clinically detected HHV-6 reactivation and disease.

How I prevent viral reactivation in high-risk patients

Preventing viral infections at an early stage is a key strategy for successfully improving transplant outcomes. Preemptive therapy and prophylaxis with antiviral agents have been successfully used to prevent clinically significant viral infections in hematopoietic cell transplant recipients. Major progress has been made over the past decades in preventing viral infections through a better understanding of the biology and risk factors, as well as the introduction of novel antiviral agents and advances in immunotherapy. High-quality evidence exists for the effective prevention of herpes simplex virus, varicella-zoster virus, and cytomegalovirus infection and disease. Few data are available on the effective prevention of human herpesvirus 6, Epstein-Barr virus, adenovirus, and BK virus infections. To highlight the spectrum of clinical practice, here we review high-risk situations that we handle with a high degree of uniformity and cases that feature differences in approaches, reflecting distinct hematopoietic cell transplant practices, such as ex vivo T-cell depletion.

Immunocompromised Host Pneumonia: Definitions and Diagnostic Criteria: An Official American Thoracic Society Workshop Report

Pneumonia imposes a significant clinical burden on people with immunocompromising conditions. Millions of individuals live with compromised immunity because of cytotoxic cancer treatments, biological therapies, organ transplants, inherited and acquired immunodeficiencies, and other immune disorders. Despite broad awareness among clinicians that these patients are at increased risk for developing infectious pneumonia, immunocompromised people are often excluded from pneumonia clinical guidelines and treatment trials. The absence of a widely accepted definition for immunocompromised host pneumonia is a significant knowledge gap that hampers consistent clinical care and research for infectious pneumonia in these vulnerable populations. To address this gap, the American Thoracic Society convened a workshop whose participants had expertise in pulmonary disease, infectious diseases, immunology, genetics, and laboratory medicine, with the goal of defining the entity of immunocompromised host pneumonia and its diagnostic criteria.

Comparing the application of mNGS after combined pneumonia in hematologic patients receiving hematopoietic stem cell transplantation and chemotherapy: A retrospective analysis

Rapid and accurate pathogen identification is essential for timely and effective treatment of pneumonia. Here, we describe the use of metagenomic next-generation sequencing (mNGS) of bronchoalveolar lavage (BALF) fluid to identify pathogens in patients with hematologic comorbid respiratory symptoms in a retrospective study with 84 patients. In the transplantation group, 8 cases (19.5%) and 47 cases (97.9%) were positive for BALF by conventional method detection and mNGS detection, respectively, and 6 cases (14.0%) and 41 cases (91.1%) in chemotherapy group, respectively. The detection rate of mNGS in both groups was significantly higher than that of conventional detection methods (all P&lt;0.05). Pseudomonas aeruginosa and Streptococcus pneumoniae were the most common bacterial infections in the transplantation and chemotherapy groups, respectively. Aspergillus was the most common fungal infection in both groups. Human betaherpesvirus 5 (HHV-5), torque teno virus and human betaherpesvirus 7 (HHV-7) were the most common pathogen species in both groups. The most common type of infection in patients in the transplantation and chemotherapy groups was the mixed infection of bacteria-virus. Most patients in the transplantation group had mixed infections based on multiple viruses, with 42 cases of viral infections in the transplantation group and 30 cases of viral infections in the chemotherapy group, which were significantly higher in the transplantation group than in the chemotherapy group (χ2 = 5.766, P=0.016). and the mixed infection of virus-virus in the transplantation group was significantly higher than that in the chemotherapy group (27.1% vs 4.4%, P=0.003). The proportion of death due to pulmonary infection was significantly higher in the transplantation group than in the chemotherapy group (76.9% vs 16.7%, χ2 = 9.077, P=0.003). This study demonstrated the value of mNGS of BALF in improving the diagnosis and prognosis of hematologic comorbid pneumonia, helping patients to obtain timely and effective treatment, and giving guidance on the overall treatment plan for patients, with particular benefit for patients with hematologic chemotherapy comorbid pneumonia.

Herpesviridae in critically ill hematology patients: HHV-6 is associated with worse clinical outcome

PURPOSE

Although viral infections are frequent among patients with hematological malignancies (HM), data about herpesviridae in critically ill hematology patients are scarce. We aimed at determining the impact of herpesviridae reactivation/infection in this population.

MATERIAL AND METHODS

We performed a single center retrospective study including all consecutive adult hematology patients admitted to our comprehensive cancer center ICU on a 6-year period. Clinical characteristics, microbiological findings, especially virus detection and outcome were recorded.

RESULTS

Among the 364 included patients, HHV-6 was the predominant retrieved herpesviridae (66 patients, 17.9%), followed by HSV1/2 (41 patients, 11.3%), CMV (38 patients, 10.4%), EBV (24 patients, 6.6%) and VZV (3 patients). By multivariable analysis, HHV-6 reactivation was independently associated with hospital mortality (OR, 2.35; 95% CI, 1.03-5.34; P = 0.042), whereas antiviral prophylaxis during ICU stay had a protective effect (OR, 0.41; 95% CI, 0.18-0.95; P = 0.037). HHV-6 pneumonitis was independently associated with 1-year mortality (OR, 6.87; 95% CI, 1.09-43.3; P = 0.04).

CONCLUSIONS

Among critically ill hematology patients, HHV-6 reactivation and pneumonitis are independent risk factors for hospital and 1-year mortality, respectively. Impact of prevention and treatment using agents active against HHV-6 should be assessed to define a consensual diagnostic and therapeutic strategy.

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.

Oral brincidofovir decreases the incidence of HHV-6B viremia after allogeneic HCT

Human herpesvirus 6B (HHV-6B) frequently reactivates after allogeneic hematopoietic cell transplantation (HCT). There are no randomized studies of antiviral treatments to prevent HHV-6B reactivation. Brincidofovir has high in vitro activity against HHV-6B and other DNA viruses, but its in vivo activity for HHV-6B has not been demonstrated. We performed a post hoc analysis of a randomized controlled trial of twice-weekly oral brincidofovir for cytomegalovirus prophylaxis after allogeneic HCT to study the effect of brincidofovir on HHV-6B reactivation. We included patients randomized within 2 weeks of HCT and who received at least 6 consecutive doses of study drug after randomization. We tested plasma for HHV-6B through week 6 post-HCT. The cohort consisted of 92 patients receiving brincidofovir and 61 receiving placebo. The cumulative incidence of HHV-6B plasma detection through day 42 post-HCT was significantly lower among patients receiving brincidofovir (14.2%) compared with placebo (32.4%; log-rank, 0.019). In an adjusted Cox model, brincidofovir exposure remained associated with a lower hazard for HHV-6B plasma detection (hazard ratio, 0.40; 95% confidence interval, 0.20-0.80). In conclusion, brincidofovir prophylaxis reduced HHV-6B reactivation after allogeneic HCT in a post hoc analysis of a randomized controlled trial. These data support the study of intravenous brincidofovir for HHV-6B prophylaxis.

Human herpesvirus 6 in transplant recipients: an update on diagnostic and treatment strategies

PURPOSE OF REVIEW

The current review article focuses on recent advances in the approach to the diagnosis and treatment of human herpesvirus 6B (HHV-6B) in hematopoietic cell and solid organ transplant recipients.

RECENT FINDINGS

Over the past few years, key studies have broadened our understanding of best practices for the prevention and treatment of HHV-6B encephalitis after transplantation. Moreover, important data have been reported that support a potential role of HHV-6B reactivation in the development of acute graft-versus-host disease and lower respiratory tract disease in transplant recipients. Finally, increasing recognition of inherited chromosomally integrated HHV-6 (iciHHV-6) and an expanding array of diagnostic tools have increased our understanding of the potential for complications related to viral reactivation originating from iciHHV-6 in donors or recipients.

SUMMARY

Recent advances in diagnostic tools, disease associations, and potential treatments for HHV-6B present abundant opportunities for improving our understanding and management of this complex virus in transplant recipients.

A Systematic Review of Sodium Disorders in HHV-6 Encephalitis

Human herpesvirus 6 (HHV-6) encephalitis has a high mortality rate. Among those who survive, ~80% develop some type of permanent neurologic disorder. Early diagnosis and treatment may help prevent long-term sequelae. There have been several case reports as well as retrospective and prospective studies associating HHV-6 encephalitis with some form of sodium imbalance, either hyponatremia or hypernatremia; however, the exact frequency post-HCT is unknown, with reports ranging from 30% to 100%. We performed a systematic review of the literature and found 34 cases of HHV-6 encephalitis reported in conjunction with sodium imbalance that documented the timing of that imbalance relative to the onset of encephalitis. Sodium imbalance occurred before or at the onset of HHV-6 encephalitis in all but 2 cases (94%). This finding supports previous suggestions that sodium imbalance can be considered an early indicator of the potential development or presence of HHV-6 encephalitis in at-risk patient populations.

An Animal Model That Mimics Human Herpesvirus 6B Pathogenesis

Human herpesvirus 6B (HHV-6B), a T-lymphotropic virus, infects almost exclusively humans. An animal model of HHV-6B has not been available. Here, we report the first animal model to mimic HHV-6B pathogenesis; the model is based on humanized mice in which human immune cells were engrafted and maintained. For HHV-6B replication, adequate human T-cell activation (which becomes susceptible to HHV-6B) is necessary in this murine model. Here, we found that an additional transfer of human mononuclear cells to humanized mice resulted in an explosive proliferation of human activated T cells, which could be representative of graft-versus-host disease (GVHD) because the primary transfer of human cells was not sufficient to increase the number and ratio of human T cells. Mice infected with HHV-6B became weak and/or died approximately 7 to 14 days later. Quantitative PCR analysis revealed that the spleen and lungs were the major sites of HHV-6B replication in this model, and this was corroborated by the detection of viral proteins in these organs. Histological analysis also revealed the presence of megakaryocytes, indicating HHV-6B infection. Multiplex analysis of cytokines/chemokines in sera from the infected mice showed secretions of human cytokines/chemokines as reported for both in vitro infection and clinical samples, indicating that the secreted cytokines could affect pathogenesis. This is the first animal model showing HHV-6B pathogenesis, and it will be useful for elucidating the pathogenicity of HHV-6B, which is related to GVHD and idiopathic pneumonia syndrome.IMPORTANCE Human herpesvirus 6B (HHV-6B) is a ubiquitous virus that establishes lifelong latent infection only in humans, and the infection can reactivate, with severe complications that cause major problems. A small-animal model of HHV-6B infection has thus been desired for research regarding the pathogenicity of HHV-6B and the development of antiviral agents. We generated humanized mice by transplantation with human hematopoietic stem cells, and here, we modified the model by providing an additional transfer of human mononuclear cells, providing the proper conditions for efficient HHV-6B infection. This is the first humanized mouse model to mimic HHV-6B pathogenesis, and it has great potential for research into the in vivo pathogenesis of HHV-6B.

Comparative Analysis of Roseoloviruses in Humans, Pigs, Mice, and Other Species

Viruses of the genus Roseolovirus belong to the subfamily Betaherpesvirinae, family Herpesviridae. Roseoloviruses have been studied in humans, mice and pigs, but they are likely also present in other species. This is the first comparative analysis of roseoloviruses in humans and animals. The human roseoloviruses human herpesvirus 6A (HHV-6A), 6B (HHV-6B), and 7 (HHV-7) are relatively well characterized. In contrast, little is known about the murine roseolovirus (MRV), also known as murine thymic virus (MTV) or murine thymic lymphotrophic virus (MTLV), and the porcine roseolovirus (PRV), initially incorrectly named porcine cytomegalovirus (PCMV). Human roseoloviruses have gained attention because they can cause severe diseases including encephalitis in immunocompromised transplant and AIDS patients and febrile seizures in infants. They have been linked to a number of neurological diseases in the immunocompetent including multiple sclerosis (MS) and Alzheimer's. However, to prove the causality in the latter disease associations is challenging due to the high prevalence of these viruses in the human population. PCMV/PRV has attracted attention because it may be transmitted and pose a risk in xenotransplantation, e.g., the transplantation of pig organs into humans. Most importantly, all roseoloviruses are immunosuppressive, the humoral and cellular immune responses against these viruses are not well studied and vaccines as well as effective antivirals are not available.