American Society for Transplantation and Cellular Therapy Series #9: Management of HHV-6B After Hematopoietic Cell Transplantation and Chimeric Antigen Receptor (CAR)-T-Cell Therapy

The Practice Guidelines Committee and the Transplant Infectious Disease Special Interest Group of the American Society for Transplantation and Cellular Therapy developed guidelines focusing on human herpes virus 6B (HHV-6B). A compendium-style approach was used to address a series of standalone frequently asked questions (FAQs), supported by tables and figures to spotlight key concepts. Adult and pediatric infectious disease and hematopoietic cell transplantation (HCT) content experts developed these FAQs, and finalized recommendations after consensus was reached. This ninth topic in the series focuses on the relevant risk factors, diagnostic considerations, prophylaxis, and treatment approaches relevant to HHV-6B infections after HCT and Chimeric Antigen Receptor (CAR)-T-Cell Therapy.

Distribution of ganciclovir in the porcine central nervous system

Ganciclovir is often used compassionately for encephalitis due to cytomegalovirus (CMV) and human herpes virus 6b (HHV-6b). Ganciclovir pharmacokinetic studies in the central nervous system (CNS) generally rely on single measurements in the cerebrospinal fluid (CSF) or homogenized brain tissue. Therefore the objective was to compare brain extracellular fluid (ECF) concentrations of ganciclovir with plasma and CSF concentrations in a porcine model, using microdialysis during a 24 h period. Six Danish landrace pigs (female, age 4 months, 31-37 kg) received two weight-adjusted intravenous doses of ganciclovir. Unbound ganciclovir concentrations were determined by microdialysis over 24 h in five compartments: CSF (lateral ventricle, cisterna magna, and lumbar) and brain ECF (cortical and subcortical). Data were compared with paired plasma samples. Ganciclovir concentrations >IC50 for CMV (1.6 µg/mL) were achieved in all compartments. Concentrations >IC90 for CMV (8.3 µg/mL) were only achieved in plasma and the lumbar CSF compartment. The concentration time curves indicated higher lumbar and cisternal CSF concentrations than ECF concentrations. The ECF compartments achieved greater maximum concentration (Cmax), area under the concentration time curve (AUC), and time >IC50 after the second dose, and an accumulation ratio (Rac) >1. The greater Cmax, AUC, time >IC50, and Rac >1 in the ECF compartments with repeated dosages suggest that therapeutic concentrations may be achieved during long-term treatment. A higher loading dose might be warranted to improve early viral inhibition.

Extracellular viral microRNAs as biomarkers of virus infection in human cells

Nucleic acid amplification tests (NAATs) have enabled fast and sensitive detection of virus infections but are unable to discriminate between live and dead/inert viral fragments or between latent and reactivated virus infections. Here, we show that extracellular viral microRNAs (viral exmiRs) are cell-free candidate biomarkers of live, latent, and reactivated virus infections, achieving fast (under 1 day) and sensitive (30 attomolar [aM]) detection by quantitative real-time reverse transcription PCR (real-time RT-qPCR). We report that spent-media-derived Epstein-Barr virus (EBV) miR-BART10-3p and herpes simplex virus 1 (HSV-1) miR-H5 are biomarkers of live EBV-2 and HSV-1 infection of T cell cultures, respectively. We identified extracellular human herpesvirus 6 (HHV-6) miR-Ro6-4 as a biomarker of endogenous latent HHV-6 in healthy human donor T cell cultures and identified human cytomegalovirus (HCMV) miR-US5-2-5p and miR-US22-5p as plasma biomarkers of endogenous latent HCMV infection. Viral exmiR profiling of spent media from EBV- and HHV-8-reactivated B cell models revealed specific signatures of elevated EBV miR-BHRF1-2-3p and HHV-8 miR-K12-10a-3p, miR-K12-10b, and miR-K12-12-3p, respectively, during virus reactivation. Our study thus suggests the utility of viral exmiR biomarkers in enabling NAAT-based detection of live, endogenous latent, and reactivated virus infections of cells.

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.

Graft Failure Incidence, Risk Factors, and Outcomes in Patients Undergoing Non-Myeloablative Allogeneic Hematopoietic Cell Transplantation Using Post-Transplant Cyclophosphamide

Graft failure (GF) is a major complication of allogeneic hematopoietic cell transplantation (alloHCT) that results in significant morbidity and mortality. Post-transplant cyclophosphamide (PTCy)-based graft-versus-host disease (GVHD) prophylaxis has emerged as an effective regimen across the spectrum of donor-match settings, but few studies have investigated the characteristics of GF in the setting of PTCy-based GVHD prophylaxis. The objective was to detail the incidence, clinical features, risk factors, and outcomes for patients with primary graft failure (PGF) and secondary graft failure (SGF). In this retrospective study at a single institution, 958 consecutive patients undergoing first nonmyeloablative (NMA) alloHCT with PTCy-based GVHD prophylaxis were analyzed. PGF was defined as a failure to achieve an ANC ≥ 500 cells/m3 by day 30 of transplant in the absence of residual disease. SGF was defined as complete loss of donor chimerism after initial engraftment. The incidences of PGF and SGF were 3.8% (n = 37) and 1.8% (n = 17), respectively. Neither PGF nor SGF were associated with HLA disparity. In a multivariate analysis, risk factors for PGF in this cohort included age ≥ 65 (OR 2.4, 95% CI 1.2 to 4.8, P = .0120), an underlying diagnosis of MDS, MPN, or MDS/MPN overlap (OR 2.8, 95% CI 1.4 to 5.7, P = .0050), post-transplant viremia with HHV-6 (OR 2.9, 95% CI 1.5 to 5.7, P = .0030), and low CD34+ dose (OR 0.7, 95% CI 0.5 to 0.9, P = .0080). Patients with PGF had poor overall survival, driven primarily by a high rate of nonrelapse mortality (59% at 36 months). SGF was associated with use of a bone marrow graft source and a diagnosis of Hodgkin lymphoma. Patients with SGF had excellent clinical outcomes with only one of seventeen patients experiencing relapse and relapse-related mortality. The incidence of PGF and SGF in patients receiving NMA conditioning and PTCy is low and is not impacted by HLA disparities between donors and recipients. PGF is more common in recipients with age ≥ 65, a diagnosis of MDS, MPN, or MDS/MPN-overlap, post-transplant HHV-6 viremia, and low CD34+ cell dose. Low total nucleated cell dose is also a risk factor for PGF in patients receiving a bone marrow graft source. Patients who experience PGF have poor outcomes due to high rates of nonrelapse mortality, whereas patients who experience SGF have excellent long-term outcomes.

COVID-19 was associated with the complications after allogeneic hematopoietic stem cell transplantation

We aimed to identify the severity and duration of COVID-19 infection on complications after allo-HSCT. Enrolled 179 hospitalized patients with COVID-19 were categorized into long-term infection (> 18 days, n = 90) or short-term infection group (≤ 18 days, n = 89) according to the median duration of COVID-19. The severity of COVID-19 was categorized as asymptomatic infection, mild, moderate, severe, and critical illness according to guidelines of National Institutes of Health. Particularly, severe illness and critical illness were classified as serious infection. Asymptomatic infection, mild illness and moderate illness were classified as non-serious infection. The 150-day probabilities of poor graft function (PGF), cytomegalovirus (CMV) pneumonia and non-relapse mortality (NRM) were significantly higher in long-term infection group. The 150-day probabilities of CMV pneumonia and NRM after COVID-19 were higher in serious infection group. The 150-day probabilities of overall survival (OS) was significantly lower in long-term and serious infection group. In multivariable analysis, the severity of COVID-19 was associated with NRM and OS, and the duration of COVID-19 was associated with PGF. In summary, our data reported that the severity and duration of COVID-19 were associated with several complications and contribute to poor outcomes after allo-HSCT.

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.

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.

Laboratory and clinical aspects of human herpesvirus 6 infections

Human herpesvirus 6 (HHV-6) is a widespread betaherpesvirus which is genetically related to human cytomegalovirus (HCMV) and now encompasses two different species: HHV-6A and HHV-6B. HHV-6 exhibits a wide cell tropism in vivo and, like other herpesviruses, induces a lifelong latent infection in humans. As a noticeable difference with respect to other human herpesviruses, genomic HHV-6 DNA is covalently integrated into the subtelomeric region of cell chromosomes (ciHHV-6) in about 1% of the general population. Although it is infrequent, this may be a confounding factor for the diagnosis of active viral infection. The diagnosis of HHV-6 infection is performed by both serologic and direct methods. The most prominent technique is the quantification of viral DNA in blood, other body fluids, and organs by means of real-time PCR. Many active HHV-6 infections, corresponding to primary infections, reactivations, or exogenous reinfections, are asymptomatic. However, the virus may be the cause of serious diseases, particularly in immunocompromised individuals. As emblematic examples of HHV-6 pathogenicity, exanthema subitum, a benign disease of infancy, is associated with primary infection, whereas further virus reactivations can induce severe encephalitis cases, particularly in hematopoietic stem cell transplant recipients. Generally speaking, the formal demonstration of the causative role of HHV-6 in many acute and chronic human diseases is difficult due to the ubiquitous nature of the virus, chronicity of infection, existence of two distinct species, and limitations of current investigational tools. The antiviral compounds ganciclovir, foscarnet, and cidofovir are effective against active HHV-6 infections, but the indications for treatment, as well as the conditions of drug administration, are not formally approved to date. There are still numerous pending questions about HHV-6 which should stimulate future research works on the pathophysiology, diagnosis, and therapy of this remarkable human virus.