Kinetics of Torque Teno Virus-DNA Plasma Load Predict Rejection in Lung Transplant Recipients

Attenuation of Torque teno viral load over time in kidney transplantation recipients treated with calcineurin inhibitors is mitigated after conversion to belatacept

Torque Teno Virus (TTV) is a non-pathogenic anellovirus, highly prevalent in healthy populations. Variations in its viral load have been associated with states of diminished immunity, as occurs after organ transplantation. It is hypothesized that TTV-load might be used as a diagnostic tool to guide prescription and dosing of immunosuppressive drugs. Not much is known about the effects of combined immunosuppressive drugs on TTV replication in renal transplantation. Belatacept was introduced to counter side-effects of calcineurin inhibitors (CNI). It was never widely adopted, mainly because its association with increased risk of rejection. To investigate the differential effects of a regimen based on calcineurin inhibitors versus belatacept on TTV-loads, we measured TTV-levels in 105 patients from two randomized controlled trials in kidney transplant recipients (KTRs). We observed that time after transplantation was inversely related to TTV-levels of patients that remained on a CNI-containing regime, whereas this decline over time was diminished after conversion to belatacept. In addition, a correlation with tacrolimus-trough levels and age were found. Our study is the first report on the impact of conversion from CNI to belatacept on TTV-levels in KTR. In conclusion, the time-related decline in TTV-levels is mitigated after conversion from CNI to belatacept.

Torque Teno Virus Load Is Associated With Centers for Disease Control and Prevention Stage and CD4+ Cell Count in People Living With Human Immunodeficiency Virus but Seems Unrelated to AIDS-Defining Events and Human Pegivirus Load

BACKGROUND

Torque teno virus (TTV) is part of the human virome. TTV load was related to the immune status in patients after organ transplantation. We hypothesize that TTV load could be an additional marker for immune function in people living with HIV (PLWH).

METHODS

In this analysis, serum samples of PLWH from the RESINA multicenter cohort were reanalyzed for TTV. Investigated clinical and epidemiological parameters included human pegivirus load, patient age and sex, HIV load, CD4+ T-cell count (Centers for Disease Control and Prevention [CDC] stage 1, 2, or 3), and CDC clinical stage (1993 CDC classification system; stage A, B, or C) before initiation of antiretroviral therapy. Regression analysis was used to detect possible associations among parameters.

RESULTS

Our analysis confirmed TTV as a strong predictor of CD4+ T-cell count and CDC class 3. This relationship was used to propose a first classification of TTV load with regard to clinical stage. We found no association with clinical CDC stages A-C. The human pegivirus load was inversely correlated with HIV load but not TTV load.

CONCLUSIONS

TTV load was associated with immunodeficiency in PLWH. Neither TTV nor HIV load were predictive for the clinical categories of HIV infection.

Amyotrophic lateral sclerosis stratification: unveiling patterns with virome, inflammation, and metabolism molecules

Amyotrophic lateral sclerosis (ALS) is an untreatable and clinically heterogeneous condition primarily affecting motor neurons. The ongoing quest for reliable biomarkers that mirror the disease status and progression has led to investigations that extend beyond motor neurons' pathology, encompassing broader systemic factors such as metabolism, immunity, and the microbiome. Our study contributes to this effort by examining the potential role of microbiome-related components, including viral elements, such as torque tenovirus (TTV), and various inflammatory factors, in ALS. In our analysis of serum samples from 100 ALS patients and 34 healthy controls (HC), we evaluated 14 cytokines, TTV DNA load, and 18 free fatty acids (FFA). We found that the evaluated variables are effective in differentiating ALS patients from healthy controls. In addition, our research identifies four unique patient clusters, each characterized by distinct biological profiles. Intriguingly, no correlations were found with site of onset, sex, progression rate, phenotype, or C9ORF72 expansion. A remarkable aspect of our findings is the discovery of a gender-specific relationship between levels of 2-ethylhexanoic acid and patient survival. In addition to contributing to the growing body of evidence suggesting altered peripheral immune responses in ALS, our exploratory research underscores metabolic diversity challenging conventional clinical classifications. If our exploratory findings are validated by further research, they could significantly impact disease understanding and patient care customization. Identifying groups based on biological profiles might aid in clustering patients with varying responses to treatments.

Polyomavirus Nephropathy in ABO Blood Group-Incompatible Kidney Transplantation: Torque Teno Virus and Immunosuppressive Burden as an Approximation to the Problem

Introduction

Earlier reports suggest that patients after ABO-incompatible kidney transplantation (ABOi) are at enhanced risk of developing BK-virus (BKV, also known as BK polyomavirus [BKPyV]) nephropathy (BKPyVAN). It remains elusive whether this is a result of more intense immunosuppression or an ABOi-associated "intrinsic attribute." To address this question, we measured Torque Teno virus (TTV) loads as a quantitative proxy for immunosuppressive depth in ABOi recipients and compared them to human leukocyte antigen-incompatible (HLAi, i.e. pretransplant donor-specific antibody-positive) and standard-risk transplant recipients.

Methods

Our retrospective study screened 2256 consecutive kidney transplantations performed between 2007 and 2020 at the Medical University of Vienna. Out of 629 in-principle eligible transplantations, we were able to include 465 patients: 42 ABOi, 106 HLAi, and 317 control recipients. Longitudinal TTV- polymerase chain reaction (PCR) and BKV-PCR was carried out at predefined timepoints and ranged from pretransplant until month 24 posttransplantation. TTV loads and immunosuppression were evaluated in the context of BKV-associated complications.

Results

ABOi recipients had a higher TTV load compared to HLAi and controls both at month 3 (median 1.5 × 109 vs. 2.4 × 108 vs. 9.1 × 107; P = 0.010) and at month 6 (3.1 × 109 vs. 1.4 × 107 vs. 6.4 × 107; P = 0.014) posttransplantation. Tacrolimus exposure was significantly higher in ABOi patients compared to HLAi and control patients (ABOi vs. HLAi: P = 0.007; ABOi vs. controls: P < 0.0001). Biopsy-proven BKPyVAN was more frequent in ABOi recipients when compared to HLAi and control recipients (11.9% vs. 2.8% vs. 4.1%; P = 0.046).

Conclusion

Our data support the assumption that ABOi patients are indeed at higher risk to develop BKPyVAN. A higher TTV load and immunosuppressive burden suggest that intense immunosuppression, rather than an "intrinsic attribute" conferred by ABOi, may contribute to this finding.

Investigation of Oral Shedding of Torquetenovirus (TTV) in Moderate-to-Severe COVID-19 Hospitalised Patients

BACKGROUND

Torquetenovirus (TTV) is a small DNA virus constituting the human virome. High levels of TTV-DNA have been shown to be associated with immunosuppression and inflammatory chronic disorders.

AIM

To assess the possible association between the salivary viral load of TTV-DNA in patients hospitalised due to COVID-19 and disease severity.

METHODS

Saliva samples collected from 176 patients infected with SARS-CoV-2 were used to investigate the presence of SARS-CoV-2 and TTV-DNA by use of real-time RT-PCR.

RESULTS

The majority of patients were male with severe COVID-19. Presence of SARS-CoV-2 was observed in the saliva of 64.77% of patients, showing TTV-DNA in 55.68% of them. Patients with impaired clinical conditions (p < 0.001), which evolved to death (p = 0.003), showed a higher prevalence of TTV-DNA. The median viral load in patients with severe condition was 4.99 log10 copies/mL, in which those who were discharged and those evolving to death had values of 3.96 log10 copies/mL and 6.27 log10 copies/mL, respectively. A statistically significant association was found between the distribution of TTV-DNA viral load in saliva samples and severity of COVID-19 (p = 0.004) and disease outcomes (p < 0.001).

CONCLUSIONS

These results indicate that TTV-DNA in saliva could be a useful biomarker of COVID-19 severity and prognosis.

Molecular characterization of plasma virome of hepatocellular carcinoma (HCC) patients

Hepatocellular carcinoma (HCC) stands as the most common cancer type, arising from various causes, and responsible for a substantial number of cancer-related fatalities. Recent advancements in viral metagenomics have empowered scientists to delve into the intricate diversity of the virosphere, viral evolution, interactions between viruses and their hosts, and the identification of viral causes behind disease outbreaks, the development of specific symptoms, and their potential role in altering the host's physiology. The present study had the objective of "Molecular Characterization of HBV, HCV, anelloviruses, CMV, SENV-D, SENV-H, HEV, and HPV viruses among individuals suffering from HCC." A total of 381 HCC patients contributed 10 cc of blood each for this study. The research encompassed the assessment of tumor markers, followed by molecular characterization of HBV, HCV, Anelloviruses (TTV, TTMV, and TTMDV), SENV-H and SENV-D viruses, HEV, CMV, and HPV, as well as histopathological examinations. The outcomes of this study revealed that majority of the HCC patients 72.4% (276/381) were male as compared to females. HCV infection, at 76.4% (291 out of 381), exhibited a significant association (p < 0.05) with HCC. Most patients displayed singular lesions in the liver, with Child Pugh Score Type B being the predominant finding in 45.2% of cases. Plasma virome analysis indicated the prevalence of TTMDV (75%), followed by TTMV (70%) and TTV (42.1%) among anelloviruses in HCC patients. Similarly, SENV-H (52%) was followed by SENV-D (20%), with co-infections at 15%. The presence of CMV and HEV among the HCC patients was recorded 5% each however 3.5% of the patients showed the presence of HPV. In conclusion, this study underscores that HCC patients serve as reservoirs for various pathogenic and non-pathogenic viruses, potentially contributing to the development, progression, and severity of the disease.

Nocardia farcinica brain abscess with torque teno virus co-infection: A case report

Background

Brain abscesses caused by Nocardia are rare and difficult to diagnose. Nocardia farcinica is among the most common species; however, the conventional diagnosis of N. farcinica infection consists of cerebrospinal fluid (CSF) and blood culture and Gram staining. These procedures prolong the time to diagnosis and initiating treatment.

Case presentation

A 69-year-old woman with diabetes mellitus presented with headaches and dizziness persisting for 2 weeks, which was initially diagnosed as a brain abscess. Due to the unusual presentation and rapid progression of symptoms, she underwent surgical resection of the brain abscess. No pathogens were detected in blood or CSF cultures. However, metagenomic next-generation sequencing (mNGS) identified N. farcinica and Torque teno virus in pus extracted from the abscesses. The patient received appropriate antibiotic therapy and recovered fully without any residual neurological deficits.

Conclusion

mNGS useful for prompt diagnosis and selection of antibiotic therapy for brain abscesses caused by Nocardia. Surgical intervention is necessary in some cases.

High Torque teno virus load and outcome of patients undergoing allogeneic hematopoietic cell transplantation

Quantification of Torque teno virus (TTV) load emerged as a marker of immunosuppression. Associations of TTV load with complications and survival after allogeneic hematopoietic cell transplantation (allo-HCT) were controversial in published studies. In this prospective study, we aimed to identify factors influencing TTV load after allo-HCT and to determine whether the TTV load is associated with complications or outcomes. Seventy allo-HCT recipients were included. TTV DNA load was quantified in 469 plasma samples of 70 patients from Day (D) 15 before D120 after transplantation. The influence of transplant characteristics on TTV load and the associations of TTV load with viral infections, acute graft versus host disease, mortality, and relapse were analyzed. More than 80% of patients were TTV DNA positive from D30 after transplantation onwards. Median TTV load increased between D30 and D60 post-transplantation. Patients with lymphoid malignancies had higher TTV load than those with myeloid malignancies. Myeloablative conditioning was associated with higher TTV loads. Patients with no measurable residual disease at transplant had higher TTV loads. High TTV load at D90 post-transplantation was associated with lower overall survival and at D120 post-transplantation was associated with higher relapse rate. In conclusion, TTV load at time points later than D90 after allo-HCT may be useful to assess prognosis.

Molecular monitoring of lung allograft health: is it ready for routine clinical use?

Maintenance of long-term lung allograft health in lung transplant recipients (LTRs) requires a fine balancing act between providing sufficient immunosuppression to reduce the risk of rejection whilst at the same time not over-immunosuppressing individuals and exposing them to the myriad of immunosuppressant drug side-effects that can cause morbidity and mortality. At present, lung transplant physicians only have limited and rather blunt tools available to assist them with this task. Although therapeutic drug monitoring provides clinically useful information about single time point and longitudinal exposure of LTRs to immunosuppressants, it lacks precision in determining the functional level of immunosuppression that an individual is experiencing. There is a significant gap in our ability to monitor lung allograft health and therefore tailor optimal personalised immunosuppression regimens. Molecular diagnostics performed on blood, bronchoalveolar lavage or lung tissue that can detect early signs of subclinical allograft injury, differentiate rejection from infection or distinguish cellular from humoral rejection could offer clinicians powerful tools in protecting lung allograft health. In this review, we look at the current evidence behind molecular monitoring in lung transplantation and ask if it is ready for routine clinical use. Although donor-derived cell-free DNA and tissue transcriptomics appear to be the techniques with the most immediate clinical potential, more robust data are required on their performance and additional clinical value beyond standard of care.

Torque Teno Virus (TTV)-A Potential Marker of Immunocompetence in Solid Organ Recipients

Torque Teno Virus (TTV), first discovered in 1997, is a non-pathogenic, highly prevalent virus with a notable presence in the human virome. TTV has garnered attention as a potential indicator of immunocompetence in recipients of solid organ transplants. In this review, we discuss the role of TTV as a potential marker for immunosuppression optimization, prediction of graft rejection, and as an indicator of opportunistic infections. We discuss TTV's behavior over the course of time after transplantation, TTV's implications in different immunosuppressive regimens, and potential utility in vaccinations. The review synthetizes findings from various studies depicting its potential clinical utility for future personalized patient care.

Kinetics of Torque Teno virus in heart transplant patients

End-stage heart failure often requires heart transplantation as a life-prolonging treatment. Immunosuppressive therapy is necessary to avoid rejection, but is associated with serious adverse effects. New approaches are needed to monitor immune function in heart transplant patients. We here report the kinetics of Torque Teno Virus (TTV) after transplantation in a large cohort of heart transplant patients and examine its possible role in predicting rejection. We included 106 patients from Aarhus University Hospital and Oslo University Hospital. Patients were followed for 3 years with clinical assessments, biopsies, TTV measurements, and flowcytometric phenotyping. We observed TTV levels reaching a maximum 3 months after transplantation for all 106 patients, after which levels gradually declined. 38 patients (38 %) had biopsy-proven rejection within the first year. We did not find evidence of an association between TTV and serum trough levels, events of rejection, nor flow cytometric immunophenotype. We report data on a large cohort of heart transplant patients and contribute to the understanding of how TTV behaves in transplant patients. Despite not finding an association with rejection, our results provide important insights into the kinetics of TTV levels after transplantation, which may be useful in future studies of immune function in heart transplant patients.

Diagnosis, Prevention, and Treatment of Infections in Kidney Transplantation

Kidney transplant often is complicated by infections in the recipient from therapy-related and patient-related risk factors. Infections in kidney transplant recipients are associated with increased morbidity, mortality, and allograft dysfunction. There is a predictable timeline after kidney transplant regarding the types of pathogens causing infections, reflecting the net state of immunosuppression. In the early post-transplant period, bacterial infections comprise two thirds of all infections, followed by viral and fungal infections. Infections occurring early after kidney transplantation are generally the result of postoperative complications. In most cases, opportunistic infections occur within 6 months after kidney transplantation. They may be caused by a new infection, a donor-derived infection, or reactivation of a latent infection. Community-acquired pneumonia, upper respiratory tract infections, urinary tract infections, and gastrointestinal infections are the most common infections in the late period after transplantation when the net immunosuppression is minimal. It is crucial to seek information on the time after transplant, reflecting the net state of immunosuppression, previous history of exposure/infections, geography, and seasonal outbreaks. It is imperative that we develop regionally specific guidelines on screening, prevention, and management of infections after kidney transplantation.

Torque teno virus viremia and QuantiFERON®-CMV assay in prediction of cytomegalovirus reactivation in R+ kidney transplant recipients

Introduction

Cytomegalovirus (CMV) is the most frequent infectious complication following solid organ transplantation. Torque teno viruses (TTV) viremia has been proposed as a biomarker of functional immunity in the management of kidney transplant recipients (KTR). The QuantiFERON^®-CMV (QF-CMV) is a commercially available assay that allows the assessment of CD8⁺ T-cell responses in routine diagnostic laboratories.

Methods

In a prospective national multicenter cohort of 64 CMV-seropositive (R+) KTR, we analyzed the value of TTV load and the two markers of the QF-CMV assay [QF-Ag (CMV-specific T-cell responses) and QF-Mg (overall T-cell responses)], alone and in combination, in prediction of CMV reactivation (≥3 log₁₀ IU/ ml) in the first post-transplant year. We compared previously published cut-offs and specific cut-offs optimized from ROC curves for our population.

Results

Using the conventional cut-off (3.45 log₁₀ copies/ml), TTV load at D0 [inclusion visit on the day of transplantation before induction (D0)], or at M1 (1-month post-transplant visit) perform better in predicting CMV viremia control than CMV reactivation. Survival analyses suggest a better performance of our optimized TTV cut-offs (3.78 log₁₀ copies/ml at D0 and 4.23 log₁₀ copies/ml at M1) for risk stratification of CMV reactivation in our R+ KTR cohort. The QF-CMV (QF-Ag = 0.2 IU/ml, and QF-Mg = 0.5 IU/ml) also appears to better predict CMV viremia control than CMV reactivation. Moreover, survival analyses suggest that the QF-Mg would perform better than the QF-Ag in stratifying the risk of CMV reactivation. The use of our optimized QF-Mg cut-off (1.27 IU/ml) at M1 further improved risk stratification of CMV reactivation. Using conventional cut-offs, the combination of TTV load and QF-Ag or TTV load and QF-Mg did not improve prediction of CMV viremia control compared to separate analysis of each marker but resulted in an increase of positive predictive values. The use of our cut-offs slightly improved risk prediction of CMV reactivation.

Conclusion

The combination of TTV load and QF-Ag or TTV load and QF-Mg could be useful in stratifying the risk of CMV reactivation in R+ KTR during the first post-transplant year and thereby have an impact on the duration of prophylaxis in these patients.

Clinical trial registration

ClinicalTrials.gov registry, identifier NCT02064699.

Understanding torquetenovirus (TTV) as an immune marker

Torquetenovirus (TTV), a small, single stranded anellovirus, is currently being explored as a marker of immunocompetence in patients with immunological impairment and inflammatory disorders. TTV has an extremely high prevalence and is regarded as a part of the human virome, the replication of which is controlled by a functioning immune system. The viral load of TTV in plasma of individuals is thought to reflect the degree of immunosuppression. Measuring and quantifying this viral load is especially promising in organ transplantation, as many studies have shown a strong correlation between high TTV loads and increased risk of infection on one side, and low TTV loads and an increased risk of rejection on the other side. As clinical studies are underway, investigating if TTV viral load measurement is superior for gauging antirejection therapy compared to medication-levels, some aspects nevertheless have to be considered. In contrast with medication levels, TTV loads have to be interpreted bearing in mind that viruses have properties including transmission, tropism, genotypes and mutations. This narrative review describes the potential pitfalls of TTV measurement in the follow-up of solid organ transplant recipients and addresses the questions which remain to be answered.

The plasma virome in longitudinal samples from pregnant patients

Introduction

Nucleic acid from viruses is common in peripheral blood, even in asymptomatic individuals. How physiologic changes of pregnancy impact host-virus dynamics for acute, chronic, and latent viral infections is not well described. Previously we found higher viral diversity in the vagina during pregnancy associated with preterm birth (PTB) and Black race. We hypothesized that higher diversity and viral copy numbers in the plasma would show similar trends.

Methods

To test this hypothesis, we evaluated longitudinally collected plasma samples from 23 pregnant patients (11 term and 12 preterm) using metagenomic sequencing with ViroCap enrichment to enhance virus detection. Sequence data were analyzed with the ViroMatch pipeline.

Results

We detected nucleic acid from at least 1 virus in at least 1 sample from 87% (20/23) of the maternal subjects. The viruses represented 5 families: Herpesviridae, Poxviridae, Papillomaviridae, Anelloviridae, and Flaviviridae. We analyzed cord plasma from 18 of the babies from those patients and found nucleic acid from viruses in 33% of the samples (6/18) from 3 families: Herpesviridae, Papillomaviridae, and Anelloviridae. Some viral genomes were found in both maternal plasma and cord plasma from maternal-fetal pairs (e.g. cytomegalovirus, anellovirus). We found that Black race associated with higher viral richness (number of different viruses detected) in the maternal blood samples (P=0.003), consistent with our previous observations in vaginal samples. We did not detect associations between viral richness and PTB or the trimester of sampling. We then examined anelloviruses, a group of viruses that is ubiquitous and whose viral copy numbers fluctuate with immunological state. We tested anellovirus copy numbers in plasma from 63 pregnant patients sampled longitudinally using qPCR. Black race associated with higher anellovirus positivity (P<0.001) but not copy numbers (P=0.1). Anellovirus positivity and copy numbers were higher in the PTB group compared to the term group (P<0.01, P=0.003, respectively). Interestingly, these features did not occur at the time of delivery but appeared earlier in pregnancy, suggesting that although anelloviruses were biomarkers for PTB they were not triggering parturition.

Discussion

These results emphasize the importance of longitudinal sampling and diverse cohorts in studies of virome dynamics during pregnancy.

Torque teno virus load as marker of rejection and infection in solid organ transplantation - A systematic review and meta-analysis

Balancing immunosuppression to prevent rejection in solid organ transplant (SOT) recipients remains challenging. Torque teno virus (TTV), a commensal non-pathogenic virus, has been proposed as marker of functional immunity: higher loads correspond to over-immunosuppression, and lower loads to under-immunosuppression. This review offers an overview of the current evidence of the association between TTV-load and infection and rejection after SOT. A systematic literature search strategy, deposited in the PROSPERO registry, resulted in 548 records. After screening, 23 original and peer-reviewed articles were assessed investigating the association between TTV-load, infection and/or rejection in SOT. The Quality in Prognostic Studies (QUIPS)-tool was used to assess the risk of bias. Meta-analysis with random-effects was performed on results with similar outcomes and exposure measures. Most of the included studies involved retrospective cohorts in which the TTV-load was measured longitudinally, within the first 2 years post-transplantation. Infection outcomes differed between studies and included viral, bacterial, parasitic and fungal infections. Rejection was defined by biopsy confirmation or initiation of rejection treatment. Twelve out of 16 studies reported an association between high TTV-load and infections, whereas 13 out of 15 reported an association between low TTV-load and rejection. Meta-analysis showed an increased risk of infection (OR: 1.16, 95% CI: 1.03-1.32; HR: 1.05, 95% CI: 0.97-1.14) and a decreased risk of rejection (OR: 0.90, 95% CI: 0.87-0.94; HR: 0.74, 95% CI: 0.71-0.76) per 1 log TTV-load increase. The qualitative assessment showed varying risks of bias in the included studies. This systematic review and meta-analysis indicates that blood TTV-load measured within the first 2 years after SOT is associated with the risk of infection or allograft rejection, although substantial risk of bias in the studies included warrant cautious interpretation. The results in this review provide a rationale for larger, prospective, studies into TTV as marker of infection and rejection after SOT.

Integrated Immunologic Monitoring in Solid Organ Transplantation: The Road Toward Torque Teno Virus-guided Immunosuppression

Potent immunosuppressive drugs have been introduced into clinical care for solid organ transplant recipients. It is now time to guide these drugs on an individual level to optimize their efficacy. An ideal tool simultaneously detects overimmunosuppression and underimmunosuppression, is highly standardized, and is straightforward to implement into routine. Randomized controlled interventional trials are crucial to demonstrate clinical value. To date, proposed assays have mainly focused on the prediction of rejection and were based on the assessment of few immune compartments. Recently, novel tools have been introduced based on a more integrated approach to characterize the immune function and cover a broader spectrum of the immune system. In this respect, the quantification of the plasma load of a highly prevalent and apathogenic virus that might reflect the immune function of its host has been proposed: the torque teno virus (TTV). Although TTV control is driven by T cells, other major immune compartments might contribute to the hosts' response. A standardized in-house polymerase chain reaction and a conformité européenne-certified commercially available polymerase chain reaction are available for TTV quantification. TTV load is associated with rejection and infection in solid organ transplant recipients, and cutoff values for risk stratification of such events have been proposed for lung and kidney transplantation. Test performance of TTV load does not allow for the diagnosis of rejection and infection but is able to define at-risk patients. Hitherto TTV load has not been used in interventional settings, but two interventional randomized controlled trials are currently testing the safety and efficacy of TTV-guided immunosuppression.

Association of post-transplantation anellovirus viral load with kidney transplant rejection in children

BACKGROUND

Post-transplantation immunosuppressive therapy reduces the risk of graft rejection but raises the risk of infection and malignancy. A biomarker of the level of immunosuppression can be helpful in monitoring immunosuppressive therapy. Inverse correlation between Torque teno virus (TTV) from the Anelloviridae (AV) family load and immune competence was described in previous studies. The aim of this study was to analyze the association between AV family viruses' kinetics and the risk for graft rejection in the first year after kidney transplantation in children.

METHODS

The titers of three genera (TTV, TTMDV, and TTMV) from the AV family were monitored by real-time PCR in consecutive samples from children before and after kidney transplantation.

RESULTS

Twenty-one children who underwent kidney transplantation were enrolled. Five out of 21 patients experienced acute graft rejection within a year from transplantation. We found that in patients who experienced graft rejection, the median titers of TTV and total AV titers at 5-6 months post-transplantation were lower than in those who did not. Using a threshold determined by ROC analysis, significant differences in TTV and total AV load were found between patients who had or did not have graft rejection (p = 0.002 and 0.004, respectively). No association was found between the dominance of any AV genus titer and the likelihood of rejection.

CONCLUSION

This pilot study suggests that children after kidney transplantation with low TTV and total AV titers 5-6 months post-transplantation are at increased risk for graft rejection within a year after transplantation. A higher resolution version of the Graphical abstract is available as Supplementary information.

Biomarker-Based Assessment for Infectious Risk Before and After Heart Transplantation

Purpose of Review

Survival outcomes for heart transplant recipients have improved in recent decades, but infection remains a significant cause of morbidity and mortality. In this review, we discuss several biological markers, or biomarkers, that may be used to monitor immunologic status in this patient population.

Recent Findings

While modest, data on the utility of immune biomarkers in heart transplant recipients suggest correlation between low level of immune response and increased infection risk. More novel assays, such as the detection of circulating levels of pathogen cell-free DNA in plasma and the use of Torque teno virus load as a surrogate for net state of immunosuppression, have potential to be additional important biomarkers.

Summary

Biomarker approaches to individualize immunosuppression therapy among heart transplant recipients is a promising area of medicine. However, additional studies are needed to inform the optimal protocol in which to incorporate these biomarkers into clinical practice.

Viruses, friends and foes: The case of Torque Teno virus and the net state of immunosuppression

New reliable biomarkers are needed to improve individual risk assessment for post-transplant infection, acute graft rejection and other immune-related complications after solid organ transplantation (SOT) and allogeneic hematopoietic stem cell transplantation (allo-HSCT). One promising strategy relies on the monitoring of replication kinetics of virome components as functional surrogate for the net state of immunosuppression. Torque Teno Virus (TTV) is a small, non-enveloped, circular, single-stranded DNA anellovirus with no attributable pathological effects. A major component of the human blood virome, TTV exhibits various features that facilitate its application as immune biomarker: high prevalence rates, nearly ubiquitous distribution, stable viral loads with little intra-individual variability, insensitivity to antiviral drugs, and availability of commercial PCR assays for DNA quantification. The present review summarizes the available studies supporting the use of post-transplant TTV viremia to predict patient and graft outcomes after SOT and allo-HSCT. Taken together, this evidence suggests that high or increasing TTV DNA levels precede the occurrence of infectious complications in the SOT setting, whereas low or decreasing viral loads are associated with the development of acute rejection. The interpretation in allo-HSCT recipients is further complicated by complex interplay with the underlying disease, conditioning regimen and timing of recovery of lymphocyte counts, although TTV kinetics may act as a marker of immunological reconstitution at the early post-transplant period. The standardization of PCR methods and reporting units for TTV DNAemia and the results from ongoing interventional trials evaluating a TTV load-guided strategy to adjust immunosuppressive therapy are achievements expected in the coming years. This article is protected by copyright. All rights reserved.

Quantification of torque teno virus (TTV) DNA in saliva and plasma samples in patients at short time before and after kidney transplantation

BACKGROUND

Several reports have proposed that the viral load of torque teno virus (TTV) in plasma is a biomarker of immune function in solid organ transplantation (SOT) and in allogeneic hematopoietic stem cell transplantation. Additionally, for the latter one, TTV-DNA quantification in saliva has also been suggested.

AIM

to investigate the correlation between the TTV viral load and immune function in paired saliva and plasma samples in patients on kidney transplantation.

MATERIALS AND METHODS

TTV-DNA viral load was quantified in paired samples of saliva and plasma from 71 patients before and a short-time after renal-transplantation by real-time PCR.

RESULTS

The data obtained from 213 paired samples showed a slight consistency in the comparison between saliva and plasma, with prevalence of TTV-DNA being 58%, 52% and 60% in saliva samples and 60%, 73% and 90% in plasma samples before and at 15-20 and 45-60 days after transplantation, respectively. Additionally, a high TTV viral load was observed in plasma at 15-20 and 45-60 days after transplantation compared to that observed in saliva at the same time.

CONCLUSIONS

Overall, monitoring TTV-DNA in saliva samples could be an additional fast non-invasive option to assess the immune functionality in SOT populations.

High-resolution Metatranscriptomic Characterization of the Pulmonary RNA Virome After Lung Transplantation

BACKGROUND

Lung transplantation provides a unique opportunity to investigate the constituents and temporal dynamics of the human pulmonary microbiome after lung transplantation. For methodological reasons, prior studies using metagenomics have detected DNA viruses but not demonstrated the presence of RNA viruses, including those that are common community acquired. In this proof-of-concept study, we aimed to further characterize the pulmonary microbiome after lung transplantation by using metagenomic next-generation sequencing (mNGS), with a particular focus on the RNA virome.

METHODS

We performed a single-center longitudinal study of lower respiratory tract RNA viruses and bacteria using bronchoalveolar lavage at postoperative day 1 and week 6 analyzed with total RNA sequencing (metatranscriptomics). Five primary and 5 repeat transplant recipients were recruited.

RESULTS

mNGS identified 5 RNA viruses (nil in the normal saline control), including 4 species of human rhinovirus not previously reported in Australia: A7 (HRV-A7), C22 (HRV-C22), B52 (HRV-B52), and B72 (HRV-B72). Overall, 12/20 specimens were virus positive in 7/10 cases. Human parainfluenza virus 3 was the most frequent virus in 7/20 specimens in 5/10 cases. In this small study, we did not detect a significant difference in abundance and diversity of RNA viruses and bacteria at postoperative day 1 and 6 wk, nor differences between retransplant recipients and primary lung transplant recipients.

CONCLUSIONS

Our study demonstrates how mNGS can also identify RNA viruses within the human pulmonary virome, including novel RNA viruses, and paves the way for a greater understanding of the complex relationships among the constituents of the pulmonary infectome.

Exploring the Diversity of the Human Blood Virome

Metagenomics is greatly improving our ability to discover new viruses, as well as their possible associations with disease. However, metagenomics has also changed our understanding of viruses in general. The vast expansion of currently known viral diversity has revealed a large fraction of non-pathogenic viruses, and offers a new perspective in which viruses function as important components of many ecosystems. In this vein, studies of the human blood virome are often motivated by the search for new viral diseases, especially those associated with blood transfusions. However, these studies have revealed the common presence of apparently non-pathogenic viruses in blood, particularly human anelloviruses and, to a lower extent, human pegiviruses (HPgV). To shed light on the diversity of the human blood virome, we subjected pooled plasma samples from 587 healthy donors in Spain to a viral enrichment protocol, followed by massive parallel sequencing. This showed that anelloviruses were clearly the major component of the blood virome and showed remarkable diversity. In total, we assembled 332 complete or near-complete anellovirus genomes, 50 of which could be considered new species. HPgV was much less frequent, but we, nevertheless, recovered 17 different isolates that we subsequently used for characterizing the diversity of this virus. In-depth investigation of the human blood virome should help to elucidate the ecology of these viruses, and to unveil potentially associated diseases.

The lung microbiome in lung transplantation

Culture-independent study of the lower respiratory tract after lung transplantation has enabled an understanding of the microbiome - that is, the collection of bacteria, fungi, and viruses, and their respective gene complement - in this niche. The lung has unique features as a microbial environment, with balanced entry from the upper respiratory tract, clearance, and local replication. There are many pressures impacting the microbiome after transplantation, including donor allograft factors, recipient host factors such as underlying disease and ongoing exposure to the microbe-rich upper respiratory tract, and transplantation-related immunosuppression, antimicrobials, and postsurgical changes. To date, we understand that the lung microbiome after transplant is dysbiotic; that is, it has higher biomass and altered composition compared to a healthy lung. Emerging data suggest that specific microbiome features may be linked to host responses, both immune and non-immune, and clinical outcomes such as chronic lung allograft dysfunction (CLAD), but many questions remain. The goal of this review is to put into context our burgeoning understanding of the lung microbiome in the postlung transplant patient, the interactions between microbiome and host, the role the microbiome may play in post-transplant complications, and critical outstanding research questions.

Torque Teno Virus load in lung cancer patients correlates with age but not with tumor stage

Background

Torque teno virus (TTV) is a ubiquitous non-pathogenic virus, which is suppressed in immunological healthy individuals but replicates in immune compromised patients. Thus, TTV load is a suitable biomarker for monitoring the immunosuppression also in lung transplant recipients. Since little is known about the changes of TTV load in lung cancer patients, we analyzed TTV plasma DNA levels in lung cancer patients and its perioperative changes after lung cancer surgery.

Material and methods

Patients with lung cancer and non-malignant nodules as control group were included prospectively. TTV DNA levels were measured by quantiative PCR using DNA isolated from patients plasma and correlated with routine circulating biomarkers and clinicopathological variables.

Results

47 patients (early stage lung cancer n = 30, stage IV lung cancer n = 10, non-malignant nodules n = 7) were included. TTV DNA levels were not detected in seven patients (15%). There was no significant difference between the stage IV cases and the preoperative TTV plasma DNA levels in patients with early stage lung cancer or non-malignant nodules (p = 0.627). While gender, tumor stage and tumor histology showed no correlation with TTV load patients below 65 years of age had a significantly lower TTV load then older patients (p = 0.022). Regarding routine blood based biomarkers, LDH activity was significantly higher in patients with stage IV lung cancer (p = 0.043), however, TTV load showed no correlation with LDH activity, albumin, hemoglobin, CRP or WBC. Comparing the preoperative, postoperative and discharge day TTV load, no unequivocal pattern in the kinetics were.

Conclusion

Our study suggest that lung cancer has no stage dependent impact on TTV plasma DNA levels and confirms that elderly patients have a significantly higher TTV load. Furthermore, we found no uniform perioperative changes during early stage lung cancer resection on plasma TTV DNA levels.

Associations Between Sputum Torque Teno Virus Load and Lung Function and Disease Severity in Patients With Chronic Obstructive Pulmonary Disease

Purpose: Viral load of Torque Teno virus (TTV) is elevated in immunosuppressed patients. The weakened immune response is typical in chronic obstructive pulmonary disease (COPD) patients. However, the relationship between TTV and COPD is still unknown.

Patients and Methods: We enrolled 91 patients admitted to hospitals with acute exacerbation of COPD (AECOPD) between January 2017 and August 2017 (ClinicalTrials.gov ID, NCT03236480). Sputum samples were gathered during hospitalization and the 120-day follow-up. TTV distribution and genogroups were assessed, and the associations between viral loads and clinical parameters were analyzed.

Results: TTV DNA was detected in 95.6% of COPD patients, and the viral load was nearly invariable at the stable and exacerbation states. Most TTV DNA-positive patients carried four distinct genotypes. Sputum load of TTV was positively associated with RV/TLC (r = 0.378, p = 0.030), and negatively correlated with FEV1/pre and FEV1/FVC (r = −0.484, −0.432, p = 0.011, 0.024, respectively). Neutral correlation between the TTV DNA load and COPD assessment test (CAT) scores (r = 0.258, p = 0.018) was observed.

Conclusion: Sputum loads of TTV DNA could be a novel indicator for lung function and disease severity assessment in COPD patients.

Torque teno viral load reflects immunosuppression in paediatric kidney-transplanted patients-a pilot study

BACKGROUND

Chronic deterioration of kidney graft function is related to inadequate immunosuppression (IS). A novel tool to assess the individual net state of IS in transplanted patients might be the monitoring of Torque teno virus (TTV) viral load. TTV is a non-pathogen virus detectable in almost all individuals. TTV level in the peripheral blood has been linked to the immune-competence of its host and should thus reflect IS after solid organ transplantation.

METHODS

TTV plasma load was quantified monthly by RT-PCR for a period of 1 year in 45 kidney-transplanted children. Post-transplant time was at least 3 months. The relation of the virus DNA levels to IS and transplant-specific clinical and laboratory parameters was analysed longitudinally.

RESULTS

TTV DNA was detectable in 94.5% of the plasma samples. There was a significant association with the post-transplant follow-up time as well as with the type of IS regimen, with lower virus loads in patients after longer post-transplant time and mTOR inhibitor-based IS. Furthermore, a significant positive correlation with the dose of prednisolone and mycophenolate mofetil was found.

CONCLUSIONS

TTV levels show an association/correlation with the strength of IS. Further studies are needed in order to evaluate TTV measurement as a tool for IS monitoring for hard clinical outcomes such as presence of donor-specific antibodies, rejections or infections-common consequences of insufficient or too intense IS.

Torque teno virus microRNA detection in cerebrospinal fluids of patients with neurological pathologies

BACKGROUND

Torque teno virus (TTV) is a widespread anellovirus that establishes persistent infections in humans and represents the most abundant component of the human virome. TTV encodes microRNAs (miRNA) which are found both in viremic and not viremic subjects being potentially ideal tools for the virus to evade the immune system response and to maintain chronic infection in the host.

OBJECTIVE

To investigate TTV-DNA loads and TTV-miRNAs expression in cerebrospinal fluids (CSF) from subjects under analysis for the assessment of neurological diseases.

STUDY DESIGN

Detection of TTV-DNA and TTV-miRNAs (e. g. miRNA t1a, t3b, and tth8) were carried out from CSF samples of 93 subjects with neurological diseases by using universal real-time PCR, real-time RT-PCR, and next-generation sequencing (NGS) analyses.

RESULTS

TTV-DNA was detected in 11 of 93 (12 %) CSFs with a mean TTV load of 155 copies/mL. Conversely, 29 CSF samples (31 %) were positive for at least one TTV-miRNA, while 15 (16 %) CSFs contained all the TTV-miRNAs examined. Overall, TTV-miRNA tth8 was detected in 62 % of samples, followed by TTV miRNA t3b (56 %), and t1a (29 %). Interestingly, TTV-miRNAs were found in CSF samples that were negative for the presence of TTV-DNA. Next-generation sequencing analysis carried out from 4 TTV-DNA negative CSF samples detected reads mapped in TTV-miRNA sequences region.

CONCLUSIONS

These results shed novel light on the relationship between TTV and the central nervous system and make compelling furthered studies for investigating the potential role of TTV-miRNAs in neurological disorders.

Clinical relevance of plasma virome dynamics in liver transplant recipients

BACKGROUND

The role of the microbiome in liver transplantation (LT) outcome has received a growing interest in the past decades. In contrast to bacteria, the role of endogenous viral communities, known as the virome, is poorly described. Here, we applied a viral metagenomic approach to study the dynamic evolution of circulating viruses in the plasma of LT recipients and its effect on the clinical course of patients.

METHODS

Patients chronically infected with hepatitis B virus (HBV) that received a LT due to endstage liver disease were included in this study. Longitudinal plasma samples were collected pre- and post-LT. Intact viral particles were isolated and sequenced on an Illumina HiSeq 2500 platform. Short read libraries were analysed with an in-house bioinformatics pipeline. Key endpoints were the dynamics of viral families and post-LT complications.

FINDINGS

The initiation of immunosuppression induced a bloom of the Anelloviridae that dominated the post-LT plasma virome. A variety of post-LT complication were observed. Nephrotoxicity was reported in 38% of the patients and was associated with a high abundance of anelloviruses. Besides nephrotoxicity, 16 (67%) patients experienced flares of viral or bacterial infections in post-transplant follow-up. These flares were recognized by an increased burden of anelloviruses (p < 0.05). Interestingly, no mortality was observed in patients infected with human pegivirus.

INTERPRETATION

These findings suggest a diagnostic potential for the Anelloviridae family in post-LT complications. Furthermore, the impact of human pegivirus infection on post-transplant survival should be further investigated.

FUNDING

This trial was supported by Gilead Sciences grant number BE-2017-000133.

Surveillance Bronchoscopy for the Care of Lung Transplant Recipients: A Retrospective Single Center Analysis

INTRODUCTION

Lung transplantation is often the only treatment for end-stage lung disease. Following lung transplantation, infections and transplant rejections are major obstacles to short- and long-term success. Therefore, close monitoring for these complications is required after lung transplantation. The role of prescheduled surveillance bronchoscopies after lung transplantation is controversial. Thus, we aimed to retrospectively analyze the therapeutic implications of surveillance bronchoscopies in 110 consecutive lung transplant recipients.

MATERIALS AND METHODS

Results of 400 prescheduled surveillance bronchoscopies of 110 consecutive lung transplant recipients were analyzed. Positive results (pathologic histology, microbiology, or virology) were further investigated for their effect on clinical decision making. Additionally, cellular composition of bronchoalveolar lavage (BAL) was analyzed.

RESULTS

Two hundred five surveillance bronchoscopies showed pathologic findings. In 81 cases clinical treatment was changed based on the results. That is, 20% of all prescheduled bronchoscopies directly influenced clinical decision making. Furthermore, analyses of BAL indicate that increased alveolar eosinophils are associated with an increased risk of transplant rejection.

CONCLUSIONS

Prescheduled surveillance bronchoscopies identify clinically unsuspected but therapeutically relevant pathologic findings in approximately 20% of cases. BAL cell composition may confer additional information, especially in cases when biopsy is not possible.

Prognostic Utility of Whole-Genome Sequencing and Polymerase Chain Reaction Tests of Ocular Fluids in Postprocedural Endophthalmitis

PURPOSE

To associate detection of potential pathogen DNA in endophthalmitis with clinical outcomes.

DESIGN

Prospective cohort study.

METHODS

Patients in whom endophthalmitis was diagnosed following an intraocular procedure were recruited. Clinical outcome data from baseline, week-1, month-1, and month-3 visits were collected. Intraocular biopsy samples were cultured by standard methods. Quantitative polymerase chain reaction (qPCR) was performed for specific pathogens and whole-genome sequencing (WGS).

RESULTS

A total of 50 patients (mean age 72 years old; 52% male) were enrolled. Twenty-four cases were culture-positive and 26 were culture-negative. WGS identified the cultured organism in 76% of culture-positive cases and identified potential pathogens in 33% of culture-negative cases. Month-1 and -3 visual acuities did not vary by pathogen-positive versus pathogen-negative cases as detected by either culture or WGS. Visual outcomes of Staphylococcus epidermidis endophthalmitis were no different than those of pathogen-negative cases, whereas the patients infected with other pathogens showed worse outcome. Higher baseline bacterial DNA loads of bacteria other than those of S epidermidis detected by WGS were associated with worse month-1 and -3 visual acuity, whereas the S epidermidis loads did not appear to influence outcomes. Torque teno virus (TTV) and Merkel cell polyomavirus (MCV) were detected by qPCR in 49% and 19% of cases, respectively. Presence of TTV at presentation was associated with a higher rate of secondary pars plana vitrectomy (P = .009) and retinal detachment (P = .022).

CONCLUSIONS

The presence and higher load of bacteria other than S epidermidis detected by WGS or DNA from TTV by qPCR in ocular fluids is associated with worse outcomes in post-procedure endophthalmitis.

Beyond Cytomegalovirus and Epstein-Barr Virus: a Review of Viruses Composing the Blood Virome of Solid Organ Transplant and Hematopoietic Stem Cell Transplant Recipients

Viral primary infections and reactivations are common complications in patients after solid organ transplantation (SOT) and hematopoietic stem cell transplantation (HSCT) and are associated with high morbidity and mortality. Among these patients, viral infections are frequently associated with viremia. Beyond the usual well-known viruses that are part of the routine clinical management of transplant recipients, numerous other viral signatures or genomes can be identified in the blood of these patients. The identification of novel viral species and variants by metagenomic next-generation sequencing has opened up a new field of investigation and new paradigms. Thus, there is a need to thoroughly describe the state of knowledge in this field with a review of all viral infections that should be scrutinized in high-risk populations. Here, we review the eukaryotic DNA and RNA viruses identified in blood, plasma, or serum samples of pediatric and adult SOT/HSCT recipients and the prevalence of their detection, with a particular focus on recently identified viruses and those for which their potential association with disease remains to be investigated, such as members of the Polyomaviridae, Anelloviridae, Flaviviridae, and Astroviridae families. Current knowledge of the clinical significance of these viral infections with associated viremia among transplant recipients is also discussed. To ensure a comprehensive description in these two populations, individuals described as healthy (mostly blood donors) are considered for comparative purposes. The list of viruses that should be on the clinicians' radar is certainly incomplete and will expand, but the challenge is to identify those of possible clinical significance.

Torque teno virus for risk stratification of graft rejection and infection in kidney transplant recipients-A prospective observational trial

The nonpathogenic and ubiquitous torque teno virus (TTV) is associated with immunosuppression in solid organ transplant recipients. Studies in kidney transplant patients proposed TTV quantification for risk stratification of graft rejection and infection. In this prospective trial (DRKS00012335) 386 consecutive kidney transplant recipients were subjected to longitudinal per-protocol monitoring of plasma TTV load by polymerase chain reaction for 12 months posttransplant. TTV load peaked at the end of month 3 posttransplant and reached steady state thereafter. TTV load after the end of month 3 was analyzed in the context of subsequent rejection diagnosed by indication biopsy and infection within the first year posttransplant, respectively. Each log increase in TTV load decreased the odds for rejection by 22% (odds ratio [OR] 0.78, 95% confidence interval [CI] 0.62-0.97; P = .027) and increased the odds for infection by 11% (OR 1.11, 95% CI 1.06-1.15; P < .001). TTV was quantified at a median of 14 days before rejection was diagnosed and 27 days before onset of infection, respectively. We defined a TTV load between 1 × 10⁶ and 1 × 10⁸ copies/mL as optimal range to minimize the risk for rejection and infection. These data support the initiation of an interventional trial assessing the efficacy of TTV-guided immunosuppression to reduce infection and graft rejection in kidney transplant recipients.

Torque Teno Virus as a Potential Biomarker for Complications and Survival After Allogeneic Hematopoietic Stem Cell Transplantation

Impaired immune reconstitution after allogeneic hematopoietic stem cell transplantation (HSCT) contributes to increased risk of cancer relapse and infection resulting in significant morbidity and mortality. Unfortunately, effective strategies to functionally assess the quality of immune reconstitution are still missing. Quantification of in vivo replication of the ubiquitous, non-pathogenic virus Torque Teno Virus (TTV) has been reported in small series as a test to functionally evaluate the quality of post-transplant immune reconstitution. In the present study, we analyzed by quantitative PCR TTV titers in plasma samples from a large cohort of 168 allogeneic HSCT recipients. Our analysis confirms that TTV titers peaked at 100 days post-transplant, followed by progressive normalization thereafter. Negative correlation of TTV titers with T cell absolute numbers during the first year post-transplant points to the restoration of an active anti-TTV immunity. Univariable and multivariable linear regression analysis demonstrated that donor CMV positive serostatus, donor type and immune suppression resulting from GVHD treatment affected the restoration of anti-TTV immunity. Importantly, higher TTV titers at 100 days after transplantation were associated with worse overall survival and higher risk of acute GVHD and infections. Our results provide new insights into the factors affecting the dynamics of TTV replication and indicate that TTV is a potentially useful biomarker to assess immune reconstitution and to predict complications and outcomes of allogeneic HSCT.

Torque teno virus in liver diseases: On the way towards unity of view

The review presents the data accumulated for more than 20 years of research of torque teno virus (TTV). Its molecular genetic structure, immunobiology, epidemiology, diagnostic methods, possible replication sites, and pathogenicity factors are described. TTV is a virus that is frequently detectable in patients with different viral hepatitides, in cases of hepatitis without an obvious viral agent, as well as in a healthy population. There is evidence suggesting that biochemical and histological changes occur in liver tissue and bile duct epithelium in TTV monoinfection. There are sufficient histological signs of liver damage, which confirm that the virus can undergo a replicative cycle in hepatocytes. Along with this, cytological hybridization in TTV-infected cells has shown no substantial cytopathic (cell-damaging) effects that are characteristic of pathogenic hepatotropic viruses. Studying TTV has led to the evolution of views on its role in the development of human pathology. The first ideas about the hepatotropism of the virus were gradually reformed as new data became available on the prevalence of the virus and its co-infection with other viruses, including the viruses of the known types of hepatitides. The high prevalence of TTV in the human population indicates its persistence in the body as a virome and a non-pathogenic virus. It has recently been proposed that the level of TTV DNA in the blood of patients undergoing organ transplantation should be used as an endogenous marker of the body’s immune status. The available data show the polytropism of the virus and deny the fact that TTV can be assigned exclusively to hepatitis viruses. Fortunately, the rare detection of the damaging effect of TTV on hepatic and bile duct epithelial cells may be indirect evidence of its conditionally pathogenic properties. The ubiquity of the virus and the variability of its existence in humans cannot put an end to its study.

Predictive tools to determine risk of infection in kidney transplant recipients

Introduction: Infection represents a major complication after kidney transplantation (KT). Therapeutic drug monitoring is essentially the only approach for the adjustment of immunosuppression in current practice, with suboptimal results. The implementation of immune monitoring strategies may contribute to minimizing the risk of adverse events attributable to over-immunosuppression without compromising graft outcomes.Areas covered: The present review (based on PubMed/MEDLINE searches from database inception to November 2019) is focused on immune biomarkers with no antigen specificity (non-pathogen-specific), including serum levels of immunoglobulins and complement factors, peripheral blood lymphocyte subpopulations, soluble CD30, intracellular ATP production by stimulated CD4⁺ T-cells, and other cell-based immune assays. We also summarized recent advances in the use of replication kinetics of latent viruses to assess the functionality of T-cell immunity, with focus on the nonpathogenic anelloviruses. Finally, the composite risk scores reported in the literature are critically discussed.Expert opinion: Notable efforts have been made to develop an enlarging repertoire of immune biomarkers and prediction models, although most of them still lack technical standardization and external validation. Preventive interventions based on these tools (prolongation of prophylaxis, tapering of immunosuppression, or immunoglobulin replacement therapy in hypogammaglobulinemic patients) remain to be defined, ideally in the context of controlled trials.

Assessment of prevalence and load of torquetenovirus viraemia in a large cohort of healthy blood donors

OBJECTIVES

Torquetenovirus (TTV) is an emerging marker of functional immune competence with the potential to predict transplant-related adverse events. A large-scale epidemiological study was performed to understand how basal values vary in healthy individuals according to age and gender.

METHODS

We tested plasma from 1017 healthy blood donors aged 18-69 years. The presence and load of TTV were determined by a real-time PCR assay. A sub-cohort of 384 donors was tested for anti-cytomegalovirus IgG antibodies, and 100 participants were also tested for TTV viraemia on a paired whole blood sample.

RESULTS

The overall prevalence of TTV was 65% (657/1017) with a mean (±SD) growth of 5 ± 4% every 10 years of age increase, but stably higher in males (465/690, 67%) than in females (192/327, 59%). Mean (±SD) TTV load was 2.3 ± 0.7 Log copies/mL with no sex difference. TTV viraemia showed modest increases along 10-year age intervals (mean ± SD: 0.3 ± 0.1). TTV viraemia in donors sampled 2 years later remained stable (mean ± SD: 2.3 ± 0.8 versus 2.2 ± 0.7 Log copies between samples). Twenty-six per cent (9/34) of blood donors with TTV-negative plasma scored positive when whole blood was tested, and the donors with positive plasma showed a mean (±SD) 1.4 ± 0.5 Log increase in copy numbers when whole blood was tested.

CONCLUSIONS

This study establishes the mean value of TTV viraemia in plasma in healthy blood donors and suggests that ageing causes only minimal increases in TTV viraemia.

Comparative evaluation of molecular methods for the quantitative measure of torquetenovirus viremia, the new surrogate marker of immune competence

BACKGROUND

Torquetenovirus (TTV) viremia is emerging as a promising tool to assess functional immune competence, to predict posttransplant immune-related complications, and eventually to customize immunosuppression.

METHODS

In this study, 327 blood samples were tested using two real-time PCR (rtPCR) assays both targeted to the untranslated region of the TTV genome. The first assay was an in-house rtPCR developed by our group, the second one was the recently marketed TTV R-GENE assay.

RESULTS

In the validation study, the TTV R-GENE showed good performances in precision and reproducibility, and sensitivity as low as 12 TTV DNA copies/mL, like previously reported for the in-house rtPCR. The Bland-Altman analysis showed that the mean difference between the two methods was -0.3 log copies/mL. In the comparison study, 69% and 72% of samples were detected positive by rtPCR and TTV R-GENE, respectively (94% concordance, κ = 0.88). Performances did not differ between the two rtPCRs by type of TTV group examined. When a newly-developed in-house digital droplet PCR was applied for TTV quantification and used as an alternative method of comparison on 94 samples, the results strongly correlated with those obtained by the two rtPCR methods (99% concordance).

CONCLUSION

In summary, all the molecular methods assayed are highly sensitive and accurate in quantitation of TTV DNA in blood samples.