Cell-free DNA donor fraction analysis in pediatric and adult heart transplant patients by multiplexed allele-specific quantitative PCR: Validation of a rapid and highly sensitive clinical test for stratification of rejection probability

Rejection Surveillance After Heart Transplantation: Is Paired Noninvasive Testing the New Gold Standard?

Rejection surveillance after heart transplantation has traditionally relied on numerous endomyocardial biopsies, most of which occur during the first posttransplant year. With the introduction of gene expression profiling and, more recently, donor-derived cell-free DNA, a great proportion of surveillance is being performed noninvasively with both tests. Although patients have welcomed the use of paired testing because of the decreased risk and inconvenience, interpretation of both tests can sometimes be challenging, particularly when the test results are discordant. Growing evidence from both single-center experiences and large national databases has given insights that have allowed the field to operationalize dual testing and provide physicians with algorithms to approach paired testing. The increased use of noninvasive testing has also begun to challenge the role of biopsy as the gold standard for graft monitoring, not only for rejection but over the life of the heart transplant. In a growing number of circumstances, cell-free DNA not only may be a better means of assessing rejection but could also redefine how clinicians approach the diagnosis and even treatment of graft injury. As the heart transplant community garners more experience and generates more data, the current paradigms of heart transplant surveillance will continue to be challenged.

Evaluating threshold for donor fraction cell-free DNA using clinically available assay for rejection in pediatric and adult heart transplantation

BACKGROUND

The aims of the study were to assess the performance of a clinically available cell-free DNA (cfDNA) assay in a large cohort of pediatric and adult heart transplant recipients and to evaluate performance at specific cut points in detection of rejection.

METHODS

Observational, non-interventional, prospective study enrolled pediatric and adult heart transplant recipients from seven centers. Biopsy-associated plasma samples were used for cfDNA measurements. Pre-determined cut points were tested for analytic performance.

RESULTS

A total of 487 samples from 160 subjects were used for the analysis. There were significant differences for df-cfDNA values between rejection [0.21% (IQR 0.12-0.69)] and healthy samples [0.05% (IQR 0.01-0.14), p < .0001]. The pediatric rejection group had a median df-cfDNA value of 0.93% (IQR 0.28-2.84) compared to 0.09% (IQR 0.04-0.23) for healthy samples, p = .005. Overall negative predictive value was 0.94 while it was 0.99 for pediatric patients. Cut points of 0.13% and 0.15% were tested for various types of rejection profiles and were appropriate to rule out rejection.

CONCLUSION

The study suggests that pediatric patients with rejection show higher levels of circulating df-cfDNA compared to adults and supports the specific cut points for clinical use in pediatric and adult patients with overall acceptable performance.

Free-Circulating Nucleic Acids as Biomarkers in Patients After Solid Organ Transplantation

A number types of extracellular DNA (eg, cell-free, cfDNA) circulate in human blood, including mitochondrial, transcriptome, and regulatory DNA, usually at low concentrations. Larger amounts of cfDNA appear in any inflammatory condition, including organ damage due to a variety of reasons. The role of cfDNA in solid organ transplantation is discussed in this review as a valuable additional tool in the standard of care of transplant patients. Post-transplant monitoring requires the use of high-quality biomarkers for early detection of graft damage or rejection to be able to apply early therapeutic intervention. CfDNA complements the traditional monitoring strategies, being a risk stratification tool and an important prognostic marker. However, improving the sensitivity and specificity of cfDNA detection is necessary to facilitate personalized patient management, warranting further research in terms of measurement, test standardization, and storage, processing, and shipping. A diagnostic test (Allosure, CareDx, Inc., Brisbane, CA) for kidney, heart and lung transplant patients is now commercially available, and validation for other organs (eg, liver) is pending. To date, donor-derived cfDNA in combination with other biomarkers appears to be a promising tool in graft rejection as it is minimally invasive, time-sensitive, and cost-effective. However, improvement of sensitivity and specificity is required to facilitate personalized patient management. Whether it could be an alternate to graft biopsy remains unclear.

Validation of donor fraction cell-free DNA with biopsy-proven cardiac allograft rejection in children and adults

OBJECTIVES

Donor-specific cell-free DNA shows promise as a noninvasive marker for allograft rejection, but as yet has not been validated in both adult and pediatric recipients. The study objective was to validate donor fraction cell-free DNA as a noninvasive test to assess for risk of acute cellular rejection and antibody-mediated rejection after heart transplantation in pediatric and adult recipients.

METHODS

Pediatric and adult heart transplant recipients were enrolled from 7 participating sites and followed for 12 months or more with plasma samples collected immediately before all endomyocardial biopsies. Donor fraction cell-free DNA was extracted, and quantitative genotyping was performed. Blinded donor fraction cell-free DNA and clinical data were analyzed and compared with a previously determined threshold of 0.14%. Sensitivity, specificity, negative predictive value, positive predictive value, and receiver operating characteristic curves were calculated.

RESULTS

A total of 987 samples from 144 subjects were collected. After applying predefined clinical and technical exclusions, 745 samples from 130 subjects produced 54 rejection samples associated with the composite outcome of acute cellular rejection grade 2R or greater and pathologic antibody-mediated rejection 2 or greater and 323 healthy samples. For all participants, donor fraction cell-free DNA at a threshold of 0.14% had a sensitivity of 67%, a specificity of 79%, a positive predictive value of 34%, and a negative predictive value of 94% with an area under the curve of 0.78 for detecting rejection. When analyzed independently, these results held true for both pediatric and adult cohorts at the same threshold of 0.14% (negative predictive value 92% and 95%, respectively).

CONCLUSIONS

Donor fraction cell-free DNA at a threshold of 0.14% can be used to assess for risk of rejection after heart transplantation in both pediatric and adult patients with excellent negative predictive value.

Nuclear Cell-Free DNA Predicts Adverse Events After Pediatric Cardiothoracic Surgery

BACKGROUND

Preoperative risk stratification in cardiac surgery includes patient and procedure factors that are used in clinical decision-making. Despite these tools, unidentified factors contribute to variation in outcomes. Identification of latent physiologic risk factors may strengthen predictive models. Nuclear cell-free DNA (ncfDNA) increases with tissue injury and drops to baseline levels rapidly. The goal of this investigation is to measure and to observe ncfDNA kinetics in children undergoing heart operations with cardiopulmonary bypass (CPB), linking biomarkers, organ dysfunction, and outcomes.

METHODS

This is a prospective observational study of 116 children <18 years and >3 kg undergoing operations with CPB. Plasma ncfDNA samples were collected and processed in a stepwise manner at predefined perioperative time points. The primary outcome measure was occurrence of postoperative cardiac arrest or extracorporeal membrane oxygenation.

RESULTS

Data were available in 116 patients (median age, 0.9 years [range, 0-17.4 years]; median weight, 7.8 kg [range, 3.2-98 kg]). The primary outcome was met in 6 of 116 (5.2%). Risk of primary outcome was 2% with ncfDNA <20 ng/mL and 33% with ncfDNA >20 ng/mL (odds ratio, 25; CI, 3.96-158; P = .001). Elevated ncfDNA was associated with fewer hospital-free days (P < .01).

CONCLUSIONS

This study analyzes ncfDNA kinetics in children undergoing operations with CPB for congenital heart disease. Elevated preoperative ncfDNA is strongly associated with postoperative arrest and extracorporeal membrane oxygenation. Further studies are needed to validate this technology as a tool to predict morbidity in children after cardiac surgical procedures.

Upregulated circulating mir-424 and its’ diagnostic value for gram-negative bacteremia after thoracic transplantation

Aims

Early post-transplant complications such as acute graft rejection and infections are associated with high morbidity and mortality of heart and lung transplant recipients who are in vital need of immunosuppressive therapy. MiR-424 is a member of the miR-16 family, which plays an important physiological role in the development of cardiovascular and respiratory pathology, is involved in the regulation of monocyte and macrophage differentiation, and has an immunosuppressive potential. The aim of the study was to determine the diagnostic value of circulating miR-424 as a potential biomarker of post-transplant complications in heart and lung transplant recipients.

Methods

The study enrolled 83 heart transplant recipients, aged 18 to 70 (48 ± 13) years; 26 lung transplant recipients, aged 10 to 74 (36 ± 16) years. The miR-424 plasma expression was detected by real-time PCR (Qiagen, USA). Significance of miR-424 level was assessed through the ΔCt method. Acute graft rejection was verified by the results of endomyocardial or transbronchial biopsy. Post-transplant infectious complications were verified through microbiological identification of bacteremia from blood cultures.

Results

Our study shows miR-424 upregulation in plasma of patients with chronic heart or respiratory failure in comparison with healthy individuals (p = 0.003 and p = 0.04 resp.). There was a direct correlation of miR-424 expression with red blood cells and hemoglobin levels in patients before heart transplantation (p = 0.01 and p = 0.03 resp.). After transplantation the expression of plasma miR-424 correlated with the level of C-reactive protein (CRP) both in heart (r = 0.75; p = 0.02) and lung (r = 0.50; p = 0.04) transplant recipients. The expression of plasma miR-424 correlated with tacrolimus blood concentration after heart transplantation (r = 0.38; p = 0.04). The miR-424 level didn't differ in heart or lung transplant recipients with and without acute graft rejection (p = 0.47 and p = 0.78 resp.), but was significantly higher in heart and lung transplant recipients with gram-negative bacteremia (p = 0.002). When the miR-424 level is above a threshold value (−5.72 fold change), the relative risk of bacteremia is RR = 3.84 [95% CI 1.94–7.61]; Se = 60.0%; Sp = 89.2%. CRP concentration above 7 mg/L in duplex test with miR-424 improves the diagnostic characteristics of miR-424 for post-transplant gram-negative bacteremia in heart and lung transplant recipients up to RR = 9.17 [95% CI 1.37–61.46]; Se = 83.3% and Sp = 90.1%.

Conclusion

MiR-424 plasma expression was upregulated in patients with chronic heart and respiratory failure and in heart and lung transplant recipients in the early post-transplant period. The duplex test, including miR-424 and CRP, has a diagnostic value for detecting the high risk of post-transplant gram-negative bacteremia in heart and lung transplant recipients.

A novel donor-derived cell-free DNA assay for the detection of acute rejection in heart transplantation

BACKGROUND

Endomyocardial biopsy (EMB), the reference surveillance test for acute rejection (AR) in heart transplant (HTx) recipients, is invasive, costly, and shows significant interobserver variability. Recent studies indicate that donor-derived cell-free DNA (dd-cfDNA), obtained non-invasively from blood, is associated with AR and could reduce the frequency of EMB surveillance. The aim of this study was to examine the performance characteristics of a novel test for detecting AR in adult HTx recipients.

METHODS

Plasma samples with contemporaneous EMBs were obtained from HTx recipients. A clinically available SNP-based massively multiplexed-PCR dd-cfDNA assay was used to measure dd-cfDNA fraction. dd-cfDNA fractions were compared with EMB-defined rejection status and test performance was assessed by constructing ROC curves and calculating accuracy measures.

RESULTS

A total of 811 samples from 223 patients with dd-cfDNA testing and contemporaneous EMB were eligible for the study. dd-cfDNA fraction was significantly higher in AR (median 0.58%, IQR, 0.13%-1.68%) compared to non-AR (median 0.04%, IQR, 0.01%-0.11%, pc < 0.001). ROC analysis produced an area under the curve (AUC-ROC) of 0.86 (95% CI, 0.77-0.96). Defining samples with dd-cfDNA fraction ≥0.15% as AR yielded 78.5% sensitivity (95% CI, 60.7%-96.3%) and 76.9% specificity (95% CI, 71.1%-82.7%). Positive and negative predictive values were 25.1% (95% CI, 18.8%-31.5%) and 97.3% (95% CI, 95.1%-99.5%) respectively, calculated using the cohort AR prevalence of 9.0% (95% CI, 5.3%-12.8%) with adjustment for repeat samples.

CONCLUSIONS

This novel dd-cfDNA test detects AR in HTx recipients with good accuracy and holds promise as a noninvasive test for AR in HTx recipients.

Relationship between donor fraction cell-free DNA and clinical rejection in heart transplantation

BACKGROUND

Clinical rejection (CR) defined as decision to treat clinically suspected rejection with change in immunotherapy based on clinical presentation with or without diagnostic biopsy findings is an important part of care in heart transplantation. We sought to assess the utility of donor fraction cell-free DNA (DF cfDNA) in CR and the utility of serial DF cfDNA in CR patients in predicting outcomes of clinical interest.

METHODS

Patients with heart transplantation were enrolled in two sequential, multi-center, prospective observational studies. Blood samples were collected for surveillance or clinical events. Clinicians were blinded to the results of DF cfDNA.

RESULTS

A total of 835 samples from 269 subjects (57% pediatric) were included for this analysis, including 28 samples associated with CR were analyzed. Median DF cfDNA was 0.43 (IQR 0.15, 1.36)% for CR and 0.10 (IQR 0.07, 0.16)% for healthy controls (p < .0001). At cutoff value of 0.13%, the area under curve (AUC) was 0.82, sensitivity of 0.86, specificity of 0.67, and negative predictive value of 0.99. There was serial decline in DF cfDNA post-therapy, however, those with cardiovascular events (cardiac arrest, need for mechanical support or death) showed significantly higher levels of DF cfDNA on Day 0 (2.11 vs 0.31%) and Day 14 (0.51 vs 0.22%) compared to those who did not have such an event (p < .0001).

CONCLUSION

DF cfDNA has excellent agreement with clinical rejection and, importantly, serial measurement of DF cfDNA predict clinically significant outcomes post treatment for rejection in these patients.

Rejection surveillance in pediatric heart transplant recipients: Critical reflection on the role of frequent and long-term routine surveillance endomyocardial biopsies and comprehensive review of non-invasive rejection screening tools

BACKGROUND

Despite significant medical advances in the field of pediatric heart transplantation (HT), acute rejection remains an important cause of morbidity and mortality. Endomyocardial biopsy (EMB) remains the gold-standard method for diagnosing rejection but is an invasive, expensive, and stressful process. Given the potential adverse consequences of rejection, routine post-transplant rejection surveillance protocols incorporating EMB are widely employed to detect asymptomatic rejection. Each center employs their own specific routine rejection surveillance protocol, with no consensus on the optimal approach and with high inter-center variability. The utility of high-frequency and long-term routine surveillance biopsies (RSB) in pediatric HT has been called into question.

METHODS

Sources for this comprehensive review were primarily identified through searches in biomedical databases including MEDLINE and Embase.

RESULTS

The available literature suggests that the diagnostic yield of RSB is low beyond the first year post-HT and that a reduction in RSB intensity from high-frequency to low-frequency can be done safely with no impact on early and mid-term survival. Though there are emerging non-invasive methods of detecting asymptomatic rejection, the evidence is not yet strong enough for any test to replace EMB.

CONCLUSION

Overall, pediatric HT centers in North America should likely be doing fewer RSB than are currently performed. Risk factors for rejection should be considered when designing the optimal rejection surveillance strategy. Noninvasive testing including emerging biomarkers may have a complementary role to aid in safely reducing the need for RSB.

Cell-free DNA as a solid-organ transplant biomarker: technologies and approaches

High-quality biomarkers that detect emergent graft damage and/or rejection after solid-organ transplantation offer new opportunities to improve post-transplant monitoring, allow early therapeutic intervention and facilitate personalized patient management. Donor-derived cell-free DNA (DD-cfDNA) is a particularly exciting minimally invasive biomarker because it has the potential to be quantitative, time-sensitive and cost-effective. Increased DD-cfDNA has been associated with graft damage and rejection episodes. Efforts are underway to further improve sensitivity and specificity. This review summarizes the procedures used to process and detect DD-cfDNA, measurement of DD-cfDNA in clinical transplantation, approaches for improving sensitivity and specificity and long-term prospects as a transplant biomarker to supplement traditional organ monitoring and invasive biopsies.

Noninvasive biomarkers in heart transplant: 2020-2021 year in review

PURPOSE OF REVIEW

Endomyocardial biopsy (EMB), the current gold standard for cardiac allograft monitoring is invasive, may have a low sensitivity and is associated with significant variability in histopathologic interpretation. Fortunately, on-going research is identifying noninvasive biomarkers that address some of these limitations. This review provides an update on noninvasive blood-based methods for rejection surveillance and diagnosis in heart transplantation.

RECENT FINDINGS

Recent studies highlight good test performance to detect acute rejection for donor-derived cell-free DNA (dd-cfDNA) and microRNAs (miR). dd-cfDNA is sensitive, nonspecific, and has a high negative predictive value for acute cellular and antibody-mediated rejection. Clinical utility trials are being planned to test its role as a rule-out test for acute rejection as compared to the EMB. miRs may have an added advantage as it may phenotype the subtypes of rejection alleviating the need for an EMB or permitting the initiation of targeted therapy while awaiting the results of the EMB.

SUMMARY

In this review, we discuss recent advances in the field of noninvasive biomarkers to detect allograft rejection after heart transplant. We provide a perspective of additional studies needed to prove their clinical utility and bring these biomarkers to widescale clinical use.

Early findings after integration of donor-derived cell-free DNA into clinical care following pediatric heart transplantation

BACKGROUND

Endomyocardial biopsy (EMB) is costly and discomforting yet remains a key component of surveillance after pediatric heart transplantation (HT). Donor-derived cell-free DNA (dd-cfDNA) has been histologically validated with high negative predictive value, offering an alternative to surveillance EMB (sEMB).

METHODS

We implemented an alternative surveillance protocol using commercially available dd-cfDNA assays in place of sEMB after pediatric HT. Recipients ≧7 months post-HT with reassuring clinical assessment were referred for dd-cfDNA. When not elevated above the manufacturers' threshold, sEMB was deferred. Subsequent clinical status and results of follow-up EMB were analyzed.

RESULTS

Over 17 months, 58 recipients [34% female, median age at HT 3.1 years (IQR 0.6-10.6)] had dd-cfDNA assessed per protocol. Median age was 14.8 years (8.4-18.3) and time from HT 6.0 years (2.2-11.2). Forty-seven (81%) had non-elevated dd-cfDNA and 11 (19%) were elevated. During a median of 8.7 months (4.2-15), all are alive without allograft loss/new dysfunction. Among those with non-elevated dd-cfDNA, 24 (51%) had subsequent sEMB at 12.1 months (6.9-12.9) with 23 showing no acute rejection (AR): grade 0R/pAMR0 (n = 16); 1R(1A)/pAMR0 (n = 7). One had AR (grade 2R(3A)/pAMR0) on follow-up sEMB after decreased immunosuppression following a diagnosis of PTLD. All 11 with elevated dd-cfDNA had reflex EMB at 19 days (12-32) with AR in 4: grade 1R(1B-2)/pAMR0 (n = 3); 1R(1B)/pAMR2 (n = 1).

CONCLUSIONS

dd-cfDNA assessment in place of selected, per-protocol EMB decreased surveillance EMB by 81% in our pediatric HT recipient cohort with no short-term adverse outcomes. Individual center approach to surveillance EMB will influence the utility of these findings.

Feasibility of Droplet Digital PCR Analysis of Plasma Cell-Free DNA From Kidney Transplant Patients

Increasing research demonstrates the potential of donor-derived cell-free DNA (dd-cfDNA) as a biomarker for monitoring the health of various solid organ transplants. Several methods have been proposed for cfDNA analysis, including real-time PCR, digital PCR, and next generation sequencing-based approaches. We sought to revise the droplet digital PCR (ddPCR)-based approach to quantify relative dd-cfDNA in plasma from kidney transplant (KTx) patients using a novel pilot set of assays targeting single nucleotide polymorphisms that have a very high potential to distinguish cfDNA from two individuals. The assays are capable of accurate quantification of down to 0.1% minor allele content when analyzing 165 ng of human DNA. We found no significant differences in the yield of extracted cfDNA using the three different commercial kits tested. More cfDNA was extracted from the plasma of KTx patients than from healthy volunteers, especially early after transplantation. The median level of donor-derived minor alleles in KTx samples was 0.35%. We found that ddPCR using the evaluated assays within specific range is suitable for analysis of KTx patients' plasma but recommend prior genotyping of donor DNA and performing reliable preamplification of cfDNA.

Increase in nuclear cell-free DNA is associated with major adverse events in adult and pediatric heart transplant recipients

BACKGROUND

Cell-free DNA is an emerging biomarker. While donor fraction may detect graft events in heart transplant recipients, the prognostic value of total nuclear cell-free DNA (ncfDNA) itself is largely unexplored.

OBJECTIVE

Explore the relationship between ncfDNA and clinical events in heart transplant recipients.

METHODS

We conducted a multi-center prospective study to investigate the value of cell-free DNA in non-invasive monitoring following heart transplantation. Over 4000 blood samples were collected from 388 heart transplant patients. Total ncfDNA and donor fraction were quantified. Generalized linear models with maximum likelihood estimation for repeated measures with subjects as clusters were used to explore the relationship of ncfDNA and major adverse events. Receiver operating characteristic curves were used to help choose cutpoints.

RESULTS

A ncfDNA threshold (50 ng/ml) was identified that was associated with increased risk of major adverse events. NcfDNA was elevated in patients who suffered cardiac arrest, required mechanical circulatory support or died post heart transplantation as well as in patients undergoing treatment for infection.

CONCLUSIONS

Elevated ncfDNA correlates with risk for major adverse events in adult and pediatric heart transplant recipients and may indicate a need for enhanced surveillance after transplant.

Cell-free DNA diagnostics in transplantation utilizing next generation sequencing

The use of Next Generation Sequencing (NGS) to interrogate cell-free DNA (cfDNA) as a transplant diagnostic provides a crucial step in improving the accuracy of post-transplant monitoring of allograft health. cfDNA interrogation provides a powerful, yet minimally invasive, biomarker for disease and tissue injury. cfDNA can be isolated from a variety of body fluids and analyzed using bioinformatics to unlock its origins. Furthermore, cfDNA characteristics can reveal the mechanisms and conditions under which it was generated and released. In transplantation, donor-derived cfDNA monitoring provides a tool for identifying active allograft injury at the time of transplant, infection, and rejection. Multiple detection and interrogation methods for cfDNA detection are now being evaluated for clinical validity and hold the promise to provide minimally invasive, quantitative, and reproducible measures of allograft injury across organ types.

Cell-free DNA in the surveillance of heart transplant rejection

BACKGROUND

Circulating cell-free deoxyribonucleic acid (cfDNA) is promptly materializing as a highly useful tool for the surveillance of solid-organ transplant rejection. Donor-specific fraction (DF) cfDNA is a potential marker of selective donor organ injury. It is emerging as a promising analytical target in the near future. The aim of this systematic review is to throw light on the importance of cfDNA and future perspective in detecting acute rejection in heart transplantation.

METHODS

An exhaustive search was carried out for this review article on the basis of literature available including scientific databases of PubMed, Embase, and ClinicalTrials.gov. The search engines were systematically explored using the search terms "cell free DNA," "Heart transplant," and "Rejection" from inception until August 2020, and narrative analysis was accomplished. Majority of the studies described endomyocardial biopsy-proven acute rejection as reference standard.

RESULTS

After initial screening of 331 articles, 11 studies were included and discussed in detail in the present review article. Majority of the studies showed prospective designs. A firm correlation was noted between acute rejection (identified on endomyocardial biopsy) and cfDNA levels by most of the studies.

CONCLUSIONS

cfDNA is a promising tool to replace repeated biopsies to detect rejection. The development in the area of digital droplet polymerase chain reaction and massive parallel sequencing, along with the overall reduction in cost of sequencing with its automation, has helped establish its role in the transplant population.

Donor-derived cell-free DNA accurately detects acute rejection in lung transplant patients, a multicenter cohort study

BACKGROUND

Acute rejection, which includes antibody-mediated rejection and acute cellular rejection, is a risk factor for lung allograft loss. Lung transplant patients often undergo surveillance transbronchial biopsies to detect and treat acute rejection before irreversible chronic rejection develops. Limitations of this approach include its invasiveness and high interobserver variability. We tested the performance of percent donor-derived cell-free DNA (%ddcfDNA), a non-invasive blood test, to detect acute rejection.

METHODS

This multicenter cohort study monitored 148 lung transplant subjects over a median of 19.6 months. We collected serial plasma samples contemporaneously with TBBx to measure %ddcfDNA. Clinical data was collected to adjudicate for acute rejection. The primary analysis consisted of computing the area-under-the-receiver-operating-characteristic-curve of %ddcfDNA to detect acute rejection. Secondary analysis determined %ddcfDNA rule-out thresholds for acute rejection.

RESULTS

ddcfDNA levels were high after transplant surgery and decayed logarithmically. With acute rejection, ddcfDNA levels rose six-fold higher than controls. ddcfDNA levels also correlated with severity of lung function decline and histological grading of rejection. %ddcfDNA area-under-the-receiver-operating-characteristic-curve for acute rejection, AMR, and ACR were 0.89, 0.93, and 0.83, respectively. ddcfDNA levels of <0.5% and <1.0% showed a negative predictive value of 96% and 90% for acute rejection, respectively. Histopathology detected one-third of episodes with ddcfDNA levels ≥1.0%, even though >90% of these events were coincident to clinical complications missed by histopathology.

CONCLUSIONS

This study demonstrates that %ddcfDNA reliably detects acute rejection and other clinical complications potentially missed by histopathology, lending support to its use as a non-invasive marker of allograft injury.

Cell-Free DNA to Detect Heart Allograft Acute Rejection

BACKGROUND

After heart transplantation, endomyocardial biopsy (EMBx) is used to monitor for acute rejection (AR). Unfortunately, EMBx is invasive, and its conventional histological interpretation has limitations. This is a validation study to assess the performance of a sensitive blood biomarker-percent donor-derived cell-free DNA (%ddcfDNA)-for detection of AR in cardiac transplant recipients.

METHODS

This multicenter, prospective cohort study recruited heart transplant subjects and collected plasma samples contemporaneously with EMBx for %ddcfDNA measurement by shotgun sequencing. Histopathology data were collected to define AR, its 2 phenotypes (acute cellular rejection [ACR] and antibody-mediated rejection [AMR]), and controls without rejection. The primary analysis was to compare %ddcfDNA levels (median and interquartile range [IQR]) for AR, AMR, and ACR with controls and to determine %ddcfDNA test characteristics using receiver-operator characteristics analysis.

RESULTS

The study included 171 subjects with median posttransplant follow-up of 17.7 months (IQR, 12.1-23.6), with 1392 EMBx, and 1834 %ddcfDNA measures available for analysis. Median %ddcfDNA levels decayed after surgery to 0.13% (IQR, 0.03%-0.21%) by 28 days. Also, %ddcfDNA increased again with AR compared with control values (0.38% [IQR, 0.31-0.83%], versus 0.03% [IQR, 0.01-0.14%]; P<0.001). The rise was detected 0.5 and 3.2 months before histopathologic diagnosis of ACR and AMR. The area under the receiver operator characteristic curve for AR was 0.92. A 0.25%ddcfDNA threshold had a negative predictive value for AR of 99% and would have safely eliminated 81% of EMBx. In addition, %ddcfDNA showed distinctive characteristics comparing AMR with ACR, including 5-fold higher levels (AMR ≥2, 1.68% [IQR, 0.49-2.79%] versus ACR grade ≥2R, 0.34% [IQR, 0.28-0.72%]), higher area under the receiver operator characteristic curve (0.95 versus 0.85), higher guanosine-cytosine content, and higher percentage of short ddcfDNA fragments.

CONCLUSIONS

We found that %ddcfDNA detected AR with a high area under the receiver operator characteristic curve and negative predictive value. Monitoring with ddcfDNA demonstrated excellent performance characteristics for both ACR and AMR and led to earlier detection than the EMBx-based monitoring. This study supports the use of %ddcfDNA to monitor for AR in patients with heart transplant and paves the way for a clinical utility study. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT02423070.

A Changing Paradigm in Heart Transplantation: An Integrative Approach for Invasive and Non-Invasive Allograft Rejection Monitoring

Cardiac allograft rejection following heart transplantation is challenging to diagnose. Tissue biopsies are the gold standard in monitoring the different types of rejection. The last decade has seen an increased emphasis on identifying non-invasive methods to improve rejection diagnosis and overcome tissue biopsy invasiveness. Liquid biopsy, as an efficient non-invasive diagnostic and prognostic oncological monitoring tool, seems to be applicable in heart transplant follow-ups. Moreover, molecular techniques applied on blood can be translated to tissue samples to provide novel perspectives on tissue and reveal new diagnostic and prognostic biomarkers. This review aims to provide a comprehensive overview of the state-of-the-art of the new methodologies in cardiac allograft rejection monitoring and investigate the future perspectives on invasive and non-invasive rejection biomarkers identification. We reviewed literature from the most used scientific databases, such as PubMed, Google Scholar, and Scopus. We extracted 192 papers and, after a selection and exclusion process, we included in the review 81 papers. The described limitations notwithstanding, this review show how molecular biology techniques and omics science could be deployed complementarily to the histopathological rejection diagnosis on tissue biopsies, thus representing an integrated approach for heart transplant patients monitoring.

The Organ Trail: A Review of Biomarkers of Organ Failure

Pediatric organ failure and transplant populations face significant risks of morbidity and mortality. The risk of organ failure itself may be disproportionately higher among pediatric oncology patients, as cancer may originate within and/or metastasize to organs and adversely affect their function. Additionally, cancer directed therapies are frequently toxic to organs and may contribute to failure. Recent reports suggest that nearly half of providers find it difficult to provide prognostic information regarding organ failure due to unknown disease trajectories. Unfortunately, there is a lack of uniform methodology in detecting the early symptoms of organ failure, which may delay diagnosis, initiation of treatment and hinder prognostic planning. There remains a wide array of outstanding scientific questions regarding organ failure in pediatrics but emerging data may change the landscape of prognostication. Liquid biopsy, in which disease biomarkers are detected in bodily fluids, offers a noninvasive alternative to tissue biopsy and may improve prompt detection of organ failure and prognostication. Here, we review potential liquid biopsy biomarkers for organ failure, which may be particularly useful among pediatric oncology patients. We synthesized information from publications obtained on PubMed, Google Scholar, clinicaltrials.gov, and Web of Science and categorized our findings based on the type of biomarker used to detect organ failure. We highlight the advantages and disadvantages specific to each type of organ failure biomarker. While much work needs to be done to advance this field and validate its applicability to pediatric cancer patients facing critical care complications, herein, we highlight promising areas for future discovery.

Non-invasive cardiac allograft rejection surveillance: reliability and clinical value for prevention of heart failure

Allograft rejection-related acute and chronic heart failure (HF) is a major cause of death in heart transplant recipients. Given the deleterious impact of late recognized acute rejection (AR) or non-recognized asymptomatic antibody-mediated rejection on short- and long-term allograft function improvement of AR surveillance and optimization of action strategies for confirmed AR can prevent AR-related allograft failure and delay the development of cardiac allograft vasculopathy, which is the major cause for HF after the first posttransplant year. Routine non-invasive monitoring of cardiac function can improve both detection and functional severity grading of AR. It can also be helpful in guiding the anti-AR therapy and timing of routine surveillance endomyocardial biopsies (EMBs). The combined use of EMBs with non-invasive technologies and methods, which allow detection of subclinical alterations in myocardial function (e.g., tissue Doppler imaging and speckle-tracking echocardiography), reveal alloimmune activation (e.g., screening of complement-activating donor-specific antibodies and circulating donor-derived cell-free DNA) and help in predicting the imminent risk of immune-mediated injury (e.g., gene expression profiling, screening of non-HLA antibodies, and circulating donor-derived cell-free DNA), can ensure the best possible surveillance and management of AR. This article gives an overview of the current knowledge about the reliability and clinical value of non-invasive cardiac allograft AR surveillance. Particular attention is focused on the potential usefulness of non-invasive tools and techniques for detection and functional grading of early and late ARs in asymptomatic patients. Overall, the review aimed to provide a theoretical and practical basis for those engaged in this particularly demanding up-to-date topic.