Adding Insult on Injury: Immunogenic Role for Donor-derived Cell-free DNA?

Defatting of donor transplant livers during normothermic perfusion-a randomised clinical trial: study protocol for the DeFat study

BACKGROUND

Liver disease is the third leading cause of premature death in the UK. Transplantation is the only successful treatment for end-stage liver disease but is limited by a shortage of suitable donor organs. As a result, up to 20% of patients on liver transplant waiting lists die before receiving a transplant. A third of donated livers are not suitable for transplant, often due to steatosis. Hepatic steatosis, which affects 33% of the UK population, is strongly associated with obesity, an increasing problem in the potential donor pool. We have recently tested defatting interventions during normothermic machine perfusion (NMP) in discarded steatotic human livers that were not transplanted. A combination of therapies including forskolin (NKH477) and L-carnitine to defat liver cells and lipoprotein apheresis filtration were investigated. These interventions resulted in functional improvement during perfusion and reduced the intrahepatocellular triglyceride (IHTG) content. We hypothesise that defatting during NMP will allow more steatotic livers to be transplanted with improved outcomes.

METHODS

In the proposed multi-centre clinical trial, we will randomly assign 60 livers from donors with a high-risk of hepatic steatosis to either NMP alone or NMP with defatting interventions. We aim to test the safety and feasibility of the defatting intervention and will explore efficacy by comparing ex-situ and post-reperfusion liver function between the groups. The primary endpoint will be the proportion of livers that achieve predefined functional criteria during perfusion which indicate potential suitability for transplantation. These criteria reflect hepatic metabolism and injury and include lactate clearance, perfusate pH, glucose metabolism, bile composition, vascular flows and transaminase levels. Clinical secondary endpoints will include proportion of livers transplanted in the two arms, graft function; cell-free DNA (cfDNA) at follow-up visits; patient and graft survival; hospital and ITU stay; evidence of ischemia-reperfusion injury (IRI); non-anastomotic biliary strictures and recurrence of steatosis (determined on MRI at 6 months).

DISCUSSION

This study explores ex-situ pharmacological optimisation of steatotic donor livers during NMP. If the intervention proves effective, it will allow the safe transplantation of livers that are currently very likely to be discarded, thereby reducing waiting list deaths.

TRIAL REGISTRATION

ISRCTN ISRCTN14957538. Registered in October 2022.

Racial Differences in Donor-Derived Cell-Free DNA and Mitochondrial DNA After Heart Transplantation, on Behalf of the GRAfT Investigators

BACKGROUND

Black heart transplant patients are at higher risk of acute rejection (AR) and death than White patients. We hypothesized that this risk may be associated with higher levels of donor-derived cell-free DNA (dd-cfDNA) and cell-free mitochondrial DNA.

METHODS

The Genomic Research Alliance for Transplantation is a multicenter, prospective, longitudinal cohort study. Sequencing was used to quantitate dd-cfDNA and polymerase chain reaction to quantitate cell-free mitochondrial DNA in plasma. AR was defined as ≥2R cellular rejection or ≥1 antibody-mediated rejection. The primary composite outcome was AR, graft dysfunction (left ventricular ejection fraction <50% and decrease by ≥10%), or death.

RESULTS

We included 148 patients (65 Black patients and 83 White patients), median age was 56 years and 30% female sex. The incidence of AR was higher in Black patients compared with White patients (43% versus 19%; P=0.002). Antibody-mediated rejection occurred predominantly in Black patients with a prevalence of 20% versus 2% (P<0.001). After transplant, Black patients had higher levels of dd-cfDNA, 0.09% (interquartile range, 0.001-0.30) compared with White patients, 0.05% (interquartile range, 0.001-0.23; P=0.003). Beyond 6 months, Black patients showed a persistent rise in dd-cfDNA with higher levels compared with White patients. Cell-free mitochondrial DNA was higher in Black patients (185 788 copies/mL; interquartile range, 101 252-422 133) compared with White patients (133 841 copies/mL; interquartile range, 75 346-337 990; P<0.001). The primary composite outcome occurred in 43% and 55% of Black patients at 1 and 2 years, compared with 23% and 27% in White patients, P<0.001. In a multivariable model, Black patient race (hazard ratio, 2.61 [95% CI, 1.35-5.04]; P=0.004) and %dd-cfDNA (hazard ratio, 1.15 [95% CI, 1.03-1.28]; P=0.010) were associated with the primary composite outcome.

CONCLUSIONS

Elevated dd-cfDNA and cell-free mitochondrial DNA after heart transplant may mechanistically be implicated in the higher incidence of AR and worse clinical outcomes in Black transplant recipients.

REGISTRATION

URL: https://www.clinicaltrials.gov; Unique identifier: NCT02423070.

Inflammasome pathway in kidney transplantation

Kidney transplantation is the best available renal replacement therapy for patients with end-stage kidney disease and is associated with better quality of life and patient survival compared with dialysis. However, despite the significant technical and pharmaceutical advances in this field, kidney transplant recipients are still characterized by reduced long-term graft survival. In fact, almost half of the patients lose their allograft after 15-20 years. Most of the conditions leading to graft loss are triggered by the activation of a large immune-inflammatory machinery. In this context, several inflammatory markers have been identified, and the deregulation of the inflammasome (NLRP3, NLRP1, NLRC4, AIM2), a multiprotein complex activated by either whole pathogens (including fungi, bacteria, and viruses) or host-derived molecules, seems to play a pivotal pathogenetic role. However, the biological mechanisms leading to inflammasome activation in patients developing post-transplant complications (including, ischemia-reperfusion injury, rejections, infections) are still largely unrecognized, and only a few research reports, reviewed in this manuscript, have addressed the association between abnormal activation of this pathway and the onset/development of major clinical effects. Finally, the regulation of the inflammasome machinery could represent in future a valuable therapeutic target in kidney transplantation.

Donor-Derived Cell-free DNA for Personalized Immunosuppression in Renal Transplantation

BACKGROUND

The long-term outcomes of solid organ transplantation remain suboptimal. Therefore, appropriate biomarkers are needed in addition to immunosuppressive drugs and other traditional approaches for graft monitoring to achieve personalized immunosuppression and reduce premature graft loss.

METHODS

Donor-derived cell-free DNA (dd-cfDNA) is a minimally invasive biomarker of cell death due to graft injury. It can be quantified using droplet digital polymerase chain reaction and next-generation sequencing. Fractional dd-cfDNA determination can be affected by changes in recipient cfDNA, such as those caused by leukopenia or infection, leading to false-positive or false-negative results, respectively. Absolute quantification of dd-cfDNA helps in overcoming this limitation.

RESULTS

Overall, there is sufficient evidence of the clinical validity of dd-cfDNA. It detects rejection episodes early at an actionable stage and reflects the severity of graft injury without being rejection-specific. Owing to its high negative predictive value, dd-cfDNA is very useful for ruling out graft injury. Dd-cfDNA complements histological findings and can help in avoiding unnecessary biopsies. It indicates a response to rejection treatment and detects underimmunosuppression.

CONCLUSIONS

Monitoring changes in dd-cfDNA over time may be helpful in adapting immunosuppression to prevent graft rejection. Moreover, serial dd-cfDNA determination may increase the effectiveness of transplant recipient surveillance and facilitate personalized immunosuppression when combined with other relevant clinical and diagnostic findings.

Expanded knowledge of cell-free DNA biology: potential to broaden the clinical utility

Noninvasive sampling of an individual's body fluids is an easy means to capture circulating cell-free DNA (cfDNA). These small fragments of DNA carry information on the contributing cell's genome, epigenome, and nuclease content. Analysis of cfDNA for the assessment of genetic risk has already revolutionized clinical practice, and a compendium of increasingly higher-resolution approaches based on epigenetic and fragmentomic cfDNA signatures continues to expand. Profiling cfDNA has unlocked a wealth of molecular information that can be translated to the clinic. This review covers the biological characteristics of cfDNA, recent advances in liquid biopsy and the clinical utility of cfDNA.

The interactions between DNA nanostructures and cells: A critical overview from a cell biology perspective

DNA nanotechnology has yielded remarkable advances in  composite materials with diverse applications in biomedicine. The specificity and predictability of building 3D structures at the nanometer scale make DNA nanotechnology a promising tool for uses in biosensing, drug delivery, cell modulation, and bioimaging. However, for successful translation of DNA nanostructures to real-world applications, it is crucial to understand how they interact with living cells, and the consequences of such interactions. In this review, we summarize the current state of knowledge on the interactions of DNA nanostructures with cells. We identify key challenges, from a cell biology perspective, that influence progress towards the clinical translation of DNA nanostructures. We close by providing an outlook on what questions must be addressed to accelerate the clinical translation of DNA nanostructures. STATEMENT OF SIGNIFICANCE: Self-assembled DNA nanostructures (DNs) offers unique opportunities to overcome persistent challenges in the nanobiotechnology field. However, the interactions between engineered DNs and living cells are still not well defined. Critical systematization of current cellular models and biological responses triggered by DNs is a crucial foundation for the successful clinical translation of DNA nanostructures. Moreover, such an analysis will identify the pitfalls and challenges that are present in the field, and provide a basis for overcoming those challenges.

Donor Derived Cell Free DNA in Kidney Transplantation: The Circa 2020–2021 Update

The routine surveillance of kidney transplant allografts has relied on imperfect non-invasive biomarkers such as creatinine and urinary indices, while the gold standard allograft biopsy is associated with risk of bleeding, organ injury and sampling errors. Donor derived cell free DNA (dd-cfDNA) is being employed as a biomarker that addresses limitations of these surveillance methods, albeit has inherent drawbacks. This review provides an update on the enhanced understanding of dd-cfDNA and its expanded use beyond the conventional indication of detecting allograft rejection.

High levels of donor-derived cell-free DNA in a case of graft-versus-host-disease following liver transplantation

The diagnosis of graft-versus-host-disease (GVHD) after solid organ transplantation is made difficult by its variable clinical presentation and lack of sensitive and specific biomarkers to evaluate the immune state of transplant recipients. Emerging noninvasive diagnostic techniques like the quantification of donor-derived cell-free DNA (dd-cfDNA) for surveillance may improve the current standard-of-care. Herein, we report the use of this methodology in a patient with GVHD and corresponding levels of dd-cfDNA without any evidence of graft injury. Correlation of dd-cfDNA levels with the clinical course and its novel application here could lead to improvements in the rapid diagnosis of GVHD and in monitoring of response to treatment.

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.

Higher levels of allograft injury in black patients early after heart transplantation

Black patients suffer higher rates of antibody-mediated rejection and have worse long-term graft survival after heart transplantation. Donor-derived cell free DNA (ddcfDNA) is released into the blood following allograft injury. This study analyzed %ddcfDNA in 63 heart transplant recipients categorized by Black and non-Black race, during the first 200 days after transplant. Immediately after transplant, %ddcfDNA was higher for Black patients (mean [SE]: 8.3% [1.3%] vs 3.2% [1.2%], p = 0.001). In the first week post-transplant, the rate of decay in %ddcfDNA was similar (0.7% [0.68] vs 0.7% [0.11], p = 0.78), and values declined in both groups to a comparable plateau at 7 days post-transplant (0.46% [0.03] vs 0.45% [0.04], p = 0.78). The proportion of Black patients experiencing AMR was higher than non-Black patients (21% vs 9% [hazard ratio of 2.61 [95% confidence interval: 0.651-10.43], p = 0.18). Black patients were more likely to receive a race mismatched organ than non-Black patients (69% vs 35%, p = 0.01), which may explain the higher levels of early allograft injury.

Validation and clinical outcome in assessing donor-derived cell-free DNA monitoring insights of kidney allografts with longitudinal surveillance (ADMIRAL) study

The use of routine monitoring of donor-derived cell-free DNA (dd-cfDNA) after kidney transplant may allow clinicians to identify subclinical allograft injury and intervene prior to development of clinically evident graft injury. To evaluate this, data from 1092 kidney transplant recipients monitored for dd-cfDNA over a three year period was analyzed to assess the association of dd-cfDNA with histologic evidence of allograft rejection. Elevation of dd-cfDNA (0.5% or more) was significantly correlated with clinical and subclinical allograft rejection. dd-cfDNA values of 0.5% or more were associated with a nearly three-fold increase in risk development of de novo donor specific antibodies (hazard ratio 2.71) and were determined to be elevated a median of 91 days (inter quartile range of 30-125 days) ahead of donor specific antibody identification. Persistently elevated dd-cfDNA (more than one result above the 0.5% threshold) predicted over a 25% decline in the estimated glomerular filtration rate over three years (hazard ratio 1.97). Therefore, routine monitoring of dd-cfDNA allowed early identification of clinically important graft injury. Biomarker monitoring complemented histology and traditional laboratory surveillance strategies as a prognostic marker and risk-stratification tool post-transplant. Thus, persistently low dd-cfDNA levels may accurately identify allograft quiescence, or absence of injury, paving the way for personalization of immunosuppression trials.

Donor-derived Cell-free DNA in Solid-organ Transplant Diagnostics: Indications, Limitations, and Future Directions

The last few years have seen an explosion in clinical research focusing on the use of donor-derived cell-free DNA (dd-cfDNA) in solid-organ transplants (SOT). Although most of the literature published so far focuses on kidney transplants, there are several recent as well as ongoing research studies on heart, lung, pancreas, and liver transplants. Though initially studied as a noninvasive means of identifying subclinical or acute rejection in SOT, it is rapidly becoming clear that instead of being a specific marker for allograft rejection, dd-cfDNA is more appropriately described as a marker of severe injury, although the most common cause of this injury is allograft rejection. Multiple studies in kidney transplants have shown that although sensitivity for the diagnosis of antibody-mediated rejection is excellent, it is less so for T-cell-mediated rejection. It is possible that combining dd-cfDNA with other novel urine- or blood-based biomarkers may increase the sensitivity for the diagnosis of rejection. Irrespective of the cause, though, elevated dd-cfDNA seems to portend adverse allograft prognosis and formation of de novo donor-specific antibody. Although current data do not lend themselves to a clear conclusion, ongoing studies may reveal the utility of serial surveillance for the management of SOT as following levels of dd-cfDNA over time may provide windows of opportunity to intervene early and before irreversible allograft injury. Finally, cost-effectiveness studies will be needed to guide the ideal incorporation of dd-cfDNA into routine clinical practice.

Association between dd-cfDNA levels, de novo donor specific antibodies, and eGFR decline: An analysis of the DART cohort

BACKGROUND

Donor-derived cell-free DNA (dd-cfDNA) is a marker of allograft injury in transplant recipients; however, the relationship between dd-cfDNA and other clinical parameters associated with adverse allograft outcomes is not well-characterized.

METHODS

We performed a retrospective analysis of kidney transplant recipients from the DART cohort (ClinicalTrials.gov Identifier: NCT02424227) to evaluate the associations between eGFR decline, de novo donor-specific antibodies (dnDSA), and dd-cfDNA.

RESULTS

Both elevated dd-cfDNA (≥1%) and dd-cfDNA variability (≥.34%) in the first post-transplant year were associated with decline in eGFR ≥25% in the second year (21.4% vs. 4.1%, P = .005; 25% vs. 3.6%, P = .002, respectively). Compared to samples from DSA negative patients, samples from patients with concurrent de novo HLA DSAs had higher dd-cfDNA levels (P < .0001).

DISCUSSION

Abnormalities in dd-cfDNA levels are associated with clinical parameters commonly used as surrogate endpoints for adverse allograft outcomes, raising the possibility that molecular injury as characterized by dd-cfDNA could help identify patients at risk of these outcomes.

Chronic Active Antibody-Mediated Rejection Following COVID-19 Infection in a Kidney Transplant Recipient: A Case Report

Kidney transplant recipients who develop coronavirus disease 2019 (COVID-19) are at increased risk of life-threatening illness, which often requires reducing immunosuppression despite the potential risk of causing an allograft rejection. Herein, we describe the clinical presentation and course of a kidney transplant recipient who acquired COVID-19 and was hospitalized with severe symptoms and hypoxemia. Upon admission, the patient was found to have elevated de novo donor-specific antibodies (DSA) yielding a positive cytotoxicity crossmatch and concurrent elevated plasma donor-derived cell-free DNA (dd-cfDNA) level, indicating a possible ongoing rejection despite improvement in his serum creatinine. Because of persistent positive COVID-19 tests and stable serum creatinine, a kidney allograft biopsy was initially deferred and his dd-cfDNA and DSA were monitored closely postdischarge. Three months later, because of persistent elevated dd-cfDNA and positive DSA, a kidney allograft biopsy was performed, which showed chronic active antibody-mediated rejection. Accordingly, the patient was treated with intravenous immunoglobulin and his maintenance immunosuppressive regimen was increased.

Cell-free DNA maps COVID-19 tissue injury and risk of death and can cause tissue injury

INTRODUCTION

The clinical course of coronavirus 2019 (COVID-19) is heterogeneous, ranging from mild to severe multiorgan failure and death. In this study, we analyzed cell-free DNA (cfDNA) as a biomarker of injury to define the sources of tissue injury that contribute to such different trajectories.

METHODS

We conducted a multicenter prospective cohort study to enroll patients with COVID-19 and collect plasma samples. Plasma cfDNA was subject to bisulfite sequencing. A library of tissue-specific DNA methylation signatures was used to analyze sequence reads to quantitate cfDNA from different tissue types. We then determined the correlation of tissue-specific cfDNA measures to COVID-19 outcomes. Similar analyses were performed for healthy controls and a comparator group of patients with respiratory syncytial virus and influenza.

RESULTS

We found markedly elevated levels and divergent tissue sources of cfDNA in COVID-19 patients compared with patients who had influenza and/or respiratory syncytial virus and with healthy controls. The major sources of cfDNA in COVID-19 were hematopoietic cells, vascular endothelium, hepatocytes, adipocytes, kidney, heart, and lung. cfDNA levels positively correlated with COVID-19 disease severity, C-reactive protein, and D-dimer. cfDNA profile at admission identified patients who subsequently required intensive care or died during hospitalization. Furthermore, the increased cfDNA in COVID-19 patients generated excessive mitochondrial ROS (mtROS) in renal tubular cells in a concentration-dependent manner. This mtROS production was inhibited by a TLR9-specific antagonist.

CONCLUSION

cfDNA maps tissue injury that predicts COVID-19 outcomes and may mechanistically propagate COVID-19–induced tissue injury.

FUNDING

Intramural Targeted Anti–COVID-19 grant, NIH.

Donor-derived cell-free DNA is associated with cardiac allograft vasculopathy

BACKGROUND

The role of donor-derived cell-free DNA (dd-cfDNA) in screening for cardiac allograft vasculopathy (CAV) is unknown. We hypothesized that dd-cfDNA correlates with CAV, markers of inflammation, and angiogenesis in stable heart transplant (HT) recipients.

METHODS

Sixty-five HT recipients ≥2 years post-transplant, without recent rejection, were stratified by high (≥0.12%) versus low levels (<0.12%) of dd-cfDNA. A targeted amplification, next-generation sequencing assay (AlloSure^® ; CareDx, Inc.) was used to detect dd-cfDNA. Peripheral blood inflammatory and angiogenesis markers were assessed using a multiplex immunoassay system (Bioplex^® ).

RESULTS

Of 65 patients, 58 patients had a known CAV status and were included. Thirty had high levels of dd-cfDNA (≥0.12%), and 28 had low levels (<0.12%). CAV was present in 63% of patients with high dd-cfDNA vs. 35% with low dd-cfDNA (p = .047). Donor-specific antibodies were present in 25% of patients with high dd-cfDNA vs. 3.8% in those with low dd-cfDNA (p = .03). There were no differences in rejection episodes, inflammatory, or angiogenesis markers. Importantly, dd-cfDNA levels were not different when stratified by time post-transplant.

CONCLUSIONS

Higher dd-cfDNA levels were associated with CAV in stable chronic HT recipients. Further studies are warranted to investigate a possible association between dd-cfDNA levels and CAV severity and whether dd-cfDNA can predict CAV progression.

Understanding and using AlloSure donor derived cell-free DNA

Renal transplant is a lifesaving and cost-effective intervention for patients with End Stage Renal Failure. Yet it is often regarded as replacement therapy rather than a cure given the overall failure rate over time. With a shortage of organs, this global issue has been further compounded by increased incidences of obesity, hypertension and diabetes, such that the disease burden and need for transplantation continues to increase. Considering the lifetime of immunosupression in transplant patients, there will also be significant associated co-morbidities By leveraging the advances in innovation in Next Generation Sequencing, the field of transplant can now monitor patients with an optimized surveillance schedule, and change the care paradigm in the post-transplant landscape. Notably, low grade inflammation is an independent risk for mortality across different disease states. In transplantation, sub-clinical inflammation enhances acute and chronic rejection, as well as accelerates pathologies that leads to graft loss. Cell free DNA has been shown to be increased in inflammatory processes as we all as provide an independent predictor of all-cause mortality. This review considers the utility of AlloSure, a donor derived cell free DNA molecular surveillance tool, which has shown new clinical insights on how best to manage renal transplant patients, and how to improve patient outcomes.

Recent Advances on Biomarkers of Early and Late Kidney Graft Dysfunction

New biomarkers of early and late graft dysfunction are needed in renal transplant to improve management of complications and prolong graft survival. A wide range of potential diagnostic and prognostic biomarkers, measured in different biological fluids (serum, plasma, urine) and in renal tissues, have been proposed for post-transplant delayed graft function (DGF), acute rejection (AR), and chronic allograft dysfunction (CAD). This review investigates old and new potential biomarkers for each of these clinical domains, seeking to underline their limits and strengths. OMICs technology has allowed identifying many candidate biomarkers, providing diagnostic and prognostic information at very early stages of pathological processes, such as AR. Donor-derived cell-free DNA (ddcfDNA) and extracellular vesicles (EVs) are further promising tools. Although most of these biomarkers still need to be validated in multiple independent cohorts and standardized, they are paving the way for substantial advances, such as the possibility of accurately predicting risk of DGF before graft is implanted, of making a “molecular” diagnosis of subclinical rejection even before histological lesions develop, or of dissecting etiology of CAD. Identification of “immunoquiescent” or even tolerant patients to guide minimization of immunosuppressive therapy is another area of active research. The parallel progress in imaging techniques, bioinformatics, and artificial intelligence (AI) is helping to fully exploit the wealth of information provided by biomarkers, leading to improved disease nosology of old entities such as transplant glomerulopathy. Prospective studies are needed to assess whether introduction of these new sets of biomarkers into clinical practice could actually reduce the need for renal biopsy, integrate traditional tools, and ultimately improve graft survival compared to current management.

The Use of Donor-Derived Cell-Free DNA for Assessment of Allograft Rejection and Injury Status

Patient monitoring after kidney transplantation (KT) for early detection of allograft rejection remains key in preventing allograft loss. Serum creatinine has poor predictive value to detect ongoing active rejection as its increase is not sensitive, nor specific for acute renal allograft rejection. Diagnosis of acute rejection requires allograft biopsy and histological assessment, which can be logistically challenging in some cases and carries inherent risk for complications related to procedure. Donor-derived cell-free DNA (dd-cfDNA), DNA of donor origin in the blood of KT recipient arising from cells undergoing injury and death, has been examined as a potential surrogate marker for allograft rejection. A rise in dd-cfDNA levels precedes changes in serum creatinine allows early detections and use as a screening tool for allograft rejection. In addition, when used in conjunction with donor-specific antibodies (DSA), it increases the pre-biopsy probability of antibody-mediated rejection (ABMR) aiding the decision-making process. Advancements in noninvasive biomarker assays such as dd-cfDNA may offer the opportunity to improve and expand the spectrum of available diagnostic tools to monitor and detect risk for rejection and positively impact outcomes for KT recipients. In this this article, we discussed the evolution of dd-cfDNA assays and recent evidence of assessment of allograft rejection and injury status of KT by the use of dd-cfDNA.