Kidney allograft surveillance biopsy practices across US transplant centers: A UNOS survey

Biomarkers of Rejection in Kidney Transplantation

Alloimmune injury is a major cause of long-term kidney allograft failure whether due to functionally stable (subclinical) or overt clinical rejection. These episodes may be mediated by immune cells (cellular rejection) or alloantibody (antibody-mediated rejection). Early recognition of immune injury is needed for timely appropriate intervention to maintain graft functional viability. However, the conventional measure of kidney function (i.e., serum creatinine) is insufficient for immune monitoring due to limited sensitivity and specificity for rejection. As a result, there is need for biomarkers that more sensitively detect the immune response to the kidney allograft. Recently, several biomarkers have been clinically implemented into the care of kidney transplant recipients. These biomarkers attempt to achieve multiple goals including (1) more sensitive detection of clinical and subclinical rejection, (2) predicting impending rejection, (3) monitoring for the adequacy of treatment response, and (4) facilitating personalized immunosuppression. In this review, we summarize the findings to date in commercially available biomarkers, along with biomarkers approaching clinical implementation. While we discuss the analytical and clinical validity of these biomarkers, we identify the challenges and limitations to widespread biomarker use, including the need for biomarker-guided prospective studies to establish evidence of clinical utility of these new assays.

Detection of Subclinical Rejection in Pediatric Kidney Transplantation: Current and Future Practices

INTRODUCTION

The successes in the field of pediatric kidney transplantation over the past 60 years have been extraordinary. Year over year, there have been significant improvements in short-term graft survival. However, improvements in longer-term outcomes have been much less apparent. One important contributor has been the phenomenon of low-level rejection in the absence of clinical manifestations-so-called subclinical rejection (SCR).

METHODS

Traditionally, rejection has been diagnosed by changes in clinical parameters, including but not limited to serum creatinine and proteinuria. This review examines the shortcomings of this approach, the effects of SCR on kidney allograft outcome, the benefits and drawbacks of surveillance biopsies to identify SCR, and new urine and blood biomarkers that define the presence or absence of SCR.

RESULTS

Serum creatinine is an unreliable index of SCR. Surveillance biopsies are the method most utilized to detect SCR. However, these have significant drawbacks. New biomarkers show promise. These biomarkers include blood gene expression profiles and donor derived-cell free DNA; urine gene expression profiles; urinary cytokines, chemokines, and metabolomics; and other promising blood and urine tests.

CONCLUSION

Specific emphasis is placed on studies carried out in pediatric kidney transplant recipients.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT03719339.

Biomarkers in Kidney Transplantation

Currently in the United States, there are more than 250,000 patients with a functioning kidney allograft and over 100,000 waitlisted patients awaiting kidney transplant, with a burgeoning number added to the kidney transplant wait list every year. Although early post-transplant care is delivered at the transplant center, the increasing number of kidney transplant recipients requires general nephrologists to actively participate in the long-term care of these patients. Serum creatinine and proteinuria are imperfect traditional biomarkers of allograft dysfunction and lag behind subclinical allograft injury. This manuscript reviews the various clinically available biomarkers in the field of kidney transplantation for a general nephrologist with a focus on the utility of donor-derived cell-free DNA, as a marker of early allograft injury. Blood gene expression profiling, initially studied in the context of early identification of subclinical rejection, awaits validation in larger multicentric trials. Urinary cellular messenger ribonucleic acid and chemokine CXCL10 hold promising potential for early diagnosis of both subclinical and acute rejection. Torque tenovirus, a ubiquitous DNA virus is emerging as a biomarker of immunosuppression exposure as peripheral blood torque tenovirus copy numbers might mirror the intensity of host immunosuppression. Although high-quality evidence is still being generated, evidence and recommendations are provided to aid the general nephrologist in implementation of novel biomarkers in their clinical practice.

The reduced function allele SLCO1B1 c.521T>C is of no practical relevance for the renal graft function over the first post-transplant year in patients treated with mycophenolic acid

OBJECTIVE

It is unclear whether renal transplant recipients treated with mycophenolic acid (MPA) who carry the reduced-function allele at polymorphism SLCO1B1 c.521T>C differ from their wild-type peers regarding renal outcomes and tolerability. We aimed to estimate the effect of this polymorphism on the graft function (estimated glomerular filtration rate, eGFR) over the first 12 post-transplant months in patients on MPA-based maintenance immunosuppression.

METHODS

In a 12-month observational cohort study, consecutive adult patients were repeatedly assessed for eGFR. The SLCO1B1 c.521C>T variant allele carriers (exposed) and wild-type subjects (controls) were balanced on a range of demographic, medical, and genetic variables at baseline, and eGFR trajectory was estimated with further adjustment for time-varying covariates. A subset of patients were assessed for exposure to MPA 5-7 days after the transplantation.

RESULTS

The adjusted eGFR slopes from day 1 to day 28 (daily), and from day 28 to day 365 (monthly) were practically identical in exposed (n = 86) and control (n = 168) patients [geometric means ratios (GMR) = 0.99, 95% confidence interval (CI) = 0.92-1.06 and GMR = 0.98, 0.94-1.01, respectively]. The rates of adverse renal outcomes and possible MPA-related adverse effects were low, and similar in exposed and controls [rate ratios (RR) = 0.94, 0.49-1.84 and RR = 1.08, 0.74-1.58, respectively]. The pharmacokinetic analysis did not signal meaningful differences regarding exposure to MPA, overall (exposed n = 23, control n = 45), if cotreated with cyclosporine (n = 17 vs. n = 26) or with tacrolimus (n = 8 vs. n = 17).

CONCLUSIONS

In patients treated with MPA, variant allele SLCO1B1 c.521T>C appears of no practical relevance regarding the 12-month renal graft function, MPA safety and exposure to MPA at early steady-state.

Subclinical rejection and allograft survival in kidney transplantation: protocol for a systematic review and meta-analysis

INTRODUCTION

Subclinical rejection (SCR) refers to the presence of acute rejection without accompanying kidney allograft dysfunction. The impact of SCR on long-term graft survival remains a subject of ongoing debate.

METHODS AND ANALYSIS

We will perform a systematic search of databases including MEDLINE, Embase and Cochrane Central, from January 1995 to November 2023. We will include English-language studies involving adult kidney transplant patients who investigated SCR. We will exclude studies focused on 'for-cause' biopsies. Both title, abstract screening and full-text screening will be performed by two or more reviewers. The primary outcome of this study will be death-censored allograft loss. The secondary outcome will include development of subsequent rejection. For time-dependent outcomes, we will prioritise HRs and the 95% CIs. In cases where HRs are unavailable, we will calculate risk ratios based on the recorded events. The risk of bias will be assessed using the Cochrane Collaboration's revised tool for assessing the risk of bias in randomised trials and the Newcastle-Ottawa scale for cohort studies. We will employ a random effects model. We will evaluate heterogeneity using the I2 variable. We will assess publication bias by funnel plots, Begg and Mazumdar test, and Egger's test.

ETHICS AND DISSEMINATION

Ethics approval does not apply as no original data will be collected. The results will be disseminated through peer-reviewed publications and conference presentations.

PROSPERO REGISTRATION NUMBER

CRD42023463536.

Immune monitoring in pediatric kidney transplant

BACKGROUND

Long-term outcomes in pediatric kidney transplantation remain suboptimal, largely related to chronic rejection. Creatinine is a late marker of renal injury, and more sensitive, early markers of allograft injury are an active area of current research.

METHODS

This is an educational review summarizing existing strategies for monitoring for rejection in kidney transplant recipients.

RESULTS

We summarize supporting currently available clinical tests, including surveillance biopsy, donor specific antibodies, and donor-derived cell free DNA, as well as the potential limitations of these studies. In addition, we review the current avenues of active research, including transcriptomics, proteomics, metabolomics, and torque tenovirus levels.

CONCLUSION

Advancing the use of noninvasive immune monitoring will depend on well-designed multicenter trials that include patients with stable graft function, include biopsy results on all patients, and can demonstrate both association with a patient-relevant clinical endpoint such as graft survival or change in glomerular filtration rate and a potential timepoint for intervention.

Inosine monophosphate dehydrogenase type 2 polymorphism IMPDH2 3757T>C (rs11706052) and 12-month evolution of the graft function in renal transplant recipients on mycophenolate-based immunosuppression

Variant allele at the inosine monophosphate dehydrogenase type 2 polymorphism IMPDH2 3757T>C has been associated with increased enzyme activity and reduced susceptibility to mycophenolic acid (MPA) in vitro. It has been suggested associated with an increased risk of acute rejection in renal transplant recipients on MPA-based immunosuppression, but not unambiguously. We assessed one-year evolution of the estimated glomerular filtration rate (eGFR) in transplanted variant allele carriers and wild-type subjects, while controlling for a number of demographic, pharmacogenetic, (co)morbidity, and treatment baseline and time-varying covariates. The eGFR slopes to day 28 (GMR = 1.01, 95% CI 0.93-1.09), and between days 28 and 365 (GMR = 1.01, 95% CI 0.99-1.02) were practically identical in 52 variant carriers and 202 wild-type controls. The estimates (95%CIs) remained within the limits of ±20% difference even after adjustment for a strong hypothetical effect of unmeasured confounders. Polymorphism IMPDH2 3757T>C does not affect the renal graft function over the 1st year after transplantation.

Very Low Frequency of Pathological Findings in One-year Protocol Biopsies of Uneventful Standard Risk Kidney Transplant Recipients: Results From the Nordic Protocol Biopsy Study

Background

The clinical significance of kidney transplant protocol biopsies has been debated. We studied the frequency of borderline changes and T cell-mediated rejection (TCMR) in 1-y protocol biopsies in standard risk kidney transplant recipients.

Methods

Consecutive non-HLA-sensitized recipients of kidney transplants between 2006 and 2017, who underwent a protocol biopsy at 1 y in 2 national transplant centers were studied retrospectively (N = 1546). Donor-specific HLA antibodies (DSAs), graft function (plasma creatinine), and proteinuria were measured at the time of 1-y protocol biopsy. The occurrence of subclinical acute TCMR (i2t2v0 or higher) or borderline changes suspicious of TCMR (i1t1v0 or higher) in the protocol biopsy was studied, together with frequency of findings causing changes in the composite score iBox.

Results

Subclinical acute TCMR was detected in 30 of 1546 (1.9%) of the protocol biopsies, and borderline or TCMR in 179 of 1546 (12%). Among patients with no history of acute rejection, and no proteinuria or DSA, TCMR was detected in only 1 of 974 (0.1%) and borderline or TCMR in only 48 of 974 (4.9%) patients at 1 y. In the absence of proteinuria (<30 mg/g, or equivalent as measured with a negative dipstick proteinuria) or DSA, or history of acute rejection, only 50 of 974 (5.1%) biopsies showed any lesions significant for the iBox score.

Conclusions

The likelihood of pathological findings in 1-y protocol biopsies in non-HLA-sensitized patients without previous immunological events is low. Clinical usefulness of protocol biopsies seems limited in these patients.

Prediction of very early subclinical rejection with machine learning in kidney transplantation

Protocol biopsy is a reliable method for assessing allografts status after kidney transplantation (KT). However, due to the risk of complications, it is necessary to establish indications and selectively perform protocol biopsies by classifying the high-risk group for early subclinical rejection (SCR). Therefore, the purpose of this study is to analyze the incidence and risk factors of early SCR (within 2 weeks) and develop a prediction model using machine learning. Patients who underwent KT at Samsung Medical Center from January 2005 to December 2020 were investigated. The incidence of SCR was investigated and risk factors were analyzed. For the development of prediction model, machine learning methods (random forest, elastic net, extreme gradient boosting [XGB]) and logistic regression were used and the performance between the models was evaluated. The cohorts of 987 patients were reviewed and analyzed. The incidence of SCR was 14.6%. Borderline cellular rejection (BCR) was the most common type of rejection, accounting for 61.8% of cases. In the analysis of risk factors, recipient age (OR 0.98, p = 0.03), donor BMI (OR 1.07, p = 0.02), ABO incompatibility (OR 0.15, p < 0.001), HLA II mismatch (two [OR 6.44, p < 0.001]), and ATG induction (OR 0.41, p < 0.001) were associated with SCR in the multivariate analysis. The logistic regression prediction model (average AUC = 0.717) and the elastic net model (average AUC = 0.712) demonstrated good performance. HLA II mismatch and induction type were consistently identified as important variables in all models. The odds ratio analysis of the logistic prediction model revealed that HLA II mismatch (OR 6.77) was a risk factor for SCR, while ATG induction (OR 0.37) was a favorable factor. Early SCR was associated with HLA II mismatches and induction agent and prediction model using machine learning demonstrates the potential to predict SCR.

The Importance of 1-Year Protocol Biopsy in the Long-Term Prognosis of Kidney Transplants-5-Years Follow-Up

BACKGROUND

Protocol biopsies are performed to detect subclinical pathologies that may lead to future graft dysfunction. However, they are not routinely performed interventions in every transplant center. There is no established regimen for performing them.

PURPOSE

The study aimed to evaluate if protocol biopsies can improve long-term patient outcomes after detecting early disorders and modifying treatment.

MATERIAL AND METHODS

Our observational study included 61 patients who underwent protocol biopsy 12 months after the transplantation. Based on the biopsy results, patients with abnormal histologic material (n = 37) were divided into 3 study groups as follows: patients with mild inflammatory lesions (n = 21), patients with interstitial fibrosis and tubular atrophy (IFTA) grade II to III (n = 12), and patients with BK virus nephropathy (n = 4). The control group (n = 24) included kidney recipients with IFTA 0 to I grade. Outcomes after 5-year follow-up were evaluated.

RESULTS

Five years after the biopsy, patients in the control group had stable graft function (5-year change in serum creatinine was -0.09 mg/dL). An increase in serum creatinine levels was observed in patients with IFTA II to III compared with the control group (0.14 mg/dL, P = .04). Immunosuppressive treatment was modified in the group with mild inflammatory changes and in the BKV group after the biopsy result. In the group with mild inflammatory lesions, renal function was stable (change of serum creatinine was -0.01 mg/dL, P = .51). In the BKV nephropathy group, there was a significant reduction in serum creatine levels (-0.48 mg/dL, P = .016). The analysis showed no diagnostic value for serum creatinine concentration (95% CI 0.49-0.78, P = .08).

CONCLUSIONS

Protocol biopsies are useful for detecting early pathologies and preventing allograft failure. They greatly benefit patients with detectable pathology that can be treated or in whom therapy modification is possible.

Assessment of Donor Derived Cell Free DNA (dd-cfDNA) at Surveillance and at Clinical Suspicion of Acute Rejection in Renal Transplantation

In our prospective, unicenter cohort study, we collected blood samples from 30 newly kidney transplanted patients, at month 1, 2, 3, and 5 for dd-cfDNA analysis, along with creatinine/eGFR and DSA monitoring, and from 32 patients who underwent an indication biopsy and whose dd-cfDNA levels were measured at the time of biopsy and 1 month afterwards. Fourteen of 32 (43.8%) patients in the biopsy group were diagnosed with TCMR and 5 of 32 (15.6%) with ABMR. Dd-cfDNA proved to be better than creatinine in diagnosing rejection from non-rejection in patients who were biopsied. When a dd-cfDNA threshold of 0.5% was chosen, sensitivity was 73.7% and specificity was 92.3% (AUC: 0.804, 0.646-0.961). In rejection patients, levels of dd-cfDNA prior to biopsy (0.94%, 0.3-2.0) decreased substantially after initiation of treatment with median returning to baseline already at 1 month (0.33%, 0.21-0.51, p = 0.0036). In the surveillance group, high levels of dd-cfDNA (>0.5%) from second month post-transplantation were correlated with non-increasing eGFR 1 year post-transplantation. The study used AlloSeq kit for kidney transplant surveillance for first time and confirmed dd-cfDNA's ability to detect rejection and monitor treatment, as well as to predict worse long-term outcomes regarding eGFR.

Effects of Treating Subclinical Rejection 2 Weeks After Kidney Transplantation, as Determined by Analyzing 1-Year Histologic Outcomes

Subclinical rejection (SCR) is associated with chronic allograft nephropathy. Therefore, early detection and treatment of SCR through a protocol biopsy (PB) can reduce the incidence of pathologic changes. This study evaluates the impact of early detection and treatment of SCR using a routine PB 2 weeks after kidney transplantation (KT) by examining histologic outcomes 1 year later. We reviewed 624 KT recipients at the Samsung Medical Center between August 2012 and December 2018. Protocol biopsy was planned 2 weeks and 1 year after transplantation. We compared the histologic changes between the 2 biopsies. After a propensity score matching analysis, we divided the patients into 2 groups: the proven normal group (n = 256) and the rejection group (n = 96) at the PB taken 2 weeks post-transplant. The rejection group showed no significant difference from the normal group in the flow of graft function or the Kaplan-Meier curve for graft survival. In the histologic outcomes, the pathologic differences between the groups significantly improved between the 2 time points. Treating SCR through a PB 2 weeks after KT can contribute to the maintenance of graft function and improve histologic changes 1 year after KT.

Subclinical rejection-free diagnostic after kidney transplantation using blood gene expression

We previously established a six-gene-based blood score associated with operational tolerance in kidney transplantation which was decreased in patients developing anti-HLA donor-specific antibodies (DSA). Herein, we aimed to confirm that this score is associated with immunological events and risk of rejection. We measured this using quantitative PCR (qPCR) and NanoString methods from an independent multicenter cohort of 588 kidney transplant recipients with paired blood samples and biopsies at one year after transplantation validating its association with pre-existing and de novo DSA. From 441 patients with protocol biopsy, there was a significant decrease of the score of tolerance in 45 patients with biopsy-proven subclinical rejection (SCR), a major threat associated with pejorative allograft outcomes that prompted an SCR score refinement. This refinement used only two genes, AKR1C3 and TCL1A, and four clinical parameters (previous experience of rejection, previous transplantation, sex of recipient and tacrolimus uptake). This refined SCR score was able to identify patients unlikely to develop SCR with a C-statistic of 0.864 and a negative predictive value of 98.3%. The SCR score was validated in an external laboratory, with two methods (qPCR and NanoString), and on 447 patients from an independent and multicenter cohort. Moreover, this score allowed reclassifying patients with discrepancies between the DSA presence and the histological diagnosis of antibody mediated rejection unlike kidney function. Thus, our refined SCR score could improve detection of SCR for closer and noninvasive monitoring, allowing early treatment of SCR lesions notably for patients DSA-positive and during lowering of immunosuppressive treatment.

Long-term immunological outcomes of early subclinical inflammation on surveillance kidney allograft biopsies

The long-term impact of early subclinical inflammation (SCI) through surveillance biopsy has not been well studied. To do this, we recruited a prospective observational cohort that included 1000 sequential patients who received a kidney transplant from 2013-2017 at our center. A total of 586 patients who underwent a surveillance biopsy in their first year post-transplant were included after excluding those with clinical rejections, and those who were unable to undergo a surveillance biopsy. Patients were classified based on their biopsy findings: 282 with NSI (No Significant Inflammation) and 304 with SCI-T (SCI and Tubulitis) which was further subdivided into 182 with SC-BLR (Subclinical Borderline Changes) and 122 with SC-TCMR (Subclinical T Cell Mediated Rejection, Banff 2019 classification of 1A or more). We followed the clinical and immunological events including Clinical Biopsy Proven Acute Rejection [C-BPAR], long-term kidney function and death-censored graft loss over a median follow-up of five years. Episodes of C-BPAR were noted at a median of two years post-transplant. Adjusted odds of having a subsequent C-BPAR was significantly higher in the SCI-T group [SC-BLR and SC-TCMR] compared to NSI 3.8 (2.1-7.5). The adjusted hazard for death-censored graft loss was significantly higher with SCI-T compared to NSI [1.99 (1.04-3.84)]. Overall, SCI detected through surveillance biopsy within the first year post-transplant is a harbinger for subsequent immunological events and is associated with a significantly greater hazard for subsequent C-BPAR and death-censored graft loss. Thus, our study highlights the need for identifying patients with SCI through surveillance biopsy and develop strategies to prevent further alloimmune injuries.

Regulatory and transitional B cells: potential biomarkers and therapeutic targets in organ transplantation

PURPOSE OF THE REVIEW

Regulatory B cells (Bregs) play a prominent role in various disease settings. While progress has been hindered by the lack of a specific Breg marker, new findings highlight their role modulating the alloimmune response and promoting allograft survival.

RECENT FINDINGS

Herein, we focus on the recent advances in Breg biology and their role in transplantation. We review studies showing that T-cell immunoglobulin and mucin domain 1 (TIM-1) is an inclusive and functional Breg marker in mice that may have human relevance. We highlight the utility of the B cell interleukin-10/tumor necrosis factor-alpha (IL-10/TNFα) ratio in identifying underlying immunological reactivity and predicting clinical outcomes in kidney transplantation. This may identify patients requiring more immunosuppression and provide insight into potential therapeutic approaches that can modulate the Breg: B effector cell (Beff) balance.

SUMMARY

Emerging data support Bregs as potent modulators of immune responses in humans. Their ability to promote allograft survival must await development of approaches to expand Bregs in vitro/in vivo . The low IL-10/TNFα ratio reflecting decreased Breg/Beff balance, predicts acute rejection (AR) and poorer outcomes in renal transplantation. It remains to be determined whether this paradigm can be extended to other allografts and whether therapy aiming to correct the relative deficiency of Bregs will improve outcomes.

Validation of a gene expression signature to measure immune quiescence in kidney transplant recipients in the CLIA setting

Aim: Allograft rejection remains a major cause of graft failure in kidney transplantation. Here the authors report the validation of a non-invasive molecular diagnostic assay, AlloMap Kidney, using peripheral blood. Methods: The AlloMap Kidney test is a gene expression profile utilizing the RNA-seq platform to measure immune quiescence in kidney transplant patients. Results/Conclusions: Analytical validation showed robust performance characteristics with an accuracy correlation coefficient of 0.997 and a precision coefficient of variation of 0.049 across testing. Clinical validation from the prospective, multi-center studies of 235 samples (66 rejection and 169 quiescence specimens) demonstrated the sensitivity of 70% and specificity of 66% for allograft rejection, while the negative predictive value was 95% to discriminate rejection from quiescence at 10% prevalence of rejection.

Emerging biomarkers in kidney transplantation and challenge of clinical implementation

PURPOSE OF REVIEW

Despite improvement in short-term outcomes after kidney transplantation, long-term outcomes remain suboptimal. Conventional biomarkers are limited in their ability to reliably identify early immunologic and nonimmunologic injury. Novel biomarkers are needed for noninvasive diagnosis of subclinical injury, prediction of response to treatment, and personalization of the care of kidney transplant recipients.

RECENT FINDINGS

Recent biotechnological advances have led to the discovery of promising molecular biomarker candidates. However, translating potential biomarkers from bench to clinic is challenging, and many potential biomarkers are abandoned prior to clinical implementation. Despite these challenges, several promising urine, blood, and tissue novel molecular biomarkers have emerged and are approaching incorporation into clinical practice.

SUMMARY

This article highlights the challenges in adopting biomarker-driven posttransplant management and reviews several promising emerging novel biomarkers that are approaching clinical implementation.

Rabbit antithymocyte globulin dose and early subclinical and clinical rejections in kidney transplantation

Antithymocyte globulin (ATG) is a commonly used induction agent in kidney transplant recipients. However, the optimal dosing has not been well defined. Our protocol aims for a 5-6 mg/kg cumulative dose. It is unclear if a dose lower than 5 mg/kg is associated with more rejection. We performed a retrospective cohort study of patients who received a kidney transplant at our center between January 1, 2013 and December 31, 2016. Primary outcome was biopsy proven acute rejection (clinical and subclinical) in the first six months after kidney transplant. CMV viremia in high risk(D+/R-) recipients and BK viremia was compared as a secondary endpoint. Of the 543 patients, the Low Dose (LD) group (n = 56) received <5 mg/kg ATG and Regular Dose (RD) group (n = 487) received ≧5 mg/kg. Patients in RD were more sensitized (higher PRA and CPRA). LD received a dose of 4 ± 1.1 mg/kg ATG whereas RD received 5.6 ± 0.3 mg/kg ATG (p < 0.001). TCMR(Banff 1A or greater) was present in 34% of patients in LD vs. 22% in RD (p = 0.04) (OR 2.1;95%CI 1.12-3.81;p = 0.019). There was no difference in the incidence of CMV or BK viremia. ATG doses lower than 5 mg/kg may be associated with a heightened risk of rejection despite a low degree of sensitization. This article is protected by copyright. All rights reserved.

Decrease in CD14++CD16+ Monocytes in Low-Immunological-Risk Kidney Transplant Patients with Subclinical Borderline Inflammation

We determined the association between CD14++CD16+ monocytes and subclinical infiltrates that do not reach the histological threshold for rejection (≥Banff IA). We studied low-immunological-risk kidney-transplant recipients in a clinical trial (NCT02284464; EudraCT 2012-003298-24) whose protocol biopsy in the third month showed no significant changes or borderline lesions (BL). Flow cytometry was used to analyze the percentage of CD14++CD16+ monocytes in peripheral blood (PB) and blood from a fine-needle-aspiration biopsy (FNAB). A protocol biopsy was performed in 81 low-immunological-risk patients, of whom 15 were excluded (BK polyomavirus and rejection). The 28 (42.4%) with borderline lesions had significantly low levels of CD14++CD16+ in PB compared to patients with normal biopsies (7.9 ± 5.4 vs. 13.0 ± 12.8; p = 0.047). Patients without significant changes had similar percentages of CD14++CD16+ monocytes in the graft blood (GB) and FNAB blood. The percentage of these monocytes in the patients with an interstitial infiltrate, however, increased significantly in the FNAB blood compared to the GB: 16.9 ± 16.6 vs. 7.9 ± 5.4; p = 0.006. A difference of 50% in CD14++CD16+ in the GB versus the PB was a significant risk factor (p = 0.002) for BL, increasing the risk seven times. A decrease in CD14++CD16+ in the PB could be associated with the recruitment of these cells to the graft tissue in cases of subclinical BL inflammatory infiltrates below the threshold for rejection.

The causes and frequency of kidney allograft failure in a low-resource setting: observational data from Iraqi Kurdistan

Background

In the developing world, transplantation is the most common long-term treatment for patients with end-stage renal disease, but rates and causes of graft failure are uncertain.

Methods

This was a retrospective outcomes study of renal transplant patients seen in Iraqi Kurdistan nephrology clinics in the year 2019. In 2019, 871 renal transplant patients were registered and outcomes followed through 12/31/2020. Indicated renal biopsies were obtained on 431 patients at 1 day to 18 years post-transplantation. Outcomes were compared with United States Renal Data System (USRDS) living donor reports.

Results

All donors were living. The recipient age was 38.5 ± 13.3 years, 98.2% were < 65 years old, 3.7% had previous transplants, and 2.8% had pretransplant donor-specific antibodies (DSA). Gehan-Breslow estimated failure rates for all-cause, return to HD, and death with functional graft were 6.0, 4.2, and 1.9% at 1 year and 18.1, 13.7, and 5.1% at 5 years post-engraftment (USRDS 2000; 1 year: 7.0, 5.0, 2.6%; 5 year: 22.3, 15.2, 10.6%. USRDS 2010; 1 year: 3.7, 2.4, 1.4%; 5 year: 15.3, 9.6, 7.3%). The median graft survival was 15 years. Acute tubular injury (ATI), infarction, and acute T cell-mediated rejection accounted for 22.2% of graft loss, with > 75% of these failures taking place in the first year. Most graft failures occurred late, at a median post-transplant time of 1125 (interquartile range, 365–2555) days, and consisted of interstitial fibrosis and tubular atrophy (IF/TA) (23.8%), transplant glomerulopathy (13.7%), and acquired active antibody-mediated rejection (12.0%). The significant predictors of graft loss were C4d + biopsies (P < 0.01) and advanced IF/TA (P < 0.001).

Conclusions

Kurdistan transplant patients had graft failure rates similar to living donors reported by the USRDS for the year 2000 but higher than reported for 2010. Compared to USRDS 2010, Kurdistan patients had a moderate excess of HD failures at one and 5 years post-engraftment. Nevertheless, prolonged survival is the norm, with chronic disorders and acquired DSA being the leading causes of graft loss.

Beyond the Biopsy: Monitoring Immune Status in Kidney Recipients

Improved long-term kidney allograft survival is largely related to better outcomes at 12 months, in association with declining acute rejection rates and more efficacious immunosuppression. Finding the right balance between under- and overimmunosuppression or rejection versus immunosuppression toxicity remains one of transplant's holy grails. In the absence of precise measures of immunosuppression burden, transplant clinicians rely on nonspecific, noninvasive tests and kidney allograft biopsy generally performed for cause. This review appraises recent advances of conventional monitoring strategies and critically examines the plethora of emerging tests utilizing tissue, urine, and blood samples to improve upon the diagnostic precision of allograft surveillance.

A new lateral flow assay to detect sIL-2R during T-cell mediated rejection after kidney transplantation

Kidney is the most frequently transplanted among all solid organs worldwide. Kidney transplant recipients (KTRs) undergo regular follow-up examinations for the early detection of acute rejections. The gold standard for proving a T-cell mediated rejection (TCMR) is a biopsy of the renal graft often occurring as indication biopsy, in parallel to an increased serum creatinine that may indicate deterioration of renal transplant function. The goal of the current work was to establish a lateral flow assay (LFA) for diagnosing acute TCMR to avoid harmful, invasive biopsies. Soluble interleukin-2 (IL-2) receptor (sIl-2R) is a potential biomarker representing the α-subunit of the IL-2 receptor produced by activated T-cells, e.g., after allogen contact. To explore the diagnostic potential of sIL-2R as a biomarker for TCMR and borderline TCMR, plasma and urine samples were collected from three independent KTR cohorts with various distinct histopathological diagnostic findings according to BANFF (containing 112 rsp. 71 rsp. 61 KTRs). Samples were analyzed by a Luminex-based multiplex technique and cut off-ranges were determined. An LFA was established with two specific sIL-2R-antibodies immobilized on a nitrocellulose membrane. A significant association between TCMR, borderline TCMR and sIL-2R in plasma and between TCMR and sIL-2R in urine of KTRs was confirmed using the Mann-Whitney U test. The LFA was tested with sIL-2R-spiked buffer samples establishing a detection limit of 25 pM. The performance of the new LFA was confirmed by analyzing urine samples of the 2^nd and 3^rd patient cohort with 35 KTRs with biopsy proven TCMRs, 3 KTRs diagnosed with borderline TCMR, 1 mixed AMR/TCMR rsp. AMR/borderline TCMR and 13 control patients with a rejection-free kidney graft proven by protocol biopsies. The new point-of-care assay showed a specificity of 84.6% and sensitivity of 87.5%, and a superior estimated glomerular filtration rate (eGFR) at the time point of biopsy (specificity 30.8%, sensitivity 85%).

Impact of Subclinical and Clinical Kidney Allograft Rejection Within 1 Year Posttransplantation Among Compatible Transplant With Steroid Withdrawal Protocol

Early acute kidney rejection remains an important clinical issue.

Methods

The current study included 552 recipients who had 1-2 surveillance or indication biopsy within the 1 y posttransplant. We evaluated the impact of type of allograft inflammation on allograft outcome. They were divided into 5 groups: no inflammation (NI: 95), subclinical inflammation (SCI: 244), subclinical T cell-mediated rejection (TCMR) (SC-TCMR: 110), clinical TCMR (C-TCMR: 83), and antibody-mediated rejection (AMR: 20). Estimated glomerular filtration rate (eGFR) over time using linear mixed model, cumulative chronic allograft scores/interstitial fibrosis and tubular atrophy (IFTA) ≥2 at 12 mo, and survival estimates were compared between groups.

Results

The common types of rejections were C-TCMR (15%), SC-TCMR (19.9%), and AMR (3.6%) of patients. Eighteen of 20 patients with AMR had mixed rejection with TCMR. Key findings were as follows: (i) posttransplant renal function: eGFR was lower for patients with C-TCMR and AMR (P < 0.0001) compared with NI, SCI, and SC-TCMR groups. There was an increase in delta-creatinine from 3 to 12 mo and cumulative allograft chronicity scores at 12 mo (P < 0.001) according to the type of allograft inflammation. (ii) Allograft histology: the odds of IFTA ≥2 was higher for SC-TCMR (3.7 [1.3-10.4]; P = 0.04) but was not significant for C-TCMR (3.1 [1.0-9.4]; P = 0.26), and AMR (2.5 [0.5-12.8]; P = 0.84) compared with NI group, and (iii) graft loss: C-TCMR accounted for the largest number of graft losses and impending graft losses on long-term follow-up. Graft loss among patient with AMR was numerically higher but was not statistically significant.

Conclusions

The type of kidney allograft inflammation predicted posttransplant eGFR, cumulative chronic allograft score/IFTA ≥2 at 12 mo, and graft loss.

Therapies for Chronic Allograft Rejection

Remarkable advances have been made in the pathophysiology, diagnosis, and treatment of antibody-mediated rejection (ABMR) over the past decades, leading to improved graft outcomes. However, long-term failure is still high and effective treatment for chronic ABMR, an important cause of graft failure, has not yet been identified. Chronic ABMR has a relatively different phenotype from active ABMR and is a slowly progressive disease in which graft injury is mainly caused by de novo donor specific antibodies (DSA). Since most trials of current immunosuppressive therapies for rejection have focused on active ABMR, treatment strategies based on those data might be less effective in chronic ABMR. A better understanding of chronic ABMR may serve as a bridge in establishing treatment strategies to improve graft outcomes. In this in-depth review, we focus on the pathophysiology and characteristics of chronic ABMR along with the newly revised Banff criteria in 2017. In addition, in terms of chronic ABMR, we identify the reasons for the resistance of current immunosuppressive therapies and look at ongoing research that could play a role in setting better treatment strategies in the future. Finally, we review non-invasive biomarkers as tools to monitor for rejection.

Advances in personalized medicine and noninvasive diagnostics in solid organ transplantation

Personalized medicine has been a mainstay and in practice in transplant pharmacotherapy since the advent of the field. Decisions pertaining to the diagnosis, selection, and monitoring of transplant pharmacotherapy are aimed toward the individual, the allograft, and the overall immunologic needs of the patient. Recent advances in pharmacogenomics, noninvasive biomarkers, and artificial intelligence (AI) technologies have the promise of transforming the way we individualize treatment and monitor allograft function. Pharmacogenomic testing can provide clinicians with additional data that can minimize toxicity and maximize therapeutic dosing in high-risk patients, leading to more informed decisions that may decrease the risk of rejection and adverse outcomes related to immunosuppressive therapies. Development of noninvasive strategies to monitor allograft function may offer safer and more convenient methods to detect allograft injury. Cell free DNA and gene expression profiling offer the potential to serve as "liquid biopsies" minimizing the risk to patients and providing clinicians with useful molecular data that may help individualize immunosuppression and rejection treatment. Use of big data in transplant and novel AI platforms, such as the iBox, hold tremendous promise in providing clinicians a "glimpse into the future" thereby allowing for a more individualized approach to immunosuppressive therapy that may minimize future adverse outcomes. Advances in diagnostics, laboratory science, and AI have made the application of personalized medicine even more tailored for solid organ transplant recipients. In this perspective, we summarize the current and emerging tools available, literature supporting use, and the horizon for future personalization of transplantation.

Kidney allograft rejection: Diagnosis and treatment practices in USA- A UNOS survey

We studied diverse rejection management strategies across centers by conducting a UNOS survey of kidney transplant program directors in 2017. There were 104 total responses from 235 kidney transplant programs representing 88 unique transplant programs (response rate 37%). Information was collected on center-specific management practices. Pertinent center-specific data were obtained from the OPTN database. Of the respondents, 33% were considered large centers (>100 transplants/year). Thymoglobulin was the most commonly used induction agent at 84%, 72% responders do rapid steroid withdrawal, and mycophenolic acid (MPA) is the major antimetabolite (100%). For diagnosing TCMR, 100% used indication biopsy, 28% used protocol biopsy, 2% used serum biomarkers, and none used urine cytokines. For ABMR, 99% used indication biopsy, 34% used protocol biopsy, 72% used DSA, 21% used C1q positive DSA, and none used gene profiling (ENDATS). The treatment of subclinical and clinical TCMR included iv/PO steroids. PP/IVIG were the commonest treatments for ABMR. The use of rituximab, bortezomib, and eculizumab increased from C4D-ABMR to recurrent ABMR. There are diverse management practices for diagnosing and treating rejection. An effort to harmonize these diverse practices for management of TCMR and ABMR will give an opportunity to pool data for evaluating clinical outcomes.

Impact of Subclinical Borderline Inflammation on Kidney Transplant Outcomes

Supplemental Digital Content is available in the text.

Background.

Surveillance biopsies permit early detection of subclinical inflammation before clinical dysfunction, but the impact of detecting early subclinical phenotypes remains unclear.

Methods.

We conducted a single-center retrospective cohort study of 441 consecutive kidney transplant recipients between 2015 and 2018 with surveillance biopsies at 6 months post-transplant. We tested the hypothesis that early subclinical inflammation (subclinical borderline changes, T cell-mediated rejection, or microvascular injury) is associated with increased incidence of a composite endpoint including acute rejection and allograft failure.

Results.

Using contemporaneous Banff criteria, we detected subclinical inflammation in 31%, with the majority (75%) having a subclinical borderline phenotype (at least minimal inflammation with mild tubulitis [>i0t1]). Overall, subclinical inflammation was independently associated with the composite endpoint (adjusted hazard ratio, 2.88; 1.11-7.51; P = 0.03). The subgroup with subclinical borderline inflammation, predominantly those meeting the Banff 2019 i1t1 threshold, was independently associated with 5-fold increased hazard for the composite endpoint (P = 0.02). Those with concurrent subclinical inflammation and subclinical chronic allograft injury had worse outcomes. The effect of treating subclinical inflammation was difficult to ascertain in small heterogeneous subgroups.

Conclusions.

Subclinical acute and chronic inflammation are common at 6 months post-transplant in kidney recipients with stable allograft function. The subclinical borderline phenotype with both tubulitis and interstitial inflammation was independently associated with poor long-term outcomes. Further studies are needed to elucidate the role of surveillance biopsies for management of allograft inflammation in kidney transplantation.

Economic analysis of screening for subclinical rejection in kidney transplantation using protocol biopsies and noninvasive biomarkers

Subclinical rejection (SCR) screening in kidney transplantation (KT) using protocol biopsies and noninvasive biomarkers has not been evaluated from an economic perspective. We assessed cost-effectiveness from the health sector perspective of SCR screening in the first year after KT using a Markov model that compared no screening with screening using protocol biopsy or biomarker at 3 months, 12 months, 3 and 12 months, or 3, 6, and 12 months. We used 12% subclinical cellular rejection and 3% subclinical antibody-mediated rejection (SC-ABMR) for the base-case cohort. Results favored 1-time screening at peak SCR incidence rather than repeated screening. Screening 2 or 3 times was favored only with age <35 years and with high SC-ABMR incidence. Compared to biomarkers, protocol biopsy yielded more quality-adjusted life years (QALYs) at lower cost. A 12-month biopsy cost $13 318/QALY for the base-case cohort. Screening for cellular rejection in the absence of SC-ABMR was less cost effective with 12-month biopsy costing $46 370/QALY. Screening was less cost effective in patients >60 years. Using biomarker twice or thrice was cost effective only if biomarker cost was <$700. In conclusion, in KT, screening for SCR more than once during the first year is not economically reasonable. Screening with protocol biopsy was favored over biomarkers.

Transplantation of Kidneys From Hepatitis C Virus-Infected Donors to Hepatitis C Virus-Negative Recipients: One-Year Kidney Allograft Outcomes

RATIONALE & OBJECTIVE

Transplant centers in the United States are increasingly willing to transplant kidneys from hepatitis C virus (HCV)-infected (HCV⁺) donors into HCV^- recipients. We studied the association between donor HCV infection status and kidney allograft function and posttransplantation allograft biopsy findings.

STUDY DESIGN

Retrospective cohort study.

SETTING & PARTICIPANTS

We examined 65 HCV^- recipients who received a kidney from a HCV⁺ donor and 59 HCV^- recipients who received a kidney from a HCV^- donor during 2018 at a single transplant center.

EXPOSURE

Predictor(s) of donor infection with HCV.

OUTCOMES

Kidney allograft function and allograft biopsy findings during the first year following transplantation.

ANALYTICAL APPROACH

We compared estimated glomerular filtration rate (eGFR), findings on for-cause and surveillance protocol biopsies, development of de novo donor-specific antibodies (DSAs), and patient and allograft outcomes during the first year following transplantation between recipients of HCV⁺ and HCV^- kidneys. We used linear regression to estimate the independent association between allograft function and HCV viremic status of the kidney donor.

RESULTS

The mean age of recipients was 52 ± 11 (SD) years, 43% were female, 19% and 80% of recipients were White and Black, respectively. Baseline characteristics were similar between the HCV⁺ and HCV^- groups. There were no statistically significant differences between the HCV⁺ and HCV^- groups in delayed graft function rates (12% vs 8%, respectively); eGFRs at 3, 6, 9, and 12 months post-transplantation; proportions of patients with cellular rejection (6% vs 7%, respectively); and proportions with antibody-mediated rejection (7% vs 10%, respectively) or de novo DSAs (31% vs 20%, respectively). HCV viremic status was not associated with eGFR at 3, 6, 9, or 12 months.

LIMITATIONS

Generalizability from a single-center study and small sample size was limited.

CONCLUSIONS

Recipients of kidneys from donors infected with HCV had similar kidney allograft function and probability of rejection in the first year after transplantation compared to those who received kidneys from donors without HCV infection.

Two-year protocol biopsy after kidney transplantation in clinically stable recipients - a retrospective study

The idea of protocol biopsy is to detect subclinical pathologies, including rejection, recurrent disease, or infection for early intervention and adjustment of immunosuppressants. Nevertheless, it is not adopted by most clinicians because of its low yield rate and uncertain long-term benefits. This retrospective study evaluated the impact of protocol biopsy on renal function and allograft survival. A two-year protocol biopsy was proposed for 190 stable patients; 68 of them accepted [protocol biopsy (PB) group], while 122 did not [nonprotocol biopsy (NPB) group]. The rejection diagnosis was made in 13 patients by protocol biopsy, and 11 of them had borderline rejection. In the following 5 years, graft survival was better in the PB group than in the NPB group (P = 0.0143). A total of 4 and 17 patients in the PB and NPB groups, respectively, had rejection events proven by indication biopsy. Renal function was better preserved in the PB group than in the NPB group (P = 0.0107) for patients with rejection events. Nevertheless, the survival benefit disappeared by a longer follow-up period (12-year, P = 0.2886). In conclusion, 2-year protocol biopsy detects subclinical pathological changes in rejection and preserves renal function by early intervention so as to prolong graft survival within 5 years.

Avoiding surveillance biopsy: Use of a noninvasive biomarker assay in a real-life scenario

PURPOSE

TruGraf™ blood test measures a specific gene expression signature in peripheral blood mononuclear cells for noninvasive assessment of kidney transplant recipients (KTRs) with stable renal function, excluding subclinical acute rejection (subAR) with high degree of confidence. Study objective was to correlate TruGraf™ test with 6-month surveillance biopsy (SBx).

METHODS

Prospective, single-center study of 116 consecutive KTRs with SBx performed at 6 months post-transplant..TruGraf™ done at time of SBx; results compared with histology (Banff 2017) for concordance.

RESULTS

Of 116 enrollees, 26 excluded, absent biopsy (n = 17), test quality control issues (n = 9), leaving 90 KTRs-66% deceased donor kidneys, 58% African American, and 59% male. TruGraf™ result negative in 67 subjects; 54 had normal biopsy, indicating SBx could have been avoided. Eight subjects had true positive result where biopsy justified. Unnecessary biopsy would have been performed in 15 subjects with false-positive TruGraf™, and subAR missed in 13 subjects with false-negative test. In overall population of 90 patients, SBx would have been avoided in 54 (60%).

CONCLUSIONS

Implementation of TruGraf™ testing in a "real-world" cohort at the time of SBx identified a significant proportion of KTRs that could have avoided SBx.

A Practical Guide to the Clinical Implementation of Biomarkers for Subclinical Rejection Following Kidney Transplantation

Noninvasive biomarkers are needed to monitor stable patients following kidney transplantation (KT), as subclinical rejection, currently detectable only with invasive surveillance biopsies, can lead to chronic rejection and graft loss. Several biomarkers have recently been developed to detect rejection in KT recipients, using different technologies as well as varying clinical monitoring strategies defined as "context of use (COU)." The various metrics utilized to evaluate the performance of each biomarker can also vary, depending on their intended COU. As the use of molecular biomarkers in transplantation represents a new era in patient management, it is important for clinicians to better understand the process by which the incremental value of each biomarkers is evaluated to determine its potential role in clinical practice. This process includes but is not limited to an assessment of clinical validity and utility, but to define these, the clinician must first appreciate the trajectory of a biomarker from bench to bedside as well as the regulatory and other requirements needed to navigate this course successfully. This overview summarizes this process, providing a framework that can be used by clinicians as a practical guide in general, and more specifically in the context of subclinical rejection following KT. In addition, we have reviewed available as well as promising biomarkers for this purpose in terms of the clinical need, COU, assessment of biomarker performance relevant to both the need and COU, assessment of biomarker benefits and risks relevant to the COU, and the evidentiary criteria of the biomarker relevant to the COU compared with the current standard of care. We also provide an insight into the path required to make biomarkers commercially available once they have been developed and validated so that they used by clinicians outside the research context in every day clinical practice.

National survey of physicians' perspectives on pharmacogenetic testing in solid organ transplantation

INTRODUCTION

Our objective was to evaluate physicians' perspectives on the clinical utility of pharmacogenetic (PGx) testing in kidney, liver, heart, and lung transplantation (KLHL-Tx).

METHODS

A 36-question web-based survey was developed and administered to medical and surgical directors of US KLHL-Tx centers.

RESULTS

There were 82 respondents (10% response rate). The majority were men (78%), non-Hispanic whites (70%), medical directors (72%), and kidney transplant physicians (35%). Although 78% of respondents reported having some PGx education, most reported lack of confidence in their PGx knowledge and ability to apply a PGx test. Participants reported mixed views about the clinical utility of PGx testing-most agreed with the efficacy of PGx testing, but not the benefits relative to the risks or standard of care. While 55% reported that testing was available at their institution, only 38% ordered a PGx test in the past year, most commonly thiopurine-S-methyltransferase. Physician-reported barriers to PGx implementation included uncertainty about the clinical value of PGx testing and patient financial burden.

CONCLUSION

Together, our findings suggest prospective PGx research and pilot implementation programs are needed to elucidate the clinical utility and value of PGx in KLHL-Tx. These initiatives should include educational efforts to inform the use of PGx testing.

Kidney Graft Surveillance Biopsy Utilization and Trends: Results From a Survey of High-Volume Transplant Centers

An e-mail-based market research survey focused on high-volume US adult transplant centers was developed and implemented to assess surveillance based on United Network for Organ Sharing/Scientific Registry of Transplant Recipients data: 51 to 100 transplants, 101 to 200 transplants, and more than 200 transplants. Eighty-three centers responded to the survey. Respondent centers represented 13,837/21,167 (65%) of the total kidney transplants in 2018. In total, 38/83 (46%) centers reported the use of surveillance biopsies-20 centers in all patients and 18 in select patients. Surveillance biopsies were performed in 37% (7/19) of centers performing 51 to 100 transplants annually, in 44% (15/34) doing 101 to 200 transplants, and in 53% (16/30) of centers doing more than 200 transplants. Of the 20 centers doing surveillance biopsies in all patients, 17/20 (85%) perform more than 100 annual transplants, and 3/20 (15%) perform less than 100 annual transplants. Of the 45 centers not currently doing surveillance biopsies, 13 (29%) used surveillance biopsies in the past; discontinuation was primarily due to patient inconvenience, adverse events, and cost. Using survey percentages, it is estimated that surveillance biopsies are performed in approximately 34% of kidney transplant recipients and that 74% of all surveillance biopsies occur in centers performing more than 100 kidney transplants per year.

The Impact of Early Clinical and Subclinical T Cell-mediated Rejection After Kidney Transplantation

BACKGROUND

We investigated the effect of clinical and subclinical T cell-mediated rejection (C-TCMR and SC-TCMR) on allograft histology, function, and progression.

METHODS

Adult kidney recipients with 2 protocol biopsies were divided into No-TCMR on biopsies (n = 104), SC-TCMR (n = 56), and C-TCMR (n = 32) in at least 1 biopsy. Chronicity (ci + ct + cg + cv) scores, renal function, and the burden of renal disease measured by area under the curve (serum creatinine, mg mo/dL) were compared.

RESULTS

Baseline characteristics were similar except for mean donor age and Kidney Donor Profile index scores. Patients with C-TCMR had higher mean serum creatinine, lower mean estimated glomerular filtration rate, and higher area under the curve with 95% confidence interval (75.2 [67.7-82.7]) as opposed to patients with SC-TCMR and No-TCMR (58.3 [53.6-62.9], 65.1 [58.8-71.5]), P = 0.0004. Chronicity scores were higher at 3 months in C-TCMR (2.30 ± 1.58) compared with SC-TCMR (2.02 ± 1.42) and No-TCMR (1.31 ± 1.18), P = 0.0001 and also at 12 months. At last follow-up, 18.8% patients with C-TCMR had ≥50% decline in estimated glomerular filtration rate from 3 months compared with 7% and 1% among No-TCMR and SC-TCMR groups (P = 0.038). Multivariate analyses revealed higher odds of Δ-creatinine ≥ 0.5 mg/dL from 3 months to last follow-up for C-TCMR (3.39 [95% confidence interval, 1.25-9.20]) versus No-TCMR (P = 0.016).

CONCLUSIONS

Kidney transplant recipients with C-/SC-TCMR have heightened early allograft chronicity and worse renal function compared with those with No-TCMR. Progressive renal dysfunction was noted among patients with C-TCMR as opposed to SC-TCMR and No-TCMR.

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.

Diagnostic yield of 18 F-FDG PET/CT imaging and urinary CXCL9/creatinine levels in kidney allograft subclinical rejection

Subclinical kidney allograft acute rejection (SCR) corresponds to "the unexpected histological evidence of acute rejection in a stable patient." SCR detection relies on surveillance biopsy. Noninvasive approaches may help avoid biopsy-associated complications. From November 2015 to January 2018, we prospectively performed positron emission tomography/computed tomography (PET/CT) after injection of F¹⁸ -fluorodeoxyglucose (¹⁸ F-FDG) in adult kidney transplant recipients with surveillance biopsy at ~3 months posttransplantation. The Banff-2017 classification was used. The ratio of the mean standard uptake value (mSUVR) between kidney cortex and psoas muscle was measured. Urinary levels of CXCL-9 were concomitantly quantified. Our 92-patient cohort was categorized upon histology: normal (n = 70), borderline (n = 16), and SCR (n = 6). No clinical or biological difference was observed between groups. The mSUVR reached 1.87 ± 0.55, 1.94 ± 0.35, and 2.41 ± 0.54 in normal, borderline, and SCR groups, respectively. A significant difference in mSUVR was found among groups. Furthermore, mSUVR was significantly higher in the SCR vs normal group. The area under the receiver operating characteristic curve (AUC) was 0.79, with 83% sensitivity using an mSUVR threshold of 2.4. The AUC of urinary CXCL-9/creatinine ratios comparatively reached 0.79. The mSUVR positively correlated with ti and acute composite Banff scores. ¹⁸ F-FDG-PET/CT helps noninvasively exclude SCR, with a negative predictive value of 98%. External validations are required.

Serial Peripheral Blood Gene Expression Profiling to Assess Immune Quiescence in Kidney Transplant Recipients with Stable Renal Function

Background

TruGraf is a blood-based biomarker test that measures differential expression of a collection of genes that have been shown to correlate with surveillance biopsy results. However, in the majority of U.S. transplant centers, surveillance biopsies are not performed. The objectives of this study were to evaluate the clinical validity of TruGraf in stable kidney transplant recipients and to demonstrate the potential clinical utility of serial TruGraf testing in a center not utilizing surveillance biopsies.

Material/Methods

Serum creatinine levels, TruGraf testing at multiple time points, and subsequent clinical follow-up were obtained for 28 patients.

Results

Overall concordance of TruGraf results, when compared with independent clinical assessment of testing, was 77% (54/70) for all tests; 79% (22/28) for test 1, 75% (21/28) for test 2, and 79% (11/14) for test 3. The negative predictive value (NPV) was 98.0%. Analysis of clinical utility indicated that 77% of TruGraf results would have been useful in patient management.

Conclusions

Our results indicate the value of serial TruGraf testing in those transplant centers that do not perform surveillance biopsies as part of their standard of care. The high negative predictive value indicates the ability of TruGraf to confirm immune quiescence with a high degree of probability in patients with a Transplant eXcellence (TX) result, without the need to perform a surveillance biopsy.

Early subclinical tubulitis and interstitial inflammation in kidney transplantation have adverse clinical implications

This prospective observational cohort study compared the impact of subclinical tubulitis with or without interstitial inflammation to interstitial inflammation alone and to no inflammation in early post kidney transplant biopsies. A study cohort of 415 patients (living and deceased donor recipients) was divided into three groups on the basis of their three-month biopsy: 149 patients with No Inflammation (NI), 83 patients with Isolated Interstitial Inflammation (IIF), and 183 patients with Tubulitis [(with or without interstitial inflammation) (TIF) but not meeting criteria for Banff IA]. TIF was further divided into 56 patients with tubulitis without interstitial inflammation (TIF0) and 127 patients with tubulitis alongside interstitial inflammation (TIF1). TIF was significantly associated with higher incidence of subsequent T-cell mediated rejection (clinical or subclinical) at one year compared to IIF (31% vs 15%) and NI (31% vs 17%). Chronicity on one-year biopsy was significantly higher in TIF compared to IIF (22% vs 11%) and NI (22% vs 7%). De novo donor-specific antibody development was significantly higher in TIF compared to NI (6% vs 0.7%). Tubulitis subgroups (TIF0 and TIF1) revealed comparable effects on de novo donor-specific antibody and interstitial fibrosis/tubular atrophy development. However, tubulitis with interstitial inflammation had a significantly higher incidence of subsequent rejection and posed an increased hazard for the composite end point (subsequent acute rejection and death censored graft loss) compared to other groups [adjusted hazard 2.1 (95% confidence interval 1.2-3.5)]. Thus, subclinical tubulitis is a marker of adverse immunological events, but tubulitis with interstitial inflammation has a worse prognosis. Hence, the Banff 1997 (TIF1) and Banff 2005 classifications (TIF) for borderline change may have different implications.

Application of TruGraf v1: A Novel Molecular Biomarker for Managing Kidney Transplant Recipients With Stable Renal Function

TruGraf v1 is a laboratory-developed DNA microarray-based gene expression blood test to enable proactive noninvasive serial assessment of kidney transplant recipients with stable renal function. It has been previously validated in patients identified as Transplant eXcellence (TX: stable serum creatinine, normal biopsy results, indicative of immune quiescence), and not-TX (renal dysfunction and/or rejection on biopsy results). TruGraf v1 is intended for use in subjects with stable renal function to measure the immune status as an alternative to invasive, expensive, and risky surveillance biopsies.

MATERIALS AND METHODS

In this study, simultaneous blood tests and clinical assessments were performed in 192 patients from 7 transplant centers to evaluate TruGraf v1. The molecular testing laboratory was blinded to renal function and biopsy results.

RESULTS

Overall, TruGraf v1 accuracy (concordance between TruGraf v1 result and clinical and/or histologic assessment) was 74% (142/192), and a result of TX was accurate in 116 of 125 (93%). The negative predictive value for TruGraf v1 was 90%, with a sensitivity 74% and specificity of 73%. Results did not significantly differ in patients with a biopsy-confirmed diagnosis vs those without a biopsy.

CONCLUSIONS

TruGraf v1 can potentially support a clinical decision enabling unnecessary surveillance biopsies with high confidence, making it an invaluable addition to the transplant physician's tool kit for managing patients. TruGraf v1 testing can potentially avoid painful and risky invasive biopsies, reduce health care costs, and enable frequent assessment of patients with stable renal function to confirm the presence of immune quiescence in the peripheral blood.

Development and clinical validity of a novel blood-based molecular biomarker for subclinical acute rejection following kidney transplant

Noninvasive biomarkers are needed to monitor stable patients after kidney transplant (KT), because subclinical acute rejection (subAR), currently detectable only with surveillance biopsies, can lead to chronic rejection and graft loss. We conducted a multicenter study to develop a blood-based molecular biomarker for subAR using peripheral blood paired with surveillance biopsies and strict clinical phenotyping algorithms for discovery and validation. At a predefined threshold, 72% to 75% of KT recipients achieved a negative biomarker test correlating with the absence of subAR (negative predictive value: 78%-88%), while a positive test was obtained in 25% to 28% correlating with the presence of subAR (positive predictive value: 47%-61%). The clinical phenotype and biomarker independently and statistically correlated with a composite clinical endpoint (renal function, biopsy-proved acute rejection, ≥grade 2 interstitial fibrosis, and tubular atrophy), as well as with de novo donor-specific antibodies. We also found that <50% showed histologic improvement of subAR on follow-up biopsies despite treatment and that the biomarker could predict this outcome. Our data suggest that a blood-based biomarker that reduces the need for the indiscriminate use of invasive surveillance biopsies and that correlates with transplant outcomes could be used to monitor KT recipients with stable renal function, including after treatment for subAR, potentially improving KT outcomes.

Investigator Assessment of the Utility of the TruGraf Molecular Diagnostic Test in Clinical Practice

BACKGROUND

TruGraf v1 is a well-validated DNA microarray-based test that analyzes blood gene expression profiles as an indicator of immune status in kidney transplant recipients with stable renal function.

METHODS

In this study, investigators assessed clinical utility of the TruGraf test in patient management. In a retrospective study, simultaneous blood tests and clinical assessments were performed in 192 patients at 7 transplant centers, and in a prospective observational study they were performed in 45 subjects at 5 transplant centers.

RESULTS

When queried regarding whether or not the TruGraf test result impacted their decision regarding patient management, in 168 of 192 (87.5%) cases the investigator responded affirmatively. The prospective study indicated that TruGraf results supported physicians' decisions on patient management 87% (39/45) of the time, and in 93% of cases physicians indicated that they would use serial TruGraf testing in future patient management. A total of 21 of 39 (54%) reported results confirmed their decision that no intervention was needed, and 17 of 39 (44%) reported that results specifically informed them that a decision not to perform a surveillance biopsy was correct.

CONCLUSIONS

TruGraf is the first and only noninvasive test to be evaluated for clinical utility in determining rejection status of patients with stable renal function and shows promise of providing support for clinical decisions to avoid unnecessary surveillance biopsies with a high degree of confidence. TruGraf is an invaluable addition to the transplant physician's tool kit for managing patient health by avoiding painful and invasive biopsies, reducing health care costs, and enabling frequent assessment of patients with stable renal function to confirm immune quiescence.

Maintaining the Health of the Renal Allograft: Laboratory and Histologic Monitoring After Kidney Transplantation

Advances in posttransplant care, including new immunosuppressive medications have led to excellent short-term renal allograft survival. However, there is a small therapeutic window within which the patient and the clinician must balance the risk of rejection, with side effects such as infection, malignancy, and toxicity. Laboratory testing plays a key role in this ongoing monitoring, which includes relatively simple tests, such as serum creatinine, to complex tests, such as solid-phase assays, used to monitor for donor-specific antibody and surveillance allograft biopsies. This article reviews the role of the laboratory tests and surveillance biopsies in posttransplant monitoring.

Subclinical inflammation phenotypes and long-term outcomes after pediatric kidney transplantation

The implementation of surveillance biopsies in pediatric kidney transplantation remains controversial. Surveillance biopsies detect subclinical injury prior to clinical dysfunction, which could allow for early interventions that prolong allograft survival. We conducted a single-center retrospective cohort study of 120 consecutive pediatric kidney recipients, of whom 103 had surveillance biopsies ≤6 months posttransplant. We tested the hypothesis that subclinical inflammation (borderline or T cell-mediated rejection without clinical dysfunction) is associated with a 5-year composite endpoint of acute rejection and allograft failure. Overall, 36% of subjects had subclinical inflammation, which was associated with increased hazard for the composite endpoint (adjusted hazard ratio 2.89 [1.27, 6.57]; P < .01). Subjects with treated vs untreated subclinical borderline rejection had a lower incidence of the composite endpoint (41% vs 67%; P < .001). Subclinical vascular injury (subclinical inflammation with Banff arteritis score > 0) had a 78% incidence of the composite endpoint vs 11% in subjects with no major surveillance abnormalities (P < .001). In summary, we showed that subclinical inflammation phenotypes were prevalent in pediatric kidney recipients without clinical dysfunction and were associated with increased acute rejection and allograft failure. Once prospectively validated, our data would support implementation of surveillance biopsies as standard of care in pediatric kidney transplantation.