Developing renal allograft surveillance strategies - urinary biomarkers of cellular rejection

Multicenter Validation of a Urine CXCL10 Assay for Noninvasive Monitoring of Renal Transplants

BACKGROUND

Urine CXCL10 (C-X-C motif chemokine ligand 10, interferon gamma-induced protein 10 [IP10]) outperforms standard-of-care monitoring for detecting subclinical and early clinical T-cell-mediated rejection (TCMR) and may advance TCMR therapy development through biomarker-enriched trials. The goal was to perform an international multicenter validation of a CXCL10 bead-based immunoassay (Luminex) for transplant surveillance and compare with an electrochemiluminescence-based (Meso Scale Discovery [MSD]) assay used in transplant trials.

METHODS

Four laboratories participated in the Luminex assay development and evaluation. Urine CXCL10 was measured by Luminex and MSD in 2 independent adult kidney transplant trial cohorts (Basel and TMCT04). In an independent test and validation set, a linear mixed-effects model to predict (log 10 -transformed) MSD CXCL10 from Luminex CXCL10 was developed to determine the conversion between assays. Net reclassification was determined after mathematical conversion.

RESULTS

The Luminex assay was precise, with an intra- and interassay coefficient of variation 8.1% and 9.3%; showed modest agreement between 4 laboratories (R 0.96 to 0.99, P < 0.001); and correlated with known CXCL10 in a single- (n = 100 urines, R 0.94 to 0.98, P < 0.001) and multicenter cohort (n = 468 urines, R 0.92, P < 0.001) but the 2 assays were not equivalent by Passing-Bablok regression. Linear mixed-effects modeling demonstrated an intercept of -0.490 and coefficient of 1.028, showing Luminex CXCL10 are slightly higher than MSD CXCL10, but the agreement is close to 1.0. After conversion of the biopsy thresholds, the decision to biopsy would be changed for only 6% (5/85) patients showing acceptable reclassification.

CONCLUSIONS

These data demonstrate this urine CXCL10 Luminex immunoassay is robust, reproducible, and accurate, indicating it can be readily translated into clinical HLA laboratories for serial posttransplant surveillance.

Getting immunosuppression just right: the role of clinical biomarkers in predicting patient response post solid organ transplantation

INTRODUCTION

Actually, immunosuppression selection isn't based on individual immune alloreactivity, and immunosuppressive drug dosing is mainly based on the development of toxicity and the achievement of specific target concentrations. Since a successful outcome requires optimal patient risk stratification and treatment, several groups have evaluated candidate biomarkers that have shown promise in the assessment of individual immune responses, the prediction of personal pharmacodynamic effects of immunosuppressive drugs and the prognosis and diagnosis of graft outcomes..

AREAS COVERED

This review includes biomarkers that the Scientific Community in Solid Organ Transplantation currently considers to have potential as diagnostic and prognostic biomarkers of graft evolution. We have focused on recent scientific advances and expert recommendations regarding the role of specific and non-specific pharmacodynamic biomarkers that are mainly involved in the T-cell-mediated response.

EXPERT OPINION

Integral pharmacologic monitoring that combines pharmacokinetics, pharmacogenetics and predictive pharmacodynamic biomarkers may provide crucial information and allow personal adjustment of immunosuppressive drugs at an early stage before severe adverse events ensue. Multicentre, randomized, prospective and interventional trials are needed to fine tune the established cut-off values for each biomarker and the optimal monitoring frequency for each biomarker and to accurately evaluate possible clinical confounding factors to enable correct clinical qualification.

Early postoperative urinary MCP-1 as a potential biomarker predicting acute rejection in living donor kidney transplantation: a prospective cohort study

We investigated the clinical relevance of urinary cytokines/chemokines reflecting intrarenal immunologic micromilieu as prognostic markers and the optimal measurement timing after living donor kidney transplantation (LDKT). This prospective cohort study included 77 LDKT patients who were followed for ≥ 5 years. Patients were divided into control (n = 42) or acute rejection (AR, n = 35) group. Early AR was defined as AR occurring within 3 months. Serum and urine cytokines/chemokines were measured serially as follows: intraoperative, 8/24/72 h, 1 week, 3 months, and 1 year after LDKT. Intrarenal total leukocytes, T cells, and B cells were analyzed with immunohistochemistry followed by tissueFAXS. Urinary MCP-1 and fractalkine were also analyzed in a validation cohort. Urinary MCP-1 after one week was higher in the AR group. Urinary MCP-1, fractalkine, TNF-α, RANTES, and IL-6 after one week were significantly higher in the early AR group. Intrarenal total leukocytes and T cells were elevated in the AR group compared with the control group. Urinary fractalkine, MCP-1, and IL-10 showed positive correlation with intrarenal leukocyte infiltration. Post-KT 1 week urinary MCP-1 showed predictive value in the validation cohort. One-week post-KT urinary MCP-1 may be used as a noninvasive diagnostic marker for predicting AR after LDKT.

Urinary CXCL10 Measurement in Late Renal Allograft Biopsies Predicts Outcome Even in Histologically Quiescent Patients

BACKGROUND

CXCL10 is a promising early noninvasive diagnostic marker for allograft rejection and predictive for long-term outcomes. However, its value when measured later in the posttransplant course has not yet been accurately analyzed.

METHODS

We investigated urinary CXCL10 in 141 patients from a prospective, observational renal transplant cohort with 182 clinically indicated allograft biopsies performed >12 months posttransplant and corresponding urines. Urinary CXCL10 was retrospectively quantified on stored urines using the MSD V-Plex Chemokine Panel 1 sandwich immunoassay (Meso Scale Discovery). The primary outcome was a composite of allograft loss/renal function decline (>30% estimated glomerular filtration rate [eGFR]-decrease between index biopsy and last follow-up).

RESULTS

Seventy-two patients (51%) reached the primary outcome, and their urinary CXCL10 levels were significantly higher at the time of their biopsy compared with patients with stable allograft function (median 9.3 ng/mmol vs 3.3 ng/mmol, P < .0001). Time-to-endpoint analyses according to high/low urinary CXCL10 demonstrated that low urinary CXCL10 (≤7.0 ng/mmol) was associated with 73% 5-year event-free graft survival compared with 48% with high urinary CXCL10 (>7.0 ng/mmol; P = .0001). Even in histologically quiescent patients, high urinary CXCL10 was associated with inferior endpoint-free graft survival (P = .003), and it was an independent predictor of the primary outcome (P = .03).

CONCLUSIONS

This study demonstrates that urinary CXCL10 has a promising diagnostic performance for detection of late allograft rejection and is an independent predictor of long-term renal allograft outcomes, even in histologically quiescent patients.

Advantages of plasmatic CXCL-10 as a prognostic and diagnostic biomarker for the risk of rejection and subclinical rejection in kidney transplantation

This study evaluate the potential of plasmatic CXCL-10 (pCXCL-10) as a pre&post transplantation prognostic and diagnostic biomarker of T-cell-mediated rejection (TCMR), antibody-mediated rejection (ABMR) and subclinical rejection (SCR) risk in adult kidney recipients considering BKV and CMV infections as possible clinical confounder factors. Twenty-eight of 100 patients included experienced rejection (TCMR:14; ABMR:14); 8 SCR; 13 and 16 were diagnosed with BKV and CMV infection, respectively. Pre-transplantation pCXCL-10 was significantly increased in TCMR and ABMR and post-transplantation in TCMR, ABMR and SCR compared with nonrejectors. All CMV⁺ patients showed pCXCL-10 levels above the cutoff values established for rejection whereas the 80% of BKV⁺ patients showed pCXCL-10 concentration < 100 pg/mL. pCXCL-10 could improve pre-transplantation patient stratification and immunosuppressive treatment selection according to rejection risk; and after kidney transplantation could be a potential early prognostic biomarker for rejection. Clinical confounding factor in BKV⁺ and particularly in CMV⁺ patients must be discarded.

[Urinary biomarkers in kidney transplant recipients: From technological innovations to clinical development]

In kidney transplantation, the assessment of individual risks remains highly imperfect and highlights the need for robust noninvasive biomarkers with the overall goal to improve patient and graft outcomes. In the field of noninvasive biomarkers discovery, urinary biomarkers are promising tools which use easily accessible biological fluid. During the past decades, the technical revolution in the fields of genetics and molecular biology, and advances in chemistry and data analysis have led to a wealth of studies using urinary cell pellets or supernatants from kidney transplant recipients. Transcriptomic, proteomic and metabonomic analyses have suggested numerous signatures for the diagnoses of acute rejection, delayed-graft function or interstitial fibrosis. Nevertheless, the translation and validation of exploratory findings and their implementation into standard clinical practice remain challenging. This requires dedicated prospective interventional trials demonstrating that the use of these biomarkers avoids invasive procedures and improves patient or transplant outcomes.

Urinary C-X-C Motif Chemokine 10 Is Related to Acute Graft Lesions Secondary to T Cell- and Antibody-Mediated Damage

Background

Non-invasive biomarkers of graft rejection are needed to optimize the management and outcomes of kidney transplant recipients. Urinary excretion of IFN-γ-related chemokine CXCL10 is clearly associated with clinical and subclinical T cell-mediated graft inflammation, but its relationship with antibody-mediated damage has not been fully addressed. Further, the variables influencing levels of urinary CXCL10 excretion are unknown.

Material/Methods

A total of 151 kidney graft biopsies (92 surveillance and 59 indication biopsies) and 151 matched urine samples obtained before biopsy were prospectively analyzed. T cell-mediated rejection (TCMR) and antibody-mediated rejection (AbMR) were defined according to the 2017 Banff classification criteria. Urinary CXCL10 levels were measured by ELISA and corrected by urinary creatinine.

Results

Banff scores ‘t’, ‘i’, ‘g’, and ‘ptc’ were significantly related to urinary CXCL10 levels. Multivariate analysis showed that ‘t’ (β=0.107, P=0.001) and ‘ptc’ (β=0.093, P=0.002) were significantly associated with urinary CXCL10. Donor-specific antibodies (DSAs) were related to the high excretion of urinary CXCL10 at 1 year after transplantation (odds ratio [OR] 17.817, P=0.003). Urinary CXCL10 showed good discrimination ability for AbMR (AUC-ROC 0.760, P=0.001). The third tertile of urinary CXCL10 remained significantly associated with AbMR (OR 4.577, 95% confidence interval 1.799–11.646, P=0.001) after multivariate regression analysis.

Conclusions

DSA was the only variable clearly related to high urinary CXCL10 levels. Urinary CXCL10 is a good non-invasive candidate biomarker of AbMR and TCMR, supplying information independent of renal function and other variables normally used to monitor kidney transplants.

Altered Phosphorylation of Cytoskeleton Proteins in Peripheral Blood Mononuclear Cells Characterizes Chronic Antibody-Mediated Rejection in Kidney Transplantation

Chronic antibody-mediated rejection (CAMR) is the major cause of kidney transplant failure. The molecular mechanisms underlying this event are still poorly defined and this lack of knowledge deeply influences the potential therapeutic strategies. The aim of our study was to analyze the phosphoproteome of peripheral blood mononuclear cells (PBMCs), to identify cellular signaling networks differentially activated in CAMR. Phosphoproteins isolated from PBMCs of biopsy proven CAMR, kidney transplant recipients with normal graft function and histology and healthy immunocompetent individuals, have been investigated by proteomic analysis. Phosphoproteomic results were confirmed by Western blot and PBMCs’ confocal microscopy analyses. Overall, 38 PBMCs samples were analyzed. A differential analysis of PBMCs’ phosphoproteomes revealed an increase of lactotransferrin, actin-related protein 2 (ARPC2) and calgranulin-B in antibody-mediated rejection patients, compared to controls. Increased expression of phosphorylated ARPC2 and its correlation to F-actin filaments were confirmed in CAMR patients. Our results are the first evidence of altered cytoskeleton organization in circulating immune cells of CAMR patients. The increased expression of phosphorylated ARPC2 found in the PBMCs of our patients, and its association with derangement of F-actin filaments, might suggest that proteins regulating actin dynamics in immune cells could be involved in the mechanism of CAMR of kidney grafts.

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.

Activity-based protein profiling guided identification of urine proteinase 3 activity in subclinical rejection after renal transplantation

Background

The pathophysiology of subclinical versus clinical rejection remains incompletely understood given their equivalent histological severity but discordant graft function. The goal was to evaluate serine hydrolase enzyme activities to explore if there were any underlying differences in activities during subclinical versus clinical rejection.

Methods

Serine hydrolase activity-based protein profiling (ABPP) was performed on the urines of a case control cohort of patients with biopsy confirmed subclinical or clinical transplant rejection. In-gel analysis and affinity purification with mass spectrometry were used to demonstrate and identify active serine hydrolase activity. An assay for proteinase 3 (PR3/PRTN3) was adapted for the quantitation of activity in urine.

Results

In-gel ABPP profiles suggested increased intensity and diversity of serine hydrolase activities in urine from patients undergoing subclinical versus clinical rejection. Serine hydrolases (n = 30) were identified by mass spectrometry in subclinical and clinical rejection patients with 4 non-overlapping candidates between the two groups (i.e. ABHD14B, LTF, PR3/PRTN3 and PRSS12). Western blot and the use of a specific inhibitor confirmed the presence of active PR3/PRTN3 in samples from patients undergoing subclinical rejection. Analysis of samples from normal donors or from several serial post-transplant urines indicated that although PR3/PRTN3 activity may be highly associated with low-grade subclinical inflammation, the enzyme activity was not restricted to this patient group.

Conclusions

There appear to be limited qualitative and quantitative differences in serine hydrolase activity in patients with subclinical versus clinical renal transplant rejection. The majority of enzymes identified were present in samples from both groups implying that in-gel quantitative differences may largely relate to the activity status of shared enzymes. However qualitative compositional differences were also observed indicating differential activities. The PR3/PRTN3 analyses indicate that the activity status of urine in transplant patients is dynamic possibly reflecting changes in the underlying processes in the transplant. These data suggest that differential serine hydrolase pathways may be active in subclinical versus clinical rejection which requires further exploration in larger patient cohorts. Although this study focused on PR3/PRTN3, this does not preclude the possibility that other enzymes may play critical roles in the rejection process.

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.

Longitudinal assessment of the CXCL10 blood and urine concentration in kidney transplant recipients with BK polyomavirus replication-a retrospective study

In kidney transplant recipients (KTRs), BK polyomavirus (BKPyV) replication may progress to polyomavirus‐associated nephropathy (PVAN). In this retrospective study, we assessed the chemokine CXCL10 in urine and blood samples consecutively acquired from 85 KTRs who displayed different stages of BKPyV replication and eventually developed PVAN. In parallel to progression toward PVAN, CXCL10 gradually increased in blood and urine, from baseline (prior to virus replication) to BKPyV DNAuria (median increase in blood: 42.15 pg/ml, P = 0.0156), from mere DNAuria to low‐ and high‐level BKPyV DNAemia (median increase: 52.60 and 87.26 pg/ml, P = 0.0010 and P = 0.0002, respectively) and peaked with histologically confirmed PVAN (median increase: 145.00 pg/ml, P < 0.0001). CXCL10 blood and urine levels significantly differed among KTRs with respect to simultaneous presence of human cytomegalovirus (P < 0.001) as well as in relation to the clinical severity of respective BKPyV DNAemia episodes (P = 0.0195). CXCL‐10 concentrations were particularly lower in KTRs in whom BKPyV DNAemia remained without clinical evidence for PVAN, as compared to individuals who displayed high decoy cell levels, decreased renal function and/or biopsy‐proven PVAN (median blood concentration: 266.97 vs. 426.42 pg/ml, P = 0.0282). In conclusion, in KTRs CXCL10 rises in parallel to BKPyV replication and correlates with the gradual development of PVAN.

Multicentre randomised controlled trial protocol of urine CXCL10 monitoring strategy in kidney transplant recipients

INTRODUCTION

Subclinical inflammation is an important predictor of death-censored graft loss, and its treatment has been shown to improve graft outcomes. Urine CXCL10 outperforms standard post-transplant surveillance in observational studies, by detecting subclinical rejection and early clinical rejection before graft functional decline in kidney transplant recipients.

METHODS AND ANALYSIS

This is a phase ii/iii multicentre, international randomised controlled parallel group trial to determine if the early treatment of rejection, as detected by urine CXCL10, will improve kidney allograft outcomes. Incident adult kidney transplant patients (n~420) will be enrolled to undergo routine urine CXCL10 monitoring postkidney transplant. Patients at high risk of rejection, defined as confirmed elevated urine CXCL10 level, will be randomised 1:1 stratified by centre (n=250). The intervention arm (n=125) will undergo a study biopsy to check for subclinical rejection and biopsy-proven rejection will be treated per protocol. The control arm (n=125) will undergo routine post-transplant monitoring. The primary outcome at 12 months is a composite of death-censored graft loss, clinical biopsy-proven acute rejection, de novo donor-specific antibody, inflammation in areas of interstitial fibrosis and tubular atrophy (Banff i-IFTA, chronic active T-cell mediated rejection) and subclinical tubulitis on 12-month surveillance biopsy. The secondary outcomes include decline of graft function, microvascular inflammation at 12 months, development of IFTA at 12 months, days from transplantation to clinical biopsy-proven rejection, albuminuria, EuroQol five-dimension five-level instrument, cost-effectiveness analysis of the urine CXCL10 monitoring strategy and the urine CXCL10 kinetics in response to rejection therapy.

ETHICS AND DISSEMINATION

The study has been approved by the University of Manitoba Health Research Ethics Board (HS20861, B2017:076) and the local research ethics boards of participating centres. Recruitment commenced in March 2018 and results are expected to be published in 2023. De-identified data may be shared with other researchers according to international guidelines (International Committee of Medical Journal Editors [ICJME]).

TRIAL REGISTRATION NUMBER

NCT03206801; Pre-results.

Recent Advancements in the Assessment of Renal Transplant Dysfunction with an Emphasis on Microarray Molecular Diagnostics

Conventional assessment of renal transplant rejection and injury through use of histology, C4d staining, and HLA antibody testing, has been the standard approach to transplant management. By many measures, these methods of conventional assessment may be considered flawed, particularly with the subjective nature of histologic diagnoses. The Alberta Transplant Applied Genomics Center has developed the Molecular Microscope diagnostic system, which uses microarrays to measure gene expression. These data are analyzed using classifiers (weighted equations) that compare the tested biopsy to a proprietary reference set of biopsies to provide objective measures of the status of the renal transplant.

The prognostic value of urinary chemokines at 6 months after pediatric kidney transplantation

Pediatric kidney transplantation is lifesaving, but long-term allograft survival is still limited by injury processes mediated by alloimmune inflammation that may otherwise be clinically silent. Chemokines associated with alloimmune inflammation may offer prognostic value early post-transplant by identifying patients at increased risk of poor graft outcomes. We conducted a single-center prospective cohort study of consecutive pediatric kidney transplant recipients (<19 years). Urinary CCL2 and CXCL10 measured at 6 months post-transplant were evaluated for association with long-term eGFR decline, allograft survival, and concomitant acute cellular rejection histology. Thirty-eight patients with a mean age of 12.4 ± 4.6 years were evaluated. Urinary CCL2 was associated with eGFR decline until 6 months (ρ -0.43; P < .01), but not at later time points. Urinary CXCL10 was associated with eGFR decline at 36 months (ρ -0.49; P < .01), risk of 50% eGFR decline (HR = 1.04; P = .02), risk of allograft loss (HR = 1.05; P = .01), borderline rejection or rejection episodes 6-12 months post-transplant (r .41; P = .02), and Banff i + t score (r .47, P < .01). CCL2 and CXCL10 were also correlated with one another (ρ 0.54; P < .01). CCL2 and CXCL10 provide differing, but complementary, information that may be useful for early non-invasive prognostic testing in pediatric kidney transplant recipients.

New developments in transplant proteomics

PURPOSE OF REVIEW

Despite modern immunosuppression, renal allograft rejection remains a major contributor to graft loss. Novel biomarkers may help improve posttransplant outcomes through the early detection and treatment of rejection. Our objective is to provide an overview of proteomics, review recent discovery-based rejection studies, and explore innovative approaches in biomarker development.

RECENT FINDINGS

Urine MMP7 was identified as a biomarker of subclinical and clinical rejection using two-dimensional liquid chromatography tandem-mass spectrometry (LC-MS/MS) and improved the overall diagnostic discrimination of urine CXCL10 : Cr alone for renal allograft inflammation. A novel peptide signature to classify stable allografts from acute rejection, chronic allograft injury, and polyoma virus (BKV) nephropathy was identified using isobaric tag for relative and absolute quantitation (TRAQ) and label-free MS, with independent validation by selected reaction monitoring mass spectrometry (SRM-MS). Finally, an in-depth exploration of peripheral blood mononuclear cells identified differential proteoform expression in healthy transplants versus rejection.

SUMMARY

There is still much in the human proteome that remains to be explored, and further integration of renal, urinary, and exosomal data may offer deeper insight into the pathophysiology of rejection. Functional proteomics may be more biologically relevant than protein/peptide quantity alone, such as assessment of proteoforms or activity-based protein profiling. Discovery-based studies have identified potential biomarker candidates, but external validation studies are required.

Urinary Hepcidin-25 Is Elevated in Patients That Avoid Acute Kidney Injury Following Cardiac Surgery

Background:

Acute kidney injury (AKI) following cardiac surgery leads to increased morbidity and mortality. Characterization and validation of early biomarkers of AKI may ultimately facilitate early therapeutic intervention. We have previously identified that elevated urinary hepcidin-25 is inversely and independently associated with the development of AKI in adult cardiac surgery patients. Hepcidin-25 is an antimicrobial peptide that sequesters iron intracellularly, and its elevation following human ischemia reperfusion injury may represent a renoprotective response to minimize renal injury.

Objective:

Our goal was to validate urinary hepcidin-25 as a non-invasive biomarker in an independent cardiac surgery cohort, within the context of clinical AKI predictors.

Design:

Prospective observational cohort study.

Setting:

Adult cardiac surgery program at St. Boniface Hospital, Winnipeg, Manitoba, Canada.

Patients:

Adult cardiac surgery patients undergoing cardiopulmonary bypass (CPB), n = 306.

Measurements:

Urine hepcidin-25, measured on post-operative day (POD) 1.

Methods:

A prospective, observational cohort of adult CPB patients (n = 306) was collected with serial perioperative urine samples. Urine hepcidin-25 at POD 1 was measured by competitive ELISA. Its diagnostic performance was evaluated in conjunction with clinical parameters and the Thakar clinical prediction score, using multivariate logistic regression.

Results:

Urinary hepcidin-25 is elevated following cardiac surgery in AKI and non-AKI patients. Elevated urinary hepcidin-25 concentration was inversely associated with AKI on both univariate (odds ratio [OR]: 0.61, 95% confidence interval [CI]: 0.45-0.83, P = .002) and multivariate analysis (OR: 0.67, 95% CI: 0.50-0.95, P = .02). A combined model with clinical risk factors demonstrated that baseline estimated glomerular filtration rate (eGFR), diabetes mellitus, and urinary hepcidin-25 concentration had an overall area under the curve (AUC) of 0.82 (0.75-0.88) for predicting subsequent AKI development, which was superior to clinical prediction alone as determined by the Thakar score.

Limitations:

(1) A single-center observational study. (2) Polyclonal antibody–based competitive ELISA.

Conclusion:

Hepcidin-25 is inversely associated with AKI in a multivariate model when combined with eGFR and diabetes mellitus, with an overall AUC of 0.82. Notably, urinary hepcidin-25 improves on clinical AKI prediction compared to the Thakar score alone.

Biomarkers and a tailored approach for immune monitoring in kidney transplantation

A literature review on immune monitoring in kidney transplantation produced dozens of research articles and a multitude of promising biomarkers, all in the quest for the much sought after - but perennially elusive - “holy grail” of kidney biomarkers able to unequivocally predict acute transplant rejection vs non-rejection. Detection methodologies and study designs were many and varied. Hence the motivation for this editorial, which espouses the notion that in today’s kidney transplantation milieu, the judicious use of disease classifiers tailored to specific patient immune risks may be more achievable and productive in the long run and confer a greater advantage for patient treatment than the pursuit of a single “omniscient” biomarker. In addition, we desire to direct attention toward greater scrutiny of biomarker publications and decisions to implement biomarkers in practice, standardization of methods in the development of biomarkers and consideration for adoption of “biomarker-driven” biopsies. We propose “biomarker-driven” biopsies as an adjunctive to and/or alternative to random surveillance (protocol) biopsies or belated indication biopsies. The discovery of a single kidney transplantation biomarker would represent a major breakthrough in kidney transplantation practice, but until that occurs - if ever it does occur, other approaches offer substantial potential for unlocking prognostic, diagnostic and therapeutic options. We conclude our editorial with suggestions and recommendations for productively incorporating current biomarkers into diagnostic algorithms and for testing future biomarkers of acute rejection in kidney transplantation.

Biomarkers in renal transplantation: An updated review

Genomics, proteomics and molecular biology lead to tremendous advances in all fields of medical sciences. Among these the finding of biomarkers as non invasive indicators of biologic processes represents a useful tool in the field of transplantation. In addition to define the principal characteristics of the biomarkers, this review will examine the biomarker usefulness in the different clinical phases following renal transplantation. Biomarkers of ischemia-reperfusion injury and of delayed graft function are extremely important for an early diagnosis of these complications and for optimizing the treatment. Biomarkers predicting or diagnosing acute rejection either cell-mediated or antibody-mediated allow a risk stratification of the recipient, a prompt diagnosis in an early phase when the histology is still unremarkable. The kidney solid organ response test detects renal transplant recipients at high risk for acute rejection with a very high sensitivity and is also able to make diagnosis of subclinical acute rejection. Other biomarkers are able to detect chronic allograft dysfunction in an early phase and to differentiate the true chronic rejection from other forms of chronic allograft nephropathies no immune related. Finally biomarkers recently discovered identify patients tolerant or almost tolerant. This fact allows to safely reduce or withdrawn the immunosuppressive therapy.

Establishing Biomarkers in Transplant Medicine: A Critical Review of Current Approaches

Although the management of kidney transplant recipients has greatly improved over recent decades, the assessment of individual risks remains highly imperfect. Individualized strategies are necessary to recognize and prevent immune complications early and to fine-tune immunosuppression, with the overall goal to improve patient and graft outcomes. This review discusses current biomarkers and their limitations, and recent advancements in the field of noninvasive biomarker discovery. A wealth of noninvasive monitoring tools has been suggested that use easily accessible biological fluids such as urine and blood, allowing frequent and sequential assessments of recipient's immune status. This includes functional cell-based assays and the evaluation of molecular expression on a wide spectrum of platforms. Nevertheless, the translation and validation of exploratory findings and their implementation into standard clinical practice remain challenging. This requires dedicated prospective interventional trials demonstrating that the use of these biomarkers avoids invasive procedures and improves patient or transplant outcomes.

Changing Paradigms in the Management of Rejection in Kidney Transplantation: Evolving From Protocol-Based Care to the Era of P4 Medicine

PURPOSE OF REVIEW

P4 medicine denotes an evolving field of medicine encompassing predictive, preventive, personalized, and participatory medicine. Using the example of kidney allograft rejection because of donor-recipient incompatibility in human leukocyte antigens, this review outlines P4 medicine's relevance to the various stages of the kidney transplant cycle.

SOURCES OF INFORMATION

A search for English articles was conducted in Medline via OvidSP (up to August 18, 2016) using a combination of subject headings (MeSH) and free text in titles, abstracts, and author keywords for the concepts kidney transplantation and P4 medicine. The electronic database search was expanded further on particular subject headings.

FINDINGS

Available histocompatibility methods exemplify current applications of the predictive and preventive domains of P4 medicine in kidney transplant recipients' care. Pharmacogenomics are discussed as means to facilitate personalized immunosuppression regimens and promotion of active patient participation as a means to improve adherence.

LIMITATIONS

For simplicity, this review focuses on rejection. P4 medicine, however, should more broadly address health concerns in kidney transplant recipients, including competing outcomes such as infections, malignancies, and cardiovascular disease. This review highlights how biomarkers to evaluate these competing outcomes warrant validation and standardization prior to their incorporation into clinical practice.

IMPLICATIONS

Consideration of all 4 domains of the P4 medicine framework when caring for and/or studying kidney transplant recipients has the potential of increasing therapeutic efficiency, minimizing adverse effects, decreasing health care costs, and maximizing wellness. Technologies to gauge immune competency, immunosuppression requirements, and early/reversible immune-mediated injuries are required to optimize kidney transplant care.

Advances in diagnostics for transplant rejection

INTRODUCTION

Identification of allograft injury, including acute clinical and subclinical injury, is vital in increasing the longevity of the transplanted organ. Acute rejection, which occurs as a result of a variety of immune and non-immune factors including the infiltration of immune cells and antibodies to the donor specific epitopes, poses a significant risk to the organ. Recent years have marked an increase in the discovery of new genomic, transcriptomic, and proteomic biomarkers in molecular diagnostics, which offer better potential for personalized management of the transplanted organ by providing earlier detection of rejection episodes. Areas covered: This review was compiled from key word searches of full-text publications relevant to the field. Expert commentary: Many of the recent advancements in the molecular diagnostics of allograft injury show much promise, but before they can be fully realized further validation in larger sample sets must be conducted. Additionally, for better informed therapeutic decisions, more work must be completed to differentiate between different causes of injury. Moreover, the diagnostics field is looking at methodologies that allow for multiplexing, the ability to identify multiple targets simultaneously, in order to provide more robust biomarkers and better understanding.

Non-invasive approaches in the diagnosis of acute rejection in kidney transplant recipients, part II: omics analyses of urine and blood samples

Kidney transplantation (KTx) represents the best available treatment for patients with end-stage renal disease. Still, the full benefits of KTx are undermined by acute rejection (AR). The diagnosis of AR ultimately relies on transplant needle biopsy. However, such an invasive procedure is associated with a significant risk of complications and is limited by sampling error and interobserver variability. In the present review, we summarize the current literature about non-invasive approaches for the diagnosis of AR in kidney transplant recipients (KTRs), including in vivo imaging, gene-expression profiling and omics analyses of blood and urine samples. Most imaging techniques, such as contrast-enhanced ultrasound and magnetic resonance, exploit the fact that blood flow is significantly lowered in case of AR-induced inflammation. In addition, AR-associated recruitment of activated leucocytes may be detectable by 18F-fluorodeoxyglucose positron emission tomography. In parallel, urine biomarkers, including CXCL9/CXCL10 or a three-gene signature of CD3ε, CXCL10 and 18S RNA levels, have been identified. None of these approaches has yet been adopted in the clinical follow-up of KTRs, but standardization of analysis procedures may help assess reproducibility and comparative diagnostic yield in large, prospective, multicentre trials.

Non-invasive approaches in the diagnosis of acute rejection in kidney transplant recipients. Part I. In vivo imaging methods

Kidney transplantation (KTx) represents the best available treatment for patients with end-stage renal disease. Still, full benefits of KTx are undermined by acute rejection (AR). The diagnosis of AR ultimately relies on transplant needle biopsy. However, such an invasive procedure is associated with a significant risk of complications and is limited by sampling error and interobserver variability. In the present review, we summarize the current literature about non-invasive approaches for the diagnosis of AR in kidney transplant recipients (KTRs), including in vivo imaging, gene expression profiling and omics analyses of blood and urine samples. Most imaging techniques, like contrast-enhanced ultrasound and magnetic resonance, exploit the fact that blood flow is significantly lowered in case of AR-induced inflammation. In addition, AR-associated recruitment of activated leukocytes may be detectable by ¹⁸F-fluoro-deoxy-glucose positron emission tomography. In parallel, urine biomarkers, including CXCL9/CXCL10 or a three-gene signature of CD3ε, IP-10 and 18S RNA levels, have been identified. None of these approaches has been adopted yet in the clinical follow-up of KTRs, but standardization of procedures may help assess reproducibility and compare diagnostic yields in large prospective multicentric trials.