Biomarker-Development Proteomics in Kidney Transplantation: An Updated Review.

Kidney transplantation (KT) is the optimal therapeutic strategy for patients with end-stage renal disease. The key to post-transplantation management is careful surveillance of allograft function. Kidney injury may occur from several different causes that require different patient management approaches. However, routine clinical monitoring has several limitations and detects alterations only at a later stage of graft damage. Accurate new noninvasive biomarker molecules are clearly needed for continuous monitoring after KT in the hope that early diagnosis of allograft dysfunction will lead to an improvement in the clinical outcome. The advent of "omics sciences", and in particular of proteomic technologies, has revolutionized medical research. Proteomic technologies allow us to achieve the identification, quantification, and functional characterization of proteins/peptides in biological samples such as urine or blood through supervised or targeted analysis. Many studies have investigated proteomic techniques as potential molecular markers discriminating among or predicting allograft outcomes. Proteomic studies in KT have explored the whole transplant process: donor, organ procurement, preservation, and posttransplant surgery. The current article reviews the most recent findings on proteomic studies in the setting of renal transplantation in order to better understand the effective potential of this new diagnostic approach.

Artificial Urinary Biomarkers for Early Diagnosis of Acute Renal Allograft Rejection.

Acute renal allograft rejection (ARAR) after kidney transplantation associated with reduced graft survival and eventual graft failure is poorly diagnosed in hospitals. Here, we report the development of Artificial bioMarker Probes (AMPros) for sensitive urinalysis of ARAR in murine models. AMPros spontaneously go to the kidneys after systemic administration, specifically react with the prodromal immune biomarkers to activate their near-infrared fluorescence signals to report cell-mediated rejection, and efficiently undergo renal excretion into urine. Thus, AMPros enable convenient optical urinalysis that detects ARAR prior to histological manifestation of rejection, which is also earlier than current diagnostic methods measuring proinflammatory cytokines and peripheral blood lymphocyte mRNAs. Due to the high kidney specificity, AMPros-based urinalysis discriminates allograft rejection against other non-alloimmune specific diseases, which is unattainable by measurement of serological biomarkers. Such a noninvasive and sensitive urine test holds great promise in continuous monitoring of renal allograft conditions at low resource settings for timely clinical interventions.

Biomarker implementation: Evaluation of the decision-making impact of CXCL10 testing in a pediatric cohort.

BACKGROUND: Children are at high risk for subclinical rejection, and kidney biopsy is currently used for surveillance. Our objective was to test how novel rejection biomarkers such as urinary CXCL10 may influence clinical decision-making to indicate need for a biopsy. METHODS: A minimum dataset for standard decision-making to indicate a biopsy was established by an expert panel and used to design clinical vignettes for use in a survey. Pediatric nephrologists were recruited to review the vignettes and A) estimate rejection risk and B) decide whether to biopsy; first without and then with urinary CXCL10/Cr level. Accuracy of biopsy decisions was then tested against the biopsy results. IRA was assessed by Fleiss Kappa (κ) for binary choice and ICC for probabilities. RESULTS: Eleven pediatric nephrologists reviewed 15 vignettes each. ICC of probability assessment for rejection improved from poor (0.28, P < .01) to fair (0.48, P < .01) with addition of CXCL10/Cr data. It did not, however, improve the IRA for decision to biopsy (K = 0.48 and K = 0.43, for the comparison). Change in clinician estimated probability of rejection with additional CXCL10/Cr data was correlated with CXCL10/Cr level (r2  = 0.7756, P < .0001). Decision accuracy went from 8/15 (53.3%) cases to 11/15 (73.3%) with CXCL10/Cr, although improvement did not achieve statistical significance. Using CXCL10/Cr alone would have been accurate in 12/15 cases (80%). CONCLUSION: There is high variability in decision-making on biopsy indication. Urinary CXCL10/Cr improves probability estimates for risk of rejection. Training may be needed to assist nephrologists in better integrate biomarker information into clinical decision-making.

Urinary Extracellular Vesicles Are a Novel Tool to Monitor Allograft Function in Kidney Transplantation: A Systematic Review.

Extracellular vesicles (EVs) are nanoparticles that transmit molecules from releasing cells to target cells. Recent studies link urinary EVs (uEV) to diverse processes such as infection and rejection after kidney transplantation. This, and the unmet need for biomarkers diagnosing kidney transplant dysfunction, has led to the current high level of interest in uEV. uEV provide non-intrusive access to local protein, DNA, and RNA analytics without invasive biopsy. To determine the added value of uEV measurements for detecting allograft dysfunction after kidney transplantation, we systematically included all related literature containing directly relevant information, with the addition of indirect evidence regarding urine or kidney injury without transplantation. According to their varying characteristics, uEV markers after transplantation could be categorized into kidney-specific, donor-specific, and immune response-related (IR-) markers. A few convincing studies have shown that kidney-specific markers (PODXL, ion cotransporters, SYT17, NGAL, and CD133) and IR-markers (CD3, multi-mRNA signatures, and viral miRNA) could diagnose rejection, BK virus-associated nephropathy, and calcineurin inhibitor nephrotoxicity after kidney transplantation. In addition, some indirect proof regarding donor-specific markers (donor-derived cell-free DNA) in urine has been demonstrated. Together, this literature review provides directions for exploring novel uEV markers' profiling complications after kidney transplantation.

Unique and specific Proteobacteria diversity in urinary microbiota of tolerant kidney transplanted recipients.

Host-microbiota interactions can modulate the immune system both at local and systemic levels, with potential consequences for organ transplantation outcomes. In this study, we hypothesized that differences in the urinary microbiome following kidney transplantation would be associated with posttransplantation status: stable, minimally immunosuppressed, or tolerant. One hundred thirteen urine samples from stable (n = 51), minimally immunosuppressed (n = 19), and spontaneously tolerant (n = 16) patients, paired with age-matched controls (n = 27) were profiled and compared to each other at a taxonomic level with special interest in the immunosuppressive regimen. All comparisons and correlations were adjusted on sex and time posttransplantation. Our results highlighted a unique and specific urinary microbiota associated with spontaneous tolerance characterized by a high diversity and a clear Proteobacteria profile. Finally, we report that this profile is (1) impacted by gender, (2) inversely correlated with immunosuppressive drugs (calcineurin inhibitors and mammalian target of rapamycin inhibitors), and (3) stable in time.

Urinary nitrate concentration as a marker for kidney transplant rejection.

BACKGROUND: Early identification and treatment of kidney transplant rejection episodes is vital to limit loss of function and prolong the life of the transplanted kidney and recipient. Current practice depends on detecting a creatinine rise. A biomarker to diagnose transplant rejection at an earlier time point than current practice, or to inform earlier decision making to biopsy, could be transformative. It has previously been shown that urinary nitrate concentration is elevated in renal transplant rejection. Nitrate is a nitric oxide (NO) oxidation product. Transplant rejection upregulates NO synthesis via inducible nitric oxide synthase leading to elevations in urinary nitrate concentration. We have recently validated a urinary nitrate concentration assay which could provide results in a clinically relevant timeframe. Our aim was to determine whether urinary nitrate concentration is a useful tool to predict renal transplant rejection in the context of contemporary clinical practice. METHODS: We conducted a prospective observational study, recruiting renal transplant participants over an 18-month period. We made no alterations to the patients' clinical care including medications, immunosuppression, diet and frequency of visits. We collected urine samples from every clinical attendance. We assessed the urinary nitrate to creatinine ratio (uNCR) between patient groups: routine attendances, biopsy proven rejection, biopsy proven no rejection and other call backs. uNCR was examined over time for those with biopsy proven transplant rejection. These four groups were compared using an ANOVA test. RESULTS: A total of 2656 samples were collected. uNCR during biopsy proven rejection, n = 15 (median 49 µmol/mmol, IQR 23-61) was not significantly different from that of routine samples, n = 164 (median 55 µmol/mmol, IQR 37-82) (p = 0.55), or biopsy proven no rejection, n = 12 (median 39 µmol/mmol, IQR 21-89) (P = 0.77). Overall uNCR was highly variable with no diagnostic threshold for kidney transplant rejection. Furthermore, within-patient uNCR was highly variable over time, and thus it was not possible to produce individualised patient thresholds to identify rejection. The total taking Tacrolimus was 204 patients, with no statistical difference between the uNCR of all those on Tacrolimus, against those not, p = 0.18. CONCLUSION: The urinary nitrate to creatinine ratio is not a useful biomarker for renal transplant rejection.

Urinary Biomarkers for Diagnosis and Prediction of Acute Kidney Allograft Rejection: A Systematic Review.

Noninvasive tools for diagnosis or prediction of acute kidney allograft rejection have been extensively investigated in recent years. Biochemical and molecular analyses of blood and urine provide a liquid biopsy that could offer new possibilities for rejection prevention, monitoring, and therefore, treatment. Nevertheless, these tools are not yet available for routine use in clinical practice. In this systematic review, MEDLINE was searched for articles assessing urinary biomarkers for diagnosis or prediction of kidney allograft acute rejection published in the last five years (from January 1, 2015 to May 31, 2020). This review follows the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) guidelines. Articles providing targeted or unbiased urine sample analysis for the diagnosis or prediction of both acute cellular and antibody-mediated kidney allograft rejection were included, analyzed, and graded for methodological quality with a particular focus on study design and diagnostic test accuracy measures. Urinary C-X-C motif chemokine ligands were the most promising and frequently studied biomarkers. The combination of precise diagnostic reference in training sets with accurate validation in real-life cohorts provided the most relevant results and exciting groundwork for future studies.

Posttransplant muscle mass measured by urinary creatinine excretion rate predicts long-term outcomes after liver transplantation.

Long-term survival in orthotopic liver transplant (OLT) recipients remains impaired because of many contributing factors, including a low pretransplant muscle mass (or sarcopenia). However, influence of posttransplant muscle mass on survival is currently unknown. We hypothesized that posttransplant urinary creatinine excretion rate (CER), an established noninvasive marker of total body muscle mass, is associated with long-term survival after OLT. In a single-center cohort study of 382 adult OLT recipients, mean ± standard deviation CER at 1 year posttransplantation was 13.3 ± 3.7 mmol/24 h in men and 9.4 ± 2.6 mmol/24 h in women. During median follow-up for 9.8 y (interquartile range 6.4-15.0 y), 104 (27.2%) OLT recipients died and 44 (11.5%) developed graft failure. In Cox regression analyses, as continuous variable, low CER was associated with increased risk for mortality (HR = 0.43, 95% CI: 0.26-0.71, P = .001) and graft failure (HR = 0.42, 95% CI: 0.20-0.90, P = .03), independent of age, sex, and body surface area. Similarly, OLT recipients in the lowest tertile had an increased risk for mortality (HR = 2.69; 95% CI: 1.47-4.91, P = .001) and graft failure (HR = 2.77, 95% CI: 1.04-7.39, P = .04), compared to OLT recipients in the highest tertile. We conclude that 1 year posttransplant low total body muscle mass is associated with long-term risk of mortality and graft failure in OLT recipients.

Circular RNAs in Urine of Kidney Transplant Patients with Acute T Cell-Mediated Allograft Rejection.

BACKGROUND: Circular RNAs (circRNAs) have recently been described as novel noncoding regulators of gene expression. They are detectable in the blood of patients with acute kidney injury. We tested whether circRNAs were present in urine and could serve as new predictors of outcome in renal transplant patients with acute rejection. METHODS: A global circRNA expression analysis using RNA from urine of patients with acute T cell-mediated renal allograft rejection and control transplant patients was performed. Dysregulated circRNAs were confirmed in a cohort of 62 patients with acute rejection, 10 patients after successful antirejection therapy, 18 control transplant patients without rejection, and 13 stable transplant patients with urinary tract infection. RESULTS: A global screen revealed several circRNAs to be altered in urine of patients with acute rejection. Concentrations of 2 circRNAs including hsa_circ_0001334 and hsa_circ_0071475 were significantly increased. These were validated in the whole cohort of patients. hsa_circ_0001334 was upregulated in patients with acute rejection compared with controls. Concentrations of hsa_circ_0001334 normalized in patients with acute rejection following successful antirejection therapy. hsa_circ_0001334 was associated with higher decline in glomerular filtration rate 1 year after transplantation. CONCLUSIONS: CircRNA concentrations are significantly dysregulated in patients with acute rejection at subclinical time points. Urinary hsa_circ_0001334 is a novel biomarker of acute kidney rejection, identifying patients with acute rejection and predicting loss of kidney function.

Histopathologic Features that Predict Transplant Glomerulopathy Progression in a Chinese Cohort.

BACKGROUND: Transplant glomerulopathy (TG) represents a major cause of long-term allograft failure and is the leading cause of overall post-transplant proteinuria. The extent to which histopathologic features predicts prognostication is uncertain. METHODS: A single-center retrospective cohort with biopsy-proven TG was investigated. Renal biopsies were scored according to Banff 2017. The primary outcome was death-censored graft failure defined as return to dialysis or estimated glomerular filtration rate (eGFR) decreased to <15 mL/min/1.73 m2. The prognostic significance of clinical and histopathologic parameters was determined using Cox proportional hazards models. RESULTS: Data from 180 cases were available for analysis with a median follow-up of 5.0 (2.6-8.2) years. In multivariable models, ci + ct score (HR 3.1; 95% CI 2.0-4.9), cg score (HR 1.7; 95% CI 1.1-2.8), eGFR (HR 2.1; 95% CI 1.4-3.2) and proteinuria (HR 2.4; 95% CI 1.6-3.7) were independent predictors of the primary outcome. Mesangial Immunoglobulin A deposition did not significantly affect allograft survival. The only significant pathologic factors for the severity of proteinuria were cg and g + ptc (adjusted R2 = 0.46) as determined by multivariable stepwise linear regression analysis. CONCLUSIONS: Severe ci + ct and cg at biopsy were predictors of unfavorable allograft prognosis in TG patients even after taking into consideration clinical characteristics. Histologic severity of cg and g + ptc was significantly associated with clinical proteinuria.

Assessment of treatment efficacy using surface-enhanced Raman spectroscopy analysis of urine in rats with kidney transplantation or kidney disease.

BACKGROUND: Individuals who have kidney disease or kidney transplants need routine assessment of their kidney damage and function, which are largely measured based on histological examination of kidney biopsies, blood test, and urinalysis. These methods are practically difficult or inconvenient, and expensive. The objective of this study was to develop a model to estimate the kidney damage and function by surface-enhanced Raman spectroscopy (SERS). METHODS: Urine samples were collected from two previous studies: renal allograft recipient Lewis rats receiving anti-TGF-ß antibody or control antibody treatment and obese diabetic ZSF1 rats with kidney disease fed with whole grape powder-containing chow or control chow. Silver nanoparticle-based SERS spectra of urine were measured. SERS spectra were analyzed using principal component analysis (PCA) combined with linear discriminant analysis (LDA) and partial least squires (PLS) analysis. RESULTS: PCA/LDA separated anti-TGF-ß antibody-treated group from control group with 90% sensitivity and 70% specificity in kidney transplants, and grape-fed group from controls with 72.7% sensitivity and 60% specificity in diabetic kidneys. The receiver operating characteristic curves showed that the integration area under the curve was 0.850 ± 0.095 (p = 0.008) in kidney transplant groups and 0.800 ± 0.097 (p = 0.02) in diabetic kidney groups. PLS predicted the biochemical parameters of kidney function using the SERS spectra, resulting in R2 = 0.8246 (p < 0.001,urine protein), R2 = 0.8438 (p < 0.001, urine creatinine), R2 = 0.9265 (p < 0.001, urea), R2 = 0.8719 (p < 0.001, serum creatinine), and R2 = 0.6014 (p < 0.001, urine protein to creatinine ratio). CONCLUSION: Urine SERS spectral analysis suggesting that it may become a convenient method for rapid assessment of renal impairment.

Urinary Human Epididymis Secretory Protein 4 as a Useful Biomarker for Subclinical Acute Rejection Three Months after Kidney Transplantation.

Kidney transplantation is the treatment of choice for patients with advanced chronic kidney disease (CKD) and end stage renal disease (ESRD). However, acute rejection (AR) is a common complication in kidney transplantation and is associated with reduced graft survival. Current diagnosis of AR relies mainly on clinical monitoring including serum creatinine, proteinuria, and confirmation by histopathologic assessment in the biopsy specimen of graft kidney. Although an early protocol biopsy is indispensable for depicting the severity of pathologic lesions in subclinical acute rejection (subAR), it is not acceptable in some cases and cannot be performed because of its invasive nature. Therefore, we examined the detection of noninvasive biomarkers that are closely related to the pathology of subAR in protocol biopsies three months after kidney transplantation. In this study, the urinary level of microtubule-associated protein 1 light chain 3 (LC3), monocyte chemotactic protein-1 (MCP-1), liver-type fatty acid-binding protein (L-FABP), neutrophil gelatinase-associated lipocalin (NGAL), and human epididymis secretory protein 4 (HE4) were measured three months after kidney transplantation. Urine samples of 80 patients undergoing kidney transplantation between August 2014 to September 2016, were prospectively collected after three months. SubAR was observed in 11 patients (13.8%) in protocol biopsy. The urinary levels of LC3, MCP-1, NGAL, and HE4 were significantly higher in patients with subAR than in those without, while those of L-FABP did not differ between the two groups. Multivariate regression models, receiver-operating characteristics (ROC), and areas under ROC curves (AUC) were used to identify predicted values of subAR. Urinary HE4 levels were able to better identify subAR (AUC = 0.808) than the other four urinary biomarkers. In conclusion, urinary HE4 is increased in kidney transplant recipients of subAR three months after kidney transplantation, suggesting that HE4 has the potential to be used as a novel clinical biomarker for predicting subAR.

GC/MS-based urine metabolomics analysis of renal allograft recipients with acute rejection.

BACKGROUND: Acute renal allograft rejection is a common complication after renal transplantation that often leads to chronic rejection and ultimate graft loss. While renal allograft biopsy remains the gold standard for diagnosis of acute rejection, the possibility of biopsy-associated complications cannot be overlooked. The development of noninvasive methods for accurate detection of acute renal allograft rejection is thus of significant clinical importance. METHODS: Gas chromatography-mass spectrometry (GC/MS) was employed for analysis of urine metabolites in 15 renal allograft recipients with acute rejection and 15 stable renal transplant recipients. Partial least squares (PLS) regression and leave-one-out analyses were performed to ascertain whether the metabolites identified could be exploited to distinguish acute rejection from stable groups as well as their sensitivity and specificity. RESULTS: Overall, 14 metabolites were significantly altered in the acute rejection group (11 and 3 metabolites displayed higher and lower levels, respectively) relative to the stable transplant group. Data from PLS and leave-one-out analyses revealed that the differential metabolites identified not only distinguished acute rejection from stable transplant recipients but also showed high sensitivity and specificity for diagnosis of renal allograft recipients with acute rejection. CONCLUSION: Urine metabolites identified with GC/MS can effectively distinguish acute rejection from stable transplant recipients, supporting the potential utility of metabolome analysis in non-invasive diagnosis of acute rejection.

Identification of a urine metabolite constellation characteristic for kidney allograft rejection.

INTRODUCTION: Allograft rejection is still an important complication after kidney transplantation. Currently, monitoring of these patients mostly relies on the measurement of serum creatinine and clinical evaluation. The gold standard for diagnosing allograft rejection, i.e. performing a renal biopsy is invasive and expensive. So far no adequate biomarkers are available for routine use. OBJECTIVES: We aimed to develop a urine metabolite constellation that is characteristic for acute renal allograft rejection. METHODS: NMR-Spectroscopy was applied to a training cohort of transplant recipients with and without acute rejection. RESULTS: We obtained a metabolite constellation of four metabolites that shows promising performance to detect renal allograft rejection in the cohorts used (AUC of 0.72 and 0.74, respectively). CONCLUSION: A metabolite constellation was defined with the potential for further development of an in-vitro diagnostic test that can support physicians in their clinical assessment of a kidney transplant patient.

Urinary microbiome associated with chronic allograft dysfunction in kidney transplant recipients.

BACKGROUND: We performed a study to identify differences in the urinary microbiome associated with chronic allograft dysfunction (CAD) and compared the urinary microbiome of male and female transplant recipients with CAD. METHODS: This case-control study enrolled 67 patients within the Deterioration of Kidney Allograft Function (DeKAF) Genomics cohort at two transplant centers. CAD was defined as a greater than 25% rise in serum creatinine relative to a 3 month post-transplant baseline. Urine samples from patients with and without CAD were analyzed using 16S V4 bacterial ribosomal DNA sequences. RESULTS: Corynebacterium was more prevalent in female and male patients with CAD compared to non-CAD female patients (P = 0.0005). A total 21 distinct Operational Taxonomic Unit (OTUs) were identified as significantly different when comparing CAD and non-CAD patients using Kruskal-Wallis (P < 0.01). A subset analysis of female patients with CAD compared to non-CAD females identified similar differentially abundant OTUs, including the genera Corynebacterium and Staphylococcus (Kruskal-Wallis; P = 0.01; P = 0.004, respectively). Male CAD vs female CAD analysis showed greater abundance of phylum Proteobacteria in males. CONCLUSION: There were differences in the urinary microbiome when comparing female and male CAD patients with their female non-CAD counterparts and these differences persisted in the subset analysis limited to female patients only.

Urinary angiotensinogen level is increased in renal transplant recipients with masked hypertension and is correlated with left ventricular mass index and albuminuria in these patients.

Activation of the local renin-angiotensin system (RAS) is an independent risk factor for the development of proteinuria and left ventricular hypertrophy (LVH) more commonly seen in masked hypertensives. It has been reported that urinary angiotensinogen (UAGT) level provides a specific index of the intrarenal RAS status. The aim of this study was to evaluate the association between UAGT and left ventricular mass index (LVMI) and urinary albumin-creatinine ratio (UACR) in renal transplant recipients (RTRs) with masked hypertension (HT). A total of 116 non-diabetic-treated hypertensive RTRs were included in this study. The patients were divided into two groups: masked hypertensives and controlled hypertensives. Forty-two (36.2%) of RTRs had masked HT. Mean UACR and LVMI levels were higher in RTRs with masked HT than in RTRs with controlled HT (P < 0.001). UAGT level was also higher in masked hypertensives compared to controlled hypertensives (P < 0.001). Multivariable regression analysis showed that UAGT was positively correlated with UACR (ß = 0.024, P = 0.001) and LVMI (ß = 0.082, P = 0.001) in masked hypertensives. Consequently, masked HT was considerably frequent (36.2%) in treated hypertensive RTRs and high UAGT levels accompanied by high albuminuria and LVMI levels were seen in these patients. Overproduction of the UAGT may play a pivotal role in the development of LVH and proteinuria in masked hypertensives.

Liquid Biopsies to Monitor Solid Organ Transplant Function: A Review of New Biomarkers.

Despite modern immunosuppressive therapy, allograft rejection remains a major cause of solid organ transplant dysfunction. For clinical care, organ transplant function is routinely monitored by measuring biomarkers that, depending on the organ transplanted, include serum creatinine, N-terminal pro-hormone of brain natriuretic peptide (NT-proBNP), and aspartate aminotransferase. All can be measured easily in clinical chemistry laboratories. The main problem with these biomarkers is that they have a low sensitivity for the detection of allograft damage and are nonspecific for the detection of allograft rejection. To diagnose rejection, histologic examination of grafted tissue is necessary, which requires an invasive biopsy procedure. There is thus an unmet need in transplantation medicine for biomarkers that are specific for rejection, identify graft injury at an early stage, and may eventually overcome the need for a transplant biopsy. Recently, tremendous progress in the field of biomarkers has been made. In this narrative review, the potential of donor-derived cell-free DNA (ddcfDNA), cell-free nucleosomes, and extracellular vesicles to act as next-generation biomarkers for solid organ transplant is discussed. Based on the fact that cell content is released during rejection, these markers could serve as very specific biomarkers for allograft injury and rejection. These markers have the potential to improve rejection monitoring, evaluate the response to antirejection therapy, and may decrease the need for invasive procedures.

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.

Evolution of renal function and urinary biomarker indicators of inflammation on serial kidney biopsies in pediatric kidney transplant recipients with and without rejection.

Urinary CXCL10 and metabolites are biomarkers independently associated with TCMR. We sought to test whether these biomarkers fluctuate in association with histological severity of TCMR over short time frames. Forty-nine pairs of renal biopsies obtained 1-3 months apart from 40 pediatric renal transplant recipients were each scored for TCMR acuity score (i + t; Banff criteria). Urinary CXCL10:Cr and TCMR MDS were obtained at each biopsy and were tested for association with changes between biopsies in acuity, estimated GFR (ΔeGFR), and 12-month ΔeGFR. Sequential biopsies were obtained 1.8 ± 0.8 months apart. Biopsy 1 was usually obtained under protocol (75%), and 62% percent had evidence of TCMR. Using each biopsy pair for comparison, ΔeGFR did not predict change in acuity. By contrast, change in acuity was significantly correlated with change in urinary CXCL10:Cr (ρ 0.45, P = .003) and MDS (ρ 0.29, P = .04) between biopsies. The 12-month ΔeGFR was not predicted by TCMR acuity or CXCL10:Cr at Biopsy 2; however, an inverse correlation was seen with urinary MDS (ρ -0.35; P = .02). Changes in eGFR correlate poorly with evolving TCMR acuity on histology. Urinary biomarkers may be superior for non-invasive monitoring of rejection, including histological response to therapy, and may be prognostic for medium-term function.

Biomarkers to detect rejection after kidney transplantation.

Detecting acute rejection in kidney transplantation has been traditionally done using histological analysis of invasive allograft biopsies, but this method carries a risk and is not perfect. Transplant professionals have been working to develop more accurate or less invasive biomarkers that can predict acute rejection or subsequent worse allograft survival. These biomarkers can use tissue, blood or urine as a source. They can comprise individual molecules or panels, singly or in combination, across different components or pathways of the immune system. This review highlights the most recent evidence for biomarker efficacy, especially from multicenter trials.