Identification of T Cell–Mediated Vascular Rejection After Kidney Transplantation by the Combined Measurement of 5 Specific MicroRNAs in Blood

Role of microRNAs in Immune Regulation with Translational and Clinical Applications

MicroRNAs (miRNAs) are 19-23 nucleotide long, evolutionarily conserved noncoding RNA molecules that regulate gene expression at the post-transcriptional level. In this review, involvement of miRNAs is summarized in the differentiation and function of immune cells, in anti-infective immune responses, immunodeficiencies and autoimmune diseases. Roles of miRNAs in anticancer immunity and in the transplantation of solid organs and hematopoietic stem cells are also discussed. Major focus is put on the translational clinical applications of miRNAs, including the establishment of noninvasive biomarkers for differential diagnosis and prediction of prognosis. Patient selection and response prediction to biological therapy is one of the most promising fields of application. Replacement or inhibition of miRNAs has enormous therapeutic potential, with constantly expanding possibilities. Although important challenges still await solutions, evaluation of miRNA fingerprints may contribute to an increasingly personalized management of immune dysregulation with a remarkable reduction in toxicity and treatment side effects. More detailed knowledge of the molecular effects of physical exercise and nutrition on the immune system may facilitate self-tailored lifestyle recommendations and advances in prevention.

MicroRNAs as Potential Graft Rejection or Tolerance Biomarkers and Their Dilemma in Clinical Routines Behaving like Devilish, Angelic, or Frightening Elements

Allograft rejection is a widespread complication in allograft recipients with chronic kidney disease. Undertreatment of subclinical and clinical rejection and later post-transplant problems are caused by an imperfect understanding of the mechanisms at play and a lack of adequate diagnostic tools. Many different biomarkers have been analyzed and proposed to detect and monitor these crucial events in transplant outcomes. In this sense, microRNAs may help diagnose rejection or tolerance and indicate appropriate treatment, especially in patients with chronic allograft rejection. As key epigenetic regulators of physiological homeostasis, microRNAs have therapeutic potential and may indicate allograft tolerance or rejection. However, more evidence and clinical validation are indispensable before microRNAs are ready for clinical prime time.

Serum TGF-β as a predictive biomarker for severe disease and fatality of COVID-19

For targeted intervention in coronavirus disease 2019 (COVID-19), there is a high medical need for biomarkers that predict disease progression and severity in the first days after symptom onset. This study assessed the utility of early transforming growth factor β (TGF-β) serum levels in COVID-19 patients to predict disease severity, fatality, and response to dexamethasone therapy. Patients with severe COVID-19 had significantly higher TGF-β levels (416 pg/mL) as compared to patients with mild (165 pg/mL, p < 0.0001) or moderate COVID-19 (241 pg/mL; p < 0.0001). Receiver operating characteristics area under the curve values were 0.92 (95% confidence interval [CI] 0.85-0.99, cut-off: 255 pg/mL) for mild versus severe COVID-19, and 0.83 (95% CI 0.65-1.0, cut-off: 202 pg/mL) for moderate versus severe COVID-19. Patients who died of severe COVID-19 had significantly higher TGF-β levels (453 pg/mL) as compared to convalescent patients (344 pg/mL), and TGF-β levels predicted fatality (area under the curve: 0.75, 95% CI 0.53-0.96). TGF-β was significantly reduced in severely ill patients treated with dexamethasone (301 pg/mL) as compared to untreated patients (416 pg/mL; p < 0.05). Early TGF-β serum levels in COVID-19 patients predict, with high accuracy, disease severity, and fatality. In addition, TGF-β serves as a specific biomarker to assess response to dexamethasone treatment.

Molecular immune monitoring in kidney transplant rejection: a state-of-the-art review

Although current regimens of immunosuppressive drugs are effective in renal transplant recipients, long-term renal allograft outcomes remain suboptimal. For many years, the diagnosis of renal allograft rejection and of several causes of renal allograft dysfunction, such as chronic subclinical inflammation and infection, was mostly based on renal allograft biopsy, which is not only invasive but also possibly performed too late for proper management. In addition, certain allograft dysfunctions are difficult to differentiate from renal histology due to their similar pathogenesis and immune responses. As such, non-invasive assays and biomarkers may be more beneficial than conventional renal biopsy for enhancing graft survival and optimizing immunosuppressive drug regimens during long-term care. This paper discusses recent biomarker candidates, including donor-derived cell-free DNA, transcriptomics, microRNAs, exosomes (or other extracellular vesicles), urine chemokines, and nucleosomes, that show high potential for clinical use in determining the prognosis of long-term outcomes of kidney transplantation, along with their limitations.

Development and validation of urinary exosomal microRNA biomarkers for the diagnosis of acute rejection in kidney transplant recipients

Introduction

Acute rejection (AR) continues to be a significant obstacle for short- and long-term graft survival in kidney transplant recipients. Herein, we aimed to examine urinary exosomal microRNAs with the objective of identifying novel biomarkers of AR.

Materials and methods

Candidate microRNAs were selected using NanoString-based urinary exosomal microRNA profiling, meta-analysis of web-based, public microRNA database, and literature review. The expression levels of these selected microRNAs were measured in the urinary exosomes of 108 recipients of the discovery cohort using quantitative real-time polymerase chain reaction (qPCR). Based on the differential microRNA expressions, AR signatures were generated, and their diagnostic powers were determined by assessing the urinary exosomes of 260 recipients in an independent validation cohort.

Results

We identified 29 urinary exosomal microRNAs as candidate biomarkers of AR, of which 7 microRNAs were differentially expressed in recipients with AR, as confirmed by qPCR analysis. A three-microRNA AR signature, composed of hsa-miR-21-5p, hsa-miR-31-5p, and hsa-miR-4532, could discriminate recipients with AR from those maintaining stable graft function (area under the curve [AUC] = 0.85). This signature exhibited a fair discriminative power in the identification of AR in the validation cohort (AUC = 0.77).

Conclusion

We have successfully demonstrated that urinary exosomal microRNA signatures may form potential biomarkers for the diagnosis of AR in kidney transplantation recipients.

Donor-derived cell-free DNA as a diagnostic tool in transplantation

There is a need to improve personalized immunosuppression in organ transplantation to reduce premature graft loss. Biomarkers are needed to better detect rejection, asymptomatic graft injury, and under-immunosuppression. Assessment of minimal necessary exposure to guide tapering and prevent immune activation is also important. There is robust clinical evidence from a large number of published studies supporting the role of dd-cfDNA for monitoring graft integrity and detection or exclusion of rejection. Dd-cfDNA indicates graft cell death without being rejection specific. It can be determined in plasma through droplet digital PCR using preselected SNPs or next generation sequencing. Changes in recipient cfDNA (e.g., by infection) can affect the results of dd-cfDNA fractional determination. This limitation can be overcome using absolute dd-cfDNA quantification. The combination of fractional and absolute determination including total cfDNA is recommended for meaningful interpretation of the results. The value proposition for the patient includes earlier transplant injury detection and intervention, less full blown rejection risk, an alternative to invasive biopsies, and personalized immunosuppression with potential for improved long-term outcome. Transplant physicians benefit from better immunosuppressive guidance and having an alternative when biopsies are refused or contraindicated. Further advantages are improved biopsy interpretation, less trial and error changes in immunosuppression, and less time dealing with complications. The laboratory medicine specialist can provide more effective services. Hospital management and insurance companies could benefit from more cost-effective surveillance of transplant recipients. Potential cost savings would result from fewer biopsies as a result of the tests’ high negative predictive value, fewer re-transplantations, and less organ failure with return to dialysis. A pathway to implementation and metrics is suggested to measure the effectiveness of dd-cfDNA testing.

MicroRNAs in kidney injury and disease

MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression by degrading or repressing the translation of their target messenger RNAs. As miRNAs are critical regulators of cellular homeostasis, their dysregulation is a crucial component of cell and organ injury. A substantial body of evidence indicates that miRNAs are involved in the pathophysiology of acute kidney injury (AKI), chronic kidney disease and allograft damage. Different subsets of miRNAs are dysregulated during AKI, chronic kidney disease and allograft rejection, which could reflect differences in the physiopathology of these conditions. miRNAs that have been investigated in AKI include miR-21, which has an anti-apoptotic role, and miR-214 and miR-668, which regulate mitochondrial dynamics. Various miRNAs are downregulated in diabetic kidney disease, including the miR-30 family and miR-146a, which protect against inflammation and fibrosis. Other miRNAs such as miR-193 and miR-92a induce podocyte dedifferentiation in glomerulonephritis. In transplantation, miRNAs have been implicated in allograft rejection and injury. Further work is needed to identify and validate miRNAs as biomarkers of graft function and of kidney disease development and progression. Use of combinations of miRNAs together with other molecular markers could potentially improve diagnostic or predictive power and facilitate clinical translation. In addition, targeting specific miRNAs at different stages of disease could be a promising therapeutic strategy.

Noninvasive Assessment of the Alloimmune Response in Kidney Transplantation

Transplantation remains the optimal mode of kidney replacement therapy, but unfortunately long-term graft survival after 1 year remains suboptimal. The main mechanism of chronic allograft injury is alloimmune, and current clinical monitoring of kidney transplants includes measuring serum creatinine, proteinuria, and immunosuppressive drug levels. The most important biomarker routinely monitored is human leukocyte antigen (HLA) donor-specific antibodies (DSAs) with the frequency based on underlying immunologic risk. HLA-DSA should be measured if there is graft dysfunction, immunosuppression minimization, or nonadherence. Antibody strength is semiquantitatively estimated as mean fluorescence intensity, with titration studies for equivocal cases and for following response to treatment. Determination of in vitro C1q or C3d positivity or HLA-DSA IgG subclass analysis remains of uncertain significance, but we do not recommend these for routine use. Current evidence does not support routine monitoring of non-HLA antibodies except anti-angiotensin II type 1 receptor antibodies when the phenotype is appropriate. The monitoring of both donor-derived cell-free DNA in blood or gene expression profiling of serum and/or urine may detect subclinical rejection, although mainly as a supplement and not as a replacement for biopsy. The optimal frequency and cost-effectiveness of using these noninvasive assays remain to be determined. We review the available literature and make recommendations.

The Role of Immune-Related miRNAs in the Pathology of Kidney Transplantation

MicroRNAs (miRNAs) are members of the non-coding regulatory RNA family that play pivotal roles in physiological and pathological conditions, including immune response. They are particularly interesting as promising therapeutic targets, prognostic and diagnostic markers due to their easy detection in body fluids and stability. There is accumulating evidence that different miRNAs provide disease-specific signatures in liquid samples of distinct kidney injuries. Using experimental models and human samples, there have been numerous suggestions that immune-related miRNAs are also important contributors to the development of different kidney diseases as well as important markers for monitoring response after kidney transplantation. However, there are limited data for understanding their function in the molecular pathways of allograft pathologies. In our review, we focused on microRNAs that are related to different aspects of immune response after kidney transplantation.

MicroRNAs: small molecules, big effects

PURPOSE OF REVIEW

In kidney transplantation, microRNAs (miRNAs) have been extensively studied over the past decade, and panels of differentially expressed miRNAs have been identified from various body fluids/tissues, including blood, plasma, urine, or allograft biopsies, and in various conditions, such as acute T-cell-mediated and antibody-mediated rejections, chronic allograft rejection, interstitial fibrosis and tubular atrophy, acute tubular necrosis or BKV nephropathy.

RECENT FINDINGS

This review outlines our current knowledge regarding the complexity of miRNA regulation in fine-tuning expression of two-thirds of the human genome and the potential of miRNAs as biomarkers, based on an increasing number of case--control studies with, however, no evidence of short-term clinical development. Instead, a progressive change in study objectives is reported, with the most recent literature using miRNA-targeted genes as entry points for studying disease pathways.

SUMMARY

Our nascent understanding of their presumed roles in alloimmunity suggests that miRNAs are key regulators in many allograft injuries. Future directions should investigate how the integration of miRNAs with other layers of molecular data, such as genomic, transcriptomic, or proteomic data, could help to characterize the cellular interactions involved in allograft rejection and whether miRNA-based therapy could be of relevance for transplant medicine.

Advances of miRNAs in kidney graft injury

Kidney transplantation is the preferred treatment for patients with end-stage renal disease. However, various types of kidney graft injury after transplantation are still key factors that affect the survival of the kidney graft. Therefore, exploring the underlying mechanisms involved is very important. Current diagnostic measures for kidney graft injury (including needle biopsy, blood creatinine, eGFR, etc.) have many limiting factors such as invasiveness, insufficient sensitivity and specificity, so they cannot provide timely and effective information to clinicians. As for kidney grafts that have occurred injury, the traditional treatment has a little efficacy and many side effects. Therefore, there is an urgent need for developing new biomarkers and targeted treatment for kidney graft injury. Recently, studies have found that miRNAs are involved in the regulation of the progression of kidney graft injury. At the same time, it has high stability in blood, urine, and other body fluids, so it is suggested to have the potential as a biomarker and therapeutic target for kidney graft injury. Here, we reviewed the miRNAs involved in the pathophysiology of kidney graft injury such as ischemia/reperfusion injury, acute rejection, drug-induced nephrotoxicity, chronic allograft dysfunction, BK virus infection, and the latest advances of miRNAs as biomarkers and therapeutic targets of kidney graft injury, then summarized the specific data of miRNAs expression level in kidney graft injury, which aims to provide a reference for subsequent basic research and clinical transformation.

Differential expression of genes related to calcineurin and mTOR signaling and regulatory miRNAs in peripheral blood from kidney recipients under tacrolimus-based therapy

Background

Genetic and epigenetics factors have been implicated in drug response, graft function and rejection in solid organ transplantation. Differential expression of genes involved in calcineurin and mTOR signaling pathway and regulatory miRNAs was analyzed in the peripheral blood of kidney recipient cohort (n=36) under tacrolimus-based therapy.

Methods

PPP3CA, PPP3CB, MTOR, FKBP1A, FKBP1B and FKBP5 mRNA expression and polymorphisms in PPP3CA and MTOR were analyzed by qPCR. Expression of miRNAs targeting PPP3CA (miR-30a, miR-145), PPP3CB (miR-10b), MTOR (miR-99a, miR-100), and FKBP1A (miR-103a) was measured by qPCR array.

Results

PPP3CA and MTOR mRNA levels were reduced in the first three months of treatment compared to pre-transplant (P<0.05). PPP3CB, FKBP1A, FKBP1B, and FKBP5 expression was not changed. In the 3^rd month of treatment, the expression of miR-99a, which targets MTOR, increased compared to pre-transplant (P<0.05). PPP3CA c.249G>A (GG genotype) and MTOR c.2997C>T (TT genotype) were associated with reduced expression of PPP3CA mRNA and MTOR, respectively. FKBP1B mRNA levels were higher in patients with acute rejection (P=0.026).

Conclusions

The expression of PPP3CA, MTOR and miR-99a in the peripheral blood of renal recipients is influenced by tacrolimus-based therapy and by PPP3CA and MTOR variants. These molecules can be potential biomarkers for pharmacotherapy monitoring.

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.

Identification of Candidate Biomarkers for Transplant Rejection from Transcriptome Data: A Systematic Review

BACKGROUND

Traditional methods for rejection control in transplanted patients are considered invasive, risky, and prone to sampling errors. Using molecular biomarkers as an alternative protocol to biopsies, for monitoring rejection may help to mitigate some of these problems, increasing the survival rates and well-being of patients. Recent advances in omics technologies provide an opportunity for screening new molecular biomarkers to identify those with clinical utility.

OBJECTIVE

This systematic literature review (SLR) aimed to summarize existing evidence derived from large-scale expression profiling regarding differentially expressed mRNA and miRNA in graft rejection, highlighting potential molecular biomarkers in transplantation.

METHODS

The study was conducted following PRISMA methodology and the BiSLR guide for performing SLR in bioinformatics. PubMed, ScienceDirect, and EMBASE were searched for publications from January 2001 to January 2018, and studies (i) aiming at the identification of transplant rejection biomarkers, (ii) including human subjects, and (iii) applying methodologies for differential expression analysis from large-scale expression profiling were considered eligible. Differential expression patterns reported for genes and miRNAs in rejection were summarized from both cross-organ and organ-specific perspectives, and pathways enrichment analysis was performed for candidate biomarkers to interrogate their functional role in transplant rejection.

RESULTS

A total of 821 references were collected, resulting in 604 studies after removal of duplicates. After application of inclusion and exclusion criteria, 33 studies were included in our analysis. Among the 1517 genes and 174 miRNAs identifed, CXCL9, CXCL10, STAT1, hsa-miR-142-3p, and hsa-miR-155 appeared to be particularly promising as biomarkers in transplantation, with an increased expression associated with transplant rejection in multiple organs. In addition, hsa-miR-28-5p was consistently decreased in samples taken from rejected organs.

CONCLUSION

Despite the need for further research to fill existing knowledge gaps, transcriptomic technologies have a relevant role in the discovery of accurate biomarkers for transplant rejection diagnostics. Studies have reported consistent evidence of differential expression associated with transplant rejection, although issues such as experimental heterogeneity hinder a more systematic characterization of observed molecular changes. Special attention has been giving to large-scale mRNA expression profiling in rejection, whereas there is still room for improvements in the characterization of miRnome in this condition.

PROSPERO REGISTRATION NUMBER

CRD42018083321.

Noninvasive biomarkers in monitoring kidney allograft health

PURPOSE OF REVIEW

A key aspect of posttransplant management is to identify and treat graft injury before it becomes irreversible. The gold-standard for detection is histology, but biopsy is uncomfortable for the patient and carries a risk of complications. Detection of changes at a molecular level may preempt histological injury, and thereby identify injury earlier.

RECENT FINDINGS

Indicators of immune system activation, such as candidate chemokines CXCL9 and CXCL10, and by-products of neutrophil activity, have been related to acute rejection and early allograft function. Transcriptomic studies of multiple-gene panels have identified candidate combinations that have proven very promising in risk-stratification and prediction of acute rejection, as well as diagnosis of both T-cell-mediated and antibody-mediated rejection. Serum and urine cell-free DNA is also a promising area of investigation, particularly in antibody-mediated rejection.

SUMMARY

Noninvasive, rapid, and accurate tests for risk-prediction and diagnosis in renal transplant allografts are urgently required. The ideal candidate is one that can be measured in either urine or blood, is cheap, and is both sensitive and specific for the condition of interest. Numerous strategies have been proposed, with varying degrees of clinical and preclinical success. A few that meet the essential criteria have been evaluated; a few have made it as far as clinical testing.

Biomarkers of rejection in kidney transplantation

PURPOSE OF REVIEW

To provide an update of the literature on the use of new biomarkers of rejection in kidney transplant recipients.

RECENT FINDINGS

The kidney allograft biopsy is currently considered the gold standard for the diagnosis of rejection. However, the kidney biopsy is invasive and could be indeterminate. A significant progress has been made in discovery of new biomarkers of rejection, and some of them have been introduced recently for potential use in clinical practice including measurement of serum donor-derived cell free DNA, allo-specific CD154 + T-cytotoxic memory cells, and gene-expression 'signatures'. The literature supports that these biomarkers provide fair and reliable diagnostic accuracy and may be helpful in clinical decision-making when the kidney biopsy is contraindicated or is inconclusive.

SUMMARY

The new biomarkers provide a promising approach to detect acute rejections in a noninvasive way.

MicroRNAs in AKI and Kidney Transplantation

MicroRNAs are epigenetic regulators of gene expression at the posttranscriptional level. They are involved in intercellular communication and crosstalk between different organs. As key regulators of homeostasis, their dysregulation underlies several morbidities including kidney disease. Moreover, their remarkable stability in plasma and urine makes them attractive biomarkers. Beyond biomarker studies, clinical microRNA research in nephrology in recent decades has focused on the discovery of specific microRNA signatures and the identification of novel targets for therapy and/or disease prevention. However, much of this research has produced equivocal results and there is a need for standardization and confirmation in prospective trials. This review aims to provide an overview of general concepts and available clinical evidence in both the pathophysiology and biomarker fields for the role of microRNA in AKI and kidney transplantation.

The regulation of interferon type I pathway-related genes RSAD2 and ETV7 specifically indicates antibody-mediated rejection after kidney transplantation

CONTEXT

Antibody-mediated rejection (ABMR) after kidney transplantation (KTx) remains the crucial obstacle to successful long-term graft function. The identification of gene signatures involved in ABMR could grant the basis for better prevention and treatment strategies.

OBJECTIVE

The identification of gene signatures in whole blood cells specific for ABMR after KTx.

MATERIALS AND METHODS

Total RNA from blood cells of 16 kidney-transplanted patients with ABMR, stable graft function (SGF), and with T-cell-mediated rejection (TCMR) was isolated. Gene expression was determined by high-throughput sequencing followed by validation and analyses of differentially expressed candidates on mRNA level and on protein level in a large patient cohort (n = 185) in patients with SGF, urinary tract infection (UTI), borderline rejection (BL), TCMR, ABMR, and interstitial fibrosis and tubular atrophy.

RESULTS

From the 570 genes detected, 111 discriminated ABMR from SGF and TCMR. A distinct enrichment of interferon (IFN) type I and type II signature gene set was observed. The expression of candidate genes IFIT1, ETV7, and RSAD2 distinguished ABMR patients from patients with SGF and also TCMR, whereas ETV7 and RSAD2 differentiated ABMR also from BL.

CONCLUSION

The IFN-inducible genes ETV7 and RSAD2 represent specific biomarkers for ABMR episodes after KTx.

MicroRNA regulation in blood cells of renal transplanted patients with interstitial fibrosis/tubular atrophy and antibody-mediated rejection

Interstitial fibrosis/tubular atrophy (IFTA) is associated with reduced allograft survival, whereas antibody-mediated rejection (ABMR) is the major cause for renal allograft failure. To identify specific microRNAs and their regulation involved in these processes, total RNA from blood cells of 16 kidney transplanted (KTx) patients with ABMR, stable graft function (SGF) and with T-cell mediated rejection (TCMR) was isolated. MicroRNA expression was determined by high-throughput sequencing. Differentially expressed candidate microRNAs were analyzed with RT-PCR in patients with SGF (n = 53), urinary tract infection (UTI) (n = 17), borderline rejection (BL) (n = 19), TCMR (n = 40), ABMR (n = 22) and IFTA (n = 30). From the 301 detected microRNAs, 64 were significantly regulated between the three cohorts. Selected candidate microRNAs miR-223-3p, miR-424-3p and miR-145-5p distinguished TCMR and ABMR from SGF, but not from other pathologies. Most importantly, miR-145-5p expression in IFTA patients was significantly downregulated and displayed a high diagnostic accuracy compared to SGF alone (AUC = 0.891) and compared to SGF, UTI, BL, TCMR and ABMR patients combined (AUC = 0.835), which was verified by cross-validation. The identification of miR-145-5p as IFTA specific marker in blood constitutes the basis for evaluating this potentially diagnostic microRNA as biomarker in studies including high numbers of patients and different pathologies and also the further analysis of fibrosis causing etiologies after kidney transplantation.

Novel non-invasive biomarkers diagnostic of acute rejection in renal transplant recipients: A systematic review

BACKGROUND AND OBJECTIVES

Acute rejection is a significant complication detrimental to kidney transplant function. Current accepted means of diagnosis is percutaneous renal biopsy, a costly and invasive procedure. There is an urgent need to detect and validate non-invasive biomarkers capable of replacing the biopsy.

DESIGN, SETTING, PARTICIPANTS AND MEASUREMENTS

Comprehensive literature searches of Medline, EMBASE and Cochrane Central Register of Controlled Trials databases were performed. Eligible studies were included as per inclusion criteria and assessed for quality using the GRADE quality of evidence tool. Outcomes evaluated included biomarker diagnostic performance, number of patients/samples, mean age and gender ratio, immunosuppression regime, in addition to clinical applications of the biomarker(s) tested. PRISMA guidelines were followed. Where possible, statistical analysis of comparative performance data was performed.

RESULTS

23 studies were included in this review, including 19 adult, 3 paediatric and 1 mixed studies. A total of 2858 participants and 50 candidate non-invasive tests were identified. Sensitivity, specificity and area under the curve performance values ranged 36%-100%, 30%-100% and 0.55-0.98, respectively.

CONCLUSIONS

Although larger, more robust multi-centre validation studies are needed before non-invasive biomarkers can replace the biopsy, numerous candidate tests have demonstrated significant promise for various facets of postoperative management. Suggested uses include: ruling out patients with a low risk of acute rejection to avoid the need for biopsy, non-invasive testing where the biopsy is contraindicated and a prompt diagnosis is needed, and integration into a serial blood monitoring protocol in conjunction with serum creatinine.

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.

Renal Protection Mediated by Hypoxia Inducible Factor-1α Depends on Proangiogenesis Function of miR-21 by Targeting Thrombospondin 1

Background

Angiogenesis contributes to the repair process after renal ischemia/reperfusion (I/R) injury. In the present study, we tested the role of miR-21 in the angiogenesis induced by hypoxia inducible factor (HIF)-1α through inhibiting a predicted target gene thrombospondin 1 (TSP-1).

Methods

To stabilize HIF-1α, hypoxia (1% O₂ for 24 hours) was performed in human umbilical vein endothelial cells and cobalt chloride (CoCl₂) was pretreated intraperitoneally 24 hours before renal I/R in mice. Locked nucleic acid modified anti-miR-21 and scrambled control was transfected with hypoxic cells or delivered into the mice via tail vein 1 hour before CoCl₂ injection. The kidneys and blood were collected at 24 hours after reperfusion.

Results

HIF-1α induced by hypoxia and CoCl₂ upregulated vascular endothelial growth factor and miR-21, and increased angiogenesis. It was found that expression of TSP-1 was inversely related with miR-21 in vitro and in vivo. Targeting of TSP-1 by miR-21 was further confirmed in vitro. Furthermore, HIF-1α improved renal function, accompanied with increased angiogenesis after I/R injury in mice. The protective effect of HIF-1α was attenuated by inhibition of miR-21.

Conclusions

HIF-1α induced angiogenesis by upregulating not only vascular endothelial growth factor but also miR-21 via inhibiting a novel target gene TSP-1. Both of them may contribute to the protective effect of HIF-1α on renal I/R injury.

Hypoxia induces HIF-1α which upregulates not only VEGF but also miR-21, and this last one inhibits a novel target gene, thrombospondin 1. Angiogenesis induced by hypoxia depends at least partially on production of VEGF and inhibition of thrombospondin 1 through miR-21.

Blood biomarkers of kidney transplant rejection, an endless search?

INTRODUCTION

The tailoring of immunosuppressive treatment is recognized as a promising strategy to improve long-term kidney graft outcome. To guide the standard care of transplant recipients, physicians need objective biomarkers that can identify an ongoing pathology with the graft or low intensity signals that will be later evolved to accelerated transplant rejection. The early identification of 'high-risk /low-risk' patients enables the adjustment of standard of caring, including managing the frequency of clinical visits and the immunosuppression dosing. Given their ease of availability and the compatibility with a large technical array, blood-based biomarkers have been widely scrutinized for use as potential predictive and diagnostic biomarkers. Areas covered: Here, the authors report on non-invasive biomarkers, such as modification of immune cell subsets and mRNA and miRNA profiles, identified in the blood of kidney transplant recipients collected before or after transplantation. Expert commentary: Combined with functional tests, the identification of biomarkers will improve our understanding of pathological processes and will contribute to a global improvement in clinical management.

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.

[The microRNAs as biomarkers: What prospects?]

MicroRNAs are nucleic acids of about twenty nucleotides that regulate about a third of the genome at the post-transcriptional level. Thanks to their different forms of transport, microRNAs are stable and can be detected in biological fluids such as blood, urine, cerebrospinal fluid, or saliva. In addition, the profile of circulating microRNAs is a specific part of the cells in which it is secreted and is modified according to the physiological or pathological conditions of these cells. MicroRNAs therefore appear as biomarkers of interest for many diseases. However, these applications face several challenges because there are currently considerable differences between the sample processing procedures, assay methods, and especially the result standardization strategies. This literature review aims to take stock of the current use of microRNAs as biomarkers mainly in biological fluids and address the perspectives that emerge from the fact that their vesicular circulating forms could be used to assess the state of the cells and the tissues that produce them.

Free microRNA levels in plasma distinguish T-cell mediated rejection from stable graft function after kidney transplantation

The potential diagnostic value of circulating free miRNAs in plasma compared to miRNA expression in blood cells for rejection processes after kidney transplantation is largely unknown, but offers the potential for better and timely diagnosis of acute rejection. Free microRNA expression of specific blood cell markers was measured in 160 plasma samples from kidney transplant patients under standard immunosuppressive therapy (steroids±mycophenolic acid±calcineurin inhibitor) with stable graft function, urinary tract infection, interstitial fibrosis and tubular atrophy, antibody-mediated rejection (ABMR), Borderline (Banff3), tubulo-interstitial (Banff4-I) and vascular rejection (Banff4-II/III) applying RT-PCR. The expression levels of specific microRNAs miR-15B, miR-103A and miR-106A discriminated patients with stable graft function significantly (p-values 0.001996, 0.0054 and 0.0019 resp.) from patients with T-cell mediated rejection (TCMR) and from patients with urinary tract infection (p-values 0.0001, <0.0001 and 0.0001, resp.). A combined measurement of several microRNAs after multivariate logistic regression improved the diagnostic value supported by subsequent cross-validation. In conclusion, the measurement of circulating microRNAs in plasma from patients with renal transplants distinguishes TCMR and urinary tract infection from stable graft function. In contrast to miRNA expression measurement in blood cells it does not allow a discrimination from ABMR or interstitial fibrosis and tubular atrophy.