Kidney Allograft Fibrosis Research Articles

Association between Kidney Allograft Fibrosis and Magnetic Resonance Elastography-Derived Stiffness in Kidney Transplant Recipients

Association between Kidney Allograft Fibrosis and Magnetic Resonance Elastography-Derived Stiffness in Kidney Transplant Recipients

Multicenter, prospective, observational study for urinary exosomal biomarkers of kidney allograft fibrosis

Severity of deceased donor kidney fibrosis impacts graft survival in deceased-donor kidney transplantation. Our aim was to identify potential miRNA biomarkers in urinary exosomes that mirror interstitial fibrosis and tubular atrophy (IFTA) severity. Among 109 urine samples from deceased donors, 34 displayed no IFTA in the zero-day biopsy (No IFTA group), while the remaining 75 deceased donor kidneys exhibited an IFTA score ≥ 1 (IFTA group). After analyzing previous reports and electronic databases, six miRNAs (miR-19, miR-21, miR-29c, miR-150, miR-200b, and miR-205) were selected as potential IFTA biomarker candidates. MiR-21, miR-29c, miR-150, and miR-205 levels were significantly higher, while miR-19 expression was significantly lower in the IFTA group. MiR-21 (AUC = 0.762; P < 0.001) and miR-29c (AUC = 0.795; P < 0.001) showed good predictive accuracy for IFTA. In the No IFTA group, the eGFR level at 1 week after transplantation was significantly higher compared to the IFTA group (41.34 mL/min/1.73m2 vs. 28.65 mL/min/1.73m2, P = 0.012). These findings signify the potential of urinary exosomal miRNAs as valuable biomarker candidates for evaluating the severity of IFTA in deceased donor kidneys before they undergo recovery.

Effect of Spironolactone on Kidney Function in Kidney Transplant Recipients (the SPIREN trial): A Randomized Placebo-Controlled Clinical Trial.

Long-term kidney allograft survival is hampered by progressive interstitial fibrosis and tubular atrophy. The SPIREN trial tested the hypothesis that the mineralocorticoid receptor antagonist spironolactone stabilizes kidney function and attenuates glomerular barrier injury in kidney transplant patients treated with calcineurin inhibitors. Randomized, placebo-controlled, double blind clinical trial including 188 prevalent kidney transplant patients. Patients were randomized to spironolactone or placebo for three years. Glomerular filtration rate was measured along with proteinuria and kidney fibrosis. The primary endpoint was change in measured glomerular filtration rate. Secondary outcomes were 24h proteinuria, kidney allograft fibrosis and cardiovascular events. Measured glomerular filtration rates, 24h proteinuria and blood pressure were determined yearly. Kidney biopsies were collected at baseline and after two years (n=48). Fibrosis was evaluated by quantitative stereology and classified according to Banff. The groups were comparable at baseline except for slightly older allografts in the spironolactone group. Spironolactone reduced measured glomerular filtration rates (up to -7.6 (95% CI -10.9;-4.3) ml/min compared to placebo) independently of time since transplantation and blood pressure with no impact on the kidney function curve over time and reduced 24h proteinuria after one year. There was no significant effect of spironolactone on the development of interstitial fibrosis. Spironolactone added to standard therapy for three years in kidney transplant patients did not improve kidney function, long-term proteinuria or interstitial fibrosis.

Dysregulated lipid metabolism is associated with kidney allograft fibrosis

BackgroundInterstitial fibrosis and tubular atrophy (IF/TA), a histologic feature of kidney allograft destruction, is linked to decreased allograft survival. The role of lipid metabolism is well-acknowledged in the area of chronic kidney diseases; however, its role in kidney allograft fibrosis is still unclarified. In this study, how lipid metabolism contributes to kidney allografts fibrosis was examined.MethodsA comprehensive bioinformatic comparison between IF/TA and normal kidney allograft in the Gene Expression Omnibus (GEO) database was conducted. Further validations through transcriptome profiling or pathological staining of human recipient biopsy samples and in rat models of kidney transplantation were performed. Additionally, the effects of enhanced lipid metabolism on changes in the fibrotic phenotype induced by TGF-β1 were examined in HK-2 cell.ResultsIn-depth analysis of the GEO dataset revealed a notable downregulation of lipid metabolism pathways in human kidney allografts with IF/TA. This decrease was associated with increased level of allograft rejection, inflammatory responses, and epithelial mesenchymal transition (EMT). Pathway enrichment analysis showed the downregulation in mitochondrial LC-fatty acid beta-oxidation, fatty acid beta-oxidation (FAO), and fatty acid biosynthesis. Dysregulated fatty acid metabolism was also observed in biopsy samples from human kidney transplants and in fibrotic rat kidney allografts. Notably, the areas affected by IF/TA had increased immune cell infiltration, during which increased EMT biomarkers and reduced CPT1A expression, a key FAO enzyme, were shown by immunohistochemistry. Moreover, under TGF-β1 induction, activating CPT1A with the compound C75 effectively inhibited migration and EMT process in HK-2 cells.ConclusionsThis study reveal a critical correlation between dysregulated lipid metabolism and kidney allograft fibrosis. Enhancing lipid metabolism with CPT1A agonists could be a therapeutic approach to mitigate kidney allografts fibrosis.

Targeted delivery of galunisertib using machine perfusion reduces fibrogenesis in an integrated ex vivo renal transplant and fibrogenesis model.

Fibrosis in kidney allografts is a major post-transplant complication that contributes to graft failure. Lately, multiple potent inhibitors of fibrosis-related pathways have been developed such as galunisertib, an inhibitor of the transforming growth factor-beta (TGF-β/TGFβ1) signalling pathway. This drug, however, poses risks for adverse effects when administered systemically. Therefore, we devised a new repurposing strategy in which galunisertib is administered ex vivo. We combined machine perfusion and tissue slices to explore the antifibrotic effects of galunisertib in renal grafts. Porcine kidneys were subjected to 30 min of warm ischaemia, 24 h of oxygenated hypothermic machine perfusion and 6 h of normothermic machine perfusion with various treatments (i.e. untreated control, TGFβ1, galunisertib or TGFβ1 + galunisertib; n = 8 kidneys per group). To determine whether effects persisted upon ceasing treatment, kidney slices were prepared from respective kidneys and incubated for 48 h. Galunisertib treatment improved general viability without negatively affecting renal function or elevating levels of injury markers or by-products of oxidative stress during perfusion. Galunisertib also reduced inflammation and, more importantly, reduced the onset of fibrosis after 48 h of incubation. Our findings demonstrate the value of using machine perfusion for administering antifibrotic drugs such as galunisertib, proving it to be an effective example of repurposing.

Single-nucleotide polymorphisms of matrix metalloproteinase genes are associated with graft fibrosis after kidney transplantation.

Further research needs to be conducted on the role of genetic variables in kidney transplantation fibrosis. In this study, we used next-generation sequencing (NGS) to examine the relationship between matrix metalloproteinase (MMP) genes and single-nucleotide polymorphisms (SNPs) in renal allograft fibrosis. This study comprised 200 patients, whose complete DNA samples were taken. The SNPs in MMP genes were identified using targeted NGS. Hardy-Weinberg equilibrium (HWE) and minor allele frequency (MAF) tests were conducted, followed by a linkage disequilibrium (LD) analysis. Finally, the SNPs and severity of kidney allograft fibrosis were evaluated using different inheritance models. In total, 41 MMP gene-related SNPs were identified using targeted sequencing, and 20 tagger SNPs were retained for further study. The general linear models (GLMs) revealed that sirolimus treatment had a substantial effect on kidney graft fibrosis. The multiple inheritance model analyses revealed that SNP rs9059 of the MMP9 gene was strongly associated with kidney graft fibrosis. The in-vitro experiments showed the MMP9 rs9509 mutation promotes the process of epithelial-mesenchymal transition (EMT) in the human kidney 2 (HK2) cells. The SNP rs9059 is associated with significant kidney allograft pathological changes by promoting EMT progression. Our findings provide insights into the etiology of renal allograft interstitial fibrosis and the MMP9 could be used as a potential treatment target in the future.

Single nuclei transcriptomics delineates complex immune and kidney cell interactions contributing to kidney allograft fibrosis

Chronic allograft dysfunction (CAD), characterized histologically by interstitial fibrosis and tubular atrophy, is the major cause of kidney allograft loss. Here, using single nuclei RNA sequencing and transcriptome analysis, we identified the origin, functional heterogeneity, and regulation of fibrosis-forming cells in kidney allografts with CAD. A robust technique was used to isolate individual nuclei from kidney allograft biopsies and successfully profiled 23,980 nuclei from five kidney transplant recipients with CAD and 17,913 nuclei from three patients with normal allograft function. Our analysis revealed two distinct states of fibrosis in CAD; low and high extracellular matrix (ECM) with distinct kidney cell subclusters, immune cell types, and transcriptional profiles. Imaging mass cytometry analysis confirmed increased ECM deposition at the protein level. Proximal tubular cells transitioned to an injured mixed tubular (MT1) phenotype comprised of activated fibroblasts and myofibroblast markers, generated provisional ECM which recruited inflammatory cells, and served as the main driver of fibrosis. MT1 cells in the high ECM state achieved replicative repair evidenced by dedifferentiation and nephrogenic transcriptional signatures. MT1 in the low ECM state showed decreased apoptosis, decreased cycling tubular cells, and severe metabolic dysfunction, limiting the potential for repair. Activated B, T and plasma cells were increased in the high ECM state, while macrophage subtypes were increased in the low ECM state. Intercellular communication between kidney parenchymal cells and donor-derived macrophages, detected several years post-transplantation, played a key role in injury propagation. Thus, our study identified novel molecular targets for interventions aimed to ameliorate or prevent allograft fibrogenesis in kidney transplant recipients.

Association between the renin-angiotensin system and chronic lung allograft dysfunction.

Chronic lung allograft dysfunction (CLAD) is the major cause of death after lung transplantation. Angiotensin II (AngII), the main effector of the renin-angiotensin system, elicits fibrosis in both kidney and lung. We identified six AngII-regulated proteins (Ras homolog family member B (RHOB), bone marrow stromal cell antigen 1 (BST1), lysophospholipase 1 (LYPA1), glutamine synthetase (GLNA), thrombospondin 1 (TSP1) and laminin subunit β2 (LAMB2)) that were increased in urine of patients with kidney allograft fibrosis. We hypothesised that the renin-angiotensin system is active in CLAD and that AngII-regulated proteins are increased in bronchoalveolar lavage fluid (BAL) of CLAD patients.We performed immunostaining of AngII receptors (AGTR1 and AGTR2), TSP1 and GLNA in 10 CLAD lungs and five controls. Using mass spectrometry, we quantified peptides corresponding to AngII-regulated proteins in BAL of 40 lung transplant recipients (stable, acute lung allograft dysfunction (ALAD) and CLAD). Machine learning algorithms were developed to predict CLAD based on BAL peptide concentrations.Immunostaining demonstrated significantly more AGTR1+ cells in CLAD versus control lungs (p=0.02). TSP1 and GLNA immunostaining positively correlated with the degree of lung fibrosis (R2=0.42 and 0.57, respectively). In BAL, we noted a trend towards higher concentrations of AngII-regulated peptides in patients with CLAD at the time of bronchoscopy, and significantly higher concentrations of BST1, GLNA and RHOB peptides in patients that developed CLAD at follow-up (p<0.05). The support vector machine classifier discriminated CLAD from stable and ALAD patients at the time of bronchoscopy (area under the curve (AUC) 0.86) and accurately predicted subsequent CLAD development (AUC 0.97).Proteins involved in the renin-angiotensin system are increased in CLAD lungs and BAL. AngII-regulated peptides measured in BAL may accurately identify patients with CLAD and predict subsequent CLAD development.

Suppression of Allograft Fibrosis by Regulation of Mammalian Target of Rapamycin-Related Protein Expression in Kidney-Transplanted Recipients Treated with Everolimus and Reduced Tacrolimus.

BackgroundAlthough renoprotective effects of everolimus (EVR) in kidney transplantation (KTx) have been widely reported, its pathophysiological mechanism remains unclear.Material/MethodsWe compared changes in eGFR (ΔGFR, ml/min/1.73 m2) and the ratio of the fibrotic area in biopsy specimens (ΔFI,%) from 3 months to 3 years after KTx between the EVR+ group (EVR addition and Tac reduction early after KTx, n=32), and the EVR− group (normal Tac without EVR, n=28). We also immunohistochemically evaluated mTOR-related protein expression.ResultsΔGFR and ΔFI in the EVR+ vs. EVR− groups were −0.27±6.8 vs. −9.8±12.8 (p<0.001) and 2.4±4.9 vs. 9.5±10.5 (p<0.001), respectively. Phosphorylated mTOR and phosphorylated 4EBP1 expression at 3 years in the EVR+ group was significantly lower than that in the EVR− group. Moreover, in the subgroup analysis comparing ΔGFR and ΔFI among groups stratified by immunosuppressive regimen and mTOR signal enhancement, the ΔFI in patients with EVR+ with decreased mTOR signal enhancement was significantly milder than that in other patients. In addition, in the multivariate analysis, EVR addition was the only independent predictor for allograft fibrosis, whereas the Tac C0 concentration at neither 1 nor 3 years proved to be a risk factor.ConclusionsThese results suggested that EVR addition and Tac reduction may attenuate kidney allograft fibrosis, and that the suppression of mTOR signaling process may be involved in the anti-fibrotic effect of this immunosuppressive regimen. These results provide suggestions of how to utilize EVR for patients with KTx and improve graft function.

ARHGDIB and AT1R autoantibodies are differentially related to the development and presence of chronic antibody-mediated rejection and fibrosis in kidney allografts

The role of non-HLA autoantibodies in chronic-active antibody-mediated rejection (c-aABMR) of kidney transplants is largely unknown. In this study, the presence and clinical relevance of non-HLA autoantibodies using a recently developed multiplex Luminex-based assay were investigated. Patients with a kidney allograft biopsy at least 6 months after transplantation with a diagnosis of c-aABMR (n = 36) or no rejection (n = 21) were included. Pre-transplantation sera and sera at time of biopsy were tested for the presence of 14 relevant autoantibodies.A significantly higher signal for autoantibodies against Rho GDP‐dissociation inhibitor 2 (ARHGDIB) was detected in recipients with c-aABMR as compared to recipients with no rejection. However, ARHGDIB autoantibodies did not associate with graft survival. Levels of autoantibodies against angiotensin II type 1-receptor (AT1R) and peroxisomal trans‐2‐enoyl‐CoA reductase (PECR) were increased in recipients with interstitial fibrosis in their kidney biopsy. Only the signal for AT1R autoantibody showed a linear relationship with the degree of interstitial fibrosis and was associated with graft survival.In conclusion, anti-ARHGDIB autoantibodies are increased when c-aABMR is diagnosed but are not associated with graft survival, while higher levels of AT1R autoantibody are specifically associated with the presence of interstitial fibrosis and graft survival.

Magnetic Resonance Imaging for Evaluation of Interstitial Fibrosis in Kidney Allografts.

This prospective trial was primarily designed to investigate whether the results of T1-weighted MRI associate with the degree of IF. Thirty-two kidney transplant recipients were subjected to 1.5-Tesla MRI scans shortly before or after routine allograft biopsies. MRI parameters [T1 and T2 relaxation times; apparent diffusion coefficient (ADC)] were assessed for cortical and medullary sections. Advanced IF (Banff ci score >1) was associated with higher cortical T1 (but not T2) values [1451 (median; interquartile range: 1331-1506) versus 1306 (1197-1321) ms in subjects with ci scores ≤1; P = 0.011; receiver operating characteristic area under the curve for prediction of ci > 1: 0.76]. In parallel, T1 values were associated with kidney function and proteinuria. There was also a relationship between IF and corticomedullary differences on ADC maps (receiver operating characteristic area under the curve for prediction of ci ≤ 1: 0.79). Our results support the use of MRI for noninvasive assessment of allograft scarring. Future studies will have to clarify the role of T1 (and ADC) mapping as a surrogate endpoint reflecting the progression of chronic graft damage.

Kidney allograft fibrosis: what we learned from latest translational research studies.

To add new molecular and pathogenetic insights into the biological machinery associated to kidney allograft fibrosis is a major research target in nephrology and organ transplant translational medicine. Interstitial fibrosis associated to tubular atrophy (IF/TA) is, in fact, an inevitable and progressive process that occurs in almost every type of chronic allograft injury (particularly in grafts from expanded criteria donors) characterized by profound remodeling and excessive production/deposition of fibrillar extracellular matrix (ECM) with a great clinical impact. IF/TA is detectable in more than 50% of kidney allografts at 2 years. However, although well studied, the complete cellular/biological network associated with IF/TA is only partially evaluated. In the last few years, then, thanks to the introduction of new biomolecular technologies, inflammation in scarred/fibrotic parenchyma areas (recently acknowledged by the BANFF classification) has been recognized as a pivotal element able to accelerate the onset and development of the allograft chronic damage. Therefore, in this review, we focused on some new pathogenetic elements involved in graft fibrosis (including epithelial/endothelial to mesenchymal transition, oxidative stress, activation of Wnt and Hedgehog signaling pathways, fatty acids oxidation and cellular senescence) that, in our opinion, could become in future good candidates as potential biomarkers and therapeutic targets.

Donor acute kidney injury and its effect on 1-year post-transplant kidney allograft fibrosis.

Transplantation of kidneys from deceased donors with acute kidney injury (AKI) can expand the donor pool. We investigated the effect of donor AKI on renal function and chronic changes on protocol biopsies at 1-year post-transplant. Donor AKI was defined according to Acute Kidney Injury Network (AKIN) criteria. Between 2013 and 2017, 333 kidneys were transplanted and subsequently biopsied after 1year. Fifty-three kidneys from AKI donors (AKIN stage I n=42, stage II n=8, stage III n=3) were compared to 280 kidneys from non-AKI donors. At 1-year follow-up, patient and graft survival were comparable. Donor AKI was not predictive of IFTA (Banff interstitial fibrosis plus tubular atrophy scores) at 1-year post-transplant biopsy (2.10±1.28 in AKI, 2.09±1.22 in non-AKI, P=.95). Donor AKI was also not associated with progression of IFTA from 3 to 12months (P=.69), or inferior glomerular filtration rate (eGFR, P=.94). In a multivariate analysis, the odds of IFTA >2 were comparable between AKI and non-AKI groups. In conclusion, the transplantation of kidneys from donors with predominantly stage I AKI results in comparable function and degree of fibrosis on protocol biopsies 1-year post-transplant. Selected grafts from donors with AKI are a valuable tool for expanding the donor pool for kidney transplantation.

Combination of Functional Magnetic Resonance Imaging and Histopathologic Analysis to Evaluate Interstitial Fibrosis in Kidney Allografts.

Recent developments indicated that functional magnetic resonance imaging (MRI) could potentially provide noninvasive assessment of kidney interstitial fibrosis in patients with kidney diseases, but direct evidence from histopathology is scarce. We aimed to explore the diagnostic utilities of functional MRI for the evaluation of kidney allograft interstitial fibrosis. We prospectively examined 103 kidney transplant recipients who underwent for-cause biopsies and 20 biopsy-proven normal subjects with functional MRI. Histomorphometric analyses of interstitial fibrosis and peritubular capillary densities were performed on digitally scanned Masson's trichrome- and CD34-stained slides, respectively. The performances of functional MRI to discriminate interstitial fibrosis were assessed by calculating the area under the curve using receiver-operating characteristic curve. Main pathologic findings in this single-center cohort were representative of common diagnostic entities in the kidney allografts, with rejection (32%) and glomerulonephritides (31%) accounting for the majority of diagnoses. Apparent diffusion coefficient from diffusion-weighted imaging correlated with interstitial fibrosis (ρ=-0.77; P<0.001). Additionally, decreased arterial spin labelings were accompanied by peritubular capillary density reductions (r=0.77; P<0.001). Blood oxygen level-dependent (BOLD) imaging demonstrated cortical hypoxia with increasing interstitial fibrosis (ρ=0.61; P<0.001). The area under the curve for the discrimination of ≤25% versus >25% interstitial fibrosis and ≤50% versus >50% interstitial fibrosis were 0.87 (95% confidence interval [95% CI], 0.79 to 0.93) and 0.88 (95% CI, 0.80 to 0.93) by apparent diffusion coefficient, 0.92 (95% CI, 0.85 to 0.97) and 0.94 (95% CI, 0.87 to 0.98) by arterial spin labeling, 0.81 (95% CI, 0.72 to 0.88) and 0.86 (95% CI, 0.78 to 0.92) by perfusion fraction, 0.79 (95% CI, 0.69 to 0.87) and 0.85 (95% CI, 0.76 to 0.92) by BOLD imaging, respectively. Functional MRI measurements were strongly correlated with kidney allograft interstitial fibrosis. The performances of functional MRI for discriminating ≤50% versus >50% interstitial fibrosis were good to excellent.

SDF‑1/CXCR4 induces epithelial‑mesenchymal transition through activation of the Wnt/β‑catenin signaling pathway in rat chronic allograft nephropathy.

Epithelial-mesenchymal transition (EMT) has been demonstrated to serve a crucial role in the progression of interstitial fibrosis, which is one of the principal pathological features of chronic allograft nephropathy (CAN). However, to the best of our knowledge, the mechanisms of EMT in CAN have not been investigated. In the present study, the effect of stromal cell-derived factor 1 (SDF-1) and the Wnt signaling pathway on the progression of EMT following kidney transplantation was investigated. The CAN model was established using Fisher 344 and Lewis rats, treated with low-dose cyclosporine with or without AMD3100. CAN was confirmed by the pathological alterations and chronic allograft damage index scoring, and EMT was confirmed by western blotting and reverse transcription-quantitative polymerase chain reaction. In the AMD3100 group, there were lower expression levels of α-SMA and higher expression levels of E-cadherin, which indicated that CAN and EMT were ameliorated by AMD3100. The kidney tissue was analyzed using an mRNA + long noncoding (lnc)RNA microarray. A total of 506 mRNAs and 404 lncRNAs were demonstrated to be significantly differentially expressed between the two groups, which revealed the involvement of SDF-1/CXC chemokine receptor 4 (CXCR4) and the Wnt pathway. SDF-1 was demonstrated to induce EMT in vitro through the upregulation of α-SMA, downregulation of E-cadherin and the wound healing assay, and in the rat renal tubular epithelial cells via the nuclear accumulation of β-catenin, which were all inhibited by either AMD3100 or DKK-1. CXXC finger protein 5 (CXXC5), a negative regulator of the Wnt pathway, was downregulated following treatment with SDF-1, which was inhibited by AMD3100 but not by DKK-1. Thus, CXXC5 may be a regulator downstream of SDF-1/CXCR4 in EMT. In conclusion, SDF-1/CXCR4 induces EMT of renal tubular epithelial cells with the involvement of the Wnt pathway, which may be a novel mechanism and therapeutic target in kidney allograft fibrosis of rats.

Urinary transglutaminase 2 as a potent biomarker to predict interstitial fibrosis and tubular atrophy of kidney allograft during early posttransplant period in deceased donor kidney transplantation.

PurposeTransglutaminase type 2 (TG2) is an extracellular matrix crosslinking enzyme with a pivotal role in kidney fibrosis. We tested whether quantification of urinary TG2 may represent a noninvasive method to estimate the severity of kidney allograft fibrosis.MethodsWe prospectively collected urine specimens from 18 deceased donor kidney transplant recipients at 1-day, 7-day, 1-month, 3-month, and 6-month posttransplant. In addition, kidney allograft tissue specimens at 0-day and 6-month posttransplant were sampled to analyze the correlation of urinary TG2 and kidney allograft fibrosis.ResultsThirteen recipients had increased interstitial fibrosis and tubular atrophy (IFTA) scores at the 6-month protocol biopsy (IFTA group). The mean level of urinary TG2 in the IFTA group was higher compared to that of 5 other recipients without IFTA (no IFTA group). Conversely, the mean level of urinary syndecan-4 in the IFTA group was lower than levels in patients without IFTA. In the IFTA group, double immunofluorescent staining revealed that TG2 intensity was significantly upregulated and colocalizations of TG2/heparin sulfate proteoglycan and nuclear syndecan-4 were prominent, usually around tubular structures.ConclusionUrinary TG2 in early posttransplant periods is a potent biomarker for kidney allograft inflammation or fibrosis.

A Composite of Urinary Biomarkers to Differentiate between Tubulointersttial Inflammation and Fibrosis in Kidney Allografts

BackgroundA composite of urinary biomarkers may be more helpful to monitor kidney allograft pathology compared with a single biomarker.MethodsAs a cross-sectional cohort study, we collected 210 urine samples from living or deceased donor kidney transplant (KT) recipients. Among them, 123 recipients

Inflammation in Fibrotic Areas (i-IF/TA) Identifies a T cell-mediated Rejection Component of IF/TA with Poor Kidney Allograft Outcome

Addressing the etiological heterogeneity of interstitial fibrosis in kidney allografts represents an important challenge to improve long-term transplant outcomes. We investigated the determinants, clinical and histological phenotype, and outcome of i-IF/TA in a prospective cohort of kidney recipients. We prospectively enrolled 1539 kidney recipients transplanted between 2004 and 2010, with systematic assessment of i-IF/TA using the i-IF/TA Banff score and of tubulitis in atrophic tubules (t-IF/TA), on allograft biopsies performed at 1 year post-transplantation. We considered donor, recipient and transplant baseline characteristics, immunosuppression, infectious diseases (CMV, pyelonephritis, BK virus), presence of donor-specific anti-HLA antibodies (DSAs) and all the biopsy-proven diagnoses (T cell-mediated rejection [TCMR], antibody-mediated rejection [ABMR], recurrence, BK virus-associated nephropathy [BKVAN], calcineurin inhibithor [CNI] toxicity, acute tubular necrosis) recorded within the first year after transplantation. We identified 946 (61%) patients with IF/TA at one year post-transplant, among whom 394 (42%) patients showed i-IFTA, which was associated with t-IF/TA in 309 (78%) patients. Patients with i-IF/TA at 1 year post-transplant had significantly decreased allograft survival at 8 years compared with patients with non-inflammatory IF/TA (81% vs 87%, P=0.002). Independent risk factors for i-IF/TA included: TCMR (OR=2.7, p<0.001), BKVAN (OR=3.3, p=0.007) and HLA B (OR=1.3, p=0.012) and DR (OR=1.2, p=0.044) mismatching, while steroid therapy (OR=0.6, p=0.039), CNI therapy (OR=0.5, p=0.011) and inosine-5'-monophosphate dehydrogenase inhibitor therapy (OR=0.5, p=0.011) had protective effects on i-IF/TA occurrence. Unsupervised hierarchical clustering based on the whole spectrum of Banff elementary lesions assessed at 1 year post-transplant showed that i-IF/TA aggregated in the TCMR cluster (i, t, ti, t-IF/TA and i-IF/TA) and not in the ABMR (g, ptc, C4d, cg) and chronicity clusters (cv, ci, ct, ah). We observed a positive gradient between increasing level of i-IF/TA and t-IF/TA Banff scores and the risk of allograft loss (p<0.001). i-IFTA may reflect a TCMR subcomponent of IF/TA related to under-immunosuppression and is associated with poor kidney transplant outcome compared to non-inflammatory IF/TA.

Non-invasive assessment of kidney allograft fibrosis with shear wave elastography: A radiological-pathological correlation analysis.

To evaluate the use of shear wave elastography in assessment of kidney allograft tubulointerstitial fibrosis. Shear wave elastography assessment was carried out by two independent operators in kidney transplant recipients who underwent allograft biopsy for clinical indications (i.e. rising creatinine >15% or proteinuria >1g/day). Allograft biopsies were interpreted by the same pathologist according to the 2013 Banff Classification. A total of 40 elastography scans were carried out (median creatinine 172.5μmol/L [interquartile range 133.8-281.8μmol/L]). Median tissue stiffness at the cortex (22.6kPa [interquartile range 18.8-25.7kPa] vs 22.3kPa [interquartile range 19.0-26.5kPa], P=0.70) and medulla (15.0kPa [interquartile range 13.7-18.0kPa] vs 15.6kPa [interquartile range 14.4-18.2kPa]) showed no significant differences between the two observers. Interobserver agreement was satisfactory (intraclass correlation coefficient of the cortex 0.84, 95% CI 0.70-0.92 and intraclass correlation coefficient of the medulla 0.88, 95% CI 0.78-0.94). The areas under the receiver operating characteristic curves for detection of tubulointerstitial fibrosis were estimated to be 0.75 (95% CI 0.61-0.89), 0.85 (95% CI 0.75-0.95) and 0.65 (95% CI 0.53-0.78) for cortical, medullary tissue stiffness and serum creatinine, respectively. Shear wave elastography can be used as a non-invasive tool to evaluate kidney allograft fibrosis with reasonable interobserver agreement and superior test performance to serum creatinine in detecting early tubulointerstitial fibrosis.

Magnetic Resonance Elastography to Assess Fibrosis in Kidney Allografts.

Fibrosis is a major cause of kidney allograft injury. Currently, the only means of assessing allograft fibrosis is by biopsy, an invasive procedure that samples <1% of the kidney. We examined whether magnetic resonance elastography, an imaging-based measure of organ stiffness, could noninvasively estimate allograft fibrosis and predict progression of allograft dysfunction. Kidney allograft recipients >1 year post-transplant undergoing an allograft biopsy first underwent free-breathing, flow-compensated magnetic resonance elastography on a 3.0-T magnetic resonance imaging scanner. Each patient had serial eGFR measurements after the elastography scan for a follow-up period of up to 1 year. The mean stiffness value of the kidney allograft was compared with both the histopathologic Banff fibrosis score and the rate of eGFR change during the follow-up period. Sixteen patients who underwent magnetic resonance elastography and biopsy were studied (mean age: 54±9 years old). Whole-kidney mean stiffness ranged between 3.5 and 7.3 kPa. Whole-kidney stiffness correlated with biopsy-derived Banff fibrosis score (Spearman rho =0.67; P<0.01). Stiffness was heterogeneously distributed within each kidney, providing a possible explanation for the lack of a stronger stiffness-fibrosis correlation. We also found negative correlations between whole-kidney stiffness and both baseline eGFR (Spearman rho =-0.65; P<0.01) and eGFR change over time (Spearman rho =-0.70; P<0.01). Irrespective of the baseline eGFR, increased kidney stiffness was associated with a greater eGFR decline (regression r2=0.48; P=0.03). Given the limitations of allograft biopsy, our pilot study suggests the potential for magnetic resonance elastography as a novel noninvasive measure of whole-allograft fibrosis burden that may predict future changes in kidney function. Future studies exploring the utility and accuracy of magnetic resonance elastography are needed.