Clinical predictors of renal allograft histopathology: a comparative study of single-lesion histology versus a composite, quantitative scoring system

Epigenetic modifications and the development of kidney graft fibrosis

PURPOSE OF REVIEW

To outline recent discoveries in epigenetic regulatory mechanisms that have potential implications in the development of renal fibrosis following kidney transplantation.

RECENT FINDINGS

The characterization of renal fibrosis following kidney transplantation has shown TGFβ/Smad signaling to play a major role in the progression to chronic allograft dysfunction. The onset of unregulated proinflammatory pathways are only exacerbated by the decline in regulatory mechanisms lost with progressive patient age and comorbidities such as hypertension and diabetes. However, significant developments in the recognition of epigenetic regulatory markers upstream of aberrant TGFβ-signaling has significant clinical potential to provide therapeutic targets for the treatment of renal fibrosis. In addition, discoveries in extracellular vesicles and the characterization of their cargo has laid new framework for the potential to evaluate patient outcomes independent of invasive biopsies.

SUMMARY

The current review summarizes the main findings in epigenetic machinery specific to the development of renal fibrosis and highlights therapeutic options that have significant potential to translate into clinical practice.

Persistent BK Polyomavirus Viruria is Associated with Accumulation of VP1 Mutations and Neutralization Escape

To investigate the relationship between neutralization escape and persistent high-level BK polyomavirus replication after kidney transplant (KTx), VP1 sequences were determined by Sanger and next-generation sequencing in longitudinal samples from KTx recipients with persistent high-level viruria (non-controllers) compared to patients who suppressed viruria (controllers). The infectivity and neutralization resistance of representative VP1 mutants were investigated using pseudotype viruses. In all patients, the virus population was initially dominated by wild-type VP1 sequences, then non-synonymous VP1 mutations accumulated over time in non-controllers. BC-loop mutations resulted in reduced infectivity in 293TT cells and conferred neutralization escape from cognate serum in five out of six non-controller patients studied. When taken as a group, non-controller sera were not more susceptible to neutralization escape than controller sera, so serological profiling cannot predict subsequent control of virus replication. However, at an individual level, in three non-controller patients the VP1 variants that emerged exploited specific “holes” in the patient’s humoral response. Persistent high-level BK polyomavirus replication in KTx recipients is therefore associated with the accumulation of VP1 mutations that can confer resistance to neutralization, implying that future BKPyV therapies involving IVIG or monoclonal antibodies may be more effective when used as preventive or pre-emptive, rather than curative, strategies.

Long Non-coding RNA Expression Profiling in Biopsy to Identify Renal Allograft at Risk of Chronic Damage and Future Graft Loss

The loss of allograft from chronic damage is still the major risk that renal transplant recipients face today. Biomarkers for early detection of chronic damage are needed to improve the long-term graft survival. This study aimed to identify long non-coding RNA (lncRNA) biomarkers associated with chronic damage and graft loss after renal transplantation. Gene Expression Omnibus (GEO) datasets including GSE57387 (n = 101), GSE21374 (n = 282), and GSE25902 (n = 24) from three high-quality studies were analyzed. By repurposing the publicly available array-based data coupled with Affymetrix Human Exon 1.0 ST and Human U133 Plus 2.0 arrays, we obtained expression profiles of 11323 and 3383 lncRNAs in biopsies after renal transplantation, respectively. The logistic regression model and Cox regression model were applied to identify lncRNAs associated with chronic damage and graft survival. High AC093673.5 expression was identified as significantly associated with the three endpoints including chronic damage, progressive chronic histological damage, and graft failure across these three datasets. A six-lncRNA signature was created to predict renal allograft at risk of chronic damage with a high predictive ability (AUC = 0.94). Gene set enrichment analysis (GSEA) indicated that our lncRNA signature was related with allograft rejection and immunity. Our study highlights the importance of lncRNAs in chronic graft damage and allograft loss, supporting their potential role as prognosis biomarkers.

Differential MicroRNA Expressions in Human Peripheral Blood Mononuclear Cells Are Predictive of Renal Allograft Function

BACKGROUND

The present diagnostic methods for detecting graft damage after kidney transplantation are either invasive or not available early enough. The microRNAs (miRNAs) in peripheral blood mononuclear cells (PBMCs) have been suggested as promising biomarkers.

METHODS

Using quantitative real-time polymerase chain reaction, we identified 9 miRNAs (miR-142-5p, miR-142-3p, miR-223, miR-211, miR-486, miR-155, miR-10b, miR-30a, and let-7c) related to the human renal allograft status in PBMCs from 104 kidney transplant recipients.

RESULTS

The miR-142-5p, miR-142-3p, and miR-223 were significantly upregulated and miR-10b was significantly downregulated in recipients with abnormal levels of serum creatinine 3 to 4 weeks after initial sample collection. Moreover, the miR-142-5p and miR-142-3p were also found to be significantly upregulated in recipients with abnormal levels of cystatin C. Through a combination of the validated miRNAs, receiver operating characteristic analyses yielded the highest area under the curve value of 0.7913 and 0.7063 in predicting the levels of serum creatinine and cystatin C, respectively. In the testing stage, the developed models correctly predicted allograft function in 16 to 17 of 22 recipients (false rate, 22.7%-27.2%).

CONCLUSIONS

miRNAs in PBMCs of recipients hold great promise to be used as predictive and noninvasive biomarkers after transplantation.

Ischemia-Induced DNA Hypermethylation during Kidney Transplant Predicts Chronic Allograft Injury

Background Ischemia during kidney transplant causes chronic allograft injury and adversely affects outcome, but the underlying mechanisms are incompletely understood. In tumors, oxygen shortage reduces the DNA demethylating activity of the ten-11 translocation (TET) enzymes, yielding hypermethylated genomes that promote tumor progression. We investigated whether ischemia similarly induces DNA hypermethylation in kidney transplants and contributes to chronic injury.Methods We profiled genome-wide DNA methylation in three cohorts of brain-dead donor kidney allograft biopsy specimens: a longitudinal cohort with paired biopsy specimens obtained at allograft procurement (preischemia; n=13), after implantation and reperfusion (postischemia; n=13), and at 3 or 12 months after transplant (n=5 each); a cross-sectional cohort with preimplantation biopsy specimens (n=82); and a cross-sectional cohort with postreperfusion biopsy specimens (n=46).Results Analysis of the paired preischemia and postischemia specimens revealed that methylation increased drastically in all allografts on ischemia. Hypermethylation was caused by loss of 5-hydroxymethylcytosine, the product of TET activity, and it was stable 1 year after transplant. In the preimplantation cohort, CpG hypermethylation directly correlated with ischemia time and for some CpGs, increased 2.6% per additional hour of ischemia. Hypermethylation preferentially affected and reduced the expression of genes involved in suppressing kidney injury and fibrosis. Moreover, CpG hypermethylation in preimplantation specimens predicted chronic injury, particularly fibrosis and glomerulosclerosis, 1 year after transplant. This finding was validated in the independent postreperfusion cohort, in which hypermethylation also predicted reduced allograft function 1 year after transplant, outperforming established clinical variables.Conclusions We highlight a novel epigenetic basis for ischemia-induced chronic allograft injury with biomarker potential.

FcγRIIa defunctioning polymorphism in paediatric patients with renal allograft

Introduction

Fc gamma receptor (FcγR) IIa is considered the most widely distributed of the three classes of Fc receptors, and it expresses an allelic polymorphism. This type of polymorphism may modify the immune response and may be an important factor for some diseases. The aim of the study reported herein was to evaluate the association between the FcγRIIa polymorphism and susceptibility to both end-stage renal disease (ESRD) and acute kidney graft rejection (AR) in children who have undergone renal transplantation.

Material and methods

The study evaluated 70 children who had undergone transplantation and 60 healthy subjects. AR was observed in 25 children.

Results

FcγRIIa genotypes and alleles were significantly different between transplantation patients and the control group. The assessment for FcγR of the groups in which AR was present showed that there was only a risk of having an acute rejection in homozygous genotype RR.

Conclusions

FcγRIIa RR genotype and allele frequency was increased in paediatric renal transplant recipients. The present findings showed that FcγRIIa genotype may be related to ESRD disease susceptibility, and FcγRIIa polymorphisms seemed to affect AR.

Kidney Fibrosis: Origins and Interventions

All causes of renal allograft injury, when severe and/or sustained, can result in chronic histological damage of which interstitial fibrosis and tubular atrophy are dominant features. Unless a specific disease process can be identified, what drives interstitial fibrosis and tubular atrophy progression in individual patients is often unclear. In general, clinicopathological factors known to predict and drive allograft fibrosis include graft quality, inflammation (whether "nonspecific" or related to a specific diagnosis), infections, such as polyomavirus-associated nephropathy, calcineurin inhibitors (CNI), and genetic factors. The incidence and severity of chronic histological damage have decreased substantially over the last 3 decades, but it is difficult to disentangle what effects individual innovations (eg, better matching and preservation techniques, lower CNI dosing, BK viremia screening) may have had. There is little evidence that CNI-sparing/minimization strategies, steroid minimization or renin-angiotensin-aldosterone system blockade result in better preservation of intermediate-term histology. Treatment of subclinical rejections has only proven beneficial to histological and functional outcome in studies in which the rate of subclinical rejection in the first 3 months was greater than 10% to 15%. Potential novel antifibrotic strategies include antagonists of transforming growth factor-β, connective tissue growth factor, several tyrosine kinase ligands (epidermal growth factor, platelet-derived growth factor, vascular endothelial growth factor), endothelin and inhibitors of chemotaxis. Although many of these drugs are mainly being developed and marketed for oncological indications and diseases, such as idiopathic pulmonary fibrosis, a number may hold promise in the treatment of diabetic nephropathy, which could eventually lead to applications in renal transplantation.

Biopsy transcriptome expression profiling to identify kidney transplants at risk of chronic injury: a multicentre, prospective study

BACKGROUND

Chronic injury in kidney transplants remains a major cause of allograft loss. The aim of this study was to identify a gene set capable of predicting renal allografts at risk of progressive injury due to fibrosis.

METHODS

This Genomics of Chronic Allograft Rejection (GoCAR) study is a prospective, multicentre study. We prospectively collected biopsies from renal allograft recipients (n=204) with stable renal function 3 months after transplantation. We used microarray analysis to investigate gene expression in 159 of these tissue samples. We aimed to identify genes that correlated with the Chronic Allograft Damage Index (CADI) score at 12 months, but not fibrosis at the time of the biopsy. We applied a penalised regression model in combination with permutation-based approach to derive an optimal gene set to predict allograft fibrosis. The GoCAR study is registered with ClinicalTrials.gov, number NCT00611702.

FINDINGS

We identified a set of 13 genes that was independently predictive for the development of fibrosis at 1 year (ie, CADI-12 ≥2). The gene set had high predictive capacity (area under the curve [AUC] 0·967), which was superior to that of baseline clinical variables (AUC 0·706) and clinical and pathological variables (AUC 0·806). Furthermore routine pathological variables were unable to identify which histologically normal allografts would progress to fibrosis (AUC 0·754), whereas the predictive gene set accurately discriminated between transplants at high and low risk of progression (AUC 0·916). The 13 genes also accurately predicted early allograft loss (AUC 0·842 at 2 years and 0·844 at 3 years). We validated the predictive value of this gene set in an independent cohort from the GoCAR study (n=45, AUC 0·866) and two independent, publically available expression datasets (n=282, AUC 0·831 and n=24, AUC 0·972).

INTERPRETATION

Our results suggest that this set of 13 genes could be used to identify kidney transplant recipients at risk of allograft loss before the development of irreversible damage, thus allowing therapy to be modified to prevent progression to fibrosis.

FUNDING

National Institutes of Health.

The Emerging Role of DNA Methylation in Kidney Transplantation: A Perspective

Allograft outcome depends on a range of factors, including donor age, the allo-immune response, ischemia-reperfusion injury, and interstitial fibrosis of the allograft. Changes in the epigenome, and in DNA methylation in particular, have been implicated in each of these processes, in either the kidney or other organ systems. This review provides a primer for DNA methylation analyses and a discussion of the strengths and weaknesses of current studies, but it is also a perspective for future DNA methylation research in kidney transplantation. We present exciting prospects for leveraging DNA methylation analyses as a tool in kidney biology research, and as a diagnostic or prognostic marker for predicting allograft quality and success. Topics discussed include DNA methylation changes in aging and in response to hypoxia and oxidative stress upon ischemia-reperfusion injury. Moreover, emerging evidence suggests that DNA methylation contributes to organ fibrosis and that systemic DNA methylation alterations correlate with the rate of kidney function decline in patients with chronic kidney disease and end-stage renal failure. Monitoring or targeting the epigenome could therefore reveal novel therapeutic approaches in transplantation and open up paths to biomarker discovery and targeted therapy.

The effect of anastomosis time on outcome in recipients of kidneys donated after brain death: a cohort study

Whether warm ischemia during the time to complete the vascular anastomoses determines renal allograft function has not been investigated systematically. We investigated the effect of anastomosis time on allograft outcome in 669 first, single kidney transplantations from brain-dead donors. Anastomosis time independently increased the risk of delayed graft function (odds ratio per minute [OR] 1.05, 95% confidence interval [CI] 1.02-1.07, p < 0.001) and independently impaired allograft function after transplantation (p = 0.009, mixed-models repeated-measures analysis). In a subgroup of transplant recipients, protocol-specified biopsies at 3 months (n = 186), 1 year (n = 189), and 2 years (n = 153) were blindly reviewed. Prolonged anastomosis time independently increased the risk of interstitial fibrosis and tubular atrophy on these protocol-specified biopsies posttransplant (p < 0.001, generalized linear models). In conclusion, prolonged anastomosis time is not only detrimental for renal allograft outcome immediately after transplantation, also longer-term allograft function and histology are affected by the duration of this warm ischemia.

siRNA technology in kidney transplantation: current status and future potential

Kidney transplantation is one of the most common transplantation operations in the world, accounting for up to 50 % of all transplantation surgeries. To curtail the damage to transplanted organs that is caused by ischemia-reperfusion injury and the recipient's immune system, small interfering RNA (siRNA) technology is being explored. Importantly, the kidney as a whole is a preferential site for non-specific systemic delivery of siRNA. To date, most attempts at siRNA-based therapy for transplantation-related conditions have remained at the in vitro stage, with only a few of them being advanced into animal models. Hydrodynamic intravenous injection of naked or carrier-bound siRNAs is currently the most common route for delivery of therapeutic constructs. To our knowledge, no systematic screens for siRNA targets most relevant for kidney transplantation have been attempted so far. A majority of researchers have arrived at one or another target of interest by analyzing current literature that dissects pathological processes taking place in transplanted organs. A majority of the genes that make up the list of 53 siRNA targets that have been tested in transplantation-related models so far belong to either apoptosis- or immune rejection-centered networks. There is an opportunity for therapeutic siRNA combinations that may be delivered within the same delivery vector or injected at the same time and, by targeting more than one pathway, or by hitting the same pathways within two different key points, will augment the effects of each other.

Intronic locus determines SHROOM3 expression and potentiates renal allograft fibrosis

Fibrosis underlies the loss of renal function in patients with chronic kidney disease (CKD) and in kidney transplant recipients with chronic allograft nephropathy (CAN). Here, we studied the effect of an intronic SNP in SHROOM3, which has previously been linked to CKD, on the development of CAN in a prospective cohort of renal allograft recipients. The presence of the rs17319721 allele at the SHROOM3 locus in the donor correlated with increased SHROOM3 expression in the allograft. In vitro, we determined that the sequence containing the risk allele at rs17319721 is a transcription factor 7-like 2-dependent (TCF7L2-dependent) enhancer element that functions to increase SHROOM3 transcription. In renal tubular cells, TGF-β1 administration upregulated SHROOM3 expression in a β-catenin/TCF7L2-mediated manner, while SHROOM3 in turn facilitated canonical TGF-β1 signaling and increased α1 collagen (COL1A1) expression. Inducible and tubular cell-specific knockdown of Shroom3 markedly abrogated interstitial fibrosis in mice with unilateral ureteric obstruction. Moreover, SHROOM3 expression in allografts at 3 months after transplant and the presence of the SHROOM3 risk allele in the donor correlated with increased allograft fibrosis and with reduced estimated glomerular filtration rate at 12 months after transplant. Our findings suggest that rs17319721 functions as a cis-acting expression quantitative trait locus of SHROOM3 that facilitates TGF-β1 signaling and contributes to allograft injury.

The impact of stem cells on electron fluxes, proton translocation, and ATP synthesis in kidney mitochondria after ischemia/reperfusion

Tissue damage by ischemia/reperfusion (I/R) results from a temporary cessation of blood flow followed by the restoration of circulation. The injury depresses mitochondrial respiration, increases the production of reactive oxygen species (ROS), decreases the mitochondrial transmembrane potential, and stimulates invasion by inflammatory cells. The primary objective of this work was to address the potential use of bone marrow stem cells (BMSCs) to preserve and restore mitochondrial function in the kidney after I/R. Mitochondria from renal proximal tubule cells were isolated by differential centrifugation from rat kidneys subjected to I/R (clamping of renal arteries followed by release of circulation after 30 min), without or with subcapsular administration of BMSCs. Respiration starting from mitochondrial complex II was strongly affected following I/R. However, when BMSCs were injected before ischemia or together with reperfusion, normal electron fluxes, electrochemical gradient for protons, and ATP synthesis were almost completely preserved, and mitochondrial ROS formation occurred at a low rate. In homogenates from cultured renal cells transiently treated with antimycin A, the coculture with BMSCs induced a remarkable increase in protein S-nitrosylation that was similar to that found in mitochondria isolated from I/R rats, evidence that BMSCs protected against both superoxide anion and peroxynitrite. Labeled BMSCs migrated to damaged tubules, suggesting that the injury functions as a signal to attract and host the injected BMSCs. Structural correlates of BMSC injection in kidney tissue included stimulus of tubule cell proliferation, inhibition of apoptosis, and decreased inflammatory response. Histopathological analysis demonstrated a score of complete preservation of tubular structures by BMSCs, associated with normal plasma creatinine and urinary osmolality. These key findings shed light on the mechanisms that explain, at the mitochondrial level, how stem cells prevent damage by I/R. The action of BMSCs on mitochondrial functions raises the possibility that autologous BMSCs may help prevent I/R injuries associated with transplantation and acute renal diseases.

Pre-existing arteriosclerotic intimal thickening in living-donor kidneys reflects allograft function

BACKGROUND

Donor shortage is a serious problem worldwide and it is now debated whether kidneys from marginal donors are suitable for renal transplantation. Recent studies have shown that the findings of preimplantation kidney biopsy are useful to evaluate vasculopathy in the donated kidney, and may predict transplant outcomes in deceased- donor kidney transplantation. However, few studies have focused on the pathological findings of preimplantation biopsy in living-donor kidney transplantation. Therefore, we investigated whether arteriosclerotic vasculopathy in living-donor kidneys at the time of transplantation predicts the recipient's kidney function (allograft function) later in life.

METHODS

We retrospectively analyzed 75 consecutive adult living-donor kidney transplants performed at Kagawa University Hospital. Renal arteriosclerotic vasculopathy was defined according to the presence of fibrous intimal thickening in the interlobular artery.

RESULTS

Forty-one kidneys exhibited mild arteriosclerotic vasculopathy on preimplantation kidney biopsies. The decreases in estimated glomerular filtration rate after donation were similar in donors with or without renal arteriosclerotic vasculopathy. Pre-existing arteriosclerotic vasculopathy did not affect graft survival rate, patient survival rate or the incidence of complications. Recipients of kidneys with arteriosclerotic vasculopathy had lower allograft function at 1 and 3 years after transplantation than the recipients of arteriosclerosis-free kidneys with or without donor hypertension. In multivariate analysis, fibrous intimal thickening on preimplantation biopsy was predictive of reduced allograft function at 1 year after transplantation.

CONCLUSIONS

The present study demonstrated that mild arteriosclerotic vasculopathy in the donated kidney is an important pathological factor that reflects future impaired function of renal allografts from marginal donors.

Connective tissue growth factor (CTGF/CCN2) ELISA: a novel tool for monitoring fibrosis

BACKGROUND

Connective tissue growth factor (CTGF) has been identified as a key factor in the pathogenesis of diseases with significant fibrosis-related complications such as hepatitis, diabetes and renal transplantation. Increasing evidence shows that CTGF levels in plasma, serum and urine have promising biomarker applicability in these disorders.

OBJECTIVE

To present an overview of current knowledge on CTGF in various patient populations and the technical aspects of CTGF measurement by enzyme-linked immunosorbent assay (ELISA).

METHOD

We performed a comprehensive literature search by using electronic bibliographic databases.

CONCLUSION

CTGF is associated with disease severity parameters and outcome in fibrotic disease and may have diagnostic and prognostic values. However, CTGF ELISA needs standardization.

Immunotherapy in elderly transplant recipients: a guide to clinically significant drug interactions

Currently, >50% of candidates for solid organ transplantation in Europe and the US are aged >50 years while approximately 15% of potential recipients are aged >or=65 years. Elderly transplant candidates are characterized by specific co-morbidity profiles that compromise graft and patient outcome after transplantation. The presence of coronary artery or peripheral vascular disease, cerebrovascular disease, history of malignancy, chronic obstructive lung disease or diabetes mellitus further increases the early post-transplant mortality risk in elderly recipients, with infections and cardiovascular complications as the leading causes of death. Not only are elderly patients more prone to developing drug-related adverse effects, but they are also more susceptible to pharmacokinetic and pharmacodynamic drug interactions because of polypharmacy. The majority of currently used immunosuppressant drugs in organ transplantation are metabolized by cytochrome P450 (CYP) or uridine diphosphate-glucuronosyltransferases and are substrates of the multidrug resistance (MDR)-1 transporter P-glycoprotein, the MDR-associated protein 2 or the canalicular multispecific organic anion transporter, which predisposes these immunosuppressant compounds to specific interactions with commonly prescribed drugs. In addition, important drug interactions between immunosuppressant drugs have been identified and require attention when choosing an appropriate immunosuppressant drug regimen for the frail elderly organ recipient. An age-related 34% decrease in total body clearance of the calcineurin inhibitor ciclosporin was observed in elderly renal recipients (aged >65 years) compared with younger patients, while older recipients also had 44% higher intracellular lymphocyte ciclosporin concentrations. Similarly, using a Bayesian approach, an inverse relationship was noted between sirolimus clearance and age in stable kidney recipients. Ciclosporin and tacrolimus have distinct pharmacokinetics, but both are metabolized by intestinal and hepatic CYP3A4/3A5 and transported across the cell membrane by P-glycoprotein. The most common drug interactions with ciclosporin are therefore also observed with tacrolimus, but the two drugs do not interact identically when administered with CYP3A inhibitors or inducers. The strongest effects on calcineurin-inhibitor disposition are observed with azole antifungals, macrolide antibacterials, rifampicin, calcium channel antagonists, grapefruit juice, St John's wort and protease inhibitors. Drug interactions with mycophenolic acids occur mainly through inhibition of their enterohepatic recirculation, either by interference with the intestinal flora (antibacterials) or by limiting drug absorption (resins and binders). Rifampicin causes a reduction in mycophenolic acid exposure probably through induction of uridine diphosphate-glucuronosyltransferases. Proliferation signal inhibitors (PSIs) such as sirolimus and everolimus are substrates of CYP3A4 and P-glycoprotein and have a macrolide structure very similar to tacrolimus, which explains why common drug interactions with PSIs are comparable to those with calcineurin inhibitors. Ciclosporin, in contrast to tacrolimus, inhibits the enterohepatic recirculation of mycophenolic acids, resulting in significantly lower concentrations and hence risk of underexposure. Therefore, when switching from tacrolimus to ciclosporin and vice versa or when reducing or withdrawing ciclosporin, this interaction needs to be taken into account. The combination of ciclosporin with PSIs requires dose reductions of both drugs because of a synergistic interaction that causes nephrotoxicity when left uncorrected. Conversely, when switching between calcineurin inhibitors, intensified monitoring of PSI concentrations is mandatory. Increasing age is associated with structural and functional changes in body compartments and tissues that alter absorptive capacity, volume of distribution, hepatic metabolic function and renal function and ultimately drug disposition. While these age-related changes are well-known, few specific effects of the latter on immunosuppressant drug metabolism have been reported. Therefore, more clinical data from elderly organ recipients are urgently required.

Ischemia/reperfusion injury in kidney transplantation: mechanisms and prevention

Ischemia has been an inevitable event accompanying kidney transplantation. Ischemic changes start with brain death, which is associated with severe hemodynamic disturbances: increasing intracranial pressure results in bradycardia and decreased cardiac output; the Cushing reflex causes tachycardia and increased blood pressure; and after a short period of stabilization, systemic vascular resistance declines with hypotension leading to cardiac arrest. Free radical-mediated injury releases proinflammatory cytokines and activates innate immunity. It has been suggested that all of these changes-the early innate response and the ischemic tissue damage-play roles in the development of adaptive responses, which in turn may lead to an acute font of kidney rejection. Hypothermic kidney storage of various durations before transplantation add to ischemic tissue damage. The final stage of ischemic injury occurs during reperfusion. Reperfusion injury, the effector phase of ischemic injury, develops hours or days after the initial insult. Repair and regeneration processes occur together with cellular apoptosis, autophagy, and necrosis; the fate of the organ depends on whether cell death or regeneration prevails. The whole process has been described as the ischemia-reperfusion (I-R) injury. It has a profound influence on not only the early but also the late function of a transplanted kidney. Prevention of I-R injury should be started before organ recovery by donor pretreatment. The organ shortage has become one of the most important factors limiting extension of deceased donor kidney transplantation worldwide. It has caused increasing use of suboptimal deceased donors (high risk, extended criteria [ECD], marginal donors) and uncontrolled non-heart-beating (NHBD) donors. Kidneys from such donors are exposed to much greater ischemic damage before recovery and show reduced chances for proper early as well as long-term function. Storage of kidneys, especially those recovered from ECD (or NHBD) donors, should use machine perfusion.

Pathogenesis and management of chronic allograft nephropathy

Chronic allograft nephropathy (CAN) is a common cause of late kidney transplant failure, characterized by progressive histological damage in the allograft. Although functional biomarkers such as creatinine are typically used to predict CAN, recent evidence suggests that composite, quantitative histological indices may be better predictors of long-term graft outcomes. Calcineurin inhibitors (CNIs) have been associated with major improvements in early rejection outcomes, but appear to cause both acute and chronic nephrotoxicity. The acute phase is associated with functional nephrotoxicity and is reversible with a reduction in CNI dosage, whereas the chronic phase is characterized by persistent histological lesions that are typically irreversible. Results from recent clinical trials suggest that converting from a CNI to sirolimus, withdrawing a CNI from a sirolimus-based regimen or using a CNI-free strategy may improve long-term outcomes by reducing CNI-related nephrotoxicity. However, in the de novo transplant setting, triple therapy with sirolimus, mycophenolate mofetil and corticosteroids is not recommended in combination with basiliximab induction. A treatment algorithm, based on the patient's histological score obtained on an allograft biopsy taken at approximately 6-12 months post-transplant, has been developed by our group and is described here.

Chronic allograft nephropathy

PURPOSE OF REVIEW

Despite dramatic declines in acute rejection and early graft failure, long-term outcomes after kidney transplantation have improved little during the past 25 years. Most late allograft failure is attributed to chronic allograft nephropathy, but this is a clinicopathological description and not a diagnosis, and its pathogenesis and treatment are largely unknown.

RECENT FINDINGS

Recent studies suggest that acute rejection during the first few months, and calcineurin inhibitor toxicity thereafter, may both contribute to chronic allograft nephropathy. There is also accumulating evidence that injury from antibody-mediated rejection may play an important pathogenic role in at least some patients with chronic allograft nephropathy, particularly those with transplant glomerulopathy. Therapeutic measures, including protocols to reduce calcineurin inhibitor exposure, remain largely unproven.

SUMMARY

Understanding why so many kidney allografts fail, despite effective preventive measures for early acute rejection, is one of the most important areas of research in kidney transplantation today.

Sirolimus versus cyclosporine therapy increases circulating regulatory T cells, but does not protect renal transplant patients given alemtuzumab induction from chronic allograft injury

BACKGROUND

In kidney transplant recipients with alemtuzumab induction maintained on mycophenolate mofetil (MMF) immunosuppression, sirolimus (SRL) promotes significant expansion of circulating CD4+CD25high regulatory T cells (Treg). This might translate into more effective protection against chronic graft injury compared to cyclosporin A (CsA), which, in the same clinical setting, does not affect Treg.

METHODS

To assess this hypothesis, in the extension of a single-center, prospective, randomized, open, blind endpoint study aimed to assess the effect of low-dose SRL or CsA on circulating Treg, we compared the outcomes of renal transplant recipients on SRL (n=11) or CsA (n=10) by per-protocol biopsies and serial measurements of glomerular filtration rate (GFR), renal plasma flow (RPF), and 24-hour proteinuria over 30 months posttransplant.

RESULTS

Despite 4-fold higher CD4+CD25high Treg counts (22.1+/-12.2% vs. 5.7+/-4.2% of CD3+CD4+ T cells), SRL-treated patients, compared to CsA-treated patients, had a significantly higher tubular C4d staining score (1.1+/-0.6 vs. 0.2+/-0.3, P<0.01), with nonsignificant trends to higher chronic allograft damage index score (5.6+/-2.4 vs. 3.7+/-3.3), faster GFR (-2.92+/-0.33 vs. -0.28+/-0.44 ml/min/1.73 m2 per year), and RPF (-10.80+/-5.45 vs. -1.86+/-3.09 ml/min/1.73 m2 per year) decline, and more clinical proteinuria (n=6 vs. 4). There was no significant correlation between Treg counts and any considered outcome variable in the study group as a whole and within each cohort.

CONCLUSIONS

These data suggest that, despite enhanced Treg expression, low-dose SRL combined to alemtuzumab induction and MMF-based steroid-free maintenance therapy, does not appreciably protect renal transplant recipients from chronic allograft injury and dysfunction.