Protocol Renal Allograft Biopsies Research Articles

Association of high intra-patient variability in tacrolimus exposure with calcineurin inhibitor nephrotoxicity in kidney transplantation

Tacrolimus intra-patient variability (IPV) is a novel predictive marker for long-term kidney transplantation outcomes. We examined the association between IPV and calcineurin inhibitor (CNI) nephrotoxicity and the impact of pharmacogenes on CNI nephrotoxicity and IPV. Among kidney transplant recipients at our hospital between January 2013 and December 2015, the records of 80 patients who underwent 1-year protocol renal allograft biopsy and agreed to donate blood samples for genetic analysis were retrospectively reviewed. The cohort was divided into the low and high IPV groups based on a coefficient variability cutoff value (26.5%). In multivariate analysis, the IPV group was involved in determining CNI nephrotoxicity (HR 4.55; 95% CI 0.05–0.95; p = 0.043). The 5-year graft survival was superior in the low IPV group than in the high IPV group (100% vs 92.4% respectively, p = 0.044). Analysis of the time above therapeutic range (TATR) showed higher CNI nephrotoxicity in the high IPV with high TATR group than in the low IPV with low TATR group (35.7% versus 6.7%, p = 0.003). Genetic analysis discovered that CYP3A4 polymorphism (rs2837159) was associated with CNI nephrotoxicity (HR 28.23; 95% CI 2.2–355.9; p = 0.01). In conclusion, high IPV and CYP3A4 polymorphisms (rs2837159) are associated with CNI nephrotoxicity.

Comparison of 2-week and 1-year protocol renal allograft biopsies regarding technical feasibility and clinical outcomes

Comparison of 2-week and 1-year protocol renal allograft biopsies regarding technical feasibility and clinical outcomes

SP438Differential protein expression in protocol renal allograft biopsies from diabetic patients

SP438Differential protein expression in protocol renal allograft biopsies from diabetic patients

Clinical Significance of Renal Allograft Protocol Biopsies: A Single Tertiary Center Experience in Malaysia.

Background The role of protocol renal allograft biopsy in kidney transplantation is controversial due to the concern with procedural-related complications; however, its role is slowly evolving. Recent evidence suggests that protocol biopsy is useful in detecting subclinical renal pathology. Early recognition and treatment of renal pathologies can improve long-term outcomes of renal allografts. Methodology A total of 362 renal allograft protocol biopsies were performed in adult recipients of kidney transplantation between 2012 and 2017. After excluding those with poor quality or those performed with a baseline serum creatinine level >200 umol/L, we analyzed 334 (92.3%) biopsies. Histology reports were reviewed and categorized into histoimmunological and nonimmunological changes. The immunological changes were subcategorized into the following: (1) no acute rejection (NR), (2) borderline changes (BC), and (3) subclinical rejection (SCR). Nonimmunological changes were subcategorized into the following: (1) chronicity including interstitial fibrosis/tubular atrophy (IFTA), chronic T-cell-mediated rejection (TCMR), unspecified chronic lesions, and arterionephrosclerosis, (2) de novo glomerulopathy/recurrence of primary disease (RP), and (3) other clinically unsuspected lesions (acute pyelonephritis, calcineurin inhibitors toxicity, postinfective glomerulonephritis, and BK virus nephropathy). Risk factors associated with SCR were assessed. Results For the histoimmunological changes, 161 (48.2%) showed NR, 145 (43.4%) were BC, and 28 (8.4%) were SCR. These clinical events were more pronounced for the first 5 years; our data showed BC accounted for 59 (36.4%), 64 (54.2%), and 22 (40.7%) biopsies within <1 year, 1-5 years, and > 5 years, respectively (p = 0.011). Meanwhile, the incidence for SCR was 6 (3.7%) biopsies in <1 year, 18 (15.3%) in 1-5 years, and 4 (7.4%) in >5 years after transplantation (p=0.003). For the nonimmunological changes, chronicity, de novo glomerulopathy/RP, and other clinically unsuspected lesions were seen in 40 (12%), 10 (3%), and 12 (3.6%) biopsies, respectively. Living-related donor recipients were associated with decreased SCR (p=0.007). Conclusions Despite having a stable renal function, our transplant recipients had a significant number of subclinical rejection on renal allograft biopsies.

Living-Donor Kidney Transplant With Preformed Donor-Specific Antibodies.

We investigated outcomes in living-donor kidney transplant recipients with preformed donor-specific antibodies (detected with flow cytometry and specified with the LABScreen single antigen test) under desensitization pretransplant and immunosuppression posttransplant. Of 15 recipients included, 8 had ABO-incompatible kidney transplant. Six patients had sensitization caused by pregnancy, 8 by blood transfusion, 5 by previous transplants, and 1 by unknown cause. Desensitization was initiated using calcineurin inhibitors, methylprednisolone, and mycophenolate mofetil 30 days pretransplant, with rituximab administered 1 and 10 days pretransplant. Patients underwent plasmapheresis 1, 3, and 5 days pretransplant. Antithymocyte globulin was admi nistered for 5 days posttransplant as induction therapy. At 3 and 12 months posttransplant, all recipients underwent protocol renal allograft biopsies, with donor-specific antibodies simultaneously measured with the single antigen test. T-cell complement-dependent cytotoxicity crossmatch was negative in all 15 recipients, but T-cell and B-cell flow cytometry was positive in 8 and 14 recipients, respectively. Anti-HLA class I antibodies became negative, except in 1 recipient 3 months posttransplant. Class II antibodies remained positive in 8 recipients 3 months posttransplant. No clinical or subclinical T-cell-mediated rejection occurred, but 1 recipient experienced clinical acute antibody-mediated rejection. At 3 and 12 months posttransplant, 8 and 5 recipients had subclinical acute antibody-mediated rejection. Cytomegalovirus test showed positivity in 14 recipients, but none developed cytomegalovirus disease. BK viremia was detected in 2 recipients, with 1 developing BK virus nephropathy, which was reversed by reducing immunosuppression. Transplant patients with preformed donor-specific antibodies showed good outcomes in terms of desensitization and immunosuppression. However, most anti-HLA class II donor-specific antibodies remained, and microvascular inflammation score could indicate long-term risk of renal allograft dysfunction.

Page Kidney Following a Nonepisode Protocol Renal Allograft Biopsy: A Case Report

Page kidney refers to a clinical condition that is characterized by the acute onset of hypertension and renal dysfunction owing to external compression of the kidney by a hematoma, tumor, lymphocele, or urinoma. We report a case in which Page kidney occurred after a nonepisode protocol renal allograft biopsy. A 31-year-old man with end-stage renal disease received a living related kidney transplant from his father. One year later, a nonepisode protocol renal allograft biopsy was performed. A day later, the patient's serum creatinine level increased to 4.23 mg/dL, and a subcapsular renal hematoma was detected using ultrasonography and computed tomography. Page kidney was diagnosed, and immediate surgical removal of the hematoma was performed. Nine days after the operation, the patient's serum creatinine level had improved to 1.89 mg/dL. Page kidney is a serious but treatable complication of renal allograft biopsies, and clinicians should pay attention to such complications, even in the setting of nonepisode protocol renal allograft biopsies.

Subclinical Antibody-Mediated Rejection

Subclinical Antibody-Mediated Rejection

Chronic renal allograft dysfunction in Egyptian population: Histopathological and immunohistochemical study.

The chronic dysfunction stands as the most common cause of renal allograft loss. During the nineties of the past century, this condition was referred to as chronic allograft nephropathy (CAN). Since 2005, CAN has been assigned by the eighth Banff schema to four main categories via histopathological and immunohistochemical findings including chronic antibodymediated rejection (CAMR), chronic T-cell-mediated rejection (CTMR), chronic cyclosporine toxicity (CNITOX), and "interstitial fibrosis (IF)/tubular atrophy; not otherwise specified (NOS)" to eliminate the term CAN. We conducted a retrospective study of renal allograft cases with biopsy-proven chronic damage diagnosed at our nephropathology units, between January 2007 and September 2013, to assign them to the defined categories. Differences between groups were tested using one-way analysis of variance. The frequencies of the diagnostic categories were as follow: CNITOX (43.1%), CAMR (27.5%), CTMR (17.6%), and NOS (11.8%). The serum creatinine level, time posttransplant, and global sclerosis frequency were insignificant among the categories. Nine categorized cases showed transplant glomerulopathy; five of them were seen in association with CAMR. There was a positive relationship between the number of interstitial CD8 + T cells and the degree of IF in CTMR cases. Two cases showed combined features of CAMR and CTMR. Protocol renal allograft biopsy starting 3 months after transplantation with proper monitoring and adjustment of the calcineurin inhibitors level may reduce the potential risk of chronic damage in renal allograft.

The Role of Macrophages in the Development of Human Renal Allograft Fibrosis in the First Year After Transplantation

The aim of this study was to investigate the role of infiltrating macrophages in renal allograft fibrosis. Forty-six protocol renal allograft biopsies obtained 1 year after transplantation were stained with Sirius red to quantify fibrosis and double stained with CD68 and CD206 to identify the proportion of alternatively activated (M2) macrophages. Biopsies were analyzed for gene expression by microarray, which was correlated with macrophage infiltration and the severity of fibrosis. The number of infiltrating CD68+ cells strongly correlated with the percentage of interstitial fibrosis (r = 0.73, p < 0.0001). Macrophage infiltration at 1 year correlated with renal dysfunction at 1, 12 and 36 months posttransplant (estimated GFR low vs. high: 1 month 78 ± 26 vs. 54 ± 19 mL/min, p < 0.01; 12 months 87 ± 29 vs. 64 ± 19 mL/min, p < 0.05; 36 months 88 ± 33 vs. 60 ± 24 mL/min, p < 0.05). Ninety-two percent of infiltrating macrophages exhibited an M2 phenotype with CD68+ CD206+ dual staining. Gene microarrays demonstrated an alloimmune response with up-regulation of interferon-γ-response genes despite the lack of rejection or inflammatory infiltrate. Consistent with this was the presence of CXCL10 in proximal tubular cells at 3 months. This suggests that M2 macrophage proliferation, or infiltration, was associated with subclinical alloimmune inflammation, tubular injury and progression of fibrosis.

Intragraft Gene Expression in Positive Crossmatch Kidney Allografts: Ongoing Inflammation Mediates Chronic Antibody-Mediated Injury

We studied intragraft gene expression profiles of positive crossmatch (+XM) kidney transplant recipients who develop transplant glomerulopathy (TG) and those who do not. Whole genome microarray analysis and quantitative rt-PCR were performed on RNA from protocol renal allograft biopsies in three groups: (1) +XM/TG+ biopsies before and after TG; (2) +XM/NoTG; and (3) negative crossmatch kidney transplants (control). Microarray comparisons showed few differentially expressed genes between paired biopsies from +XM/TG+ recipients before and after the diagnosis of TG. Comparing +XM/TG+ and control groups, significantly altered expression was seen for 2447 genes (18%) and 3200 genes (24%) at early and late time points, respectively. Canonical pathway analyses of differentially expressed genes showed inflammatory genes associated with innate and adaptive immune responses. Comparing +XM/TG+ and +XM/NoTG groups, 3718 probe sets were differentially expressed but these were over-represented in only four pathways. A classic accommodation phenotype was not identified. Using rt-PCR, the expression of inflammatory genes was significantly increased in +XM/TG+ recipients compared to the +XM/NoTG and control groups. In conclusion, pretransplant donor-specific anti-HLA antibodies results in a gene expression profile characterized by inflammation and cellular infiltration and the majority of +XM grafts are exposed to chronic injury.

Enhanced resolution of interstitial fibrosis in pediatric renal allograft biopsies using image analysis of trichrome stain

The Banff classification is ill suited to detect subtle histologic progression in renal allografts. We present image analysis methodology to precisely quantify IF in pediatric renal allograft biopsies routinely stained with MT. The mean area %IF was determined in 105 pediatric renal allograft biopsies. Associations between %IF or Banff ci scores and estimated GFR were determined using GEE modeling. Logistic regression was used to estimate IF progression. Percent IF (mean ± s.d.) was 6.83% ± 3.94, 10.39 ± 5.23%, and 20.53 ± 8.74 in patients with ci0, ci1, and ci2, respectively. The difference in %IF between biopsies with ci0, ci1, and ci2 was not proportionately incremental: compared to ci2, ci0 had 67% less IF (p < 0.0001), while ci1 had 48% less IF (p < 0.0001). AR had no impact on the precision of %IF measurements. Each 0.5% decrement in %IF was associated with a 1 mL/min per 1.73 m² increase in GFR (p < 0.004). Histologic progression was demonstrated by increasing %IF values (p < 0.0001) and could be estimated by IF = 2.61 × (months) + 6.43. This readily adaptable methodology may be used for the longitudinal assessment of IF in pediatric protocol renal allograft biopsies.

Intragraft Tubular Vimentin and CD44 Expression Correlate With Long-Term Renal Allograft Function and Interstitial Fibrosis and Tubular Atrophy

Development of interstitial fibrosis and tubular atrophy (IF/TA) is the main histologic feature involved in renal allograft deterioration. The aim of this study was to validate whether de novo tubular expression of CD44 (transmembrane glycoprotein) and vimentin (mesenchymal cell marker), both involved in renal fibrosis, can operate as surrogate markers for late IF/TA and renal function. Furthermore, we wanted to establish the interrater reproducibility for the scoring system, which can be a problem in histologic assessments. Six-month protocol renal allograft biopsies (n=30 for matching 12 months estimated glomerular filtration rate (eGFR) from which 20 matched the 12-month protocol biopsy) were immunostained for CD44 and vimentin, semiquantitatively scored by three observers of two centers, and correlated with IF/TA and eGFR at 12 months. The interobserver agreement was excellent for CD44 (Kendall's W-coefficient: 0.69; P<0.001) and vimentin (Kendall's W-coefficient: 0.79; P<0.001). CD44 and vimentin expression at 6 months were significantly correlated with IF/TA (rho=0.481 for CD44 and rho=0.619 for vimentin) and eGFR (rho=-0.569 for CD44 and rho=-0.376 for vimentin) at 12 months. Summarizing, de novo tubular expression of CD44 and vimentin can function as surrogate marker for IF/TA and eGFR at 12 months. Further area under receiver operator characteristic curve analysis has to establish the predictive value for both biomarkers.

Patterns of Chronic Injury in Pediatric Renal Allografts

In pediatric recipients, the pathophysiology of chronic renal allograft injury is poorly understood. We studied the evolution and determinants of tubulointerstitial, vascular, and glomerular injury in 240 pediatric protocol renal allograft biopsies during the first 5 years posttransplant. Chronic tubulointerstitial injury (ci, ct) developed predominantly during the first 12 months posttransplant, whereas chronic vascular damage (cv, and arteriolar hyalinosis [ah]) and global glomerulosclerosis (gs) became increasingly prevalent at 25 to 36 months and beyond. Chronic interstitial lesions were associated with acute rejection and borderline histology (odds ratio [OR] 2.3, P<0.04), recipient body surface area less than 1.0 m2 (OR 3.6, P<0.05), and obesity (OR 2.0, P<0.03). Determinants of ct were acute rejection (OR 2.6, P=0.02) and acute tubular necrosis (OR 2.8, P<0.04). Vascular fibrous intimal thickening and ah were associated with donor hypertension (OR 3.6, P=0.001) and recipient body surface area less than 1.0 m (OR 2.6, P=0.02), respectively. The severity of ah correlated with the incidence of gs (r=0.32, P<0.0001), with 7.8% gs for ah0, 14.3% gs for ah1, 60.0% gs for ah2, and 95.5% gs for ah3 (median values). Antibody induction conferred protection from ci (OR 0.31, P=0.008), ct (OR 0.33, P=0.002), and ah (OR 0.12, P<0.001) progression. By 5 years posttransplant, pediatric renal allografts manifest a substantial burden of tubulointerstitial and microvascular injury. These lesions are associated with donor hypertension, acute inflammation, renal hypoperfusion, obesity, and calcineurin inhibitor toxicity. The pervasiveness and rapid progression of microvascular lesions at 25 to 36 months suggest that attempts at reducing calcineurin inhibitor exposure should be made before two years posttransplant.

Calcineurin inhibitor toxicity in renal allografts: Morphologic clues from protocol biopsies

Calcineurin inhibitors (cyclosporine and tacrolimus) are important constituents of post renal transplant immunosuppression. However, renal toxicity limits their utility. Histological features of calcineurin inhibitor toxicity (CNIT) have been the subject of few studies using protocol biopsy samples, and consensus on diagnostic criteria is still evolving. To analyze the spectrum of histological changes in protocol renal allograft biopsies with evidence of CNIT and identify additional features that are likely to help the pathologist in arriving at a diagnosis. One hundred and forty protocol allograft biopsies performed at 1, 6 and 12 months post renal transplant were studied. The defining features of CNIT included: isometric vacuolization of proximal tubular cells, arteriolar hyalinosis with medial/peripheral nodules and striped pattern of tubular atrophy/interstitial fibrosis. Other features such as global glomerulosclerosis, vacuolization of smooth muscle cells of arterioles, tubular microcalcinosis, ischemic shrinkage of glomeruli and hyperplasia of juxtaglomerular apparatus (JGA) were also analyzed and graded semiquantitatively. CNIT was seen in 17/140 protocol biopsies (12.1%). In addition to the diagnostic criteria, arteriolar hyalinosis, smooth muscle cell vacuolization of arterioles and hyperplasia of JGA were found to be useful indicators of CNIT. There is a relatively high incidence of CNIT in protocol allograft biopsies. A critical analysis of renal biopsy in adequate number of serial step sections to identify these features is mandatory, as many of these features are subtle and are likely to be missed if not specifically sought.

Ultrastructural alterations in endothelial mitochondria are associated with enhanced nitrotyrosine accumulation and progressive reduction of VEGF expression in sequential protocol renal allograft biopsies with calcineurin inhibitor toxicity

Calcineurin inhibitors (cyclosporine and tacrolimus; CNIs) continue to be used as constituents of post-transplant immunosuppression in most centers. However, renal toxicity associated with the use of these drugs remains a problem adversely affecting the long-term graft survival. Fifteen adequate protocol renal allograft biopsies, with histological features of CNI toxicity among 140 protocol biopsies performed at 1-, 6-, and 12-month post-transplant, were included. Mitochondrial alterations in the tubular epithelial cells and endothelia of glomerular, peritubular capillaries and arterioles were graded semiquantitatively and further ultrastructural morphometric evaluation of numerical density and area of the mitochondria was performed. Immunohistochemical staining for nitrotyrosine (marker of peroxynitrite formation) and vascular endothelial growth factor (VEGF) was performed and expression graded semiquantitatively. Higher grades of alterations were seen in endothelial mitochondria as compared with tubular mitochondria in biopsies with calcineurin inhibitor toxicity (CNIT). Endothelial mitochondrial numerical density showed progressive decline over 1-, 6- and 12-month biopsies while area showed progressive increase in biopsies with CNIT as compared with controls. Upregulation of nitrotyrosine was seen even at 1-month post-transplant, persisted at 6 and 12 months, and was significantly greater than that in control biopsies. Intense VEGF expression was noted in early CNIT while progressive reduction was seen in 6- and 12-month protocol biopsies. This study shows a relatively high incidence of CNIT in protocol renal allograft biopsies, indicating that this might be an important mechanism of background damage to the allograft. Structural alterations in endothelial mitochondria are consistent findings in protocol biopsies with CNIT and this relatively specific mitochondrial damage may stem from the peroxynitrite-mediated damage associated with progressive loss of protective function of VEGF.

Subclinical toxicity of calcineurin inhibitors in repeated protocol biopsies: an independent risk factor for chronic kidney allograft damage

The purpose of the prospective study was to determine the prevalence of subclinical toxicity of calcineurin inhibitors (CI) in repeated protocol renal allograft biopsies and to assess its impact on the development of chronic graft changes. A total of 424 biopsies were conducted in a cohort of 158 patients; of these biopsies, 158 were in the third week, 142 were in the third month and 124 were in the first year after transplantation. Histological signs of toxicity occurred in the third week in 33 (20.1%) patients, with persistence after CI dose reduction in the third month in 27 (19.0%) and in the first year in 23 (18.5%) patients. Of the toxic changes, 52% were clinically silent. At the end of the one-year follow-up, both subclinical and clinically manifest toxicity resulted in a similar progression of chronic changes quantified by Banff chronicity score and they significantly differed from the control group (P< 0.05). Subclinical toxicity affects a significant percentage of grafts; it occurs independently of dosage, blood level and type of applied CI. It is associated with the progression of chronic changes as early as in the first year after transplantation and represents an independent risk factor for chronic allograft damage. We report here our clinical approach to toxicity.

Interstitial Fibrosis and Tubular Atrophy in Renal Allograft Protocol Biopsies as a Surrogate of Graft Survival

Interstitial fibrosis and tubular atrophy (IF/TA) evaluated in protocol renal allograft biopsies are associated with decreased graft survival, especially when associated with transplant vasculopathy, subclinical rejection, or transplant glomerulopathy. IF/TA evaluated in protocol biopsies has been used as a secondary efficacy variable in clinical trials, some of which have shown that the prevalence of IF/TA depends on the type of immunosuppressive treatment. These observations suggest that IF/TA may be considered a surrogate of graft survival. However, there is an important difference between a predictive and a surrogate variable. A predictive variable is associated only with the main outcome variable, whereas in case of a surrogate variable, an additional condition must be accomplished; that is, modifications of the predictive variable as a result of treatment imply changes in the main outcome variable. In a trial of cyclosporine withdrawal from a cyclosporine-sirolimus-prednisone regimen, cyclosporine discontinuation was associated with less severe chronic lesions in protocol biopsies at 3 years and also with improved graft survival at 4 years. This observation suggest that IF/TA may be a surrogate of survival. This conclusion must be confirmed in other trials before accepting IF/TA as a real surrogate of graft outcome.

Pseudoaneurysm Complicating Protocol Renal Transplant Biopsies: Case Reports

Pseudoaneurysm is a rare complication of a renal biopsy procedure. We describe two cases of kidney transplant recipients who were diagnosed with a pseudoaneurysm more than 48 hours after protocol renal allograft biopsy and were successfully treated by selective embolization of the afferent artery.

Immunephenotype of Glomerular and Interstitial Infiltrating Cells in Protocol Renal Allograft Biopsies and Histological Diagnosis

Patients with a protocol renal allograft biopsy simultaneously displaying interstitial fibrosis/tubular atrophy (IF/TA) and subclinical rejection (SCR) have a shortened graft survival than patients with a normal biopsy, or with a biopsy only displaying IF/TA or SCR. The poor outcome of these patients could be related with a more severe inflammation. We evaluate the immunophenotype of infiltrating cells in these diagnostic categories. Nonexhausted paraffin blocks from protocol biopsies done during the first year were stained with anti-CD45, CD3, CD20, CD68 and CD15 monoclonal antibodies. Glomerular and interstitial positive cells were counted. C4d deposition in peritubular capillaries was evaluated. Histological diagnoses were: normal (n = 80), SCR (n = 17), IF/TA (n = 42) and IF/TA + SCR (n = 17). Only interstitial CD20 positive cells were significantly increased in patients displaying IF/TA + SCR; normal (137 +/- 117), SCR (202 +/- 145), IF/TA (208 +/- 151) and IF/TA + SCR (307 +/- 180 cells/mm(2)), p < 0.01. The proportion of biopsies displaying C4d deposition was not different among groups. The upper tertile of CD20 positive interstitial cells was associated with a decreased death-censored graft survival (relative risk: 3.01, 95% confidence interval: 1.23-7.35; p = 0.015). These data suggest that B-cell interstitial infiltrates are associated with histological damage and outcome, but do not distinguish whether these infiltrates were the cause or the consequence of chronic tubulo-interstitial damage.

Do We Have to Treat Subclinical Rejections in Early Protocol Renal Allograft Biopsies?

The aim of the present study was to evaluate whether treatment of subclinical, borderline rejections (SR/BR) or histological findings of chronic allograft nephropathy (CAN) in protocol biopsies in the first month posttransplantation after living related kidney transplantation has a beneficial effect on graft histology and renal function at 6 months. Among the 40 paired biopsies, only 6/80 showed no histological lesions. BR was found in 13/40 and 12/40, and SR in 15/40 and 21/40 of patients on the 1- and 6-month biopsies, respectively. The mean histological index/total sum of scores for acute and chronic changes (HI) increased at 6-month biopsy: 5.3 ± 2.9 vs 7.8 ± 3.6 ( P < .001). Similarly, the mean sum of histological markers for chronicity (CAN score) of 2.1 ± 1.5 increased to 4.6 ± 2.3 ( P < .001) on the 6-month biopsy. When divided according to whether there was treatment of BR and SR, the treated BR/SR group on 1-month biopsy had a mean HI score of 7.11 ± 1.9, which remained almost the same (7.11 ± 2.32) at 6 months. Among the untreated BR/SR group it increased from 4.95 ± 1.99 to 8.16 ± 4.30. However, there was no difference in graft function between the groups from 1 to 6 months. In conclusion, a protocol 1-month biopsy may be valuable to establish the prevalence of BR/SR in stable allografts. The presence of an untreated BR/SR upon a 1-month biopsy showed greater susceptibility for histological deterioration on the 6-month biopsy due to an accelerated CAN process.