Kidney Allograft Research Articles

Detection of Subclinical Rejection in Pediatric Kidney Transplantation: Current and Future Practices.

The successes in the field of pediatric kidney transplantation over the past 60 years have been extraordinary. Year over year, there have been significant improvements in short-term graft survival. However, improvements in longer-term outcomes have been much less apparent. One important contributor has been the phenomenon of low-level rejection in the absence of clinical manifestations-so-called subclinical rejection (SCR). Traditionally, rejection has been diagnosed by changes in clinical parameters, including but not limited to serum creatinine and proteinuria. This review examines the shortcomings of this approach, the effects of SCR on kidney allograft outcome, the benefits and drawbacks of surveillance biopsies to identify SCR, and new urine and blood biomarkers that define the presence or absence of SCR. Serum creatinine is an unreliable index of SCR. Surveillance biopsies are the method most utilized to detect SCR. However, these have significant drawbacks. New biomarkers show promise. These biomarkers include blood gene expression profiles and donor derived-cell free DNA; urine gene expression profiles; urinary cytokines, chemokines, and metabolomics; and other promising blood and urine tests. Specific emphasis is placed on studies carried out in pediatric kidney transplant recipients. ClinicalTrials.gov: NCT03719339.

Clinical Value of Peripheral Blood Gene Expression Profile and Donor-Derived Cellfree DNA for Identifying Persistent Rejection.

Persistent rejection is an increasingly recognized barrier to long-term kidney allograft survival. A noninvasive method to help identify patients with persistent rejection in need of biopsy would be valuable. This was a post-hoc analysis of a multicenter observational study. Subjects that had a biopsy-proven acute rejection and had another biopsy within 9 months (270 days) and had a biopsy-paired biomarker sample were included. A total of 64 "index" rejections in 58 subjects with repeat biopsies were identified with a median time to repeat biopsy of 100 days. Persistent rejection was present in 61%; 69% of follow-up biopsies were performed in clinically stable patients. Peripheral blood gene expression profile (GEP) demonstrated 59% sensitivity, 76% specificity, PPV of 79%, and NPV of 54%. Donor-derived cell-free DNA (dd-cfDNA) demonstrated sensitivity of 62%, specificity of 86%, PPV of 88%, and NPV of 56%. For repeat biopsies within 90 days of rejection in clinically stable patients (63% of repeat biopsies), both GEP and dd-cfDNA had specificities and PPVs of 100%. GEP was more likely to be positive in TCMR, while dd-cfDNA was more likely to be positive in AMR. Both GEP and dd-cfDNA may have utility at identifying clinically stable patients with persistent rejection in need of biopsy, however they identify different types of rejection.

Pre-transplant anti-nephrin antibodies are specific predictors of recurrent diffuse podocytopathy in the kidney allograft

Pre-transplant anti-nephrin antibodies are specific predictors of recurrent diffuse podocytopathy in the kidney allograft

The Microscope and Beyond: Current Trends in the Characterization of Kidney Allograft Rejection From Tissue Samples.

The Banff classification is regularly updated to integrate recent advances in the characterization of kidney allograft rejection, gathering novel diagnostic, prognostic, and theragnostic data into a diagnostic and pathogenesis-based framework. Despite ongoing research on noninvasive biomarkers of kidney rejection, the Banff classification remains, to date, biopsy-centered, primarily relying on a semiquantitative histological scoring system that overall lacks reproducibility and granularity. Besides, the ability of histopathological injuries and transcriptomics analyses from bulk tissue to accurately infer the pathogenesis of rejection is questioned. This review discusses findings from past, current, and emerging innovative tools that have the potential to enhance the characterization of allograft rejection from tissue samples. First, the digitalization of pathological workflows and the rise of deep learning should yield more reproducible and quantitative results from routine slides. Additionally, novel histomorphometric features of kidney rejection could be discovered with an overall genuine clinical implementation perspective. Second, multiplex immunohistochemistry enables in-depth in situ phenotyping of cells from formalin-fixed samples, which can decipher the heterogeneity of the immune infiltrate during kidney allograft rejection. Third, transcriptomics from bulk tissue is gradually integrated into the Banff classification, and its specific context of use is currently under extensive consideration. Finally, single-cell transcriptomics and spatial transcriptomics from formalin-fixed and paraffin-embedded samples are emerging techniques capable of producing up to genome-wide data with unprecedented precision levels. Combining all these approaches gives us hope for novel advances that will address the current blind spots of the Banff system.

Evaluation of non-invasive biomarkers of kidney allograft rejection in a prospective multicenter unselected cohort study (EU-TRAIN)

Non-invasive biomarkers are promising tools for improving kidney allograft rejection monitoring, but their clinical adoption requires more evidence in specifically designed studies. To address this unmet need, we designed the EU-TRAIN study, a large prospective multicentric unselected cohort funded by the European Commission. Here, we included consecutive adult patients who received a kidney allograft in nine European transplant centers between November 2018 and June 2020. We prospectively assessed gene expression levels of 19 blood messenger RNAs, four antibodies targeting non-human leukocyte antigen (HLA) endothelial antigens, together with circulating anti-HLA donor-specific antibodies (DSA). The primary outcome was allograft rejection (antibody-mediated, T cell-mediated, or mixed) in the first year post-transplantation. Overall, 412 patients were included, with 812 biopsies paired with a blood sample. CD4 gene expression was significantly associated with rejection, while circulating anti-HLA DSA had a significant association with allograft rejection and a strong association with antibody-mediated rejection. All other tested biomarkers, including AKR1C3, CD3E, CD40, CD8A, CD9, CTLA4, ENTPD1, FOXP3, GZMB, ID3, IL7R, MS4A1, MZB1, POU2AF1, POU2F1, TCL1A, TLR4, and TRIB1, as well as antibodies against angiotensin II type 1 receptor, endothelin 1 type A receptor, C3a and C5a receptors, did not show significant associations with allograft rejection. The blood messenger RNAs and non-HLA antibodies did not show an additional value beyond standard of care monitoring parameters and circulating anti-HLA DSA to predict allograft rejection in the first year post-transplantation. Thus, our results open avenues for specifically designed studies to demonstrate the clinical relevance and implementation of other candidate non-invasive biomarkers in kidney transplantation practice.

Trained immunity suppression determines kidney allograft survival

The innate immune system plays an essential role in regulating the immune responses to kidney transplantation, but the mechanisms through which innate immune cells influence long-term graft survival are unclear. The current study highlights the vital role of trained immunity in kidney allograft survival. Trained immunity describes the epigenetic and metabolic changes that innate immune cells undergo following an initial stimulus, allowing them have a stronger inflammatory response to subsequent stimuli. We stimulated healthy peripheral blood mononuclear cells with pretransplant and posttransplant serum of kidney transplant patients and immunosuppressive drugs in an in vitro trained immunity assay and measured tumor necrosis factor and interleukin 6 cytokine levels in the supernatant as a readout for trained immunity. We show that the serum of kidney transplant recipients collected 1 week after transplantation can suppress trained immunity. Importantly, we found that kidney transplant recipients whose serum most strongly suppressed trained immunity rarely experienced graft loss. This suppressive effect of posttransplant serum is likely mediated by previously unreported effects of immunosuppressive drugs. Our findings provide mechanistic insights into the role of innate immunity in kidney allograft survival, uncovering trained immunity as a potential therapeutic target for improving graft survival.

Tertiary lymphoid organs contribute to kidney allograft rejection.

Tertiary lymphoid organs contribute to kidney allograft rejection.

Cysteine as an Innovative Biomarker for Kidney Injury.

Kidney transplantation is a widely used treatment for end-stage kidney disease. Nevertheless, the incidence of acute kidney injury (AKI) in deceased donors poses a potential hazard because it significantly increases the risk of delayed graft function and potentially exerts an influence on the kidney allograft outcome. It is crucial to develop a diagnostic model capable of assessing the existence and severity of AKI in renal grafts. However, no suitable kidney injury markers have been developed thus far. We evaluated the efficacy of the molecular probe NPO-B, which selectively responds to cysteine, as a new diagnostic tool for kidney injury. We used an in vitro model using ischemia/reperfusion injury human kidney-2 cells and an in vivo ischemia/reperfusion injury mouse model. Additionally, cysteine was investigated using urine samples from deceased donors and living donors to assess the applicability of detection techniques to humans. This study confirmed that the NPO-B probe effectively identified and visualized the severity of kidney injury by detecting cysteine in both in vitro and in vivo models. We observed that the fluorescence intensity of urine samples measured using NPO-B from the deceased donors who are at a high risk of renal injury was significantly stronger than that of the living donors. If implemented in clinical practice, this new diagnostic tool using NPO-B can potentially enhance the success rate of kidney transplantation by accurately determining the extent of AKI in renal grafts.

Relevance of Proteinuria in Kidney Transplant Recipients and Allograft Outcomes

BackgroundThe onset of proteinuria in renal allograft recipients is frequently associated with an increased risk for both graft failure and mortality. We investigated the risk associated with post-transplant proteinuria and its time-dynamics in a select group treated for biopsy proven antibody-mediated rejection (ABMR). MethodsEighty-five patients who underwent transplantation were enrolled in our study and followed up from transplantation until October 31, 2020, death, or the date of the return to dialysis. We created two main groups: the ABMR group (n = 19) and an ABMR-negative control group with stable kidney function (n = 52) without donor-specific antibodies (DSA) and a subgroup with DSAs but stable graft function (n = 14) without ABMR. Differences in patient, donor, and transplant graft characteristics between the groups were assessed by Fisher's exact test for categorical variables. Death-censored graft loss was evaluated with the help of Kaplan-Meier analysis using log risk statistics. ResultsProteinuria decreased after treatment in the ABMR group (P < .0009). Pre-treatment every 10 mg/mmol increase in proteinuria was associated with a 7% increase in the risk for graft failure in the ABMR group. The estimated 3-year graft survival was 87.5% in the ABMR group, compared to 93% in the group without ABMR but with pre-formed DSA, and 100% in the DSA negative subgroup (log-rank probe P < .0666). ConclusionProteinuria is an independent predictor for graft failure, can be lowered by treatment for ABMR but ABMR is associated with lower graft survival in our study population.

Simultaneous Liver and Kidney Transplantation in Patients Aged 70 y and Older: Proceed With Caution.

The number of elderly patients aged 70 y and older with liver and kidney failure is increasing, mainly because of increasing prevalence of metabolic dysfunction-associated steatohepatitis. At present, limited data are available on the outcomes of elderly patients who fit the criteria for dual organ transplantation since the implementation of the simultaneous liver and kidney (SLK) allocation policy. We performed a retrospective analysis of the Organ Procurement and Transplantation Network database of adults aged 18 y and older undergoing SLK and kidney transplantation only from August 11, 2017, to December 31, 2022. We examined patient and graft survivals and compared the outcomes of the recipients aged 70 y and older undergoing SLK transplantation to those who received kidney transplant alone and kidney after liver transplant. During the study period, there has been a significant rise in the number of patients aged 70 y and older undergoing SLK transplantation, with 6 patients undergoing SLK transplantation in 2017 and 63 in 2021. Patients aged 70 y and older had significantly lower survival with 82.9% at 1 y and 66.5% at 3 y compared with 89.3% and 78.8% in the 50-69 y age group and 93.2% and 88.6% in the 18-49 y age group, respectively. Overall, kidney allograft survival was significantly lower in the 70 y and older group, with 80.9% at 1 y and 66.4% at 3 y compared with 91.1% and 75.5%, respectively, in those undergoing kidney transplant alone. There was no difference in kidney allograft survival in those undergoing SLK and kidney after liver transplantation. Although the outcomes are inferior in recipients of SLK transplant aged 70 y and older, chronologic age should not preclude them from undergoing transplantation. Kidney transplantation after liver transplantation could be considered to avoid futile transplants.

Subclinical rejection and allograft survival in kidney transplantation: protocol for a systematic review and meta-analysis

IntroductionSubclinical rejection (SCR) refers to the presence of acute rejection without accompanying kidney allograft dysfunction. The impact of SCR on long-term graft survival remains a subject of ongoing debate.Methods and...

Urinary Chemokines CXCL9 and CXCL10 Are Non-Invasive Biomarkers of Kidney Transplant Rejection.

BACKGROUND Rejection is the main cause of kidney allograft failure, and kidney biopsy is the criterion standard method to diagnose it. However, non-invasive techniques to detect kidney transplant rejection are necessary. This study aimed to evaluate urinary chemokines CXCL9 and CXCL10 as potential biomarkers of kidney transplant rejection and to analyze chemokine association with allograft prognosis. MATERIAL AND METHODS We collected 117 urine samples from kidney transplant recipients undergoing allograft biopsy. CXCL9 and CXCL10 levels were measured by ELISA and the ratio to urine creatinine was calculated. Histology and other clinical data were collected from medical records. RESULTS The diagnostic performance of urinary CXCL9/cre in discriminating rejection from all other histological groups showed an ROC AUC value of 0.728 (95% CI 0.632-0.824, p<0.001), and a cut-off value 0.11 ng/mmol had the best sensitivity (76.9%) and specificity (73.1%). The ability of CXCL10/cre to discriminate transplant rejection from all other histological groups had ROC AUC value 0.73 (95% CI 0.63-0.84, P<0.001), the cut-off value 0.42 ng/mmol with best sensitivity (71.4%) and specificity (84.6%). CXCL9 and CXCL10 levels were also increased in patients with polyoma BK virus, recurrent AA amyloidosis, and thrombotic microangiopathy. Patients with higher CXCL9/cre (≥0.11 ng/mmol) and CXCL10/cre (≥0.42 ng/mmol) levels were at increased risk of transplant progression to ESRD (HR 3.25, 95% CI=1.27-8.36, P=0.01), irrespective of serum creatinine at the time of biopsy. CONCLUSIONS Urinary CXCL9/cre and CXCL10/cre were able to distinguished between patients with transplant rejection and those without rejection. High levels of urinary CXCL9/cre and CXCL10/cre were associated with worse allograft survival.

Protocol biopsy of kidney allograft enables early detection of BK virus nephropathy to preserve kidney allograft function.

The Banff Working Group has updated the histological classification of BK virus nephropathy (BKVN), highlighting the importance of early detection. However, an early detection strategy for BKVN using biopsy has not yet been established. Our investigation aimed to assess the efficacy of protocol biopsy for the diagnosis of BKVN. We performed a retrospective cohort study of 314 patients who had undergone kidney transplantation between 2006 and 2021. Kidney allograft biopsies were performed as part of a protocol biopsy at 3 months and 1 year post-transplantation. Following the diagnosis of BKVN, the immunosuppressant dose was reduced. Twelve patients (3.8%) were diagnosed with BKVN by biopsy. Most diagnoses are established during the early stages of BKVN (polyomavirus nephropathy class 1 in six, class 2 in five, and class 3 in one). Following the reduction in immunosuppressant dose, kidney allograft function did not deteriorate in any patients. Additionally, test for BK virus DNA in the blood was negative. All but one patient demonstrated histological resolution of BKVN, and the other had a very slight positivity for the simian virus 40 large T antigen. The median follow-up time after BKVN diagnosis was 6 years. One patient developed de novo donor-specific antibody and subclinical acute antibody-mediated rejection that was successfully cured. Our analysis indicates that protocol biopsy may enable the early detection of BKVN, resulting in the preservation of kidney function.

1004 Urgent Explant of Infected Aortic Stent Graft in a Patient with Kidney Transplant Using Biological Aortoiliac Reconstruction and a Temporary Axillo-Femoral Perfusion Shunt: 6-Year Follow-Up and Literature Review

Abstract Background Written consent obtained for case report. A 59-year-old male who was 3-months post-EVAR repair under immunosuppression for kidney transplantation and anti-retroviral HIV treatment presented to ED in 2017 with abdominal pain and fever. CTAP revealed pyelonephritis in renal allograft. Blood cultures were positive for staphylococcus epidermidis. PETCT showed high-intensity uptake around endograft. Urgent explant of endograft and insitu biological aorto-biiliac graft reconstruction with bench prepared bilateral long saphenous veins were performed. Results The predicted challenges were locating source of infection, immunosuppressed state, and allograft preservation. Dacron graft was used as temporary perfusion shunt (left axillary artery to right superficial femoral artery) for renal allograft on right external iliac vessels. Endograft was removed via rooftop incision with visceral rotation. Supra-celiac and supra-superior mesenteric artery clamping times were 15 and 35 minutes. The source of infection was from infected appendix proximal to graft with erosion of right external iliac artery resulting in appendectomy in the same operation. Following 12-weeks of OPAT antibiotic-therapy, repeat PETCT revealed low-grade uptake around aortic graft and inflammatory markers were back to baseline. At 6 years in 2023, patient remains clinically well with ∼20% allograft function. Maintaining kidney allograft perfusion in the setting of elective non-infected aortic graft explant was previously reported, but with ENROUTE system (Rasheed et al., 2018). Conclusions The satisfactory long-term outcomes discussed here demonstrated with MDT planning involving vascular surgery, infectious diseases, renal medicine and patient, explant of infected graft with insitu biological graft reconstruction in renal transplant patients presenting with complex aortic-graft infection is feasible.

Oxidized ATP Suppresses B Lymphocyte Activity to Attenuate Antibody-mediated Rejection of Kidney Allografts in Mice

Background. Antibody-mediated rejection (AMR) is a major cause of renal allograft dysfunction and loss. Targeting B cells and/or donor-specific antibody removal using plasma exchange and anti-CD20 antibodies are increasingly used in clinical practice, but the efficacy remains limited. Recent studies suggest that targeting purinergic P2X7 receptor/ATP axis can have profound immune regulatory effects in transplant models, but the mechanisms involved remain incompletely defined. Methods. Purified B cells were isolated from the spleen of Balb/C mice and cultured with oxidized ATP at different concentrations. Proliferation and differentiation of B cells were examined. Effects of oxidized ATP were examined in a presensitized animal model where kidney allograft rejection mimics aspects of clinical AMR. Histopathology was assessed at the time of rejection or on day 5 after kidney transplantation. Infiltrating immune cells in renal allografts were detected by flow cytometry. Results. Oxidized ATP inhibited B-cell activation and proliferation in vitro, significantly attenuated histological signs of graft injury and prolonged kidney allograft survival. Mechanistically, oxidized ATP inhibited antibody secretion by activated B cells in response to lipopolysaccharide stimulation and markedly suppressed the production of donor-specific antibody in kidney allograft recipients. Oxidized ATP also reduced graft infiltration by other inflammatory cells. Conclusions. These findings provide evidence for the involvement of the purinergic P2X7 receptor pathway in AMR and suggest that targeting this pathways may have important clinical implications.

Effect of Hydroxychloroquine Treatment on Kidney Allograft Rejection and Graft Failure

Kidney allograft rejection is a major issue because it causes graft failure and because immunosuppressive treatments used for its prevention increase the risk of infections and cancers. In systemic lupus patients, hydroxychloroquine is used to prevent immune flares with decreased doses of immunosuppressants. Hydroxychloroquine can be safely used in kidney transplant recipients when indicated for autoimmune disease, but its effect on allograft rejection is unknown. We hypothesized that it may prevent kidney allograft rejection. We conducted a nationwide retrospective propensity-matched study on kidney transplantations of patients treated with hydroxychloroquine in France between 2008 and 2018. We analyzed the incidence of allograft rejection or failure within the first year after transplantation. The rates of rejection or allograft failure were not different between the 188 patients treated with hydroxychloroquine at the time of transplantation and their propensity matched controls. Hydroxychloroquine treatment in association with standard immunosuppressive treatment does not prevent rejection in kidney allograft recipients.

Significant Long-Term Prevention of High Sensitization After Kidney Allograft Failure by Maintaining Calcineurin Inhibitor-Based Immunosuppression.

Broad national or international programs contribute to mitigating the expected longer waiting list (WL) time for sensitized patients but with minor benefits for highly sensitized subjects. Therefore, strategies to prevent high sensitization are urgently required. In this study, we investigated the risk of developing highly sensitized patients with different immunosuppressive (IS) handling after kidney allograft failure (KAF). Data from 185 patients with KAF, retransplanted/relisted from 2010 to 2020 in two regions of Italy that share the same regional WL, were analyzed. Patients were categorized according to IS management at 12 months after KAF as follows: patients maintaining IS with calcineurin inhibitors (CNI) (late withdrawal group [LWG], n = 58) and those who withdrew all IS therapy or were on steroids only (early withdrawal group [EWG], n = 127). Patients in the LWG showed lower panel reactive antibodies (PRA) at 12 (29.0%vs. 85.5%, p < 0.001) and 24 months (61.0%vs. 91.0%, p = 0.001), reduced risk of high sensitization (PRA ≥90%) at 12 (9.4%vs. 40.7%, p < 0.001, OR = 0.15) and 24 months (25.6%vs. 57.3%, p = 0.001, OR = 0.26) and almost no very high sensitization (PRA ≥ 98%) at 12 months (1.9%vs. 18.6%, p=0.003, OR=0.08) after KAF. In the LWG subgroup analysis, patients who maintained IS for up to 24 months after KAF did not show very high sensitization. The LWG showed shorter active WL times (406vs. 813 days, p = 0.001) without an increased risk of complications. CNI maintenance for at least 12 months after KAF could be a useful approach to prevent high sensitization and reduce WL times in patients who are offered retransplantation, without a higher burden of complications.

A comparative analysis of kidney allograft outcomes in steroid use versus steroid discontinuation after basiliximab and ATG induction: AUNOS database study.

The relative safety and efficacy of early steroid withdrawal in kidney transplant patients after basiliximab compared to anti-thymocyte globulin (ATG) induction therapy is unknown. We aimed to compare kidney allograft outcomes in steroid use versus steroid discontinuation after basiliximab and ATG induction from the United Network for Organ Sharing (UNOS) database. We conducted a retrospective cohort analysis of the UNOS database and included first kidney transplant recipients who received ATG or basiliximab induction therapy. We compared graft and patient outcomes in those who received steroid maintenance and those who were discharged off steroids. Of 106,061 patients, 25,344 (86.7%) received basiliximab induction and were maintained on steroids (B-Sm), and 3,880 (13.3%) were on a steroid-free regimen (B-Sf). Graft failure rate was significantly higher in the B-Sf compared to B-Sm at 1-year (4.1 vs. 1.8%, p<0.001), 3-year (6.0 vs. 4.3%, p<0.001) and 5-year follow-up (7.7 vs. 6.4%, p=0.0004). The mortality rate was significantly higher in B-Sf at 1-year (3.3 vs. 2.4%, p=0.0005), 3-year (7.6 vs. 5.5%, p<0.001) and 5-year follow-up (11.5 vs. 8.8%, p<0.001) when compared to the B-Sm. 76,837 recipients received ATG induction therapy, 51,745 (72.4%) were on steroid maintenance therapy (A-Sm) and 25,092 (32.6%) were on a steroid-free regimen (A-Sf). The graft failure rate was significantly higher in A-Sf compared to A-Sm at 1-year follow-up (2.6 vs. 2.3%, p=0.0006), however, there was no difference at 3-year (5.0 vs. 5.0%, p=0.53) or 5-year follow-up (7.2 vs. 8.1%, p=0.17). There was no difference in mortality rates between A-Sf vs. A-Sm at 1 year (2.5 vs. 2.4%, p=0.98) and at 3 years (5.5 vs. 5.4%, p=0.45), respectively. Patients who were maintained on steroids after basiliximab induction had better 5-year allograft survival and patient survival compared to those who were not maintained on steroids. However, steroid maintenance conferred no additional benefit after ATG induction and was associated with higher mortality.

Doppler Ultrasonographic Indexes and Its Relation to Transplanted Kidney (Allograft) Function in Sulaimani City Centre

Doppler Ultrasonographic Indexes and Its Relation to Transplanted Kidney (Allograft) Function in Sulaimani City Centre

A universal urinary cell gene signature of acute rejection in kidney allografts

IntroductionAcute rejection (AR) undermines the life-extending benefits of kidney transplantation and is diagnosed using the invasive biopsy procedure. T cell-mediated rejection (TCMR), antibody-mediated rejection (ABMR), or concurrent TCMR + ABMR (Mixed Rejection [MR]) are the three major types of AR. Development of noninvasive biomarkers diagnostic of AR due to any of the three types is a useful addition to the diagnostic armamentarium. MethodsWe developed customized RT-qPCR assays and measured urinary cell mRNA copy numbers in 145 biopsy-matched urine samples from 126 kidney allograft recipients. We determined whether the urinary cell three-gene signature diagnostic of TCMR (Suthanthiran et al., 2013) discriminates patients with no rejection biopsies (NR, n = 50) from those with ABMR (n = 28) or MR (n = 20) biopsies. ResultsThe urinary cell three-gene signature discriminated all three types of rejection biopsies from NR biopsies (P < 0.0001, One-way ANOVA). Dunnett's multiple comparisons test yielded P < 0.0001 for NR vs. TCMR; P < 0.001 for NR vs. ABMR; and P < 0.0001 for NR vs. MR. By bootstrap resampling, optimism-corrected area under the receiver operating characteristic curve (AUC) was 0.749 (bias-corrected 95% confidence interval [CI], 0.638 to 0.840) for NR vs. TCMR (P < 0.0001); 0.780 (95% CI, 0.656 to 0.878) for NR vs. ABMR (P < 0.0001); and 0.857 (95% CI, 0.727 to 0.947) for NR vs. MR (P < 0.0001). All three rejection categories were distinguished from NR biopsies with similar accuracy (all AUC comparisons P > 0.05). ConclusionThe urinary cell three-gene signature score discriminates AR due to TCMR, ABMR or MR from NR biopsies in human kidney allograft recipients.