Allograft Biopsies Research Articles

Pathological Approach to Kidney Allograft Infection.

Infectious agents can pose a significant challenge in kidney transplantation, as they have the potential to cause direct infections in the transplanted kidney. These infections can lead to a decline in kidney function and reduce the longevity of the transplanted kidney. Common post-transplant allograft infections include bacterial pyelonephritis and the BK virus infection, while adenovirus, JC virus, and cytomegalovirus are less frequent but can also lead to significant allograft dysfunctions. The histopathological features of these infections are characterized by the infiltration of inflammatory cells in the kidney interstitial area and the presence of viral nuclear inclusions or cytopathic changes in the renal tubular epithelial cells. The confirmation of causative organisms can be achieved by immunohistochemical staining or the visualization of viral particles using electron microscopic examination. However, these methods typically require a longer turnaround time and are not readily available in developing countries, unlike standard hematoxylin-eosin staining. Notably, the differential diagnosis of interstitial inflammation in kidney allografts almost always includes T cell-mediated rejection, which has a different treatment approach than allograft infections. The aim of this review was to prompt clinicians to identify diverse pathological alterations as observed in kidney allograft biopsies, thereby facilitating further investigations and the management of suspected kidney allograft infections.

#5691 BK POLYOMAVIRUS VIREMIA AND VIRURIA ARE ASSOCIATED WITH SEVERE INFLAMMATION AND FIBROSIS IN RENAL ALLOGRAFT, BUT NOT WITH GRAFT SURVIVAL

Abstract Background and Aims Infection of the renal allograft by Polyomavirus BK (BKV) causes tubular cell injury and interstitial inflammation, which leads to subsequent interstitial fibrosis and tubular atrophy (IFTA). The presence and degree of inflammation within these areas (i-IFTA) is associated with worse outcomes in kidney transplant (KT) patients. The aim of this study was to investigate the association between BKV viremia and viruria and the presence of IFTA and i-IFTA, decline of renal function, and graft loss. Method We conducted a single-center retrospective case-control study, which included all patients who underwent an allograft biopsy between January 2018 and December 2022. All biopsies were made for-cause (allograft dysfunction with increased serum creatinine). Real-time polymerase chain reaction was used to detect and quantitate BK viral load in serum and urine samples. Patients were included if they had at least 6 months since KT and if they had serial evaluation of BKV viremia and viruria previously to the biopsy. We evaluated, in the graft biopsy, the percentage of IFTA, and also i-IFTA. Estimated glomerular filtration rate (eGFR) was obtained at baseline and 1 year after the biopsy. Graft loss was evaluated at 6 months and 1 year after the biopsy. Results Mean age of the population was 53,5 years and 67% were males. A total of 116 biopsies were performed during the studied period and 72 met the inclusion criteria. Ten percent of patients developed persistent (≥ 3 months) BKV viremia, 24% developed persistent BKV viruria, and 18% developed persistent JCV viruria. Five cases of polyomavirus-associated nephropathy were diagnosed. The other most common diagnoses were T cell-mediated rejection (24%), antibody-mediated rejection (15%), and focal segmental glomerulosclerosis (15%). In patients with persistent BKV viremia, a higher viral load had a strong positive association with the degree of i-IFTA (r=0.954; P = .001). Patients with BKV viremia and/or viruria were more likely to present more severe IFTA (≥ 40%) and i-IFTA (grade ≥2) in allograft biopsy (P = .03). Patients with higher degrees of IFTA and i-IFTA were more likely to experience graft loss 1 year after the biopsy (P = .01). There was no significant association between the presence of BKV viremia and/or viruria and the decline of eGFR, nor with the incidence of graft loss 1 year after the biopsy. In multivariable analysis adjusted for age, eGFR at the time of biopsy, the presence of donor-specific antibodies and the main diagnosis of allograft biopsy, the presence of BK viremia and/or viruria was a significant predictor of more severe IFTA and i-IFTA (P = .04). Conclusion In our population, higher BK viremia loads were associated with more extensive inflammation within areas of IFTA. Patients with BK viremia and/or viruria, independently of the main diagnosis of the biopsy, were more likely to exhibit more severe IFTA and i-IFTA in allograft biopsies, but no association with the incidence of dialysis at 1 year was shown. Longer prospective studies are needed to investigate whether BKV infection treatment/ reduction of immunosuppression can slow down fibrosis progression and minimizes i-IFTA.

#6147 BELATACEPT OUTCOMES IN PEDIATRIC KIDNEY TRANSPLANTATION: AN INTERNATIONAL MULTICENTER STUDY

Abstract Background and Aims Belatacept is a co-stimulation blocker associated with better long-term outcomes in adult patients compared to CNI based regimens. Data on its use in older children and young adults are lacking. We are the 1st to report outcomes for 45 pediatric kidney transplant recipients converted to belatacept. Method 45 patients were included from 4 centers (USA and France) between 05/2018 and 12/2021. Patients received an induction with basiliximab (n = 39) or ATG (n = 6). Maintenance immunosuppression included CNI, MMF +/− steroids. Patients’ viral status (EBV, CMV) were monitored monthly and allograft biopsies were performed prior and ∼6 months after starting belatacept. The first 5 belatacept injections were administered at 5 mg/kg/dose (10 mg/kg/dose if early conversion) every 2 weeks, then monthly. CNI were progressively reduced and stopped. MMF doses were also increased at CNI withdrawal. Results Median age at conversion was 17.7 y (range 10.3-20.6). 7/45 patients received an early conversion (median: 1 month post-transplant, IQR 0.5-1.2): 6 patients because of delayed graft function and 1 to avoid CNI toxicity (post-transplant diabetes). 38/45 patients were converted after a median of 4.1 years post-transplant (IQR 1.7-6.0). Conversion indication was based on the need for long term CNI avoidance: either because of toxicity (histology, post-transplant diabetes, tremors; n = 13) or sub-optimal creatinine (n = 12) or to improve adherence (e.g. monthly IV-treatment, n = 13). CNI were withdrawn in 42/45 patients by a median of 2.4 months (IQR 1.4-6.0). GFR was stable or improved over a median follow-up time of 1.6 years (IQR 1.1-2.4), Fig 1 A. Rejection episodes were observed in 10/45 patients (22%) after a median of 10.2 months (IQR 6.1-15.8) and included 7 TCMR, 2 ABMR and 1 mixed rejection. None of these patients were converted early (<3 m), 5 had been converted for non-adherence, 4 had pre-existing DSA and 4 had prior history of rejection. Evolution of GFR in rejectors is shown in Fig 1 B. CNI were reintroduced for 6/10 and belatacept stopped for 3/10. Regarding viral complications, 1 severe BKv nephropathy required the discontinuation of belatacept. All patients were EBV+ at conversion (4 were EBV- at the time of transplant). No EBV replication was observed. Conclusion Selected pediatric kidney recipients benefit from long-term CNI toxicity avoidance, but selection criteria need to be refined to avoid rejection under costimulation blockade.

#4743 OMNIGRAF (COMBINED GENE EXPRESSION AND DD-CF DNA) USE IN MONITORING RENAL ALLOGRAFT REJECTION IN MULTIORGAN TRANSPLANT RECIPIENTS

Abstract Background and Aims To date there is no clinically available non-invasive biomarker to monitor for renal allograft rejection in multiorgan transplant recipients. TruGraf (Gene expression profile) and TRAC (dd-cf DNA), as part of the biomarker panel OmniGraf, have shown to be reliable “rule out” tests for subclinical rejection in stable kidney transplant recipients. However, the validity and utility of these tests in monitoring for renal allograft rejections in the setting of multiorgan transplants has yet to be assessed. The aim of this study is to assess the feasibility of using the biomarkers individually, as well as together in the OmniGraf biomarker panel, to assist in making the decision to perform a renal allograft biopsy in multiorgan transplant recipients. Method This is an ongoing prospective, observational sample collection study in any multiorgan (kidney + non-renal organ) undergoing a renal allograft biopsy. Biopsies were considered positive if they showed rejection in the kidney based on Banff 2019 and included borderline changes as positive results. Copper-Pearson 95% CI were used for sensitivity, specificity, and accuracy; standard logit CIs were used for NPV and PPV. For TruGraf, (TX = negative result) and (not-TX = positive test). For TRAC, 0.7% was used as the threshold for all organs except for those that had a liver transplant, where a threshold of 15% was used to determine positive vs. negative. Results Paired renal allograft surveillance biopsies and biomarker samples were available for 20 patients. Of the 20, 9 (45%) were liver-kidney transplants, 6 (30%) were heart-kidney transplants, and 5 (25%) were kidney-pancreas transplants. Nine (45%) of the patients were male, 14 (70%) were White, 5 (25%) were Black, and 1 patient was Hispanic. The mean age was 50 ± 13 years. Average SrCr was 1.3 ± 0.5 mg/dL. Of the 20 paired biopsies and samples, 2 (10%) had only TruGraf results, while the other 18 (90%) had OmniGraf (TruGraf and TRAC). There were 2 rejections (borderline changes). Diagnostic performance is presented in tables 1–4. Both TruGraf and TRAC individually had NPV of 89% and 85%, respectively, and PPV of 65% and 73%, respectively. When analyzing the performance of the OmniGraf biomarker panel, OmniGraf +/+ showed a 100% PPV and OmniGraf -/- showed a 100% NPV. Conclusion In this analysis of renal allograft biopsies in a multiorgan transplant cohort, TruGraf, TRAC (when using organ-dependent thresholds) had reasonable diagnostic performance as a “rule out” test. When the tests are combined into OmniGraf, the PPV and NPV were 100% when both tests agreed with each other. These outcomes justify potential use and the need for continued analysis of the utility of the OmniGraf biomarker panel in monitoring renal allograft in multiorgan transplant recipients.

#6709 DONOR-DERIVED CELL-FREE DNA (DD-CDNA) AS A NON-INVASIVE BIOMARKER OF KIDNEY ALLOGRAFT REJECTION IN PEDIATRIC KIDNEY TRANSPLANTATION

Abstract Background and Aims Rejection remains the first cause of allograft loss in pediatric kidney transplant (pkTx) recipients. Detection of rejection currently relies on kTx biopsies performed either because of allograft dysfunction with the risk of late diagnosis or per surveillance protocols allowing early detection of subclinical rejection but resulting in many unnecessary biopsies. Dd-cfDNA was reported as a new non-invasive biomarker with the potential to improve rejection detection and guide biopsy indications. We aim to assess the association of dd-cfDNA levels with biopsy results in a large cohort of pediatric kTx recipients. Method All pediatric kTx patients with at least one dd-cfDNA assessment at the time of a biopsy at a single pediatric transplant center were included. Clinical, biological and histological data were collected from medical reports. Dd-cfDNA were retrospectively measured from plasma samples biobanked at the time of allograft biopsy between 2015 and 2020 or collected in patients who received regular dd-cfDNA testing as part as clinical care between 2021 and 2022. Results 170 cfDNA measurements in 132 pkTx recipients were available at the time of a biopsy, including 100 performed for surveillance. Mean age at biopsy was 16 years with a median time from kTx of 21 [11;38] months. Median eGFR was 62 [48;83] mL/min/1.73 m2, median UPCR 0,21 [0,14;0,36] g/g, and 20% had DSA at the time of the biopsy. Biopsy findings included: 109 normal, 30 borderline, 15 TCMR, 11 AMR and 5 mixed rejections. Median cfDNA level was 0,64 [0,31;1,80] %. We found a strong association between cfDNA levels and active tubule-interstitial and microvascular Banff lesions (Figure 1). cfDNA levels were significantly increased in cases with rejection (Figure 2). Using the proposed cut-off of 0.5%, performances of the test to detect rejection were Se 84%, Spe 51%, PPV 33%, NPV 92%. Among the borderline cases, 17 (57%) had cfDNA>0.5%. Conclusion We confirm in the largest pediatric kTx cohort to date, the association of dd-cfDNA levels with allograft rejection and its potential interest as a non-invasive biomarker in children. Further studies are needed to assess the added value of dd-cfDNA monitoring to the current standard of care and its ability to reduce unnecessary surveillance biopsies and improve outcomes.

#2794 ISOLATED GLOMERULITIS IS STRONGLY ASSOCIATED WITH THE ABSENCE OF ANTIBODY-MEDIATED REJECTION BY MOLECULAR DIAGNOSTICS

Abstract Background and Aims According to the 2018 Banff classification, the Molecular Microscope Diagnostic System (MMDx) is indicated in cases when histology is insufficient to diagnose antibody-mediated rejection (ABMR) due to an absence of diagnostic criteria groups 2 and/or 3. The impact of isolated glomerulitis (g>0, ptc0) on the likelihood of ABMR diagnosis by the MMDx appears critical to the implementation of this new biomarker. Method We analyzed 251 kidney allograft biopsies by histology and molecular diagnostics at the University Hospital Zurich from October 2018 to November 2022. Histologic findings were classified concerning the absence of (1) diagnostic criteria groups 2 and 3 (n = 18), (2) diagnostic criteria group 2 only (n = 18), and (3) diagnostic criteria group 3 only (n = 28). In addition, cases with histologically proven ABMR were used for comparison (n = 65). High-resolution re-typing was performed from the kidney allograft biopsies if necessary. Results The MMDx diagnosed ABMR in 1 of 18 cases (6%) with absent diagnostic criteria groups 2 and 3, 4 of 18 cases (22%) with absent diagnostic criteria groups 2, and 19 of 28 cases (68%) with absent diagnostic criteria groups 3. On the contrary, MMDx confirmed the diagnosis of ABMR in 42 of 65 cases (65%) with histologically proven ABMR but did not in 23 of 65 cases (35%). Among 28 cases with absent diagnostic criteria group 3, only 2 of 19 cases (11%) with ABMR by MMDx but 6 of 9 cases (67%) with no ABMR by MMDx showed isolated glomerulitis (p = 0.0048). Among 65 cases with histologically proven ABMR, only 7 of 42 cases (17%) with ABMR by MMDx but 14 of 23 cases (61%) with no ABMR by MMDx showed isolated glomerulitis (p<0.001). Overall, 14 of 65 cases (21%) with isolated glomerulitis showed ABMR diagnosis by MMDx. Conclusion Isolated glomerulitis is strongly associated with the absence of ABMR by MMDx not only when diagnostic criteria group 2 is missing but also when diagnostic criteria 3 is missing or ABMR is proven by histology. Our results may help to guide the indication for MMDx in clinical practice. However, the clinical significance of these results needs further investigation.

#4610 LACK OF EFFICACY AND SAFETY OF ECULIZUMAB FOR TREATMENT OF ANTIBODY-MEDIATED REJECTION FOLLOWING RENAL TRANSPLANTATION

Abstract Background and Aims We evaluated the efficacy and safety of eculizumab in comparison with plasmapheresis and intravenous immunoglobulin therapy in renal transplant recipients diagnosed with antibody-mediated rejection (AMR). Method This was a multicenter, open-label, prospective, randomized analysis. The patients were randomized by therapy type (eg, eculizumab infusions or standard of care [SOC]: plasmapheresis/intravenous immunoglobulin). The patients (ie, eculizumab arm: 7 patients, SOC arm: 4 patients) were evaluated for the continued presence of donor-specific antibodies (DSAs) and C4d (staining on biopsy), as well as histologic evidence, using repeat renal biopsy after treatment. Results The allograft biopsies revealed that eculizumab did not prevent the progression to transplant glomerulopathy. Cases of AMR were diagnosed in the early post-transplantation period in 2 patients (eculizumab arm: 1 patient, SOC arm: 1 patient) and in the late period in 9 patients. Most of the reports show that eculizumab, in combination with other therapeutic measures such as PP and/or IVIG, effectively reversed rejection. However, eculizumab alone could not treat AMR effectively. Only 2 patients in the SOC arm experienced rejection reversal, and no graft losses occurred in either group. After AMR treatment, the DSA titers generally decreased compared to titers taken at the time of AMR diagnosis. There were no serious adverse effects in the eculizumab arm. Conclusion Eculizumab alone cannot treat AMR effectively and does not prevent acute AMR from progressing to chronic AMR or transplant glomerulopathy. However, it should be considered as a potential alternative therapy because it may be associated with decreased DSA levels.

#2795 PROSPECTIVE ASSESSMENT OF THE NEED FOR AND ADDED VALUE OF MOLECULAR DIAGNOSTICS OF KIDNEY ALLOGRAFT BIOPSIES: AN EVALUATION IN CLINICAL PRACTICE

Abstract Background and Aims The Molecular Microscope Diagnostic System (MMDx) may resolve inconclusive histology findings, as preserved biopsy material can be examined after histology findings have been obtained. The extent to which this proposed approach can be implemented in clinical practice remains an open question. Method We prospectively analyzed 104 consecutive indication kidney allograft biopsies by histology and molecular diagnostics at the University Hospital Zurich from April 2022 to December 2022. Pathologists and clinicians with experience in molecular diagnostics assessed the need for MMDx by questionnaire when the histology report was available. Clinicians then assessed the added value of the molecular diagnostics by questionnaire when the MMDx report was available. Results 29 of 104 cases (28%) showed rejection by histology, 42 of 104 cases (40%) showed no rejection by histology, and 33 of 104 cases (32%) showed histologic findings insufficient to diagnose ABMR due to an absence of diagnostic criteria groups 2 and/or 3. Pathologists considered molecular diagnostics indicated in 42 of 104 cases (40%), 9 cases to give extra confidence, and 33 cases for diagnostic clarification concerning rejection. Clinicians considered molecular diagnostics indicated in 54 of 104 (52%) cases, 5 cases to give extra confidence, and 49 for diagnostic clarification concerning rejection. In 33 cases with histologic findings insufficient to diagnose ABMR, molecular diagnostics were considered indicated by pathologists and clinicians. Molecular diagnostics allowed the diagnosis of ABMR in 8 of 33 cases (24%). In addition, 11 of 104 cases (11%) showed a discrepancy between the histologic findings and the molecular diagnosis. Clinicians considered adjustment of treatment based on the MMDx report in 3 of 11 discrepant cases. Pathologists and clinicians considered molecular diagnostics indicated in 2 of 11 and 3 of 11 discrepant cases, respectively. Conclusion The need for molecular diagnostics goes beyond the recommendation of the 2018 Banff classification for histologic findings insufficient to diagnose ABMR. However, the added value of molecular diagnostics appears to be largely limited to these cases.

#3654 ABO-INCOMPATIBLE KIDNEY TRANSPLANTATION LOWERS INCIDENCES OF DE NOVO DONOR-SPECIFIC ANTIBODIES AND CHRONIC ANTIBODY-MEDIATED REJECTION

Abstract Background and Aims ABO-incompatible kidney transplantation has been associated with an increased risk for antibody-mediated rejection (ABMR) and early graft loss attributable to isoagglutinins. Its impact on the development of de novo donor-specific HLA antibodies (DSA) and DSA-induced chronic ABMR, however, remains less well studied. Method We analyzed 297 kidney transplant recipients (KTRs) who underwent living donor transplantation at the University Hospital Zurich from 2009 to 2021. 58 ABO-incompatible (iABO) KTRs were compared to 239 ABO-compatible (cABO) KTRs concerning the development of de novo donor-specific antibodies (DSA) and antibody-mediated rejection (ABMR). ABO desensitization was performed using rituximab and antigen-specific immunoadsorption. The HLA-derived epitope-mismatches were calculated per HLA-locus and in total using the Predicted Indirectly Recognizable HLA-Epitopes (PIRCHE-II) algorithm. High-resolution re-typing was performed from protocol kidney allograft biopsies if necessary. Results The incidence of TCMR/ABMR in the first post-transplant year was comparable between iABO KTRs (19%) and cABO KTRs (13%; p = 0.207). De novo DSA were detected in only 1 of 58 iABO KTRs but 12 of 239 cABO KTRs in the first post-transplant year and 2 of 58 iABO KTRs but 50 of 239 cABO KTRs in the long-term follow-up (p = 0.001). ABMR was diagnosed in only 1 of 58 iABO KTRs but 28 of 239 cABO KTRs after the first post-transplant year (p = 0.021). iABO kidney transplantation decreased the risk of de novo DSA development (HR 7.222, CI 1.755-29.722, p = 0.006) and ABMR (HR 7.362, CI 1.000-54.239; p = 0.050) after the first-post-transplant year independent from the presence of preformed DSA. Total PIRCHE-II scores and PIRCHE-II scores per locus were not associated with the development of de novo DSA in all 297 living-donor KTRs (p>0.05). Conclusion Our findings suggest that iABO kidney transplantation is associated with a lower incidence of de novo DSA and ABMR in the long term, independent from the HLA-derived epitope mismatch load. Whether this protective effect offers new therapeutic options against kidney allograft injury needs to be investigated in future studies.

#4487 AN UNEXPECTED CASE OF 2,8-DIHYDROXYADENINE NEPHROPATHY AFTER KIDNEY TRANSPLANTATION RELATED TO NEW VARIANTS OF ADENINE PHOSPHORIBOSILTRANSFERASE GENE

Abstract Background and Aims Adenine phosphoribosyltransferase (APRT) deficiency is a rare autosomal recessive disorder of the purine metabolism which results in the conversion of adenine into 2,8 dihydroxyadenine (DHA) due to the activity of the xanthine oxidoreductase (XOR). Patients affected by APRT deficiency if not treated with inhibitors of XOR may develop 2,8-DHA nephropathy that might progress to end-stage kidney disease (ESKD) with the need of kidney transplant. The high rate of misdiagnosis of 2,8-DHA nephropathy in native kidneys could lead to the failure of kidney graft in transplanted patients affected by APRT deficiency. Method Here, we report the case of a female, 63-years old patient with ESKD of unknown cause on regular hemodialysis treatment from 2018 after a period of three years on peritoneal dialysis, who underwent kidney transplantation in our Center in 2022. Her medical history showed a metabolic syndrome. She did not experience episodes of renal colic whereas family history reported a brother affected by frequent renal colic of unknown cause. In March 2022, she underwent kidney transplantation from a deceased death brain donor. Induction therapy includes basiliximab, tacrolimus, mycophenolic acid and steroids. Due to the persistence of delay graft function, ten days after kidney transplantation an allograft biopsy has been performed. The histological examination revealed tubular damage surrounded by inflammation cells and intratubular crystals in the renal cortex. The crystals were reddish brown tinged in hematoxylin and eosin stain and were birefringent under polarized light Fig. 1 A, B, so they were strongly related to the hypothesis of DHA crystals. Consistently, the urinalysis showed yellow-brown crystals of DHA. Thus, a genetic analysis of APRT gene has been performed showing two novel heterozygous variants c.388_397p.(Leu130ValfsTer4) and exon 3 deletion, expected pathogenic. The patient was treated with bolus of methylprednisolone (4mg/kg alternate to 50 mg) and a therapy with febuxostat 80 mg/die was started to reduce the amount of plasma DHA. In addition, based on our previous experience of recurrence DHA nephropathy after transplantation, we treated the patient with six consecutive hemodiafiltration (HDF) sessions without ultrafiltration, to promptly remove the serum DHA avoiding their precipitation in the graft while waiting for the lowering effect of febuxostat. At discharge the patient showed an increase of the urine output not associated with a complete recovery of kidney function (sCr 3.88 mg/dl, uric acid 1.6 mg/dl), so two other hemodialysis treatments were performed in the next two weeks. Results At present, almost one year after kidney transplant, the patient is doing well and the graft function is stable with a sCr of 1.6 mg/dl without significant presence of DHA crystals in the urine. Conclusion In conclusion, we find out an unexpected recurrence of 2,8-DHA nephropathy due to novel expected pathogenetic variants of APRT gene in patient without medical history of kidney stones successfully treated with steroid, febuxostat and hemodiafiltration.

#6440 C1Q-BINDING ANTI-HLA DONOR-SPECIFIC ANTIBODIES AND LONG-TERM KIDNEY GRAFT OUTCOMES

Abstract Background and Aims Immunological response mediated by anti-HLA donor specific antibodies plays an important role in renal allograft injury in kidney transplant recipients. Several characteristics of donor-specific antibodies such as HLA class, specificity, mean fluorescence intensity, IgG subclass and C1q-binding capacity can be assessed. The aim of this study was to determine the impact of circulating anti-HLA donor-specific and their characteristics, including C1q-binding capacity, on long-term kidney graft outcomes. Method One hundred eight patients from our transplant center, who underwent kidney allograft biopsy within three to twenty-four months after renal transplantation from brain-dead deceased donor between 2018 and 2020, were included in the study. At the time of biopsy patients’ sera were collected and stored for analysis. Samples were tested for anti-HLA donor-specific antibodies and their characteristics. Antibodies with mean fluorescence intensity > 500 were considered positive. Results Median time of follow-up of patients was thirty-nine months. Out of nineteen patients with detected donor-specific antibodies, ten patients were identified with immunodominant donor-specific antibodies with C1q-binding capacity (out of them, six patients had anti-HLA donor-specific antibodies detected also before transplantation). C1q-binding antibodies were IgG1 (six patients), IgG3 (three patients) and IgG1+IgG3 (one patient). Presence at the time of biopsy of donor-specific antibodies and their C1q-binding capacity were independent predictors (HR = 5.13, p < 0.001 and HR = 14.64, p < 0.001; respectively) of inferior kidney graft outcomes (composite of 30% reduction from eGFR at biopsy or death-censored graft loss). Conclusion Detection of donor-specific antibodies and their C1q-binding capacity might provide prognostic information in post-transplant monitoring in kidney transplant recipients.

Clinicopathological Results of Percutaneous Transplant Kidney Biopsies: Single Center Nine Years' Experience

Background: Based on clinical criteria alone, the cause of graft dysfunction cannot be accurately predicted in 40-70% of cases. Therefore, renal allograft biopsy is still the gold standard for accurate diagnosis. We performed this study to evaluate the causes of renal graft dysfunction detected in renal allograft biopsies in our center.
 Methods: The results of 90 patients who underwent renal allograft biopsy between May 2013 and June 2022 from kidney transplant patients were evaluated retrospectively.
 Results: It was determined that 92 biopsies were performed from 90 patients and all were ‘cause’’ biopsies. The mean age was 40.03±14.29 years. 82 of the kidney transplants were from living donors. 21 patients had preemptive transplantation. The type of renal replacement therapy before transplantation was hemodialysis in 52 patients, PD in 3 patients, PD and HD in 3 patients. The reason for biopsy was high creatinine in 67 patients, proteinuria in 23 patients, and BKV viremia in 2 patients. The mean discharge creatinine value was 1.64±1.11mg/dl, and the mean creatinine before biopsy was 3.06±2.07mg/dl. Although there was kidney tissue in one of the allograft biopsies, there was no glomeruli. The mean number of cores taken was 2.94±0.61, and the number of glomeruli was 21.33±11.64. In one of the 92 biopsies performed, bleeding requiring transfusion developed. No other biopsy-related complications were observed. Graft loss was observed in 46 of 90 patients during the follow-up period.
 Conclusions: Evaluation of serum creatinine and urinalysis may be useful in predicting histological graft diagnosis, but an allograft biopsy is necessary for definitive diagnosis.

Arteriovenous fistula in a renal allograft with gross hematuria and subsequent acute kidney injury due to urinary tract obstruction: a case report

BackgroundArteriovenous fistula (AVF) due to renal allograft biopsy is mechanical trauma resulting from the penetration of small arteries and veins by a core needle. Most AVFs are reported to resolve asymptomatically and spontaneously. This report presents a patient with acute kidney injury (AKI) due to urinary tract obstruction caused by a bleeding AVF in a renal allograft.Case presentationA 22-year-old Japanese woman who underwent living-donor kidney transplantation (KT) at 3 years due to end-stage renal disease caused by focal segmental glomerulosclerosis (FSGS) presented with a renal transplant AVF (gourd-shaped; 42 × 19 × 20 mm). The AVF was unexpectedly discovered by ultrasound before a surveillance biopsy at 10 years after KT. The patient had a history of recurrent FSGS, had undergone several renal allograft biopsies after KT, and did not experience symptoms or growth of the AVF for years. Nineteen years after KT, the patient developed AKI with sudden, asymptomatic, gross hematuria and anuria. Plain computed tomography revealed a hematoma in the pelvis of the renal allograft and bladder tamponade. The AVF was successfully treated by coil embolization. Hemodialysis was performed for AKI, and graft function was gradually recovered.ConclusionsUnexpected bleeding from a renal transplant AVF may lead to transplant dysfunction. Angiographic embolization against the ruptured renal transplant AVF may prevent rebleeding and rescue the renal allograft.

Evaluation of Interstitial Fibrosis and Tubular Atrophy (IFTA) in Renal Allograft Biopsies:- Comparison of Visual Analysis with Morphometric Quantification and its Correlation with Renal Function

ABSTRACT Introduction: With the increase in number of allografts being performed, the frequency of chronic allograft nephropathy (CAN) has also increased. It is characterized clinically by a progressive decline in glomerular filtration rate, and histologically, by a progressive interstitial fibrosis (IF) and tubular atrophy (TA) which can even be seen in recipients with good allograft function. Objectives: To compare visual analysis with morphometric quantification of interstitial fibrosis and tubular atrophy (IFTA) in renal allograft biopsies and its correlation with renal function. Materials and Methods: A total of 29 renal allograft biopsies were evaluated for fibrosis and tubular atrophy by light microscopy by visual method on Masson’s trichrome-stained and PAS-stained sections, respectively, as well as by computer-assisted morphometry. IFTA was graded as per Banff working classification of renal allograft pathology, which includes a four-point estimate of the prevalence of IF (ci score) and for tubular atrophy (ct score). The estimation of IF and TA by the two methods was correlated with the renal function state; the serum creatinine level. Result: The percentage of IFTA showed statistically significant correlation between manual and morphometric methods (P < 0.001). Each of the method was correlated with serum creatinine level. IF showed a good correlation with serum creatinine by both the methods; however, no correlation could be established between TA and serum creatinine by either method. Conclusion: When calculating scoring IFTA as per Banff criteria, by either the visual method or the morphometric method, there was a significant correlation between the two methods. However when expressed only as a percentage of total area, the visual method was associated with slight overestimation of both the parameters.

The Trend of Serum Creatinine Does Not Predict Follow-Up Biopsy Findings Among Kidney Transplant Recipients With Antibody-Mediated Rejection.

We included all cases of AMR at our program between March 2016 and July 2020 who had a follow-up biopsy after the index biopsy, with initial diagnosis of AMR. We trended the Scr and change in Scr (delta Scr) and its association with being a responder (microvascular inflammation, MVI ≤1) or nonresponder (MVI >1), as well as graft failure. A total of 183 kidney transplant recipients were included, 66 in the responder group and 177 in the nonresponder group. The MVI scores and sum chronicity scores, along with transplant glomerulopathy scores, were higher in the nonresponder group. However, Scr at index biopsy was similar in responders (1.74 ± 0.70) versus nonresponders (1.83 ± 0.65; P = 0.39), as were the delta Scr at various time points. After adjustment for multiple variables, delta Scr was not associated with being a nonresponder. Also, delta Scr value at follow-up biopsy compared with index biopsy among responders was 0 ± 0.67 (P = 0.99) and among nonresponders was -0.01 ± 0.61 (P = 0.89). Being a nonresponder was significantly associated with an increased risk of graft failure at the last follow-up in univariate analysis but was not in multivariate analysis (hazard ratio 1.35; 95% confidence interval, 0.58-3.17; P = 0.49). We found that Scr is not a good predictor of the resolution of MVI, supporting the utility of follow-up biopsies after treatment of AMR.

Interleukin-21 promotes Type-1 activation and cytotoxicity of CD56dimCD16bright natural killer cells during kidney allograft antibody–mediated rejection showing a new link between adaptive and innate humoral allo-immunity

The role of Natural killer (NK) cells during kidney allograft antibody-mediated rejection (ABMR) is increasingly recognized, but an in-depth characterization of mechanisms that contribute to such immune response is still under investigation. Here, we characterized phenotypic, functional, and transcriptomic profiles of peripheral blood circulating and allograft infiltrating CD56dimCD16bright NK cells during anti-HLA donor-specific antibody (DSA)+ ABMR. Cross-sectional analyses performed in 71 kidney transplant recipients identified a unique phenotypic circulating CD56dimCD16bright NK cell cluster expanded in DSA+ ABMR. This cluster co-expressed high levels of the interleukin-21 Receptor (IL-21R); Type-1 transcription factors T-bet and EOMES, CD160 and natural killer group 2D cytotoxic and activating co-stimulatory receptors. CD160+ IL-21R+ NK cells correlated with elevated plasma IL-21, Ki-67+ ICOS+ (CD278) IL-21-producing circulating T follicular helper cells, enhanced Type-1 pro-inflammatory cytokines, NK cell cytotoxicity, worse microvascular inflammation and graft loss. Single-cell transcriptomic analysis of circulating NK cells delineated an expanded cluster in DSA+ ABMR characterized by elevated pro-inflammatory/cytotoxic pathways, IL-21/STAT3 signaling, and leukocyte trans-endothelial migration pathways. Infiltration of CD160+ IL-21R+ NK cells with similar transcriptomic profile was detected in DSA+ ABMR allograft biopsies, potentially contributing to allograft injury. Thus, the IL-21/IL-21R axis, linking adaptive and innate humoral allo-immunity, or NK cells may represent appealing immunotherapy targets in DSA+ ABMR.

A case of kidney transplantation for complete C4 deficiency with recurrent IgM-monoclonal gammopathy of renal significance (MGRS) associated nephropathy

We present a rare case of a patient with complete C4 deficiency who underwent kidney transplantation and experienced immunoglobulin M-monoclonalgammopathyofrenalsignificance (IgM-MGRS) recurrence after the procedure. A 45-year-old male patient presented with end-stage renal failure due to membranoproliferative glomerulonephritis (MPGN). The initial immunosuppressive regimen consisted of tacrolimus, steroids, mycophenolate mofetil, basiliximab, and rituximab. He underwent ABO-incompatible kidney transplantation from his mother in August 2021. The clinical course after kidney transplantation was uneventful for a month. A biopsy of the transplanted kidney was performed due to decreased renal function. The allograft biopsy result led to the suspicion of primary macroglobulinemia-associated nephropathy. Bone marrow biopsy revealed an increase in plasma cells; however, no diagnosis of primary macroglobulinemia was made. At this point, IgM-MGRS was diagnosed instead of primary macroglobulinemia. A follow-up allograft biopsy was performed, and IgM-MGRS-associated nephropathy was diagnosed. Eventually, his retrieved autologous kidney biopsy from the initial examination showed that the primary disease was not MPGN but recurrent IgM-MGRS-associated nephropathy. Dexamethasone, rituximab, and cyclophosphamide (DRC) were started to treat IgM-MGRS due to worsening renal function (serum creatinine levels were in the 4–5 mg/dL range). Additional doses of DRC with 20 cycles of plasma exchange were introduced. Severe side effects occurred but did not result in death.

Renal Transplantation in Antineutrophil Cytoplasmic Antibody-Associated Vasculitis: A Single-Center 10-Year Experience

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a common cause of rapidly progressive glomerulonephritis resulting in end-stage renal disease. The optimal timing of kidney transplantation for end-stage renal disease due to AAV and the risk of relapse after kidney are poorly defined. Our study aimed to evaluate the clinical outcomes of AAV after kidney transplantation, namely the risk of relapse, rejection, and oncologic disease. This retrospective study included all patients with AAV submitted to a kidney transplant between January 2011 and December 2020. Twenty-seven patients (20 males/7 females; mean age 47 years) received a kidney transplant for end-stage renal disease secondary to microscopic polyangiitis (n=25) or granulomatosis with polyangiitis (n=2). All patients were in clinical remission at the time of the kidney transplant, but 11 patients were ANCA-positive. A vasculitis relapse after kidney transplantation occurred in only 1 patient (3.7%). Rejection episodes, proven by allograft biopsy, were present in 3 patients (11.1%), with graft losses in 2 (66.7%). The median time until the graft was lost after the initial rejection diagnosis was 27 ± 8 months. Oncologic complications were present in 9 patients (33.3%). Five patients died (18.5%), and the main cause of death was cardiovascular disease (n=3, 60.0%), followed by oncologic disease (n=2, 40.0%). Kidney transplantation is a safe and effective option for treating end-stage renal disease secondary to AAV. Current immunosuppression regimens make relapses and rejection infrequent but place oncologic complications at a higher incidence.

Significance of C4d expression in peritubular capillaries concurrent with microvascular inflammation in for-cause biopsies of ABO-incompatible renal allografts.

Pathologic diagnosis of antibody-mediated rejection (ABMR) in ABO-incompatible (ABOi) transplantation patients is often challenging because patients without ABMR are frequently immunopositive for C4d. The aim of this study was to determine whether C4d positivity with microvascular inflammation (MVI), in the absence of any detectable donor-specific antibodies (DSAs) in ABOi patients, could be considered as ABMR. A retrospective study of 214 for-cause biopsies from 126 ABOi kidney transplantation patients was performed. Patients with MVI score of ≥2 and glomerulitis score of ≥1 (n = 62) were divided into three groups: the absolute ABMR group (DSA-positive, C4d-positive or C4d-negative; n = 36), the C4d-positive group (DSA-negative, C4d-positive; n = 22), and the C4d-negative group (DSA-negative, C4d-negative; n = 4). The Banff scores, estimated glomerular filtration rates (eGFRs), and graft failure rates were compared among groups. C4d-positive biopsies showed higher glomerulitis, peritubular capillaritis, and MVI scores compared with C4d-negative specimens. The C4d-positive group did not show significant differences in eGFRs and graft survival compared with the absolute ABMR group. The results indicate that C4d positivity, MVI score of ≥2, and glomerulitis score of ≥1 in ABOi allograft biopsies may be categorized and treated as ABMR cases.

Isolated arterial mucoid intimal thickening lesion in early post-transplant kidney allograft biopsies.

Thrombotic microangiopathy (TMA) on kidney biopsy shows a variable combination of features: arterial mucoid intimal thickening, acellular closure of glomerular capillary loops, fragmented red blood cells, fibrin thrombi, and arterial fibrinoid necrosis. However, some early post-transplant kidney biopsies show only arterial mucoid intimal thickening. We aimed to elucidate the importance of this finding. We identified 19 biopsies showing isolated arterial mucoid intimal thickening and compared them with 22 bona fide TMA biopsies identified based on the pathological findings (excluding rejection) (2011-2020). Additionally, delayed graft function (DGF) (n=237), and no DGF (control, n=1314) groups were included for survival analysis. Seven of 19 cases with isolated arterial mucoid intimal thickening showed peripheral blood schistocytes but no other systemic features of TMA. Eight patients underwent adjustments in maintenance immunosuppression (mainly calcineurin inhibitors). None of the cases progressed to full-blown TMA on consecutive biopsies. The overall and death-censored graft survival rates in this group were comparable to the DGF group, but significantly better than the TMA group (P=.005 and .04, respectively). Isolated arterial mucoid intimal thickening in early post-transplant biopsies may be an early/mild form of TMA, probably requiring adjustment in immunosuppressive regimen. Careful exclusion of known causes of TMA, and donor-derived arterial injury are important.