Kidney Allograft Research Articles

#2324 Do urinary tract infections trigger chronic inflammation in the kidney allograft? Interleukin 17 levels in the urine of kidney recipients

Abstract Background and Aims Urinary tract infections (UTI) represent the most common complication following kidney transplantation. Their role in triggering immune phenomena in kidney allograft remains unclear. Interleukin 17 (IL17) represents the significant branch in antimicrobial immunity. At the same time IL17 has been found associated with autoimmune inflammatory disorders. The triggering role of infections in autoimmunity as well as the similarities between autoimmunity and post-transplant immunity have been postulated. The aim of the study was to analyze the levels of urine IL 17A levels in relation to prior UTI history and the timeframe after the last UTI episode. Method The group of 91 kidney recipients who received kidney transplantation between 2016 and 2019 was analyzed. The set of 233 urine samples (109 from females and 124 from males) obtained within first 24 months post-transplant was investigated, among these 144 samples from the patients with no previous UTI history and 89 samples from the patients with previous UTI history (1-22 months after the last episode, average 6.7 ± SD 5.7). Furthermore, 18 samples obtained at the time of an UTI episode and 29 samples from healthy controls were included. Urine IL 17A levels were measured with Human IL 17 ELISA Kit (Sigma Aldrich) and urine IL/creatinine concentrations ratio was calculated for each value. Szapiro-Wilk test was used to assess data distribution, Kruskal-Wallis test was used to assess the differences between independent groups and two proportions Z test was used to compare the groups compositions. Results Interleukin 17A appeared detectable in 105 out of the 233 investigated samples (45%), with significantly higher frequency in samples from the recipients with previous UTI history (p = 0.02). The difference was not significant in the group who underwent recurrent UTI episodes vs. these after a single UTI episode. Among the samples in which IL 17A was detected, the period between the last UTI episode and sample collection was divided into three timeframes: 1-3 months, 4-12 months and 12-24 months. Urine IL17A levels appeared significantly higher independently in each timeframe post-UTI when compared to the samples from the recipients without UTI history and controls (p = 0.0001). Fig. 1 It was apparent within the whole group but also in males and females separately. Further, urine IL17A levels were significantly higher in males 1-3 months after the last UTI episode than in females in the analogous period (p = 0.001). Conclusion Interleukin 17A was more frequently detected in urine samples from kidney recipients with previous UTI history. UTI history impacted IL17A urine levels in the analyzed kidney recipients. Within the first 24 months post-transplant, these were higher in the recipients with UTI history prior to the sample collection and it was independent on the timeframe between the last UTI episode and the sample collection. The factors other than UTI history which influence urine IL17A detectability are not fully recognized and remain under investigation.

#153 The risk of post-transplant recurrent immunoglobulin A nephropathy: the association with post-transplant steroid use

Abstract Background and Aims Immunoglobulin A nephropathy (IgAN) is the most common cause of kidney failure among glomerulopathies worldwide and it is reported that approximately 6-7% of all kidney transplantation is due to IgAN. It is well known that IgAN can recur in the kidney allograft and previous studies suggest that recurrent IgAN is the third most common cause of graft loss in patients with IgAN as primary disease. There is currently no effective treatment for recurrent IgAN, and the main goal is therefore to prevent recurrence in the allograft. Post-transplant steroid therapy is a cornerstone in many immunosuppressive regimens, but steroid treatment also come with several side effects leading to the use of steroid-free protocols. Controversy remains as to whether the use of steroid affects the risk of recurrent IgAN. Previous, retrospective studies report widely divergent associations between the use of steroids and the risk of recurrent IgAN and thus, more research on the association between steroid use and the risk of recurrent IgAN is warranted. We examined this by taking advantage of the fact that two different standard immunosuppression protocols have been employed at two Danish transplantation centers, of which one included steroids and the other did not. The patients treated at the two transplantations centers were otherwise similar with respect to ethnicity, socio-economic status and other aspects of treatment differing only by regional residency. This provided a unique opportunity to compare the association between steroid use, recurrence rate and graft survival. We furthermore aimed to identify potential risk factors for recurrent IgAN. Method A retrospective cohort study including all adult patients (age ≥ 18 years) with biopsy-proven IgAN and a first-time kidney-only transplantation from 1990 to 2020 at either Aarhus University Hospital or Odense University Hospital using a steroid containing or a steroid free post-transplant immunosuppressive protocol, respectively. Renal transplant patients with IgAN were identified from the Danish Nephrology Registry and data on medical treatment, graft survival and histopathological evidence of recurrent IgAN were extracted from electronic medical journals. Data is presented by Aalen-Johansen and Kaplan-Meier plot, and associations between risk factors for recurrent IgAN were analyzed by cox-regression. Results A total of 120 first-time kidney recipients were included in the study. Biopsy-proven, recurrent IgAN was identified in 17 (14.2%) recipients. The median time from transplantation to recurrence was 2.91 years (IQR 0.89−5.60). Only one of 18 (15%) recipients adhering to steroid-free protocol was diagnosed with recurrent IgAN during the study period. The accumulated use of steroid as part of the immunosuppression regime was not associated with the risk of recurrent IgAN (unadjusted HR (95% CI) =1.02 (0.94−1.12)). Transplantation with genetically related living donor was associated with a greater risk of recurrent IgAN compared with non-genetically related ((unadjusted HR (95% CI) = 3.90 (1.37−11.10)) and recipients with recurrent IgAN were more likely to be younger at time of been diagnosed with IgAN and had a shorter time from being diagnosed to kidney failure when compared to recipients with non-recurrent IgAN. There were no associations between the risk of recurrent IgAN and induction therapy or HLA-mismatches. The 10-year death censored graft survival was 45% for recipients with recurrent IgAN, compared to 80% for recipients with non-recurrent IgAN. Conclusion The risk of recurrent IgAN after kidney transplantation was not associated with the use of steroids as part of the immunosuppression protocol, whereas recipients receiving a kidney from a genetic related donor appeared to have a higher risk of recurrent IgAN.

#2478 Multiparametric magnetic resonance imaging predicts decline of kidney function but does not perform better than diffusion-weighted MRI alone

Abstract Background and Aims Renal cortical interstitial fibrosis, typically measured by biopsy, is a critical factor for kidney function prognosis. Diffusion-weighted magnetic resonance imaging (DW-MRI) has emerged as a novel promising non-invasive method to assess the degree of fibrosis. We have previously shown that there is a strong correlation between the cortico-medullary apparent diffusion coefficient difference (ΔADC) and histologically assessed fibrosis. We also developed a model based on ΔADC, eGFR and proteinuria that calculates a risk score for future renal function decline. Multiparametric MRI combines DW-MRI with other sequences and can provide synchronized insights into perfusion, diffusion, oxygenation, and tissue characterization (T1 and T2 mappings). Our current research evaluates whether additional multiparametric MRI sequences increase the power of the DW-MRI based model to predict renal function decline. Method We used data from 197 patients with either chronic kidney disease (42) or allograft kidneys (155). Each participant underwent a biopsy followed by a multiparametric MRI within the following week. The median follow-up period was 2.2 years, during which laboratory parameters were recorded. The primary endpoint was defined as a rapid decline in kidney function, characterized by a reduction in eGFR of over 30%, or the initiation of dialysis. Prognostic factors for the primary outcome were analyzed using both univariable and multivariable Cox regression models, incorporating MRI parameters (ΔADC, cortical and ΔT1, cortical and ΔT2), eGFR, and proteinuria. Results At baseline, mean eGFR was 54.5 ml/min/1.73 m2 (SD 23.8) and mean proteinuria was 0.90 g/24 h (SD 2.4). Rapid decline of renal function occurred in 54 patients after a median time of 1.1 years (interquartile range, 0.9–2.1 years). In univariable survival analysis, cortical T1 measure and cortico-medullar difference ΔT2 have showed the best association to rapid kidney function decline. Compared to our previously established model incorporating ΔADC, eGFR, and proteinuria, adding cortical T1 did not significantly improve the hazard ratio (from 4.62 (95% CI: 1.56–13.67) to 4.36 (95% CI: 1.46–13.02) with cortical T1 inclusion). Harrell's C-index marginally increased with cortical T1, suggesting no significative improvement in prognostic capacity (0.77 versus 0.79 with cortical T1). Additionally, adjusting the regression model for ΔT2 yielded no enhancement in predictive power. Conclusion Our results did not demonstrate an enhancement of the prognostic power of the composite score with the inclusion of additional MRI sequences. Consequently, no clear benefit of multiparametric MRI on top of DW-MRI was observed. Additional research is required to investigate this issue more thoroughly.

#2894 pre-mRNA FOXP3 levels after transplant do not reflect risk of rejection

Abstract Background and Aims Forkhead box P3 (FOXP3) is the master gene regulator of T regulatory cells, and is crucial for their suppressive function. In kidney transplant recipients, low post-transplant levels of FOXP3 in peripheral blood has been associated with increased risk of kidney allograft rejection. However, it is unknown if low post-transplant levels of FOXP3 pre-mRNA is also associated with increased risk of kidney allograft rejection. Here we aim to test if pre-mRNA FOXP3 levels are associated with the risk of rejection post-transplant in kidney transplant recipients. Method We collected blood samples from incident kidney transplant recipients the first day after transplantation. From these, we extracted peripheral blood mononuclear cell ribonucleic acid and measured pre-mRNA FOXP3 transcripts with quantitative reverse transcription polymerase chain reaction. Pre-mRNA FOXP3 levels were normalized to β-actin, and converted to a logarithmic scale. We collected data concerning rejection episodes through medical record review. Kidney transplant recipients that had at least one recorded acute kidney allograft rejection episode within the first three months post-transplant were defined as recipients with a rejection episode. Data is presented as median [interquartile range] and tested with Wilcoxon rank sum test. Results We measured pre-mRNA FOXP3 in 515 incident kidney transplant recipients, 52 experienced a rejection episode within the first three months post-transplant. Pre-mRNA levels did not differ between recipients with vs without rejection, logarithmic value of normalized pre-mRNA FOXP3 −4.48 [−4.63 to −4.10] vs −4.41 [−4.69 to −4.11], p = 0.80. The pattern persisted regardless of donor type, deceased recipients with rejection (N = 25) vs deceased recipients without—(N = 268), −4.47 [−4.62 to −4.26] vs −4.46 [−4.71 to −4.25], p = 0.90. Living ABO-compatible recipients with rejection (N = 19) vs living ABO-compatible recipients without—(N = 139), −4.49 [−4.64 to −4.14] vs −4.35 [−4.65 to −3.93], p = 0.30. Living ABO-incompatible recipients with rejection (N = 8) vs living ABO-compatible recipients without—(N = 56), −4.13 [−4.48 vs −3.88] vs −4.20 [−4.61 to −3.88], p = 0.70. Conclusion In kidney transplant recipients, early post-transplant abundance of pre-mRNA FOXP3 transcripts were similar regardless of risk of kidney allograft rejection post-transplant.

#665 Comparison of outcomes between kidney transplant-naïve and post-transplant graft failure peritoneal dialysis patients

Abstract Background and Aims Despite progress in kidney transplant medicine, there are still patients experiencing graft failure and returning to dialysis therapy. Data regarding the prognosis of these patients remain conflicting. This study was conducted to compare clinical outcomes between transplant-naïve peritoneal dialysis (PD) patients and those returning to PD after a failed allograft. Method In this retrospective cohort study during 2006 and 2016, we included a total of 786 patients on chronic PD. Of them 679 were transplant-naïve, 76 patients underwent a successful transplantation, and 32 patients returned to PD after a failed kidney allograft. Baseline demographics and clinical characteristics were analyzed in relation to the outcomes of all-cause mortality and peritonitis rate. We employed the Kaplan-Meier method and Cox proportional hazards model to evaluate survival, while Poisson regression was utilized to estimate rate ratios for peritonitis. Results During a median follow-up of 6.37 years, 56.68 % death and 146.62 episodes of peritonitis/patient-year were observed. Compared with patients who received a kidney graft, transplant-naïve patients were older, more with diabetes and having higher mortality (58.6 ± 15.8, 40.5% and 57.73%, p < 0.0001). After accounting for age, gender, and comorbidities, the adjusted hazards ratios were 0.26 (95% CI 0.13-0.53) in patients with a functioning graft and 1.12 (95% CI 0.61-2.06) in patients returning to PD after graft failure, compared respectively with concurrent PD patients without kidney transplant. The adjusted relative risk of peritonitis in patients resuming PD after graft failure was comparable to those without kidney transplant (95% CI 0.22-1.14). Conclusion Successful kidney transplant reduced the risk of overall mortality among patients on long-term PD. Patients returning to PD after graft loss showed outcomes similar to transplant-naïve counterparts. These data support reactivation of PD as a viable option for patients with a failed kidney transplant.

#1453 EZH2 is an epigenetic regulator of renal gluconeogenesis in chronic kidney disease through downregulation of PCK1

Abstract Background and Aims Impaired renal gluconeogenesis has been recently identified as a hallmark of chronic kidney diseases (CKD), and is tightly correlated with the progression of renal tubulointerstitial fibrosis. The methyltransferase enhancer of zeste homolog 2 (EZH2) is an epigenetic regulator playing an important role in renal tubulointerstitial fibrosis. Whether renal gluconeogenesis can be epigenetically regulated is currently unknown. In the current study, we studied EZH2-mediated epigenetic regulation of renal gluconeogenesis in three different mouse models of renal fibrosis. Method Mouse models of renal fibrosis were established by unilateral ureteral obstruction (UUO) operation, unilateral ischemia reperfusion injury or folic acid (FA) injection. Human proximal tubular cell line (HK2), primary tubular cells or primary tubules was used as an in vitro or ex vivo model. EZH2 was conditional knockout or inhibited by 3-DZNeP in mice. Inhibition of EZH2 by 3-DZNeP or overexpressed by adenovirus was performed in vitro. RNA sequencing and cleavage under targets and tagmentation (CUT&Tag) sequencing analysis were performed and followed by quantitative PCR, CUT&Tag and Western blotting analysis. Glucogenic metabolites were measured and systemic glucose metabolism was assessed by tolerance tests. Results By deletion of Ezh2 gene in mice through a ubiquitous expressed Cre/Esr1 system, we confirmed the pro-fibrotic effect of EZH2 in unilateral ureteral obstruction (UUO) kidneys. Through RNA sequencing and CUT&Tag sequencing analysis, we found that the phosphoenolpyruvate carboxykinase 1 (PCK1), a critical enzyme in gluconeogenesis, is negatively regulated by the methyltransferase EZH2 in fibrotic kidneys, which was further confirmed by quantitative PCR, CUT&Tag and Western blotting analysis in renal cells and UUO or FA kidneys. We further showed that pharmaceutical inhibition of EZH2 by 3-DZNeP enhances PCK1 expression in fibrotic kidneys of three mouse models. Moreover, the concentration of lactate, a glucogenic metabolic intermediate, was increased in mouse fibrotic kidneys, which was reduced by EZH2 inhibition. A further experiment showed that systemic glucose metabolism was impaired in UUO mice and restored by EZH2 inhibition as assessed by insulin or glucose tolerance test. Upregulated EZH2 in UUO kidneys is colocalized with the proximal tubular marker as shown by immunofluorescent staining. The direct anti-gluconeogenesis effect of EZH2 on renal proximal epithelial cells and primary renal tubules was shown by analysis of gluconeogenic gene expression and production of glucose or lactate in human HK2 cells treated with EZH2 inhibitor or exogeneous expression of EZH2 by adenovirus transfection. Importantly, we further confirmed the direct effect of tubular EZH2 on gluconeogenesis in tubular specific deleted EZH2 mice (Ezh2fl/fl;Cdh16-Cre). Moreover, inhibition of PCK1 by 3-mercaptopropionic acid abrogated the pro-gluconeogenic effect and anti-fibrotic effect of EZH2 inhibitor in renal cells and UUO kidneys. Finally, RNA sequencing data from kidney allograft biopsies showed that EZH2 is progressively increased in CKD patients. Conclusion We conclude that EZH2 promotes renal tubulointerstitial fibrosis through epigenetic inhibition of PCK1. Our study suggests that therapeutic restoration of the impaired renal gluconeogenesis is beneficial to CKD.

#1776 Distinct changes in gut microbiota of patients with kidney graft rejection

Abstract Background and Aims Kidney graft rejection still represents the major cause of graft loss in kidney transplant recipients. Of growing interest is the bidirectional relationship between gut microbiome and immune system suggesting that gut microbiota can affect allograft outcome. Method In this cross-sectional case control study, we characterized the gut microbial profile of adult renal transplant recipients with and without graft rejection in order to define a cohort-specific microbial fingerprint through 16S rRNA gene sequencing. We used very strict inclusion and exclusion criteria to address confounder of microbiota composition. Results Different relative abundances in several gut microbial taxa were detectable in control patients compared to patients with kidney allograft rejection. Alpha diversity was lower in the rejection group and beta diversity revealed dissimilarity between patients with and without kidney graft rejection (P < .01). When the rejection group was stratified according to different types of allograft rejection, major changes were identified between patients with chronic T cell mediated rejection (cTCMR) and controls. Changes in alpha diversity within the gut microbiome were related to the probability of cTCMR (P < .05). Kidney transplant patients without rejection showed significant enrichment of rather anti-inflammatory taxa whereas in the rejection group bacteria well known for their role in chronic inflammation were increased. For example, ASV 362 belonging to the genus Bacteroides and ASV 312 belonging to Tanerrelaceae were enriched in no rejection (P < .001 and P < .01) whereas ASV 365 was enriched in patients with allograft rejection (P = .04). Looking at metagenomic functions, a higher abundance of genes coding for enzymes involved in bacterial multidrug resistance and processing of short chain fatty acids was found in patients without rejection but an increase in enzymes involved in NADPH production was seen in patients with allograft rejection. Conclusion A distinct microbial fingerprint of patients with allograft rejection might serve as non-invasive biomarker in the future.

#2132 Recipient outcomes after laparoscopic versus open living donor nephrectomy: a propensity score-matched cohort study

Abstract Background and Aims Kidney transplantation is the optimal treatment for end-stage renal disease. To meet the growing demand for kidney allografts and to ensure the well-being of donors, laparoscopic nephrectomy has been adopted leading to superior donor outcomes. However, data on recipient outcomes of laparoscopically retrieved grafts are underreported. The aim of the study is to estimate the impact of laparoscopic compared to open living donor nephrectomy (LDN, ODN) on recipient outcomes in the first-year post-transplant. Method This was an observational cohort study of primary data on 396 recipients who had undergone living kidney transplantation from January 2011 to December 2021 at the Clinic of Nephrology and Renal Transplantation of ‘Laiko’ hospital. Since October 2018 laparoscopic surgery has supplanted ODN in the reporting center. Graft function, the risk of adverse events, patient and graft survival within the first-year post-transplantation, were evaluated. A propensity score analysis was applied (2:1 nearest-neighbor matching, with a caliper width of 0.05). As a robustness check, the analysis was rerun on the sub-groups of low and high immunological risk patients. Results After propensity score matching, 389 patients were analyzed. One-year post-transplantation, renal function (−0.074 mg/dl, p: 0.063) patient (99.44% vs 100%, p: 0.27) and graft (99.43% vs 100%, p: 0.13) survival were statistically equal among LDN and ODN recipients. Laparoscopically retrieved grafts demonstrated statistically higher risk of delayed graft function (10.1%, p: 0.032) and higher risk for transfusion (12.9%, p:0.022). The risk for acute rejection, surgical complications and infections (Fig. 1), as well as the length of hospital stay did not differ between the two groups. Kidney function at one year was similar in LDN and ODN patients, regardless of the immunological risk. Low immunological risk patients demonstrated comparable risk of adverse events in the first post-transplant year. High-immunological risk patients after LDN after LDN exhibited greater risk for reoperation (16%, p: 0.0078) urologic complications (19.6%, p: 0.042) and bacterial infections (7.1%, p: 0.027) compared to ODN recipients during the first year after transplantation. Conclusion The results indicate that one-year post-transplantation, renal function, patient and graft survival are equivalent among recipients of allografts procured either laparoscopically or by open surgery, with similar risk of adverse events.

#725 Incorporating molecular rejection patterns to differentiate histologic activity and chronicity features in antibody-mediated rejection

Abstract Background and Aims Biopsy-based transcripts associated with antibody-mediated rejection (AMR) hold promise as substitutes for C4d positivity, according to the Banff Meeting Report of 2022. However, incorporating histologic and molecular features of disease activity and chronicity is crucial to potentially guide patient management. Method We analyzed 365 kidney allograft biopsies by histology and the Molecular Microscope Diagnostic System (MMDx) at the University Hospital Zurich from July 2021 to November 2023. Histologic findings were classified according to Banff 2022 into (1) active AMR (n = 24), (2) chronic active AMR (MVI, n = 47), and (3) chronic AMR (n = 30). The corresponding histologic subgroups with DSA negativity were used for comparison. Results Fourteen out of 24 cases (58%) with active AMR, 28 of 47 cases (60%) with chronic active AMR, but only 1 of 30 cases (3%) with chronic AMR showed molecular AMR. Among cases with molecular AMR the sum of the fully-developed AMR-related (R5) and late-stage AMR-related (R6) phenotype scores was significantly higher in chronic active AMR compared to active AMR cases (p = 0.0017). This finding was even more pronounced in chronic active AMR cases with double contours (cg)>1 (p = 0.00062). Similarly, in the cases without molecular AMR the sum of the fully-developed AMR-related (R5) and late-stage AMR-related (R6) phenotype scores was higher in chronic active AMR compared to active AMR cases (p = 0.039) and more pronounced in cases with cg>1 (p = 0.008). However, rejection phenotype scores (R1-R6) among chronic AMR cases did not differ from DSA-positive or DSA-negative cases without microvascular inflammation (p = 0.705 for R5+R6). Conclusion Incorporating molecular rejection phenotype patterns may further differentiate disease activity and chronicity in cases with active and chronic active AMR by histology. However, molecular subthreshold findings do not appear relevant in chronic AMR cases.

#1038 Progressive multifocal leukoencephalopathy in kidney transplant recipients: a retrospective multicenter nationwide cohort study

Abstract Background and Aims Progressive multifocal leukoencephalopathy (PML) is a serious opportunistic infectious disease affecting the central nervous system caused by JC virus. While extensively studied in patients with HIV infection, haematological malignancies, or undergoing immunotherapies, there is a lack of data concerning kidney transplant recipients (KTRs). Method We performed a retrospective, multicentric, nationwide study. We contacted all kidney transplantation centres in France to gather all cases of PML. We obtained the count of patients with a functional kidney allograft using the registry of the French regulatory agency. Results We collected 24 cases of PML. Between 2012 and 2021, the estimated minimal nationwide incidence of PML was 4.7/100 000 patient-years. The median duration from kidney transplantation to PML was 88 months (interquartile range: 9 to 355). Eight patients (33%) had been exposed to belatacept (median exposure: 18.5 months). Almost all patients underwent reduction or withdrawal of immunosuppressive drug doses and 13 (54%) received a specific treatment. Fifteen patients (65%) died within one year after diagnosis. Conclusion In this nationwide study, PML incidence rate in KTRs was at least 4.7/100 000 patient-years resulting in an alarming 65% mortality rate within a year despite immunosuppressants doses decrease or withdrawal. Further investigations are warranted to demonstrate the efficacy of specific treatments and confirm a potential association between belatacept exposure and PML occurrence, as suggested by our study.

#2082 Effectiveness of a surveillance protocol and early mTORi conversion according to Urine BK viral load in Thai kidney transplant recipients

Abstract Background and Aims BK viral nephropathy (BKVN) is a crucial cause of early kidney allograft failure. Early detection and prompt treatment in the case of a high urine viral load might be more advantageous than waiting until BK viremia occurs. Data regarding outcome of BK infection based on adjustments of immunosuppression according to urine viral load is limited. Method A prospective cohort study of kidney transplant (KT) recipients at Siriraj Hospital, conducted between January 2015 and June 2020, involved monitoring urine BK viral load (RT-PCR) at 1, 2, 3, 6, 12, 18, and 24 months after KT. Determination of BK viremia and adjustments to immunosuppression were performed in patients with urine BK viral loads exceeding 1,000,000 copies/ml or demonstrating progressive increments in BK viruria. Initially, mycophenolate (MPA) dosage was reduced, and subsequently, conversion to mTOR inhibitors was considered for non-responsive cases. Data on the overall incidence and risk factors of BK viremia and/or BKVN were collected. Results Out of a total of 339 enrolled patients, 234 (69%) underwent deceased KT, and 49 (14.5%) received induction therapy with anti-thymocyte globulin. The incidence of BK viruria, viremia, and BKVN were 38.6% (131 patients), 9.7% (33 patients), and 4.1% (14 patients), respectively. The median time of occurrence for BK viruria and BKVN was 3 (IQR 1-12) and 4.5 (IQR 3–18) months after KT, respectively. Most BKVN cases (71.4%) developed within the first six months post KT. We did not find any significant risk factors associated with the occurrence of BK viremia or BKVN. Regarding the adjustment of immunosuppression, the initial reduction of MPA dosage was effective in 48 out of 92 patients (52.17%). In cases with an extremely high urine BK viral load or no response to MPA reduction, 46 patients received a change from MPA to everolimus, which was successful in 38 patients (82.6%). No graft loss due to BKVN was observed throughout the study. Conclusion The incidence of BK infection after KT in Thai recipients is high, comparable to western population. A surveillance protocol with urine BK viral load and early mTORi conversion is effective for prevention of allograft loss from BKVN.

#2859 Clinical and morphological characteristics of biopsy-proven kidney graft rejection in Latvia

Abstract Background and Aims Kidney transplantation is a treatment for many patients with end stage renal disease leading to increased quality of life. In last decades results in kidney transplantation have been improving, but allograft rejection remains an important clinical problem. Graft biopsy remains the gold standard to assess the cause of kidney transplant status. This study aimed to determine clinical and histopathological characteristics, treatment and short-term outcomes of biopsy-proved kidney graft rejection in Latvia. Method In this retrospective observational study all kidney allograft biopsies performed in Pauls Stradins Clinical University Hospital from January 2014 till December 2022 was reviewed. Biopsies with rejection, ≥7 glomeruli, patients ≥18 years old were included. Acute rejection was diagnosed according to clinical, laboratory and biopsy-proven acute rejection (BPAR) histological criteria. BPAR was classified and subdivided using Banff criteria. All recipients universally received either depleting or non-depleting induction therapy. Most of the patient (82%) for maintenance immunosuppression (MI) received triple therapy with calcineurin inhibitor, mycophenolate mofetil, and prednisone, others—in different combinations with above and mammalian target of rapamycin (mTOR), azathioprine. Graft function was evaluated according to glomerular filtration rate (GFR), calculated with the CKD-EPI Creatinine, 2021 equation. Treatment strategies, laboratory data at the time of biopsy and after 1 year follow-up were analysed. Repeated-control biopsies after receiving therapy were excluded. Data were analysed using descriptive statistics and T-test. Results From all 523 biopsies, further included and analysed were 153 (total 146 patients). 58% were males, average patient age was 45.5 years. Most 84% of the grafts were from deceased, 8%—living donors. Mean time from transplantation to biopsy was 32 months. Acute antibody-mediated rejection (AAMR) was diagnosed in 41% cases, chronic-active antibody mediated (CAAMR)—25%, followed by mixed 16%, acute cellular (ACR) 10% and borderline 8% rejection. Besides augmented MI for almost all patients, pulse steroids (GCS) were the most commonly 70% administered treatment, followed by plasma exchange 59% (PEX), rituximab (RTX) 50%, immunoglobulins (IG) 24% and anti-thymocyte globulin (ATG) 10% in different, mostly non-homogenous combinations. Non adherence, advanced fibrotic changes in biopsy and serious comorbidities were the main reasons patients did not receive specific treatment besides intensified MI. The most favourable outcomes were in ACR where mean allograft GFR increased +20.7 ml/min after one year, compared to the worst outcome CAAMR group where GFR decreased −4.7 ml/min (p = 0.03). In ACR group 92% graft function stayed the same or improved, moreover 54% graft function increased ≥20% from baseline; similarly in mixed and AAMR group GFR increase ≥20% were for 45% and 48%, compared to CAAMR where it was only for 6% of patient. Furthermore, the CAAMR group was with the most patients (48%) who returned to dialysis or died. In AAMR and mixed rejection groups mean GFR changes were close +13.4 ml/min and +12.9 ml/min (p = 0.95). There were no statistically significant associations between treatment outcomes in PEX+RTX+GCS vs PEX+RTX+GCS+IG in the AAMR group (p = 0.382). Overall, 3.9% of patients died. Conclusion Overall BPAR prevalence between kidney graft biopsies was high (29%). Antibody mediated rejection was diagnosed most often with least favourable short-term outcomes in CAAMR group. Despite various improvements in immunosuppression, CAAMR remains a serious cause of transplant dysfunction or loss.

#1134 Molecular rejection phenotype patterns differentiate between probable AMR, DSA-negative microvascular inflammation, and AMR

Abstract Background and Aims Biopsy-based transcripts associated with antibody-mediated rejection (AMR) hold promise as substitutes for C4d positivity, according to the latest Banff Meeting Report of 2022. However, patterns and strength of rejection phenotype scores remain inadequately studied within the new subgroups along the AMR continuum. Method We analyzed 365 kidney allograft biopsies by histology and the Molecular Microscope Diagnostic System (MMDx) at the University Hospital of Zurich from July 2021 to November 2023. Histologic findings were classified according to Banff 2022 into (1) probable AMR (n = 32), (2) donor-specific antibodies (DSA)-negative C4d-negative microvascular inflammation (MVI, n = 32), and (3) AMR (n = 60). A control group of 118 cases without MVI was used for comparison. Results 10 out of 32 cases (31%) with probable AMR, 20 of 32 cases (63%) with DSA-negative C4d-negative MVI, and 31 of 60 cases (52%) with AMR showed molecular AMR. Among cases with molecular AMR the sum of the TCMR-related (R2) and late-stage AMR-related (R6) phenotype scores was significantly higher in probable AMR and DSA-negative MVI cases compared to AMR cases (p = 0.029). In contrast, the sum of the mixed rejection (R3), early-stage AMR (R4), fully-developed AMR (R5) phenotype scores was higher in AMR compared to probable AMR (p = 0.063). Among cases without molecular AMR the all AMR phenotype score was significantly higher in AMR and DSA-negative MVI compared to probable AMR and the control group without MVI (p = 0.012, p < 0.001). Conclusion Our results identify different molecular rejection phenotype patterns between cases with probable AMR, DSA-negative MVI, and AMR. Sub-threshold findings appear relevant along the AMR continuum.

Cherry on Top or Real Need? A Review of Explainable Machine Learning in Kidney Transplantation.

Research on solid organ transplantation has taken advantage of the substantial acquisition of medical data and the use of artificial intelligence (AI) and machine learning (ML) to answer diagnostic, prognostic, and therapeutic questions for many years. Nevertheless, despite the question of whether AI models add value to traditional modeling approaches, such as regression models, their "black box" nature is one of the factors that have hindered the translation from research to clinical practice. Several techniques that make such models understandable to humans were developed with the promise of increasing transparency in the support of medical decision-making. These techniques should help AI to close the gap between theory and practice by yielding trust in the model by doctors and patients, allowing model auditing, and facilitating compliance with emergent AI regulations. But is this also happening in the field of kidney transplantation? This review reports the use and explanation of "black box" models to diagnose and predict kidney allograft rejection, delayed graft function, graft failure, and other related outcomes after kidney transplantation. In particular, we emphasize the discussion on the need (or not) to explain ML models for biological discovery and clinical implementation in kidney transplantation. We also discuss promising future research paths for these computational tools.

Effect of End-Stage Renal Disease Prospective Payment System on Utilization of Peritoneal Dialysis in Patients with Kidney Allograft Failure

Introduction: The Center for Medicare and Medicaid Services introduced an End-Stage Renal Disease Prospective Payment System (PPS) in 2011 to increase the utilization of home dialysis modalities, including peritoneal dialysis (PD). Several studies have shown a significant increase in PD utilization after PPS implementation. However, its impact on patients with kidney allograft failure remains unknown. Methods: We conducted an interrupted time series analysis using data from the US Renal Data System (USRDS) that include all adult kidney transplant recipients with allograft failure who started dialysis between 2005 and 2019. We compared the PD utilization in the pre-PPS period (2005–2010) to the fully implemented post-PPS period (2014–2019) for early (within 90 days) and late (91–365 days) PD experience. Results: A total of 27,507 adult recipients with allograft failure started dialysis during the study period. There was no difference in early PD utilization between the pre-PPS and the post-PPS period in either immediate change (0.3% increase; 95% CI: −1.95%, 2.54%; p = 0.79) or rate of change over time (0.28% increase per year; 95% CI: −0.16%, 0.72%; p = 0.18). Subgroup analyses revealed a trend toward higher PD utilization post-PPS in for-profit and large-volume dialysis units. There was a significant increase in PD utilization in the post-PPS period in units with low PD experience in the pre-PPS period. Similar findings were seen for the late PD experience. Conclusion: PPS did not significantly increase the overall utilization of PD in patients initiating dialysis after allograft failure.

Urinary Dickkopf 3 Is Not an Independent Risk Factor in a Cohort of Kidney Transplant Recipients and Living Donors.

Urinary dickkopf 3 (uDKK3) is a marker released by kidney tubular epithelial cells that is associated with the progression of chronic kidney disease (CKD) and may cause interstitial fibrosis and tubular atrophy. Recent evidence suggests that uDKK3 can also predict the loss of kidney function in CKD patients and kidney transplant recipients, regardless of their current renal function. We conducted a prospective study on 181 kidney transplant (KTx) recipients who underwent allograft biopsy to determine the cause, analyzing the relationship between uDKK3 levels in urine, histological findings, and future allograft function progression. Additionally, we studied 82 living kidney donors before unilateral nephrectomy (Nx), 1-3 days after surgery, and 1 year post-surgery to observe the effects of rapid kidney function loss. In living donors, the uDKK3/creatinine ratio significantly increased 5.3-fold 1-3 days after Nx. However, it decreased significantly to a median level of 620 pg/mg after one year, despite the absence of underlying primary kidney pathology. The estimated glomerular filtration rate (eGFR) decreased by an average of 29.3% to approximately 66.5 (±13.5) mL/min/1.73 m2 after one year, with no further decline in the subsequent years. uDKK3 levels increased in line with eGFR loss after Nx, followed by a decrease as the eGFR partially recovered within the following year. However, uDKK3 did not correlate with the eGFR at the single time points in living donors. In KTx recipients, the uDKK3/creatinine ratio was significantly elevated with a median of 1550 pg/mg compared to healthy individuals or donors after Nx. The mean eGFR in the recipient group was 35.5 mL/min/1.73 m2. The uDKK3/creatinine ratio was statistically associated with the eGFR at biopsy but was not independently associated with the eGFR one year after biopsy or allograft loss. In conclusion, uDKK3 correlates with recent and future kidney function and kidney allograft survival in the renal transplant cohort. Nevertheless, our findings indicate that the uDKK3/creatinine ratio has no prognostic influence on future renal outcome in living donors and kidney recipients beyond the eGFR, independent of the presence of acute renal graft pathology, as correlations are GFR-dependent.

Association between Body Mass Index and Early Renal Function after Kidney Transplantation: Observational and Mendelian Randomization Study

Introduction: The relationship between BMI and early renal function recovery after kidney transplantation is important due to the rising global obesity rates. Methods: A retrospective study on 320 patients who received allograft kidney transplantation at Guangxi Medical University Hospital explored the BMI-kidney function relationship using various statistical methods. Mendelian randomization (MR) was also employed to investigate causality. Results: Based on the univariate analysis, multivariate linear regression models, and trend analysis, it was found that there were significant positive correlations between BMI and creatinine, urea, and cystatin C on the 7th day after kidney transplantation (p < 0.05). The sensitivity analysis further confirmed these correlations in different gender stratification, adolescents, and adults. However, the positive correlation with cystatin C was only significant in males. Additionally, after conducting smooth curve fitting analysis and threshold saturation analysis, it was revealed that the negative correlation between early renal function recovery was most significant when BMI was between 22.0 and 25.5 kg/m2, and early postoperative renal function may be optimal when BMI was at 22.2 kg/m2. Finally, the MR analysis confirmed a causal relationship between BMI and renal failure, as indicated by the IVW method (p = 0.003), as well as the weighted median estimator (p = 0.004). Conclusion: This study on kidney transplant patients found that maintaining a BMI within the range of 22.0–25.5 kg/m2, with an optimal BMI of 22.2 kg/m2, improves early renal function recovery. This correlation holds true for different age-groups and genders. Monitoring and controlling BMI in high-risk patients can enhance post-transplantation renal function.

The innate immune cells at the heart of kidney allograft rejection

The innate immune cells at the heart of kidney allograft rejection

Treatment of allograft’ ureteral stones with percutaneous laser lithotripsy in a patient post-kidney-transplant: A case report

IntroductionUrolithiasis in transplanted kidneys is a rare complication. The management of urolithiasis in transplant patients is similar to that in the general population. Case presentationA 51-year-old man with end-stage renal failure due to diabetic nephropathy underwent ABO-compatible living-donor kidney transplantation using his younger sister as a donor. The postoperative clinical course was uneventful and the function of the transplanted kidney was excellent during follow-up. In late May 2022, the patient visited our institution with fever, malaise, and oliguria. The function of the transplanted kidney had decreased, with a serum creatinine level of 6.39 mg/dL. Computed tomography demonstrated allograft hydronephrosis and allograft distal ureteral stone. The patient was diagnosed with acute renal failure due to allograft distal ureteral calculi. Moreover, calculous pyelonephritis was also observed. A percutaneous allograft nephrostomy was performed followed by a percutaneous ureteral lithotripsy in early June 2022. The patient underwent an antegrade disposable flexible ureteroscopy, holmium laser lithotripsy, and basket extraction. All stone fragments were surgically removed. After the successful treatment, the allograft kidneys functioned well. ConclusionPercutaneous laser lithotripsy was successfully performed without complications.

A quantitative comparison of urine centrifugation and filtration for the isolation and analysis of urinary nucleic acid biomarkers

Urine is a rich source of nucleic acid biomarkers including cell-free DNA (cfDNA) and RNA for monitoring the health of kidney allografts. In this study, we aimed to evaluate whether urine filtration can serve as an alternative to the commonly used method of centrifugation to collect urinary fluid and cell pellets for isolating cfDNA and cellular messenger RNA (mRNA). We collected urine specimens from kidney allograft recipients and obtained the urine supernatant and cell pellet from each specimen using both filtration and centrifugation for paired analyses. We performed DNA sequencing to characterize the origin and properties of cfDNA, as well as quantitative PCR of mRNAs extracted from cell fractions. Our results showed that the biophysical properties of cfDNA, the microbial DNA content, and the tissues of origin of cfDNA were comparable between samples processed using filtration and centrifugation method. Similarly, mRNA quality and quantity obtained using both methods met our criteria for downstream application and the Ct values for each mRNA were comparable between the two techniques.The Ct values demonstrated a high degree of correlation. These findings suggest that urine filtration is a viable alternative to urine centrifugation for isolation of nucleic acid biomarkers from urine specimens.