Renal Allograft Histology at 10 Years After Transplantation in the Tacrolimus Era: Evidence of Pervasive Chronic Injury

Improving long‐term renal allograft survival remains an important unmet need. To assess the extent of histologic injury at 10 years after transplantation in functioning grafts, we studied 575 consecutive adult solitary renal transplants performed between 2002 and 2005: 77% from living donors and 81% maintained on tacrolimus‐based immunosuppression. Ten‐year graft survival was 59% and death‐censored graft survival was 74%. Surveillance allograft biopsies were assessed at implantation, 5 years, and 10 years from 145 patients who reached 10 years. At implantation, 5% of biopsies had major histologic abnormalities (chronic transplant glomerulopathy score > 0, other chronic Banff scores ≥ 2, global glomerulosclerosis > 20%, or mesangial sclerosis ≥ 2). This increased to 54% at 5 years and 82% at 10 years. Major lesions at 10 years included the following: arteriolar hyalinosis (66%), mesangial sclerosis (67%), and global glomerulosclerosis > 20% (43%), with 48% of grafts having more than one major lesion. Transplant glomerulopathy and moderate‐to‐severe interstitial fibrosis were uncommon (12% each). Major lesions were associated with increased proteinuria and decreased graft function. In patients with diabetes at baseline, 52% had diabetic nephropathy/mesangial sclerosis at 10 years. We conclude that almost all renal allografts sustain major histologic injury by 10 years after transplantation. Much damage appears nonimmunologic, suggesting that new approaches are needed to decrease late injury.     

Early Macrophage Infiltration and Sustained Inflammation in Kidneys From Deceased Donors Are Associated With Long‐Term Renal Function

Kidney transplants from living donors (LDs) have a better outcome than those from deceased donors (DDs). Different factors have been suggested to justify the different outcome. In this study, we analyzed the infiltration and phenotype of monocytes/macrophages and the expression of inflammatory and fibrotic markers in renal biopsy specimens from 94 kidney recipients (60 DDs and 34 LDs) at baseline and 4 months after transplantation. We evaluated their association with medium‐ and long‐term renal function. At baseline, inflammatory gene expression was higher in DDs than in LDs. These results were confirmed by the high number of CD68‐positive cells in DD kidneys, which correlated negatively with long‐term renal function. Expression of the fibrotic markers vimentin, fibronectin, and α–smooth muscle actin was more elevated in biopsy specimens from DDs at 4 months than in those from LDs. Gene expression of inflammatory and fibrotic markers at 4 months and difference between 4 months and baseline correlated negatively with medium‐ and long‐term renal function in DDs. Multivariate analysis point to transforming growth factor‐β1 as the best predictor of long‐term renal function in DDs. We conclude that early macrophage infiltration, sustained inflammation, and transforming growth factor‐β1 expression, at least for the first 4 months, contribute significantly to the difference in DD and LD transplant outcome.     

Intra‐Abdominal Cooling System Limits Ischemia–Reperfusion Injury During Robot‐Assisted Renal Transplantation

Robot‐assisted kidney transplantation is feasible; however, concerns have been raised about possible increases in warm ischemia times. We describe a novel intra‐abdominal cooling system to continuously cool the kidney during the procedure. Porcine kidneys were procured by standard open technique. Groups were as follows: Robotic renal transplantation with (n = 11) and without (n = 6) continuous intra‐abdominal cooling and conventional open technique with intermittent 4°C saline cooling (n = 6). Renal cortex temperature, magnetic resonance imaging, and histology were analyzed. Robotic renal transplantation required a longer anastomosis time, either with or without the cooling system, compared to the open approach (70.4 ± 17.7 min and 74.0 ± 21.5 min vs. 48.7 ± 11.2 min, p‐values < 0.05). The temperature was lower in the robotic group with cooling system compared to the open approach group (6.5 ± 3.1°C vs. 22.5 ± 6.5°C; p = 0.001) or compared to the robotic group without the cooling system (28.7 ± 3.3°C; p < 0.001). Magnetic resonance imaging parenchymal heterogeneities and histologic ischemia–reperfusion lesions were more severe in the robotic group without cooling than in the cooled (open and robotic) groups. Robot‐assisted kidney transplantation prolongs the warm ischemia time of the donor kidney. We developed a novel intra‐abdominal cooling system that suppresses the noncontrolled rewarming of donor kidneys during the transplant procedure and prevents ischemia–reperfusion injuries.     

Uremia‐Associated Premature Aging of T Cells Does Not Predict Infectious Complications After Renal Transplantation

Patients with end‐stage renal disease have prematurely aged T cell systems. We tested whether T cell aging parameters were associated with the risk of infections after renal transplantation (RTx). We studied 188 patients over 1 year. Peripheral T cells were analyzed before and at 3 and 6 mo after RTx for frequency of recent thymic emigrants, relative telomere length and differentiation status. These parameters were related to the occurrence of opportunistic and serious infections. Overall, 84 patients developed an infection. In this group, 50 developed an opportunistic infection and 53 developed a serious infection. T cell aging parameters assessed before RTx were not associated with infection risk. The memory T cells showed a decrease within the first 3 mo in both groups (p < 0.001). The CD4⁺ memory T cells increased between 3 and 6 mo within the infection group (p = 0.015). The number of CD8⁺ memory T cells increased in both groups (p < 0.001) but reached baseline levels only in the infection group. In the infection group, the CD8⁺CD28^null T cell percentage increased between 3 and 6 mo (p = 0.024), tending to be higher than at baseline (p = 0.061). These differences in post‐RTx dynamics resulted from infections. Parameters of uremia‐associated premature aging of peripheral T cells do not predict posttransplant infections.     

Anti‐CD47 monoclonal antibody therapy reduces ischemia‐reperfusion injury of renal allografts in a porcine model of donation after cardiac death

We investigated whether blockade of the CD47 signaling pathway could reduce ischemia‐reperfusion injury (IRI) of renal allografts donated after cardiac death (DCD) in a porcine animal model of transplantation. Renal allografts were subjected to 30 minutes of warm ischemia, 3.5 hours of cold ischemia, and then perfused with a humanized anti‐CD47 monoclonal antibody (CD47mAb) in the treatment group or HTK solution in the control group (n = 4/group). The animals were euthanized five days after transplantation. At the time of reperfusion, indocyanine green‐based in vivo imaging showed that CD47mAb‐treated organs had greater and more uniform reperfusion. On post‐transplant days 3‐5, the treatment group had lower values compared to the control for creatinine and blood urea nitrogen. Histological examination of allograft tissues showed a significant decrease of acute tubular injury in the CD47mAb‐treated group compared to control. Compared to the control group, CD47mAb treatment significantly decreased genes expression related to oxidative stress (sod‐1, gpx‐1, and txn), the inflammatory response (il‐2, il‐6, inf‐g, and tgf‐b), as well as reduced protein levels of BAX, Caspase‐3, MMP2, and MMP9. These data demonstrate that CD47mAb blockade decreases IRI and subsequent tissue injury in DCD renal allografts in a large animal transplant model.     

Thrombalexins: Cell‐Localized Inhibition of Thrombin and Its Effects in a Model of High‐Risk Renal Transplantation

Allograft transplantation into sensitized recipients with antidonor antibodies results in accelerated antibody‐mediated rejection (AMR), complement activation, and graft thrombosis. We have developed a membrane‐localizing technology of wide applicability that enables therapeutic agents, including anticoagulants, to bind to cell surfaces and protect the donor endothelium. We describe here how this technology has been applied to thrombin inhibitors to generate a novel class of drugs termed thrombalexins (TLNs). Using a rat model of hyperacute rejection, we investigated the potential of one such inhibitor (thrombalexin‐1 [TLN‐1]) to prevent acute antibody‐mediated thrombosis in the donor organ. TLN‐1 alone was able to reduce intragraft thrombosis and significantly delay rejection. The results confirm a pivotal role for thrombin in AMR in vivo. This approach targets donor organs rather than the recipient and is intended to be directly translatable to clinical use.     

Urinary MicroRNA as Biomarker in Renal Transplantation

Urine represents a noninvasive source in which proteins and nucleic acids can be assessed. Such analytes may function as biomarkers to monitor kidney graft pathology at every desired frequency, thereby providing a time window to prevent graft damage by therapeutic intervention. Recently, several proteins have been measured in urine as markers of graft injury. However, the specificity is limited, and measuring urinary proteins generally lacks the potential to predict early kidney graft damage. Currently, urinary mRNA and microRNA are being investigated to evaluate the prognostic value of changes in gene expression during the initial stages of graft damage. At such time point, a change in treatment regimen and dosage is expected to have maximum potency to minimize future decline in graft function. Both mRNA and microRNAs have shown promising results in both detection and prediction of graft injury. An advantage of microRNAs compared to mRNA molecules is their stability, a characteristic that is beneficial when working with urine samples. In this review, we provide the current state of urinary biomarkers in renal transplantation, with a focus on urinary microRNA. In addition, we discuss the methods used to study urinary microRNA expression.     

Protecting the Kidney in Liver Transplant Candidates: Practice‐Based Recommendations From the American Society of Transplantation Liver and Intestine Community of Practice

Acute kidney injury (AKI) and chronic kidney disease (CKD) are common in patients awaiting liver transplantation, and both have a marked impact on the perioperative and long‐term morbidity and mortality of liver transplant recipients. Consequently, we reviewed the epidemiology of AKI and CKD in patients with end‐stage liver disease, highlighted strategies to prevent and manage AKI, evaluated the changing liver transplant waiting list's impact on kidney function, delineated important considerations in simultaneous liver–kidney transplant selection, and projected possible future transplant policy changes and outcomes. This review was assembled by experts in the field and endorsed by the American Society of Transplantation Liver and Intestinal Community of Practice and Board of Directors and provides practice‐based recommendations for preservation of kidney function in patients with end‐stage liver disease.     

Triptolide inhibits donor‐specific antibody production and attenuates mixed antibody‐mediated renal allograft injury

Donor‐specific antibodies (DSAs) are major mediators of renal allograft injury, and strategies to inhibit DSAs are important in promoting long‐term graft survival. Triptolide exhibits a wide spectrum of antiinflammatory and immunosuppressive activities, and in autoimmune diseases it inhibits autoantibody levels. In this study, we investigated the suppressive role of triptolide in the generation of DSAs in transplant recipients. We found that triptolide treatment of skin allograft recipients in mice significantly suppressed the development of circulating anti‐donor‐specific IgG and effectively alleviated DSA‐mediated renal allograft injury, which led to prolonged allograft survival. In vitro studies revealed that triptolide inhibited the differentiation of B cells into CD138⁺CD27⁺⁺ plasma cells; reduced the levels of IgA, IgG, and IgM secreted by plasma cells; and repressed somatic hypermutation and class switch recombination of B cells. Moreover, triptolide‐treated recipients showed reduced numbers of B cells, plasma cells, and memory B cells in spleens and decreased numbers of T, B, natural killer (NK) cells, and macrophages infiltrating grafts. These findings highlight the importance of triptolide in suppressing DSAs and establish triptolide as a novel therapeutic agent for antibody‐mediated allograft rejection.     

Pretransplant Numbers of CD16+ Monocytes as a Novel Biomarker to Predict Acute Rejection After Kidney Transplantation: A Pilot Study

Acute rejection is one of the major immunological determinants of kidney graft function and survival. Early biomarkers to predict rejection are lacking. Emerging evidence reveals a crucial role for the monocyte/macrophage lineage cells in the pathogenesis of rejection. We hypothesized that higher pretransplant numbers of proinflammatory CD16+ monocytes can predict rejection. The study cohort consisted of 104 kidney transplant recipients (58 with no rejection and 46 with biopsy‐proven rejection) and 33 healthy persons. Posttransplant median follow‐up time was 14.7 mo (interquartile range 0.3–34 mo). Pretransplantation blood samples were analyzed by flow cytometry for monocyte immunophenotypes. Groups were compared by Cox regression models for the occurrence of acute rejection. We documented a significantly increased absolute number of pretransplant CD16+ monocytes in patients who developed biopsy‐proven rejection after transplantation compared with those with no rejection (hazard ratio [HR] 1.60, 95% CI 1.28–2.00, p < 0.001) and healthy persons (HR 1.47, 95% CI 1.18–1.82, p < 0.001). In parallel, significantly fewer absolute numbers of CD16? monocytes were observed at pretransplant time points in rejectors versus nonrejectors (HR 0.74, 95% CI 0.58–0.94, p < 0,014). A higher pretransplant number of CD16+ monocytes is significantly associated with a higher risk of acute rejection after kidney transplantation.     

Recurrent 2,8‐Dihydroxyadenine Nephropathy: A Rare but Preventable Cause of Renal Allograft Failure

Adenine phosphoribosyltransferase (APRT) deficiency is a rare autosomal recessive enzyme defect of purine metabolism that usually manifests as 2,8‐dihydroxyadenine (2,8‐DHA) nephrolithiasis and more rarely chronic kidney disease. The disease is most often misdiagnosed and can recur in the renal allograft. We analyzed nine patients with recurrent 2,8‐DHA crystalline nephropathy, in all of whom the diagnosis had been missed prior to renal transplantation. The diagnosis was established at a median of 5 (range 1.5–312) weeks following the transplant procedure. Patients had delayed graft function (n = 2), acute‐on‐chronic (n = 5) or acute (n = 1) allograft dysfunction, whereas one patient had normal graft function at the time of diagnosis. Analysis of allograft biopsies showed birefringent 2,8‐DHA crystals in renal tubular lumens, within tubular epithelial cells and interstitium. Fourier transformed infrared microscopy confirmed the diagnosis in all cases, which was further supported by 2,8‐DHA crystalluria, undetectable erythrocyte APRT enzyme activity, and genetic testing. With allopurinol therapy, the allograft function improved (n = 7), remained stable (n = 1) or worsened (n = 1). At last follow‐up, two patients had experienced allograft loss and five had persistent chronic allograft dysfunction. 2,8‐DHA nephropathy is a rare but underdiagnosed and preventable disorder that can recur in the renal allograft and may lead to allograft loss.     

Twenty‐four–hour normothermic perfusion of discarded human kidneys with urine recirculation

Transportable normothermic kidney perfusion for 24 hours or longer could enable viability assessment of marginal grafts, increased organ use, and improved transplant logistics. Eleven clinically declined kidneys were perfused normothermically, with 6 being from donors after brain death (median cold ischemia time 33 ± 36.9 hours) and 5 being from donors after circulatory death (36.2 ± 38.3 hours). Three kidneys were perfused using Ringer’s lactate to replace excreted urine volume, and 8 kidneys were perfused using urine recirculation to maintain perfusate volume without fluid replenishment. In all cases, normothermic perfusion either maintained or slightly improved the histopathologically assessed tubular condition, and there was effective urine production in kidneys from both donors after brain death and donors after circulatory death (2367 ± 1798 mL vs 744.4 ± 198.4 mL, respectively; P = .44). Biomarkers, neutrophil gelatinase–associated lipocalin, and kidney injury molecule‐1 were successfully detected and quantified in the perfusate. All kidneys with urine recirculation were readily perfused for 24 hours (n = 8) and exhibited physiological perfusate sodium levels (140.7 ± 1.2 mmol/L), while kidneys without urine recirculation (n = 3) achieved a reduced normothermic perfusion time of 7.7 ± 1.5 hours and significantly higher perfusate sodium levels (159.6 ± 4.63 mmol/:, P < .01). Normothermic machine perfusion of human kidneys for 24 hours appears to be feasible, and urine recirculation was found to facilitate the maintenance of perfusate volume and homeostasis.     

Anti‐LG3 Antibodies Aggravate Renal Ischemia–Reperfusion Injury and Long‐Term Renal Allograft Dysfunction

Pretransplant autoantibodies to LG3 and angiotensin II type 1 receptors (AT1R) are associated with acute rejection in kidney transplant recipients, whereas antivimentin autoantibodies participate in heart transplant rejection. Ischemia–reperfusion injury (IRI) can modify self‐antigenic targets. We hypothesized that ischemia–reperfusion creates permissive conditions for autoantibodies to interact with their antigenic targets and leads to enhanced renal damage and dysfunction. In 172 kidney transplant recipients, we found that pretransplant anti‐LG3 antibodies were associated with an increased risk of delayed graft function (DGF). Pretransplant anti‐LG3 antibodies are inversely associated with graft function at 1 year after transplantation in patients who experienced DGF, independent of rejection. Pretransplant anti‐AT1R and antivimentin were not associated with DGF or its functional outcome. In a model of renal IRI in mice, passive transfer of anti‐LG3 IgG led to enhanced dysfunction and microvascular injury compared with passive transfer with control IgG. Passive transfer of anti‐LG3 antibodies also favored intrarenal microvascular complement activation, microvascular rarefaction and fibrosis after IRI. Our results suggest that anti‐LG3 antibodies are novel aggravating factors for renal IRI. These results provide novel insights into the pathways that modulate the severity of renal injury at the time of transplantation and their impact on long‐term outcomes.     

Renal Allograft Fibrosis: Biology and Therapeutic Targets

Renal tubulointerstitial fibrosis is the final common pathway of progressive renal diseases. In allografts, it is assessed with tubular atrophy as interstitial fibrosis/tubular atrophy (IF/TA). IF/TA occurs in about 40% of kidney allografts at 3–6 months after transplantation, increasing to 65% at 2 years. The origin of renal fibrosis in the allograft is complex and includes donor‐related factors, in particular in case of expanded criteria donors, ischemia‐reperfusion injury, immune‐mediated damage, recurrence of underlying diseases, hypertensive damage, nephrotoxicity of immunosuppressants, recurrent graft infections, postrenal obstruction, etc. Based largely on studies in the non‐transplant setting, there is a large body of literature on the role of different cell types, be it intrinsic to the kidney or bone marrow derived, in mediating renal fibrosis, and the number of mediator systems contributing to fibrotic changes is growing steadily. Here we review the most important cellular processes and mediators involved in the progress of renal fibrosis, with a focus on the allograft situation, and discuss some of the challenges in translating experimental insights into clinical trials, in particular fibrosis biomarkers or imaging modalities.     

Protecting the Kidney in Liver Transplant Recipients: Practice‐Based Recommendations From the American Society of Transplantation Liver and Intestine Community of Practice

Both acute and chronic kidney disease are common after liver transplantation and result in significant morbidity and mortality. The introduction of the Model for End‐stage Liver Disease score has directly correlated with an increased prevalence of perioperative renal dysfunction and the number of simultaneous liver–kidney transplantations performed. Kidney dysfunction in this population is typically multifactorial and related to preexisting conditions, pretransplantation renal injury, perioperative events, and posttransplantation nephrotoxic immunosuppressive therapies. The management of kidney disease after liver transplantation is challenging, as by the time the serum creatinine level is significantly elevated, few interventions affect the course of progression. Also, immunological factors such as antibody‐mediated kidney rejection have become of greater interest given the rising liver–kidney transplant population. Therefore, this review, assembled by experts in the field and endorsed by the American Society of Transplantation Liver and Intestine Community of Practice, provides a critical assessment of measures of renal function and interventions aimed at preserving renal function early and late after liver and simultaneous liver–kidney transplantation. Key points and practice‐based recommendations for the prevention and management of kidney injury in this population are provided to offer guidance for clinicians and identify gaps in knowledge for future investigations.     

Tailoring the Endovascular Management of Transplant Renal Artery Stenosis

In this study we analyze the different types of endovascular interventions (EVIs) in de novo transplant renal artery stenosis (TRAS) and its anatomical subtypes to examine any variation in recovery of allograft function, blood pressure control, EVI patency and allograft survival with respect to EVI type (DES: drug‐eluting stent, BMS: bare‐metal stent, PTA: percutaneous transluminal angioplasty). Forty‐five patients underwent a total of 50 primary EVIs (DES: 18, BMS: 26, PTA: 6). Patients were stratified according to medical co‐morbidities, graft characteristics, biopsy results, clinical presentation and TRAS anatomic subtypes (anastomotic: 26, postanastomotic: 17, bend‐kink: 2). There was significant improvement in allograft function and mean arterial blood pressure (MAP) control across all interventions (pre‐EVI‐creatinine [CR]: 2.8 ± 1.4, post‐EVI‐Cr: 2.1 ± 0.7, p < 0.001; pre‐EVI‐MAP: 117 ± 16, post‐EVI‐MAP: 112 ± 17, p = 0.03) with no significant difference among EVI types. There was no significant difference in allograft survival with respect to EVI type. Patency was significantly higher in EVIs performed with DES and BMS compared to PTA (p = 0.001). In the postanastomotic TRAS subtype, patency rates were significantly higher in DES compared to BMS (p = 0.012) in vessels of comparable reference diameter (≤5 mm).