Marko J.K. Mallat

Early versus late acute rejection episodes in renal transplantation.

Background. Acute rejection is a major complication after renal transplantation and the most important risk factor for chronic rejection. We investigated whether the timing of the last treated acute rejection episode (ARE) influences long-term outcome and compared the risk profiles of early versus late ARE. Methods. A cohort of 654 patients who underwent cadaveric renal transplants (1983–1997) that functioned for more than 6 months was studied. In 384 of 654 transplant recipients, one or more treated AREs were documented; the last ARE occurred in 297 of 384 transplant recipients within 3 months and in 87 of 384 after 3 months. Applying multivariate logistic regression analysis, we compared the predictor variables of the two groups with transplants without AREs. Results. Ten-year graft survival rates censored for causes of graft loss other than chronic rejection were 94%, 86%, and 45% for patients without ARE, with early ARE, and with late ARE, respectively. Delayed graft function, odds ratio (OR) 2.37 (1.55–3.62), and major histocompatibility complex (MHC) class II incompatibility, OR 2.28 (1.62–3.20) per human leukocyte antigen (HLA)-DR mismatch, were independent risk factors for early ARE. In contrast, recipient age, OR 0.75 (0.61–0.93) per 10-year increase, donor age, OR 1.28 (1.07–1.53) per 10-year increase, female donor gender, OR 1.74 (1.03–2.94), and MHC class I incompatibility, OR 1.35 (1.07–1.72) per mismatch of cross reactive groups, were associated with late ARE. Conclusions. Late ARE has a detrimental impact on long-term graft survival and is associated with MHC class I incompatibility, whereas early ARE is correlated with HLA-DR mismatches and has a better prognosis. These data are consistent with the role of direct and indirect allorecognition in the pathophysiology of early and late ARE, respectively.

Association Between Mannose‐Binding Lectin Levels and Graft Survival in Kidney Transplantation

The mannose‐binding lectin (MBL) pathway of complement is activated by pattern recognition. Genetic MBL variants are frequent and associated with low MBL serum levels. Higher MBL levels may be associated with more complement‐mediated damage resulting in inferior graft survival.

Effect of obesity on the outcome of kidney transplantation: a 20-year follow-up.

Background. Cardiovascular disease is both a major threat to the life expectancy of kidney transplant recipients and an important determinant of late allograft loss. Obesity is an important risk factor for cardiovascular disease. Methods. We investigated the relation between both pretransplant and 1-year posttransplant body mass index (BMI) with patient and renal graft survival in a cohort of 1810 adult patients. Sixty-one percent of all patients were men; median age (interquartile range [IQR]) was 46 years (35–56 years); median (IQR) pretransplant BMI was 23.0 kg/m2 (20.8–25.6 kg/m2); 1 year after transplantation, the median (IQR) BMI had increased 1.6 kg/m2 (0.3–3.2 kg/m2) and median (IQR) follow-up time was 8.3 years (5.3–12.0 years). We categorized BMI as follows: less than or equal to 20, more than 20 to less than or equal to 25 (normal), more than 25 to less than or equal to 30, and more than 30 (obesity) kg/m2. Results. Using a Cox proportional hazards model, after adjustment for cardiovascular risk factors, the relative risks (95% confidence intervals) of death and death-censored graft failure during all follow-up for pretransplant obesity compared with normal BMI were 1.22 (0.86–1.74) and 1.34 (1.02–1.77), respectively; for obesity 1 year after transplantation compared with normal BMI, it was 1.39 (1.05–1.86) and 1.39 (1.10–1.74), respectively; and for change in BMI (per 5 kg/m2 increment) during the first year after transplantation, it was 1.23 (1.01–1.50) and 1.18 (1.01–1.38), respectively. Conclusions. One year posttransplant BMI and BMI increment are more strongly related to death and graft failure than pretransplant BMI among kidney transplant recipients. Patients with BMI more than 30 kg/m2 compared with a normal BMI have approximately 20% to 40% higher risk for death and graft failure.

No Difference in Degree of Interstitial Sirius Red–Stained Area in Serial Biopsies from Area under Concentration-over-Time Curves–Guided Cyclosporine versus Tacrolimus-Treated Renal Transplant Recipients at One Year

Interstitial fibrosis is the main characteristic of chronic allograft nephropathy and long-term graft failure. Cyclosporin (CsA) is thought to be more fibrogenic than tacrolimus. In a prospective, randomized, multicenter trial using a calcineurin-sparing regimen, renal interstitial volume was compared in CsA- and tacrolimus-treated renal transplant recipients by image analysis of Sirius red (SR)-stained cortical areas in protocol biopsies obtained at 6 mo (n = 94) and 12 mo (n = 97) after transplantation. Immunosuppression consisted of CsA or tacrolimus, CD25 mAb, mycophenolate mofetil, and prednisolone. CsA therapy increased the 6-mo risk for subclinical rejection. The prevalence of subclinical rejection was 38.8% in the CsA-treated and 15.2% in the tacrolimus-treated patient group (P = 0.012). Strikingly, no difference in the degree of interstitial SR-stained area was detectable between the two treatment groups. In particular, previous subclinical rejection episodes did not influence the degree of interstitial volume. Also, no difference in GFR occurred at 1 yr, when the mean GFR mounted 63 ml/min. No significant differences in the degree of interstitial SR-stained area could be observed at 6 and 12 mo between CsA- and tacrolimus-treated renal transplant recipients. Although CsA-treated patients developed significantly more subclinical rejections at 6 mo, this did not influence the degree of SR staining or the change in renal function at 1 yr.

Low Pretransplantation Mannose-Binding Lectin Levels Predict Superior Patient and Graft Survival after Simultaneous Pancreas-Kidney Transplantation

Simultaneous pancreas-kidney transplantation (SPKT) is the treatment of choice for patients with type 1 diabetes and renal failure. However, this procedure is characterized by a high rate of postoperative infections, acute rejection episodes, and cardiovascular mortality. The lectin pathway of complement activation contributes to cardiovascular disease in diabetes and may play an important role in inflammatory damage after organ transplantation. This study therefore sought to determine how mannose-binding lectin (MBL), a major recognition molecule of the lectin pathway of complement activation, influences outcome after SPKT. MBL serum levels were determined in 99 and MBL genotypes in 97 consecutive patients who received an SPKT from 1990 through 2000 and related to patient and graft survival. At 12 yr, cumulative death-censored kidney graft survival was 87.5% in patients with an MBL level <400 ng/ml and 74.8% in the group with MBL levels >400 ng/ml (P = 0.021). Pancreas graft survival was significantly better in patients with low MBL levels (P = 0.016). MBL levels >400 ng/ml were associated with a hazard ratio of 6.28 for patient death (95% confidence interval 1.8 to 20.3; P = 0.003). Accordingly, survival was significantly better in recipients with MBL gene polymorphisms associated with low MBL levels. These findings identify MBL as a potential risk factor for graft and patient survival in SPKT. It is hypothesized that MBL contributes to the pathogenesis of inflammation-induced vascular damage both in the transplanted organs and in the recipients native blood vessels.

Untreated Rejection in 6-Month Protocol Biopsies Is Not Associated with Fibrosis in Serial Biopsies or with Loss of Graft Function

Donor age, calcineurin inhibitor nephrotoxicity, and acute rejection are the most significant predictors of chronic allograft nephropathy. Protocol biopsies, both in deceased- and living-donor renal grafts, have shown that cortical tubulointerstitial fibrosis correlates with graft survival and function. The impact of not treating subclinical acute rejection (SAR) is less clear. In this study, 126 de novo renal transplant recipients were randomly assigned to receive area-under-the-curve-controlled exposure of either a cyclosporine or a tacrolimus-based immunosuppressive regimen that included steroids, mycophenolate mofetil, and basiliximab induction. Protocol biopsies were taken before and 6 and 12 mo after transplantation. The prevalence of SAR was determined retrospectively. Fibrosis was evaluated by quantitative digital analysis of Sirius red staining in serial biopsies. Donor age correlated significantly with tubulointerstitial fibrosis in pretransplantation biopsies and inferior graft function at month 6 (rtau = -0.26; P = 0.033). Acute rejection incidence was 11.5%, and no clinical late rejection occurred. The prevalence of SAR at 6 mo was 30.8% but was not associated with differences in serial quantitative Sirius red staining at 6 or 12 mo, proteinuria, or progressive loss of GFR up to 2 yr. No differences were found in donor variables, histocompatibility, rejection history, or exposure of immunosuppressants. Controlled individualized calcineurin inhibitor exposure and subsequent tapering resulted in a low early acute rejection rate and prevented late acute rejection. Because, by design, we did not treat SAR, these results provide evidence that asymptomatic infiltrates in 6-mo surveillance biopsies may not be deleterious in the intermediate term. There is need for reliable biomarkers to prove that not all cell infiltrates are equivalent or that infiltrates may change with time.

Calcium levels as a risk factor for delayed graft function.

Background. Delayed graft function (DGF) occurs in up to 50% of renal transplants. Hypercalcemia and hyperparathyroidism are associated with impaired renal function. Little is known on the effects of serum calcium levels on DGF. This issue was addressed in the current study. Methods. Patients receiving a cadaveric renal transplant between 1986 and 1996 were studied. Data on calcium metabolism and histologic characteristics of nephrocalcinosis, acute tubular necrosis (ATN), and acute rejection in biopsies taken within the first week were related to the occurrence of DGF. Results. The incidence of DGF in a cohort of 585 cadaveric transplants was 31%. DGF correlated independently with serum calcium levels (odds ratio [OR] 1.14 [95% confidence interval (CI) 1.04–1.26] per 0.1 mmol/L). The use of calcium channel blockers before transplantation protected against DGF (OR 0.5 [95% CI 0.29– 0.87]). In this selected group, we found an association with histologic signs of ATN and DGF. However, most of the biopsies also had features of acute rejection or nephrocalcinosis. Nephrocalcinosis was found in 12 of 71 biopsies and was not associated with serum calcium levels or the occurrence of DGF. Conclusions. In this study, serum calcium levels were independently associated with DGF. This could not be explained by the presence of microscopic nephrocalcinosis. Therefore, DGF is attributed to high intracellular calcium levels. Because calcium supplementation and vitamin D analogues are commonly used in dialysis practice, hypercalcemia influences long-term graft outcome by its effect on DGF. The pretransplant use of calcium channel blockers has a protective effect on the occurrence of DGF.

Simpler and equitable allocation of kidneys from postmortem donors primarily based on full HLA-DR compatibility.

Background. The introduction of human leukocyte antigen (HLA)-matching in nonliving kidney transplantation has resulted into a better graft outcome, but also in an increase of waiting time, especially for patients with rare HLA phenotypes. We addressed the question of the differential influence of HLA-DR-matching versus HLA-A,B in clinical kidney transplantation. Methods. We used Kaplan-Meier product limit method to estimate survival rates, and Cox proportional hazard regression for the estimation of relative risks (Hazard-ratios) for different variables. Results. A single center study (n=456 transplants, performed between 1985 and 1999) showed that full HLA-DR compatibility leads to a lower incidence of biopsy confirmed acute rejections in the first 180 posttransplantation days. These results were substantiated using the Eurotransplant database (n=39,205 transplants performed between 1985 and 2005) where graft survival in the full HLA-DR compatible group was significantly better than in the incompatible. An additional positive effect of HLA-A,B matching was only found in the full HLA-DR compatible group. In both studies, the introduction of a single HLA-DR incompatibility eliminates the HLA-A,B matching effect. Conclusions. We propose to allocate postmortem kidneys only to patients with full HLA-DR compatibility, and use HLA-A,B compatibility as an additional selection criterion. All patients, irrespective of their ethnic origin, will profit since the polymorphism of HLA-DR is by far lower than that of HLA-A,B. Excessive kidney travel and cold ischemia time will be significantly reduced.

Circulating MicroRNAs Associate With Diabetic Nephropathy and Systemic Microvascular Damage and Normalize After Simultaneous Pancreas–Kidney Transplantation

Because microvascular disease is one of the most important drivers of diabetic complications, early monitoring of microvascular integrity may be of clinical value. By assessing profiles of circulating microRNAs (miRNAs), known regulators of microvascular pathophysiology, in healthy controls and diabetic nephropathy (DN) patients before and after simultaneous pancreas–kidney transplantation (SPK), we aimed to identify differentially expressed miRNAs that associate with microvascular impairment. Following a pilot study, we selected 13 candidate miRNAs and determined their circulating levels in DN (n = 21), SPK‐patients (n = 37), healthy controls (n = 19), type 1 diabetes mellitus patients (n = 15) and DN patients with a kidney transplant (n = 15). For validation of selected miRNAs, 14 DN patients were studied longitudinally up to 12 months after SPK. We demonstrated a direct association of miR‐25, ‐27a, ‐126, ‐130b, ‐132, ‐152, ‐181a, ‐223, ‐320, ‐326, ‐340, ‐574‐3p and ‐660 with DN. Of those, miR‐25, ‐27a, ‐130b, ‐132, ‐152, ‐320, ‐326, ‐340, ‐574‐3p and ‐660 normalized after SPK. Importantly, circulating levels of some of these miRNAs tightly associate with microvascular impairment as they relate to aberrant capillary tortuosity, angiopoietin‐2/angiopoietin‐1 ratios, circulating levels of soluble‐thrombomodulin and insulin‐like growth factor. Taken together, circulating miRNA profiles associate with DN and systemic microvascular damage, and might serve to identify individuals at risk of experiencing microvascular complications, as well as give insight into underlying pathologies.

Infectious Complications After Simultaneous Pancreas-Kidney Transplantation : A Role for the Lectin Pathway of Complement Activation

Background. Mannose-binding lectin (MBL) is a recognition molecule of the lectin pathway of complement activation, and its serum levels are largely determined by frequently occurring polymorphisms of the MBL gene. We questioned whether MBL deficiency influences infectious complications in patients after simultaneous pancreas-kidney transplantation (SPKT). Methods. Infectious complications in the first year after transplantation were scored retrospectively in 152 consecutive SPKT patients who received their transplant at our center between 1990 and 2005. Pretransplant serum MBL levels were determined with enzyme-linked immunosorbent assay. Results. Every 500 ng/mL increase in baseline MBL was associated with an odds ratio of 0.83 (P=0.045) for urinary tract infections and an odds ratio of 0.68 (P=0.029) for urosepsis. Urosepsis was significantly more common in patients with low baseline MBL (<400 ng/mL) compared with those with greater MBL levels (22.7% vs. 8.3%, P=0.015). No significant influence of MBL on the occurrence of wound infections and cytomegalovirus disease could be demonstrated. Conclusions. With the current study, we show that high levels of serum MBL are associated with protection against urinary tract infections and, more specifically, against urosepsis after SPKT. These data indicate an important role for the lectin pathway of complement activation in antimicrobial defense in these transplant recipients.