Yohann Foucher

Pretransplant Sensitization Against Angiotensin II Type 1 Receptor Is a Risk Factor for Acute Rejection and Graft Loss

The angiotensin II type 1 receptor (AT1R) is an emerging target of functional non‐HLA antibodies (Ab). We examined the potential of determining the degree of presensitization against AT1R as a risk factor for graft survival and acute rejection (AR). The study included 599 kidney recipients between 1998 and 2007. Serum samples were analyzed in a blinded fashion for anti‐AT1R antibodies (AT1R‐Abs) using a quantitative solid‐phase assay. A threshold of AT1R‐Ab levels was statistically determined at 10 U based on the time to graft failure. An extended Cox model determined risk factors for occurrence of graft failure and a first AR episode. AT1R‐Abs >10 U were detected in 283 patients (47.2%) before transplantation. Patients who had a level of AT1R‐Abs >10 U had a 2.6‐fold higher risk of graft failure from 3 years posttransplantation onwards (p = 0.0005) and a 1.9‐fold higher risk of experiencing an AR episode within the first 4 months of transplantation (p = 0.0393). Antibody‐mediated rejection (AMR) accounted for 1/3 of AR, whereby 71.4% of them were associated with >10 U of pretransplant AT1R‐Abs. Pretransplant anti‐AT1R‐Abs are an independent risk factor for long‐term graft loss in association with a higher risk of early AR episodes.

Each additional hour of cold ischemia time significantly increases the risk of graft failure and mortality following renal transplantation

Although cold ischemia time has been widely studied in renal transplantation area, there is no consensus on its precise relationship with the transplantation outcomes. To study this, we sampled data from 3839 adult recipients of a first heart-beating deceased donor kidney transplanted between 2000 and 2011 within the French observational multicentric prospective DIVAT cohort. A Cox model was used to assess the relationship between cold ischemia time and death-censored graft survival or patient survival by using piecewise log-linear function. There was a significant proportional increase in the risk of graft failure for each additional hour of cold ischemia time (hazard ratio, 1.013). As an example, a patient who received a kidney with a cold ischemia time of 30 h presented a risk of graft failure near 40% higher than a patient with a cold ischemia time of 6 h. Moreover, we found that the risk of death also proportionally increased for each additional hour of cold ischemia time (hazard ratio, 1.018). Thus, every additional hour of cold ischemia time must be taken into account in order to increase graft and patient survival. These findings are of practical clinical interest, as cold ischemia time is among one of the main modifiable pre-transplantation risk factors that can be minimized by improved management of the peri-transplantation period.

Kidney and Recipient Weight Incompatibility Reduces Long-Term Graft Survival

Long-term function of kidney allografts depends on multiple variables, one of which may be the compatibility in size between the graft and the recipient. Here, we assessed the long-term consequences of the ratio of the weight of the kidney to the weight of the recipient (KwRw ratio) in a multicenter cohort of 1189 patients who received a transplant between 1995 and 2006. The graft filtration rate increased by a mean of 5.74 ml/min between the third and sixth posttransplantation months among patients with a low KwRw ratio (<2.3 g/kg; P<0.0001). In this low KwRw ratio group, the graft filtration rate remained stable between 6 months and 7 years but then decreased at a mean rate of 3.17 ml/min per yr (P<0.0001). In addition, low KwRw ratios conferred greater risk for proteinuria, more antihypertensive drugs, and segmental or global glomerulosclerosis. Moreover, a KwRw ratio<2.3 g/kg associated with a 55% increased risk for transplant failure by 2 years of follow-up. In conclusion, incompatibility between graft and recipient weight is an independent predictor of long-term graft survival, suggesting that avoiding kidney and recipient weight incompatibility may improve late clinical outcome after kidney transplantation.

Tribbles-1 as a Novel Biomarker of Chronic Antibody-Mediated Rejection

Diagnosis of the specific cause of late allograft injury is necessary if more personalized and efficient immunosuppressive regimens are to be introduced. This study sought previously unrecognized biomarkers for specific histologic diagnoses of late graft scarring by comparison of gene sets from published microarray studies. Tribbles-1 (TRIB1), a human homolog of Drosophila tribbles, was identified to be a potentially informative biomarker. For testing this, mRNA expression in 76 graft biopsies, 71 blood samples, and 11 urine samples were profiled from independent cohorts of renal transplant patients with different histologic diagnoses recruited at two European centers. TRIB1 but not TRIB2 or TRIB3 was found to be a potential blood and tissue biomarker of chronic antibody-mediated rejection, an active immune-mediated form of chronic allograft failure associated with a poor prognosis. TRIB1 mRNA levels in peripheral blood mononuclear cells discriminated patients with chronic antibody-mediated rejection from those with other types of late allograft injury with high sensitivity and specificity. TRIB1 was also upregulated in a rodent model of chronic cardiac vasculopathy, suggesting that this biomarker may be useful in other solid-organ transplants and across species. It was determined that TRIB1 is expressed primarily by antigen-presenting cells and activated endothelial cells. Overall, these data support the potential use of TRIB1 as a biomarker of chronic antibody-mediated allograft failure.

Impact of graft mass on the clinical outcome of kidney transplants

The effect of nephronic mass reduction of kidney transplants has not been analyzed specifically in a large cohort. Transplant injuries in cadaver kidney graft may have led to an underestimation of the magnitude of this factor. The aim of this study was to analyze the consequences of kidney mass reduction on transplantation outcome. The weights of 1142 kidney grafts were collected prospectively immediately before grafting. Donors and recipients <15 yr of age, simultaneous kidney/pancreas grafts, and technical failures before day 7 were excluded from the analysis. The analysis was performed on Cockroft-calculated creatinine clearance and proteinuria in 964 patients for whom all of the necessary information was available. This study reports that the smallest kidneys transplanted into the largest recipients (donor kidney weight/recipient body weight [DKW/RBW] <2 g/kg, n = 88) increased their clearance by 2.38 ml/min every month for 6 mo (P < 0.0001) and by 0.27 ml/min thereafter (P < 0.0001). Conversely, creatinine clearance did not change for the largest kidneys transplanted into the smallest recipients (DKW/RBW ratios >/=4 g/kg). Next, using a Cox model analysis, it was shown that the risk of having a proteinuria >0.5 g/kg was significantly increased for the low DKW/RBW ratios <2 g/kg with 50% of patients having a proteinuria, compared with DKW/RBW ratios >/=4 g/kg (P < 0.001). In cadaver transplant recipients, graft mass has a rapid impact on graft filtration rate and proteinuria. Avoiding major kidney/recipient inadequacy should have a significant influence on long-term transplant function.

The Natural History of Clinical Operational Tolerance After Kidney Transplantation Through Twenty-Seven Cases

We report here on a European cohort of 27 kidney transplant recipients displaying operational tolerance, compared to two cohorts of matched kidney transplant recipients under immunosuppression and patients who stopped immunosuppressive drugs and presented with rejection. We report that a lower proportion of operationally tolerant patients received induction therapy (52% without induction therapy vs. 78.3%[p = 0.0455] and 96.7%[p = 0.0001], respectively), a difference likely due to the higher proportion (18.5%) of HLA matched recipients in the tolerant cohort. These patients were also significantly older at the time of transplantation (p = 0.0211) and immunosuppression withdrawal (p = 0.0002) than recipients who rejected their graft after weaning. Finally, these patients were at lower risk of infectious disease. Among the 27 patients defined as operationally tolerant at the time of inclusion, 19 still display stable graft function (mean 9 ± 4 years after transplantation) whereas 30% presented slow deterioration of graft function. Six of these patients tested positive for pre‐graft anti‐HLA antibodies. Biopsy histology studies revealed an active immunologically driven mechanism for half of them, associated with DSA in the absence of C4d. This study suggests that operational tolerance can persist as a robust phenomenon, although eventual graft loss does occur in some patients, particularly in the setting of donor‐specific alloantibody.

Early Structural Valve Deterioration of Mitroflow Aortic Bioprosthesis Mode, Incidence, and Impact on Outcome in a Large Cohort of Patients

Background— Structural valve deterioration (SVD) is a major flaw of bioprostheses. Early SVD has been suspected in the last models of Mitroflow bioprosthesis. We sought to assess the incidence, mode, and impact of SVD on outcome in a large series of Mitroflow aortic valve replacement. Methods and Results— Six hundred seventeen consecutive patients (aged 76.1±6.3 years) underwent aortic valve replacement with a Mitroflow prosthesis (models 12A/LX) between 2002 and 2007. By echocardiography, 39 patients developed early SVD (1.66% per patient-year), with stenosis as the main mode (n=36). Mean delay to SVD was only 3.8±1.4 years, and 5-year SVD-free survival was 91.6% (95% confidence interval [CI], 88.7–94.7) for the whole cohort and 79.8% (95% CI, 71.2–89.4) and 94.0% (95% CI, 90.3–97.8) for 19- and 21-mm sizes, respectively. Among the 39 patients with SVD, 13 patients (33%) had an accelerated SVD once the mean gradient exceeded 30 mm Hg. Valve-related death was 46.2% in this SVD subgroup. Five-year overall survival was 69.6% (95% CI, 65.7–73.9). In multivariable analysis, SVD was the strongest correlate of overall mortality (hazard ratio=7.7; 95% CI, 4.4–13.6). Conclusions— Early SVD is frequent in Mitroflow bioprosthesis (models 12A/LX), especially for small sizes (19 and 21 mm), and reduces overall survival. An unpredictable accelerated pattern of SVD constitutes a life-threatening condition. In view of the large number of Mitroflow valves implanted worldwide, one can expect an epidemic of SVD and valve-related deaths, which represents a major public health issue, especially in the elderly. Hence, a close follow-up with yearly echocardiography after Mitroflow implantation is advisable. An urgent reoperation should be discussed in patients with severe SVD even though they are still asymptomatic.Background— Structural valve deterioration (SVD) is a major flaw of bioprostheses. Early SVD has been suspected in the last models of Mitroflow bioprosthesis. We sought to assess the incidence, mode, and impact of SVD on outcome in a large series of Mitroflow aortic valve replacement. Methods and Results— Six hundred seventeen consecutive patients (aged 76.1±6.3 years) underwent aortic valve replacement with a Mitroflow prosthesis (models 12A/LX) between 2002 and 2007. By echocardiography, 39 patients developed early SVD (1.66% per patient-year), with stenosis as the main mode (n=36). Mean delay to SVD was only 3.8±1.4 years, and 5-year SVD-free survival was 91.6% (95% confidence interval [CI], 88.7–94.7) for the whole cohort and 79.8% (95% CI, 71.2–89.4) and 94.0% (95% CI, 90.3–97.8) for 19- and 21-mm sizes, respectively. Among the 39 patients with SVD, 13 patients (33%) had an accelerated SVD once the mean gradient exceeded 30 mm Hg. Valve-related death was 46.2% in this SVD subgroup. Five-year overall survival was 69.6% (95% CI, 65.7–73.9). In multivariable analysis, SVD was the strongest correlate of overall mortality (hazard ratio=7.7; 95% CI, 4.4–13.6). Conclusions— Early SVD is frequent in Mitroflow bioprosthesis (models 12A/LX), especially for small sizes (19 and 21 mm), and reduces overall survival. An unpredictable accelerated pattern of SVD constitutes a life-threatening condition. In view of the large number of Mitroflow valves implanted worldwide, one can expect an epidemic of SVD and valve-related deaths, which represents a major public health issue, especially in the elderly. Hence, a close follow-up with yearly echocardiography after Mitroflow implantation is advisable. An urgent reoperation should be discussed in patients with severe SVD even though they are still asymptomatic. # CLINICAL PERSPECTIVE {#article-title-37}

Expression of miR-142-5p in peripheral blood mononuclear cells from renal transplant patients with chronic antibody-mediated rejection.

In renal transplantation, the unresponsiveness of patients undergoing chronic antibody mediated rejection (CAMR) to classical treatment stress on the need for accurate biomarkers to improve its diagnosis. We aim to determine whether microRNA expression patterns may be associated with a diagnosis of CAMR. We performed expression profiling of miRNAs in peripheral blood mononuclear cells (PBMC) of kidney transplant recipients with CAMR or stable graft function. Among 257 expressed miRNAs, 10 miRNAs associated with CAMR were selected. Among them, miR-142-5p was increased in PBMC and biopsies of patients with CAMR as well as in a rodent model of CAMR. The lack of modulation of miR-142-5p in PBMC of patients with renal failure, suggests that its over-expression in CAMR was associated with immunological disorders rather than renal dysfunction. A ROC curve analysis performed on independent samples showed that miR-142-5p is a potential biomarker of CAMR allowing a very good discrimination of the patients with CAMR (AUC = 0.74; p = 0.0056). Moreover, its expression was decreased in PHA-activated blood cells and was not modulated in PBMC from patients with acute rejection, excluding a non-specific T cell activation expression. The absence of modulation of this miRNA in immunosuppressed patients suggests that its expression was not influenced by treatment. Finally, the analysis of miR-142-5p predicted targets under-expressed in CAMR PBMC in a published microarray dataset revealed an enrichment of immune-related genes. Altogether, these data suggest that miR-142-5p could be used as a biomarker in CAMR and these finding may improve our understanding of chronic rejection mechanisms.

Regulatory, Effector, and Cytotoxic T Cell Profiles in Long-Term Kidney Transplant Patients

Animal studies have suggested a potential role for regulatory T cells (Tregs) in allograft tolerance, but these FOXP3+ cells seem to be an inherent component of acute rejection (AR) in human recipients of renal transplants. The balance between regulatory cells and effector/cytotoxic cells may determine graft outcome; this balance has not been described for chronic allograft injury. We investigated the expression of key regulatory, effector, and cytotoxic transcripts (i.e., FOXP3, T-bet, and granzyme B, respectively) in the grafts and peripheral blood of long-term-surviving renal transplant patients. We found that, whereas neither intragraft nor peripheral blood FOXP3 or T-bet mRNA could distinguish between rejection and nonrejection status, granzyme B (GrzB) mRNA could: It was significantly increased in the graft and significantly decreased in the peripheral blood of patients with chronic antibody-mediated rejection (CAMR). Quantifying peripheral blood GrzB mRNA demonstrated potential to aid in the noninvasive diagnosis of CAMR. In summary, these data affirm GrzB as a marker not only for AR but also for CAMR. In addition, we identified several previously unreported clinical or demographic factors influencing regulatory/effector/cytotoxic profiles in the peripheral blood, highlighting the necessity to consider confounding variables when considering the use of potential biomarkers, such as FOXP3, for diagnosis or prognosis in kidney transplantation.

BAFF and BAFF-R levels are associated with risk of long-term kidney graft dysfunction and development of donor-specific antibodies.

There are lines of evidence that B cells may play a role in transplantation. B cell activating factor, BAFF, is a homotrimer that has been shown to play a role in B cell survival, maturation and activation. To date, little is known of the role of BAFF and its receptors in transplantation. We analyzed the level of BAFF mRNA and its soluble protein, as well as transcripts coding for its receptors, BAFF‐R, TACI and BCMA, in the blood of 143 patients with stable kidney transplant function 5 years or more posttransplantation. Three endpoints were analyzed: the time to renal dysfunction, the time to appearance of anti‐HLA antibodies and the time to development of donor‐specific antibodies. We established threshold values for BAFF and BAFF‐R and showed that (1) stable patients with high BAFF‐R levels had a higher risk of developing graft dysfunction, (2) patients with lower levels of BAFF transcripts or a higher level of soluble BAFF had a significantly higher risk of developing donor‐specific antibodies. These data suggest that BAFF constitutes a risk factor for renal graft dysfunction and development of donor‐specific antibodies. They also suggest that agents targeting BAFF‐R interactions may offer new therapeutic opportunities in transplantation.