Héloïse Cardinal

Antiperlecan antibodies are novel accelerators of immune-mediated vascular injury.

Acute vascular rejection (AVR) is characterized by immune‐mediated vascular injury and heightened endothelial cell (EC) apoptosis. We reported previously that apoptotic ECs release a bioactive C‐terminal fragment of perlecan referred to as LG3. Here, we tested the possibility that LG3 behaves as a neoantigen, fuelling the production of anti‐LG3 antibodies of potential importance in regulating allograft vascular injury. We performed a case–control study in which we compared anti‐LG3 IgG titers in kidney transplant recipients with AVR (n = 15) versus those with acute tubulo‐interstitial rejection (ATIR) (n = 15) or stable graft function (n = 30). Patients who experienced AVR had elevated anti‐LG3 titers pre and posttransplantation compared to subjects with ATIR or stable graft function (p < 0.05 for both mediators). Elevated pretransplant anti‐LG3 titers (OR: 4.62, 95% CI: 1.08–19.72) and pretransplant donor‐specific antibodies (DSA) (OR 4.79, 95% CI: 1.03–22.19) were both independently associated with AVR. To address the functional role of anti‐LG3 antibodies in AVR, we turned to passive transfer of anti‐LG3 antibodies in an animal model of vascular rejection based on orthotopic aortic transplantation between fully MHC‐mismatched mice. Neointima formation, C4d deposition and allograft inflammation were significantly increased in recipients of an ischemic aortic allograft passively transferred with anti‐LG3 antibodies. Collectively, these data identify anti‐LG3 antibodies as novel accelerators of immune‐mediated vascular injury and obliterative remodeling.

The Perlecan Fragment LG3 Is a Novel Regulator of Obliterative Remodeling Associated With Allograft Vascular Rejection

Rationale: Endothelial apoptosis is increased in association with acute and chronic vascular rejection (VR) of solid allografts. Apoptotic endothelial cells (EC) release LG3, a C-terminal fragment of perlecan of potential importance in vascular remodeling and neointima formation. Objective: Our 2 goals were to determine whether circulating levels of LG3 are increased in association with acute VR of renal allografts and to evaluate the impact of LG3 on vascular remodeling. Methods and Results: We conducted a case-control study to compare serum LG3 levels in human renal transplant patients with acute VR, tubulo-interstitial rejection (ATIR) and normal graft function. Aorta transplantation between fully MHC-mismatched mice in association with intravenous LG3 injection was used to characterize the impact of LG3 on vascular remodeling. Scratch assays evaluated the promigratory activity of LG3 on vascular smooth muscle cells (VSMC) in vitro. Serum LG3 levels were significantly elevated in human renal transplant patients with acute VR (n=16) compared to ATIR (n=16) and normal graft function (n=32, P=0.004). In patients with acute VR, graft loss was associated with elevated LG3 levels. Increasing LG3 serum levels in aortic allograft recipients significantly increased neointima formation. LG3 injection fostered accumulation of &agr;-smooth muscle actin–positive cells and decreased the number of CD31 positive EC. LG3 increased the migration of VSMC through extracellular signal-regulated kinases 1/2-dependent pathways. Conclusion: These results indicate that LG3 is a novel regulator of obliterative vascular remodeling during rejection.

The 20S proteasome core, active within apoptotic exosome-like vesicles, induces autoantibody production and accelerates rejection

Exosome-like vesicles containing an active 20S proteasome core contribute to autoimmunity and vascular allograft inflammation. Friendly fire from organ failure Despite advances in organ transplantation, rejection still poses a substantial risk. Autoantibodies contribute to rejection, but how these autoantibodies are generated remains unknown. Dieudé et al. found that injection of apoptotic exosome-like vesicles apoExo stimulated autoantibody production in mice, which led to increased graft rejection after transplant. The apoExo contained active 20S proteasome core complexes, and inhibition of proteasome activity decreased the immunogenicity of apoExo and graft rejection in transplanted mice. Circulating apoExo and increased anti-autoantibody titers were also observed in mouse models of ischemia-reperfusion injury, suggesting that the same organ failure that necessitates the transplant might increase the risk of rejection. Therefore, proteasome inhibitors could provide a new therapeutic avenue for graft rejection. Autoantibodies to components of apoptotic cells, such as anti-perlecan antibodies, contribute to rejection in organ transplant recipients. However, mechanisms of immunization to apoptotic components remain largely uncharacterized. We used large-scale proteomics, with validation by electron microscopy and biochemical methods, to compare the protein profiles of apoptotic bodies and apoptotic exosome-like vesicles, smaller extracellular vesicles released by endothelial cells downstream of caspase-3 activation. We identified apoptotic exosome-like vesicles as a central trigger for production of anti-perlecan antibodies and acceleration of rejection. Unlike apoptotic bodies, apoptotic exosome-like vesicles triggered the production of anti-perlecan antibodies in naïve mice and enhanced anti-perlecan antibody production and allograft inflammation in mice transplanted with an MHC (major histocompatibility complex)–incompatible aortic graft. The 20S proteasome core was active within apoptotic exosome-like vesicles and controlled their immunogenic activity. Finally, we showed that proteasome activity in circulating exosome-like vesicles increased after vascular injury in mice. These findings open new avenues for predicting and controlling maladaptive humoral responses to apoptotic cell components that enhance the risk of rejection after transplantation.

The risk of thromboembolic events in kidney transplant patients

Little is known about the risk of venous thrombosis following kidney transplant. To determine this we estimated the risk of thromboembolic events (TEs) in a cohort of consecutive patients who underwent kidney transplantation at a single tertiary care center over an 11-year period and calculated standardized incidence ratios (SIRs) for a first TE in kidney transplant recipients compared with the general population. We then performed a nested case-control study and compared patients with and without TEs to identify risk factors for thrombosis. Among 913 kidney transplant recipients (KTRs), 68 patients developed these events. The SIR for TEs in KTRs compared with the general population was 7.9 over the duration of follow-up. The risk was particularly higher in the first post-transplant year (SIR 26.1) but remained elevated afterward (SIR 5.2). Hospitalization, use of sirolimus, low hemoglobin level, and use of renin-angiotensin system inhibitors were independently associated with these events. When cases of TEs that occurred during hospitalization were excluded, the risk of these events remained elevated. The risk of TEs in KTRs was eightfold higher than in the general population but not fully explained by the increased risk associated with hospitalization. Our results underscore the important risk of thrombosis in patients who received a kidney transplant, making vigilance mandatory especially during hospitalization.

Effect of cinacalcet availability and formulary listing on parathyroidectomy rate trends

BackgroundRecent trends in parathyroidectomy rates are not known. Our objective was to investigate the trend in parathyroidectomy rates between 2001 and 2010, and to evaluate if the availability and reimbursement of cinacalcet modified that trend.MethodsUsing a provincial administrative database, we included all adult patients receiving chronic dialysis treatments between 2001 and 2010 (incident and prevalent) in a time series analysis. The effect of cinacalcet availability on parathyroidectomy bimonthly rates was modeled using an ARIMA intervention model using different cut-off dates: September 2004 (Health Canada cinacalcet approval), January 2005, June 2005, January 2006, June 2006 (date of cinacalcet provincial reimbursement), and January 2007.ResultsA total of 12 795 chronic dialysis patients (mean age 64 years, 39% female, 82% hemodialysis) were followed for a mean follow-up of 3.3 years. During follow-up, 267 parathyroidectomies were identified, translating to an average rate of 7.0 per 1000 person-years. The average parathyroidectomy rate before cinacalcet availability was 11.4 /1000 person-years, and 3.6 /1000 person-years after cinacalcet public formulary listing. Only January 2006 as an intervention date in the ARIMA model was associated with a change in parathyroidectomy rates (estimate: -5.58, p = 0.03). Other intervention dates were not associated with lower parathyroidectomy rates.ConclusionsA reduction in rates of parathyroidectomy was found after January 2006, corresponding to cinacalcet availability. However, decreased rates may be due to other factors occurring simultaneously with cinacalcet introduction and further studies are needed to confirm these findings.

Evaluation of a Preemptive Strategy for BK Polyomavirus-Associated Nephropathy Based on Prospective Monitoring of BK Viremia: A Kidney Transplantation Center Experience

INTRODUCTION BK polyomavirus-associated nephropathy (BKPVAN) is a major cause of renal failure early after kidney transplantation. The present study reports the preliminary results of prospective monitoring including a preemptive strategy for BKPVAN during the first year after kidney transplantation. METHODS We monitored BK virus DNA in blood at months 1, 2, 3, 6, 9, and 12 among 92 subjects who received induction therapy (basiliximab or antithymocyte globulin), and maintenance immunosuppression with prednisone, mycophenolate mofetil, and tacrolimus. Patients with two or more consecutive measurements of viral load >10(4) copies/mL were treated with a stepwise approach including dose reduction or discontinuation of mycophenolate mofetil eventually followed by reduction of tacrolimus and introduction of leflunomide. RESULTS Within 1 year, seven (7%) patients displayed sustained BK viremia at a median of 92 days after transplantation. Among 68 patients who underwent a renal allograft biopsy, seven were diagnosed as BKPVAN at a median of 15 weeks after transplantation. The diagnosis was achieved by a surveillance biopsy in four patients with stable renal function. BKPVAN was preceded by asymptomatic viremia except for two cases in whom BK viremia occurred at 6 or 11 months, after the histological diagnosis. At 12 months, six patients had cleared their viremia. Serum creatinine levels had stabilized in six recipients with BKPVAN estimated renal function was 43.7 ± 16.3 mL/min in patients with viremia and/or BKPVAN versus 61.3 ± 20.1 mL/min among patients who never became viremic (P = .03). None of the patients with viremia and/or BKPVAN lost the allograft. CONCLUSION BKPVAN may occur early after kidney transplantation, at a low or undetectable viremia or at some weeks after the first positive viremia. Intensive monitoring during the first 4 months after transplantation together with early protocol biopsies or interventions prompted by BK viremia may optimize BKPVAN diagnosis at a subclinical stage, thus avoiding renal dysfunction.

Usefulness of Soluble Fas Levels for Improving Diagnostic Accuracy and Prognosis for Acute Coronary Syndromes

Although both inflammation and apoptosis occur in acute coronary syndromes (ACSs), previous studies have not tested the diagnostic and prognostic utility of an approach that measures circulating markers of these pathways. The aim of the present study was to assess whether measuring soluble Fas (sFas) and high-sensitivity C-reactive protein (hs-CRP), as markers of apoptosis and inflammation, improve ACS diagnostic and prognostic accuracy. In a prospective cohort of consecutive subjects admitted to the hospital for suspicion of ACS, we measured sFas, hs-CRP, and troponin T in those who had a final noncardiac chest pain diagnosis (n = 100), those who had an ACS diagnosis and experienced (n = 218) or did not experience (n = 170) recurrent cardiac events during 1 year of follow-up. sFas was strongly and independently associated with a discharge diagnosis of an ACS versus noncardiac chest pain during the index hospitalization (odds ratio 16.16 for the second vs first tertile, 95% confidence interval [CI] 7.07 to 36.91; and odds ratio 25.40 for the third vs first tertile, 95% CI 9.38 to 68.75). However, hs-CRP was not. sFas significantly improved the diagnostic accuracy for ACSs (C statistic increased from 0.85 to 0.93, difference +0.08, 95% CI for the difference 0.05 to 0.11). The sFas levels were high and did not vary with time in the subjects having early versus late measurements (beta 0.00 ln pg/ml/hour, 95% CI -0.01 to 0.01). In contrast, troponin increased with time since the beginning of the symptoms (beta 0.07 ln microg/L/hour, 95% CI 0.04 to 0.10). Baseline sFas and hs-CRP did not predict recurrent cardiac events. In conclusion, our results suggest that in suspected ACS cases, sFas, but not hs-CRP, helps to improve the diagnostic accuracy and timeliness over and above standard diagnostic criteria.

Complement factor H deficiency in acute allograft glomerulopathy and post-transplant hemolytic uremic syndrome.

Acute allograft glomerulopathy (AAG) is a distinct form of allograft rejection characterized by cytotoxic T‐cell‐mediated injury to the renal glomerular and arteriolar endothelium. Acute allograft glomerulopathy is characterized by mononuclear cell infiltration of glomerular capillary tufts in association with endothelial cell hypertrophy and injury. Intra‐glomerular thrombi have been described in AAG, suggesting that overlapping features of AAG and post‐transplant thrombotic microangiopathy (TMA) may coexist. We present a case suggesting that complement factor H deficiency, a known hereditary risk factor for TMA, may also favor development of AAG. We discuss the potential implications of factor H deficiency in the pathophysiology of renal allograft microvascular injury, leukocyte infiltration and formation of intraglomerular platelet thrombi. We propose that unopposed complement activation is a risk factor for both immune and nonimmune forms of microvascular injuries in renal allografts.

The Emerging Importance of Non-HLA Autoantibodies in Kidney Transplant Complications

Antibodies that are specific to organ donor HLA have been involved in the majority of cases of antibody-mediated rejection in solid organ transplant recipients. However, recent data show that production of non-HLA autoantibodies can occur before transplant in the form of natural autoantibodies. In contrast to HLAs, which are constitutively expressed on the cell surface of the allograft endothelium, autoantigens are usually cryptic. Tissue damage associated with ischemia-reperfusion, vascular injury, and/or rejection creates permissive conditions for the expression of cryptic autoantigens, allowing these autoantibodies to bind antigenic targets and further enhance vascular inflammation and renal dysfunction. Antiperlecan/LG3 antibodies and antiangiotensin II type 1 receptor antibodies have been found before transplant in patients with de novo transplants and portend negative long-term outcome in patients with renal transplants. Here, we review mounting evidence suggesting an important role for autoantibodies to cryptic antigens as novel accelerators of kidney dysfunction and acute or chronic allograft rejection.

The incidence, management, and evolution of rapamycin-related side effects in kidney transplant recipients

Conversion from a calcineurin‐inhibitor‐based immunosuppression to a rapamycin‐based immunosuppression may preserve kidney graft function. The side effects of rapamycin can limit its usefulness, but their management and evolution are rarely reported in clinical trials. We performed a retrospective cohort study in patients transplanted before December 31, 2008 and who received rapamycin to replace calcineurin inhibitors. In 219 patients studied, 98% presented ≥1 side effects after starting rapamycin. Side effects occurring in ≥10% of patients were dyslipidemia (52%, 95% confidence interval (CI): 45–59%), peripheral edema (37%, 95%CI: 31–43%), cytopenia (36%, 95% CI: 30–42%), acne (29%, 95% CI: 23–35%), proteinuria (23%, 95% CI: 17–29%), and oral ulcers 14% (95% CI: 10–18%). Proteinuria, ulcers, and edema were difficult to manage and were more likely to cause cessation of rapamycin. Rapamycin was discontinued in 46% of patients (95% CI: 40–52%). Age (odds ratio [OR] per 10‐yr increase: 1.29, 95% CI: 1.05–1.59) and obesity (OR: 2.57, 95% CI: 1.10–6.01) were independently associated with cessation of rapamycin. We conclude that successful control of dyslipidemia and cytopenia can be achieved without discontinuing rapamycin. Most other side effects are harder to manage. Leaner and younger patients are less likely to discontinue rapamycin due to side effects.