J.W. de Fijter

A randomized double-blind, multicenter plasma concentration controlled study of the safety and efficacy of oral mycophenolate mofetil for the prevention of acute rejection after kidney transplantation.

BACKGROUND Adding a fixed dose of 1 g b.i.d. of mycophenolate mofetil (MMF) to an immunosuppressive regimen consisting of cyclosporine and prednisone results in a 50% reduction in the incidence of acute rejection after kidney transplantation. This study was designed to investigate the relationship between pharmacokinetic data (mycophenolic acid area under the curve; MPA AUC) and the prevention of rejection after kidney transplantation. METHODS A total of 154 adult recipients of a primary or secondary cadaveric kidney graft were randomly allocated, in this double-blind trial, to receive MMF treatment aimed at three predefined target MPA AUC values (16.1, 32.2, and 60.6 microg x hr/ml). During the first 6 months after transplantation, plasma samples for nine AUCs were collected. After analysis of the samples, a coded dose adjustment advice was generated using a Bayesian algorithm, maintaining the double blinding. Immunosuppressive therapy further consisted of cyclosporine and prednisone. The primary end point of this study was the occurrence of biopsy-proven acute rejection within the 6-month study period. RESULTS A total of 150 patients were eligible for analysis. Although after day 21, the mean MMF dose was reduced, the mean MPA AUC gradually increased and target MPA AUC values were exceeded in all three groups. The incidences of biopsy-proven acute rejection in the low, intermediate, and high target MPA AUC groups were 14 of 51 (27.5%), 7 of 47 (14.9%), and 6 of 52 (11.5%), respectively. The incidences of premature withdrawal from the study due to adverse events in the three groups were 4 of 51 (7.8%), 11 of 47 (23.4%), and 23 of 52 (44.2%), respectively. Logistic regression analysis showed a highly statistically significant relationship between median ln(MPA AUC) and the occurrence of a biopsy-proven rejection (P<0.001). The logistic regression using median ln(Cpredose) was also statistically significant for this relationship (P=0.01), whereas it was not when using mean MMF dose (P=0.082). In contrast, the logistic regression using mean MMF dose for comparison of patients who successfully completed the study versus patients experiencing premature withdrawal due to adverse events was highly significant (P<0.001), whereas this was not significant when using median ln(Cpredose) (P=0.512) or median ln(MPA AUC) (P=0.434). CONCLUSION MPA Cpredose and MPA AUC are significantly related to the incidence of biopsy-proven rejection after kidney transplantation, whereas MMF dose is significantly related to the occurrence of adverse events.

UGT1A9 −275T>A/−2152C>T Polymorphisms Correlate With Low MPA Exposure and Acute Rejection in MMF/Tacrolimus‐Treated Kidney Transplant Patients

Mycophenolate mofetil (MMF) is an immunosuppressive drug commonly used in the context of kidney transplantation. Exposure to the active metabolite mycophenolic acid (MPA) is associated with risk of allograft rejection. MPA pharmacokinetics varies between individuals, the potential cause being the presence of genetic polymorphisms in key enzymes. We genotyped 338 kidney transplant patients for UGT1A8, UGT1A9, UGT2B7, and MRP2 polymorphisms and recorded MPA exposure and biopsy‐proven acute rejections (BPARs) during a 1‐year follow‐up. Tacrolimus‐treated patients who were UGT1A9 −275T>A and/or −2152C>T carriers displayed a 20% lower MPA area under the concentration–time curve from 0 to 12 h (AUC0–12) (P = 0.012). UGT1A9*3 carriers displayed a 49% higher MPA AUC0–12 when treated with tacrolimus and a 54% higher MPA AUC0–12 when treated with cyclosporine (P < 0.005). Cyclosporine‐treated UGT1A8*2/*2 (518GG) patients had an 18% higher MPA AUC0–12 compared with noncarriers. Carrying the UGT1A9 −275T>A and/or −2152C>T polymorphism significantly predicted acute rejection in fixed‐dose (FD) MMF‐treated patients receiving tacrolimus (odds ratio 13.3, 95% confidence interval 1.1–162.3; P < 0.05). UGT1A9 −275T>A and/or −2152C>T genotyping may identify patients at risk of MPA underexposure and acute rejection when receiving treatment with MMF and tacrolimus.

Plasma concentrations of mycophenolic acid acyl glucuronide are not associated with diarrhea in renal transplant recipients

The aim of this study was to determine whether plasma concentrations of the acyl (AcMPAG) and phenolic (MPAG) glucuronide metabolites of mycophenolic acid (MPA) were related to diarrhoea in renal transplant patients on mycophenolate mofetil (MMF) with cyclosporine (CsA) or tacrolimus (TCL). Blood samples (0, 30, 120 min) were taken at days 3, 10, week 4, months 3, 6 and 12 for determination of MPA, MPAG and AcMPAG. MPA‐AUC was estimated using validated algorithms. Two hour AUCs were calculated for MPAG and AcMPAG. Immunosuppressive therapy consisted of CsA/MMF (n= 110) and of TCL/MMF (n= 180). In 70/290 (24%) patients 86 episodes of diarrhoea were recorded during 12 months. Significantly more patients on TCL (31.1%) suffered from diarrhea compared to CsA (12.7%). MMF dose, MPA‐AUC and the 2 h AUCs of MPAG and AcMPAG did not differ between patients with and without diarrhoea. Plasma AcMPAG and MPAG concentrations were substantially higher in patients on CsA compared with TCL, while MPA‐AUC was lower in the former group. These data support the concept that CsA inhibits the biliary excretion of MPAG and AcMPAG, thereby potentially reducing the risk of intestinal injury through enterohepatic recycling of MPA and its metabolites.

Mannan-binding lectin mediates renal ischemia/reperfusion injury independent of complement activation.

Ischemia/reperfusion injury (IRI) remains a major problem in renal transplantation. Clinical studies have identified that high serum levels of Mannan‐binding lectin (MBL), the initiator of the lectin pathway of complement activation, are associated with inferior renal allograft survival. Using a rat model, we identified an entirely novel role for MBL in mediating renal IRI. Therapeutic inhibition of MBL was protective against kidney dysfunction, tubular damage, neutrophil and macrophage accumulation, and expression of proinflammatory cytokines and chemokines. Following reperfusion, exposure of tubular epithelial cells to circulation‐derived MBL resulted in internalization of MBL followed by the rapid induction of tubular epithelial cell death. Interestingly, this MBL‐mediated tubular injury was completely independent of complement activation since attenuation of complement activation was not protective against renal IRI. Our identification that MBL‐mediated cell death precedes complement activation strongly suggests that exposure of epithelial cells to MBL immediately following reperfusion is the primary culprit of tubular injury. In addition, also human tubular epithelial cells in vitro were shown to be susceptible to the cytotoxic effect of human MBL. Taken together, these data reveal a crucial role for MBL in the early pathophysiology of renal IRI and identify MBL as a novel therapeutic target in kidney transplantation.

Effect of CYP3A4*22, CYP3A5*3, and CYP3A Combined Genotypes on Cyclosporine, Everolimus, and Tacrolimus Pharmacokinetics in Renal Transplantation

Cyclosporine, everolimus, and tacrolimus are the cornerstone of immunosuppressive therapy in renal transplantation. These drugs are characterized by narrow therapeutic windows, highly variable pharmacokinetics (PK), and metabolism by CYP3A enzymes. Recently, the decreased activity allele, CYP3A4*22, was described as a potential predictive marker for CYP3A4 activity. This study investigated the effect of CYP3A4*22, CYP3A5*3, and CYP3A combined genotypes on cyclosporine, everolimus, and tacrolimus PK in renal transplant patients. CYP3A4*22 carriers showed a significant lower clearance for cyclosporine (−15%), and a trend was observed for everolimus (−7%) and tacrolimus (−16%). Patients carrying at least one CYP3A5*1 allele had 1.5‐fold higher tacrolimus clearance compared with noncarriers; however, CYP3A5*3 appeared to be nonpredictive for everolimus and cyclosporine. CYP3A combined genotype did not significantly improve prediction of clearance compared with CYP3A5*3 or CYP3A4*22 alone. These data suggest that dose individualization of cyclosporine, everolimus, or tacrolimus therapy based on CYP3A4*22 is not indicated.

Early Renal Ischemia‐Reperfusion Injury in Humans Is Dominated by IL‐6 Release from the Allograft

The pathophysiology of ischemia/reperfusion (I/R) injury is complex, and current knowledge of I/R injury in humans is incomplete. In the present study, human living‐donor kidney transplantation was used as a highly reproducible model to systematically study various processes potentially involved in early I/R injury. Unique, direct measurements of arteriovenous concentration differences over the kidney revealed massive release of interleukin (IL)‐6 in the first 30 minutes of graft reperfusion and a modest release of IL‐8. Among the assessed markers of oxidative and nitrosative stress, only 15(S)‐8‐iso‐PGF2α was released. When assessing cell activation, release of prothrombin factor 1 + 2 indicated thrombocyte activation, whereas there was no release of markers for endothelial activation or neutrophil activation. Common complement activation complex sC5b‐9 was not released into the bloodstream, but was released into urine rapidly after reperfusion. To investigate whether IL‐6 plays a modulating role in I/R injury, a mouse experiment of renal I/R injury was performed. Neutralizing anti‐IL‐6 antibody treatment considerably worsened kidney function. In conclusion, this study shows that renal I/R in humans is dominated by local IL‐6 release. Neutralization of IL‐6 in mice resulted in a significant aggravation of renal I/R injury.

Maturation-resistant dendritic cells induce hyporesponsiveness in alloreactive CD45RA+ and CD45RO+ T-cell populations.

Dendritic cells (DCs) play a crucial role in the induction of antigen‐specific immunity and tolerance. Considering in vivo application of DCs prior to human organ transplantation, a protocol to develop tolerogenic DCs that not only induce unresponsiveness in naive (CD45RA+) T cells, but also in alloreactive memory (CD45RO+) T cells is required. The present study shows that dexamethasone (Dex) alters the differentiation of human monocyte‐derived DCs. DexDCs cocultured with allogeneic CD4+ T cells induced low proliferating and low IFNγ producing T cells. This is caused by lack of both costimulation via CD28 and hampered production of a soluble factor, as well as additional active suppression via B7‐H1 and IL‐10. T cells primed by DexDCs demonstrated hyporesponsiveness upon restimulation with mature DCs seemingly via the induction of anergy, since these cells showed no enhanced apoptosis and only a limited suppressive capacity. Interestingly, not only cocultures of allogeneic CD45RA+, but also of CD45RO+ T cells with DexDCs rendered T‐cell populations hyporesponsive to restimulation with mature DCs. The finding that also alloreactive memory T cells can be regulated supports the rationale of cell‐based therapies to obtain allograft‐specific tolerance in transplant recipients.

KIR-Ligand Mismatches Are Associated With Reduced Long-Term Graft Survival in HLA-Compatible Kidney Transplantation

Natural killer (NK) cells are cytotoxic lymphocytes of the innate immune system with the ability to detect HLA class I disparities via killer‐cell immunoglobulin‐like receptors (KIR). To test whether such KIR‐ligand mismatches contribute to the rejection of human solid allografts, we did a retrospective cohort study of 397 HLA‐DR‐compatible kidney transplantations and determined the KIR and HLA genotypes of recipients and the HLA genotypes of donors. In transplantations compatible for HLA‐A, HLA‐B and HLA‐DR (n = 137), in which a role for T cells and HLA antibodies in rejection was minimized, KIR‐ligand mismatches were associated with an approximately 25% reduction in 10‐year death‐censored graft survival (p = 0.043). This effect was comparable to the effect of classical HLA‐A and HLA‐B incompatibility, and in HLA‐A,‐B‐incompatible transplantations (n = 260) no significant additional effect of KIR‐ligand mismatches was observed. Multivariate Cox regression analysis confirmed the effect of KIR‐ligand mismatching as an independent risk factor in HLA‐A,‐B,‐DR‐compatible transplantations (hazard ratio 2.29, range 1.03–5.10, p = 0.043). This finding constitutes the first indication that alloreactive NK cells may thwart the success of HLA‐compatible kidney transplantations, and suggests that suppression of NK‐cell activity can improve the survival of such kidney grafts.

Successful outcome with a "quintuple approach" of posttransplant lymphoproliferative disorder.

Background. The treatment of posttransplant lymphoproliferative disorder (PTLD) remains empirical. We review our treatment of seven cases of PTLD consisting of five interventions: 1) reduction of immunosuppression; 2) antiviral drugs; 3) interferon-&agr;; 4) gamma-globulins; and 5) anti-CD19 monoclonal antibodies. Methods and Results. Seven consecutive patients who had undergone a simultaneous pancreas-kidney, liver, heart, or kidney transplantation were treated. One patient acquired a primary EBV infection with an oligoclonal immunoblastic lymphoma early after pancreas-kidney transplantation; all others developed a monoclonal polymorphic or immunoblastic lymphoma 2 to 123 months after transplantation. In all patients extranodal sites were involved, in three the graft was also involved. Five patients received the full quintuple approach and all rapidly obtained a complete remission (CR) with a median follow-up of 31 months (7-74 months). Of the two patients who did not receive interferon-&agr; for fear of graft rejection one responded slowly with a CR after 7 months, and the other obtained a rapid CR followed by a relapse at 4 months. All three patients with a liver or heart transplant could keep their graft. All patients are still alive with a median follow-up of 31 months (7-74 months). Conclusion. This combined approach resulted in a favorable outcome in patients with high risk monoclonal PTLD after solid organ transplantation.

Risk factors for Pneumocystis jirovecii pneumonia in kidney transplant recipients and appraisal of strategies for selective use of chemoprophylaxis.

M.G.J. de Boer, F.P. Kroon, S. le Cessie, J.W. de Fijter, J.T. van Dissel. Risk factors for Pneumocystis jirovecii pneumonia in kidney transplant recipients and appraisal of strategies for selective use of chemoprophylaxis.
Transpl Infect Dis 2011: 13: 559–569. All rights reserved