End-to-side versus end-to-end uretero-ureteral anastomosis in preemptive kidney transplantation from living donors: A monocentric experience

PURPOSE

End-to-end (ETE) pyeloureterostomy is an alternative to ureteroneocystostomy for urinary anastomosis during kidney transplantation (KT). In preemptive KT from living donors (PKT-LD), end-to-side (ETS) uretero-ureteral anastomosis could have the benefits of pyeloureterostomy without ligation of the native kidney ureter. This study aimed to compare ETS to ETE uretero-ureteral anastomosis in PKT-LD.

METHODS

A monocentric retrospective 8-year study included all consecutive cases of PKT-LD, excluding ureteroneocystomy anastomosis and homolateral nephrectomy. Two groups were compared: ETS and ETE. Perioperative data on graft function and urological complications were collected.

RESULTS

One hundred and six patients were included: 48 patients in the ETS group and 58 patients in the ETE group. Median follow-up was 37.5 months [17.3; 57.5]. The estimated glomerular filtration rate at postoperative day ten and 3 months was similar in both groups. The overall complication rate was 16%, with no significant difference between the 2 groups. There was one ureteral stenosis in each group. None of the patients in the ETS group presented urinary fistula, whereas it occurred in one (1.7%) in the ETE group. Back pain due to native kidney obstruction occurred in 5 patients in the ETE group (8.6%), but not in the ETS group.

CONCLUSION

In preemptive kidney transplantation from living donors, urinary anastomosis can safely be performed as an end-to-side uretero-ureteral anastomosis, with low urological complications. It could prevent symptoms and complications due to native kidney obstruction.

LEVEL OF EVIDENCE

IV.

Predictive Modeling of Tacrolimus Dose Requirement Based on High-Throughput Genetic Screening

Any biochemical reaction underlying drug metabolism depends on individual gene-drug interactions and on groups of genes interacting together. Based on a high-throughput genetic approach, we sought to identify a set of covariant single-nucleotide polymorphisms predictive of interindividual tacrolimus (Tac) dose requirement variability. Tac blood concentrations (Tac C₀ ) of 229 kidney transplant recipients were repeatedly monitored after transplantation over 3 mo. Given the high dimension of the genomic data in comparison to the low number of observations and the high multicolinearity among the variables (gene variants), we developed an original predictive approach that integrates an ensemble variable-selection strategy to reinforce the stability of the variable-selection process and multivariate modeling. Our predictive models explained up to 70% of total variability in Tac C₀ per dose with a maximum of 44 gene variants (p-value <0.001 with a permutation test). These models included molecular networks of drug metabolism with oxidoreductase activities and the multidrug-resistant ABCC8 transporter, which was found in the most stringent model. Finally, we identified an intronic variant of the gene encoding SLC28A3, a drug transporter, as a key gene involved in Tac metabolism, and we confirmed it in an independent validation cohort.

Genome-Wide Association Study of Acute Renal Graft Rejection

Acute renal rejection is a major risk factor for chronic allograft dysfunction and long-term graft loss. We performed a genome-wide association study to detect loci associated with biopsy-proven acute T cell-mediated rejection occurring in the first year after renal transplantation. In a discovery cohort of 4127 European renal allograft recipients transplanted in eight European centers, we used a DNA pooling approach to compare 275 cases and 503 controls. In an independent replication cohort of 2765 patients transplanted in two European countries, we identified 313 cases and 531 controls, in whom we genotyped individually the most significant single nucleotide polymorphisms (SNPs) from the discovery cohort. In the discovery cohort, we found five candidate loci tagged by a number of contiguous SNPs (more than five) that was never reached in iterative in silico permutations of our experimental data. In the replication cohort, two loci remained significantly associated with acute rejection in both univariate and multivariate analysis. One locus encompasses PTPRO, coding for a receptor-type tyrosine kinase essential for B cell receptor signaling. The other locus involves ciliary gene CCDC67, in line with the emerging concept of a shared building design between the immune synapse and the primary cilium.

Urinary mRNA for the Diagnosis of Renal Allograft Rejection: The Issue of Normalization

Urinary messenger RNA (mRNA) quantification is a promising method for noninvasive diagnosis of renal allograft rejection (AR), but the quantification of mRNAs in urine remains challenging due to degradation. RNA normalization may be warranted to overcome these issues, but the strategies of gene normalization have been poorly evaluated. Herein, we address this issue in a case-control study of 108 urine samples collected at time of allograft biopsy in kidney recipients with (n = 52) or without (n = 56) AR by comparing the diagnostic value of IP-10 and CD3ε mRNAs-two biomarkers of AR-after normalization by the total amount of RNA, normalization by one of the three widely used reference RNAs-18S, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and Hypoxanthine-guanine phosphoribosyltransferase (HPRT)-or normalization using uroplakin 1A (UPK) mRNA as a possible urine-specific reference mRNA. Our results show that normalization based on the total quantity of RNA is not substantially improved by additional normalization and may even be worsened with some classical reference genes that are overexpressed during rejection. However, considering that normalization by a reference gene is necessary to ensure polymerase chain reaction (PCR) quality and reproducibility and to suppress the effect of RNA degradation, we suggest that GAPDH and UPK1A are preferable to 18S or HPRT RNA.

Early Low Urinary CXCL9 and CXCL10 Might Predict Immunological Quiescence in Clinically and Histologically Stable Kidney Recipients

We monitored the urinary C-X-C motif chemokine (CXCL)9 and CXCL10 levels in 1722 urine samples from 300 consecutive kidney recipients collected during the first posttransplantation year and assessed their predictive value for subsequent acute rejection (AR). The trajectories of urinary CXCL10 showed an early increase at 1 month (p = 0.0005) and 3 months (p = 0.0009) in patients who subsequently developed AR. At 1 year, the AR-free allograft survival rates were 90% and 54% in patients with CXCL10:creatinine (CXCL10:Cr) levels <2.79 ng/mmoL and >2.79 ng/mmoL at 1 month, respectively (p < 0.0001), and 88% and 56% in patients with CXCL10:Cr levels <5.32 ng/mmoL and >5.32 ng/mmoL at 3 months (p < 0.0001), respectively. CXCL9:Cr levels also associate, albeit less robustly, with AR-free allograft survival. Early CXCL10:Cr levels predicted clinical and subclinical rejection and both T cell- and antibody-mediated rejection. In 222 stable patients, CXCL10:Cr at 3 months predicted AR independent of concomitant protocol biopsy results (p = 0.009). Although its positive predictive value was low, a high negative predictive value suggests that early CXCL10:Cr might predict immunological quiescence on a triple-drug calcineurin inhibitor-based immunosuppressive regimen in the first posttransplantation year, even in clinically and histologically stable patients. The clinical utility of this test will need to be addressed by dedicated prospective clinical trials.

Fibrosis progression according to epithelial-mesenchymal transition profile: a randomized trial of everolimus versus CsA

Markers of epithelial-mesenchymal transition (EMT) may identify patients at high risk of graft fibrogenesis who could benefit from early calcineurin inhibitor (CNI) withdrawal. In a randomized, open-label, 12-month trial, de novo kidney transplant patients received cyclosporine, enteric-coated mycophenolate sodium (EC-MPS) and steroids to month 3. Patients were stratified as EMT+ or EMT- based on month 3 biopsy, then randomized to start everolimus with half-dose EC-MPS (720 mg/day) and cyclosporine withdrawal (CNI-free) or continue cyclosporine with standard EC-MPS (CNI). The primary endpoint was progression of graft fibrosis (interstitial fibrosis/tubular atrophy [IF/TA] grade increase ≥1 between months 3-12) in EMT+ patients. 194 patients were randomized (96 CNI-free, 98 CNI); 153 (69 CNI-free, 84 CNI) were included in histological analyses. Fibrosis progression occurred in 46.2% (12/26) CNI-free EMT+ patients versus 51.6% (16/31) CNI EMT+ patients (p = 0.68). Biopsy-proven acute rejection (BPAR, including subclinical events) occurred in 25.0% and 5.1% of CNI-free and CNI patients, respectively (p < 0.001). In conclusion, early CNI withdrawal with everolimus initiation does not prevent interstitial fibrosis. Using this CNI-free protocol, in which everolimus exposure was relatively low and administered with half-dose EC-MPS, CNI-free patients were overwhelmingly under-immunosuppressed and experienced an increased risk of BPAR.

Dramatic improvement of severe cryptococcosis-induced immune reconstitution syndrome with adalimumab in a renal transplant recipient

In solid organ transplant recipients, immune reconstitution inflammatory syndrome (IRIS) is a rare complication of cryptococcosis, which may require steroids in its most severe forms. Here, we report the case of a renal transplant recipient who developed severe cryptococcal meningitis-associated IRIS 1 week after immunosuppression reduction. High-dose steroids failed to improve the disease. Finally, a recombinant human monoclonal tumor necrosis factor-α (TNF-α) antagonist, adalimumab, was prescribed, and the patient rapidly experienced dramatic neurological improvement. No IRIS relapse occurred within 14 months following adalimumab discontinuation.

Risk of antibody-mediated rejection in kidney transplant recipients with anti-HLA-C donor-specific antibodies

Anti-HLA donor-specific antibodies (DSAs) cause acute and chronic antibody-mediated rejection (AMR). However, the clinical relevance of anti-HLA-C antibodies remains unclear. We evaluated the clinical relevance of the presence of anti-HLA-C DSA at day 0 in renal transplant recipients. In this retrospective, case-controlled study, 608 patients who underwent kidney transplantation between August 2008 and March 2012 were screened for the presence of isolated anti-HLA-C DSA at day 0. A total of 22 renal transplant recipients were selected and followed for a period of 1 year. AMR was classified according to the Banff classification. The 22 patients were compared with 88 immunized patients. Acute AMR was diagnosed in six patients (27.3%). The median level of DSA at day 0 was 1179 (530-17,941). The mean fluorescence intensity in the anti-C group was 4966 (978-17,941) in the AMR group and 981 (530-8012) in the group of patients without AMR. Acute AMR was diagnosed less frequently in the 88 immunized individuals (9.1%) than in the DSA anti-C group (p = 0.033). The level of DSA at day 0 was predictive for AMR (p = 0.017). Patients with a high level of pretransplant anti-HLA-C DSAs are likely to develop acute AMR during the first year after transplantation.

Eculizumab improves posttransplant thrombotic microangiopathy due to antiphospholipid syndrome recurrence but fails to prevent chronic vascular changes

Thrombotic microangiopathy (TMA) is one of the hallmark vascular lesions of antiphospholipid syndrome nephropathy (APSN). These lesions are at high risk of recurrence after kidney transplantation. The complement pathway is thought to be active in this process. We used eculizumab to treat three consecutive kidney transplant recipients with posttransplant TMA due to APSN recurrence that was resistant to plasmapheresis and explored the complement deposition and apoptotic and vascular cell markers on the sequential transplant biopsies. Treatment with eculizumab resulted in a rapid and dramatic improvement of the graft function in all three patients and in improvement of the TMA lesions within the graft. None of these patients had TMA flares after eculizumab was withdrawn. At the time of TMA diagnosis, immunofluorescence studies revealed intense C5b-9 and C4d depositions at the endothelial cell surface of the injured vessels. Moreover, C5b-9 colocalized with vessels exhibiting a high rate of apoptotic cells. Examination of sequential biopsies during eculizumab therapy showed that TMA lesions, C4d and apoptotic markers were rapidly cleared but the C5b-9 deposits persisted for several months as a footprint of the TMA. Finally, we noticed that complement inhibition did not prevent the development of the chronic vascular changes associated with APSN. Eculizumab seems to be an efficient method for treating severe forms of posttransplant TMA due to APSN recurrence. Terminal complement inhibition does not prevent the development of chronic APSN.

Metabolic stress promotes renal tubular inflammation by triggering the unfolded protein response

The renal epithelium contributes to the development of inflammation during ischemic injury. Ischemia induces endoplasmic reticulum (ER) stress and activates the unfolded protein response (UPR). Ischemic tissues generate distress signals and inflammation that activates fibrogenesis and may promote adaptive immunity. Interestingly, the UPR may activate inflammation pathways. Our aim was to test whether the UPR is activated during metabolic stress and mediates a tubular inflammatory response. Glucose deprivation, not hypoxia and amino acids deprivation, activated the UPR in human renal cortical tubular cells in culture. This stress activated NF-κB and promoted the transcription of proinflammatory cytokines and chemokines, including IL-6, IL-8, TNF-α, RANTES and MCP-1. The protein kinase RNA (PKR)-like ER kinase signaling pathway was not required for the induction of inflammation but amplified cytokine. Inositol-requiring enzyme 1 activated NF-κB signaling and was required for the transcription of proinflammatory cytokines and chemokines following metabolic stress. Moreover, acute ischemia activated ER stress and inflammation in rat kidneys. Finally, the ER stress marker GRP78 and NF-κB p65/RelA were coexpressed in human kidney transplants biopsies performed before implantation, suggesting that ER stress activates tubular inflammation in human renal allografts. In conclusion, this study establishes a link between ischemic stress, the activation of the UPR and the generation of a tubular inflammatory response.

Significance of C4d Banff scores in early protocol biopsies of kidney transplant recipients with preformed donor-specific antibodies (DSA)

The significance of C4d-Banff scores in protocol biopsies of kidney transplant recipients with preformed donor-specific antibodies (DSA) has not been determined. We reviewed 157 protocol biopsies from 80 DSA+ patients obtained at 3 months and 1 year post-transplant. The C4d Banff scores (1,2,3) were associated with significant increments of microcirculation inflammation (MI) at both 3 months and 1 year post-transplant, worse transplant glomerulopathy and higher class II DSA-MFI (p < 0.01). Minimal-C4d had injury intermediate between negative and focal, while focal and diffuse-C4d had the same degree of microvascular injury. A total of 54% of patients had variation of C4d score between 3 months and 1 year post-transplant. Cumulative (3 month + 1 year) C4d scores correlated with long-term renal function worsening (p = 0.006). However, C4d staining was not a sensitive indicator of parenchymal disease, 55% of C4d-negative biopsies having evidence of concomitant MI. Multivariate analysis demonstrated that the presence of MI and class II DSA at 3 months were associated with a fourfold increased risk of progression to chronic antibody-mediated rejection independently of C4d (p < 0.05). In conclusion, the substantial fluctuation of C4d status in the first year post-transplant reflects a dynamic humoral process. However, C4d may not be a sufficiently sensitive indicator of activity, MI and DSA being more robust predictors of bad outcome.

Severe vascular lesions and poor functional outcome in kidney transplant recipients with lupus anticoagulant antibodies

The impact of antiphospholipid antibodies (APA) on clinical outcome and graft histology following renal transplantation remains poorly known and controversial. We retrospectively explored the functional and histological significance of APA, primarily lupus anticoagulant (LA), in kidney transplant recipients using a systematic evaluation of 3- and 12-month posttransplant screening biopsies and glomerular filtration rate measurements (mGFR). During the study period, 37 patients had APA (2.7%), primarily LA, and 12 fulfilled antiphospholipid syndrome (APS) diagnostic criteria (0.8%) at the time of transplantation. Early after transplantation, 4 of the 12 APS patients died. Early thrombosis of graft vessels and deep venous thrombosis occurred more frequently in APA+ patients than in controls (27% vs. 7%, p < 0.05 and 35% vs. 14%, p < 0.05, respectively). The survival rate was significantly lower in patients with APS. Strikingly, the hallmark lesions of APS-associated nephropathy (APSN) were found in most of screening graft biopsies in APA+ patients but not in the controls. Accordingly, APA+ patients had a dramatic increase in chronic vascular scores and a faster decline in mGFR at 1 year. In conclusion, renal transplantation may be life-threatening in APS patients, and the presence of LA at the time of transplantation is associated with a high rate of allograft APSN and poor transplantation outcomes.

Bortezomib as the sole post-renal transplantation desensitization agent does not decrease donor-specific anti-HLA antibodies

Persistence of donor-specific anti-HLA antibodies (DSA) associated with antibody-mediated graft injuries following kidney transplantation predicts evolution toward chronic humoral rejection and reduced graft survival. Targeting plasma cells, the main antibody-producing cells, with the proteasome inhibitor bortezomib may be a promising desensitization strategy. We evaluated the in vivo efficacy of one cycle of bortezomib (1.3 mg/m(2)x 4 doses), used as the sole desensitization therapy, in four renal transplant recipients experiencing subacute antibody-mediated rejection with persisting DSA (>2000 [Mean Fluorescence Intensity] MFI). Bortezomib treatment did not significantly decrease DSA MFI within the 150-day posttreatment period in any patient. In addition, antivirus (HBV, VZV and HSV) antibody levels remained stable following treatment suggesting a lack of efficacy on long-lived plasma cells. In conclusion, one cycle of bortezomib alone does not decrease DSA levels in sensitized kidney transplant recipients in the time period studied. These results underscore the need to evaluate this new desensitization agent properly in prospective, randomized and well-controlled studies.

Kidney transplantation at Necker Hospital: the most recent 5-year period (2004-2009)

The results of our last 5 years activity in kidney transplantation clearly show that it is possible to perform high-risk transplantations with very acceptable results: ECD kidneys, dual transplantation, recipients with DSAs. In depth statistical analysis of these data should allow a clearer definition of the best strategies to use in these situations.

Outcome of subclinical antibody-mediated rejection in kidney transplant recipients with preformed donor-specific antibodies

This study describes clinical relevance of subclinical antibody-mediated rejection (SAMR) in a cohort of 54 DSA-positive kidney transplant recipients receiving a deceased donor. In 3 months screening biopsies, 31.1% of patients met the criteria of SAMR. A total of 48.9% had an incomplete form of SAMR (g+/ptc+/C4d-negative) whereas 20% had no humoral lesions. Patients with SAMR at 3 months had at 1 year: a higher C4d score, ptc score, and arteriosclerosis score, higher rate of IFTA (100% vs. 33.3%, p < 0.01) and a higher rate of transplant glomerulopathy (43% vs. 0%, p = 0.02) compared to patients without 3-month SAMR. Patients with SAMR at 3 months exhibited at 1 year a higher class II MFImax-DSA and a lower mGFR compared to patients without SAMR (39.2 +/- 13.9 vs. 61.9 +/- 19.2 mL/min/1.73 m(2) respectively, p < 0.01). The group of patients with C4d-negative SAMR at 3 months developed more ptc and IFTA lesions, and lower GFR at 1 year in comparison to biopsies without humoral lesions. SAMR is a frequent entity in KTR with preexisting DSAs and promotes subsequent GFR impairment and development of chronic AMR. C4d-negative SAMR patients displayed an intermediate course between the no-SAMR group and the C4d+ SAMR group. Screening biopsies may be useful to recognize patients more likely to develop SAMR.

Incidence, risk factors and clinical consequences of neutropenia following kidney transplantation: a retrospective study

Neutropenic episodes in kidney transplant patients are poorly characterized. In this retrospective study, neutropenia was experienced by 112/395 patients (28%) during the first year posttransplant. The only factor found to be significantly associated with the occurrence of neutropenia was combined tacrolimus-mycophenolate therapy (p < 0.001). Neutropenic patients experienced more bacterial infections (43% vs. 32%, p = 0.04). Grade of neutropenia correlated with the global risk of infection. Discontinuation of mycophenolic acid (MPA) due to neutropenia was associated with an increased incidence of acute rejection (odds ratios per day 1.11, 95% confidence intervals 1.02-1.22) but not with reduced renal function at 1 year. The time from onset of neutropenia to MPA discontinuation correlated with the duration of neutropenia. Granulocyte colony-stimulating factor (G-CSF) administration was safe and effective in severely neutropenic kidney graft recipients, with absolute neutrophil count >1000/microL achieved in a mean of 1.5+/-0.5 days. Neutropenia is an important and frequent laboratory finding that may exert a significant influence on outcomes in kidney transplantation. As well as leading to an increased incidence of infection, it is associated with a higher rate of allograft rejection if MPA is discontinued for >6 days (p = 0.02). G-CSF accelerates recovery of neutropenia and may be a good therapeutic alternative for severely neutropenic patients.

Intensive and prolonged treatment of focal and segmental glomerulosclerosis recurrence in adult kidney transplant recipients: a pilot study

No treatment has consistently induced long-term remission of proteinuria in adult patients with focal segmental glomerulosclerosis (FSGS) recurrence after kidney transplantation. We undertook an open-label, nonrandomized pilot trial of intensive and prolonged treatment of FSGS recurrence. Over an 18-month period, 10 adult kidney transplant recipients with FSGS recurrence received concomitantly high-dose steroids, intravenous cyclosporine for 14 days followed by oral cyclosporine therapy, and an intensive and prolonged course of plasma exchanges (PE). We compared this treatment with those of a control group of 19 patients with a FSGS recurrence transplanted between 1997 and 2005. Complete, rapid (mean 23 +/- 7 days) and sustained remission was obtained in 9/10 patients (90%) as opposed to 27% in the control group. At month 3 and month 12, proteinuria was 0.16 g/day (range 0.05-0.3 g/day) and 0.19 g/day (range 0.05-1 g/day) respectively. Only one patient remained in partial remission at month 12 but he had already lost two previous grafts due to FSGS recurrence. PEs were stopped at month 9 in all patients except for the patient with a partial remission who remains PE-dependent. This small pilot study provides very encouraging results demonstrating that this treatment rapidly achieves complete and sustained remission in a high proportion of patients.

Cyclosporine-induced endoplasmic reticulum stress triggers tubular phenotypic changes and death

The molecular mechanisms by which cyclosporine induces chronic nephrotoxicity remain poorly understood. A previous transcriptomic study suggested that cyclosporine might induce endoplasmic reticulum (ER) stress in human tubular cells. The aim of the present study was to characterize the features of tubular ER stress induced by cyclosporine and to investigate its effects on cell differentiation and viability. Using primary cultures of human tubular cells, we confirmed that cyclosporine is responsible for ER stress in vitro. This was also confirmed in vivo in the rat. In vitro, cyclosporine and other ER stress inducers were responsible for epithelial phenotypic changes leading to the generation of protomyofibroblasts, independent of transforming growth factor-beta signaling. RNA interference directed against cyclophilin A supported the role of its inhibition in triggering ER stress as well as epithelial phenotypic changes induced by cyclosporine. Salubrinal, which is known to protect cells from ER stress, significantly reduced epithelial phenotypic changes and cytotoxicity induced by cyclosporine in vitro. Salubrinal also reduced cyclosporine nephrotoxicity in rat kidneys. Thus, we describe a novel mechanism that initiates dedifferentiation and tubular cell death upon cyclosporine treatment. These results provide an interesting framework for further nephroprotective therapies by targeting ER stress.

A simple clinico-histopathological composite scoring system is highly predictive of graft outcomes in marginal donors

The predictive value of pre-implantation biopsies versus clinical scores has not been studied extensively in marginal donors. Pre-implantation biopsies were performed in 313 kidneys from donors that were > or = 50 years of age (training set, n = 191; validation set, n = 122). The value of the donor clinical parameters and histological results in predicting 1-year estimated glomerular filtration rate (eGFR) <25 mL/min/1.73 m(2) was retrospectively evaluated. In multivariate analysis, the only clinical parameters associated with low eGFR were donor hypertension and a serum creatinine level > or =150 micromol/L before organ recovery. Clinical scores (Nyberg and Pessione) were not significantly associated with graft function. Regarding histological parameters, univariate analysis showed that glomerulosclerosis (GS) (p = 0.02), arteriolar hyalinosis (p = 0.03) and the Pirani (p = 0.02) and chronic allograft damage index (CADI) (p = 0.04) histological scores were associated with low eGFR. The highest performance in predicting low eGFR was achieved using a composite score that included donor serum creatinine (> or =150 micromol/L or <150 micromol/L), donor hypertension and GS (> or =10% or <10%). The validation set confirmed the critical importance of taking into account biopsy and clinical parameters during marginal donor evaluation. In conclusion, clinical scores are weak predictors of graft outcomes with marginal donors. Instead, a simple and convenient composite score strongly predicts graft function and survival and may facilitate optimal allocation of marginal donors.

Sirolimus may reduce fertility in male renal transplant recipients

Assessment of sex hormones in organ transplant recipients suggests that sirolimus may impair testicular function. The aim of this study was to evaluate the frequency and severity of sirolimus-associated alterations in sperm parameters and their impact on fathered pregnancy rate. An observational study was carried out in male patients aged 20-40 years who received a kidney transplant during 1995-2005. Patients were sent a questionnaire by post, and sperm analysis was proposed. The fathered pregnancy rates according to the immunosuppressive regimen were estimated and compared using the Poisson model. Complete information was obtained from 95 out of 116 recipients. Patients treated with sirolimus throughout the post-transplant period had a significantly reduced total sperm count compared to patients who did not receive sirolimus (28.6 +/- 31.2 x 10(6) and 292.2 +/- 271.2 x 10(6), respectively; p = 0.006), and a decreased proportion of motile spermatozoa (22.2 +/- 12.3% and 41.0 +/- 14.5%, p = 0.01). Moreover, the fathered pregnancy rate (pregnancies/1000 patient years) was 5.9 (95% CI, 0.8-42.1) and 92.9 (95% CI, 66.4-130.0) in patients receiving sirolimus-based and sirolimus-free regimens, respectively (p = 0.007). Of six patients in whom sirolimus treatment was interrupted, only three showed a significant improvement in sperm parameters. Sirolimus is associated with impaired spermatogenesis and, as a corollary, may reduce male fertility.

Pharmacogenetics of Tacrolimus and Sirolimus in Renal Transplant Patients: From Retrospective Analyses to Prospective Studies

The promises of pharmacogenetics are to elucidate the inherited basis of differences between individual responses to drugs in order to identify the right drug and dose for each patient. The recent identification of genetic polymorphisms in drug-metabolizing enzymes and drug transporters led to the hypothesis that genetic factors may be implicated in the interindividual variability of the pharmacokinetic or pharmacodynamic characteristics of immunosuppressive drugs, major side effects, and efficacy. The purpose of this study was to provide a short overview of recent results obtained in the field of pharmacogenetics of tacrolimus and sirolimus, both substrates of the cytochrome P450 3A (CYP3A) enzymes and of the efflux pump P-glycoprotein, the product of the Multidrug Resistance-1 (MDR1) genes. A number of retrospective studies that demonstrated a link between the polymorphisms governing the CYP3A5 protein expression, with more conflicting results with the MDR1 gene polymorphisms, related to the daily dose necessary to achieve adequate blood tacrolimus levels. The CYP3A5 polymorphisms have also been associated with sirolimus pharmacokinetics. One challenge is to investigate the combined effect of a number of different polymorphisms in various genes to define genetic backgrounds with different pharmacokinetic profiles using high throughput technologies. Another challenge is to move toward prospective randomized studies to explore whether a pharmacogenetic approach, taking into account a limited number of polymorphisms prior to drug treatment, could be used on an individual basis to guide initial dosing of a given drug. The last challenge is based on "target" pharmacogenetics to investigate the role of the polymorphisms of other genes implicated in the efficacy and/or safety of the drug.