Differential effects of donor-specific HLA antibodies in living versus deceased donor transplant.

The presence of donor-specific anti-HLA antibodies (DSAs) is associated with increased risk of graft failure after kidney transplant. We hypothesized that DSAs against HLA class I, class II, or both classes indicate a different risk for graft loss between deceased and living donor transplant. In this study, we investigated the impact of pretransplant DSAs, by using single antigen bead assays, on long-term graft survival in 3237 deceased and 1487 living donor kidney transplants with a negative complement-dependent crossmatch. In living donor transplants, we found a limited effect on graft survival of DSAs against class I or II antigens after transplant. Class I and II DSAs combined resulted in decreased 10-year graft survival (84% to 75%). In contrast, after deceased donor transplant, patients with class I or class II DSAs had a 10-year graft survival of 59% and 60%, respectively, both significantly lower than the survival for patients without DSAs (76%). The combination of class I and II DSAs resulted in a 10-year survival of 54% in deceased donor transplants. In conclusion, class I and II DSAs are a clear risk factor for graft loss in deceased donor transplants, while in living donor transplants, class I and II DSAs seem to be associated with an increased risk for graft failure, but this could not be assessed due to their low prevalence.

How can we reduce costs of solid-phase multiplex-bead assays used to determine anti-HLA antibodies?

Solid-phase multiplex-bead assays are widely used in transplantation to detect anti-human leukocyte antigen (HLA) antibodies. These assays enable high resolution detection of low levels of HLA antibodies. However, multiplex-bead assays are costly and yield variable measurements that limit the comparison of results between laboratories. In the context of a Dutch national Consortium study we aimed to determine the inter-assay and inter-machine variability of multiplex-bead assays, and we assessed how to reduce the assay reagents costs. Fifteen sera containing a variety of HLA antibodies were used yielding in total 7092 median fluorescence intensities (MFI) values. The inter-assay and inter-machine mean absolute relative differences (MARD) of the screening assay were 12% and 13%, respectively. The single antigen bead (SAB) inter-assay MARD was comparable, but showed a higher lot-to-lot variability. Reduction of screening assay reagents to 50% or 40% of manufacturers' recommendations resulted in MFI values comparable to 100% of the reagents, with an MARD of 12% or 14%, respectively. The MARD of the 50% and 40% SAB assay reagent reductions were 11% and 22%, respectively. From this study, we conclude that the reagents can be reliably reduced at least to 50% of manufacturers' recommendations with virtually no differences in HLA antibody assignments.

Cervicovaginal HPV infection in female renal transplant recipients: an observational, self-sampling based, cohort study.

Immunosuppressive treatment of organ transplant recipients is associated with an increase in the occurrence of human papillomavirus (HPV) related anogenital (pre)malignancies. This cohort study investigated the genotype-specific prevalence of HPV infections in a large cohort of female renal transplant recipients (RTRs). Participants self-collected a cervicovaginal sample for detection and genotyping of HPV. Besides, they completed a questionnaire regarding sociodemographic variables, medical data and sexual behavior. Anogenital screening was offered to all HPV-positive participants. A total number of 218 female RTRs was included. The prevalence of mucosal HPV infections was 27.1% and 17.4% for high risk HPV in particular. The studied cohort showed a broad range of HPV genotypes and multiple HPV genotypes were found in 27.1% of HPV-positive patients. Seven participants were identified with occult premalignant anogenital lesions. In conclusion, this study shows a high point-prevalence of HPV in female RTRs (age-matched West-European general population: 9-10%) with a shift in the distribution of genotypes as compared with the general population. Moreover, a substantial number of patients with occult premalignancies was identified. The introduction of self-sampling for HPV positivity can help in early detection of (pre)malignant anogenital lesions in this vulnerable population.

The Maastricht Transplant Center: clinical setting and epitope searches in HLA class II molecules: does the structural localization of a polymorphic site contribute to its immunogenicity?

Our understanding of the immunological processes influencing the clinical outcome after kidney transplantation has advanced majorly over the last few decades. However, many factors still restrict graft and patient survival. Within the Maastricht transplant center we have successfully implemented an alternative immunosuppressive regimen involving Tacrolimus monotherapy in order to minimize the adverse effects associated with long-term use of immunosuppressive drugs. This clinical development has an impact on pre-transplant risk stratification which requires that patients are closely monitored immunologically. In this review we will elaborate on our strategy regarding the analysis of epitopes in HLA-DQ and HLA-DP molecules. In this respect we have also looked at the immunodominance of certain epitopes by assessing their structural localization, conformation and physiochemical properties.

Preservation of kidneys from controlled donors after cardiac death.

BACKGROUND: Donation after cardiac death (DCD) expands the pool of donor kidneys, but is associated with warm ischaemic injury. Two methods are used to preserve kidneys from controlled DCD donors and reduce warm ischaemic injury: in situ preservation using a double-balloon triple-lumen catheter (DBTL) inserted via the femoral artery and direct cannulation of the aorta after rapid laparotomy. The aim of this study was to compare these two techniques. METHODS: This was a retrospective cohort study of 165 controlled DCD procedures in two regions in the Netherlands between 2000 and 2006. RESULTS: There were 102 donors in the DBTL group and 63 in the aortic group. In the aortic group the kidney discard rate was lower (4·8 versus 28·2 per cent; P < 0·001), and the warm (22 versus 27 min; P < 0·001) and the cold (19 versus 24 h; P < 0·001) ischaemia times were shorter than in the DBTL group. Risk factors for discard included preservation with the DBTL catheter (odds ratio (OR) 5·19, 95 per cent confidence interval 1·88 to 14·36; P = 0·001) and increasing donor age (1·05, 1·02 to 1·07; P < 0·001). Warm ischaemia time had a significant effect on graft failure (hazard ratio 1·04, 1·01 to 1·07; P = 0·009), and consequently graft survival was higher in the aortic cannulation group (86·2 per cent versus 76·8 per cent in the DBTL group at 1 year; P = 0·027). CONCLUSION: In this retrospective study, direct aortic cannulation appeared to be a better method to preserve controlled DCD kidneys.

HLA-DP antibodies before and after renal transplantation.

Human leukocyte antigen (HLA)-DP is considered a target for humoral immune response in clinical transplantation. This study analyses the incidence of HLA-DP antibodies in renal patients. Development and epitope specificity of donor-specific antibodies (DSA) and non-DSA (NDSA) were examined. Pre- and posttransplant sera of 338 patients were screened for HLA-DP antibodies using the luminex single antigen assay. Positive patients, partners and/or kidney donors were HLA-DP typed by sequence-specific oligonucleotides. Potential epitopes were mapped by comparing the amino acid sequences of HLA-DP hypervariable regions (HVR) A-F of recipient, partner and/or donor. Specificities in the sera were aligned to deduce the HVR motif responsible for the antibodies. HLA-DP antibodies were detected in 14% of the patients (48/338). Before transplantation, the antibodies were shown in 23% (10 females and 1 male) and 77% were found after transplantation (30 in patients after the first, 7 after the second graft). Specificities were never restricted to individual mismatched antigens; broad HLA-DP sensitization was found as a rule. A single HVR mismatch was present in 80% of the DSA and in 79% of the NDSA. No HLA-DPA specific antibodies were found. Our findings confirm that HLA-DP antibodies are specific for epitopes shared by different HLA-DP antigens, indicating that only a restricted number of mismatched epitopes are recognized by the recipients immune system. Matching for immunogenic HLA-DP epitopes for renal transplantation seems to be functionally more relevant than classical matching at the allelic level.

Clinical relevance of Luminex donor-specific crossmatches: data from 165 renal transplants.

The clinical significance of the presence of donor-specific anti-human leucocyte antigen (HLA) antibodies (DSA) prior to renal transplantation detected solely by solid-phase techniques remains unclear. This study was designed to determine the clinical relevance of the recently introduced bead-based Luminex donor-specific crossmatch (LumXm). A group of 165 patients transplanted between 1997 and 2001 were tested. Of 165 recipients transplanted with a negative complement-dependent cytotoxicity crossmatch, 32 proved to have a positive Luminex crossmatch. Sixteen were positive for class I, 15 were positive for class II, 1 was both class I and II positive and 133 recipients were negative. Acute rejection (AR)-free survival for all recipients was 77%, and there was no difference in AR-free survival between LumXm-positive and LumXm-negative recipients. Overall graft survival after a median follow-up time of 8 years was 56%. Recipients with a positive class I LumXm had worse long-term graft survival (P = 0.006). In recipients with a positive class I LumXm, 5-year graft survival was 41% vs 70% in negative patients and 10-year graft survival was 27% vs 56%. Positivity for class II LumXm was not a significant risk factor for graft failure (P = 0.7). In conclusion, pretransplant DSA detected by the LumXm had no impact on AR episodes. Class II LumXm positivity proved no significant risk factor for graft failure, but the value of the class II LumXm is questionable. A positive class I LumXm resulted in worse long-term graft survival compared with a negative one.

Histological assessment of preimplantation biopsies may improve selection of kidneys from old donors after cardiac death.

Kidneys from old donors after cardiac death (DCD) may increase the donor pool but the prognosis of these kidneys is unsatisfactory. To improve these results, we retrospectively evaluated the diagnostic utility of published selection algorithms for old donor kidneys. We studied all DCD kidney transplantations between January 1, 1994 and July 1, 2005 at our institution (n = 199). Selection algorithms were evaluated in the subset of kidney transplantations from donors aged 60 years or older (n = 52). For histological assessment of kidney biopsies, glomerulosclerosis, tubular atrophy, interstitial fibrosis and vascular narrowing were blindly scored. Functional kidney weight was calculated as renal mass multiplied by the fraction of nonsclerosed glomeruli. Graft function and survival of kidneys from DCD aged 60 years or older were inferior to those from younger DCD. Histological scores were associated with kidney function and graft survival of old DCD kidney transplantations. Functional kidney weight was associated with kidney function but not graft survival, while donor glomerular filtration rate (GFR), donor age and machine perfusion characteristics were associated with neither of the clinical outcomes of interest. We conclude that histological assessment of preimplantation biopsies may improve the selection of kidneys from old DCD and may therefore contribute to expansion of the donor pool.

Luminex donor-specific crossmatches.

In Luminex bead-based screening assays, color-coded microspheres coated with human leukocyte antigens (HLA) are used to identify both complement-binding and non-complement-binding HLA class I and II antibodies in recipient sera. Many laboratories rely on their specificity detection and use the information obtained for allocation of donor organs. A donor-specific crossmatch in the Luminex technique (LumXm) is for that reason desirable. A LumXm, in which the actual donor HLA are coated onto specific capture beads, was tested for 88 pre- and posttransplant sera of 18 recipients. The results were compared with previously published flow cytometric crossmatch (FCXm) results for the same donor-recipient combinations. All sera were also examined by Luminex single antigen (SA) tests. Class I LumXm detected 24 of 27 T-cell positive FCXm (89%) and class II 15 of 22 B-cell positive FCXm (68%). Sensitivity of LumXm for class I and II was 89% and 68% and specificity was 98% and 97%, respectively. Discrepant LumXm results were obtained in 13 sera of nine patients (15%). In general, based on SA testing, FCXm showed false-positive results for class I and LumXm gave false-negative and positive results for class II. The LumXm test was proven not to react with recipient sera containing DQ antibodies only, also DP detection was insufficient. The validity of the LumXm has been shown for class I, but its value for class II is uncertain. HLA-DR is most probably correctly identified, the validity for DQ and DP is doubtful.

Do blood pressure and arterial wall properties change after conversion from cyclosporine to tacrolimus?

Cardiovascular disease is the leading cause of death in renal transplant recipients. Arterial wall properties are surrogate markers for arteriosclerosis. Previous investigations have shown that the cardiovascular risk profile is better with tacrolimus compared to cyclosporine. Renal function, blood pressure, and lipid levels improve. The hypothesis is that arterial wall properties will improve after conversion from cyclosporine to tacrolimus. Thirty-four stable renal recipients were converted from cyclosporine microemulsion to tacrolimus without changing concomitant medication. Before and after conversion we performed wall track ultrasounds of the carotid and the brachial arteries; pulse wave velocity (PWV); laboratory investigations; 24-hour ABPM; estimates of renal function; and Framingham risk scores. After conversion the 24-hour ambulatory blood pressure monitoring (ABPM) did not change. Total cholesterol, LDL cholesterol, and triglycerides improved significantly. Renal function (Cockroft) improved. There were no significant changes in arterial wall properties, or in PWV. Framingham comparative risk scores improved only significantly in patients not receiving statins. In conclusion, 3 months after conversion from cyclosporine to tacrolimus total cholesterol, LDL cholesterol, and triglycerides were significantly decreased and renal function significantly improved. Contrary to expectation, ABPM did not change, probably due to prolonged use (>10 years) of cyclosporine. There was also no difference in arterial wall properties.

Metabolic aspects of tacrolimus in renal transplantation. Consequences for the choice of an immunosuppressive regimen and for the management of post-transplant diabetes mellitus.

The occurrence of post-transplant diabetes mellitus (PTDM) is an important complication after renal transplantation associated with an increased risk of chronic transplant dysfunction and of cardiovascular morbidity and mortality. Both tacrolimus and cyclosporine have been associated with PTDM. In the initial studies, PTDM seemed to occur more often in tacrolimus treated patients than in cyclosporine treated patients. The mechanism by which tacrolimus could cause PTDM was unknown and the relative roles of tacrolimus and corticosteroids, which are often prescribed concomitantly with tacrolimus, were unknown. In several studies we used fasting glucose and insulin levels to assess (peripheral) insulin resistance, and intravenous glucose tolerance tests to assess insulin secretion by the pancreatic b-cells in response to a stimulus (glucose load). Thus, we evaluated the mechanism by which tacrolimus causes glucose metabolic disorders, risk factors for glucose metabolic disorders during tacrolimus treatment, the relative roles of corticosteroids and tacrolimus trough levels in glucose metabolic disorders, and also differences in glucose metabolism between patients using tacrolimus versus patients using cyclosporine. Based on the results of these studies and the available literature, the consequences for the choice of a primary immunosuppressive agent and guidelines for the treatment of PTDM during tacrolimus-based immunosuppression are discussed.