The role of HLA in renal transplantation

Incidence and risk factors of kidney allograft loss due to BK nephropathy in the pediatric population: A retrospective analysis of the UNOS/OPTN database

BACKGROUND

BK virus infection can lead to graft dysfunction and loss in kidney transplant recipients. Risk factors for BKV and BKVN have been inadequately studied in children. Here, we evaluate the incidence and risk factors of allograft loss due to BKVN in the pediatric population of the UNOS data set.

METHODS

We conducted a retrospective cohort analysis of the UNOS database and identified all pediatric recipients of kidney transplantation between 2000 and 2018. We compared donor and recipient characteristics, including cause of ESRD, among patients who lost their graft due to BKVN or other causes, and those with functioning allograft. Kaplan-Meier curve and Cox regression analysis were performed to evaluate the risk factors.

RESULTS

A total of 66 patients (0.47%) suffered graft failure from BKVN. Older age, male gender, HLA mismatch, and rejection at 1 year were significantly associated with BKVN graft failure, compared to recipients with functioning allograft. In comparison with graft loss due to other causes, male gender, higher HLA mismatch, rejection in 1st year and tacrolimus use at discharge were significantly associated with BKVN graft loss. Recipients who received mycophenolate at time of discharge were at reduced risk for BKVN graft failure. Compared to graft failure from other causes, BKVN graft failure had shorter death censored graft survival [P = .001]. ESRD due to urologic causes and Alport syndrome had higher rate of BKVN graft failure.

CONCLUSION

Incidence of graft loss from BKVN in the pediatric population was 10.2 per 10 000 patient-years in this study. BKVN is associated with early allograft failure in the pediatric population, compared to other causes of graft loss. Male gender, HLA mismatch, rejection in 1st year, and urological cause of ESRD are risk factors for graft failure from BKVN in children.

Impact of human leukocyte antigen and calculated panel reactive antibody on BK viremia in kidney transplant recipients: A single-center experience and literature review

BACKGROUND

The aim of this retrospective analysis was to investigate the effect of human leukocyte antigen (HLA) and calculated panel reactive antibody (cPRA) on BK virus activation as evidenced by BK viremia (BKV).

PATIENTS AND METHODS

At our institution, 649 kidney transplant patients were screened for BKV from 2009 to 2017. Patients were considered to have BKV if they had >10 000 copies/mL of BK DNA in their blood. Donor and recipient HLA and cPRA, demographic, clinical and laboratory data, as well as immunosuppressive medications were collected.

RESULTS

We identified 122 BK positive and 527 BK negative patients. Only 25% of the patients had cPRA of 20% or more, and 64% had more than three HLA-A, -B, and -DR mismatches. In both univariate and multivariate analyses, male gender, age, and maintenance of steroid therapy significantly increased the risk of BKV (P = 0.005, 0.005 and <0.001, respectively). The degree of cPRA and the individual HLA allele and HLA allele matching did not significantly affect BKV.

CONCLUSION

Neither the degree of HLA mismatching nor cPRA appears to affect BKV. Moreover, no specific HLA allele, HLA allele matching, or cPRA were associated with BKV.

BK Virus Nephropathy in Pediatric Renal Transplant Recipients: An Analysis of the North American Pediatric Renal Trials and Collaborative Studies (NAPRTCS) Registry

BACKGROUND AND OBJECTIVES

There is limited information regarding BK virus nephropathy in pediatric kidney transplantation. The objective of this study was to evaluate cases of BK virus nephropathy in the North American Pediatric Renal Trials and Collaborative Studies database.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Using a questionnaire that was sent to North American Pediatric Renal Trials and Collaborative Studies centers, we assessed the incidence, risk factors, clinical features, and outcomes of BK virus nephropathy in pediatric renal transplant recipients who received a transplant between 2000 and 2004.

RESULTS

BK virus nephropathy was reported in 25 (4.6%) of 542 patients at a median onset of 10.1 mo after transplantation. The median age was 11 yr. All patients who were tested reported BK viruria, and 19 (91%) of 21 who had plasma tested reported BK viremia. Treatment of BK virus nephropathy included reduction of immunosuppression (84%), cidofovir (24%), leflunomide (8%), and intravenous Ig (20%). Simultaneous rejection treatment was reported in four (16%). The median creatinine was 2.0 mg/dl at a mean follow-up of 24 mo. There were six (24%) graft failures in the patients with BK virus nephropathy at a mean of 24 mo after diagnosis. Rejection occurred in eight (32%) after diagnosis. Multivariate analysis showed that use of polyclonal induction therapy and zero HLA DR mismatch were associated with the development of BK virus nephropathy.

CONCLUSIONS

This first multicenter, retrospective, cohort study of BK virus nephropathy in pediatric renal transplant recipients found a BK virus nephropathy incidence of 4.6% and identified polyclonal induction and zero HLA DR mismatch as significant risk factors for BK virus nephropathy.

Detection and analysis of HLA class I and class II specific alloantibodies in the sera of dialysis recipients waiting for a renal retransplantation

The objective of this study was to evaluate the specificities of HLA class I (-A,-B) and class II (-DR,-DQ) antibodies (Ab) detected in the sera of alloimmunized patients waiting for a subsequent renal transplantation. The study group consisted of 62 dialysis patients (42 men and 20 women, mean age: 43 +/- 18 yr) on waiting list for a subsequent kidney transplant (52 for a second and 10 for a third transplant) at S. Martino Hospital Transplant Centre in Genoa/Italy, who were enrolled from 2002 to 2004 for HLA antibody screening. Complement dependent cytotoxicity (CDC) technique was used firstly to select anti-HLA class I sensitized patients; indeed sera from 50 individuals out of 62 (80.6%) were found to display persistent HLA class I PRA (panel reactive antibody) values >4% (range: 20-100). ELISA technique was subsequently adopted to analyze HLA class I Ab positive sera for the presence also of HLA class II Ab and to characterize class I and class II Ab specificities. Anti-class I immunized patients were divided in three groups according to the type of class I Ab specificities, that were classified as private, public, and multispecific. The first group included 35 patients (70% of the total number of positive patients) showing only antibodies directed against private HLA class I specificities, represented in 33 cases by those expressed by graft donors (first or second transplant). In this group anti-class I PRA% values ranged from 20% to 60%. HLA class II Ab, with an heterogeneous specificity pattern (private, public or multispecific), were present in 25 (78.1%) out of the 32 patients, whose sera were also available for this analysis. The second group comprised 12 patients (24%) who displayed antibodies directed against class I public epitopes belonging to CREGs (Cross reactive Groups) or an association of anti-private and anti-public antibodies. In this group PRA values ranged from 25% to 90%. Five patients (46.7%) were positive for HLA class II Ab, whose specificity pattern appeared also heterogeneous (private or multispecific). The third group was represented by three patients (6%) displaying multispecific antibodies with PRA values > or = 90%. No multispecific class II Ab were found in this group, where only two patients had class II Ab showing anti-private or anti-private plus public specificities. Globally, 74% of anti-class I Ab positive patients, having at least one HLA class II antigen mismatch, appeared also positive for class II Ab. These results indicate that: (i) a large proportion of patients, waiting for a kidney retransplantation, display in their sera alloantibodies specific for graft mismatched HLA class I (80.6%) and class II antigens (54.2); (ii) the immunogenic determinants, mainly involved in HLA class I and II specific Ab production, were, in a significant rate, private specificities of mismatched HLA antigens (70% for class I and 59.4% for class II), and in a lesser percentage by public (CREG) epitopes (24% for class I and 34.3% for class II). In a few patients only no HLA class I and class II Ab specificities could be determined, as they displayed multispecific antibodies (6% for class I and 6.2% for class II). These findings may have important implications to improve donor-recipient matching in dialysis recipients waiting for a subsequent renal transplantation.

Detection and specification of noncomplement binding anti-HLA alloantibodies

The aim of the study was to investigate the distribution of human leukocyte antigen (HLA) -specific immunoglobulin (Ig) isotypes/subclasses in alloimmunized patients awaiting a kidney retransplant. Sera from 102 patients were analyzed for the presence of anti-HLA-A, anti-HLA-B alloantibodies by complement-dependent cytotoxicity test with the addition of dithiothreitol (CDC+DTT). Furthermore, anti-HLA class I and class II alloantibodies were determined using a commercial solid-phase (enzyme-linked immunosorbent assay [ELISA]) system. The respective isotypes/subclasses were defined by replacing the IgG1-4 secondary antibody with IgG1-, IgG2-, IgG3-, IgG4-, IgA1-, IgA2-, and IgM-specific antibodies. The HLA specificities of the noncomplement-binding IgG2 and IgG4 antibodies were determined and compared with the mismatches from the failed transplants. Thirty-eight of 102 (37%) sera were positive in the class I CDC+DTT, in contrast to 41 of 102 (40%) detected by class I ELISA and 47 of 102 (46%) by class II ELISA. Seventeen of 102 (17%) positive reaction were observed for the IgM-isotype, whereas none were detected for the IgA-isotype. Twenty-five of 102 (25 %) sera contained noncomplement-binding IgG2 and/or IgG4 antibodies; in the majority of the cases, 22 of 25 (88%) were directed against the organ donor antigen. These data show that donor-specific, noncomplement-binding IgG2 and IgG4 alloantibodies exist with high prevalence in HLA-immunized retransplant candidates. Therefore, a thorough antibody screening workup, including CDC with or without DTT and ELISA screening should be performed for patients before they reenter the waiting list. Defining the Ig isotypes and subclasses can be helpful to explain inconsistent results.

HLA mismatching increases the risk of BK virus nephropathy in renal transplant recipients

BK virus (BKV) nephropathy is a serious complication in kidney transplant recipients that may lead to irreversible graft failure. We have analyzed the degree of donor/recipient HLA compatibility and HLA antigen association in 40 kidney transplant patients with BKV nephropathy in comparison with a control group of 404 unaffected transplant recipients who were on tacrolimus-based immunosuppression with no induction. HLA compatibility was assessed by determining the number of HLA-A, -B, -DR-mismatched antigens. BK virus nephropathy was diagnosed histologically and confirmed by immunochemistry. Univariate and multiple logistic regression statistical analyses have shown a significant association between BKV nephropathy and HLA mismatching. This analysis showed also that BKV nephritis is associated with a greater number of rejection episodes and a higher incidence of steroid-resistant rejection requiring antilymphocyte treatment. There was no association between BKV nephropathy and any specific HLA allele. We propose that HLA mismatching promotes the development of BKV nephropathy through rejection-related inflammatory processes and heavy immunosuppression which cause virus reactivation and injury of the tubular epithelium.

A sequencing-based typing method for HLA-DQA1 alleles

Sequencing-based typing (SBT) is the most comprehensive method for characterizing human leukocyte antigen gene polymorphisms. Development of a SBT method for DQA1 is hampered because of a deletion of codon 56 in nearly half of the known DQA1 alleles. Sequence electropherograms of heterozygous samples comprising a deletion allele and a non-deletion allele display misalignment after codon 56 because of a three base-pair shift in the deletion allele. To overcome this problem, we have designed three group-specific primer sets to selectively amplify the deletion alleles from the nondeletion alleles. DNA samples are initially polymerase chain reaction (PCR)-typed using these primer sets along with an internal positive control primer set specific to growth hormone gene 1 (hGH1). The positive group-specific PCR reactions were selectively repeated without hGH1 control primers, and the amplicons were used as template in sequencing reactions. The sequence data were analyzed to obtain DQA1 types using ABI MatchTools software as well as the newly available Conexio Genomics Assign SBT Genotyping Software. The method was validated using a panel of reference DNA from the University of California, Los Angeles, International DNA Exchange Program. We conclude that the present SBT method is a technically simple and robust procedure to characterize the sequence polymorphisms in exon 2 of DQA1 gene.

Immunologic monitoring

The development of reliable in vitro assays that could allow the quantitation and characterization of anti-donor alloimmune responses has always been a goal in clinical transplantation, both to predict presensitization to the transplanted tissue and to be able to identify rejection without resorting to more invasive tests. With recent development in our understanding of transplantation biology and therapeutics, there is a real expectation that these tests may be used to identify tolerance as much as to predict rejection. The traditional limiting dilution assays still have a contribution to make and are being complemented by an array of tools, such as ELISpot, flow cytometry-based techniques, and microarray analysis. The assays that have been informative, to date, are discussed in this review. This information will lead, at least, to a better understanding of how and when the rejection process occurs. More interestingly, the objective is to apply this information to evaluate tolerance-inducing strategies or to identify patients that have become tolerant to their graft and can be weaned of immunosuppression. Of course sensitive, accurate and specific immunologic monitoring has applications well beyond the field of transplantation.

Loss of direct and maintenance of indirect alloresponses in renal allograft recipients: implications for the pathogenesis of chronic allograft nephropathy

Chronic allograft nephropathy (CAN) is the principal cause of late renal allograft failure. This complex process is multifactorial in origin, and there is good evidence for immune-mediated effects. The immune contribution to this process is directed by CD4(+) T cells, which can be activated by either direct or indirect pathways of allorecognition. For the first time, these pathways have been simultaneously compared in a cohort of 22 longstanding renal allograft recipients (13 with good function and nine with CAN). CD4(+) T cells from all patients reveal donor-specific hyporesponsiveness by the direct pathway according to proliferation or the secretion of the cytokines IL-2, IL-5, and IFN-gamma. Donor-specific cytotoxic T cell responses were also attenuated. In contrast, the frequencies of indirectly alloreactive cells were maintained, patients with CAN having significantly higher frequencies of CD4(+) T cells indirectly activated by allogeneic peptides when compared with controls with good allograft function. An extensive search for alloantibodies has revealed significant titers in only a minority of patients, both with and without CAN. In summary, this study demonstrates widespread donor-specific hyporesponsiveness in directly activated CD4(+) T cells derived from longstanding recipients of renal allografts, whether they have CAN or not. However, patients with CAN have significantly higher frequencies of CD4(+) T cells activated by donor Ags in an indirect manner, a phenomenon resembling split tolerance. These findings provide an insight into the pathogenesis of CAN and also have implications for the development of a clinical tolerance assay.

Prospective study of microchimerism in renal allograft recipients: association between HLA-DR matching, microchimerism and acute rejection

The presence of donor-derived hematopoietic cells in blood and various tissues of the organ recipients, termed allogeneic microchimerism, has been considered to play an essential role in establishment of organ acceptance. In this study, we prospectively determined the presence of peripheral blood microchimerism (PBM) in 20 male-to-female renal allograft recipients up to 30 months post-transplantation. Recipients were categorized according to the pattern of microchimerism into microchimeric and nonmicrochimeric groups, and then state of human leukocyte antigens (HLA) Class II (DR/DQ) matching, episodes of acute rejection, age at transplantation, renal function, and history of blood transfusion were compared. DNA was extracted from donor, pre-transplant, and post-transplant (1 wk; 1, 3, 6, 12, 18, 24, and 30 months) peripheral blood samples. We analyzed PBM using nested polymerase chain reaction (PCR) amplification specific for the SRY region of the Y chromosome with a sensitivity up to 1:1 000 000. Microchimerism was detected in 13 (65%) of 20 recipients at various intervals. The highest frequency of microchimerism was at 1 wk (55%). Among microchimeric recipients, none were positive on all post-transplant analyses. Interestingly, nonmicrochimeric cases were negative throughout the study. The three recipients with an episode of acute rejection during the first week after transplantation were all in the nonmicrochimeric group with completely mismatched HLA-DR antigens. HLA-DR incompatibility was significantly lower (t-test, p<0.05) in microchimeric cases (1.0+/-0.58) than in nonmicrochimeric ones (1.9+/-0.38). But regarding HLA-DQ and other clinical parameters mentioned above, significant difference was not observed. We propose that there is an association between HLA-DR matching, microchimerism and acute graft rejection in our recipients. Our study demonstrates that, with routine immunosuppressive protocols, higher compatibility of HLA-DR antigens facilitates microchimerism induction. Then, development of new stronger immunosuppressive protocols (including conditioning) or augmentation of chimeric state (by donor-specific bone marrow infusion), especially in completely mismatched HLA-DR renal allograft recipients, may be useful for graft acceptance.

Time dependency of factors affecting renal allograft survival

The function of renal transplants can deteriorate at any time posttransplant, but the risks and mechanisms may differ at different times posttransplant. Survival of 522 consecutive cadaveric renal transplant recipients followed for at least 6 mo were analyzed, with patient death censored. The overall risk factors in univariate analysis were acute rejection requiring antibody therapy (AR), delayed graft function, elevated serum creatinine at 6 mo, high panel-reactive antibodies, and donor age > or =55 yr, with borderline effects of recipient age and female gender. These risks were studied in each of three intervals posttransplantation: < or =6 mo, 6 mo to 5 yr, and >5 yr. Of the 135 graft failures, 53 occurred < or =6 mo, 61 between 6 mo and 5 yr, and 21 beyond 5 yr. By multivariate analysis. the risks for graft failure in interval < or =6 mo were AR (hazard ratio (HR) = 4.86, P < 0.001); delayed graft function (HR = 1.47, P = 0.06): and high panel-reactive antibodies (HR = 2.04, P = 0.0(3). Between 6 mo and 5 yr, the risks for graft loss were AR (HR = 2.87, P < 0.001) and serum creatinine at 6 mo > or =150 micromol/L (HR = 3.69, P < 0.001). Beyond 5 yr the risk factors were donor age > or =55 yr (HR = 5.87, P = 0.002), with a borderline effect of kidneys from female donors (HR = 2.28, P = 0.07). HLA-A, -B, and -DR matching and presensitization had most of their effect through early AR and impaired function. The results indicate that risks for graft loss are time-dependent: early losses correlate with injury and rejection, but late events correlate with donor age and possibly workload.