Donor-specific Antibody Formation Research Articles

Eplet Mismatch Load and De Novo Occurrence of Donor-Specific Anti-HLA Antibodies, Rejection, and Graft Failure after Kidney Transplantation: An Observational Cohort Study.

In kidney transplantation, evaluating mismatches of HLA eplets-small patches of surface-exposed amino acids of the HLA molecule-instead of antigen mismatches might offer a better approach to assessing donor-recipient HLA incompatibility and improve risk assessment and prediction of transplant outcomes. To evaluate the effect of number of eplet mismatches (mismatch load) on de novo formation of donor-specific HLA antibodies (DSAs) and transplant outcomes, we conducted a cohort study that included consecutive adult kidney recipients transplanted at a single center from March 2004 to February 2013. We performed retrospective high-resolution genotyping of HLA loci of 926 transplant pairs and used the HLAMatchmaker computer algorithm to count HLA eplet mismatches. De novo DSAs occurred in 43 (4.6%) patients. Multivariable analysis showed a significant independent association between antibody-verified eplet mismatch load and de novo DSA occurrence and graft failure, mainly explained by DQ antibody-verified eplet effects. The association with DQ antibody-verified eplet mismatches was linear, without a safe threshold at which de novo DSA did not occur. Odds for T cell- or antibody-mediated rejection increased by 5% and 12%, respectively, per antibody-verified DQ eplet mismatch. Eplet mismatches in HLA-DQ confer substantial risk for de novo DSA formation, graft rejection, and graft failure after kidney transplantation. Mismatches in other loci seem to have less effect. The results suggest that antibody-verified HLA-DQ eplet mismatch load could be used to guide personalized post-transplant immunosuppression. Adoption of molecular matching for DQA1 and DQB1 alleles could also help to minimize de novo DSA formation and potentially improve transplant outcomes.

The meaning of borderline rejection in kidney transplantation

Borderline T cell-mediated rejection is a diagnostic category of the Banff schema that uses a lower diagnostic threshold. Subclinical borderline T cell-mediated rejection detected by surveillance sampling is not entirely benign. Studies demonstrate increased rates of late rejection, progressive nephron loss, functional impairment, donor-specific antibody formation, and allograft failure. It can be conceptualized as a failure to control the cellular alloimmune response. Mixed results are reported for its treatment, and randomized controlled trials are needed.

Predictive value of HLAMatchmaker and PIRCHE-II scores for de novo donor-specific antibody formation after adult and pediatric liver transplantation

Production of de novo DSA (dnDSA) is associated with an increased risk of antibody mediated rejection after liver transplantation. Antibodies not only recognize the entire antigen but are able to bind specific functional epitopes present on the HLA molecule surface. The HLAMatchmaker and the PIRCHE-II (predicted indirectly recognizable HLA epitopes) algorithms are able to determine predictive epitope mismatches scores and de novo DSA (dnDSA) synthesis based on alloreactive eplets' identification. The aim of the present study was to assess, for the first time in liver transplantation, the complementarity between these two algorithms. We retrospectively analyzed a cohort of 407 adult and 133 pediatric liver transplant patients without preformed DSA, transplanted between 1991 and 2019 in Lyon and Montpellier. HLA antibodies were detected by single antigen bead assay. HLA typing of the donor-recipient pair was achieved by serological and/or DNA-based techniques. PIRCHE-II and HLAMatchmaker algorithms were then applied on both groups. During follow-up, 27.3% of adults and 38.3% of children developed dnDSA. HLA-DRB1 and DQB1-PIRCHE-II and HLAMatchmaker scores were significantly higher in dnDSA group compared to no DSA group for both pediatric and adult patients (except for PIRCHE-II HLA-DRB1 locus score in pediatrics). ROC curves allowed determining score thresholds classifying patients in low- and high-risk of dnDSA synthesis. The two algorithms' Kaplan-Meier curves showed a predicted incidence of dnDSA 20 years after transplantation significantly lower in the low-risk group compare with the high-risk group (log rank <0.05), in both cohorts, with a good negative predictive value. In conclusion, HLAMatchmaker and PIRCHE-II algorithms both are effective tools to identify anti-HLA immunization risk and to predict dnDSA formation after liver transplantation.

HLA-EMMA: A user-friendly tool to analyse HLA class I and class II compatibility on the amino acid level.

In renal transplantation, polymorphic amino acids on mismatched donor HLA molecules can lead to the induction of de novo donor‐specific antibodies (DSA), which are associated with inferior graft survival. To ultimately prevent de novo DSA formation without unnecessarily precluding transplants it is essential to define which polymorphic amino acid mismatches can actually induce an antibody response. To facilitate this, we developed a user‐friendly software program that establishes HLA class I and class II compatibility between donor and recipient on the amino acid level. HLA epitope mismatch algorithm (HLA‐EMMA) is a software program that compares simultaneously the HLA class I and class II amino acid sequences of the donor with the HLA amino acid sequences of the recipient and determines the polymorphic solvent accessible amino acid mismatches that are likely to be accessible to B cell receptors. Analysis can be performed for a large number of donor‐recipient pairs at once. As proof of principle, a previously described study cohort of 191 lymphocyte immunotherapy recipients was analysed with HLA‐EMMA and showed a higher frequency of DSA formation with higher number of solvent accessible amino acids mismatches. Overall, HLA‐EMMA can be used to analyse compatibility on amino acid level between donor and recipient HLA class I and class II simultaneously for large cohorts to ultimately determine the most immunogenic amino acid mismatches.

Relationship between 2-Hour Tacrolimus Concentrations and Clinical Outcomes in Long Term Kidney Transplantation.

Background: Tacrolimus is routinely monitored using trough concentrations, however, recent data have suggested that area under the curve (AUC) provides better correlation with toxicity and efficacy. Area under the curve is cumbersome to measure, but studies have demonstrated that surrogate time points such as 2-hour concentrations are well correlated with AUC. Methods: This is a single center, retrospective study of adult kidney transplant recipients with 2-hour tacrolimus concentrations measured over three years post-transplant. The primary outcome was to determine the difference in serum creatinine (Scr) in those with 2-hour tacrolimus concentrations greater than 20 ng/mL versus those less than or equal to 20 ng/mL. Results: A total of 150 kidney transplant recipients were included. The mean Scr and glomerular filtration rate were 1.49 ± 1.01 mg/dL and 59 ± 23.2 mL/min/1.73 m2, respectively, for the entire cohort. The rate of donor specific antibody formation was 2% and 8% experienced biopsy-proven rejection. The rate of cytomegalovirus viremia was 2% and BK viremia was 13%. There was no significant difference in kidney function over 36 months for the groups specified a priori. Conclusions: Long-term outcomes of maintaining tacrolimus 2-hour concentrations over 20 ng/mL is favorable with minimal opportunistic infections.

Evaluation of Induction Strategies in Heart Transplant at a Single Center

Immunosuppression induction is commonly utilized in heart transplant (HT) to prevent acute rejection and/or delay calcineurin inhibitor (CNI) initiation. However, guidance on whether to use induction and preferred agent(s) are not well defined. This is reflected by high practice variability across centers. According to ISHLT registry data, 54% of adult HT cases utilized induction, 31% with an IL-2R antagonist and 23% with a T-cell depleting agent. Our center has primarily utilized 3 strategies based on rejection risk and need to delay CNI: IL-2R antagonist (basiliximab), T-cell depleting (anti-thymocyte globulin, rabbit (rATG)), or no induction. Our study's objective was to compare these strategies' safety and effectiveness. A retrospective chart review was conducted at a large academic medical center, including HT cases performed between January 2015 and April 2019. Patients were stratified by induction strategy used at the time of transplant. The primary outcomes were rate of biopsy-proven acute cellular rejection (ACR) grade 2R or higher, treated antibody mediated rejection (AMR), and any infection within one year of transplantation. From January 2015 to April 2019, 145 total HTs were included in our study (123 heart, 20 heart-kidney, and 2 heart-liver). rATG was the most common induction strategy used (36%), followed by no induction (35%), and basiliximab (26%). Four patients (3%) received 1 dose of basiliximab but were switched to rATG. ACR rates were not statistically different among induction groups: 22% with no induction, 11% with basiliximab, 17% with rATG, and 0% with combination (p = 0.51). AMR rates were also not statistically different: 6% with no induction, 5% with basiliximab, 4% with rATG, and 0% with combination (p = 0.93). There was no difference detected in donor-specific antibody (DSA) formation at 1 year (p = 0.81). The percentages of patients with any infection were: 53% with no induction, 55% with basiliximab, 62% with rATG, and 75% with combination (p = 0.90). Incidences of ACR, AMR, DSA formation, and infection were not statistically different among induction strategies at one year post-transplant. It may be beneficial to individualize induction strategies based on recipient factors at the time of transplantation. Long term outcomes in this patient cohort are yet to be determined.

Can Avoiding So-Called HLA High Risk Epitope Mismatches (REM) Improve Lung Transplant (LTx) Outcomes?

HLA epitope mismatches can determine risk of graft rejection and de novo Donor Specific Antibodies (dnDSA) formation. Recently (McCaughan 2018) noted some epitopes posed a greater risk of developing dnDSA post-LTx and assumed this correlated with CLAD and survival. Using these reported REM we aim to determine associations between REM and actual LTx outcomes. We retrospectively analysed all 310 primary LTx undertaken Aug 2008-Dec 2015, with both patients and donors' high resolution HLA typed for all HLA loci. Using HLAMatchmaker (v2.1), LTx were assessed for the presence of REM (45GE3 or 45EV/55PP) and DQA1*05. BOS and RAS were determined using the most recent 2019 ISHLT guidelines. Kaplan Meier analysis with log-ranked tests compared groups. Within our cohort, 82 (27%) LTx occurred in the presence of a REM from the donor. Of these, 43 developed CLAD (BOS n=28 RAS n=15). REM was not a predictor of overall patient survival (fig 1a) (p=0.52) or time to CLAD (fig 1b) (p=0.32). As previously published (McCaughan 2018) the development of dnDSA directed to HLA-DQ was frequent (ie 75% of those tested post-LTx) this did not correlate to time to CLAD or overall patient survival in our cohort. Although avoiding REM has been reported to reduce risk of dnDSA following LTx, in our cohort this does not strongly correlate to overall patient survival or time to CLAD. Further studies are still warranted to identify the riskiest of epitopes to avoid in LTx and how the correlate to LTx outcomes.

The role of HLA-DP mismatches and donor specific HLA-DP antibodies in kidney transplantation: a case series

Background: The impact of HLA-DP mismatches on renal allograft outcome is still poorly understood and is suggested to be less than that of the other HLA loci. The common association of HLA-DP donor-specific antibodies (DSA) with other DSA obviates the evaluation of the actual effect of HLA-DP DSA.Methods: From a large multicenter data collection, we retrospectively evaluated the significance of HLA-DP DSA on transplant outcome and the immunogenicity of HLA-DP eplet mismatches with respect to the induction of HLA-DP DSA. Furthermore, we evaluated the association between the MFI of HLA-DP antibodies detected in Luminex assays and the outcome of flowcytometric/complement-dependent cytotoxicity (CDC) crossmatches.Results: In patients with isolated pretransplant HLA-DP antibodies (N = 13), 6 experienced antibody-mediated rejection (AMR) and 3 patients lost their graft. In HLAMatchmaker analysis of HLA-DP mismatches (N = 72), HLA-DP DSA developed after cessation of immunosuppression in all cases with 84DEAV (N = 14), in 86% of cases with 85GPM (N = 6/7), in 50% of cases with 56E (N = 6/12) and in 40% of cases with 56A mismatch (N = 2/5). Correlation analysis between isolated HLA-DP DSA MFI and crossmatches (N = 90) showed negative crossmatch results with HLA-DP DSA MFI <2000 (N = 14). Below an MFI of 10,000 CDC crossmatches were also negative (N = 33). Above these MFI values both positive (N = 35) and negative (N = 16) crossmatch results were generated.Conclusions: Isolated HLA-DP DSA are rare, yet constitute a significant risk for AMR. We identified high-risk eplet mismatches that can lead to HLA-DP DSA formation. We therefore recommend HLA-DP typing to perform HLA-DP DSA analysis before transplantation. HLA-DP DSA with high MFI were not always correlated with positive crossmatch results.

Conversion to belatacept within 1-year of renal transplantation in a diverse cohort including patients with donor-specific antibodies.

Early conversion from a calcineurin inhibitor to belatacept has the potential to improve long-term renal allograft function; however, there remains limited experience with this strategy among African Americans and patients with preformed donor-specific antibodies (DSA). To examine these subgroups, we performed a single-center review of kidney transplant recipients converted to belatacept within 1-year of transplant between 01/2011 and 10/2017. All patients received lymphocyte-depleting induction with maintenance tacrolimus and mycophenolate +/- corticosteroids. Patients were switched to belatacept for clinical indication and followed from date of conversion until allograft failure or study conclusion. The primary endpoint at 1-year was a composite of allograft loss, biopsy proven rejection, de novo DSA formation, proteinuria, and declining renal function. Thirty-two patients were included in the review. The majority were African American, and 28.1% had DSA at transplant. Patient and allograft survival at 1-year was 96.9% and 93.8%, respectively, and estimated glomerular filtration rate improved from 41.9 to 58.4mL/min. No African Americans or patients with pretreatment DSA developed rejection or allograft failure within 1-year. The only clinical variable correlated with suboptimal allograft function was baseline weight ≥80kg (OR=6.2; 95% CI, 1.2-32.3). Early conversion to belatacept appears safe for select patients with DSA and African Americans receiving lymphocyte-depleting induction.

High levels of dd-cfDNA identify patients with TCMR 1A and borderline allograft rejection at elevated risk of graft injury.

The clinical importance of subclinical, early T cell–mediated rejection (Banff TCMR 1A and borderline lesions) remains unclear, due, in part to the fact that histologic lesions used to characterize early TCMR can be nonspecific. Donor‐derived cell‐free DNA (dd‐cfDNA) is an important molecular marker of active graft injury. Over a study period from June 2017 to May 2019, we assessed clinical outcomes in 79 patients diagnosed with TCMR 1A/borderline rejection across 11 US centers with a simultaneous measurement of dd‐cfDNA. Forty‐two patients had elevated dd‐cfDNA (≥0.5%) and 37 patients had low levels (<0.5%). Elevated levels of dd‐cfDNA predicted adverse clinical outcomes: among patients with elevated cfDNA, estimated glomerular filtration rate declined by 8.5% (interquartile rate [IQR] −16.22% to −1.39%) (−3.50 mL/min/1.73 m2 IQR −8.00 to −1.00) vs 0% (−4.92%, 4.76%) in low dd‐cfDNA patients (P = .004), de novo donor‐specific antibody formation was seen in 40% (17/42) vs 2.7% (P < .0001), and future or persistent rejection occurred in 9 of 42 patients (21.4%) vs 0% (P = .003). The use of dd‐cfDNA may complement the Banff classification and to risk stratify patients with borderline/TCMR 1A identified on biopsy.

Exploring predicted indirectly recognizable HLA epitopes (PIRCHE-II) in liver transplant recipients on calcineurin inhibitor-free maintenance immunosuppression. A retrospective single center study

The PIRCHE (Predicted Indirectly ReCognizable HLA Epitopes) score is an HLA epitope matching algorithm. PIRCHE algorithm estimates the level of presence of T-cell epitopes in mismatched HLA. The PIRCHE-II numbers associate with de novo donor-specific antibody (dnDSA) formation following liver transplantation and kidney allograft survival following renal transplantation. The aim of our study was to assess the PIRCHE-II score in calcineurin inhibitor (CNI)-free maintenance immunosuppression recipients.This was a retrospective study of forty-one liver transplant recipients on CNI-free immunosuppression and with available liver allograft biopsies. Donors and recipients were HLA typed. The HLA-derived mismatched peptide epitopes that could be presented by the recipient's HLA-DRB1 molecules were calculated using PIRCHE-II algorithm. The associations between PIRCHE-II scores and graft immune-mediated events were assessed using receiver operating characteristics curves and subsequent univariate and multivariate analyses.CNI-free patients with cellular rejection, humoral rejection, or severe portal inflammation had higher mean PIRCHE-II scores compared to patients with normal liver allografts. PIRCHE-II score and donor age were independent risk factors for liver graft survival in CNI-free patients (HR: 8.0, 95% CI: 1.3–49, p = .02; and HR: 0.88, 95% CI: 0.00–0.96, p = .007, respectively).PIRCHE-II scores could be predictive of liver allograft survival in CNI-free patients following liver transplantation. Larger studies are needed to confirm these results.

Anti-BAFF Treatment Interferes With Humoral Responses in a Model of Renal Transplantation in Rats.

B-cell-activating factor (BAFF) is associated with donor-specific antibodies (DSA) and poorer outcomes after renal transplantation (RTx). We examined the effects of anti-BAFF treatment on B cells, expression of costimulatory molecules and cytokines, germinal centers (GCs), and DSA formation in an RTx model in rats. Anti-BAFF antibody was injected on days 3, 17, 31, and 45 after allogeneic RTx. Rats received reduced dose cyclosporine A for 28 or 56 days to allow chronic rejection and DSA formation. Leukocytes, B-cell subsets, and DSA were measured using flow cytometry; expression of cytokines and costimulatory molecules was measured by quantitative polymerase chain reaction, and GCs and T follicular helper were assessed using immunohistochemistry. Rejection was evaluated by a nephropathologist. Anti-BAFF treatment reduced the frequency of B cells in allografts and spleen. Naive B cells were strongly reduced by anti-BAFF treatment in all compartments. Messenger RNA expression of interleukin-6 and the costimulatory molecules CD40 and inducible T cell costimulator ligand was significantly reduced in anti-BAFF-treated rats. GC area was smaller and plasmablasts/plasma cell numbers lower in anti-BAFF-treated rats, which was reflected by less DSA in certain IgG subclasses. Anti-BAFF treatment interferes with humoral responses at multiple levels in this model of allogeneic RTx.

Novel insights into non-HLA alloimmunity in kidney transplantation.

SummaryRecognition of non‐self structures on donor cells represents the main immunological barrier in solid organ transplantation. The human leukocyte antigens (HLA) are considered the most important non‐self (allo)antigens in transplantation. Long‐term graft attrition is mainly caused by the formation of alloreactive antibodies that are directed against non‐self structures (i.e., epitopes) on cell surface proteins. Recently published data provided evidence for a similar importance of non‐HLA mismatches between donors and recipients in acute rejection as well as long‐term kidney allograft survival. These data suggest a broader concept of immunological non‐self that goes beyond HLA incompatibility and expands the current concept of polymorphic non‐self epitopes on cell surface molecules from HLA to non‐HLA targets. Amino acid substitutions caused by single nucleotide variants in protein‐coding genes or complete loss of gene expression represent the basis for polymorphic residues in both HLA and non‐HLA molecules. To better understand these novel insights in non‐HLA alloimmunity, we will first review basic principles of the alloimmune response with a focus on the HLA epitope concept in donor‐specific antibody formation before discussing key publications on non‐HLA antibodies.

Endothelial Cell-Derived Interleukin-18 Released During Ischemia Reperfusion Injury Selectively Expands T Peripheral Helper Cells to Promote Alloantibody Production.

Ischemia reperfusion injury (IRI) predisposes to the formation of donor-specific antibodies, a factor contributing to chronic rejection and late allograft loss. We describe a mechanism underlying the correlative association between IRI and donor-specific antibodies by using humanized models and patient specimens. IRI induces immunoglobulin M-dependent complement activation on endothelial cells that assembles an NLRP3 (NOD-like receptor pyrin domain-containing protein 3) inflammasome via a Rab5-ZFYVE21-NIK axis and upregulates ICOS-L (inducible costimulator ligand) and PD-L2 (programmed death ligand 2). Endothelial cell-derived interleukin-18 (IL-18) selectively expands a T-cell population (CD4+CD45RO+PD-1hiICOS+CCR2+CXCR5-) displaying features of recently described T peripheral helper cells. This population highly expressed IL-18R1 and promoted donor-specific antibodies in response to IL-18 in vivo. In patients with delayed graft function, a clinical manifestation of IRI, these cells were Ki-67+IL-18R1+ and could be expanded ex vivo in response to IL-18. IRI promotes elaboration of IL-18 from endothelial cells to selectively expand alloreactive IL-18R1+ T peripheral helper cells in allograft tissues to promote donor-specific antibody formation.

The Epidemiologic Burden of Tacrolimus Variability among Kidney Transplant Recipients in the United States

Background: Within-patient tacrolimus level variability >30% has been shown to be a risk factor for de novo donor-specific antibody formation and death-censored graft failure among kidney transplant recipients. The burden of tacrolimus variability and the correlation between variability and subtherapeutic tacrolimus levels were examined in a large national data set. Methods: All tacrolimus levels drawn at LabCorp® facilities in the United States with a diagnosis code for kidney transplant between November 2011 and September 2017 were examined, excluding values that could represent new allografts. Tacrolimus variability was calculated if at least 3 levels were available. The percentage of subtherapeutic (<4.0 ng/dL) tacrolimus levels (%subT) was also calculated. Interdependence between %subT and tacrolimus variability was assessed with correlation analysis and linear regression. Results: There were 410,257 tacrolimus levels among 27,375 patients, who had 11 (interquartile range [IQR] 6–20) tacrolimus levels over a median follow-up of 26.5 (IQR 12.8–46.1) months. Median tacrolimus variability was 30.6%, and 51.6% of patients exceeded 30% variability. Median %subT was 11.1% (IQR 0–30.8%), and 34.3% of patients had no subtherapeutic levels. The correlation coefficient between tacrolimus variability and %subT was 0.253 (p< 0.001). In linear regression, tacrolimus variability increased 1.86% for each 10% increase in %subT (p < 0.001), but R-squared for this model was only 0.06. Conclusion: More than half of established kidney transplant patients from a large national sample exhibited levels of tacrolimus variability that have been associated with inferior transplant outcomes. Tacrolimus variability has a weak association with subtherapeutic levels, but represents a more complicated constellation of clinical factors.

Circulating T follicular helper cells are a biomarker of humoral alloreactivity and predict donor-specific antibody formation after transplantation.

Donor-specific antibodies (DSAs) contribute to renal allograft loss. However, biomarkers to guide clinical management of DSA posttransplant or detect humoral alloimmune responses before alloantibodies develop are not available. Circulating T follicular helper (cTfh) cells are CD4+ CXCR5+ Tfh-like cells in the blood that have been associated with alloantibodies in transplant recipients, but whether they precede antibody formation for their evaluation as a predictive biomarker in transplant is unknown. To evaluate the ability of cTfh cells to predict DSA, we used murine transplant models to determine the temporal relationship between cTfh cells, germinal center formation, and DSA development. We observed that donor-reactive CD4+ CXCR5+ cTfh cells expand after allotransplant. These cTfh cells were equivalent to graft-draining lymph node-derived Tfh cells in their ability to provide B cell help for antibody production. cTfh cell expansion and differentiation into ICOS+ PD-1+ cells temporally correlated with germinal center alloreactivity and preceded the generation of DSAs in instances of modified and unmodified alloantibody formation. Importantly, delayed costimulation blockade initiated after the detection of ICOS+ PD-1+ cTfh cells prevented DSAs. These findings suggest that cTfh cells could serve as a biomarker for humoral alloreactivity before the detection of alloantibodies and inform therapeutic approaches to prevent DSAs.

Alemtuzumab Treatment Leads to Delayed Recovery of T Follicular Regulatory Cells, and May Therefore Predispose Patients to de novo Donor-Specific Antibody Formation

Background - T follicular helper (Tfh) and regulatory (Tfr) cells are key players in the formation of long-lived antibody responses. Their circulating counterparts, cTfh and cTfr, are often used as biomarkers because longitudinal sampling of secondary lymphoid tissues is unfeasible in clinical studies. This is the first study to track cTfh and cTfr cells following therapeutic lymphocyte depletion with alemtuzumab, an anti-CD52 monoclonal antibody, to infer the influence of this treatment on the germinal centre response. Methods - Samples from 61 transplant recipients were taken at the time of transplant, and regular intervals post-transplant for both flow-cytometric immunophenotyping, and Luminex-based donor-specific antibody (DSA) assessment. Results - Patients treated with alemtuzumab (42/61, 69%) had a significantly lower ratio of cTfr to cTfh at all time points post-transplant. We found that, despite a high proportion of Tregs in the recovering cell population, cTfr cells did not repopulate in alemtuzumab treated patients, while cTfh cells reconstituted to higher than pre-transplant levels over the 2-year follow-up. Conclusions - Alemtuzumab has been used as first-line induction immunosuppression and treatment for steroid-resistant rejection in transplantation; our data suggests alemtuzumab-treated patients have a lower cTfr to cTfh ratio even 2 years post-transplant, and may therefore be at higher risk of de novo DSA formation.

Allosensitization after transplant failure: the role of graft nephrectomy and immunosuppression - a retrospective study.

There are conflicting data about the role of transplant nephrectomy and immunosuppression withdrawal on the development of allosensitization and the impact on re-transplantation. We divided 109 first graft recipients into two groups according to whether they underwent nephrectomy (NX+, n=61) or their graft was left insitu (NX-, n=48). Sera were assessed for HLA-A/B/Cw/DR/DQ antibodies at the time of NX/transplant failure and after 3, 6, 12, 24months. The NX+ group showed a higher rate of donor specific antibody (DSA) and non-DSA human leukocyte antigen (HLA) antibody production at all the time points. Multivariable analysis showed that nephrectomy was a strong, independent risk factor for the development of DSAs after 12 and 24months (P=0.005 and 0.008). In the NX- group, low tacrolimus levels correlated with DSA formation (AUC 0.817, P=0.002; best cut-off level 2.9ng/ml). Analysis with a standardized pool of UK donors showed a more difficult grade of HLA matchability following nephrectomy compared with the NX- group. Nephrectomy is followed by the long-term production of DSA and non-DSA HLA antibodies and negatively impacts on the chances of finding a HLA-compatible kidney. Tacrolimus levels ≥3ng/ml are protective against the development of allosensitization and could facilitate re-transplantation in the NX- group.

The clinical impact of donor-specific antibodies on antibody-mediated rejection and long-term prognosis after heart transplantation.

Outcomes after cardiac transplantation have improved over past decades, but long-term graft survival remains limited in part because of uncertainty regarding clinical implications of donor-specific antibodies (DSAs). The purpose of this review is to consolidate recent advances in knowledge on the topic of DSA and their potential to impact long-term prognosis after heart transplantation. The presence of persistent DSA increases the risk of poor outcome after heart transplantation, including development of antibody-mediated rejection (AMR), graft failure, cardiac allograft vasculopathy, and mortality. Importantly, different DSA vary in clinical significance. DSA capable of activating the complement cascade portend a higher risk of developing AMR. human leukocyte antigen class I and class II antigens are expressed differently within the heart, and so, clinical manifestations of class I and class II DSA vary accordingly. Further, compared with class I, class II DSA carry an increased risk of graft loss and mortality. When comparing preexisting DSA with formation of de-novo DSA, de-novo DSA are associated with worse outcome. DSAs are generally associated worse long-term prognosis after heart transplantation but vary in their clinical significance. Recognition of specific risk profiles is essential for guiding posttransplant antibody management.

Graft vasculopathy of vascularized composite allografts in humans: a literature review and retrospective study.

Mechanisms of chronic rejection of vascularized composite allografts (VCA) remain poorly understood and likely present along a spectrum of highly varied clinicopathological findings. Across both animal and human VCA however, graft vasculopathy (GV) has been the most consistent pathological finding resulting clinically in irreversible allograft dysfunction and eventual loss. A literature review of all reported clinical VCA cases with documented GV up to December 2018 was thus performed to elucidate the possible mechanisms involved. Relevant data extracted include C4d deposition, donor-specific antibody (DSA) formation, extent of human leukocyte antigen (HLA) mismatch, pretransplant panel reactive antibody levels, induction and maintenance immunosuppression used, the number of preceding acute rejection episodes, and time to histological confirmation of GV. Approximately 6% (13 of 205) of all VCA patients reported to date developed GV at a mean of 6 years post-transplantation. 46% of these patients have either lost or had their VCAs removed. Neither C4d nor DSA alone was predictive of GV development; however, when both are present, VCA loss appears inevitable due to progressive GV. Of utmost concern, GV in VCA does not appear to be abrogated by currently available immunosuppressive treatment and is essentially irreversible by the time of diagnosis with allograft loss a likely eventuality.