Development Of anti-HLA Antibodies Research Articles

Safety and Immunogenicity of SARS-CoV-2 mRNA Vaccine Booster Doses in Kidney Transplant Recipients: Results of a 12-mo Follow-up From a Prospective Observational Study.

Booster doses of SARS-CoV-2 mRNA vaccines are commonly used in kidney transplant recipients (KTRs). However, there is uncertainty regarding the waning of vaccination responses and immunological safety in KTRs. A total of 123 KTRs were included in the final analysis of this prospective observational cohort study. The aim was to evaluate the immunogenicity and immunological safety. SARS-CoV-2 antispike IgG antibodies and anti-HLA antibodies were measured at baseline and then at months 3, 6, and 12 after vaccination with the first booster dose (ie, the third vaccine dose). Antibodies against S1 and S2 subunits of SARS-CoV-2 were evaluated using an immunochemiluminescent assay (cutoff 9.5 AU/mL, sensitivity 91.2%, and specificity 90.2%). Anti-HLA antibodies were analyzed using single-antigen bead technology. Seroconversion was reached in 65% of KTRs previously nonresponding to 2-dose mRNA vaccination; the overall seroconversion rate 3 mo after the first booster dose was 83%. Vaccination induced a durable humoral response, and the antibody levels were stable during the 12-mo study follow-up. Higher age (exponentiated beta coefficient [eβ] 0.97; 95% confidence interval [CI], 0.943-0.997) and a full dose of mycophenolate (eβ 0.296; 95% CI, 0.089-0.984) were negatively associated with SARS-CoV-2 IgG antibody levels, whereas better graft function (eβ1.021; 95% CI, 1.005-1.037) was associated positively. There were no systematic signs of anti-HLA antibody development after vaccination. However, during the follow-up, there was a nonsignificant signal of an increase in anti-HLA antibodies in those who developed COVID-19. Additional booster doses of SARS-CoV-2 mRNA vaccines induce durable antibody response even in a large subset of previous nonresponders and are not associated with the risk of allosensitization. Furthermore, a signal linking COVID-19 to the development of anti-HLA antibodies was observed, and this should be confirmed and further examined (NCT05483725).

Prevalence of Anti-HLA Antibodies in Multiply Transfused Patients with Hematologic Malignancy

Background: Human leukocyte antigen (HLA) alloimmunization can be induced by exposure to non-self HLA molecules, such as foreign tissue during transplantation, pregnancy, and blood products. Antibodies against HLA lead to serious complications in patients receiving blood transfusions. Objective: The present study aimed to determine the prevalence and risk factors for HLA alloimmunization in multiple transfused patients with hematologic malignancies at Siriraj Hospital. Materials and Methods: The present research was a cross-sectional study. The samples comprised 100 cases of hematologic malignancy patients who had a history of at least three episodes of transfusion with cellular blood components. All patients were tested for anti-HLA class I and class II antibodies by Luminex assay. Results: The overall prevalence of HLA alloimmunization in multiple transfused patients with hematologic malignancies was 40%. Anti-HLA class I, class II, and both class I and class II antibodies were detected in 35%, 30%, and 25% of the patients, respectively. Factors related to the development of anti-HLA antibodies were previous pregnancy (OR 4.82, 95% CI 1.62 to 14.35, p=0.005), five or more transfusions (OR 7.82, 95% CI 2.22 to 27.55, p=0.001), and diagnoses with myelodysplastic syndromes (MDS) antibodies (OR 5.88, 95% CI 1.98 to 17.47, p=0.001). Conclusion: Patients with hematologic malignancies who required long-term blood transfusion support could be at high risk for the development of anti-HLA antibodies. Important risk factors are pregnancy, multiple transfusions, and MDS. Keywords: HLA alloimmunization, Anti-HLA antibodies, Blood transfusions, Hematologic malignancy

Effect of blood transfusion post kidney transplantation on de novo human leukocytes antigen donor-specific antibody development and clinical outcomes in kidney transplant recipients: A systematic review and meta-analysis

The relationship between blood transfusion following kidney transplantation (KT) and the development of de novo donor-specific antibodies (dnDSA) is controversial. This was investigated by conducting a meta-analysis of studies on patients who underwent KT with or without blood transfusion, and by evaluating the effect of post-KT blood transfusion on clinical outcomes of kidney transplant recipients. Relevant studies in the PubMed, EMBASE, and Cochrane Library databases were identified from inception to July 1, 2022. Two reviewers independently extracted data from the selected articles and estimated study quality. A fixed effects or random effects model was used to pool data according to the heterogeneity among studies. Data included in the meta-analysis were derived from 11 studies with a total of 19,543 patients including 6191 with and 13,352 without blood transfusion post-KT. We assessed the pooled associations between blood transfusion and occurrence of dnDSA and clinical outcomes of transplant recipients. Blood transfusion was strongly correlated with the development of dnDSA (relative risk [RR] = 1.40, 95% confidence interval [CI]: 1.17–1.67; P < 0.05). Patients with blood transfusion had a higher risk of developing anti-human leukocyte antigen (HLA) class I dnDSA than non-transfused patients (RR = 1.75, 95% CI: 1.14–2.69; P < 0.05) as well as significantly higher rates of antibody-mediated rejection (AMR) (RR = 1.41, 95% CI: 1.21–2.35; P < 0.05) and graft loss (RR = 1.75, 95% CI: 1.30–2.35; P < 0.05). There were no statistically significant differences between the two groups in the development of anti-HLA antibodies, anti-HLA class II dnDSA, and anti-HLA class I and II dnDSA; delayed graft function; T cell-mediated rejection; acute rejection; borderline rejection; or patient death. Our results suggest that blood transfusion was associated with dnDSA development in KT recipients. The findings of this systematic review also suggest that post-KT blood transfusion recipients have a higher risk of AMR, and graft loss compared with non-transfused patients. Evidence from this meta-analysis indicates that the use of blood transfusion post-KT is associated with a significantly higher risk of immunological sensitization. More and higher quality results from large randomized controlled trials are still needed to inform clinical practice.

DETERMINATION OF THE PRA POSITIVITY PERCENTAGE IN MALE PATIENTS WITH CHRONIC KIDNEY DISEASE BY USING FLOW CYTOMETRY TECHNIQUE.

The antibodies directed against human leukocyte antigen (HLA) molecules, which play a crucial role in allograft histocompatibility, are called anti-HLA antibodies. Anti-HLA antibodies against foreign HLA molecules may be present in patients with chronic kidney disease even before transplantation. The panel reactive antibody (PRA) test is used to measure the renal transplant candidate's immune sensitivity to HLA molecules other than their own HLA molecules by assessing the diversity of anti-HLA antibodies in the blood of these patients. This study aimed to determine the PRA values and the percentage of PRA positivity of Turkish male patients with chronic kidney disease (CKD), who had not been sensitized by the major known causes (those with no history of organ or tissue transplantation, those with no history of blood transfusion), who had not been diagnosed with any autoimmune diseases, and who had not been under immunosuppressive treatment. The study included 60 male patients aged over 18 years. All of the patients were followed up with a diagnosis of CKD at the Nephrology Clinic, Internal Medicine Department, Akdeniz University Medical Faculty Hospital. None of the patients included in the study was sensitized by a known mechanism previously (they did not have blood transfusion or organ transplantation). Glomerular filtration rate (GFR) levels of all patients were below the level of 60 mL/min/1.73 m2. Patient data including their age information, etiology of CKD, accompanying diseases, and information about dialysis modalities were recorded. HLA antibody percentage was determined by the flow cytometry technique. Statistical data analysis was performed by using SPSS 22.0 (Statistical Package for Social Sciences, Version 22.0). The values of p less than 0.05 were considered statistically significant. Twenty patients were receiving dialysis treatment due to end-stage renal disease. Of the 60 patients included in the study, 25% showed PRA positivity; 28.3% of all study patients were found to be positive for anti-HLA class I antibodies and 26.7% of all study patients were found to be positive for anti-HLA class II antibodies on separate analysis for anti-HLA class I and anti-HLA class II antibody positivity. When the patients were categorized as PRA negative and PRA positive in two groups, there were no differences between the groups according to mean age, percentage of hemodialysis patients, percentage of peritoneal dialysis patients and presence of accompanying chronic diseases (such as hypertension, type 2 diabetes mellitus, hyperlipidemia, nephrolithiasis, coronary artery disease). In addition to this, evaluation of the GFR levels showed that the PRA positive group contained a significantly higher percentage of end-stage renal disease patients (GFR <15 mL/min/1.73 m2) as compared with the PRA negative group. Detailed analysis of the percentages of PRA levels in the PRA positive patients, which was carried out to determine the degree of sensitization, showed that the PRA values were over 80% in 11.77% of the patients positive for anti-HLA class I antibodies. On the other hand, PRA values were within the range of 15%-80% in 88.23% of the patients who had anti-HLA class II antibodies. The PRA values were below 80% in all of the patients positive for anti-HLA class II antibodies and those positive for both anti-HLA class I and class II antibodies. In conclusion, PRA levels of the candidates for kidney transplantation should always be measured to assess their state of sensitization before transplantation, even though they have no risk factors known to cause anti-HLA antibody development.

HLA Sensitization in the Era of COVID-19: Single-Center Experience

It is well known that several viral infections are capable of triggering the formation of HLA antibodies; however, association between SARS-CoV-2 and the development of anti-HLA antibodies is not yet confirmed. In this study, we compared the prevalence of HLA antibody before and after COVID-19 infection in a cohort of three groups included 58 healthy non-sensitized employees (HNE), 130 kidney transplanted recipients (KTR) and 62 kidney transplant candidates (KTC). There was no significant changes observed in HLA-class I antibodies in any of the groups but evaluation of antibodies to HLA-class II revealed significant change in KTR group (p=0.0184) after acquiring COVID-19 infection and in the HNE group (p=0.0043) when compared to the reported prevalence in similar population. Although we observed emergence of convalescent de-novo donor specific antibodies in two patients, we did not encounter any rejection episodes in the KTR group. Finally, the results of flow cytometry crossmatch in the HNE group were not consistent with the state of antibodies. In conclusion, COVID-19 infection has the potential to produce Class II antibodies but with little effect on pre-existing sensitization. These antibodies are likely to be transient and not necessarily causing positive crossmatch with the corresponding antigens at the proper MFI and therefore, should not affect access to transplantation. There is a need for further evaluation to ascertain these antibodies genuineness and their exact impact on transplant readiness and outcomes.

Infusion of Allogeneic Mesenchymal Stromal Cells After Liver Transplantation: A 5-Year Follow-Up.

Various properties of mesenchymal stromal cells (MSCs) might be particularly of interest after liver transplantation (LT). In this article, we report the long-term results of a prospective, controlled, and first-in-human phase 1 study evaluating the safety of a single MSC infusion after LT. A total of 10 LT recipients treated with standard immunosuppression received 1.5 to 3×106 /kg third-party unrelated MSCs on postoperative day 3and were prospectively compared with a control group of 10 LT recipients. Primary endpoints were set to prospectively detect potentially delayed adverse effects of MSC infusion, particularly the occurrence of infections and cancers. Secondary endpoints of liver graft and patient survival, graft rejection and function, occurrence of bile duct complications, and development of donor-specific anti-human leukocyte antigen (HLA) antibodies (DSA) against liver or MSC donors were studied. The median follow-up was 85months. There was no difference in overall rates of infection or cancer at 5years of follow-up between the 2 groups. There was also no difference in secondary endpoints. The prevalence of de novo liver DSAs related to HLA mismatches was twice as high in the MSC group compared with the control group. All of the de novo class II HLA antibodies against MSCs were linked to a shared HLA mismatch between the liver and MSCs. This study confirms the safety of a single MSC infusion after LT. The potential benefits of MSC injections in the context of organ transplantation have yet to be demonstrated by larger prospective studies. The development of anti-HLA antibodies against an MSC donor should be further evaluated, especially in cases of shared HLA mismatches between graft and MSC donors, despite the fact that no deleterious effect has been detected.

The effect of paracorporeal pulsatile biventricular assist devices on allosensitization in adults: A comparison with left ventricular assist devices

Ventricular assist devices (VADs) have been associated with the development of anti-HLA antibodies (‘allosensitization’), but data on devices providing biventricular support in adults are limited. We sought to characterize differences in anti-HLA antibody formation in adult patients receiving left- (LVAD) versus biventricular- (BiVAD) assist devices as bridge to transplantation (BTT) by retrospectively reviewing the records of adult patients who have undergone VAD implantation at our institution. We assessed 82 patients supported with a pulsatile-flow paracorporeal BiVAD and compared them with 40 patients receiving LVAD till 2018. Forty-eight (58.5%) of the BiVAD and 23 (57.5%) of the LVAD patients were eventually transplanted (p = 0.91) with an average time to transplantation 559 and 598 days, respectively (p = 0.73). Evidence of sensitization pre-VAD was found in 11.0% of the BiVAD patients and 15.0% of the LVAD ones (p = 0.53); these percentages rose to 43.9% (p < 0.001) and 40.0% (p = 0.01), respectively. The post-VAD sensitization status was not significantly different between the BiVAD and the LVAD group (p = 0.68). De novo sensitization was comparable between the two groups (p = 0.55). Post-transplantation outcomes regarding rejections and cardiac allograft vasculopathy were also similar. Conclusively, BiVAD- and LVAD- induced allosensitization do not appear to differ significantly.

Antibodies to human leukocyte antigens and their association with blood product exposures in pediatric patients undergoing cardiac transplantation

Previous blood product exposures may result in the development of antibodies to human leukocyte antigens (HLA). Pediatric heart transplant recipients who have these antibodies experience increased morbidity and mortality after transplantation. In this study, our aims were to confirm the association of previous allogeneic blood product exposures with the formation of anti-HLA antibodies, determine which blood components pose the greatest risk of developing antibodies, and assess differences in outcomes after transplantation between patients who had anti-HLA antibodies and those who did not. This retrospective investigation included all children who underwent cardiac transplantation at Children's Healthcare of Atlanta from January 1, 2015 through December 31, 2018. Chart reviews were performed to collect pertinent data. Anti-HLA antibodies were detected by single antigen bead testing. Antibody burden was tabulated using the calculated panel reactive antibody (cPRA) score immediately prior to transplantation. Statistical analyses were conducted to examine differences based on HLA antibody status and identify associations with outcomes of interest. Our results show a significant association between pretransplant blood product exposures and HLA antibody status. Children with a pretransplant blood product exposure had 7.98 times the odds of developing an anti-HLA antibody compared to those without a pretransplant blood product exposure (p=.01). We also found a significant association between a previous red blood cell (RBC) exposure and HLA antibody status (p=.01) which was not found for other blood component exposures. Patients who were HLA antibody positive were more likely to develop a donor-specific antibody (DSA) after transplantation (p=.04). Exposure to previous allogeneic blood products affects the development of anti-HLA antibodies in children presenting for heart transplantation. Previous RBC exposures resulted in HLA antibody positivity more than other blood component exposures. Importantly, the presence of HLA antibodies was associated with the development of DSAs post-transplantation. Developing transfusion strategies to reduce allogeneic blood product exposures in children who may need future cardiac transplantation should be a high priority.

Sensitization and Desensitization in Vascularized Composite Allotransplantation.

Vascularized composite allotransplantation (VCA) is a field under research and has emerged as an alternative option for the repair of severe disfiguring defects that result from severe tissue loss in a selected group of patients. Lifelong immunosuppressive therapy, immunosuppression associated complications, and the effects of the host immune response in the graft are major concerns in this type of quality-of-life transplant. The initial management of extensive soft tissue injury can lead to the development of anti-HLA antibodies through injury-related factors, transfusion and cadaveric grafting. The role of antibody-mediated rejection, donor-specific antibody (DSA) formation and graft rejection in the context of VCA still remain poorly understood. The most common antigenic target of preexisting alloantibodies are MHC mismatches, though recognition of ABO incompatible antigens, minor histocompatibility complexes and endothelial cells has also been shown to contribute to rejection. Mechanistically, alloantibody-mediated tissue damage occurs primarily through complement fixation as well as through antibody-dependent cellular toxicity. If DSA exist, activation of complement and coagulation cascades can result in vascular thrombosis and infarction and thus rejection and graft loss. Both preexisting DSA but especially de-novo DSA are currently considered as main contributors to late allograft injury and graft failure. Desensitization protocols are currently being developed for VCA, mainly including removal of alloantibodies whereas treatment of established antibody-mediated rejection is achieved through high dose intravenous immunoglobulins. The long-term efficacy of such therapies in sensitized VCA recipients is currently unknown. The current evidence base for sensitizing events and outcomes in reconstructive transplantation is limited. However, current data show that VCA transplantation has been performed in the setting of HLA-sensitization.

O40: PRE-OPERATIVE MANAGEMENT AND SENSITISATION IN VASCULARIZED COMPOSITE ALLOTRANSPLANTATION: A SYSTEMATIC REVIEW

Abstract Introduction Vascularised composite allotransplantation (VCA) permits like-for-like reconstruction following extensive soft tissue injuries. The initial management of extensive soft tissue injury can lead to the development of anti-HLA antibodies through injury, transfusion and cadaveric grafting. The role of antibody-mediated rejection, donor-specific antibodies and graft rejection in the context of VCA remains unclear. This systematic review aimed to determine whether pre-operative management strategies influence immunological outcome following VCA. Method A systematic review of MEDLINE, EMBASE and CINAHL using a PRISMA-compliant methodology up to February 2019 was conducted. Pre-operative, procedural and long-term outcome data were collected and recorded for all VCA recipients on an individual patient basis. Result The search revealed 3,847 records of which 114 met inclusion criteria and reported clinical data related to 100 patients who underwent 129 VCA transplants. Trauma (50%) and burns (15%) were the most frequent indications for VCA. Of all 114 studies, only one reported acute resuscitative management. Fifteen patients (14.7%) were sensitized prior to reconstructive transplantation with an 80% incidence of acute rejection in the first post-operative year. Seven patients demonstrated graft vasculopathy, only one of whom had demonstrated panel reactive antibodies. Conclusion Currently employed acute management strategies predispose to the development of anti-HLA antibodies, adding to the already complex immunological challenge of VCA. Early appropriate care is warranted in patients with extensive soft tissue loss where the resuscitative needs should be balanced against strategies to mitigate the immunological burden, particularly as reconstructive transplantation becomes a feasible option for future soft tissue coverage. Take-home message Acute resuscitative management may sensitise potential transplant recipients following major soft tissue injury. Early appropriate care is warranted.

Characteristics and Sensitization Risk Factors in Kidney Transplant Wait List Candidates: Panel Reactive Antibodies Status Is Crucial for Successful Kidney Allocation Systems in Turkey.

Kidney transplant is the treatment of choice for end-stage renal disease. Because of the insufficient supply of donor organs for transplant, the number of patients on the transplant wait list is increasing. We analyzed demographic and clinical factors including sensitization status of patients on the kidney transplant wait list in our center. Patients on the kidney transplant wait list at Ankara University School of Medicine by July 2018 were evaluated. Data on demographics, comorbidities, treatment characteristics, and immunologic properties were collected. The study included 528 kidney transplant candidates whose mean time on the deceased donor organ wait list was 57 ± 47 months. Enlisted patients were aged 53 ± 13 years, and 95% of them were on dialysis. Dialysis vintage was longer and percentage of patients who had anti-HLA antibodies was higher in women than men (P = .004 and P < .001, respectively). Levels for median fluorescence intensity were higher in women compared with men (class I, P < .001; and class II, P = .011). Transfusion (P < .001), pregnancy (P = .001), transplant (P < .001), longer dialysis vintage (P = .021), and longer time on wait list (P = .001) were associated with anti-HLA antibody positivity. Multiple regression analysis revealed that a history of transplant and blood transfusion were independent risk factors of a positive panel reactive antibodies. In our kidney transplant candidates on the wait list, sensitization by transplant has a significant impact on development of anti-HLA antibodies. Updates of the organ allocation system to consider sensitized candidates and strategies to expand the deceased donor organ pool and donation rates are needed to increase the rate of deceased donor kidney transplant in Turkey.

P1739IMMUNOSUPPRESSION WITH CALCINEURIN INHIBITOR AFTER RENAL TRANSPLANT FAILURE PREVENTS ALLOSENSITIZATION

Abstract Background and Aims Retransplantation is an important option to consider in patients who return to dialysis after graft failure since it reduces mortality. HLA allosensitization hinders retransplantation, and immunosuppression withdrawal after graft failure seems to favor sensitization. There are no established protocols on the immunosuppressive treatment that should be maintained after transplant failure in order to reduce the development of anti-HLA antibodies. The aim of the study is to evaluate the effect of immunosuppression withdrawal on the development of anti-HLA antibodies after graft loss. Method A retrospective analysis including 77 patients who lost their first renal graft between 1/1/2006-12/31/2015 was performed. 22 patients with preemptive second kidney transplant were included. Maintenance immunosuppression was collected in months 1, 3 and 6 after graft failure. Patients were divided into two groups according to the presence or not of calcineurin inhibitor (CNI) as maintenance treatment. Two sera were analyzed per patient, one immediately prior to graft loss and another one after graft failure (Luminex®, Single Antigen). In patients in whom transplantectomy was performed, the selected serum after transplant failure was already after graft nephrectomy. PRA was calculated (cPRA) in each serum and the development of de novo donor-specific antibodies (dnDSA) was evaluated. Results Selected sera were extracted 1.0 month before graft failure (interquartile range 0.3-2.0) and 7.6 months after transplant failure (interquartile range 6.0-12.2). By multivariate logistic regression analysis, graft nephrectomy was an independent risk factor for cPRA&amp;gt;75% after transplant failure (OR 4.9, CI 95% 1.0-22.2, p=0.038). Similarly, the absence of CNI at 6 months after graft failure was significantly related to cPRA&amp;gt;75% in the multivariate analysis (OR 4.8, CI 95% 1.5-15.0, p=0.006). It was possible to analyze dnDSA formation in 73 patients. The absence of CNI at 6 months after graft loss was an independent risk factor for dnDSA development (OR 23.2, CI 95% 5.3-100.6, p &amp;lt;0.001). There were no differences in the management of other immunosuppressive drugs. Conclusion The absence of maintenance treatment with CNI at the sixth month after graft loss is a risk factor for sensitization. Therefore, immunosuppressive maintenance treatment based on CNI after transplant failure should be considered, since it seems to prevent HLA allosensitization.

Factors influencing transfusion‐associated HLA sensitization in patients bridged to heart transplantation using ventricular assist device

Bridging heart failure patients with mechanical ventricular assist devices (VAD) enables access to transplantation. However, VAD is associated with increased risk for anti-HLA antibodies associated with rejection of subsequent allografts. Factors determining alloantibody formation in these patients remain undefined. We performed a single-center retrospective cohort study of 164 patients undergoing heart transplantation from 2014 to 2017. Medical records including use of VAD, transfused blood products, anti-HLA antibody testing, crossmatch, and time to transplant were evaluated. Patients received an average of 13.8 red blood cell and 1.9 single-donor platelet units associated with VAD. There was a 28.7% increase in the incidence of anti-HLA antibodies after VAD. Development of anti-HLA antibodies did not correlate with volume or type of blood products, but with pre-VAD HLA sensitization status; relative risk of new alloantibodies in patients with pre-VAD antibodies was 3.5-fold higher than those without prior antibodies (P=.008). Development of new anti-HLA antibodies was associated with an increased time to transplant (169 vs 330days, P=.013). Our findings indicate that the presence of anti-HLA antibodies pre-VAD was the most significant risk factor for developing additional antibodies post-VAD, suggesting that a subset of patients may be predisposed to alloantibody formation.

P6314Left- versus Bi-Ventricular Assist Device-mediated anti-HLA alloantibody induction in bridge-to-transplantation patients

Abstract Background Presence of anti-Human Leukocyte Antigen (anti-HLA) alloantibodies (allosensitization) in a heart transplantation candidate impedes the chance of finding a compatible transplant. Left Ventricular Assist Devices (LVADs) have been shown to induce allosensitization. Purpose The purpose of this study is to characterize anti-HLA allosensitization in adult patients receiving left (LVAD) versus biventricular- (BiVAD) assist devices as bridge to transplantation (BTT). Methods This study retrospectively assessed anti-HLA antibody induction in all adult patients who have received either LVAD or BiVAD as BTT at our institution. Anti-HLA alloantibody screening was performed before, and at multiple time-points after VAD implantation. Anti-HLA antibody detection was performed with a cytotoxic panel-reactive antibody (PRA) method until 2003, enzyme-linked immunoassay (ELISA) method from 2003 to 2005 and SAB assays on the Luminex platform from 2005 to 2017. Sensitization was defined either as PRA &gt;10%, or as peak anti-HLA antibody mean fluorescence intensity (MFI) values of more than 1000. Baseline characteristics and sensitization in the two patient groups were evaluated using descriptive statistics. Results Between 2003 and 2018, 154 patients were placed on VAD support at our institution as BTT. Sensitization data were available for 130 patients. Fifty five (36.6%) patients were supported with an LVAD (median age, 48 years, 26% female) and 95 (63.4%) with a BiVAD (median age, 45 years, 28% female). Twenty-five (45.4%) of the LVAD and 49 (51.2%) of the BiVAD patients were eventually transplanted (p=0.47) with an average time to transplantation 588 and 562 days respectively. Fifteen (27.2%) LVAD and 35 (36.8%) BiVAD patients died before transplantation (p=0.23) with an average time on VAD support before death 269 and 302 days respectively. Evidence of sensitization pre-VAD was found in 17.1% of the LVAD and 12.5% of the BiVAD patients (p=0.53); these percentages rose to 40.0% (p=0.001) and 43.7% (p=0.0001) respectively at 2 to 12 months post-VAD implantation. However, the post-VAD allosensitization status was not statistically different between the LVAD and the BiVAD group. Among the 25 LVAD patients who were transplanted 7 (30.4%) were sensitized immediately before transplantation, compared to 22 (46.8%) out of 49 BiVAD patients (p=0.16). Conclusion Both LVADs and BiVADs are a factor of de novo anti-HLA antibody development in adult patients after implantation. Sensitization pattern does not seem to differ between LVAD and BiVAD patients. Additionally, patients supported by LVAD or BiVAD have similar chances of finding a suitable donor heart.

P124 De novo development of anti-HLA antibodies in lung transplant recipients with preexisting DSA is related to pirche-II score

P124 De novo development of anti-HLA antibodies in lung transplant recipients with preexisting DSA is related to pirche-II score

Tacrolimus Variability: A Cause of Donor-Specific Anti-HLA Antibody Formation in Children.

The most important determinant of long-term graft survival in renal transplantation is adequate immunosuppression. Inadequate immunosuppression may lead to graft loss due to the presence of anti-HLA antibody. The aim of this study was to investigate the effect of variability in tacrolimus blood concentration on anti-HLA antibody development in pediatric recipients of living-donor renal transplants. Pediatric recipients of living-donor renal transplants were retrospectively evaluated. Patients with a minimum of two years of follow-up who were administered tacrolimus were included in the study. Patients who had pretransplant anti-HLA antibody were excluded. Variability in tacrolimus blood concentration was assessed using the coefficient of variation ("tacrolimus CV") method. Tacrolimus CV was calculated separately for the first 6months post-transplant, between 6 and 12months post-transplant, and from the end of the first year post-transplant to the last follow-up. We constructed receiver operating characteristic (ROC) curves of the tacrolimus CV for each group to find the best cutoff value. A total of 67 patients (including 48 males; 72%) with a mean age of 15.16 ± 4.43years were included in the study. Anti-HLA antibody positivity was detected in 12 patients (18%). More than three HLA mismatches and the presence of acute cellular rejection correlated with the development of anti-HLA antibody (p = 0.056, 0.009). Tacrolimus CVs for the three periods were 0.37 ± 0.11, 0.31 ± 0.18, and 0.35 ± 0.12, respectively. The cutoff value of tacrolimus CV for anti-HLA antibody development was calculated as 0.32 with a sensitivity of 90.91% and specificity of 50.94% [AUC (area under the curve) 0.713, p = 0.023]. During the second 6-month period and after a year post-transplant, the percentage of patients with tacrolimus CV >0.32 was significantly higher in the anti-HLA antibody positive group than in the antibody negative group (67% vs 31%, p = 0.027; 83% vs 47%, p = 0.033). The eGFR (estimated glomerular filtration rate) was similar for the anti-HLA antibody negative and positive groups (78.72 ± 2.86 vs 77.45 ± 8.08, p > 0.05). High tacrolimus concentration variability appears to be associated with anti-HLAantibody formation in pediatric recipients of living-donor renal transplants.

Pregnancy and donor-specific HLA-antibody-mediated rejection after liver transplantation: “Liaisons dangereuses”?

BackgroundRisk factors for the development of anti-HLA antibodies include blood transfusion, organ transplantation, and pregnancy. Humoral rejection, mediated by donor-specific anti-HLA antibodies (DSA), has been studied in all kind of solid organ transplantations, and several studies have suggested that post-liver transplantation (LT) DSA may play a role in acute and chronic rejection. ObjectiveThe aim of the present study was to assess the impact of pregnancy on the occurrence of DSA and the impact of DSA in a large population of young female LT recipients. MethodsThis single center retrospective study included all female patients who underwent a first LT between January 1990 and December 2010 and who were of childbearing age during post-LT follow-up (i.e. 18 to 40 years old). ResultsThe study population consisted in 73 patients, and the mean age at LT was 20.9 years (0.6–39.9); 32 patients were transplanted during childhood. The global incidence of de novo DSA was 42.5% (31/73), after a median delay of 15.5 years (1–25) of follow-up after LT. Most de novo DSA were anti-class II alone (90.3%), and included anti-DQ for 80.6%. From the 73 patients, 33 presented at least one pregnancy after LT (45.2%) and before DSA screening. Multivariate analysis disclosed that history of pregnancy (OR = 6.37; 95%CI, 2.17–18.63, p = 0.001) and younger age at LT (OR = 0.96; 95%CI:0.92–0.99, p = 0.033) were significantly associated with de novo DSA. Among the 31 patients who had de novo DSA, the diagnosis of antibody-mediated rejection was made in 8 patients (25.8%), after a median delay of 74 months after LT; 6/8 (75.0%) had history of pregnancy. During follow-up, 3 of these 8 patients lost their liver graft and died. ConclusionThe results of the present study suggest that close monitoring of DSA in young women with history of pregnancy should be recommended regarding the risk of DSA-mediated rejection.

Anti-HLA Antibody: The Role of Epitopes in Organ Transplantation.

Recent developments have been achieved for better matching in solid-organ transplantation by epitope matching. HLA matching remains a standard immunologic strategy to determine organ compatibility for recipients. Advancements in tissue typing have introduced HLA matching at the epitope level. For this, B cells are able to recognize polymorphic amino acid configurations, which are named epitopes. However, antibody production against these epitopes may be a leading cause of rejection. Although data to support the added clinical benefit of epitope matching over traditional antigen matching are still lacking, there are at least 2 theoretical reasons for epitope matching: (1) to avoid future allosensitization with the development of anti-HLA antibodies and (2) to allow selection of a suitable allograft for highly sensitized patients through virtual crossmatch. Sensitive antibody tests with a comprehensive panel of single alleles have yielded informative, donor-specific antibody reactivity patterns that can be analyzed with a computer algorithm. This program (HLAMatchmaker) uses structurally defined eplets to describe epitopes that can react with specific antibodies. Although low mean fluorescence intensity levels by Luminex (Austin, TX, USA) assay are usually considered low risk for solid organ transplant, it could be important in posttransplant humoral rejection. Thus, specific shared eplets should always be investigated with respect to previous transplant mismatches. Epitopes are present on a single HLA (private epitope) or shared by multiple antigens (public epitope). The phenomenon of crossreactivity in HLA testing, often explained as crossreactive groups of antigens with antibody, can be clearly explained now by public epitopes, an antibody targeting an epitope that shows positive reaction with all antigens sharing the epitope. A better understanding of the immunogenicity and structural characteristics of HLA epitopes will guide us to consider epitope matching as an important parameter for donor selection in kidney transplant in the near future.

Antibody response to HBV vaccination on dialysis does not correlate with the development of deNovo anti-HLA antibodies after renal transplantation

BackgroundResponse to Hepatitis B virus (HBV) vaccination can be diminished in some (50–80%) but not all dialysis patients. We hypothesized, that the response to vaccination on dialysis may correlate with the development of anti-HLA antibodies after renal transplantation and might therefore be a valuable parameter to predict alloresponses. MethodsThe response to HBV vaccination on dialysis and the development of deNovo anti-HLA antibodies post-transplant was analyzed in 188 non-immunized renal transplant recipients. The response to HBV vaccination was evaluated by measuring the anti-HBs titer at time of transplantation. Anti-HLA antibodies post-transplant were monitored by serial measurements by means of Luminex. Acute rejection episodes, graft loss and renal dysfunction were assessed within a median follow-up of 5.5years. ResultsOne hundred and forty-one patients (75%) exhibited an adequate immune response to HBV vaccination on dialysis. Vaccine responder (R) and none responder (NR) did not differ with respect to age, gender and BMI, while R spend significantly more time on dialysis before transplantation (4.58±3.35 vs 3.23±2.55 years, p=0.033). More NR developed deNovo anti-HLA antibodies (27.7 vs 22.7%, p=0.554) and donor-specific anti-HLA antibodies (23.4 vs 14.2%, p=0.173) in comparison to R. Accordingly, the number of acute rejections was higher in NR as compared to R (36.1 vs 24.1%, p=0.130) while graft survival was similar in both groups. ConclusionContrary to our hypothesis antibody response to HBV vaccination on dialysis does not predict the development of anti-HLA antibodies post transplant.

Clinical and immunological relevance of antibodies in solid organ transplantation.

The two important issues affecting recipients of solid organ transplants and of importance to immunologists are (i) sensitization of the recipient to HLA antigens and the resultant humoral immune response leading to the development of anti-HLA antibodies; and ii) development of robust assays for early detection of humoral rejection post-transplant. Evidence from several studies clearly indicates that presence of circulating anti-HLA antibodies especially donor specific leads to early graft loss and high titres of DSA may even lead to hyperacute or accelerated acute rejection. Long-term graft survival too is adversely affected by the presence of either pre- or post-transplant DSA. HLA matching status of the recipient - donor pair - is an important factor in the modulation of humoral response following transplantation and in a way affects de novo development of DSA. Data collected over the past decade clearly indicate significantly lower level of DSAs in optimally matched donor-recipient pairs. HLA mismatches especially those on HLA-DR and HLA-C loci have wider implications on post-transplant graft survival. The presence of circulating anti-HLA antibodies leads to endothelial damage in the newly grafted organ through complement dependent or independent pathways. Although detection of C4d deposition in renal biopsies serves as an important indicator of humoral rejection, its absence does not preclude the presence of DSAs and humoral rejection, and hence, it cannot be relied upon in every case. The emergence of epitope-based screening for anti-HLA antibodies on Luminex platform with high degree of sensitivity has revolutionized the screening for anti-HLA antibodies and DSAs. Studies indicate that humoral response to non-HLA antigens might also have a detrimental effect on allograft survival. High titres of such circulating antibodies may even lead to hyperacute rejection. Pre-emptive testing of solid organ recipients, especially kidney transplant recipients for anti-HLA and non-HLA antibodies and aggressive post-transplant monitoring of allograft function to detect DSAs using Luminex-based tests, is highly recommended.