Clinical relevance of anti-HLA antibodies detected by flow-cytometry bead-based assays--single-center experience

The correlation of results of panel reactive antibody, identification, and single antigen beads in detection of anti-HLA antibodies: Istanbul Faculty of Medicine, tissue typing laboratory experience

BACKGROUND

We have performed a retrospective analysis of anti-HLA class I MHC and class II MHC antibodies measured using a single antigen bead (SAB) assay and a panel reactive antibody (PRA) assay.

MATERIAL AND METHODS

A group of 256 patients with end-stage renal disease (ESRD) was tested for anti-HLA antibodies in the tissue typing laboratory between 2017 and 2020. In the cohort, the serum samples of patients waiting for transplantation were tested. Both the PRA and SAB tests of these patients were analyzed using the Luminex (Immucor) method. The threshold of positivity was accepted as median fluorescence intensities (MFI) ≥1000 for PRA screening and MFI ≥750 for SAB screening.

RESULTS

Overall, antibodies to HLA antigens were detected in 202 (78.9%) out of 256 patients in the PRA study. Antibodies against both class I/II antigens were detected only in 15.6% of these patients, whereas antibodies against only against class I HLA in 31.3% and only against class II HLA in 32.0%. By comparison, the SAB study found that 66.8% of patients were positive for HLA antigens. Furthermore, donor-specific antibodies (DSA) were detected in 52.0% of PRA-positive patients and 52.6% of SAB-positive patients. It was shown that 168 patients (83.2%) out of 202 PRA-positive patients were found to be SAB-positive. In addition, 51 patients negative in the SAB assay (94.4%) were also negative in the PRA assay. Statistical analysis established a significant correlation between the PRA and SAB positivity (p > 0.001). It was also shown that MFI ≥3000 PRA positivity for class I HLA antigens (p = 0.049) and MFI ≥5000 PRA positivity for class II antigens (p < 0.001) correlated with the SAB positivity in patients.

CONCLUSION

Our results showed the importance of both PRA and SAB assays to define the status of sensitization in patients.

Correlation of Luminex-Based Single Antigen Based Results With Complement-Dependent Cytotoxicity Crossmatch and Flow Cytometry Crossmatch Results: A Single-Center Experience From Istanbul

BACKGROUND

This study aimed to retrospectively investigate the correlation of mean Class I donor-specific antibody (DSA) intensity values detected in Luminex-based techniques with the results of complement-dependent cytotoxicity crossmatch (CDC-XM) and flow cytometry crossmatch (FC-XM) results.

METHODS

A total of 335 patients with kidney failure and their living donors whose CDC-XM, FC-XM, and single antigen based (SAB) tests were studied between 2018 and 2020 for transplant preparation from living donor candidates were included in the study. Patients were divided into 4 groups according to their mean fluorescence intensity (MFI) values of SAB assay.

RESULTS

Anti-HLA antibodies (class I and/or class II) were detected using SAB in 91.6% patients included in the study (MFI >1000). Class I DSA was positive in 34.8% of patients with anti-HLA antibodies. When CDC-XM and FC-XM results were evaluated in the 4 groups separated according to MFI values, 3 patients with DSA MFI <1000 had negative CDC-XM and T-B-FC-XM results. Of 32 patients with DSA-MFI between 1000 and 3000, 93.75% (n = 30) had T-B-FC-XM or CDC-XM-negative results, and 6.25% (n = 2) had B-FC-XM-positive results. The CDC-XM, T, and B-FC-XM were negative in all 17 patients with DSA-MFI between 3000 and 5000. Our results showed that MFI >5834 DSA values were significantly correlated with positive T-FC-XM (P < .001), and MFI >6016 values were significantly correlated with positive CDC-XM (P = .002). In addition, MFI values >5000 were associated with both CDC-XM and FC-XM in our study.

CONCLUSIONS

The MFI values >5000 correlated with both CDC-XM and FC-XM.

Dynamic Behaviour of Donor Specific Antibodies in the Early Period Following HLA Incompatible Kidney Transplantation

In HLA-incompatible kidney transplantation, monitoring donor-specific antibodies (DSA) plays a crucial role in providing appropriate treatment and increases kidney survival times. This work aimed to determine if early post-transplant DSA dynamics inform graft outcome over and above other predictive factors. Eighty-eight cases were classified by unsupervised machine learning into five distinct DSA response groups: no response, fast modulation, slow modulation, rise to sustained and sustained. Fast modulation dynamics gave an 80% rate for early acute rejection, whereas the sustained group was associated with the lowest rejection rates (19%). In complete contrast, the five-year graft failure was lowest in the modulation groups (4–7%) and highest in the sustained groups (25–31%). Multivariable analysis showed that a higher pre-treatment DSA level, male gender and absence of early acute rejection were strongly associated with a sustained DSA response. The modulation group had excellent five-year outcomes despite higher rates of early rejection episodes. This work further develops an understanding of post-transplant DSA dynamics and their influence on graft survival following HLA-incompatible kidney transplantation.

C3d-positive donor-specific antibodies have a role in pretransplant risk stratification of cross-match-positive HLA-incompatible renal transplantation: United Kingdom multicentre study

Anti-HLA-antibody characteristics aid to risk-stratify patients and improve long-term renal graft outcomes. Complement activation by donor-specific antibody (DSA) is an important characteristic that may determine renal allograft outcome. There is heterogeneity in graft outcomes within the moderate to high immunological risk cases (cross-match-positive). We explored the role of C3d-positive DSAs in sub-stratification of cross-match-positive cases and relate to the graft outcomes. We investigated 139 cross-match-positive living-donor renal transplant recipients from four transplant centres in the United Kingdom. C3d assay was performed on serum samples obtained at pretreatment (predesensitization) and Day 14 post-transplant. C3d-positive DSAs were found in 52 (37%) patients at pretreatment and in 37 (27%) patients at Day 14 post-transplant. Median follow-up of patients was 48 months (IQR 20.47-77.57). In the multivariable analysis, pretreatment C3d-positive DSA was independently associated with reduced overall graft survival, the hazard ratio of 3.29 (95% CI 1.37-7.86). The relative risk of death-censored five-year graft failure was 2.83 (95% CI 1.56-5.13). Patients with both pretreatment and Day 14 C3d-positive DSAs had the worst five-year graft survival at 45.5% compared with 87.2% in both pretreatment and Day 14 C3d-negative DSA patients with the relative risk of death-censored five-year graft failure was 4.26 (95% CI 1.79, 10.09). In this multicentre study, we have demonstrated for the first time the utility of C3d analysis as a distinctive biomarker to sub-stratify the risk of poor graft outcome in cross-match-positive living-donor renal transplantation.

Role of de novo DQ donor-specific antibody in antibody-mediated rejection in renal transplant recipient: A case study

The human leukocyte antigen (HLA) matching plays an important role in determining the clinical outcome of renal transplantation. The development of donor specific antibodies (DSA) against HLA is associated with antibody mediated allograft tissue injury, poor outcome and rejection. The DQ-DSA develops in a denovo pattern and its unfavorable impact on renal transplantation has not yet been widely reported. We investigated the clinical significance of DQ-DSA in a patient diagnosed with hypertension, CKD stage V on maintenance hemodialysis (MHD) for second renal transplant. The histocompatibility workup before the first transplant included low resolution HLA-A, B, DR typing of both patient and donor. HLA type of the patient was HLA-A*29, 68, HLAB*44, 44, DRB1*07, 11. HLA type of the donor was HLA-A*03, 68, HLA-B*39, 44, DRB1*07, 10 with a 3/6 match. The HLA antibody screen and complement dependent cytotoxicity crossmatch (CDC) were found to be negative. No therapeutic plasma exchanges (TPE) were done during stay and post-transplant the patient was on triple immunosuppressant therapy. After four years the patient was diagnosed with recurrent membranoproliferative glomerulonephritis and second renal transplant was planned, therefore, histocompatibility workup was initiated. HLA antibody screen was found to be positive for HLA class II. Initially only HLA-A, B, DR typing was performed and that too only low resolution, further, high resolution HLA typing was done for HLA-DR and DQ to rule out if these antibodies are de-novo DQ/DR DSA. We analyzed that the patient had developed de-novo DSA against HLA-DRB1* 10:01 (DR10), MFI-2374 and DQB1*06:01 (DQ6), MFI-15315. This study suggests the role of DQ antibodies in determining the graft survival and to highlight the need of HLA DQ typing as a routine of the diagnostic work-up in a solid organ transplant.

Frequency of Human Leukocyte Antigens and Donor Specific Antibodies in Long-Term Living Donor Kidney Transplantation

PURPOSE

HLA antibodies have been shown to be associated with late graft loss. In this study, we defined the incidence and profiles of anti-HLA antibodies and their impact on graft outcome in long-term kidney recipients.

METHODS

The sera of 118 kidney transplant recipients were screened for anti-HLA antibody presence. The antigen specificity of the detected HLA class I and class II antibodies was identified using a Luminex assay (Luminex Corp, Austin, TX, United States). Presence of donor specific antibodies (DSA) was examined in individuals with anti-HLA antibodies using the Luminex method.

RESULTS

Anti-HLA class I and/or class II antibodies were detected in serum of 16.1% of the kidney transplant patients. The antibodies were directed against HLA class I antigens in 4 patients (21.1%), HLA class II antigens in 9 patients (47.4%), and both class I and class II antigens in 6 patients (31.6%). The overall prevalence of DSA was 10.2%. Anti-HLA antibodies were significantly associated with higher rate of cyclosporine use. Presence of DSA was associated with a lower rate of tacrolimus use, a higher rate of cyclosporine use, and lower donor age. Presence of anti-HLA antibodies was associated with higher acute cellular rejection and higher chronic active humoral rejection rates. Presence of DSA was associated with chronic active humoral rejection.

CONCLUSION

The presence of either HLA antibodies or DSA significantly correlated with lower graft survival, poor transplant function, and proteinuria.

Donor-specific Antibody Surveillance and Graft Outcomes in Pediatric Kidney Transplant Recipients

BACKGROUND

The development of de novo donor-specific antibodies (dnDSA) has been associated with rejection and graft loss in kidney transplantation, and DSA screening is now recommended in all kidney transplant recipients. However, the clinical significance of dnDSA detected by screening patients with a stable creatinine remains unclear.

METHODS

One hundred three patients younger than 18years receiving a first, kidney alone transplant between December 1, 2007, and December 31, 2013, underwent DSA screening every 3months for 2years posttransplant, with additional testing as clinically indicated. No treatment was given for DSAs in the absence of biopsy-proven rejection.

RESULTS

Twenty (19%) patients had dnDSA first detected on a screening test, and 13 (13%) patients had dnDSA first detected on a for-cause test. Mean follow-up time posttransplant was 4.4years. Screening-detected dnDSA was associated with an increased risk of rejection within 3years, microvascular inflammation, and C4d staining on a 2-year protocol biopsy. In a Cox proportional hazards regression, screening-detected dnDSA was not associated with time to 30% decline in estimated glomerular filtration rate (adjusted hazard ratio, 0.88; 95% confidence interval [CI], 0.30-2.00; P=0.598) or graft loss. dnDSA first detected on for-cause testing was associated with a 2.8 times increased risk of decline in graft function (95% CI, 1.08-7.27; P=0.034) and a 7.34 times increased risk of graft loss (95% CI, 1.37-39.23 P=0.020) compared with those who did not develop dnDSA.

CONCLUSIONS

The clinical setting in which dnDSA is first detected impacts the association between dnDSA and graft function. Further research is needed to clarify the role of dnDSA screening in pediatric kidney transplantation.

Flow Cytometry Panel-Reactive Antibody Screening of Anti-HLA Antibodies in the Waiting List Significantly Reduces the Occurrence of Acute Rejection After Kidney Transplantation

INTRODUCTION

The presence of preformed HLA-reactive antibodies in recipient serum before transplantation has long been recognized as a prominent risk factor for a generally worse graft outcome. Screening and identification of HLA antibodies can be used to stratify patients into high- and low-risk categories.

MATERIALS AND METHODS

We determined patients' anti-HLA antibodies using flow cytometry panel-reactive antibody (flowPRA) screening, specifying more than 5% after positive screening. According to the results of the screening test, patients were allocated to the induction immunosuppressive protocol according to the actual immunologic risk.

RESULTS

In the group of 78 patients, screening with flowPRA of anti-HLA antibodies was done twice a year. Patients were divided into 2 groups of immunologic risk (low or medium), and we chose the induction immunosuppressive protocol according to the risk. Stratification of the risk was correct, because the only predictor for development of acute rejection in the monitored period of 12 months was delayed graft function (odds ratio 33.2501; 95% confidence interval 10.0095-110.4508; P < .0001). The occurrence of acute rejection upon implementing the screening was reduced in our transplant center from 44% to 19% (P < .0001). No difference was recorded in the 12-month survival of grafts and patients according to the applied induction immunosuppressive protocol.

CONCLUSION

We confirmed significantly reduced occurrence of acute rejection in the follow-up period of 12 months by using individualized induction according to flowPRA screening of anti-HLA antibodies. FlowPRA screening represents a suitable alternative for screening and specification of anti-HLA antibodies in case the Luminex methodology is unavailable.

Association Between HLA Antibodies and Different Sensitization Events in Renal Transplant Candidates

BACKGROUND

Human leukocyte antigen (HLA) allo-immunization is caused by various events such as blood transfusions, pregnancies, or organ transplantations, which can lead to sensitization. In this retrospective study, we evaluated different sensitization models and their effects on panel-reactive antibody (PRA) profiles of renal transplantation candidates.

METHODS

Anti-HLA class I/II antibody screening tests were performed in 906 renal transplantation candidates with the use of a microbead-based assay (Luminex).

RESULTS

Two hundred ninety-seven (32.8%) of the patients were determined as positive in terms of PRA, and 609 (67.2%) were negative. Sensitized and non-sensitized patients were compared separately in terms of each sensitization type. The anti-HLA class I, II, and I+II positivity rates in patients sensitized only by blood transfusion were 13.1%, 6.3%, and 14.1%, the rates with pregnancy sensitization were 35.5%, 29%, and 45.2%, and rates with previous transplantation sensitization were 15.6%, 34.4%, and 38.9%, respectively. Prevalence of PRA positivity was significantly higher in patients with previous pregnancy than with transplantation and transfusion (odds ratio, 1.003; 95% confidence interval, 0.441-2.281; P = .031). The risk of developing HLA class I antibodies was higher in pregnancies (P < .001), and the risk of developing anti-HLA class II antibodies was higher in patients who had undergone a previous transplantation (P < .001). The rate of developing HLA-B antibodies in patients sensitized by pregnancy were significantly higher compared with sensitization after transfusion (P = .015), as was the rate of developing HLA-DQ antibodies in patients sensitized by previous transplantation compared with sensitization through pregnancy (P = .042).

CONCLUSIONS

In patients who are waiting for kidney transplantation, sensitization by pregnancy and transplantation have a significant impact on development of HLA class I and class II antibodies.

Corrected Panel-Reactive Antibody Positivity Rates for Hypersensitized Patients in Turkish Population With Calculated Panel-Reactive Antibody Software

INTRODUCTION

High rates of panel-reactive antibody (PRA) may decrease the chance of kidney transplantation and may result in long waiting periods before transplantation. The calculated PRA (cPRA) is performed based on unacceptable HLA antigens. These antigens are identified by a program that was created based on the antibodies that developed against the HLA antigens circulating in serum and on the risk of binding of these antibodies to antigens. The antigen profile of the population and antigen frequencies can be measured, and more realistic cPRA positivity rates may be obtained using this method.

MATERIALS AND METHODS

We developed a program based on the HLA antigens of 494 blood donors in 2 European Federation for Immunogenetics-accredited Tissue Typing Laboratories in Turkey. Next-generation sequencing-based tissue typing (HLA-A, -B, -C, -DR, -DQ, 4 digits) of the samples was performed. The PRA screening test was performed on 380 patients who were waiting for organ transplant from a cadaver in Istanbul Faculty of Medicine. The single antigen bead assay testing was performed to identify the antibody profiles on 48 hypersensitized patients.

RESULTS

The PRA testing results using the current methods were 44.6% ± 18.5%, and the cPRA rate was 86.2% ± 5.1%. The mean PRA positivity of the sensitized patients using the current methods was 44.6%; however, the rate was 86.2% using the cPRA.

DISCUSSION

cPRA shows the rate of the rejected donors according to all unacceptable antigens. The need for a list of unacceptable antigens in place of the PRA positivity rate is a real change in the sensitization-dependent calculation as cPRA positivity rate.

CONCLUSION

In principal, implementation of cPRA will encourage many centers and laboratories to adopt a standard measurement of sensitization in Turkey. It will increase the chances of better donor match, particularly for hypersensitized patients, by the creation of an unacceptable mismatch program using cPRA software.

Donor-specific HLA antibodies and graft function in kidney-transplanted children - the Vienna cohort

In the pediatric population, little is known on de novo DSA development, its impact on graft function, and association with suboptimal IS. We assessed the prevalence of de novo DSA in the Vienna cohort of 40 renal transplanted children and adolescents and prospectively followed its association with clinical parameters, graft function, and proteinuria for one yr. At the cross-sectional analysis (median post-transplant time of five yr), 17% of the patients had developed de novo DSA. All HLA-Ab were anti-HLA class II antibodies and persisted in 85% of the cases until the follow-up screening performed within one yr. Basic clinical and laboratory parameters did not differ between DSA-negative and DSA-positive patients at the time of HLA-Ab screening. Suboptimal IS due to reduced medication or non-adherence could not be proven in DSA-positive patients. The changes in eGFR did not differ during the prospective study period, but there was a significantly higher proteinuria in the DSA-positive patients during the follow-up. Our data demonstrate an overall prevalence of 17% of de novo DSA in a pediatric renal transplant cohort. During 12 months of prospective follow-up time, we could demonstrate a significant impact of de novo DSA presence on proteinuria.

HLA epitope based matching for transplantation

As important risk factors for transplant rejection and failure, HLA antibodies are now recognized as being specific for epitopes which can be defined structurally with amino acid differences between HLA alleles. Donor-recipient compatibility should therefore be assessed at the epitope rather than the antigen level. HLAMatchmaker is a computer algorithm that considers each HLA antigen as a series of small configurations of polymorphic residues referred to as eplets as essential components of HLA epitopes. It includes epitopes on antigens encoded by all HLA-A, B, C, DR, DQ and DP loci as well as MICA. HLA epitopes have two characteristics namely antigenicity, i.e. the reactivity with antibody and immunogenicity, i.e. the ability of eliciting an antibody response. This article addresses the relevance of determining epitope-specificities of HLA antibodies, the effect of epitope structure on technique-dependent antibody reactivity and the identification of acceptable mismatches for sensitized patients considered for transplantation. Permissible mismatching for non-sensitized patients aimed to prevent or reduce HLA antibody responses could consider epitope loads of mismatched antigens and the recently developed nonself-self paradigm of epitope immunogenicity.

Incidence and clinical significance of de novo donor specific antibodies after kidney transplantation

Kidney transplantation has evolved over more than half a century and remarkable progress has been made in patient and graft outcomes. Despite these advances, chronic allograft dysfunction remains a major problem. Among other reasons, de novo formation of antibodies against donor human leukocyte antigens has been recognized as one of the major risk factors for reduced allograft survival. The type of treatment in the presence of donor specific antibodies (DSA) posttransplantation is largely related to the clinical syndrome the patient presents with at the time of detection. There is no consensus regarding the treatment of stable renal transplant recipients with circulating de novo DSA. On the contrast, in acute or chronic allograft dysfunction transplant centers use various protocols in order to reduce the amount of circulating DSA and achieve long-term graft survival. These protocols include removal of the antibodies by plasmapheresis, intravenous administration of immunoglobulin, or depletion of B cells with anti-CD20 monoclonal antibodies along with tacrolimus and mycophenolate mofetil. This review aims at the comprehension of the clinical correlations of de novo DSA in kidney transplant recipients, assessment of their prognostic value, and providing insights into the management of these patients.

Detection of anti-HLA antibodies in maternal blood in the second trimester to identify patients at risk of antibody-mediated maternal anti-fetal rejection and spontaneous preterm delivery

PROBLEM

Maternal anti-fetal rejection is a mechanism of disease in spontaneous preterm labor. The objective of this study was to determine whether the presence of human leukocyte antigen (HLA) panel-reactive antibodies (PRA) during the second trimester increases the risk of spontaneous preterm delivery.

METHODS OF STUDY

This longitudinal case-control study included pregnant women with spontaneous preterm deliveries (n = 310) and control patients with normal term pregnancies (n = 620), matched for maternal age and gravidity. Maternal plasma samples obtained at 14-16, 16-20, 20-24, and 24-28 weeks of gestation were analyzed for HLA class I and class II PRA positivity using flow cytometry. The fetal HLA genotype and maternal HLA alloantibody epitope were determined for a subset of patients with positive HLA PRA.

RESULTS

(i) Patients with spontaneous preterm delivery were more likely to exhibit HLA class I (adjusted OR = 2.54, P < 0.0001) and class II (adjusted OR = 1.98, P = 0.002) PRA positivity than those delivering at term; (ii) HLA class I PRA positivity for patients with spontaneous preterm delivery between 28 and 34 weeks (adjusted OR = 2.88; P = 0.001) and after 34 weeks of gestation (adjusted OR = 2.53; P < 0.0001) was higher than for those delivering at term; (iii) HLA class II PRA positivity for patients with spontaneous preterm delivery after 34 weeks of gestation was higher than for those delivering at term (adjusted OR = 2.04; P = 0.002); (iv) multiparous women were at a higher risk for HLA class I PRA positivity than nulliparous women (adjusted OR = 0.097, P < 0.0001 for nulliparity); (v) nulliparous women had a higher rate of HLA class I PRA positivity with advancing gestational age (P = 0.001); and (vi) 78% of women whose fetuses were genotyped had alloantibodies specific against fetal HLA class I antigens.

CONCLUSION

Pregnant women with positive HLA class I or class II PRA during the second trimester are at an increased risk of spontaneous preterm delivery due to antibody-mediated maternal anti-fetal rejection.

Detection of anti-HLA antibodies by solid-phase assay in kidney transplantation: friend or foe?

Pre-formed and de novo anti-human leukocyte antigen (HLA) antibodies induce antibody-mediated rejection and are also involved in mechanisms leading to chronic graft nephropathy. The detection of anti-HLA antibodies by solid-phase assay (SPA) has revolutionized the management of immunized patients before and after kidney transplantation. Characterized by high sensitivity and specificity, the clinical relevance of anti-HLA antibodies by SPA has to be clarified. The presence of donor-specific antibody at the epitope level, their titer, and the use of different crossmatch technologies could help to determine which of the anti-HLA antibodies are friends and which are foes in kidney transplantation. In this review, we summarize the current state of the art on this debated topic, and give clinical guidelines for the management of antibody detection pre- and post-transplantation, based on these evidences and our own clinical expertise.

Humoral alloimmunity in transplantation: relevance of HLA epitope antigenicity and immunogenicity

HLA mismatching is an important risk factor for antibody-mediated rejection and transplant failure. With the realization HLA antibodies recognize epitopes rather than antigens, it has become apparent that donor-recipient compatibility should be assessed at the epitope level. Recent developments have increased our understanding of the structural basis of HLA antigenicity, i.e., the reactivity with specific antibody and, immunogenicity, i.e., the ability to induce an antibody response. HLAMatchmaker is a computer algorithm that considers each HLA antigen as a series of small configurations of polymorphic residues referred to as eplets as essential components of HLA epitopes. This article addresses the relevance of determining epitope-specificities of HLA antibodies in the identification of acceptable mismatches for sensitized patients considered for transplantation. Permissible mismatching for non-sensitized patients aimed to prevent or reduce HLA antibody responses could consider epitope loads of mismatched antigens and the recently developed non-self–self paradigm of epitope immunogenicity.

CD4+ T cells and complement independently mediate graft ischemia in the rejection of mouse orthotopic tracheal transplants

RATIONALE

While microvascular injury is associated with chronic rejection, the cause of tissue ischemia during alloimmune injury is not yet elucidated.

OBJECTIVE

We investigated the contribution of T lymphocytes and complement to microvascular injury-associated ischemia during acute rejection of mouse tracheal transplants.

METHODS AND RESULTS

Using novel techniques to assess microvascular integrity and function, we evaluated how lymphocyte subsets and complement specifically affect microvascular perfusion and tissue oxygenation in MHC-mismatched transplants. To characterize T cell effects on microvessel loss and recovery, we transplanted functional airway grafts in the presence and absence of CD4(+) and CD8(+) T cells. To establish the contribution of complement-mediated injury to the allograft microcirculation, we transplanted C3-deficient and C3-inhibited recipients. We demonstrated that CD4(+) T cells and complement are independently sufficient to cause graft ischemia. CD8(+) T cells were required for airway neovascularization to occur following CD4-mediated rejection. Activation of antibody-dependent complement pathways mediated tissue ischemia even in the absence of cellular rejection. Complement inhibition by CR2-Crry attenuated graft hypoxia, complement/antibody deposition on vascular endothelium and promoted vascular perfusion by enhanced angiogenesis. Finally, there was a clear relationship between the burden of tissue hypoxia (ischemia×time duration) and the development of subsequent airway remodeling.

CONCLUSIONS

These studies demonstrated that CD4(+) T cells and complement operate independently to cause transplant ischemia during acute rejection and that sustained ischemia is a precursor to chronic rejection.

Flow cytometric crossmatching and panel-reactive antibodies in chronic renal failure patients

AIM

Anti-donor antibodies, denoted as "panel-reactive antibodies" (PRAs), are one of the most important factors influencing graft survival after renal transplantation. PRA is generally analyzed with enzyme-linked immunosorbent assay or flow cytometry (FC), which identify the HLA antigen specific for the preformed antibody.

PATIENTS AND METHODS

We tested 66 patients for FC crossmatch (FCXM) when they were called for cadaveric renal transplantation. Thirty of 66 patients were FCXM-positive; 36 were FCXM-negative. Among the FCXM positive crossmatches, 21 were T- and B-cell positive; seven B positive; and two T positive. The HLA antibodies in the sera of FCXM-positive patients were reanalyzed using flow-PRA.

RESULTS

We detected HLA antibodies in 28/66 sera with flow PRA. The sera of 16/21 T-/B-, FCXM-positive patients contained both class I and II anti-HLA antibodies, five had only class I anti-HLA antibodies. One out of seven B-cell FCXM-positive patients had class I and class II anti-HLA antibodies, three, class I and 1 class II anti-HLA antibodies; the other two were negative. Class I and class II HLA antibodies were observed in two T-cell FCXM-positive patients. Four of 36 patients who were FCXM-negative were flow PRA positive: one had both class I and class II HLA antibodies and three, only class I HLA antibody. The comparison of FCXM and flow PRA results was significant (P = .001).

CONCLUSION

FCXM results may be confirmed by flow PRA tests, an important method to differentiate HLA versus non-HLA antibodies.

Antibody-reactive epitope determination with HLAMatchmaker and its clinical applications

Antibodies against allogeneic human leukocyte antigen (HLA) molecules are important impediments to the success of different clinical procedures including transplantation and platelet transfusion. In these settings, characterization of the repertoire of immunogenic epitopes is important for permissible mismatch determination and the identification of acceptable mismatches for sensitized patients. HLAMatchmaker is a computer algorithm that considers small configurations of polymorphic residues referred to as eplets as essential components of HLA epitopes. This review critically elaborates the concepts underlying the HLAMatchmaker and describes the usefulness of HLAMatchmaker in the clinical setting. Recent developments have increased our understanding of structural basis of HLA antigenicity (i.e. reactivity with specific antibody) and immunogenicity (i.e. its ability to induce an antibody response).

Anti-HLA I antibodies induce VEGF production by endothelial cells, which increases proliferation and paracellular permeability

Anti-human leukocyte antigen class I (HLA I) antibodies were shown to activate several protein kinases in endothelial cells (ECs), which induces proliferation and cell survival. An important phenomenon in antibody-mediated rejection is the occurrence of interstitial edema. We investigated the effect of anti-HLA I antibodies on endothelial proliferation and permeability, as one possible underlying mechanism of edema formation. HLA I antibodies increased the permeability of cultured ECs isolated from umbilical veins. Anti-HLA I antibodies induced the production of vascular endothelial growth factor (VEGF) by ECs, which activated VEGF receptor 2 (VEGFR2) in an autocrine manner. Activated VEGFR2 led to a c-Src-dependent phosphorylation of vascular endothelial (VE)-cadherin and its degradation. Aberrant VE-cadherin expression resulted in impaired adherens junctions, which might lead to increased endothelial permeability. This effect was only observed after cross-linking of HLA I molecules by intact antibodies. Furthermore, our results suggest that increased endothelial proliferation following anti-HLA I treatment occurs via autocrine VEGFR2 activation. Our data indicate the ability of anti-HLA I to induce VEGF production in ECs. Transactivation of VEGFR2 leads to increased EC proliferation and paracellular permeability. The autocrine effect of VEGF on endothelial permeability might be an explanation for the formation of interstitial edema after transplantation.

HLAMatchmaker-defined triplet matching is not associated with better survival rates of patients with class I HLA allele mismatched hematopoietic cell transplants from unrelated donors

This report addresses the concept that permissible HLA mismatching, that is, mismatches that do not generate an allogeneic response, in hematopoietic stem cell transplantation (HCT) can be determined with structural similarity of polymorphic regions. We have applied the triplet version of a structural algorithm called HLAMatchmaker, which considers short sequences involving polymorphic amino acid residues on the molecular surface as key elements of immunogenic epitopes. The triplet matching effect was analyzed in a National Marrow Donor Program dataset consisting of 744 unrelated hematopoietic cell transplantation cases with 1 HLA-A, -B, or -C mismatch and 1690 fully HLA-A, -B, -C, -DR, or -DQ allele matched cases. In multivariate models adjusting for other significant clinical risk factors, the degree of triplet mismatching did not significantly correlate with patient survival, engraftment, or acute graft-versus-host disease (aGVHD). Other structurally based strategies should be pursued to identify permissible HLA mismatches in HCT.

Poor graft outcome in recipients with de novo donor-specific anti-HLA antibodies after living related kidney transplantation

Antibody-mediated rejection (AMR) is now widely recognized as a major problem in organ transplantation. This study was conducted to investigate the relationship between newly developing anti-HLA antibodies post-transplantation (de novo Abs) and the outcome of living related kidney transplantation (LRKT). The subjects included 87 patients who had received living donor kidney allografts at our institution. Panel reactive Ab assay (Flow-PRA) and graft biopsies were performed in all the recipients before and 6 months after the LRKT. The incidence of AMR, the donor specificity and time of appearance of the de novo Abs were retrospectively studied. Among the 87 LRKT recipients, 47 (54%) showed negative/negative (N/N) results, 15 (17%) showed positive/positive (P/P) results, 12 (14%) showed positive/negative results (P/N), and 13 (15%) showed negative/positive (N/P) results (de novo Abs) in the pre-/post-transplant Flow-PRA analysis. Among the 13 cases with de novo Abs, 5 (38%) had donor-specific Abs (DSA) and the remaining 8 (62%) had nondonor-specific Abs, as determined by LAB single antigen analysis. Eighty percent of the recipients with DSA showed evidence of AMR in the graft biopsies. The 5-year graft survival rate of the recipients with de novo Abs (N/P) was 69%, as compared with 96% in the N/N, 88% in the P/N and 93% in the P/P recipient groups (P = 0.009). LRKT recipients developing de novo Abs, especially those with DSA, showed a much higher incidence of AMR and a worse prognosis. Cautious monitoring for the appearance of anti-HLA Abs should be adopted after transplantation, even in patients without anti-HLA Abs prior to the transplantation.

Comparison of acute non-haemolytic transfusion reactions in female and male patients receiving female or male blood components

To study the relationship between antibodies detected in patients’ and/or donors’ sera and the clinical features of acute non-haemolytic transfusion reactions (ANHTRs), and to determine any gender-related difference. ANHTRs range from urticaria to transfusion-related acute lung injury (TRALI). Antibodies to human leukocyte antigen (HLA), granulocytes, platelets, and/or plasma proteins are implicated in some of the ANHTRs. A higher antibody positivity is expected for females than for males. A comparative study of ANHTRs for antibody positivity and their clinical features between females and males for both patients and donors is helpful for characterizing ANHTRs including TRALI more clearly, but such studies are few and outdated. Two hundred and twenty-three ANHTR cases reported by 45 hospitals between October 2000 and July 2005 were analysed. The patients and 196 donors of suspect blood products were screened for antibodies to HLA Class I, HLA Class II, granulocytes, and platelets. The patients were also screened for anti-plasma protein antibodies. The types and severity of ANHTR did not differ significantly between female and male patients. The frequency of the anti-HLA antibodies, but not that of the non-HLA antibodies, was significantly higher in females. Non-HLA antibodies were significantly associated with severe reactions in females. All the TRALI cases had predisposing risk factors for acute lung injury, and 60% of the cases showed anti-leucocyte antibodies. Although the anti-HLA antibodies were detected more frequently in females than males, no significant association of ANHTRs including TRALI with gender, not only for patients, but also for donors, could be shown in this study.

Retransplant candidates have donor-specific antibodies that react with structurally defined HLA-DR,DQ,DP epitopes

This report describes a detailed analysis how donor-specific HLA class II epitope mismatching affects antibody reactivity patterns in 75 solid organ transplant recipients with an in situ allograft and who were considered for retransplantation. Sera were tested for antibodies in a sensitive antigen-binding assay (Luminex) with single class II alleles. Their reactivity was analyzed with HLAMatchmaker, a structural matching algorithm that considers so-called eplets to define epitopes recognized by antibodies. Only 24% of the patients showed donor-specific anti-DRB1 antibodies and there was a significant correlation with a low number of mismatched DRB1 eplets. This low detection rate of anti-DRB1 antibodies may also be due to allograft absorption. In contrast, antibodies to DRB3/4/5 mismatches were more common. Especially, 83% of the DRB4 (DR53) mismatches resulted in detectable antibodies against an eplet uniquely found on DR53 antigens. Donor-specific DQB mismatches led to detectable anti-DQB antibodies with a frequency of 87%. Their specificity correlated with eplets uniquely found on DQ1-4. The incidence of antibodies induced by 2-digit DQA mismatches was 64% and several eplets appeared to play a dominant role. These findings suggest that both alpha and beta chains of HLA-DQ heterodimers have immunogenic epitopes that can elicit specific antibodies. About one-third of the sera had anti-DP antibodies; they reacted primarily with two DPB eplets and an allelic pair of DPA eplets. These data demonstrate that HLA class II reactive sera display distinct specificity patterns associated with structurally defined epitopes on different HLA-D alleles.