Detection of Donor-Specific Anti-HLA Class I and II Antibodies Using Antibody Monitoring System

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.

Donor-specific HLA antibodies in predicting crossmatch outcome: Comparison of three different laboratory techniques

The virtual crossmatch, which is based on single antigen bead technology, is used in the prediction of crossmatch results. However, this assay differs in sensitivity and specificity from crossmatch methods. In our study, the results of physical crossmatches, performed with three different methods, were assessed against virtual crossmatch results. The aim was to determine the potential cut-off values for donor specific antibodies (DSA) that would predict the crossmatch results obtained by different methods. The results of different crossmatch techniques were correlated with the virtual crossmatch. The receiver operating characteristic (ROC) analysis revealed the Flow cytometric crossmatch (FCXM) and Luminex crossmatch (LXM) to be the most accurate, with area under curve (AUC) values of 0.861 and 0.805, respectively. While we found that the virtual crossmatch correlated well with all the crossmatch results, FCXM produced the best results (83% of the DSA detected). LXM outperformed the other tests in terms of the accuracy in separating class II DSA.

Sensitive solid-phase detection of donor-specific antibodies as an aid highly relevant to improving allograft outcomes

Transplant recipients who have had sensitizing events such as pregnancies, blood transfusions and previous transplants often develop antibodies directed against human leukocyte antigen (HLA)-molecules of the donor tissue. These pre-formed donor-specific antibodies (DSA) represent a high risk of organ failure as a consequence of antibody-mediated hyper-acute or acute allograft rejection. As a first assay to detect DSA, the complement-dependent lymphocytotoxicity assay (CDC) was established more than 40 years ago. However, this assay is characterized by several drawbacks such as a low sensitivity and a high susceptibility to various artificial factors generally not leading to valid and reliable outcomes under several circumstances that are reviewed in this article. Furthermore, only those antibodies that exert complement-fixing activity are detected. As a consequence, novel procedures that act independently of the complement system and that do not represent functional assays were generated in the format of solid phase assays (SPAs) (bead- or ELISA-based). In this article, we review the pros and cons of these sensitive SPA in comparison with the detection of DSA through the use of the traditional methods such as CDC and flow cytometric analyses. Potential drawbacks of the alternative methodological approaches comprising high background reactivity, susceptibility to environmental factors and the possible influence of subjective operators' errors concerning the interpretation of the results are summarized and critically discussed for each method. We provide a forecast on the future role of SPAs reliably excluding highly deleterious DSA, thus leading to an improved graft survival.

The clinical significance of human leukocyte antigen antibody development in kidney transplantation

BACKGROUND

This retrospective study uses the LAT-M (One Lambda Inc., Calif) screen assay to reexamine the impacts (a), of pretransplant human leukocyte antigen (HLA) antibody on long-term graft survival; (b) posttransplant HLA antibody on long-term graft survival and (c) immunosuppressive regimen on posttransplant HLA antibody development.

PATIENTS AND METHODS

Pretransplant sera from 222 renal transplant recipients and posttransplant sera from 216 renal transplant recipients were studied for the impact of HLA antibody on long-term graft survival.

RESULTS

Among the patients who did not display pretransplant HLA antibodies, 85% enjoyed 5-year and 59% 10-year graft survival, whereas the patients who tested positive were 83% and 83% (P = .5596). Among the patients who did not show posttransplant HLA antibodies, 99% enjoyed 5-, 91% 10-, and 65% 15-year graft survival, whereas for the 44 patients who tested positive they were 59%, 44%, and 30%, respectively (P < .0001). Patients prescribed cyclosporine + myfortic (odds ratio 0.17, P = .05) or FK + Cellcept (odds ratio 0.36, P = .04) showed the lowest posttransplant HLA antibody development.

CONCLUSION

Both regimens improve graft survival.

B-cell complement dependent cytotoxic crossmatch positivity is an independent risk factor for long-term renal allograft survival

The clinical significance of positive B-cell complement-dependent cytotoxicity crossmatching (B-CDC) in renal transplant recipients remains unclear. We reviewed 20 recipients with isolated B-CDC positivity at the time of transplantation. We compared the clinical characteristics, acute rejection and long-term graft survival between positive and negative B-CDC patients (n = 602). The number of retransplant recipients and positivity for T- and B-flowcytometric crossmatch was greater in positive B-CDC patients than in negative B-CDC patients. The overall acute rejection rate of positive B-CDC patients was significantly higher (P < 0.001), and Banff grade II or III cellular rejection was more frequently observed in positive B-CDC patients (P = 0.037). Compared with negative B-CDC patients, acute cellular rejection as a cause of graft loss was more prevalent (P = 0.020) and rescue rejection therapy was more frequently needed in positive B-CDC patients (P = 0.007). The allograft survival rate of positive B-CDC patients was significantly lower than that of negative B-CDC patients (P < 0.001), and B-CDC positivity independently increased the risk of allograft failure 2.31-fold (95% CI 1.15-4.67; P = 0.019) according to multivariate analysis. In conclusion, isolated B-CDC positivity is an independent long-term prognostic factor for allograft survival.

Novel solid phase-based ELISA assays contribute to an improved detection of anti-HLA antibodies and to an increased reliability of pre- and post-transplant crossmatching

Antibodies directed against HLA antigens of a given organ donor represent the dominating reason for hyper-acute or acute allograft rejections. In order to select recipients without donor-specific antibodies, a standard crossmatch (CM) procedure, the complement-dependent cytotoxicity assay (CDC), was developed. This functional assay strongly depends on the availability of isolated vital lymphocytes of a given donor. However, the requirements of the donor’s material may often not be fulfilled, so that the detection of the antibodies directed against HLA molecules is either impaired or becomes completely impossible. To circumvent the disadvantages of the CDC procedure, enzyme-linked immunosorbent assay (ELISA)-based and other solid phase-based ELISA-related techniques have been designed to reliably detect anti-HLA antibodies in recipients. Due to the obvious advantages of these novel technologies, when compared with the classical CDC assay, there is an urgent need to implement them as complementary methods or even as a substitution for the conventional CDC crossmatch that is currently being applied by all tissue typing laboratories.

Association of HLA phenotypes of end-stage renal disease patients preparing for first transplantation with anti-HLA antibody status

Patients with pre-transplantation high levels of panel reactive antibody (PRA) have an increased risk of graft failure, and renal transplantation in sensitized patients remains a highly significant challenge worldwide. The influence of anti-human leukocyte antigen (HLA) antibodies on the development of rejection episodes depends on patient-specific clinical factors and differs from patient to patient. The HLA typing of the recipient might influence the development of anti-HLA antibodies. Some HLA antigens appear to be more immunogenic than others. The aim of this study is to demonstrate the distribution of HLA phenotypes in PRA-positive and PRA-negative end-stage renal disease (ESRD) patients on the basis of having sensitizing events or not. Our study included 642 (mean age: 41.54; female/male: 310/332) ESRD patients preparing for the first transplantation and who are on the cadaveric kidney transplantation waiting list of Istanbul Medical Faculty in 2008-2009. Class I HLA-A,B typing was performed by complement-dependent cytotoxicity (CDC) method, whereas class II HLA-DRB1 typing was performed by low-resolution polymerase chain reaction (PCR)-sequence-specific primer (SSP). All serum samples were screened for the presence of IgG type of anti-HLA class I- and II-specific antibodies by enzyme-linked-immunosorbent assay (ELISA). PRA-negative group consisted of 558 (86.9%) and PRA-positive group included 84 (13.1%) patients. We have found statistically significant frequency of HLA-A3 (p=0.018), HLA-A66 (p=0.04), and HLA-B18 (p=0.006) antigens in PRA-positive patients and DRB1*07 (p=0.02) having the highest frequency in patients with sensitizing event history but no anti-HLA development suggesting that DRB1*07 might be associated with low risk of anti-HLA antibody formation.

Anti-HLA antibody profile of Turkish patients with end-stage renal disease

Exposure to human leukocyte antigens (HLA) via blood transfusions, pregnancies, and previous transplantations can result in anti-HLA antibody production. The presence of anti-HLA antibodies in recipient sera before transplantation is an important risk factor. To demonstrate the anti-HLA antibody status of Turkish end-stage renal disease (ESRD) patients, 674 patients (mean age, 40.35 +/- 13.15 years; female/male, 328/346) were enrolled into the study. Anti-HLA antibody screening and identification tests were performed using an enzyme-linked immunosorbent assay (ELISA) method. The panel-reactive antibody (PRA)-negative group consisted of 564 (83.6%) and the PRA-positive group consisted of 110 (17.3%) patients. Of the 110 (17.3%) PRA-positive patients, 43 (6.4%) were class I (+) and class II (-); 19 (2.8%) were class I (-) and class II (+); 48 (7.1%) were both class I and II (+). The most frequent antibodies were directed against the A2 crossreactive group (CREG) and the A10 CREG with less frequent reactions against the B7 CREG, indicating antibodies to both frequent (members of A2 CREG) and relatively rare (members of A10 CREG and B7 CREG antigens). These data also suggested that some antibodies occur at greater than expected frequency because of shared epitopes. Our findings confirmed the significant correlation between female gender, pregnancy, failed graft history, long dialysis duration, and blood transfusions with PRA positivity (P < .05).

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.

Reappraisal of HLA antibody analysis and crossmatching in kidney transplantation

Enzyme-linked immunosorbent assay (ELISA) and flow cytometric techniques have been introduced to overcome the limited sensitivity and specificity of the CDC assay. This retrospective study used lambda antigen tray-mixed screening and Luminex HLA class I and II specificity assays to re-examine: (1) the accuracy with which detection of HLA antibody and specificity by ELISA predicts pretransplantation National Institutes of Health (NIH)/Centers for Disease Control and Prevention (CDC) crossmatch; and (2) a comparison of Luminex and ELISA methods to detect HLA antibodies. Sera from 481 patients awaiting kidney transplantation were tested using the ELISA method lambda antigen tray-mixed and using NIH-CDC to determine how well HLA antibodies detected using ELISA predicted crossmatches using CDC. Pretransplantation sera from 48 patients with follow-up data were retested using both ELISA lambda antigen tray-mixed and Luminex to compare the efficacy of the 2 methods.

Successful renal transplantation with desensitization in highly sensitized patients: a single center experience

Intravenous immunoglobulin (IVIG) and/or plasmapheresis (PP) are effective in preventing antibody-mediated rejection (AMR) of kidney allografts, but AMR is still a problem. This study reports our experience in living donor renal transplantation in highly sensitized patients. Ten patients with positive crossmatch tests or high levels of panel-reactive antibody (PRA) were included. Eight patients were desensitized with pretransplant PP and low dose IVIG, and two were additionally treated with rituximab. Allograft function, number of acute rejection (AR) episodes, protocol biopsy findings, and the presence of donor-specific antibody (DSA) were evaluated. With PP/IVIG, six out of eight patients showed good graft function without AR episodes. Protocol biopsies revealed no evidence of tissue injury or C4d deposits. Of two patients with AR, one was successfully treated with PP/IVIG, but the other lost graft function due to de novo production of DSA. Thereafter, rituximab was added to PP/IVIG in two cases. Rituximab gradually decreased PRA levels and the percentage of peripheral CD20+ cells. DSA was undetectable and protocol biopsy showed no C4d deposits. The graft function was stable and there were no AR episodes. Conclusively, desensitization using PP/IVIG with or without rituximab increases the likelihood of successful living donor renal transplantation in sensitized recipients.