Clinical relevance of Luminex donor-specific crossmatches: data from 165 renal transplants

Donor-Specific Antibody Detection by Single-Antigen Bead Assay for Renal Transplantation: A 2-Year Experience from South India

Introduction

Recipient sensitization against donor human leukocyte antigens (HLA) plays a key role in transplant rejection, and this risk is best minimized by efficient pre transplant antibody detection. Determination of antibody specificity with the highest sensitivity and degree of resolution to the allelic antigen level is achieved by using single-antigen bead (SAB) assay.

Methods

This study evaluated the correlation of Luminex cross match (LXM) with SAB assay for detection of donor-specific antibodies (DSA). A total of 2075 renal transplant patients were screened for the presence of DSA by LXM, complement-dependent cytotoxicity (CDC) cross match, and 125 patients for SAB from January 2018 to December 2019.

Results

There was a male preponderance among recipients (P < 0.0001), and the most affected age group was 21-40 years. HLA typing was done in 550/2075 by DNA PCR-reverse sequence-specific oligonucleotide probes (SSOP) method. HLA DSA by LXM was detected in 16.3% of recipients (338/2075). Majority 180/338 (53.2%) of the patients were class II DSA positive, (P < 0.0001). Among the class II DSA positive patients, 20/180 (11.1%) samples gave false-positive results by LXM. SAB for class I and class II HLA IgG antibodies was done in 125/338 renal transplant recipients, which included 20 recipients with false-positive class II Luminex DSA, to check whether the DSA detected were really donor specific or not. The results showed that although 20/125 patients had some antibodies detected in their serum, they were not against the donor HLA antigens, as per the HLA typing reports of the donors. When compared to SAB assay, LXM showed more discrepant results, particularly to class II DSA.

Conclusion

In conclusion, LXM, if used in combination with SAB assay and HLA typing of donors if necessary for virtual cross match, will help in avoiding unnecessary exclusion of donors for renal transplant recipients and also for post transplant monitoring of recipients, especially in cadaveric donor transplants.

Evaluation of three different laboratory methods to detect preformed human leukocyte antigen antibodies in a South African kidney transplant population

Background

Anti-human leukocyte antigen antibodies (anti-HLA) play a crucial role in graft. Detection of anti-HLA, both pre- and post-transplant is a crucial investigation in clinical organ transplantation.

Objectives

Three methodologies for the detection of lymphocytotoxic antibodies were compared to establish which of these is best suited to optimise pre-transplant donor-recipient matching.

Methods

Serum samples from 15 renal transplant patients were tested for the presence of anti-HLA by i) cytotoxic-dependent cross-match (CDCXM), ii) flow cytometric cross-match (FCXM) and iii) Luminex-based donor specific antibody cross-match (DSAXM) method, Confirmatory tests for the presence of preformed HLA antibodies were tested using Luminex methodology.

Results

Two (13%) of the 15 patients had positive HLA Class I antibodies (Ab) using all 3 methods. An additional 2 HLA Class I Ab were identified with FCXM/CDCXM. DSAXM identified 1 HLA Class I positive, not indicated by CDCXM/FCXM.

High HLA Class II positivity (40%), identified by CDCXM, while DSAXM and FCXM identified two and one patients, respectively. CDCXM produced 4 false-positive results confirmed by lymphocyte single antigen (LSA) assay.

Conclusions

The DSAXM method appears to add value in pre-transplantation screening to identify pre-sensitised patients that may not reject the donor graft due to the absence of donor-specific antibodies.

Discrepant Antibody Testing Results: Which One to Believe?

The impact of solid-phase immunoassay for HLA antibody detection on the field of transplantation has been extremely significant by providing the most sensitive and precise method for characterization of HLA antibodies. However, despite all the benefits, technical limitations and inherent artifacts represent significant challenges, particularly with Luminex-based single-antigen bead (SAB) assay. Discordant results between antibody detection (screening assay) and identification (SAB) is not uncommon. Positive SAB assay in the context of negative screening testing is well documented and attributed to altered tertiary structure of HLA molecules exposing new epitopes or detection of naturally occurring antibodies. However, there are few reports that addressed the opposite scenario when negative SAB appeared in the context of positive screening assay. In such discrepant results, unmissed HLA antibody has to be excluded with certainty by other tests; however, with the availability of variable assays it may be difficult to choose the best combinations that clarify discrepancy without adding more confusion. Here we describe the results of correlation between 2 antibody screening solid-phase immunoassays (LABScreen Mixed using Luminex and FlowPRA Screen) on conventional flow cytometry and compare their outcomes with SAB and crossmatch results.

Positive Luminex and negative flow cytometry in kidney transplantation: a systematic review and meta-analysis

The presence of pre-formed donor-specific antibodies (DSAs) in kidney transplantation is associated with worse overall outcomes compared with DSA-negative transplantation. A positive complement-dependant cytotoxic crossmatch presents a high immunological risk, while a negative flow cytometry crossmatch is at the lower end of the risk spectrum. Yet, the presence of low-level DSA detected by Luminex alone, that is, positive Luminex and negative flow (PLNF) cytometry crossmatch lacks robust scientific exploration. In this systematic review and pooled analysis, we investigate the glomerular filtration rate, acute rejection (AR), graft survival and patient survival of PLNF transplants compared with DSA-negative transplants. Our analysis identified seven retrospective studies consisting of 429 PLNF transplants and 10 677 DSA-negative transplants. Pooled analysis identified no significant difference in the incidence of AR at 1 year [relative risk (RR) = 1.35, 95% confidence interval (CI) 0.90–2.02, Z = 1.46, P = 0.14, I2 = 0%], graft failure at 1 year (RR = 1.66, 95% CI 0.94–2.94, Z = 1.75, P = 0.08, I2 = 23%), graft failure at 5 years (RR = 1.29, 95% CI 0.90–1.87, Z = 1.38, P = 0.17, I2 = 0%), patient mortality at 1 year (RR = 0.89, 95% CI 0.31–2.56, Z = 0.22, P = 0.82, I2 = 0%) and patient mortality at 5 years (RR = 1.76, 95% CI 0.48–6.48, Z = 0.85, P = 0.39, I2 = 61%). Pooled analysis of graft function was not possible due to insufficient data. Current evidence suggests that low-level DSA detected by Luminex alone does not pose significant risk at least in the short–medium term. Considering the shortage of kidney transplants and the ever-increasing waiting time, the avoidance of PLNF transplants may be unwarranted especially in patients who have been enlisted for a long time.

Comparative analysis of two methods to detect donor-specific anti-HLA antibodies after kidney transplant

Preformed anti-human leukocyte antigen (HLA) antibodies may be present in the blood of kidney transplant candidates. The production of these antibodies may occur in the post-transplant period, with the possible development of donor-specific antibodies (DSA). Luminex-based tests, such as the single antigen (SA) assay and the Luminex crossmatch (Xm-DSA) assay are the most commonly used tools to detect anti-HLA antibodies, due to their high sensitivity and specificity. This cross-sectional study aimed to compare the findings of two methods for the detection of DSAs after kidney transplant: SA and Xm-DSA. A total of 122 patients who underwent deceased donor kidney transplant at Hospital de Clínicas de Porto Alegre were included. The SA assay detected anti-class I HLA DSAs in 17 patients (13.9%) and anti-class II HLA DSAs in 22 patients (19.6%), whereas the Xm-DSA detected DSAs in 18 patients (14.8%) both against class I and class II antigens. There was agreement between the two methods for class I (kappa = 0.66, p = 0.001) and class II (kappa = 0.54, p = 0.025) antigens. The incidence of DSAs as obtained by the SA assay was 15.57%, and the most prevalent DSAs were those against HLA-DR antigens. Patient survival at 3 years was 92%. The two techniques assessed in this study provide important information on the presence of DSAs and may help in the post-transplant patient monitoring and in immunosuppressive strategy.

The good, the bad, and the ugly of luminex donor-specific crossmatch

The presence of donor-specific antibodies directed against human leukocyte antigen significantly influences renal transplant because of antibody-mediated rejection. We performed the screening of pre-renal transplant patients for preformed anti-HLA antibodies using anti-human globulin augmented-complement-dependent lymphocytotoxicity crossmatch (AHG-CDCXm), luminex donor-specific crossmatch (LumXm) and HLA antibody screening. Seven hundred and fifty-four patients were assessed for LumXm. HLA antibody screening was possible in 325 out of 754 cases. All the three investigations viz. CDCXm, HLA antibody screening and LumXm was performed in 325 patients. All CDCXm positive patients (10/325, 3.08%) were also positive with LumXm and HLA antibody screen whereas 14 cases (4.31%) with CDCXm negative were positive with luminex-based assays. LumXm and HLA antibody screening were both positive in 24 (7.38%) cases, LumXm and HLA antibody screening were both negative in 275 (84.63%) cases and LumXm negative and HLA antibody screening was positive in 22 (6.76%) cases. However, there were four cases (1.23%) which were positive in LumXm in spite of being negative in HLA antibody testing. Single Antigen Bead (SAB) assay was performed in all patients positive for HLA antibody test. We suggest that LumXm is a useful and sensitive technique for the detection of anti-HLA antibodies in pre-transplant renal patients. However, other measures such as luminex antibody screen, SAB assay, history of the donor, and the class of antibodies involved should be taken into consideration for pre-transplant work up of renal patients.

Impact of persistent and cleared preformed HLA DSA on kidney transplant outcomes

Preformed HLA donor-specific antibodies (DSA) only detected with Luminex have been associated with increased risk of antibody-mediated rejection (ABMR) and graft failure after kidney transplantation (KT). Their evolution after KT may modify this risk. We analyzed postransplant evolution of preformed DSA identified retrospectively and their impact on outcomes of 370 KT performed 2006-2014. Antibodies were monitored prospectively at 1-3-5 years after KT and if any dysfunction. Early acute ABMR was more frequent among patients with preformed DSA class-I or I + II than isolated class-II (29.4% vs 4.5%, p = 0.02). One year post-KT, 20 of 34 patients with functioning KT had persistent DSA. Preformed DSA class-II persisted more frequently than class-I/I + II (66.7% vs 33.3%; p = 0.031). The only risk factor independently associated with persistence was pretransplant MFI. Patients with de novo DSA had the highest risk of ABMR (HR 22.2 [CI 6.1-81.2]). Although recipients with persisting preformed DSA had significantly increased ABMR risk (HR 14.7 [CI 6.5-33.0]), those with cleared preformed DSA also had a higher risk than those without DSA (HR 7.01 [CI 2.2-21.8]). Preformed DSA are a very important risk factor for ABMR and graft loss. Patients who clear preformed DSA still show an increased risk of ABMR and graft loss after KT.

Unexpected Positive Prospective Crossmatches in Organ Transplant

Preformed donor-specific antibodies against human leukocyte antigen can induce antibody-mediated rejection after organ transplant. Hence, future transplant recipients undergo pretransplant screening for preformed antibodies (ie, virtual crossmatch). Subsequently, prospective (analytic) crossmatching is performed using conventional, complement-dependent cytotoxicity assays and/or flow cytometry-based methods. The present article reviews factors that must be considered when unexpected, positive, prospective crossmatches are observed. First, the prozone effect caused by the interference of complement or immunoglobulin M must be abrogated by treating the serum with moderate heat, dilution, hypotonic dialysis, EDTA, or dithiothreitol. Second, the physician must check for the presence of potentially interfering autoantibodies (in a context of autoimmune disease or human immunodeficiency virus infection) or therapeutic antibodies (such as rituximab and antithymocyte globulin). In conclusion, knowledge of each assay's technical characteristics will enable the physician to reliably interpret any discrepancies. The reasons for an unexpected, positive, prospective crossmatch must be elucidated before transplant to ensure efficient organ allocation and optimize patient outcomes.

Detection of HLA Antibodies in Organ Transplant Recipients - Triumphs and Challenges of the Solid Phase Bead Assay

This review outlines the development of human leukocyte antigen (HLA) antibody detection assays and their use in organ transplantation in both antibody screening and crossmatching. The development of sensitive solid phase assays such as the enzyme-linked immunosorbent assay technique, and in particular the bead-based technology has revolutionized this field over the last 10-15 years. This revolution however has created a new paradigm in clinical decision making with respect to the detection of low level pretransplant HLA sensitization and its clinical relevance. The relative sensitivities of the assays used are discussed and the relevance of conflicting inter-assay results. Each assay has its advantages and disadvantages and these are discussed. Over the last decade, the bead-based assay utilizing the Luminex® fluorocytometer instrument has become established as the "gold standard" for HLA antibody testing. However, there are still unresolved issues surrounding this technique, such as the presence of denatured HLA molecules on the beads which reveal cryptic epitopes and the issue of appropriate fluorescence cut off values for positivity. The assay has been modified to detect complement binding (CB) in addition to non-complement binding (NCB) HLA antibodies although the clinical relevance of the CB and NCB IgG isotypes is not fully resolved. The increase sensitivity of the Luminex® bead assay over the complement-dependent cytotoxicity crossmatch has permitted the concept of the "virtual crossmatch" whereby the crossmatch is predicted to a high degree of accuracy based on the HLA antibody specificities detected by the solid phase assay. Dialog between clinicians and laboratory staff on an individual patient basis is essential for correct clinical decision making based on HLA antibody results obtained by the various techniques.

HLA Mismatching Strategies for Solid Organ Transplantation - A Balancing Act

HLA matching provides numerous benefits in organ transplantation including better graft function, fewer rejection episodes, longer graft survival, and the possibility of reduced immunosuppression. Mismatches are attended by more frequent rejection episodes that require increased immunosuppression that, in turn, can increase the risk of infection and malignancy. HLA mismatches also incur the risk of sensitization, which can reduce the opportunity and increase waiting time for a subsequent transplant. However, other factors such as donor age, donor type, and immunosuppression protocol, can affect the benefit derived from matching. Furthermore, finding a well-matched donor may not be possible for all patients and usually prolongs waiting time. Strategies to optimize transplantation for patients without a well-matched donor should take into account the immunologic barrier represented by different mismatches: what are the least immunogenic mismatches considering the patient’s HLA phenotype; should repeated mismatches be avoided; is the patient sensitized to HLA and, if so, what are the strengths of the patient’s antibodies? This information can then be used to define the HLA type of an immunologically optimal donor and the probability of such a donor occurring. A probability that is considered to be too low may require expanding the donor population through paired donation or modifying what is acceptable, which may require employing treatment to overcome immunologic barriers such as increased immunosuppression or desensitization. Thus, transplantation must strike a balance between the risk associated with waiting for the optimal donor and the risk associated with a less than optimal donor.

Casting a smaller net into a bigger donor pool: A single center's experience with the new kidney allocation system

The new kidney allocation system (KAS) provides additional allocation points for candidates with broad HLA sensitization in an effort to increase transplant rates for this underserved population. Following the implementation of KAS, our center lowered the HLA antibody threshold for listing unacceptable antigens from a cytotoxicity crossmatch level to a flow cytometric crossmatch level increasing Calculated Panel Reactive Antibody (CPRA) values and allocation points, yet restricting acceptable donor HLA phenotypes. As a result, many sensitized candidates were transitioned from 50% to 98% CPRA categories into the 99% CPRA regional share and 100% CPRA national share categories. Exposure to these larger donor pools significantly increased transplantation with compatible donors for 100% CPRA candidates, but regional sharing was not sufficient to increase transplantation rates for our 99% CPRA candidates. Competition within the 100% CPRA cohort identified inequities for 99.99-100.0% CPRA candidates and highlighted the continued need for desensitization therapies to reduce immunological barriers and provide transplant opportunities for the most highly sensitized candidates.

Nonspecific positivity on the Luminex crossmatch assay for anti-human leukocyte antigen antibodies due to antibodies directed against the antibody coated beads

Two cases are described of previously unreported false positivity on the Luminex crossmatch assay due to non HLA specific antibodies directed against the beads. In both cases the Luminex crossmatch indicated the presence of donor specific antibodies to class II HLA antigens, which was not substantiated by the clinical scenario or other assays. We could demonstrate the non specificity of these antibodies through using the same assay in a modified form where beads were unexposed to cell lysate and therefore did not carry HLA antigens at all. These cases further serve to emphasize the absolute necessity of correlating positive results with the priming history, and confirming their relevance using other platforms.

Development of antidonor antibody directed toward non-major histocompatibility complex antigens in tolerant animals

BACKGROUND

The clinical significance of antibodies directed against antigens other than major histocompatibility complex (MHC) antigens is poorly understood, and there are few large animal models in which such antibodies can be examined. We studied, both retrospectively and prospectively, the development of antibodies to non-MHC antigens in tolerant miniature swine.

METHODS

Our database was assessed for cases of antidonor antibody formation in tolerant animals over the last 20 years. Flow cytometry, absorption assays, and familial analyses for inheritance pattern of the gene(s) potentially responsible for the antibody reactivities were carried out, and an animal determined to be negative for this reactivity was immunized by a skin graft and subcutaneous injections of peripheral blood monocyte cells from an antigen-positive donor.

RESULTS

Sixteen of 469 tolerant animals tested were found to have developed antidonor antibodies. These antibodies were found to be specific for the same, presumably single, non-MHC antigen. Familial analyses indicated that the gene encoding this antigen was expressed in an autosomal-dominant manner in approximately 95% of the herd. In a prospective study, antidonor antibodies with the same specificity as those observed retrospectively were successfully induced in an antigen-negative animal after immunization with peripheral blood monocyte cells.

CONCLUSION

To our knowledge, this is the first report of the development of antibodies to a highly prevalent, non-MHC antigen present on peripheral blood mononuclear cells and developing in tolerant animals without signs of graft dysfunction. Considering the concern often raised by the appearance of antidonor antibodies in transplant recipients, these data could have important implications for clinical transplantation.

Methodological aspects of anti-human leukocyte antigen antibody analysis in solid organ transplantation

Donor human leukocyte antigen (HLA)-specific antibodies (DSA) play an important role in solid organ transplantation. Preexisting IgG isotype DSA are considered a risk factor for antibody mediated rejection, graft failure or graft loss. The post-transplant development of DSA depends on multiple factors including immunogenicity of mismatched antigens, HLA class II typing of the recipient, cytokine gene polymorphisms, and cellular immunoregulatory mechanisms. De novo developed antibodies require special attention because not all DSA have equal clinical significance. Therefore, it is important for transplant clinicians and transplant immunologists to accurately characterize DSA. In this review, the contemporary immunological techniques for detection and characterization of anti-HLA antibodies and their pitfalls are described.

Histocompatibility testing for organ transplantation purposes in Albania: a single center experience

BACKGROUND

Histocompatibility testing (HT) which includes donor-recipient human leukocyte antigen (HLA) matching, cross-match testing (XMT) and anti-HLA antibody searching are crucial examinations in solid organ transplantation aiming to avoid the hyperacute graft rejection and also to predict the immunological outcome of the graft.

AIMS

The aim of this study was to analyse the tissue typing data collected at the Laboratory of Immunology and Histocompatibility of the University Hospital Center of Tirana, Albania, in order to define those actions that should be taken for improvements in the situation of kidney transplantation in Albania.

STUDY DESIGN

Descriptive study.

METHODS

The donor/recipient cross-match testing was performed through a standard complement-dependent cytotoxicity (CDC) assay using separated donor T and B cells that were tested in parallel with the recipient serum sample. All recipient sera were screened for anti-Class I and anti-Class II HLA antibodies using a bead based Luminex anti-HLA antibody screening test. In the case of detected positivity, an allele-specific anti-HLA antibody determination was conducted with the respective Luminex anti-Class I and Class II HLA antibody determination kits.

RESULTS

A total of 174 recipients and 202 donors were typed for the purpose of living donor kidney transplantation at our laboratory between January 2006 and December 2012. The mean age and female gender proportion of patients were 34.9 years and 34.5%, respectively, and 48.0 years and 65.3% for the donors, respectively. Here, 25.9% of the patients reported a positive complement-dependent cytotoxicity cross-match test and/or a positive anti-HLA antibody testing result. Eighteen patients that were negative for the complement-dependent cytotoxicity cross-match test were positive for anti-HLA antibodies.

CONCLUSION

The predominant causes of end-stage renal disease (ESRD) in our patient population are chronic pyelonephritis and glomerulonephritis. The female gender is significantly more frequent among donors, which emphasises the need for more gender equity as far as the altruistic willingness for organ donation is concerned. The significant number of patients with Luminex anti-HLA antibody positivity combined with complement-dependent cytotoxicity cross-match negative results underlines the necessity of using additional methods like cell-based flow cytometry or bead-based Luminex anti-HLA antibody assays for the detection of anti-donor-specific antibodies. We also suggest that the number of kidney transplantations in Albania needs to be increased significantly by expanding it with paired exchange living donation and also by implementing an efficient deceased donor kidney transplantation program.

Assessing immunologic risk factors in transplantation

The innate and adaptive immune systems, together, represent the largest impediment to good and long-lasting graft function. Although improved immunosuppressive agents and expanded and enhanced diagnostic tools have led to better prevention and treatment of acute rejection, chronic rejection remains a serious threat to long-term graft survival. Immunologic heterogeneity among patients, variability in treatment protocols and unforeseen events following transplantation translate into different levels of risk among patients. While one cannot predict with certainty the short- and long-term outcomes of a particular transplant, it is possible to identify immunologic risk factors that can affect outcome.

Cross-validation of IFN-γ Elispot assay for measuring alloreactive memory/effector T cell responses in renal transplant recipients

Assessment of donor-specific alloreactive memory/effector T cell responses using an IFN-γ Elispot assay has been suggested to be a novel immune-monitoring tool for evaluating the cellular immune risk in renal transplantation. Here, we report the cross-validation data of the IFN-γ Elispot assay performed within different European laboratories taking part of the EU RISET consortium. For this purpose, development of a standard operating procedure (SOP), comparisons of lectures of IFN-γ plates assessing intra- and interlaboratory assay variability of allogeneic or peptide stimuli in both healthy and kidney transplant individuals have been the main objectives. We show that the use of a same SOP and count-settings of the Elispot bioreader allow low coefficient variation between laboratories. Frozen and shipped samples display slightly lower detectable IFN-γ frequencies than fresh samples. Importantly, a close correlation between different laboratories is obtained when measuring high frequencies of antigen-specific primed/memory T cell alloresponses. Interestingly, significant high donor-specific alloreactive T cell responses can be similarly detected among different laboratories in kidney transplant patients displaying histological patterns of acute T cell mediated rejection. In conclusion, assessment of circulating alloreactive memory/effector T cells using an INF-γ Elispot assay can be accurately achieved using the same SOP, Elispot bioreader and experienced technicians in kidney transplantation.

Correlation between Luminex donor-specific crossmatches and levels of donor-specific antibodies in pretransplantation screening

Before kidney transplantation, recipients are routinely screened for preformed antibodies and prospective crossmatches. In this study, we compared prospective Luminex donor-specific crossmatches (LumXm) with the levels of identified, donor-specific antibodies (DSAs). LumXm was performed for 108 patient sera, 84 of which were positive for preformed antibodies and 24 of which were negative. Although LumXm can detect class I DSAs (anti-A and anti-B) with a mean fluorescence intensity (MFI) as low as 2300, the assay has a 'grey zone' for MFIs up to 4000 with a sensitivity of 54% and a specificity of 100%. LumXm can detect a class II DSA (anti-DRB1) with an MFI as low as 1300 and a sensitivity of 93% and a specificity of 99%. However, these correlations were obtained with two precautions: autocrossmatching and single-antigen bead assay with denaturing buffer were performed in discordant cases. Moreover, LumXm failed to detect anti-Cw and anti-DP in the 10 cases studied. LumXm, therefore, displays certain discrepancies with respect to single-bead assays--especially for antibodies with a low MFI. Unfortunately, LumXm has a low sensitivity for anti-A and anti-B class I antibodies.

Dynamic challenges inhibiting optimal adoption of kidney paired donation: findings of a consensus conference

While kidney paired donation (KPD) enables the utilization of living donor kidneys from healthy and willing donors incompatible with their intended recipients, the strategy poses complex challenges that have limited its adoption in United States and Canada. A consensus conference was convened March 29-30, 2012 to address the dynamic challenges and complexities of KPD that inhibit optimal implementation. Stakeholders considered donor evaluation and care, histocompatibility testing, allocation algorithms, financing, geographic challenges and implementation strategies with the goal to safely maximize KPD at every transplant center. Best practices, knowledge gaps and research goals were identified and summarized in this document.

Donor-specific antibodies adversely affect kidney allograft outcomes

The effect of low titers of donor-specific antibodies (DSAs) detected only by sensitive solid-phase assays (SPAs) on renal transplant outcomes is unclear. We report the results of a systematic review and meta-analysis of rejection rates and graft outcomes for renal transplant recipients with such preformed DSAs, defined by positive results on SPA but negative complement-dependent cytotoxicity and flow cytometry crossmatch results. Our search identified seven retrospective cohort studies comprising a total of 1119 patients, including 145 with isolated DSA-SPA. Together, these studies suggest that the presence of DSA-SPA, despite a negative flow cytometry crossmatch result, nearly doubles the risk for antibody-mediated rejection (relative risk [RR], 1.98; 95% confidence interval [CI], 1.36-2.89; P<0.001) and increases the risk for graft failure by 76% (RR, 1.76; 95% CI, 1.13-2.74; P=0.01). These results suggest that donor selection should consider the presence of antibodies in the recipient, identified by the SPA, even in the presence of a negative flow cytometry crossmatch result.

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.

Luminex and antibody detection in kidney transplantation

Preformed anti-human leukocyte antigen (HLA) antibodies have a negative effect on kidney transplantation outcome with an increased rejection rate and reduction in survival. Posttransplantation production of donor-specific anti-HLA antibodies is indicative of an active immune response and risk of transplantation rejection. For many years the primary technique for anti-HLA antibody detection was complement-dependent cytotoxicity (CDC), which has been integrated by solid-phase assays as HLA antigen-coated bead methods (Luminex). This new technological approach has allowed identification of anti-HLA antibodies, not detectable using conventional CDC method, in patients awaiting kidney transplantation. Moreover, use of Luminex technology has enabled better definition of acceptable or unacceptable antigens favoring transplantation in highly immunized patients. However, there are still many unresolved issues, including the clinical relevance of antibodies detected with this system.

Donor-specific antibody levels and three generations of crossmatches to predict antibody-mediated rejection in kidney transplantation

BACKGROUND

This study evaluated the prognostic impact of pretransplant donor-specific anti-human leukocyte antigen antibodies (DSA) detected by single-antigen beads and compared the three generations of crossmatch (XM) tests in kidney transplantation.

METHODS

Thirty-seven T-cell complement-dependent cytotoxicity crossmatch (CXM) negative living donor kidney recipients with a retrospectively positive antihuman leukocyte antigen antibody screening assay were included. A single-antigen bead test, a flow cytometry XM, and a Luminex XM (LXM) were retrospectively performed, and the results were correlated with the occurrence of antibody-mediated rejections (AMRs) and graft function.

RESULTS

We found that (1) pretransplant DSA against class I (DSA-I), but not against class II, are predictive for AMR, resulting in a sensitivity of 75% and a specificity of 90% at a level of 900 mean fluorescence intensity (MFI); (2) with increasing strength of DSA-I, the sensitivity for AMR is decreasing to 50% and the specificity is increasing to 100% at 5200 MFI; (3) the LXM for class I, but not for class II, provides a higher accuracy than the flow cytometry XM and the B-cell CXM. The specificity of all XMs is increased greatly in combination with DSA-I values more than or equal to 900 MFI.

CONCLUSIONS

In sensitized recipients, the best prediction of AMR and consecutively reduced graft function is delivered by DSA-I alone at high strength or by DSA-I at low strength in combination with the LXM or CXM.

Solid phase HLA antibody detection technology--challenges in interpretation

The introduction into routine diagnostic laboratories of solid phase assays for human leukocyte antigen (HLA) antibody detection has resulted in the application of new laboratory matching algorithms in clinical organ transplantation which have improved pre-transplant detection of immunization, in turn resulting in avoidance of rejection in many cases which until their introduction would not have been possible using the historical complement dependent serological techniques. There have been two generations of solid phase assays introduced into routine practice, namely, the enzyme-linked immunosorbent assay (ELISA) technique and the use of fluorescent beads with HLA molecules bound to their surface which can either be used in conventional flow cytometry or in conjunction with Luminex instrumentation, the latter having become the most popular approach. The use of the fluorescent bead techniques has raised interesting questions both with respect to technical performance and the interpretation of the results obtained. The advantages of bead technology for HLA antibody determination and the technical issues requiring resolution are the subject of this review.