Detection of HLA-specific antibodies by PRA-STAT and their association with transplant outcome

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.

Antibodies, isotypes and complement in allograft rejection

PURPOSE OF REVIEW

Classical complement activation is a key step in the process of antibody-mediated rejection. Emphasizing novel diagnostic strategies, this study will discuss recent studies highlighting the particular relevance of alloantibodies with complement-fixing ability.

RECENT FINDINGS

Reinforcing the pivotal role of complement, numerous studies have shown tight associations of capillary C4d deposition, a 'footprint' of alloantibody-triggered complement activation, with the occurrence of allograft injury. Distribution patterns of immunoglobulin isotypes or subclasses, which strongly differ in their ability to activate complement, may not adequately reflect the actual pathogenetic relevance of detected allosensitization. This fact may be explained by the finding that other variables, such as antibody-binding density or a synergism of antibodies against different epitopes of the same antigen, may contribute to complement activation. An attractive approach to distinguish between complement-fixing and presumably less harmful noncomplement-fixing alloreactivities could be the detection of C4d deposition in vitro. Applying such techniques, recent studies have shown that human leukocyte antigen reactivity with C4d-fixing ability, in contrast to noncomplement-fixing sensitization, may strongly predict antibody-mediated rejection and inferior graft survival.

SUMMARY

Considering the pivotal role of complement, technologies that uncover the complement-fixing ability of alloantibodies may be of particular interest for the selective detection of deleterious sensitization.

No association of kidney graft loss with human leukocyte antigen antibodies detected exclusively by sensitive Luminex single-antigen testing: a Collaborative Transplant Study report

BACKGROUND

It is unclear whether kidney transplant recipients with preformed donor-specific human leukocyte antigen (HLA) antibodies (DSA) detectable only in the highly sensitive Luminex single-antigen (LSA) assay are at an increased risk of graft failure.

METHODS

We studied 3148 patients who received a deceased donor kidney graft between 1996 and 2008 and were enrolled in the prospective serum project of the Collaborative Transplant Study. There were 118 patients with graft loss during the first 3 years after transplantation on whom recipient and donor DNA was available for complete HLA typing. We compared the incidence of LSA-detected DSA in these patients with graft failure and matched controls with functioning grafts. All patients were found negative in the less-sensitive complement-dependent lymphocytotoxicity and enzyme-linked immunosorbent assays.

RESULTS

When mean fluorescence intensity (MFI) of greater than or equal to 1000 was used as a cutoff for Luminex positivity, 118 patients with graft loss did not show a higher incidence of DSA against HLA-A, -B, -C, -DRB1/3/4/5, -DQA1, -DQB1, -DPA1, or -DPB1 antigens than 118 matched controls without graft loss (for all loci P not significant). The incidence of strong DSA (MFI ≥2000 or MFI ≥3000) detected only by LSA was low (for all loci between 0% and 5%) and did not identify unacceptable antigens that were relevant for graft loss within the first 3 years after transplantation.

CONCLUSION

We conclude that, given currently practiced crossmatch procedures and immunosuppressive regimens, exclusion of donor organs carrying "unacceptable" HLA based exclusively on sensitive LSA antibody testing is not justified.

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.

Determinants of the complement-fixing ability of recipient presensitization against HLA antigens

BACKGROUND

The presence of preformed alloantibodies with the ability to activate complement may pose a particular risk for kidney allograft rejection. The aim of this study was to evaluate variables that determine the complement-fixing capability of human leukocyte antigen (HLA) sensitization.

METHODS

Sixty-five sensitized patients with > or =10% pretransplant panel-reactive antibody (PRA) levels uncovered by immunoglobulin G [IgG]FlowPRA HLA class I and/or class II screening were included. Applying modified FlowPRA screening, sera were evaluated for patterns of alloreactive IgG subclasses and IgM, and, in parallel, for their complement-activating ability assessed by flow cytometric detection of human complement split product deposition ([C4d]FlowPRA).

RESULTS

Approximately two-thirds (68%) of tested sera were found to contain complement-fixing alloreactivity (> or =10%[C4d]FlowPRA). IgG1 type panel reactivity was predominant (detectable HLA class I and II reactivity in 93% and 91% of IgG-positive sera), followed by IgG3 (49%/44%), IgG2 (44%/27%), and IgG4 (19%/11%). Applying partial correlation we found an independent correlation of both %[IgG1]FlowPRA and %[IgG3]FlowPRA with %[C4d]FlowPRA reactivities (P< or =0.01). In addition, for IgG1 a contribution of the amount of bound alloantibody to complement-fixation was observed. Complement-fixation was also favored by the simultaneous presence of alloreactive IgG1, IgG3, and IgM. Previous grafting, but not pregnancy and transfusion, was independently associated with complement-fixing sensitization (P<0.05), presumably due to increased IgG1 type reactivity.

CONCLUSIONS

Anti-HLA antibody-triggered complement activation is dependent on both the pattern of Ig reactivities and the amount of bound antibody. Previous transplantation represents a major risk factor for the development of complement-fixing sensitization.

Effect of Panel-Reactive Antibody in Predicting Crossmatch Selection of Cadaveric Kidney Recipients

AIM

The influence of panel-reactive antibody level (%PRA) on crossmatch results was evaluated among 866 patients on the waiting list for cadaveric renal allografting from January 2001 to August 2005. We evaluated the results for 124 potential donors for a kidney, including 2008 crossmatches. Four hundred eighteen patients were tested against only 1 donor.

METHODS

Serum samples were screened for anti-HLA antibodies using immunoglobulin (Ig)G enzyme-linked immunosorbent assay (ELISA) PRA kit and the %PRA of the most reactive sample (peak) was used for patient stratification, according to sensitization level. Crossmatches were performed on fresh donor T lymphocytes from peripheral lymph nodes, using classical and anti-human-globulin enhanced complement-dependent cytotoxicity (CDC-T) methods. The tests were performed using peak and current patient sera before and after dithiothreitol treatment. The crossmatch was assumed to be negative when no reactivity was observed in all tests.

RESULTS

The incidences of positive crossmatch were as follows: 72.3%, 14.6%, and 7.2%, among patients with PRA >50%, PRA </=50%, and PRA = 0%, respectively. A negative crossmatch was observed in 6.5% (4 of 62) of the tests among 100% PRA patients.

CONCLUSION

Although %PRA level reflects the HLA sensitization of the patient, IgG ELISA PRA and CDC-T crossmatch may not reflect the same antibodies, and both results must be considered in a transplantation decision.

Luminex technology for anti-HLA antibody screening: Evaluation of performance and of impact on laboratory routine

The recent introduction of new technologies such as Luminex has provided alternative methods to the Complement Dependent Cytotoxicity (CDC) test for HLA specific antibody detection. In this study we compared the results obtained with CDC to those obtained using a Luminex method with the aim of evaluating the impact of this new technology on antibody screening policies in our transplant setting.A total of 1,421 sera, acquired from patients on the waiting list for a kidney transplant or following transplantation, were tested by both methodologies. CDC was performed using a whole lymphocyte population comprising a panel of 52 cells. The percentage panel reactive antibodies (PRA) and antibody specificity were evaluated using Lambda Scan Analysis software. For the Luminex method sera screening and identification of antibody specificity were carried out using the LABScreen Mixed and LABScreen PRA respectively. The overall concordance between the results obtained using the CDC and the Luminex methods was 85%. HLA antibody specificity was confirmed in 96% of the sera which tested positive using the Luminex system and serum positivity corresponded with a previous sensitisation event in these individuals. Using the Luminex method 18% of patients on the waiting list were considered and managed as sensitised as compared to 7% when testing with CDC alone. The Luminex method was able to detect a number of antibody specificities significantly more frequently than the CDC method and in addition the CDC method failed to detect some of the antibody specificities detected by the Luminex system. Based on this comparison study we have incorporated the Luminex methodology into our screening strategy.

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

The antibody monitoring system (AMS, GTI Inc) is a solid enzyme-linked immunosorbent assay (ELISA) crossmatch test for the detection of immunoglobulin G (IgG) antibody to donor-specific solubilized HLA class I and class II antigens. The objective of this study was to compare the results of the AMS assay with donor-specific anti-HLA IgG antibodies (DS-HLA Abs), as determined by ELISA panel reactive antibody (PRA) and the flow cytometric crossmatch test (FCXM). A total of 107 sera were screened for the presence of HLA Abs by ELISA PRA (LAT-M, One-Lambda Inc), the DS-HLA Abs were determined in 34 serum samples (31.8%) by an ELISA panel (LAT class I and class II, One-Lambda Inc) and FCXM. The FCXM and AMS assays were performed with matched lymphocytes from 56 donors. There was a significant degree of concordance (89.7%) between the two tests (P < .001). The sensitivity, specificity, positive predictive value, and negative predictive value of AMS assay to detect DS-HLA Abs was 88.2%, 94.5%, 88.2%, and 94.5%, respectively. The AMS is a simple, objective test, which has several advantages over the cell-based crossmatch test, such as elimination of non-HLA antibody reactivity, elimination of non-donor-specific antibody reactivity, no need for viable cells, and preparation of the donor's HLA antigens in advance. In summary, this study suggested that AMS may be useful as a supportive crossmatch test or as a monitoring test after transplantation to detect class I or class II DS-HLA Abs.

Anti-HLA alloantibodies in pediatric solid organ transplantation

An increasing number of studies demonstrate the clinical impact of preformed and de novo anti-human leucocyte antigen alloantibody (HLA-Ab) in solid organ transplantation (Tx). The screening of HLA-Ab in candidates and transplant recipients has evolved over time, with continuous improvement in the sensitivity and specificity of assays for HLA-Ab detection. Furthermore, histologic markers of complement activation pathways are currently implemented in the diagnosis of antibody-mediated rejection (AMR). Therapeutic strategies, including depletion of HLA-Ab and B cells, have allowed Tx across antibody barriers, or have rescued patients with AMR. The purpose of the present review is to summarize the state-of-the-art of HLA-Ab detection, clinical significance and therapeutic strategies in pediatric solid organ Tx.

The repercussions of implementing flow cytometry as a single HLA antibody screening technique in prospective renal transplant recipients

In an effort to replace the complement-dependent cytotoxicity test (CDC) with a more sensitive single technique we looked at flow cytometry as a possible replacement. The Flow PRA Bead technique (One Lambda) performed well in our laboratory. Although as expected this technique was more sensitive and specific than CDC, there remained 11 samples from eight patients which were flow negative, CDC positive. The results of various antibody identification tests on these samples prompted us to alter the positive selection criteria which we had been using on our routine screening with the Flow PRA Beads and persuaded us that the initial CDC result was correctly positive in nine of the 11 samples.

Human Leukocyte Antigen Antibodies for Monitoring Transplant Patients

Human leukocyte antigen (HLA) antibody-mediated hyperacute rejection has dramatically decreased since the clinical introduction of crossmatch technology. However, the role of HLA antibody in acute and chronic rejection remains unclear. In this article, we cite publications to show the correlation between HLA antibody and allograft rejection. Potential pathological mechanisms of antibody-mediated rejection are also proposed and the rationale of commonly used HLA antibody detection techniques are introduced. The advantages and disadvantages of these technologies are further discussed in detail. We conclude that owing to the recent availability of improved antibody detection methods, a causal relationship between HLA antibodies and allograft rejection is now considered to exist.

Impact of ELISA-Detected Anti-HLA Antibodies on Pediatric Cardiac Allograft Outcome

In this study, we determine whether the presence of enzyme-linked immunosorbent assay (ELISA) detected anti-human leukocyte antigen (HLA) antibodies correlates with acute and chronic rejection in pediatric heart transplantation (Tx). Forty-five patients, who had serial ELISA pre- and posttransplantation, were studied. Age at Tx was 8.2 +/- 7.2 years. Acute rejection (AR) was defined as International Society for Heart and Lung Transplantation Grade > or =3a. Patients were defined as rejectors (22 cases) if they had recurrent AR or steroid-resistant AR within the first year post-Tx; the other cases (23) were defined as nonrejectors. Overall, 219 samples were analyzed. Twenty-two of the 45 had pre- or post-Tx anti-HLA antibodies: 77% in rejectors (17/22) and only 22% in nonrejectors (5/23), p = 0.0002. Pre-Tx HLA antibodies were present in 12 cases (27%). Presensitization was more frequent in rejectors (11/22, 50%) than in nonrejectors (1/23, 4%, p = 0.0005). Nineteen cases retained (9 cases) or developed (10 cases) anti-HLA antibodies post-Tx: 14 in rejectors (63.6%) and 5 in nonrejectors (21.7%), p = 0.003. Four of eight cases with coronary artery disease (50%) had preformed anti-HLA antibodies compared with 8 of 37 without coronary artery disease (25.6%) (p = 0.09). Preformed, persistent, and de novo ELISA-detected anti-HLA antibodies were correlated with first-year acute rejection profile.

Humoral Theory of Transplantation: Mechanism, Prevention, and Treatment

We discuss the potential mechanisms of antibody-induced primary endothelium injury, which includes complement-dependent pathway (membrane attack complex formation, recruitment of inflammatory cells, and complement-complement receptor-mediated phagocytosis) and complement independent pathway antibody-dependent cell cytotoxicity. Secondary to endothelium injury, the following pathological reactions are found to be responsible for progressive tissue injury and final graft function loss: platelet activation and thrombosis, pathological smooth muscle and endothelial cell proliferation, and humoral and/or cellular infiltrate-mediated parenchyma damage after endothelium injury. We also introduce three categories of therapeutic strategy in the prevention and treatment of antibody-mediated rejection: (1) inhibition and depletion of antibody producing cells (immunosuppressants, antilymphocyte antibodies, splenectomy); (2) removal or blockage of preexisting or newly developed antibodies (immunoadsorption, plasmapheresis/plasma exchange, intravenous immunoglobulin); and (3) impediment or postponement of antibody-mediated primary and secondary tissue injury (anticoagulation, glucosteroids). In conclusion, because alloantibodies have destructive effect on allografts, alloantibody monitoring becomes extremely important. It will help clinicians to determine a patient's humoral responses against allograft and will therefore direct clinicians to optimize and/or minimize immunosuppressive drug therapy.

Immunological profile of patients awaiting a renal transplant

BACKGROUND

A renal transplant is the best possible treatment for patients with terminal renal failure. Advances in the development of techniques of screening of pre-formed antibodies have contributed to a notable improvement in the results obtained with allogenic transplants.

METHODS

The aim of the present work is to study the nature, class, isotype and specificity of antibodies detected in patients awaiting renal transplantation at Complejo Hospitalario Universitario Juan Canalejo, as well as their relation with the level of anti-human leucocyte antigen (HLA) sensitization.

RESULTS

In all patient groups, there was a predominance of IgG. The distribution of anti-HLA antibody class showed that the most frequent pattern corresponded to a mixture of class I and class II antibodies for all groups. The study of specificity of anti-HLA antibody showed that of the patients with at least one previous transplant, 72% developed specific anti-HLA antibodies against some of the incompatible antigens of the donor, 12% against HLA antigens not related with the phenotype of the donor and in 16% it was not possible to determine their specificity. Most patients developed antibodies against antigens of locus B, probably because of that the number of incompatibilities contributed by the donors is also greater for locus B.

CONCLUSIONS

The exhaustive study of sera of patients on a waiting list for transplantation with respect to the nature, isotype, class and specificity of the antibody is important since it is possible that different antibodies can bring about, in the transplant, events that will have different consequences for the survival of the graft.

Incidence and specificity of HLA antibodies in multitransfused patients with acquired aplastic anemia

BACKGROUND

This study aimed to establish the prevalence and characteristics of anti-HLA in antibody acquired aplastic anemia patients following cessation of antithymocyte globulin therapy and to characterize antibody in terms of epitope specificity.

STUDY DESIGN AND METHODS

One hundred and fifty multitransfused, untransplanted patients from eight European centers were investigated by serologic methods.

RESULTS

Sixty-two percent were antibody positive. Eighteen HLA-Class-I-specific antibodies (15 IgG, 3 IgM) were identified in 13 patients; 13 antibodies were specific for HLA-A epitopes and 5 for HLA-B. Epitope analysis identified significant correlation between serum reactivity and amino acid substitutions associated with HLA-Class-I epitopes. An excess of antibodies to HLA-A1-associated cross-reactive groups was identified. There was no significant difference in antibody frequency in patients taking cyclosporine compared to those who were not.

CONCLUSION

Data suggested a contribution from B cell memory of alloantigens introduced during pregnancy. In some cases, antibody production continued many years after the last transfusion, and although the target varied between individual patients, the antibody to HLA was focused on a few specific Class I epitopes, the majority of which mapped to the HLA-A molecule.

Monitoring Anti-HLA Class I IgG antibodies in renal transplant recipients

Anti-HLA class I IgG antibodies play an important role in hyperacute rejection but the significance of its de novo appearance or increase in levels during the posttransplant period remains controversial. The purpose of this study was to determine the correlation between the anti-HLA class I IgG antibodies and posttransplant events during the first 4 months after renal transplantation. From 200 renal allograft recipients, 549 serum samples were retrospectively evaluated. Patients who experienced graft dysfunction confirmed by biopsy had three serum samples tested: before, during (within 24 hours), and after the event. The presence of anti-HLA antibodies was observed in recipients with chronic allograft nephropathy (60%); acute rejection (clinical criteria without biopsy 57.1%); rejection types IIA (7.1%), IIB (40%), and III (50%); borderline changes (42.8%); acute tubular necrosis (34.4%); infarction (25%); and no rejection (12.5%). We observed a high incidence of anti-HLA class I IgG antibodies during acute tubular necrosis, borderline changes, acute rejection types IIB and III, and chronic allograft nephropathy.

The detection and definition of IgM alloantibodies in the presence of IgM autoantibodies using flowPRA beads

We have developed a flow cytometry-based screening method using FlowPRA (One Lambda) human leukocyte antigen (HLA) class I panel beads and FlowPRA (One Lambda) HLA class I specificity beads for the detection and definition of immunoglobulin (Ig)M HLA-specific antibodies in the presence of IgM autoantibodies. Forty-six autoantibody-positive patients who were on the waiting list for a renal transplant (56 sera) were tested in parallel with FlowPRA (One Lambda) HLA class I beads and FlowPRA (One Lambda) control beads. Sera that were positive for IgM HLA class I antibodies were subsequently tested with FlowPRA HLA class I specificity beads to determine the HLA specificities. Thirteen of the 46 patients were positive for IgM HLA class I-specific antibodies. Eleven of the 13 had previous failed transplants and 2 were awaiting a primary transplant. For 9 of the 13 positive patients, IgM HLA class I specificities were defined. We have demonstrated the presence of IgM HLA-specific antibodies in patients with IgM autoantibodies. This study demonstrates the value of FlowPRA HLA class I panel and specificity beads for the detection and definition of IgM HLA class I-specific antibodies.

Relationship of donor-specific class-I anti-HLA antibodies detected by ELISA after kidney transplantation on the development of acute rejection and graft survival

BACKGROUND

The objective of this study was to evaluate the role of post-transplant donor-specific anti-HLA antibodies (DS-HLA Abs) detected by an ELISA method on long-term graft survival.

METHODS

The serum pre-/post-transplant profile of anti-HLA Abs was analysed in 71 renal transplant patients by ELISA. The HLA specificity of positive sera was analysed by a different ELISA method. According to the results, patients were classified into two different groups: those who either developed DS-HLA Abs or significantly increased their panel-reactive antibody (PRA) (group A) and those who did not (group B).

RESULTS

Thirteen out of 71 patients showed post-transplant DS-HLA Abs and were included in group A, whereas the remaining 58 were placed in group B. The incidence of acute rejection (AR) was significantly higher in group A than in group B (77 vs 10%). In addition, seven out of eight patients from group A had graft loss secondary to AR, whereas one of nine grafts lost in group B was due to AR. When analysing the clinical outcome according to HLA class specificity, only patients with HLA-I Abs lost their grafts due to vascular AR. The remaining patients with HLA-II Abs who lost their grafts also had HLA-I Abs. In four of the eight patients who lost their grafts, DS HLA-I Abs were detected several days before AR.

CONCLUSIONS

The detection of DS HLA-I Abs in the post-transplant period may provide a good marker for AR and graft loss due to immunological origin. Monitorization of these Abs by ELISA may be a useful tool for tailoring immunosuppression after kidney transplantation.

Formation of donor-specific human leukocyte antigen antibodies after kidney transplantation: correlation with acute rejection and tapering of immunosuppression

BACKGROUND

Before kidney transplantation, a serological crossmatch is routinely performed between donor and recipient to prevent hyperacute rejection by donor-specific anti-human leukocyte antigen (HLA) antibodies. After transplantation, the presence of these antibodies is not routinely monitored. We wanted to know whether donor-specific anti-HLA antibodies are detectable during acute rejection (AR), before or after reduction of immunosuppression in kidney transplant recipients who were converted from cyclosporine A (CsA) to the less nephrotoxic azathioprine (AZA) or mycophenolate mofetil (MMF) at 1 year after transplantation.

METHODS

Plasma samples were collected before transplantation, at several time points after transplantation, and during AR. Antibodies were measured in 29 patients: 5 patients with AR during the first year after transplantation (before conversion), 14 patients with AR after conversion or dose-reduction of AZA or MMF, and a control group of 10 patients without AR during a follow-up of 2 years (1 year before and 1 year after conversion of immunosuppression). Antibodies were measured by complement-dependent cytotoxicity assay, enzyme-linked immunosorbent assay (ELISA), and flow-cytometry in a crossmatch with donor spleen cells.

RESULTS

Donor-specific antibodies were not detectable after transplantation in the control group without AR, nor in patients with AR shortly after transplantation during CsA therapy. After conversion from CsA to AZA or MMF, antibodies appeared only in one patient after graft failure followed by transplantectomy and in patients during AR on AZA but not on MMF therapy.

CONCLUSION

In this patient group, we could not detect donor-specific antibodies during CsA treatment, not even at the time of AR using three different techniques. Donor-specific antibodies were primarily present during AR in patients converted from CsA to AZA and were not found in the sera from patients converted to MMF.

Comparison of different techniques for detection of anti-HLA antibodies in sera from patients awaiting kidney transplantation

The aim of the present study was to compare different techniques of HLA antibody detection in patients waiting for a transplant. Two methods of HLA antibody screening were compared: the complement-dependent cytotoxicity (CDC) test and the enzyme-linked immunosorbent solubility assay (ELISA). Three different commercial kits for the latter assay were tested: the kits were produced by One Lambda (O.L.) and SANG STAT for prescreening and specificity determination, and GTI only for prescreening. Of the two techniques, only CDC can detect IgM. The study included 207 serum samples selected from 192 patients waiting for a first kidney transplant. The conclusions are that O.L. is more sensitive than CDC and the other ELISA kits and is much faster for analysing a serum (taking only a few hours), but costs about 16 times more than CDC and does not detect IgM antibodies, so can be used only in support of CDC.

Kidney graft failure and presensitization against HLA class I and class II antigens

BACKGROUND

It is well known that kidney transplant recipients with preformed lymphocytotoxic antibodies against HLA antigens have an increased graft rejection rate. However, the individual contribution of anti-HLA class I and class II antibodies to this phenomenon is poorly understood. We investigated the clinical relevance of preformed anti-HLA class I and class II antibodies on graft outcome in more than 4000 kidney recipients.

METHODS

Pretransplant sera of 4136 cadaver kidney recipients from 28 transplant centers were tested in ELISA for IgG-anti-HLA class I and IgG-anti-HLA class II antibodies. The influence of antibody reactivity on graft survival was analyzed.

RESULTS

Four hundred eighty of the anti-HLA class I antibody-positive recipients had a graft survival rate at 2 years of 77+/-2%, compared with an 84+/-1% rate in 3656 anti-HLA class I antibody-negative recipients (P<0.0001), and 770 anti-HLA class II-positive recipients had a graft survival rate of 79+/-2%, compared with an 84+/-1% rate in 3366 anti-HLA class II-negative patients (P<0.0001). Importantly, good 2-year graft survival rates of 85+/-3% and 84+/-2%, respectively, were observed in 206 anti-HLA class I-positive/class II-negative and 496 anti-HLA, class I-negative/class II-positive recipients. In contrast, the 274 recipients positive for both types of antibodies showed a poor graft survival rate of 71+/-3% (P<0.0001). Among 853 patients who received a well-matched kidney (0 or 1 HLA-A+B+DR mismatch), sensitization against either class I or class II, or both, had no deleterious effect. However, in 113 class I and class II antibody-positive patients who received a kidney with > or =3 HLA-A+B+DR mismatches, the 2-year graft survival rate was only 60+/-5%.

CONCLUSION

Presensitization of first kidney transplant recipients against either HLA class I or class II is of no clinical consequence, whereas sensitization against both HLA class I and class II results in increased rejection of HLA mismatched grafts.

HLA-antibody testing: the immune phagocytosis inhibition test is superior to the PRA-STAT and NIH lymphocytotoxic test with respect to specificity

We compared the specificity and sensitivity of four different methods for the detection of antibodies specific for HLA antigens. The NIH version of the complement-dependent cytotoxic test (CDC) was used as the gold standard to which we compared two Fcgamma receptor (FcgammaR)-dependent immune phagocytosis inhibition tests (IPI) and one commercial enzyme-labelled immunosorbent assay (ELISA) with soluble HLA class I-antigen preparations bound to the plate (PRA-STAT). Both IPI tests are based on the fact that HLA-antibodies specifically bind to antigens on the monocyte surface via their Fab portion, and in so doing block a neighbouring FcgammaR with their Fc region. This blockade prevents phagocytosis of IgG-coated red blood cells (RBCs), which can be measured either microscopically (IPIm) or photometrically (IPIp). The four assays were used in blind tests on 20 human alloantisera or monoclonal antibodies with known HLA-antigen reactivities. Additionally, two monoclonal antibodies and one human serum were titrated to elucidate the sensitivity of each test. After all tests were completed, the identities of the samples were disclosed. Both IPI methods detected and identified all clinically relevant HLA class I and class II specific antibodies. In contrast, the CDC was not able to detect noncytotoxic HLA-antibodies and HLA class II specific antibodies; however, it detected clinically insignificant IgM lymphocytotoxins. The PRA-STAT assay enabled identification of all cytotoxic and noncytotoxic IgG antibodies with specificity for HLA-class I antigens. With respect to sensitivity, the CDC and the IPI methods were superior to the PRA-STAT. These facts demonstrate the advantage of IPI methods in the detection of clinically relevant HLA-antibodies.

Platelet alloantibodies in transfused patients

BACKGROUND

Patients receiving cellular blood components may form HLA antibodies and platelet-specific alloantibodies.

STUDY DESIGN AND METHODS

Serum samples from a cohort of 252 patients with hematologic or oncologic diseases who are receiving cellular blood components were studied for platelet-reactive antibodies. Specificity of platelet alloantibodies was determined with a panel of typed platelets

RESULTS

Platelet-reactive antibodies were detected in the sera of 113 patients (44.8% of 252), HLA antibodies in the sera of 108 (42.9%), and platelet-specific antibodies in the sera of 20 (8%). The following platelet-specific antibodies were identified: anti-HPA-5b (n = 10), anti-HPA-1b (n = 4), anti-HPA-5a (n = 2), anti-HPA-1a (n = 1), anti-HPA-2b (n = 1), anti-HPA-1b+5b (n = 1), and anti-HPA-1b+2b (n = 1). Fifteen sera from the 108 patients with anti-HLA (13.9%) contained additional platelet-specific alloantibodies, while in 5 sera, platelet-specific alloantibodies only were detected: anti-HPA-5b (n = 4) and anti-HPA-1a (n = 1). Of the 108 sera with HLA antibodies, 29 (26.9%) showed discordant results when studied with the lymphocytotoxicity test and the glycoprotein-specific immunoassay. Ten sera contained panreactive antibodies against platelet glycoproteins (GP) IIb/IIIa, GPIa/IIa, and/or GPIb/IX. Alloimmunization occurred in 58.3 percent of female patients with previous pregnancies, but in only 23.3 percent of those without previous pregnancies (p = 0.0049).

CONCLUSION

Platelet alloantibody specificities in transfused patients (predominantly anti-HPA-5b and -1b with antigen frequencies <30% among whites) differ significantly from those observed in patients with neonatal alloimmune thrombocytopenia or posttransfusion purpura, in whom anti-HPA-1a (antigen frequency >95%) is the most prevalent specificity. HLA antibody detection yields discordant results when the lymphocytotoxicity assay and a glycoprotein-specific immunoglobulin-binding assay are used.

REJECTION OF A KIDNEY TRANSPLANT DOES NOT ALWAYS LEAD TO PRIMING OF CYTOTOXIC T CELLS AGAINST MISMATCHED DONOR HLA CLASS I ANTIGENS1

BACKGROUND

Previous studies showed that graft rejection is often associated with the presence of primed cytotoxic T cells (CTLs) with a high avidity for donor cells. Similar high avidity CTLs have been found in individuals who have formed IgG anti-HLA antibodies. The presence of such CTLs to a specific HLA mismatch is therefore considered to be a reflection of an activated immune system, and a contraindication for retransplantation with a donor sharing this particular HLA class I mismatch.

METHODS

In our study we investigated whether patients have always primed CTLs against all individual HLA class I mismatches present on a rejected graft. Therefore, 14 patients who had undergone transplantectomy after irreversible kidney graft rejection were analyzed with respect to donor-specific CTLp frequencies and the presence or absence of high avidity CTLs directed against HLA class I mismatches present on the rejected graft.

RESULTS

Patients, who have not formed anti-HLA antibodies against the donor have mainly naive CTLs. Most of the patients, that have developed IgG anti-HLA antibodies against a donor mismatch, have primed CTLs directed against that particular mismatch. However, patients with IgM anti-HLA antibodies only, and patients with IgG anti-HLA antibodies in historical sera but no IgG anti-HLA antibodies in current sera, have mainly naive CTLs against the donor HLA mismatch.

CONCLUSION

Our results suggest that it is not always necessary to exclude repeated HLA class I mismatches for a subsequent transplantation. In addition to good anti-HLA antibody screening, the CTLp-assay may be a useful tool for donor-selection in retransplant candidates.

Detection of HLA-specific IGG antibodies using single recombinant HLA alleles: the MonoLISA assay

BACKGROUND

Because of the presence of confounding antigens, the assignment of HLA antibody specificity is difficult in highly sensitized patients, and the definition of an acceptable HLA mismatch requires a significant workload per patient. We describe a new ELISA method, monoLISA, for detection of immunoglobulin (Ig)G HLA antibody using single recombinant HLA class I monomers bound to microtiter plates.

METHODS

HLA-A2 and -B8 monomers were synthesized and used as screening targets for 85 sera from renal patients. The sera contained various IgG and IgM HLA-specific antibodies, including anti-A2 and anti-B8,defined in a conventional complement-dependent cytotoxicity test (CDC). Investigations were performed to determine possible effects on antibody binding of differential monomer peptide presentation as well as lack of glycosylation.

RESULTS

A good correlation was found between CDC-defined specificities and the reactivity observed with HLA monomers. MonoLISA attained means of 100% sensitivity and 92.5% specificity compared with CDC. Neither the presence of different peptides, nor the absence of glycosylation of the monomer affected the ability of monoLISA to detect antibody.

CONCLUSION

This study demonstrates that the mono-LISA method for HLA antibody detection is valid. Because this has the potential to reduce the work involved in screening sensitized patients awaiting transplantation for HLA antibodies, resources aimed at increasing the number of constructed monomers would be well targeted.

Involvement of antibody-dependent apoptosis in graft rejection

BACKGROUND

Both humoral factors and apoptosis have been recently suggested to play a role in chronic allograft rejection. However, a link between alloantibodies and grafted cell apoptosis has never been proposed. Using the aortic allograft model in the rat, we have previously demonstrated the presence of IgG associated with the disappearance of donor endothelial and medial smooth muscle cells. In the present study, we tested the interaction between recipient allosera, enriched with antibodies by presensitization, and primary culture of cardiovascular cells of donor origin.

METHODS

For this purpose endothelial cells, smooth muscle cells, adventitial fibroblasts, and cardiac myocytes of donor origin were cultured. Binding of alloantisera to these cells was analyzed by flow cytometry. Apoptosis of donor cells was evaluated by Tdt-mediated d' UTP-FITC nick end labeling, 4',6-diamidino-2-phenylindole and DNA ladder techniques. The alloantisera were compared with anti-MHC class I monoclonal antibodies. Finally the colocalization of antibodies and apoptosis was investigated in vivo.

RESULTS

In vitro, alloantisera bind to cardiovascular cells of donor origin. These cells expressed MHC class I but not MHC class II. There was a partial competition between anti-MHC I mouse monoclonal antibody and alloantisera mainly of the IgG isotype. Alloantisera bound to, but did not induce lysis of, donor RBC. Alloantisera induced apoptosis of donor cardiovascular cells as assessed by the typical morphological aspect of the donor cells after 24 hr of incubation. These data were confirmed by the Tdt-mediated d' UTP-FITC nick end labeling positivity of the cells and the fragmentation of the nucleus visualized by 4',6-diamidino-2-phenylindole and DNA ladder techniques. Similar apoptosis was induced by specific monoclonal antibodies directed against the MHC class I of donor cells. Primary culture of similar vascular cells of recipient origin was insensitive to alloantisera directed against donor alloantigens. Finally, in vivo, using allopresentization and aortic allografts, an association of alloantibody binding and endothelial cell apoptosis was observed at day 5, and a similar association with smooth muscle cell apoptosis on day 12 after grafting.

CONCLUSION

These data demonstrate the role of humoral injury in chronic allograft rejection and suggest new therapeutical approaches focused on the induction of resistance to antibody-dependent apoptosis.

Detection of HLA class I and II antibodies by ELISA and complement-dependent cytotoxicity before and after transplantation

BACKGROUND

Anti-class I IgG can be detected by complement-dependent cytotoxicity (CDC) and by ELISA. We compared ELISA and CDC for both class I and class II antibodies on method agreement and relation to rejection-free and graft survival.

METHODS

Peak, current, and posttransplant sera (n=429) of 143 renal allograft patients were tested by National Institutes of Health technique (NIHT), two-color fluorescence (TCF), and ELISA. Method agreement was assessed by intraclass correlation coefficient (ICC). Rejection and graft survival were analyzed by uni- and multivariate techniques. The screening results for each serum were compared, as was the change in result of current to posttransplant serum.

RESULTS

The ICC of ELISA and NIHT was insufficient; it was lower for TCF than NIHT. Graft survival was not related to the result of any assay. Rejection-free survival was related to ELISA and NIHT in current and posttransplant serum. With the NIHT, the change in percent panel-reactive antibody (%PRA) correlated better with rejection than it did with ELISA. The combined antibody status of current and posttransplant serum was a risk factor for rejection in all assays, and for TCF also in multivariate analysis. The rejection rate was higher if the posttransplant serum was ELISA-negative/CDC-positive, rather than ELISA-positive/CDC-negative. For ELISA, class I specificities (and not %PRA) in peak and current sera were related to rejection, even if the antibodies were not donor-directed. In the case of the National Institutes of Health technique (NIHT), %PRA and not specificity was related to rejection. Class II antibodies were never related to rejection.

CONCLUSIONS

ELISA and NEIT are complementary screening techniques in this patient population. They are of equal predictive value for rejection. The optimal strategy in combining these techniques must be determined.

The application of flow cytometry to histocompatibility testing

Flow cytometry is a powerful technique that enables the sensitive and quantitative detection of both cellular antigens and bound biological moieties. This article reviews how flow cytometry is increasingly being used as histocompatibility laboratories for the analysis of antibody specificity and HLA antigen expression. A basic description of flow cytometry principles and standardisation is given, together with an outline of clinical application in the areas of pre-transplant cross-matching, antibody screening, post-transplant antibody monitoring and HLA-B27 detection. It is concluded that flow cytometry is a useful multi-parametric analytical tool, yielding clinical benefit especially in the identification of patients at risk of early transplant rejection.

Anti-HLA antibodies after solid organ transplantation

We have cited more than 23 studies showing that de novo development of anti-HLA antibodies is associated with increased acute and chronic rejection and decreased graft survival in kidney, heart, lung, liver, and corneal transplants. Antibodies to both HLA class I and class II antigens seem to be detrimental. Antibodies of the IgG isotype and possibly the IgM isotype were clinically relevant. Most studies showed that donor-specific antibodies were associated with rejection and graft loss. Therefore, HLA antibodies provide a clinical readout for patient alloreactivity that may have the ability to distinguish graft dysfunction due to immunologic and nonimmunologic causes. Antibody may act as a critical trigger for rejection of allografts and may serve as an early indicator of a slowly smoldering chronic rejection that is not manifested at a given time by biochemical measures such as serum creatinine levels. The effectiveness of various drugs on chronic rejection should be evaluable by their effects on HLA antibody production. We predict that recently developed ELISA and flow cytometry techniques using purified HLA antigen will increase the clinical relevance of posttransplantation HLA antibody monitoring by (1) allowing the detection of low levels of donor antibody; (2) easily distinguishing the isotype and target (HLA class I or class II) of the antibodies; and (3) correlating the antibody with specific graft pathology.

Utilization of crossmatch techniques for renal transplantation

The pre-transplant cytotoxic crossmatch test is a necessary requirement for renal transplantation to proceed. However, there is no universally accepted policy on the clinical significance of a positive flow-cytometric crossmatch despite the increasing use of this technique. Differences in clinical significance found by different groups may be due to the outcome measures used and differences in the technique. The definition of a positive crossmatch can affect the results and investigators may gain information of clinical importance by considering changes in antibody levels over a series of samples from individual patients. The use of sensitive screening methods may assist in the interpretation of crossmatch results. Pre- and post-transplant crossmatching may provide data which can be used to modify immunosuppression in patients at risk of graft dysfunction.