Characterization of lymphocytotoxic antibodies causing a positive crossmatch in renal transplantation. Relationship to primary and regraft outcome

HLA in transplantation

The human major histocompatibility complex is a family of genes that encodes HLAs, which have a crucial role in defence against foreign pathogens and immune surveillance of tumours. In the context of transplantation, HLA molecules are polymorphic antigens that comprise an immunodominant alloreactive trigger for the immune response, resulting in rejection. Remarkable advances in knowledge and technology in the field of immunogenetics have considerably enhanced the safety of transplantation. However, access to transplantation among individuals who have become sensitized as a result of previous exposure to alloantigens is reduced proportional to the breadth of their sensitization. New approaches for crossing the HLA barrier in transplantation using plasmapheresis, intravenous immunoglobulin and kidney paired donation have been made possible by the relative ease with which even low levels of anti-HLA antibodies can now be detected and tracked. The development of novel protocols for the induction of tolerance and new approaches to immunomodulation was also facilitated by advances in HLA technology. Here, we review the progress made in understanding HLAs that has enabled organ transplantation to become a life-saving endeavour that is accessible even for sensitized patients. We also discuss novel approaches to desensitization, immunomodulation and tolerance induction that have the potential to further improve transplantation access and outcomes.

Reason and Resolution of High Negative Control Beads in Solid-Phase Immunoassay

OBJECTIVES

The Luminex technology is the most sensitive diagnostic method for HLA antibody detection and identification. However, the interpretation of immunoassays is commonly affected by the artifact, and non-specific background. Sera from some patients show high negative control bead (NC) value, which makes assessing and interpretation of HLA antibodies difficult. In this study, we evaluated the effect of Adsorb Out reagent, dithiothreitol (DTT), and Ethylenediaminetetraacetic acid (EDTA) on the NC median fluorescence intensity value by comparing treated versus untreated patient sera. In addition, we wanted to identify whether kidney disease and administered medication influenced high NC median fluorescence intensity values by comparing patient versus control results.

MATERIALS AND METHODS

HLA antibody screening was performed on 3500 serum samples. Sera were analyzed using the standard protocol for Luminex antibody screening. Sera with high NC values were preincubated with Adsorb Out, DTT, and EDTA. Screening of these sera was then performed.

RESULTS

We found that 4% of samples showed high NC values. Adsorb Out, DTT, and EDTA decreased the NC values at 723.5 (299.25-1443) versus 85 (34-218; P < .001), at 723.5 (299.25-1443) versus 184 (106-597; P < .001), and at 723.5 (299.25-1443) versus 455 (131-1177; P = .004). These succeeded in bringing back NC values to normal range in 69.2%, 43%, and 30% of treated sera, respectively. In addition, the differences of corticoids, immunosuppressive, and heparin drugs between patients and controls were statistically significant (P < .001, < .001, and = .043). However, presence of kidney disease was not significant between these groups.

CONCLUSIONS

All pretreatments had an important effect in decreasing negative control values, with Adsorb Out having highest efficiency. Serum-specific components could contribute to high negative control bead median fluorescence intensity values. Further studies are needed to determine the adequate pretreatment of patient sera.

The Humoral Theory of Transplantation: Epitope Analysis and the Pathogenicity of HLA Antibodies

Central to the humoral theory of transplantation is production of antibodies by the recipient against mismatched HLA antigens in the donor organ. Not all mismatches result in antibody production, however, and not all antibodies are pathogenic. Serologic HLA matching has been the standard for solid organ allocation algorithms in current use. Antibodies do not recognize whole HLA molecules but rather polymorphic residues on the surface, called epitopes, which may be shared by multiple serologic HLA antigens. Data are accumulating that epitope analysis may be a better way to determine organ compatibility as well as the potential immunogenicity of given HLA mismatches. Determination of the pathogenicity of alloantibodies is evolving. Potential features include antibody strength (as assessed by antibody titer or, more commonly and inappropriately, mean fluorescence intensity) and ability to fix complement (in vitro by C1q or C3d assay or by IgG subclass analysis). Technical issues with the use of solid phase assays are also of prime importance, such as denaturation of HLA antigens and manufacturing and laboratory variability. Questions and controversies remain, and here we review new relevant data.

Effect of Heart Valve Decellularization on Xenograft Rejection

OBJECTIVES

Endothelial cells harbor many antigenic determinants that may be targets for the immune system. The aim of this study was to determine the immunologic effects of decellularization, using 3 different methods, on xenograft rejection.

MATERIALS AND METHODS

In a sterile plate containing phosphate-buffered saline, fresh sheep aortic heart valves were decellularized using 3 different enzymatic methods: with 900 μg/mL of collagenase at 40°C (method A), with 450 μg/mL of collagenase at 4°C (method B), and with 900 μg/mL of collagenase at 4°C (method C). Intact and decellularized valves were implanted subdermally into inbred male albino rabbits and extracted after 21 days (extra valve pieces were also extracted after 60 days, as control samples, for assessing chronic rejection). Valves were histologically analyzed for inflammatory cell infiltration. Subendothelial structure integrity was determined using surface electron microscope.

RESULTS

No inflammatory cell infiltration was seen around the decellularized valve with method A, and no subendothelial structure change was observed by surface electron microscope. Infiltration of immune cells involved in rejection was not seen around valves decellularized with method B, although the subendothelial structure was relatively preserved and valve stiffness was increased. With method C, we observed a foreign body-type reaction around the intact valve and the decellularized valve.

CONCLUSIONS

Method A is considered the optimal method of decellularization in our study, as this method significantly reduced the immune response to xenograft tissue, while maintaining subendothelial tissue.

[Immunological monitoring in kidney transplantation: 13 years experience of a Moroccan histocompatibility laboratory]

PURPOSE OF STUDY

The quality of the immunological monitoring is crucial because it determines the success of the kidney transplantation. The scope of this work is to describe the experience of the department of immunological unity of the Ibn Sina university hospital in Rabat regarding the immunological monitoring of patients transplanted between 2001 and 2014.

PATIENTS AND METHODS

Patient samples were collected from nephrology services of different public and private hospitals of Morocco. The tests conducted in the context of immunological monitoring are ABO typing, HLA-A, B, DR, DQ typing, anti-HLA antibodies detection and identification and cross-match.

RESULTS

One hundred and fourteen benefited from a pre- and post-transplant immunological monitoring in our laboratory. The percentage of recipients having between 2 and 5 stored sera is 60.5 before transplantation and 56.1 after transplantation. Immunized patients account for 22.8% before the transplant and 17.6% after transplantation. Ninety-seven patients still have a functional graft, while 4 of them had DSA of low intensity before transplantation. Five immunological rejections were reported while the cross-match were negative and no DSA was identified before transplantation. Patient survival and graft at 1 year was 98.2% and 92.7% respectively.

CONCLUSION

Conducting regular immunological monitoring is sometimes difficult in our context, however, the results are satisfactory in terms of graft and patients survival.

Utility of HLA Antibody Testing in Kidney Transplantation

HLA antigens are polymorphic proteins expressed on donor kidney allograft endothelium and are critical targets for recipient immune recognition. HLA antibodies are risk factors for acute and chronic rejection and allograft loss. Solid-phase immunoassays for HLA antibody detection represent a major advance in sensitivity and specificity over cell-based methods and are widely used in organ allocation and pretransplant risk assessment. Post-transplant, development of de novo donor-specific HLA antibodies and/or increase in donor-specific antibodies from pretransplant levels are associated with adverse outcomes. Although single antigen bead assays have allowed sensitive detection of recipient HLA antibodies and their specificities, a number of interpretive considerations must be appreciated to understand test results in clinical and research contexts. This review, which is especially relevant for clinicians caring for transplant patients, discusses the technical aspects of single antigen bead assays, emphasizes their quantitative limitations, and explores the utility of HLA antibody testing in identifying and managing important pre- and post-transplant clinical outcomes.

Detection of donor-specific antibodies in kidney transplantation

INTRODUCTION

Precise and timely detection of human leukocyte antigen (HLA) donor-specific antibodies (DSAs) is vital for evaluating humoral immune status of patients pre- and post-transplantation.

SOURCE OF DATA

Clinically relevant articles on theory, development, methodology and application of HLA-DSA testing in kidney transplantation.

AREAS OF AGREEMENT AND CONTROVERSY

The availability of solid phase HLA-antibody testing revolutionized our ability to detect HLA-DSA and to appreciate their significance in kidney transplant outcome. The best approach to determine the strength, immunogenicity and pathogenicity of HLA antibodies still remains controversial.

GROWING POINTS

Assays to identify complement-binding antibodies were developed. Their clinical utilization, pre- and post-transplantation, is currently under investigation. Appreciation of the complexity of HLA-DQ antibodies should lead to better assignment of unacceptable antibodies and cPRA calculation.

AREAS TIMELY FOR DEVELOPING RESEARCH

Characterization of HLA-antibody epitopes, and utilization of epitope matching to better define compatible donors could contribute to better transplant outcomes.

Desensitization for solid organ and hematopoietic stem cell transplantation

Desensitization protocols are being used worldwide to enable kidney transplantation across immunologic barriers, i.e. antibody to donor HLA or ABO antigens, which were once thought to be absolute contraindications to transplantation. Desensitization protocols are also being applied to permit transplantation of HLA mismatched hematopoietic stem cells to patients with antibody to donor HLA, to enhance the opportunity for transplantation of non-renal organs, and to treat antibody-mediated rejection. Although desensitization for organ transplantation carries an increased risk of antibody-mediated rejection, ultimately these transplants extend and enhance the quality of life for solid organ recipients, and desensitization that permits transplantation of hematopoietic stem cells is life saving for patients with limited donor options. Complex patient factors and variability in treatment protocols have made it difficult to identify, precisely, the mechanisms underlying the downregulation of donor-specific antibodies. The mechanisms underlying desensitization may differ among the various protocols in use, although there are likely to be some common features. However, it is likely that desensitization achieves a sort of immune detente by first reducing the immunologic barrier and then by creating an environment in which an autoregulatory process restricts the immune response to the allograft.

Complement-dependent cytotoxicity crossmatch

The complement-dependent cytotoxic crossmatch is an informative test that detects alloantibodies in pre- and post-transplant patients, which may dictate clinical management of transplant patients. While challenging to perform, the cytotoxic crossmatch represents the only assay that provides direct evidence for the presence of potentially pathologic (i.e., cytotoxic) alloantibodies. The cytotoxic crossmatch combines patient (recipient) serum and donor cells. If donor-reactive alloantibodies are present in patient serum, these antibodies can bind donor cells. Antibody-antigen complexes, in turn, can activate the complement cascade, leading to complement-mediated cytotoxicity. Two commonly performed cytotoxic crossmatches, using donor lymphocytes as target cells, are described.

The role of complement in antibody-mediated rejection in kidney transplantation

Over the past decade, several studies have suggested that the complement system has an active role in both acute and chronic allograft rejection. These studies have been facilitated by improved techniques to detect antibody-mediated organ rejection, including immunohistological staining for C4d deposition in the allograft and solid-phase assays that identify donor-specific alloantibodies (DSAs) in the serum of transplant recipients. Studies with eculizumab, a humanized monoclonal antibody directed against complement component C5, have shown that activation of the terminal complement pathway is necessary for the development of acute antibody-mediated rejection in recipients of living-donor kidney allografts who have high levels of DSAs. The extent to which complement activation drives chronic antibody-mediated injury leading to organ rejection is less clear. In chronic antibody-mediated injury, early complement activation might facilitate chemotaxis of inflammatory cells into the allograft in a process that later becomes somewhat independent of DSA levels and complement factors. In this Review, we discuss the different roles that the complement system might have in antibody-mediated allograft rejection, with specific emphasis on renal transplantation.

The Induction of IgM and IgG Antibodies against HLA or MICA after Lung Transplantation

The production of IgG HLA antibodies after lung transplantation (LTx) is considered to be a major risk factor for the development of chronic rejection, represented by the bronchiolitis obliterans syndrome (BOS). It has recently been observed that elevated levels of IgM HLA antibodies also correlates with the development of chronic rejection in heart and kidney transplantation. This study investigates the relationship between IgM and IgG antibodies against HLA and MICA after lung transplantation. Serum was collected from 49 patients once prior to transplantation and monthly for up to 1 year after lung transplantation was analyzed by Luminex to detect IgM and IgG antibodies against HLA and MICA. The presence of either IgM or IgG HLA and/or MICA antibodies prior to or after transplantation was not related to survival, gender, primary disease, or the development of BOS. Additionally, the production of IgG alloantibodies was not preceded by an increase in levels of IgM, and IgM levels were not followed by an increase in IgG. Under current immune suppressive regimen, although the presence of IgM antibodies does not correlate with BOS after LTx, IgM ^high IgG ^low HLA class I antibody titers were observed more in patients with BOS compared to patients without BOS.

Interpretation of positive flow cytometric crossmatch in the era of the single-antigen bead assay

BACKGROUND

Prognosis of renal transplants with positive flow cytometric crossmatch (FCXM) remains controversial.

METHODS

We analyzed the outcome of these kidney transplant recipients by human leukocyte antigen (HLA) donor-specific antibodies (HLA-DSA) using single-antigen bead (SAB) assays in major histocompatibility complex classes I and II. We compared them with controls with a negative FCXM.

RESULTS

Forty-five patients consecutively transplanted with a positive FCXM had significantly more acute rejection episodes than the control patients (33.3% vs. 8.9%, P=0.002). Risk of acute rejection was increased with day 0 (D0) positive T-cell FCXM (odds ratio [OR]=9.04, P=0.002), D0 positive B-cell FCXM (OR=7.43, P=0.02), and D0 HLA-DSA identified by SAB assay (OR=6.5, P=0.03). The 21 patients with D0 positive FCXM and D0 HLA-DSA had more acute rejection (62%, P=0.0001) and a lower estimated glomerular filtration rate 1-year posttransplantation (P=0.0001), when compared with controls. Mainly anti-Cw and anti-DP HLA-DSA were found in patients displaying acute rejection. The remaining FCXM-positive patients displayed short-term outcomes similar to controls. The presence of HLA-DSA detected only by the SAB assay in the context of a negative FCXM crossmatch was not associated with increased risk of acute rejection.

CONCLUSION

Identification of HLA-DSA in D0 sera by the two sensitive techniques FCXM and SAB assay indicates which patients are at highest risk of subsequent acute allograft rejection and chronic allograft dysfunction.

Blood group O recipients associated with early graft deterioration in living ABO-incompatible kidney transplantation

BACKGROUND

Blood group O individuals are known to have larger amounts of anti-ABO blood group (anti-A/B) IgG antibodies than A or B individuals. Therefore, in ABO-incompatible (ABOI) kidney transplantation (KTX), it is expected that blood group O recipients are more likely to suffer graft damage, because anti-A/B IgG antibodies are believed to be responsible for worse graft outcomes.

METHODS

This study assessed the graft outcomes between blood group O and non-O recipients in ABOI-KTX. A total of 164 consecutive recipients who underwent ABOI-KTX between 1990 and 2007 under three different immunosuppressive protocols were enrolled in this study. The study population was divided into two groups: (i) recipients with blood group O (n=87) and (ii) recipients with blood group A or B (non-O) (n=77).

RESULTS

High anti-A/B IgG titers were predominant in the O group (P<0.001), whereas no significant difference was observed in the IgM titers. The overall graft survival rate did not differ between the two groups; however, the 6-month graft survival rate was significantly lower in the O group (86% vs. 97%, P=0.011). Among 14 recipients who suffered graft loss within 6 months after transplantation, 12 (86%) were O recipients. The cumulative incidence of acute antibody-mediated rejection was significantly higher in the O group (60 days, 31 vs. 14%, P=0.013).

CONCLUSION

Our results may indicate that being a blood group O recipient is at great risk for experiencing early allograft deterioration, probably caused by anti-A/B IgG antibodies in ABOI-KTX.

Detection of immunoglobulin G human leukocyte antigen-specific alloantibodies in renal transplant patients using single-antigen-beads is compromised by the presence of immunoglobulin M human leukocyte antigen-specific alloantibodies

BACKGROUND

Luminex-based single-antigen human leukocyte antigen (HLA) antibody detection beads (SAB) are a major advance for the characterization of HLA-specific antibodies but their clinical utility is limited unless the analysis is performed and interpreted optimally. Here, we identify problems encountered in routine monitoring of antibody levels that may give rise to misleading results, and describe how these can be overcome to provide more meaningful clinical information.

METHODS AND RESULTS

HLA class I specific antibody-binding levels were determined using SAB in the sera of 42 highly sensitized patients awaiting renal transplantation. Normalization of the results against the HLA class I specific monoclonal antibody W6/32 overcame the problems caused by variation in antigen density on SAB and also suggested the presence of alloantibodies directed against multiple HLA class I epitopes of a given specificity. Routine analysis using undiluted sera gave an incomplete assessment of antibody levels. On serum dilution, three patterns of antibody binding became apparent: most sera showed a sequential reduction in immunoglobulin G (IgG) binding levels but several sera displayed antibody binding which remained unchanged (suggesting antigen saturation) or increased IgG binding on serum dilution (suggesting inhibition of IgG binding using neat serum). The presence of immunoglobulin M (IgM) HLA-specific antibodies in sera correlated with inhibition of IgG antibody binding for the corresponding specificity and treatment of sera with dithiothreitol to eliminate IgM HLA-specific blocking antibodies restored maximum IgG antibody binding levels.

CONCLUSION

When using SAB to monitor HLA-specific antibody binding levels, sera should be pretreated with dithiothreitol to eliminate blocking IgM HLA-specific antibodies that may mask clinically relevant allosensitization.

A reevaluation of the role of IgM Non-HLA antibodies in cardiac transplantation

BACKGROUND

Preexisting IgG antibodies to donor human leukocyte antigens (HLA) are a risk factor for rapid allograft rejection. However, non-HLA antibodies, of the IgM class, also called autoreactive antibodies, are not believed to affect graft survival. The aim of this study was to determine the incidence and clinical relevance of pretransplant lymphocytotoxic non-HLA IgM antibodies on long-term cardiac allograft survival.

METHODS

A retrospective study of 616 adult recipients of cardiac allografts, transplanted at this center between 1991 and 2003, has been performed. Antibodies in pretransplant sera were initially defined using complement-dependent cytotoxicity assays, and subsequently analyzed for HLA specificities using solid phase assays.

RESULTS

HLA antibodies were present in 69 of 616 heart recipients (58 IgG, 11 IgM); in 22 of these, the antibodies were donor-specific. Non-HLA IgM antibodies were detected in 59 of 616 recipients who did not have HLA-specific antibodies; these patients had a 1, 2, 5, and 10 year survival of 55.9%, 54.2%, 49.9%, and 43.3% compared with 75.8%, 73.7%, 66.6%, and 52.8% for those without antibodies (P=0.0085 log-rank test). Multivariate analysis demonstrated pretransplant non-HLA IgM antibodies to be an independent risk factor for mortality (P=0.0001). Myocardial histology of postmortem heart and cardiac biopsies suggested an association with ischemic damage and "primary" allograft failure.

CONCLUSIONS

We propose the hypothesis that the presence of cytotoxic IgM antibodies to non-HLAs before heart transplantation maybe a risk factor for early allograft failure.

Back to the future: application of contemporary technology to long-standing questions about the clinical relevance of human leukocyte antigen-specific alloantibodies in renal transplantation

Luminex technology allows the accurate identification of human leukocyte antigen (HLA) class I and class II-specific antibodies at levels below the threshold detectable by either conventional complement-dependent lymphocytotoxicity or flow cytometry. The technology enables the analysis of complex antibody profiles in sensitized patients and gives improved definition of acceptable and unacceptable HLA specificities to guide donor kidney allocation. This helps to facilitate virtual cross-matching and avoid inappropriate shipping of kidneys for incompatible patients in distant centers. Luminex allows the cause of a positive cross-match test to be determined in a clinically relevant time scale and, when used in conjunction with lymphocytotoxic and flow cytometric cross-matching, it provides an assessment of the level of immunological risk in patients being considered as potential recipients for a particular donor kidney. Information is now emerging to enable the full clinical potential of Luminex to be realized.

[Transplantation strategies in immunized and hyperimmunized patients]

The rate of access to transplantation of hyperimmunized patients has improved thanks to a modification of the organ allocation rule in 2002 and the initiation of the Acceptable Mismatch program. Transplantation of immunized patients must be now preceded by a fine description of the characteristics of pretransplantation immunization using sensitive techniques and by an indispensable clinical and biological discussion to choose the best transplantation strategy, taking into account the risk/benefit balance for the patient of each strategy. Whichever transplantation strategy is adopted, immunosuppression should be adapted to the immunological status of the patient, often using the new therapeutic strategies (IVIg, rituximab, plasma exchange) with a specific follow-up, notably for anti-HLA antibodies, checking their evolution post treatment.

Relevance of MICA and other non-HLA antibodies in clinical transplantation

The clinical importance of HLA-specific antibodies for organ allograft outcome is well established. In the past few years, there has been an increasing interest in non-HLA antigens as targets of injury in organ transplant recipients. This increased interest has been spurred by the fact that HLA-identical kidney transplants also undergo immunological rejections. Polymorphisms within non-HLA genes associated with evoking an immune response to alloantigens are currently being studied for their association with transplant outcome. Non-HLA antigens, such as the polymorphic MHC class I-related chain A (MICA), expressed on endothelial cells have been implicated in the pathogenesis of hyperacute, acute and chronic organ allograft rejections. Use of endothelial cells as targets may clarify the specificities of other clinically relevant non-HLA antibodies in graft rejections. This review summarizes past and current knowledge of the clinical importance and specificities of non-HLA antibodies, and mechanisms by which these antibodies may contribute to graft destruction in clinical transplantation. The aims of current research into the role of non-HLA antigens and their genetics in predicting outcome are to develop an improved insight into the basic science of transplantation and to develop a risk or prognostic index for use in the clinical setting. Non-HLA antibody responses are receiving increasing interest in acute and chronic rejection and specificity, affinity, and pathogenicity need to be investigated to estimate their contribution. Undoubtedly, this will continue to be an area of interest in terms of fully understanding the role of non-HLA antigens as targets of immune-mediated injury and the potential for clinical intervention.

Detecting and monitoring human leukocyte antigen-specific antibodies

Renewed awareness of the relevance of HLA-specific antibodies to transplantation and the development of protocols to reduce or eliminate sensitization have made monitoring of antibodies and accurate interpretation of test results increasingly important. Here we review the various tests available and provide guidelines for the development of monitoring protocols.

Immunoglobulin Class (IgG, IgM) Determination by Dithiothreitol in Sensitized Kidney Transplant Candidates

Immunoglobulin class plays an important role in the histocompatibility crossmatch test to predict hyperacute rejection in kidney transplantation. The existing data indicates that immunoglobulin (Ig) M antibodies, particularly when they are autoantibodies, are not deleterious to the renal allograft. We used the reducing agent dithiotreitol (DTT) to inactivate IgM but not IgG in the crossmatch assay to help sensitized patients have the chance for successful transplantation. In this descriptive study, 57 candidates for kidney transplantation with final positive crossmatches who had a history of panel-reactive antibody (PRA) greater than 30% were selected. Two of 57 patients had systemic lupus erythematous (SLE). The sera of patients were treated by DTT and then measured for cytotoxicity against donor lymphocytes and a panel of 12 cells using the complement-dependent cytotoxicity (CDC) method. Autocrossmatch was also performed to differentiate autoantibodies and alloantibodies by the CDC method. Of the 57 patients, six subjects (10.53%) had IgM and 51 patients (89.47%) IgG in their serum against donor lymphocytes. Also against panel cells, 39 of 57 patients (68.43%) had IgG, three patients (5.26%) had IgM, and 15 patients (26.31%) had both IgG and IgM antibodies. Autolymphocytotoxic antibodies were detected in 1.75% patients (1 of 57) who had SLE. According to our results, 5.26% of the patients who were IgM-positive and IgG-negative for both crossmatch and PRA assays may experience successful kidney transplantation.

Endothelial cells as targets of allograft rejection

Endothelial cells harbor many antigenic determinants that may be targets for antibodies and, as such, induce acute or chronic antibody-mediated rejections. In certain cases of organ transplantation, antibodies reacting with endothelial cells, but not with ABO or human leukocyte antigens, can be observed and these are probably responsible for the rejection of the graft. The antigenic targets, however, are still poorly defined and the mechanisms of action of such antibodies would appear to be diverse, leading to the lack of a relevant in vitro assay for the detection of those antibodies. Increasing data suggest that, apart from direct alloimmune responses, autoimmune mechanisms might be triggered by alloreactivity and also play a significant role in the pathogenesis of the vascular lesions, the so-called chronic rejection, observed in organ allografts.

Preformed cytotoxic antibodies in potential allograft recipients: recent data

Presensitization to donor human leukocyte antigen (HLA) remains a major barrier to cell and organ transplantation, thereby contributing to patient mortality. The risks associated with transplantation in the presence of preformed antidonor HLA antibodies range from hyperacute rejection and increased frequency and severity of rejection to no appreciable effect on transplant outcome. Recent evidence has emphasized the importance of immunologic history, anti-HLA antibody class and titer, and differential organ susceptibility to antibody-mediated damage to explain differences in risk for antibody-mediated rejection. Furthermore, in studies of endothelial cells, ligation of class I molecules by subsaturating concentrations of antibodies stimulated expression of cell survival proteins, raising the possibility that, under certain conditions, antibodies promote graft accommodation providing a mechanism for the endothelium to resist immune and inflammatory damage. The discovery of capillary-bound C4d as a robust diagnostic marker for antibody-mediated rejection, coupled with the development of solid-phase assays for the identification of HLA-specific antibodies, has enhanced our ability to detect antibody-mediated rejection and interpret cross-match results. With new diagnostic tools and immunosuppression regimens such as plasmapheresis and intravenous immunoglobulin therapy targeting the humoral immune response, it is time for a concerted effort to reassess the role of alloantibodies in acute and chronic rejection.

Alemtuzumab (CAMPATH 1H) induction therapy in cadaveric kidney transplantation--efficacy and safety at five years

Alemtuzumab is a powerful lymphocyte depleting antibody currently being evaluated in solid organ transplantation. This paper describes 5-year results of a single center study of alemtuzumab as induction in renal transplantation. Thirty-three renal transplant recipients received 20 mg alemtuzumab on day 0 and 1, followed by half-dose cyclosporin monotherapy (trough concentration 75-125 ng/mL) from day 3. They were compared in a retrospective contemporaneous-controlled manner with 66 kidney transplant recipients transplanted in the same period and center who received conventional immunosuppression with cyclosporin, azathioprine and prednisolone. In the alemtuzumab group 12% of recipients died compared to 17% in the control group (p = 0.48); likewise graft loss was similar in both groups (21% vs. 26%, respectively, p = 0.58). Incidence of acute rejection was also comparable at 5 years (31.5% vs. 33.6%), although the pattern of rejection was different with 14% patients in the alemtuzumab group experiencing rejection over 1 year post-transplant compared to none in the control group. There was no significant difference between groups in terms of infection or serious adverse events. While acknowledging the limitations of a relatively small single-center study, results suggest that alemtuzumab induction allowed satisfactory long-term patient and graft survival equivalent to that seen with standard triple immunosuppression, while avoiding steroid therapy.

Antidonor Antibodies and Transplantation: How to Deal with Them Before and After Transplantation

The presence of antibodies directed against the donor has usually been considered as an absolute contraindication to transplantation. However, recent advances both in the ABO and human leukocyte antigen settings, detailed in this paper, have led to successful transplantations in the presence of antidonor antibodies, with preliminary evidence of accommodation.

Consensus opinion from the antibody working group on the diagnosis, reporting, and risk assessment for antibody-mediated rejection and desensitization protocols

During the past few decades, much of the experimental and clinical effort in solid-organ transplantation has been directed toward ameliorating or abrogating T-cell-mediated responses. As a result, universally understood and accepted nomenclature and diagnostic criteria have evolved. Humoral immunity in transplantation has yet to undergo a similar renaissance. Readers of transplant journals regularly find it difficult and often impossible to interpret data on the diagnosis and management of antibody-mediated rejection. The Antibody Working Group was assembled in an attempt to provide guidelines for the standardization of nomenclature, diagnostic criteria, reporting, antibody profiling, and risk assessment.

Comparison of allogeneic and xenogeneic in vitro T-cell proliferative responses in sensitized patients awaiting kidney transplantation

Highly sensitized patients awaiting kidney transplantation may be potential candidates for future clinical trials using pig organ donors. Because of crossreactivity between human leucocyte antigens (HLA) and swine leucocyte antigens (SLA), such patients might have heightened T-cell responses to porcine xenoantigens. We determined whether lymphocytes from allo-sensitized patients displayed secondary (cyclosporine resistant) T-cell proliferative responses against porcine xenoantigens. Lymphocytes from six non-sensitized, seven sensitized [immunoglobulin G (IgG) panel reactive antibodies (PRA) 11 to 84%], 14 highly sensitized patients (IgG PRA > 84%) and 12 healthy individuals were tested [in the presence and absence of Cyclosporin A (CsA)] to determine their proliferative response to human (allogeneic) and to porcine (xenogeneic) stimulator cells. Lymphocytes from all study groups showed a strong proliferative response to allogeneic and xenogeneic stimulator cells with no significant difference between non-sensitized and sensitized individuals. Addition of CsA (100 and 500 ng/ml) inhibited (>90%) proliferation of lymphocytes from all non-sensitized patients to both allogeneic and xenogeneic stimulators. CsA was less effective at inhibiting proliferation of lymphocytes from sensitized patients and highly sensitized patients to allogeneic stimulators [29% (n=21) and 50% (n=42) respectively were resistant to CsA inhibition (100 ng/ml)]. In contrast, cyclosporine inhibited proliferation of lymphocytes from the majority of sensitized and highly sensitized patients to xenogeneic stimulator cells [14% (n=21) and 14% (n=42) respectively were resistant to CsA inhibition (100 ng/ml)]. HLA sensitized patients awaiting renal transplantation display cyclosporine resistant proliferative T-cell responses to allogeneic stimulators but proliferative responses to xenogeneic stimulators are more amenable to suppression by CsA. This finding suggests that humoral sensitisation to HLA antigens is not necessarily indicative of a heightened in vitro T-cell response to SLA antigens.

Activated HLA class I-reactive cytotoxic T lymphocytes associated with a positive historical crossmatch predict early graft failure

BACKGROUND

Preexisting alloantibodies against the mismatched HLA class I antigens of the donor, when present in current sera, are believed to be detrimental for kidney graft survival. The relevance of a positive crossmatch with historical sera only is still a matter of debate. Previous studies showed a correlation between the presence of alloantibodies and the presence of alloactivated cytotoxic T lymphocytes (CTLs). We wondered whether the persistence of activated CTLs might explain the poor results in a proportion of patients with a historical positive crossmatch.

METHODS

We tested 10 sensitized patients to determine whether activated CTLs persist when the antibodies disappear. Limiting dilution assays were performed in the presence and absence of cyclosporine (CsA) to distinguish between activated (primed) (CsA resistant) and naive (CsA sensitive) CTLs. To test the clinical relevance of the persisting CTLs, eight sensitized patients, who underwent a kidney transplantation across a positive historical crossmatch, were retrospectively tested for the presence or absence of activated donor-specific CTLs at the day of transplantation.

RESULTS

In the first group, four patients had CsA-sensitive CTLs, three patients had CsA-resistant CTLs, and three other patients had CsA-sensitive CTLs for a particular HLA antigen and CsA-resistant CTLs for another HLA antigen. In the transplant group, four patients with CsA-sensitive CTLs at the day of transplantation were found to have a good graft function. In the other four patients, the presence of CsA-resistant donor-specific CTLs was associated with rejection and early graft loss.

CONCLUSION

The present study suggests that determining the activation state of CTLs specific for the HLA mismatch against which antibodies were present in historical sera, may be relevant to transplant outcome in patients who undergo transplantation across a positive historical crossmatch.

Primed CTLs specific for HLA class I may still be present in sensitized patients when anti-HLA antibodies have disappeared: relevance for donor selection

BACKGROUND

The presence of donor-specific HLA antibodies is generally considered to be a contraindication for transplantation, even when these antibodies are only present in historical sera. Previous studies showed that donor-specific antibodies in current sera were associated with the presence of primed cytotoxic T cells (CTLs) with a high avidity for donor HLA class I antigens. The presence of these CTLs is considered to be a reflection of an activated immune system and a contraindication for transplantation with a donor sharing these particular HLA antigens.

METHODS

In the present study we compared the incidence of primed CTLs in patients with anti-HLA antibodies in current sera and in patients with anti-HLA antibodies in historical sera only. Cytotoxic T lymphocyte precursor (CTLp) frequencies and the incidence of primed CTLs directed against HLA class I antigens to which the patient had formed antibodies were studied in 37 sensitized renal patients. As controls, antigens to which a patient has never formed antibodies were tested.

RESULTS

In patients with antibodies in current sera mainly primed CTLs were detected, whereas in patients where the antibodies had disappeared mainly naive CTLs were detected. However, in four patients primed CTLs persisted despite the fact that the HLA antibodies had disappeared.

CONCLUSION

Considering the previously described association between primed CTLs and graft rejection, these findings may be relevant for the selection of patients who can be transplanted across a positive historical crossmatch. If the antibodies have disappeared and only naive CTLs are present, a successful transplantation should be feasible. A prospective study will reveal whether this is indeed the case.

B-Cell crossmatching and kidney allograft outcome in 9031 United States transplant recipients

The predictive power of a positive B-cell crossmatch remains controversial due to the presence of cofactors, such as sensitization and human leukocyte antigen (HLA) mismatch levels. UNOS OPTN/Scientific Registry data were analyzed on 9031 cadaveric kidney graft recipients who were B-cell crossmatched during 1994 and 1995 for graft outcome. This 2-year time period was chosen so that most US transplant recipients in this study would have had a similar regimen of immunosuppression consisting of prednisone, Sandimmune, and azathioprine The two patient groups that were analyzed were B-pos (n = 336) and B-neg (n = 8,695). All T-cell crossmatches were negative. Data analyzed included donor-recipient demographics, sensitization levels, B-cell crossmatch techniques, histocompatibility mismatching, graft rejection incidence, early graft loss, cause of graft failure, and statistical analyses (univariate and multivariate) in primary and repeat graft recipients. Significant factors in both crossmatch groups included pretransplant transfusions, peak and most recent class I PRA levels, a previous kidney graft, histocompatibility mismatching at HLA-A plus -B, urine in first 24 h, and rejection incidence between discharge and 6 months post-transplantation. Class II antibody specificities and panel reactive antibody (PRA) levels were not available from the UNOS database. Fifty-seven percent of 15,896 (1994-1995) transplant recipients (n 9031) were B-cell crossmatched, and 336 of 9031 recipients (3.7%) were transplanted with a B-pos crossmatch. Sixteen percent of B-pos recipients experienced early graft loss (< 6 months) compared with 11% of B-neg recipients (p < 0.001). Both primary and repeat grafts with B-pos crossmatches experienced an increase in rejection incidence (p = 0.023) and early graft loss (p < 0.001). In the sensitized (PRA > 10%) recipient subset (n = 2,789), both primary (n = 93) and regraft (n = 52) recipients with B-pos crossmatches had a higher incidence of early graft loss at 3 months, p < 0.001 and p = 0.016, respectively. HLA-DR mismatch levels in both patient groups were not different (p = 0.109). There was a 68% increase in the odds of 3-month graft loss in B-pos versus B-neg recipients (multivariate logistic regression analysis p = 0.054, 95% confidence interval 0.99-2.85). In conclusion, a B-pos crossmatch in primary and regraft recipients, including a sensitized subset, is predictive of inferior kidney graft outcome.

Sensitisation to swine leukocyte antigens in patients with broadly reactive HLA specific antibodies

We have previously shown that IgG HLA specific antibodies in the sera of highly sensitised patients awaiting renal transplantation can cross-react with swine leukocyte antigens (SLA). In this study we determined the frequency of patient serum IgG HLA specific antibody binding to a porcine lymphocyte panel and the likelihood of locating a cross-match negative pig donor for sensitised patients. Serum samples (n = 82) were obtained from 35 sensitised [current IgG panel reactive antibodies (PRA) > 10%] and seven nonsensitised patients awaiting renal transplantation at Addenbrooke's Hospital, Cambridge, UK. Fifty sera had IgG HLA specific PRA of 11-84%, 20 had IgG PRA of >84% and 12 had 0% PRA (negative controls). Sera were absorbed with porcine erythrocytes to remove xenoreactive natural antibodies and tested for cross-reactive IgG HLA specific antibody binding by flow cytometry against a panel of porcine lymphocytes obtained from 23 human decay accelerating factor (hDAF) transgenic pigs. A total of 1,884 cross-match combinations were tested and 369 (20%) gave a positive porcine lymphocyte cross-match. For sera from sensitised patients with IgG PRA (11-64%), only 6 of 805 (0.75%) cross-match tests were positive. In contrast, for sera from patients with high IgG PRA (>64%), 363 of 805 (45%) cross-match tests were positive (p < 0.0001). There was no difference in the frequency of positive cross-matches between patient sera with IgG PRA 65-84% and highly sensitised patient sera with IgG PRA 85-100% [156/345 (45%) vs. 207/460 (45%)]. This study demonstrates that only patient sera with broadly reactive IgG HLA specific PRA (>64%) cross-react with porcine lymphocytes. If future clinical trials of xenotransplantation are undertaken, it may be of value to select a cross-match-negative pig organ donor for such patients.

Long-term kidney graft survival across a positive historic but negative current sensitized cross-match

BACKGROUND

The sensitive cross-match (XM) techniques that have been introduced for clinical transplantation can detect anti-donor immune reactivity despite a negative standard National Institute of Health (NIH) cross-match. One of them uses anti-kappa human light chain globulins (AHG). But there is some discussion about the clinical consequences of a positive AHG-XM in the historical sera that became negative in the sera collected just before the transplantation (pretransplant sera). This study was intended to assess the risk of kidney graft failure associated with a positive historic but negative pretransplant AHG-XM in allosensitized patients having a negative historic NIH-XM.

METHODS

This retrospective study includes 90 consecutive renal transplants in immunized patients performed at one center between 1985 and 1991. All of the patients had negative historical and pretransplant standard NIH lymphocytotoxic cross-matches and received the same immunosuppressive regimen. The AHG-XMs were done retrospectively using peak historic and sera collected on the day of the transplantation.

RESULTS

The AHG cross-match (AHG-XM) was positive in 17 patients, although the standard NIH cross-match was negative. Fourteen of them had a positive historical but negative pretransplant AHG-XM. The actuarial graft survival in this group of 14 patients was 100% at 1 year and 78% at 9 years compared with 90 and 67%, respectively, in patients with negative historical AHG-XM. In addition, the number of rejection episodes per patient as well as renal function at 1, 2, and 5 years were similar in the two groups. IgG anti-donor HLA class I accounted for the XM positivity in 12 of the 14 patients; most rapidly lost all antibody reactivity by NIH technique in an average time of 8 months before the transplantation. In conclusion, this study suggests that transplant patients having a negative historic NIH-XM but a positive historic AHG-XM may not be at high risk of graft failure especially if there is a well-documented sera history showing a marked decrease in PRA level before transplantation and a negative pretransplant AHG-XM.

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.

A retrospective flow cytometric crossmatch study in transplant recipients with autoreactive lymphocytotoxic antibodies

Our previous data shows renal transplant recipients with autoreactive lymphocytotoxic antibodies to have a reduced transplant survival when compared to patients without autoantibodies. This could have been due to the presence of weak IgG antibodies inhibited by the dithiothreitol used to remove IgM antibodies in the pretransplant cytotoxicity crossmatch. That possibility was investigated in a retrospective study of 52 recipients of 57 renal transplants who were recrossmatched using a more sensitive flow cytometry crossmatch (FCXM) to detect recipient IgG antibodies to donor T and/or B cell splenic lymphocytes. Fourteen of the 57 (24%) transplants failed. Six losses were within the 1st month posttransplant and four of these were immunological failures. None of the transplant failures had a positive pretransplant FCXM. These results showed that the recipients with autoantibodies did not have pretransplant IgG anti-donor antibodies. The transplant failures did not, therefore, relate to the presence of antibodies undetected by the dithiothreitol-treated cytotoxicity crossmatch.

Plasmapheresis and intravenous immune globulin provides effective rescue therapy for refractory humoral rejection and allows kidneys to be successfully transplanted into cross-match-positive recipients

BACKGROUND

Hyperacute rejection (HAR) and acute humoral rejection (AHR) remain recalcitrant conditions without effective treatments, and usually result in graft loss. Plasmapheresis (PP) has been shown to remove HLA- specific antibody (Ab) in many different clinical settings. Intravenous gamma globulin (IVIG) has been used to suppress alloantibody and modulate immune responses. Our hypothesis was that a combination of PP and IVIG could effectively and durably remove donor-specific, anti-HLA antibody (Ab), rescuing patients with established AHR and preemptively desensitizing recipients who had positive crossmatches with a potential live donor.

METHODS

The study patients consisted of seven live donor kidney transplant recipients who experienced AHR and had donor-specific Ab (DSA) for one or more mismatched donor HLA antigens. The patients segregated into two groups: three patients were treated for established AHR (rescue group) and four cross-match-positive patients received therapy before transplantation (preemptive group).

RESULTS

Using PP/IVIG we have successfully reversed established AHR in three patients. Four patients who were cross-match-positive (3 by flow cytometry and 1 by cytotoxic assay) and had DSA before treatment underwent successful renal transplantation utilizing their live donor. The overall mean creatinine for both treatment groups is 1.4+/-0.8 with a mean follow up of 58+/-40 weeks (range 17-116 weeks).

CONCLUSIONS

In this study, we present seven patients for whom the combined therapies of PP/IVIG were successful in reversing AHR mediated by Ab specific for donor HLA antigens. Furthermore, this protocol shows promise for eliminating DSA preemptively among patients with low-titer positive antihuman globulin-enhanced, complement-dependent cytotoxicity (AHG-CDC) cross-matches, allowing the successful transplantation of these patients using a live donor without any cases of HAR.