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

Acute and chronic antibody-mediated rejection in pediatric kidney transplantation

Acute antibody-mediated rejection is a diagnostic challenge in renal transplantation medicine. However, it is an important diagnosis to make, since chronic antibody-mediated rejection (CAMR) is the main cause of long-term graft loss. Antibody-mediated rejection is diagnosed by detecting donor-specific antibodies (DSAs) in the blood in combination with observing typical histomorphological signs in kidney biopsy, as described in the Banff classification. Therapy is based on the removal of DSAs by administering intravenous immunoglobulins (IVIGs), plasmapheresis, or immunoadsorption. Reoccurrence of antibodies is diminished by the use of rituximab, increased immunosuppression, and in some cases additional experimental substances. A combination of these techniques has been shown to be successful in the majority of cases of acute and chronic antibody-mediated rejection. Routine DSA monitoring is warranted for early detection of antibody-mediated rejection.

Denatured class I human leukocyte antigen antibodies in sensitized kidney recipients: prevalence, relevance, and impact on organ allocation

BACKGROUND

Single antigen flow beads assays may overestimate sensitization because of the detection of supposedly irrelevant antibodies recognizing denatured class I human leukocyte antigens (HLAs).

METHODS

Sera of 323 HLA-sensitized kidney transplant candidates positive with a class I HLA single antigen flow beads assay were retested after acid treatment of the beads. Denatured HLA antibodies were identified according to ratio between the measured fluorescence intensity for treated and nontreated beads. T-lymphocyte flow cytometry crossmatches were performed to characterize the ability of these antibodies to recognize HLA on normal cells as a surrogate of their potential clinical relevance. Their impact on organ allocation was evaluated through a calculated panel reactive antibody. The utility of single antigen flow beads largely devoid of denatured HLA (iBeads) was also evaluated.

RESULTS

Denatured HLA antibodies were detected in 39% of the patients. They provided much less positive flow cytometry crossmatches than anti-native HLA antibodies (16% vs. 83%, P<0.0001). Removing the HLA-A and HLA-B antigens targeted by denatured HLA antibodies from unacceptable antigens lowered the calculated panel reactive antibody for 90 patients, sometimes dramatically. The iBeads assay demonstrated nearly the same ability to predict crossmatch results than the acid treatment assay.

CONCLUSION

Denatured class I HLA antibodies are common, but the antigens they target should not be considered as unacceptable in most cases, because they negatively impact access to a transplant while predominantly providing negative sensitive crossmatches. The iBeads assay seems to be a valuable alternative to better define unacceptable antigens.

Survival in sensitized lung transplant recipients with perioperative desensitization

Donor-specific HLA antibodies (DSA) have an adverse effect on short-term and long-term lung transplant outcomes. We implemented a perioperative strategy to treat DSA-positive recipients, leading to equivalent rejection and graft survival outcomes. Pretransplant DSA were identified to HLA-A, B, C, DR and DQ antigens. DSA-positive patients were transplanted if panel reactive antibody (PRA) ≥30% or medically urgent and desensitized with perioperative plasma exchange, intravenous immune globulin, antithymocyte globulin (ATG), and mycophenolic acid (MPA). PRA-positive/DSA-negative recipients received MPA. Unsensitized patients received routine cyclosporine, azathioprine and prednisone without ATG. From 2008-2011, 340 lung-only first transplants were performed: 53 DSA-positive, 93 PRA-positive/DSA-negative and 194 unsensitized. Thirty-day survival was 96 %/99%/96% in the three groups, respectively. One-year graft survival was 89%/88%/86% (p = 0.47). DSA-positive and PRA-positive/DSA-negative patients were less likely to experience any ≥ grade 2 acute rejection (9% and 9% vs. 18% unsensitized p = 0.04). Maximum predicted forced expiratory volume (1 s) (81%/74%/76%, p = NS) and predicted forced vital capacity (81%/77%/78%, respectively, p = NS) were equivalent between groups. With the application of this perioperative treatment protocol, lung transplantation can be safely performed in DSA/PRA-positive patients, with similar outcomes to unsensitized recipients.

Impact of donor mismatches at individual HLA-A, -B, -C, -DR, and -DQ loci on the development of HLA-specific antibodies in patients listed for repeat renal transplantation

We have analyzed the relationship between donor mismatches at each HLA locus and development of HLA locus-specific antibodies in patients listed for repeat transplantation. HLA antibody screening was undertaken using single-antigen beads in 131 kidney transplant recipients returning to the transplant waiting list following first graft failure. The number of HLA mismatches and the calculated reaction frequency of antibody reactivity against 10,000 consecutive deceased organ donors were determined for each HLA locus. Two-thirds of patients awaiting repeat transplantation were sensitized (calculated reaction frequency over 15%) and half were highly sensitized (calculated reaction frequency of 85% and greater). Antibody levels peaked after re-listing for repeat transplantation, were independent of graft nephrectomy and were associated with length of time on the waiting list (odds ratio 8.4) and with maintenance on dual immunosuppression (odds ratio 0.2). Sensitization was independently associated with increasing number of donor HLA mismatches (odds ratio 1.4). All mismatched HLA loci contributed to the development of HLA locus-specific antibodies (HLA-A: odds ratio 3.2, HLA-B: odds ratio 3.4, HLA-C: odds ratio 2.5, HLA-DRB1: odds ratio 3.5, HLA-DRB3/4/5: odds ratio 3.9, and HLA-DQ: odds ratio 3.0 (all significant)). Thus, the risk of allosensitization following failure of a first renal transplant increases incrementally with the number of mismatches at all HLA loci assessed. Maintenance of re-listed patients on dual immunosuppression was associated with a reduced risk of sensitization.

Concordance and discordance in anti-HLA antibody testing

BACKGROUND

Correct identification of the specificity of antibodies directed against HLA using single antigen Luminex beads (SALB) is essential in current HLA laboratory practice for transplantation. The aim of this study was to investigate the magnitude of concordance and discordance among laboratories in testing for anti-HLA antibodies using SALB.

METHOD

35 sera were distributed by the ASHI Proficiency Testing Program to HLA laboratories worldwide. We analyzed 4335 test results submitted between April 2010 and April 2013 by participating laboratories.

RESULTS

SALB was used by approximately 94% of the participating laboratories, yet concordant assignment of antibody specificity was imperfect. For each serum, the assignment of an average of 10 antibody specificities was discordant. Disagreement was observed for antibodies directed against common as well as uncommon antigens. The assignment of an average of 15 antibody specificities in each "positive" serum appeared to be influenced by vendor-dependent causes. Inter-vendor concordance was lower than intra-vendor concordance, indicating that vendor dependent factors may be a central cause for disagreement.

CONCLUSIONS

Our study illustrates the prevalence of concordance and discordance, also affected by unpremeditated causes, in reporting SALB antibody results. Insufficient concordance and standardization in antibody testing may have practical implications for organ allocation and organ sharing programs.

HLA antibody detection with solid phase assays: great expectations or expectations too great?

Alloantibodies directed against HLA antigens, are a barrier to long-term solid organ allograft survival. The clinical impact of preformed, donor-directed HLA alloantibodies range from acceptable risk to unequivocal contraindication for organ transplantation. HLA antibodies are key factors that limit patient access to donor organs. Serological methods were once the only approach to identify HLA antigens and antibodies. Limitations in these technologies led to the development of solid phase approaches. In the early 1990s, the development of the polymerase chain reaction enabled DNA-based HLA antigen testing to be performed. By the mid-1990s, microparticle-based technology that utilized flow cytometry for analysis was developed to detect both classes I and II HLA antibodies. These methodologies revolutionized clinical histocompatibility testing. The strengths and weaknesses of these assays are described in detail in this review.

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.

The role of donor-specific HLA alloantibodies in liver transplantation

The impact of donor-specific HLA alloantibodies (DSA) on short- and long-term liver transplant outcome is not clearly defined. While it is clear that not all levels of allosensitization produce overt clinical injury, and that liver allografts possess some degree of alloantibody resistance, alloantibody-mediated adverse consequences are increasingly being recognized. To better define the current state of this topic, we assembled experts to provide insights, explore controversies and develop recommendations for future research on the consequences of DSA in liver transplantation. This article summarizes the proceedings of this inaugural meeting. Several insights emerged. Acute antibody-mediated rejection (AMR), although rarely diagnosed, is increasingly understood to overlap with T cell-mediated rejection. Isolated liver allograft recipients are at increased risk of early allograft immunologic injury when preformed DSA are high titer and persist posttransplantation. Persons who undergo simultaneous liver-kidney transplantation are at risk of renal AMR when Class II DSA persist posttransplantation. Other under-appreciated DSA associations include ductopenia and fibrosis, plasma cell hepatitis, biliary strictures and accelerated fibrosis associated with recurrent liver disease. Standardized DSA testing and diagnostic criteria for both acute and chronic AMR are needed to distil existing associations into etiological processes in order to develop responsive therapeutic strategies.

HLA antibody screening in kidney transplantation: current guidelines

BACKGROUND

In organ transplantation, the introduction of the solid phase immunoassay technology radically changed the practice of antibody monitoring against human leukocyte antigens (HLA).

PURPOSE

Precise identification of antibody specificities in complex sera of sensitized patients and monitoring of low levels of donor-specific HLA antibodies in the posttransplant phase became possible. However, at the same time, new technical problems and great variation emerged in the interpretation of test results, indicating a need for standardization.

CONCLUSION

In May 2012, The Transplantation Society (TTS) recruited a panel of laboratory and clinical experts to discuss emerging testing and clinical management issues that are associated with antibody testing in organ transplantation. In this article, we provide a summary of the TTS recommendations formulated in this international effort on the standardization of antibody monitoring in kidney transplantation.

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.

Kidney transplantation in immunologically high-risk patients

An increased number of sensitized patients await kidney transplantation (KTx). Sensitization has a major impact on patient mortality and morbidity due to prolonged waiting time and may preclude live donor transplantation. However, recent reports have shown that KTx can be performed successfully using novel immunosuppressive protocols. This study presents our experience with patients displaying donor-specific antibody (DSA) (+). We enrolled 5 lymphocyte cross-match (LCM) negative (complement-dependent cytotoxicity) and panel-reactive antibody (PRA) plus DSA-positive patients mean fluorescein intensity [MFI] > 1000) who underwent living kidney donor procedures. All subjects were females and their mean age was 36.7 years. In our protocol, we started mycophenolate mofetil (2 g/d), tacrolimus (0.01 mg/kg) and prednisolone (0.5 mg/kg) on day -6. We performed 2 sessions of total plasma exchange (TPE) with albumin replacement and administered 2 doses of IVIG (5 g/d). On day -1, we added rituximab (200 mg). On the operation day and on day +4, the patients received doses of basiliximab. Serum samples were taken on days -6, 0, and 30 as well as at 1 year after transplantation. All patients displayed immediate graft function. Mean basal DSA titer was 5624 MFI. After desensitization, the MFI titers decreased at the time of transplantation to 2753 MFI, and were 2564 MFI at the 1st month and 802 MFI at 1st year. Three patients experienced acute rejection episodes (60%). After treatment for rejection, the average follow-up was 17 months and last creatinine levels were 0.6-0.8 mg/dL (minimum-maximum). In conclusion, KTx can be succesfully performed in sensitized patients displaying DSA. However, there seems to be a greater acute rejection risk. There is no consensus regarding adequate doses of IVIG or plasmapheresis treatments; furthermore, more studies are needed to clarify the safe MFI titer of the DSA.

Technical aspects of HLA antibody testing

PURPOSE OF REVIEW

Since the landmark studies of Patel and Terasaki, pretransplant identification of donor-directed HLA alloantibodies (DSAs) has been a critical prelude to renal allograft transplantation. Pretransplant, DSAs may be an acceptable risk or an unconditional contraindication to transplantation depending on the particular donor : recipient combination. Posttransplant, DSAs are associated with episodes of acute rejection, chronic rejection, and graft loss. Thus, monitoring for such antibodies is an important aspect of patient care.

RECENT FINDINGS

The development of solid-phase antibody detection assays significantly enhanced our ability to identify HLA antibodies, taking virtual crossmatching from concept to reality. At the root of these detection assays are two questions that have been asked for almost 50 years: are donor-directed HLA antibodies present and, if so, are they clinically relevant? While the technology related to solid-phase antibody detection has seemingly allowed the first question to be answered with exquisite sensitivity and specificity, can the same be said for question 2?

SUMMARY

Solid-phase antibody detection assays have clear benefits over historical approaches to antibody identification, but are not flawless. In fact, the limitations of these assays are frequently ignored. Herein, the strengths and weaknesses of solid-phase antibody detection are highlighted.

Different impact of pretransplant anti-HLA antibodies detected by Luminex in highly sensitized renal transplanted patients

It is well know that anti-HLA antibodies are an important obstacle in kidney transplantation. Our aim was to study the clinical impact of pretransplant donor specific anti-HLA antibodies (HLA-DSA), in highly sensitized (HS) patients. We analyzed retrospectively the day-of-transplant sera by Luminex Single Antigen Assay (LSA) in HS patients, and the results were correlated with episodes of humoral and cellular rejection as well as with graft and patient survival. All HS subjects received the same induction therapy and rejection episodes were biopsy proven. Thirteen patients (56.5%) preformed HLA-DSA, and we observed higher incidence of acute rejection in aforementioned patients than in the pre-transplant negatives DSA recipients (77% versus 30%, P = 0.03). The one-year graft survival was significantly reduced in positive pre-transplant HLA-DSA patients (60% versus 100%, P = 0.01 Breslow). The positive predicted value of HLA-DSA in relation to rejection reached 100% if patients lost their previous graft in the first year after transplant. Among anti-HLA antibodies present in patients before transplant, HLA-DSA were significantly associated with high risk of acute humoral and cellular rejection and reduced graft survival in posttransplant outcome. The negative impact of these antibodies was even higher when patients suffered an early loss of the previous transplant.

Influence of test technique on sensitization status of patients on the kidney transplant waiting list

The exquisitely sensitive single antigen bead (SAB) technique was shown to detect human leukocyte antigen (HLA) antibodies in sera of healthy male blood donors. Such false reactions can have an impact on critical decisions, especially with respect to the determination of unacceptable HLA-antigen mismatches in patients awaiting a kidney transplant. We tested pretransplant sera of 534 patients on the kidney waiting list using complement-dependent cytotoxicity (CDC), enzyme-linked immunosorbent assay (ELISA) and SAB in parallel. Evidence of HLA antibodies was obtained in 5% of patients using CDC, 14% using ELISA, and 81% using SAB. Among patients without history of an immunizing event, 77% showed evidence of HLA antibodies in SAB. In contrast 98% of these patients were negative in ELISA and CDC. In patients without an immunizing event, SAB-detected antibodies reacted not always weakly but with mean fluorescence intensity (MFI) values as high as 14 440. High-MFI-value antibodies were found in some of these patients with HLA specificities that are rather common in general population, consideration of which would lead to unjustified exclusion of potential kidney donors. False SAB reactions can be unveiled by testing with additional antibody assays. Denial of donor kidneys to recipients based on HLA-antibody specificities detected exclusively in the SAB assay is not advisable.

Report of the second joint meeting of ESOT and AST: current pipelines in biotech and pharma

Following the first joint meeting organized by the European (ESOT) and American (AST) Societies of Transplantation in 2010, a second joint meeting was held in Nice, France, on October 12-14, 2012 at the Palais de la Mediterannee. Co-chairs of the scientific advisory committee were Dr. Flavio Vincenti (AST) and Dr. Teun Van Gelder (ESOT). The goal was to discuss the key unmet needs in solid organ transplantation with the opportunity to interrelate current basic research efforts with clinical translation. Thus, the topic of this second meeting "Transformational therapies and diagnostics in transplantation" was devised and a summary of this meeting follows.

Solid phase assay measuring C4d deposition to determine complement fixation by HLA-specific antibodies

The definition of HLA-specific antibodies in solid organ transplant patients is a necessary tool for recipient selection prior to transplantation and monitoring for rejection post transplant. Solid phase assays can detect both complement fixing and non-complement fixing HLA-specific antibodies. Here we describe a method for determining the presence of complement fixing HLA-specific antibodies using a sensitive solid phase assay.

Algorithms for the determination of unacceptable HLA antigen mismatches in kidney transplant recipients

One of the major tasks of human leukocyte antigen (HLA) laboratories is the pretransplant determination of unacceptable HLA antigen mismatches (UAM) in organ transplant recipients. HLA antigen specificities are determined against which the patient has circulating alloantibodies that are expected to harm the transplanted organ. Using the information on UAM, negative crossmatch (XM) prediction or 'virtual XM' is possible when a potential donor's complete HLA typing is available. Before the introduction of solid-phase antibody detection assays, UAM were determined using the complement-dependent cytotoxicity methodology. After the introduction of the single antigen bead technique, however, various UAM determination algorithms have emerged. In this report, six different laboratories worldwide present how they determine UAM in their collective of kidney transplant recipients in the pretransplant phase and proceed thereafter to transplantation.

Four-year allograft survival in a highly sensitized combined liver-kidney transplant patient despite unsuccessful anti-HLA antibody reduction with rituximab, splenectomy, and bortezomib

Although donor-specific lymphocytotoxic antibodies are regarded as a contraindication for kidney transplantation (KTx), the data available for liver or combined liver or kidney transplantation (cLKTx) are scarce. Here, we report a case of a highly sensitized young man receiving his sixth liver and second kidney graft. Multiple anti-HLA antibodies were present at the time of transplantation. As a result of suspected antibody-mediated graft damage, the patient was treated with rituximab, plasmapheresis, intravenous immunoglobulins, splenectomy, and bortezomib to decrease the antibody production. So far, patient and allograft survival has reached 4 years despite failure to achieve a permanent reduction of anti-HLA antibodies, and particularly nondonor directed antibodies.

Lung transplantation in patients with pretransplantation donor-specific antibodies detected by Luminex assay

BACKGROUND

New methods of solid-phase assays, such as Luminex assay, with high sensitivity in detecting anti-human leukocyte antigen (HLA) antibodies (Abs), have increased the proportion of sensitized candidates waiting for lung transplantation (LTx). However, how to apply these results clinically during graft allocation is debated: strict exclusion of candidates with Luminex-positive results can lead to lost opportunities for Tx. We retrospectively analyzed the clinical impact of pre-LTx Luminex-detected Abs on post-LTx outcomes for patients who underwent LTx before the availability of Luminex assay.

METHODS

We analyzed data for 56 successive patients who underwent LTx before 2008 and were considered to not have anti-HLA Abs by then-available methods of detection at the date of their LTx. Pre-LTx sera from these patients were retested by Luminex assay. Using log-rank test, freedom from bronchiolitis obliterans syndrome (BOS) and graft survival were compared between patients with and without pre-LTx Luminex-detected anti-HLA Abs classes I and II and donor-specific Abs (DSA) classes I and II.

RESULTS

Freedom from bronchiolitis obliterans syndrome was lower, and mortality was higher for patients with than those without pre-LTx Luminex-detected DSA class II (P=0.004 and P=0.007, respectively) but did not differ for patients with and without DSA class I or anti-HLA Abs class I or II.

CONCLUSIONS

It suggests to avoid attributing graft with forbidden antigens to sensitized candidates with Luminex-detected DSA class II and to evaluate the role of specific posttransplantation protocols for LTx candidates who require emergency LTx.

Systematic comparison of four cell- and Luminex-based methods for assessment of complement-activating HLA antibodies

BACKGROUND

Efforts to increase the specificity and sensitivity of human leukocyte antigen (HLA) antibody detection assays recently led to the establishment of two novel Luminex bead-based assays to detect complement-activating antibodies by the assessment of complement products C1q or C4d. Here, we present a systematic comparison of the four methods, complement-dependent lymphocytotoxicity (CDC) and C1q-, C4d-, and IgG-Luminex, to assess or predict the complement-binding capability of HLA IgG antibodies.

METHODS

Forty-five sera of highly immunized patients have been assessed by in-house modified C1q- and C4d-Luminex assays and compared with standard CDC and IgG-Luminex.

RESULTS

Antibody specificities assigned by the C1q- and C4d-Luminex assay revealed an excellent concordance of 94% and 97% for HLA class I and II, respectively. Complement-fixing HLA class II antibodies were found less frequently among IgG antibodies compared with class I. Both C1q- and C4d-Luminex detected, on average, three times more specificities than CDC. Although we found a high correlation of mean fluorescence intensity values between C1q- and C4d-Luminex assays, IgG mean fluorescence intensity was not a suitable surrogate marker for the prediction of complement binding.

CONCLUSIONS

C1q- and C4d-Luminex assays are characterized by an increased sensitivity and specificity compared with CDC, the current standard in detecting complement-fixing HLA antibodies. Pretransplantation risk assessment for transplantation but also posttransplantation monitoring are important applications for both assays to improve overall allograft survival.

Role and Value of Luminex(®)-Detected HLA Antibodies before and after Kidney Transplantation

SUMMARY

The complement-dependent lymphocytotoxicity (CDC) method has been the classical technique to detect human leukocyte antigen (HLA) antibodies in sera of patients who are listed for kidney transplantation. Because of the drawbacks of CDC, such as low sensitivity and low resolution in characterizing antibody specificities, the more specific ELISA technology was introduced in the 1990s which utilizes solubilized HLA molecules instead of lymphocytes. During the last 10 years, the introduction of the Luminex-based single antigen bead (L-SAB) technology, which uses recombinant single HLA molecules, allows detection and characterization of HLA antibodies at greater sensitivity than CDC and ELISA. A drawback associated with this technique is that the interpretation of results is demanding and requires comprehensive experience in HLA antibody diagnostics. Herein we discuss the current role and value of L-SAB technology in the clinical management of sensitized kidney transplant recipients.

Consensus guidelines on the testing and clinical management issues associated with HLA and non-HLA antibodies in transplantation

BACKGROUND

The introduction of solid-phase immunoassay (SPI) technology for the detection and characterization of human leukocyte antigen (HLA) antibodies in transplantation while providing greater sensitivity than was obtainable by complement-dependent lymphocytotoxicity (CDC) assays has resulted in a new paradigm with respect to the interpretation of donor-specific antibodies (DSA). Although the SPI assay performed on the Luminex instrument (hereafter referred to as the Luminex assay), in particular, has permitted the detection of antibodies not detectable by CDC, the clinical significance of these antibodies is incompletely understood. Nevertheless, the detection of these antibodies has led to changes in the clinical management of sensitized patients. In addition, SPI testing raises technical issues that require resolution and careful consideration when interpreting antibody results.

METHODS

With this background, The Transplantation Society convened a group of laboratory and clinical experts in the field of transplantation to prepare a consensus report and make recommendations on the use of this new technology based on both published evidence and expert opinion. Three working groups were formed to address (a) the technical issues with respect to the use of this technology, (b) the interpretation of pretransplantation antibody testing in the context of various clinical settings and organ transplant types (kidney, heart, lung, liver, pancreas, intestinal, and islet cells), and (c) the application of antibody testing in the posttransplantation setting. The three groups were established in November 2011 and convened for a "Consensus Conference on Antibodies in Transplantation" in Rome, Italy, in May 2012. The deliberations of the three groups meeting independently and then together are the bases for this report.

RESULTS

A comprehensive list of recommendations was prepared by each group. A summary of the key recommendations follows. Technical Group: (a) SPI must be used for the detection of pretransplantation HLA antibodies in solid organ transplant recipients and, in particular, the use of the single-antigen bead assay to detect antibodies to HLA loci, such as Cw, DQA, DPA, and DPB, which are not readily detected by other methods. (b) The use of SPI for antibody detection should be supplemented with cell-based assays to examine the correlations between the two types of assays and to establish the likelihood of a positive crossmatch (XM). (c) There must be an awareness of the technical factors that can influence the results and their clinical interpretation when using the Luminex bead technology, such as variation in antigen density and the presence of denatured antigen on the beads. Pretransplantation Group: (a) Risk categories should be established based on the antibody and the XM results obtained. (b) DSA detected by CDC and a positive XM should be avoided due to their strong association with antibody-mediated rejection and graft loss. (c) A renal transplantation can be performed in the absence of a prospective XM if single-antigen bead screening for antibodies to all class I and II HLA loci is negative. This decision, however, needs to be taken in agreement with local clinical programs and the relevant regulatory bodies. (d) The presence of DSA HLA antibodies should be avoided in heart and lung transplantation and considered a risk factor for liver, intestinal, and islet cell transplantation. Posttransplantation Group: (a) High-risk patients (i.e., desensitized or DSA positive/XM negative) should be monitored by measurement of DSA and protocol biopsies in the first 3 months after transplantation. (b) Intermediate-risk patients (history of DSA but currently negative) should be monitored for DSA within the first month. If DSA is present, a biopsy should be performed. (c) Low-risk patients (nonsensitized first transplantation) should be screened for DSA at least once 3 to 12 months after transplantation. If DSA is detected, a biopsy should be performed. In all three categories, the recommendations for subsequent treatment are based on the biopsy results.

CONCLUSIONS

A comprehensive list of recommendations is provided covering the technical and pretransplantation and posttransplantation monitoring of HLA antibodies in solid organ transplantation. The recommendations are intended to provide state-of-the-art guidance in the use and clinical application of recently developed methods for HLA antibody detection when used in conjunction with traditional methods.

Living donor kidney transplantation in patients with donor-specific HLA antibodies enabled by anti-CD20 therapy and peritransplant apheresis

OBJECTIVE

Due to increasing waiting times for deceased donor kidneys, living donor kidney transplantation is increasingly performed in the presence of donor-specific antibodies (DSA).

METHODS

Twenty-three patients with Luminex-detected DSA were successfully desensitized by anti-CD20 therapy and immunoadsorption (N = 19) or plasmapheresis (N = 4) and received a kidney transplant from a living donor. Twelve of the 23 patients (52%) had a positive CDC and/or ELISA crossmatch result before desensitization. Six patients were negative in CDC as well as ELISA screening but positive in Luminex for DSA.

RESULTS

The 23 patients received a median of 8 apheresis treatments before and 5 treatments after transplantation. Induction therapy was performed with either thymoglobulin (N = 11) or basiliximab (N = 12). The 2-year graft survival rate was 100%. At last follow up, a median of 12 months after transplantation, median serum creatinine was 1.42 mg/dL, median MDRD-GFR 59.5 mL/min/1.73 m(2), and median urinary protein-to-creatinine ratio 0.12. Ten out of fourteen patients (71%) who had completed the first year after transplantation by the time of analysis had no DSA by day 360. Acute T-cell mediated rejection was diagnosed in one patient (4%), and antibody-mediated changes were found in 5 patients (22%). Four out of these 5 patients showed evidence of persistent (N = 2) or reemerging plus/minus de novo DSA (N = 2) on day 360, and the 2 patients with persistent DSA lost their allograft subsequently on days 750 and 810, respectively. Infectious complications were infrequent.

CONCLUSIONS

Our previously described treatment algorithm for desensitization of living donor kidney transplant recipients with DSA results in good graft outcomes with a low rate of side effects.

Inter and intra laboratory concordance of HLA antibody results obtained by single antigen bead based assay

Single antigen bead based assays (SAB) to identify antibodies to HLA are marketed as a qualitative test, however often used as a quantitative test as the results provide mean fluorescence intensity (MFI) which is found to correlate with the strength/avidity of the antibody. We studied the between and within laboratory variability in performing the SAB from one manufacturer. Ten samples were tested at four laboratories according to the manufacturer's suggested protocol. Additionally same samples were tested on four consecutive days in one laboratory. All tests were performed using the same lot of beads and secondary antibody. Results were classified as positive at four different MFI cutoffs: 1000, 5000, 8000 and 10,000. MFI values across and within the laboratory were compared in a pair-wise fashion with Pearson's correlations. Overall concordance for Class-I was 97% between laboratories and 98% within laboratory at all cutoffs. Pair-wise Pearson correlation between laboratories was 0.989-0.99, while within laboratory it was 0.998-0.999. For Class-II, overall concordance between and within laboratory was 98%. Pair-wise Pearson correlation between laboratories was 0.991-0.997, while within laboratory it was 0.997-0.999. There is good correlation between laboratories and within laboratory using the same manufacturer, same lot and same protocol while performing SAB.

Prevention of antibody-mediated kidney transplant rejection

There is increasing evidence that antibody-mediated rejection is the major cause of late kidney graft failure. Prevention of antibody-mediated allograft damage has therefore become an important issue in kidney transplantation. Such prevention starts already before transplantation with the avoidance of sensitizing events. When a patient is already sensitized, precise characterization of alloantibodies and exact HLA typing of the donor at the time of transplantation are mandatory. To ensure timely and successful transplantation of highly sensitized patients, desensitization, and inclusion in special programs such as the Eurotransplant Acceptable Mismatch Program should be considered. After transplantation, close monitoring of kidney function, testing for the de novo development or changing characteristics of alloantibodies, and attention to non-adherence to immunosuppression is obligatory. In the current overview, we discuss the currently available measures for the prevention of antibody-mediated kidney graft rejection.

Pretransplant donor-specific HLA class-I and -II antibodies are associated with an increased risk for kidney graft failure

Pretransplant risk assessment of graft failure is important for donor selection and choice of immunosuppressive treatment. We examined the relation between kidney graft failure and presence of IgG donor specific HLA antibodies (DSA) or C1q-fixing DSA, detected by single antigen bead array (SAB) in pretransplant sera from 837 transplantations. IgG-DSA were found in 290 (35%) sera, whereas only 30 (4%) sera had C1q-fixing DSA. Patients with both class-I plus -II DSA had a 10 yr graft survival of 30% versus 72% in patients without HLA antibodies (p < 0.001). No significant difference was observed in graft survival between patients with or without C1q-fixing DSA. Direct comparison of both assays showed that high mean fluorescence intensity values on the pan-IgG SAB assay are generally related to C1q-fixation. We conclude that the presence of class-I plus -II IgG DSA as detected by SAB in pretransplant sera of crossmatch negative kidney recipients is indicative for an increased risk for graft failure, whereas the clinical significance of C1q-fixing IgG-DSA could not be assessed due to their low prevalence.

Donor-specific HLA antibodies and graft function in children after renal transplantation

BACKGROUND

The presence of circulating donor-specific human leukocyte antigen antibodies (HLA-DSA) has been associated with chronic antibody-mediated rejection, leading to progressive graft dysfunction and poor graft survival.The aim of this study was to investigate the incidence and significance of HLA-DSA in paediatric renal transplantation(RTx) patients.

METHODS

A total of 294 post-transplant serum samples from 123 RTx patients were retrospectively analysed for HLA antibodies. Positive samples were further tested for HLADSA by a Luminex Single Antigen bead assay. The antibody findings were correlated to measured glomerular filtration rate(GFR) and clinical outcome.

RESULTS

HLA antibodies were detected in half of the routine samples (140/294) taken 1 month to 10 years after RTx, and 40% (62/140) of these were HLA-DSA. Overall, one-third(42/123) of the patients had HLA-DSA, which mostly(65%) reacted against class II antigens. Detection of HLADSA was not associated with poor GFR at the time of sampling, and no exceptional deterioration of GFR after the HLA-DSA detection was noted in individual patients regardless of the antibody level. The presence of HLA-DSA in the first 2 years posttransplantation was not associated with poorer graft function later on.

CONCLUSION

Detection of HLA antibodies is common in children after RTx, and this finding, as such, does not predict any deterioration of graft function.

Chronic alloantibody mediated rejection

Alloantibodies clearly cause acute antibody mediated rejection, and all available evidence supports their pathogenic etiology in the development of chronic alloantibody mediated rejection (CAMR). But the slow evolution of this disease, the on-going immunosuppression, the variations in titer of alloantibodies, and variation in antigenic targets all complicate identifying which dynamic factors are most important clinically and pathologically. This review highlights the pathological factors related to the diagnosis of CAMR, the time course and natural history of this disease. What is known about CAMR pathogenesis is discussed including alloantibodies, the role of complement, gene activation, and Fc effector cell function. Therapy, which is problematic for this disease, is also discussed, including on-going and potential therapies and their limitations.

Living donor kidney transplantation in crossmatch-positive patients enabled by peritransplant immunoadsorption and anti-CD20 therapy

Living donor kidney transplantation in crossmatch-positive patients is a challenge that requires specific measures. Ten patients with positive crossmatch results (n = 9) or negative crossmatch results but strong donor-specific antibodies (DSA; n = 1) were desensitized using immunoadsorption (IA) and anti-CD20 antibody induction. IA was continued after transplantation and accompanied by HLA antibody monitoring and protocol biopsies. After a median of 10 IA treatments, all patients were desensitized successfully and transplanted. Median levels of mean fluorescence intensity (MFI) of Luminex-DSA before desensitization were 6203 and decreased after desensitization and immediately before transplantation to 891. Patients received a median of seven post-transplant IA treatments. At last visit, after a median follow-up of 19 months, 9 of 10 patients had a functioning allograft and a median Luminex-DSA of 149 MFI; serum creatinine was 1.6 mg/dl, and protein to creatinine ratio 0.1. Reversible acute antibody-mediated rejection was diagnosed in three patients. One allograft was lost after the second post-transplant year in a patient with catastrophic antiphospholipid syndrome. We describe a treatment algorithm for desensitization of living donor kidney transplant recipients that allows the rapid elimination of DSA with a low rate of side effects and results in good graft outcome.

Algorithm to manage highly sensitized kidney transplant recipients in Poland

OBJECTIVE

Programs for immunized transplant recipients are essential to achieve graft survivals comparable to those of non-immunized recipients. The threshold in Poland is a PRA by the complement-dependent cytotoxicity (CDC) method greater than 50%, which includes approximately 3.8% of the patients. At the same time the United Network for Organ Sharing there recipients represent approximately 16% of the waiting list in the United Network for Organ Sharing (UNOS). The underestimation of the immunized group in Poland may be due to differences in laboratory techniques to assess alloantibodies.

MATERIALS AND METHODS

This study investigated 55 potential recipients with a PRA by CDC>50%. We used the following algorithm to assess their immunization: Luminex screening test for an HLA antibody; specificity assessed with Luminex Single Antigen, vPRA (evaluation of immunization of the patient); and analysis of acceptable HLA incompatibilities (HLAMatchmaker).

RESULTS

All recipients were positive class I anti-HLA antibodies and 94.5% were positive for class II. For the groups of subjects with PRA-CDC from 50% to 79% versus those greater than 80%, the average values of PRA-CDC were 62.2% and 89.5%, respectively. The virtual PRA results for these groups were 95.7% and 97.2%, respectively. In addition, anti-HLA-Cw, anti-DQ and anti-DP antibodies were detected in 77%, 84%, and 51% of recipients, respectively. Immunized recipients reported to the next transplant were characterized by the antibodies against mismatch only in 68%. For all potential recipients, additional acceptable non-compliance was determined with HLAMatchmaker: 152 specificity for locus A and 252 for locus B.

CONCLUSIONS

Evaluation of immunization status of recipient candidates should be routinely performed using tests to assess class and specificity as well as level of alloantibodies to enable determination of a safe potential donor. As a routine test, PRA-CDC underestimates the number of highly immunized patients. Exclusion from the list of patients with repeated non-compliance is a simplification, which reduces their chance for transplantation.