Anti-HLA donor-specific antibodies detected in positive B-cell crossmatches by Luminex predict late graft loss

Development of the Crossmatch Test in Kidney Transplantation Up to the Virtual Level

The Human Leukocyte Antigen (HLA) system forms the central part of the immune system and is crucial in the recognition and elimination of "non-self" antigens. While this role of the HLA system is essential in the effective defense of the organism against pathogens, it is undesirable in organ and tissue transplantation because it enables the recognition of mismatched HLA molecules of the donor as being foreign and stimulates the graft rejection reaction. Organ transplantation involves the introduction of antigens that are more or less mismatched to the recipient; therefore, in order to achieve the best possible match in the HLA system between the recipient and the donor, a whole series of immunogenetic tests is performed, including crossmatching (XM). If performed before kidney transplantation, it represents the final in vitro test to rule out the presence of donor-specific antibodies, which may cause graft rejection and which may not have been detected by earlier serum screening. The beginning of XM was marked by the complement-dependent cytotoxicity (CDC) method developed by Terasaki and colleagues in 1964. Later, as a result of advances in technology and the need for methods that overcome the limitations of CDC, flow cytometry and Luminex XM assays were developed. The introduction of solid-phase technology brought a new dimension to the detection of low-level HLA antibodies and the determination of their specificities, which enabled the development and implementation of the virtual XM test (vXM). It is an in silico test that assesses the immunological match between the recipient and the organ donor based on the analysis of the specificity of the antibodies present in the recipient's serum and the HLA typing of the organ donor. Each method has its own advantages and limitations, which are described below and need to be taken into account, considering their significant impact on clinical application in kidney transplantation.

HLA Compatibility and Graft Survival Rates Among Related and Unrelated Donors in Renal Transplantation

Human leukocyte antigen (HLA) compatibility between donors and recipients plays a critical role in graft survival in renal transplantation. This study evaluates the impact of HLA mismatching on graft survival and rejection among renal transplant recipients with related and unrelated donors, considering factors such as age, sex, ABO blood type, and anti-HLA antibodies. We investigated the graft survival rates between related and unrelated donors in a prospective cohort study conducted from 2018 to 2020 at Cho Ray Hospital and People's Hospital 115 in Vietnam, involving 126 related and 82 unrelated donor-recipient pairs. Over 32 months of follow-up, there was no significant difference in the rates of suspected graft rejection (P = .75) or graft loss (P = .095) between the 2 groups. However, related donors exhibited significantly higher overall survival (P = .0086) and better event-free survival (P = .0025) compared with unrelated donors. HLA matching and ABO type did not show any association with suspected graft rejection in either group. Notably, unrelated donors older than 5 years increased the risk of suspected graft rejection (hazard ratio, 4.22), and positive anti-HLA antibodies also increased this risk (hazard ratio, 4.5). Conversely, male-male donor-recipient pairs significantly decreased the risk of graft rejection by 88% compared with female-female pairs. The study concludes that although HLA matching is not different for related and unrelated donor groups, factors such as donor age, same-sex pairs, and the presence of anti-HLA antibodies are significant risk factors for graft rejection in unrelated donors. Enhancing monitoring and developing strategies for unrelated donors are essential to improve graft survival outcomes in renal transplantation.

The utility of cytolytic flow cytometry crossmatch before kidney transplantation

The donor/recipient matching in kidney transplantation is based on approved laboratory tests, which are complement-dependent cytotoxic crossmatch (CDC-XM) and flow cytometry crossmatch (FCXM). Both have some disadvantages: CDC-XM has low sensitivity, whereas FCXM does not differentiate between lytic vs. non-lytic alloantibodies. To find an improved method, we have developed a new crossmatch technique of cytolytic flow cytometry crossmatch (cFCXM), which allows for sensitive detection of clinically relevant complement-binding antibodies. The cFCXM assay detects dead cells with viability dye that ensue from the binding of allospecific lytic antibodies. In our study, 135 unsensitized kidney transplant recipients were recruited based on the CDC-XM and FCXM results and the clinical utility of cFCXM was evaluated. The 5-year follow-up for acute rejection incidents revealed that cFCXM could verify the clinical relevance of positive FCXM results as recipients with positive FCXM but negative CDC-XM had the same risk of rejection as patients with both negative CDC-XM/FCXM results. These findings suggest that cFCXM assay may provide more precise immunological risk assessment in kidney transplant recipients.

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

Background

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

Objectives

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

Methods

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

Results

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

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

Conclusions

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

A virtual crossmatch-based strategy for perioperative desensitisation in lung transplant recipients with preformed donor-specific antibodies: 3-year outcome

BACKGROUND

Preformed donor-specific antibodies (DSAs) are associated with worse outcome after lung transplantation (LTx) and migvaht limit access to LTx. A virtual crossmatch (CXM)-based strategy for perioperative desensitisation protocol has been used for immunised LTx candidates since 2012 at Foch hospital. We compared the outcome of desensitised LTx candidates with high DSA mean fluorescence intensity (MFI) and those with low or no preformed DSAs, not desensitised.

METHODS

For all consecutive LTx recipients (January-2012/March-2018), freedom from CLAD and graft survival were assessed by Kaplan-Meier analysis and Cox multivariate analysis.

RESULTS

We compared outcomes for desensitised patients with high preformed DSAs (n=39) and those with no (n=216) or low pre-formed DSAs (n=66). The desensitisation protocol decreased the level of immunodominant DSA (class I/II) at 1, 3, and 6 month post-LTx (p<0.001, p<0.01, p<0.001, respectively). Freedom from CLAD and graft survival at 3 years was similar in the desensitised group as a whole and other groups. Nevertheless, incidence of CLAD was higher with persistent high- than cleared high-level (p=0.044) or no DSAs (p=0.014). Conversely, graft survival was better with cleared high DSAs than persistent high-, low-level, and no pre-formed DSAs (p=0.019, p=0.025, and p=0.044, respectively). On multivariate analysis, graft survival was associated with cleared high DSAs (HR: 0.12 [95%CI: 0.02-0.85] versus no DSAs, p=0.035) and CLAD with persistent DSAs (HR: 3.04 [1.02-9.17] versus no preformed DSAs, p=0.048).

CONCLUSION

The desensitisation protocol in LTx recipients with high preformed DSAs was associated with satisfactory outcome, with cleared high pre-formed DSAs after desensitisation identified as an independent predictor of graft survival.

Red herrings in crossmatching kidneys for transplant

Crossmatching of prospective renal transplant donors against recipients is a mandatory component of the transplant workup, being performed for over 40 years now. Allografting patients with human leukocyte antigens which are recognized by preformed antibodies constitutes the main cause of hyperacute or acute rejections. The existence of these donor-specific anti-human leukocyte antigen antibodies (DSAs) is regarded as a contraindication for graft trans-plantation, both cadaveric and live kidney. We present two unusual cases in which both complement-dependent cytotoxicity crossmatch and DSA by Luminex were falsely positive due to autoimmune and infectious causes, but single-antigen bead assay showed these antibodies to be against nondonor antigens. After treating their basic disease, thought to be responsible for false-positive DSA, these patients became DSA negative and underwent transplantation with an uneventful posttransplant period. Our aim through these examples is to highlight the problem of false-positive crossmatch in potential renal allograft transplant recipients. Further, we propose antigenic determination of donor-specific antibodies in such patients where we suspect the immune system to be chronically activated to pick up false-positive cases and therefore increase the donor pool without compromising the transplant outcome.

Out with the old, in with the new: Virtual versus physical crossmatching in the modern era

The virtual crossmatch (VXM) is gaining acceptance as an alternative approach to assess donor:recipient compatibility prior to transplantation. In contrast to a physical crossmatch, the virtual crossmatch does not require viable donor cells but rather relies on complete HLA typing of the donor and current antibody assessment of the recipient. Thus, the VXM can be performed in minutes which allows for faster transplant decisions thereby increasing the likelihood that organs can be shipped across significant distances yet safely transplanted. Here, we present a brief review of the past 50 years of histocompatibility testing; from the original complement-dependent cytotoxicity crossmatch in 1969 to the new era of molecular HLA typing, solid-phase antibody testing and virtual crossmatching. These advancements have shaped a paradigm shift in our approach to transplantation. That is, foregoing a prospective physical crossmatch in favor of a VXM. In this review, we undertake an in-depth analysis of the pros- and cons- of physical and virtual crossmatching.Finally, we provide objective data on the selected use of the VXM which demonstrate the value of a VXM in lieu of the traditional physical crossmatch for safe and efficient organ transplantation.

Pretransplant Single Antigen Bead-Detected HLA Antibodies in Kidney Transplant Long-term Outcome: A Single-Center Cohort Experience

Single-antigen bead (SAB) platform permits the identification of antibodies not detectable by complement-dependent lymphocytotoxicity test, but their clinical significance is not completely understood. The aim of this study was to evaluate whether the presence of pretransplant SAB-detected antibodies is associated with the development of allograft failure. This is a single-center cohort study with 10-year follow-up in which 573 kidney recipients with negative pretransplant complement-dependent lymphocytotoxicity crossmatch who received transplants at the Kidney Transplant Center of Policlinico, Milan, from deceased donors between 1996 and 2005 were evaluated. Pretransplant plasma samples were retrospectively analyzed by SAB assay. Survival analyses were performed to assess the risk of allograft failures by SAB-detected antibodies. Pretransplant antibodies were found in 160 (28.0%) recipients, of whom 42 subsequently developed an allograft failure for a survival rate of 70.9% (95% confidence interval [CI), 63.5-78.4). Among those without antibodies, 58 (14.0%) returned to dialysis with a survival rate of 84.7% (95% CI, 81.0-88.4). In Cox regression analyses, patients with SAB-positivity had 2-fold higher risk of allograft failure than those who were SAB-negative (hazard ratio, 2.07; 95% CI, 1.39-2.79). Results did not change after adjustment for putative confounders. In conclusion, in this single-center cohort, 10-year allograft survival rate was significantly influenced by the presence of SAB-detected antibodies.

Combining Sensitive Crossmatch Assays With Donor/Recipient Human Leukocyte Antigen Eplet Matching Predicts Living-Donor Kidney Transplant Outcome

Introduction

Despite the different assays available for immune-risk stratification before living-donor kidney transplantation (LDKT), the precise type and number of tests to perform remain uncertain.

Methods

In a cohort of 330 consecutive LDKT patients, all of which were complement-dependent cytotoxicity (CDC)−crossmatch negative, we retrospectively analyzed the impact on main clinical outcomes of most sensitive immunoassays (complement-dependent cytotoxicity−panel-reactive antibody [CDC-PRA], flow cytometry crossmatch [FC-XM], donor-specific antibodies [DSAs], and their complement-binding capacity DSA-C3d]), together with donor/recipient HLA eplet matching. Mean follow-up was 67 months (range 24−190 months).

Results

Of 330 patients, 35 (11%) showed a CDC-PRA >20%; 17 (5%) FC-XM+; 30 (9%) DSA+, 18(5%) DSA-C3d+, with low overlapping results (10 patients positive in all donor-specific tests). Unlike HLA allele compatibility, the mean number of HLA class II eplet mismatches was higher in LDKT patients with positive baseline test results. DSA-C3d+ showed higher mean fluorescence intensity (MFI) DSA, with a cut-off MFI of 6192 accurately predicting complement fixation (area under the curve = 0.85, P = 0.008). Although all assays were associated with acute rejection (AR), only DSA-C3d+ (odds ratio [OR] = 6.64, P = 0.038) or high MFI-DSA (OR = 7.54, P = 0.038) independently predicted AR. Likewise, poorly HLA class II eplet−matched patients were at higher risk for AR, particularly patients with negative baseline test results (OR = 1.14, P = 0.019). Finally, previous AR and FC-XM+/DSA+, regardless of C3d positivity, independently predicted graft loss.

Conclusion

Combining FC-XM and solid-phase assays with the evaluation of donor/recipient HLA eplet mismatches, are most accurate tools for immune-risk stratification prior LDKT.

Positive Rates of Preliminary Crossmatches Among Transplantation Candidates Waitlisted for Different Organs in the Korean Network for Organ Sharing

OBJECTIVE

For deceased-donor organ transplantations, negative T cell crossmatches (XMs) are mandatory for kidney and pancreas allocation in the Korean Network for Organ Sharing (KONOS) organ allocation system. Submission and periodic renewal of serum to the KONOS is required for all transplantation candidates of kidney or pancreas and these sera are distributed to 23 laboratories for preliminary XMs. We have investigated how sensitization status varies among transplantation candidates waitlisted for different organs.

METHODS

Positive rates of T cell XMs performed during recent 1-year period (from March 2014 to February 2015) in the Korea Organ Donation Agency laboratory have been analyzed according to different organs. For 163 cases of deceased donors, 3605 recipients (22.1 recipients per one donor) were crossmatched using both of National Institutes of Health and antihuman globulin complement-dependent cytotoxicity (CDC) methods and flow cytometry method.

RESULTS

T cell XM positive rates varied among transplantation candidates for different organs. The positive rate was high for kidney (485/3,145, 15.4%), and low for pancreas or kidney/pancreas (7/200, 3.5%), lung (0/41, 0%), and heart (11/221, 5.0%). Among XM-positive individuals, nearly two-thirds of the kidney transplantation candidates showed strong sensitization status with CDC+/flow+ results (64.5%), whereas pancreas or kidney/pancreas transplantation candidates more commonly showed weaker sensitization status with CDC-/flow+ results (85.7%).

CONCLUSION

Kidney transplantation candidates show a much higher positive rate and stronger sensitization status than candidates for other organs. The results of this study would be useful for determining the number of candidates to be crossmatched for different organs.

Donor-specific antibodies require preactivated immune system to harm renal transplant

BACKGROUND

It is an unresolved issue why some kidney transplant recipients with pretransplant donor-specific HLA antibodies (DSA) show a high transplant failure rate, whereas in other patients DSA do not harm the graft. We investigated whether help from preactivated T-cells might be necessary for DSA to exert a deleterious effect.

METHODS

The impact of pretransplant DSA and immune activation marker soluble CD30 (sCD30) on 3-year graft survival was analyzed in 385 presensitized kidney transplant recipients.

FINDINGS

A deleterious influence of pretransplant DSA on graft survival was evident only in patients who were positive for the immune activation marker sCD30. In the absence of sCD30 positivity, 3-year graft survival was virtually identical in patients with or without DSA (83.1±3.9% and 84.3±2.8%, P=0.81). A strikingly lower 3-year graft survival rate of 62.1±6.4% was observed in patients who were both sCD30 and DSA positive (HR 2.92, P<0.001). Even in the presence of strong DSA with ≥5000 MFI, the 3-year graft survival rate was high if the recipients were sCD30 negative.

INTERPRETATION

Pretransplant DSA have a significantly deleterious impact on graft survival only in the presence of high pretransplant levels of the activation marker sCD30.

Effect of Different Sensitization Events on HLA Alloimmunization in Kidney Transplantation Candidates

BACKGROUND

HLA alloimmunization is caused by sensitization events (SEs), such as transfusion, pregnancy, or previous organ transplantation, and the effects of particular SEs have not been thoroughly studied. Our aim was to evaluate how each SE affected HLA alloimmunization by considering Luminex assays.

METHODS

Sera from 722 kidney transplantation candidates were screened per protocol by means of Luminex assays to determine the presence of anti-HLA class I/II antibodies; positive sera underwent single-antigen assay to determine the presence of specific antibodies against HLA A, B, C, DR, DQ, DP loci (positivity if median fluorescence intensity values were >1,000). The effect of each SE was analyzed considering only patients exposed to 1 kind of sensitization.

RESULTS

In the 453 candidates with ≥1 SE, anti-HLA class I positivity rates were significantly higher in patients with previous transfusion (18.9%; P = .014), pregnancy (38.3%; P < .001) or transplant (75%; P < .001) compared with those with no SE (similar results for class II). The strength (median fluorescence intensity) of specific antibodies was significantly higher in patients with previous transplantation than in those with previous transfusion for HLA-A (8,017 vs 2,302; P = .02), HLA-B (7,765 vs 2,901; P = .018), and HLA-DR (9,835 vs 2,060; P = .003). Other anti-HLA antibody strengths were similar between patients with previous pregnancy or transplantation.

CONCLUSIONS

Presence of any SE analyzed was associated with a higher prevalence of anti-HLA antibodies for class I ± II compared with nonsensitized patients. Transplantation had the strongest immunization effect on both classes, followed by pregnancy and then transfusion.

HLA gene dosage effect on renal allograft survival

BACKGROUND

Human leukocyte antigen (HLA)-A, HLA-B, and HLA-DR matching has beneficial long-term effects on renal allograft survival. However, the gene dosage effect of mismatched HLA on transplant outcomes is not known. We investigated the HLA gene dosage effects on allograft survival in kidney transplant recipients (KTRs).

METHODS

We analyzed HLA typing of KTRs and kidney donors at Kyungpook National University Hospital from January 1982 to December 2012. KTRs were divided into 2 groups: recipients from homozygous HLA donors and recipients from heterozygous HLA donors. Death-censored graft survival of KTRs was compared according to allele state of kidney donors.

RESULTS

In this study, 697 KTRs were enrolled. According to Kaplan-Meier analysis, graft survival in KTRs of HLA-DR and HLA-B heterozygous donors was longer than that in KTRs of HLA-DR and HLA-B homozygous donors (P = .007 and P < .0001, respectively). Multivariate Cox proportional hazards model analysis showed that HLA-DR and HLA-B donor homozygosity was an independent risk factor for death-censored graft survival (P = .019 and P = .022, respectively). Death-censored graft survival was not associated with HLA-A and HLA-A, B, DR allele states.

CONCLUSIONS

Compared with HLA donor mismatch caused by HLA-DR and HLA-B heterozygosity, HLA donor mismatch caused by HLA-DR and HLA-B homozygosity was associated with significantly increased risk of graft failure. In addition to the number of HLA mismatch between KTRs and donors, the donor allele state should be considered to predict transplant outcomes.

Peripheral natural killer cell and allo-stimulated T-cell function in kidney transplant recipients associate with cancer risk and immunosuppression-related complications

Reducing immunosuppression has been proposed as a means of preventing cancer in kidney transplant recipients but this can precipitate graft rejection. Here we tested whether anti-tumor natural killer (NK) cell and allo-responsive T-cell function in kidney transplant recipients may predict cancer risk and define risk of rejection. NK cell function was measured by the release of lactate dehydrogenase and T-cell allo-response by interferon-γ quantification using a panel of reactive T-cell enzyme-linked immunospot (ELISPOT) in 56 kidney transplant recipients with current or past cancer and 26 kidney transplant recipients without cancer. NK function was significantly impaired and the allo-response was significantly lower in kidney transplant recipients with cancer. With prospective follow-up, kidney transplant recipients with poor NK cell function had a hazard ratio of 2.1 (95% confidence interval 0.97-5.00) for the combined end point of metastatic cancer, cancer-related death, or septic death. Kidney transplant recipients with low interferon-γ release were also more likely to reach this combined end point. Thus, posttransplant monitoring of allo-immunity and NK cell function is useful for assessing the risk of over immunosuppression for the development of malignancy and/or death from cancer or sepsis.

The relative benefits and costs of solid phase bead technology to detect preformed donor specific antihuman leukocyte antigen antibodies in determining suitability for kidney transplantation

BACKGROUND

Screening for donor-specific anti-HLA antibodies (DSA) using bead-based multiplex assays to determine transplant suitability is standard practice in many countries. We compared the health benefits and costs of screening preformed DSA using bead-based assay as an add-on test to complement-dependent cytotoxicity (CDC) crossmatch with CDC crossmatch alone, and determined the optimal threshold to determine transplant suitability.

METHODS

Three probabilistic Markov models were developed to compare bead-based assay with CDC and CDC alone. The model assumed a hypothetical cohort of 10,000 patients who received only a single kidney transplant and terminated when all patients were deceased.

RESULTS

Assuming transplantation was permitted for recipients with no DSA or with a DSA mean fluorescence intensity (MFI) value of 500 or less, screening by bead-based assay and CDC saved 6.5 grafts and U.S. $1,192,303 per 100 transplants compared with CDC alone. If the thresholds were increased to an MFI of 2000 or less and 5000 or less, an extra 6.4 and 6.1 grafts would be saved, with cost savings of U.S. $867,203 and U.S. $830,664 per 100 transplants compared with CDC alone. The total number of kidney transplants performed would have increased by 8 and 9, respectively, but at the expense of an extra 0.1 and 0.4 graft lost per 100 transplants after 5 years.

CONCLUSIONS

Screening using bead-based assay is cost-saving and improves graft outcomes. The greatest benefits and cost-savings are achieved if transplantation occurs at a threshold of MFI of 500 or less or in those without preformed DSA. Increasing the threshold to an MFI of 2000 or less may provide an acceptable balance for improving transplant eligibility without compromising longer-term outcomes.

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.

Analysis of preformed donor-specific anti-HLA antibodies characteristics for prediction of antibody-mediated rejection in kidney transplantation

BACKGROUND

The relevance of preformed donor specific antibodies (DSA) detected by Luminex assays, with a negative complement-dependent cytotoxicity (CDC) crossmatch, remains unsettled in kidney transplantation (KT). We aimed to analyze the impact of preformed DSA characteristics on kidney graft outcomes.

METHODS

In 462 patients that received a kidney graft in our unit, between 2007 and 2012, pre-transplant sera were analyzed by Luminex screening assay to determine the presence of anti-human leukocyte antigen (HLA) antibodies and single-antigen bead assay [positive if mean fluorescence intensity (MFI) ≥ 1000] to assign anti-HLA specificities.

RESULTS

Anti-HLA antibodies were present in 95 patients (20.6%), but only 40 (8.7%) had DSA. Antibody-mediated rejection (AMR) at 1-year was higher in patients with DSA (35.0%) than in those without them (0.9%) (P < 0.001). Only DSA with a MFI of >3000 were significantly associated with AMR occurrence. Receiver operator curves revealed that a MFI of >4900 in the highest DSA bead had a high sensitivity (85.7%) and that the sum of all DSA beads MFI > 11,000 had a high specificity (92.3%) for AMR prediction. Anti-thymocyte globulin versus basiliximab induction was more frequent in DSA+ AMR- (65.4%) versus DSA+ AMR+ (34.6%) patients (P = 0.072). Five-year censored graft survival was lower in DSA+ than in DSA- patients (respectively, 84.8% versus 94.9%, P = 0.006), although survival was only reduced in DSA+ AMR+ (68.8%) versus DSA+ AMR- (96.0%) patients (P = 0.038).

CONCLUSIONS

Preformed DSA is associated with kidney graft loss, in relation with AMR occurrence. DSA strength may be used to improve immunological risk stratification of sensitized patients and their clinical management.

Immune profiling and cancer post transplantation

Half of all long-term (> 10 year) australian kidney transplant recipients (KTR) will develop squamous cell carcinoma (SCC) or solid organ cancer (SOC), making cancer the leading cause of death with a functioning graft. At least 30% of KTR with a history of SCC or SOC will develop a subsequent SCC or SOC lesion. Pharmacological immunosuppression is a major contributor of the increased risk of cancer for KTR, with the cancer lesions themselves further adding to systemic immunosuppression and could explain, in part, these phenomena. Immune profiling includes; measuring immunosuppressive drug levels and pharmacokinetics, enumerating leucocytes and leucocyte subsets as well as testing leucocyte function in either an antigen specific or non-specific manner. Outputs can vary from assay to assay according to methods used. In this review we define the rationale behind post-transplant immune monitoring assays and focus on assays that associate and/or have the ability to predict cancer and rejection in the KTR. We find that immune monitoring can identify those KTR of developing multiple SCC lesions and provide evidence they may benefit from pharmacological immunosuppressive drug dose reductions. In these KTR risk of rejection needs to be assessed to determine if reduction of immunosuppression will not harm the graft.

Pre-transplant low level HLA antibody shows a composite poor outcome in long-term outcome of renal transplant recipients

To determine the significance of low-level DSA (donor specific antibody) in patients transplanted with negative cytotoxicity AHG (antihuman immunoglobulin) crossmatch, data from 279 patients who received a kidney transplant between July 1999 and March 2006 were collected. All kidney recipients received ABO-compatible donors. A poor outcome was defined as any one of the following: death, Cr>2.0 mmol/L, occurrence of a rejection episode. Luminex Screening and Single Antigen assays from Tepnel Life Codes were used to detect human leukocyte antigen antibodies on pre-transplant sera retrospectively. Twenty-four out of 279 recipients demonstrated the presence of solid-phase DSA (MFI>1000) present pre-transplant. In DSA+ group, the accumulated good versus poor outcome rate was 0.30 versus 0.70, respectively. These rates were 0.49 and 0.51, respectively, in the DSA- group. The difference in composite poor outcome between DSA+ versus DSA- group was significant (p=0.030). The DSA- group had no difference in patient survival as compared to the DSA+ group (p=0.061). There is no statistically significant difference for either mortality or outcome results between high MFI (>2000) and low MFI (≤2000) groups. Our data suggest that solid-phase antibodies which are not strong enough to elicit a positive T-AHG crossmatch may influence long-term graft outcome.

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

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

Impact of the baseline anti-A/B antibody titer on the clinical outcome in ABO-incompatible kidney transplantation

BACKGROUND/AIMS

We investigated the impact of the baseline anti-A/B antibody titer on the clinical outcome in ABO-incompatible kidney transplantation (IKT).

METHODS

We included 183 patients who had undergone KT (40 ABO IKT and 143 ABO-compatible KT). Eight patients with a baseline titer of ≥1:512 were assigned to the high-titer group and 32 patients with a baseline titer of ≤1:256 were assigned to the low-titer group. Patients who underwent ABO-compatible KT were used as the control group. We compared the clinical outcomes of the three groups.

RESULTS

Before transplantation, the high-titer group displayed more frequent antibody rebound, as shown in a lower titer reduction rate, and more difficulty reaching the target titer (1:16) than the low-titer group. During the postoperative period and out-clinic follow-up, antibody rebound was more frequent, and the rate of acute rejection and infection were significantly higher and allograft function was lower in the high-titer group than in the low-titer and control groups. Multivariate analysis showed that high baseline antibody titer was an independent risk factor for acute rejection.

CONCLUSION

ABO IKT in the high-titer group (baseline titer ≥1:512) required greater caution compared to the low-titer group because of the higher tendency of antibody rebound and the risk for acute rejection.

An update on the impact of pre-transplant transfusions and allosensitization on time to renal transplant and on allograft survival

Background

Blood transfusions have the potential to improve graft survival, induce sensitization, and transmit infections. Current clinical practice is to minimize transfusions in renal transplantation candidates, but it is unclear if the evidence continues to support pre-transplant transfusion avoidance. Changes in the Medicare prospective payment system may increase transfusion rates. Thus there is a need to re-evaluate the literature to improve the management options for renal transplant candidates.

Methods

A review applying a systematic approach and conducted using MEDLINE^®, Embase^®, and the Cochrane Library for English-language publications (timeframe: 01/1984–03/2011) captured 180 studies and data from publically available registries and assessed the impact of transfusions on allosensitization and graft survival, and the impact of allosensitization on graft survival and wait time.

Results

Blood transfusions continued to be a major cause of allosensitization, with allosensitization associated with increased rejection and graft loss, and longer wait times to transplantation. Although older studies showed a beneficial effect of transfusion on graft survival, this benefit has largely disappeared in the post-cyclosporine era due to improved graft outcomes with current practice. Recent data suggested that it may be the donor-specific antibody component of allosensitization that carried the risk to graft outcomes.

Conclusions

Results of this review indicated that avoiding transfusions whenever possible is a sound management option that could prevent detrimental effects in patients awaiting kidney transplantation.

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

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

Superiority of AbCross enzyme-linked immunosorbent assay cross-match over the B-cell complement-dependent lymphocytotoxicity cross-match

BACKGROUND

The AbCross enzyme-linked immunosorbent assay (ELISA) cross-match is a recently introduced solid phase cross-match technique with several technical advantages over the currently available Antibody Monitoring System ELISA cross-match.

METHODS

In the present study, we investigated the potential superiority of AbCross over the traditional complement-dependent lymphocytotoxicity (CDC) B-cell cross-match (BXM). Pretransplant sera of 271 kidney transplant recipients who were transplanted at our center between 1998 and 2010 were tested in ELISA screening for the presence of human leukocyte antigen (HLA) antibodies and in AbCross and CDC for antibody reactivity against solubilized donor HLA class I and II antigens and donor B cells, respectively.

RESULTS

Patients positive for HLA class I or II antibodies on ELISA screening had a significantly poorer graft outcome 2 years after transplantation than recipients who were negative for HLA antibodies (21% vs 6% graft loss; P = .002). Corresponding with this finding, 37 recipients positive for HLA antibodies in AbCross against donor HLA class I or II antigens had a 2-year post-transplant graft loss rate of 19%, which is significantly higher than the 8% rate in 186 recipients who were negative for both antibody classes in AbCross (P = .043). The 2-year graft loss rate in 34 AbCross positive but BXM negative patients was 21%, compared with 7% in 172 AbCross and BXM negative patients (P = .012) and 9% in 11 AbCross negative but BXM positive patients (P = .39).

CONCLUSIONS

Our data indicate that the AbCross ELISA cross-match is superior to the CDC BXM, most likely because it detects antibodies against donor HLA antigens at a higher sensitivity.

Alloantibody and autoantibody monitoring predicts islet transplantation outcome in human type 1 diabetes

Long-term clinical outcome of islet transplantation is hampered by the rejection and recurrence of autoimmunity. Accurate monitoring may allow for early detection and treatment of these potentially compromising immune events. Islet transplant outcome was analyzed in 59 consecutive pancreatic islet recipients in whom baseline and de novo posttransplant autoantibodies (GAD antibody, insulinoma-associated protein 2 antigen, zinc transporter type 8 antigen) and donor-specific alloantibodies (DSA) were quantified. Thirty-nine recipients (66%) showed DSA or autoantibody increases (de novo expression or titer increase) after islet transplantation. Recipients who had a posttransplant antibody increase showed similar initial performance but significantly lower graft survival than patients without an increase (islet autoantibodies P < 0.001, DSA P < 0.001). Posttransplant DSA or autoantibody increases were associated with HLA-DR mismatches (P = 0.008), induction with antithymocyte globulin (P = 0.0001), and pretransplant panel reactive alloantibody >15% in either class I or class II (P = 0.024) as independent risk factors and with rapamycin as protective (P = 0.006) against antibody increases. DSA or autoantibody increases after islet transplantation are important prognostic markers, and their identification could potentially lead to improved islet cell transplant outcomes.

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.

Preformed and de novo donor specific antibodies in visceral transplantation: long-term outcome with special reference to the liver

Despite improvement in early outcome, rejection particularly chronic allograft enteropathy continues to be a major barrier to long-term visceral engraftment. The potential role of donor specific antibodies (DSA) was examined in 194 primary adult recipients. All underwent complement-dependent lymphocytotoxic crossmatch (CDC-XM) with pre- and posttransplant solid phase HLA-DSA assay in 156 (80%). Grafts were ABO-identical with random HLA-match. Liver was included in 71 (37%) allografts. Immunosuppression was tacrolimus-based with antilymphocyte recipient pretreatment in 150 (77%). CDC-XM was positive in 55 (28%). HLA-DSA was detectable before transplant in 49 (31%) recipients with 19 continuing to have circulating antibodies. Another 19 (18%) developed de novo DSA. Ninety percent of patients with preformed DSA harbored HLA Class-I whereas 74% of recipients with de novo antibodies had Class-II. Gender, age, ABO blood-type, cold ischemia, splenectomy and allograft type were significant DSA predictors. Preformed DSA significantly (p < 0.05) increased risk of acute rejection. Persistent and de novo HLA-DSA significantly (p < 0.001) increased risk of chronic rejection and associated graft loss. Inclusion of the liver was a significant predictor of better outcome (p = 0.004, HR = 0.347) with significant clearance of preformed antibodies (p = 0.04, OR = 56) and lower induction of de novo DSA (p = 0.07, OR = 24). Innovative multifaceted anti-DSA strategies are required to further improve long-term survival particularly of liver-free allografts.

Crossmatching by complement-dependent lymphocytotoxicity

The presence of preformed donor-specific HLA antibodies detected by Complement-dependent cyto-toxicity (CDC) crossmatch assay is associated with a high incidence of hyperacute or accelerated rejection and remains one of the gold standard tests pre-transplant. The standard CDC crossmatch detects IgG1, IgG3, and IgM antibody, i.e. complement fixing, bound to the native viable cell surface of lymphocytes. The crossmatch can be enhanced with the addition of anti-human-globulin to detect non-complement fixing antibodies (IgG2 and IgG4), and sensitivity can be improved with prolonged incubation times.

Tolerogenic therapies in transplantation

Since the concept of immunologic tolerance was discovered in the 1940s, the pursuit of tolerance induction in human transplantation has led to a rapid development of pharmacologic and biologic agents. Short-term graft survival remains an all-time high, but successful withdrawal of immunosuppression to achieve operational tolerance rarely occurs outside of liver transplantation. Collaborative efforts through the NIH sponsored Immune Tolerance Network and the European Commission sponsored Reprogramming the Immune System for Establishment of Tolerance consortia have afforded researchers opportunity to evaluate the safety and efficacy of tolerogenic strategies, investigate mechanisms of tolerance, and identify molecular and genetic markers that distinguish the tolerance phenotype. In this article, we review traditional and novel approaches to inducing tolerance for organ transplantation, with an emphasis on their translation into clinical trials.

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.

Hidden perils in a highly sensitized kidney transplant recipient

Highly sensitised patients are at increased risk for antibody mediated rejection (AMR) and reduced graft survival. Highly sensitive assays for detecting recipient preformed anti-HLA antibodies have been developed and identify high immunological risk donors. A 62yo male with end stage renal failure secondary to glomerulonephritis received a T-cell crossmatch negative, deceased donor, renal transplant mismatched at 3 of 6 HLA loci. A donor specific antibody (DSAb) to DR17 (MFI 2073) was present. Given his advancing age, multiple medical comorbidities and broad HLA sensitisation the transplant was accepted, however, shortly before transplantation two atypical results were made available. Firstly a B-cell crossmatch was performed and found to be negative in current serum but strongly positive in peak serum, secondly a further potential DSAb was predicted based on linkage disequilibrium with known donor HLA typing. The donor HLA typing would not be clarified until after the transplant. Despite the increased risk of AMR the transplant proceeded with pre-emptive plasma exchange. The patient developed severe AMR requiring extensive therapy. Incomplete prospective donor HLA typing can generate uncertainty in the interpretation of the virtual crossmatch performed for deceased donor transplants. This may result in clinically relevant sequelae. Advances in antibody detection techniques need to be matched by timely donor HLA typing for its full benefit to be realised.

Clinical relevance of pretransplant HLA class II donor-specific antibodies in renal transplantation patients with negative T-cell cytotoxicity crossmatches

Background

We evaluated the clinical relevance of pretransplant donor-specific HLA antibodies (DSA) in renal transplantation patients who had negative T-cell cytotoxicity crossmatches.

Methods

From 328 consecutive renal transplant recipients, we selected 28 patients who had positive pretransplant (historical or at the time of transplantation) flow cytometry crossmatches, but negative T-cell cytotoxicity crossmatches at the time of transplantation. The presence of DSA and its level at the time of transplantation were retrospectively tested using Luminex single antigen assays.

Results

DSA was present in 16 (57.1%) of 28 patients. Biopsy-proven acute rejection (9 patients) occurred more frequently in patients with DSA than in those without DSA (56.3% vs. 0.0%; P=0.003). The positivity rate of class II DSA was significantly higher in patients with antibody-mediated rejection (AMR) than in those without AMR (100% vs. 21.7%; P=0.003). However, the positivity rate of class I DSA was not different between the two groups (40% vs. 40.9%). Among patients with class II DSA, those with AMR tended to have higher antibody levels (median fluorescence intensity, MFI) than those without AMR (16,359 vs. 5,910; P=0.056). A cut-off MFI value of 4,487 for class II DSA predicted the occurrence of AMR with good sensitivity and specificity (100% and 87.0%).

Conclusions

In patients with negative T-cell cytotoxicity crossmatches, the presence of class II DSA and its level at the time of transplantation were associated with the occurrence of AMR. Pretransplant DSA measurement with Luminex single antigen assay would be useful in renal transplantation.

Clinical relevance and IgG subclass determination of non-HLA antibodies identified using endothelial cell precursors isolated from donor blood

BACKGROUND

ABO and human leukocyte antigen (HLA) alloantibodies provide major immunologic barriers to successful transplantation; however, there is increasing recognition for the role of anti-endothelial cell antibodies (AECAs) in allograft rejection. We investigated the relationship between AECAs identified using donor-derived endothelial cell precursors (ECPs) and kidney allograft rejection and function.

METHODS

Sixty live donor kidney recipients were tested pretransplant for AECAs and HLA-antibodies using flow cytometric crossmatch tests and solid-phase bead immunoassays. Renal allograft function was assessed by serum creatinine (SCr) values collected at early (mean, 50 days) and late (mean, 815 days) time points posttransplant and by incidence and type of rejection. Immunoglobulin G (IgG) subtype determination of both AECAs and HLA antibodies bound to ECPs was performed using flow cytometry.

RESULTS

Fourteen patients (23%) tested positive for donor-reactive IgG AECAs and had statistically higher SCr values and incidences of cellular rejection early posttransplant compared with 46 patients who tested negative (P=0.014 and P<0.05). SCr values were not statistically different late posttransplant. IgG subclass determination showed AECAs to be enriched for IgG2 and IgG4, subclasses that do not activate complement effectively. Detection of donor-reactive immunoglobulin M (IgM) AECAs did not correlate with increased SCr or incidence of rejection.

CONCLUSION

Crossmatch tests performed using donor-derived ECPs allow for the identification of alloantibodies that are associated with cellular rejection and are distinct from alloantibodies detected using lymphocytes.

Combined liver-kidney transplants: allosensitization and recipient outcomes

BACKGROUND

A pretransplant positive crossmatch in combined liver kidney transplants (CLK) is not considered a contraindication based on the reported immunoprotection conferred by the liver allograft. However, antibody-mediated rejection of the kidney in CLK has been reported recently. This prompted our study to investigate the impact of presensitization on CLK recipient outcomes.

METHODS

We examined kidney allograft and patient survival by indication of sensitization using Scientific Registry of Transplant Recipients data on CLK performed from 1995 to 2008. We defined sensitization as panel reactive antibody (PRA) more than 10% or a positive T-cell crossmatch (TXM).

RESULTS

Among 2484 CLK recipients with available PRA or TXM information, 30% had positive TXM or PRA more than 10%. Among those with TXM information, 12% had a positive crossmatch (n=234). In univariate analyses, patient (P=0.002) and overall kidney graft survival (P=0.015) were significantly diminished among sensitized patients. Differences in patient survival translated to estimated half-lives of 10.3 years among nonsensitized recipients versus 7.8 years among sensitized recipients, In multivariable Cox models, allosensitization was independently associated with patient death (adjusted hazard ratio=1.22, 95% CI, 1.04-1.43) and overall kidney graft loss (adjusted hazard ratio=1.16, 95% CI, 1.00-1.36).

CONCLUSIONS

These results suggest a negative impact of presensitization on patient and overall renal allograft survival in CLK. Accordingly, presensitization may need to be considered in risk stratification and clinical management of CLK.

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.

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

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

Desensitization for renal transplantation: depletion of donor-specific anti-HLA antibodies, preservation of memory antibodies, and clinical risks

Desensitization protocols reduce donor-specific anti-HLA antibodies (DSA) and enable renal transplantation in patients with a positive complement-dependent cytotoxic cross-match (CDC-CXM). The effect of this treatment on protective antibody and immunoglobulin levels is unknown. Thirteen patients with end-stage renal disease, DSA and positive CDC-CXM underwent desensitization. Sera collected pre- and post-transplantation were analysed for anti-tetanus and anti-pneumococcal antibodies, total immunoglobulin (Ig) levels and IgG subclasses and were compared to healthy controls and contemporaneous renal transplant recipients treated with standard immunosuppression alone. Ten patients developed negative CDC-CXM and enzyme-linked immunosorbent assay (ELISA) and underwent successful transplantation. Eight recipients achieved good graft function without antibody-mediated or late rejection, BK virus or cytomegalovirus infection. One patient had primary non-function due to recurrent oxalosis, and one patient with immediate graft function died from septicaemia. Seven recipients required post-operative transfusion and three developed septicaemia. DSA remained negative by ELISA at 12 months, but were detectable by Luminex(®) . Anti-tetanus and anti-pneumococcal antibodies, total Ig and IgG subclasses were below the normal range but comparable to levels in renal transplant recipients who had not undergone desensitization. Desensitization protocols effectively reduce DSA and allow successful transplantation. Post-operative bleeding and short-term infectious risk is increased. Protective antibody and serum immunoglobulin levels are relatively preserved.

Surveillance of alloantibodies after transplantation identifies the risk of chronic rejection

The monitoring of the levels of alloantibodies following transplantation might facilitate early diagnosis of chronic rejection (CR), the leading cause of renal allograft failure. Here, we used serial alloantibody surveillance to monitor patients with preoperative positive flow cytometric crossmatch (FCXM). Sixty-nine of 308 renal transplant patients in our center had preoperative positive FCXM. Blood was collected quarterly during the first postoperative year and tested by FCXM and single antigen bead luminometry, more sensitive techniques than complement-dependent cytotoxic crossmatching. Distinct post-transplant profiles emerged and were associated with different clinical outcomes. Two-thirds of patients showed complete elimination of FCXM and solid-phase assay reactions within 1 year, had few adverse events, and a 95% 3-year graft survival. In contrast, the remaining third failed to eliminate flow FCXM or solid-phase reactions directed against HLA class I or II antibodies. The inferior graft survival (67%) with loss in this latter group was primarily due to CR. Thus, systematic assessment of longitudinal changes in alloantibody levels, either by FCXM or solid-phase assay, can help identify patients at greater risk of developing CR.

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

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

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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