Humoral theory of transplantation

A clinical scoring system highly predictive of long-term kidney graft survival

Determining early surrogate markers of long-term graft outcome is important for optimal medical management. In order to identify such markers, we used clinical information from a cross-validated French database (Données Informatisées et VAlidées en Transplantation) of 2169 kidney transplant recipients to construct a composite score 1 year after transplantation. This Kidney Transplant Failure Score took into account a series of eight accepted pre- and post-transplant risk factors of graft loss, and was subsequently evaluated for its ability to predict graft failure at 8 years. This algorithm outperformed the traditional surrogates of serum creatinine and the estimated graft filtration rate, with an area under the receiver-operator characteristic curve of 0.78. Validation on an independent database of 317 graft recipients had the same predictive capacity. Our algorithm was also able to stratify patients into two groups according to their risk: a high-risk group of 81 patients with 25% graft failure and a low-risk group of 236 patients with an 8% failure rate. Thus, although this clinical composite score predicts long-term graft survival, it needs validation in different patient groups throughout the world.

Peritransplant immunoadsorption for positive crossmatch deceased donor kidney transplantation

Various desensitization protocols were shown to enable successful living donor kidney transplantation across a positive complement-dependent cytotoxicity crossmatch (CDCXM). Positive crossmatch transplantation, however, is less well established for deceased donor transplantation. We report a cohort of 68 deceased donor renal allograft recipients who, on the basis of broad sensitization (lymphocytotoxic panel reactivity ≥40%), were subjected to a protocol of peritransplant immunoadsorption (IA). Treatment consisted of a single session of immediate pretransplant IA (protein A) followed by posttransplant IA and antilymphocyte antibody therapy. Twenty-one patients had a positive CDCXM, which could be rendered negative by pretransplant apheresis. Solid phase HLA antibody detection revealed preformed donor-specific antibodies (DSA) in all 21 CDCXM-positive and in 30 CDCXM-negative recipients. At 5 years, overall graft survival, death-censored graft survival and patient survival were 63%, 76% and 87%, respectively, without any differences between CDCXM-positive, CDCXM-negative/DSA-positive and CDCXM-negative/DSA-negative recipients. Furthermore, groups did not differ regarding rates of antibody-mediated rejection (24% vs. 30% vs. 24%, p = 0.84), cellular rejection (14% vs. 23% vs. 18%, p = 0.7) or allograft function (median 5-year serum creatinine: 1.3 vs. 1.8 vs. 1.7 mg/dL, p = 0.62). Our results suggest that peritransplant IA is an effective strategy for rapid desensitization in deceased donor transplantation.

Association of HLA phenotypes of end-stage renal disease patients preparing for first transplantation with anti-HLA antibody status

Patients with pre-transplantation high levels of panel reactive antibody (PRA) have an increased risk of graft failure, and renal transplantation in sensitized patients remains a highly significant challenge worldwide. The influence of anti-human leukocyte antigen (HLA) antibodies on the development of rejection episodes depends on patient-specific clinical factors and differs from patient to patient. The HLA typing of the recipient might influence the development of anti-HLA antibodies. Some HLA antigens appear to be more immunogenic than others. The aim of this study is to demonstrate the distribution of HLA phenotypes in PRA-positive and PRA-negative end-stage renal disease (ESRD) patients on the basis of having sensitizing events or not. Our study included 642 (mean age: 41.54; female/male: 310/332) ESRD patients preparing for the first transplantation and who are on the cadaveric kidney transplantation waiting list of Istanbul Medical Faculty in 2008-2009. Class I HLA-A,B typing was performed by complement-dependent cytotoxicity (CDC) method, whereas class II HLA-DRB1 typing was performed by low-resolution polymerase chain reaction (PCR)-sequence-specific primer (SSP). All serum samples were screened for the presence of IgG type of anti-HLA class I- and II-specific antibodies by enzyme-linked-immunosorbent assay (ELISA). PRA-negative group consisted of 558 (86.9%) and PRA-positive group included 84 (13.1%) patients. We have found statistically significant frequency of HLA-A3 (p=0.018), HLA-A66 (p=0.04), and HLA-B18 (p=0.006) antigens in PRA-positive patients and DRB1*07 (p=0.02) having the highest frequency in patients with sensitizing event history but no anti-HLA development suggesting that DRB1*07 might be associated with low risk of anti-HLA antibody formation.

Chronic humoral rejection of human kidney allografts associates with broad autoantibody responses

BACKGROUND

Chronic humoral rejection (CHR) is a major complication after kidney transplantation. The cause of CHR is currently unknown. Autoantibodies have often been reported in kidney transplant recipients alongside antidonor human leukocyte antigen antibodies. Yet, the lack of comprehensive studies has limited our understanding of this autoimmune component in the pathophysiology of CHR.

METHODS

By using a series of ELISA and immunocytochemistry assays, we assessed the development of autoantibodies in 25 kidney transplant recipients with CHR and 25 patients with stable graft function. We also compared the reactivity of five CHR and five non-CHR patient sera with 8027 recombinant human proteins using protein microarrays.

RESULTS

We observed that a majority of CHR patients, but not non-CHR control patients, had developed antibody responses to one or several autoantigens at the time of rejection. Protein microarray assays revealed a burst of autoimmunity at the time of CHR. Remarkably, microarray analysis showed minimal overlap between profiles, indicating that each CHR patient had developed autoantibodies to a unique set of antigenic targets.

CONCLUSION

The breadth of autoantibody responses, together with the absence of consensual targets, suggests that these antibody responses result from systemic B-cell deregulation.

Effect of the proteasome inhibitor bortezomib on humoral immunity in two presensitized renal transplant candidates

BACKGROUND

Recipient presensitization represents a major hurdle to successful renal transplantation. Previous case series have suggested that the proteasome inhibitor bortezomib directly affects the alloantibody-secreting plasma cells in rejecting allograft recipients. However, the ability of this agent to desensitize nonimmunosuppressed transplant candidates before transplantation is currently unknown.

METHODS

In this analysis, two sensitized hemodialysis patients were selected to receive two subsequent bortezomib cycles. Bortezomib was given at 1.3 mg/m(2) on days 1, 4, 8, and 11. Dexamethasone was added to the second cycle to enhance treatment efficiency. Serial immune monitoring included cytotoxic panel reactive antibody testing, Luminex single antigen testing for anti-human leukocyte antigen (HLA) IgG with or without C4d-fixing capability, and ABO antibody detection.

RESULTS

During a half-year follow-up period, cytotoxic panel reactive antibody decreased from 87% to 80% (patient 1) and 37% to 13% (patient 2). Patient 1 showed a 40% reduction in binding intensities of identified Luminex HLA single antigen reactivities and, in parallel, slight reductions in ABO blood group antibody and total immunoglobulin levels. In patient 2, bortezomib did not affect circulating antibody levels in a meaningful way. Both patients showed a more than 50% reduction in the levels of anti-HLA antibody-triggered C4d deposition to Luminex beads.

CONCLUSION

Our initial experience suggests that, without additional immunosuppressive measures, bortezomib has modest effects on circulating antibodies against HLA or blood group antigens. The reduced levels of antibody-triggered complement fixation, however, imply potential clinical relevance of proteasome inhibition for recipient desensitization.

Increased erythrocyte C4D is associated with known alloantibody and autoantibody markers of antibody-mediated rejection in human lung transplant recipients

BACKGROUND

Immune responses to mismatched donor human leukocyte antigens (HLA) are important in the pathogenesis of chronic rejection. This study evaluated whether erythrocyte-bound C4d (E-C4d) is associated with known alloimmune and autoimmune markers of antibody-mediated rejection after human lung transplantation (LTx).

METHODS

Flow cytometry was used to analyze 22 LTx recipients and 15 healthy individuals for E-C4d. Development of antibodies to donor-mismatched HLA (donor-specific antibody [DSA]) and antibodies to HLA were determined using the solid-phase method by Luminex. Development of antibodies to self-antigens, K-alpha-1-tubulin (KA1T) and collagen V (Col-V), were measured by enzyme-linked immunosorbent assay. C3d deposition in lung biopsy specimens was determined by immunohistochemical staining.

RESULTS

Percent E-C4d (%E-C4d) levels were 19.9% in LTx patients vs 3.7% in healthy individuals (p = 0.02). DSA+ patients had higher E-C4d levels than DSA- patients (34.1% vs 16.7%, p = 0.02). In 5 patients with preformed anti-HLA, E-C4d levels were not significantly different vs 13 patients without detectable anti-HLA (p = 0.1). E-C4d levels were higher in patients who developed antibodies to KA1T (p = 0.02) and Col-V (p = 0.03). Recipients with C3d-positive tissue deposition had higher E-C4d levels than patients with C3d-negative biopsy results (p = 0.01).

CONCLUSIONS

Increased %E-C4d levels are found in patients with positive DSA, high antibody titers to KA1T and Col-V, and have C3d+ lung biopsy findings. Therefore, %E-C4d can serve as a potential marker for antibody-mediated rejection after LTx.

Detecting adaptive immunity: applications in transplantation monitoring

In recent decades, continuous improvements in immunosuppressive therapy have led to a significant increase in kidney allograft survival. Despite innovative developments and improvements in immunosuppression, chronic allograft injury and late graft loss still remain major causes of morbidity and mortality. In clinical practice, long-term immunosuppression is adapted and fine-tuned according to drug levels, kidney function, and biopsy results. As an invasive procedure, indication biopsy still represents an indispensible diagnostic gold standard. However, in an effort to further improve outcomes on the basis of individualized treatment, there is an urgent need for noninvasive assays, as well as biomarkers, to more accurately monitor allogeneic responses and predict the risk of acute and chronic allograft rejection. This article discusses strategies for immune monitoring of T-cell responsiveness and humoral alloreactivity. Furthermore, new microarray and gene profiling data are highlighted, which may identify hyporesponsive transplant recipients who could benefit from a reduction or even withdrawal of immunosuppression. Finally, supplementary transplant risk assessment markers, such as soluble CD30 and urinary effector molecule analysis, are discussed as promising new tools. Recent developments and improvements in test principles to monitor and predict allograft immunity are encouraging and may herald the transition of present empiric immunosuppression to individualized immunosuppressive treatment. Nonetheless, before implementation of immune monitoring in routine clinical practice, there is still a need for prospective trials designed to clarify the actual diagnostic potential of individual test systems in a therapeutic context.

Role of T cells in graft rejection and transplantation tolerance

Transplantation is the most effective treatment for end-stage organ failure, but organ survival is limited by immune rejection and the side effects of immunosuppressive regimens. T cells are central to the process of transplant rejection through allorecognition of foreign antigens leading to their activation, and the orchestration of an effector response that results in organ damage. Long-term transplant acceptance in the absence of immunosuppressive therapy remains the ultimate goal in the field of transplantation and many studies are exploring potential therapies. One promising cellular therapy is the use of regulatory T cells to induce a state of donor-specific tolerance to the transplant. This article first discusses the role of T cells in transplant rejection, with a focus on the mechanisms of allorecognition and the alloresponse. This is followed by a detailed review of the current progress in the field of regulatory T-cell therapy in transplantation and the translation of this therapy to the clinical setting.

Prevention trumps treatment of antibody-mediated transplant rejection

Belying the spectacular success of solid organ transplantation and improvements in immunosuppressive therapy is the reality that long-term graft survival rates remain relatively unchanged, in large part due to chronic and insidious alloantibody-mediated graft injury. Half of heart transplant recipients develop chronic rejection within 10 years - a daunting statistic, particularly for young patients expecting to achieve longevity by enduring the rigors of a transplant. The current immunosuppressive pharmacopeia is relatively ineffective in preventing late alloantibody-associated chronic rejection. In this issue of the JCI, Kelishadi et al. report that preemptive deletion of B cells prior to heart transplantation in cynomolgus monkeys, in addition to conventional posttransplant immunosuppressive therapy with cyclosporine, markedly attenuated not only acute graft rejection but also alloantibody elaboration and chronic graft rejection. The success of this preemptive strike implies a central role for B cells in graft rejection, and this approach may help to delay or prevent chronic rejection after solid organ transplantation.

Development of antibodies to human leukocyte antigen precedes development of antibodies to major histocompatibility class I-related chain A and are significantly associated with development of chronic rejection after human lung transplantation

The development of antibodies (Abs) to major histocompatibility (MHC) class I-related chain A (MICA) and human leukocyte antigen (HLA) and their role in the immunopathogenesis of chronic rejection (bronchiolitis obliterans syndrome [BOS]) after human lung transplantation (LTx) was analyzed. Sera from 80 LTx recipients were analyzed for anti-MICA and anti-HLA Abs using Luminex and flow PRA (panel reactive assay). Development of Abs either to MICA alone or MICA and HLA together significantly correlated (p < 0.01) with development of BOS. Kinetic analysis in the post-LTx period revealed that development of anti-HLA Abs (7.6 +/- 4.7 months) preceded the development of anti-MICA Abs (10.0 +/- 3.5 months). Abs to MICA alleles (*001 and *009) developed approximately 6 months after LTx and peak titers were present at the time of clinical diagnosis of BOS (16.3 +/- 2.7 months). The development of Abs to both MICA and HLA was strongly associated with the development of BOS thereby suggesting a synergistic effect. Furthermore, immune response to mismatched HLA can lead to development of Abs to other MHC related antigens expressed on the airway epithelial cells. Cumulatively, these immune responses contribute to the pathogenesis of chronic rejection following human LTx.

Anti-HLA antibody profile of Turkish patients with end-stage renal disease

Exposure to human leukocyte antigens (HLA) via blood transfusions, pregnancies, and previous transplantations can result in anti-HLA antibody production. The presence of anti-HLA antibodies in recipient sera before transplantation is an important risk factor. To demonstrate the anti-HLA antibody status of Turkish end-stage renal disease (ESRD) patients, 674 patients (mean age, 40.35 +/- 13.15 years; female/male, 328/346) were enrolled into the study. Anti-HLA antibody screening and identification tests were performed using an enzyme-linked immunosorbent assay (ELISA) method. The panel-reactive antibody (PRA)-negative group consisted of 564 (83.6%) and the PRA-positive group consisted of 110 (17.3%) patients. Of the 110 (17.3%) PRA-positive patients, 43 (6.4%) were class I (+) and class II (-); 19 (2.8%) were class I (-) and class II (+); 48 (7.1%) were both class I and II (+). The most frequent antibodies were directed against the A2 crossreactive group (CREG) and the A10 CREG with less frequent reactions against the B7 CREG, indicating antibodies to both frequent (members of A2 CREG) and relatively rare (members of A10 CREG and B7 CREG antigens). These data also suggested that some antibodies occur at greater than expected frequency because of shared epitopes. Our findings confirmed the significant correlation between female gender, pregnancy, failed graft history, long dialysis duration, and blood transfusions with PRA positivity (P < .05).

The yin and yang of B cells in graft rejection and tolerance

Various lineages of B cells are being increasingly recognized as important players in the etiology and prognosis of both acute and chronic graft rejection. The role of immature, chronically activated B cells, as efficient antigen-presenting cells, supporting recalcitrant cell-mediated graft rejection and late lineage B cells driving humoral rejections, is being increasingly recognized. This review captures the recent literature on this subject and discusses the various roles of the B cell in renal graft rejection and conversely, also in graft tolerance, both in animal and human studies. In addition, novel therapies targeting specific B-cell lineages in graft rejection are also discussed, with a view to developing more targeted therapies for graft rejection.

A flow cytometric crossmatch test for simultaneous detection of antibodies against donor lymphocytes and endothelial precursor cells

Complement-dependent cytotoxicity or flow cytometric lymphocyte crossmatch (LXM) tests may fail to detect clinically significant antibodies (Abs) against non-human leukocyte antigen (HLA). A flow cytometric endothelial precursor cell crossmatch (EPCXM) test (XM-ONE) is available for detection of Abs against donor endothelial precursor cells (EPCs). We showed that lymphocytes co-purified with EPCs can be used in LXM tests allowing simultaneous detection of Abs reactive with donor EPCs and lymphocytes. The lymphocyte population co-purified with EPCs on anti-Tie-2 Ab-coupled magnetic beads contained CD 8(+) and CD 4(+) T-cells, B-cells, and natural killer (NK)- and natural killer T (NKT)-cells. HLA class I antigen expression was slightly higher on CD 3(+) lymphocytes co-purified on Tie-2 Ab beads than on unseparated lymphocytes, whereas HLA class I and II antigen levels on CD 19(+) lymphocytes were not significantly different. Sera from 10 patients with panel-reactive Abs were tested on cells from nine donors using flow cytometric LXM and EPCXM tests. There was a very good correlation (R(2) = 0.94) between the channel shift values obtained on unseparated and Tie-2 Ab bead-isolated T-lymphocytes, whereas the correlation between the channel shift values obtained on the two B-lymphocyte populations was lower (R(2) = 0.71). T- and B-lymphocytes co-purified with EPCs can be used in LXM tests enabling simultaneous detection of donor lymphocyte- and EPC-reactive Abs in a single-tube XM-ONE assay.

Advances in research on antibody-mediated rejection after liver transplantation

T cell- and antibody-mediated immunity are also called cellular and humoral immunity, respectively. Both cellular and humoral immunity are known to mediate the rejection after allogeneic/xenogeneic organ transplantation. Liver transplantation is the most common type of organ transplantation. At present, many studies have shown that antibody-mediated immunity plays an important role in the development of rejection after liver transplantation. In this article, we will review the recent advances in understanding the basic theory, mechanism, pathological diagnosis and treatment of antibody-mediated rejection after liver transplantation.

HLA class I antibodies provoke graft arteriosclerosis in human arteries transplanted into SCID/beige mice

Antibodies toward HLA class I and/or MICA are commonly observed in transplanted patients suffering from allograft arteriosclerosis, also called chronic vascular rejection (CVR). The relative importance of cellular versus humoral alloreactivity for CVR is still disputed. We demonstrate that antibodies toward HLA class I provoke lesions typical for CVR in human arteries in vivo in the absence of cellular immunity. To show this, we grafted segments of human mesenteric arteries from 8 deceased organ donors into 36 immunodeficient SCID/beige mice in the infrarenal aortic position. Three mice died postoperatively. The remaining 33 mice received weekly i.v. injections of either a monoclonal antibody toward HLA class I, toward MICA or an irrelevant monoclonal antibody. At sacrifice after 6 weeks, mice receiving the HLA antibody showed a significant neointimal thickening in the grafted artery due to smooth muscle cell (SMC) proliferation while control mice receiving anti-MICA or irrelevant antibody showed little or no thickening. Whereas antibodies toward HLA class I were mitogenic to SMC in vitro, those directed toward MICA did not have any effect. Humoral alloreactivity toward HLA may thus play a causal role for the development of CVR and this opens new possibilities for the treatment of CVR.

De novo donor-specific antibody at the time of kidney transplant biopsy associates with microvascular pathology and late graft failure

We studied whether de novo donor-specific antibodies (DSA) in sera from patients undergoing kidney transplant biopsies associate with specific histologic lesions in the biopsy and prognosis. DSA were assessed in 145 patients at the time of biopsy between 7 days to 31 years posttransplant. DSA was detected in 54 patients (37%), of which 32 represented de novo DSA. De novo DSA was more frequent in patients having late biopsies (34%) versus early biopsies (4%), and was usually either against class II alone or class I and II but rarely against class I alone. Microcirculation inflammation (glomerulitis, capillaritis) and damage (glomuerulopathy, capillary basement membrane multilayering), and C4d staining were associated with de novo DSA. However, the degree of scarring, arterial fibrosis and tubulo-interstitial inflammation did not correlate with the presence of de novo DSA. De novo DSA correlated with reduced graft survival after the biopsy. Thus, de novo DSA at the time of a late biopsy for clinical indication is primarily against class II, and associates with microcirculation changes in the biopsy and subsequent graft failure. We propose careful assessment of de novo DSA, particularly against class II, be performed in all late kidney transplant biopsies.

Lack of effect of MICA antibodies on graft survival following heart transplantation

Little is known about the effect of MICA antibodies (Abs) on cardiac allograft function and survival. Pretransplant and posttransplant serum from 491 and 196 adult cardiac allograft recipients, respectively, has been investigated for MICA Abs, donor specificity and the effect of MICA Abs on graft survival, acute rejection episodes (AR) and cardiac allograft vasculopathy (CAV). Patients with HLA Abs (11.6%) were excluded from the analysis. A total of 11.8% of patients had MICA Abs, without HLA Abs, before their transplant. Actuarial graft survival demonstrated slightly better survival of patients with donor-specific MICA Abs at 1 and 5 years (88.9% and 83.3%) than patients negative for MICA Abs (72% and 63.7%, p = 0.051). After transplantation, 15.8% of patients produced MICA Abs, and in 17 patients these were produced de novo. There was no effect of pretransplant or posttransplant production of MICA Abs on numbers of AR episodes in year 1, or CAV assessed at years 3 and 5. Immunocytochemistry of cardiac biopsies from 11 patients did not demonstrate a presence of MICA. Sera from only 4/69 patients with MICA Abs fixed complement prior to transplantation and from 7/38 patients following transplantation. In conclusion, this study suggests that MICA Abs do not adversely affect the outcome of cardiac transplantation.

The pathogenesis and treatment of chronic allograft nephropathy

Despite improvements in immunosuppressive therapy, long-term allograft survival after kidney transplantation remains as low as 50%. Chronic allograft nephropathy (CAN) is a major cause of late graft loss in renal transplant recipients. The histopathologic signs of CAN-interstitial fibrosis, tubular atrophy, glomerulopathy and vasculopathy-are nonspecific; therefore, the 2007 Banff classification dispensed with the term CAN in favor of 'interstitial fibrosis and tubular atrophy without evidence of any specific etiology'. In this Review, however, the term CAN is used to describe a clinical syndrome that is characterized by progressive decline in renal function from 3 months after transplantation, accompanied by the development of proteinuria and hypertension. The pathogenesis of CAN is complex and incompletely understood, and involves several immunological and non-immunological factors. We discuss the contributory roles of acute rejection, donor age, anti-human-leukocyte-antigen antibodies, calcineurin inhibitor nephrotoxic effects, viral infection, hypertension and hyperlipidemia. The prevention and treatment of CAN needs multidisciplinary strategies. Early detection by means of protocol biopsy and calculation of glomerular filtration rate is the first step, followed by management of modifiable risk factors.

Anti-human leukocyte antigen and donor-specific antibodies detected by luminex posttransplant serve as biomarkers for chronic rejection of renal allografts

BACKGROUND

Although the incidence of early acute rejection could have been diminished in the past, the long-term renal allograft survival could not benefit from the introduction of more effective immunosuppressive regimens mainly aiming at cellular rejection mechanisms. The cause of chronic rejection is still discussed controversially. Here, we demonstrate to what extent human leukocyte antigen (HLA) antibodies (HLAab) posttransplant contribute to late graft outcome.

METHODS

A total of 1014 deceased kidney transplant recipients transplanted at the Charité hospital were monitored in a cross-sectional manner for the development of HLAab using Luminex Single Antigen beads. Patients with stable kidney function at a median of 5-years posttransplant were tested once for HLAab and monitored for 5.5 years after testing.

RESULTS

Thirty percent of recipients showed HLAab. Donor-specific antibodies (DSA) were found in 31% of antibody positive patients. The presence of DSA was associated with a significantly lower graft survival of 49% vs. 83% in the HLAab negative group (P< or =0.0001). Non-DSAs also had an adverse effect on graft survival (70% vs. 83%; P=0.0001). In a prospective analysis of 195 patients with repeatedly no detectable HLAab, the survival probability was 94% as opposed to 79% survival among patients who developed HLAab de novo after the first testing (P=0.05).

CONCLUSIONS

We confirmed that HLAab produced even late after transplantation are detrimental to graft outcome. DSA were proven to have a strong adverse impact on graft survival. The results indicate that a posttransplant HLAab monitoring routine could be appropriate to improve long-term results.

Effects of blood transfusions given after renal transplantation

BACKGROUND

Human leukocyte antigen (HLA) antibodies produced after transplantation are frequently measured in transplant recipients, because they are strongly associated with humoral rejection and graft loss. However, antibodies can be induced by posttransplant blood transfusions rather than by the graft, casting doubts about the possible role of antibodies in a patient with graft dysfunction.

METHODS

We recorded the posttransplant transfusions in 746 patients transplanted during a 6-year period. Rejection episodes were evaluated after exclusion of patients who were transfused proximate to the time of rejection. Specimens for solid-phase HLA antibody testing were available in 199 patients.

RESULTS

The frequency of transfusions was 45%, but it was higher in deceased donor transplants (51%) than in live donor transplants (30%). Almost 80% of the transfusions were given during the first month after transplant. However, the incidence of posttransplant antibodies was similar in patients transfused and not transfused, and only 1 of 12 patients who received more than 10 transfusions produced antibodies. There was no evidence that posttransplant antibodies not directed to donor antigens were triggered by transfusions. The incidence of rejection episodes, allograft nephropathy, and graft loss was slightly more in transfused patients but the differences were not statistically significant.

CONCLUSIONS

When HLA antibodies are detected posttransplant, they are likely induced by the graft rather than by any transfusions the patient may have received. The results suggest that posttransplant transfusions do not have the sensitizing or down-regulatory effects of pretransplant transfusions.

Anti-HLA I antibodies induce VEGF production by endothelial cells, which increases proliferation and paracellular permeability

Anti-human leukocyte antigen class I (HLA I) antibodies were shown to activate several protein kinases in endothelial cells (ECs), which induces proliferation and cell survival. An important phenomenon in antibody-mediated rejection is the occurrence of interstitial edema. We investigated the effect of anti-HLA I antibodies on endothelial proliferation and permeability, as one possible underlying mechanism of edema formation. HLA I antibodies increased the permeability of cultured ECs isolated from umbilical veins. Anti-HLA I antibodies induced the production of vascular endothelial growth factor (VEGF) by ECs, which activated VEGF receptor 2 (VEGFR2) in an autocrine manner. Activated VEGFR2 led to a c-Src-dependent phosphorylation of vascular endothelial (VE)-cadherin and its degradation. Aberrant VE-cadherin expression resulted in impaired adherens junctions, which might lead to increased endothelial permeability. This effect was only observed after cross-linking of HLA I molecules by intact antibodies. Furthermore, our results suggest that increased endothelial proliferation following anti-HLA I treatment occurs via autocrine VEGFR2 activation. Our data indicate the ability of anti-HLA I to induce VEGF production in ECs. Transactivation of VEGFR2 leads to increased EC proliferation and paracellular permeability. The autocrine effect of VEGF on endothelial permeability might be an explanation for the formation of interstitial edema after transplantation.

Clinical significance of anti-HLA antibodies detected by Luminex: enhancing the interpretation of CDC-BXM and important post-transplantation monitoring tools

B-cell crossmatch (BXM) was originally introduced to increase the sensitivity to detect anti-HLA antibodies of conventional CDC crossmatch in renal transplantation. Newer techniques such as Luminex((R)) have greater sensitivity in detecting anti-HLA antibodies but have not been directly evaluated versus BXM. We discuss our experience with Luminex testing and the significance of donor-specific antibodies (DSA) defined by Luminex in three populations, as compared with the CDC crossmatch. In the general transplant population, Luminex-defined DSA were found in only one third of positive CDC-BXM and were associated with graft rejection. Luminex testing enhanced the interpretation of CDC-BXM and identified patients with clinically relevant BXM. In the highly sensitized transplant population, Luminex-defined DSA were found in two thirds of positive BXM and were a better predictor of graft rejection. Therefore, Luminex assays rather than CDC-BXM should be used to facilitate kidney allocation in highly sensitized patients. In the post-transplantation population, Luminex antibody monitoring for DSA was shown to be important, as it defined low-level de novo DSA that were associated with development of transplant glomerulopathy and a significant predictor of graft loss in those patients. Thus Luminex testing facilitated the interpretation of CDC-BXM and provided a useful predictive tool for the detection of clinically significant DSA in post-transplantation antibody monitoring.

Emerging role of donor-specific anti-human leukocyte antigen antibody determination for clinical management after solid organ transplantation

Preformed and de novo donor-specific HLA antibodies (DSA) have been associated with allograft dysfunction and failure. The application of solid-phase methods have increased the sensitivity and specificity of antibody detection; however the clinical significance of these DSA is under evaluation. In the present study, we summarize six cases (four renal transplant recipients, one multivisceral recipient, and one heart-and-lung transplant recipient) to illustrate the role of the histocompatibility laboratory in providing the most comprehensive workup to assess the risk of graft dysfunction associated with antibody-mediated rejection (AMR). These cases illustrate the potential risk assessment for AMR in various situations: (1) in patients exhibiting low levels of DSA pretransplantation; (2) protocol immunosuppression minimization during stepwise weaning; and (3) desensitization protocols. Furthermore, increased sensitivity of DSA determination is indicated for the interpretation of focal C4d and its clinical significance. The clinical relevance of monitoring for circulating DSA with solid-phase single-antigen assays is also discussed. These cases exemplify the rationale for all patients to be monitored for DSA post-transplantation, with the frequency adjusted based on the individual risk for AMR.

Correlations between Terasaki's HLA class II epitopes and HLAMatchmaker-defined eplets on HLA-DR and -DQ antigens

Human leukocyte antigen (HLA) class II-specific antibodies increase the risk of transplant failure, and their characterization must consider epitopes rather than antigens. There are two strategies to determine HLA epitope structure. Terasaki's group has analyzed antibody reactivity patterns with single antigen panels with a computer program based on shared amino acid residues of reactive alleles. HLAMatchmaker is a theoretical algorithm that predicts HLA epitopes on the HLA molecular surface from stereochemical modeling of epitope-paratope interfaces of antigen-antibody complexes. Our epitope repertoire is based on so-called 'eplets' representing 3-A patches of at least one polymorphic residue on the molecular surface. This report describes how 49 of 53 Terasaki's HLA-DR epitopes correspond to HLAMatchmaker-defined eplets. Most of them are equivalent to single eplets (n = 33) or two or more possible eplets (n = 10), but six had corresponding eplet pairs. There were 10 cases whereby eplets have permissible residue combinations, and in 5 cases, we found that eplet specificity might be influenced by nearby hidden residues. We could assign corresponding eplets to 17 of 18 Terasaki's HLA-DQ epitopes. This study demonstrates how the HLAMatchmaker interpretation of amino acid residues shared between antibody-reactive antigens can increase our understanding of the structural basis of HLA epitopes.

Donor-directed HLA antibodies before and after transplantectomy detected by the luminex single antigen assay

BACKGROUND

Donor-directed antibodies (DDA) have been shown to result in poor graft survival. This study was designed to analyze antibody appearance and patient and graft characteristics related to antibody formation in patients who lost their graft at different time points after transplantation.

METHODS

Pre- and posttransplant sera of 56 DDA-negative first transplant patients were screened for human leukocyte antigen (HLA) class I and II DDA by the Luminex single antigen assay (LSA). All patients were treated with calcineurine inhibitor-based immunosuppression.

RESULTS

Three of 56 patients proved DDA positive by LSA before transplantation. Eighty-one percent of the remaining 53 patients became DDA class I or II positive or both; 16% before and 84% after transplantectomy. Class I antibodies were produced in 84% and class II in 77% of the recipients. Based on time of transplantectomy, three groups were created as follows: less than or equal to 1 month, 1 to 6 months, and more than 6 months. The groups proved to be significantly different for HLA class II mismatch and acute rejection. All recipients in group 1 to 6 months proved to be DDA positive. Logistic regression analysis showed that DDA positivity for class I was related to higher donor age and donor type (nonheart beating), class II to higher donor age and class II mismatch.

CONCLUSIONS

Donor-directed HLA antibodies after transplantation were demonstrated in 81% of first transplant recipients, all of whom were DDA negative by LSA before transplantation. The majority of the antibodies was found after transplantectomy. These findings may have to be taken into consideration in the allocation of organs of marginal donors such as older or nonheart beating kidneys.

Multicenter evaluation of a novel endothelial cell crossmatch test in kidney transplantation

BACKGROUND

Despite their clinical importance, clinical routine tests to detect anti-endothelial cell antibodies (AECA) in organ transplantation have not been readily available. This multicenter prospective kidney transplantation trial evaluates the efficacy of a novel endothelial cell crossmatch (ECXM) test to detect donor-reactive AECA associated with kidney allograft rejection.

METHODS

Pretransplant serum samples from 147 patients were tested for AECA by a novel flow cytometric crossmatch technique (XM-ONE) using peripheral blood endothelial progenitor cells as targets. Patient enrolment was based on acceptance for transplantation determined by donor lymphocyte crossmatch results.

RESULTS

Donor-reactive AECA were found in 35 of 147 (24%) patients. A significantly higher proportion of patients with a positive ECXM had rejections (16 of 35, 46%) during the follow-up of at least 3 months compared with those without AECA (13 of 112, 12%; P<0.00005). Both IgG and IgM AECAs were associated with graft rejections. Mean serum creatinine levels were significantly higher in patients with a positive ECXM test at 3 and 6 months posttransplant.

CONCLUSIONS

XM-ONE is quick, easy to perform on whole blood samples and identifies patients at risk for rejection and reduced graft function not identified by conventional lymphocyte crossmatches.

Specificity and sensitivity of screening for anti-HLA antibodies in kidney allograft dysfunction

BACKGROUND

Prospective testing for posttransplant circulating anti-HLA antibodies seems to be a critical noninvasive tool, but confirmatory data are lacking.

MATERIALS AND METHODS

Over the last 3 years, peritubular capillary (PTC) C4d deposition was prospectively sought by an immunofluorescence technique applied to frozen tissue in biopsies obtained for allograft dysfunction. Screening for circulating anti-HLA class I/II alloantibodies (AlloAb) by the flow cytometric test was performed simultaneously.

RESULTS

We evaluated 132 sets of biopsies and simultaneous serum samples. PTC C4d deposition was demonstrated in 15.9% (21/132) of biopsies. Circulating anti-HLA I/II AlloAb were detected in 25% (33/132) of serum samples. Employing receiver-operator characteristic (ROC) curves for all C4d-positive biopsies, screening for AlloAb showed a global specificity of 82% and sensitivity of 61.9%. When this analysis was restricted to biopsies obtained in the first month posttransplantation, the sensitivity increased to 81.8%, but the specificity decreased to 76.9%. After the first month posttransplantation, we observed sensitivity of 40.0% and a specificity of 86.4%. In the first month posttransplantation, all patients with a diagnosis of acute antibody-mediated rejection displayed circulating anti-HLA class I/II, but not always at the same time as the C4d-positive biopsy.

CONCLUSIONS

In the first month posttransplantation, prospective monitoring of anti-HLA antibodies may be useful. The high sensitivity allows the identification of patients at risk, affording an earlier diagnosis of antibody-mediated rejection. After the first month, the test can be used to evaluate allograft dysfunction episodes, since positivity is highly suggestive of an antibody-mediated process.