Humoral theory of transplantation

Autologous and Allogenous Antibodies in Lung and Islet Cell Transplantation

The field of organ transplantation has undoubtedly made great strides in recent years. Despite the advances in donor-recipient histocompatibility testing, improvement in transplantation procedures, and development of aggressive immunosuppressive regimens, graft-directed immune responses still pose a major problem to the long-term success of organ transplantation. Elicitation of immune responses detected as antibodies to mismatched donor antigens (alloantibodies) and tissue-restricted self-antigens (autoantibodies) are two major risk factors for the development of graft rejection that ultimately lead to graft failure. In this review, we describe current understanding on genesis and pathogenesis of antibodies in two important clinical scenarios: lung transplantation and transplantation of islet of Langerhans. It is evident that when compared to any other clinical solid organ or cellular transplant, lung and islet transplants are more susceptible to rejection by combination of allo- and autoimmune responses.

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

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

Unraveling the Role of Allo-Antibodies and Transplant Injury

Alloimmunity driving rejection in the context of solid organ transplantation can be grossly divided into mechanisms predominantly driven by either T cell-mediated rejection (TCMR) and antibody-mediated rejection (ABMR), though the co-existence of both types of rejections can be seen in a variable number of sampled grafts. Acute TCMR can generally be well controlled by the establishment of effective immunosuppression (1, 2). Acute ABMR is a low frequency finding in the current era of blood group and HLA donor/recipient matching and the avoidance of engraftment in the context of high-titer, preformed donor-specific antibodies. However, chronic ABMR remains a major complication resulting in the untimely loss of transplanted organs (3-10). The close relationship between donor-specific antibodies and ABMR has been revealed by the highly sensitive detection of human leukocyte antigen (HLA) antibodies (7, 11-15). Injury to transplanted organs by activation of humoral immune reaction in the context of HLA identical transplants and the absence of donor specific antibodies (17-24), strongly suggest the participation of non-HLA (nHLA) antibodies in ABMR (25). In this review, we discuss the genesis of ABMR in the context of HLA and nHLA antibodies and summarize strategies for ABMR management.

[Immunology and immunosuppression in kidney transplantation. ABO and HLA incompatible kidney transplantation]

OBJECTIVES

To perform a state of the art about immunological features in renal transplantation, immunosuppressive drugs and their mechanisms of action and immunologically high risk transplantations such as ABO and HLA-incompatible transplantation.

MATERIAL AND METHODS

An exhaustive systematic review of the scientific literature was performed in the Medline database (http://www.ncbi.nlm.nih.gov) and Embase (http://www.embase.com) using different associations of the following keywords (MESH): "allogenic response; allograft; immunosuppression; ABO incompatible transplantation; donor specific antibodies; HLA incompatible; desensitization; kidney transplantation". Publications obtained were selected based on methodology, language, date of publication (last 10 years) and relevance. Prospective and retrospective studies, in English or French, review articles; meta-analysis and guidelines were selected and analyzed. This search found 4717 articles. After reading titles and abstracts, 141 were included in the text, based on their relevance.

RESULTS

The considerable step in comprehension and knowledge allogeneic response this last few years allowed a better used of immunosuppression and the discover of news immunosuppressive drugs. In the first part of this article, the allogeneic response will be described. The different classes of immunosuppressive drugs will be presented and the actual management of immunosuppression will be discussed. Eventually, the modalities and results of immunologically high-risk transplantations such as ABO and HLA incompatible transplantations will be reported.

CONCLUSIONS

The knowledge and the control of allogeneic response to allogeneic graft allowed the development of renal transplantation.

Impact of Early Blood Transfusion After Kidney Transplantation on the Incidence of Donor-Specific Anti-HLA Antibodies

Little is known about the impact of posttransplant blood transfusion on the sensitization of anti-HLA antibodies and the formation of donor-specific antibodies (DSAs). The aims of our study were to determine the 1-year incidence of DSAs (assessed using a solid-phase assay) and antibody-mediated rejection (AMR) in kidney transplant patients who had or had not received a blood transfusion during the first year after transplantation. Included were 390 non-HLA-sensitized patients who had received an ABO-compatible kidney transplant and had not previously or simultaneously received a nonkidney transplant. Overall, 64% of patients received a red blood cell transfusion within the first year after transplantation, most within the first month. The overall 1-year incidence of DSAs was significantly higher in patients that had undergone transfusion (7.2% vs. 0.7% in patients with no transfusion, p < 0.0001). AMR occurred more often in the transfusion group (n = 15, 6%) compared with the nontransfusion group (n = 2, 1.4%; p = 0.04). Blood transfusion was an independent predictive factor for de novo DSA formation but not for AMR. Patients who had a transfusion and developed DSAs were more often treated with cyclosporin A (n = 10, 55.5%) rather than tacrolimus (n = 45, 19.4%; p = 0.0001). In conclusion, early posttransplant blood transfusion may increase immunological risk, especially in underimmunosuppressed patients.

Association of C1q Binding Status With De Novo HLA Antibody Clinical Features and Allograft Function in Kidney Transplantation Patients During Eight Years of Dynamic Follow-up

BACKGROUND

C1q-binding donor-specific antibody (DSA) is detrimental to transplanted kidney function. However, the factors that affect C1q binding status are unclear.

METHODS

A total of 519 samples from 129 consecutive kidney transplantation patients during 8 years of dynamic follow-up were collected for HLA antibody (Ab) screening and C1q detection.

RESULTS

Among the detected HLA Abs, the majority were class II, and the DQ subtypes composed the highest proportion. The C1q-binding Abs were all HLA-II, and the DQ subtypes had the highest rate of C1q positivity. With a cutoff mean fluorescence intensity (MFI) value of 7349, the sensitivity and specificity of detecting C1q-binding Abs from all HLA-II Abs were 84.48% and 83.56%, respectively. Additionally, C1q is more likely to be bound by DSA than non-donor-specific antibody (NDSA). Compared with free DSA/NDSA, the MFI values of C1q-binding DSA/NDSA are more closely correlated with serum creatinine levels and reflect the effect of anti-antibody-mediated rejection treatment more sensitively.

CONCLUSIONS

HLA-II Abs (particularly DQ subtypes), high titers of Abs, and DSA are important relevant factors of C1q positivity. The MFI value of C1q-binding DSA may be a useful clinical indicator of HLA antibody-mediated graft injury before the appearance of histologically typical humoral rejection.

The Complement System and Antibody-Mediated Transplant Rejection

Complement activation is an important cause of tissue injury in patients with Ab-mediated rejection (AMR) of transplanted organs. Complement activation triggers a strong inflammatory response, and it also generates tissue-bound and soluble fragments that are clinically useful markers of inflammation. The detection of complement proteins deposited within transplanted tissues has become an indispensible biomarker of AMR, and several assays have recently been developed to measure complement activation by Abs reactive to specific donor HLA expressed within the transplant. Complement inhibitors have entered clinical use and have shown efficacy for the treatment of AMR. New methods of detecting complement activation within transplanted organs will improve our ability to diagnose and monitor AMR, and they will also help guide the use of complement inhibitory drugs.

Immune response and histology of humoral rejection in kidney transplantation

The adaptive immune response forms the basis of allograft rejection. Its weapons are direct cellular cytotoxicity, identified from the beginning of organ transplantation, and/or antibodies, limited to hyperacute rejection by preformed antibodies and not as an allogenic response. This resulted in allogenic response being thought for decades to have just a cellular origin. But the experimental studies by Gorer demonstrating tissue damage in allografts due to antibodies secreted by B lymphocytes activated against polymorphic molecules were disregarded. The special coexistence of binding and unbinding between antibodies and antigens of the endothelial cell membranes has been the cause of the delay in demonstrating the humoral allogenic response. The endothelium, the target tissue of antibodies, has a high turnover, and antigen-antibody binding is non-covalent. If endothelial cells are attacked by the humoral response, immunoglobulins are rapidly removed from their surface by shedding and/or internalization, as well as degrading the components of the complement system by the action of MCP, DAF and CD59. Thus, the presence of complement proteins in the membrane of endothelial cells is transient. In fact, the acute form of antibody-mediated rejection was not demonstrated until C4d complement fragment deposition was identified, which is the only component that binds covalently to endothelial cells. This review examines the relationship between humoral immune response and the types of acute and chronic histological lesion shown on biopsy of the transplanted organ.

Functional Immune Anatomy of the Liver-As an Allograft

The liver is an immunoregulatory organ in which a tolerogenic microenvironment mitigates the relative "strength" of local immune responses. Paradoxically, necro-inflammatory diseases create the need for most liver transplants. Treatment of hepatitis B virus, hepatitis C virus, and acute T cell-mediated rejection have redirected focus on long-term allograft structural integrity. Understanding of insults should enable decades of morbidity-free survival after liver replacement because of these tolerogenic properties. Studies of long-term survivors show low-grade chronic inflammatory, fibrotic, and microvascular lesions, likely related to some combination of environment insults (i.e. abnormal physiology), donor-specific antibodies, and T cell-mediated immunity. The resultant conundrum is familiar in transplantation: adequate immunosuppression produces chronic toxicities, while lightened immunosuppression leads to sensitization, immunological injury, and structural deterioration. The "balance" is more favorable for liver than other solid organ allografts. This occurs because of unique hepatic immune physiology and provides unintended benefits for allografts by modulating various afferent and efferent limbs of allogenic immune responses. This review is intended to provide a better understanding of liver immune microanatomy and physiology and thereby (a) the potential structural consequences of low-level, including allo-antibody-mediated injury; and (b) how liver allografts modulate immune reactions. Special attention is given to the microvasculature and hepatic mononuclear phagocytic system.

Cellular immune profile of kidney transplant patients developing anti-HLA antibodies during childhood

BACKGROUND

In the field of kidney transplantation, identifying early signatures of humoral rejection is a key challenge.

METHODS

We investigated the presence of anti-HLA antibodies and the distribution of lymphocyte subpopulations in 77 kidney-transplanted children and young adults compared to 23 healthy controls. Moreover, we tested whether the presence of anti-HLA antibodies could be related to modification in lymphocyte phenotype. Finally, we correlated the presence of anti-HLA antibodies and specific alteration of lymphocyte subsets with clinical outcomes.

RESULTS

In kidney-transplanted children who developed anti-HLA antibodies, we observed an expansion of double-negative B cells (CD19 + CD27-IgD-), indicating premature aging of this compartment. Moreover, we reported signs of impaired B cell regulation, indicated by a higher IL-21R+ B cell frequency associated with an abnormal increase of follicular helper T cells. Finally, a considerable reduction in CD8+ effector T and invariant Natural killer T (NKT) cells was observed. The stability of graft function over time is significantly correlated with the frequency of peripheral effector CD4+ and CD8+ T cells and invariant NKT cells.

CONCLUSIONS

This study supports the usefulness of lymphocyte subset as one of a spectrum of early diagnostic tools required to identify patients at risk of developing donor alloimmune response.

Immune mechanisms of acute and chronic rejection

With the currently available immunosuppression, severe T-cell mediated rejection has become a rare event. With the introduction of modern antibody-detection techniques, such as the L-SAB technology, acute or hyperacute antibody-mediated rejection of the kidney are also seen infrequently. In contrast, chronic antibody-mediated rejection is considered to be a major contributor to graft loss in the late posttransplant phase. Problems in the management of chronic antibody-mediated rejection are effective prevention of the development of alloantibodies against donor HLA and the early identification of patients at risk for this entity. Finally, today there is still noeffective strategy to treat this indolent and slowly progressing form of antibody-mediated rejection. Herein, we review the pathomechanisms of the different forms of rejection and the clinical significance of these entities in human kidney transplantation.

High-grade proteinuria as a cardiovascular risk factor in renal transplant recipients

BACKGROUND

Proteinuria is a marker of graft damage and is closely associated with a higher risk of morbidity, mortality, and cardiovascular disease in kidney transplant recipients (KTRs). Arterial stiffness is a well-known predictor of vascular calcification and systemic arteriosclerosis. In our study, we aimed to investigate the association between proteinuria and graft/patient survival and to determine whether proteinuria may be a predictor for cardiovascular disease in our KTR population.

METHODS

Ninety KTRs (31 women; age, 38.7 ± 11 years, with 45.9 ± 9.6 months post-transplantation period) with normal graft functions in the 3 to 5 years of the post-transplantation period were enrolled. All patients were evaluated for their standard clinical (age, sex, and duration of hemodialysis) parameters. High-grade proteinuria was defined as proteinuria >500 mg/day in the 24-hour urine collection. All patients were evaluated by means of pulse-wave velocity (PWV) measurement at the initiation of the study.

RESULTS

Patients were divided into 2 groups: group 1 (high-grade proteinuria) patients with ≥500 mg/24 hours (n = 30) and group 2 (low-grade proteinuria) patients with <500 mg/24 hours (n = 60). High-grade proteinuria was correlated with higher PWV measurements and lower estimated glomerular filtration levels. Proteinuria appears to precede the elevation of serum creatinine and thus may be a useful marker of renal injury and may also be a contributing factor on deterioration of the graft.

CONCLUSIONS

High-grade (>500 mg/day) proteinuria in KTRs is strongly associated with poor graft survival and increased risk of cardiovascular events. In our study, we proved the significant difference between high-grade and low-grade proteinuric patients, and we suggest 500 mg/day as the threshold of proteinuria in KTR population.

Late Failing Heart Allografts: Pathology of Cardiac Allograft Vasculopathy and Association With Antibody-Mediated Rejection

In heart transplantation, there is a lack of robust evidence of the specific causes of late allograft failure. We hypothesized that a substantial fraction of failing heart allografts may be associated with antibody-mediated injury and immune-mediated coronary arteriosclerosis. We included all patients undergoing a retransplantation for late terminal heart allograft failure in three referral centers. We performed an integrative strategy of heart allograft phenotyping by assessing the heart vascular tree including histopathology and immunohistochemistry together with circulating donor-specific antibodies. The main analysis included 40 explanted heart allografts patients and 402 endomyocardial biopsies performed before allograft loss. Overall, antibody-mediated rejection was observed in 19 (47.5%) failing heart allografts including 16 patients (40%) in whom unrecognized previous episodes of subclinical antibody-mediated rejection occurred 4.5 ± 3.5 years before allograft loss. Explanted allografts with evidence of antibody-mediated rejection demonstrated higher endothelitis and microvascular inflammation scores (0.89 ± 0.26 and 2.25 ± 0.28, respectively) compared with explanted allografts without antibody-mediated rejection (0.42 ± 0.11 and 0.36 ± 0.09, p = 0.046 and p < 0.0001, respectively). Antibody-mediated injury was observed in 62.1% of failing allografts with pure coronary arteriosclerosis and mixed (arteriosclerosis and atherosclerosis) pattern, while it was not observed in patients with pure coronary atherosclerosis (p = 0.0076). We demonstrate that antibody-mediated rejection is operating in a substantial fraction of failing heart allografts and is associated with severe coronary arteriosclerosis. Unrecognized subclinical antibody-mediated rejection episodes may be observed years before allograft failure.

Characterisation of Tertiary Lymphoid Organs in Explanted Rejected Donor Kidneys

PURPOSE

Tertiary lymphoid organs (TLOs) have been described within organ allografts, but whether they promote destructive or beneficial alloimmune responses remains controversial. This study aimed to characterize TLO distribution in human chronically rejected renal allografts and to explore their functions.

METHODS

A total of 29 explanted chronically rejected and 12 acutely rejected renal allografts were analyzed by immunohistochemistry. The distribution of TLOs, T cells, follicular dendritic cells, B cells, and follicular regulatory T (Tfr) cells, as well as Ki67, peripheral lymph node addressin (PNAd), podoplanin, AID, IL-17, IL-21, IL-10, and C4d expression were detected by immunohistochemistry. Correlations between lymphoid neogenesis and the expression of IL-17, IL-21, C4d, podoplanin, IL-10, and Foxp3 were evaluated. In addition, the duration of graft function was compared between allografts that harbored or lacked TLOs.

RESULTS

TLOs were detected in 27.6% of chronically rejected renal grafts, but they rarely had germinal centers. Lymphoid neogenesis negatively correlated with CXCR5 expression, and almost completely correlated with IL-17 expression. Those grafts that harbored a TLO functioned for an average of 5.98 years and those without a TLO lasted only about half as long with an average of 2.91 years. However, in grafts that harbored a TLO, Foxp3(+) cells were comparitively less than those without a TLO. Foxp3(+)CXCR5(+) Tfr cells and IL-10(+) cells were rare in grafts, irrespective of the presence of a TLO.

CONCLUSION

TLOs in chronically rejected kidney allografts may be an epiphenomenon of the inflammatory process that is related to graft duration.

Improved flow cytometry based cytotoxicity and binding assay for clinical antibody HLA crossmatching

The presence of preformed donor-specific HLA antibodies leads to early antibody mediated kidney allograft rejection. Therefore, detection and avoidance of donor reactive HLA antibodies prior to transplantation is of outmost importance in order to minimize the risk of rejection. Detection of pre-formed HLA antibodies is currently performed using complement-dependent cytotoxicity (CDC) assay alone or together with a flow cytometry based crossmatch (FCXM). This study was initiated to further evaluate our recently developed flow cytometry based procedure for determination of both cytotoxicity of and IgG binding to donor-derived lymphocytes by HLA antibodies. Highly enriched immuno-magnetic bead purified T and B lymphocytes were used as target cells for patient sera using 96-well plates. Importantly, the assay shows high sensitivity and specificity as determined by HLA typed donor cells and serum with defined HLA antibody IgG and C1q. Based on this and additional data generated in this paper, such as evaluation of appropriate serum and complements incubation times and assay reproducibility and stability, will enable us to more rapidly implement this assay in our clinical laboratory routines. In addition, we demonstrate that FCtox crossmatching of deceased donor cells has superior specificity compared to conventional CDC assay especially regarding high frequencies of false-positive reactions.

Detection of alloantibody-mediated complement activation: A diagnostic advance in monitoring kidney transplant rejection?

OBJECTIVE

Antibody-mediated rejection (ABMR) is an important cause of kidney allograft injury. In the last two decades, detection of complement split product C4d along transplant capillaries, a footprint of antibody-mediated classical complement activation, has evolved as a useful diagnostic marker of ABMR. While it was recognized that ABMR may occur also in the absence of C4d, numerous studies have shown that C4d deposition may indicate a more severe rejection phenotype associated with poor graft survival. Such studies suggest a possible diagnostic benefit of ex vivo monitoring the complement-activating capability of circulating alloantibodies.

DESIGN AND METHODS

We reviewed the literature between 1993 and 2015, focusing on in vivo (biopsy work-up) and in vitro detection (modified bead array technology) of HLA antibody-triggered classical complement activation in kidney transplantation.

RESULTS

Precise HLA antibody detection methods, in particular Luminex-based single antigen bead (SAB) assays, have provided a valuable basis for the design of techniques for in vitro detection of HLA antibody-triggered complement activation reflected by C1q, C4 or C3 split product deposition to the bead surface. Establishing such assays it was recognized that deposition of complement products to SAB, which critically depends on antibody binding strength, may be a cardinal trigger of the prozone effect, a troublesome in vitro artifact caused by a steric interference with IgG detection reagents. False-low IgG results, especially on SAB with extensive antibody binding, have to be considered when interpreting studies analyzing the diagnostic value of complement in relation to standard IgG detection. Levels of complement-fixing donor-specific antibodies (DSA) were shown to correlate with the results of standard crossmatch tests, suggesting potential application for crossmatch prediction. Moreover, while the utility of pre-transplant complement detection, at least in crossmatch-negative transplant recipients, is controversially discussed, a series of studies have shown that the appearance of post-transplant complement-fixing DSA may be associated with C4d deposition in transplant capillaries and a particular risk of graft failure.

CONCLUSIONS

The independent value of modified single antigen bead assays, as compared to a careful analysis of standard IgG detection, which may be affected considerably by complement dependent artifacts, needs to be clarified. Whether they have the potential to improve the predictive accuracy of our current diagnostic repertoire warrants further study.

[Ten years' experience in the research of abdominal compartment syndrome (2004-2014)]

Intra-abdominal hypertension and abdominal compartment syndrome are frequent findings among severe surgical ill patients. In spite of the fast diagnostic methods and effective therapeutic procedures the mortality is high. The causing factors lead to increased intra-abdominal pressure and abdominal compartment syndrome. It can be defined as adverse physiologic consequences that occur as a result of an acute increase in the intra-abdominal pressure. The most common causes are retroperitoneal haemorrhage, pancreatitis, bowel obstruction, tense ascites, peritonitis and serious visceral edema due to massive fluid resuscitation. The affected systems are cardiovascular, respiratory, renal, central nervous systems, splanchnic organs, and finally the whole body. The diagnostic method is the intra-abdominal pressure monitoring. The bases of the treatment are adequate fluid resuscitation, non-surgical management and decompression. The authors review the topic including the international and Hungarian references based on their ten years experience.

Antibody-mediated rejection in young kidney transplant recipients: the dilemma of noncompliance and insufficient immunosuppression

BACKGROUND

Antibody-mediated rejection (ABMR) is a recognized cause of late kidney allograft loss. Although ABMR may occur despite appropriate chronic immunosuppressive therapy, non-adherence both facilitates and accelerates the activation of the effector phase of the humoral immune response against the donor tissue, leading in turn to progressive kidney allograft rejection. Given the poor efficacy of rescue therapies for both acute and chronic late ABMR, establishing appropriate preventive strategies at different times before and after transplantation is a critical management goal.

CASE-DIAGNOSIS/TREATMENT

In this report, we discuss the differential diagnoses and management of ABMR based on the clinical case report of a young kidney transplant recipient with progressive ABMR due to poor immunosuppressive adherence. In the absence of sensitive and specific non-invasive monitoring tools for alloimmune activation, the clinical dilemma in the management of the adolescent patient lies in differentiating between suboptimal prescribed immunosuppression and deliberate non-adherence to adequate immunosuppression dosing. Despite the advent of therapies to reduce ABMR injury, the graft is destined for untimely functional loss.

CONCLUSIONS

New biomarkers and tools for the accurate characterization of alloimmune risk before and after transplantation, and serial testing for de novo changes in circulating donor-specific alloantibodies, are urgently needed to support the delivery of optimized immunosuppression exposure.

Personalization of the immunosuppressive treatment in renal transplant recipients: the great challenge in "omics" medicine

Renal transplantation represents the most favorable treatment for patients with advanced renal failure and it is followed, in most cases, by a significant enhancement in patients’ quality of life. Significant improvements in one-year renal allograft and patients’ survival rates have been achieved over the last 10 years primarily as a result of newer immunosuppressive regimens. Despite these notable achievements in the short-term outcome, long-term graft function and survival rates remain less than optimal. Death with a functioning graft and chronic allograft dysfunction result in an annual rate of 3%–5%. In this context, drug toxicity and long-term chronic adverse effects of immunosuppressive medications have a pivotal role. Unfortunately, at the moment, except for the evaluation of trough drug levels, no clinically useful tools are available to correctly manage immunosuppressive therapy. The proper use of these drugs could potentiate therapeutic effects minimizing adverse drug reactions. For this purpose, in the future, “omics” techniques could represent powerful tools that may be employed in clinical practice to routinely aid the personalization of drug treatment according to each patient’s genetic makeup. However, it is unquestionable that additional studies and technological advances are needed to standardize and simplify these methodologies.

Matching for Human Leukocyte Antigens (HLA) in corneal transplantation - to do or not to do

As many patients with severe corneal disease are not even considered as candidates for a human graft due to their high risk of rejection, it is essential to find ways to reduce the chance of rejection. One of the options is proper matching of the cornea donor and recipient for the Human Leukocyte Antigens (HLA), a subject of much debate. Currently, patients receiving their first corneal allograft are hardly ever matched for HLA and even patients undergoing a regraft usually do not receive an HLA-matched graft. While anterior and posterior lamellar grafts are not immune to rejection, they are usually performed in low risk, non-vascularized cases. These are the cases in which the immune privilege due to the avascular status and active immune inhibition is still intact. Once broken due to infection, sensitization or trauma, rejection will occur. There is enough data to show that when proper DNA-based typing techniques are being used, even low risk perforating corneal transplantations benefit from matching for HLA Class I, and high risk cases from HLA Class I and probably Class II matching. Combining HLA class I and class II matching, or using the HLAMatchmaker could further improve the effect of HLA matching. However, new techniques could be applied to reduce the chance of rejection. Options are the local or systemic use of biologics, or gene therapy, aiming at preventing or suppressing immune responses. The goal of all these approaches should be to prevent a first rejection, as secondary grafts are usually at higher risk of complications including rejections than first grafts.

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.

Vascular endothelium as a target of immune response in renal transplant rejection

This review of clinical and experimental studies aims at analyzing the interplay between graft endothelium and host immune system in renal transplantation, and how it affects the survival of the graft. Graft endothelium is indeed the first barrier between self and non-self that is encountered by host lymphocytes upon reperfusion of vascularized solid transplants. Endothelial cells (EC) express all the major sets of antigens (Ag) that elicit host immune response, and therefore represent a preferential target in organ rejection. Some of the Ag expressed by EC are target of the antibody-mediated response, such as the AB0 blood group system, the human leukocyte antigens (HLA), and MHC class I related chain A antigens (MICA) systems, and the endothelial cell-restricted Ag; for each of these systems, the mechanisms of interaction and damage of both preformed and de novo donor-specific antibodies are reviewed along with their impact on renal graft survival. Moreover, the rejection process can force injured EC to expose cryptic self-Ag, toward which an autoimmune response mounts, overlapping to the allo-immune response in the damaging of the graft. Not only are EC a passive target of the host immune response but also an active player in lymphocyte activation; therefore, their interaction with allogenic T-cells is analyzed on the basis of experimental in vitro and in vivo studies, according to the patterns of expression of the HLA class I and II and the co-stimulatory molecules specific for cytotoxic and helper T-cells. Finally, as the response that follows transplantation has proven to be not necessarily destructive, the factors that foster graft endothelium functioning in spite of rejection, and how they could be therapeutically harnessed to promote long-term graft acceptance, are described: accommodation that is resistance of EC to donor-specific antibodies, and endothelial cell ability to induce Foxp3+ regulatory T-cells, that are crucial mediators of tolerance.

Clinical relevance of HLA antibody monitoring after kidney transplantation

In kidney transplantation, antibody-mediated allograft injury caused by donor HLA-specific antibodies (DSA) has recently been identified as one of the major causes of late graft loss. This paper gives a brief overview on the impact of DSA development on graft outcome in organ transplantation with a focus on risk factors for de novo alloantibody induction and recently published guidelines for monitoring of DSA during the posttransplant phase.

Methodological aspects of anti-human leukocyte antigen antibody analysis in solid organ transplantation

Donor human leukocyte antigen (HLA)-specific antibodies (DSA) play an important role in solid organ transplantation. Preexisting IgG isotype DSA are considered a risk factor for antibody mediated rejection, graft failure or graft loss. The post-transplant development of DSA depends on multiple factors including immunogenicity of mismatched antigens, HLA class II typing of the recipient, cytokine gene polymorphisms, and cellular immunoregulatory mechanisms. De novo developed antibodies require special attention because not all DSA have equal clinical significance. Therefore, it is important for transplant clinicians and transplant immunologists to accurately characterize DSA. In this review, the contemporary immunological techniques for detection and characterization of anti-HLA antibodies and their pitfalls are described.

Pretransplant IgG reactivity to apoptotic cells correlates with late kidney allograft loss

Preexisting serum antibodies have long been associated with graft loss in transplant recipients. While most studies have focused on HLA-specific antibodies, the contribution of non-HLA-reactive antibodies has been largely overlooked. We have recently characterized mAbs secreted by B cell clones derived from kidney allograft recipients with rejection that bind to apoptotic cells. Here, we assessed the presence of such antibodies in pretransplant serum from 300 kidney transplant recipients and examined their contribution to the graft outcomes. Kaplan-Meier survival analysis revealed that patients with high pretransplant IgG reactivity to apoptotic cells had a significantly increased rate of late graft loss. The effect was only apparent after approximately 1 year posttransplant. Moreover, the association between pretransplant IgG reactivity to apoptotic cells and graft loss was still significant after excluding patients with high reactivity to HLA. This reactivity was almost exclusively mediated by IgG1 and IgG3 with complement fixing and activating properties. Overall, our findings support the view that IgG reactive to apoptotic cells contribute to presensitization. Taking these antibodies into consideration alongside anti-HLA antibodies during candidate evaluation would likely improve the transplant risk assessment.

Predictive factors of allosensitization in renal transplant patients switched from calcineurin to mTOR inhibitors

Conversion of kidney-transplant recipients from calcineurin inhibitors to mTOR inhibitors has been suggested to be a risk factor for increased alloimmune response. We have analyzed the development of new HLA-antibodies (HLA-Abs) early after conversion in 184 patients converted in stable phase at our hospital and compared with a control group of nonconverted comparable 63 transplants. Using single-antigen solid-phase immunoassay analysis, a preconversion and a 3-6 months postconversion sera were prospectively analyzed in every patient for the appearance of new HLA-Abs. Renal function at 2 years postconversion and cumulative graft survival were compared between groups. In 16 patients, new HLA-Abs (3-DSA and 13-NonDSA), not present at the moment of conversion, were detected (8.7% vs. 3.1% in the control group). The type of mTORi used, type of CNI preconversion, the presence of steroids, time of conversion, or indication for conversion did not have influence on this effect but the presence of HLA-Abs before conversion highly correlated with the appearance of new specificities. Patients with de novo HLA-Abs showed a trend to worst graft function and survival. In conclusion, conversion to mTORi can be followed by early appearance of de novo HLA-Abs, especially in patients with HLA-Abs preconversion, and this complication should be screened early after conversion.

Preformed donor-specific antibodies and risk of antibody-mediated rejection in repeat renal transplantation

BACKGROUND

Allograft outcomes in patients undergoing repeat renal transplantation are inferior compared to first-time transplant recipient outcomes. Donor-specific antibodies detected by solid-phase assays (DSA-SPA) may contribute to the worse prognosis. The influence of DSA-SPA on repeat renal transplantation outcomes has not been previously studied in detail.

DESIGN

This study reports the findings in 174 patients who underwent repeat renal transplantation between years 2007 and 2012. These included 62 patients with preformed DSA-SPA detected by Luminex at the time of transplantation. Patients received standard and consistent immunosuppression and were monitored closely for evidence of rejection. Recipients who underwent desensitization were excluded from this analysis. Endpoints included development of biopsy-proven acute rejection and analysis of graft survival and function.

RESULTS

Patients in the DSA-SPA-positive and DSA-SPA-negative groups received similar immunosuppression, and a similar proportion of recipients had a peak panel reactive antibody greater than 20%; the two groups differed with respect to human leukocyte antigen mismatches (4.7 ± 1.1 vs. 4.1 ± 1.7, P=0.024). Recipients with preformed DSA-SPA had higher rejection rates (54.8% vs. 34.8%, P=0.01), including higher rates of antibody-mediated rejection (AMR) (32.3% vs. 7.1%, P<0.001). Recipients who were DSA-SPA-positive and flow cytometry crossmatch (FCXM)-positive had a higher incidence of both AMR (OR 4.6, P=0.009) and of acute rejection (OR 3.57, P=0.02) as compared to those who were DSA-SPA-positive and FCXM-negative. Overall allograft survival was similar in the DSA-SPA-positive and DSA-SPA-negative groups (log-rank test=0.63, P=0.428). Differences in allograft function were detectable after 2 years (32.8 ± 13.1 vs. 47 ± 20.2 mL/min/1.73 m(2), P=0.023) and may be reflective of more AMR among DSA-SPA-positive patients.

CONCLUSIONS

This analysis suggests that DSA-SPA increases the overall risk of acute rejection but does not appear to adversely impact allograft survival during the early follow-up period. Close monitoring of renal function and early biopsy for AMR detection appear to allow for satisfactory short-term allograft outcomes in repeat transplant recipients.

Kidney transplant recipients treated with belatacept exhibit increased naïve and transitional B cells

Phase III clinical studies have shown that kidney transplant (KT) recipients treated with the costimulation blocker belatacept exhibited a better renal allograft function and lower donor-specific anti-HLA immunization when compared to recipients treated with calcineurin inhibitors (CNI). We analyzed B cell phenotype in KT recipients treated with belatacept and stable renal function (N = 13). Results were compared to those observed in stable patients treated with CNI (N = 12), or with chronic antibody-mediated rejection (N = 5). Both transcriptional profile and phenotypic characterization of peripheral B cells were performed by real-time polymerase chain reaction and flow cytometry, respectively. In belatacept group, the frequency and absolute number of transitional B cells as defined by both phenotypes: CD19(+) CD24(hi) CD38(hi) and CD19(+) IgD(hi) CD38(hi) CD27(-) , as well as naïve B cells were significantly higher compared with CNI group. B cell activating factor (BAFF) and BAFF receptor mRNA levels were significantly lower in belatacept group than in CNI group. These results show for the first time that belatacept influences B cell compartment by favoring the occurrence of transitional B cells with potential regulatory properties, as described in operational tolerant patients. This role may explain the lower alloimmunization rate observed in belatacept-treated patients.

Bortezomib in late antibody-mediated kidney transplant rejection (BORTEJECT Study): study protocol for a randomized controlled trial

Background

Despite major advances in transplant medicine, improvements in long-term kidney allograft survival have not been commensurate with those observed shortly after transplantation. The formation of donor-specific antibodies (DSA) and ongoing antibody-mediated rejection (AMR) processes may critically contribute to late graft loss. However, appropriate treatment for late AMR has not yet been defined. There is accumulating evidence that the proteasome inhibitor bortezomib may substantially affect the function and integrity of alloantibody-secreting plasma cells. The impact of this agent on the course of late AMR has not so far been systematically investigated.

Methods/design

The BORTEJECT Study is a randomized controlled trial designed to clarify the impact of intravenous bortezomib on the course of late AMR. In this single-center study (nephrological outpatient service, Medical University Vienna) we plan an initial cross-sectional DSA screening of 1,000 kidney transplant recipients (functioning graft at ≥180 days; estimated glomerular filtration rate (eGFR) >20 ml/minute/1.73 m²). DSA-positive recipients will be subjected to kidney allograft biopsy to detect morphological features consistent with AMR. Forty-four patients with biopsy-proven AMR will then be included in a double-blind placebo-controlled intervention trial (1:1 randomization stratified for eGFR and the presence of T-cell-mediated rejection). Patients in the active group will receive two cycles of bortezomib (4 × 1.3 mg/m² over 2 weeks; 3-month interval between cycles). The primary end point will be the course of eGFR over 24 months (intention-to-treat analysis). The sample size was calculated according to the assumption of a 5 ml/minute/1.73 m² difference in eGFR slope (per year) between the two groups (alpha: 0.05; power: 0.8). Secondary endpoints will be DSA levels, protein excretion, measured glomerular filtration rate, transplant and patient survival, and the development of acute and chronic morphological lesions in 24-month protocol biopsies.

Discussion

The impact of anti-humoral treatment on the course of late AMR has not yet been systematically investigated. Based on the hypothesis that proteasome inhibition improves the outcome of DSA-positive late AMR, we suggest that our trial has the potential to provide solid evidence towards the treatment of this type of rejection.

Trial registration

Clinicaltrials.gov: NCT01873157.

Everolimus inhibits anti-HLA I antibody-mediated endothelial cell signaling, migration and proliferation more potently than sirolimus

Antibody (Ab) crosslinking of HLA I molecules on the surface of endothelial cells triggers proliferative and pro-survival intracellular signaling, which is implicated in the process of chronic allograft rejection, also known as transplant vasculopathy (TV). The purpose of this study was to investigate the role of mammalian target of rapamycin (mTOR) in HLA I Ab-induced signaling cascades. Everolimus provides a tool to establish how the mTOR signal network regulates HLA I-mediated migration, proliferation and survival. We found that everolimus inhibits mTOR complex 1 (mTORC1) by disassociating Raptor from mTOR, thereby preventing class I-induced phosphorylation of mTOR, p70S6K, S6RP and 4E-BP1, and resultant class I-stimulated cell migration and proliferation. Furthermore, we found that everolimus inhibits class I-mediated mTORC2 activation (1) by disassociating Rictor and Sin1 from mTOR; (2) by preventing class I-stimulated Akt phosphorylation and (3) by preventing class I-mediated ERK phosphorylation. These results suggest that everolimus is more effective than sirolimus at antagonizing both mTORC1 and mTORC2, the latter of which is critical in endothelial cell functional changes leading to TV in solid organ transplantation after HLA I crosslinking. Our findings point to a potential therapeutic effect of everolimus in prevention of chronic Ab-mediated rejection.

Prevalence and risk factors for early chronic allograft nephropathy in a live related renal transplant program

BACKGROUND

Chronic allograft nephropathy (CAN) is a common cause of delayed allograft failure throughout the world. Its prevalence and risk factors vary depending on a number of factors. There is little information on the prevalence and risk factors for early CAN in live related renal transplant patients.

OBJECTIVES

We aimed to determine the prevalence and the risk factors of early CAN in our setup.

PATIENTS AND METHODS

The study was conducted at Sindh Institute of Urology & Transplantation (SIUT), Karachi, from 2002 to 2005 on patients who had live related kidney transplantation and underwent at least one allograft biopsy within 18 months of transplantation. The biopsies were performed and prepared in accordance with established indications and guidelines. The Banff 97 classification and its updates were used to diagnose and categorize the biopsy pathology. Patients were divided into two groups depending on the presence or absence of CAN on biopsies. Following parameters were compared among the groups: age, sex, human leukocyte antigen (HLA) match, immunosuppression used, acute rejection (AR) episodes, urinary tract infections (UTIs), viral infections, cyclosporine levels, early and late graft function monitored by serum creatinine.

RESULTS

A total of 164 patients fulfilled the study inclusion criteria. The mean age of recipients and donors was relatively young. The majority of the donors were siblings. The overall prevalence of CAN was 25.6% (42/164), between 3 and 18 months post transplantation. The median time to the appearance of CAN was 9 months post-transplant. The prevalence of CAN increased as post-transplant duration increased. In 39 (92.8%) subjects, CAN was detected on the second or subsequent graft biopsy. Only 3 (7.2%) patients showed CAN on the first graft biopsy. The majority of cases belonged to moderate degree or grade II CAN. The mean serum creatinine values were higher in the CAN group at the time of discharge and all times post-transplantation.

CONCLUSIONS

In conclusion, the results show that serum creatinine at the time of discharge is a useful predictor of later development of chronic changes in the allograft. Further studies are needed to identify the risk factors for the early development of chronic changes in living related renal transplant program.

Maternal microchimerism in biliary atresia: are maternal cells effector cells, targets, or just bystanders?

The etiology of biliary atresia (BA) is unknown; however, the liver histology is similar to that observed in immune-mediated hepatic disorders. Liver fibrosis in BA progresses even after bile drainage has been achieved by the Kasai operation. Maternal microchimerism has been purported to play a part in the pathogenesis of BA as well as certain autoimmune diseases. However, the role of maternal cells has not yet been determined in BA. Specifically, it is unknown whether these maternal cells function as maternal effector T lymphocytes, or targets or bystanders. We currently hypothesize that the first hit is due to GvHD interaction by engrafted maternal effector T lymphocytes. Furthermore, we suggest that the secondary effects that are manifested by progressive cirrhosis are caused either by maternal chimeric effector T lymphocytes (e.g., GvHD interaction) or targets (e.g., HvGD interaction). Based on our hypothesis, mixed lymphocyte reactions between patients and their mothers might shed light on the etiopathogenesis and prognostic indicators.

Trends and characteristics in early glomerular filtration rate decline after posttransplantation alloantibody appearance

BACKGROUND

Approximately 7% to 9% of patients with donor-specific anti-human leukocyte antigen (HLA) antibodies (DSA) fail within 1 year post-DSA onset. However, little is known as to how this DSA-associated failure temporally progresses. This longitudinal study investigates DSA's temporal relationship to allograft dysfunction and identifies predictors of allograft function's progressive deterioration post-DSA.

METHODS

A cohort of 175 non-HLA identical patients receiving their first transplant between March 1999 and March 2006 were analyzed. Protocol testing for DSA via single antigen beads was done before transplantation and at 1, 3, 6, 9, and 12 months after transplantation then annually. Estimated glomerular filtration rate (eGFR) was analyzed before and after DSA onset.

RESULTS

Forty-two patients developed DSA and had adequate eGFR information for analysis. Before DSA onset, the 42 patients had stable eGFR. By 1 year post-DSA, the cohort's eGFR was significantly lower (P<0.001); however, 30 of 42 had stable function. Twelve patients had failure or early allograft dysfunction (eGFR decline >25% from DSA onset). Those who failed early (by 1 year post-DSA) had more antibody-mediated rejection than stable patients (P=0.03). Late failures (after 1 year post-DSA) were predictable with evidence of early allograft dysfunction (eGFR decline >25% by 1 year post-DSA; P<0.001). Early allograft dysfunction preceded late failure by nearly 1 year.

CONCLUSIONS

DSA is temporally related to allograft function deterioration. However, in many cases, late allograft failures are preceded by early allograft dysfunction. Therefore, monitoring for early allograft dysfunction provides treating physicians with a window of opportunity for treatment or continued monitoring.

Issues in solid-organ transplantation in children: translational research from bench to bedside

In this review, we identify important challenges facing physicians responsible for renal and cardiac transplantation in children based on a review of the contemporary medical literature. Regarding pediatric renal transplantation, we discuss the challenge of antibody-mediated rejection, focusing on both acute and chronic antibody-mediated rejection. We review new diagnostic approaches to antibody-mediated rejection, such as panel-reactive antibodies, donor-specific cross-matching, antibody assays, risk assessment and diagnosis of antibody-mediated rejection, the pathology of antibody-mediated rejection, the issue of ABO incompatibility in renal transplantation, new therapies for antibody-mediated rejection, inhibiting of residual antibodies, the suppression or depletion of B-cells, genetic approaches to treating acute antibody-mediated rejection, and identifying future translational research directions in kidney transplantation in children. Regarding pediatric cardiac transplantation, we discuss the mechanisms of cardiac transplant rejection, including the role of endomyocardial biopsy in detecting graft rejection and the role of biomarkers in detecting cardiac graft rejection, including biomarkers of inflammation, cardiomyocyte injury, or stress. We review cardiac allograft vasculopathy. We also address the role of genetic analyses, including genome-wide association studies, gene expression profiling using entities such as AlloMap®, and adenosine triphosphate release as a measure of immune function using the Cylex® ImmuKnow™ cell function assay. Finally, we identify future translational research directions in heart transplantation in children.