Post-transplantation antibody monitoring and HLA antibody epitope identification

Immunosuppressive protocols after laryngeal transplantation: a systematic review

BACKGROUNDS

Larynx transplantation has been successfully performed four times, in 1998, 2010, 2015 and 2023 remained the ultimate goal of voice, feeding and breathing rehabilitation.

OBJECTIVE

Immunosuppressive protocols used during the previous successful larynx allotransplantation are detailed.

MATERIAL AND METHODS

A systematic review of the literature on PUBMED/Medline, Cochrane and Embase was conducted. Articles relating to actual human larynx transplantations were included.

RESULTS

Bibliography search gathered N = 10 publications related to the performance and follow-up of human laryngeal transplantations. N = 8 publications were included corresponding to N = 3 actual human larynx transplantations performed in 1998 and 2010 in the USA and in 2015 in Poland. Immunosuppression protocols, induction and maintenance strategies, rejection monitoring and history of all the three previous laryngeal grafts were detailed.

CONCLUSIONS

Beyond the surgical prowess, larynx transplantation is feasible and associated with a reasonably successful outcome when compared to other solid organ transplants. Immunosuppressive regimen protocols and technologies for the monitoring of the organ viability have evolved.

SIGNIFICANCE

The reevaluation of this surgical option serves as the reminder of the critical necessity to implement a meticulous immunosuppression protocol when transplanting this inherently immunogenic composite organ, the larynx.

DSA-FXM: Accelerated Donor-specific Flow Crossmatch Discriminating Class I and II Antibody Specifically and Only to Donor HLA for Determining True Incompatibility

BACKGROUND

Worldwide, a final crossmatch is the gold standard for determining compatibility between patient and donor before solid organ transplantation and preventing hyperacute rejection. In the absence of autoantibodies, an incompatible crossmatch in a sensitized patient is attributed to mismatched donor HLA. However, current physical crossmatch methods cannot distinguish reactivity to HLA from other clinically irrelevant cell surface targets nor the class of HLA if it is the target. Result interpretation is difficult or impossible when autoantibodies, alloantibodies, or therapeutic antibodies coexist.

METHODS

Herein, we describe a unique donor-specific flow crossmatch (DSA-FXM) that distinguishes HLA class I or II donor-specific antibody bound to HLA antigens on the donor cell surface in their native conformation that is not impacted by rituximab, anti-thymocyte globulin (after absorption), or autoantibodies. It is HLA specific.

RESULTS

We compared the results of single-antigen antibody testing, autoreactive and alloreactive flow cytometry crossmatches (FXM) using traditional FXM and our DSA-FXM method from 94 patients (enriched for auto+/allo+ pairs; n = 64) against 110 donors (338 tests) and show that, in our cohort, positive traditional FXM results are not directed to donor HLA 60.25% of the time and negative traditional FXM results are missing HLA donor-specific antibody 36.2% of the time based on the DSA-FXM.

CONCLUSIONS

We demonstrate that the DSA-FXM is able to define categorically distinct and clinically important HLA antibody profiles in half the time required for the standard FXM, potentially shortening cold ischemia time and providing clinicians with unambiguous essential information regarding HLA compatibility when time is critical.

Characterizing pre-transplant and post-transplant kidney rejection risk by B cell immune repertoire sequencing

Studying immune repertoire in the context of organ transplant provides important information on how adaptive immunity may contribute and modulate graft rejection. Here we characterize the peripheral blood immune repertoire of individuals before and after kidney transplant using B cell receptor sequencing in a longitudinal clinical study. Individuals who develop rejection after transplantation have a more diverse immune repertoire before transplant, suggesting a predisposition for post-transplant rejection risk. Additionally, over 2 years of follow-up, patients who develop rejection demonstrate a specific set of expanded clones that persist after the rejection. While there is an overall reduction of peripheral B cell diversity, likely due to increased general immunosuppression exposure in this cohort, the detection of specific IGHV gene usage across all rejecting patients supports that a common pool of immunogenic antigens may drive post-transplant rejection. Our findings may have clinical implications for the prediction and clinical management of kidney transplant rejection.

Defining the structural basis for human alloantibody binding to human leukocyte antigen allele HLA-A*11:01

Our understanding of the conformational and electrostatic determinants that underlie targeting of human leukocyte antigens (HLA) by anti-HLA alloantibodies is principally based upon in silico modelling. Here we provide a biochemical/biophysical and functional characterization of a human monoclonal alloantibody specific for a common HLA type, HLA-A*11:01. We present a 2.4 Å resolution map of the binding interface of this antibody on HLA-A*11:01 and compare the structural determinants with those utilized by T-cell receptor (TCR), killer-cell immunoglobulin-like receptor (KIR) and CD8 on the same molecule. These data provide a mechanistic insight into the paratope−epitope relationship between an alloantibody and its target HLA molecule in a biological context where other immune receptors are concomitantly engaged. This has important implications for our interpretation of serologic binding patterns of anti-HLA antibodies in sensitized individuals and thus, for the biology of human alloresponses.

Anti-human leukocyte antigen (HLA) antibodies are important mediators of alloresponses, but structural insights on antibody:HLA interaction are still lacking. Here the authors provide a 2.4 Å structure of antibody:HLA complex, and also analyse HLA features important for other HLA-interacting molecules, to enhance our understanding of alloimmunity.

HLA epitope matching in pediatric renal transplantation

Chronic graft loss due to antibody-mediated rejection (AMR) and the difficulty of re-transplanting highly sensitized patients are two of the major long-term challenges in pediatric renal transplantation. Treatments for AMR are often ineffective and desensitization protocols can be a high risk, making prevention a highly appealing strategy. Insights into the structural determinants of humoral alloantigenicity present an exciting opportunity to reassess our current paradigm of tissue matching and potentially preventing these complications. We review the theory behind human leukocyte antigen (HLA) B cell epitopes and the various systems that have been proposed to define them, including eplets. There is a growing body of clinical evidence suggesting that epitope-based tissue matching may be superior to traditional HLA antigen matching at predicting a range of clinical outcomes. However, additional studies are required to better understand the biological relevance of these systems of defining epitopes and their role in pediatric transplantation.

Are We Ready for Epitope-Based HLA Matching in Clinical Organ Transplantation?

This overview describes recent developments demonstrating the significance of epitopes in HLA antibody responses and matching for organ transplantation. HLA epitopes are defined by molecular modeling and amino acid comparisons between HLA alleles and the HLAMatchmaker algorithm considers eplets as essential components. Each allele represents a distinct string of eplets and matching is done by aligning donor and recipient strings. Evidence is summarized how mismatched eplet loads affect antibody responses and transplant outcomes. Epitope-based matching has been applied not only to identify acceptable mismatches for sensitized transplant candidates but also to identify more suitably mismatched donors for nonsensitized patients. Three recently proposed theories will further our understanding of the immunogenicity of individual HLA eplets.It has become apparent that epitope-based matching is superior to antigen matching; we should be ready soon to apply this principle in the clinical transplant setting very soon.

A Novel Method for Anti-HLA Antibody Detection Using Personalized Peptide Arrays

Background

HLA mismatches are the primary cause of alloantibody-mediated rejection (AMR) in organ transplantation. To delineate antigenic and immunogenic potentials among individual HLA mismatches, information regarding antibody specificity at the epitope level, instead of the allelic level, is needed.

Methods

This study explores a direct screening method for HLA linear epitopes in kidney transplant patients. We custom synthesized a large panel of 15-residue HLA peptides in an array format and measured alloantibody reactivity to these peptides from the sera of post and/or pretransplant patients. Two design concepts for the arrays were followed: a standard array of a fixed panel of peptides or personalized arrays. The standard array contains 420 peptides derived from a predetermined set of HLA-DQ allelic antigens based on templates also used in the single-antigen beads assay.

Results

The array detected distinct antiserum patterns among transplant subjects and revealed epitope levels of specificity largely in accordance with the single-antigen results. Two personalized arrays that each included donor-derived peptides of HLA-A, -B, -C, -DQ, and -DR sequences were separately designed for 2 transplant subjects. The personalized arrays detected de novo antibodies following transplantation. The new method also showed superior sensitivity to a single-antigen assay in one of the cases whose pathological diagnosis of AMR occurred before single-antigen assay could detect antibodies.

Conclusions

This pilot study proved the feasibility of using personalized peptide arrays to achieve detection of alloantibodies for linear HLA epitopes associated with distinct donor-recipient mismatches. Single or multiple reactive epitopes may occur on an individual HLA molecule, and donor-specific HLA-DQ-reactivity among 5 kidney transplant subjects revealed patterns of shared epitopes.

Many de novo donor-specific antibodies recognize β2 -microglobulin-free, but not intact HLA heterodimers

Solid‐phase single antigen bead (SAB) assays are standard of care for detection and identification of donor‐specific antibody (DSA) in patients who receive solid organ transplantation (SOT). While several studies have documented the reproducibility and sensitivity of SAB testing for DSA, there are little data available concerning its specificity. This study describes the identification of antibodies to β₂‐microglobulin‐free human leukocyte antigen (β₂‐m‐fHLA) heavy chains on SAB arrays and provides a reassessment of the clinical relevance of DSA testing by this platform. Post‐transplant sera from 55 patients who were positive for de novo donor‐specific antibodies on a SAB solid‐phase immunoassay were tested under denaturing conditions in order to identify antibodies reactive with β₂‐m‐fHLA or native HLA (nHLA). Antibodies to β₂‐m‐fHLA were present in nearly half of patients being monitored in the post‐transplant period. The frequency of antibodies to β₂‐m‐fHLA was similar among DSA and HLA antigens that were irrelevant to the transplant (non‐DSA). Among the seven patients with clinical or pathologic antibody‐mediated rejection (AMR), none had antibodies to β₂‐m‐fHLA exclusively; thus, the clinical relevance of β₂‐m‐fHLA is unclear. Our data suggests that SAB testing produces false positive reactions due to the presence of β₂‐m‐fHLA and these can lead to inappropriate assignment of unacceptable antigens during transplant listing and possibly inaccurate identification of DSA in the post‐transplant period.

[New aspects of HLA compatibility in organ transplantation]

In organ transplantation, HLA compatibility between a donor and a recipient is currently assessed through the comparison of their HLA antigens and the sole count of incompatible HLA antigens. Similarly, antibodies were originally described as antigenic-specific. With solid phase assays detection of anti-HLA antibodies and crystallographic studies, it is now recognized that anti-HLA antibodies are not specific for antigens, but for epitopes, i.e. short polymorphic sequences of amino acids that are more often in positions accessible to allo-antibodies. These epitopes, due to the distribution of HLA molecules polymorphism, may be shared by different HLA antigens. This explains why an immunization towards a given HLA antigen can lead to synthesis of antibodies reactive towards other antigens sharing one or more epitopes. Similarly, structural comparison of the HLA molecules of a recipient and his donor defines the epitope load, i.e. the number of incompatible epitopes. This epitope load is correlated with the risk of developing antibodies specific for the donor after transplantation. New tools, such as the HLAMatchmaker software, allow to determine the epitopic load and to analyze the epitopic specificity of alloantibodies. These tools will possibly lead to rethink the method of graft allocation, or at least to take differently into account HLA compatibility in allocation algorythms.

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.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Laryngotracheal transplantation: technical modifications and functional outcomes

OBJECTIVES/HYPOTHESIS

Laryngeal transplantation offers the potential for patients without a larynx to recover their voice, which is critical in our communication age. We report clinical and functional outcomes from a laryngotracheal transplant. Widespread adoption of this technique has been slowed due to the ethical concerns of life-long immunosuppression after a nonvital organ transplant. Our patient was already on immunosuppressive medication from prior kidney-pancreas transplantation, and therefore was not exposed to added long-term risk. We describe the unique technical advances, clinical course, and rehabilitation of this patient and the implications for future laryngeal transplantation.

STUDY DESIGN

Case report.

METHODS

A laryngotracheal transplantation was performed in a 51-year-old prior kidney-pancreas transplant recipient presenting with complete laryngotracheal stenosis. Surgical modifications were made in the previously described technique related to retrieval, vascular supply, and reinnervation. This resulted in a robustly vascularized organ with well-perfused long-segment tracheal transplant and early return of motor reinnervation.

RESULTS

A multidisciplinary approach resulted in a successful transplant without evidence of rejection to date. Postoperatively, the patient continues to rely on a tracheotomy but has had the return of an oral and nasal airway, vocalization, smell, and taste, all experienced for the first time in 11 years.

CONCLUSIONS

We have demonstrated that our methods may result in a successful laryngotracheal transplant. We describe the preparation, surgical technique, rehabilitation, and interventions employed in achieving optimal outcomes. This report contributes valuable information on this rarely performed composite transplant.

Anti-donor immune responses elicited by allogeneic mesenchymal stem cells: what have we learned so far?

Mesenchymal stem (stromal) cells (MSCs) have potent anti-inflammatory/immunosuppressive properties which underlie much of their therapeutic potential. This fact has led to the widely accepted belief that MSCs from genetically unrelated individuals (allogeneic (allo)-MSCs) can be used therapeutically with equal efficacy to autologous MSCs and without triggering the donor-specific immune responses that are typically associated with allo-transplants. In this article, we critically review available experimental data to determine whether good in vivo evidence exists in support of the 'immune privileged' status of allo-MSCs. We also examine published studies regarding the immunogenicity of allo-MSCs following activation ('licensing') by inflammatory stimuli or following differentiation. Among the identified studies which have addressed in vivo immunogenicity of allo-MSCs, there was substantial variability as regards experimental species, disease model, route of MSC administration, cell dose and stringency of the immunological assays employed. Nonetheless, the majority of these studies has documented specific cellular (T-cell) and humoral (B-cell/antibody) immune responses against donor antigens following administration of non-manipulated, interferon-γ-activated and differentiated allo-MSCs. The consequences of such anti-donor immune responses were also variable and ranged from reduced in vivo survival of allo-MSCs with accelerated rejection of subsequent allogeneic transplants to apparent promotion of donor-specific tolerance. On the basis of these findings and on existing knowledge of allo-antigen recognition from the field of transplant immunology, we propose that the concept of the immune privileged nature of allo-MSCs should be reconsidered and that the range and clinical implications of anti-donor immune responses elicited by allo-MSCs be more precisely studied in human and animal recipients.

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

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

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Evaluation of humoral immune response to donor HLA after implantation of cellularized versus decellularized human heart valve allografts

We have evaluated the development of antibodies in response to donor allograft valve implant in patients who received cellularized and decellularized allografts and determined possible immunogenic epitopes considered responsible for antibodies reactivity. Serum samples from all recipients who received cellularized allografts or decellularized allografts were collected before valve replacement and at 5, 10, 30 and 90 days post-operatively and frozen until required. Tests were performed using the Luminex-based single human leukocyte antigen (HLA)-A, -B, -C and HLA-DR, -DQ antigen microsphere assay. To determine possible immunogenic epitopes, we used the HLAMatchmaker (HLAMM) software if applicable. Decellularized grafts elicited lower levels of anti-HLA class I and II antibody formation after implantation than cellularized allografts. All patients from cellularized group presented donor-specific antibodies class I and II within 3 months of observation period. In HLAMM analysis, the cellularized group had significantly higher numbers of immunogenic epitopes than decellularized group for both class I and II (p: 0.002 - cl I / p: 0.009 - cl II / p: 0.004 - cl I and II). Our findings demonstrate that the anti-HLA antibodies detected in the cellularized group were against donor HLA possible immunogenic epitopes and that in the decellularized group the anti-HLA antibodies were not against donor HLA possible immunogenic epitopes. These findings lead us to suggest that choosing sodium dodecyl sulfate decellularization process is the best alternative to decrease the immunogenicity of allograft valve transplant.

Luminex and antibody detection in kidney transplantation

Preformed anti-human leukocyte antigen (HLA) antibodies have a negative effect on kidney transplantation outcome with an increased rejection rate and reduction in survival. Posttransplantation production of donor-specific anti-HLA antibodies is indicative of an active immune response and risk of transplantation rejection. For many years the primary technique for anti-HLA antibody detection was complement-dependent cytotoxicity (CDC), which has been integrated by solid-phase assays as HLA antigen-coated bead methods (Luminex). This new technological approach has allowed identification of anti-HLA antibodies, not detectable using conventional CDC method, in patients awaiting kidney transplantation. Moreover, use of Luminex technology has enabled better definition of acceptable or unacceptable antigens favoring transplantation in highly immunized patients. However, there are still many unresolved issues, including the clinical relevance of antibodies detected with this system.

Novel C1q assay reveals a clinically relevant subset of human leukocyte antigen antibodies independent of immunoglobulin G strength on single antigen beads

It has been known for 40 years that cytotoxic human leukocyte antigen (HLA) antibodies are associated with graft rejection. However, the complement-dependent cytotoxicity assay (CDC) used to define these clinically deleterious antibodies suffers from a lack of sensitivity and specificity. Recently, methods exploiting immunoglobulin G (IgG) antibody binding to HLA single antigen beads (SAB) have overcome sensitivity and specificity drawbacks but introduced a new dilemma: which of the much broader set of antibodies defined by these methods are clinically relevant. To address this, we developed a complement-fixing C1q assay on the HLA SAB that combines sensitivity, specificity, and functional potential into one assay. We compared the CDC, IgG, and C1q assays on 96 sera having 2,118 defined antibodies and determined that CDC detects only 19% of complement-fixing antibodies detected by C1q, whereas C1q detects only 47% of antibodies detected by IgG. In the same patient, there is no predictability by IgG mean fluorescence intensity (MFI) as to which of the antibodies will bind C1q because fixation is independent of MFI values. In 3 clinical studies, C1q(+) antibodies appear to be more highly correlated than those detected by IgG alone for antibody-mediated rejection in hearts as well as for kidney transplant glomerulopathy and graft failure.

A role for antibodies to human leukocyte antigens, collagen-V, and K-α1-Tubulin in antibody-mediated rejection and cardiac allograft vasculopathy

BACKGROUND

We determined the role of donor-specific antibodies (DSA) and antibodies (Abs) to self-antigens, collagen-V (Col-V), and K-α1-Tubulin (KAT) in pathogenesis of acute antibody-mediated rejection (AMR) and cardiac allograft vasculopathy (CAV) after human heart transplantation (HTx).

METHODS

One hundred thirty-seven HTx recipients, with 60 early period (≤ 12 months) and 77 late period (>12 months), were enrolled in this study. Circulating DSA was determined using LUMINEX. Abs against Col-I, II, IV, V, and KAT were measured using ELISA. Frequency of CD4+T helper cells (CD4+Th) secreting interferon (IFN)-γ, interleukin (IL)-5, -10, or -17 specific to self-antigens were determined using Enzyme Linked Immunosorbent Spot assay.

RESULTS

A significant association between AMR and DSA was demonstrated. Development of DSA in AMR patients correlated well with the development of auto-Abs to Col-V (AMR[+]: 383 ± 72 μg/mL, AMR[-]: 172 ± 49 μg/mL, P=0.033) and KAT (AMR[+]: 252 ± 49 μg/mL, AMR[-]: 61 ± 21 μg/mL, P=0.014). Patients who developed AMR demonstrated increased frequencies of CD4+Th secreting IFN-γ and IL-5 with reduction in IL-10 specific for Col-V/KAT. Patients diagnosed with CAV also developed DSA and auto-Abs to Col-V (CAV[+]: 835 ± 142 μg/mL, CAV[-]: 242 ± 68 μg/mL, P=0.025) and KAT (CAV[+]: 768 ± 206 μg/mL, CAV[-]: 196 ± 72 μg/mL, P=0.001) with increased frequencies of CD4+Th secreting IL-17 with reduction in IL-10 specific for Col-V/KAT. CONCLUSIONS.: Development of Abs to human leukocyte antigens and self-antigens are associated with increases in CD4+Th secreting IFN-γ and IL-5 in AMR and IL-17 in CAV, with reduction in CD4+Th secreting IL-10 in both AMR and CAV.

The generation and maintenance of serum alloantibody

Donor-specific alloantibodies (DSA) mediate hyperacute and acute antibody-mediated rejection (AMR), which can lead to early graft damage and loss, and are also associated with chronic AMR and reduced long-term graft survival. Such alloantibodies can be generated by previous exposure to major histocompatibility (MHC) antigens (usually via blood transfusions, previous allografts or pregnancy) or can occur de novo after transplantation. Recent studies also suggest that non-MHC antibodies, including those recognising major histocompatibility complex class I-related chain A (MICA), MICB, vimentin, angiotensin II type I receptor may also have an adverse impact on allograft outcomes. In this review, we consider how the dose, route and context of antigen exposure influences DSA induction and describe factors which control the generation, maintenance and survival of alloantibody-producing plasma cells. Finally, we discuss the implications of these variables on therapeutic approaches to DSA.

Donor-specific antibodies to human leukocyte antigens are associated with and precede antibodies to major histocompatibility complex class I-related chain A in antibody-mediated rejection and cardiac allograft vasculopathy after human cardiac transplantation

Humoral immune responses to mismatched donor human leukocyte antigen (HLA) and major histocompatibility complex (MHC) class I-related chain A (MICA) have been reported to contribute to immunopathogenesis of antibody-mediated rejection (AMR) in the early period and cardiac allograft vasculopathy (CAV) in the late period after cardiac transplantation (HTx). The goal of this study is to define the roles of donor-specific antibodies (DSA) and anti-MICA in AMR and CAV. A total of 95 post-HTx recipients were enrolled; 43 patients in the early period (≤ 12 months post-HTx) and 52 patients in the late period (>12 months post-HTx). Development of DSA and anti-MICA were serially monitored using Luminex. Development of DSA (AMR+: n = 6/8.75%, AMR-: n = 4/35.11%, p = 0.009) and anti-MICA (AMR+: n = 5/8.63%, AMR-: n = 4/35.11%, p = 0.002) was significantly associated with AMR. AMR+DSA+ patients demonstrated increased anti-MICA levels compared with AMR+DSA- patients (p=0.01). Serial monitoring revealed DSA (2.7 ± 1.4 months) preceded development of anti-MICA (6.5 ± 2.1 months) in recipients diagnosed with AMR at 8.3 ± 2.5 months post-HTx. Development of DSA (CAV+: n = 8/12.67%, CAV-: n = 5/40.13%, p = 0.004) and anti-MICA (CAV+: n = 9/12.75%, CAV-: n = 5/40.13%, p = 0.001) was significantly associated with CAV. CAV+DSA+ patients demonstrated increased anti-MICA levels compared with CAV+DSA- patients (p = 0.01). Antibodies to HLA are associated with and precede development of anti-MICA in AMR and CAV. Therefore, DSA and anti-MICA can be used as noninvasive markers for monitoring AMR and CAV.

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.

Correlations between Terasaki's HLA class I epitopes and HLAMatchmaker-defined eplets on HLA-A, -B and -C antigens

Although the determination of human leukocyte antigen (HLA) antibody specificity has traditionally been directed toward HLA antigens, there is now increasing attention to structurally defined HLA epitopes. An understanding of the HLA epitope repertoire is important to acceptable mismatching for sensitized patients and to a new epitope-based matching algorithm aimed to reduce antibody-mediated rejection. There are two strategies to determine the HLA epitope repertoire. Terasaki's group has used an empirical method to analyze the reactivity of single allele Luminex panels with mouse monoclonal antibodies (mAbs) and absorbed/eluted alloantibodies with a computer program based on shared residues in the amino acid sequences 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. A comparative analysis has shown that 81/103 Terasaki's HLA class I epitopes are equivalent to individual eplets (n = 50) or pairs of eplets (n = 31) separated far enough to serve as potential contact sites for two complementarity-determining regions of antibody. An additional 12 Terasaki's epitopes (TerEps) correspond to eplets with permissible residue combinations that do not seem to affect epitope specificity. We could not identify corresponding eplets for the remaining 10 TerEps, including 8 that might be considered xeno-epitopes defined by mouse mAbs. Conversely, HLAMatchmaker has 38 additional eplets in well-exposed surface positions that do not have equivalent TerEps, and for many of them, we have found specific antibodies. These findings strengthen the concept that eplets are essential basic units of HLA epitopes and that they provide a better understanding of HLA immunogenicity (i.e. ability to induce an antibody response) and antigenicity (i.e. reactivity with specific antibody).

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.