Detection of donor-specific antibodies in kidney transplantation

Hybrid structural modeling of alloantibody binding to human leukocyte antigen with rapid and reproducible cross-linking mass spectrometry

Alloantibody recognition of donor human leukocyte antigen (HLA) is associated with poor clinical transplantation outcomes. However, the molecular and structural basis for the alloantibody-HLA interaction is not well understood. Here, we used a hybrid structural modeling approach on a previously studied alloantibody-HLA interacting pair with inputs from ab initio, in silico, and in vitro data. Highly reproducible cross-linking mass spectrometry data were obtained with both discovery- and targeted mass spectrometry-based approaches approaches. The cross-link information was then used together with predicted antibody Fv structure, predicted antibody paratope, and in silico-predicted interacting surface to model the antibody-HLA interaction. This hybrid structural modeling approach closely recapitulates the key interacting residues from a previously solved crystal structure of an alloantibody-HLA-A∗11:01 pair. These results suggest that a predictive-based hybrid structural modeling approach supplemented with cross-linking mass spectrometry data can provide functionally relevant structural models to understand the structural basis of antibody-HLA mismatch in transplantation.

Clinical Outcome of Kidney Transplant Recipients with C1q-Binding De Novo Donor Specific Antibodies: A Single-Center Experience

Complement activation by HLA antibodies is a key component of immune-mediated graft injury. We examined the clinical outcomes of kidney transplant recipients with complement-fixing de novo donor-specific antibodies (dnDSA) who were followed in our center. The C1q-binding ability was retrospectively assessed in 69 patients with dnDSA and mean fluorescence intensity (MFI) values > 2000 out of the 1325 kidney transplant recipients who were screened for DSA between 2015 and 2019. Luminex IgG single antigen beads (SAB)and C1q-SAB assays (One Lambda) were used. C1q-binding dnDSA was identified in 32/69 (46.4%) of the patients. Significantly higher MFI values were observed in C1q-positive DSA (18,978 versus 5840, p < 0.001). Renal graft biopsies were performed in 43 of the kidney transplant recipients (62.3%) with allograft dysfunction. Antibody-mediated rejection (ABMR) was detected in 29/43 (67.4%) of the patients. The incidence of ABMR was similar among patients with C1q-binding and non-C1q-binding DSA (51.7% vs. 48.3%, p = 0.523). Graft loss occurred in 30/69 (43.5%) of the patients at a median time of 82.5 months (IQR 45-135) from DSA detection. C1q-binding DSA was present in more patients who experienced graft loss (53.1% vs. 35.1%, p = 0.152). Higher MFI values and inferior clinical outcomes occurred in most of the kidney transplant recipients with C1q-binding dnDSA.

Small Extracellular Vesicles in Transplant Rejection

Small extracellular vesicles (sEV), which are released to body fluids (e.g., serum, urine) by all types of human cells, may stimulate or inhibit the innate and adaptive immune response through multiple mechanisms. Exosomes or sEV have on their surface many key receptors of immune response, including major histocompatibility complex (MHC) components, identical to their cellular origin. They also exhibit an ability to carry antigen and target leukocytes either via interaction with cell surface receptors or intracellular delivery of inflammatory mediators, receptors, enzymes, mRNAs, and noncoding RNAs. By the transfer of donor MHC antigens to recipient antigen presenting cells sEV may also contribute to T cell allorecognition and alloresponse. Here, we review the influence of sEV on the development of rejection or tolerance in the setting of solid organ and tissue allotransplantation. We also summarize and discuss potential applications of plasma and urinary sEV as biomarkers in the context of transplantation. We focus on the attempts to use sEV as a noninvasive approach to detecting allograft rejection. Preliminary studies show that both sEV total levels and a set of specific molecules included in their cargo may be an evidence of ongoing allograft rejection.

B cells in transplant tolerance and rejection: friends or foes?

Our understanding of the role of B cells in organ transplantation remains incomplete and continues to grow. The majority of research has focused on the detrimental role of antibodies that drive the development of pathogenesis of the transplanted organ. However, it has been shown that not all donor-specific antibodies are harmful and in some circumstances can even promote tolerance through the mechanism of accommodation. Furthermore, B cells can have effects on transplanted organs through their interaction with T cells, namely antigen presentation, cytokine production, and costimulation. More recently, the role and importance of Bregs was introduced to the field of transplantation. Due to this functional and ontogenetic heterogeneity, targeting B cells in transplantation may bring undesired immunologic side effects including increased rejection. Therefore, the selective control of B cells that contribute to the humoral response against donor antigens will continue to be an important and challenging area of research and potentially lead to improved long-term transplant outcomes.

Case Report: A five-year follow up after pediatric renal transplantation using flow cytometry crossmatch and HLA immunophenotyping based on DNA for screening test

Background: There are three methods for renal replacement therapy for end stage chronic kidney disease; dialysis, continuous ambulatory peritoneal dialysis, and renal transplantation which is the best because of the least morbidity rate, the best survival rates, the best quality of life, and the best improvement in activities of daily living. In the field, flow cytometry serves a well-established role in pre- and post-transplant crossmatching, and if it is combined with human leukocyte antigen (HLA) immunophenotyping based on DNA, it will produce a more sensitive prediction of the chronic graft rejection compared to complement-dependent cytotoxicity crossmatching and can eliminate irrelevant antibody (IgM). This is the first experience using this method in our hospital. The survival rate at one, five and ten years has been shown to be 99%, 97% and 96%, respectively; therefore, we wanted to find out the five year follow up of the patient. Case presentation: We evaluated a 20-year-old female with a history of pediatric renal transplantation five years previously due to end stage renal disease caused by bilateral parenchymatous renal disease. She had a history of hypertension since December 2014 and underwent hemodialysis for three months. The transplantation took place in March 2015. A kidney from her mother was transplanted to recipient using end-to-side anastomoses. After five years, the patient was routinely monitored at the urology clinic, with creatinine serum results between 1.5 and 2 mg/dL, urea and electrolyte serum levels within normal limits and she could resume normal life. Conclusions: Survival five years after the procedure showed a beneficial outcome of the method used.

KDIGO Clinical Practice Guideline on the Evaluation and Management of Candidates for Kidney Transplantation

The 2020 Kidney Disease: Improving Global Outcomes (KDIGO) Clinical Practice Guideline on the Evaluation and Management of Candidates for Kidney Transplantation is intended to assist health care professionals worldwide who evaluate and manage potential candidates for deceased or living donor kidney transplantation. This guideline addresses general candidacy issues such as access to transplantation, patient demographic and health status factors, and immunological and psychosocial assessment. The roles of various risk factors and comorbid conditions governing an individual's suitability for transplantation such as adherence, tobacco use, diabetes, obesity, perioperative issues, causes of kidney failure, infections, malignancy, pulmonary disease, cardiac and peripheral arterial disease, neurologic disease, gastrointestinal and liver disease, hematologic disease, and bone and mineral disorder are also addressed. This guideline provides recommendations for evaluation of individual aspects of a candidate's profile such that each risk factor and comorbidity are considered separately. The goal is to assist the clinical team to assimilate all data relevant to an individual, consider this within their local health context, and make an overall judgment on candidacy for transplantation. The guideline development process followed the Grades of Recommendation Assessment, Development, and Evaluation (GRADE) approach. Guideline recommendations are primarily based on systematic reviews of relevant studies and our assessment of the quality of that evidence, and the strengths of recommendations are provided. Limitations of the evidence are discussed with differences from previous guidelines noted and suggestions for future research are also provided.

Safety and Efficacy of a Steroid Avoidance Immunosuppression Regimen in Renal Transplant Patients With De Novo or Preformed Donor-Specific Antibodies: A Single-Center Study

Although interest in the role of donor-specific antibodies (DSAs) in kidney transplant rejection, graft survival, and histopathological outcomes is increasing, their impact on steroid avoidance or minimization in renal transplant populations is poorly understood. Primary outcomes of graft survival, rejection, and histopathological findings were assessed in 188 patients who received transplants between 2012 and 2015 at the Scripps Center for Organ Transplantation, which follows a steroid avoidance protocol. Analyses were performed using data from the United Network for Organ Sharing. Cohorts included kidney transplant recipients with de novo DSAs (dnDSAs; n = 27), preformed DSAs (pfDSAs; n = 15), and no DSAs (nDSAs; n = 146). Median time to dnDSA development (classes I and II) was shorter (102 days) than in previous studies. Rejection of any type was associated with DSAs to class I HLA (P < .05) and class II HLA (P < .01) but not with graft loss. Although mean fluorescence intensity (MFI) independently showed no association with rejection, an MFI >5000 showed a trend toward more antibody-mediated rejection (P < .06), though graft loss was not independently associated. Banff chronic allograft nephropathy scores and a modified chronic injury score were increased in the dnDSA cohort at 6 months, but not at 2 years (P < .001 and P < .08, respectively). Our data suggest that dnDSAs and pfDSAs impact short-term rejection rates but do not negatively impact graft survival or histopathological outcomes at 2 years. Periodic protocol post-transplant DSA monitoring may preemptively identify patients who develop dnDSAs who are at a higher risk for rejection.

Defining the structural basis for human leukocyte antigen reactivity in clinical transplantation

The current state-of-the-art technology employed to assess anti-human leukocyte antigen antibodies (Anti-HLA Ab) for donor-recipient matching and patient risk stratification in renal transplantation is the single antigen bead (SAB) assay. However, there are limitations to the SAB assay as it is not quantitative and due to variations in techniques and reagents, there is no standardization across laboratories. In this study, a structurally-defined human monoclonal alloantibody was employed to provide a mechanistic explanation for how fundamental alloantibody biology influences the readout from the SAB assay. Performance of the clinical SAB assay was evaluated by altering Anti-HLA Ab concentration, subclass, and detection reagents. Tests were conducted in parallel by two internationally accredited laboratories using standardized protocols and reagents. We show that alloantibody concentration, subclass, laboratory-specific detection devices, subclass-specific detection reagents all contribute to a significant degree of variation in the readout. We report a significant prozone effect affecting HLA alleles that are bound strongly by the test alloantibody as opposed to those bound weakly and this phenomenon is independent of complement. These data highlight the importance for establishing international standards for SAB assay calibration and have significant implications for our understanding of discordance in previous studies that have analyzed its clinical relevance.

Characterization of the C1q-Binding Ability and the IgG1-4 Subclass Profile of Preformed Anti-HLA Antibodies by Solid-Phase Assays

Humoral alloimmunity, particularly that triggered by preformed antibodies against human leukocyte antigens (HLA), is associated with an increased prevalence of rejection and reduced transplant survival. The high sensitivity of solid phase assays, based on microbeads coated with single antigens (SAB), consolidated them as the gold-standard method to characterize anti-HLA antibodies, ensuring a successful allograft allocation. Mean fluorescence intensity (MFI) provided by SAB is regularly used to stratify the immunological risk, assuming it as a reliable estimation of the antibody-level, but it is often limited by artifacts. Beyond MFI, other properties, such as the complement-binding ability or the IgG1-4 subclass profile have been examined to more accurately define the clinical relevance of antibodies and clarify their functional properties. However, there are still unresolved issues. Neat serum-samples from 20 highly-sensitized patients were analyzed by SAB-panIgG, SAB-IgG1-4 subclass and SAB-C1q assays. All 1:16 diluted serum-samples were additionally analyzed by SAB-panIgG and SAB-IgG1-4 subclass assays. A total of 1,285 anti-HLA antibodies were identified as positive, 473 (36.8%) of which were C1q-binding. As expected, serum-dilution enhanced the correlation between the C1q-binding ability and the antibody-strength, measured as the MFI (r_neat = 0.248 vs. r_diluted = 0.817). SAB-subclass assay revealed at least one IgG1-4 subclass in 1,012 (78.8%) positive antibody-specificities. Among them, strong complement-binding subclasses, mainly IgG1, were particularly frequent (98.9%) and no differences were found between C1q- and non-C1q-binding antibodies regarding their presence (99.4 vs. 98.5%; p = 0.193). In contrast, weak or non-C1q-binding subclasses (IgG2/IgG4) were more commonly detected in C1q-binding antibodies (78.9 vs. 38.6%; p < 0.001). Interestingly, a strong association was found between the C1q-binding ability and the IgG1 strength (r_IgG1dil = 0.796). Though lower, the correlation between the IgG2 strength and the C1q-binding ability was also strong (r_IgG2dil = 0.758), being both subclasses closely related (r_IgG1−IgG2 = 0.817). We did not find any correlation with the C1q-binding ability considering the remaining subclasses. In conclusion, we demonstrate that a particular profile of IgG subclasses (IgG1/IgG3) itself does not determine at all the ability to bind complement of anti-HLA antibodies assessed by SAB-C1q assay. It is the IgG subclass strength, mainly of IgG1, which usually appears in combination with IgG2, that best correlates with it.

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.

Comparison of Physical Crossmatch and Virtual Crossmatch to Identify Preexisting Donor-Specific Human Leukocyte Antigen (HLA) Antibodies and Outcome Following Kidney Transplantation

Background

Physical crossmatch (PXM) and virtual crossmatch (VXM) are applied to identify preexisting donor-specific human leukocyte antigen (HLA) antibodies in patients awaiting kidney transplantation. Recently, high-resolution epitope analysis has emerged as a novel strategy for VXM. A retrospective clinical study compared PXM with VXM before kidney transplantation and recipient outcome following transplantation.

Material/Methods

Between August 2017 and March 2018, 239 patients underwent crossmatching and 94 patients received a donor kidney. A complement-dependent cytotoxicity (CDC) PXM assay and VXM using serological and epitope analysis identified donor-specific antibodies (DSA). Crossmatch results and clinical outcome at 3 months were compared.

Results

VXM identified serological DSA (sDSA), verified epitope DSA, and total epitope DSA in 74 (31.0%), 39 (16.3%), and 49 (20.5%) cases, respectively. Eleven cases (4.6%) had a positive PXM detected by the CDC assay. Of 94 kidney transplant recipients, 21 had preexisting sDSA but were negative in PXM; there was 1 case of delayed graft function (DGF) and no cases of hyperacute rejection or acute rejection. Of the rest of the 73 recipients who were negative for sDSA, 8 had acute rejection (P=0.253) and 19 had DGF (P=0.037). No significant differences were found in graft survival at 3 months.

Conclusions

High-resolution epitope analysis identified fewer cases with DSA compared with serological analysis. Because patients with and without sDSA had a similar short-term outcome in the setting of a negative PXM, the presence of preexisting sDSA, determined by VXM, should not be an absolute contraindication for kidney transplantation.

Contemporary Strategies and Barriers to Transplantation Tolerance

The purpose of this review is to discuss immunologic tolerance as it applies to solid organ transplantation and to identify barriers that hinder the achievement of this long-term goal. First, the definition of tolerance and an introduction of mechanisms by which tolerance exists or can be achieved will be discussed. Next, a review of contemporary attempts at achieving transplant tolerance will be described. Finally, a discussion of the humoral barriers to transplantation tolerance and potential ways to overcome these barriers will be presented.

The good, the bad, and the ugly of luminex donor-specific crossmatch

The presence of donor-specific antibodies directed against human leukocyte antigen significantly influences renal transplant because of antibody-mediated rejection. We performed the screening of pre-renal transplant patients for preformed anti-HLA antibodies using anti-human globulin augmented-complement-dependent lymphocytotoxicity crossmatch (AHG-CDCXm), luminex donor-specific crossmatch (LumXm) and HLA antibody screening. Seven hundred and fifty-four patients were assessed for LumXm. HLA antibody screening was possible in 325 out of 754 cases. All the three investigations viz. CDCXm, HLA antibody screening and LumXm was performed in 325 patients. All CDCXm positive patients (10/325, 3.08%) were also positive with LumXm and HLA antibody screen whereas 14 cases (4.31%) with CDCXm negative were positive with luminex-based assays. LumXm and HLA antibody screening were both positive in 24 (7.38%) cases, LumXm and HLA antibody screening were both negative in 275 (84.63%) cases and LumXm negative and HLA antibody screening was positive in 22 (6.76%) cases. However, there were four cases (1.23%) which were positive in LumXm in spite of being negative in HLA antibody testing. Single Antigen Bead (SAB) assay was performed in all patients positive for HLA antibody test. We suggest that LumXm is a useful and sensitive technique for the detection of anti-HLA antibodies in pre-transplant renal patients. However, other measures such as luminex antibody screen, SAB assay, history of the donor, and the class of antibodies involved should be taken into consideration for pre-transplant work up of renal patients.

Kidney Transplantation: The Challenge of Human Leukocyte Antigen and Its Therapeutic Strategies

Kidney transplantation remains the treatment of choice for end-stage renal failure. When the immune system of the recipient recognizes the transplanted kidney as a foreign object, graft rejection occurs. As part of the host immune defense mechanism, human leukocyte antigen (HLA) is a major challenge for graft rejection in transplantation therapy. The impact of HLA mismatches between the donor and the potential recipient prolongs the time for renal transplantation therapy, tethered to dialysis, latter reduces graft survival, and increases mortality. The formation of pretransplant alloantibodies against HLA class I and II molecules can be sensitized through exposures to blood transfusions, prior transplants, and pregnancy. These preformed HLA antibodies are associated with rejection in kidney transplantation. On the other hand, the development of de novo antibodies may increase the risk for acute and chronic rejections. Allograft rejection results from a complex interplay involving both the innate and the adaptive immune systems. Thus, further insights into the mechanisms of tissue rejection and the risk of HLA sensitization is crucial in developing new therapies that may blunt the immune system against transplanted organs. Therefore, the purpose of this review is to highlight facts about HLA and its sensitization, various mechanisms of allograft rejection, the current immunosuppressive approaches, and the directions for future therapy.

Donor-Specific Antibodies in Kidney Transplant Recipients

Donor-specific antibodies have become an established biomarker predicting antibody-mediated rejection. Antibody-mediated rejection is the leading cause of graft loss after kidney transplant. There are several phenotypes of antibody-mediated rejection along post-transplant course that are determined by the timing and extent of humoral response and the various characteristics of donor-specific antibodies, such as antigen classes, specificity, antibody strength, IgG subclasses, and complement binding capacity. Preformed donor-specific antibodies in sensitized patients can trigger hyperacute rejection, accelerated acute rejection, and early acute antibody-mediated rejection. De novo donor-specific antibodies are associated with late acute antibody-mediated rejection, chronic antibody-mediated rejection, and transplant glomerulopathy. The pathogeneses of antibody-mediated rejection include not only complement-dependent cytotoxicity, but also complement-independent pathways of antibody-mediated cellular cytotoxicity and direct endothelial activation and proliferation. The novel assay for complement binding capacity has improved our ability to predict antibody-mediated rejection phenotypes. C1q binding donor-specific antibodies are closely associated with acute antibody-mediated rejection, more severe graft injuries, and early graft failure, whereas C1q nonbinding donor-specific antibodies correlate with subclinical or chronic antibody-mediated rejection and late graft loss. IgG subclasses have various abilities to activate complement and recruit effector cells through the Fc receptor. Complement binding IgG3 donor-specific antibodies are frequently associated with acute antibody-mediated rejection and severe graft injury, whereas noncomplement binding IgG4 donor-specific antibodies are more correlated with subclinical or chronic antibody-mediated rejection and transplant glomerulopathy. Our in-depth knowledge of complex characteristics of donor-specific antibodies can stratify the patient's immunologic risk, can predict distinct phenotypes of antibody-mediated rejection, and hopefully, will guide our clinical practice to improve the transplant outcomes.

Luminex Solid-Phase Crossmatch for De Novo Donor-Specific Antibodies in Living-Donor Related Transplants

OBJECTIVES

There are no reports of de novo donor-specific antibody monitoring by a low-cost solid-phase crossmatch assay using donor lysate after renal transplant.

MATERIALS AND METHODS

We prospectively evaluated 121 complement-dependant cytotoxicity crossmatch-negative living-donor kidney transplant recipients for development of de novo donor-specific antibodies (class I and II HLA) by solid-phase crossmatch Luminex assay after transplant.

RESULTS

Of 121 recipients in our study group, 26 (21.5%) developed de novo donor-specific antibody within 3 months after transplant. Fifteen (58%) of these 26 recipients developed class II de novo donor-specific antibody, 8 patients (30%) developed class I, and 3 (12%) developed both class I and class II. Of the remaining 95 patients (79%) who did not develop de novo donor-specific antibody, 6 (33.3%) had antibody-mediated rejection with glomerulitis (2 with C4d-positive disease). Donor-specific antibody was detected by Luminex solid-phase crossmatch in 18 patients (5 with class I, 11 with class II, and 2 with both class I and II), all with no evidence of clinical rejection. Development of de novo donor-specific antibody detected by solid-phase crossmatch was associated with more acute rejection (31% in de novo donor-specific antibody-positive group versus 19% in the negative group). The positive group had more antibody-mediated rejection (75% of acute rejections), whereas only 33.3% of acute rejections in the negative group were antibody-mediated rejection. Of 12 patients with antibody-mediated rejection, 9 were C4d negative (75%) and were diagnosed by donor-specific antibody positivity detected by solid-phase cros?match testing and histologic findings. The use of donor lysate in solid-phase crossmatch assays is more economical than the single-antigen bead Luminex assay (per test cost of US $45.20 vs $403.20).

False negative single antigen bead assay: Is it always an effect of prozone?

BACKGROUND

Bead based flow cytometry and Luminex play a major role in identification of alloantibodies in renal transplant work-up. Strong sensitization events may lead to prozone phenomenon that can affect single antigen bead (SAB) assay and result in false negativity. However, this can also be due to high titer of other blocking antibodies. While methods like, heat inactivation, C1 inhibitor, Ethylene diamine tetra-acetic-acid and Dithio threitol treatment can remove interfering antibodies of complement and IgM, these methods are not optimal if false negativity is due to prozone effect, which is high titer of antibodies alone.

METHODS

We hereby present a case of a highly sensitized renal transplant recipient with 64% panel reactive antibody positivity (PRA) and a subsequent negative SAB assay. This paradoxical finding hinted at SAB being a false negative result and serial dilutions were used to perform further tests.

RESULTS

Serum dilutions lead to positive flow based panel reactive antibody (PRA) and flow cytometry crossmatch (FCXM), with an increasing trend in FCXM.

CONCLUSIONS

In highly sensitized patients serial dilution should be considered during a transplant work-up to avoid missing any underlying antibodies. Serum dilution can be used as first option to circumvent prozone. Also, interference of other antibodies should not be labeled as prozone effect.

Human Pooled Immunoglobulin as Treatment of Active Antibody-Mediated Rejection of Transplanted Kidney

BACKGROUND

Antibody-mediated rejection (ABMR) has emerged as the leading cause of renal graft loss. The optimal treatment protocol in ABMR remains unknown. This study aimed to assess the efficacy of intravenous immunoglobulin (IVIG) for treatment of ABMR in renal recipients.

METHODS

Thirty-nine ABO-compatible cross-match-negative renal recipients with biopsy-proven ABMR composed the study group. Pulses of methylprednisolone (MP) and appropriate enhancement of net state of immunosuppression were applied in all individuals; 17/39 recipients were administered IVIG (IVIG group); the remaining 22/39 patients, identified to be nonadherent or unsatisfactorily immunosuppressed, were kept on the initial treatment (MP group). Serum creatinine concentration was obtained at each of 10 intended visits, and glomerular filtration rate (GFR) was estimated with the use of the standard Modification of Diet in Renal Disease (MDRD) formula. Generalized linear mixed model was used for statistical analysis.

RESULTS

Renal function (modeled as linear slope of MDRD-based GFR change over time, separately for the pre- and post-intervention periods) improved significantly in IVIG-treated recipients. Pre-intervention slopes were -0.72 and -0.46 mL/min/mo for IVIG and MP groups, respectively (P = NS), whereas post-intervention the slopes changed to -0.03 and -0.47 mL/min/mo (IVIG and MP, respectively; P < .005). Within-group changes of slopes at the time of intervention were 0.69 and -0.01 mL/min/mo in IVIG (P < .01) and MP (P = NS) groups, respectively. The relative slope change (pre- to post-intervention) was 0.7 mL/min/mo in favor of the IVIG group (P < .033). None of the classic immunologic or nonimmunologic graft function predictors influenced GFR during 12 months of follow-up.

CONCLUSIONS

IVIG improved graft function in renal recipients diagnosed with ABMR.

The XIIIth Banff Conference on Allograft Pathology: The Banff 2015 Heart Meeting Report: Improving Antibody-Mediated Rejection Diagnostics: Strengths, Unmet Needs, and Future Directions

The 13th Banff Conference on Allograft Pathology was held in Vancouver, British Columbia, Canada from October 5 to 10, 2015. The cardiac session was devoted to current diagnostic issues in heart transplantation with a focus on antibody-mediated rejection (AMR) and small vessel arteriopathy. Specific topics included the strengths and limitations of the current rejection grading system, the central role of microvascular injury in AMR and approaches to semiquantitative assessment of histopathologic and immunophenotypic indicators, the role of AMR in the development of cardiac allograft vasculopathy, the important role of serologic antibody detection in the management of transplant recipients, and the potential application of new molecular approaches to the elucidation of the pathophysiology of AMR and potential for improving the current diagnostic system. Herein we summarize the key points from the presentations, the comprehensive, open and wide-ranging multidisciplinary discussion that was generated, and considerations for future endeavors.

Donor-Specific Antibody Monitoring: Where Is the Beef?

This review paper discusses the impact of de novo donor-specific antibodies (DSA) to donor HLA antigens in kidney transplantation and summarizes the benefits and challenges that exist with DSA monitoring. Post-transplant DSA is associated with worse allograft outcomes and its detection may precede or coincide with clinical, biochemical, and histologic allograft dysfunction. There are no absolute features of DSA testing results that perfectly discriminate between states of disease and health. In a state of antibody-associated graft dysfunction, removal or reduction in DSA may only provide clinical benefit for some. Furthermore, various factors influence test results, and detection of HLA antibodies must be interpreted within the appropriate clinical and laboratory context. The utility of DSA monitoring is further affected by the limited effectiveness of treatment for antibody-mediated rejection. Although DSA monitoring is potentially beneficial in some circumstances, the optimal screening and treatment strategies are still to be defined.

HLA epitopes as viewed by antibodies: what is it all about?

The need for new approaches to define HLA antibodies, in the context of organ transplantation, is intensely debated among HLA professionals. In this review, we sought to provide background and perspective to current understanding of the immunogenicity of HLA mismatches with respect to the humoral alloimmune response and the definition of B cell epitopes. Initial data suggest that epitope matching not only assists in defining better matches for the current transplant, but also minimizes the risk of developing de novo HLA-donor-specific-antibodies posttransplant. In other words, other than lowering the risk of current graft rejection, epitope matching is likely to lower overall future sensitization levels and thus increases the likelihood of finding a compatible donor when the need for a retransplantation arises. More detailed knowledge of epitopes makes it possible to investigate what constitutes permissible versus non-permissible HLA mismatches. The currently available evidence suggest that epitope matching is the most rational way to decrease the risk of HLA-linked transplant rejection. This review is aimed at stimulating further and more intense collaborative effort in this field.

Utility of HLA Antibody Testing in Kidney Transplantation

HLA antigens are polymorphic proteins expressed on donor kidney allograft endothelium and are critical targets for recipient immune recognition. HLA antibodies are risk factors for acute and chronic rejection and allograft loss. Solid-phase immunoassays for HLA antibody detection represent a major advance in sensitivity and specificity over cell-based methods and are widely used in organ allocation and pretransplant risk assessment. Post-transplant, development of de novo donor-specific HLA antibodies and/or increase in donor-specific antibodies from pretransplant levels are associated with adverse outcomes. Although single antigen bead assays have allowed sensitive detection of recipient HLA antibodies and their specificities, a number of interpretive considerations must be appreciated to understand test results in clinical and research contexts. This review, which is especially relevant for clinicians caring for transplant patients, discusses the technical aspects of single antigen bead assays, emphasizes their quantitative limitations, and explores the utility of HLA antibody testing in identifying and managing important pre- and post-transplant clinical outcomes.