Comparison of human leukocyte antigen immunologic risk stratification methods in lung transplantation

Outcomes after lung transplantation (LTx) remain poor, despite advances in sequencing technology and development of algorithms defining immunologic compatibility. Presently, there is no consensus regarding the best approach to define human leukocyte antigen (HLA) compatibility in LTx. In this study, we compared 5 different HLA compatibility tools in a high-resolution HLA-typed, clinically characterized cohort, to determine which approach predicts outcomes after LTx. In this retrospective single-center study, 277 donor-recipient transplant pairs were HLA-typed using next generation sequencing. HLA compatibility was defined using HLAMatchmaker, HLA epitope mismatch algorithm (HLA-EMMA), predicted indirectly recognizable HLA epitopes (PIRCHE), electrostatic mismatch score (EMS), and amino acid mismatches (AAMMs). Associations with HLA mismatching and survival, chronic lung allograft dysfunction (CLAD), and anti-HLA donor-specific antibody (DSA) were calculated using adjusted Cox proportional modeling. Lower HLA class II mismatching was associated with improved survival as defined by HLAMatchmaker (P < .01), HLA-EMMA (P < .05), PIRCHE (P < .05), EMS (P < .001), and AAMM (P < .01). All approaches demonstrated that HLA-DRB1345 matching was associated with freedom from restrictive allograft syndrome and HLA-DQ matching with reduced DSA development. Reducing the level of HLA mismatching, in T cell or B cell epitopes, electrostatic differences, or amino acid, can improve outcomes after LTx and potentially guide immunosuppression strategies.

An Integrated Approach Using HLAMatchmaker and Pirche II for Epitopic Matching in Pediatric Kidney Transplant-A Romanian Single-Center Study

(1) Background: Renal transplantation (KT) is the most efficient treatment for chronic kidney disease among pediatric patients. Antigenic matching and epitopic load should be the main criteria for choosing a renal graft in pediatric transplantation. Our study aims to compare the integration of new histocompatibility predictive algorithms with classical human leukocyte antigen (HLA) matching regarding different types of pediatric renal transplants. (2) Methods: We categorized our cohort of pediatric patients depending on their risk level, type of donor and type of transplantation, delving into discussions surrounding their mismatching values in relation to both the human leukocyte antigen Matchmaker software (versions 4.0. and 3.1.) and the most recent version of the predicted indirectly identifiable HLA epitopes (PIRCHE) II score. (3) Results: We determined that the higher the antigen mismatch, the higher the epitopic load for both algorithms. The HLAMatchmaker algorithm reveals a noticeable difference in eplet load between living and deceased donors, whereas PIRCHE II does not show the same distinction. Dialysis recipients have a higher count of eplet mismatches, which demonstrates a significant difference according to the transplantation type. Our results are similar to those of four similar studies available in the current literature. (4) Conclusions: We suggest that an integrated data approach employing PIRCHE II and HLAMatchmaker algorithms better predicts histocompatibility in KT than classical HLA matching.

Formation of donor-specific antibodies depends on the epitope load of mismatched hlas in lung transplant recipients: A retrospective single-center study

The development of donor-specific antibodies (DSA) has a significant impact on graft outcome in solid organ transplantation. Mismatched HLAs are recognized directly and indirectly by the recipient immune system. Both pathways occur in parallel and result in the generation of plasma cells, DSA, cytotoxic and T helper lymphocytes. Here, we present the results of an analysis of the epitope load of mismatched HLAs in a cohort of 220 lung transplant recipients using two in silico algorithms, HLAMatchmaker and PIRCHE-II (Predicted Indirectly ReCognizable HLA Epitopes). De novo DSA (dnDSA) were detected by single antigen bead assays. The percentage of recipients who developed dnDSA was significantly higher in the group of patients who received lung transplants with a mismatching score above the detected threshold than in the group of patients who received lung transplants with a mismatching score below the threshold. In a multivariate Cox proportional hazard analysis, the PIRCHE-II score appeared to be a superior predictor of dnDSA formation. In addition, PIRCHE-II technology was shown to be useful in predicting separate dnDSA1 and dnDSA2 formation. We conclude that both algorithms can be used for the evaluation of the epitope load of mismatched HLAs and the prediction of DSA development in lung transplant recipients. This article is protected by copyright. All rights reserved.

Impact of HLA Epitope Matching on Outcomes After Unrelated Bone Marrow Transplantation

The significance of antibody-identified epitopes stimulating humoral alloimmunity is not well understood in the identification of non-permissive human leukocyte antigen (HLA) mismatching patterns in hematopoietic stem cell transplantation (HSCT). This was a retrospective study in a cohort of 9,991 patients who underwent their first HSCT for hematologic malignancies from unrelated bone marrow donors in the Transplant Registry Unified Management Program (TRUMP). HLA eplet mismatches (EMM) were quantified using HLAMatchmaker (HLAMM). The median age of patients was 48 years (range, 16 to 77). The number of EMM in recipient-donor pairs in our study population ranged from 0 to 37 in HLA class I (median, 0) and 0 to 60 in HLA class II (median, 1). In addition to the known high-risk mismatch patterns in the Japanese cohort, HLA-C EMM in the GVH direction was associated with a significantly higher risk for grade III-IV aGVHD, leading to a higher risk of non-relapse mortality and lower overall survival (compared with HLA-C matched patients, HR 1.67, 95% CI 1.44–1.95; HR 1.39, 95% CI 1.25–1.54; HR 1.20, 95% CI 1.10–1.30, respectively). HLAMM-based epitope matching might be useful for identifying patients who are at high risk for serious complications after HSCT from HLA mismatched unrelated donors.

Human Leukocyte Antigen-Based Risk Stratification in Heart Transplant Recipients-Implications for Targeted Surveillance

Background

Human leukocyte antigen (HLA) matching isn't routinely performed in heart transplantation. Novel allograft perfusion methods may make HLA matching feasible. The purpose of this study is to reexamine whether HLA mismatch may be used in risk stratification to improve outcomes in heart transplantation.

Methods and Results

We analyzed 34 681 recipients undergoing heart transplantation between 1987 and 2013. We used HLAMatchmaker to quantify HLA eplet mismatches and Cox regression for analysis of time to graft loss. Recipients with 4 mismatched HLA‐DR/DQ alleles and >40 eplets reached an adjusted hazard ratio (HR) for graft loss of 1.17 (95% CI 1.07–1.28) and 1.11 (95% CI 1.03–1.21), respectively. We found significant interaction between recipient age and numbers of HLA‐DR/DQ allele and eplet mismatches resulting in an adjusted HR of 1.78 (95% 1.13–2.80) and 1.82 (95% CI, 1.23–2.70), respectively. HR for both interaction terms was 0.99 (95% CI, 0.98–1.00). Risk of graft loss was more pronounced after 1 year, where recipient <40 years with 4 mismatched HLA‐DR/DQ alleles and >40 eplets had an adjusted HR of 1.51 (95% CI 1.12–2.03) and 1.32 (95% CI 1.02–1.70), respectively. Pre‐sensitized recipients with panel reactive antibodies >10% had an adjusted HR=1.27 (95% CI 1.16–1.40) for graft loss within 1 year but not thereafter. HLA eplet mismatch was independent of panel reactive antibodies on reduction of graft loss within and after 1 year, P (interaction)=0.888 and 0.389.

Conclusions

HLA mismatch may be used in risk stratification for intensified post‐transplant surveillance and therapy.

Case report: A transplant candidate with unexpected serum reactivity against the 45KE eplet on HLA-B alleles

This case report describes the serum antibody specificity against the 45KE eplet which had not been yet shown to be antibody-verified. This antibody was produced by a 41-year-old European male with Berger's disease. His serum had HLA class I antibody reactivity as determined in IgG binding assays with single allele panels (OneLambda, ThermoFisher, Lot 8 and Lot 9). The HLAMatchmaker analysis revealed reproducible serum reactivity only with alleles carrying the 45KE eplet. The cause of this 45KE-specific immunization is unknown because this male patient had never been transfused nor received a previous transplant, Moreover, his mother's HLA type did not have any 45KE-carrying allele. This finding might be related to observations reported in the literature about the appearance of HLA-reactive antibodies following influenza vaccination but this possibility could not be investigated.

The clinical significance of epitope mismatch load in kidney transplantation: A multicentre study

Since the advent of kidney transplantation a key strategy for maximising graft survival by avoiding allorecognition has been to minimise HLA mismatching between donor and recipient. As HLA antibodies are now recognised as being specific for epitopes and donor-recipient HLA mismatch at the amino acid level can now be determined, HLA epitope mismatch load could be a better predictor for dnDSA development than classical HLA antigen mismatch calculation. This hypothesis has been investigated by other studies and the aim of our multicentre study was to confirm this observation in our population. Two algorithms, HLAMatchmaker and PIRCHE-II, were used to determine the HLA epitope mismatch load between donor and recipient. We have shown a significant association between the number of HLA epitope mismatches and the development of dnDSA and we have confirmed the earlier observations.

Inaccuracies in epitope repertoire estimations when using Multi-Locus Allele-Level hla genotype imputation tools

BACKGROUND

Limited availability of allele-level HLA genotypes prompts their imputation from allele-group genotypes to estimate epitope mismatches. We evaluated the accuracy of epitope load and repertoire assignment when imputing allele-level HLA genotypes.

METHODS

Analyses were conducted on 175 hematopoietic stem cell (HSC) donors from the Héma-Québec registry (HQR) and 57 HSC donor-recipient pairs from McGill University Health Centre (MUHC), Québec, Canada, genotyped for HLA-A, -B, -C, -DRB1 and -DQB1. Multi-locus allele-level imputation was performed using HaploStats. Disagreement in B- and T-cell epitope assignment and epitope mismatches were ascertained for imputed vs. measured allele-level HLA genotypes in HSC donors and donor-recipient pairs, respectively.

RESULTS

Imputation resulted in no differences in overall eplet mismatches and PIRCHE-II for HLA-A, -B, and -C in 83.4% and 93.7% of HQR donors and 87.7% and 87.7% of MUHC donors, respectively. HLA-DRB1- and -DQB1-derived eplet mismatches and PIRCHE-II were correctly assigned in 72.0% and 85.1% of HQR donors and 70.2% and 71.9% of MUHC donors, respectively. No discrepancies in eplet load or PIRCHE-II were observed in 96.5% and 86.0% of HSC donor-recipient pairs and in 70.2% and 70.1% of pairs for HLA-A, -B and -C and -DRB1 and -DQB1, respectively. Kappa statistics of 0.9708 and 0.9725, 0.8724 and 0.8177, 0.9827 and 0.9022, 0.5644 and 0.4939, 0.5085 and 0.6361 were demonstrated when assessing agreement between eplet mismatches and PIRCHE-II of imputed vs. measured HLA-A, -B, -C, -DRB1 and -DQB1 types, respectively.

CONCLUSIONS

To avoid inaccuracies in epitope compatibility estimation, mainly for class II HLA, multi-locus allele-level genotype measurement is recommended. This article is protected by copyright. All rights reserved.

Should epitope-based HLA compatibility be used in the kidney allocation system?

The new kidney allocation system (KAS) still applies donor-recipient HLA compatibility mostly at the antigen level and although some four-digit alleles have been included. This system is used to record unacceptable mismatches for sensitized transplant candidates with serum HLA antibodies. Since the reactivities of such antibodies are specifically associated with epitopes rather than HLA antigens, a more scientifically accurate assessment of mismatch acceptability could be based on epitopes. HLA class I and class II epitope specificity analyses can now be readily performed with serum antibody assays with single allele panels. This report describes an epitope-based HLA compatibility system for KAS and involves recipient and donor HLA typing at the four-digit allele level. It focuses on sensitized patients who have serum antibodies specific for HLA epitopes that can be entered as unacceptable mismatches in the transplant candidate database. Newly developed software programs could readily identify compatible HLA types.

Epitope analysis of DQ6-reactive antibodies in sera from a DQ6-positive transplant candidate sensitized during pregnancy

This case report describes DQ6-reactive serum antibody reactivity in a patient who types as DQ6. DNA typing showed DQB1*06:09 on the antibody producer and serum reactivity with DQB1*06:01, *06:02 and *06:03 but not with *06:04 and *06:09. HLAMatchmaker serum analysis showed antibody reactivity with a new antibody-verified 85VA eplet on DQB but additional reactivity with DQB1*02:01 could not be readily interpreted. After applying the nonself-self algorithm of HLA immunogenicity we have identified a new DQB epitope structurally described as 140A2+130R+135D and shared by DQB1*02:01 and DQB1*05:01 and DQB1*06:02 of the immunizer.

Antibody-defined epitopes on HLA-DQ alleles reacting with antibodies induced during pregnancy and the design of a DQ eplet map

The concept that HLA antibodies recognize epitopes is leading to new approaches of HLA matching at the epitope level. HLA-DQ plays an important role and many studies have identified structurally defined DQ epitopes specifically recognized by antibodies; they have been recorded in the International HLA Epitope Registry http://www.epregistry.com.br but the list is still incomplete. Pregnancy offers an attractive model to study antibody responses to HLA epitopes. The current analysis was done on 42 DQ-reactive post-pregnancy sera tested in binding assays with a panel of DQ heterodimers. The reactivity of 29 sera corresponded fully to the presence of antibody-verified DQA and DQB epitopes recorded in the Registry. Analysis of the remaining 13 sera led to the identification of additional antibody-defined DQB and DQA epitopes. We have designed the first version of an eplet map for DQ alleles which includes antibody-defined DQA and DQB epitopes and shows sequence positions with polymorphic residues which can be used in HLA epitology studies to identify new antibody-defined DQ epitopes.

Antibody-reactive class I epitopes defined by pairs of mismatched eplets and self-eplets

The identification of human leukocyte antigen (HLA) antibodies in the sera of candidates awaiting organ transplantation has evolved over time. This has been possible because of the introduction of more sensitive techniques and to the increasing focus on the structural aspects of the HLA epitopes. The use of the HLAMatchmaker algorithm in the analysis of positive sera and the verification of HLA ABC epitopes in the HLA Epitope Registry website provide new stimuli on the interpretation of antibody reactivity. The epitopes defined by eplet pairs often involve a nonself-eplet and a self-eplet (nonself-self paradigm), suggesting that the antibody response to an HLA mismatch must have an auto-reactive component. Here, we report an application of the nonself-self paradigm that provides a basis for better knowledge and interpretation of HLA-antibody reactivity in Luminex assays with single alleles.

Usefulness of the Nonself-Self Algorithm of HLA Epitope Immunogenicity in the Specificity Analysis of Monospecific Antibodies Induced during Pregnancy

BACKGROUND

HLAMatchmaker is a program to analyze the epitope specificities of HLA antibodies. It considers each HLA allele as a string of eplets. Intralocus and interlocus comparisons between donor and recipient alleles offer a structural assessment of compatibility and an analysis of allele panel reactivity patterns can generate information about epitope specificities of HLA antibodies. However, HLAMatchmaker cannot always generate conclusive interpretations of reactivity patterns of all monospecific antibodies, which by definition recognize single epitopes.

HYPOTHESIS

We have therefore developed a new antibody analysis approach that utilizes the nonself-self algorithm of HLA epitope immunogenicity. It is based on the concept that HLA antibodies originate from B-cells with immunoglobulin receptors to self-HLA epitopes on one given allele and which can be activated by epitopes defined by a few nonself residue differences whereas the remainder of the structural epitope of the immunizing allele consists of self residues.

METHODS

Three human monoclonal class I antibodies from HLA typed women sensitized during pregnancy were tested in Ig-binding assays with single alleles on a Luminex platform.

FINDINGS

Three new HLA epitopes were identified; they are defined by combinations of nonself- and self-residues for one allele of the antibody producer.

CONCLUSION

The nonself-self paradigm of HLA epitope immunogenicity offers a second approach to analyze HLA antibody specificities.

Epitope-specificities of HLA antibodies: the effect of epitope structure on Luminex technique-dependent antibody reactivity

The search of HLA antibodies is currently more accessible by solid-phase techniques (Luminex) in the immunized patients leading to an expansion of the antibody patterns. The aim of this study was to investigate low median fluorescence intensity value in unexpected reactivity patterns. Here, we performed HLAMatchmaker analyses to evaluate the potential functional epitopes that can elicit HLA-specific alloantibody responses in a pregnancy-sensitized woman with an epitope defined by the 82LR. Surprisingly, in according to the registry of HLA epitopes, we found that 82LR epitope covered all allelic specificities of our unexpected antibody patterns, shared between Bw4-positive HLA-B antigen and HLA-A23, -A24, -A25 and -A32. This finding is consistent with the verification of HLA ABC epitope recorded in the website-based HLA Epitope Registry and addresses the importance of determining HLA antibody epitope-specificities on Luminex technique-dependent antibody reactivity.

HLA epitope based matching for transplantation

As important risk factors for transplant rejection and failure, HLA antibodies are now recognized as being specific for epitopes which can be defined structurally with amino acid differences between HLA alleles. Donor-recipient compatibility should therefore be assessed at the epitope rather than the antigen level. HLAMatchmaker is a computer algorithm that considers each HLA antigen as a series of small configurations of polymorphic residues referred to as eplets as essential components of HLA epitopes. It includes epitopes on antigens encoded by all HLA-A, B, C, DR, DQ and DP loci as well as MICA. HLA epitopes have two characteristics namely antigenicity, i.e. the reactivity with antibody and immunogenicity, i.e. the ability of eliciting an antibody response. This article addresses the relevance of determining epitope-specificities of HLA antibodies, the effect of epitope structure on technique-dependent antibody reactivity and the identification of acceptable mismatches for sensitized patients considered for transplantation. Permissible mismatching for non-sensitized patients aimed to prevent or reduce HLA antibody responses could consider epitope loads of mismatched antigens and the recently developed nonself-self paradigm of epitope immunogenicity.

Humoral alloimmunity in transplantation: relevance of HLA epitope antigenicity and immunogenicity

HLA mismatching is an important risk factor for antibody-mediated rejection and transplant failure. With the realization HLA antibodies recognize epitopes rather than antigens, it has become apparent that donor-recipient compatibility should be assessed at the epitope level. Recent developments have increased our understanding of the structural basis of HLA antigenicity, i.e., the reactivity with specific antibody and, immunogenicity, i.e., the ability to induce an antibody response. HLAMatchmaker is a computer algorithm that considers each HLA antigen as a series of small configurations of polymorphic residues referred to as eplets as essential components of HLA epitopes. This article addresses the relevance of determining epitope-specificities of HLA antibodies in the identification of acceptable mismatches for sensitized patients considered for transplantation. Permissible mismatching for non-sensitized patients aimed to prevent or reduce HLA antibody responses could consider epitope loads of mismatched antigens and the recently developed non-self–self paradigm of epitope immunogenicity.