Predictive value of HLAMatchmaker and PIRCHE-II scores for de novo donor-specific antibody formation after adult and pediatric liver transplantation

Indirect presentation of mismatched human leukocyte antigen-B associates with outcomes of cord blood transplantation

Cord blood transplantation (CBT) is a valuable donor source for patients without human leukocyte antigen (HLA)-matched donors. While CBT has a lower risk of graft-versus-host disease and requires less stringent histocompatibility, it is associated with a higher transplantation-related mortality (TRM) compared to other donor sources. We hypothesized that assessing the immunogenicity of mismatched HLA could reveal non-permissive mismatches contributing to increased TRM. We retrospectively analysed 1498 single-unit CBT cases from 2000 to 2018 across eight Japanese institutions, evaluating the immunogenicity of mismatched HLA using the PIRCHE algorithm to examine binding affinities of HLA-derived epitopes to donor or recipient HLA. Results indicated that Class I epitopes from mismatched recipient HLA-B were significantly associated with poor outcomes due to higher TRM and lower neutrophil engraftment, particularly when presented on matched HLA class I. Notably, epitopes from HLA-B exon 1 showed stronger prognostic significance, with HLA-B alleles carrying M-type leader peptides exhibiting higher affinity for these epitopes. Patients with a matched M-type HLA-B and Class I epitopes derived from mismatched HLA-B exon 1 had worse outcomes. These findings suggest that immunogenicity-informed donor selection could improve CBT outcomes.

Association analysis of T and B-cell epitopes with humoral alloimmunisation in kidney transplantation: A Tunisian cohort study

INTRODUCTION

HLA matching is critical for successful kidney transplantation. This study aimed to investigate the impact of eplet mismatches and Predicted Indirectly Recognizable HLA Epitopes (PIRCHE-II) scores on the development of de novo donor-specific antibodies (dnDSA) and graft survival in a Tunisian cohort, characterized by a high prevalence of living donors and significant genetic diversity in HLA profiles.

METHODS

This retrospective study included 112 adult kidney transplant recipients who underwent transplantation between 2012 and 2018. Donor and recipient HLA typing was performed using One Lambda Labtype PCR-SSO and PCR-SSP kits, with high-resolution typing inferred using validated tools and reference datasets. Luminex DSA screening (One Lambda) was conducted at transplantation, during follow-up for graft dysfunction or proteinuria, and at the study's conclusion. Eplet mismatches and PIRCHE-II scores were calculated using EpVix and PIRCHE-II software.

RESULTS

Nineteen patients (17 %) developed dnDSA, predominantly targeting HLA-DQ, with a median detection timeframe of 50 months (range: 11-106 months) post-transplantation. Male donor sex was negatively associated with dnDSA development, while prolonged cold ischemia time was a significant risk factor. Molecular HLA-DQ mismatches and high PIRCHE-II scores were significantly associated with dnDSA. Factors independently associated with reduced death-censored graft survival included history of transfusion after transplantation, allelic DRB1 mismatch, dnDSA development, and elevated PIRCHE-II score.

CONCLUSION

Our findings highlight the critical role of HLA-DQ compatibility in kidney transplantation and suggest that molecular HLA-DQ matching should be considered in kidney allocation strategies to minimise alloimmune responses and improve long-term graft outcomes.

Characteristics of mismatched eplets affecting de novo donor-specific antibody production and antibody-mediated rejection after kidney transplantation

De novo donor-specific antibody (dnDSA) generation is the most important marker of antibody-mediated rejection (AMR). However, not all dnDSAs induce AMR. The effects of mismatched eplets on dnDSA production and the occurrence AMR remain controversial. We analyzed 64 cases of dnDSA positive kidney transplantation that occurred between 2017 and 2021 at our center to reveal the relationships between mismatched eplet and dnDSA generation and the characteristics of antibody-specific and AMR associated mismatched eplets. Among the 64 dnDSA positive cases, 114 dnDSA were produced. Both the average production time and medium fluorescence index (MFI) value of human leukocyte antigen (HLA) II dnDSA were higher than those of HLA I (time, p = 0.024; MFI, p = 0.032). More HLA II dnDSAs were generated in the AMR group (p < 0.001). The frequency of HLA II dnDSAs was higher in cases of longer antibody generation time, higher MFI, and AMR( p < 0.05). The differences in the numbers of mismatched HLA I and II eplets were statistically significant between the rejection and no rejection groups (p = 0.030). dnDSA-specific and AMR associated mismatched eplets were strongly correlated (p < 0.0001). The dominant mismatched eplets included 41 T, 163R, 25Q, 78 V, 47QL and 55PP. dnDSA-specific eplets accounted for majority of the total mismatched eplets of donors and recipients. The amino acids with increased proportions of dnDSA-specific eplets were mainly non-polarity amino acids (p < 0.0001). AMR-associated mismatched eplets accounted for majority of the dnDSA-specific mismatched eplets. Arginine, histidine, glutamine, glutamate, lysine and asparagine levels increased significantly in the rejection group compared with the no rejection group (p < 0.001). The amino acids with increased proportions of AMR-associated mismatched eplets were all polar (p < 0.0001) and mainly positively charged (p < 0.0001). The polarity and charge of amino acids in mismatched eplets may be the key factors affecting the occurrence of AMR after kidney transplantation.

Improving long-term kidney allograft survival by rethinking HLA compatibility: from molecular matching to non-HLA genes

Optimizing immunologic compatibility in organ transplantation extends beyond the conventional approach of Human Leukocyte Antigen (HLA) antigen matching, which exhibits significant limitations. A broader comprehension of the roles of classical and non-classical HLA genes in transplantation is imperative for enhancing long-term graft survival. High-resolution molecular HLA genotyping, despite its inherent challenges, has emerged as the cornerstone for precise patient-donor compatibility assessment. Leveraging understanding of eplet biology and indirect immune activation, eplet mismatch calculators and the PIRCHE-II algorithm surpass traditional methods in predicting allograft rejection. Understanding minor histocompatibility antigens may also present an opportunity to personalize the compatibility process. While the application of molecular matching in deceased donor organ allocation presents multiple technical, logistical, and conceptual barriers, rendering it premature for mainstream use, several other areas of donor-recipient matching and post-transplant management are ready to incorporate molecular matching. Provision of molecular mismatch scores to physicians during potential organ offer evaluations could potentially amplify long-term outcomes. The implementation of molecular matching in living organ donation and kidney paired exchange programs is similarly viable. This article will explore the current understanding of immunologic matching in transplantation and the potential applications of epitope and non-epitope molecular biology and genetics in clinical transplantation.

Association of HLA B- and T-cell molecular mismatches with HLA antibodies, rejection, and graft survival in pediatric kidney transplantation

BACKGROUND

Optimizing graft survival and diminishing human leukocyte antigen (HLA) sensitization are essential for pediatric kidney transplant recipients. More precise HLA matching predicting epitope mismatches could reduce alloreactivity. We investigated the association of predicted HLA B- and T-cell molecular mismatches with the formation of de novo donor-specific antibodies, HLA antibodies, rejection, and graft survival.

METHODS

Forty-nine pediatric kidney transplant recipients transplanted from 2009 to 2020 were retrospectively studied. Donors and recipients were high-resolution HLA typed, and recipients were screened for HLA antibodies posttransplant. HLA-EMMA (HLA Epitope MisMatch Algorithm) and PIRCHE-II (Predicted Indirectly ReCognizable HLA Epitopes) predicted the molecular mismatches. The association of molecular mismatches and the end-points was explored with logistic regression.

RESULTS

Five recipients (11%) developed de novo donor-specific antibodies. All five had de novo donor-specific antibodies against HLA class II, with four having HLA-DQ antibodies. We found no associations between PIRCHE-II or HLA-EMMA with de novo donor-specific antibodies, HLA sensitization, graft loss, or rejection. However, we did see a tendency towards an increased odds ratio in PIRCHE-II predicting de novo donor-specific antibodies formation, with an odds ratio of 1.12 (95% CI: 0.99; 1.28) on HLA class II.

CONCLUSION

While the study revealed no significant associations between the number of molecular mismatches and outcomes, a notable trend was observed - indicating a reduced risk of dnDSA formation with improved molecular match. It is important to acknowledge, however, that the modest population size and limited observed outcomes preclude us from making definitive conclusions.

High-resolution HLA genotyping improves PIRCHE-II assessment of molecular mismatching in kidney transplantation

HLA matching in solid organ transplant is performed with the aim of assessing immunologic compatibility in order to avoid hyperacute rejection and assess the risk of future rejection events. Molecular mismatch algorithms are intended to improve granularity in histocompatibility assessment and risk stratification. PIRCHE-II uses HLA genotyping to predict indirectly presented mismatched donor HLA peptides, though most clinical validation studies rely on imputing high resolution (HR) genotypes from low resolution (LR) typing data. We hypothesized that use of bona fide HR typing could overcome limitations in imputation, improving accuracy and predictive ability for donor-specific antibody development and acute rejection. We performed a retrospective analysis of adult and pediatric kidney transplant donor/recipient pairs (N = 419) with HR typing and compared the use of imputed LR genotyping verses HR genotyping for PIRCHE-II analysis and outcomes. Imputation success was highly dependent on the reference population used, as using historic Caucasian reference populations resulted in 10 % of pairs with unsuccessful imputation while multiethnic reference populations improved successful imputation with only 1 % unable to be imputed. Comparing PIRCHE-II analysis with HR and LR genotyping produced notably different results, with 20 % of patients discrepantly classified to immunologic risk groups. These data emphasize the importance of using multiethnic reference panels when performing imputation and indicate HR HLA genotyping has clinically meaningful benefit for PIRCHE-II analysis compared to imputed LR typing.

Role of HLA in cardiothoracic transplantation

In current clinical practice, transplant clinicians create collaborative working relationships with histocompatibility laboratory scientists to identify the risk of long-term graft failure, which may assist in establishing strategies for treatment and surveillance. Transplant immunology research also focuses on optimizing human leukocyte antibody tissue typing and defines the most effective test for detecting the presence of donor-specific antibodies. Although several studies have been conducted, data on pediatric heart transplant recipients are limited. Epitope load information may be utilized to identify donors with permissible human leukocyte antibody mismatches to increase transplant success. Although current guidelines do not consider human leukocyte antibody epitope-based matching tools, these guidelines could be useful for identifying recipients at a high risk of donor-specific antibody production, which would be appropriate for routine donor-specific antibody screening to initiate early interventions to prevent antibody-mediated rejection. Human leukocyte antibody matching at the epitope level offers an effective approach for identifying acceptable mismatches in sensitized patients and provides information about epitope loads. In the future, eplet matching may be used to define the best immunosuppressive therapy protocol for cardiothoracic organ transplantation. This report provides an overview of the role of human leukocyte antibodies in heart and lung transplantation.

PIRCHE-II Risk and Acceptable Mismatch Profile Analysis in Solid Organ Transplantation

To optimize outcomes in solid organ transplantation, the HLA genes are regularly compared and matched between the donor and recipient. However, in many cases a transplant cannot be fully matched, due to widespread variation across populations and the hyperpolymorphism of HLA alleles. Mismatches of the HLA molecules in transplanted tissue can be recognized by immune cells of the recipient, leading to immune response and possibly organ rejection. These adverse outcomes are reduced by analysis using epitope-focused models that consider the immune relevance of the mismatched HLA.PIRCHE, an acronym for Predicted Indirectly ReCognizable HLA Epitopes, aims to categorize and quantify HLA mismatches in a patient-donor pair by predicting HLA-derived T cell epitopes. Specifically, the algorithm predicts and counts the HLA-derived peptides that can be presented by the host HLA, known as indirectly-presented T cell epitopes. Looking at the immune-relevant epitopes within HLA allows a more biologically relevant understanding of immune response, and provides an expanded donor pool for a more refined matching strategy compared with allele-level matching. This PIRCHE algorithm is available for analysis of single transplantations, as well as bulk analysis for population studies and statistical analysis for comparison of probability of organ availability and risk profiles.

Predictive value of molecular matching tools for the development of donor specific HLA-antibodies in patients undergoing lung transplantation

Molecular matching is a new approach for virtual histocompatibility testing in organ transplantation. The aim of our study was to analyze whether the risk for de novo donor-specific HLA antibodies (dnDSA) after lung transplantation (LTX) can be predicted by molecular matching algorithms (MMA) and their combination. In this retrospective study we included 183 patients undergoing LTX at our center from 2012-2020. We monitored dnDSA development for 1 year. Eplet mismatches (epMM) using HLAMatchmaker were calculated and highly immunogenic eplets based on their ElliPro scores were identified. PIRCHE-II scores were calculated using PIRCHE-II algorithm (5- and 11-loci). We compared epMM and PIRCHE-II scores between patients with and without dnDSA using t-test and used ROC-curves to determine optimal cut-off values to categorize patients into four groups. We used logistic regression with AIC to compare the predictive value of PIRCHE-II, epMM, and their combination. In total 28.4% of patients developed dnDSA (n = 52), 12.5% class I dnDSA (n = 23), 24.6% class II dnDSA (n = 45), and 8.7% both class II and II dnDSA (n = 16). Mean epMMs (p-value = 0.005), mean highly immunogenic epMMs (p-value = 0.003), and PIRCHE-II (11-loci) (p = 0.01) were higher in patients with compared to without class II dnDSA. Patients with highly immunogenic epMMs above 30.5 and PIRCHE-II 11-loci above 560.0 were more likely to develop dnDSA (31.1% vs. 14.8%, p-value = 0.03). The logistic regression model including the grouping variable showed the best predictive value. MMA can support clinicians to identify patients at higher or lower risk for developing class II dnDSA and might be helpful tools for immunological risk assessment in LTX patients.

Seeking Standardized Definitions for HLA-incompatible Kidney Transplants: A Systematic Review

BACKGROUND

There is no standard definition for "HLA incompatible" transplants. For the first time, we systematically assessed how HLA incompatibility was defined in contemporary peer-reviewed publications and its prognostic implication to transplant outcomes.

METHODS

We combined 2 independent searches of MEDLINE, EMBASE, and the Cochrane Library from 2015 to 2019. Content-expert reviewers screened for original research on outcomes of HLA-incompatible transplants (defined as allele or molecular mismatch and solid-phase or cell-based assays). We ascertained the completeness of reporting on a predefined set of variables assessing HLA incompatibility, therapies, and outcomes. Given significant heterogeneity, we conducted narrative synthesis and assessed risk of bias in studies examining the association between death-censored graft failure and HLA incompatibility.

RESULTS

Of 6656 screened articles, 163 evaluated transplant outcomes by HLA incompatibility. Most articles reported on cytotoxic/flow T-cell crossmatches (n = 98). Molecular genotypes were reported for selected loci at the allele-group level. Sixteen articles reported on epitope compatibility. Pretransplant donor-specific HLA antibodies were often considered (n = 143); yet there was heterogeneity in sample handling, assay procedure, and incomplete reporting on donor-specific HLA antibodies assignment. Induction (n = 129) and maintenance immunosuppression (n = 140) were frequently mentioned but less so rejection treatment (n = 72) and desensitization (n = 70). Studies assessing death-censored graft failure risk by HLA incompatibility were vulnerable to bias in the participant, predictor, and analysis domains.

CONCLUSIONS

Optimization of transplant outcomes and personalized care depends on accurate HLA compatibility assessment. Reporting on a standard set of variables will help assess generalizability of research, allow knowledge synthesis, and facilitate international collaboration in clinical trials.

Clinical recommendations for posttransplant assessment of anti-HLA (Human Leukocyte Antigen) donor-specific antibodies: A Sensitization in Transplantation: Assessment of Risk consensus document

Although anti-HLA (Human Leukocyte Antigen) donor-specific antibodies (DSAs) are commonly measured in clinical practice and their relationship with transplant outcome is well established, clinical recommendations for anti-HLA antibody assessment are sparse. Supported by a careful and critical review of the current literature performed by the Sensitization in Transplantation: Assessment of Risk 2022 working group, this consensus report provides clinical practice recommendations in kidney, heart, lung, and liver transplantation based on expert assessment of quality and strength of evidence. The recommendations address 3 major clinical problems in transplantation and include guidance regarding posttransplant DSA assessment and application to diagnostics, prognostics, and therapeutics: (1) the clinical implications of positive posttransplant DSA detection according to DSA status (ie, preformed or de novo), (2) the relevance of posttransplant DSA assessment for precision diagnosis of antibody-mediated rejection and for treatment management, and (3) the relevance of posttransplant DSA for allograft prognosis and risk stratification. This consensus report also highlights gaps in current knowledge and provides directions for clinical investigations and trials in the future that will further refine the clinical utility of posttransplant DSA assessment, leading to improved transplant management and patient care.

Assessment of human leukocyte antigen matching algorithm PIRCHE-II on liver transplantation outcomes

For liver transplantations, human leukocyte antigen (HLA) matching is not routinely performed because observed effects have been inconsistent. Nevertheless, long-term liver transplantation outcomes remain suboptimal. The availability of a more precise HLA-matching algorithm, Predicted Indirectly Recognizable HLA Epitopes II (PIRCHE-II), now enables robust assessment of the association between HLA matching and liver transplantation outcomes. We performed a single-center retrospective cohort study of 736 liver transplantation patients. Associations between PIRCHE-II and HLAMatchmaker scores and mortality, graft loss, acute and chronic rejection, ischemic cholangiopathy, and disease recurrence were evaluated with Cox proportional hazards models. Associations between PIRCHE-II with 1-year, 2-year, and 5-year outcomes and severity of acute rejection were assessed with logistic and linear regression analyses, respectively. Subgroup analyses were performed for autoimmune and nonautoimmune indications, and patients aged 30 years and younger, and older than 30 years. PIRCHE-II and HLAMatchmaker scores were not associated with any of the outcomes. However, patients who received transplants for autoimmune disease showed more acute rejection and graft loss, and these risks negatively associated with age. Rhesus mismatch more than doubled the risk of disease recurrence. Moreover, PIRCHE-II was inversely associated with graft loss in the subgroup of patients aged 30 years and younger with autoimmune indications. The absence of associations between PIRCHE-II and HLAMatchmaker scores and the studied outcomes refutes the need for HLA matching for liver (stem cell) transplantations for nonautoimmune disease. For autoimmune disease, the activated immune system seems to increase risks of acute rejection and graft loss. Our results may suggest the benefits of transplantations with rhesus matched but PIRCHE-II mismatched donor livers.

Mismatch epitope load predicts de novo-DSA-free survival in pediatric liver transplantation

BACKGROUND

Our knowledge of de novo anti-HLA donor-specific antibodies (dnDSA) in liver transplantation continues to be defined. We hypothesized that differences of HLA-DR/DQ mismatches can improve precision in alloimmune risk categorization and be applied to tailor immunosuppression.

METHODS

A retrospective chart review of 244 pediatric patients consecutively transplanted at our center between 2003 and 2019 was performed to identify patients tested for dnDSA. Records were queried for: demographics, pre-transplant diagnosis, biopsy-proven T-cell-mediated rejection (TCMR), radiology proven biliary complications, tacrolimus trough levels, dnDSA characteristics, and HLA typing. The eplet mismatch analyses were performed using HLAMatchmaker^™ 3.1. All statistical analyses were conducted using R software version 3.40.

RESULTS

There were 99 dnDSA-negative patients and 73 dnDSA-positive patients (n = 70 against class II and n = 3 against class I and II). ROC analysis identified optimal cutoff of eplet mismatch load for dnDSA and defined risk groups for an alloimmune outcome. Kaplan-Meier curves and log-rank tests showed high eplet mismatch load was associated with shorter dnDSA-free survival (log-rank p = .001). Multivariable Cox regression models showed that tacrolimus coefficient of variation and tacrolimus mean levels were significantly associated with dnDSA-free survival (p < .001 and p = .036). Fisher's exact test showed that dnDSA was associated with an increased likelihood of TCMR (OR 14.94; 95% CI 3.65 - 61.19; p < .001). Patients without TCMR were more likely to have dnDSA to HLA-DQ7 and less likely to have dnDSA to HLA-DQ2 (p = .03, p = .080).

CONCLUSIONS

Mismatched epitope load predicts dnDSA-free survival in pediatric liver transplant, while dnDSA specificity may determine alloimmune outcome.

Impact of calcineurin inhibitor-free immunosuppression on de novo donor-specific antibody formation in liver transplant recipients

BACKGROUND & AIMS

Low calcineurin inhibitor (CNI) levels expose liver transplant recipients to rejection episodes and potentially to antibody-mediated rejection. There are little data on the impact of CNI-free immunosuppression on de novo donor-specific HLA antibody (dnDSA) development. Here we evaluated the prevalence of dnDSA in liver transplant recipients on CNI-free maintenance regimens and their associations with histopathological abnormalities of allografts.

METHODS

Seven hundred and twenty-seven liver transplant recipients underwent a first liver transplant between 2000 and 2018 in three French transplant centres and had protocolized follow-up with dnDSA screening and allograft biopsy 1, 5 and 10 years after transplantation.

RESULTS

CNIs were withdrawn in 166 (22.8%) patients with or without conversion to mammalian target of rapamycin inhibitors and/or maintenance with mycophenolic acid. DSA were present after withdrawal in 30.1% (50/166) patients on CNI-free immunosuppression compared with 16% (90/561) on CNI maintenance therapy (p < 0.001). The cumulative incidence of dnDSA 10 years after transplant was 20% in the CNI group versus 28% in the CNI-free group (p < 0.01). dnDSAs were associated with histological graft abnormalities (significant allograft fibrosis or rejection) (HR 2.24, 95% CI 1.2-4.1; p = 0.01). In univariate Cox regression analysis, being on a CNI-free regimen did not impact graft histology.

CONCLUSIONS

Patients on a CNI-free IS regimen have a higher prevalence of dnDSA than patients on a standard IS regimen. dnDSAs but not CNI-free immunosuppression were associated with abnormal allograft histology.

Implementation of molecular matching in transplantation requires further characterization of both immunogenicity and antigenicity of individual HLA epitopes

Over the past decade, high HLA epitope mismatch scores have been associated with inferior transplant outcomes using several tools, of which HLAMatchmaker is most well-known. This software uses theoretically defined polymorphic amino acid configurations, called eplets, for HLA compatibility analysis. Although consideration of eplet mismatch loads has potential for immunological risk stratification of transplant patients, the use of eplet matching in organ allocation algorithms is hindered by lacking knowledge of the immunogenicity of individual eplets, and the possibility that single mismatched amino acids, rather than complete eplets, are responsible for HLA antibody induction. There are several approaches to define eplet immunogenicity, such as antibody verification of individual eplets, and data-driven approaches using large datasets that correlate specific eplet mismatches to donor specific antibody formation or inferior transplant outcomes. Data-driven approaches can also be used to define whether single amino acid mismatches may be more informative than eplet mismatches for predicting HLA antibody induction. When using epitope knowledge for the assignment of unacceptable antigens, it important to realize that alleles sharing an eplet to which antibodies have formed are not automatically all unacceptable since multiple contact sites determine the binding strength and thus biological function and pathogenicity of an antibody, which may differ between reactive alleles. While the future looks bright for using HLA epitopes in clinical decision making, major steps need to be taken to make this a clinical reality.

Peptides Derived From Mismatched Paternal Human Leukocyte Antigen Predicted to Be Presented by HLA-DRB1, -DRB3/4/5, -DQ, and -DP Induce Child-Specific Antibodies in Pregnant Women

Predicted Indirectly ReCognizable Human Leukocyte Antigen (HLA) Epitopes (PIRCHE) are known to be a significant risk factor for the development of donor HLA-specific antibodies after organ transplantation. Most previous studies on PIRCHE limited their analyses on the presentation of the HLA-DRB1 locus, although HLA-DRB3/4/5, -DQ, and -DP are also known for presenting allopeptides to CD4+ T cells. In this study, we analyzed the impact of predicted allopeptides presented by these additional loci on the incidence of HLA-specific antibodies after an immunization event. We considered pregnancy as a model system of an HLA immunization and observed child-specific HLA antibody (CSA) development of 231 mothers during pregnancy by samples being taken at delivery. Our data confirm that PIRCHE presented by HLA-DRB1 along with HLA-DRB3/4/5, -DQ, and -DP are significant predictors for the development of CSA. Although there was limited peptidome overlap observed within the mothers’ presenting HLA proteins, combining multiple presenting loci in a single predictor improved the model only marginally. Prediction performance of PIRCHE further improved when normalizing scores by the respective presenters’ binding promiscuity. Immunogenicity analysis of specific allopeptides could not identify significant drivers of an immune response in this small cohort, suggesting confirmatory studies.

Progress and challenges in diagnosis and treatment of rejection following liver transplantation

PURPOSE OF REVIEW

Liver biopsy remains the most widely utilized method for diagnosis of allograft rejection following liver transplantation. However, associated risks and limitations present an opportunity for emerging noninvasive diagnostic techniques to improve upon the current standard of care. This review evaluates progress toward development of new noninvasive methods for the monitoring and diagnosing of allograft rejection.

RECENT FINDINGS

Recent studies investigate the potential of a variety of analytes. Quantification of dd-cfDNA and of DSA show potential to indicate status of allograft rejection and aid in immunosuppression modulation. Moreover, mRNA microarray profiling of differentially expressed genes, as well as characterization of cytokine responses and immunophenotypic shifts following liver transplantation, may predict and recognize rejection events.

SUMMARY

Noninvasive methods are not yet ready to replace liver biopsy as the standard of care for diagnosis of allograft rejection, though several assays and biomarkers have shown promising preliminary results. As noninvasive techniques become validated in clinical settings, their integration with current diagnostic methods is likely to foster increased sensitivity, specificity, and reliability of diagnosis.

Molecular Mismatch Predicts T Cell-Mediated Rejection and De Novo Donor-Specific Antibody Formation After Living Donor Liver Transplantation

Human leukocyte antigen (HLA) molecular mismatch (MM) analysis improves the prediction of clinical outcomes in kidney transplantation compared with prediction via traditional antigen MM. However, it remains unclear whether the level of MM can be used for risk stratification among liver transplantation (LT) recipients. A retrospective observational study of 45 living donor LTs was performed to evaluate eplet MM as a risk factor for both T cell-mediated rejection (TCMR) in the first month and de novo donor-specific antibody (dnDSA) formation. A total of 9 (20%) patients displayed TCMR. HLA-A, HLA-B, HLA-C, and HLA-DRB1 eplet MM numbers were not associated with TCMR. By contrast, HLA-DQB1 eplet MM (DQB1-EpMM) number was significantly high in patients with TCMR. The predicted indirectly recognizable HLA epitopes (PIRCHE-II) score for the HLA-DQB1 locus (DQB1-PIRCHE-II) was also significantly higher in the TCMR group than in the no-TCMR group. There was a high probability for TCMR to occur with either a DQB1-EpMM ≥7 or a DQB1-PIRCHE-II ≥13. Pretransplant mixed lymphocyte response analyses indicated that there were no significant differences between the antidonor T cell proliferation activities of patients with low-number (<7) and high-number (≥7) DQB1-EpMMs. However, the proportion of CD25 expression on proliferating antidonor CD8⁺ T cells, used as a cytotoxic activity marker, was high in DQB1-EpMMs ≥7. Moreover, both DQB1-EpMMs ≥9 and DQB1-PIRCHE-II ≥3 were predictors of dnDSA formation. Thus, MM analysis may be applied toward tailored immunosuppression based on individual risks.

Matchmaker, matchmaker make me a match: Opportunities and challenges in optimizing compatibility of HLA eplets in transplantation

The development of donor-specific antibodies (DSAs) is a major complication in transplantation, which is associated with inferior graft survival, impaired quality of life, and increased healthcare costs. DSA develop upon recognition of nonself HLA by the recipient's immune system. HLA molecules contain epitopes, which are the surface regions of HLA molecules recognized by antibodies. HLAMatchmaker is an algorithm for assessing donor:recipient HLA compatibility at the level of structurally defined HLA targets called eplets. The consideration of eplets, rather than the whole HLA molecule, could offer some advantages when classifying the immune risk associated with particular donor:recipient pairs. Assessing compatibility at the level of HLA eplets could decrease misclassification of post-transplant immune risk by improving specificity, when antibodies are confirmed to be directed against donor eplets missing from the recipient's repertoire of eplets. Consideration of eplets may also increase the sensitivity of immune risk assessment, when identifying mismatched eplets that could give rise to new, not previously detected, donor-specific antibodies post-transplant. Eplet matching can serve as a rational strategy for immune risk mitigation. Herein, we review the evolution of HLA (in) compatibility assessment for organ allocation. We outline challenges in the implementation of eplet-based donor:recipient matching, including unavailability of allele-level donor genotypes for 11 HLA loci at the time of organ allocation and difficulty in assessing the hierarchy of immune risk associated with particular HLA eplet mismatches. Opportunities to address some of the current shortcomings of donor genotyping and HLAMatchmaker are also discussed. While there is a demonstrated benefit in the application of HLAMatchmaker for donor: recipient HLA (in)compatibility assessment, evolving long-read genotyping methods, compilation of large data sets with allele-level genotypes, and standardization of methods to verify eplets as determinants of immune-mediated injuries are required before HLA eplet matching is implemented in organ allocation to improve upon transplant outcomes.