Epitope Mismatches Research Articles

Precision in post-transplant management: Revealing epitope mismatch analysis for enhanced graft survival prediction

Precision in post-transplant management: Revealing epitope mismatch analysis for enhanced graft survival prediction

Permissible HLA mismatches in 9/10 unrelated donor pediatric stem cell transplants using HLA-EMMA: an EBMT Inborn Errors Working Party study

AbstractAllogeneic hematopoietic stem cell transplantation (HSCT) with mismatched unrelated donors (MMUD) is associated with inferior outcome compared with matched unrelated donors (MUDs). We aimed to identify permissible mismatches using HLA epitope mismatch algorithm, which determines permissibility by analyzing amino acid sequences, in a single-center cohort of 70 pediatric 9/10 MMUD HSCTs and 157 10/10 MUDs for comparison. Amino acid matching was evaluated for the whole HLA protein, the α-helices, and the β-sheets, in both host vs graft (HvG) and graft vs host (GvH) direction. Superior event-free survival (EFS) was found in 13 patients permissibly mismatched in the HvG direction (totalHvG, 92% vs 58% at 1 year; P = .009) and in 21 patients matched on the α-helices (αHvG, 90% vs 53%; P = .002). These rates were similar to EFS rates in patients with 10/10 MUDs (90% vs 80%; P = .60). EFS was not related to β-sheet amino acid matching, nor to matching in the GvH direction. Overall survival (OS) rates trended similarly to those of EFS for amino acid mismatches (totalHvG, 92% vs 74%; P = .075; αHvG, 90% vs 71%; P = .072). These findings were reproduced in an EBMT Registry inborn errors cohort of 271 pediatric 9/10 MMUD HSCTs and 929 10/10 MUD HSCTs, showing a significant effect of αHvG matching on both OS and EFS and similar OS and EFS between αHvG matched MMUDs and 10/10 MUDs. In summary, HvG amino acid matching on the α-helices identifies 9/10 MMUDs with permissible mismatches, which are correlated with favorable transplant outcomes similar to those of matched donors.

HLA Genotype Imputation Results in Largely Accurate Epitope Mismatch Risk Categorization Across Racial Groups.

Biomarkers that predict posttransplant alloimmunity could lead to improved long-term graft survival. Evaluation of the number of mismatched epitopes between donor and recipient HLA proteins, termed molecular mismatch analysis, has emerged as an approach to classify transplant recipients as having high, intermediate, or low risk of graft rejection. When high-resolution genotypes are unavailable, molecular mismatch analysis requires algorithmic assignment, or imputation, of a high-resolution genotyping. Although imputation introduces inaccuracies in molecular mismatch analyses, it is unclear whether these inaccuracies would impact the clinical risk assessment for graft rejection. Using renal transplant patients and donors from our center, we constructed cohorts of surrogate donor-recipient pairs with high-resolution and low-resolution HLA genotyping that were racially concordant or discordant. We systemically assessed the impact of imputation on molecular mismatch analysis for cohorts of 180-200 donor-recipient pairs for each of 4 major racial groups. We also evaluated the effect of imputation for a racially diverse validation cohort of 35 real-world renal transplant pairs. In the surrogate donor-recipient cohorts, imputation preserved the molecular mismatch risk category for 90.5%-99.6% of racially concordant donor-recipient pairs and 92.5%-100% of racially discordant pairs. In the validation cohort, which comprised 72% racially discordant pairs, we found that imputation preserved the molecular mismatch risk category for 97.1% of pairs. Overall, these data demonstrate that imputation preserves the molecular mismatch risk assessment in the vast majority of cases and provides evidence supporting imputation in the performance of molecular mismatch analysis for clinical assessment.

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

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. 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. 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. 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.

#1130 Biopsy-based transcript diagnostics identify early antibody-mediated rejection phenotypes in biopsies with subclinical donor-specific antibodies

Abstract Background and Aims Biopsy based transcript diagnostics using the molecular microscope diagnostic system (MMDx) have the potential to add diagnostic clarification in the antibody mediated rejection (AMR) continuum. While de novo donor specific antibody (dnDSA) or preformed DSA accompanied by allograft function deterioration are accepted indications for allograft biopsy with therapeutic implications, management strategy for subclinical DSA lacks consensus. MMDx might show clinical utility in this controverse scenario by helping with therapeutic decisions. Method In this single-center cohort of 326 indication kidney transplant biopsies assessed by histology and MMDx at the University Hospital Zurich, we analyzed 58 cases with subclinical DSA as biopsy indication. Cases with (n = 44) and without (n = 14) histopathologic features of AMR according to Banff 2022 were compared for molecular AMR rejection transcripts. Results When biopsied for subclinical DSA, all 14 cases without histopathologic features of AMR showed absence of molecular AMR. In contrast, molecular AMR was detected in 6/19 (32%) cases with histopathologic diagnosis of AMR and 2/25 (8%) with probable AMR (p = 0.059), Fig. 1. Microvascular inflammation below threshold with C4d negativity was significantly associated with absence of molecular AMR (p < 0.0001). Higher number of calculated epitope mismatch load for HLA class II as measured by PIRCHE II Score was significantly associated with molecular AMR (p = 0.01). In cases with molecular AMR, early AMR scores predominated (R4 vs R6, 0.0002 and R4 vs R5 0.051). Conclusion No molecular AMR was observed in absence of histopathologic AMR. Yet, in cases with histopathologic features of AMR, only 8/44 showed molecular AMR. Predominance of early AMR rejection phenotype in cases with molecular AMR transcripts allows hope for MMDx to identify treatment amenable cases with subclinical DSA. Discrepant cases call for re-biopsy to guide therapeutic decisions.

PIRCHE application major versions 3 and 4 lead to equivalent T cell epitope mismatch scores in solid organ and stem cell transplantation modules

PIRCHE scores in organ and stem cell transplantation have been shown to correlate with increased risk of donor-specific HLA antibodies and graft-versus-host disease, respectively. With advancements of the PIRCHE application server, it is critical to compare the predicted scores with previous versions. This manuscript compares the newly introduced PIRCHE version 4.2 with its predecessor version 3.3, which was widely used in retrospective studies, using a virtual cohort of 10,000 transplant pairs. In the stem cell transplantation module, both versions yield identical results in 100% of the test population. In the solid organ module, 97% of the test population has identical PIRCHE scores. The deviating cases (3%) were attributed to refinements in the PIRCHE algorithm’s specification. Furthermore, the magnitude of the difference is likely to be below the detection limit for clinical effects, confirming the equivalence in PIRCHE scores between versions 3.3 and 4.2.

Positive Long-Term Outcome of Kidney Allocation via Acceptable Mismatch Program in Highly Sensitized Patients

Introduction: Eurotransplant established the acceptable mismatch (AM) program to facilitate timely kidney transplantations of highly sensitized patients, but long-term granular clinical and immunological outcomes regarding overall graft survival and de novo DSA (dnDSA) formation are still intensively researched. The right choice of induction therapy in patients with differing immunological risk is not conclusively determined, as well as the impact of human leukocyte antigen (HLA) epitope matching on dnDSA formation. Methods: This monocentric, retrospective study analyzed 94 patients transplanted within the AM program between 2000 and 2019 compared to case-control matched cohorts of non- (PRA 0–5%; PRA-0) and intermediately sensitized (PRA 6–84%; PRA-6/84) patients transplanted through Eurotransplant Kidney Allocation System. Results: Estimated 10-year overall graft survival between the PRA-0 and AM cohorts was similar, whereas PRA-6/84 was significantly disadvantageous compared to PRA-0. Estimated 10-year incidence of antibody-mediated rejection rates was significantly lower in the PRA-0 group compared to AM and PRA-6/84 groups. Compared to the AM group, estimated incidence of de novo donor-specific antibody (dnDSA) was significantly lower in PRA-0 patients, with no differences between the AM and PRA-6/84 cohorts. The PRA-6/84 cohort was the only subgroup in which interleukin-2 receptor antagonist (IL2RA) induction was associated with longer overall graft survival, patient survival, and graft survival compared to depleting induction (ATG or OKT3). Broad HLA-A, -B, -DR mismatches (mmABDR) and HLA epitope mismatches determined by Eplets and PIRCHE-II were predictive for dnDSA formation in the total cohort, and the AM subgroup. Discussion: The high efforts expended on AM patients are justified to allow timely organ transplantation with acceptable risk profile and non-inferior outcomes. IL2RA induction in intermediately sensitized patients is associated with superior overall graft survival, patient survival, and graft survival compared to ATG/OKT3 induction, without negative effects on rejection episodes or dnDSA formation. In silico epitope matching might further help reduce dnDSA formation, particularly in high-risk AM patients.

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.

Investigation of non-human leukocyte antigen antibodies and epitope mismatch in kidney transplant recipients with chronic antibody-mediated rejection

Investigation of non-human leukocyte antigen antibodies and epitope mismatch in kidney transplant recipients with chronic antibody-mediated rejection

Early progression of chronic histologic lesions in kidney transplant biopsies is not associated with HLA histocompatibility.

Early progression of chronic histologic lesions in kidney allografts represents the main finding in graft attrition. The objective of this retrospective cohort study was to elucidate whether HLA histocompatibility is associated with progression of chronic histologic lesions in the first year post-transplant. Established associations of de novo donor-specific antibody (dnDSA) formation with HLA mismatch and microvascular inflammation (MVI) were calculated to allow for comparability with other study cohorts. We included 117 adult kidney transplant recipients, transplanted between 2016 and 2020 from predominantly deceased donors, who had surveillance biopsies at 3 and 12 months. Histologic lesion scores were assessed according to the Banff classification. HLA mismatch scores [i.e. eplet, predicted indirectly recognizable HLA-epitopes algorithm (PIRCHE-II), HLA epitope mismatch algorithm (HLA-EMMA), HLA whole antigen A/B/DR] were calculated for all transplant pairs. Formation of dnDSAs was quantified by single antigen beads. More than one-third of patients exhibited a progression of chronic lesion scores by at least one Banff grade in tubular atrophy (ct), interstitial fibrosis (ci), arteriolar hyalinosis (ah) and inflammation in the area of interstitial fibrosis and tubular atrophy (i-IFTA) from the 3- to the 12-month biopsy. Multivariable proportional odds logistic regression models revealed no association of HLA mismatch scores with progression of histologic lesions, except for ah and especially HLA-EMMA DRB1 [odds ratio (OR)=1.10, 95% confidence interval (CI) 1.03-1.18]. Furthermore, the established associations of dnDSA formation with HLA mismatch and MVI (OR=5.31, 95% CI 1.19-22.57) could be confirmed in our cohort. These data support the association of HLA mismatch and alloimmune response, while suggesting that other factors contribute to early progression of chronic histologic lesions.

P121 Correlation of HLA epitope mismatches with de novo donor-specific antibody formation in renal transplant recipients – A comparison of snowflake to HLAMatchmaker and PIRCHE scores

P121 Correlation of HLA epitope mismatches with de novo donor-specific antibody formation in renal transplant recipients – A comparison of snowflake to HLAMatchmaker and PIRCHE scores

O17 HLA genotype imputation results in largely accurate epitope mismatch risk categorization across racial groups

O17 HLA genotype imputation results in largely accurate epitope mismatch risk categorization across racial groups

#3823 CAN HLA MOLECULAR MISMATCH GUIDE CLINICAL DECISION IN PAEDIATRIC KIDNEY TRANSPLANT RECIPIENTS: A RETROSPECTIVE STUDY

Abstract Background and Aims Optimizing graft survival and diminishing anti-HLA sensitization are essential in paediatric kidney transplant recipients (KTRs) facing multiple retransplantations. Improved pretransplant risk stratification and donor selection using in silico molecular HLA matching could enhance personalized immunosuppression and improve outcomes. HLA EMMA is a new in silico method to predict B cell epitope mismatches, and its clinical applicability needs confirmation in paediatric transplantation. We investigated the association of HLA B cell epitope (HLA EMMA) and predicted HLA T cell epitope (PIRCHE) mismatches with de novo donor specific antibodies (dnDSA), anti-HLA antibodies, rejection, and graft survival. Method We retrospectively analysed 49 consecutive paediatric KTRs aged 1 to 16 transplanted from 2009-2020 at a single Danish centre. The centre has a long tradition of steroid-free kidney transplantations in immunologically uncomplicated recipients, and 80% of the KTRs did not receive steroids. Donors and recipients were all high-resolution HLA typed, and HLA EMMA (v 1.00) and PIRCHE (v 3.3.60) predicted the molecular mismatches. KTRs were screened with mixed and single bead antigen kits after the transplantation. Logistic regression analyses were performed to explore the association of molecular mismatches and dnDSA, sensitization, graft loss, and rejection. Results The median age of the KTRs was 11 years (IQR 8), with a median follow-up time of 5 years (IQR 5). 11.36% developed dnDSA (60% class II, 40% class I and II) within a median of 3.91 years (IQR 2.28; range: 2.22-9.20). 57.45% had detectable anti-HLA antibodies during follow-up. Six KTRs lost their graft. None of the graft losses were related to alloimmunity, and 5-year death censored (one KTR died) graft survival was 88%. The cumulative incidence of rejection was 4% (95% CI: -1.5; 5.5) after one year and 10% (95% CI: 1.6; 18.7) after five years. The mean PIRCHE score was 368.47 (95% CI: 316.79; 420.15), the mean HLA EMMA class I mismatch was 20.33 (95% CI: 17.56; 23.09), and the mean HLA EMMA class II mismatch was 30.02 (95% CI: 24.99; 35.05). We found no association between PIRCHE or HLA EMMA with dnDSA, sensitization, graft loss, or rejection in the logistic regression models. We did see a tendency towards an increased odds ratio in PIRCHE predicting dnDSA (odds ratio: 1.31 (95% CI: 0.96; 1.80)) (Figure 1). Conclusion We did not find evidence to support the inclusion of the prediction of molecular mismatches in our clinical practice. The role of molecular mismatches in a clinical setting has yet to be established.

#3654 ABO-INCOMPATIBLE KIDNEY TRANSPLANTATION LOWERS INCIDENCES OF DE NOVO DONOR-SPECIFIC ANTIBODIES AND CHRONIC ANTIBODY-MEDIATED REJECTION

Abstract Background and Aims ABO-incompatible kidney transplantation has been associated with an increased risk for antibody-mediated rejection (ABMR) and early graft loss attributable to isoagglutinins. Its impact on the development of de novo donor-specific HLA antibodies (DSA) and DSA-induced chronic ABMR, however, remains less well studied. Method We analyzed 297 kidney transplant recipients (KTRs) who underwent living donor transplantation at the University Hospital Zurich from 2009 to 2021. 58 ABO-incompatible (iABO) KTRs were compared to 239 ABO-compatible (cABO) KTRs concerning the development of de novo donor-specific antibodies (DSA) and antibody-mediated rejection (ABMR). ABO desensitization was performed using rituximab and antigen-specific immunoadsorption. The HLA-derived epitope-mismatches were calculated per HLA-locus and in total using the Predicted Indirectly Recognizable HLA-Epitopes (PIRCHE-II) algorithm. High-resolution re-typing was performed from protocol kidney allograft biopsies if necessary. Results The incidence of TCMR/ABMR in the first post-transplant year was comparable between iABO KTRs (19%) and cABO KTRs (13%; p = 0.207). De novo DSA were detected in only 1 of 58 iABO KTRs but 12 of 239 cABO KTRs in the first post-transplant year and 2 of 58 iABO KTRs but 50 of 239 cABO KTRs in the long-term follow-up (p = 0.001). ABMR was diagnosed in only 1 of 58 iABO KTRs but 28 of 239 cABO KTRs after the first post-transplant year (p = 0.021). iABO kidney transplantation decreased the risk of de novo DSA development (HR 7.222, CI 1.755-29.722, p = 0.006) and ABMR (HR 7.362, CI 1.000-54.239; p = 0.050) after the first-post-transplant year independent from the presence of preformed DSA. Total PIRCHE-II scores and PIRCHE-II scores per locus were not associated with the development of de novo DSA in all 297 living-donor KTRs (p&amp;gt;0.05). Conclusion Our findings suggest that iABO kidney transplantation is associated with a lower incidence of de novo DSA and ABMR in the long term, independent from the HLA-derived epitope mismatch load. Whether this protective effect offers new therapeutic options against kidney allograft injury needs to be investigated in future studies.

Specific human leucocyte antigen-DQ risk epitope mismatches are associated with chronic lung allograft dysfunction after lung transplantation

A high-risk epitope mismatch (REM) (found in DQA1∗05 + DQB1∗02/DQB1∗03:01) is associated with de novo donor specific antibodies after lung transplantation (LTx). Chronic lung allograft dysfunction (CLAD) remains a barrier to LTx survival. This study aimed to measure the association between DQ REM and the risk of CLAD and death after LTx. A retrospective analysis of LTx recipients at a single center was conducted between January 2014 and April 2019. Molecular typing at human leucocyte antigen-DQA/DQB identified DQ REM. Multivariable competing risk and Cox regression models were used to measure the association between DQ REM, time-to-CLAD, and time-to-death. DQ REM was detected in 96/268 (35.8%), and DQ REM de novo donor specific antibodies were detected in 34/96 (35.4%). CLAD occurred in 78 (29.1%), and 98 (36.6%) recipients died during follow-up. When analyzed as a baseline predictor, DQ REM status was associated with CLAD (subdistribution hazard ratio (SHR), 2.19; 95% confidence interval [CI], 1.40-3.43; P = .001). After adjustment for time-dependent variables, DQ REM dn-DSA (SHR, 2.43; 95% CI, 1.10-5.38; P = .029) and A-grade rejection score (SHR, 1.22; 95% CI, 1.11-1.35; P = <.001), DQ REM status was not independently associated with CLAD. DQ REM was not associated with death (hazard ratio, 1.18; 95% CI, 0.72-1.93; P = .51). Classification of DQ REM may identify patients at risk of poor outcomes and should be incorporated into clinical decision-making.

Immunologic risk stratification of pediatric heart transplant patients by combining HLA-EMMA and PIRCHE-II.

Human leukocyte antigen (HLA) molecular mismatch is a powerful biomarker of rejection. Few studies have explored its use in assessing rejection risk in heart transplant recipients. We tested the hypothesis that a combination of HLA Epitope Mismatch Algorithm (HLA-EMMA) and Predicted Indirectly Recognizable HLA Epitopes (PIRCHE-II) algorithms can improve risk stratification of pediatric heart transplant recipients. Class I and II HLA genotyping were performed by next-generation sequencing on 274 recipient/donor pairs enrolled in the Clinical Trials in Organ Transplantation in Children (CTOTC). Using high-resolution genotypes, we performed HLA molecular mismatch analysis with HLA-EMMA and PIRCHE-II, and correlated these findings with clinical outcomes. Patients without pre-formed donor specific antibody (DSA) (n=100) were used for correlations with post-transplant DSA and antibody mediated rejection (ABMR). Risk cut-offs were determined for DSA and ABMR using both algorithms. HLA-EMMA cut-offs alone predict the risk of DSA and ABMR; however, if used in combination with PIRCHE-II, the population could be further stratified into low-, intermediate-, and high-risk groups. The combination of HLA-EMMA and PIRCHE-II enables more granular immunological risk stratification. Intermediate-risk cases, like low-risk cases, are at a lower risk of DSA and ABMR. This new way of risk evaluation may facilitate individualized immunosuppression and surveillance.

Association between PIRCHE‐II scores and de novo allosensitization after reduction of immunosuppression during SARS‐CoV‐2 infection in kidney transplant recipients

Before the availability of mRNA vaccines, many transplant centers chose to significantly reduce maintenance immunosuppression in kidney transplant recipients (KTRs) with SARS-CoV-2 infection. The extent to which this increases the risk of allosensitization is unclear. In this observational cohort study, we analyzed 47 KTRs from March 2020 to February 2021 who underwent substantial reduction of maintenance immunosuppression during SARS-CoV-2 infection. KTRs were followed at 6 and 18 months concerning the development of de novo donor-specific anti-HLA (human leukocyte antigen) antibodies (DSA). The HLA-derived epitope mismatches were calculated using the predicted indirectly recognizable HLA-epitopes (PIRCHE-II) algorithm. In total, 14 of 47 KTRs (30%) developed de novo HLA antibodies after the reduction of maintenance immunosuppression. KTRs with higher total PIRCHE-II scores and higher PIRCHE-II scores for the HLA-DR locus were more likely to develop de novo HLA antibodies (p=.023, p=.009). Furthermore, 4 of the 47 KTRs (9%) developed de novo DSA after reduction of maintenance immunosuppression, which were exclusively directed against HLA-class II antigens and also showed higher PIRCHE-II scores for HLA-class II. The cumulative mean fluorescence intensity of 40 KTRs with preexisting anti-HLA antibodies and 13 KTRs with preexisting DSA at the time of SARS-CoV-2 infection remained stable after the reduction of maintenance immunosuppression (p=.141; p=.529). Our data show that the HLA-derived epitope mismatch load between donor and recipient influences the risk of de novo DSA development when immunosuppression is temporarily reduced. Our data further suggest that reduction in immunosuppression should be made more cautiously in KTRs with high PIRCHE-II scores for HLA-class II antigens.

Epitope Mismatch at HLA-DRB1 Associates with Reduced Relapse Risk in Cord Blood Transplantation for Standard-Risk Hematologic Malignancy

Cord blood transplantation (CBT) is an attractive therapeutic option for patients with hematological malignancies. CBT tolerates HLA mismatches between donors and recipients, but which HLA mismatches generate graft-versus-tumor (GVT) effects is unknown. Given that HLA molecules contain epitopes comprising polymorphic amino acids that determine their immunogenicity, we investigated associations between epitope-level HLA mismatches and relapse following single-unit CBT. A total of 492 patients with hematological malignancies who received single unit, T cell replete CBT were included in this multi-center retrospective study. HLA epitope mismatches (EM) were quantified using HLA matchmaker software from donor and patient HLA-A, B, C and DRB1 allele data. Patients were dichotomized by median EM value and divided into groups transplanted in complete/partial remission (standard stage: 62.4%) and others (advanced stage: 37.6%). Median EM numbers in the graft-versus-host direction (GVH-EM) at HLA-class I and HLA-DRB1 were 3 (range, 0-16) and 1 (range, 0-7), respectively. Higher HLA-class I GVH-EM increased non-relapse mortality (NRM) in the advanced stage group (adjusted hazard ratio [HR], 2.12; p=0.021), with no significant advantage for relapse in either stage. On the other hand, higher HLA-DRB1 GVH-EM was associated with better disease-free survival in the standard stage group (adjusted HR, 0.63; p=0.020), which was attributed to lower relapse risk (adjusted HR, 0.46; p=0.014). These associations were also observed even within HLA-DRB1 allele-mismatched transplants in the standard stage group, indicating that EM might have impacts on relapse risk independently of allele mismatch. High HLA-DRB1 GVH-EM did not increase NRM in either stage. High HLA-DRB1 GVH-EM may lead to potent GVT effects and favorable prognosis following CBT especially in the patients transplanted in the standard stage. This approach may facilitate appropriate unit selection and improve the overall prognosis of patients with hematological malignancies who receive CBT.

Determining Clinical Thresholds for Donor HLA Eplet Compatibility to Predict Best Outcomes Following Lung Transplantation.

Background.Currently, the assessment of immunological risk in lung transplantation (LTx) does not completely consider HLA compatibility at the molecular level. We have previously demonstrated the association of HLA eplets in predicting chronic lung allograft dysfunction following LTx; however, the associations between HLA eplet mismatch (epMM) loads and overall survival are unknown.Methods.In this retrospective, single-center study, 277 LTx donor-recipient pairs were high resolution HLA typed and analyzed for HLA epMMs using HLAMatchmaker (version 3.1). LTx pairs were also assessed for the presence of the previously described risk epitope mismatches DQ2-DQA1*05 and DQ7-DQA1*05.Results.HLA class I epMMs were not associated with deleterious outcomes; however, lower HLA class II (≤19), DQA1 (≤2), and combined HLA class I and II (≤29) epMM demonstrated an association with increased time to chronic lung allograft dysfunction and improved overall survival. The presence of a risk epitope mismatch was not associated with worse clinical outcomes.Conclusions.HLA epMM can risk-stratify LTx recipients and potentially guide donor-recipient matching and immunosuppression strategies.

316.11: HLA-DPB1 Molecular Mismatches Are Associated With Acute Rejection and Long-term Graft Function in First Kidney Transplants

Introduction: It is generally accepted that HLA-DP mismatches (MM) do not impact the survival of first transplants but that they may exert a deleterious effect in retransplants. This study aimed to investigate the impact of HLA-DPB1 allele and molecular MM (mMM) on the occurrence of acute rejection (AR) and low 5-year graft function (5-yGF) in first kidney transplants (KT). Method: HLA-DPB1 allele and mMM were determined in 130 first KT from deceased donors, performed between 2014 and 2016. The following mMM models were investigated: expression MM, with the high expression G allele in the donor, T cell epitope (TCE) MM, classified as permissive and nonpermissive MM, epitope MM (EMM), considering all six HLA-DPB1 hypervariable regions (EMM-ABCDEF HVR) or only ABEF regions (EMM-ABEF HVR), Eplet MM (EpMM), considering all or only antibody-verified (AbVer) eplets, and solvent accessible amino acid MM (SAMM). EMM, EpletMM and SAMM loads were categorized using thresholds determined by ROC analysis for each outcome. The outcomes were AR and 5-yGF (estimated by CKD-EPI). Logistic and Cox regressions were used to investigate variables associated with 5-yGF and AR, respectively. Results: 119 (91.5%) KT were performed with one or two HLA-DPB1 allele MM. The overall incidence of AR was 17.7% and the median 5-yGF was 40.3 (27.0 - 51.7) mL/min/1.73m2. No association between HLA-DPB1 allele MM and 5-yGF or rejection was observed. Considering only recipients of standard criteria donor, five logistic models for 5-yGF were built including variables that reached a p-value <0.10 in the univariable analysis (age and donor sex, cause of brain death, ABDR MM and AR) and the mMM (TCE, SAMM, all and AbVer EpMM, EMM-ABCDEF and ABEF HVR). In the model 2, variables associated with 5-yGF≤ 40 were donor age (OR=1.08; CI95%=1.02-1.14; p=0.005) and SAMM≥7 (OR=4.40; CI95%=1.56-12.36, p<0.005), while in the model 4, donor age (OR= 1.09; CI95%=1.03-1.15; p=0.003) and EpMM(AbVer≥2 (OR=3.39; CI95%=1.2-9.45, p=0.02) were associated with low GF. The AUC-ROC for predicting 5-yGF was 0.83 (0.75-0.92) for the model 2, and 0.68 (0.57-0.79) for the model 4. Lastly, for the outcome AR in all recipients, beyond the final donor creatinine, the following mMM models were statistically significant: TCE (HR=3.01; CI95%=1.33-6.84; p=0.008), SAMM≥5 (HR=2.69; CI95%=1.10-6.56; p=0.03), AbVerEpMM ≥3 (HR=3.38; 95%CI=1.32-8.70; p=0.01), and EMM-ABCDEF HVR ≥ 6 (HR=5.08; 95%CI=2.19-11.82; p<0.001). Conclusion: To the best of our knowledge, this is the first study that shows that some mMM, in contrast to classical allele HLA-DPB1 MM, are associated with acute rejection and long-term graft function in a population of exclusively first kidney transplants.