Comparative evaluation of biological human leukocyte antigen DPB1 mismatch models for survival and graft-versus-host disease prediction after unrelated donor hematopoietic cell transplantation

HLA-DPB1 genotype variants predict DP molecule cell surface expression and DP donor specific antibody binding capacity

The contribution of alloresponses to mismatched HLA-DP in solid organ transplantation and hematopoietic stem cell transplantation (HCT) has been well documented. Exploring the regulatory mechanisms of DPB1 alleles has become an important question to be answered. In this study, our initial investigation focused on examining the correlation between the rs9277534G/A SNP and DPB1 mRNA expression. The result showed that there was a significant increase in DPB1 mRNA expression in B lymphoblastoid cell lines (BLCLs) with the rs9277534GG genotype compared to rs9277534AA genotype. In addition, B cells with the rs9277534GG exhibited significantly higher DP protein expression than those carrying the rs9277534AA genotype in primary B cells. Furthermore, we observed a significant upregulation of DP expression in B cells following treatment with Interleukin 13 (IL-13) compared to untreated B cells carrying rs9277534GG-linked DPB1 alleles. Fluorescence in situ hybridization (FISH) analysis of DPB1 in BLCL demonstrated significant differences in both the cytoplasmic (p=0.0003) and nuclear (p=0.0001) localization of DP mRNA expression comparing DPB1*04:01 (rs9277534AA) and DPB1*05:01 (rs9277534GG) homozygous cells. The study of the correlation between differential DPB1 expression and long non-coding RNAs (lncRNAs) showed that lnc-HLA-DPB1-13:1 is strongly associated with DP expression (r=0.85), suggesting the potential involvement of lncRNA in regulating DP expression. The correlation of DP donor specific antibody (DSA) with B cell flow crossmatch (B-FCXM) results showed a better linear correlation of DP DSA against GG and AG donor cells (R2 = 0.4243, p=0.0025 and R2 = 0.6172, p=0.0003, respectively), compared to DSA against AA donor cells (R2 = 0.0649, p=0.4244). This explained why strong DP DSA with a low expression DP leads to negative B-FCXM. In conclusion, this study provides evidence supporting the involvement of lncRNA in modulating HLA-DP expression, shedding lights on the intricate regulatory mechanisms of DP, particularly under inflammatory conditions in transplantation.

Assessment of HLA-DPB1 genetic variation using an HLA-DP tool and its implications in clinical transplantation

HLA-DP is a classic transplantation antigen that mediates alloreactivity through T-cell epitope (TCE) diversity and expression levels. A current challenge is to integrate these functional features into the prospective selection of unrelated donor candidates for transplantation. Genetically, HLA-DPB1 exon 2 defines the permissive and nonpermissive TCE groups, and exons 2 and 3 (in linkage with rs9277534) indicate low- and high-expression allotypes. In this study, we analyzed 356 272 exon 2-exon 3-phased sequences from individuals across 5 self-identified race and ethnicity categories: White, Hispanic, Asian or Pacific Islander, Black or African American, and American Indian or Alaskan Native. This sequence data set revealed the complex relationship between TCE and expression models and the importance of exon 3 sequence data. We also studied archived donor search lists for 2545 patients who underwent transplantation from an HLA-11/12 unrelated donor mismatched for a single HLA-DPB1 allele. Depending on the order in which the TCE and expression criteria were considered, some patients had different TCE- and expression-favorable donors. In addition, this data set revealed that many expression-favorable alternatives existed in the search lists. To improve the selection of candidate donors, we provide, disseminate, and automate our findings through our multifaceted tool called Expression of HLA-DP Assessment Tool, consisting of a public web application, Python package, and analysis pipeline.

Analysis of biological models to predict clinical outcomes based on HLA-DPB1 disparities in unrelated transplantation

HLA compatibility is a key factor for survival after unrelated hematopoietic stem cell transplantation (HSCT). HLA-A, -B, -C, -DRB1, and -DQB1 are usually matched between donor and recipient. By contrast, HLA-DPB1 mismatches are frequent, although it is feasible to optimize donor selection and DPB1 matching with prospective typing. Because classical DPB1 allele mismatches are often unavoidable, however, several biological models have been developed to predict the optimal DPB1 mismatch combination for less graft-versus-host disease (GVHD) and better overall survival. In 909 recipient/donor pairs, we analyzed the role of 3 biological models: T-cell epitopes (TCEs) based on the immunogenicity of DPB1, cell surface expression of DPB1 molecules based on a single-nucleotide polymorphism located in the 3' untranslated region, and the Predicted Indirectly ReCognizable HLA Epitopes (PIRCHE) model based on the presentation of allogeneic peptides derived from mismatched HLA, compared with the classical allele mismatch. Matching for both DPB1 alleles remains the best option to prevent acute GVHD. In the situation of one DPB1 allele mismatch, the donor associated with the lowest acute GVHD risks is mismatched for an allele with a low expression profile in the recipient, followed by a permissive TCE3/4 mismatch and/or the absence of PIRCHE II potential against the recipient. In the context of 2 DPB1 mismatches, the same considerations apply for a permissive TCE3/4 mismatch and no PIRCHE II. By combining the biological models, the most favorable DPB1 constellation can be defined. This approach will help optimize donor selection and improve post-HSCT complications and patient prognosis.

Use of DPB1 T-cell epitope algorithm among italian transplant centers: A survey on behalf of Associazione Italiana di Immunogenetica e Biologia dei Trapianti

The HLA-DPB1 locus has been demonstrated to have a significant role on patients' outcome after allogeneic HSCT, and the so-called T-cell epitope (TCE) algorithm has been incorporated in international guidelines for the selection of unrelated donors. The purpose of the present study is to measure, through a national survey conducted on behalf of the Associazione Italiana di Immunogenetica e Biologia dei Trapianti (AIBT), the extent of awareness and use of HLA-DPB1 TCE-based algorithms during the donor search. 89% of the HLA laboratories answered to a short questionnaire and the results showed a progressive increase of the laboratories typing DPB1 in patients and their potential donors during the search (from 44% to 79% during the 2010-2019 period) as well as the application of a TCE-based algorithm for the donor choice whenever possible (from 24% to 65% during the same period). The DP-permissiveness status is detailed in the official HLA typing report by 12%, 32% and 50% of laboratories in 2010, 2015 and 2019, respectively. The present data indicate an encouraging raise in the awareness of the HLA-DPB1 role in unrelated donor selection; noteworthy, mentioning the TCE-based permissiveness status in the HLA typing report of each potential unrelated donor represents a notable mean to raise awareness among transplant physicians and to support them in their task of choosing the best donor. Nonetheless, despite the compelling evidence of the predictive ability of TCE-based algorithms, further efforts are still needed to extend its application to all transplant centers in Italy.

Allelic HLA Matching and Pair Origin Are Favorable Prognostic Factors for Unrelated Hematopoietic Stem Cell Transplantation in Neoplastic Hematologic Diseases: An Italian Analysis by the Gruppo Italiano Trapianto di Cellule Staminali e Terapie Cellulari, Italian Bone Marrow Donor Registry, and Associazione Italiana di Immunogenetica e Biologia dei Trapianti

HLA molecules are important for immunoreactivity in allogeneic hematopoietic stem cell transplantation (HSCT). The Gruppo Italiano Trapianto di Cellule Staminali e Terapie Cellulari, Italian Bone Marrow Donor Registry, and Associazione Italiana di Immunogenetica e Biologia dei Trapianti promoted a retrospective observational study to evaluate HLA matching and the impact of allelic HLA mismatching and non-HLA factors on unrelated Italian HSCT outcomes. From 2012 to 2015, 1788 patients were enrolled in the study. The average donor age was 29 years and the average recipient age was 49 years. As a conditioning regimen, 71% of the patients received myeloablative conditioning. For GVHD prophylaxis, 76% received either antithymocyte or anti-T lymphocyte globulin, cyclosporine A, and methotrexate. Peripheral blood was the stem cell source in 80%. The median duration of follow-up was 53 months. Regarding HLA matching, 50% of donor-recipient pairs were 10/10 matched, 38% had 1 mismatch, and 12% had 2 or more mismatches. A total of 302 pairs shared Italian origin. Four-year overall survival (OS), progression-free survival, GVHD-free relapse-free survival, and relapse rates were 49%, 40%, 22%, and 34%, respectively. The 4-year NRM was 27%, and the 100-day cumulative incidence of grade ≥II acute GVHD (aGVHD) was 26%. In multivariate analysis, 9/10 and ≤8/10 HLA allele-matched pairs were associated with worse OS (P = .04 and .007, respectively), NRM (P = .007 and P < .0001, respectively), and grade III-IV aGVHD (P = .0001 and .01, respectively). Moreover, the incidences of grade II-IV aGVHD (P = .001) and chronic GVHD (P = .002) were significantly lower in Italian pairs. In conclusion, 10/10 HLA matching is a favorable prognostic factor for unrelated HSCT outcome in the Italian population. Moreover, the presence of 2 HLA-mismatched loci was associated with a higher NRM (P < .0001) and grade II-IV aGVHD (P = .006) and a poorer OS (P = .001) compared with 1 HLA-mismatched locus in early or intermediate disease phases. Finally, we found that Italian donor and recipient origin is a favorable prognostic factor for GVHD occurrence.

Role of HLA-DP Expression in Graft-Versus-Host Disease After Unrelated Donor Transplantation

PURPOSE

The main aim of this study was to evaluate the significance of HLA-DPB1 expression in acute graft-versus-host disease (GVHD) after hematopoietic cell transplantation (HCT) from HLA-A, -B, -C, -DRB1, -DQB1-matched and -mismatched unrelated donors.

PATIENTS AND METHODS

Between January 1, 2017, and January 10, 2019, we assessed 19,136 patients who received HCT from an HLA-A, -B, -C, -DRB1, -DQB1-matched or -mismatched unrelated donor performed in Australia, the European Union, Japan, North America, and the United Kingdom between 1988 and 2016. Among transplant recipients with one HLA-DPB1 mismatch, the patient's mismatched HLA-DPB1 allotype was defined as low or high expression. Multivariable regression models were used to assess risks of GVHD associated with high expression relative to low expression HLA-DPB1 mismatches. The effect of increasing numbers of HLA-DPB1 mismatches on clinical outcome was assessed in HLA-mismatched transplant recipients.

RESULTS

In HLA-A, -B, -C, -DRB1,-DQB1-matched transplant recipients, donor mismatching against one high-expression patient HLA-DPB1 increased moderate (odds ratio [OR], 1.36; P = .001) and severe acute GVHD (OR, 1.32; P = .0016) relative to low-expression patient mismatches, regardless of the expression level of the donor's mismatched HLA-DPB1. Among transplant recipients with one HLA-A, -B, -C, -DRB1, or -DQB1 mismatch, the odds of acute GVHD increased with increasing numbers of HLA-DPB1 mismatches (OR, 1.23 for one; OR, 1.40 for two mismatches relative to zero mismatches for moderate GVHD; OR, 1.19 for one; OR, 1.40 for two mismatches relative to zero for severe GVHD), but not with the level of expression of the patient's mismatched HLA-DPB1 allotype.

CONCLUSION

The level of expression of patient HLA-DPB1 mismatches informs the risk of GVHD after HLA-A, -B, -C, -DRB1, -DQB1-matched unrelated HCT, and the total number of HLA-DPB1 mismatches informs the risk of GVHD after HLA-mismatched unrelated HCT. Prospective consideration of HLA-DPB1 may help to lower GVHD risks after transplantation.

Selection of matched unrelated donors moving forward: from HLA allele counting to functional matching

Matched unrelated donors (URD) are the most frequent source of stem cells for allogeneic hematopoietic cell transplantation (HCT) to date, with HCT performed mainly under conventional immunosuppression by methotrexate and cyclosporine. In this setting, every single allelic donor-recipient mismatch for HLA-A, -B, -C, -DRB1 (8/8), but not for HLA-DQB1, -DPB1, has a significant negative effect on overall survival (OS). When several 8/8 HLA-matched URD are available, donor age is the most important factor impacting OS. Moving forward from the traditional way of counting the number of donor-recipient HLA allele mismatches to biology-driven algorithms for functional matching has led to the unraveling of an association between permissive, low-risk HLA-DPB1 mismatches and improved outcome after URD HCT for malignant disease but not for nonmalignant disease. Functional HLA matching might prove to have increasing importance for URD selection in the era of new immunosuppressive regimens that have the potential to substantially reshuffle the role of HLA mismatches in URD HCT.