Impact ofHLA-DPB1allelic and single amino acid mismatches on HSCT

Promiscuity of Peptides Presented in HLA-DP Molecules from Different Immunogenicity Groups Is Associated With T-Cell Cross-Reactivity

In the context of HLA-DP-mismatched allogeneic stem cell transplantation, mismatched HLA-DP alleles can provoke profound allo-HLA-DP-specific immune responses from the donor T-cell repertoire leading to graft-versus-leukemia effect and/or graft-versus-host disease in the patient. The magnitude of allo-HLA-DP-specific immune responses has been shown to depend on the specific HLA-DP disparity between donor and patient and the immunogenicity of the mismatched HLA-DP allele(s). HLA-DP peptidome clustering (DPC) was developed to classify the HLA-DP molecules based on similarities and differences in their peptide-binding motifs. To investigate a possible categorization of HLA-DP molecules based on overlap of presented peptides, we identified and compared the peptidomes of the thirteen most frequently expressed HLA-DP molecules. Our categorization based on shared peptides was in line with the DPC classification. We found that the HLA-DP molecules within the previously defined groups DPC-1 or DPC-3 shared the largest numbers of presented peptides. However, the HLA-DP molecules in DPC-2 segregated into two subgroups based on the overlap in presented peptides. Besides overlap in presented peptides within the DPC groups, a substantial number of peptides was also found to be shared between HLA-DP molecules from different DPC groups, especially for groups DPC-1 and -2. The functional relevance of these findings was illustrated by demonstration of cross-reactivity of allo-HLA-DP-reactive T-cell clones not only against HLA-DP molecules within one DPC group, but also across different DPC groups. The promiscuity of peptides presented in various HLA-DP molecules and the cross-reactivity against different HLA-DP molecules demonstrate that these molecules cannot be strictly categorized in immunogenicity groups.

Tools for optimizing risk assessment in hematopoietic cell transplant - What can we get away with?

Unrelated allogeneic hematopoietic cell transplant (HCT) is a critical modality to treat hematologic malignancies. The current objective of donor selection is to match donor and recipient at the HLA (human leukocyte antigen) peptide-binding region which should lower the risk of graft-versus-host disease. However, depending on the patient's ethnicity/race, finding a matched donor is challenging, especially for HLA-DPB1 which is due to the weak linkage disequilibrium between HLA-DPB1 and the other HLA class II loci. Recent evidence, on the molecular level, has shown that certain HLA mismatches carry lower clinical risk. More specifically, there is an increasing understanding of polymorphisms of the innate and adaptive immune systems and their impact on transplant outcomes, allowing us to expand our "toolkit" for optimization of donor selection in HCT. Therefore, in this review we discuss matching strategies based on comparing donor and recipient polymorphisms that may influence innate and adaptive immune response genes in allorecognition and the role of single nucleotide polymorphisms in non-HLA genes that have the potential for providing additional tools to refine risk stratification.

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.

Impact of HLA-DPB1 Matching on Outcome of Unrelated Transplant for Hematologic Malignant Diseases: A Systematic Review and Meta-analysis

OBJECTIVE

Human leukocyte antigen match is the most important donor factor affecting transplant outcome. The HLA-DPB1 mismatch on the clinical outcome of hematopoietic stem cell transplant (HSCT) is less clear. This study is the first meta-analysis to investigate the impact of HLA-DPB1 loci mismatch on clinical outcome after unrelated donor HSCT for hematologic malignant disease.

METHODS

We electronically searched the PubMed, EMBASE, Cochrane Central Register of Controlled Trials, and a related database (January 1995-December 2018) for all relevant articles. Comparative studies were carried out to investigate the impact of HLA-DPB1 loci mismatch on clinical outcome after unrelated donor HSCT, that is, the disease-free survival, engraftment, graft-vs-host disease, relapse, and transplant-related mortality (TRM). We performed a meta-analysis using Review Manager 5.3.5 software and adopted funnel plot regression to assess the publication bias.

RESULTS

A total of 1570 articles were retrieved; 21 studies including 27,852 patients were assessed. Pooled comparisons of studies found that the HLA-DPB1-mismatched group had a lower rate of disease-free survival than the DPB1-matched group and lower overall survival in non-T cell-depleted transplant than the DPB1-matched group. The DPB1-mismatched group has higher incidence of acute graft-vs-host disease (aGVHD) and severe (≥ III degree) aGVHD, lower relapse rate, and higher TRM. Moreover, compared with 1-antigen mismatch, 2-antigen mismatch in DPB1 had a higher risk of TRM and a lower relapse rate, and the nonpermissive DPB1 mismatch had significantly higher rate of severe aGvHD and lower rate of disease relapse.

CONCLUSIONS

This analysis confirmed that HLA-DPB1 has important influence on survival and transplant-related complications during unrelated donor HSCT, and HLA-DPB1 donor selection strategies have been proposed based on personalized algorithm.

Extended HLA Haplotypes and Their Impact on DPB1 Matching of Unrelated Hematologic Stem Cell Transplant Donors

Although HLA-DPB1 has long been considered of lesser importance in the selection of an unrelated donor (URD) hematologic stem cell transplantation, currently in many instances the DPB1 type of the donor is relevant or even critical. At present, however, only a minority of registry donors are DPB1 typed. It is also unclear to what extent the DPB1 alleles are linked to the 5-locus HLA-A-, B-, C-, DRB1, -DQB1 haplotypes. We sought to study whether there is such a linkage by using donors in the Finnish Stem Cell Registry as the study population. The 6-locus HLA-A, -B, -C, -DRB1, -DQB1, -DPB1 haplotype frequencies were estimated from a group of 43,365 Finnish registry donors using the German National Bone Marrow Registry algorithm. Five-locus haplotype (HLA-A, -B, -C, -DRB1, -DQB1) and HLA-DPB1 allele frequencies were calculated as marginal frequencies of the estimated 6-locus haplotype frequencies. The Finnish average frequency of individual DPB1 alleles was compared with their respective frequencies in association with individual 5-locus HLA haplotypes (haplotype-specific frequencies). Finally, the probability of DPB1 matching in 10/10 matched URD transplants was assessed. Haplotype-specific DPB1 frequencies differed significantly from the average DPB1 frequencies in 81 of 100 most frequent Finnish 5-locus HLA haplotypes, including some infrequent DPB1 alleles that were associated almost exclusively with certain individual 5-locus haplotypes. Five-locus haplotypes that are enriched in Finland but rare among other Europeans carried stronger DPB1 associations than haplotypes that are frequent European-wide. Finally, 10/10 matched transplants from domestic registry donors were significantly more likely to also be DPB1 matched than those from foreign donors. The results indicate an extension of linkage disequilibrium in the MHC complex in the Finnish population. With continuing upfront DPB1 typing of registry donors, it will be possible to perform similar extended 6-locus haplotype frequency estimations also in other registries. The associations are likely to be population specific but may be weaker in more heterogeneous populations. In the future the results might be used to predict the probability of DPB1 match or permissive/nonpermissive DPB1 mismatch for non-DPB1 typed donors in registry donor searches.

Clinical implications of HLA locus mismatching in unrelated donor hematopoietic cell transplantation: a meta-analysis

It remains controversial that the impacts of individual HLA locus mismatches on clinical outcomes of patients receiving unrelated-donor hematopoietic cell transplantation (HCT), as compared to HLA allele matched controls. We conducted a meta-analysis to address these issues. Four databases (PubMed, Embase, Web of Science and the Cochrane Library) were searched to select eligible studies. All donor-recipient pairs were high-resolution typing for HLA-A, -B, -C, -DRB1, DQB1 and DPB1 loci. Multivariate-adjusted hazard ratios (HRs) were extracted and pooled using a random-effects model. A total of 36 studies were included, with 100,072 patients receiving HCT. Surprisingly, we found that HLA-DQB1 locus mismatches had no significantly increased risk of multiple outcomes including acute and chronic graft-versus-host disease (GVHD), overall mortality and disease relapse (HR, 1.07; P = .153; HR, 1.07; P = .271; HR, 1.09; P = .230; HR, 1.07; P = .142 and HR, 1.02; P = .806, respectively). Mismatched HLA-DPB1 was significantly associated with a reduced risk of disease relapse (HR, 0.74; P < .001) but not with increased risks of transplant-related mortality (TRM) and overall mortality (HR, 1.09; P = .591; I² = 74.2% and HR, 1.03; P = .460, respectively). In conclusion, HLA-DQB1 locus mismatches is a permissive mismatching. HLA-DPB1 locus mismatches significantly protect against leukemia relapse. Refining effects of individual HLA locus mismatches contributes to predicting prognosis of patients receiving unrelated donor HCT.

Impact of HLA-Mismatch in Unrelated Donor Hematopoietic Stem Cell Transplantation: A Meta-Analysis

The magnitude of risk associated with 9/10 mismatched unrelated donor (MMURD) hematopoietic stem cell transplantation and that of mismatches at the individual HLA loci remain unclear. We performed a meta-analysis to assess the difference in clinical outcomes between matched unrelated donor (MUD) and MMURD transplantation. A comprehensive search of Medline and Embase for manuscripts regarding transplantation outcomes in primarily adult patients with hematologic malignancies was performed. The pooled effect estimates were calculated using DerSimonian-Laird random effects models. A total of 13 studies were included, reporting on 13,446 transplants. 9/10 MMURD transplantation was associated with worse overall survival compared to 10/10 MUD transplantation (pooled HR: 1.27, 95% CI: 1.12-1.45; n = 7 studies). Mismatch at HLA-A, -B, or -C was associated with significantly worse overall survival compared to MUD transplantation, while there was no significant difference associated with -DQ or -DPB1 mismatch. Inferior survival associated with HLA-DRB1 mismatch could not be ruled out. Data on acute and chronic graft-versus-host disease were scarce but favored MUD transplantation. In summary, this meta-analysis of the available literature favored MUD over MMURD transplantation in hematologic malignancies and further quantifies the risks associated with specific HLA-allele mismatches. Am. J. Hematol. 91:551-555, 2016. © 2016 Wiley Periodicals, Inc.

How to select the best available related or unrelated donor of hematopoietic stem cells?

Recognition of HLA incompatibilities by the immune system represents a major barrier to allogeneic hematopoietic stem cell transplantation. HLA genotypically identical sibling donors are, therefore, the gold standard for transplantation purposes, but only 30% patients have such a donor. For the remaining 70% patients alternative sources of stem cells are a matched unrelated adult volunteer donor, a haploidentical donor or a cord blood unit. The definition of 'HLA matching' depends on the level of resolution and on which loci are tested. The development of HLA molecular typing technologies and the availability of more than 27 million donors in the international database has greatly facilitated unrelated donor searches. The gold standard is high resolution typing at the HLA-A, -B, -C, -DRB1, and -DQB1 loci (10/10 match). Single disparities for HLA-A, -B, - C, or -DRB1 are associated with increased risk of post-transplant complications, but less so in patients with advanced disease, and in those undergoing T-cell-depleted allografting. HLA-DQB1 mismatches seem to be better tolerated and some HLA-C, -DRB1 and -DPB1 disparities are potentially less immunogenic. HLA typing by next-generation sequencing methods is likely to change matching algorithms by providing full sequence information on all HLA loci in a single step. In most European populations a 10/10 matched donor can be found for at least 50% of patients and an additional 20-30% patients may have a 9/10 matched donor. Genetic factors that help in identifying donors with less immunogenic mismatches are discussed. Haploidentical donors are increasingly used as an alternative source of stem cells for those patients lacking a matched unrelated donor.

Functional distance between recipient and donor HLA-DPB1 determines nonpermissive mismatches in unrelated HCT

The role of HLA amino acid (AA) polymorphism for the outcome of hematopoietic cell transplantation (HCT) is controversial, in particular for HLA class II. Here, we investigated this question in nonpermissive HLA-DPB1 T-cell epitope (TCE) mismatches reflected by numerical functional distance (FD) scores, assignable to all HLA-DPB1 alleles based on the combined impact of 12 polymorphic AAs. We calculated the difference in FD scores (ΔFD) of mismatched HLA-DPB1 alleles in patients and their 10/10 HLA-matched unrelated donors of 379 HCTs performed at our center for acute leukemia or myelodysplastic syndrome. Receiver-operator curve-based stratification into 2 ΔFD subgroups showed a significantly higher percentage of nonpermissive TCE mismatches for ΔFD >2.665, compared with ΔFD ≤2.665 (88% vs 25%, P < .0001). In multivariate analysis, ΔFD >2.665 was significantly associated with overall survival (hazard ratio [HR], 1.40; 95% confidence interval [CI], 1.05-1.87; P < .021) and event-free survival (HR, 1.39; 95% CI, 1.05-1.82; P < .021), compared with ΔFD ≤2.665. These associations were stronger than those observed for TCE mismatches. There was a marked but not statistically significant increase in the hazards of relapse and nonrelapse mortality in the high ΔFD subgroup, whereas no differences were observed for acute and chronic graft-versus-host disease. Seven nonconservative AA substitutions in peptide-binding positions had a significantly stronger impact on ΔFD compared with 5 others (P = .0025), demonstrating qualitative differences in the relative impact of AA polymorphism in HLA-DPB1. The novel concept of ΔFD sheds new light onto nonpermissive HLA-DPB1 mismatches in unrelated HCT.

Mismatched unrelated alternative donors for hematological malignancies

For the majority of hematologic malignancies allogeneic hematopoietic cell transplantation (HCT) is the only curative treatment option. Sibling donors have been the standard for adult patients. Since there is not a suitable family donor for all patients, the need for alternative donors for HCT is great. Fortunately, the availability of unrelated volunteer donor registries has expanded over the years and the results of HCT with matched unrelated donors (MUD) are comparable to the results with matched related donors (MRD). Nevertheless, there are many patients lacking a well-matched donor. To increase the applicability of transplantation, alternative donors such as mismatched unrelated donors (MMURD), cord blood stem cell products and haploidentical related donors have been widely used. This review seeks to give insights into the use of MMUD donors for HCT and summarize the existing data.

High-resolution HLA matching in unrelated donor transplantation in Switzerland: differential impact of class I and class II mismatches may reflect selection of nonimmunogenic or weakly immunogenic DRB1/DQB1 disparities

Unrelated donor searches in Switzerland require high-resolution HLA typing for HLA-A/B/C/DRB1/DRB3,4/DQB1 loci. We evaluated this strategy accepting donors with ⩾9/10 match. Of 802 unrelated donor transplants in 2000-2013, 570 were 10/10 matched, 31 were DRB3/4 mismatched, 261 were single-allele mismatched and 13 had 2 allele mismatches. Of the 261 single-allele disparities, 60 concerned HLA-A/-B, 55 HLA-C and 73 HLA-DRB1/-DQB1 loci. Transplants were reduced intensity conditioning (289, 36%), marrow (187, 23%), EBMT risk score was low in 39, intermediate I in 331, intermediate II in 333 and high in 99 patients. Five-year survival was 48±4%. HLA affected survival in the multivariate model adjusted for risk score. HLA-A/-B and HLA-C mismatches had twice the mortality risks, whereas HLA-DRB1/-DQB1 mismatches were similar to matched transplants. HLA-DRB3/4 mismatches were associated with a nonsignificant increased mortality risk. HLA-DRB3/4 mismatches had higher graft-versus-host disease and transplant-related mortality risks and lower relapse rates compared with matched transplants. We show significant effects of HLA class I, but not HLA class II, mismatches. The lack of impact of DRB1 disparities may be related to the lower immunogenicity of the DRB1*11:01/11:04 and DRB1*14:01/14:54 mismatches, representing 46% of DRB1 incompatibilities. These results support a matching algorithm that prioritizes mismatches considered as more permissive.

Is there any impact of HLA-DPB1 disparity in 10/10 HLA-matched unrelated hematopoietic SCT? Results of a French multicentric retrospective study

We retrospectively analyzed the impact of HLA-DPB1 mismatches in a large cohort of 1342 French patients who underwent 10/10 HLA-matched unrelated HSCT. A significant impact of HLA-DPB1 allelic mismatches (2 vs 0) was observed in severe acute GVHD (aGVHDIII-IV) (risk ratio (RR)=1.73, confidence interval (CI) 95% 1.09-2.73, P=0.019) without impact on OS, TRM, relapse and chronic GVHD (cGVHD). According to the T-cell epitope 3 (TCE3)/TCE4 HLA-DPB1 disparity algorithm, 37.6% and 58.4% pairs had nonpermissive HLA-DPB1, respectively. TCE3 and TCE4 disparities had no statistical impact on OS, TRM, relapse, aGVHD and cGVHD. When TCE3/TCE4 disparities were analyzed in the graft-vs-host or host-vs-graft (HVG) direction, only a significant impact of TCE4 nonpermissive disparities in the HVG direction was observed on relapse (RR=1.34, CI 95% 1.00-1.80, P=0.048). In conclusion, this French retrospective study shows an adverse prognosis of HLA-DPB1 mismatches (2 vs 0) on severe aGVHD and of nonpermissive TCE4 HVG disparities on relapse after HLA-matched 10/10 unrelated HSCT.

Hematopoietic stem cell transplantation donor sources in the 21st century: choosing the ideal donor when a perfect match does not exist

Most patients who require allogeneic stem cell transplantation do not have a matched sibling donor, and many patients do not have a matched unrelated donor. In an effort to increase the applicability of transplantation, alternative donors such as mismatched adult unrelated donors, haploidentical related donors, and umbilical cord blood stem cell products are frequently used when a well matched donor is unavailable. We do not yet have the benefit of randomized trials comparing alternative donor stem cell sources to inform the choice of donor; however, the existing data allow some inferences to be made on the basis of existing observational and phase 2 studies. All 3 alternative donor sources can provide effective lymphohematopoietic reconstitution, but time to engraftment, graft failure rate, graft-versus-host disease, transplant-related mortality, and relapse risk vary by donor source. These factors all contribute to survival outcomes and an understanding of them should help guide clinicians when choosing among alternative donor sources when a matched related or matched unrelated donor is not available.

HLA allele and haplotype polymorphisms among Croatian patients in an unrelated hematopoietic stem cell donor search program

The aim of the present study was to investigate HLA alleles and haplotypes among Croatian patients in an unrelated HSCT program, and to analyze HLA matching in patient/donor pairs. Analysis was performed on a group of 105 patients and their donors, and 4000 unrelated donors from our registry (CBMDR) served as controls. PCR-SSO and PCR-SSP high-resolution methods for HLA-A, -B, -C, -DRB1, and -DQB1 loci were used for typing patient/donor pairs. Donors from CBMDR were tested for HLA-A, -B, and -DRB1 by PCR-SSO. No difference in frequency at HLA tested loci among patients and donors from CBMDR was observed. A fully matched donor (10/10) was found for 68 (64.8%) patients, and the highest number of mismatches was found for HLA-DRB1 and HLA-C alleles. The presence of HLA-B alleles (B*15:01, B*18:01, and B*51:01) associated with two or more HLA-C alleles as well as the presence of unusual HLA-B/HLA-C (B*35:01-C*07:01 and B*35:01-C*14:02) combinations resulted in mismatches at the HLA-C locus. Additionally, mismatches at the DRB1 locus were in most cases found for DRB1*11 alleles. The results suggest that the DRB1*11:04 allele might be considered as a limiting factor in finding a 10/10 matched donor. These data may help in the improvement of the searching protocol for unrelated donors for Croatian patients.

Tick-borne encephalitis (TBE) and hepatitis B nonresponders feature different immunologic mechanisms in response to TBE and influenza vaccination with involvement of regulatory T and B cells and IL-10

Low responsiveness/nonresponsiveness is characterized by an insufficient immune response upon primary and/or booster vaccination and affects 1-10% of vaccinees. In the current study, we aimed to investigate whether nonresponsiveness is an Ag/vaccine-specific phenomenon and to clarify underlying immunological mechanisms. Nonresponders to tick-borne encephalitis (TBE) or hepatitis B Ag with a history of previous TBE vaccinations were booster vaccinated with TBE and influenza vaccine and compared with TBE high responders in terms of humoral and cellular immune response. Postboosters in TBE high responder existing TBE titers increased, and solid humoral responses to influenza vaccine were induced. In TBE nonresponders, low to undetectable prevaccination TBE titers remained low, whereas sufficient influenza Abs were induced. In both TBE groups, a positive correlation of humoral and cellular immune response was seen as high/low TBE titers were associated with sufficient/lack of Ag-specific T cell proliferation. Furthermore, responses to influenza were robust in terms of Abs and cytokine production. In contrast, in hepatitis B nonresponders, sufficient humoral responses to TBE and influenza Ags were induced despite lacking specific IL-2 and IFN-γ production. Importantly, these patients showed high IL-10 baseline levels in vitro. HLA-DR subtypes associated with hepatitis B nonresponsiveness were overrepresented in this group, and high IL-10 levels were linked to these subtypes. Whereas TBE and hepatitis B nonresponders had increased IL-10-producing FOXP3(+) T regulatory cells upon vaccination, only in hepatitis B nonresponders, showing elevated prevaccination IL-10 levels, a prominent population of B regulatory cells was detected. We conclude that immunological pathways of nonresponsiveness follow different patterns depending both on vaccine Ag and genetic predisposition of the vaccinee.

Investigation of the impact of HLA-DPB1 matching status in 10/10 HLA matched unrelated hematopoietic stem cell transplantation: results of a French single center study

The impact of HLA-DPB1 mismatches after unrelated hematopoietic stem cell transplantation (HSCT) remains controversial. We retrospectively analyzed the impact of permissive/non-permissive HLA-DPB1 mismatches on the outcome of 141 patients who underwent 10/10 HLA allelic-matched unrelated HSCT. Each pair was classified according to the 3 (TCE3) and 4-group (TCE4) algorithm based on DPB1 alleles immunogenicity. Outcome analysis revealed that TCE3 and TCE4 non-permissive HLA-DPB1 disparities were not associated with worsened overall survival, relapse risk neither risk of acute GvHD. Overall, this single center retrospective study does not confirm the adverse prognostic of non-permissive HLA-DPB1 mismatches.

Effect of T-cell-epitope matching at HLA-DPB1 in recipients of unrelated-donor haemopoietic-cell transplantation: a retrospective study

BACKGROUND

The risks after unrelated-donor haemopoietic-cell transplantation with matched HLA-A, HLA-B, HLA-C, HLA-DRB1, HLA-DQB1 alleles between donor and recipient (10/10 matched) can be decreased by selection of unrelated donors who also match for HLA-DPB1; however, such donors are difficult to find. Classification of HLA-DPB1 mismatches based on T-cell-epitope groups could identify mismatches that might be tolerated (permissive) and those that would increase risks (non-permissive) after transplantation. We did a retrospective study to compare outcomes between permissive and non-permissive HLA-DPB1 mismatches in unrelated-donor haemopoietic-cell transplantation.

METHODS

HLA and clinical data for unrelated-donor [corrected] transplantations submitted to the International Histocompatibility Working Group in haemopoietic-cell transplantation were analysed retrospectively. HLA-DPB1 T-cell-epitope groups were assigned according to a functional algorithm based on alloreactive T-cell crossreactivity patterns. Recipients and unrelated donors matching status were classified as HLA-DPB1 match, non-permissive HLA-DPB1 mismatch (those with mismatched T-cell-epitope groups), or permissive HLA-DPB1 mismatch (those with matched T-cell-epitope groups). The clinical outcomes assessed were overall mortality, non-relapse mortality, relapse, and severe (grade 3-4) acute graft-versus-host disease (aGvHD).

FINDINGS

Of 8539 transplantations, 5428 (64%) were matched for ten of ten HLA alleles (HLA 10/10 matched) and 3111 (36%) for nine of ten alleles (HLA 9/10 matched). Of the group overall, 1719 (20%) were HLA-DPB1 matches, 2670 (31%) non-permissive HLA-DPB1 mismatches, and 4150 (49%) permissive HLA-DPB1 mismatches. In HLA 10/10-matched transplantations, non-permissive mismatches were associated with a significantly increased risk of overall mortality (hazard ratio [HR] 1·15, 95% CI 1·05-1·25; p=0·002), non-relapse mortality (1·28, 1·14-1·42; p<0·0001), and severe aGvHD (odds ratio [OR] 1·31, 95% CI 1·11-1·54; p=0·001), but not relapse (HR 0·89, 95% CI 0·77-1·02; p=0·10), compared with permissive mismatches. There were significant differences between permissive HLA-DPB1 mismatches and HLA-DPB1 matches in terms of non-relapse mortality (0·86, 0·75-0·98; p=0·03) and relapse (1·34, 1·17-1·54; p<0·0001), but not for overall mortality (0·96, 0·87-1·06; p=0·40) or aGvHD (OR 0·84, 95% CI 0·69-1·03; p=0·09). In the HLA 9/10 matched population, non-permissive HLA-DPB1 mismatches also increased the risk of overall mortality (HR 1·10, 95% CI 1·00-1·22; p=0·06), non-relapse mortality (1·19, 1·05-1·36; p=0·007), and severe aGvHD (OR 1·37, 95% CI 1·13-1·66; p=0·002) compared with permissive mismatches, but the risk of relapse was the same in both groups (HR 0·93, 95% CI 0·78-1·11; p=0·44). Outcomes for HLA 10/10-matched transplantations with non-permissive HLA-DPB1 mismatches did not differ substantially from those for HLA 9/10-matched transplantations with permissive HLA-DPB1 mismatches or HLA-DPB1 matches.

INTERPRETATION

T-cell-epitope matching defines permissive and non-permissive HLA-DPB1 mismatches. Avoidance of an unrelated donor with a non-permissive T-cell-epitope mismatch at HLA-DPB1 might provide a practical clinical strategy for lowering the risks of mortality after unrelated-donor haemopoietic-cell transplantation.

FUNDING

National Institutes of Health; Associazione Italiana per la Ricerca sul Cancro; Telethon Foundation; Italian Ministry of Health; Cariplo Foundation; National Cancer Institute; National Heart, Lung and Blood Institute; National Institute of Allergy and Infectious Diseases; Office of Naval Research; IRGHET Paris; Swedish Cancer Society; Children's Cancer Foundation; Swedish Research Council; Cancer Society in Stockholm; Karolinska Institutet; and Leukemia and Lymphoma Society.

Impact of HLA-DPB1 haplotypes on outcome of 10/10 matched unrelated hematopoietic stem cell donor transplants depends on MHC-linked microsatellite polymorphisms

Hematopoietic stem cell transplantation (HSCT) with HLA-A, -B, -C, -DRB1, -DQB1 allele matched (10 of 10) unrelated donors is still associated with a significant rate of posttransplantation complications. In order to disclose additional immunogenetic factors, we analyzed the impact of HLA-DPB1 disparities and major histocompatibility complex (MHC)-resident microsatellite polymorphisms in 246 HLA 10 of 10 matched HSCT patients. First we showed that patients with more frequent/conserved HLA haplotypes had a higher 5-year survival (55% ± 18% versus 39% ± 18%, P = .021). In addition, DPB1 incompatibilities and 3 microsatellite alleles were associated with outcome. In a Cox regression model adjusting for European Blood and Marrow Transplant (EBMT) risk score, T cell depletion, and year of treatment, HSCT with a tumor necrosis factor d (TNFd) 4/d5-positive donor was associated with increased mortality (hazard ratio [HR] = 2.03; confidence interval [CI] 1.25-3.31; P = .004), whereas the D6S510-184 allele was protective (HR = 0.44; CI 0.22-0.87; P = .018). The 2 MHC-linked genetic donor factors, DPB1 mismatch (MM), and TNFd4/d5-positivity, acted in synergy with the EBMT risk score with an always lower survival (HR = 2.97; CI 1.27-6.92; P = .012). These data show that multiple MHC-linked genetic donor factors impact on outcome after unrelated donor HSCT. Their additive and potentially divergent effects could explain previous discrepant results, particularly with respect to the role of HLA-DPB1 disparities. We conclude that HLA-DPB1 typing combined with a simple TNFd microsatellite genotyping assay may significantly help in pretransplantation risk assessment for graft-versus-host disease and mortality, particularly for patients with several potential 10 of 10 matched donors.

Predictions in the face of clinical reality: HistoCheck versus high-risk HLA allele mismatch combinations responsible for severe acute graft-versus-host disease

HLA polymorphism remains a major hurdle for hematopoietic stem cell transplantation (HSCT). In 2004, Elsner et al. proposed the HistoCheck Web-based tool to estimate the allogeneic potential between HLA-mismatched stem cell donor/recipient pairs expressed as a sequence similarity matching (SSM). SSM is based on the structure of HLA molecules and the functional similarity of amino acids. According to this algorithm, a high SSM score represents high dissimilarity between MHC molecules, resulting in a potentially more deleterious impact on stem cell transplant outcomes. We investigated the potential of SSM to predict high-risk HLA allele mismatch combinations responsible for severe acute graft-versus-host disease (aGVHD grades III and IV) published by Kawase et al., by comparing SSM in low- and high-risk combinations. SSM was calculated for allele mismatch combinations using the HistoCheck tool available on the Web (www.histocheck.org). We compared ranges and means of SSM among high-risk (15 combinations observed in 722 donor/recipient pairs) versus low-risk allele combinations (94 combinations in 3490 pairs). Simulation scenarios were created where the recipient's HLA allele was involved in multiple allele mismatch combinations with at least 1 high-risk and 1 low-risk mismatch combination. SSM values were then compared. The mean SSM for high- versus low-risk combinations were 2.39 and 2.90 at A, 1.06 and 2.53 at B, 16.60 and 14.99 at C, 4.02 and 3.81 at DRB1, and 7.47 and 6.94 at DPB1 loci, respectively. In simulation scenarios, no predictable SSM association with high- or low-risk combinations could be distinguished. No DQB1 combinations met the statistical criteria for our study. In conclusion, our analysis demonstrates that mean SSM scores were not significantly different, and SSM distributions were overlapping among high- and low-risk allele combinations within loci HLA-A, B, C, DRB1, and DPB1. This analysis does not support selecting donors for HSCT recipients based on low HistoCheck SSM scores.

HLA-DPB1 mismatching results in the generation of a full repertoire of HLA-DPB1-specific CD4+ T cell responses showing immunogenicity of all HLA-DPB1 alleles

Clinical studies have indicated that HLA-DPB1 functions as a classical transplantation antigen in allogeneic stem cell transplantation. Mismatching for HLA-DPB1 was associated with an increased risk of graft-versus-host disease (GVHD), but also a decreased risk of disease relapse. However, specific HLA-DPB1 mismatches were associated with poor clinical outcome. It was suggested that this unfavorable effect was caused by a difference in immunogenicity between HLA-DPB1 alleles. To analyze whether immunogenicity of HLA-DPB1 mismatches could be predicted based on the presence or absence of specific amino acid sequences we developed a model to generate allo-HLA-DPB1 responses in vitro. We tested in total 48 different stimulator/responder combinations by stimulating CD4(+) T cells from 5 HLA-DPB1 homozygous individuals with the same antigen-presenting cells transduced with different allo-HLA-DPB1 molecules. HLA-DPB1 molecules used for stimulation comprised 76% to 99% of HLA-DPB1 molecules present in different ethnic populations. We show that all HLA-DPB1 mismatches as defined by allele typing resulted in high-frequency immune responses. Furthermore, we show that crossrecognition of different HLA-DPB1 molecules is a broadly observed phenomenon. We confirm previously described patterns in crossrecognition, and demonstrate that a high degree in similarity between HLA-DPB1 molecules is predictive for crossrecognition, but not for immunogenicity.

Minor ABO-mismatches are risk factors for acute graft-versus-host disease in hematopoietic stem cell transplant patients

We investigated the impact of ABO and Rhesus (Rh) blood group matching on the outcome of hematopoietic stem cell transplantation (HSCT) of 154 patients matched at 10/10 HLA loci with unrelated donors. ABO and Rh, as potential risk factors, were modeled with the clinical outcome--acute and chronic graft-versus-host disease (aGVHD, cGVHD), relapse, treatment-related mortality (TRM), and overall survival (OS)--by simple, multiple, and competing risk analyses. We found that minor ABO-mismatches represent a significant risk factor for aGVHD (II-IV) with an estimated risk increase of almost 3-fold (hazard ratio [HR]=2.92, 95% confidence interval [CI]: 1.43-5.95, P=.003), and even 4-fold for aGVHD (III-IV) (HR=4.24, 95% CI: 1.70-10.56, P=.002), but not for other transplant endpoints. No significant association of the Rh matching status with any of the HSCT endpoints was seen. These results suggest that ABO minor mismatches may play a role in aGvHD pathophysiology, possibly by providing the setting for T cell activation and antibody mediated damage. To decrease the risk of aGVHD, ABO matching should be considered in HSCT.

Nonpermissive HLA-DPB1 disparity is a significant independent risk factor for mortality after unrelated hematopoietic stem cell transplantation

The importance of donor-recipient human leukocyte antigen (HLA)-DPB1 matching for the clinical outcome of unrelated hematopoietic stem cell transplantation (HSCT) is controversial. We have previously described an algorithm for nonpermissive HLA-DPB1 disparities involving HLA-DPB1*0901,*1001,*1701,*0301,*1401,*4501, based on T-cell alloreactivity patterns. By revisiting the immunogenicity of HLA-DPB1*02, a modified algorithm was developed and retrospectively tested in 621 unrelated HSCTs facilitated through the Italian Registry for oncohematologic adult patients. The modified algorithm proved to be markedly more predictive of outcome than the original one, with significantly higher Kaplan-Meier probabilities of 2-year survival in permissive compared with nonpermissive transplantations (55% vs 39%, P = .005). This was the result of increased adjusted hazards of nonrelapse mortality (hazard ratio [HR] = 1.74; confidence interval [CI], 1.19-2.53; P = .004) but not of relapse (HR = 1.02; CI, 0.73-1.42; P = .92). The increase in the hazards of overall mortality by nonpermissive HLA-DPB1 disparity was similar in 10 of 10 (HR = 2.12; CI, 1.23-3.64; P = .006) and 9 of 10 allele-matched transplantations (HR = 2.21; CI, 1.28-3.80; P = .004), both in early-stage and in advanced-stage disease. These data call for revisiting current HLA matching strategies for unrelated HSCT, suggesting that searches should be directed up-front toward identification of HLA-DPB1 permissive, 10 of 10 or 9 of 10 matched donors.