Alloresponses to HLA-DP detected in the primary MLR: correlation with a single amino acid difference

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.

The allogeneic HLA-DP-restricted T-cell repertoire provoked by allogeneic dendritic cells contains T cells that show restricted recognition of hematopoietic cells including primary malignant cells

Stem cell grafts from 10/10 HLA-matched unrelated donors are often mismatched for HLA-DP. In some patients, donor T-cell responses targeting the mismatched HLA-DP allele(s) have been found to induce a specific graft-versus-leukemia effect without coinciding graft-versus-host disease, whereas in other cases significant graft-versus-host disease occurred. Cell-lineage-specific recognition patterns within the allogeneic HLA-DP-specific donor T-cell repertoire could explain the differential clinical effects mediated by donor T cells after HLA-DP-mismatched allogeneic stem cell transplantation. To unravel the composition of the HLA-DP T-cell repertoire, donor T-cell responses were provoked by in vitro stimulation with allogeneic HLA-DP-mismatched monocyte-derived dendritic cells. A strategy including depletion of reactivity against autologous dendritic cells allowed efficient identification and enrichment of allo-reactive T cells upon stimulation with HLA-DP-mismatched dendritic cells. In this study we elucidated that the allogeneic HLA-DP-restricted T-cell repertoire contained T cells with differential cell-lineage-specific recognition profiles. As expected, some of the allogeneic HLA-DP-restricted T cells showed broad recognition of a variety of hematopoietic and non-hematopoietic cell types expressing the targeted mismatched HLA-DP allele. However, a significant proportion of the allogeneic HLA-DP-restricted T cells showed restricted recognition of hematopoietic cells, including primary malignant cells, or even restricted recognition of only myeloid cells, including dendritic cells and primary acute myeloid leukemia samples, but not of other hematopoietic and non-hematopoietic cell types. These data demonstrate that the allogeneic HLA-DP-specific T-cell repertoire contains T cells that show restricted recognition of hematopoietic cells, which may contribute to the specific graft-versus-leukemia effect without coinciding graft-versus-host disease.

Alloreactive T Cell Receptor Diversity against Structurally Similar or Dissimilar HLA-DP Antigens Assessed by Deep Sequencing

T cell alloreactivity is mediated by a self-human leukocyte antigen (HLA)-restricted T cell receptor (TCR) repertoire able to recognize both structurally similar and dissimilar allogeneic HLA molecules (i.e., differing by a single or several amino acids in their peptide-binding groove). We hypothesized that thymic selection on self-HLA molecules could have an indirect impact on the size and diversity of the alloreactive response. To test this possibility, we used TCR Vβ immunophenotyping and immunosequencing technology in a model of alloreactivity between self-HLA selected T cells and allogeneic HLA-DPB1 (DPB1) differing from self-DPB1*04:02 by a single (DPB1*02:01) or several (DPB1*09:01) amino acids in the peptide-binding groove. CD4+ T cells from three different self-DPB1*04:01,*04:02 individuals were stimulated with HeLa cells stably transduced with the relevant peptide processing machinery, co-stimulatory molecules, and HLA-DP. Flow cytometric quantification of the DPB1-specific T cell response measured as upregulation of the activation marker CD137 revealed significantly lower levels of alloreactivity against DPB1*02:01 compared with DPB1*09:01 (mean CD4+CD137+ frequency 35.2 ± 9.9 vs. 61.5 ± 7.7%, respectively, p < 0.0001). These quantitative differences were, however, not reflected by differences in the breadth of the alloreactive response at the Vβ level, with both alloantigens eliciting specific responses from all TCR-Vβ specificities tested by flow cytometry, albeit with higher levels of reactivity from most Vβ specificities against DPB1*09:01. In line with these observations, TCRB-CDR3 immunosequencing showed no significant differences in mean clonality of sorted CD137+CD4+ cells alloreactive against DPB1*02:01 or DPB1*09:01 [0.39 (0.36–0.45) and 0.39 (0.30–0.46), respectively], or in the cumulative frequencies of the 10 most frequent responding clones (55–67 and 58–62%, respectively). Most of the clones alloreactive against DPB1*02:01 (68.3%) or DPB1*09:01 (75.3%) were characterized by low-abundance (i.e., they were not appreciable among the pre-culture T cells). Interestingly, however, their cumulative frequency was lower against DPB1*02:01 compared with DPB1*09:01 (mean cumulative frequency 35.3 vs. 50.6%, respectively). Our data show that, despite lower levels of alloreactivity, a similar clonal diversity can be elicited by structurally similar compared with structurally dissimilar HLA-DPB1 alloantigens and demonstrate the power of TCRB immunosequencing in unraveling subtle qualitative changes not appreciable by conventional methods.

ATPase4A Autoreactivity and Its Association With Autoimmune Phenotypes in the Type 1 Diabetes Genetics Consortium Study

Autoantibodies targeting the H+/K+-ATPase proton pump of the gastric parietal cell (parietal cell antibodies [PCA]) are diagnostic of atrophic body gastritis (ABG) leading to pernicious anemia (PA). PCA, ABG, and PA occur in increased frequency in patients with type 1 diabetes and their relatives and are considered "minor" components of forms of autoimmune polyglandular syndrome (APS). A customized radioimmunoprecipitation assay was applied to 6,749 samples from the Type 1 Diabetes Genetics Consortium to measure ATP4A autoreactivity. Autoantibody prevalence was correlated with variants in HLA class II, PTPN22, and CTLA4 genes. With an ATP4A radioimmunoprecipitation assay, PCA were detected in sera from 20.9% of affected individuals. PCA prevalence increased with age and was greater in females (25.3%) than males (16.5%) and among Hispanics (36.3%) and blacks (26.2%) compared with non-Hispanic whites (20.8%) and Asians (16.7%). PCA and other organ-specific autoantibodies GAD65, IA-2, thyroid peroxidase (TPO), 21-hydroxylase (21-OH), and transglutaminase (TG) clustered within families with heritability estimates from 71 to 95%. PCA clustered with TPO, 21-OH, and persistent GAD65 autoantibodies but not with celiac (TG) or IA-2 autoantibodies. PCA-positive subjects showed an increased frequency of DRB1*0404, DPB1*0201, and PTPN22 R620W (rs2476601-T) and a decreased frequency of DRB1*0101, DPB1*0301, and CTLA4 CT60 (rs3087243-T). Genetic variants accounted for 4-5% of the heritable risk for PCA. The same alleles were associated with other autoantibody phenotypes in a consistent pattern. Whereas most of the heritable risk for PCA and other antibodies reflects genetic effects that are tissue specific, parietal cell autoimmunity is a major pathogenetic contributor in APS2.

Genetic variants in human leukocyte antigen-DP influence both hepatitis C virus persistence and hepatitis C virus F protein generation in the Chinese Han population

Chronic hepatitis C is a serious liver disease that often results in cirrhosis or hepatocellular carcinoma. The aim of this study was to assess the association of human leukocyte antigen-DP (HLA-DP) variants with risk of chronic hepatitis C virus (HCV) or anti-F antibody generation. We selected two single nucleotide polymorphisms (SNPs) in a region including HLA-DPA1 (rs3077) and HLA-DPB1 (rs9277534) and genotyped SNPs in 702 cases and 342 healthy controls from the Chinese population using TaqMan SNP genotyping assay. Moreover, the exon 2 of the HLA-DPA1 and HLA-DPB1 genes were amplified and determined by sequencing-based typing (SBT). The results showed that rs3077 significantly increased the risk of chronic HCV infection in additive models and dominant models (odds ratio (OR) = 1.32 and 1.53). The rs3077 also contributed to decrease the risk of anti-F antibody generation in additive models and dominant models (OR = 0.46 and 0.56). Subsequent analyses revealed the risk haplotypes (DPA1*0103-DPB1*0501 and DPA1*0103-DPB1*0201) and protective haplotypes (DPA1*0202-DPB1*0501 and DPA1*0202-DPB1*0202) to chronic HCV infection. Moreover, we also found that the haplotype of DPA1*0103-DPB1*0201 and DPA1*0202-DPB1*0202 were associated with the anti-F antibody generation. Our findings show that genetic variants in HLA-DP gene are associated with chronic HCV infection and anti-F antibody generation.

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.

Genetics of the HLA region in the prediction of type 1 diabetes

Type 1 diabetes (T1D) is one of the most widely studied complex genetic disorders, and the genes in HLA are reported to account for approximately 40-50% of the familial aggregation of T1D. The major genetic determinants of this disease are polymorphisms of class II HLA genes encoding DQ and DR. The DR-DQ haplotypes conferring the highest risk are DRB1*03:01-DQA1*05:01-DQB1*02:01 (abbreviated "DR3") and DRB1*04:01/02/04/05/08-DQA1*03:01-DQB1*03:02/04 (or DQB1*02; abbreviated "DR4"). The risk is much higher for the heterozygote formed by these two haplotypes (OR = 16.59; 95% CI, 13.7-20.1) than for either of the homozygotes (DR3/DR3, OR = 6.32; 95% CI, 5.12-7.80; DR4/DR4, OR = 5.68; 95% CI, 3.91). In addition, some haplotypes confer strong protection from disease, such as DRB1*15:01-DQA1*01:02-DQB1*06:02 (abbreviated "DR2"; OR = 0.03; 95% CI, 0.01-0.07). After adjusting for the genetic correlation with DR and DQ, significant associations can be seen for HLA class II DPB1 alleles, in particular, DPB1*04:02, DPB1*03:01, and DPB1*02:02. Outside of the class II region, the strongest susceptibility is conferred by class I allele B*39:06 (OR =10.31; 95% CI, 4.21-25.1) and other HLA-B alleles. In addition, several loci in the class III region are reported to be associated with T1D, as are some loci telomeric to class I. Not surprisingly, current approaches for the prediction of T1D in screening studies take advantage of genotyping HLA-DR and HLA-DQ loci, which is then combined with family history and screening for autoantibodies directed against islet-cell antigens. Inclusion of additional moderate HLA risk haplotypes may help identify the majority of children with T1D before the onset of the disease.

Evaluation of genetic susceptibility loci for chronic hepatitis B in Chinese: two independent case-control studies

Background

A recent genome-wide scan has identified two genetic variants in the HLA-DP region strongly associated with hepatitis B infection in Japanese. This study evaluates the effects of these risk variants in Chinese, where the HBV infection is the most popular in the world.

Methods and Findings

We have assessed the relationship between these two single nucleotide polymorphisms (rs3077 and rs9277535) and chronic hepatitis B infection in two independent case-control studies. The first population in Chinese Han included 736 patients and 782 spontaneously recovered controls. The second set was established in Chinese Zhuang minority of 177 patients and 208 controls. Both A alleles of rs3077 and rs9277535 significantly deceased the risk to CHB in Chinese Han (OR = 0.540, 95%CI: 0.464–0.628, P = 4.068×10⁻¹⁶ and OR = 0.696, 95%CI: 0.601–0.806, P = 1.062×10⁻⁶, respectively). Conceivably, rs9277535 was found to be associated with decreased risk of the disease in Chinese Zhuang, with an OR of 0.606 (95%CI, 0.441–0.833, P = 0.002).

Conclusion

Chronic hepatitis B susceptibility loci in HLA-DP region (rs3077 and rs9277535) identified by genome-wide scan in Japanese population were validated in Chinese population. These findings might provide clues to develop screening and surveillance strategies.

HLA DPA1, DPB1 alleles and haplotypes contribute to the risk associated with type 1 diabetes: analysis of the type 1 diabetes genetics consortium families

OBJECTIVE

To determine the relative risk associated with DPA1 and DPB1 alleles and haplotypes in type 1 diabetes.

RESEARCH DESIGN AND METHODS

The frequency of DPA1 and DPB1 alleles and haplotypes in type 1 diabetic patients was compared to the family based control frequency in 1,771 families directly and conditional on HLA (B)-DRB1-DQA1-DQB1 linkage disequilibrium. A relative predispositional analysis (RPA) was performed in the presence or absence of the primary HLA DR-DQ associations and the contribution of DP haplotype to individual DR-DQ haplotype risks examined.

RESULTS

Eight DPA1 and thirty-eight DPB1 alleles forming seventy-four DPA1-DPB1 haplotypes were observed; nineteen DPB1 alleles were associated with multiple DPA1 alleles. Following both analyses, type 1 diabetes susceptibility was significantly associated with DPB1*0301 (DPA1*0103-DPB1*0301) and protection with DPB1*0402 (DPA1*0103-DPB1*0402) and DPA1*0103-DPB1*0101 but not DPA1*0201-DPB1*0101. In addition, DPB1*0202 (DPA1*0103-DPB1*0202) and DPB1*0201 (DPA1*0103-DPB1*0201) were significantly associated with susceptibility in the presence of the high risk and protective DR-DQ haplotypes. Three associations (DPB1*0301, *0402, and *0202) remained statistically significant when only the extended HLA-A1-B8-DR3 haplotype was considered, suggesting that DPB1 alone may delineate the risk associated with this otherwise conserved haplotype.

CONCLUSIONS

HLA DP allelic and haplotypic diversity contributes significantly to the risk for type 1 diabetes; DPB1*0301 (DPA1*0103-DPB1*0301) is associated with susceptibility and DPB1*0402 (DPA1*0103-DPB1*0402) and DPA1*0103-DPB1*0101 with protection. Additional evidence is presented for the susceptibility association of DPB1*0202 (DPA1*0103-DPB1*0202) and for a contributory role of individual amino acids and DPA1 or a gene in linkage disequilibrium in DR3-DPB1*0101 positive haplotypes.

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.

The degree of matching at HLA-DPB1 predicts for acute graft-versus-host disease and disease relapse following haematopoietic stem cell transplantation

The importance of matching for HLA-DPB1 in unrelated donor haematopoietic stem cell (HSC) transplantation is little understood. Most transplant centres do not, currently, prospectively match for DPB1, but emerging data show that DPB1 matching does play a role in determining outcome. We studied the impact of HLA-DPB1 matching on outcome in 143 recipients of T-cell depletion transplants, who matched with their respective unrelated donors (allelic level) at HLA-A, -B, -C, -DRB1 and -DQB1. Of those matched at DPB1, 47.2% (17/36) developed acute graft-versus-host disease (aGvHD) as compared to 66.3% (55/83) of those who were mismatched. This led to a 19.1% (95% CI 0.1-38.3%) increase in the chance of developing aGvHD in mismatched patients (P=0.049). Relapse of the original disease occurred in 51 recipients; 23 of 37 (62%) matched at both DPB1 alleles, 28 of 82 (34%) were mismatched at one or two DPB1 alleles. Thus, there was a significantly higher relapse rate (P=0.0011) in transplant recipients who matched at both DPB1 alleles. In conclusion, a donor/recipient DPB1 match was associated with a significantly lower incidence of aGvHD and a significantly higher incidence of disease relapse. This study provides further evidence for an immunogenic role of HLA-DPB1 in HSC transplants.

HLA-DP4, the most frequent HLA II molecule, defines a new supertype of peptide-binding specificity

Among HLA-DP specificities, HLA-DP4 specificity involves at least two molecules, HLA-DPA1*0103/DPB1*0401 (DP401) and HLA-DPA1*0103/DPB1*0402 (DP402), which differ from each other by only three residues. Together, they are present worldwide at an allelic frequency of 20-60% and are the most abundant human HLA II alleles. Strikingly, the peptide-binding specificities of these molecules have never been investigated. Hence, in this study, we report the peptide-binding motifs of both molecules. We first set up a binding assay specific for the immunopurified HLA-DP4 molecules. Using multiple sets of synthetic peptides, we successfully defined the amino acid preferences of the anchor residues. With these assays, we were also able to identify new peptide ligands from allergens and viral and tumor Ags. DP401 and DP402 exhibit very similar patterns of recognition in agreement with molecular modeling of the complexes. Pockets P1 and P6 accommodate the main anchor residues and interestingly contain only two polymorphic residues, beta86 and beta11, respectively. Both positions are almost dimorphic and thus produce a limited number of pocket combinations. Taken together, our results support the existence of three main binding supertypes among HLA-DP molecules and should significantly contribute to the identification of universal epitopes to be used in peptide-based vaccines for cancer, as well as for allergic or infectious diseases.

DPB1 disparities contribute to severe GVHD and reduced patient survival after unrelated donor bone marrow transplantation

In order to evaluate the impact of HLA-DBP1 incompatibilities on the occurrence of acute graft-versus-host disease (GVHD) in unrelated hematopoietic cell transplantation, we studied 57 donor/recipient pairs characterized by their allelic identity for HLA-A, B, C, DRB1 and DQB1 and also for DRB3, 4, 5 loci and aimed to correlate DPB1 mismatches to already described risk factors for GVHD using multivariate Cox regression analysis. DPB1 identity between donor and recipient was observed in 24% and DPB1 compatibility (GVHD vector) in 42%. Two factors were independently associated with severe acute GVHD: two DP incompatibilities (RR = 8.25, 95% confidence interval (CI): 1.67-40.10, P = 0.010) and disease risk (RR = 10.23, 95% CI: 1.12-93.13, P = 0.012). Two DPB1 incompatibilities appeared also to be a factor in poorer survival independent of its effect on acute GVHD (RR = 4.97, 95% Cl: 1.80-13.71, P = 0.002). A correlation between acute GVHD and matching for each individual DPB1 polymorphic region and for residue 69 of the DP beta molecule, which seems to be a key residue in the alloimmune response, was not observed. Our data indicate that the outcome of unrelated hematopoietic cell transplantation in terms of GVHD but also survival, could be improved through HLA-DPB1 matching or at least by avoiding two DPB1 mismatches.

Improving the outcome of unrelated donor stem cell transplantation by molecular matching

Volunteer unrelated donor (VUD) stem cell transplantation is now a well-established procedure in the treatment for many haematological and other disorders. The improved success of this modality of treatment is related, in part, to the existence of large volunteer donor registries (with well characterized tissue typing), as well as to the improved understanding of the molecular factors that have an influence on transplantation outcome. It is clear that close attention to human leukocyte antigen (HLA) matching is essential in ensuring a satisfactory transplant outcome, however the extent to which donor-recipient pairs need to be matched is not yet clear. There is also an increased understanding that factors other than HLA do affect clinical outcome. The ability to perform high resolution molecular typing techniques has allowed researchers to begin assessing the significance of mismatches at particular loci against an otherwise matched background, and in this way highlight the effects of individual genetic factors on transplantation outcome.

HLA-DPA1 and DPB1 polymorphism in four Pacific Islands populations determined by sequencing based typing

Class II HLA-DP antigens are heterodimers comprised of alpha and beta chains coded by HLA-DPA1 and HLA-DPB1 genes. Both genes are polymorphic with substantial variation between different populations world wide. This work describes DPA1 and DPB1 polymorphism in four Pacific Island populations of Cook Islands, Samoa, Tokelau and Tonga, living in New Zealand. Using sequencing based typing four DPA1 alleles and twelve DPB1 alleles were observed in total among the four populations. There are two predominant DPA1 alleles DPA1*01031 and DPA1*02022 and three predominant DPB1 alleles DPB1*02012, DPB1*0401 and DPB1*0501. Fourteen DPA1-DPB1 haplotypes in total are present in these four populations with three predominant haplotypes: DPA1*02022-DPB1*0501, DPA1*01031-DPB1*02012, and DPA1*01031-DPB1*0401. Strong positive and negative disequilibrium was observed for individual DPA1-DPB1 haplotypes. Significant differences in DPA1 and DPB1 allele and haplotype frequencies were observed between Tokelauan and other three populations. Phylogenetic analysis of genetic distances between the four Pacific Island populations and other Asian Oceanian populations have shown that Cook Islanders, Samoans and Tongans are more closely related to Asian populations whereas Tokelauans cluster towards non-Austronesian populations of Papua New Guinea Highlanders and Australian Aborigines.

Polymorphism in the regulatory regions of the HLA-DPB1 gene

Nucleotide sequencing of approximately 400 basepairs upstream from exon 1 of the DPB1 gene and sequence specific oligonucleotide hybridisation identified eight nucleotide positions to be polymorphic which were in linkage disequilibrium (LD) with DPA1 and DPB1 alleles. Substitutions at two sites (-230 and -224) formed three genotypes (DP-PRO1-3). DP-PRO 1 was the most common genotype and was in LD with DPA1*0103, *0202 and DPB1*0401, *0501. DP-PRO 2 was observed in LD with DPB1*02012, *1601, *1701 and DPA1*0104. DP-PRO3 was in LD with DPB1*0901, *1001 and DPA1*0201. Electrophoretic Mobility Shift Assays (EMSA) performed with restriction enzyme fragments showed substitutions at -230 and -224 not to be involved in binding nuclear proteins. Six substitutions were found on a single genotype (DP-PRO4) which was observed in seven samples; 67% of DP-PRO4 inferred haplotypes were HLA-A2-B46, DRB1*0901, DQB1*03032, DPA1*0401, DPB1*1301. Three of the substitutions occurred in conserved regulatory region boxes, W', X and Y, and three in the signal and leader sequences. EMSA competitive binding assays performed with oligonucleotide probes for the substitutions showed no difference in binding affinity for W' and X probes. The DP-PRO4 Y box had a decreased nuclear protein binding affinity compared to DP-PRO1-3. Whether the sum of the differences in DP-PRO4 relate to a change in the cell surface expression of HLA-DP is yet to be determined.

Matching for HLA DPA1 and DPB1 alleles in unrelated bone marrow transplantation

The impact of donor-recipient DPA1 and DPB1 matching was examined in 122 unrelated bone marrow transplant pairs. All pairs were serologically matched at the time of transplantation for HLA class I and II and a majority also DRB1 allele matched. Retrospective A, B, C, DRB1, DQA1, DQB1 in addition to DPA1 and DPB1 allele matching was performed by molecular techniques. The percentage of pairs that were allele matched was as follows; HLA-A = 91% (n = 80), HLA-B = 94% (n = 80), HLA-C = 78% (n = 80), HLA-DRB1 = 96% (n = 122), HLA-DQA1 = 99% (n = 80), HLA-DQB1 = 92% (n = 122). 92 recipient/donor pairs with informative clinical data were available for analysis. DPA1 identity (no incompatibility in either direction) was observed in 57% and DPA1 compatibility in 76% of pairs with no apparent beneficial effect of matching on patient survival or Graft Versus Host Disease (GVHD). DPB1 identity was observed in 11% and compatibility in 27% of pairs. A significant improvement in patient survival was observed in DPB1 matched compared to one DPB1 mismatch (p < 0.01) and combined one and two DPB1 mismatched transplants (p = 0.03). This beneficial effect remained when allele mismatches at HLA-A, B, C, DRB1, DQA1, DQB1 were excluded (p = 0.05, p = 0.03, respectively). There was a significant association of increased frequency of severe GVHD (grades III-IV) compared to mild GVHD (grades I-II) with DPB1 mismatched transplants compared to DPB1 matched transplants (p = 0.04). In DPB1 mismatched transplants an association between patient survival and matching for individual DPB1 polymorphic regions was not observed; however in the HLA-A, B, DRB1, DQA1, DQB1 allele matched transplants a non significant increase in the frequency of Grade IV GVHD was observed in recipients who were negative compared to those who were positive for DPB1 alleles coding for glutamic acid at position 69.

HLA-DPbeta residue 69 plays a crucial role in allorecognition

To investigate the contribution to allorecognition of the individual polymorphic positions Glu 69 and Val 36 from the DPB1*02012 allele, DPB1*02012 cDNA was subjected to site-directed mutagenesis and alleles expressing Lys at 69 and Ala at 36 were generated. The lymphoblastoid cell line (LCL) 45.EM1, a previously generated mutant B-LCL which expresses normal levels of DPA mRNA but is not able to transcribe DPB, was transfected with wild-type or mutant DPB1*02012 cDNAs. The ability of two HLA-DPw2 alloreactive CD4+ cytotoxic T-lymphocyte (CTL) clones to lyse the panel of DPB1*02012 wild-type and site-directed mutant B-cell lines was tested. Both CTL clones (8.3 and 8.9) lysed the B-LCL 45.1, which is haploid for HLA and expresses wild-type DPB1*02012, and transfectants expressing Ala at 36 instead of Val, indicating that this polymorphic residue is not critical for T-cell recognition. However, the change of Glu to Lys at 69 prevented recognition by clones 8.3 and 8.9. These data demonstrate that the residue at peptide-binding position 69 is crucial for T-cell receptor recognition and suggest the requirement for a negatively charged residue at this position for allostimulation of these T-cell clones. The side chain of DPbeta-69 is predicted to point into the peptide-binding groove, and the existence of positive(Lys) or negative (Glu) residues probably leads to substantial differences in the allo- or auto-DP-bound peptides or to differences in the conformation of the peptide-MHC complex, which would therefore be responsible for specific DPw2 allorecognition. The binding of a panel of monomorphic and polymorphic anti-HLA-DP monoclonal antibodies (mAbs) to these transfectants was also tested by flow cytometry. The changes at Glu 69 and Val 36 did not affect recognition by any of the monomorphic antibodies tested. However, the binding pattern of some of the polymorphic mAbs was clearly modified. Therefore, even though it is not crucial for T-cell allorecognition, polymorphic residue 36 must be involved in epitopes recognized by some polymorphic anti-DP antibodies, while residue 69 of the DPB molecule is crucial both for T-cell allorecognition and recognition by some mAbs.