The importance of establishing genetic phase in clinical medicine.

Haplotyping or determination of genetic phase has always played a pivotal role in MHC (HLA studies) both in helping to understand inheritance patterns in diseases such as type 1 diabetes (T1D) and in ensuring better matching in transplantation scenarios such as haematopoietic stem cell transplantation (HSCT), using donors genetically related to the patient. In recent years the need to establish genetic phase in a number of clinical scenarios has become apparent. These include: Genetic phasing for hematopoietic stem cell transplants using unrelated donors, where the HLA haplotypes are not known but where haplotype-matched recipients fare better clinically than allele matched, but haplotype mismatched patients. The use of checkpoint inhibitors is one of the most innovative and exciting developments in cancer treatment in years. An example is the use of the monoclonal ipilimumab to block the CTLA-4 receptor which is known to contain polymorphic sites. Until the phase of these polymorphisms is known it will not be possible to determine how effectively this monoclonal will perform in individual patients. The role of miRNA single strand molecules and their effect on gene expression. Thousands of non-coding genes have been identified and have been shown to be polymorphic, as have their target genes. Genetic phasing of polymorphism both in the miRNA source genes and their targets is clearly a fertile area of research In areas such a drug metabolism where the polymorphic family of CYP genes is responsible for the metabolism of the majority of prescription drugs, determining phase of SNPs is critical to understanding drug metabolism and efficacy. In multigenic disease studies combinations of single nucleotide polymorphisms (SNPs) in participating genes require accurate phasing in order to fully appreciate their role in the disease process. In addition, the level of expression of genes (point 3) is also important in understanding disease processes at the functional level. This review outlines the techniques that are currently available for approximating phase and discusses the clinical relevance of establishing genetic phase in areas of clinical medicine outlined in points 1-3.

Human leukocyte antigen class I-restricted activation of CD8+ T cells provides the immunogenetic basis of a systemic drug hypersensitivity.

The basis for strong immunogenetic associations between particular human leukocyte antigen (HLA) class I allotypes and inflammatory conditions like Behçet's disease (HLA-B51) and ankylosing spondylitis (HLA-B27) remain mysterious. Recently, however, even stronger HLA associations are reported in drug hypersensitivities to the reverse-transcriptase inhibitor abacavir (HLA-B57), the gout prophylactic allopurinol (HLA-B58), and the antiepileptic carbamazepine (HLA-B*1502), providing a defined disease trigger and suggesting a general mechanism for these associations. We show that systemic reactions to abacavir were driven by drug-specific activation of cytokine-producing, cytotoxic CD8+ T cells. Recognition of abacavir required the transporter associated with antigen presentation and tapasin, was fixation sensitive, and was uniquely restricted by HLA-B*5701 and not closely related HLA allotypes with polymorphisms in the antigen-binding cleft. Hence, the strong association of HLA-B*5701 with abacavir hypersensitivity reflects specificity through creation of a unique ligand as well as HLA-restricted antigen presentation, suggesting a basis for the strong HLA class I-association with certain inflammatory disorders.

The effect of folinic acid on methylenetetrahydrofolate reductase polymorphisms in methotrexate-treated allogeneic hematopoietic stem cell transplants.

This study examined the contribution single nucleotide polymorphisms (SNPs) of the 5,10-methylenetetrahydrofolate reductase (MTHFR) gene have on clinical outcomes in hematopoietic stem cell transplant patients treated with the antiproliferative drug methotrexate. Two common SNPs, 677C>T and 1298A>C, were genotyped by polymerase chain reaction-restriction fragment-length polymorphism (PCR-RFLP) from samples obtained from patient DNA samples. Eleven clinical outcomes including survival and graft-versus-host disease (GVHD) were assessed against donor and recipient MTHFR genotypes against pretransplantation variables. Folinic acid (FA) as treatment for oral mucositis toxicity was used at investigator discretion in 72 of 140. Donor MTHFR 1298AA genotype was associated with decreased 5-year survival (P = .03) and event-free survival (EFS) (P = .02) in patients withheld FA. Donor MTHFR 677CC genotype was associated with earlier GVHD (P = .003), and more severe acute GVHD (P = 0.02). FA was significantly associated with decreased survival (P = 0.02) in patients given a donor MTHFR 677CT transplant. FA was significantly associated with decreased survival (P = .04), EFS (P = .009) in patients given a donor MTHFR 1298AC transplant MTHFR gene polymorphisms indicate a potentially useful gene for donor selection where more than one donor is available. Use of FA following transplantation should be reconsidered in the context of patient and donor MTHFR genotypes.

A naturally selected dimorphism within the HLA-B44 supertype alters class I structure, peptide repertoire, and T cell recognition.

HLA-B*4402 and B*4403 are naturally occurring MHC class I alleles that are both found at a high frequency in all human populations, and yet they only differ by one residue on the alpha2 helix (B*4402 Asp156-->B*4403 Leu156). CTLs discriminate between HLA-B*4402 and B*4403, and these allotypes stimulate strong mutual allogeneic responses reflecting their known barrier to hemopoeitic stem cell transplantation. Although HLA-B*4402 and B*4403 share >95% of their peptide repertoire, B*4403 presents more unique peptides than B*4402, consistent with the stronger T cell alloreactivity observed toward B*4403 compared with B*4402. Crystal structures of B*4402 and B*4403 show how the polymorphism at position 156 is completely buried and yet alters both the peptide and the heavy chain conformation, relaxing ligand selection by B*4403 compared with B*4402. Thus, the polymorphism between HLA-B*4402 and B*4403 modifies both peptide repertoire and T cell recognition, and is reflected in the paradoxically powerful alloreactivity that occurs across this "minimal" mismatch. The findings suggest that these closely related class I genes are maintained in diverse human populations through their differential impact on the selection of peptide ligands and the T cell repertoire.

Natural HLA class I polymorphism controls the pathway of antigen presentation and susceptibility to viral evasion.

HLA class I polymorphism creates diversity in epitope specificity and T cell repertoire. We show that HLA polymorphism also controls the choice of Ag presentation pathway. A single amino acid polymorphism that distinguishes HLA-B*4402 (Asp116) from B*4405 (Tyr116) permits B*4405 to constitutively acquire peptides without any detectable incorporation into the transporter associated with Ag presentation (TAP)-associated peptide loading complex even under conditions of extreme peptide starvation. This mode of peptide capture is less susceptible to viral interference than the conventional loading pathway used by HLA-B*4402 that involves assembly of class I molecules within the peptide loading complex. Thus, B*4402 and B*4405 are at opposite extremes of a natural spectrum in HLA class I dependence on the PLC for Ag presentation. These findings unveil a new layer of MHC polymorphism that affects the generic pathway of Ag loading, revealing an unsuspected evolutionary trade-off in selection for optimal HLA class I loading versus effective pathogen evasion.

HLA genotyping in the international Type 1 Diabetes Genetics Consortium.

BACKGROUND: Although human leukocyte antigen (HLA) DQ and DR loci appear to confer the strongest genetic risk for type 1 diabetes, more detailed information is required for other loci within the HLA region to understand causality and stratify additional risk factors. The Type 1 Diabetes Genetics Consortium (T1DGC) study design included high-resolution genotyping of HLA-A, B, C, DRB1, DQ, and DP loci in all affected sibling pair and trio families, and cases and controls, recruited from four networks worldwide, for analysis with clinical phenotypes and immunological markers. PURPOSE: In this article, we present the operational strategy of training, classification, reporting, and quality control of HLA genotyping in four laboratories on three continents over nearly 5 years. METHODS: Methods to standardize HLA genotyping at eight loci included: central training and initial certification testing; the use of uniform reagents, protocols, instrumentation, and software versions; an automated data transfer; and the use of standardized nomenclature and allele databases. We implemented a rigorous and consistent quality control process, reinforced by repeated workshops, yearly meetings, and telephone conferences. RESULTS: A total of 15,246 samples have been HLA genotyped at eight loci to four-digit resolution; an additional 6797 samples have been HLA genotyped at two loci. The genotyping repeat rate decreased significantly over time, with an estimated unresolved Mendelian inconsistency rate of 0.21%. Annual quality control exercises tested 2192 genotypes (4384 alleles) and achieved 99.82% intra-laboratory and 99.68% inter-laboratory concordances. LIMITATIONS: The chosen genotyping platform was unable to distinguish many allele combinations, which would require further multiple stepwise testing to resolve. For these combinations, a standard allele assignment was agreed upon, allowing further analysis if required. CONCLUSIONS: High-resolution HLA genotyping can be performed in multiple laboratories using standard equipment, reagents, protocols, software, and communication to produce consistent and reproducible data with minimal systematic error. Many of the strategies used in this study are generally applicable to other large multi-center studies.

Review article: Luminex technology for HLA antibody detection in organ transplantation.

Since its inception in the early 1960s, the serologically based complement-dependent cytotoxicity (CDC) assay has been the cornerstone technique for the detection of human leucocyte antigen (HLA) antibodies, not only in pre-transplant renal patients, but also in other forms of organ transplantation. Recently, solid phase assays have been developed and introduced for this purpose, and in particular the Flow-based bead assays such as the Luminex system. This latter assay has proved to be far more sensitive than the CDC assay and has revealed pre-sensitization in potential transplant recipients not detected by other methods of HLA antibody detection. However, the clinical implications of this increased sensitivity have not been convincingly demonstrated until recently. This technology for HLA antibody detection permits the evaluation of the clinical importance of antibodies directed at, for example, HLA-DPB1 and HLA-DQA1, which has not been possible to date. There are Luminex issues, however, requiring resolution such as the ability to distinguish between complement fixing and non-complement fixing antibodies and determination of their relative clinical significance. Luminex technology will permit a re-evaluation of the role of HLA antibodies in both early and late antibody-mediated rejection.

Human leukocyte antigen mismatch and other factors affecting cryopreserved allograft valve function.

The causes of cryopreserved allograft heart valve degeneration are poorly understood. We investigated HLA mismatch and other factors implicated in allograft valve degeneration. For this study we recruited 110 adult recipients of allograft heart valves who underwent surgery between June 1998 and March 2003 in the state of Victoria, Australia. Recipients and donors were HLA typed using serological and molecular methods. Valve function at most recent echocardiographic follow-up was examined for an association with the following variables using univariate and multivariate methods: HLA-A,-B, and -DR donor-recipient mismatch; HLA class I mismatch; total HLA mismatch; valve ischemic time; recipient age; donor age; ABO blood group donor-recipient match; and allograft size. Mean recipient age was 45 years (18-75 years), 75% were men. Seventy-four pulmonary (62 Ross procedure) and 36 aortic allografts were examined. Median valve ischemic time was 31 hours, range 20-48 hours. Echocardiographic follow-up was complete at a mean of 41 (+/-18) months, range 6-85 months. At univariate analysis longer ischemic time and younger recipient age were associated with valve dysfunction. HLA-A, -B, or DR mismatch, HLA class I mismatch, total HLA mismatch, donor age, ABO mismatch, and allograft size were not associated with valve dysfunction. Only younger recipient age remained significant at multivariate analysis. In conclusion, longer ischemic times and younger patient age predicted valve dysfunction at a mean of 3 years follow-up. Recipient age remained the strongest predictor of valve dysfunction. These results indicate that allograft ischemic times should be minimized.

Anti-HLA antibodies after cryopreserved allograft valve implantation does not predict valve dysfunction at three-year follow up.

BACKGROUND AND AIM OF THE STUDY: As the cause of allograft heart valve degeneration is poorly understood, the study aim was to investigate the host antibody response to allograft valve implantation. METHODS: Sera were obtained from 92 recipients of allograft heart valves (61 pulmonary, 31 aortic). Sera were tested for anti-HLA class I antibodies by ELISA and complement-dependent cytotoxicity (CDC) methods, and anti-HLA class II antibodies by ELISA. Specificities of recipient anti-HLA class I antibodies were defined by standard CDC testing against a panel of T lymphocytes from 80 blood donors. Donor valve HLA typing was performed on stored donor DNA samples using molecular methods. The presence of donor-specific anti-HLA class I antibodies was hence defined in recipient sera. The presence of anti-HLA antibodies and donor-specific anti-HLA class I antibodies were correlated with function of allograft valves at the most recent echocardiographic follow up. RESULTS: At a mean of 3.0 years (range: 0.3-5.4 years) after allograft implantation, 96% (87/92) and 82% (75/92) of patients were positive for anti-HLA class I and II antibodies, respectively, by ELISA testing. Some 68% (61/90) of patients were positive for anti-HLA class I antibody (PRA > 5%) by CDC testing. PRA levels decreased with greater postoperative interval (r = -0.31, p = 0.003). In 68 recipients where donor HLA type was defined, 54% (37/68) of patients had antibodies specific to at least one donor HLA class I antigen. In 87 patients with a recent echocardiographic examination available for analysis (at a mean of 3.5 +/- 1.6 years postoperatively), there was no association between valve dysfunction and antibody status. CONCLUSION: Anti-HLA class I and II antibodies were detected by ELISA methods in most patients after allograft implantation extending to 5.4 years. The clinical significance of these findings is unclear, as no correlation was found between the prevalence of anti-HLA antibody and echocardiographic parameters of valve dysfunction at a mean of 3.5 years follow up.

Detection of HLA Antibodies in Organ Transplant Recipients - Triumphs and Challenges of the Solid Phase Bead Assay.

This review outlines the development of human leukocyte antigen (HLA) antibody detection assays and their use in organ transplantation in both antibody screening and crossmatching. The development of sensitive solid phase assays such as the enzyme-linked immunosorbent assay technique, and in particular the bead-based technology has revolutionized this field over the last 10-15 years. This revolution however has created a new paradigm in clinical decision making with respect to the detection of low level pretransplant HLA sensitization and its clinical relevance. The relative sensitivities of the assays used are discussed and the relevance of conflicting inter-assay results. Each assay has its advantages and disadvantages and these are discussed. Over the last decade, the bead-based assay utilizing the Luminex® fluorocytometer instrument has become established as the "gold standard" for HLA antibody testing. However, there are still unresolved issues surrounding this technique, such as the presence of denatured HLA molecules on the beads which reveal cryptic epitopes and the issue of appropriate fluorescence cut off values for positivity. The assay has been modified to detect complement binding (CB) in addition to non-complement binding (NCB) HLA antibodies although the clinical relevance of the CB and NCB IgG isotypes is not fully resolved. The increase sensitivity of the Luminex® bead assay over the complement-dependent cytotoxicity crossmatch has permitted the concept of the "virtual crossmatch" whereby the crossmatch is predicted to a high degree of accuracy based on the HLA antibody specificities detected by the solid phase assay. Dialog between clinicians and laboratory staff on an individual patient basis is essential for correct clinical decision making based on HLA antibody results obtained by the various techniques.

Haplotyping the human leukocyte antigen system from single chromosomes.

We describe a method for determining the parental HLA haplotypes of a single individual without recourse to conventional segregation genetics. Blood samples were cultured to identify and sort chromosome 6 by bivariate flow cytometry. Single chromosome 6 amplification products were confirmed with a single nucleotide polymorphism (SNP) array and verified by deep sequencing to enable assignment of both alleles at the HLA loci, defining the two haplotypes. This study exemplifies a rapid and efficient method of haplotyping that can be applied to any chromosome pair, or indeed all chromosome pairs, using a single sorting operation. The method represents a cost-effective approach to complete phasing of SNPs, which will facilitate a deeper understanding of the links between SNPs, gene regulation and protein function.

Allocation of cadaver donor kidneys in Australia.

The national allocation of kidneys in Australia is based on a combination of human leukocyte antigen (HLA) matching and equity factors designed to make transplantation accessible to as many patients as possible. A points system has been designed that deducts points for HLA mismatches but adds points for factors such as levels of HLA sensitization, waiting time on dialysis, and a loading for pediatric patients. Kidneys that do not reach the level of matching required for national allocation are transplanted in the donor state using both matching and waiting time criteria, which caters to minority groups with rare HLA types.

Closer association of IA-2 humoral autoreactivity with HLA DR3/4 than DQB1*0201/*0302 in Korean T1D patients.

The HLA DQB1*0302 allele on DR4 haplotypes is a well-known marker for T1D susceptibility. The contribution of this DQ molecule to overall disease susceptibility may be genotype dependent. On Asian DR4 haplotypes, not only DQB1*0302, but also DQB1*0401 confer susceptibility to T1D, which is mediated by DRB1*0405 on the same haplotype. To analyze further the association of DQB1*0302 and DQB1*0401 haplotypes in Asian patients with T1D, we investigated HLA DR and DQ alleles with the presence or the persistence of GAD, ICA, and IA-2 autoantibodies in 121 Korean T1D patients. In Korean patients, there was an association of IA-2 autoantibodies with DR4 as well as DR3, but not with DQA1*0301-DQB1*0302. GAD autoantibodies were not associated with the DR3-DQB1*0201, DQA1*0301-DQB1*0302, or DR4. In this low-risk population, autoantibodies to islet-cell antigens were associated with different HLA molecules. In different populations, the immune response to different beta cell autoantigens is mediated via varying HLA class II molecules from different loci. Design of the antigen-specific immunointervention trials should take into account such HLA DR and DQ association.

Consensus guidelines on the testing and clinical management issues associated with HLA and non-HLA antibodies in transplantation.

BACKGROUND: The introduction of solid-phase immunoassay (SPI) technology for the detection and characterization of human leukocyte antigen (HLA) antibodies in transplantation while providing greater sensitivity than was obtainable by complement-dependent lymphocytotoxicity (CDC) assays has resulted in a new paradigm with respect to the interpretation of donor-specific antibodies (DSA). Although the SPI assay performed on the Luminex instrument (hereafter referred to as the Luminex assay), in particular, has permitted the detection of antibodies not detectable by CDC, the clinical significance of these antibodies is incompletely understood. Nevertheless, the detection of these antibodies has led to changes in the clinical management of sensitized patients. In addition, SPI testing raises technical issues that require resolution and careful consideration when interpreting antibody results. METHODS: With this background, The Transplantation Society convened a group of laboratory and clinical experts in the field of transplantation to prepare a consensus report and make recommendations on the use of this new technology based on both published evidence and expert opinion. Three working groups were formed to address (a) the technical issues with respect to the use of this technology, (b) the interpretation of pretransplantation antibody testing in the context of various clinical settings and organ transplant types (kidney, heart, lung, liver, pancreas, intestinal, and islet cells), and (c) the application of antibody testing in the posttransplantation setting. The three groups were established in November 2011 and convened for a "Consensus Conference on Antibodies in Transplantation" in Rome, Italy, in May 2012. The deliberations of the three groups meeting independently and then together are the bases for this report. RESULTS: A comprehensive list of recommendations was prepared by each group. A summary of the key recommendations follows. Technical Group: (a) SPI must be used for the detection of pretransplantation HLA antibodies in solid organ transplant recipients and, in particular, the use of the single-antigen bead assay to detect antibodies to HLA loci, such as Cw, DQA, DPA, and DPB, which are not readily detected by other methods. (b) The use of SPI for antibody detection should be supplemented with cell-based assays to examine the correlations between the two types of assays and to establish the likelihood of a positive crossmatch (XM). (c) There must be an awareness of the technical factors that can influence the results and their clinical interpretation when using the Luminex bead technology, such as variation in antigen density and the presence of denatured antigen on the beads. Pretransplantation Group: (a) Risk categories should be established based on the antibody and the XM results obtained. (b) DSA detected by CDC and a positive XM should be avoided due to their strong association with antibody-mediated rejection and graft loss. (c) A renal transplantation can be performed in the absence of a prospective XM if single-antigen bead screening for antibodies to all class I and II HLA loci is negative. This decision, however, needs to be taken in agreement with local clinical programs and the relevant regulatory bodies. (d) The presence of DSA HLA antibodies should be avoided in heart and lung transplantation and considered a risk factor for liver, intestinal, and islet cell transplantation. Posttransplantation Group: (a) High-risk patients (i.e., desensitized or DSA positive/XM negative) should be monitored by measurement of DSA and protocol biopsies in the first 3 months after transplantation. (b) Intermediate-risk patients (history of DSA but currently negative) should be monitored for DSA within the first month. If DSA is present, a biopsy should be performed. (c) Low-risk patients (nonsensitized first transplantation) should be screened for DSA at least once 3 to 12 months after transplantation. If DSA is detected, a biopsy should be performed. In all three categories, the recommendations for subsequent treatment are based on the biopsy results. CONCLUSIONS: A comprehensive list of recommendations is provided covering the technical and pretransplantation and posttransplantation monitoring of HLA antibodies in solid organ transplantation. The recommendations are intended to provide state-of-the-art guidance in the use and clinical application of recently developed methods for HLA antibody detection when used in conjunction with traditional methods.

The ever-expanding list of HLA alleles: changing HLA nomenclature and its relevance to clinical transplantation.

Since the discovery of the HLA system 51 years ago, both the techniques for the detection of HLA antigens and the method of nomenclature for cataloguing them have changed dramatically. Initially serology was the sole technological tool available to describe the polymorphism of the class 1 and later the class 2 loci. Numbers were assigned to antigens as they were described and as serologic techniques that improved "subtypes" of the original antigens were described. With sequencing of HLA alleles, further polymorphisms were described, and it became evident that the degree of polymorphism was much greater than had hitherto been realized. Sequence differences were detected between alleles, which did not appear to provoke antibody responses but were clearly recognized by responding T cells. A new method of nomenclature was devised, which assigned 2 sets of numbers to each allele. The first 2 numbers indicated the serologic group to which the allele belonged, whereas the second set of 2 numbers was assigned in a numerical progression as each new allele was described. In addition, letters were introduced at the end of each allele where they were known to be nonexpressed or have low levels of cell expression. The limitation of this system is that it only caters for 99 alleles in each serologic group, and this has now been exceeded in some cases. The World Health Organization Nomenclature Committee for factors of the HLA system introduced a modification of the current nomenclature in April 2010 which uses colons to separate the numbers that has the effect of delimiting the number of alleles, which can be assigned to each serologic group. Due to the extensive polymorphism of the HLA genes, sequencing frequently results in ambiguous combinations of alleles and also "strings" of possible alleles due to polymorphisms in nonsequenced gene locations. The reporting in such instances has been simplified to some extent by the introduction of a lettering system to indicate a particular "string." The nomenclature of the HLA system can be confusing to those outside the HLA scientific community. It is important, however, that physicians, particularly those involved in transplantation, have a working knowledge of the nomenclature. It is important in solid organ transplantation in terms of interpreting the relevance of HLA antibodies in cases where there are clear demonstrations in patients of allele-specific antibodies. It is critical in hematopoietic stem cell transplantation where allele level matching is imperative and where decisions have to be made regarding the likelihood of possible sequence mismatches and the clinical relevance of nonexpression or low expression of HLA allelic products.

Quantitative and functional diversity of cross-reactive EBV-specific CD8+ T cells in a longitudinal study cohort of lung transplant recipients.

BACKGROUND: Cross-reactive antiviral memory T cells constitute a significant proportion of the alloresponse, potentially playing a pivotal role in adverse posttransplant outcomes in human leukocyte antigen (HLA)-mismatched allografts. We explored the longitudinal dynamics of cross-reactive HLA-B8-restricted Epstein-Barr virus-specific CD8+ T cells directed toward the EBNA3A epitope FLRGRAYGL (FLR) in lung transplant recipients (LTRs) to determine whether their corecognition of HLA-B*4402 expressed on the allograft contributed to poorer posttransplant outcomes. METHODS: Cross-reactive FLR-specific CD8+ T cells were measured in the peripheral blood mononuclear cells and bronchoalveolar lavage fluid in 11 HLA-B8+ LTR, who had received HLA-B44+ lung allograft, after in vitro autologous (FLR pulsed) or allogeneic stimulation by multiparameter flow cytometry. RESULTS: FLR-specific CD8+ T cells were detectable ex vivo and after 13 days following in vitro peptide stimulation of peripheral blood mononuclear cells. Individual LTR and demonstrated diverse functional profiles of either cytokine production and/or cytotoxic potential (interferon-g+, interferon-g+CD107a+ and CD107a+ subsets). However, cells isolated from bronchoalveolar lavage exhibited a skewed functional phenotype toward CD107a expression alone, indicating cytotoxic-producing but not cytokine-producing capabilities. In addition, our findings suggested that the presence of cross-reactive FLR-specific CD8+ T cells may influence the alloreactive hierarchy directed against the allograft, although they were not associated with poorer short- or long-term clinical outcomes in the absence of Epstein-Barr virus reactivation and in the setting of current immunosuppression and antiviral prophylaxis protocols. CONCLUSION: We report, for the first time, the longitudinal measurement of cross-reactive FLR-specific CD8 T cells within a clinical transplantation framework.

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.

A polymorphism in the HLA-DPB1 gene is associated with susceptibility to multiple sclerosis.

We conducted an association study across the human leukocyte antigen (HLA) complex to identify loci associated with multiple sclerosis (MS). Comparing 1927 SNPs in 1618 MS cases and 3413 controls of European ancestry, we identified seven SNPs that were independently associated with MS conditional on the others (each P ≤ 4 x 10(-6)). All associations were significant in an independent replication cohort of 2212 cases and 2251 controls (P ≤ 0.001) and were highly significant in the combined dataset (P ≤ 6 x 10(-8)). The associated SNPs included proxies for HLA-DRB1*15:01 and HLA-DRB1*03:01, and SNPs in moderate linkage disequilibrium (LD) with HLA-A*02:01, HLA-DRB1*04:01 and HLA-DRB1*13:03. We also found a strong association with rs9277535 in the class II gene HLA-DPB1 (discovery set P = 9 x 10(-9), replication set P = 7 x 10(-4), combined P = 2 x 10(-10)). HLA-DPB1 is located centromeric of the more commonly typed class II genes HLA-DRB1, -DQA1 and -DQB1. It is separated from these genes by a recombination hotspot, and the association is not affected by conditioning on genotypes at DRB1, DQA1 and DQB1. Hence rs9277535 represents an independent MS-susceptibility locus of genome-wide significance. It is correlated with the HLA-DPB1*03:01 allele, which has been implicated previously in MS in smaller studies. Further genotyping in large datasets is required to confirm and resolve this association.