Reference Grade Characterization of Polymorphisms in Full-Length HLA Class I and II Genes With Short-Read Sequencing on the ION PGM System and Long-Reads Generated by Single Molecule, Real-Time Sequencing on the PacBio Platform

HLA Genetics for the Human Diseases

Highly polymorphic human leukocyte antigen (HLA) molecules (alleles) expressed by different classical HLA class I and class II genes have crucial roles in the regulation of innate and adaptive immune responses, transplant rejection and in the pathogenesis of numerous infectious and autoimmune diseases. To date, over 35,000 HLA alleles have been published from the IPD-IMGT/HLA database, and specific HLA alleles and HLA haplotypes have been reported to be associated with more than 100 different diseases and phenotypes. Next generation sequencing (NGS) technology developed in recent years has provided breakthroughs in various HLA genomic/gene studies and transplant medicine. In this chapter, we review the current information on the HLA genomic structure and polymorphisms, as well as the genetic context in which numerous disease associations have been identified in this region.

HLA/MHC and KIR characterization in humans and non-human primates using Oxford Nanopore Technologies and Pacific Biosciences sequencing platforms

The gene products of the HLA/MHC and KIR multigene families are important modulators of the immune system and are associated with health and disease. Characterization of the genes encoding these receptors has been integrated into different biomedical applications, including transplantation and reproduction biology, immune therapies and in fundamental research into disease susceptibility or resistance. Conventional short-read sequencing strategies have shown their value in high throughput typing, but are insufficient to uncover the entire complexity of the highly polymorphic HLA/MHC and KIR gene systems. The implementation of single-molecule and real-time sequencing platforms, offered by Pacific Biosciences (PacBio) and Oxford Nanopore Technologies (ONT), revolutionized the fields of genomics and transcriptomics. Using fundamentally distinct principles, these platforms generate long-read data that can unwire the plasticity of the HLA/MHC and KIR genes, including high-resolution characterization of genes, alleles, phased haplotypes, transcription levels and epigenetics modification patterns. These insights might have profound clinical relevance, such as improved matching of donors and patients in clinical transplantation, but could also lift disease association studies to a higher level. Even more, a comprehensive characterization may refine animal models in preclinical studies. In this review, the different HLA/MHC and KIR characterization approaches using PacBio and ONT platforms are described and discussed.

Human leukocyte antigen super-locus: nexus of genomic supergenes, SNPs, indels, transcripts, and haplotypes

The human Major Histocompatibility Complex (MHC) or Human Leukocyte Antigen (HLA) super-locus is a highly polymorphic genomic region that encodes more than 140 coding genes including the transplantation and immune regulatory molecules. It receives special attention for genetic investigation because of its important role in the regulation of innate and adaptive immune responses and its strong association with numerous infectious and/or autoimmune diseases. In recent years, MHC genotyping and haplotyping using Sanger sequencing and next-generation sequencing (NGS) methods have produced many hundreds of genomic sequences of the HLA super-locus for comparative studies of the genetic architecture and diversity between the same and different haplotypes. In this special issue on 'The Current Landscape of HLA Genomics and Genetics', we provide a short review of some of the recent analytical developments used to investigate the SNP polymorphisms, structural variants (indels), transcription and haplotypes of the HLA super-locus. This review highlights the importance of using reference cell-lines, population studies, and NGS methods to improve and update our understanding of the mechanisms, architectural structures and combinations of human MHC genomic alleles (SNPs and indels) that better define and characterise haplotypes and their association with various phenotypes and diseases.

Sequence Variations Within HLA-G and HLA-F Genomic Segments at the Human Leukocyte Antigen Telomeric End Associated With Acute Graft-Versus-Host Disease in Unrelated Bone Marrow Transplantation

Acute graft-versus-host disease (aGVHD) is defined as a syndrome of an immunological response of graft to the host that occurs early after allogeneic hematopoietic stem cell transplantation (HCT). This disease is frequently observed even in HCT matched for human leukocyte antigen (HLA) alleles at multiple gene loci. Although the HLA region represents complex and diverse genomic characteristics, detailed association analysis is required for the identification of uncharacterized variants that are strongly associated with aGVHD. We genotyped three loci, OR2H2, HLA-F-AS1, and HLA-G, that are located in the 460 kb of HLA telomeric region and statistically analyzed the genotypes including HLA-DPB1 with clinical and transplantation outcomes using 338 unrelated bone marrow transplantation (UR-BMT) patient–donor pairs who were matched for HLA-A, HLA-B, HLA-C, HLA-DRB1, and HLA-DQB1 (HLA-10/10). Multivariate analyses demonstrated that HLA-F-AS1 and HLA-DPB1 mismatches were associated with grade II–IV aGVHD (hazard ratio (HR), 1.76; 95% CI, 1.07–2.88; p = 0.026; and HR, 1.59; CI, 1.02–2.49; p = 0.042, respectively). There was no confounding between HLA-F-AS1 and HLA-DPB1 (p = 0.512), suggesting that the HLA-F-AS1 mismatch has a strong effect on aGVHD independently of HLA-DPB1. Moreover, a stratified analysis suggested possible associations of HLA-F-AS1, HLA-DPB1, and/or HLA-G mismatches with grade II–IV aGVHD and the more severe grade III–IV aGVHD. These findings provide new insights into understanding the molecular mechanism of aGVHD caused by HLA-matched UR-BMT.

A novel swab storage gel is superior to dry swab DNA collection, and enables long-range high resolution NGS HLA typing from buccal cell samples

HLA sequence-based DNA typing (SBT) by long-range PCR amplification (LR PCR) and next-generation sequencing (NGS) is a high-throughput DNA sequencing method (LR-NGS-SBT) for the efficient and sensitive detection of novel and null HLA alleles to the field-4 level of allelic resolution without phase ambiguity. However, the accuracy and reliability of the HLA typing results using buccal cells (BCs) and saliva as genetic source materials for the LR-NGS-SBT method are dependent largely on the quality of the extracted genomic DNA (gDNA) because a large degree of gDNA fragmentation can result in insufficient PCR amplification with the incorrect assignment of HLA alleles due to allele dropouts. In this study, we developed a new cost-efficient swab storage gel (SSG) for wet swab collection of BCs (BC-SSG) and evaluated its usefulness by performing different DNA analytical parameters including LR-NGS-SBT to compare the quality and quantity of gDNA extracted from BCs (in SSG or air dried), blood and saliva of 30 subjects. The BC-SSG samples after 5 days of storage revealed qualitative and quantitative DNA values equivalent to that of blood and/or saliva and better than swabs that were only air-dried (BC-nSSG). Moreover, all the gDNA extracted from blood, saliva and BC-SSG samples were HLA-typed successfully to an equivalent total of 408 alleles for each sample type. Therefore, the application of BC-SSG collection media for LR-NGS-SBT has benefits over BC dried samples (dry swabs) such as reducing retesting and the number of untestable BC samples due to insufficient DNA amplification. This article is protected by copyright. All rights reserved.

Haplotype structures and polymorphisms of dog leukocyte antigen (DLA) class I loci shaped by intralocus and interlocus recombination events

The dog leukocyte antigen (DLA) class I genomic region is located on chromosome 12, and the class I genomic region is composed of at least two distinct haplotypic gene structures, DLA-88-DLA-12 and DLA-88-DLA-88L. However, detailed information of the genomic differences among DLA-88, DLA-12, and DLA-88L are still lacking at the full-length gene level, and therefore, DLA allelic sequences classified for each of these loci are limited in number so far. In this study, we determined the DNA sequence of a 95-kb DLA class I genomic region including DLA-88, DLA-12/88L, and DLA-64 with three DLA homozygous dogs and of 37 full-length allelic gene sequences for DLA-88 and DLA-12/88L loci in 26 DLA class I homozygous dogs. Nucleotide diversity profiles of the 95-kb regions and sequence identity scores of the allelic sequences suggested that DLA-88L is a hybrid gene generated by interlocus and/or intralocus gene conversion between DLA-88 and DLA-12. The putative minimum conversion tract was estimated to be at least an 850-bp segment in length located from the 5´flanking untranslated region to the end of intron 2. In addition, at least one DLA-12 allele (DLA-12*004:01) was newly generated by interlocus gene conversion. In conclusion, the analysis for the occurrence of gene conversion within the dog DLA class I region revealed intralocus gene conversion tracts in 17 of 27 DLA-88 alleles and two of 10 DLA-12 alleles, suggesting that intralocus gene conversion has played an important role in expanding DLA allelic variations.

Clinical Characteristics and Outcome Analysis for HLA Loss Patients Following Partially Mismatched Related Donor Transplantation Using HLA Chimerism for Loss of Heterozygosity Analysis by Next-Generation Sequencing

Genomic loss of mismatched human leukocyte antigen (HLA loss) is one of the most vital immune escape mechanisms of leukemic cells after allogeneic hematopoietic stem cell transplantation (allo-HSCT). However, the methods currently used for HLA loss analysis have some shortcomings. Limited literature has been published, especially in lymphoid malignancies. This study aims to evaluate the incidences, risk factors of HLA loss, and clinical outcomes of HLA loss patients. In all, 160 patients undergoing partially mismatched related donor (MMRD) transplantation from 18 centers in China were selected for HLA loss analysis with the next-generation sequencing (NGS)-based method, which was validated by HLA-KMR. Variables of the prognostic risk factors for HLA loss or HLA loss–related relapse were identified with the logistic regression or the Fine and Gray regression model. An HLA loss detection system, HLA-CLN [HLA chimerism for loss of heterozygosity (LOH) analysis by NGS], was successfully developed. Forty (25.0%) patients with HLA loss were reported, including 27 with myeloid and 13 with lymphoid malignancies. Surprisingly, 6 of those 40 patients did not relapse. The 2-year cumulative incidences of HLA loss (22.7% vs 22.0%, P = 0.731) and HLA loss–related relapse (18.4% vs 20.0%, P = 0.616) were similar between patients with myeloid and lymphoid malignancies. The number of HLA mismatches (5/10 vs <5/10) was significantly associated with HLA loss in the whole cohort [odds ratio (OR): 3.15, P = 0.021] and patients with myeloid malignancies (OR: 3.94, P = 0.021). A higher refined-disease risk index (OR: 6.91, P = 0.033) and donor–recipient ABO incompatibility (OR: 4.58, P = 0.057) contributed to HLA loss in lymphoid malignancies. To sum up, HLA-CLN could overcome the limitations of HLA-KMR and achieve a better HLA coverage for more patients. The clinical characteristics and outcomes were similar in patients with HLA loss between myeloid and lymphoid malignancies. In addition, the results suggested that a patient with HLA loss might not always relapse.

Aminipila luticellarii sp. nov., an anaerobic bacterium isolated from the pit mud of strong aromatic Chinese liquor, and emended description of the genus Aminipila

A novel mesophilic, aerotolerant anaerobic bacterium, designated JN-18^T, was isolated from the pit mud of a strong aromatic Chinese liquor. According to a 16S rRNA gene sequence analysis, it had the highest sequence similarity to Aminipila butyrica DSM 103574^T (95.69%). The G+C content of its genomic DNA was 43.39 mol%. The cells were Gram-stain-negative, slightly curved rods with flagella. Optimum growth was observed at 37 °C, pH 6.5 and without extra addition of NaCl. Strain JN-18^Tutilized amino acids (l-alanine, l-arginine, l-asparagine, l-lysine, l-methionine, l-serine and l-threonine), malate and pyruvate, and used l-arginine and l-lysine to produce acetate, butyrate, H₂, and CO₂. The major cellular fatty acids of strain JN-18^T were C_14:0, C_16:0 DMA and C_18:1 cis-9 DMA. The carbohydrate composition of the cell wall predominantly included galactose, glucose and rhamnose. Based on its phylogenetic, phenotypic, physiological and biochemical characteristics, strain JN-18^T was classified as a representative of a novel species within the genus Aminipila, for which the name Aminipila luticellarii sp. nov. is proposed. The type strain is JN-18^T (=CCAM 412^T=JCM 39126^T).

Haplotype Shuffling and Dimorphic Transposable Elements in the Human Extended Major Histocompatibility Complex Class II Region

The major histocompatibility complex (MHC) on chromosome 6p21 is one of the most single-nucleotide polymorphism (SNP)-dense regions of the human genome and a prime model for the study and understanding of conserved sequence polymorphisms and structural diversity of ancestral haplotypes/conserved extended haplotypes. This study aimed to follow up on a previous analysis of the MHC class I region by using the same set of 95 MHC haplotype sequences downloaded from a publicly available BioProject database at the National Center for Biotechnology Information to identify and characterize the polymorphic human leukocyte antigen (HLA)-class II genes, the MTCO3P1 pseudogene alleles, the indels of transposable elements as haplotypic lineage markers, and SNP-density crossover (XO) loci at haplotype junctions in DNA sequence alignments of different haplotypes across the extended class II region (∼1 Mb) from the telomeric PRRT1 gene in class III to the COL11A2 gene at the centromeric end of class II. We identified 42 haplotypic indels (20 Alu, 7 SVA, 13 LTR or MERs, and 2 indels composed of a mosaic of different transposable elements) linked to particular HLA-class II alleles. Comparative sequence analyses of 136 haplotype pairs revealed 98 unique XO sites between SNP-poor and SNP-rich genomic segments with considerable haplotype shuffling located in the proximity of putative recombination hotspots. The majority of XO sites occurred across various regions including in the vicinity of MTCO3P1 between HLA-DQB1 and HLA-DQB3, between HLA-DQB2 and HLA-DOB, between DOB and TAP2, and between HLA-DOA and HLA-DPA1, where most XOs were within a HERVK22 sequence. We also determined the genomic positions of the PRDM9-recombination suppression sequence motif ATCCATG/CATGGAT and the PRDM9 recombination activation partial binding motif CCTCCCCT/AGGGGAG in the class II region of the human reference genome (NC_ 000006) relative to published meiotic recombination positions. Both the recombination and anti-recombination PRDM9 binding motifs were widely distributed throughout the class II genomic regions with 50% or more found within repeat elements; the anti-recombination motifs were found mostly in L1 fragmented repeats. This study shows substantial haplotype shuffling between different polymorphic blocks and confirms the presence of numerous putative ancestral recombination sites across the class II region between various HLA class II genes.

Challenges in the application of NGS in the clinical laboratory

Next-generation sequencing (NGS), also known as massively parallel sequencing, has revolutionized genomic research. The current advances in NGS technology make it possible to provide high resolution, high throughput HLA typing in clinical laboratories. The focus of this review is on the recent development and implementation of NGS in clinical laboratories. Here, we examine the critical role of NGS technologies in clinical immunology for HLA genotyping. Two major NGS platforms (Illumina and Ion Torrent) are characterized including NGS library preparation, data analysis, and validation. Challenges of NGS implementation in the clinical laboratory are also discussed, including sequencing error rate, bioinformatics, result interpretation, analytic sensitivity, as well as large data storage. This review aims to promote the broader applications of NGS technology in clinical laboratories and advocate for the novel applications of NGS to drive future research.

Genetic risk factors for autoimmune hepatitis: implications for phenotypic heterogeneity and biomarkers for drug response

Autoimmune hepatitis (AIH) is a rare chronic progressive liver disease with autoimmune features. It mainly affects middle-aged women. AIH is occasionally complicated with liver cirrhosis that worsens the prognosis. Genetic and environmental factors are involved in the pathogenesis of AIH. Genetic studies of other diseases have been revealing of pathogenesis and drug efficacy. In this review, we summarize the genetic risk factors for AIH, including human leukocyte antigen (HLA) and non-HLA genes. A genome-wide association study (GWAS) on European AIH revealed the strongest associations to be with single nucleotide variants (SNVs) in HLA. Predisposing alleles for AIH were DRB1*03:01 and DRB1*04:01 in Europeans; DRB1*04:04, DRB1*04:05, and DRB1*13:01 in Latin Americans; and DRB1*04:01 and DRB1*04:05 in Japanese. Other risk SNVs in non-HLA genes for AIH were found by a candidate gene approach, but several SNVs were confirmed in replication studies. Some genetic factors of AIH overlapped with those of other autoimmune diseases. Larger-scale GWASs of other ethnic groups are required. The results of genetic studies might provide an explanation for the phenotypic heterogeneity of AIH and biomarkers for drug responses.

Review on Databases and Bioinformatic Approaches on Pharmacogenomics of Adverse Drug Reactions

Pharmacogenomics has been used effectively in studying adverse drug reactions by determining the person-specific genetic factors associated with individual response to a drug. Current approaches have revealed the significant importance of sequencing technologies and sequence analysis strategies for interpreting the contribution of genetic variation in developing adverse reactions. Advance in next generation sequencing and platform brings new opportunities in validating the genetic candidates in certain reactions, and could be used to develop the preemptive tests to predict the outcome of the variation in a personal response to a drug. With the highly accumulated available data recently, the in silico approach with data analysis and modeling plays as other important alternatives which significantly support the final decisions in the transformation from research to clinical applications such as diagnosis and treatments for various types of adverse responses.

Probably Correct: Rescuing Repeats with Short and Long Reads

Ever since the introduction of high-throughput sequencing following the human genome project, assembling short reads into a reference of sufficient quality posed a significant problem as a large portion of the human genome-estimated 50-69%-is repetitive. As a result, a sizable proportion of sequencing reads is multi-mapping, i.e., without a unique placement in the genome. The two key parameters for whether or not a read is multi-mapping are the read length and genome complexity. Long reads are now able to span difficult, heterochromatic regions, including full centromeres, and characterize chromosomes from "telomere to telomere". Moreover, identical reads or repeat arrays can be differentiated based on their epigenetic marks, such as methylation patterns, aiding in the assembly process. This is despite the fact that long reads still contain a modest percentage of sequencing errors, disorienting the aligners and assemblers both in accuracy and speed. Here, I review the proposed and implemented solutions to the repeat resolution and the multi-mapping read problem, as well as the downstream consequences of reference choice, repeat masking, and proper representation of sex chromosomes. I also consider the forthcoming challenges and solutions with regards to long reads, where we expect the shift from the problem of repeat localization within a single individual to the problem of repeat positioning within pangenomes.

A Novel Framework for Characterizing Genomic Haplotype Diversity in the Human Immunoglobulin Heavy Chain Locus

An incomplete ascertainment of genetic variation within the highly polymorphic immunoglobulin heavy chain locus (IGH) has hindered our ability to define genetic factors that influence antibody-mediated processes. Due to locus complexity, standard high-throughput approaches have failed to accurately and comprehensively capture IGH polymorphism. As a result, the locus has only been fully characterized two times, severely limiting our knowledge of human IGH diversity. Here, we combine targeted long-read sequencing with a novel bioinformatics tool, IGenotyper, to fully characterize IGH variation in a haplotype-specific manner. We apply this approach to eight human samples, including a haploid cell line and two mother-father-child trios, and demonstrate the ability to generate high-quality assemblies (>98% complete and >99% accurate), genotypes, and gene annotations, identifying 2 novel structural variants and 15 novel IGH alleles. We show multiplexing allows for scaling of the approach without impacting data quality, and that our genotype call sets are more accurate than short-read (>35% increase in true positives and >97% decrease in false-positives) and array/imputation-based datasets. This framework establishes a desperately needed foundation for leveraging IG genomic data to study population-level variation in antibody-mediated immunity, critical for bettering our understanding of disease risk, and responses to vaccines and therapeutics.

Capturing Differential Allele-Level Expression and Genotypes of All Classical HLA Loci and Haplotypes by a New Capture RNA-Seq Method

The highly polymorphic human major histocompatibility complex (MHC) also known as the human leukocyte antigen (HLA) encodes class I and II genes that are the cornerstone of the adaptive immune system. Their unique diversity (>25,000 alleles) might affect the outcome of any transplant, infection, and susceptibility to autoimmune diseases. The recent rapid development of new next-generation sequencing (NGS) methods provides the opportunity to study the influence/correlation of this high level of HLA diversity on allele expression levels in health and disease. Here, we describe the NGS capture RNA-Seq method that we developed for genotyping all 12 classical HLA loci (HLA-A, HLA-B, HLA-C, HLA-DPA1, HLA-DPB1, HLA-DQA1, HLA-DQB1, HLA-DRA, HLA-DRB1, HLA-DRB3, HLA-DRB4, and HLA-DRB5) and assessing their allelic imbalance by quantifying their allele RNA levels. This is a target enrichment method where total RNA is converted to a sequencing-ready complementary DNA (cDNA) library and hybridized to a complex pool of RNA-specific HLA biotinylated oligonucleotide capture probes, prior to NGS. This method was applied to 161 peripheral blood mononuclear cells and 48 umbilical cord blood cells of healthy donors. The differential allelic expression of 10 HLA loci (except for HLA-DRA and HLA-DPA1) showed strong significant differences (P < 2.1 × 10-15). The results were corroborated by independent methods. This newly developed NGS method could be applied to a wide range of biological and medical questions including graft rejections and HLA-related diseases.

Highly accurate mtGenome haplotypes from long-read SMRT sequencing can distinguish between monozygotic twins

Discriminating between monozygotic twins (MZ) remains a challenge in the field of forensics globally. It is very difficult to find sequence variants within MZ twins, despite using ultra-deep next generation sequencing (NGS) for nuclear DNA. However, mitochondrial DNA might be a potential marker owing to its higher mutation rate and easier sequencing via NGS. Here, we aimed to introduce a long-read single molecule real-time sequencing (SMRT) strategy, with better continuity and fewer alignment errors, to obtain more accurate mitochondrial genome (mtGenome) sequence on the Sequel platform. Compared to Ion Torrent Personal Genome Machine (PGM), the long-read SMRT sequencing strategy generated highly accurate and mapped circular consensus sequence (CCS) reads and exhibited robust performance in terms of reliable repeatability, consistent coverage pattern, and balanced strands in mtGenome recovery. Moreover, the long-read SMRT strategy exhibited superior ability to not only identify accurate haplotypes but also discover a total of 785 low-level variants within 16 MZ twin pairs with threshold of 2% and 20 CCS reads with Q30 quality. Taken together, our findings suggested the long-read SMRT technology as an appreciable strategy for obtaining accurate mitotypes and providing a promising solution for distinguishing between MZ twin pairs in forensic genetics.

Genome-Wide Association Study of Lean Nonalcoholic Fatty Liver Disease Suggests Human Leukocyte Antigen as a Novel Candidate Locus

Nonalcoholic fatty liver disease (NAFLD) is supposed to manifest its metabolic phenotype in the liver, but it is common to have lean individuals diagnosed with NAFLD, known as lean NAFLD. We conducted a two-stage analysis to identify NAFLD-associated loci in Japanese patients. In stage I, 275 metabolically healthy normal-weight patients with NAFLD were compared with 1,411 non-NAFLD controls adjusted for age, sex, and alcohol consumption by a genome-wide association study (GWAS). In stage II, human leukocyte antigen (HLA) in chromosome 6 (chr6) (P = 6.73E-08), microRNA (MIR) MIR548F3 in chr7 (P = 4.25E-07), myosin light chain 2 (MYL2) in chr12 (P = 4.39E-07), and glycoprotein precursor (GPC)6 in chr13 (P = 5.43E-07), as suggested by the GWAS, were assessed by single nucleotide polymorphism (SNP) association analysis of whole NAFLD against non-NAFLD in 9,726 members of the general population. A minor allele of the secondary lead SNP in chr6, rs2076529, was significantly associated (odds ratio [OR], 1.19; 95% confidence interval [CI], 1.11-1.28; P = 2.10E-06) and the lead SNP in chr7 was weakly associated (OR 1.15; 95% CI, 1.04-1.27; P = 6.19E-03) with increased NAFLD risk. Imputation-based typing of HLA showed a significant difference in the distribution of HLA-B, HLA-DR-beta chain 1 (DRB1), and HLA-DQ-beta chain 1 (DQB1) alleles in lean NAFLD GWAS. Next-generation sequence-based typing of HLA in 5,649 members of the general population replicated the significant difference of HLA-B allele distribution and the significant increase of the HLA-B*54:01 allele in whole NAFLD. Fecal metagenomic analysis of 3,420 members of the general population showed significant dissimilarity in beta-diversity analysis of rs2076529 and HLA-B*54:01 allele carriers from noncarriers. Veillonellaceae was increased but Verrucomicrobia was decreased in rs2076529 minor allele and HLA-B*54:01 allele carriers as in NAFLD. Conclusion: HLA was identified as a novel locus associated with NAFLD susceptibility, which might be affected by the alteration of gut microbiota.

Defining Blood Group Gene Reference Alleles by Long-Read Sequencing: Proof of Concept in the ACKR1 Gene Encoding the Duffy Antigens

Background

In the novel era of blood group genomics, (re-)defining reference gene/allele sequences of blood group genes has become an important goal to achieve, both for diagnostic and research purposes. As novel potent sequencing technologies are available, we thought to investigate the variability encountered in the three most common alleles of ACKR1, the gene encoding the clinically relevant Duffy antigens, at the haplotype level by a long-read sequencing approach.

Materials and Methods

After long-range PCR amplification spanning the whole ACKR1 gene locus (∼2.5 kilobases), amplicons generated from 81 samples with known genotypes were sequenced in a single read by using the Pacific Biosciences (PacBio) single molecule, real-time (SMRT) sequencing technology.

Results

High-quality sequencing reads were obtained for the 162 alleles (accuracy >0.999). Twenty-two nucleotide variations reported in databases were identified, defining 19 haplotypes: four, eight, and seven haplotypes in 46 ACKR1*01, 63 ACKR1*02, and 53 ACKR1*02N.01 alleles, respectively.

Discussion

Overall, we have defined a subset of reference alleles by third-generation (long-read) sequencing. This technology, which provides a "longitudinal" overview of the loci of interest (several thousand base pairs) and is complementary to the second-generation (short-read) next-generation sequencing technology, is of critical interest for resolving novel, rare, and null alleles.

Identification of HLA-A*02:06:01 as the primary disease susceptibility HLA allele in cold medicine-related Stevens-Johnson syndrome with severe ocular complications by high-resolution NGS-based HLA typing

Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are life-threatening acute inflammatory vesiculobullous reactions of the skin and mucous membranes. These severe cutaneous drug reactions are known to be caused by inciting drugs and infectious agents. Previously, we have reported the association of HLA-A*02:06 and HLA-B*44:03 with cold medicine (CM)-related SJS/TEN with severe ocular complications (SOCs) in the Japanese population. However, the conventional HLA typing method (PCR-SSOP) sometimes has ambiguity in the final HLA allele determination. In this study, we performed HLA-disease association studies in CM-SJS/TEN with SOCs at 3- or 4-field level. 120 CM-SJS/TEN patients with SOCs and 817 Japanese healthy controls are HLA genotyped using the high-resolution next-generation sequencing (NGS)-based HLA typing of HLA class I genes, including HLA-A, HLA-B, and HLA-C. Among the alleles of HLA class I genes, HLA-A*02:06:01 was strongly associated with susceptibility to CM-SJS/TEN (p = 1.15 × 10⁻¹⁸, odds ratio = 5.46). Four other alleles (HLA-A*24:02:01, HLA-B*52:01:01, HLA-B*46:01:01, and HLA-C*12:02:02) also demonstrated significant associations. HLA haplotype analyses indicated that HLA-A*02:06:01 is primarily associated with susceptibility to CM-SJS/TEN with SOCs. Notably, there were no specific disease-causing rare variants among the high-risk HLA alleles. This study highlights the importance of higher resolution HLA typing in the study of disease susceptibility, which may help to elucidate the pathogenesis of CM-SJS/TEN with SOCs.

Bioinformatics Strategies, Challenges, and Opportunities for Next Generation Sequencing-Based HLA Genotyping

The advent of next generation sequencing (NGS) has altered the face of genotyping the human leukocyte antigen (HLA) system in clinical, stem cell donor registry, and research contexts. NGS has led to a dramatically increased sequencing throughput at high accuracy, while being more time and cost efficient than precursor technologies. This has led to a broader and deeper profiling of the key genes in the human immunogenetic make-up. The rapid evolution of sequencing technologies is evidenced by the development of varied short-read sequencing platforms with differing read lengths and sequencing capacities to long-read sequencing platforms capable of profiling full genes without fragmentation. Concomitantly, there has been development of a diverse set of computational analyses and software tools developed to deal with the various strengths and limitations of the sequencing data generated by the different sequencing platforms. This review surveys the different modalities involved in generating NGS HLA profiling sequence data. It systematically describes various computational approaches that have been developed to achieve HLA genotyping to different degrees of resolution. At each stage, this review enumerates the drawbacks and advantages of each of the platforms and analysis approaches, thus providing a comprehensive picture of the current state of HLA genotyping technologies.

HLA class I allele lineages and haplotype frequencies in Arabs of the United Arab Emirates

The high degree of polymorphism of the HLA system provides suitable genetic markers to study the diversity and migration of different world populations and is beneficial for forensic identification, anthropology, transplantation and disease associations. Although the United Arab Emirates (UAE) population of about nine million people is heterogeneous, information is limited for the HLA class I allele and haplotype frequencies of the Bedouin ethnic group. We performed low-resolution PCR-SSP genotyping of three HLA class I loci at HLA-A, -B and -C for 95 unrelated healthy Bedouins from the cities of Al Ain and Abu Dhabi in the UAE. A total of 54 HLA allele lineages were detected; the most frequent low-resolution allele lineages at each HLA locus were A*02 (0.268), B*51 (0.163) and C*07 (0.216). The inferred estimates for the two most frequent HLA-A and HLA-B haplotypes were HLA-A*02 ~ HLA-B*50 (0.070) and HLA-A*02 ~ HLA-B*51 (0.051), and the most frequent 3-locus haplotype was HLA-A*02 ~ HLA-B*50 ~ HLA-C*06 (0.068). The HLA allele lineage frequencies of the UAE Arabs were compared to those previously reported for 70 other world populations, and a strong genetic similarity was detected between the UAE Arabs and the Saudi Arabians from the west with evidence of a limited gene flow between the UAE Arabs and Pakistani across the Gulf from the east, and the UAE Arabs and Omani from the south of the Gulf Peninsula.