HLA-genotyping of clinical specimens using Ion Torrent-based NGS

Phenomic landscape and pharmacogenomic implications for HLA region in a Taiwan Han Chinese population

BACKGROUND

The human leukocyte antigen (HLA) genes, exhibiting significant genetic diversity, are associated with susceptibility to various clinical diseases and diverse in drug responses. High costs of HLA sequencing and the population-specific architecture of this genetic region necessitate the establishment of a population-specific HLA imputation reference panel. Moreover, there is a lack of understanding about the genetic and phenotypic landscape of HLA variations within the Taiwanese population.

METHODS

We created models for a Taiwanese-specific HLA imputation reference panel. These models were trained with the array genotype data and HLA sequencing data from 845 Taiwanese subjects. HLA imputation was applied for 59,448 Taiwanese subjects to characterize the HLA allele and haplotype frequencies. Additionally, a phenome-wide association study (PheWAS) was conducted to identify the phenotypes associated with HLA variations. The association of the biallelic HLA variants with the binary and quantitative traits were evaluated with additive logistic and linear regression models, respectively. Furthermore, an omnibus test with likelihood-ratio test was applied for each HLA amino acid position in the multiallelic HLA amino acid polymorphisms to compare the difference between a fitted model and a null model following a χ2 distribution of n-1 degree of freedom at a position with n residues. Finally, we estimated the prevalence of adverse drug reactions (ADR)-related HLA alleles in the Taiwanese population.

RESULTS

In this study, the reference panel models displayed remarkable accuracy, with averages of 99.3%, 98.9%, and 99.1% for 2-, 4-, 6-digit alleles of the eight classical HLA genes, respectively. For PheWAS, a total of 18,136 significant associations with HLA variants across 26 phenotypes are identified (p < 5×10-8), highlighting the pleiotropy feature of the HLA region. Among the independent signals, 15 are novel, including the association of HLA-B pos 138 variation with ankylosing spondylitis (AS), and rs9266290 and rs9266292 with allergy. Through an analysis spanning the entire HLA region, we identified clusters of phenotype correlations. Finally, the carriers of pharmacogenomic related HLA alleles, including HLA-C*01:02 (35.86%), HLA-B*58:01 (20.9%), and HLA-B*15:02 (8.38%), were characterized in the Taiwanese general population.

CONCLUSIONS

We successfully delivered the HLA imputation for 59,448 Taiwanese subjects and characterized the genetic and phenotypic landscapes of the HLA variations. In addition, we quantified the estimated prevalence of the ADR-related HLA alleles in the Taiwanese population. The developed HLA imputation reference panel could be used for estimation of population HLA allele frequencies, which can facilitate further studies in the role of HLA variants in a wider range of phenotypes in the population.

Advancements in HLA Typing Techniques and Their Impact on Transplantation Medicine

HLA typing serves as a standard practice in hematopoietic stem cell transplantation to ensure compatibility between donors and recipients, preventing the occurrence of allograft rejection and graft-versus-host disease. Conventional laboratory methods that have been widely employed in the past few years, including sequence-specific primer PCR and sequencing-based typing (SBT), currently face the risk of becoming obsolete. This risk stems not only from the extensive diversity within HLA genes but also from the rapid advancement of next-generation sequencing and third-generation sequencing technologies. Third-generation sequencing systems like single-molecule real-time (SMRT) sequencing and Oxford Nanopore (ONT) sequencing have the capability to analyze long-read sequences that span entire intronic-exonic regions of HLA genes, effectively addressing challenges related to HLA ambiguity and the phasing of multiple short-read fragments. The growing dominance of these advanced sequencers in HLA typing is expected to solidify further through ongoing refinements, cost reduction, and error rate minimization. This review focuses on hematopoietic stem cell transplantation (HSCT) and explores prospective advancements and application of HLA DNA typing techniques. It explores how the adoption of third-generation sequencing technologies can revolutionize the field by offering improved accuracy, reduced ambiguity, and enhanced assessment of compatibility in HSCT. Embracing these cutting-edge technologies is essential to advancing the success rates and outcomes of hematopoietic stem cell transplantation. This review underscores the importance of staying at the forefront of HLA typing techniques to ensure the best possible outcomes for patients undergoing HSCT.

The Genetics of Primary Biliary Cholangitis: A GWAS and Post-GWAS Update

Primary biliary cholangitis (PBC) is a chronic, progressive cholestatic liver disease in which the small intrahepatic bile ducts are destroyed by autoimmune reactions. Among autoimmune diseases, which are polygenic complex traits caused by the combined contribution of genetic and environmental factors, PBC exhibits the strongest involvement of genetic heritability in disease development. As at December 2022, genome-wide association studies (GWASs) and associated meta-analyses identified approximately 70 PBC susceptibility gene loci in various populations, including those of European and East Asian descent. However, the molecular mechanisms through which these susceptibility loci affect the pathogenesis of PBC are not fully understood. This study provides an overview of current data regarding the genetic factors of PBC as well as post-GWAS approaches to identifying primary functional variants and effector genes in disease-susceptibility loci. Possible mechanisms of these genetic factors in the development of PBC are also discussed, focusing on four major disease pathways identified by in silico gene set analyses, namely, (1) antigen presentation by human leukocyte antigens, (2) interleukin-12-related pathways, (3) cellular responses to tumor necrosis factor, and (4) B cell activation, maturation, and differentiation pathways.

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.

Recent Advances of Human Leukocyte Antigen (HLA) Typing Technology Based on High-Throughput Sequencing

The major histocompatibility complex (MHC) in humans is a genetic region consisting of cell surface proteins located on the short arm of chromosome 6. This is also known as the human leukocyte antigen (HLA) region. The HLA region consists of genes that exhibit complex genetic polymorphisms, and are extensively involved in immune responses. Each individual has a unique set of HLAs. Donor-recipient HLA allele matching is an important factor for organ transplantation. Therefore, an established rapid and accurate HLA typing technology is instrumental to preventing graft-verses-host disease (GVHD) in organ recipients. As of recent, high-throughput sequencing has allowed for an increase read length and higher accuracy and throughput, thus achieving complete and high-resolution full-length typing. With more advanced nanotechnology used in high-throughput sequencing, HLA typing is more widely used in third-generation single-molecule sequencing. This review article summarizes some of the most widely used sequencing typing platforms and evaluates the latest developments in HLA typing kits and their clinical applications.

HLA Class I Molecules as Immune Checkpoints for NK Cell Alloreactivity and Anti-Viral Immunity in Kidney Transplantation

Natural killer (NK) cells are innate lymphocytes that can kill diseased- or virally-infected cells, mediate antibody dependent cytotoxicity and produce type I immune-associated cytokines upon activation. NK cells also contribute to the allo-immune response upon kidney transplantation either by promoting allograft rejection through lysis of cells of the transplanted organ or by promoting alloreactive T cells. In addition, they protect against viral infections upon transplantation which may be especially relevant in patients receiving high dose immune suppression. NK cell activation is tightly regulated through the integrated balance of signaling via inhibitory- and activating receptors. HLA class I molecules are critical regulators of NK cell activation through the interaction with inhibitory- as well as activating NK cell receptors, hence, HLA molecules act as critical immune checkpoints for NK cells. In the current review, we evaluate how NK cell alloreactivity and anti-viral immunity are regulated by NK cell receptors belonging to the KIR family and interacting with classical HLA class I molecules, or by NKG2A/C and LILRB1/KIR2DL4 engaging non-classical HLA-E or -G. In addition, we provide an overview of the methods to determine genetic variation in these receptors and their HLA ligands.

Cataloguing experimentally confirmed 80.7 kb-long ACKR1 haplotypes from the 1000 Genomes Project database

Background

Clinically effective and safe genotyping relies on correct reference sequences, often represented by haplotypes. The 1000 Genomes Project recorded individual genotypes across 26 different populations and, using computerized genotype phasing, reported haplotype data. In contrast, we identified long reference sequences by analyzing the homozygous genomic regions in this online database, a concept that has rarely been reported since next generation sequencing data became available.

Study design and methods

Phased genotype data for a 80.6 kb region of chromosome 1 was downloaded for all 2,504 unrelated individuals of the 1000 Genome Project Phase 3 cohort. The data was centered on the ACKR1 gene and bordered by the CADM3 and FCER1A genes. Individuals with heterozygosity at a single site or with complete homozygosity allowed unambiguous assignment of an ACKR1 haplotype. A computer algorithm was developed for extracting these haplotypes from the 1000 Genome Project in an automated fashion. A manual analysis validated the data extracted by the algorithm.

Results

We confirmed 902 ACKR1 haplotypes of varying lengths, the longest at 80,584 nucleotides and shortest at 1,901 nucleotides. The combined length of haplotype sequences comprised 19,895,388 nucleotides with a median of 16,014 nucleotides. Based on our approach, all haplotypes can be considered experimentally confirmed and not affected by the known errors of computerized genotype phasing.

Conclusions

Tracts of homozygosity can provide definitive reference sequences for any gene. They are particularly useful when observed in unrelated individuals of large scale sequence databases. As a proof of principle, we explored the 1000 Genomes Project database for ACKR1 gene data and mined long haplotypes. These haplotypes are useful for high throughput analysis with next generation sequencing. Our approach is scalable, using automated bioinformatics tools, and can be applied to any gene.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12859-021-04169-6.

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.

High-resolution HLA typing by long reads from the R10.3 Oxford nanopore flow cells

Nanopore sequencing has been investigated as a rapid and cost-efficient option for HLA typing in recent years. Despite the lower raw read accuracy, encouraging typing accuracy has been reported, and long reads from the platform offer additional benefits of the improved phasing of distant variants. The newly released R10.3 flow cells are expected to provide higher read-level accuracy than previous chemistries. We examined the performance of R10.3 flow cells on the MinION device in HLA typing after enrichment of target genes by multiplexed PCR. We also aimed to mimic a 1-day workflow with 8-24 samples per sequencing run. A diverse collection of 102 unique samples were typed for HLA-A, -B, -C, -DPA1, -DPB1, -DQA1, -DQB1, -DRB1, -DRB3/4/5 loci. The concordance rates at 2-field and 3-field resolutions were 99.5% (1836 alleles) and 99.3% (1710 alleles). We also report important quality metrics from these sequencing runs. Continued research and independent validations are warranted to increase the robustness of nanopore-based HLA typing for broad clinical application.

A long road/read to rapid high-resolution HLA typing: The nanopore perspective

Next-generation sequencing (NGS) has been widely adopted for clinical HLA typing and advanced immunogenetics researches. Current methodologies still face challenges in resolving cis-trans ambiguity involving distant variant positions, and the turnaround time is affected by testing volume and batching. Nanopore sequencing may become a promising addition to the existing options for HLA typing. The technology delivered by the MinION sequencer of Oxford Nanopore Technologies (ONT) can record the ionic current changes during the translocation of DNA/RNA strands through transmembrane pores and translate the signals to sequence reads. It features simple and flexible library preparations, long sequencing reads, portable and affordable sequencing devices, and rapid, real-time sequencing. However, the error rate of the sequencing reads is high and remains a hurdle for its broad application. This review article will provide a brief overview of this technology and then focus on the opportunities and challenges of using nanopore sequencing for high-resolution HLA typing and immunogenetics research.

Performance of a multiplexed amplicon-based next-generation sequencing assay for HLA typing

BACKGROUND

Next-generation sequencing (NGS) has enabled efficient high-resolution typing of human leukocyte antigen (HLA) genes with minimal ambiguity. Most commercially available assays amplify individual or subgroup of HLA genes by long-range PCR followed by library preparation and sequencing. The AllType assay simplifies the workflow by amplifying 11 transplant-relevant HLA genes in one PCR reaction. Here, we report the performance of this unique workflow evaluated using 218 genetically diverse samples.

METHODS

Five whole genes (HLA-A/B/C/DQA1/DPA1) and six near-whole genes (HLA-DRB1/DRB345/DQB1/DPB1; excluding exon 1 and part of intron 1) were amplified in a multiplexed, long-range PCR. Manual library preparation was performed per manufacturer's protocol, followed by template preparation and chip loading on the Ion Chef, and sequencing on the Ion S5 sequencer. Pre-specified rules for quality control and repeat testing were followed; technologists were blinded to the reference results. The concordance between AllType and reference results was determined at 2-field resolution. We also describe the ranges of input DNA and library concentrations, read number per sample and per locus, and key health metrics in relation to typing results.

RESULTS

The concordance rates were 98.6%, 99.8% and 99.9% at the sample (n = 218), genotype (n = 1688), and allele (n = 3376) levels, respectively. Three genotypes were discordant, all of which shared the same G group typing results with the reference. Most ambiguous genotypes (116 out of 144, 80.6%) were due to the lack of exon 1 and intron 1 coverage for HLA-DRB1/DRB345/DQB1/DPB1 genes. A broad range of input DNA concentrations and library concentrations were tolerated. Per sample read numbers were adequate for accurate genotyping. Per locus read numbers showed some inter-lot variations, and a trend toward improved inter-locus balance was observed with later lots of reagents.

CONCLUSION

The AllType assay on the Ion Chef/Ion S5 platform offers a robust and efficient workflow for clinical HLA typing at the 2-field resolution. The multiplex PCR strategy simplifies the laboratory procedure without compromising the typing accuracy.

Next-generation sequencing of HLA: validation and identification of new polymorphisms in a Brazilian population

BACKGROUND

Next-generation sequencing (NGS) is the most modern sequencing technique that has revolutionized HLA typing, providing high-resolution results with low ambiguity rates. This study aimed to show the experiences and challenges of an HLA laboratory in the validation process of the NGS methodology for HLA typing and show the use of this method for the study of HLA genetic diversity.

METHODS

We used 115 samples that comprised a comprehensive testing panel for validation of the NGS methodology using the AllType kit (One Lambda, Canoga Park, California) on the Ion Torrent S5 NGS platform. All quality metrics were analyzed. During validation, two new HLA sequences were identified and named by the HLA Nomenclature Committee.

RESULTS

A total of 1380 alleles from the HLA-A, -B, -C, -DRB1, -DQB1, and -DPB1 loci were examined by NGS. This validation panel provided a wide range of HLA sequence variations, including non-CWD HLA alleles, new variants, and homozygous alleles. The concordance rate with Sanger sequencing-based typing was 100.0% for HLA-A, -B, -C, -DRB1, -DQB1, and 99.93% for HLA-DPB1. The newly identified HLA alleles were HLA-B*14:69N and HLA-DQB1*02:145.

CONCLUSION

We have successfully validated NGS HLA typing despite numerous challenges, contributing to the identification of novel alleles that impact on HLA matching and antibody evaluation in organ and tissue transplantation.

Rapid High-Resolution Typing of Class I HLA Genes by Nanopore Sequencing

Nanopore sequencing, enabled initially by the MinION device from Oxford Nanopore Technologies (ONT), is the only technology that offers portable, single-molecule sequencing and ultralong reads. The technology is ideal for the typing of human leukocyte antigen (HLA) genes for transplantation and cancer immunotherapy. However, such applications have been hindered by the high error rate of nanopore sequencing reads. We developed the workflow and bioinformatic pipeline, Athlon (accurate typing of human leukocyte antigen by Oxford Nanopore), to perform high-resolution typing of Class I HLA genes by nanopore sequencing. The method features a novel algorithm for candidate allele selection, followed by error correction through consensus building. Here, we describe the protocol of using Athlon packaged in a VirtualBox image for the above application.

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.

Deciphering the fine nucleotide diversity of full HLA class I and class II genes in a well-documented population from sub-Saharan Africa

With the aim to understand how next‐generation sequencing (NGS) improves both our assessment of genetic variation within populations and our knowledge on HLA molecular evolution, we sequenced and analysed 8 HLA loci in a well‐documented population from sub‐Saharan Africa (Mandenka). The results of full‐gene NGS‐MiSeq sequencing compared with those obtained by traditional typing techniques or limited sequencing strategies showed that segregating sites located outside exon 2 are crucial to describe not only class I but also class II population diversity. A comprehensive analysis of exons 2, 3, 4 and 5 nucleotide diversity at the 8 HLA loci revealed remarkable differences among these gene regions, notably a greater variation concentrated in the antigen recognition sites of class I exons 3 and some class II exons 2, likely associated with their peptide‐presentation function, a lower diversity of HLA‐C exon 3, possibly related to its role as a KIR ligand, and a peculiar molecular diversity of HLA‐A exon 2, revealing demographic signals. Based on full‐length HLA sequences, we also propose that the most frequent DRB1 allele in the studied population, DRB1*13:04, emerged from an allelic conversion involving 3 potential alleles as donors and DRB1*11:02:01 as recipient. Finally, our analysis revealed a high occurrence of the DRB1*13:04‐DQA1*05:05:01‐DQB1*03:19 haplotype, possibly resulting from a selective sweep due to protection to Onchorcerca volvulus, a prevalent pathogen in West Africa. This study unveils highly relevant information on the molecular evolution of HLA genes in relation to their immune function, calling for similar analyses in other populations living in contrasting environments.

Suitability of dried DNA for long-range PCR amplification and HLA typing by next-generation sequencing

Storage and stable shipment of genomic DNA are of great concern to laboratories that may need to perform testing off archived samples. There are some dry-state storage methods that are available that have the potential to provide a way to store samples at room temperature for long periods of time as well as offer a means to ship DNA to other facilities without the same safety concerns that come with shipping liquid samples. The recovered DNA should be of sufficient integrity such that downstream applications can be performed without concern of the sample quality. This work describes sample properties between two methods of DNA storage, dried (room temperature) and traditional (-80 °C). DNA was evaluated for purity, fragment length, and the ability to generate HLA typing using next-generation sequencing.

Evaluation of Ion Torrent sequencing technology for rapid clinical human leucocyte antigen typing

The development of techniques to define the human leucocyte antigen (HLA) region has proven to be challenging due to its high level of polymorphism. Within a clinical laboratory, a technique for high-resolution HLA typing, which is rapid and cost effective is essential. NGS has provided a rapid, high-resolution HLA typing solution, which has reduced the number of HLA ambiguities seen with other typing methods. In this study, the One Lambda NXType NGS kit was tested on the Ion Torrent PGM platform. A total of 362 registry donors from four ethnic populations (Europeans, South Asians, Africans and Chinese) were NGS HLA typed across 9-loci (HLA-A, -B, -C, -DRB1,-DRB345 -DQB1 and -DPB1). Concordance rates of 91%-98% were obtained (for HLA-A, -B, -C, -DRB1, -DQB1 and -DPB1) when compared to historical PCR-SSO HLA types, and the identification of uncommon alleles such as A*24:07:01 and C*04:82 were observed. A turnaround time of four days was achieved for typing 44 samples. However, some limitations were observed; primer locations did not allow all ambiguities to be resolved for HLA Class II where Exon I and IV amplification are needed (HLA-DRB1*04:07:01/04:92, HLA-DRB1*09:01:02/*09:21 and HLA-DRB1*12:01:01/*12:10). This study has demonstrated high-resolution typing by NGS can be achieved in an acceptable turnaround time for a clinical laboratory; however, the Ion Torrent workflow has some technical limitations that should be addressed.

Using Exome and Amplicon-Based Sequencing Data for High-Resolution HLA Typing with ATHLATES

ATHLATES (accurate typing of human leukocyte antigen through exome sequencing) was originally developed to analyze whole-exome sequencing (exome-seq) data from the Illumina platform and to predict the HLA genotype at 2-field or higher resolution. HLA locus-specific reads are first collected by stringent read mapping to the IMGT/HLA database. ATHLATES then performs read assembly, candidate allele identification, and genotype inference. Here, we describe the protocol of using ATHLATES for the above purpose and expand the application to analyze targeted sequencing data using amplicons of full HLA genes.

Application of High-Throughput Next-Generation Sequencing for HLA Typing on Buccal Extracted DNA

Next-generation sequencing (NGS) is increasingly recognized for its ability to deliver high-resolution and high-throughput HLA genotyping. As a result, there is active interest in applying NGS technologies to perform high volume bone marrow donor recruitment typing. Currently, buccal-based DNA specimens are considered a noninvasive and cost-effective method for registry typing. Here, we describe the feasibility of using long-range PCR and clonal sequencing by Illumina MiSeq to deliver unambiguous HLA typing on buccal-based donor recruitment samples.

The use of next-generation sequencing for the determination of rare blood group genotypes

OBJECTIVES

Next-generation sequencing (NGS) for the determination of rare blood group genotypes was tested in 72 individuals from different ethnicities.

BACKGROUND

Traditional serological-based antigen detection methods, as well as genotyping based on specific single nucleotide polymorphisms (SNPs) or single nucleotide variants (SNVs), are limited to detecting only a limited number of known antigens or alleles. NGS methods do not have this limitation.

METHODS

NGS using Ion torrent Personal Genome Machine (PGM) was performed with a customised Ampliseq panel targeting 15 different blood group systems on 72 blood donors of various ethnicities (Caucasian, Hispanic, Asian, Middle Eastern and Black).

RESULTS

Blood group genotypes for 70 of 72 samples could be obtained for 15 blood group systems in one step using the NGS assay and, for common SNPs, are consistent with previously determined genotypes using commercial SNP assays. However, particularly for the Kidd, Duffy and Lutheran blood group systems, several SNVs were detected by the NGS assay that revealed additional coding information compared to other methods. Furthermore, the NGS assay allowed for the detection of genotypes related to VEL, Knops, Gerbich, Globoside, P1PK and Landsteiner-Wiener blood group systems.

CONCLUSIONS

The NGS assay enables a comprehensive genotype analysis of many blood group systems and is capable of detecting common and rare alleles, including alleles not currently detected by commercial assays.

High-Throughput Sequencing of the Major Histocompatibility Complex following Targeted Sequence Capture

The Human Major Histocompatibility Complex (MHC) is a highly polymorphic region full of immunoregulatory genes. The MHC codes for the human leukocyte antigens (HLA), proteins that present on the cellular surface and that are involved in self-non-self recognition. For matching donors and recipients for organ and stem-cell transplants it is important to know an individual's HLA haplotype determinable in this region. Now, as next-generation sequencing (NGS) platforms mature and become more and more accepted as a standard method, NGS applications have spread from research laboratories to the clinic, where they provide valid genetic insights. Here, we describe a cost-effective microarray-based sequence capture, enrichment, and NGS sequencing approach to characterize MHC haplotypes. Using this approach, ~4 MB of MHC sequence for four DNA samples (donor, recipient and the parents of the recipient) were sequenced in parallel in one NGS instrument run. We complemented this approach using microarray-based genome-wide SNP analysis. Taken together, the use of recently developed tools and protocols for sequence capture and massively parallel sequencing allows for detailed MHC analysis and donor-recipient matching.

Application of High-Throughput Next-Generation Sequencing for HLA Typing on Buccal Extracted DNA: Results from over 10,000 Donor Recruitment Samples

Background

Unambiguous HLA typing is important in hematopoietic stem cell transplantation (HSCT), HLA disease association studies, and solid organ transplantation. However, current molecular typing methods only interrogate the antigen recognition site (ARS) of HLA genes, resulting in many cis-trans ambiguities that require additional typing methods to resolve. Here we report high-resolution HLA typing of 10,063 National Marrow Donor Program (NMDP) registry donors using long-range PCR by next generation sequencing (NGS) approach on buccal swab DNA.

Methods

Multiplex long-range PCR primers amplified the full-length of HLA class I genes (A, B, C) from promotor to 3’ UTR. Class II genes (DRB1, DQB1) were amplified from exon 2 through part of exon 4. PCR amplicons were pooled and sheared using Covaris fragmentation. Library preparation was performed using the Illumina TruSeq Nano kit on the Beckman FX automated platform. Each sample was tagged with a unique barcode, followed by 2×250 bp paired-end sequencing on the Illumina MiSeq. HLA typing was assigned using Omixon Twin software that combines two independent computational algorithms to ensure high confidence in allele calling. Consensus sequence and typing results were reported in Histoimmunogenetics Markup Language (HML) format. All homozygous alleles were confirmed by Luminex SSO typing and exon novelties were confirmed by Sanger sequencing.

Results

Using this automated workflow, over 10,063 NMDP registry donors were successfully typed under high-resolution by NGS. Despite known challenges of nucleic acid degradation and low DNA concentration commonly associated with buccal-based specimens, 97.8% of samples were successfully amplified using long-range PCR. Among these, 98.2% were successfully reported by NGS, with an accuracy rate of 99.84% in an independent blind Quality Control audit performed by the NDMP. In this study, NGS-HLA typing identified 23 null alleles (0.023%), 92 rare alleles (0.091%) and 42 exon novelties (0.042%).

Conclusion

Long-range, unambiguous HLA genotyping is achievable on clinical buccal swab-extracted DNA. Importantly, full-length gene sequencing and the ability to curate full sequence data will permit future interrogation of the impact of introns, expanded exons, and other gene regulatory sequences on clinical outcomes in transplantation.