Molecular typing of human leukocyte antigen and related polymorphisms following whole genome amplification

Reliable, high-resolution genotyping of human leukocyte antigen (HLA) polymorphisms is often compromised by DNA samples of suboptimal quality or limited quantity. We tested the feasibility of molecular typing for variants at HLA and neighboring loci using whole genome amplification (WGA) strategy facilitated by the Phi29 DNA polymerase. With little (5-100 ng) starting genomic DNA of varying quality and source materials, WGA was deemed successful in 167 of 169 DNA from 47 cell lines, 100 European Americans, and 22 native Africans. The Phi29-processed DNA provided adequate templates for polymerase chain reaction (PCR)-based analyses of several HLA (A, B, C, DRB1, and DQB1) and related loci (HFE, MICA, and 10 microsatellites) in the 6p24.3-6p21.3 region, with PCR amplicons ranging from 92 to 2200 bp. Five different genotyping techniques resolved and confirmed 364 genotypes when both original and Phi29-processed DNA worked in PCRs. General population genetic analyses provided additional evidence that WGA may represent a reliable and simple approach to securing ample genomic DNA for typing HLA, MICA, and related variants.     

两种全基因组扩增方法用于微量检材STR基因座分型比较

目的 应用多重置换扩增(MDA)技术和改进型扩增前引物延伸（IPEP）技术对法医学微量DNA进行全基因组扩增，比较两种方法的STR分型效果及法医学应用价值。 方法 用MDA、IPEP方法分别对不同模板量DNA进行扩增，扩增产物用实时荧光定量PCR技术定量、用AmpFLSTR® Identifiler®试剂盒检测基因型。 结果 MDA方法可对模板DNA增加103～106倍，IPEP方法可增加25～310倍。为获得完整准确的分型结果，MDA最低需1ng基因组DNA，IPEP最低需0.05ng基因组DNA。当基因组DNA为0.01ng～0.1ng时，IPEP产物、MDA产物的平均基因座检出数均高于未经全基因组扩增的DNA，其中IPEP产物的平均基因座检出数高于MDA产物。 结论 MDA方法、IPEP方法均可提高微量检材的STR分型效果。MDA方法的产量高于IPEP方法；IPEP方法的灵敏度高于MDA方法，且对微量DNA的STR分型效果优于MDA方法，因此更适于法医学痕量DNA检测。     

多重置换扩增在植入前遗传学诊断中的应用及展望

多重置换扩增是一种新兴的全基因组扩增技术,能对单个细胞进行全基因扩增,产生大量的优质DNA,具有高扩增效率和高保真性等特点.多重置换扩增联合常规PCR已被成功用于植入前遗传学诊断,进一步扩展了后者的应用范围.     

A gene-specific primer extension and liquid bead array system for killer-cell immunoglobulin-like receptor genotyping

A simple and accurate method for killer-cell immunoglobulin-like receptor (KIR) genotyping is developed using KIR gene-specific primer extension (GSPE) followed by bead array hybridization (GSPE method). After amplification of exons 4, 5, and 9, KIR GSPE and bead array hybridization were performed to verify the presence or absence of 16 KIR subfamilies. GSPE method was validated with natural killer/KIR reference panel I consisting of 48 cell types provided by 13th International Histocompatibility Working Group (IHWG) and genomic DNA from 17 peripheral blood cells, 8 cell lines, and 8 buccal cells. The results of reference panel from GSPE method were 100% concordant with the IHWG reference typing information. All genomic DNAs except reference panel were typed for KIR genes with sequence-specific primer methods and showed 100% identical typing results using this novel system. In addition, GSPE method can obtain results in 8 h from DNA with 10 ng genomic DNA in a 96-well-based assay format.     

HLA DNA typing: past, present, and future

The human leukocyte antigen (HLA) class I and class II loci are the most polymorphic genes in the human genome, with a highly clustered and patchwork pattern of sequence motifs. In the three decades since the first HLA gene was isolated by molecular cloning (a cDNA clone of HLA-B7), thousands of alleles have been identified and the names and sequences of all known alleles have been curated in the IMGT/HLA database. This extensive allelic diversity made and continues to make high-resolution HLA DNA typing very challenging. The first attempt at HLA DNA typing involved restriction fragment length polymorphism (RFLP) analysis, but this approach had many limitations. The development of PCR in 1985 allowed for the amplification of the polymorphic exons of the HLA class I and class II genes and the analysis of the polymorphic sequence motifs with sequence-specific oligonucleotide (SSO) hybridization probes. The immobilization of these probes on membranes and later on beads, along with primer sets for sequence-specific priming (SSP), gave rise to the current set of HLA typing reagents. Sanger sequencing has provided high-resolution typing but, in many cases, genotyping 'ambiguity' remains an issue. In the past few years, the introduction of next-generation sequencing, with the critical properties of massively parallel and clonal sequencing, has significantly reduced HLA genotyping ambiguity. Here, our lab's efforts to develop high-resolution and high-throughput HLA DNA typing using the 454 Sequencing System are reviewed, and the potential future developments and applications of HLA DNA typing are discussed.     

HLA class II DRB high resolution genotyping by pyrosequencing: comparison of group specific PCR and pyrosequencing primers

Sequencing of alleles of the highly polymorphic, multiple loci HLA-DRB gene family was performed by pyrosequencing using purified DNA from the 11(th) International Histocompatibility Workshop human lymphoblastiod cell lines as well as genomic DNA isolated from blood samples obtained from healthy adult volunteers. Genomic DNA was prepared from donors whose blood had been stored either frozen or as dried blood spots. Pyrosequence-based typing was optimized for identifying alleles of the HLA-DRB1, -3, -4, and -5 genes. The procedure should be applicable to other HLA loci including the class I genes HLA-A and -B that, along with HLA-DRB, are crucial for histocompatibility matching of tissue antigens during transplantation. Computer simulation of pyrosequencing data suggest that alleles of HLA-DRB1, -3, -4, and -5 were readily identifiable by pyrosequencing as were their heterozygous allelic combinations. Pyrosequencing primers were designed to specifically sequence HLA loci of interest even in a background of other amplified, closely related sequences such as alleles of the pseudogene HLA-DRB6, -7, -8, and -9. Polymorphic residues of HLA-DRB genes were identified within each pyrosequencing reaction, obtained by 50 to 70 nucleotide read lengths. Heterozygous allelic combinations of HLA genes were analyzed and compared successfully to genotyping of alleles by sequence-specific oligonucleotide probe hybridization as well as allele specific polymerase chain reaction protocols. Pyrosequence-based typing is compatible with genotyping of allelic combinations expected from heterozygous individuals, resulting in nucleotide resolution of the highly polymorphic HLA system. Using a single pyrosequence instrument, complete typing of HLA-DRB genes can be performed daily on hundreds of individuals for high resolution histocompatibility genotyping studies.     

Use of dried blood spots for the determination of genetic variation of interleukin-10, killer immunoglobulin-like receptor and HLA class I genes

Optimal methods for using dried blood spots (DBSs) for population genetics-based studies have not been well established. Using DBS stored for 8 years from 21 pregnant South African women, we evaluated three methods of gDNA extraction with and without whole-genome amplification (WGA) to characterize immune-related genes: interleukin-10 (IL-10), killer immunoglobulin-like receptors (KIRs) and human leukocyte antigen (HLA) class I. We found that the QIAamp DNA mini kit yielded the highest gDNA quality (P< 0.05; Wilcoxon signed rank test) with sufficient yield for subsequent analyses. In contrast, we found that WGA was not reliable for sequence-specific primer polymerase chain reaction (SSP-PCR) analysis of KIR2DL1, KIR2DS1, KIR2DL5 and KIR2DL3 or high-resolution HLA genotyping using a sequence-based approach. We speculate that unequal template amplification by WGA underrepresents gene repertoires determined by sequence-based approaches.     

Low-resolution DNA typing for HLA-B using sequence-specific primers in allele- or group-specific ARMS/PCR

Abstract: The products of the human major histocompatibility complex (HLA Class I and II) have historically been detected using serological or cellular assays. With the availability of DNA sequence information for alleles of the HLA system, and with the development of molecular biological techniques it has become possible to tissue type for allelic differences in the HLA genes themselves. We describe here a polymerase chain reaction (PCR) system, based on the principle of the amplification refractory mutation system (ARMS), for low-resolution DNA typing of the HLA-B gene. The technique involves a one-step PCR from genomic DNA using sequence-specific primers in particular combinations that determine the specificity of each reaction. A low-resolution primer panel has been designed, based on published HLA-B gene nucleotide sequences, consisting of 34 sequence-specific primers (SSP) in 24 PCR reactions which cover all known HLA-B alleles, to give allele-specific or group-specific amplification of DNA fragments of defined size (344–784bp). Advantages of the system are that it can be performed in under 4 hours including DNA extraction, results are easy to interpret and it does not require viable cells.     

Multiple displacement amplification to create a long-lasting source of DNA for genetic studies

In many situations there may not be sufficient DNA collected from patient or population cohorts to meet the requirements of genome-wide analysis of SNPs, genomic copy number polymorphisms, or acquired copy number alternations. When the amount of available DNA for genotype analysis is limited, high performance whole-genome amplification (WGA) represents a new development in genetic analysis. It is especially useful for analysis of DNA extracted from stored histology slides, tissue samples, buccal swabs, or blood stains collected on filter paper. The multiple displacement amplification (MDA) method, which relies on isothermal amplification using the DNA polymerase of the bacteriophage phi29, is a recently developed technique for high performance WGA. This review addresses new trends in the technical performance of MDA and its applications to genetic analyses. The main challenge of WGA methods is to obtain balanced and faithful replication of all chromosomal regions without the loss of or preferential amplification of any genomic loci or allele. In multiple comparisons to other WGA methods, MDA appears to be most reliable for genotyping, with the most favorable call rates, best genomic coverage, and lowest amplification bias.     

The use of modified primer competitors to enhance yields and specificity of HLA class I amplification by polymerase chain reaction (PCR)

Various PCR based techniques have been developed for genomic HLA typing. The fidelity of these techniques is highly dependent upon the specificity of the primers for the given HLA locus. Due to the high degree of homology between HLA class I loci, few primer sites that selectively amplify genes at a given HLA class I locus may be identified. To avoid coamplification of homologous loci, we designed and applied primer competitors for PCR amplification of HLA-A, -B and -C loci. Primer competitors identical to the 3' end of the specific primers and completely degenerate in the 5' end were designed and titrated into the respective HLA-locus PCR mixtures. We found that inclusion of primer competitors in the PCR reaction increased the specificity and yields of HLA class I amplifications, in particular when crude DNA preparation was used as template. This was particularly true for DNA preparations of low quality. The method described here may be useful for various protocols for downstream genomic typing of HLA-A, -B and -C alleles. In particular the method is useful when DNA is in scarce supply (i.e., for extensive PCR based allelic typing) or when high yields and locus specificity of amplicons are needed (i.e., sequencing-based typing).     

Physical separation of HLA-A alleles by denaturing high-performance liquid chromatography

Genomic typing of polymorphic loci may be hampered by ambiguous typing results. Moreover, robust methods for simultaneous sequencing of two alleles present in a given sample may be difficult to establish. We used denaturing high-performance liquid chromatography (DHPLC) for physical separation of HLA-A alleles before sequence-based genomic typing (SBT). Physical separation was achieved by resolution of heteroduplexes between the sample alleles and a modified reference probe by DHPLC followed by selective reamplification of the sample alleles present in heteroduplexes. Complementary strands of the reference probe and sample alleles for heteroduplex induction were obtained by lambda-exonuclease digestion. HLA-A genotyping of 101 individuals using DHPLC-SBT yielded better typing resolution compared with serological typing and genotyping by the sequence-specific primer-polymerase chain reaction (SSP-PCR) method. Physical separation of alleles using a modified reference probe allows for development of fully automated methods for genomic typing of highly polymorphic loci such as HLA.     

Assessment of multiple displacement amplification for polymorphism discovery and haplotype determination at a highly polymorphic locus, MC1R

The identification of common genetic variants such as single nucleotide polymorphisms (SNPs) in the human genome has become central in human population genetics and evolution studies, as well as in the study of the genetic basis of complex traits and diseases. Crucial for the accurate identification of genetic variants is the availability of high quality genomic DNA (gDNA). Since popular sources of gDNA (buccal cells, lymphocytes, hair bulb) often do not yield sufficient quantities of DNA for molecular genetic applications, whole genome amplification methods have recently been introduced to generate a renewable source of double-stranded linear DNA. Here, we assess the fidelity of one method, multiple displacement amplification (MDA), which utilizes bacteriophage Phi29 DNA polymerase to generate amplified DNA from an original source of gDNA, in a representative SNP discovery and genetic association study at the melanocortin 1 receptor (MC1R) locus, a highly polymorphic gene in humans involved in skin and hair pigmentation. We observed that MDA has high fidelity for novel SNP discovery and can be a valuable tool in generating a potentially indefinite source of DNA. However, we observed an allele amplification bias that causes genotype miscalls at heterozygous sites. At loci with multiple polymorphic sites in linkage disequilibrium, such as at MC1R, this bias can create a significant number of heterozygote genotype errors that subsequently misrepresents haplotypes.     

Rapid HLA-DRB1 genotyping by nested PCR amplification

State of the art genotyping of HLA class II alleles with group-specific DNA amplification by the polymerase chain reaction (PCR) (1) and subsequent probing with sequence-specific oligonucleotides (2-4) is not suitable for typing cadaveric organ donors since the typing procedure takes far more than one working day. We designed specific oligonucleotide primer sets for nested PCR amplification which allowed typing for all serological HLA-DR specificities (DR1-DRw18) solely by the detection of amplified DNA in the reaction mixtures after agarose gel electrophoresis. Exon 2 of the DRB genes and a DRw52-group-specific part of DRB1 exon 2 was amplified directly from cell lysates without prior DNA extraction. The amplified DNA was subjected to a second round of amplification, which employed a set of 18 nested allele- or group-specific primer pairs. All alleles which have at least a single mismatched base at the terminal 3'-nucleotide of one primer were completely refractory to amplification. This assay is easy to perform and takes less than one working day to complete. Thus, this method may prove to be suitable for DNA typing of organ donors for prospective HLA-DR matching in renal transplantation.     

Rapid DNA typing utilizing immobilized oligonucleotide probe and a nonradioactive detection system. Application to HLA-DR typing of the Japanese population.

We established a rapid and simple method of HLA-DR genotyping, and applied it for analysis of the Japanese population. Our method includes rapid preparation of DNA samples from buccal mucosa, incorporation of biotin-dATP into DRB genes during amplification by the polymerase chain reaction, hybridization with sequence-specific oligonucleotide (SSO) probes immobilized on nylon membranes via poly (dT) tails, and detection of the hybridization signal as chemiluminescence. We carried out DR typing of 30 Japanese donors using 20 different immobilized SSO probes, and obtained unambiguous typing signals showing perfect correlation with their serologic DR types. The genotyping also enabled us to identify several DR types unique to the Japanese population, such as DRw12b (DRB1*1202), DRw14c (DRB1*1405), and serology blank type, DR'JX6' (DRB1*1403). The method presented here would be suitable for routine DR typing in tissue-typing laboratories.     

多重置换扩增——一种新的全基因组扩增技术

全基因组扩增技术用于扩增大量的DNA以满足遗传检测的需要。在高通量的遗传分型中，处理有限的临床样本的基因组DNA，一直是个瓶颈问题。一种新方法—多重置换扩增，能高度忠实的复制整个基因组DNA，扩增出10–100 kb大小的片段，能提供大量均一完整的全基因组序列。MDA是一种简单、有效的方法，非常适用于遗传研究，法医学和临床诊断的需要。     

Comparison of yield and genotyping performance of multiple displacement amplification and OmniPlex whole genome amplified DNA generated from multiple DNA sources

The promise of whole genome amplification (WGA) is that genomic DNA (gDNA) quantity will not limit molecular genetic analyses. Multiple displacement amplification (MDA) and the OmniPlex PCR-based WGA protocols were evaluated using 4 and 5 ng of input gDNA from 60 gDNA samples from three tissue sources (mouthwash, buffy coat, and lymphoblast). WGA DNA (wgaDNA) yield and genotyping performance were evaluated using genotypes determined from gDNA and wgaDNA using the AmpFlSTR Identifiler assay and N = 49 TaqMan SNP assays. Short tandem repeat (STR) and SNP genotyping completion and concordance rates were significantly reduced with wgaDNA from all WGA methods compared with gDNA. OmniPlex wgaDNA exhibited a greater reduction in genotyping performance than MDA wgaDNA. Reduced wgaDNA genotyping performance was due to allelic (all protocols) and locus (OmniPlex) amplification bias leading to heterozygote and locus dropout, respectively, and %GC sequence content (%GC) was significantly correlated with TaqMan assay performance. Lymphoblast wgaDNA exhibited higher yield (OmniPlex), buffy coat wgaDNA exhibited higher STR genotyping completion (MDA), whereas mouthwash wgaDNA exhibited higher SNP genotyping discordance (MDA). Genotyping of wgaDNA generated from < or = 5 ng gDNA, e.g., from archaeological, forensic, prenatal diagnostic, or pathology samples, may require additional genotyping validation with gDNA and/or more sophisticated analysis of genotypes incorporating observed reductions in genotyping performance.     

Rapid HLA-DQB typing by eight polymerase chain reaction amplifications with sequence-specific primers (PCR-SSP)

Molecular genotyping of HLA class II genes using group-specific DNA amplification by the PCR followed by probing with (PCR-SSO) probes is too time consuming for the typing of cadaveric organ donors. Recently, amplification of DNA using PCR-SSP has proved a reliable and rapid method for typing HLA-DRB1 genes. PCR-SSP takes 2 hours to perform and is therefore suitable for the genotyping of cadaveric donors. We have designed a set of primers that in eight PCR reactions will positively identify the HLA-DQB1 alleles corresponding o the serologically defined series HLA-DQ2, DQ4, DQ5, DQ6, DQ7, DQ8, and DQ9. Presently, 30 homozygous cell lines and 138 individuals have been typed by the DQB1 PCR-SSP technique and compared with a combination of serology and RFLP with 100% concordance. No false-negative or false-positive amplifications were recorded. All combinations of DQB1 can be readily identified. DQB1 PCR-SSP can take as little as 130 minutes from start to finish, including DNA preparation.     

DETERMINATION OF DQB1 ALLELES USING PCR AMPLIFICATION AND ALLELE-SPECIFIC PRIMERS

Molecular genotyping of HLA class II genes is commonly carried out using polymerase chain reaction (PCR) in combination with sequence-specific oligotyping (PCR-SSO) or a combination of the PCR and restriction fragment length polymorphism methods (PCR-RFLP). However, the identification of the DQB1 type by PCR-SSO and PCR-RFLP is very time-consuming which is disadvantageous for the typing of cadaveric organ donors. We have developed a DQB1 typing method using PCR in combination with allele-specific amplification (PCR-ASA), which allows the identification of the 17 most frequent alleles in one step using seven amplification mixtures. PCR allele-specific amplification HLA-DQB1 typing is easy to perform, and the results are easy to interpret in routine clinical practice. The PCR-ASA method is therefore better suited to DQB1 typing for organ transplantation than other methods.     

Approaches to genotyping individual miracidia of Schistosoma japonicum

Molecular genetic tools are needed to address questions as to the source and dynamics of transmission of the human blood fluke Schistosoma japonicum in regions where human infections have reemerged, and to characterize infrapopulations in individual hosts. The life stage that interests us as a target for collecting genotypic data is the miracidium, a very small larval stage that consequently yields very little DNA for analysis. Here, we report the successful development of a multiplex format permitting genotyping of 17 microsatellite loci in four sequential multiplex reactions using a single miracidium held on a Whatman Classic FTA indicating card. This approach was successful after short storage periods, but after long storage (>4 years), considerable difficulty was encountered in multiplex genotyping, necessitating the use of whole genome amplification (WGA) methods. WGA applied to cards stored for long periods of time resulted in sufficient DNA for accurate and repeatable genotyping. Trials and tests of these methods, as well as application to some field-collected samples, are reported, along with the discussion of the potential insights to be gained from such techniques. These include recognition of sibships among miracidia from a single host, and inference of the minimum number of worm pairs that might be present in a host.     

Real-time molecular epidemiology of tuberculosis by direct genotyping of smear-positive clinical specimens

We applied MIRU-VNTR (mycobacterial interspersed repetitive-unit-variable-number tandem-repeat typing) to directly analyze the bacilli present in 61 stain-positive specimens from tuberculosis patients. A complete MIRU type (24 loci) was obtained for all but one (no amplification in one locus) of the specimens (98.4%), and the allelic values fully correlated with those obtained from the corresponding cultures. Our study is the first to demonstrate that real-time genotyping of Mycobacterium tuberculosis can be achieved, fully transforming the way in which molecular epidemiology techniques can be integrated into control programs.