Patent Application
20220098642
The instant application contains a Sequence Listing, which has been submitted in ASCII format via EFS-Web and is hereby incorporated by reference in its entirety. Said ASCII copy, created on Nov. 26, 2019, is named RICEP0058WO_ST25.txt and is 145.6 kilobytes in size.
The present invention relates generally to the fields of molecular biology and medicine. More particularly, it concerns compositions and methods for multiplexed copy number variation detection and allele ration quantitation using quantitative amplicon sequencing.
Copy number variations (CNVs) are important cancer biomarkers contributing to cancer formation and progression. They are present in a significant percentage of tumors, between 3% and 98% depending on the cancer type. Many CNVs confer sensitivity or resistance to targeted therapies, for example, MET amplification confers increased sensitivity to MET TKIs in non-small cell lung cancer, and PTEN deletion confers BRAF inhibitor resistance in melanoma. In tumor samples, CNV of a specific gene may exist only in a small fraction (<10%) of cells, due to tumor heterogeneity and normal cell contamination.
Unlike mutations and indels, CNVs have no unique sequence, thus detection of CNV requires accurate quantitation. This quantitation is difficult due to stochasticity in sampling of DNA molecules. For example, the standard deviation (a) of sampling 1200 molecules per locus (i.e. 1200 haploid genomic copies from 600 normal cells, 4 ng of genomic DNA) can be estimated by Poisson distribution: σ=√{square root over (1200)}=35, corresponding to 3% of molecule number. In this case, detecting 1% of extra copies is not possible. Theoretically, increasing the number of input molecules or analyzing more loci can equally decrease the variance, and the a can be estimated as σ=√{square root over (haploid genomic copies×loci number)}. If genomic copy number or loci number increase by 100×, σ will be decreased to 0.3%, and 1% of extra copies will be detectable.
Current standard method for CNV detection in molecular diagnostics is in situ hybridization (ISH), which can determine CNV status based on observation of a small number of cells. However, ISH technologies lack the ability to perform simultaneous analysis of multiple genomic regions, due to the limited number of distinguishable colors in both fluorescence and bright-field microscopy. Additionally, ISH is a complex process that needs to be performed by specialized labs, preventing it from being widely adopted.
Another method for CNV detection is droplet digital PCR (ddPCR), which is a PCR-based method for absolute quantitation of DNA molecules. However, its limit of detection (LoD) for CNV is about 20% extra copies with a large number of replicated experiments. Like ISH, ddPCR also suffers from an inability to be multiplexed due to the limited number of fluorescence channels. Microarray-based methods, including array comparative genomic hybridization and SNP arrays, are highly multiplexed methods used for screening of large CNVs and aneuploidies. However, they are not as good in detecting smaller CNVs <40 kb or low-frequency CNVs at <30% extra copies.
Next-generation sequencing (NGS) is a high-throughput technology that has seen rapidly decreasing costs over the past decade. NGS is popular in the field of cancer molecular diagnostics. Highly multiplexed mutation detection with an LoD of <0.1% variant allele frequency has been achieved and commercialized on NGS platforms. However, current LoD of NGS methods for CNV detection is not as good: whole-exome sequencing (WES) has been used for CNV discovery at a level of ≈30% extra copies, but is expensive, and requires even more NGS reads (with a proportional increase in cost) to achieve lower LoD. Smaller hybrid-capture panels, such as the FoundationOne commercial panel, can reach an LoD of ≈30% extra copies at lower costs.
In NGS panels for diagnostics, target enrichment is needed to reduce NGS reads wasted on unrelated genomic regions. Two popular methods for target enrichment are hybrid-capture and multiplexed PCR. Current NGS-based CNV panels are mostly hybrid-capture-based, which means target regions are captured by biotinylated nucleic acid probes and separated from the rest of the genome using streptavidin magnetic beads. Hybrid-capture panels have low on-target rates when the panel size is small, so most panels are >100 kb (i.e. >1000 probes or loci); this is due to nonspecific binding of unwanted DNA on bead surfaces, probes, and captured targets. Due to the large number of loci, the coverage of hybrid-capture panels is not uniform: the 95% and 5% percentile loci differ by at least 30-fold, which introduces another layer of bias in quantitation. Hybrid-capture panels also suffer from low conversion rates (i.e., the percentage of input molecules sequenced) caused by imperfect end-repair and ligation, causing biased sampling processing and contributing to variation.
Provided herein are methods of quantitative amplicon sequencing, for labeling each strand of targeted genomic loci in a DNA sample with an oligonucleotide barcode sequence by polymerase chain reaction, and amplifying the genomic region(s) for high-throughput sequencing. The methods can be used for the simultaneous detection of copy number variation (CNV) in a set of genes of interest, by quantitating the frequency of extra copies of each gene. In addition, these methods provide for the quantitation of the allele ratio of different genetic identities for targeted genomic loci using multiplexed PCR.
In one embodiment, provided herein are methods for preparing targeted regions of genomic DNA for high-throughput sequencing, the method comprising: (a) obtaining a genomic DNA sample; (b) amplifying at least a portion of the genomic DNA sample by performing two cycles of PCR using: (i) a first oligonucleotide comprising, from 5′ to 3′, a first region, a second region having a length between 0 and 50 nucleotides (e.g., 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50 nucleotides), a third region comprising at least four degenerate nucleotides (e.g., 4, 5, 6, 7, 8, 9, 10, 11, or 12 degenerate nucleotides), and a fourth region comprising a sequence that is complementary to a first target genomic DNA region; and (ii) a second oligonucleotide comprising, from 5′ to 3′, a fifth region, a sixth region having a length between 0 and 50 nucleotides (e.g., 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50 nucleotides), and a seventh region comprising a sequence that is complementary to a second target genomic DNA region; (c) amplifying a product of step (b) by performing at least three cycles of PCR with an annealing temperature that is 0-10° C. (e.g., 1-10, 2-10, 3-10, 4-10, 5-10, 1-9, 1-8, 1-7, 1-6, 1-5, 2-9, 2-8, 2-7° C. or any range or value derivable therein) higher than an annealing temperature used in step (b) and using: (i) a third oligonucleotide comprising a sequence that is able to hybridize to the reverse complement of at least a portion of the first region; and (ii) a fourth oligonucleotide comprising a sequence that is able to hybridize to the reverse complement of at least a portion of the fifth region; and (d) amplifying a product of step (c) by performing at least one cycle of PCR using a fifth oligonucleotide comprising, from 5′ to 3′, an eighth region, a ninth region having a length between 0 and 50 nucleotides (e.g., 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50 nucleotides), and a tenth region comprising a sequence that is complementary to a third target genomic DNA region, wherein the third target genomic DNA region is at least one nucleotide closer to the first target genomic DNA region than the second target genomic DNA region.
In some aspects, methods are methods for preparing between 1 and 10,000 targeted regions (e.g., at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 75, 100, 250, 500, 750, 1,000, 2,000, 3,000, 4,000 or 5,000 and at most 10,000, 9,000, 8,000, 7,000, 6,000, 5,000, 4,000, 3,000, 2,000, 1,000, 750, 500, 250, 100, 75, or 50 targeted regions, or any range or value derivable therein) of genomic DNA for high-throughput sequencing. In some aspects, the third region is a unique molecular identifier (UMI). In some aspects, the third target genomic DNA region is 1-10 (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10) bases closer to the first target genomic DNA region than the second target genomic DNA region. In some aspects, the first region and the eighth region are universal primer binding sites. In some aspects, the first region and the eighth region comprise a full or partial NGS adapter sequence. In some aspects, the fifth region comprises a sequence that cannot be found in the human genome. In some aspects, the fifth region comprises a sequence that is different from an NGS adapter sequence. In some aspects, the melting temperatures of the first region and the fifth region are 0-10° C. (e.g., 1-10, 2-10, 3-10, 4-10, 5-10, 1-9, 1-8, 1-7, 1-6, 1-5, 2-9, 2-8, 2-7° C. or any range or value derivable therein) higher than the melting temperatures of the fourth region and the seventh region. In some aspects, the degenerate nucleotides in the third region each independently are one of A, T, or C. In some aspects, none of the degenerate nucleotides in the third region are G. In some aspects, there is a population of first oligonucleotides each having a unique third region.
In some aspects, the methods further comprise purifying the product of step (c). In some aspects, purifying comprises SPRI purification or column purification. In some aspects, the methods further comprise purifying the product of step (d). In some aspects, purifying comprises SPRI purification or column purification. In some aspects, the methods further comprise (e) amplifying the product of step (d) by PCR using primers that hybridize to the first region and the eighth region, wherein the primers comprise an index sequence for next-generation sequencing. In some aspects, the methods further comprise purifying the product of step (e). In some aspects, purifying comprises SPRI purification or column purification. In some aspects, the methods further comprise (f) performing high-throughput DNA sequencing of the produce of step (e). In some aspects, high-throughput DNA sequencing comprises next-generation sequencing.
In some aspects, the first target genomic DNA region and the second target genomic DNA region are on opposite strands of the genomic DNA. In some aspects, the first target genomic DNA region and the second target genomic DNA region are separated by between 40 nucleotides and 500 nucleotides (e.g., by 40, 45, 50, 55, 60, 65, 70, 75, 80, 90, 100, 125, 150, 175, 200, 225, 250, 275, 300, 325, 350, 375, 400, 425, 450, 475, or 500 nucleotides, or any value derivable therein). In some aspects, step (b) comprises an extension time of about 30 minutes (e.g., 27, 28, 29, 30, 31, 32, or 33 minutes). In some aspects, step (c) comprises an extension time of about 30 seconds (e.g., 27, 28, 29, 30, 31, 32, or 33 seconds). In some aspects, step (d) comprises an extension time of about 30 minutes (e.g., 27, 28, 29, 30, 31, 32, or 33 minutes).
In one embodiment, provided herein are methods for quantifying the frequency of extra copies (FEC) of at least one target gene, the method comprising: (a) obtaining a genomic DNA sample; (b) preparing the genomic DNA for high-throughput sequencing according to a method of any one of the present embodiments, wherein the sequences of the fourth region, the seventh region, and the tenth region hybridize to the at least one target gene; (c) performing high-throughput sequencing according to a method of any one of the present embodiments; and (d) calculating the FEC for the at least one target gene based on the sequencing information obtained in step (c).
In some aspects, the methods are methods for quantifying the FEC for a set of target genes, wherein the set of target genes comprises between 2 and 1000 target genes (e.g., at least 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 75, 100, 250, 500, or 750, and at most 1,000, 900, 800, 750, 700, 650, 600, 550, 500, 450, 400, 350, 300, 250, 200, 150, 100, 75, 50, 25, 20, 15, 10, 9, 8, 7, 6, 5, 4, or 3 targeted regions, or any range or value derivable therein). In some aspects, step (b) is performed using a population of first oligonucleotides, a population of second oligonucleotides, and a population of fifth oligonucleotides, wherein a portion of each of the populations of first, second, and fifth oligonucleotides comprise fourth, seventh, and tenth regions, respectively, that are complementary to one of the set of target genes. In some aspects, each of the fourth, seventh, and tenth regions comprises sequences that are only found once in the human genome. In some aspects, each first oligonucleotide that hybridizes to one target gene has a unique third region compared to each other first oligonucleotide that hybridizes to the same target gene. In some aspects, step (b) is performed using a first oligonucleotide, a second oligonucleotide, and a fifth oligonucleotide comprising fourth, seventh, and tenth regions, respectively, that are complementary to a reference gene. In some aspects, step (b) prepares a portion of each target gene or reference gene for high-throughput sequencing, wherein the portion is between 40 nucleotides and 500 nucleotides (e.g., by 40, 45, 50, 55, 60, 65, 70, 75, 80, 90, 100, 125, 150, 175, 200, 225, 250, 275, 300, 325, 350, 375, 400, 425, 450, 475, or 500 nucleotides, or any value derivable therein) long. In some aspects, FEC is defined as:
In some aspects, step (d) comprises: (i) aligning NGS reads to the targeted portions of each target gene and grouping the NGS reads into subgroups based on the loci to which they align; (ii) dividing the NGS read at each locus based on their UMI sequences such that all NGS reads carrying the same UMI sequence are grouped as one UMI family; (iii) removing UMI families resulting from PCR errors or NGS errors; (iv) counting the number of unique UMI sequences at each locus; and (v) calculating the FEC based on the number of unique UMI sequences for each locus in each target gene and reference gene. In some aspects, step (d)(iii) comprises removing UMI sequences that do not meet the UMI degenerate base design. In some aspects, step (d)(iii) comprises removing UMI families with a UMI family size less than Fmin, wherein the UMI family size is the number of reads carrying the same UMI, wherein Fmin is between 2 and 20 (e.g., 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20). In some aspects, step (d)(iv) comprises removing UMI sequences that differ by only one or two bases from another UMI sequence with a larger family size.
In some aspects, FEC is defined as:
where Σi=1u NTar,i is the sum of unique UMI number for all or part of the target gene loci, u is the number of loci to consider, u is no more than the total number of loci in the target gene; Σj=1wΣi=1vNRef,i,j is the sum of unique UMI number for all or part of Reference loci, v is the number of loci to consider for one reference, v is no more than the total number of loci in the reference; w is the number of reference to consider, w is no more than the total number of reference; and k is determined by experimental calibration. In some aspects, the FEC is used to identify the copy number variation (CNV) status of the target gene.
In one embodiment, provided herein are methods for quantifying the allele ratio of different genetic identities for an at least one target genomic locus, the method comprising: (a) obtaining a genomic DNA sample; (b) preparing the genomic DNA for high-throughput sequencing according to a method of any one of the present embodiments, wherein the sequences of the fourth region, the seventh region, and the tenth region hybridize to the genomic DNA near the at least one target genomic locus; (c) performing high-throughput sequencing according to a method of any one of the present embodiments; and (d) calculating the allele ratio of different genetic identities for the at least one target genomic locus on the sequencing information obtained in step (c).
In some aspects, the methods are methods for quantifying the allele ratio of different genetic identities for a set of target genomic loci, wherein the set of target genomic loci comprises between 2 and 10,000 target genomic loci (e.g., at least 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 75, 100, 250, 500, 750, 1,000, 2,000, 3,000, 4,000 or 5,000 and at most 10,000, 9,000, 8,000, 7,000, 6,000, 5,000, 4,000, 3,000, 2,000, 1,000, 750, 500, 250, 100, 75, or 50 target genomic loci, or any range or value derivable therein). In some aspects, step (b) is performed using a population of first oligonucleotides, a population of second oligonucleotides, and a population of fifth oligonucleotides, wherein a portion of each of the populations of first, second, and fifth oligonucleotides comprise fourth, seventh, and tenth regions, respectively, that are complementary to the genomic DNA near the at least one of the set of target genomic loci. In some aspects, each of the fourth, seventh, and tenth regions comprises sequences that are not able to hybridize with non-target regions of the genomic DNA under the conditions of step (b). In some aspects, each first oligonucleotide that hybridizes to the genomic DNA near one target genomic locus has a unique third region compared to each other first oligonucleotide that hybridizes to the genomic DNA near the same target genomic locus. In some aspects, each target genomic locus is between 40 nucleotides and 500 nucleotides (e.g., by 40, 45, 50, 55, 60, 65, 70, 75, 80, 90, 100, 125, 150, 175, 200, 225, 250, 275, 300, 325, 350, 375, 400, 425, 450, 475, or 500 nucleotides, or any value derivable therein) long.
In some aspects, step (d) comprises: (i) aligning NGS reads to the targeted genomic loci and grouping the NGS reads into subgroups based on the loci to which they align; (ii) dividing the NGS read at each locus based on their UMI sequences such that all NGS reads carrying the same UMI sequence are grouped as one UMI family; (iii) removing UMI families resulting from PCR errors or NGS errors; (iv) calling the genetic identity for each remaining UMI family; (v) counting the number of unique UMI sequences at each locus; and (vi) calculating the allele ratio. In some aspects, step (d)(iii) comprises removing UMI sequences that do not meet the UMI degenerate base design. In some aspects, step (d)(iii) comprises removing UMI families with a UMI family size less than Fmin, wherein the UMI family size is the number of reads carrying the same UMI, wherein Fmin is between 2 and 20 (e.g., 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20). In some aspects, step (d)(iii) comprises removing UMI sequences that differ by only one or two bases from another UMI sequence with a larger family size. In some aspects, step (d)(iv) comprises calling the genetic identity only if at least 70% (e.g., 70%, 75%, 80%, 85%, 90%, 95%, or 98%) of the reads in a UMI family are the same on the genetic locus of interest. In some aspects, the allele ratio is defined as Rallele=N1/N2, where N1 is unique UMI number for the first genetic identity, and N2 is unique UMI number for the second genetic identity.
In some aspects, step (d)(iv) comprises identifying the consensus sequence of each UMI family. In some aspects, the consensus sequence is the sequence appearing the highest number of times in the UMI family. In some aspects, step (d)(iv) further comprises comparing the consensus sequence to the wild-type sequence for that locus, thereby identifying mutations in the consensus sequence. In some aspects, the methods further comprise calculating the variant allele frequency (VAF) of the identified mutation. In some aspects, the VAF of the identified mutation is defined as Number of UMI families with the mutation/Total number of UMI families.
As used herein, “essentially free,” in terms of a specified component, is used herein to mean that none of the specified component has been purposefully formulated into a composition and/or is present only as a contaminant or in trace amounts. The total amount of the specified component resulting from any unintended contamination of a composition is therefore well below 0.05%, preferably below 0.01%. Most preferred is a composition in which no amount of the specified component can be detected with standard analytical methods.
As used herein the specification, “a” or “an” may mean one or more. As used herein in the claim(s), when used in conjunction with the word “comprising,” the words “a” or “an” may mean one or more than one.
The use of the term “or” in the claims is used to mean “and/or” unless explicitly indicated to refer to alternatives only or the alternatives are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and “and/or.” As used herein “another” may mean at least a second or more.
Throughout this application, the term “about” is used to indicate that a value includes the inherent variation of error for the device, the method being employed to determine the value, or the variation that exists among the study subjects.
Other objects, features and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
The following drawings form part of the present specification and are included to further demonstrate certain aspects of the present invention. The invention may be better understood by reference to one or more of these drawings in combination with the detailed description of specific embodiments presented herein.
where Σi=1u NTar,i is the sum of unique UMI number for all or part of the target gene loci, u is the number of loci to consider: Σj=1wΣi=1v NRef,i,j is the sum of unique UMI number for all or part of Reference loci, v is the number of loci to consider for one reference; w is the number of reference to consider; and k is determined by experimental calibration. CNV status is determined based on FEC. (
Provided herein are methods of quantitative amplicon sequencing, for labeling each strand of targeted genomic loci in the original DNA sample with an oligonucleotide barcode sequence by polymerase chain reaction, and amplifying the genomic region(s) for high-throughput sequencing. Also provided herein are methods to allow the simultaneous detection of copy number variation (CNV) in a set of genes of interest, by quantitating the frequency of extra copies of each gene. Quantitation of the allele ratio of different genetic identities for targeted genomic loci using multiplexed PCR is also provided by the disclosed methods. These methods can be applied to the detection of CNV for gene(s) of interest in tumor samples, guiding the choice of targeted therapy, and helping the understanding of cancer formation and progression.
Current standard method for prenatal diagnosis of monogenic diseases is to sequence the fetal genetic material obtained from invasive and risky chorionic villus sampling or amniocentesis. Genetic noninvasive prenatal testing (NIPT) of monogenic disease is based on the circulation of fetal-derived cell-free DNA (cfDNA) in maternal plasma. Due to the presence of background maternal DNA, it becomes challenging to confidently detect the allele ratio change arising from fetal cfDNA, especially when the maternal DNA is heterozygous at the locus of interest. Droplet digital PCR (ddPCR) has been used to quantify the allele ratio between mutant alleles carrying disease-causing mutations and wild type alleles for NIPT (Lun et al., 2008), but the practical feasibility is limited by precision and reliability of the technology. QASeq enables absolute quantitation of DNA molecule by adding unique molecular identifier to each strand of original input molecules, and can be applied to allele ratio quantitation for NIPT. As such, QASeq can also be used for allele ratio quantitation. Allele ratio quantitation aims to quantify the ratio of DNA molecules with different genetic identities. Accurate allele ratio quantitation is key to NIPT of monogenic diseases, such as β-thalassemia and cystic fibrosis.
The frequency of extra copies (FEC) of a CNV in a genomic DNA sample is defined herein as:
A positive value of FEC indicates amplification of the target genomic region in the sample, and a negative value of FEC indicates deletion of the target genomic region in the sample.
While QASeq can be used to quantitate FEC, it does not provide information on the percentage of cells containing CNV in the tumor tissue sample. For example, if 1% of cells in a tumor sample contain 4 copies of ERBB2, and the rest 99% of cells contain 2 copies, the FEC is 1%; if 0.5% of cells in the sample contain 6 copies of ERBB2, and the rest 99.5% of cells contain 2 copies, the FEC is still 1%. Additionally, QASeq does not provide information on the genomic locations of the extra copies.
In a QASeq multiplexed PCR panel, one target gene needs M (M=1˜1000) sets of primers, each amplifying a non-overlapping small region (40 nt to 500 nt, usually ≤200 nt) in the target gene region. If the panel has multiple target genes, the number of primer sets used for each gene is similar (≈M). The panel also contains a similar number (≈M) of primer sets amplifying reference genomic regions. The reference loci serve as internal standards for the amount of genomic DNA (gDNA) loaded, so that accurate quantitation of DNA concentration in the sample is not needed. At least one reference primer set may be used for each panel. Because increasing the number of input molecules or loci in the target gene can both decrease variations in random sampling, a greater number of primer sets per gene can be used to improve the LoD for sample types containing smaller amounts of DNA; the number of reference primer sets needs to be increased proportionally in this case.
Each primer set contains three different oligos: a Specific Forward Primer (SfP), a Specific Reverse Primer A (SrPA), and a Specific Reverse Primer B (SrPB) (see
When designing primers, single nucleotide polymorphisms (SNPs) with significant minor allele frequency (MAF) should be avoided in the primer-binding regions, so that the primers' binding affinities will not likely be affected by nucleotide sequence variations in different patient samples. In addition, whole human genome nucleotide sequences should be searched to ensure that the primers are not prone to nonspecific amplification of non-target regions.
In an example panel targeting CNVs of ERBB2 in Formalin-Fixed Paraffin-Embedded (FFPE) specimen of tumor samples, 10 sets of primers, each amplifying a 60 to 70 nt amplicon, were designed in the ERBB2 gene region. In addition, 10 sets of reference primers were designed, each amplifying a region in a different housekeeping gene from different chromosomes (Table 1). Primers were designed automatically using a Matlab code to satisfy the above-mentioned design principles while minimize primer interactions. In addition, non-pathogenic SNPs with >0.2% MAF in the population were avoided. Online tool Primer-BLAST was used to ensure that each primer set only has one amplicon in the human genome. Primer sequences are shown in Table 2.
In the NGS library preparation process, PCR amplification steps can significantly increase the quantitation variation, making it difficult to differentiate small changes in original molecule number. UMI technology may be used to reduce PCR bias and achieve absolute quantitation of original DNA molecules. The concept of UMI is to give every original DNA molecule a different DNA sequence as a “barcode,” so that the origin of each NGS read can be tracked based on the barcode sequence. Given enough NGS reads, the number of unique UMIs found in the NGS output can reflect the number of original DNA molecules. Previously, UMI technology was mostly used for error correction in NGS-based detection of low-frequency mutations; it has also been applied to quantitation. Labeling each original molecule uniquely is achieved by using a large number of different UMI sequences; for example, using 109 different UMI sequences for 100,000 original molecules will generate <0.006% molecules carrying repeated UMIs.
DNA sequences containing degenerate bases, such as poly(N) (i.e., a mix of A, T, C, or G at each position), are often used as UMI sequences. In QASeq, poly(H) (A, T, or C) is used as the UMI because it has weaker cross-binding energy compared to poly(N) or a mix of S (C or G) and W (A or T) bases, as indicated by simulation (
PCR efficiency varies for amplicons with different sequences. Because UMIs consist of many different sequences, a spacer between the primer and the variable UMI region may be used to achieve more uniform PCR efficiency.
NGS was carried out to evaluate the influence of spacer on PCR bias (
UMI family size distribution was compared to evaluate the significance of spacers on PCR bias (
A schematic of the QASeq NGS library preparation workflow is shown in
All types of DNA polymerases and PCR supermixes can be used. The standard annealing, extension, and denaturation temperature for the specific polymerase used should be followed (except for the universal PCR step, in which the annealing temperature is raised).
The workflow may be performed using SW and SrPB to add UMIs using two cycles of PCR, and then directly adding index primers for index PCR. To test this, twenty sets of SW and SrPB were used in the same reaction. The experimental on-target rate of this method is very low (0.5%), and thus this method may not be useful in an NGS assay for diagnostics (
The primary workflow includes a final index PCR step to add index sequences and the sequencer's P5/P7 sequences to the ends of the amplicon; however, there are alternative workflows that add the abovementioned sequences during UMI addition, universal PCR, or adapter replacement steps, and thus do not require the index PCR step.
An alternative QASeq primer design and workflow is shown in
A schematic of the data analysis workflow for CNV detection is shown in
Then, all the reads aligned to the same locus are further divided by the UMI sequences, i.e., reads carrying the same UMI are grouped as one UMI family UMI family size is the number of reads carrying the same UMI, and unique UMI number is the total count of different UMI sequences at one locus (
FEC of a target gene may be calculated as:
where Σi=1u NTar,i is the sum of unique UMI number for all or part of the target gene loci, u is the number of loci to consider, u is no more than the total number of loci in the target gene; Σj=1w Σi=1v NRef,i,j is the sum of unique UMI number for all or part of Reference loci, v is the number of loci to consider for one reference, v is no more than the total number of loci in the reference; w is the number of reference to consider, w is no more than the total number of reference; and k is determined by experimental calibration. Before testing the QASeq panel on a clinical sample, calibration experiments were performed on DNA samples with well-characterized CNV status of the target gene. gDNA extracted from normal and cancer cell lines with CNV status characterized by ddPCR can be used for calibration. The FEC of normal calibration samples should be 0. The LoD of the assay is also determined by the calibration experiments; LoD is the smallest frequency of extra copies detectable by the assay. When testing a clinical sample, the FEC for a gene of interest will be used to infer the CNV status; if FEC>LoD, the sample is inferred to contain amplification of the target gene; if FEC≤LoD, the sample is inferred to contain deletion of the target gene.
QASeq can be applied to quantifying the allele ratio of different genetic identities for 1-10,000 genomic loci using multiplexed PCR. The multiplexed PCR panel design for targeted genomic loci, and the experimental workflow for labeling each strand of targeted genomic loci with an oligonucleotide barcode sequence by PCR, followed by amplification of the genomic regions for high-throughput sequencing are similar to CNV detection.
A schematic of data analysis workflow for allele ratio quantitation is shown in
The genetic identity (wild type or mutation) for each remaining UMI family is called based on majority vote; the genetic identity needs to be supported by at least 70% of the members (reads) in the same UMI family. As an example in
Next, the unique UMI number N (the total count of different UMI sequences at one locus) is counted for each different genetic identity at the targeted locus; N indicates the number of original strands. Allele ratio of a target locus is calculated as Rallele=N1/N2, where N1 is unique UMI number for the first genetic identity, and N2 is unique UMI number for the second genetic identity.
“Amplification,” as used herein, refers to any in vitro process for increasing the number of copies of a nucleotide sequence or sequences. Nucleic acid amplification results in the incorporation of nucleotides into DNA or RNA. As used herein, one amplification reaction may consist of many rounds of DNA replication. For example, one PCR reaction may consist of 30-100 “cycles” of denaturation and replication.
“Polymerase chain reaction,” or “PCR,” means a reaction for the in vitro amplification of specific DNA sequences by the simultaneous primer extension of complementary strands of DNA. In other words, PCR is a reaction for making multiple copies or replicates of a target nucleic acid flanked by primer binding sites, such reaction comprising one or more repetitions of the following steps: (i) denaturing the target nucleic acid, (ii) annealing primers to the primer binding sites, and (iii) extending the primers by a nucleic acid polymerase in the presence of nucleoside triphosphates. Usually, the reaction is cycled through different temperatures optimized for each step in a thermal cycler instrument. Particular temperatures, durations at each step, and rates of change between steps depend on many factors well-known to those of ordinary skill in the art, e.g., exemplified by the references: McPherson et al., editors, PCR: A Practical Approach and PCR2: A Practical Approach (IRL Press, Oxford, 1991 and 1995, respectively).
“Primer” means an oligonucleotide, either natural or synthetic that is capable, upon forming a duplex with a polynucleotide template, of acting as a point of initiation of nucleic acid synthesis and being extended from its 3′ end along the template so that an extended duplex is formed. The sequence of nucleotides added during the extension process is determined by the sequence of the template polynucleotide. Usually primers are extended by a DNA polymerase. Primers are generally of a length compatible with its use in synthesis of primer extension products, and are usually are in the range of between 8 to 100 nucleotides in length, such as 10 to 75, 15 to 60, 15 to 40, 18 to 30, 20 to 40, 21 to 50, 22 to 45, 25 to 40, and so on, more typically in the range of between 18-40, 20-35, 21-30 nucleotides long, and any length between the stated ranges. Typical primers can be in the range of between 10-50 nucleotides long, such as 15-45, 18-40, 20-30, 21-25 and so on, and any length between the stated ranges. In some embodiments, the primers are usually not more than about 10, 12, 15, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 35, 40, 45, 50, 55, 60, 65, or 70 nucleotides in length.
“Incorporating,” as used herein, means becoming part of a nucleic acid polymer.
The term “in the absence of exogenous manipulation” as used herein refers to there being modification of a nucleic acid molecule without changing the solution in which the nucleic acid molecule is being modified. In specific embodiments, it occurs in the absence of the hand of man or in the absence of a machine that changes solution conditions, which may also be referred to as buffer conditions. However, changes in temperature may occur during the modification.
A “nucleoside” is a base-sugar combination, i.e., a nucleotide lacking a phosphate. It is recognized in the art that there is a certain inter-changeability in usage of the terms nucleoside and nucleotide. For example, the nucleotide deoxyuridine triphosphate, dUTP, is a deoxyribonucleoside triphosphate. After incorporation into DNA, it serves as a DNA monomer, formally being deoxyuridylate, i.e., dUMP or deoxyuridine monophosphate. One may say that one incorporates dUTP into DNA even though there is no dUTP moiety in the resultant DNA. Similarly, one may say that one incorporates deoxyuridine into DNA even though that is only a part of the substrate molecule.
“Nucleotide,” as used herein, is a term of art that refers to a base-sugar-phosphate combination. Nucleotides are the monomeric units of nucleic acid polymers, i.e., of DNA and RNA. The term includes ribonucleotide triphosphates, such as rATP, rCTP, rGTP, or rUTP, and deoxyribonucleotide triphosphates, such as dATP, dCTP, dUTP, dGTP, or dTTP.
The term “nucleic acid” or “polynucleotide” will generally refer to at least one molecule or strand of DNA, RNA, DNA-RNA chimera or a derivative or analog thereof, comprising at least one nucleobase, such as, for example, a naturally occurring purine or pyrimidine base found in DNA (e.g., adenine “A,” guanine “G,” thymine “T” and cytosine “C”) or RNA (e.g. A, G, uracil “U” and C). The term “nucleic acid” encompasses the terms “oligonucleotide” and “polynucleotide.” “Oligonucleotide,” as used herein, refers collectively and interchangeably to two terms of art, “oligonucleotide” and “polynucleotide.” Note that although oligonucleotide and polynucleotide are distinct terms of art, there is no exact dividing line between them and they are used interchangeably herein. The term “adaptor” may also be used interchangeably with the terms “oligonucleotide” and “polynucleotide.” In addition, the term “adaptor” can indicate a linear adaptor (either single stranded or double stranded) or a stem-loop adaptor. These definitions generally refer to at least one single-stranded molecule, but in specific embodiments will also encompass at least one additional strand that is partially, substantially, or fully complementary to at least one single-stranded molecule. Thus, a nucleic acid may encompass at least one double-stranded molecule or at least one triple-stranded molecule that comprises one or more complementary strand(s) or “complement(s)” of a particular sequence comprising a strand of the molecule. As used herein, a single stranded nucleic acid may be denoted by the prefix “ss,” a double-stranded nucleic acid by the prefix “ds,” and a triple stranded nucleic acid by the prefix “ts.”
A “nucleic acid molecule” or “nucleic acid target molecule” refers to any single-stranded or double-stranded nucleic acid molecule including standard canonical bases, hypermodified bases, non-natural bases, or any combination of the bases thereof. For example and without limitation, the nucleic acid molecule contains the four canonical DNA bases—adenine, cytosine, guanine, and thymine, and/or the four canonical RNA bases—adenine, cytosine, guanine, and uracil. Uracil can be substituted for thymine when the nucleoside contains a 2′-deoxyribose group. The nucleic acid molecule can be transformed from RNA into DNA and from DNA into RNA. For example, and without limitation, mRNA can be created into complementary DNA (cDNA) using reverse transcriptase and DNA can be created into RNA using RNA polymerase. A nucleic acid molecule can be of biological or synthetic origin. Examples of nucleic acid molecules include genomic DNA, cDNA, RNA, a DNA/RNA hybrid, amplified DNA, a pre-existing nucleic acid library, etc. A nucleic acid may be obtained from a human sample, such as blood, serum, plasma, cerebrospinal fluid, cheek scrapings, biopsy, semen, urine, feces, saliva, sweat, etc. A nucleic acid molecule may be subjected to various treatments, such as repair treatments and fragmenting treatments. Fragmenting treatments include mechanical, sonic, and hydrodynamic shearing. Repair treatments include nick repair via extension and/or ligation, polishing to create blunt ends, removal of damaged bases, such as deaminated, derivatized, abasic, or crosslinked nucleotides, etc. A nucleic acid molecule of interest may also be subjected to chemical modification (e.g., bisulfite conversion, methylation/demethylation), extension, amplification (e.g., PCR, isothermal, etc.), etc.
Nucleic acid(s) that are “complementary” or “complement(s)” are those that are capable of base-pairing according to the standard Watson-Crick, Hoogsteen or reverse Hoogsteen binding complementarity rules. As used herein, the term “complementary” or “complement(s)” may refer to nucleic acid(s) that are substantially complementary, as may be assessed by the same nucleotide comparison set forth above. The term “substantially complementary” may refer to a nucleic acid comprising at least one sequence of consecutive nucleobases, or semiconsecutive nucleobases if one or more nucleobase moieties are not present in the molecule, are capable of hybridizing to at least one nucleic acid strand or duplex even if less than all nucleobases do not base pair with a counterpart nucleobase. In certain embodiments, a “substantially complementary” nucleic acid contains at least one sequence in which about 70%, about 71%, about 72%, about 73%, about 74%, about 75%, about 76%, about 77%, about 77%, about 78%, about 79%, about 80%, about 81%, about 82%, about 83%, about 84%, about 85%, about 86%, about 87%, about 88%, about 89%, about 90%, about 91%, about 92%, about 93%, about 94%, about 95%, about 96%, about 97%, about 98%, about 99%, to about 100%, and any range therein, of the nucleobase sequence is capable of base-pairing with at least one single or double-stranded nucleic acid molecule during hybridization. In certain embodiments, the term “substantially complementary” refers to at least one nucleic acid that may hybridize to at least one nucleic acid strand or duplex in stringent conditions. In certain embodiments, a “partially complementary” nucleic acid comprises at least one sequence that may hybridize in low stringency conditions to at least one single or double-stranded nucleic acid, or contains at least one sequence in which less than about 70% of the nucleobase sequence is capable of base-pairing with at least one single or double-stranded nucleic acid molecule during hybridization.
The term “non-complementary” refers to nucleic acid sequence that lacks the ability to form at least one Watson-Crick base pair through specific hydrogen bonds.
The term “degenerate” as used herein refers to a nucleotide or series of nucleotides wherein the identity can be selected from a variety of choices of nucleotides, as opposed to a defined sequence. In specific embodiments, there can be a choice from two or more different nucleotides. In further specific embodiments, the selection of a nucleotide at one particular position comprises selection from only purines, only pyrimidines, or from non-pairing purines and pyrimidines.
“Sample” means a material obtained or isolated from a fresh or preserved biological sample or synthetically-created source that contains nucleic acids of interest. Samples can include at least one cell, fetal cell, cell culture, tissue specimen, blood, serum, plasma, saliva, urine, tear, vaginal secretion, sweat, lymph fluid, cerebrospinal fluid, mucosa secretion, peritoneal fluid, ascites fluid, fecal matter, body exudates, umbilical cord blood, chorionic villi, amniotic fluid, embryonic tissue, multicellular embryo, lysate, extract, solution, or reaction mixture suspected of containing immune nucleic acids of interest. Samples can also include non-human sources, such as non-human primates, rodents and other mammals, other animals, plants, fungi, bacteria, and viruses.
As used herein in relation to a nucleotide sequence, “substantially known” refers to having sufficient sequence information in order to permit preparation of a nucleic acid molecule, including its amplification. This will typically be about 100%, although in some embodiments some portion of an adaptor sequence is random or degenerate. Thus, in specific embodiments, substantially known refers to about 50% to about 100%, about 60% to about 100%, about 70% to about 100%, about 80% to about 100%, about 90% to about 100%, about 95% to about 100%, about 97% to about 100%, about 98% to about 100%, or about 99% to about 100%.
A. Amplification of DNA
A number of template-dependent processes are available to amplify the nucleic acids present in a given template sample. One of the best known amplification methods is the polymerase chain reaction (referred to as PCR™) which is described in detail in U.S. Pat. Nos. 4,683,195, 4,683,202, and 4,800,159 and in Innis et al., 1990, each of which is incorporated herein by reference in their entirety. Briefly, two synthetic oligonucleotide primers, which are complementary to two regions of the template DNA (one for each strand) to be amplified, are added to the template DNA (that need not be pure), in the presence of excess deoxynucleotides (dNTP's) and a thermostable polymerase, such as, for example, Taq (Thermus aquaticus) DNA polymerase. In a series (typically 30-35) of temperature cycles, the target DNA is repeatedly denatured (around 90° C.), annealed to the primers (typically at 50-60° C.) and a daughter strand extended from the primers (72° C.). As the daughter strands are created they act as templates in subsequent cycles. Thus, the template region between the two primers is amplified exponentially, rather than linearly.
B. Sequencing of DNA
Methods are also provided for the sequencing of the library of adaptor-linked fragments. Any technique for sequencing nucleic acids known to those skilled in the art can be used in the methods of the present disclosure. DNA sequencing techniques include classic dideoxy sequencing reactions (Sanger method) using labeled terminators or primers and gel separation in slab or capillary, sequencing-by-synthesis using reversibly terminated labeled nucleotides, pyrosequencing, 454 sequencing, allele specific hybridization to a library of labeled oligonucleotide probes, sequencing-by-synthesis using allele specific hybridization to a library of labeled clones that is followed by ligation, real time monitoring of the incorporation of labeled nucleotides during a polymerization step, and SOLiD sequencing.
The nucleic acid library may be generated with an approach compatible with Illumina sequencing such as a Nextera™ DNA sample prep kit, and additional approaches for generating Illumina next-generation sequencing library preparation are described, e.g., in Oyola et al. (2012). In other embodiments, a nucleic acid library is generated with a method compatible with a SOLiD™ or Ion Torrent sequencing method (e.g., a SOLiD® Fragment Library Construction Kit, a SOLiD® Mate-Paired Library Construction Kit, SOLiD® ChIP-Seq Kit, a SOLiD® Total RNA-Seq Kit, a SOLiD® SAGE™ Kit, a Ambion® RNA-Seq Library Construction Kit, etc.). Additional methods for next-generation sequencing methods, including various methods for library construction that may be used with embodiments of the present invention are described, e.g., in Pareek (2011) and Thudi (2012).
In particular aspects, the sequencing technologies used in the methods of the present disclosure include the HiSeg™ system (e.g., HiSeg™ 2000 and HiSeg™ 1000), the NextSeg™ 500, and the MiSeg™ system from Illumina, Inc. The HiSeg™ system is based on massively parallel sequencing of millions of fragments using attachment of randomly fragmented genomic DNA to a planar, optically transparent surface and solid phase amplification to create a high density sequencing flow cell with millions of clusters, each containing about 1,000 copies of template per sq. cm. These templates are sequenced using four-color DNA sequencing-by-synthesis technology. The MiSeg™ system uses TruSeq™, Illumina's reversible terminator-based sequencing-by-synthesis.
Another example of a DNA sequencing technique that can be used in the methods of the present disclosure is 454 sequencing (Roche) (Margulies et al., 2005). 454 sequencing involves two steps. In the first step, DNA is sheared into fragments of approximately 300-800 base pairs, and the fragments are blunt ended. Oligonucleotide adaptors are then ligated to the ends of the fragments. The adaptors serve as primers for amplification and sequencing of the fragments. The fragments can be attached to DNA capture beads, e.g., streptavidin-coated beads using, e.g., Adaptor B, which contains 5′-biotin tag. The fragments attached to the beads are PCR amplified within droplets of an oil-water emulsion. The result is multiple copies of clonally amplified DNA fragments on each bead. In the second step, the beads are captured in wells (pico-liter sized). Pyrosequencing is performed on each DNA fragment in parallel. Addition of one or more nucleotides generates a light signal that is recorded by a CCD camera in a sequencing instrument. The signal strength is proportional to the number of nucleotides incorporated.
Another example of a DNA sequencing technique that can be used in the methods of the present disclosure is SOLiD technology (Life Technologies, Inc.). In SOLiD sequencing, genomic DNA is sheared into fragments, and adaptors are attached to the 5′ and 3′ ends of the fragments to generate a fragment library. Alternatively, internal adaptors can be introduced by ligating adaptors to the 5′ and 3′ ends of the fragments, circularizing the fragments, digesting the circularized fragment to generate an internal adaptor, and attaching adaptors to the 5′ and 3′ ends of the resulting fragments to generate a mate-paired library. Next, clonal bead populations are prepared in microreactors containing beads, primers, template, and PCR components. Following PCR, the templates are denatured and beads are enriched to separate the beads with extended templates. Templates on the selected beads are subjected to a 3′ modification that permits bonding to a glass slide.
Another example of a DNA sequencing technique that can be used in the methods of the present disclosure is the IonTorrent system (Life Technologies, Inc.). Ion Torrent uses a high-density array of micro-machined wells to perform this biochemical process in a massively parallel way. Each well holds a different DNA template. Beneath the wells is an ion-sensitive layer and beneath that a proprietary Ion sensor. If a nucleotide, for example a C, is added to a DNA template and is then incorporated into a strand of DNA, a hydrogen ion will be released. The charge from that ion will change the pH of the solution, which can be detected by the proprietary ion sensor. The sequencer will call the base, going directly from chemical information to digital information. The Ion Personal Genome Machine (PGM™) sequencer then sequentially floods the chip with one nucleotide after another. If the next nucleotide that floods the chip is not a match, no voltage change will be recorded and no base will be called. If there are two identical bases on the DNA strand, the voltage will be double, and the chip will record two identical bases called. Because this is direct detection—no scanning, no cameras, no light—each nucleotide incorporation is recorded in seconds.
Another example of a sequencing technology that can be used in the methods of the present disclosure includes the single molecule, real-time (SMRT™) technology of Pacific Biosciences. In SMRT™, each of the four DNA bases is attached to one of four different fluorescent dyes. These dyes are phospholinked. A single DNA polymerase is immobilized with a single molecule of template single stranded DNA at the bottom of a zero-mode waveguide (ZMW). A ZMW is a confinement structure which enables observation of incorporation of a single nucleotide by DNA polymerase against the background of fluorescent nucleotides that rapidly diffuse in and out of the ZMW (in microseconds). It takes several milliseconds to incorporate a nucleotide into a growing strand. During this time, the fluorescent label is excited and produces a fluorescent signal, and the fluorescent tag is cleaved off. Detection of the corresponding fluorescence of the dye indicates which base was incorporated. The process is repeated.
A further sequencing platform includes the CGA Platform (Complete Genomics). The CGA technology is based on preparation of circular DNA libraries and rolling circle amplification (RCA) to generate DNA nanoballs that are arrayed on a solid support (Drmanac et al. 2009). Complete genomics' CGA Platform uses a novel strategy called combinatorial probe anchor ligation (cPAL) for sequencing. The process begins by hybridization between an anchor molecule and one of the unique adapters. Four degenerate 9-mer oligonucleotides are labeled with specific fluorophores that correspond to a specific nucleotide (A, C, G, or T) in the first position of the probe. Sequence determination occurs in a reaction where the correct matching probe is hybridized to a template and ligated to the anchor using T4 DNA ligase. After imaging of the ligated products, the ligated anchor-probe molecules are denatured. The process of hybridization, ligation, imaging, and denaturing is repeated five times using new sets of fluorescently labeled 9-mer probes that contain known bases at the n+1, n+2, n+3, and n+4 positions.
The technology herein includes kits for analyzing copy number variation or allele frequencies in a DNA sample. A “kit” refers to a combination of physical elements. For example, a kit may include, for example, one or more components such as nucleic acid primers, enzymes, reaction buffers, an instruction sheet, and other elements useful to practice the technology described herein. These physical elements can be arranged in any way suitable for carrying out the invention.
The components of the kits may be packaged either in aqueous media or in lyophilized form. The container means of the kits will generally include at least one vial, test tube, flask, bottle, syringe or other container means, into which a component may be placed, and preferably, suitably aliquoted (e.g., aliquoted into the wells of a microtiter plate). Where there is more than one component in the kit, the kit also will generally contain a second, third or other additional container into which the additional components may be separately placed. However, various combinations of components may be comprised in a single vial. The kits of the present invention also will typically include a means for containing the nucleic acids, and any other reagent containers in close confinement for commercial sale. Such containers may include injection or blow molded plastic containers into which the desired vials are retained. A kit will also include instructions for employing the kit components as well the use of any other reagent not included in the kit. Instructions may include variations that can be implemented.
The following examples are included to demonstrate preferred embodiments of the invention. It should be appreciated by those of skill in the art that the techniques disclosed in the examples which follow represent techniques discovered by the inventor to function well in the practice of the invention, and thus can be considered to constitute preferred modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention.
An exemplary calibration experiment of the ERBB2 QASeq panel was performed on a normal cell line gDNA sample NA18562, which should not contain ERBB2 amplifications, to analyze the quantitation variability and potential LoD. The workflow was as described in the “QASeq Workflow” section. Taq polymerase was used in all the PCR steps. Denaturation was performed at 95° C., and annealing/extension was performed at 60° C. (except for the universal PCR step, in which annealing/extension was performed at 68° C.). Because all original molecules with UMIs attached need to be present in the NGS output, 15 reads were reserved for each molecule/UMI. For an input of 2500 haploid genomic copies and a 20-amplicon panel, the total reads needed is about 2×2500×20×15=1,500,000. Note that each of the strands in one DNA duplex carries a different UMI in this workflow, so 2500 haploid genomic copies=5000 molecule number=8.3 ng gDNA. This experiment was performed on an Illumina MiSeq instrument.
Exact string match was used to align NGS reads to the amplicon sequences; the alignment rate was between 50% and 70% for different libraries. Next, the UMI family sizes and unique UMI numbers were analyzed. The distribution of UMI family size peaked at ≈20 for most loci (
In order to estimate the LoD of this assay, libraries were prepared for four different DNA inputs: 75, 250, 750, and 2500 haploid genomic copies; each condition was replicated five times. The CNV ratio of the sample was calculated as described in the “Data Analysis Workflow” section. The standard deviation of CNV ratio (σCNV ratio) across five replicates was used to evaluate quantitation variability; the LoD of the assay can be estimated as 3σCNV ratio. Simulations were also performed to calculate the theoretical σCNV ratio; note that the σCNV ratio and LoD should decrease if the input molecule number increases. The σCNV ratio was higher than the theoretical value (
Two FFPE slides were analyzed using the example ERBB2 panel described in the “Multiplexed PCR Panel Design” section and Example 1. The FFPE slides (purchased from Asterand) were from the same lung cancer tumor, which is not expected to contain ERBB2 CNV. First, DNA was extracted using a QIAamp DNA FFPE Tissue Kit (Qiagen), and >6 μg of DNA per sample was obtained. The libraries were prepared using the same methods as described in Example 1. 8.3 ng extracted DNA was used for each library, which is equivalent to 2500 haploid genomic copies and 5000-molecule input. The number of NGS reads reserved for each library (1,500,000 reads) was the same as 2500 haploid genomic copies input cell line gDNA libraries.
Data analysis was performed using the same methods as described in Example 1. A similar pattern of UMI family size distribution to the cell line gDNA libraries was obtained (
The calculated CNV ratios of the FFPE samples are shown in
A 100-plex QASeq panel was used to quantitate the ploidy of ERBB2 in breast cancer FFPE samples. 50-plex were in the ERBB2 gene region (see Table 3 for primer sequences; primer names have “ERBB2” in them), and 50-plex were in the short arm of Chromosome 17 as the Reference (see Table 3 for primer sequences; primer names have “Ref” in them).
Two previously characterized FFPE DNA samples (1 “normal” sample and 1 “ERBB2 amplified abnormal” sample) were mixed to generate 2.5%, 5%, and 10% ERBB2 FEC samples. The “normal” sample DNA was extracted from a FFPE lung cancer sample (purchased from Asterand), which should not have ERBB2 amplification (FEC=0%); the “ERBB2 amplified abnormal” sample DNA was extracted from a FFPE breast cancer sample (purchased from OriGene), which has a ERBB2 FEC of 78%. The sample input was 8.3 ng DNA per library (quantitated by qPCR). The “normal” sample was tested with 5 replicated NGS libraries prepared separately, each with 8.3 ng DNA input. The experimental normalized FEC values are shown in
Normalized FECsample=(1+FECsample)/(1+FECnormal sample)−1
The FECnormal sample was the average of 5 replicates. The LoD of the CNV panel was estimated as:
FECLoD=3×σnormal sample/(1+FECnormal sample)=0.85%
Here, the σnormal sample was the standard deviation of 5 replicates. CNV was successfully detected in 2.5%, 5%, and 10% ERBB2 FEC samples, because their calculated FEC are outside the 3 standard deviation range (see
The method presented (QASeq) can not only be used for CNV quantitation, but also for NGS error correction and mutation quantitation. In each QASeq amplicon, the region between the 3′ of fP and the 3′ of rPin is the Mutation Detection Region (MDR); any small variations (including base substitutions, deletions, and insertions smaller than 500 bp) in the MDR can be detected with an LoD of 0.1%-0.3%. This is much better than standard non-UMI NGS methods for mutation detection, which has an LoD 1%.
A 179-plex comprehensive panel was developed and tested for both mutation and CNV quantitation in breast cancer samples. Every plex contains 3 primers: fP (a.k.a. SW), rPin (a.k.a SrPB), and rPout (a.k.a. SrPA) as stated in previous sections. 95 primer sets were used solely for CNV quantitation, including 45 in gene ERBB2, and 50 in the short arm of Chromosome 17 as the reference. 5 primer sets in the ERBB2 gene were used for both CNV and mutation quantitation. Another 79 primer sets were used for mutation quantitation only. UfP and UrP were used for universal amplification (see Table 3 for sequences).
CNV quantitation was done the same way as described in previous sections; data processing workflow for mutation quantitation is summarized in
This 179-plex panel was tested on the Multiplex I cfDNA Reference Standard Set from Horizon Discovery. Three replicated NGS libraries of the Wild Type cfDNA Reference Standard and three replicates of the 0.3% cfDNA Reference Standard (created by mixing 0.1% cfDNA Reference Standard and 1% cfDNA Reference Standard) were tested. The sample input was 8.3 ng DNA per library (quantitated by qPCR).
The overall on-target rate was greater than 50% (i.e. >50% of the NGS reads can be aligned to the amplicons) for all the libraries; the conversion rate (i.e., the percentage of input molecules sequenced) has an average of 62%, and 97% of the plexes have >10% conversion rate (see
All of the methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the compositions and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit and scope of the invention. More specifically, it will be apparent that certain agents which are both chemically and physiologically related may be substituted for the agents described herein while the same or similar results would be achieved. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims.
The following references, to the extent that they provide exemplary procedural or other details supplementary to those set forth herein, are specifically incorporated herein by reference.
The present application claims the priority benefit of U.S. provisional application No. 62/788,375, filed Jan. 4, 2019, the entire contents of which is incorporated herein by reference.
This invention was made with government support under Grant No. R01 HG008752 awarded by the National Institutes of Health. The government has certain rights in the invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2020/012089 | 1/2/2020 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62788375 | Jan 2019 | US |
