Patent Application
20230323489
The present invention relates to methods and kits for detecting and sequencing of nucleic acids (e.g., RNA or DNA), particularly to detecting and sequencing of nucleic acids (e.g., RNA or DNA) in samples with low concentrations of nucleic acid or poor quality samples. The present invention also features methods and kits for detecting and sequencing viral RNA of viruses such as but not limited to human immunodeficiency virus (HIV), hepatitis C virus, hepatitis B virus, influenza virus, etc.
In repositories around the world, there are countless medical, veterinary, and museum specimens that would be valuable for the elucidation of the history and evolution of pathogens if (a) the pathogen can be detected and (b) genomic material of the pathogen can be amplified in sufficient length to be of phylogenetic use. For example, there are thousands of serum/plasma samples in storage worldwide from putative AIDS cases that go back to the 1970s and 1980s, and that could elucidate both the epidemiological and evolutionary history of HIV. There are also thousands of samples that pre-date the recognition of AIDS, such as from hepatitis B studies, that can yield valuable data regarding HIV, hepatitis C, and other pathogens.
However, samples like those described above may have a low titer, e.g., the samples are degraded and/or may not be of the pathogen's target tissue. Some samples may have a low functional titer, e.g., there may be nucleic acids in the sample that represent the complete pathogen genome, but because of degradation, there may be no nucleic acids long enough to complete a given PCR reaction, thus giving the sample an effective titer of zero (PCR-negative). Or, a given aliquot of sample nucleic acids used for testing may not contain the target sequence even though the sequence is present in the nucleic acid pool. In some cases, samples may have “cryptic” sequences (e.g., sequences that differ at some sites compared to known strains). For example, particularly with RNA viruses, there may be an issue related to sequence evolution. If one wants to investigate a sample that is 50 years old, and only modern sequences are available for primer design, then any given primer pair designed is only a rough guess as to the actual target sequence. Without wishing to limit the present invention to any theory or mechanism, it is believed that it in cases such as these, a single RT-PCR assay is liable to a miss, and designing around ‘conserved regions’ may also be inadequate. Another issue for samples is the limited quantity of the sample. In some cases, antiquated samples cannot be replicated and are often quite small.
Current or traditional strategies for detecting RNA and/or for phylogenetically viable amplification are discussed herein. qPCR or single-step RT and PCR assays are commercially available for many pathogens. They are designed to amplify a relatively short stretch of conserved sequence and so work well with some, but not all, samples of low functional titer and cryptic sequence. Because of their design, they do not yield helpful phylogenetic data. Conventional RT-PCR (e.g., long-form PCR) can be used for generating phylogenetically valuable data. Attempts are often made to amplify PCR fragments greater than 1000 bp. This method faces problems with poor sample quality since no such long template molecules may survive intact in such samples. Next Generation Sequencing (NGS) can develop long sequences, (often) whole genomes, from highly fractured specimens, and because amplification is not sequence based or has no issues with cryptic sequence. However, there is a minimum RNA titer that can be successfully amplified by NGS library technology (e.g., Ovation RNA Seq FFPE requires 100 to 200 ng RNA, see User Guide of Ovation RNA-Seq FFPE, pg. 8, “Total FFPE-derived RNA input must be in the range of 100 to 200 ng . . . input under 100 ng may result in insufficient yield for analysis.”). There can also be problems with NGS if there is a low pathogen titer amongst a high titer of background (e.g., host) RNA.
Inventors surprisingly discovered methods and systems for detecting RNA and sequencing RNA in a wide range of samples, e.g., samples with low concentrations of nucleic acid, samples with degraded nucleic acid, samples that would not otherwise be amenable to conventional sequencing or RNA detection methods, poor quality samples, high-quality samples in which rare mutations are sought (e.g., drug-resistant clones), formalin-fixed paraffin-embedded (FFPE) samples, blood samples (e.g., serum or plasma samples), etc. For example, despite samples having no quantifiable RNA (thus being unusable according to NGS methods), Inventors were able to detect RNA and sequence RNA in said samples using methods of the present invention.
Briefly, methods of the present invention may use paired, large panels of primers (e.g., primer pools) to amplify many short fragments that overlap between (but not within) each panel. In some embodiments, each panel's amplicon set fills the gaps between those of the opposing panel, thereby providing complete gene or genomic coverage. A preliminary, multiplex amplification step (e.g., a pre-amplification step), amplifies target RNA for all downstream reactions (including but not limited to Sanger sequencing, cloning, and NGS).
Inventors have tried conventional methods for recovering RNA in archival serum, plasma, or FFPE samples. For example, 53 serum samples from putative HIV infected individuals (1978, 1979) were tested with conventional PCR, which failed. RNA from samples was unquantifiable; thus it was not possible to use NGS. Using methods of the present invention, near full-length sequences were generated from 9 samples. The results of this study were published in the leading science journal Nature in 2016 to wide acclaim (Nature 539(7627) . October 2016). Additionally, forty-eight plasma or serum samples from patients displaying AIDS symptoms in Kinshasa in 1983 were serologically HIV-1-positive. Still, no HIV-1 RNA was recoverable using conventional PCR approaches at NIH, and the samples were deemed to be of no value. An initial screening run using methods of the present invention (based on non-overlapping 200 bp PCR fragments) designed to produce approximately 1300 bp of data generated greater than 75% of the sequence target on the first run through in 46 samples (96%). Subsequently, a randomly selected 10 of these samples were subjected to a full panel of primer pools designed to cover the entire HIV coding region. The average yield after a first pass was 79% of the total target sequences (high of 91%, low of 69%). It should be noted that these samples represent a wide variety of HIV subtypes, including heretofore unknown subtypes indicating that this method is quite universal for HIV. These results indicate that it may be possible not only to recover HIV-1 RNA but also to generate near full-length sequences in the vast majority of such samples, even though they may appear to contain no recoverable RNA by previous methods. It should also be noted here that while this process is being done manually, currently available robotics, DNA quantification technology, and automatic sequencing makes this technology highly scalable and automatable. FFPE samples from DRC, circa 1958-1966 were screened using an 8 primer assay (70-110 bp target length). HIV was detected in two samples (DRC60, DRC66). NGS sequencing of DRC66 has generated poor results to date. Approximately 450bp of non-overlapping sequence was generated from DRC60 after extensive efforts using standard methods. Re-screening of the sample pool using methods of the present invention revealed an additional positive result, one of which was PCR-negative using previously applied conventional methods. Moreover, methods of the present invention with 192 primer pairs generated a near full-length sequence from DRC66 (>7000 bp).
The methods of the present invention may be used for a variety of applications. Applications may include but are not limited to: detecting RNA or DNA, detecting viral RNA (e.g., HIV RNA, etc.), detecting the presence (or absence) of a particular RNA or DNA, sequencing RNA or DNA, sequencing of RNA or DNA in a historical or poor quality sample, sequencing a plurality of variants of a particular RNA or DNA, e.g., viral RNA variants within a single sample, including rare, drug-resistant variants, etc. In some embodiments, the methods, systems and kits of the present invention may be used for determining a range of hosts and vectors that may be susceptible to virus infection, the early and ongoing detection of viruses in emerging geographic ranges via rapid RT-PCR and sequencing of human and mosquito samples; bulk screening of travelers; and screening novel sources, for purposes of virus surveillance and tracking, e.g., municipal wastewater; screening protocols allowing for screening of pools samples containing large numbers of individual organisms/mosquitos. Other applications may include but are not limited to: testing or screening whole blood samples (e.g., donated blood), e.g., providing higher sensitivity as compared to traditional methods, being capable of detecting the presence of viruses earlier than serological testing or currently available nucleic acid testing; RNA detection, sequencing, or screening in cases where resources may be limited, since methods such as NGS may be too expensive; clinical diagnostics (e.g., HCV detection); vaccine research (e.g., for testing old, rare samples); kits for sequencing whole genomes; liquid biopsies (e.g., cancer biopsies); FFPE sample testing, etc.
The present invention is not limited to detection and/or sequencing of RNA. For example, the present invention also features methods for detecting and/or sequencing DNA. For example, the pre-amplification step may be used for detecting DNA viruses or other DNA targets.
As used herein, the term “conventional” may refer to Next Generation sequencing (NGS) protocols that typically involve an RT-PCR amplification step of a sizable viral genomic fragment, prior to Next Gen sequencing. A non-limiting example of a conventional method may include fluorometers (e.g., Qubit Fluorometers) or spectrophotometers (e.g,. UV-Vis spectrophotometers; e.g., a Nanodrop).
The present invention features methods for detecting a target nucleic acid (e.g., RNA, DNA) in a sample or methods for sequencing a target nucleic acid (e.g., RNA, DNA) in a sample. In some embodiments, the method comprises subjecting the sample to reverse transcription (RT) using reverse transcriptase and one primer from each of one or more pairs of primers. The method may further comprise subjecting the sample from the previous step to polymerase chain reaction (PCR) amplification using Taq polymerase and the other primer of each of the one or more pairs of primers (e.g., a preamplification step). The method may further comprise subjecting a portion of the sample from the previous step to PCR amplification using Taq polymerase and both of the primers from each of the one or more pairs of primers. The method may further comprise making detectable the amplified product of the PCR amplification (e.g., second PCR amplification with both of the primers from each of the pairs of primers. Detectable amplified products may be indicative of the presence of the target (e.g., RNA, DNA) in the sample.
The methods of the present invention are extremely sensitive and can detect unknown sequences, allowing for characterization of viruses (e.g., HIV) and other pathogens. The methods herein are sensitive enough to detect RNA even in samples without detectable (i.e., non-detectable) RNA.
As used herein, the terms “non-detectable” or “undetectable” may be used interchangeably and refer to a target nucleic acid sequence that is not measurable by conventional (e.g., standard) nucleic acid quantitation/quantification methods (e.g., spectrophotometers and/or fluorometers) or a target nucleic acid sequence that is not observable in conventional (e.g., standard) sequencing reads (e.g., deep-sequencing approaches; e.g., next-generation sequencing (NGS)).
In some embodiments, the present invention features a method of sequencing a target nucleic acid sequence in a sample. The method may comprise a) aliquoting the sample into at least two portions, b) subjecting each sample portion to a polymerase chain reaction (PCR) amplification (e.g., a multiplex PCR reaction) using a thermostable polymerase and one or more primer pairs, and c) sequencing the amplified fragment from (b).
In some embodiments, the present invention may further feature kits for use in a method as described herein. The kit may comprise at least two primer pairs, each pair comprising a first primer and a second primer. In some embodiments, the at least two primer pairs are separated into at least two primer pools such that each primer pool has different primer pairs. The primer pairs in each of the at least two primer pools amplify fragments of the target nucleic acid sequence. Within each primer pool, there are non-overlapping amplified fragments.
In some embodiments, the method may comprise subjecting the sample to reverse transcription using reverse transcriptase and a first primer from each of two or more pairs of primers comprising the first primer and a second primer, wherein the first primers are non-overlapping with respect to each other, and the second primers are non-overlapping with respect to each other. The method may further comprise the sample from the previous step to polymerase chain reaction (PCR) amplification using Taq polymerase and the second primers of each of the pairs of primers. The method may further comprise subjecting a portion of the sample from the previous step to PCR amplification using Taq polymerase and both of the primers from each of the pairs of primers. The method may further comprise sequencing amplified products from the previous step.
The sample may be a sample of low quality. For example, the sample may not have quantifiable nucleic acid (e.g., RNA). In some embodiments, the sample comprises a low concentration of nucleic acid. In some embodiments, the sample comprises a degraded nucleic acid. In some embodiments, the sample has low viral density. In some embodiments, the sample comprises a formalin-fixed paraffin-embedded (FFPE) sample. In some embodiments, the sample comprises serum or plasma.
In some embodiments, the primers have the same annealing temperature or are within 5 degrees of an average annealing temperature. The pairs of primers may each be adapted to amplify a fragment of the target from 60 nt to 300 nt (e.g., 60 to 70 nt, 70 to 80 nt, 80 to 100 nt, 100 to 150 nt, 150 to 200 nt, 200 to 300 nt, etc.) in length. In some embodiments, the fragment of the target from 60 nt to 300 nt in length includes the primer. The pairs of primers may each be adapted to amplify a fragment of the target from 60 nt to 600 nt (e.g., 60 to 70 nt, 70 to 80 nt, 80 to 100 nt, 100 to 150 nt, 150 to 200 nt, 200 to 300 nt, 300 to 400 nt, 400 to 500 nt, 500 to 600 nt, etc.) in length. In some embodiments, the fragment of the target from 60 nt to 600 nt in length includes the primer.
In some embodiments, the primers used in the reverse transcription (RT) step are non-overlapping. In some embodiments, the Taq polymerase is proofreading Taq polymerase.
In some embodiments, the target is a Retrovirus, e.g., human immunodeficiency virus (e.g., HIV-1, HIV-2). In some embodiments, the target is a Hepadnavirus (e.g., hepatitis B virus (HBV)). In some embodiments, the target is a Hepacivirus (e.g., hepatitis C virus (HCV)). In some embodiments, the target is a Flavivirus (e.g., yellow fever virus, West Nile virus, dengue fever virus, Zika virus (ZIKV), etc.) In some embodiments, the target is a Filovirus, e.g., an Ebolavirus (e.g., EBOV) or a Marburg virus (MARV). In some embodiments, the target is an Orthomyxovirus, e.g., an influenza virus (e.g., influenza virus A, influenza virus B, influenza virus C). In some embodiments, the target is a Paramyxovirus (e.g., Mumps virus (MuV), measles virus (MeV)). In some embodiments, the target is a Pneumovirus (e.g., a respiratory syncytial virus (RSV)). In some embodiments, the target is a Bunyavirus. In some embodiments, the target is a Togavirus (e.g., rubella virus). The present invention is not limited to the aforementioned targets or viruses since the methods of the present invention may be applied to any appropriate RNA (or DNA) detection application.
In some embodiments, the method further comprises isolating RNA from the sample prior to performing the RT step. In some embodiments, the method further comprises subjecting the sample to DNAse prior to the RT step.
The present invention also features kits for detecting or sequencing a target (e.g., RNA, DNA) in a sample. In some embodiments, the kit comprises two or more pairs of primers, as described herein. For example, the pairs of primers comprise a first primer and a second primer. The pairs of primers may each be adapted to amplify a fragment of the target (e.g., RNA, DNA) from 60 nt to 600 nt (e.g., 60 to 70 nt, 70 to 80 nt, 80 to 100 nt, 100 to 150 nt, 150 to 200 nt, 200 to 300 nt, 300 to 400 nt, 400 to 500 nt, 500 to 600 nt, etc.). The first primers may be non-overlapping with respect to each other, and the second primers may be non-overlapping with respect to each other. The kit may further comprise reverse transcriptase. The kit may further comprise Taq polymerase. The kit may comprise 2 or more, 3 or more, 4 or more, 5 or more, 6 or more, 7 or more, 8 or more, 9 or more, 10 or more, 20 or more, 30 or more, 40 or more, 50 or more, 100 or more, etc., pairs of primers.
Any feature or combination of features described herein are included within the scope of the present invention provided that the features included in any such combination are not mutually inconsistent as will be apparent from the context, this specification, and the knowledge of one of ordinary skill in the art. Additional advantages and aspects of the present invention are apparent in the following detailed description and claims.
The features and advantages of the present invention will become apparent from a consideration of the following detailed description presented in connection with the accompanying drawings in which:
For purposes of summarizing the disclosure, certain aspects, advantages, and novel features of the disclosure are described herein. It is to be understood that not necessarily all such advantages may be achieved in accordance with any particular embodiments of the disclosure. Thus, the disclosure may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein.
Additionally, although embodiments of the disclosure have been described in detail, certain variations and modifications will be apparent to those skilled in the art, including embodiments that do not provide all the features and benefits described herein. It will be understood by those skilled in the art that the present disclosure extends beyond the specifically disclosed embodiments to other alternative or additional embodiments and/or uses and obvious modifications and equivalents thereof. Moreover, while a number of variations have been shown and described in varying detail, other modifications, which are within the scope of the present disclosure, will be readily apparent to those of skill in the art based upon this disclosure. It is also contemplated that various combinations or sub-combinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the present disclosure. Accordingly, it should be understood that various features and aspects of the disclosed embodiments can be combined with or substituted for one another in order to form varying modes of the present disclosure. Thus, it is intended that the scope of the present disclosure herein disclosed should not be limited by the particular disclosed embodiments described herein.
As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Furthermore, to the extent that the terms “including,” “includes,” “having,” “has,” “with,” or variants thereof are used in either the detailed description and/or the claims, such terms are intended to be inclusive in a manner similar to the term “comprising.”
Referring now to
Methods of the present invention may be used for the detection and phylogenetically relevant amplification of pathogens (e.g., RNA viruses) for which sequence data can only be guessed and are difficult, fractured, and low titer samples. For example, when attempting to detect and amplify sequences from, for example, fifty-year-old HIV samples, modern sequences can be of only limited use in designing primers.
The present invention features a method of sequencing a target nucleic acid sequence in a sample. The method may comprise a) aliquoting the sample into at least two portions, b) subjecting each sample portion to a polymerase chain reaction (PCR) amplification (e.g., a multiplex PCR reaction) using a thermostable polymerase and one or more primer pairs, and c) sequencing the amplified fragment from (b).
In some embodiments, the present invention features a method of sequencing a target nucleic acid sequence in a sample. The method may comprise a) aliquoting the sample into at least two portions, b) subjecting each sample portion to a multiplex polymerase chain reaction (PCR) amplification using a thermostable polymerase and one or more primer pairs, and c) subjecting each sample portion in b) to PCR amplification (e.g., a multiplex PCR reaction) using the thermostable polymerase and one or more primer pairs; and d) sequencing the amplified fragment from (c).
In some embodiments, the present invention features a method of sequencing a target nucleic acid sequence in a sample. The method may comprise a) aliquoting the sample into at least two portions, b) subjecting each portion of the sample to a reverse transcription (RT) reaction, c) adding at least one primer (e.g., a first primer; e.g., a reverse primer) from a primer pair to each sample portion, wherein the sample portions have different primer pairs, d) subjecting each sample portion to a multiplex polymerase chain reaction (PCR) amplification using a thermostable polymerase and both primers of the primer pair, e) subjecting each sample portion in (d) to PCR amplification using the thermostable polymerase and the primer pair.
In some embodiments, the method comprises a) aliquoting the sample into at least two portions, b) subjecting each portion of the sample to a reverse transcription (RT) reaction, c) adding at least one primer from a primer pair to each sample portion, wherein the sample portions have different primer pairs, d) subjecting each sample portion to a multiplex polymerase chain reaction (PCR) amplification using a thermostable polymerase and both primers of the primer pair, and e) subjecting each sample portion in (d) to PCR amplification using the thermostable polymerase and the primer pair.
The aforementioned methods may further comprise detecting and sequencing amplified products from the final step.
Each primer pair comprises a first primer and a corresponding second primer. In some embodiments, the first primer comprises a reverse primer, and the second primer comprises a corresponding forward primer.
Each sample portion has different primer pairs (i.e., different sets of primers). In some embodiments, the one or more primer pairs in each sample portion amplify a fragment of the target nucleic acid sequence. Within each sample portion, there are non-overlapping amplified fragments, such that there are gaps between the non-overlapping amplified fragments. In some embodiments, the amplified fragments overlap between each sample portion but not within each sample portion.
Without wishing to limit the present invention to any theory or mechanism, it is believed that the overlapping amplified fragments between each sample portion fill in non-overlapping gaps in the target nucleic acid sequence such that a complete gene or genomic coverage is obtained (
In some embodiments, the methods herein comprise aliquoting the sample into at least three portions. In some embodiments, the methods herein comprise aliquoting the sample into at least four portions. In some embodiments, the methods herein comprise aliquoting the sample into at least five portions. In some embodiments, the methods herein comprise aliquoting the sample into at least ten portions. In some embodiments, the methods herein comprise aliquoting the sample into at least twenty portions. In some embodiments, the methods herein comprise aliquoting the sample into at least fifty portions. In some embodiments, the methods herein comprise aliquoting the sample into at least 100 portions. The present invention is not limited to the aforementioned examples, and more than 100 sample portions may be used in accordance with the present invention.
In some embodiments, the methods herein comprise aliquoting the sample into two portions. In some embodiments, the methods herein comprise aliquoting the sample into three portions. In some embodiments, the methods herein comprise aliquoting the sample into four portions. In some embodiments, the methods herein comprise aliquoting the sample into five portions. In some embodiments, the methods herein comprise aliquoting the sample into ten portions. In some embodiments, the methods herein comprise aliquoting the sample into twenty portions. In some embodiments, the methods herein comprise aliquoting the sample into fifty portions. In some embodiments, the methods herein comprise aliquoting the sample into 100 portions. The present invention is not limited to the aforementioned examples, and more than 100 sample portions may be used in accordance with the present invention.
In some embodiments, the target nucleic acid sequence is a target RNA sequence or a target DNA sequence. If the target nucleic acid sequence is a target RNA sequence, the methods described herein further comprise subjecting each portion of the sample from (a) (e.g., after aliquoting the sample into portions) to a reverse transcription (RT) reaction. In some embodiments, the reverse transcription reaction in each sample portion comprises i) a reverse transcriptase and ii) a primer for reverse transcription of all fragments to be amplified in subsequent PCR amplification(s).
The primer may comprise one or more primers (e.g., a set of primers) for reverse transcription of fragments to be amplified, or a first primer of the one or more primer pairs (e.g., a first primer from each of the one or more primer pairs). In some embodiments, the primer comprises a random primer (e.g., a random hexamer). In some embodiments, the primer for the reverse transcription may comprise both the set of primers and the first primer of the one or more primer pairs.
In some embodiments, the reverse transcription reaction in each sample portion comprises i) a reverse transcriptase and ii) a first primer from each of the one or more primer pairs. In some embodiments, the reverse transcription reaction in each sample portion comprises i) a reverse transcriptase and ii) a random primer (e.g., a random hexamer). In some embodiments, the reverse transcription reaction in each sample portion comprises i) a reverse transcriptase and ii) both a first primer from each of the one or more primer pairs and a random primer.
In some embodiments, if the reverse transcription reaction comprises the first primer of the one or more primer pairs, then the second primer of the primer pair is added to the PCR amplification (e.g., the PCR amplification in step b). In some embodiments, if the reverse transcription reaction does not have the first primer, then both primers of the primer pair are added to the PCR amplification (e.g., the PCR amplification in step b). In some embodiments, if the reverse transcription reaction comprises the random primer (e.g., a random hexamer), then both primers of the primer pair are added to the PCR amplification (e.g., the PCR amplification in step b).
The present invention may also feature a kit for the use in methods described herein. The kit may comprise at least two primer pairs, each pair comprising a first primer and a second primer. The at least two primer pairs are separated into at least two primer pools (e.g., panels of primers) such that each primer pool has different primer pairs. In some embodiments, the primer pairs in each of the at least two primer pools amplify fragments of the target nucleic acid sequence. Within each primer pool, there are non-overlapping amplified fragments. In some embodiments, the amplified fragments overlap between the primer pools (e.g., panels) but not within the primer pools (e.g., panels).
The present invention may also feature a kit for detecting and sequencing a target nucleic acid sequence in a sample. The kit may comprise two or more primer pairs, each pair comprising a first primer and a second primer. The at least two primer pairs are separated into at least two primer pools (e.g., a panel of primers) such that each primer pool has different primer pairs. In some embodiments, the primer pairs in each of the at least two primer pools amplify fragments of the target nucleic acid sequence. Within each primer pool, there are non-overlapping amplified fragments. In some embodiments, the amplified fragments overlap between the primer pools (e.g., panels) but not within the primer pools (e.g., panels). The kit may further comprise a set of instructions (e.g., methods described herein) for amplifying the target nucleic acid sequence in the sample.
In some embodiments, the instructions comprise a) aliquoting the sample into at least two portions, b) subjecting each sample portion to a polymerase chain reaction (PCR) amplification (e.g., a multiplex PCR amplification) using a thermostable polymerase and one or more primer pairs, and optionally subjecting each sample portion in (b) to PCR amplification using the thermostable polymerase and one or more primer pairs. Each sample portion has different primer pairs. In some embodiments, the one or more primer pairs in each sample portion amplify a fragment of the target nucleic acid sequence. The instructions may further comprise detecting or sequencing amplified fragments from either of the PCR amplification steps. In some embodiments, within each sample portion, there are non-overlapping amplified fragments. In some embodiments, the amplified fragments overlap between but not within each sample portion.
The kit may further comprise a reverse transcriptase, a thermostable polymerase, or a combination thereof. In some embodiments, the thermostable polymerase comprises a Taq polymerase.
Methods and kits of the present invention feature using panels of primer pairs (e.g., primer pools). For example, in some embodiments, the methods of the present invention use panels (e.g., primer pools; e.g., eight to ten panels) of primer pairs (e.g., degenerate primers, non-degenerate primers or a combination thereof) for detection (e.g., sequencing) of a target nucleic acid sequence. In some embodiments, the methods of the present invention use panels (e.g., primer pools; e.g., eight to ten panels) of non-degenerate primers (or a mix of degenerate and non-degenerate primers) for detection (e.g., sequencing) of a target nucleic acid sequence.
In some embodiments, the methods and/or kits of the present invention use 50-200 primer pairs (e.g., degenerate, non-degenerate, a combination thereof) for near full-length sequencing. Methods and/or kits of the present invention may also feature a pre-amplification step of RT products so as to increase titer prior to final PCR. This helps allow for adequate sequence yield from some samples that have immeasurably low yields of RNA and/or are highly fractured. Because methods of the present invention may be designed to amplify 1000-1500 bp of sequence from a given aliquot of native RNA, the sample size may be much less a factor than if each PCR fragment was generated from a separate RT reaction. In the case of the 1978 and 1979 serum samples mentioned above, a near full-length sequence could be generated using only 30 μl of 50 μl serum eluate generated from 50-100 μl of serum.
The present invention also features methods and kits for detecting or sequencing genetic variations of a target nucleic acid sequence, e.g., RNA (e.g., variations of the RNA within the same sample), e.g., detecting within-host viral genetic variation with phenotypic consequences (e.g., on drug resistance, pathogenesis, cell/tissue tropism, transmissibility to secondary hosts, etc.). Without wishing to limit the present invention to any theory or mechanism, it is believed that the methods of the present invention may help to detect genetic variations that are not necessarily apparent when large amplicons are generated. For example, variations in primer regions in some clones may prevent them from being amplified. Also, the effective template number of large amplicons may be much smaller than small amplicons (e.g., there may only be one or a few template molecules 1000 nt in length in a degraded sample, whereas there may be more template molecules shorter in length). In the present invention, if several 100 nt regions within that same region are separately assayed, there may be orders of magnitude more template molecules and thus a chance to observe within-patient diversity that may otherwise be invisible when aiming for a larger fragment.
As previously discussed, the methods of the present invention feature targeting several small fragments of the target nucleic acid sequence, e.g., an RNA. For example, in some embodiments, the fragment that is targeted is about 70 nt in length. In some embodiments, the fragment is about 80 nt in length. In some embodiments, the fragment is about 90 nt in length. In some embodiments, the fragment is about 100 nt in length. In some embodiments, the fragment is about 110 nt in length. In some embodiments, the fragment is from 65 to 90 nt in length. In some embodiments, the fragment is from 70 to 100 nt in length. In some embodiments, the fragment is from 70 to 110 nt in length. In some embodiments, the fragment is from 80 to 100 nt in length. In some embodiments, the fragment is from 100 to 200 nt in length. In some embodiments, the fragment is from 70 to 200 nt in length. The present invention is not limited to the aforementioned examples. For example, in some embodiments, the fragment is more than 200 nt in length, e.g., from 200 to 250 nt, from 200 to 300 nt, from 300 to 400 nt, from 400 to 500 nt, etc. Fragment size may depend on the quality of the sample.
In some embodiments, at least two primer pairs are used per primer pool (e.g., panel). In some embodiments, at least three primer pairs are used per primer pool (e.g., panel). In some embodiments, at least four primer pairs are used per primer pool (e.g., panel). In some embodiments, at least five primer pairs are used per primer pool (e.g., panel). In some embodiments, at least six primer pairs are used per primer pool (e.g., panel). In some embodiments, at least seven primer pairs are used per primer pool (e.g., panel). In some embodiments, at least eight primer pairs are used per primer pool (e.g., panel). In some embodiments, at least nine primer pairs are used per primer pool (e.g., panel). In some embodiments, at least ten primer pairs are used per primer pool (e.g., panel). In some embodiments, at least 20 primer pairs are used per primer pool (e.g., panel). In some embodiments, at least 30 primer pairs are used per primer pool (e.g., panel). In some embodiments, at least 40 primer pairs are used per primer pool (e.g., panel). In some embodiments, at least 50 primer pairs are used per primer pool (e.g., panel). In some embodiments, at least 75 primer pairs are used per primer pool (e.g., panel). In some embodiments, at least 100 primer pairs are used per primer pool (e.g., panel). In some embodiments, at least 150 primer pairs are used per primer pool (e.g., panel). In some embodiments, at least 200 primer pairs are used per primer pool (e.g., panel). The present invention is not limited to the aforementioned examples, and more than 200 primer pairs may be used per primer pool (e.g., panel).
In some embodiments, two primer pairs are used per primer pool (e.g., panel). In some embodiments, three primer pairs are used per primer pool (e.g., panel). In some embodiments, four primer pairs are used per primer pool (e.g., panel). In some embodiments, five primer pairs are used per primer pool (e.g., panel). In some embodiments, six primer pairs are used per primer pool (e.g., panel). In some embodiments, seven primer pairs are used per primer pool (e.g., panel). In some embodiments, eight primer pairs are used per primer pool (e.g., panel). In some embodiments, nine primer pairs are used per primer pool (e.g., panel). In some embodiments, ten primer pairs are used per primer pool (e.g., panel). In some embodiments, 11 primer pairs are used per primer pool (e.g., panel). In some embodiments, 12 primer pairs are used per primer pool (e.g., panel). In some embodiments, 13 primer pairs are used per primer pool (e.g., panel). In some embodiments, 14 primer pairs are used per primer pool (e.g., panel). In some embodiments, 15 primer pairs are used per primer pool (e.g., panel). In some embodiments, 16 primer pairs are used per primer pool (e.g., panel). In some embodiments, 17 primer pairs are used per primer pool (e.g., panel). In some embodiments, 18 primer pairs are used per primer pool (e.g., panel). In some embodiments, 19 primer pairs are used per primer pool (e.g., panel). In some embodiments, 20 primer pairs are used per primer pool (e.g., panel). In some embodiments, 21 primer pairs are used per primer pool (e.g., panel). In some embodiments, 22 primer pairs are used per primer pool (e.g., panel). In some embodiments, 23 primer pairs are used per primer pool (e.g., panel). In some embodiments, 24 primer pairs are used per primer pool (e.g., panel). In some embodiments, 25 primer pairs are used per primer pool (e.g., panel). In some embodiments, 26 primer pairs are used per primer pool (e.g., panel). In some embodiments, 27 primer pairs are used per primer pool (e.g., panel). In some embodiments, 28 primer pairs are used per primer pool (e.g., panel). In some embodiments, 29 primer pairs are used per primer pool (e.g., panel). In some embodiments, 30 primer pairs are used per primer pool (e.g., panel). In some embodiments, 40 primer pairs are used per primer pool (e.g., panel). In some embodiments, 50 primer pairs are used per primer pool (e.g., panel). In some embodiments, 100 primer pairs are used per primer pool (e.g., panel). In some embodiments, 200 primer pairs are used per primer pool (e.g., panel). As previously discussed, the present invention is not limited to the aforementioned examples, and more than 200 primer pairs may be used.
The primer pairs may be divided into at least two primer pools. In some embodiments, two primer pools are used. In some embodiments, three primer pools are used. In some embodiments, four primer pools are used. In some embodiments, five primer pools are used. In some embodiments, six primer pools are used. In some embodiments, seven primer pools are used. In some embodiments, eight primer pools are used. In some embodiments, nine primer pools are used. In some embodiments, ten primer pools are used. In some embodiments, more than ten primer pools are used. In some embodiments, primer pools have about ten primers each.
For example, in some embodiments, when attempting to detect the presence of a particular RNA, about 8 to 10 primer pairs may be used. In some embodiments, when attempting to sequence a particular RNA, about 50 primer pairs may be used. However, the present invention is not limited to the aforementioned examples.
In some embodiments, the target nucleic acid sequence is a whole genome. In some embodiments, the target nucleic acid sequence is a viral nucleic acid. In some embodiments, the target nucleic acid sequence is a whole viral genome. In some embodiments, the method and kits described herein detect genetic variations in the viral nucleic acid.
In some embodiments, the target nucleic acid sequence is an RNA sequence, wherein the RNA sequence comprises a sequence from a human immunodeficiency virus (HIV), a hepatitis C virus (HCV), a hepatitis B virus (HBV), an influenza virus, an ebolavirus, or severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).
In some embodiments, the sample may comprise a biological sample or an environmental sample. In some embodiments, the sample comprises a formalin-fixed paraffin-embedded (FFPE) sample, a serum sample, a plasma sample, a nasal sample, an oral sample, a dental sample (e.g., plaque), a throat sample, a gargle sample, a fecal sample, a saliva sample, a tear sample, a sweat sample, a breath sample, a blood sample, a hair sample, a semen sample, a vaginal sample (e.g., a cervicovaginal lavage), a pus sample, a urine sample. In some embodiments, the sample may comprise a tissue sample or an organ sample. In some embodiments, the sample may be collected during a biopsy or an autopsy (e.g., a biopsy sample or an autopsy sample). In some embodiments, the sample may comprise a wastewater sample, a soil sample, an environmental sample, an air sample, or an air filter sample.
As previously discussed, the present invention may help sequence RNAs in historical samples of unknown subtypes, as well as sequence variants of an RNA. Without wishing to limit the present invention to any theory or mechanism, it is believed that the use of multiple, small fragments may be advantageous for sequencing unknown subtypes or RNAs with polymorphisms.
The present invention may also feature an amplified product produced by a method of amplifying a target nucleic acid sequence in a sample, wherein the amplified product comprises a plurality of amplified fragments. The method may comprise a) aliquoting the sample into at least two portions, b) subjecting each sample portion to a polymerase chain reaction (PCR) amplification (e.g., a multiplex PCR reaction) using a thermostable polymerase and one or more primer pairs, and c) sequencing the amplified fragment from (b).
In some embodiments, the method comprises a) aliquoting the sample into at least two portions, b) subjecting each sample portion to a multiplex polymerase chain reaction (PCR) amplification using a thermostable polymerase and both primers of the primer pair (e.g., a pre-amplification reaction), c) subjecting each sample portion in (b) to PCR amplification using the thermostable polymerase and the primer pair. The primers of the primer pair in each sample portion amplify a fragment of the target nucleic acid sequence. Within each sample portion, there are non-overlapping amplified fragments. In some embodiments, within each sample portion, there are non-overlapping amplified fragments. In some embodiments, the amplified fragments overlap between but not within each sample portion
In some embodiments, the method comprises a) aliquoting the sample into at least two portions, b) subjecting each portion of the sample to a reverse transcription (RT) reaction, c) adding at least one primer from a primer pair to each sample portion, wherein the sample portions have different primer pairs, d) subjecting each sample portion to a multiplex polymerase chain reaction (PCR) amplification using a thermostable polymerase and both primers of the primer pair, e) subjecting each sample portion in (d) to PCR amplification using the thermostable polymerase and the primer pair. The primers of the primer pair in each sample portion amplify a fragment of the target nucleic acid sequence. Within each sample portion, there are non-overlapping amplified fragments. In some embodiments, within each sample portion, there are non-overlapping amplified fragments. In some embodiments, the amplified fragments overlap between but not within each sample portion.
Example 1 describes an example of a protocol for plasma/serum samples. The present invention is not limited to the details of Example 1. This example describes a procedure for working up a sample using 40 overlapping primer pairs designed to generate products of approximately 200 bp. This will provide 6000+ bp of sequence. The actual amount of sequence is a function of how much overlap is designed into the primers. For FFPE samples or severely degraded liquid samples, 70-100 bp primer pairs may be designed. High quality proof-reading Taq is used. This protocol uses Promega Goscript and RNAsin plus for RT. Taq is Accustart.
Below shows a non-limiting example of 4 primer pools (A, B, C, D) and each comprises different primer pairs. Each primer pair within a primer pool amplifies non-overlapping fragments; however, the amplified fragments between the 4 primer pools (A, B, C, and D) overlap, such that a whole sequence of a target nucleic acid may be obtained. The following schematic may be used:
Reverse Transcription: For each sample to be amplified, the following may be used: Primer/dNTP: Make up 4 reverse primer/dNTP pools, one for each of A, B, C, D. (1) Primer—9 ul, (2) dNTP—3 ul. Add 4 ul of ‘A’ to wells 1 and 5 of an 8 place strip. Add ‘B’ to wells 2 and 6 and etc. Then add 6 ul sample to each of wells 1-4 and 6 ul control to wells 5-8. Mix well. Incubate at 70 C for 5′. Ice. RT mix: (1) 5× buffer—36 ul; (2) 25 mM Mg—36 ul; (3) RNasin—9 ul; (4) Goscript—9 ul. Add 10 ul per sample, mix well and incubate at 42 C for 2 hours, followed by 10′ at 85 C.
Preliminary amplification: The following may be used: Add 4 ul ‘A’ forward primer pool to wells 1 and 5 of an 8 place strip, and 4 ul of CB' to wells 2 and 6 and etc. Master mix: 10×—45ul; 50 mM Mg—18 ul; dNTP—9 ul; Taq—4 ul; Water—252 ul. 36 ul mix into each well. Add 10 ul individual RT reactions in the appropriate well. Mix well. Amplify for 30 cycles in a standard PCR program at the appropriate annealing temperature (e.g., primers may be designed around 52 degrees C.).
Final amplification: The following may be used: Make up 5×8 well strips with individual primer pairs in numerical order as in the schema below (e.g., 2 ul primer total per well). One may want one set for the sample and one for the control.
Make up 8 Master mixes, four for samples (A, B, C, D) and four for controls (A, B, C, D). Master mix: 10×—27.5 ul; 50 mM Mg—11 ul; dNTP—5.5 ul; Taq—1 ul; Pre-amp product—22 ul; Water—187 ul. Add 23 ul of Sample ‘A’ master mix to primer wells 1 and 5 of each strip, Master mix Sample ‘B’ to wells 2 and 6 and etc. as per schema above. Mix well. Amplify for 40 cycles at appropriate annealing temperature.
In some embodiments, this protocol, e.g., when used in conjunction with appropriately designed primers, may generate 70-90% of the target sequence on the first go through. Note that some products may be double banded with a contaminating human band, so some gel clipping may be required unless going to NGS sequencing. Note that when the first go round is done, there is 10 ul leftover RT reaction for each pool of each sample. This can be used to pre-amp and amp on an alternative cycling program such as a Touchdown program to generate bands that cover some of the blank spots. In some embodiments, this step is done before going to sequencing. Once sequencing is done and the sequences are lined up with the primers, new primers may be designed to match missing sequence. Note also that this protocol may help ensure that no given amplification is exposed to confounding internal primers from the primer pairs immediately upstream or downstream of the amplification. This may help ensure that mis-incorporation of primers doesn't compromise the data.
Methods of the present invention for recovering viral RNA were used test 1970s HIV serum samples (degraded archival samples). Example 2 describes the recovery of eight near-full-length genomes from US serum samples from 1978-79—eight of the nine oldest HIV-1 group M genomes to date. Example 2 also describes recovery of the HIV-1 genome from the individual known as Patient 0′ (Auerbach et al, 1984, Am J Med 76: 487-492) (showing there is neither biological nor historical evidence he was the primary case in the US or for subtype B as a whole).
HIV-1 serological screening of serum samples from San Francisco from 1978. 2231 samples collected from the cohort of gay and bisexual men in San Francisco in 1978 (Jaffe et al., 1985, Ann Intern Med 103: 210-214) were tested, and 83 WB-positives were detected (3.7% prevalence). Samples were first screened by GS HIV-1/HIV-2 Plus O EIA (Bio-Rad Laboratories, Redmond WA) and reactive samples were further tested by WB Genetic Systems HIV-1 Western Blot (Bio-Rad Laboratories, Redmond WA).
HIV-1 nucleic acid amplification. A total of 33 samples of frozen serum previously identified as positive for antibody to HIV-1 (Stevens et al, 1986, JAMA 255: 2167-2172; Szmuness et al, 1981, Hepatology 1: 377; Koblin et al., 1992, J Epidemiology 136:646-656) were assayed from New York City; a total of 20 frozen serum samples from San Francisco (Jaffe et al., 1985, Ann Intern Med 103: 210-214), identified as part of the present study as positive for antibody to HIV-1, were assayed. The New York City samples were from 1978 and 1979 though no complete genomic sequences from 1978 were developed. The San Francisco samples were all from 1978. Additionally, a sample of PMBC and a sample of serum were both assayed; these had been collected from a single individual in 1983 (Patient 0), and the samples were stored at CDC Atlanta. Other than Patient 0, now deceased, the data recorded were unlinked to individual identifiers and the work was approved by the Human Subjects Protection Program at the University of Arizona.
Four panels of degenerate primers were designed using a suite of North American subtype B sequences. Primers were designed to be able to amplify both conserved regions and predictably variable sites. Primers within each panel were designed to generate sequence from the 5′ end of gag to the 3′ end of nef and were designed to amplify overlapping fragments. Two panels “HIVL” (N=25) and “HIVLb” (N=22) were designed to amplify fragments of ˜500-650 bases in length. Two other panels “HIVm” (N=50) and “HIVr” (N=46) were designed to amplify fragments of ˜200-320 bases in length. Nucleic acids from 100 ul aliquots of serum (or PMBCs in the case of Patient 0) were isolated using the QIAamp Viral RNA Mini Kit (Qiagen, Gaithersburg, MD) with 5mcg added carrier RNA. Serum samples were then treated with DNase I (Invitrogen, Life Technologies, Carlsbad, CA) prior to reverse transcription. PMBC nucleic acids were left untreated. Proviral DNA from Patient 0′s PMBCs was amplified with all four primer panels and from multiple separate isolations. Amplification was achieved using Invitrogen Platinum Taq DNA polymerase High Fidelity (Life Technologies, Carlsbad, CA) and run for 55 cycles at an annealing temperature of 52° C. Additionally, attempts were made to amplify longer fragments using PCR SuperMix High Fidelity (Life Technologies, Carlsbad, CA) and forward and reverse primers matched from the HIVLb primer panel for long fragment length followed by nesting with primers for slightly shorter fragment length. A single fragment of slightly more than 7000 bases was generated after multiple attempts with multiple primer combinations and cloned using the Invitrogen TOPO XL PCR Cloning Kit (Life Technologies, Carlsbad, CA). Fragments of individual clones were then amplified using HIVLb forward and reverse primers matched to give approximately 1000-base overlapping fragments and then sequenced.
Methods of the present invention using the serum samples proceeded as follows: Aliquots of isolated RNA were reverse transcribed using the GoScript Reverse Transcription System (Promega, Madison, WI) using a program of 4 cycles of 50° C. for 30′ followed by 55° C. for 30′ and an 85° C. final incubation. Primers used were pools of reverse primers from widely spaced amplicons, abrogating the possibility of incorporation of an internal primer into any given amplicon. RT products were then briefly amplified in multiplex reactions (denaturation for 3′ at 94° C. followed by 30 cycles of 94° C. for 30″, 52° C. for 30″, 68° C. for 30″, and a final extension of 68° C. for 5′) with matching forward primer pools and then amplified via single primer pairs (denaturation for 3′ at 94° C. followed by 40 cycles of 94° C. for 30″, 52° C. for 30″, 68° C. for 30″, and a final extension of 68° C. for 5′). Two separate isolates were amplified from each sample in this manner with a minimum of one amplification with each primer panel per isolate. Sequencing was performed at the University of Arizona Genetics Core using an ABI 3730XL. The Patient 0 sample contained considerable heterogeneity (mixed bases) both in proviral assembly and in viral RNA amplifications. Heterogeneity in the NY and SF samples (all sequences derived from viral RNA) was low. In all cases consensus sequences were used in the phylogenetic analyses.
Example 3 describes the development of viral enrichment and multiplex RT-PCR viral genetic screening assays that are more sensitive than existing RT-PCR protocols for detection of viral RNA. The methods of the present invention could allow recovery of viral genomic information from challenging source material (e.g., specimens with low concentration of template viral RNA, samples containing no viable (culturable) virus, etc.). The methods of the present invention may be useful in conventional samples as well, e.g., for conventional samples in resource-limited settings where culturing of virus may be precluded but RT-PCR may be possible. Without wishing to limit the present invention to any theory or mechanism, it is believed that the methods of the present invention may allow for detection of viral RNA with very high sensitivity (e.g., up to 100% specificity after sequencing). Thus, this may allow for the use of the methods of the present invention in resource-limited settings (e.g., without the need for culturing viral isolates), for detecting viral RNA in low-concentration, damaged or otherwise challenging samples (e.g., pooled mosquito specimens, archival human specimens, or perhaps even municipal influent (e.g., sewage) samples), etc.
In some embodiments, the methods of the present invention feature RNA (or DNA capturing, e.g., for concentration of viral nucleic acids from large pooled samples. This may increase the chances of finding the target sequence and may be effective at sequestering target nucleic acids away from potential inhibitors.
Referring to
This technique allows for HIV detection that is not otherwise detectable using previous techniques (see
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Various modifications of the invention, in addition to those described herein, will be apparent to those skilled in the art from the foregoing description. Such modifications are also intended to fall within the scope of the appended claims. Each reference cited in the present application is incorporated herein by reference in its entirety.
Although there has been shown and described the preferred embodiment of the present invention, it will be readily apparent to those skilled in the art that modifications may be made thereto which do not exceed the scope of the appended claims. Therefore, the scope of the invention is only to be limited by the following claims. Reference numbers recited in the claims are exemplary and for ease of review by the patent office only, and are not limiting in any way. In some embodiments, the figures presented in this patent application are drawn to scale, including the angles, ratios of dimensions, etc. In some embodiments, the figures are representative only and the claims are not limited by the dimensions of the figures. In some embodiments, descriptions of the inventions described herein using the phrase “comprising” includes embodiments that could be described as “consisting of”, and as such the written description requirement for claiming one or more embodiments of the present invention using the phrase “consisting of” is met.
This application is a continuation-in-part and claims benefit of U.S. patent application Ser. No. 16/089,658 filed Sep. 28, 2018, which is a 371 and claims benefit of PCT Application No. PCT/US17/28591 filed Apr. 20, 2017, which claims benefit of U.S. Provisional Application No. 62/325,320 filed Apr. 20, 2016, the specifications of which are incorporated herein in their entirety by reference.
This invention was made with government support under Grant No. RO1 A1084691 awarded by National Institutes of Health. The government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 62325320 | Apr 2016 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 16089658 | Sep 2018 | US |
| Child | 18329152 | US |
