Nucleic acid oligomeric sequences and in vitro nucleic acid amplification and detection methods for detecting the presence of HAV RNA sequences in samples are disclosed. Kits comprising nucleic acid oligomers for amplifying and detecting HAV nucleic acid sequences are disclosed.

Description of the Invention

The present invention includes methods of detecting HAV present in samples. These samples may be biological samples derived from humans (e.g., feces, blood, serum, saliva or urine), environmental samples (e.g., water, soil) or other materials (e.g., foodstuffs) that are potentially contaminated with HAV. A sample includes any liquid that may contain HAV or solid that may contain or have surface HAV. Samples include, for example, those from environmental sources such as water, biological sources such a human fluids or wastes, and food, packaging materials, or other components used in food processing. A biological sample includes any tissue or material derived from a living or dead human which may contain HAV or HAV nucleic acid, including, for example, saliva, blood, plasma, serum, biopsy tissue, gastrointestinal tissue, urine, feces, or other body fluids, tissues or materials. A sample may be treated to physically or mechanically disrupt its physical state to release HAV particles or HAV RNA into an aqueous solution or solvent by using standard methods.

The present invention encompasses nucleic acid compositions, such as oligomers that hybridize specifically to HAV RNA or nucleic acids derived from HAV RNA, e.g., cDNA or amplified sequences made from HAV RNA. One such composition is a capture oligomer used to purify HAV RNA from a complex mixture such as a sample by hybridizing specifically to HAV RNA and attaching the hybridized HAV RNA to a capture support that permits separation of the captured HAV RNA from other sample components. The method of purification that uses such a capture oligomer is generally referred to as target capture, where HAV RNA is the specific target nucleic acid. Another oligomer of the invention is a nucleic acid amplification oligomer (sometimes referred to as a primer). Additional embodiments include probe oligomers that hybridize specifically to HAV RNA or amplified HAV nucleic acid sequences to provide a signal that detects the presence of an HAV specific sequence. These nucleic acid sequences are useful for capturing, amplifying and detecting HAV specific sequences and, thus, function together for detecting the presence of HAV in a sample.

The methods are based on detecting the presence of HAV nucleic acid sequences by amplifying in vitro a region of the HAV genome and detecting the amplified nucleic acid by using a probe that binds specifically to a sequence in the amplified nucleic acid. One embodiment of the method includes a step of isolating or purifying HAV nucleic acid from a sample before the step of amplifying a region of the HAV genome. This embodiment isolates HAV genomic RNA by using a capture oligomer that binds specifically to a sequence in the HAV genome, preferably outside of the region of the HAV genome that is amplified, and separating the complex made up of the capture oligomer and the bound HAV RNA from other sample components by using a capture support, such as a particle to which the capture oligomer also binds. Amplifying a portion of the HAV genomic sequence uses one or more amplification oligomers that bind specifically to HAV RNA or a complementary sequence, and enzymatic synthesis in vitro to make additional copies of a portion of the HAV genomic sequence or a complementary sequence by using the amplification oligomers as primers for synthesis of the additional copies. A preferred embodiment uses an isothermal amplification reaction to make additional copies of a portion of the HAV genomic sequence. The amplified HAV sequence is then detected by specifically binding one or more probe oligomers to the amplified nucleic acid and detecting a signal that results from the probe oligomer bound to the amplified sequence. Detection of a signal resulting from the probe oligomer bound to the amplified HAV sequence indicates the presence of HAV in the sample. These method are useful for detecting the presence of HAV in a variety of samples, such as biological samples used to diagnose a HAV infection in a human, or HAV-contaminated environmental samples to prevent the spread of HAV resulting from use or consumption of the contaminated source. These methods are also useful for testing human fluid samples for the presence of HAV, such as in serum or plasma, to prevent subsequent HAV infections resulting from use of the human fluid in transfusion or for preparation of therapeutic factors. The methods of the present invention are also useful for screening human tissue or organs for the presence of HAV to prevent their use in transplantation therapy. Thus, these methods are especially important for detecting HAV contamination in human samples or products derived from human tissue.

Nucleic acids include DNA or an analog thereof, RNA or an analog thereof, or mixed DNA-RNA polymers or oligomers, made up of at least two, and preferably ten or more bases linked by a backbone structure. DNA and RNA may be made up of the common bases (A, T, G and C for DNA, and A, G, C and U for RNA), although base analogs (e.g., inosine) and abasic positions (i.e., a phosphodiester backbone that lacks a nucleotide at one or more positions, see U.S. Pat. No. 5,585,481) are also included in these terms. Polymers may be many hundreds or thousands of nucleotides long, whereas oligomers generally refer to nucleic acids of 1,000 or fewer linked nucleotides, and often comprise two to about 100 linked nucleotides. Oligomers generally fall in a size range having a lower limit of about 10 bases and an upper limit of about 150 bases, preferably in a size range of about 15 to about 70 bases. Oligomers may be purified from naturally occurring biological sources, but preferably are synthesized in vitro using any of a variety of well-known enzymatic or chemical methods (e.g., Caruthers et al., 1987, Methods in Enzymol., 154: 287).

A nucleic acid backbone refers to groups or linkages known in the art (Eschenmoser, 1999, Science 284:2118-2124), e.g., sugar-phosphodiester linkages, 2'-O-methyl linkages, guanidine linkers in DNA ("DNG"), S-methylthiourea linkers, methylphosphonate linkages, phosphoramidate-linkages, amide backbone modifications as in polyamide or peptide nucleic acids (PNA), phosphorothioate linkages, phosphonic ester nucleic acid linkages, pyranosyl oligonucleotide linkages, bicyclo- and tricyclo-nucleic acid linkages, formacetal and 3'-thioformacetal linkages, morpholino linkages, or other modifications of the natural phosphodiester internucleoside bond, or combinations thereof (Majlessi et al., 1998, Nucl. Acids Res. 26(9):2224-2229; Dempcy et al., 1995, Proc. Natl. Acad. Sci. USA 92:6097-6101; Browne et al., 1995, Proc. Natl. Acad. Sci. USA 92:7051-7055; Arya & Bruice, 1998, J. Am. Chem. Soc. 120:6619-6620; Reynolds et al., 1996, Nucl. Acids Res. 24(22):4584-4591; Gryaznov & Chen, 1994, Am. Chem. Soc. 116:3143-3144; Chaturvedi et al., 1996, Nucl. Acids Res. 24(12):2318-2323; Hyrup & Nielsen, 1996, Bioorg. & Med. Chem. 4:5-23; Hydig-Hielsen et al., PCT Pat. App. WO 95/32305; Mesmaeker et al., Syn. Lett., November 1997:1287-1290; Peyman et al., 1996, Angew. Chem. Int. Ed. Engl. 35(22):2636-2638; Aerschot et al., 1995, Angew. Chem. Int. Ed. Engl. 34(12):1338-1339; Koshkin et al., 1998, J. Am. Chem. Soc. 120:13252-13253; Steffens & Leumann, 1997, J. Am. Chem. Soc. 119:11548-11549; Jones et al., 1993, J. Org. Chem. 58:2983-2991; Summerton & Weller, 1997, Antisense & Nucl. Acid Drug Dev. 7:187-195; Stirchak et al., 1989, Nucl. Acids Res. 17(15):6129-6141). A nucleic acid backbone may include a mixture of linkages in the same oligomer or polymer (e.g., one or more sugar-phosphodiester linkages and one or more 2'-O-methyl linkages in the strand) or may have the same linkages throughout the strand (e.g., all 2'-O-methyl or all amide modification linkages).

A target, target sequence, or target nucleic acid may refer to a large sequence (e.g., greater than 1000 nt) or a smaller sequence within a larger nucleic acid, to which another sequence binds, e.g., by using standard complementary base pairing. A target nucleic acid may be RNA or DNA, which is naturally occurring or made synthetically. For example, a target may be a relatively large nucleic acid such as the HAV genome, or a target may be a smaller subsequence contained in HAV RNA, its complement, or an amplification product made from it, which binds specifically another sequence in an oligomer. Those skilled in the art will appreciate that a target nucleic acid may exist in any form, e.g., a sense or antisense (+ or -) strand.

Complementary nucleic acids (or nucleic acid complementarity) refers to a base sequence in one strand of nucleic acid that, due to orientation of its functional groups, binds to a base sequence in an opposing strand, e.g., by hydrogen bonding between A and T or U bases, and between C and G bases. Substantially complementary means that a base sequence in one strand is not completely or perfectly complementary to a base sequence in an opposing strand, but that sufficient bonding occurs between bases of the two strands to form a stable hybridized complex in a set of conditions (e.g., salt concentration in an aqueous solution, or a temperature). Such conditions may be predicted by using the base sequences and standard mathematical calculations known to those skilled in the art for determining the melting temperature (Tm) at which 50% of hybridized strands are denatured, or by empirical determination of Tm by using routine methods (e.g., see Sambrook et al., Molecular Cloning, A Laboratory Manual, 2nd Ed., (Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y., 1989), at 9.50-51, 11.46-49, 11.55-57).

A hybridization condition refers to the cumulative environment in which one nucleic acid strand bonds to a second nucleic acid strand by complementary strand interactions to produce a hybridization complex. Such conditions include, e.g., temperature, chemical components and concentrations of compounds (e.g., salts, buffers, chelating agents, organic compounds) in aqueous and/or organic solutions that contain the nucleic acids. Other factors, such incubation time or reaction chamber dimensions may contribute to hybridization conditions, which are well known in the art (e.g., see Sambrook et al., Id., at 1.90-1.91, 9.47-9.51, 11.47-11.57).

A label refers to a molecular moiety that is detectable or produces a detectable response directly or indirectly, e.g., by catalyzing a reaction that produces a signal. Labels include luminescent moieties (e.g., fluorescent, bioluminescent, or chemiluminescent compounds), radioisotopes, members of binding pairs (e.g., biotin and avidin or streptavidin), enzymes or enzyme substrates, reactive groups or chromophores, e.g., a dye or particle that results in a detectable color. A detectable response or signal is any perceptible or measurable output that indicates the presence of a label, e.g., light, color, radioactive decay emission, electrical signal, magnetic field, or signal blockage, such as from quenching or turbidity.

An immobilized oligomer or probe refers to an oligomer that is connected or attached, covalently or noncovalently, to a capture support matrix, which provides a means for joining a capture hybrid containing a target nucleic acid to the capture support. A preferred immobilized probe is an oligomer that binds, directly or indirectly, to a target nucleic acid to facilitate separation of the bound target nucleic acid from unbound sample materials. In one embodiment, the target is indirectly bound to the immobilized probe via a capture probe that links the target and immobilized probe in a hybridization complex (see U.S. Pat. Nos. 6,110,678 and 6,280,952, Weisburg et al.). Any of a variety of supports may be used, such as matrices or particles made of, e.g., nitrocellulose, nylon, glass, polyacrylate, mixed polymers, polystyrene, silane polypropylene, and magnetic materials. Monodisperse magnetic particles of relatively uniform size that can be readily retrieved from solution by applying a magnetic force are a preferred embodiment of a support.

A capture oligomer or probe joins a target nucleic acid and an immobilized probe, i.e., by using a target-specific moiety that binds the target sequence and a moiety that attaches the capture probe to an immobilized probe. In one embodiment, both attachments result from hybridization of complementary base sequences, i.e., hybridization of a target sequence with a target-complementary sequence of the capture probe, and hybridization of another portion of the capture probe to a complementary sequence of the immobilized probe. In other embodiments, one or more attachments may occur by using members of a specific binding pair (e.g., biotin and avidin or streptavidin), which are well-known in the art. Compositions and methods that use capture probes are known (U.S. Pat. No. 6,110,678).

Separating or purifying refers to removing one or more components of a sample from other sample components. Sample components include nucleic acids in a generally aqueous solution phase, which may also include materials such as proteins, carbohydrates, lipids, and other compounds. Preferably, separating or purifying a nucleic acid removes at least about 70%, more preferably at least about 90% and, even more preferably, at least about 95% of the nucleic acid from other sample components.

An amplification oligonucleotide or oligomer refers to an oligomer that hybridizes to a target nucleic acid, or its complementary sequence, and participates in a nucleic acid amplification reaction by serving as a primer for synthesis of nucleic acid in vitro. Amplification oligomers may contain additional functional sequences, such a promoter sequence that binds an RNA polymerase in an oligomer referred to as a promoter primer. An amplification oligonucleotide generally contains at least about 10 contiguous bases, and preferably at least about 12 contiguous bases, that are complementary to a target sequence (or a complementary strand thereof). The contiguous bases are preferably at least about 80%, more preferably at least about 90%, and most preferably about 100% complementary to the sequence that binds to the amplification oligomer. An amplification oligomer may be RNA, DNA, or mixed DNA-RNA bases, and optionally may include modified nucleotides or backbone linkages.

A primer refers to an oligonucleotide that hybridizes to a template nucleic acid and which has an end (usually 3') that can be extended in a polymerization reaction catalyzed by an enzyme. The 5' region of the primer may be non-complementary to the target nucleic acid, e.g., as in a promoter primer that includes a 5' promoter sequence that is not present in the target sequence. Those skilled in the art will appreciate that a promoter primer may function as a primer independent of its promoter sequence (i.e., with or without the promoter sequence) and that any amplification oligomer may be modified to include a 5' promoter sequence, and thus function as a promoter primer.

Amplification refers to any known procedure for obtaining multiple copies of a target sequence, its complement, or fragments thereof. Amplification of fragments refers to production of an amplified nucleic acid that contains less than the complete target nucleic acid sequence or its complement, e.g., amplification of a portion of the complete HAV genome. Amplification of a fragment or portion of the complete target may result from using an amplification oligomer that which hybridizes to, and initiates polymerization from an internal position of the target nucleic acid. Known amplification methods include, e.g., transcription-mediated amplification (TMA), replicase-mediated amplification, the polymerase chain reaction (PCR), ligase chain reaction (LCR) and strand-displacement amplification (SDA). Replicase-mediated amplification uses self-replicating RNA molecules, and a replicase such as QB-replicase (e.g., U.S. Pat. No. 4,786,600 Kramer et al.). PCR uses a DNA polymerase, multiple primers and thermal cycling to synthesize many copies of two complementary strands of DNA or cDNA (e.g., U.S. Pat. Nos. 4,683,195, 4,683,202, and 4,800,159, Mullis et al.). LCR uses at least four separate oligomers to amplify a target and its complementary strand by using multiple cycles of hybridization, ligation, and denaturation (e.g., U.S. Pat. Nos. 5,427,930 Biekenmeyer et al., and 5,494,810 Barany et al.). SDA uses a primer that contains a recognition site for a restriction endonuclease and the endonuclease nicks one strand of a hemimodified DNA duplex that includes the target sequence, followed by a series of primer extension and strand displacement steps (e.g., U.S. Pat. No. 5,422,252 Walker et al.) Transcription-mediated or transcription-associated amplification reactions use a polymerase to make a complementary strand to the target in a double-stranded form that contains a functional promoter for a specific RNA polymerase that makes transcripts that can cycle isothermically to produce additional copies of transcripts that are detectable amplification products.

Transcription-mediated or transcription-associated amplification uses an RNA polymerase to produce multiple RNA transcripts from a nucleic acid template in isothermal reactions that use an RNA polymerase, a DNA polymerase, deoxyribonucleoside triphosphates, ribonucleoside triphosphates, and a promoter-primer, and optionally may include one or more additional oligonucleotides. These methods of amplification and reaction conditions have been described in detail previously (e.g., see U.S. Pat. Nos. 5,399,491 and 5,554,516 Kacian et al., U.S. Pat. No. 5,437,990 Burg et al., PCT Nos. WO 88/01302 and WO 88/10315 Gingeras et al., U.S. Pat. No. 5,130,238 Malek et al., U.S. Pat. Nos. 4,868,105 and 5,124,246 Urdea et al.).

Preferred embodiments of the present invention use transcription-mediated amplification (TMA, described in U.S. Pat. Nos. 5,399,491 and 5,554,516). It will, however, be apparent to one skilled in the art that the methods and oligonucleotide primer sequences described herein are readily applicable to use with any nucleic acid amplification method that synthetically extends primers by using a polymerase.

A detection probe is an oligomer that binds to a specific target sequence and, by binding, produces, directly or indirectly, a detectable signal that indicates the presence of the target sequence. A detection probe need not be labeled to produce a detectable signal, an example of such is an electrical impulse that results from the probe binding to the target. A labeled probe is made up of an oligomer that is linked, directly or indirectly, to a label. Methods of making and/or using labeled probes are well known (e.g., Sambrook et al., id., Chapt. 10; U.S. Pat. Nos. 6,361,945 Becker et al., 5,658,737 Nelson et al., 5,656,207 Woodhead et al., 5,547,842 Hogan et al., 5,283,174 Arnold et al., 4,581,333 Kourilsky et al., and 5,731,148 Becker et al.). Detection probes may include a synthetic linker (U.S. Pat. Nos. 5,585,481 and 5,639,604 Arnold et al.), and a chemiluminescent label, such as an acridinium ester (AE) compound (U.S. Pat. Nos. 5,185,439, 5,656,207, and 5,658,737).

A homogeneous detectable label is a label that can be detected in a homogeneous manner depending on whether the label is bound or unbound to a target. That is, detection of a label in a homogeneous reaction does not require physical separation of unbound forms of the label from the mixture in which the signal is detected. It will be appreciated by skilled artisans that a homogeneous reaction may occur in solution or on a support, e.g. on an array, biochip or gene chip. Homogeneous detectable labels and conditions for their detection are well known (e.g., U.S. Pat. Nos. 5,283,174, 5,656,207 and 5,658,737).

By "consisting essentially of" is meant that additional component(s), composition(s) or method step(s) that do not materially change the basic and novel characteristics of the present invention may be included in the compositions, kits, or methods of the present invention. Such characteristics include the ability to detect specifically the presence of HAV nucleic acid in a sample with a sensitivity of at least 80% for samples containing 25 to 30 copies of HAV per ml by using a combination of capture probe, amplification primers, and detection probe oligomers as described herein. Any component(s), composition(s), or method step(s) that have a material effect on the specificity and/or sensitivity of detection of HAV present in a sample by using the nucleic acid oligomers and in vitro methods described herein, would fall outside of this term.

Unless defined otherwise, all scientific and technical terms used herein have the same meaning as commonly understood by those skilled in the relevant art. Definitions of many of the terms used herein are provided in, e.g., Dictionary of Microbiology and Molecular Biology, 2nd ed. (Singleton et al., 1994, John Wiley & Sons, New York, N.Y.), The Encyclopedia of Molecular Biology (Kendrew, Ed., 1994, Blackwell Science Ltd., Cambridge, Mass.), or The Harper Collins Dictionary of Biology (Hale & Marham, 1991, Harper Perennial, New York, N.Y.). Unless mentioned otherwise, the techniques employed or contemplated herein are standard methodologies well known to one of ordinary skill in the art. Examples are included to illustrate some embodiments of the invention.

The present invention includes compositions (nucleic acid amplification oligomers, detection probes, and optionally capture oligomers) and methods for detecting HAV nucleic acid in a sample. To select sequences appropriate for use as the oligomers disclosed herein, known HAV genomic sequences (Beneduce, et al., 1995, Virus Res. 36 (2-3): 299-309, Fujiwara, et al., 2001, J. Hepatol. 35 (1): 112-119, Hu, et al., 2002, Acta Virol. 46 (3): 153-157), including those of different isolates, partial sequences, and complementary sequences available on a public database (e.g., GenBank accession nos. AB020564 to AB020569) were aligned by matching regions of the same or similar sequences and the aligned sequences were compared using well known techniques. Although sequence comparisons may be facilitated by use of algorithms, those skilled in the art can readily perform such comparisons manually and visually. Portions of HAV sequences that contain relatively few sequence variants between the compared sequences were chosen as a basis for designing synthetic oligomers suitable for use in the capture, amplification and detection steps described herein. Other well-known sequence characteristics, such as the GC content and the relative abundance of predicted secondary structures (e.g., hairpin turns or intramolecular pairing), were also considered in selecting the oligomer sequences.

Based on these analyses, regions of the HAV genome around nucleotides 200, 3700, 4700, 5700, 5800, 6000, and 7000 were chosen as potential target regions for detection of amplified HAV sequences. For each region, oligomers were designed for use in capturing the HAV RNA from a sample to purify it from other sample components, as amplification oligomers, and as probe sequences. Preferred embodiments of target regions are in portions of 0 to 305 nt, 4714 to 4765 nt, 5495 to 5788 nt, 5788 to 6069 nt, and 6952 to 7413 nt of the HAV genome.

Capture oligomer sequences generally include a sequence that binds specifically to a sequence near the target region to be amplified and a "tail" region used in attaching the hybridization complex that includes the target to a solid support, for example via hybridization to an immobilized oligomer (e.g., U.S. Pat. No. 6,110,678). Preferred capture oligomers include a target-specific sequence that binds specifically to a HAV RNA sequence and a covalently attached tail sequence (e.g., dT.sub.3dA.sub.30), as shown in SEQ ID NOS:1 to 7. Those skilled in the art will understand that the target-specific portion of a capture oligomer (SEQ ID NOS:8 to 14) or its RNA equivalent may be linked to any moiety that allows it to bind to an immobilized probe (e.g., a different tail sequence or a member of a binding pair, such as biotin or avidin). Any backbone may link the base sequence of a capture oligomer. Some embodiments use 2'-O-methyl linkages in the target-specific portion of a capture oligomer and standard DNA linkages in the tail portion. A polynucleotide tail sequence may be any sequence complementary to a sequence of an immobilized probe, and generally has a sequence length of about 5 to 50 residues, and is preferably a substantially homopolymeric sequence in a range of about 10 to about 40 residues (e.g., C.sub.10 to C.sub.40) that is complementary to an immobilized homopolymeric sequence (e.g., G.sub.15).

Primer sequences bind specifically to an HAV RNA target sequence or a complementary strand and flank a target sequence that is amplified, although primer sequences may contain additional sequences that do not bind to the target or its complementary sequence. A primer may be a promoter primer and include a 5' promoter sequence, such as a T7 RNA polymerase promoter (SEQ ID NO:19). Embodiments of promoter primers include those of SEQ ID NOS:20 to 49. Other embodiments of HAV-specific primers may include ancillary sequences, such as restriction endonuclease recognition sequences (SEQ ID NOS:132 to 135). Those skilled in the art will appreciate that a target-specific sequence of a primer, with or without an attached promoter or ancillary sequence, may serve as a primer in a variety of in vitro amplification conditions. Amplification oligomers were designed for sequences in targeted regions of the HAV genome (e.g., around nucleotide positions 200, 3700, 4700, 5700, 5800, 6000, and 7000). Those skilled in the art will appreciate that these numbers refer to HAV target regions that are approximate only and that oligomers may function in an assay for more than one target region. That is, the identifying target region numbers provided here merely as a convenient shorthand reference for grouping preferred embodiments of the invention does not functionally restrict these oligomers. Amplification oligomers may be synthesized as DNA, RNA, complementary DNA or RNA sequences, or mixed DNA and RNA sequences, and may include one or more non-standard nucleic acid backbone linkages. For example, an oligomer of SEQ ID NO:106 was synthesized with RNA bases and 2'-O-methyl linkages at residues 1 to 4 and standard DNA bases and linkages at the other residues.

For a first HAV target region (around position 200), amplification oligomers include those in a size range of about 23 to 26 nt that are contained in the sequence of SEQ ID NO:138, and include at least the sequence of SEQ ID NO:139 or SEQ ID NO:140. Embodiments of such oligomers includes those of SEQ ID NO:51 to SEQ ID NO:57. Embodiments of promoter primers for this region, in a size range of about 50 to 53 nt, are those that include target-specific portions of SEQ ID NOS:21 to 27. Amplification oligomers for this target region also include those in a size range of about 19 to 25 nt contained in SEQ ID NO:141, and contain at least the sequence of any one of SEQ ID NOS:142 to 146. Embodiments of amplification oligomers for this target region include those of SEQ ID NOS:15 to 18, 20 to 27, 50 to 57, and 80 to 85.

For a second HAV target region (around position 3700), amplification oligomers include those in a size range of about 21 to 27 nt, contained in the sequence of SEQ ID NO:60, or in SEQ ID NO:86 and include at least SEQ ID NO:156. Embodiments of promoter primers that include such target-specific portions for this region and are in a size range of about 48 to 54 nt include those of SEQ ID NOS:29 to 32. Embodiments of amplification oligomers for this target region include those of SEQ ID NOS:28 to 30, 58 to 60, and 86 to 88.

For a third HAV target region (around position 4700), amplification oligomers include those in a size range of about 24 to 30 nt that are contained in SEQ ID NO:147 and include at least the sequence of SEQ ID NO:148, or are contained in SEQ ID NO:157 and include at least the sequence of SEQ ID NO:158. Embodiments of amplification oligomers for this target region include those of SEQ H) NOS:31, 32, 61, 62, 89, 90, and 91, of which SEQ ID NO:31 and SEQ ID NO:32 are promoter-primer embodiments that include a 5' promoter sequence attached to the target-specific sequence.

For a fourth HAV target region (around position 5700), amplification oligomers include those in a size range of about 18 to 27 nt that are contained in the sequence of SEQ ID NO:93 or SEQ ID NO:95. Embodiments of such oligomers include those that contain at least any one of SEQ ID NO:97, SEQ ID NO:159, and SEQ ID NO:160. Embodiments of amplification oligomers for this target region include those of SEQ ID NOS:33, 63, and 92 to 97, of which SEQ ID NO:33 is a promoter primer embodiment that includes a 5' promoter sequence attached to the target-specific sequence.

For a fifth HAV target region (around position 5800), amplification oligomers include those in a size range of about 19 to 31 nt that are contained in SEQ ID NO:149 and include at least the sequence of SEQ ID NO:150. Embodiments of promoter primers, in a size range of about 51 to 56 nt, that include such target-specific portions are those of SEQ ID NOS:34 to 40. Other embodiments of amplification oligomers for this target region include those of SEQ ID NOS:64 to 70, and 97.

For a sixth HAV target region (around position 6000), amplification oligomers include those of about 24 to 28 nt contained in the sequence of SEQ ID NO:161 and include the sequence of SEQ ID NO:162. Embodiments of amplification oligomers for this target region include those of SEQ ID NOS:41, 42, 71, 72, 98, 99, and 101, of which SEQ ID NOS:41 and 42 are embodiments of promoter primers that include a 5' promoter sequence attached to the target-specific sequence.

For a seventh HAV target region (around position 7000), amplification oligomers include those in a size range of about 20 to 30 nt contained in SEQ ID NO:151 and that include at least any one of the sequences of SEQ ID NO:152 to SEQ ID NO:155. Other embodiments of amplification oligomers for this target region are contained in SEQ ID NO:163 and include at least the sequence of SEQ ID NO:164. Additional embodiments are amplification oligomers that are contained in SEQ ID NO:165 and include at least any one of the sequences of SEQ ID NOS:166 to 168. Embodiments of promoter primers, in a size range of about 51 to 56 nt, that include HAV target-specific portions for this region are SEQ ID NOS:43 to 49. Other embodiments of amplification oligomers for this region include those of SEQ ID NOS:73 to 79, and 102 to 108.

Oligomers were designed to hybridize to and detect amplified HAV sequences, which include the detection probes of SEQ ID NOS:109, 111, 113, 115, 117, 119, 121, 122, 123, 124, and 126 to 130. Those skilled in the art will appreciate that a detection probe will be chosen to hybridize to a sequence contained within an amplified sequence that is determined by the combination of amplification oligomers that are used. Detection probe oligomers may be synthesized as DNA, RNA, or mixed DNA and RNA polymers, and may include alternative backbone linkages such as 2'-O-methyl linkages. For example, oligomers of SEQ ID NOS:109, 111, 117, 119, 121, 122, 128, and 130 were synthesized with 2'-O-methyl linkages, and oligomers of SEQ ID NOS:124 and 127 were synthesized as mixed DNA and RNA nucleotides with 2'-O-methyl linkages from the second residue to the 3' terminal residue. Preferred embodiments of detection probes have an attached chemiluminescent label, preferably an acridinium ester (AE) compound (U.S. Pat. Nos. 5,185,439, 5,639,604, 5,585,481, and 5,656,744), which in preferred embodiments are attached to the probe by a non-nucleotide linker (see U.S. Pat. Nos. 5,585,481, 5,656,744, and 5,639,604, particularly at column 10, line 6 to column 11, line 3, and Example 8). Embodiments of the probe oligomers were labeled by using known methods with an AE compound between residues 9 and 10 for SEQ ID NOS:119, 121 and 124, between residues 10 and 11 for SEQ ID NOS:115, 117, 126, 127 and 128, between residues 11 and 12 for SEQ ID NOS:109, 111, 123, 124 and 130, between residues 12 and 13 for SEQ ID NOS:113, 122 and 129, and between residues 13 and 14 for SEQ ID NO:122. Probe oligomers were tested and characterized by hybridization with complementary oligomer sequences, by using standard methods for determining Tm and/or differential hydrolysis of the acridinium ester in a hybridization complex (described in detail in U.S. Pat. No. 5,283,174). For example, hybridizations were performed by using complementary pairs of sequences of SEQ ID NO:109 and SEQ ID NO:110, SEQ ID NO:111 and SEQ ID NO:112, SEQ ID NO:113 and SEQ ID NO:114, SEQ ID NO:115 and SEQ ID NO:116, SEQ ID NO:117 and SEQ ID NO:118, SEQ ID NO:119 and SEQ ID NO:120, SEQ ID NO:124 and SEQ ID NO:125, SEQ ID NO:128 and SEQ ID NO:100, and SEQ ID NO:130 and SEQ ID NO:131. Hybridization testing may be performed by using other complementary sequences, such as SEQ ID NO:124 with SEQ ID NO:137, and SEQ ID NO:129 with SEQ ID NO:136.

Compositions of the present invention include kits for detecting HAV nucleic acid sequences. Such kits include amplification oligomers as disclosed herein that function as primers for amplifying HAV nucleic acid sequences in vitro. Exemplary kits include a first amplification oligomer that hybridizes specifically to a sequence in a target region of the HAV RNA genome or its complementary sequence, and a second amplification oligomer that hybridizes specifically to another HAV sequence in the target region, preferably one complementary to the HAV RNA genomic sequence. Embodiments of kits include amplification oligomers that are combinations of primers and promoter primers as described herein. Kits may also contain one or more oligomers that serve as detection probes for detecting amplified HAV sequences of the target region of the primers selected for the kit. Embodiments of kits that include of probe oligomers use one or more of the detection probe sequences as described herein, which may include a label attached directly or indirectly to the probe oligomer. Kits may also contain oligomers that serve as capture oligomers for purifying a target HAV RNA from a sample. Embodiments of such capture oligomers as described herein may contain a covalently attached tail sequence or other binding moiety used in target capture. Kits useful for practicing the methods described herein are also included in the invention, and preferred embodiments include at least two amplification oligomers as described herein, and may also include reagents for performing in vitro amplification, e.g., enzymes, salt solutions, and nucleic acid synthesis substrate compounds. Oligomers described herein may be packaged in a variety of different embodiments, and thus, those skilled in the art will appreciate that the invention embraces many different kit configurations. For example, a kit may include amplification oligomers for only one target region of the HAV genome, or it may include amplification oligomers for multiple HAV target regions. Those skilled in the art will appreciate that a kit that includes a detection probe will include a probe that binds to a sequence amplified by the amplification oligomers of the kit. That is, selection of amplification oligomers and detection probe oligomers for a kit will be linked by their intended target region.

An embodiment of the assay to detect HAV nucleic acid in a sample includes the steps of capturing the HAV target nucleic acid from a sample by using a capture oligomer, amplifying a region of the captured HAV nucleic acid by using a combination of at least two primers, and detecting the amplified HAV sequence by specifically hybridizing it with a detection probe oligomer and detecting a signal that results from the probe bound to the amplified HAV sequence. Preferred embodiments use a transcription-associated or transcription-mediated amplification reaction. Either the amplified nucleic acid or the probe may be labeled, or both may be unlabeled and a detectable signal results from an indirect label or response associated with the hybridization complex, such as an electrical impulse resulting from hybridization of the probe and the amplified nucleic acid.

The capturing step preferably uses a capture oligomer that includes a target-specific sequence (e.g., SEQ ID NOS:8 to 14) that specifically hybridizes to a HAV target sequence and a moiety that permits the hybridized target nucleic acid to be separated from other sample components. The capturing step may use a capture oligomer that also includes a tail portion, e.g. as in SEQ ID NOS:1 to 7, that serve as the moiety that allows the target nucleic acid to be separated from other sample components by hybridization of the tail portion to an immobilized probe, as previously described (U.S. Pat. No. 6,110,678). Preferred embodiments use supports that are magnetic spheres that are monodisperse (i.e., uniform in size.+-.about 5%) with covalently attached or immobilized poly-dT oligomers that hybridize to a complementary tail sequence of the capture oligomer. The hybridization complex that includes at least the target nucleic acid and the capture oligomer, and preferably also includes the immobilized probe, is separated from the other sample components by using standard physical separation methods (e.g., application of magnetic force, filtration, or centrifugation) and the captured target nucleic acid may be washed one or more times to further purify the target nucleic acid from other sample components. For example, particles with the attached target nucleic acid in a hybridization complex are suspended one or more times in a washing solution that maintains the complex and then the particles with the attached complex are retrieved from the washing solution as described above.

Amplifying the captured HAV target sequence uses an in vitro amplification reaction that uses at least two primers that flank the sequence to be amplified, e.g., an HAV sequence flanked by SEQ ID NO:66 and SEQ ID NO:95, or their complementary sequences. One embodiment uses a transcription-associated amplification reaction that makes many RNA copies of a sequence in substantially isothermal conditions (as described previously in U.S. Pat. Nos. 5,399,491 and 5,554,516). Transcription-associated amplification uses two types of primers (one a promoter primer that contains a promoter sequence for an RNA polymerase), enzymes (a reverse transcriptase and an RNA polymerase), substrates (deoxyribonucleoside triphosphates, ribonucleoside triphosphates) and appropriate salts and buffers in solution to produce multiple RNA transcripts from a nucleic acid template. Briefly, a promoter primer hybridizes specifically to a target RNA sequence and reverse transcriptase creates a first strand cDNA by extension from the 3' end of the promoter primer and degrades the template strand in the resulting DNA:RNA duplex by using RNase H activity. A second primer binds to the cDNA and another DNA strand is synthesized by the reverse transcriptase from the end of the second primer, to create a double-stranded DNA with a functional promoter sequence to which the RNA polymerase binds. Multiple RNA transcripts ("amplicons") are transcribed and each can be a template in a new round of replication as described above, thus generating large amounts of single-stranded amplified sequence (e.g., about 100 to 3,000 transcripts from a single template). Embodiments of the invention that use a transcription-associated amplification reaction may use promoter primers (SEQ ID NOS:20 to 49) with other primers (SEQ ID NOS:15 to 18, 80 to 99, and 101 to 108) to amplify selected HAV sequences for detection.

The detecting step uses at least one probe that binds specifically to the amplified HAV sequences. Embodiments may use any know detection method (e.g., detection of a radioactive, fluorescent, enzymatic, calorimetric, electrical, or luminescent signal) to detect binding of the detection probe to the amplified HAV sequences, and the detected signal indicates the presence of HAV in the sample. Embodiments of probe oligomers (SEQ ID NOS:109, 111, 113, 115, 117, 119, 121, 122 to 124, 126 to 130) may be unlabeled or labeled using any of a variety of known labels. In preferred embodiments, the detection step is performed in a homogeneous detection reaction without removing the unbound detection probe from the mixture. Embodiments of the probe oligomers for use in homogeneous detection reactions are preferably labeled with one of a variety of AE compounds, which produce a chemiluminescent signal that is detected as described in detail previously (U.S. Pat. Nos. 5,283,174, 5,656,744, and 5,658,737).

A preferred assay embodiment generally includes the following steps. A HAV-containing sample is provided, which may be prepared by using standard laboratory methods to make a substantially aqueous solution or suspension that contains HAV. An aliquot (0.5 ml) of the sample solution or suspension is mixed with about an equal volume (0.4 to 0.5 ml) of a target capture reagent, i.e., a solution that contains one or more capture oligomers (4 pmol/reaction), magnetic particles with attached immobilized probes complementary to a portion of the capture oligomers, and salt compounds to provide a hybridization condition. The target capture reagent preferably includes a detergent or other chaotropic agent that disrupts the HAV particles and releases HAV RNA for hybridization with capture oligomers. The mixture is incubated 20-30 min at 60.deg.C. to allow hybridization of the target-specific portion of the capture oligomer to the HAV target sequence and then at room temperature for 20-30 min to allow binding of the capture oligomer and immobilized probe. A magnetic field is applied to the outside of the reaction container for about 10 min to separate the particles with the attached hybridization complexes that include HAV RNA, and the solution phase containing other sample components is aspirated away. To wash the particles with attached hybridization complexes, they are suspended in 1 ml of a wash buffer, separated from the solution substantially as described above, and the solution is removed. Particles with attached hybridization complexes that include the purified HAV RNA are mixed with a solution that contains amplification reagents (buffers, salts, dXTP and XTP substrates), and a combination of amplification oligomers (a promoter primer and a primer combination, each at 3 to 30 pmol, generally 15 pmol each), and covered with oil (0.2 ml of filtered silicon oil) to prevent evaporation, and incubated for 10 min at 60.deg.C., then for 10 min at 42.deg.C., and then enzymes are added (reverse transcriptase and RNA polymerase), and the mixture is incubated for 60 min at 42.deg.C. For detection, the amplification reaction mixture is incubated with at least one acridinium labeled detection probe oligomer to provide a maximum detectable signal (relative light units or RLU) of 2 million or less, as detected by using standard methods on a luminometer (e.g., Gen-Probe Leader.RTM., Gen-Probe Incorporated, San Diego, Calif.). Detection probe is mixed with undiluted or a diluted aliquot of the amplification reaction mixture in a hybridization solution, incubated for 20 min at 60.deg.C. to allow hybridization of the probe oligomer to the amplified target sequence. Then, label on unbound probes is hydrolyzed by using a selection reagent (e.g., a base) and incubated for 10 min at 60.deg.C., followed by adding a detection reagent (e.g., H.sub.2O.sub.2) to produce chemiluminescence, followed by pH neutralization (e.g., by adding acid), and detecting the chemiluminescent signal (RLU) on a luminometer (e.g., 1-5 sec).

For use in the methods described above, capture oligomers, amplification oligomers and detection probes may be synthesized using standard methods to produce DNA, RNA, or mixed DNA and RNA polymers. Such oligomers may include standard or modified linkages and/or naturally occurring nucleosides (A, T or U, G, C), analogs (e.g., inosine), or synthetic purine and pyrimidine derivatives (e.g., P or K bases) (Lin & Brown, 1989, Nucl. Acids Res. 17:10373-83; Lin & Brown, 1992, Nucl. Acids Res. 20: 5149-52).

The general principles of the present invention may be more fully appreciated by reference to the following examples describe some embodiments of the present invention. In addition to the specific components described in the examples, generally the following reagents were used in the experiments described below. Target capture reagent was made up of 790 mM HEPES, 680 mM LiOH, 10% (v/v) lithium lauryl sulfate (LLS), 230 mM succinic acid, 0.03% (v/v) anti-foaming agent, 100 .micro.g/ml magnetic particles (1 micron SERA-MAG.sup..TM. particles, Seradyn, Inc. Indianapolis, Ind.) with covalently attached poly-dT.sub.14, and one or more capture oligomers, each at 4 pmol per 400 .micro.l. Wash buffer was made up of 150 mM NaCl, 10 mM HEPES, 6.5 mM NaOH, 1 mM EDTA, 0.3% (v/v) ethanol, 0.1% SDS, 0.02% (w/v) methyl paraben, 0.01% (w/v) propyl paraben, at pH 7.5. Amplification reagent was made up of 11.6 mM Tris base, 15 mM Tris-HCl, 22.7 mM MgCl.sub.2, 23.3 mM KCl, 3.33% glycerol, 0.05 mM Zn-acetate, 0.665 mM dATP, 0.665 mM dCTP, 0.665 mM dGTP, 0.665 mM dTTP, 5.32 mM ATP, 5.32 mM CTP, 5.32 mM GTP, and 5.32 mM UTP, at pH 7. Enzyme reagent was made up of 140 U/.micro.l T7 RNA polymerase, 224 RTU/.micro.l of Moloney Murine Leukemia Virus reverse transcriptase (MMLV-RT), 16 mM HEPES, 70 mM N-acetyl-L-cysteine, 3 mM EDTA, 0.05% (w/v) Na-azide, 20 mM Tris, 50 mM KCl, 20% (v/v) glycerol, 10% (v/v) TRITON.RTM. X-102, 150 mM trehalose, at pH 7, (Enzyme units typically are 1 U of T7 RNA polymerase incorporates 1 nmol of ATP into RNA in 1 hr at 37.deg.C. using a DNA template containing a T7 promoter, and 1 U of MMLV-RT incorporates 1 nmol of dTTP in 10 min at 37.deg.C. using 200-400 .micro.M oligo-dt primer and poly-A template.) Probe reagent was made up of 100 mM succinic acid, 2% (w/v) LLS, 230 mM LiOH, 15 mM Aldrithiol-2, 1.2 M LiCl, 20 mM EDTA, 20 mM EGTA, 3% (v/v) ethanol, adjusted to pH 4.7 with LiOH. Selection reagent was made up of 600 mM boric acid, 182 mM NaOH, 1% (v/v) octoxynol (TRITON.RTM. X-100), at pH 8.5. Detection reagents were Detect Reagent I, which contained 1 mM nitric acid and 32 mM H.sub.2O.sub.2, and Detect Reagent II (to neutralize pH), which was 1.5 M NaOH (see U.S. Pat. No. 5,283,174 for details).
 

Claim 1 of 26 Claims

1. A combination of at least two oligomers for amplifying a hepatitis A virus (HAV) target region, wherein at least one amplification oligomer is selected from: an oligomer of about 20 to 30 contiguous nucleotides contained in the sequence of SEQ ID NO: 151 and which contains at least the sequence of SEQ ID NO:152; and wherein an additional amplification oligomer is selected from an oligomer of about 21-29 contiguous nucleotides contained in SEQ ID NO:165 and which contains at least the sequence of SEQ ID NO:166.

____________________________________________
If you want to learn more about this patent, please go directly to the U.S. Patent and Trademark Office Web site to access the full patent.