COMPOSITIONS AND METHODS FOR DETECTING RARE SEQUENCE VARIANTS
In some aspects, the present disclosure provides methods for identifying sequence variants in a nucleic acid sample. In some embodiments, a method comprises identifying sequence differences between sequencing reads and a reference sequence, and calling a sequence difference that occurs in at least two different circular polynucleotides, such as two circular polynucleotides having different junctions, as the sequence variant. In some aspects, the present disclosure provides compositions and systems useful in the described methods.
1 - 52 . (canceled)
53 . A method of distinguishing a sequence variant from an error in a nucleic acid sample comprising a plurality of cell-free deoxyribonucleic acid (DNA) polynucleotides, each cell-free DNA polynucleotide of the plurality having a 5′ end and a 3′ end, the method comprising:
(a) denaturing the plurality of cell-free DNA polynucleotides into a plurality of cell-free single-stranded DNA (ssDNA) polynucleotides;
(b) joining an adapter polynucleotide to a 5′ end, a 3′ end, or both a 5′ end and a 3′ end of each of the cell-free ssDNA polynucleotides;
(c) circularizing individual cell-free ssDNA polynucleotides of the plurality to form a plurality of circular ssDNA polynucleotides;
(d) amplifying the circular ssDNA polynucleotides of (c) to produce a plurality of concatemers;
(e) sequencing the amplified polynucleotides to produce a plurality of sequencing reads; and
(f) identifying a sequence difference between sequencing reads and a reference sequence as the sequence variant only when the sequence difference occurs in at least two copies of the circular ssDNA polynucleotide in the concatemers and not when the sequence difference occurs in only one copy of the circular ssDNA polynucleotide in the concatemers distinguishing the sequence variant from the error.
54 . The method of claim 53 , wherein at least a portion of the sequence of the adapter polynucleotide is known.
55 . The method of claim 53 , wherein the adapter polynucleotide is a ssDNA polynucleotide or a labeled nucleotide.
56 . The method of claim 53 , wherein an identical adapter polynucleotide is joined to both the 5′ end and the 3′ end of each of the cell-free ssDNA polynucleotides.
57 . The method of claim 53 , wherein different adapter polynucleotides are joined to the 5′ end and the 3′ end of each of the cell-free ssDNA polynucleotides.
58 . The method of claim 53 , wherein the adapter polynucleotide is used as a sequencing primer.
59 . The method of claim 53 , wherein the circularizing is effected by subjecting the cell-free ssDNA polynucleotides to a ligation reaction using a ligase.
60 . The method of claim 59 , wherein ligation is effected by a ligase, and the method further comprises degrading the ligase prior to the amplifying of (d).
61 . The method of claim 53 , wherein the sequence variant is a single nucleotide polymorphism.
62 . The method of claim 53 , wherein the reference sequence is a consensus sequence formed by aligning the sequencing reads with one another.
63 . The method of claim 53 , wherein the reference sequence is a known reference sequence.
64 . The method of claim 53 , wherein (d) comprises performing a primer extension reaction selected from the group consisting of, reverse transcription, polymerase chain reaction, isothermal amplification, and combinations thereof.
65 . The method of claim 53 , wherein the amplifying is effected by using a polymerase having strand-displacement activity.
66 . The method of claim 53 , wherein the amplifying comprises subjecting the circular polynucleotide to an amplification reaction mixture comprising random primers.
67 . The method of claim 53 , wherein the amplifying comprises subjecting the circular polynucleotide to an amplification reaction mixture comprising one or more primers, each of which specifically hybridizes to a different target sequence via sequence complementarity.
68 . The method of claim 53 , wherein the concatemers are subjected to the sequencing step without enrichment.
69 . The method of claim 53 , further comprising performing an enrichment on the concatemers or derivatives thereof to enrich one or more target polynucleotides.
70 . The method of claim 69 , wherein the enrichment comprises amplifying a target sequence comprising sequence A and sequence B oriented in a 5′ to 3′ direction in an amplification reaction mixture, the reaction mixture comprising:
(a) the concatemers;
(b) a first primer comprising sequence A′, wherein the first primer specifically hybridizes to sequence A of the target sequence via sequence complementarity between sequence A and sequence A′;
(c) a second primer comprising sequence B, wherein the second primer specifically hybridizes to sequence B′ present in a complementary polynucleotide comprising a complement of the target sequence via sequence complementarity between B and B′; and
(d) a polymerase that extends the first primer and the second primer to produce amplified polynucleotides;
wherein the distance between a 5′ end of sequence A and a 3′ end of sequence B of the target sequence is 75 nt or less; and
wherein sequence A and sequence B′ are present in the cell-free polynucleotide.
71 . The method of claim 53 , wherein the cell-free polynucleotide comprises cell-free tumor DNA.
72 . The method of claim 53 , wherein identifying the sequence difference is performed by a computer system based on the sequencing reads and the reference sequence.