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, or two different sheared polynucleotides as the sequence variant. In some aspects, the present disclosure provides compositions and systems useful in the described method.
1. A method of identifying a sequence variant in a nucleic acid sample comprising a plurality of polynucleotides, each polynucleotide of said plurality of polynucleotides having a 5′ end and a 3′ end, said method comprising:
(a) in a reaction mixture, circularizing individual polynucleotides of said plurality of polynucleotides to form a plurality of circular polynucleotides using a ligase, each of which having junction between said 5′ end and said 3′ end;
(b) adding a heat labile protease to said reaction mixture to degrade said ligase;
(c) amplifying said plurality of circular polynucleotides after step (b) without isolating said circular polynucleotides from said reaction mixture between steps (a) and (c) to produce amplified polynucleotides;
(d) sequencing said amplified polynucleotides to produce a plurality of sequencing reads; and
(e) comparing said plurality of sequencing reads to a reference sequence to identify said sequence variant,
wherein said method yields an increased number of unique sequences amplified from said plurality of polynucleotides as compared to performing a rolling circle amplification comprising steps (a) and (c) alone.
2. The method of claim 1 , wherein said plurality of polynucleotides are single-stranded.
3. The method of claim 1 , wherein said sequence variant is a single nucleotide polymorphism (SNP), a deletion/insertion polymorphism (DIP), a copy number variant (CNV), a short tandem repeat (STR), a simple sequence repeat (SSR), a variable number of tandem repeat (VNTR), an amplified fragment length polymorphism (AFLP), a retrotransposon-based insertion polymorphism, a sequence specific amplified polymorphism, or a methylation difference.
4. The method of claim 1 , wherein said reference sequence is a consensus sequence formed by aligning said sequencing reads with one another.
5. The method of claim 1 , wherein circularizing comprises the step of joining an adapter polynucleotide to said 5′ end, said 3′ end, or both said 5′ end and said 3′ end of an individual polynucleotide of said plurality of polynucleotides.
6. The method of claim 1 , wherein amplifying is effected by using a polymerase having strand-displacement activity.
7. The method of claim 1 , wherein amplifying comprises contacting said circular polynucleotides to an amplification reaction mixture comprising random primers.
8. The method of claim 1 , wherein amplifying comprises contacting said circular polynucleotides to an amplification reaction mixture comprising one or more primers, each of which specifically hybridizes to a different target sequence via sequence complementarity.
9. The method of claim 1 , wherein said amplified polynucleotides are subjected to the sequencing step without enrichment.
10. The method of claim 1 , further comprising enriching one or more target polynucleotides from said amplified polynucleotides by performing an enrichment step prior to sequencing.
11. The method of claim 1 , wherein a microbial contaminant is identified based on said comparing step.
12. The method of claim 1 , wherein said nucleic acid sample is obtained from a sample from a subject.
13. The method of claim 12 , wherein said sample is urine, stool, blood, saliva, tissue, or bodily fluid.
14. The method of claim 12 , wherein said sample comprises tumor cells.
15. The method of claim 12 , wherein said sample is a formalin-fixed paraffin embedded (FFPE) sample.
16. The method of claim 1 , wherein said sequence variant is associated with a type or stage of cancer.
17. The method of claim 1 , wherein said plurality of polynucleotides comprises cell-free polynucleotides.
18. The method of claim 17 , wherein said cell free polynucleotides comprise circulating tumor DNA.
19. The method of claim 2 , further comprising, following step (c) and prior to step (d), shearing said amplified polynucleotides to produce sheared polynucleotides, each sheared polynucleotide comprising one or more shear points at a 5′ end and/or a 3′ end.