HLA typing using selective amplification and sequencing
Presented herein are methods and compositions for determining haplotypes in a sample. The methods are useful for obtaining sequence information regarding, for example, HLA type and haplotype. Also presented herein are methods of determining haplotypes in a sample based on a plurality sequence reads.
1. A method of determining haplotypes in a sample comprising:
(a) selectively amplifying a nucleic acid molecule from an individual, said nucleic acid molecule comprising
(i) at least a portion of a first exon of an HLA gene;
(ii) at least a portion of a second exon of said HLA gene; and
(iii) the intron between said first and second exons, thereby generating an amplified exon pair;
(b) carrying out a sequencing read of a first region of the amplified exon pair, said first region comprising at least a portion of said first exon and a portion of the intron adjacent to said first exon;
(c) carrying out a sequencing read of a second region of the amplified exon pair, said second region comprising at least a portion of said second exon and a portion of the intron adjacent to said second exon;
(d) performing steps (b) and (c) a plurality of times to generate a plurality of paired sequencing reads of said HLA gene, said plurality of paired sequencing reads comprising sequence information from at least two different haplotypes;
(e) partitioning each sequencing read into one of two different haplotypes, wherein partitioning comprises computer implemented steps (f)-(i):
(f) randomly selecting a first and second paired sequencing read and designating said reads as haplotype 1 and haplotype 2, respectively;
(g) assigning each remaining paired sequencing read in said plurality of paired sequencing reads to said haplotype 1 or said haplotype 2 based on sequence similarity to either haplotype 1 or haplotype 2;
(h) computing a consensus sequence for haplotype 1 and a consensus sequence for haplotype 2 using the paired sequence reads assigned to each haplotype; and
(i) designating said consensus sequences as haplotypes 1 and 2 and repeating steps (g)-(h) until said consensus sequences no longer change;
thereby determining haplotypes in said sample.
2. The method of claim 1 , wherein said partitioning comprises application of a k-means clustering algorithm.
3. The method of claim 1 , wherein said partitioning comprises application of an expectation-maximization clustering algorithm.
4. The method of claim 1 , further comprising repeating steps (f)-(i) at least 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or at least 20 times and selecting the consensus sequences that minimize the number of mismatches between the consensus sequence and the reads assigned to the haplotype assigned to the consensus sequence.
5. The method of claim 1 , wherein said assigning comprises computing the number of base mismatches between said sequencing read and the sequence of haplotypes 1 and 2.
6. The method of claim 1 , wherein of said HLA gene is a Class I gene.
7. The method of claim 1 , wherein of said HLA gene is a Class II gene.
8. The method of claim 1 , wherein said HLA gene is selected from the group consisting of: HLA-A, HLA-B and HLA-C.
9. The method of claim 1 , wherein said first region comprises at least 280, 290 or 300 nucleotides from the 5′ end of said amplified exon pair.
10. The method of claim 1 , wherein said second region comprises at least 280, 290 or 300 nucleotides from the 3′ end of said amplified exon pair.
11. The method of claim 1 , further comprising performing steps (b) and (c) a plurality of times.
12. The method of claim 1 , wherein said selectively amplifying comprises an extension-ligation reaction.
13. The method of claim 1 , wherein said selectively amplifying comprises a polymerase chain reaction.
14. The method of claim 1 , wherein said sequencing reads are carried out in a sequencing-by-synthesis (SBS) reaction.