Haplotying of HLA loci with ultra-deep shotgun sequencing
Methods are provided to determine the entire genomic region of a particular HLA locus including both intron and exons. The resultant consensus sequences provides linkage information between different exons, and produces the unique sequence from each of the two genes from the individual sample being typed. The sequence information in intron regions along with the exon sequences provides an accurate HLA haplotype.
1. A method for determining a haplotype of an HLA locus, the method comprising: amplifying an entire HLA gene with nested PCR to amplify a genomic area covering the entire HLA gene including all introns and exons in a single reaction with target-specific primers that hybridize to regions flanking the entire HLA gene; sequencing the amplified gene: and performing deconvolution analysis by chromatid sequence alignment to resolve the haplotype of the locus, wherein the chromatid sequence alignment comprises the steps of: counting “central reads” for any given nucleotide, where central reads are empirically defined as mapped reads for which a ratio between a length of a left arm and that of a right arm related to a particular nucleotide is between 0.5 and 2; computing minimum coverage of overall reads (MCOR) and minimum coverage of central reads (MCCR) for each reference sequence: eliminating references with an MCOR less than 20 and an MCCR less than 10: enumerating all combinations of one reference sequence (homozygous allele) or two reference sequences (heterozygous alleles) of a same locus from the remaining reference sequences; counting distinct reads that map to each combination; wherein member(s) in the combination with maximum number of distinct reads is assigned as a genotype of a sample.
2. The method of claim 1 , wherein the primers are selected from those set forth in SEQ ID NO:1-68.
3. The method of claim 1 , wherein the amplified gene is fragmented and ligated to barcode oligonucleotides comprising (i) a target specific identifier for a source of the genomic DNA; (ii) a target specific identifier for the gene, and (iii) a sequencing adaptor.
4. The method of claim 3 , wherein the fragmented amplified gene is sequenced to a depth of at least 100 reads per sequence.
5. The method of claim 3 , wherein the fragmented amplified gene is sequenced to a depth of at least 1000 reads per sequence.
6. The method of claim 1 , wherein the locus is an HLA Class I locus.
7. The method of claim 6 , wherein the HLA Class I locus includes one or more of HLA-A, HLA-B and HLA-C.
8. The method of claim 1 , wherein the locus in an HLA Class II locus.
9. The method of claim 8 , wherein the HLA Class II locus is a DR locus.