HLA Analysis and Next Generation Sequencing

Henry Erlich, Ph.D.Cherie Holcomb, Ph.D.Roche Molecular Systems

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NGS and EFI, May 14, 2013

Library preparation strategies for NGS for HLA typing

• Amplify gene (multiple Kb)/cleave and ligate universal 454 adaptors/emPCR/sequence

• Sequence capture (NimbleGen)/cleave and ligate universal 454 adaptors/emPCR/sequence

• Amplify exons (and introns) with MID primers/emPCR/sequence (“fusion” or Fluidigm system primers)

• Sequencing HLA genes vs. HLA typing by sequencing

Incompletely ExtendedPCR Product

5’ 3’

Schematic of PCR Crossover FormationIncreased probability in long amplicon PCR

Crossover Product

5’

3’ 5’Template 1 PCR cycle

“n”

5’

3’ 5’ Template 2

PCR cycle “n+1”

3

The Benefits of Clonal Sequencing for HLA Genotyping

• Sets phase for linked polymorphisms within amplicon (reduces ambiguity)

• Allows amplification and sequencing of multiple members of multi-gene family (ie DRB1, DRB3, DRB4, DRB5) with generic (DRB) primers

• Allows for the separation of co-amplified sequences (pseudo-genes, related genes as “noise”) from target sequence (“signal”)

• Allows for the “digital” analysis (counting sequence reads) of mixtures and, with “deep” sequencing, for the detection of rare variants

Phasing across amplicons

Exon 2 seq 1

Exon 2 seq 2

Exon 3 seq 1

Exon 3 seq 2

2-1, 3-1

2-1, 3-2

2-2, 3-2

2-1, 3-2

Note: Assumes all HLA class I alleles in IMGT/HLA database have exon 2 and exon 3 sequences. If one of the 4 combinations is absent from the sequence database, an unambiguous inference of phase can be made. Physical direct phasing can be accomplished with longer amplicons or “bridging “amplicons.

NGS Applications for HLA Sequencing

• High Resolution: many amplicons/many exons per gene

• High Throughput: many samples per run

• Deep Sequencing: many reads per sample for detection of rare variants; analysis of mixtures

Neurosis is the inability to tolerate ambiguity

-Sigmund Freud