Library preparation using FFPE-derived tumor DNA for high-throughput hybridization-based targeted or exome sequencing

Abstract

The use of next generation sequencing (NGS) to profile tumor genomes for the presence of diagnostic, prognostic, or therapeutically targetable variants is revolutionizing the practice of oncology and is increasingly utilized in clinical laboratory settings. Beginning with the isolation of DNA of sufficient quality and quantity from a tumor specimen, the creation of a library of genomic fragments representing the portion of the genome of interest, ranging from a few genes to the entire exome, is the first step required in the sequencing process. Fixed tumor tissue in the form of a tissue block is the most commonly encountered specimen for analysis in a clinical setting. Special precautions must be employed to ensure that material isolated from these specimens is suitable for use. Once DNA is obtained, one of the most commonly used methods for library preparation involves fluid phase hybridization-based capture of the genomic regions to be interrogated. This multistep process involves fragmentation of the DNA to a uniform size distribution, ligating adapter molecules which are labeled with specific barcodes to enable downstream sequencing and sample identification, and the use of a multiplexed pool of biotinylated single stranded RNA or DNA hybridization probes to recognize and capture the targeted genomic regions. Fragments which are not specifically captured during the hybridization process are removed via a series of wash steps, and a final low cycle amplification is used to prepare the library of captured fragments for sequencing. In this chapter, we provide a step-by-step guide to the preparation of fixed tissue-derived DNA libraries for sequencing via the Illumina process and highlight some of the precautions necessary when working with these types of specimens.