Contrived Materials in Liquid Biopsy Assay Development
When a test needs to be sensitive enough to distinguish a few particles of cancerous DNA from billions of non-target molecules, extensive testing and validation is critical. Finding enough samples to achieve this, and having enough of the right kind of samples—perhaps with varying amounts of cancerous DNA, or with difficult-to-detect cancer mutations—can be a big problem. And what happens when you need to compare the performance of your test with another manufacturer’s? How can you be sure that differences in detection are due to the specifics of your test rather than differences in the blood samples you’re using? Every patient sample, even those taken repeatedly from the same donor, is unique, and all patient samples are precious.
Luckily, we have options for liquid biopsy test validation beyond collecting countless blood samples. Contrived materials, also called commercially available reference materials, are a class of product meant to mimic a biological human sample and are a great option for assay testing when blood samples are in short supply or don’t meet testing needs. Manufacturers such as SeraCare and Horizon Discovery Ltd are major suppliers of these products. Contrived materials are manufactured using human genomic DNA from cell lines, with known amounts of cancerous DNA spiked in. The variant allele fraction (i.e. proportion of cancerous DNA) and mutation type can be specified and customized, and some types of contrived materials are also formulated to mimic human plasma.
Contrived materials are generally manufactured using human cell line DNA, with the desired variant alleles incorporated in known amounts. Image created using Biorender.com
Learning how best to use contrived materials in combination with patient samples, how test performance compares on these different types of samples, and what types of data can be generated using contrived materials for the purposes of FDA review are open questions that the field is still investigating. BLOODPAC’s Just Freaking Do It working group is actively working on clarifying how contrived materials can and should be used in the validation process. The group’s recent study in the Journal of Molecular Diagnostics tackles the use of contrived materials in comparing different types of liquid biopsy tests across different clinical laboratories, and future studies will focus on further characterization of the role of these types of reference materials in the test development and approval process.
