XDx uses modern genomics and bioinformatics technology to develop molecular diagnostic assays based on gene expression patterns in blood cells that provide clinically useful information. Gene expression patterns reflect the activity of genes in the various blood cells types at the time the sample was taken. Overall gene activity in a blood sample can be affected by drugs, immune activation, inflammation, or by recruitment of new cells from the bone marrow.
Developing these novel in vitro diagnostic tools requires analysis of carefully characterized blood samples to find marker genes that are differentially expressed, either at a higher or lower level, in different disease states.
Gene expression is initially evaluated using microarrays, which take advantage of the recently defined sequence of the entire human genome to assess the expression of most genes in the genome on a single glass slide. Using sophisticated bioinformatic tools, candidate marker genes are identified from among the more than 41 thousand features assessed in the microarray data. The most promising candidates are then tested using quantitative real-time PCR (qRT-PCR), which is a more sensitive and reproducible technique for measuring gene expression levels than microarrays, to find markers where differential expression is confirmed in the two clinical states. From this list of confirmed marker genes, computer algorithms are used to identify the combination that best discriminates one clinical state from the other.
The final product of the development process is a list of genes to be assessed, their corresponding qRT-PCR assays, and a mathematical algorithm that combines the resulting expression levels into a score that provides information regarding the clinical state that existed when the blood sample was collected.