What is Cell-Free DNA?

What is Cell-Free DNA?

Recent medical breakthroughs in the early 2000s have discovered cell-free DNA as a new diagnostic marker in the circulating blood in humans. As the name implies, cell-free indicates DNA that are found freely in the blood without a nucleus, as DNA is usually found in a cell enclosed in a nucleus. Though cell-free DNA can also be found in the circulatory system of healthy individuals, their concentrations are at very low to negligible concentrations. However studies have found that the concentrations in cancer patients can reach high levels to substantiate diagnostic significance. With numerous studies conducted, it is now a well recognized fact that tumour DNA is liberated into the circulatory system during necrosis and apoptosis.

Furthermore the diagnostic significance of this cell-free DNA is not limited to just cancer patients; as other medical conditions such as graft rejection, stroke, trauma and burns where cellular damage is present, have similar observations too.

Medical and Diagnostic Significance of Cell-Free DNA

Cell-Free DNA can be excreted into the blood stream by both normal and tumour cells usually through either necrosis and/or apoptosis.

Apoptosis is a highly regulated process to “remove” cells that have reached their senescence stage and are replaced by new functionally healthy cells to prevent “over-population” of cells. In an average adult, between 50 and 70 billion cells reach senescence each day and undergo apoptosis. Apoptosis in normal tissues consequentially cleaves DNA into small 185-200bp fragments.

Tumour cells usually undergo necrosis which is an uncontrolled cell death resulting in loss of cell membrane integrity, resulting in the release of DNA fragments in various sizes and can be longer than 200bp.

Early detection has always been a focal point to improve cancer cure rates. Hence there is an increase in interest in looking for assays that can detect Cell-Free DNAthat correlates with specific cancer cells.

Image 1: In normal circumstances, DNA is usually enclosed in a nucleus in cells. However during apoptosis, both normal and tumour cells will release DNA fragments into the blood stream. The presence of these free circulating DNA can be of diagnostic values if the right assays are created to detect or identify the DNA sequence.

Streck Cell-Free DNA BCT

Previously, there are some major challenges to overcome before any research can be done on the cell-free DNA. This is mainly due to lysis of cells found in the blood, especially from leukocytes as these cells contain their individual genomic DNA. These cells are susceptible to losing their cellular genomic DNA into the plasma during blood processing, storage and shipping leading to contamination of the cell-free DNA of interest in the plasma. Furthermore, traditional cell-stabilising reagents such as formaldehyde and glutaraldehyde have the potential to damage the double helical structure of DNA.

Streck came out with a specialized blood collection tube that eliminates the aforementioned challenges. This Streck Cell-Free DNA BCT is a 10ml draw tube that contains K EDTA as anti-coagulant to allow plasma to be collected upon centrifugation. The signature feature of this product is the stabilising agent; a formaldehyde-free patented preservative that stabilises the blood cells, eliminating the possible contamination of genomic DNA from the leukocytes and most importantly maintain the cell-free DNA structures without interference in the downstream PCR testing.

Image 2: Streck Cell-Free DNA is a specialized vacutainer tube that can be used for direct blood draw. This tube can contains the necessary reagents that can allow immediate extraction of plasma after centrifuging.

Author:

Ivan Medical Technologist I http://textbookhaematology4medical-scientist.blogspot.sg/ Covance Asia Pte Ltd 1 International Business Park, Singapore 609917

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