A previously unknown function of platelets to 'hoover up' and store DNA in the blood could improve cancer diagnosis and prenatal screening.
The analysis of cell-free DNA (cfDNA) in the blood is used in screening methods, including non-invasive prenatal testing and 'liquid biopsy' tests (see BioNews 1273). However, current approaches only examine cfDNA in blood plasma. A study, led by the University of Oxford revealed that platelets – blood cells primarily known for their role in blood clotting – internalise and store extracellular and cancer DNA circulating in the blood.
Dr Lauren Murphy, lead author of the study published in Science, said the research 'indicates that current liquid biopsy screening methods are overlooking valuable genetic information that is contained within platelets'.
'Platelets do not have any DNA of their own, and it's interesting and potentially important that they can internalise cancer DNA circulating in the bloodstream,' said Dr David Crosby, head of prevention and early detection research at Cancer Research UK, which funded the study.
When cells die, they release DNA fragments into the bloodstream, which – in higher concentrations – can trigger unwanted immune responses or other health problems. Until now, scientists have not fully understood how the body clears these fragments.
In a mouse experiment, removal of platelets increased the concentration of circulating DNA within blood, and live imaging showed that platelets internalise these DNA fragments.
In humans, analysis of platelet DNA from a simple blood test was found to reveal the presence of cancerous and pre-cancerous changes, as well as evidence of fetal DNA in the platelets of pregnant women.
One of the limiting factors of non-invasive tests is the very low concentration of cfDNA in the blood plasma. The DNA collected by platelets is protected from being degraded, and could increase the amount of DNA available for analysis – possibly even double it according to senior author Professor Beth Psaila.
'This discovery means that many more parts of a blood sample could be used to find cancers earlier, long before any symptoms appear,' said Dr Crosby. 'It may find clues of cancer that have previously been overlooked.'
If successful, added Dr Murphy, the approach would be easy to implement, 'because it's just a small change in the initial processing of the blood sample.'
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