Clinical utility and biological impact of platelet-restricted clonal haematopoiesis

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This project aims to understand the links between abnormally expanded blood stem cells, blood clots (venous thromboembolism) and ischemic heart disease. Blood stem cells have the capacity to self-renew and to develop into all the mature blood cells, such as white blood cells (that fight infection) and platelets (essential for blood clotting). As we age, DNA copying mistakes (mutations) are acquired, but most of these are inconsequential. However, sometimes these stem cells acquire mutations that give their progeny a survival advantage and their numbers expand. Such expanded populations are referred to as a clone; the process is termed clonal haematopoiesis. As you might expect, clonal haematopoiesis is found more frequently in the ageing population, in around 10-20% of people over 70 years. Clonal haematopoiesis is associated with a 10-fold increased risk of developing blood cancers. However, it has more recently been shown to be associated with a twofold increased risk of blood clots and heart disease. The underlying cause of this association between expanded clones and blood clots/heart disease is unknown, but it is thought to be entwined with the chronic inflammation which accompanies aging. It is thought that, due to abnormal immune responses, the expanded clone is associated with an inflammatory response which is known to contribute to these diseases. The detection of clonal haematopoiesis, a 'pre-cancer' state, in people with blood clots and heart disease could lead to new ways to prevent progression to blood cancer, as well as reduce risk of further blood clots or heart disease.There is evidence that many stem cells have offspring which only contribute to the platelet lineage, although they are still capable of becoming any type of blood cell. Furthermore, this 'platelet-bias' seems to occur more with advancing age. The standard techniques to detect stem cell clones look for specific mutations in mature white blood cells, but preliminary work in our lab shows that 10% of people over the age of 70 have clones detectable only in platelets as opposed to white blood cells; this is an entirely new finding. We don't yet know if these platelet-biased stem cell clones have links with blood clots and heart disease, as all of the evidence proving these links have used the standard white blood cell detection methods. Platelets are key to normal blood clotting and are implicated in inflammation and cancer, so we hypothesise that platelet-biased stem cell clones play an important role in this association. To investigate this, we aim:1. To determine if there is an association between platelet-biased clonal haematopoiesis and venous thromboembolism and heart disease. We will screen for the presence of platelet-biased CH in patients with blood clots and heart disease.2. To investigate the mechanisms by which platelet-biased clonal haematopoiesis drives increased blood clots and heart disease. This will include functional studies such as platelet activation studies, to determine if platelet-biased CH is associated with abnormal platelet activation. We will also analyse the bone marrow (where stem cells are made) of 5-10 patients to examine the cellular origins of these aberrant platelets. 3. To look for novel mutations that are specifically associated with platelet-biased clonal haematopoiesis, in case these are different to the mutations currently recognised to cause clonal haematopoiesis in white blood cells ie. the standard CH detection method.A key aim of the planned work is to develop expertise in clonal haematopoiesis which would support new CH clinics (already set up in the US but not the UK). Once detected, these patients could be counselled on how to reduce the risks associated with such clones. Through our work in understanding the mechanisms of these associations, we hope to identify targets for drug development to reduce the risk of diseases developing in these patients.