Scientists have identified a new type of bone marrow stem cell in mice that is primed to produce large numbers of vital blood-clotting platelets. The breakthrough may eventually lead to the development of new treatments to restore platelets in patients who have undergone chemotherapy or a bone marrow transplant. The research was led by the Medical Research Council Weatherall Institute of Molecular Medicine (WIMM),at the University of Oxford.
Blood cells are made by a small pool of stem cells in the bone marrow,which replenish the blood at a rate of millions of cells per second. These cells can self-renew (copy themselves) and give rise to all the different cell types that make up the blood system,including white and red blood cells,and platelets. Platelets help the blood to clot by clumping together at the site of bleeding. Having too few platelets can result in excessive bleeding and is a common side effect in cancer patients,whose natural reservoir of platelets has been destroyed by the disease or by treatment.
This can be life-threatening in the weeks immediately following chemotherapy or a bone marrow transplant as it takes time for blood stem cells to replenish platelets to safe levels. Scientists believed there was just one type of blood stem cell. This study,led by Professors Sten Eirik W Jacobsen and Claus Nerlov,has revealed a previously undiscovered subset of platelet-primed blood stem cells that can self-renew and produce some other cell types that make up the blood,but are particularly geared towards platelet production. The researchers also found that different subtypes of blood stem cell are organised into a hierarchy,with platelet-primed cells at the top. These platelet-primed cells are able to also replenish other stem cell types that mostly generate the vital blood cells of the immune system.
Transplanting just one platelet-primed stem cell into mice that lacked their own bone marrow was enough to stably restore more than 10 per cent of their platelets,suggesting that these cells can generate a huge number of platelets in a sustainable manner. Future studies by the group will focus on whether or not this can be achieved quickly enough to benefit patients in a clinical transplantation setting. The study was published in journal Nature.