Science As We Know It

By Maria Jassinskaja

Everyone who has donated blood or had a deep cut knows that losing blood can make you feel dizzy and weak for a while. Usually this feeling doesn’t last for too long, and we have the hematopoietic stem cells (HSCs) to thank for that. Their name is derived from the Greek word “hematopoiesis” which quite literally means “to make blood”. HSCs are multipotent and can produce red blood cells, platelets and immune cells (white blood cells). Like all stem cells, HSCs have the capability to self-renew by creating copies of themselves, which enables them to sustain life-long blood production. HSCs appear in the embryo at around week four of human pregnancy. They are formed from epithelial (“skin-like”) cells in the aorta of the embryo through a process called endothelial-to-hematopoietic transition. After this, the newly formed HSCs join the blood circulation and begin to divide and grow in numbers to build up the blood system of the embryo. In adult mammals, HSCs can be found in the bone marrow. Like most other adult stem cells, HSCs in the bone marrow are normally in a resting state where they don’t divide that much, but can be activated in response to blood loss or infection to produce the cells required to deal with the injury.¹

HSC transplantation (sometimes referred to as bone marrow transplantation) is the only stem cell therapy that is used regularly in the clinic. The first HSC transplantation was performed already in the 1950s. HSC transplantation is used to treat a number of different conditions, such as blood cancer (leukemia), blood deficiency (anemia) and some autoimmune diseases. The most common way of performing HSC transplantation is to give the donor a drug that makes HSCs exit the bone marrow and circulate in the blood. The blood is collected and given to the patient who has been pre-treated with radiation to remove their own, diseased, HSCs. Through a process called homing, the donated cells find their way to the bone marrow where they go on to rebuild a new and healthy blood system in the patient. HSC transplantation is a life-saving procedure and for some severe diseases, it is the only treatment option. Like in all other types of organ donations, it is important that the donor and the patient’s immune systems are compatible with each other. If not, the newly transplanted cells can begin to attack the patient’s body and cause a disease called Graft-versus-Host.² For this reason, it is important that there are many bone marrow donors available to choose from to be able to find the right match for each patient. In Sweden, people interested in donating bone marrow can register themselves at Tobiasregistret.