cells contained in the blood and bone marrow. For decades, scientists have been using this type of adult stem cell to treat patients with diseases such as leukemia, sickle cell anemia, bone marrow damage, and some metabolic disorders and immunodeficiencies where the body has lost its ability to replenish its own set of healthy blood cells. Hematopoietic stem cells give rise to all the blood cell types, from infection-fighting white blood cells to blood-clotting platelets. Preliminary results have suggested that they may also be able to produce other cell types not found in blood, but this is not yet proven. WHY STEM CELL RESEARCH IS BEING PURSUED In the past, the only way to use hematopoietic stem cells for therapies was through bone marrow transplants. Extracting bone marrow is an uncomfortable and invasive procedure, and in order for a transplant to work, the donor and recipient must be genetically similar. If they are too genetically different, the blood cells produced from the transplanted marrow may recognize the patient’s body as foreign and fight against the patient’s own cells and organs. Additionally, the patient’s immune system may reject the transplant, causing a dangerous “war” within the patient’s body. More recently, scientists have developed ways to derive hematopoietic stem cells from the blood contained in the umbilical cord and placenta at birth. The stem cells isolated from a person’s own umbilical cord blood and placenta, if used for therapies later in life, would be less likely to cause an “internal war” within the recipient’s body. They are also more accessible than the stem cells in bone marrow because the extraction of this blood poses no risk to the mother or infant. The Changed Face of Skin Grafts For many years, scientists have been harnessing the regenerative capabilities of human skin to treat victims of severe burns using skin transplants. Skin transplants are possible because of the existence of stem cells located just under the top layer of skin. Every day, thousands of new skin cells are produced to replace those that have been shed. When someone suffers severe burns that destroy the source of these stem cells, their skin can no longer regenerate on its own. Traditionally, doctors treated severe burns by transplanting sections of skin from undamaged areas of the body onto the burned areas, but if doctors could not find enough unharmed skin to cover the burned areas, the patient could die. Now, scientists can grow vast sheets of new skin by culturing the stem cells from small pieces of healthy skin. This practice, which is a type of tissue engineering, has become routine for treating burn victims over the past 20 years. Recently, scientists have identified other types of stem cells in hair follicles and deeper layers of the skin. The inclusion of these new stem cells into engineered skin should help create more natural-looking skin transplants in the future. 14 WHY STEM CELL RESEARCH IS BEING PURSUED Stem Cells Found in Umbilical Cord Blood In 2005, the National Academies issued a report, Cord Blood: Establishing a National Hematopoietic Stem Cell Bank Program, which recommended that a national cord blood “bank” be established to harness the medical potential of this source of stem cells. Such a bank would not only benefit the people from whom the blood was collected but anyone in need of blood transplants. As with blood banks for blood transfusions, scientists could screen the bank to find the best match for each patient, providing a safer, more personalized living-cell therapy. Possible Future Treatment for Parkinson’s Disease? When most people reach for a pen, their body acts in one smooth and controlled movement. This is because the instant a person thinks of grabbing the pen, a series of nerve cells fire in an orchestrated symphony from the brain to the muscles responsible for that action. For the movement to be precise and smooth, all the nerve cells in the “grabbing-the-pen network” must function properly, including cells that tell unneeded muscles to stay still. In Parkinson’s disease, the brain cells responsible for keeping unneeded muscles from moving degenerate and die. This results in progressively more dramatic and uncontrolled movements, tremors, and spasms. To date, there is no cure for Parkinson’s disease because no one has figured out a way to bring back the specialized nerve cells that have died. Are the Promises of Stem Cell Therapies Realistic? The list of medical achievements stem cells could offer seems to be expanding at an incredible pace. The role of stem cells in medicine is already very real, but there is a danger of exaggerating the promise of new medical developments. What tend to be “over-promised” are not only the potential outcomes of both embryonic and adult stem cell research, but also the time scales that are involved. The basic research needed to develop viable therapeutic options is a lengthy process that may extend over many years and decades. Even after science has moved from basic research to developing medical applications, it still takes many years to thoroughly test those applications and demonstrate that they are safe to prescribe for patients. This is true for all medical treatments, including the development of new drugs, procedures, and medical equipment, and is not specific to the living cell therapies made possible by stem cell research.