By Anthony L. Komaroff, M.D.
Brigham and Women's Hospital

Both adult and umbilical cord stem cells already are used to treat disease.

Adult stem cells:

For many years, doctors have used adult stem cells successfully to treat human disease, through bone marrow transplantation (also known as hematopoietic stem cell transplantation). Most often, this treatment is used to treat cancers of the blood—lymphomas and leukemias. When all other treatments have failed, the only hope for a cure is to wipe out all of the patient’s blood cells—the cancerous ones and the healthy ones—and to give a patient an entirely new blood system. The only way to do this is to transplant blood stem cells—cells that can reproduce themselves indefinitely and turn into all types of specialized blood cells.

Here's how it's done. First, the doctors need to collect blood stem cells from a patient's bone marrow, and let them multiply.

Second, the patient is given a dose of chemotherapy that kills all of the cancer cells — a dose that, unfortunately, also kills the cells in the patient's bone marrow.

Third, the blood stem cells—the cells designed to give the patient a whole new blood system—are given to the patient through an intravenous catheter. Hopefully, the blood stem cells then travel through the blood to the bone marrow, where they take up residence and start to make a new blood system.

Where do the blood stem cells come from? Most of the time, they come from the patient himself. They are sucked out of the patient’s bone marrow through a needle, or taken from the patient’s blood (some blood stem cells travel in the blood). So the blood stem cells are outside the patient’s body, growing in a laboratory dish, when the patient is given the chemotherapy that kills all the blood cells still inside the body.

Sometimes the patient’s own blood stem cells cannot be used, and blood cells from another person must be used. When the procedure works, the bone marrow stem cells begin making the new blood cells the patient needs — and the cancer is cured.

Although bone marrow transplantation is a common example of using a particular type of adult stem cell — bone marrow blood-forming stem cells — to replace dead cells, it currently is the only such common example. If you need to replace cells in any organ other than the blood — your brain, heart, liver, kidneys — there is currently no stem cell therapy.

Umbilical cord stem cells:

In recent years, umbilical cord stem cells also have been used for transplantation in place of bone marrow adult stem cells. Compared with bone marrow cells, they are less likely to have certain major side effects and are at least as likely to successfully grow into healthy adult blood cells.

Umbilical cord stem cells can be easily extracted at the time of a baby's birth and frozen for years. For example, if you needed a transplantation for blood cancer or other condition later in life, your umbilical cord cells that have been frozen and stored since the day you were born, could be transplanted into you without fear of rejection by the immune system — because they come from you, not from someone who is genetically different from you. Some companies offer parents the service of collecting and freezing a baby's umbilical cord blood. While there may be cases where that makes sense — such as a baby born to a family that seems to have a high rate of blood cancer — most experts do not think there are currently many circumstances under which it is appropriate to collect and freeze a baby's cord stem cells at birth.

Anthony L. Komaroff, M.D., is professor of medicine and editor-in-chief of Harvard Health Publications at Harvard Medical School. Dr. Komaroff also is senior physician and was formerly director of the Division of General Medicine at Brigham and Women's Hospital. Dr. Komaroff has served on various advisory committees to the federal government, and is an elected Fellow of the American Association for the Advancement of Science.