Last reviewed and revised on May 20, 2013

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 bloodlymphomas and leukemias. When all other treatments have failed, the only hope for a cure is to wipe out all of the patients blood cellsthe cancerous ones and the healthy onesand to give a patient an entirely new blood system. The only way to do this is to transplant blood stem cellscells 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 cellsthe cells designed to give the patient a whole new blood systemare 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 patients bone marrow through a needle, or taken from the patients blood (some blood stem cells travel in the blood). So the blood stem cells are outside the patients body, growing in a laboratory dish, when the patient is given the chemotherapy that kills all the blood cells still inside the body.

Read more:
Special Harvard Commentary: How Stem Cells Help Treat Human Disease