The term "stem cell" refers to a cell that can give rise to a variety of other cells, like the stem of a flower can give rise to leaves, other stems and flowers. There are many different kinds of stem cells.
Embryonic Stem Cells
One type that has received a lot of attention in the media is the "embryonic" stem cell. These cells are usually isolated from an unborn fetus and, under the right circumstances, have the ability to make virtually any cell in our bodies. The use of this kind of stem cell is an exciting future prospect though there are certain moral issues that cloud the research.
Blood Stem Cells (Hematopoietic Stem Cells)
Another type of stem cell is the blood stem cell (also known as hematopoietic stem cells). This kind of stem cell can be isolated from fully formed individuals and has the capability to make all of the cells in our blood and immune system, including infection-fighting white blood cells, oxygen-carrying red blood cells and blood-clotting platelets. The hematopoietic stem cell is what our transplant program uses when we perform a "stem cell" transplant. In adults, these cells are found chiefly in the bone marrow but, under the right circumstances, they can be induced to go out into the blood stream.
Harvesting the Stem Cells
Because hematopoetic stem cells are found in the marrow, they were historically collected through a bone marrow harvesting procedure in the operating room before we learned that we could "mobilize" them into the blood using certain drugs. Bone marrow is harvested in an operating room procedure using anesthesia. Today, stem cells are more commonly obtained from the bloodstream by an outpatient process called apheresis after being "mobilized." Both bone marrow harvesting and apheresis provide stem-cell support that allows doctors to give intensive therapy without permanently harming a cancer patient's immune system or causing irreversible marrow damage.
Cord Blood Stem Cells
Hematopoietic stem cells also can be isolated from a newborn baby's umbilical cord blood. These "cord blood" stem cells can be used for transplant but, because they are low in number and the infant's immune system is not fully formed, they are more difficult transplants for adults. Our program is not currently using cord blood stem cells.