Stem Cell Transplant (Peripheral Blood, Bone Marrow, and Cord Blood Transplants)

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What are stem cells and why are they transplanted?

All of the blood cells in your body start out as young (immature) cells called hematopoietic stem cells. (Hematopoietic means blood-forming, and is pronounced he-muh-toe-poi-ET-ick.) Even though they are called stem cells, they are not the same as the embryos’ stem cells that are studied in cloning and other types of research. Here, the words stem cells refer to blood-forming stem cells.

Stem cells mostly live in the bone marrow (the spongy center of certain bones), where they divide to make new blood cells. Once blood cells mature, they leave the bone marrow and enter the bloodstream. A small number of stem cells also get into the bloodstream. These are called peripheral blood stem cells.

Stem cell transplants are used to restore the stem cells when the bone marrow has been destroyed by disease, chemotherapy (chemo), or radiation. Depending on the source of the stem cells, this procedure may be called a bone marrow transplant, a peripheral blood stem cell transplant, or a cord blood transplant. They can all be called hematopoietic stem cell transplants.

Today hundreds of thousands of patients have had stem cell transplants. Transplant teams are better able to care for transplant patients and doctors know more about which patients are likely to have better results after transplant.

What makes stem cells so important?

Stem cells make the 3 main types of blood cells: red blood cells, white blood cells, and platelets.

We need all of these types of blood cells to keep us alive. And for these blood cells to do their jobs, you need to have enough of each type in your blood.

Red blood cells (erythrocytes)

Red blood cells (RBCs) carry oxygen from the lungs to all of the cells in the body, and then bring carbon dioxide back from the cells to the lungs to be exhaled. A blood test called a hematocrit shows how much of your blood is made up of RBCs. The normal range is about 35% to 50% for adults. People whose hematocrit is below this level have anemia. This can make them look pale and feel weak, tired, and short of breath.

White blood cells (leukocytes)

White blood cells (WBCs) are a crucial part of the immune system. They help fight infections caused by bacteria, viruses, and fungi.

There are different types of WBCs. Neutrophils are the most important type in fighting bacterial infections. The absolute neutrophil count (ANC) is a measure of the neutrophils in your blood. When your ANC drops below 1,000 per cubic millimeter (1,000/mm3) you have neutropenia, and you have a higher risk of serious infection. The danger is greatest when levels are below 500/mm3.

Stem cells make another type of white blood cell called lymphocytes. There are different kinds of lymphocytes, such as T lymphocytes (T cells), B lymphocytes (B cells), and natural killer (NK) cells. Some lymphocytes make antibodies to help fight infections. The body depends on lymphocytes to recognize its own cells and reject cells that don’t belong to the body, such as invading germs or cells that are transplanted from someone else.

Platelets (thrombocytes)

Platelets are pieces of cells that seal damaged blood vessels and help blood clot, both of which are important in stopping bleeding. A normal platelet count is usually between 150,000/cubic mm and 450,000/cubic mm, depending on the lab that does the test. A person whose platelet count drops below normal is said to have thrombocytopenia, and may bruise more easily, bleed longer, and have nosebleeds or bleeding gums. Spontaneous bleeding (bleeding with no known injury) can happen if a person’s platelet count drops lower than 20,000/mm3. This can be dangerous if bleeding occurs in the brain, or if blood begins to leak into the intestine or stomach.

More information on blood counts and what the numbers mean is available in our document called Understanding Your Lab Test Results.


Last Medical Review: 10/02/2013
Last Revised: 10/02/2013