Why do we have bone marrow? Why would a person need a bone marrow transplant?

Bone Marrow
What is a bone marrow transplant and how does it work?

Peggy finds out why bone marrow matches are so rare.
Segment length: 6:45


Inside your bones is a thick mass of cells called bone marrow. Every hour, a small number of stem cells in it create all other kinds of blood cells that exist in your body, including leukocytes, erythrocytes, and platelets. These cells are essential to your health-leukocytes fight infection, erythrocytes carry oxygen, and platelets help the blood clot.

When a person has a blood disease, such as aplastic anemia or leukemia, doctors may perform bone marrow transplants to re-establish a healthy blood supply. Many transplants occur after a patient has received chemotherapy or radiation treatment to destroy cancerous or other disease-causing cells. Both abnormal and normal cells are killed by these treatments, including stem cells. A bone marrow transplant starts the blood production process from scratch with normal stem cells.

An allogeneic transplant-where another person's bone marrow is given to a patient-doesn't always work because of rejection or because of graft-versus-host disease. Rejection of the donor's marrow occurs because our bodies fight off invading foreign cells. If a donor's marrow doesn't match perfectly, the recipient's immune system may identify the new cells as foreign and destroy them, leaving the patient unable to create new blood.

Graft-versus-host disease occurs because the new immune system from the donor's marrow may identify the patient's body as foreign and try to destroy it. When the donor's immune cells in the marrow attack the patient, many symptoms may result and, in severe cases, the patient could die.

Doctors decrease these risks by trying to select a patient/donor pair whose immune cells will identify each other as "self." An identical twin's cells will see the other twin's cells as self. But most patients do not have an identical twin. So doctors look at a person's human leukocyte antigens (HLA) to match donor and patient bone marrow. These are proteins present on the surface of our cells. They play a big role in telling immune cells that other cells are either foreign or "friendly" self cells.

Doctors will look at HLA antigens on your siblings' cells, because you have a 25 percent chance of having an HLA match with a brother or sister. Among unrelated people, only one in 20,000 people will be an acceptable match.


1. How would the ability to create blood in a lab affect the availability of marrow transplants?
2. In an autologous bone marrow transplant, a patient's bone marrow is extracted and then reintroduced into the body. What transplant problems might this eliminate? What new complications might occur?

Key Words

aplastic anemia blood deficiency whereby reduced levels of red blood cells, platelets, and leukocytes result in a shortage of oxygen in the blood, bleeding, and infection
chemotherapy using chemicals to treat disease by poisoning the disease-producing cells
erythrocytes red blood cells that transport oxygen in the blood to the tissues
leukemia cancer of the blood characterized by excessive production of white blood cells
leukocytes white blood cells that fight off infection or destroy foreign cells
platelets cells in the blood that cause it to clot after an injury
radiation treatment using energy from a radiation source to eliminate disease
stem cells unspecialized cells that create specialized cells
transfusion transfer of blood from one person to another


  1. A transplant program looks to black donors. (1993, Mar 23) The New York Times, p. B6.
  2. Altman, L.K. (1994, July 19) Baboon cells might repair AIDS-ravaged immune system. The New York Times, p. C3.
  3. Brooks, A.C. (1994, Dec 10) Bone marrow transplants: Upping the odds. Science News, p. 391.
  4. Coghlan, A. (1993, Apr 10) Blood cell 'factory' aims to end transfusions. New Scientist, p. 17.
  5. Maugh, T.H. (1994, Dec 1) New tactic may ease transplants of bone marrow. Los Angeles Times, p. A1.
  6. Stewart, S.K. (1994) Bone marrow transplants: A book of basics for patients (rev. ed.). Highland Park, IL: BMT Newsletter.
  7. Wiegner, K. (1994, Dec 7) He's not my brother. Los Angeles Times,
    p. D10.

Additional resource
NEWTON'S APLE Show 1012 (blood typing). GPN: (800) 228-4630. Or call your local PBS station to find out when it will be rerun.

Additional sources of information

  1. BMT Newsletter
    1985 Spruce Ave.
    Highland Park, IL 60035
    (708) 831-1913
  2. National Marrow Donor Program
    3433 Broadway St. NE, #400
    Minneapolis, MN 55413
    (800) 627-7692

Main Activity

What Are the Odds?
Find the connection between rolling dice and a genetic match.

What are the chances of getting a match at random from an unrelated donor? In this activity, you will learn about probability using a pair of dice.


1. If you rolled a pair of dice, what chance would you have of getting matching numbers? Write down how many times you think you'd have to try before you got a match.
2. The first concept you need to know is that the probability of something happening is expressed in this simple equation:

probability = number of favorable outcomes
number of possible outcomes
In this example, you're trying to get an outcome where the two dice match. A die is a cube with six possibilities: you can roll either a 1, 2, 3, 4, 5, or 6. So with one die, your probability of rolling a 5 is:

1 (number of
probability = favorable outcomes)
6 (number of
possible outcomes)

3. Next, you have to figure out how your probability changes when you roll a pair of dice. First, consider what the new number of possible outcomes is. Before, there were six. Now, there are many more combinations possible. Below is a chart listing all the possible rolls for your dice, naming them Die A and Die B. We started the chart to help you figure it out. Fill in the missing numbers to complete all the possible die rolls.
4. Count how many possible outcomes you can have when rolling two dice. If we wanted to calculate our chances of rolling a 5 on either or both dice, we would have to rewrite our probability equation:

probability = 3 (Die A=5, Die B=5, or both=5)
(fill in your count from above)

5. Now use what you've learned and the chart you've completed to calculate the chances of rolling matching die.

1. The HLA proteins are determined by genes on chromosome 6. Each parent has two of these chromosomes, and these four HLA types are almost always different. You inherited one HLA type from each parent, as did your siblings. What is the probability that one of your siblings inherited the same HLA types that you did?

There are four different blood types: O, A, B, and AB. Try to find out the blood type for everyone in your family, including yourself. To whom could you donate blood? Who could donate blood to you?

Create a simple model showing how your blood cells are suspended in plasma, making blood. Fill a glass jar with corn syrup to represent plasma and add tea leaves, bits of confetti, and pepper to act as blood cells. Put the lid on tightly and shake the jar to get an idea of how blood cells travel in plasma through your system. What happens when you let the "blood" sit for a while? Does the heart's pumping action do more than just transport blood?

Die A Die B Die A Die B Die A Die B Die A Die B Die A Die B Die A Die B
1 1 2 1 3 1 4 1 5 1 6 1
1 2 2 2 3 2 4
1 3 2 3 3 3
1 4 2 4 3
1 5 2 5
1 6 2

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