What Is a Blood and Marrow Stem Cell Transplant?

A blood and marrow stem cell transplant replaces a person's abnormal or faulty stem cells with healthy ones from another person (a donor). This procedure allows the recipient to get new stem cells that work properly.

Stem cells are found in bone marrow—a sponge-like tissue inside the bones. Stem cells develop into the three types of blood cells that the body needs:

• Red blood cells carry oxygen through the body.
• White blood cells fight infection.
• Platelets (PLATE-lets) help blood clot.

Small numbers of stem cells also are found in the blood and in the umbilical cord (the cord that connects a fetus to its mother's placenta).

Another type of stem cell, called an embryonic (em-bre-ON-ik) stem cell, can develop into any type of cell in the body. These cells aren't found in bone marrow.

Overview

Doctors use stem cell transplants to treat people who have:

• Certain types of cancer, such as leukemia (lu-KE-me-ah). The high doses of chemotherapy and radiation used to treat some cancers can severely damage or destroy bone marrow. A transplant replaces the stem cells that the treatment destroyed.
• Severe blood diseases, such as thalassemia (thal-a-SE-me-ah), aplastic anemia (uh-NEE-me-eh), and sickle cell anemia. In these diseases, the body doesn't make enough red blood cells or they don't work properly.
• Certain immune-deficiency diseases that prevent the body from making some kinds of white blood cells. Without these cells, a person can develop life-threatening infections. A transplant provides stem cells that replace the missing white blood cells.

Types of Transplants

Two main types of stem cell transplants are autologous (aw-TOL-o-gus) and allogenic (a-LO-jen-ik).

For an autologous transplant, a person's own stem cells are collected and stored for use later on. This works best when a person still has enough healthy stem cells even though he or she is sick. For a person with cancer, doctors also make sure that cancer cells are removed or destroyed from the collected cells.

For an allogenic transplant, a person gets stem cells from a donor. The donor can be a relative (like a brother or sister) or an unrelated person. A person also may get stem cells from umbilical cord blood donated by an unrelated person.

To prevent problems, the donor's stem cells should match the recipient's as closely as possible. Donors and recipients are matched through a blood test called HLA tissue typing.

Collection Process

Stem cells used in transplants are collected from donors in several ways. They can be collected:

• Through a type of blood donation called apheresis (a-fer-E-sis). A needle is placed in the donor's arm to draw blood. Then, his or her blood is passed through a machine that removes the stem cells from the blood. The rest of the blood is returned to the donor.
• Directly from a donor's pelvis. This procedure isn't used very much anymore because it must be done in a hospital using local or general anesthesia. A hollow needle is inserted repeatedly into the pelvis, and marrow is sucked out of the bone.
• From an umbilical cord and placenta. Blood containing stems cells may be collected from an umbilical cord and placenta after a baby is born. The blood is frozen and stored at a cord blood bank for future use.

Outlook

Stem cell transplants have serious risks. Some complications are life threatening. For some people, however, a stem cell transplant is the best hope for a cure or a longer life.

September 2007