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 that carry oxygen through the body
• White blood cells that fight infection
• Platelets that help blood clot

Doctors use stem cell transplants to treat people who have:

• Certain types of cancer, such as leukemia
• Severe blood diseases, such as thalassemia, aplastic anemia, and sickle cell anemia
• Certain immune-deficiency diseases that prevent the body from making some kinds of white blood cells

Two main types of stem cell transplants are autologous and allogenic.

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 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.

Stem cells used in transplants are collected from donors in several ways. They can be collected through a blood donation, directly from a donor’s pelvis or from an umbilical cord or placenta.
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.