About Stem Cell Transplants
Hematopoietic stem cells are immature cells that are capable of developing into the three types of blood cells:
- red blood cells that carry oxygen
- white blood cells that fight infection
- platelets that help blood to clot
Hematopoietic stem cells can be found in bone marrow (the spongy tissue inside bones), the bloodstream, or the umbilical cord blood of newborn babies.
A stem cell transplant can replenish a child's supply of healthy hematopoietic stem cells. It's used to treat a wide range of diseases, including cancers like leukemia, lymphoma, neuroblastoma, Wilms tumor, and certain testicular or ovarian cancers; blood disorders; immune system diseases; and bone marrow syndromes.
Transplanted hematopoietic stem cells are introduced (or infused) into the bloodstream through an intravenous (IV) line, much like a blood transfusion. Once in the body, they can produce healthy new blood and immune system cells.
Types of Transplants
The two main types of stem cell transplants are autologous and allogeneic. The type of transplant needed will depend on the child's specific medical condition and the availability of a matching donor.
- Autologous hematopoietic stem cell transplant. With this type of transplant, patients act as their own donor. That is, a child who is about to undergo cancer treatment will have his or her own stem cells removed (harvested) and frozen for later use. After the child receives chemotherapy and/or radiation, the stem cells are thawed and put back into the child's body. This procedure may be done once or many times, depending on the need. Sometimes doctors will use extra-high doses of chemotherapy during treatment (to kill as many cancer cells as possible) if they know a patient will be getting a stem cell transplant soon after.
- Allogeneic hematopoietic stem cell transplant. With an allogeneic transplant, the stem cells come from a donor — often a sibling but sometimes another volunteer — whose cells are considered a "match" for the patient. The process of finding a match is called tissue typing (or HLA [human leukocyte antigen] typing). HLA is a protein on the surface of blood cells. Basically, the more "HLA markers" a child and the potential donor have in common, the greater the chance that the transplant will be successful.
Unlike with an autologous transplant, there is a risk of rejection. Sometimes, despite the donor being a good match, the transplant simply may not take. Other times, the donor cells can begin to make immune cells that attack the recipient's body. This condition is called graft-versus-host disease, and can be quite serious. Fortunately, most cases are successfully treated with steroids and other medications.
Sometimes, an upside of graft-versus-host disease is that the newly transplanted cells recognize the body's cancer cells as different or foreign, and actually work to fight them.
