Stem cells are cells in the body that have the potential to turn into anything, such as a skin cell, a liver cell, a brain cell, or a blood cell. Stem cells that turn into blood cells are called hematopoietic stem cells. These cells 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 (sometimes called a bone marrow transplant) can replenish a child's supply of healthy hematopoietic stem cells after they have been depleted. 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 put 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.
Autologoushematopoietic stem celltransplant. 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.
Allogeneichematopoietic stem celltransplant. 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 a child's body rejecting the donated cells. 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.
Stem cell transplantation is a very complex process that may span several months. A team of doctors is usually involved in determining if a child is a candidate and, if so, whether the transplant will be autologous or allogeneic.
For an allogeneic transplant, a compatible donor will be sought among family members or through a national registry of volunteers. Once a match is found, the donor's stem cells will be harvested. Three different types of hematopoietic stem cells can be collected or harvested:
Peripheral blood stem cells are harvested from donated blood. The stem cells are separated and collected and the rest of the blood is returned to the donor.
Bone marrow stem cells are collected from the donor's hip bone through a surgical procedure.
Cord blood stem cells are collected from a mother's placenta immediately after a child is born.
While all three types can replenish a patient's blood and bone marrow cells, there are advantages and disadvantages to each. The doctor will suggest the best type of stem cell for your child's illness.
The next step in the transplantation process is conditioning therapy, which kills unhealthy cells (like cancer cells) to make room for stem cells to grow and/or weakens the immune system so that there’s less chance of the body rejecting the new cells. One type of conditioning therapy delivers high doses of chemotherapy and/or radiation to kill cells, destroy the bone marrow, and weaken the immune system. Most kids will get this type of therapy. Another type of conditioning therapy delivers lower doses of chemotherapy, radiation, or another treatment to weaken the immune system. The doctor will decide which type of conditioning therapy is best.
Soon after the conditioning phase, the transplant itself will be done through infusion and healthy stem cells will be introduced to the child's body. After the infusion, the child will be watched very closely to make sure the new stem cells are settling into the marrow and beginning to manufacture new blood cells (called engrafting). Doctors will watch for any signs of rejection as well as graft-verses-host disease in kids with allogeneic transplants.
Engrafting takes an average of 2 weeks, but can be as quick as 1 week or as long as 6 weeks. Your child will receive medicines to promote engrafting and prevent rejection and graft-verses-host disease.
Kids who receive stem cell transplants have a high risk of infection because during conditioning therapy and while the transplant is grafting, their immune systems are weakened and unable to fight bacteria and other germs that enter the body. Children who receive an allogeneic transplant have an even greater risk of infection because they require medications to further suppress their immune systems to reduce the chance of rejection.
Because of these risks, a child who's had a stem cell transplant will not be released from the hospital until doctors are sure the transplant has successfully engrafted and the child is otherwise doing well.
Once released, a child needs very close monitoring and follow-up care. School and other public indoor areas may be off limits for 3 months to a year, and other places might be restricted as well. This is because for kids with a compromised immune system, even a simple infection like a common cold can be serious and even life threatening if untreated.
The stress of having a child who is being treated for cancer or another serious condition can be overwhelming for a family. That stress can be magnified when treatment requires a long "isolation period," as is necessary with a stem cell transplant.
To find out what support is available to you and your child, talk to your doctor, a hospital social worker, or child life specialist. Many resources are available that can help you get through this difficult time.