Types of Bone Marrow Transplants
The main distinction between the two major types of bone marrow transplant (BMT) has to do with whose stem cells are being transplanted—the child’s own cells or cells from a donor.
Autologous Bone Marrow Transplant
In autologous transplants, the transplanted stem cells come from the body of the child having the transplant. The doctors remove the stem cells from the child, store them, and then put these cells back after destroying the cancer or diseased cells with conditioning.
If your child is having an autologous transplant, you do not need a donor; the child acts as his or her own donor. However, your child will have to undergo either bone marrow harvesting or stem cell mobilization in order to gather the stem cells.
The advantage of using the child’s own stem cells is that he or she will not face the complication of graft-versus-host disease (when donated white blood cells attack the child’s healthy cells). However, with an autologous transplant the child does not have the same graft-versus-tumor benefits (when the donated white blood cells attack the child’s diseased cells). As a result, there is a higher relapse rate with autologous transplants, and this type is not suitable for some diseases or patients.
Allogeneic Bone Marrow Transplant
For some diseases, the transplanted stem cells come from another person, called a donor. Donor transplants are called allogeneic transplants. Why use another person’s stem cells? Often the child’s own blood cells are simply too diseased to be given back to them. In other cases, the donated stem cells are far more aggressive in killing the patient’s diseased cells (the graft-versus-tumor effect described above).
For these reasons, in certain serious conditions, allogeneic transplants can boost the chances of a child’s long-term recovery. However, allogeneic transplants can be riskier than autologous transplants because the cells of the donor and the recipient mix, which can lead to graft-versus-host disease. Finding a donor who is related to your child—a brother or sister, for example—can reduce some of this risk. So can using stem cells from an unrelated donor whose cells closely match your child’s.
As part of your family’s preparation for an allogeneic transplant, our doctors will pick a donor whose tissue most closely matches your child’s tissue. The closer the match, the greater the chances for a positive outcome. If your child does not have a closely matched relative who can donate bone marrow or stem cells, we will work with the international registries to find an unrelated donor.
If your child is having an allogeneic transplant, your donor will undergo stem cell mobilization and collection or bone marrow harvesting—or if the transplanted stem cells come from a baby’s umbilical cord and placenta, the cells are collected and frozen at the time of the baby’s birth.
There are several types of allogeneic transplants, with different names based on the source of the donor cells.
Related Donor Transplant
Having many relatives as potential donors is ideal because the likelihood of a very close match reduces the risk of problems. Siblings are likely to be the closest match. Identical twins are an exact match.
Matched Unrelated Donor Transplant
When no matching relative is available, doctors can search an international registry for an unrelated donor who is a match for your child. (Learn more about finding or becoming a donor.)
Half-Matched Family Member Donor Transplant
Parents are always half-matched for their children. Siblings have a 50 percent chance of being half-matched. Although not as ideal as matched sibling transplants, half-matched (haploidentical) transplants are now done routinely for children who need another option.
Cord Blood Transplants
Another new option for those without a matched donor is blood from the umbilical cord of a newborn. The immune cells in cord blood are still “naïve,” meaning they have not yet become active in attacking other cells. This immaturity makes them less likely to attack the transplant recipient’s tissues—therefore, cord blood stem cells do not need to be such a close match.