There are several types of allogeneic transplants:
Donor and patient are identical twins. They are considered to be perfect matches because they have identical genetic types.
Matched Related Transplant
Donor and patient share the same or similar genetic types – usually a brother or sister (rarely a parent or cousin). The chance of matching a brother or sister is 25% for each sibling. Typing of the siblings is performed if they are healthy and according to a priority based on the sex of the patient and potential donors, as well as age.
If there is not a complete match, the term “mismatched” is used. A complete match is preferred, but in certain situations, a related donor and patient can be mismatched to some degree. If there is too much mismatching, severe, usually fatal, GVHD will occur.
Matched or Partially Matched Unrelated Transplant
Donor and patient are not related. Some of us share similar genetic backgrounds, so it is possible that someone unrelated may have a similar genetic type.
Cord Blood Transplant (CBT)
Stem cells are obtained from the umbilical cord of a donor to a patient. Umbilical cord blood, like bone marrow, is rich in stem cells. These stem cells can be collected from related or unrelated donors, frozen and infused into a patient. CBT has been performed mainly on children and young adults weighing less than 90 pounds. However, larger adults have been transplanted successfully.
CBT may have potential advantages over a BMT: