Alternative Donors

When There’s No Good Match

Alternative Donors for Pediatric Stem Cell Transplants

Not every child who needs a stem cell transplant can find a donor — either a relative or someone unrelated — whose tissue matches their tissue closely enough to expect a good chance of success. But with recent advances in transplant protocols, the percentage of children put at a disadvantage is shrinking. Researchers at Fred Hutchinson Cancer Research Center, a parent organization of Seattle Cancer Care Alliance (SCCA), are working hard to improve what are called “alternative donor transplants” — transplants using stem cells from cord blood or from haploidentical donors.

Both methods can succeed even when the recipient’s and donor’s tissue types do not closely match. This is especially important for patients who belong to ethnic minorities or have mixed ethnicity, because they often have trouble finding a donor whose tissue type closely matches their own.

What Does Matching Mean?
It’s important to closely match the tissue of a donor with the tissue of a transplant recipient to decrease the chance that the recipient’s body will reject the transplanted cells (called host-versus-graft disease) or that the transplanted cells will attack the recipient’s tissues (called graft-versus-host disease). To match donors and recipients, doctors conduct tests to determine and compare their human leukocyte antigen (HLA) haplotype.

A haplotype is a set of closely linked genes that are inherited together. Children get one HLA haplotype from their mother and one HLA haplotype from their father. Tissue-typing tests look at five points on each HLA haplotype, for a total of ten points. To be considered a good match for a transplant, the donor and recipient normally must match each other on at least nine of these ten points.

The Search Begins
When doctors perform a stem cell transplant, their first choice is to use a donor who is related to the recipient and whose tissue is closely matched. Often relatives who are a match are willing to donate, and they usually can be enlisted in the process quickly. Time can be of the essence when a transplant becomes necessary.

If there is no matched relative who can take part, doctors search international volunteer donor banks for a close match. This takes more time, usually a matter of weeks to months. Though the delay is less than ideal, there is the possibility that the search will yield someone who matches closely enough to go forward with the transplant.

“Our Center has the most experience in the world doing unrelated donor transplants,” says Dr. Ann Woolfrey, the director of unrelated donor programs for pediatric transplants at the Hutchinson Center. “For pediatric patients with malignant diseases, our unrelated donor transplants have the same outcome as our transplants using matched, related donors. Most places cannot achieve that outcome. One of our strengths is that since we have done so many unrelated transplants, we are very good at it.”

Cord Blood and Haploidentical Transplants
If the search for an unrelated donor produces no options, doctors may turn to a cord blood transplant or a haploidentical transplant. These options are an important area of focus for Woolfrey and others at the Hutchinson Center. Several protocols have been developed for using these types of transplants for treating both malignant and nonmalignant diseases.

Read information on cord blood protocols 2030, 2010, and 2012, and haploidentical protocols 2032 and 1667.

Cord blood transplants use stem cells from the blood that remains in the umbilical cord when a mother and newborn are separated. Because the infant’s immune system is immature, a cord blood transplant can succeed even if there’s a greater disparity between the infant’s tissue and the recipient’s tissue than would be allowed in a bone marrow or peripheral blood stem cell transplant.

A haploidentical transplant uses cells from a relative whose tissue is not considered a suitable match according to usual tissue-typing standards. Haploidentical donors have one haplotype in common with the recipient, so they match on at least five out of ten points. A haploidentical match may be the best option for patients without a closely matched unrelated donor, especially those who urgently need a transplant. Parents and children are haploidentical, and some siblings are haploidentical. So if a child needs a transplant, the child’s parents or partially matched siblings may be able to donate cells.

Each of these methods opens up the option of a potentially life-saving transplant to many more children. To find out more about all stem cell transplant services available through SCCA, contact us toll-free at (800) 804-8824 or by calling (206) 288-SCCA (7222).

August 2006