Does it matter if the stem cell donor is related to the child with ALL?

This study examined the effect of different stem cell donor types on clinical outcomes in children with high-risk acute lymphoblastic leukemia (ALL). Researchers reported similar survival and relapse rates, regardless of matched related or unrelated donor type.

ALL is a type of cancer in which the bone marrow makes too many lymphoblasts (a type of immature white blood cell). This type of cancer usually gets worse quickly if it is not treated. Treatments for ALL, such as chemotherapy, kill cancer cells. Unfortunately, they are also toxic to the bone marrow. Without the stem cells (immature cells) in the bone marrow, new red or white blood cells cannot be produced. Healthy stem cells must be reintroduced (transplanted) following treatment. Stem cell transplantation is considered the most effective treatment for children with high-risk ALL who have achieved complete remission.

Stem cells can be harvested from the patient’s bone marrow or blood, or they can be harvested from a donor (allogeneic transplant). Ideally, the donor is genetically similar to the patient, such as a sibling. In some cases, stem cells from a matched unrelated donor may be used. An unrelated donor will not be a close genetic match, because they do not share the same parents as the patient.  

The aim of this study was to examine the effect of stem cell donor type on clinical outcomes in children with ALL.

411 children with high-risk ALL were included in this study. Patients underwent a stem cell transplant during the first or later remissions. 105 patients received a transplant from a sibling donor. 306 received a transplant from a matched unrelated donor. Clinical outcomes were compared over an average period of 4.2 years.

Engraftment was significantly faster with sibling donors (17 days) compared to unrelated donors (22 days). Engraftment refers to the process of donated stem cells starting to make new blood cells. At 30 days, engraftment was observed in 76% of transplants from sibling donors. This was significantly higher compared to transplants from unrelated donors (44%).

The proportion of patients who did not experience a treatment-related event such as progression, death, or discontinuation of treatment at 4 years was similar between donor types. It was 71% for patients that received a transplant from a sibling donor and 67% for those who received a transplant from an unrelated donor. Relapse rates over 4 years were also similar between sibling donor transplants (24%) and unrelated donor transplants (22%). Mortality without documented relapse occurred in 3% of patients with a sibling donor and in 10% of patients with an unrelated donor. How closely matched the unrelated donor was did not affect survival or relapse rates.

No significant differences in the incidence or severity of graft-versus-host disease (when donor cells attack the organs of the patient) were observed between donor types. Extensive graft-versus-host disease occurred in 14% of cases involving a sibling donor and in 6% of cases involving an unrelated donor. Serious cases of infection or lung complications were significantly more common after a transplant from an unrelated donor.

Researchers concluded that survival is not significantly affected by matched related or unrelated donor type in children with high-risk ALL.