Haploidentical stem cell transplantation: An effective option for high-risk ALL patients lacking an identical donor match

This study examined the outcomes of haploidentical stem cell transplantation (haplo-SCT) in adults with high-risk acute lymphoblastic leukemia (ALL). Researchers reported favorable outcomes with haplo-SCT for patients in the early stage of their disease. 

ALL is a type of cancer in which the bone marrow makes too many lymphocytes (a type of 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 patients with high-risk ALL who have achieved complete remission.

Stem cell transplantations require patients to be matched with a donor, ideally someone with a similar genetic background (like a sibling). Some patients cannot find an identical match. Haploidentical stem cell transplantation (haplo-SCT) uses stem cells from a donor who is a 50% match. More studies are needed to examine this option in adult high-risk ALL patients.

The records of 208 adults with high-risk ALL treated with haplo-SCT were analyzed. All patients had achieved remission (no sign of active disease). 44% of patients were in their first remission. Stem cells were harvested from the donor’s bone marrow in 43% of transplants. The stem cell source in the other 57% was peripheral blood. 66% of patients were treated with full-strength chemotherapy (also called myeloablative conditioning) before transplantation. 34% were treated with reduced intensity conditioning. Outcomes were followed for an average of 31 months.

92% of patients achieved engraftment (process where the donor stem cells begin to make new blood cells). The average time to engraftment was 17 days.

17.3% of patients who received stem cells from the donor’s bone marrow experienced serious graft-versus-host disease (when donor cells attack the organs of the patient). This was significantly lower compared to cases where the stem cell source was peripheral blood (40.8%).

The relapse rate at 3 years was 37%. It was 24% for patients in their first remission and 32% for those in their second remission. Relapse rate was significantly higher among patients with advanced disease before the transplant (60%). Cases where the donor was female and the recipient male were associated with a 61% reduced risk of relapse.

135 patients died during the study period. Of these, 31% died due to disease recurrence. The remaining deaths occurred without documented relapse.

The 3-year overall survival rate (proportion who have not died from any cause since treatment) was 33%. 31% of patients were leukemia-free at 3 years. 26% of patients were both leukemia-free and free of graft-versus-host disease at 3 years. Being in a later remission status was consistently associated with poorer outcomes. The use of peripheral blood as a stem cell source also had a negative effect on survival rates.

Researchers concluded that haplo-SCT is a valid treatment option for adults with high-risk ALL who are lacking an identical donor match. They suggested that haplo-SCT should be used preferably among patients in the early stage of their disease. 

Studies that randomly allocate patients to different treatment groups are needed to confirm these findings.