This study included 50 patients -- ages 4 to 30 -- with acute lymphoblastic leukemia who received CAR T-cell therapy. The treatment genetically modifies a patient's own immune cells to make them more effective at killing cancer. CAR is shorthand for chimeric antigen receptor.

While CAR-T cell therapy provides complete remission in between 60% and 100% of patients initially, many relapse. One study found that more than 40% had relapsed 13 months after treatment.

This study investigated whether stem cell transplants could help prevent relapses in patients who had undergone CAR T-cell treatment.

Of 21 patients who received a transplant of donor stem cells after CAR T-cell therapy, 9.5% had relapsed 24 months later, the study found. All of the patients who didn't have a stem cell transplant had relapsed by that point.

The findings -- published recently in the Journal of Clinical Oncology -- suggest that stem cell transplants offer long-term benefits for young patients who get CAR T-cell therapy, according to the University of Virginia researchers.

"More than 50% of kids in other studies with a different CAR relapse, with the majority of them losing the target the CAR goes after," said Dr. Daniel Lee, a pediatric oncologist and director of Pediatric Stem Cell Transplant and Immunotherapy at UVA Children's Hospital in Charlottesville.

"Most of these kids have a single shot at this life-saving and paradigm-changing therapy called CAR T-cells. We should do all we can to maximize the chance for a cure, and right now that means a transplant after CAR therapy for most," Lee added.

He noted that many parents turn to CAR T-cells in hopes of avoiding a stem cell transplant.

"But," he added, "there is a window of opportunity after CARs to cure more of these incurable kids with a transplant; our study demonstrates this."