(Press-News.org) (ORLANDO, Dec. 6, 2025) Preliminary results from two trials of the gene therapy exagamglogene autotemcel (exa-cel) suggest the therapy offers an effective cure for beta-thalassemia and sickle cell disease in children younger than 12. Researchers say the therapy’s potential to offer a cure at an early age – before organ damage accumulates – could make exa-cel even more beneficial in children than adults.
“All younger patients with sufficient follow-up met the primary endpoint of being transfusion independent in those with beta thalassemia and free of vaso-occlusive crises for those with sickle cell disease,” said lead study author Haydar Frangoul, MD, medical director of pediatric hematology/oncology at Sarah Cannon Research Institute at TriStar Centennial Children’s Hospital in Nashville, Tennessee. “A 100% success rate is rare in anything that we do.”
Exa-cel is approved for patients 12 years and older who have transfusion-dependent beta-thalassemia or sickle cell disease with recurrent vaso-occlusive crises (when blood cells become lodged in the vessels, causing severe pain and tissue damage). Both conditions are caused by genetic abnormalities that affect the ability for blood to carry oxygen throughout the body; exa-cel works by genetically modifying a patient’s own blood stem cells to correct this abnormality.
For the treatment, patients undergo a procedure to harvest their blood stem cells, which are then genetically edited in the lab using CRISPR/Cas9. The patient then undergoes a chemotherapy-based conditioning regimen to clear the bone marrow before the genetically edited stem cells are implanted back into the body, where they begin making healthy blood cells.
Researchers report preliminary results from two trials of exa-cel that are underway in children 5-11 years old. To date, the CLIMB THAL-141 trial has dosed 13 patients with beta-thalassemia, and the CLIMB SCD-151 trial has dosed 11 patients with sickle cell disease.
In CLIMB THAL-141, six of 13 patients to date have been evaluated for the primary endpoint of transfusion independence for 12 consecutive months, meaning that they maintained a weighted average hemoglobin of 9 g/dL or higher without a red blood cell infusion. All six met this endpoint. In addition, participants showed increases in hemoglobin and fetal hemoglobin production.
In CLIMB SCD-151, 4 of 11 patients to date have been evaluated for the primary endpoint of freedom from severe vaso-occlusive crises and the secondary endpoint of freedom from inpatient treatment for severe vaso-occlusive crises for 12 consecutive months. All four met these endpoints. No study participants have experienced a vaso-occlusive crisis after their exa-cel infusion to date. Increases in fetal hemoglobin production have been similar to the levels in teens and adults in previous studies, with mean total hemoglobin reaching a normal level by month six and remaining stable thereafter.
According to researchers, the results not only provide evidence that the gene therapy works in younger patients, but suggest it could be even more beneficial in this age group. “We think treating them at an earlier age may be better because you could potentially prevent some irreversible complications that lead to chronic issues,” said Dr. Frangoul.
Based on experiences to date, the safety profile of the therapy in these pediatric trials also appears to be consistent with trials in adolescents and adults and with the known side effects and complications associated with autologous stem cell transplantation and busulfan conditioning. One study participant in CLIMB THAL-141 developed severe veno-occlusive disease, related to busulfan, with fatal multi-organ failure. Veno-occlusive disease is a known risk of busulfan that occurs more frequently in children. Despite several decades of research on busulfan and alternative conditioning regimens in the context of stem cell transplantation, there is no known strategy to completely eliminate this risk.
The CLIMB THAL-141 and CLIMB SCD-151 trials will continue to accrue participants and track outcomes to assess the safety and efficacy of the therapy over a longer period of time and in a larger patient group. Dr. Frangoul noted that a future study could test the therapy in children two to four years old.
The CLIMB THAL-141 and CLIMB SCD-151 trials are sponsored by Vertex Pharmaceuticals Incorporated and CRISPR Therapeutics.
Haydar Frangoul, MD, of Sarah Cannon Research Institute at TriStar Centennial Children’s Hospital, will present this study on Saturday, December 6, 2025, at 4:00 p.m. Eastern time in W320 of the Orange County Convention Center.
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The American Society of Hematology (ASH) (hematology.org) is the world’s largest professional society of hematologists dedicated to furthering the understanding, diagnosis, treatment, and prevention of disorders affecting the blood. Since 1958, the Society has led the development of hematology as a discipline by promoting research, patient care, education, training, and advocacy in hematology. Join the #Fight4Hematology by visiting hematology.org/fight4hematology.
The Blood journals (https://ashpublications.org/journals) are the premier source for basic, translational, and clinical hematologic research. The Blood journals publish more peer-reviewed hematology research than any other academic journals worldwide.
The ASH Center for Sickle Cell Disease Initiatives (hematology.org/ash-center-for-sickle-cell-disease-initiatives) is committed to progressing research in sickle cell disease by targeting critical needs and generating powerful, real-world evidence to create impact and change.
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Early results suggest exa-cel gene therapy works well in children
2025-12-06
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