Vertex Presents Transformative Gene Therapy Data in Children with Sickle Cell Disease and Thalassemia

BOSTON–(BUSINESS WIRE)–Dec. 6, 2025– Vertex Pharmaceuticals Incorporated (NASDAQ:VRTX) presented new clinical data at the 2025 American Society of Hematology (ASH) Annual Meeting, demonstrating the profound clinical benefits and safety profile of Casgevy (exagamglogene autotemcel) in children and adults with severe sickle cell disease (SCD) or transfusion-dependent beta thalassemia (TDT).

The presentations included the first clinical data ever reported for Casgevy, a revolutionary CRISPR/Cas9 gene-edited cell therapy, in children aged 5 to 11 years.

Transformative Results in Pediatric Patients (Ages 5-11)

The results across two Phase 3 studies demonstrated Casgevy’s potential to functionally cure these severe inherited blood disorders in younger patients.

Sickle Cell Disease (SCD)

SCD is a severe inherited blood disease that causes painful vaso-occlusive crises (VOCs) and limits oxygen delivery.

• Primary Endpoint Achieved: All four patients with sufficient follow-up in the Phase 3 CLIMB-151 study achieved the primary endpoint of VOC-free for at least 12 consecutive months (VF12).

• VOC-Free Status: No patient has experienced a VOC following infusion with Casgevy, with the longest duration of VOC-free status approaching two years.

Transfusion-Dependent Beta Thalassemia (TDT)

TDT is a life-threatening genetic condition requiring regular blood transfusions.

• Transfusion Independence: All six patients with sufficient follow-up in the Phase 3 CLIMB-141 study achieved the primary endpoint of transfusion independence for at least 12 consecutive months (TI12) while maintaining adequate hemoglobin levels.

• Transfusion-Free Status: Following Casgevy infusion, 12 out of 13 patients are transfusion-free, with the longest duration of transfusion independence lasting nearly two years.

The safety profile in children is consistent with the established profile in older patients, involving myeloablative conditioning (busulfan) and autologous transplant. The data showed durable increases in fetal hemoglobin (HbF) and stable allelic editing, the therapeutic goal of the gene-edited therapy.

“These results, the first clinical data ever presented on any genetic therapy for children ages 5-11 years with SCD, again demonstrate the transformative potential of CASGEVY,” said Carmen Bozic, M.D., Chief Medical Officer at Vertex.

Longer-Term Durability in Older Patients

Vertex also presented new, longer-term data in SCD and TDT patients aged 12 years and older, confirming the durable clinical benefits seen in the initial pivotal studies as of the April 2025 data cut-off:

• SCD (Ages 12+): 100% of patients (45/45) achieved VF12 across pivotal studies, with a mean duration of VOC-free status of 35.3 months.

• TDT (Ages 12+): 98.2% of patients (55/56) achieved TI12, with a mean duration of transfusion independence of 41.4 months.