Vertex’s CRISPR therapy CASGEVY eliminates symptoms in young kids, eyes FDA expansion

Vertex Pharmaceuticals (NASDAQ:VRTX) announced highly anticipated clinical data demonstrating that its CRISPR-based gene-editing therapy, CASGEVY, matches its highly successful adult profile when used in younger children.

The Boston-based biotech presented interim results from two pivotal Phase 3 trials at the European Hematology Association (EHA) Congress, with simultaneous publication in the New England Journal of Medicine.

The data focus on children ages 5 to 11 living with severe sickle cell disease (SCD) or transfusion-dependent beta thalassemia (TDT), offering hope for early-life intervention before irreversible organ damage sets in.

In the CLIMB-151 study evaluating children with severe SCD, CASGEVY achieved a 100% success rate among evaluable patients.

All 11 children dosed with the therapy remained entirely free of painful vaso-occlusive crises (VOCs)—the agonizing, dangerous blood flow blockages characteristic of the disease.

Furthermore, 100% of the patients (8 out of 8) with sufficient follow-up met the primary endpoint of staying crisis-free for at least 12 consecutive months, boasting a mean crisis-free duration of 19 months.

The therapy yielded equally powerful results in the CLIMB-141 study for children with TDT.

Out of 15 children dosed, all 8 who reached the timeline threshold achieved total transfusion independence for at least a year.

These patients successfully maintained a stable, weighted average hemoglobin level of 9 grams per deciliter or higher without needing external blood donations.

The mean duration of transfusion independence among these children reached 23.4 months.

The safety profile in the younger cohort aligns with what doctors expect from a myeloablative conditioning regimen, which uses the chemotherapy drug busulfan to clear space in the bone marrow for the modified gene-edited cells.

One previously disclosed death occurred in the TDT trial; investigators determined it was unrelated to CASGEVY itself, but rather a severe liver complication (veno-occlusive disease) triggered by the standard busulfan conditioning process.

CASGEVY is already commercially approved in multiple markets for patients ages 12 and older.

Armed with these new pediatric findings and a National Priority Voucher, Vertex has submitted applications to the FDA, the UK's MHRA, and Saudi Arabian regulatory bodies to expand the drug's label to children as young as 5.