The Food and Drug Administration on July 1 granted a supplemental approval expanding the label for Casgevy (exagamglogene autotemcel) to patients as young as two years old with sickle cell disease and recurrent vaso-occlusive crises, or with transfusion-dependent beta thalassemia. The therapy, developed jointly by Vertex Pharmaceuticals and CRISPR Therapeutics, was previously cleared only for patients aged 12 and older. This is the first CRISPR/Cas9 gene-editing therapy authorized for use in children this young for either indication.

Casgevy works by editing a patient’s own hematopoietic stem cells outside the body, using CRISPR/Cas9 technology to disrupt a genetic switch called BCL11A. That edit reactivates production of fetal hemoglobin, which does not carry the sickled shape that causes the pain crises, organ damage and early mortality associated with the disease. The edited cells are then reinfused as a one-time treatment following myeloablative conditioning, allowing them to engraft in the bone marrow and permanently supply corrected blood cells.

Supporting data submitted to the agency came from an expansion cohort of children aged five to twelve enrolled in the pivotal CLIMB-121 program. All eight evaluable patients in that younger cohort achieved freedom from severe vaso-occlusive crises for at least twelve consecutive months following infusion, a result consistent with what the companies reported in adolescents and adults. The FDA’s decision to extend the label down to age two rested on a combination of this pediatric data and pharmacokinetic modeling bridging the age groups, given the practical and ethical constraints of running large randomized studies in toddlers with a rare, life-threatening disease.

Sickle cell disease affects roughly 100,000 people in the United States, with the highest burden falling on Black and Hispanic communities, and symptoms typically begin to manifest well before a child turns five. Physicians and patient advocacy groups have long argued that earlier intervention, before repeated vaso-occlusive episodes cause cumulative organ damage, could meaningfully change the disease’s long-term trajectory. Extending eligibility to two-year-olds directly addresses that argument, though the therapy still requires myeloablative conditioning chemotherapy, a regimen that carries its own risks in very young children and will require careful management by treating centers.

Vertex has continued to build out a network of authorized treatment centers capable of performing the stem cell collection, editing logistics and conditioning required for Casgevy, and the company said pediatric-capable centers will be prioritized as part of this expansion. Pricing has been a persistent point of scrutiny for gene therapies in this class; Casgevy carries a list price above two million dollars per patient, and payer negotiations over access for a now-larger pediatric population are likely to intensify.

The approval also keeps pressure on bluebird bio’s competing gene therapy Lyfgenia, which uses a lentiviral vector rather than gene editing and has faced slower uptake since its 2023 approval. With CRISPR-based correction now available to children years younger than before, referral patterns among pediatric hematologists may shift further toward Casgevy, reinforcing Vertex and CRISPR Therapeutics’ position in the rare disease gene-editing market they helped pioneer.