MHRA Extends Casgevy Gene Therapy to Children Aged Five

The UK's medicines regulator has lowered the age floor for the world's first licensed CRISPR-based gene-editing therapy. The Medicines and Healthcare products Regulatory Agency announced on 30 October 2026 that it has extended the UK authorisation for Casgevy (exagamglogene autotemcel, exa-cel) to children aged five and over with severe sickle-cell disease or transfusion-dependent beta-thalassemia who meet the existing eligibility criteria — down from the minimum age of 12 set when the therapy was first authorised in November 2023.

What changed

Casgevy, developed by Vertex Pharmaceuticals and CRISPR Therapeutics, edits a patient's own hematopoietic stem cells outside the body — using CRISPR/Cas9 to disrupt a regulatory region of the BCL11A gene — so that, once reinfused after conditioning chemotherapy, the edited cells produce functioning fetal hemoglobin. The MHRA authorised it in November 2023 for SCD and TDT patients aged 12 and over, the first global regulatory authorisation for a CRISPR-based medicine. The extension announced this week keeps the same clinical criteria — severe disease, no available or willing matched donor for an alternative stem-cell transplant, among other factors in the full label — but opens eligibility to children from age five.

The pediatric evidence

CLIMB-151 and CLIMB-141 are Vertex's ongoing open-label Phase 3 studies in SCD and TDT, enrolling patients aged two to eleven with roughly two years of planned follow-up after infusion. The 5-to-11 cohort data, first previewed at the American Society of Hematology meeting in December 2025, showed 8 of 8 evaluable children with SCD free of vaso-occlusive crises for 12 consecutive months while maintaining hemoglobin at or above 9 g/dL, and 6 of 6 evaluable children with TDT achieving transfusion independence for at least 12 months. Vertex presented a fuller dataset at the European Hematology Association congress in June 2026, published simultaneously in the New England Journal of Medicine, describing efficacy and safety as consistent with the outcomes seen in adults and adolescents. One death occurred among the pediatric TDT patients — a child who developed severe veno-occlusive disease attributed to busulfan conditioning chemotherapy, not to Casgevy itself, according to the company's reporting of the safety profile. Enrollment and dosing in the 5-to-11 cohort are complete; Vertex has said it plans to extend study enrollment to children aged two to four.

A narrower path than the FDA's

The MHRA's extension is the UK's second pediatric expansion for a therapy already being lowered in age elsewhere. The FDA expanded exa-cel's US approval to patients as young as two on 1 July 2026, reviewing the supplemental application in 53 days under the agency's National Priority Voucher pilot program — the eighth therapy selected for that accelerated pathway. Critically, the FDA's two-and-older expansion rested on extrapolation: the US pediatric trial data available at the time covered children aged five to eleven, and the agency extended eligibility down to age two based on product characteristics and clinical pharmacology rather than direct trial evidence in two-to-four-year-olds. The MHRA's move this week is narrower by comparison — age five, not two — but is grounded in its own Phase 3 data in the 5-to-11 band rather than extrapolation, a distinction worth noting for RA/QA teams comparing how the two agencies handled essentially the same evidence package.

What RA/QA teams should watch

• Licensing is not funding. MHRA's extension changes who can legally be prescribed Casgevy in the UK; it does not by itself change who the NHS will pay for. Casgevy's existing NHS access for patients 12 and over runs through a NICE-approved managed access arrangement negotiated separately from MHRA licensing. Whether and on what terms that arrangement extends to the newly eligible five-to-eleven age band was not confirmed in MHRA's own announcement, and sponsors and treatment centers should confirm current NICE/NHS England guidance before assuming automatic access.
• Conditioning-regimen risk stays separate from the gene-editing therapy itself. The one pediatric death reported in the TDT cohort was attributed to busulfan conditioning chemotherapy — a required pretreatment step for any autologous stem-cell gene therapy, not a Casgevy-specific safety signal. Centers offering exa-cel to younger, lower-body-weight patients should expect conditioning-regimen risk management, not the edited cell product, to be the focus of incremental pediatric safety monitoring.
• Transatlantic divergence on age is now two licenses wide. With the FDA at two-and-over (via extrapolation) and the MHRA at five-and-over (via direct trial data), sponsors running comparable pediatric gene-therapy programs elsewhere should expect regulators to weigh extrapolated versus directly observed pediatric evidence differently, even from the same underlying trials.

Frequently asked questions

What did the MHRA approve on 30 October 2026?

An extension to Casgevy's UK marketing authorisation, lowering the minimum treatable age from 12 to five for patients with severe sickle-cell disease or transfusion-dependent beta-thalassemia who meet the existing eligibility criteria.

What evidence supported the extension?

Phase 3 data from CLIMB-151 (SCD) and CLIMB-141 (TDT) in patients aged 2 to 11, with the 5-to-11 cohort results presented at EHA in June 2026 and published in the New England Journal of Medicine.

How does this compare with the US?

The FDA expanded exa-cel to patients as young as two on 1 July 2026 via extrapolation under its National Priority Voucher pilot program; the MHRA's extension to age five is narrower but grounded in direct Phase 3 pediatric data.

Does NHS funding automatically cover the newly eligible age group?

Not confirmed. MHRA licensing and NHS funding are handled separately in the UK; whether the existing NICE-approved managed access arrangement for ages 12 and over extends to the 5-to-11 band was not addressed in MHRA's announcement.