CRISPR therapy freed young children from transfusions and sickle crises

The first CRISPR-based medicine to reach patients, exagamglogene autotemcel (exa-cel), has now been tested in children as young as five — and the early results show the same striking efficacy seen in older patients, alongside a safety profile that is anything but trivial [s1]. Every child followed long enough to be judged met the trial's goal, but all of them had a serious adverse event, and one died of a complication of the chemotherapy needed to make the treatment work [s1].

What the therapy is

Exa-cel is not a pill or an infusion of a drug; it is a one-time cell therapy made from a patient's own blood-forming cells. Doctors collect the child's CD34+ haematopoietic stem cells and, in the laboratory, use CRISPR-Cas9 gene editing to switch off a control region of the BCL11A gene [s1]. That change reawakens fetal haemoglobin, the oxygen-carrying protein normally silenced after birth, which can compensate for the defective adult haemoglobin that causes both sickle cell disease and transfusion-dependent β-thalassaemia [s1]. In earlier phase 3 studies in participants aged 12 to 35, exa-cel eliminated vaso-occlusive crises in sickle cell disease and abolished the need for red-cell transfusions in β-thalassaemia [s1][s2][s3].

What the new studies did

The new report covers two ongoing, open-label, single-group phase 3 studies in children 5 to 11 years old — one in transfusion-dependent β-thalassaemia, one in sickle cell disease [s1]. Before the edited cells are returned, each child undergoes myeloablative conditioning with busulfan, a powerful chemotherapy that clears the bone marrow to make room for the engineered cells [s1]. The primary endpoints were demanding: transfusion independence for at least 12 consecutive months in the thalassaemia study, and freedom from severe vaso-occlusive crises for at least 12 consecutive months in the sickle cell study [s1].

What it found

A total of 15 children with transfusion-dependent β-thalassaemia and 11 with sickle cell disease received exa-cel, with median follow-up of 16.0 months (range 2.2 to 32.1) and 16.9 months (range 7.6 to 33.1), respectively [s1]. Among the thalassaemia group, of 8 children followed to at least 16 months, all 8 were transfusion independent; the status of the remaining 7 was not yet evaluable [s1]. Among the sickle cell group, of 8 children followed to at least 16 months, all 8 were free of vaso-occlusive crises, with the remaining 3 not yet evaluable [s1]. In other words, every child who had reached the assessment window had responded — a near-perfect early signal, if a small one.

The safety data are where honesty is required. All the children had at least one grade 3 or 4 adverse event [s1]. Two children with thalassaemia developed severe veno-occlusive liver disease — a known, serious complication of busulfan conditioning — and one of them died [s1]. That death is a reminder that much of the risk of this therapy comes not from the gene editing but from the harsh chemotherapy that precedes it.

How to read it

Two things are true at once. The efficacy is remarkable: a single treatment appears to lift young children off lifelong transfusions or out from under the recurrent agony of sickle crises, and it does so in the age range where a lifetime of avoided organ damage is most valuable [s1]. And the therapy is not gentle: these are small numbers, follow-up is still short, and the conditioning regimen carries a real risk of death [s1]. The trials are single-group and open-label — there is no comparison arm — so efficacy is judged against each child's own history rather than against a control, which is reasonable for diseases with such predictable courses but is not the same as a randomised comparison.

Funding is worth stating plainly: the studies were funded by Vertex Pharmaceuticals and CRISPR Therapeutics, the companies that developed and market exa-cel [s1]. That does not make the results wrong, but it is the reason independent long-term registries matter for a one-time therapy whose durability and late effects can only be known with years of follow-up.

For families weighing this option, the trade-off is stark and personal: a potentially curative, one-time treatment against the front-loaded danger of myeloablative chemotherapy and the unknowns of a very new technology. This article describes research and is not medical advice; whether a child is a candidate is a decision for a specialist transplant and haematology team.

What to watch

The central open questions are durability and safety at scale — whether the responses hold for years, and whether the conditioning-related risks can be reduced, perhaps with gentler, antibody-based conditioning now in development [s1]. Access is the other frontier: a bespoke, hospital-intensive therapy with a high list price will reach only a fraction of the children worldwide who carry these diseases, most of whom live where the infrastructure for it does not yet exist [s1].

Sources

• Exa-cel in Children with Transfusion-Dependent β-Thalassemia or Sickle Cell Disease — New England Journal of Medicine, 11 June 2026
• Exagamglogene Autotemcel for Severe Sickle Cell Disease — New England Journal of Medicine, 24 April 2024
• Exagamglogene Autotemcel for Transfusion-Dependent β-Thalassemia — New England Journal of Medicine, 24 April 2024