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Casgevy is made from your own blood stem cells. Doctors collect them, an editing team disables a genetic switch called BCL11A that normally shuts off fetal haemoglobin after birth, and the edited cells are given back after chemotherapy has cleared space in the bone marrow. Fetal haemoglobin comes back, and because it does not sickle, the disease largely stops. It is given once, and it is a major undertaking — weeks in hospital, and chemotherapy with permanent consequences of its own.
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Exagamglogene autotemcel is an autologous CD34+ haematopoietic stem and progenitor cell product in which CRISPR-Cas9 disrupts the erythroid-specific enhancer of BCL11A, de-repressing gamma-globin and inducing fetal haemoglobin. Manufactured from mobilised autologous cells and infused after myeloablative busulfan conditioning. Developed by Vertex Pharmaceuticals and CRISPR Therapeutics.
Regulatory history
| Jurisdiction | Indication | Date |
|---|---|---|
| United Kingdom (MHRA) | Sickle cell disease and transfusion-dependent beta thalassemia, 12+ | November 2023 — the world's first CRISPR medicine authorisation |
| United States (FDA) | Sickle cell disease with recurrent vaso-occlusive crises, 12+ | December 2023 |
| United States (FDA) | Transfusion-dependent beta thalassemia, 12+ | January 2024 |
| European Union (EMA) | Both indications, 12+, where transplant is appropriate and no matched donor is available | February 2024 |
Authorisations differ in wording and in the patient populations they cover; the table summarises rather than reproduces them.
What the trials showed
In the pivotal sickle cell study, the large majority of evaluable participants were free of severe vaso-occlusive crises for at least 12 consecutive months. In transfusion-dependent beta thalassemia, the great majority of participants achieved transfusion independence. These are substantial results in conditions where the alternative for most patients was lifelong management of a severe disease.
Follow-up is measured in a few years. Because the edit is permanent, long-term follow-up studies continue and are a regulatory requirement, not an optional extra.
What it involves for a patient
- Stem cell mobilisation and collection by apheresis, usually over several cycles.
- Manufacturing of the edited cell product, which takes weeks.
- Myeloablative conditioning with busulfan — chemotherapy that clears the bone marrow.
- Infusion of the edited cells, then a period of profound low blood counts.
- Weeks in hospital while the marrow recovers, then long-term monitoring.
Cost and access
The list price in the United States was announced at $2.2 million per patient, excluding the hospital, conditioning and supportive care around it. Delivery requires a qualified treatment centre with apheresis and transplant capability.
Roughly three-quarters of babies born with sickle cell disease each year are born in sub-Saharan Africa. The distance between that fact and this price is the defining access problem of gene-editing medicine, and it is not a problem the science solves.
Common questions
Is Casgevy a cure?
It produced sustained freedom from severe pain crises in most sickle cell trial participants and transfusion independence in most thalassemia participants, and the edit is permanent. Whether that is a cure depends on how long 'permanent' has been observed for — follow-up is a few years, and long-term studies are required. This site describes the outcome rather than using the word.
How much does Casgevy cost?
The announced US list price is $2.2 million, which does not include the hospitalisation, chemotherapy conditioning and supportive care the treatment requires. What any individual or health system actually pays depends on confidential negotiated arrangements.
Why does it need chemotherapy?
The edited cells have to engraft in the bone marrow, and there is no room until the existing marrow is cleared. Busulfan conditioning does that. It is also where most of the treatment's toxicity comes from, and reducing or replacing it — with antibody-based conditioning, for example — is an active area of research.
Sources
- U.S. Food and Drug Administration · 2023
FDA approves first gene therapies to treat patients with sickle cell disease ↗ - European Medicines Agency · 2024
Casgevy — European public assessment report ↗ - New England Journal of Medicine (Frangoul et al.) · 2024
Exagamglogene autotemcel for severe sickle cell disease ↗