CRISPR’s cure is real and it is holding. Last year, 64 people received it.

The effect is large, and it is holding

On 8 December 2023 the US Food and Drug Administration approved Casgevy (exagamglogene autotemcel) for sickle cell disease in patients 12 and older — the first medicine anywhere to use CRISPR/Cas9 genome editing.¹ It does not repair the sickle mutation. Instead it edits a patient’s own blood stem cells at the erythroid enhancer of the BCL11A gene, releasing a brake on fetal haemoglobin — the oxygen-carrying form present before birth — so that it is produced again in adult red blood cells.³

The measured results are unusually clean for a first-in-class therapy. In the completed pivotal trial (CLIMB SCD-121, a single-arm, open-label phase 3 study in patients aged 12 to 35 with at least two severe crises in each of the two prior years), 29 of 30 evaluable patients — 96.7% — had no severe vaso-occlusive crisis for at least 12 consecutive months, and all 30 avoided hospitalisation for one over the same period.⁴

Longer follow-up has not eroded the effect. In data presented to the American Society of Hematology, 39 of 42 evaluable sickle cell patients (93%) were crisis-free for at least 12 months, and 53 of 54 evaluable thalassemia patients (98%) became transfusion-independent for at least 12 months. The longest follow-up now runs beyond five years, with fetal haemoglobin levels and allelic editing stable over time.⁵

Even the shortfall is instructive. Of the three sickle cell patients who did not reach the endpoint, Vertex reports that each still cut their rate of hospitalisation for crises — by 91%, 71% and 100% respectively.⁵ This is a therapy whose failures still look like substantial clinical benefit.

Editing has left the lab in four different forms at once

In 2023 there was one approved gene-editing medicine. By mid-2026 there are four distinct modalities with human data, and they differ in ways that matter for access.

Ex vivo cutting is Casgevy’s approach: remove cells, edit outside the body, put them back. Ex vivo base editing rewrites a single DNA letter without cutting both strands. Beam Therapeutics’ risto-cel (ristoglogene autogetemcel, formerly BEAM-101) uses it to raise fetal haemoglobin in sickle cell; interim BEACON phase 1/2 data covering 31 patients, with follow-up from 0.3 to 20.4 months, were published in the New England Journal of Medicine.¹¹

In vivo editing dispenses with the cell-collection step entirely: the editor is infused and finds its target inside the patient. Intellia’s lonvo-z reported the first positive phase 3 result for any in vivo gene-editing therapy in April 2026, cutting monthly hereditary angioedema attacks by 87% against placebo, with 62% of treated patients free of both attacks and therapy over six months versus 11% on placebo.⁸ Fourth, and most novel, is the bespoke, one-patient therapy.

That fourth form is the one that changes the shape of the problem. In August 2024 an infant known as KJ Muldoon was born with severe carbamoyl phosphate synthetase 1 (CPS1) deficiency, a urea-cycle disorder that lets ammonia accumulate to levels that damage the brain or kill. He was too small for the standard treatment, a liver transplant. A team at Children’s Hospital of Philadelphia and Penn Medicine designed, manufactured and administered a base-editing therapy targeted at his specific variant, delivered to the liver in lipid nanoparticles. He received the first infusion on 25 February 2025, aged between six and seven months; the case was reported in the New England Journal of Medicine that May.⁶

A year on, CHOP reported that KJ was walking and talking.⁷ The clinically important qualifier is that he was not cured: his physicians describe a much milder form of the disease rather than its elimination, and one clinician has publicly credited his outcome substantially to a neonatologist who checked his ammonia at 36 hours old, before any editing was contemplated.⁷ A single patient cannot establish efficacy. What the case establishes is a timeline: roughly six months from identifying a private mutation to infusing a drug made for one person.

Sixty thousand people are eligible. In 2025, sixty-four were infused.

Vertex reports more than 60,000 eligible patients across the ten countries where Casgevy is licensed — approximately 37,000 in North America and Europe, and more than 23,000 in the Middle East.² Against that denominator, the treated numerator is small enough to be startling. In the whole of 2025, 64 people worldwide received a Casgevy infusion, 30 of them in the fourth quarter. Over the same year, 147 people had a first cell collection.² Cumulatively, by the first quarter of 2026, more than 500 people globally had begun the treatment journey at all.⁹

Those 500 are about 0.8% of the eligible population in countries where the therapy is actually approved. The 64 infused in 2025 are 0.11% — roughly one in every 938 eligible people.

The global denominator is larger still. The FDA puts the US sickle cell population at roughly 100,000.¹ Beam Therapeutics, citing global estimates, puts the number living with sickle cell worldwide at about eight million — concentrated in sub-Saharan Africa and India, where Casgevy is not licensed, where authorised treatment centres do not exist, and where, as researchers writing in The CRISPR Journal have argued, even hydroxyurea — a generic approved in 1998 — remains out of reach for most patients.¹² The 60,000 eligible are, on that estimate, well under 1% of the people who have the disease.

It is not mainly the centres, and in the US it is not mainly the cheque

The intuitive explanation for a 0.11% treatment rate is that there is nowhere to go and no one to pay. Both are weaker than they look.

On geography: Vertex reported more than 75 activated authorised treatment centres in the United States alone as of 1 July 2026, having earlier passed 65 globally against a target of about 75.³ On payment: as of the end of 2025, approximately 90% of US patients had reimbursed access to Casgevy, which is also reimbursed in the UK, Italy, Austria, Denmark, Luxembourg, Saudi Arabia, Bahrain, the UAE and Kuwait, with Scotland added in January 2026.²

This is the desk’s reading, not a sourced causal finding: if roughly nine in ten American patients can have it paid for, and there are more than 75 places to receive it, then the near-term constraint in approved markets is chiefly the clinical pathway itself rather than the list price or the map. The label makes the pathway explicit. Stem cells must be mobilised and collected by apheresis, often over multiple cycles; hydroxyurea must stop at least eight weeks beforehand; the patient then undergoes full myeloablative conditioning with busulfan — chemotherapy that destroys the existing bone marrow — before infusion and engraftment. Every treated patient in the trials experienced grade 3 or 4 neutropenia and thrombocytopenia; mucositis and febrile neutropenia were the commonest severe reactions; and infertility has been observed with the conditioning.¹⁵

Reporting by STAT attributes the slow rollout substantially to difficulties collecting enough stem cells, and notes that inpatient conditioning capacity has been a rate-limiting step.¹³ That account is consistent with the company’s own numbers: 147 first cell collections in 2025 produced 64 infusions in the same year. Vertex is now advancing preclinical work on gentler conditioning, which it says could broaden the eligible population.²

$2.2m against a lifetime bill that is larger

Vertex set Casgevy’s US list price at $2.2m; bluebird bio priced its non-CRISPR competitor Lyfgenia at $3.1m.¹⁴ The list price covers the edited cells, not the apheresis, conditioning, inpatient stay or follow-up around them.

Vertex also reports that people with sickle cell and recurrent crises in the US face a median age of death of about 45, and those with transfusion-dependent thalassemia about 37.³ Casgevy generated $115.8m of revenue in 2025, against $10.0m in 2024.² That is a rounding error for a company with $12.0bn of total revenue — which is itself part of the story: at current throughput, a cure for two diseases is not yet a business, and the incentive to solve the pathway is commercial as well as moral.

What the wall is made of

Credible sources genuinely disagree about what limits access. The two disputes below are different in kind, and only one of them is the sort of question evidence can eventually settle.

Every figure in this piece

What this piece left out

• Gentler conditioning. Busulfan myeloablation is what makes Casgevy a months-long hospital undertaking with infertility risk. Vertex reports preclinical work on conditioning that could broaden eligibility; antibody-based alternatives across the field would change the access arithmetic more than any price cut. Left out for length.
• The n-of-1 regulatory question. Bespoke therapies need a pathway that does not demand a separate application per mutation. KJ’s team has signalled plans for a trial spanning several urea-cycle disorders, and regulators have been consulting on frameworks for individualised genomic therapies. We did not assess those proposals here.
• Germline editing. A separate and contested strand: work on base editing in human embryos has begun appearing in preprints. This piece deals only with somatic editing — changes that are not inherited.
• Lyfgenia and the lentiviral alternative. bluebird bio’s competing sickle cell therapy carries a boxed warning for blood cancer and a higher price; its commercial trajectory is a story in itself.
• Hydroxyurea and the unglamorous baseline. The largest near-term gains in global sickle cell mortality probably come not from editing but from delivering a 1998 generic to people who cannot get it.