Long-term follow-up

Gene therapy is given once, but it is not finished once. Follow-up runs for years, and the reason is honest: nobody yet knows what this looks like over a lifetime.

How long the benefit has been shown to last

In the trials that led to approval, people were followed for around two years on average.

• Sickle cell disease: 28 of 29 people had no severe pain crises for at least 12 months in a row.

• Beta thalassaemia: 39 of 42 people kept their haemoglobin up without needing transfusions for at least 12 months in a row.

Since then the same participants have been followed for longer, and results presented at conferences suggest the benefit has held for five to six years. Those are conference reports funded by the manufacturer rather than fully peer-reviewed papers, so they carry a little less weight than the figures above, but they point the same way.

The longest anyone has been followed is about six years. That is the honest answer to "how long does it last?", it has held up for as long as anyone has been watching, and nobody can yet tell you about year twenty.

Why you stay under follow-up for 15 years

The European regulator requires a 15-year registry study of everyone treated. Patients are asked to enrol, and the UK product information says the same in principle without naming a length.

This is not because something is expected to go wrong. It is because gene editing is new, and there is a theoretical risk that the editing tool made a change somewhere it was not meant to. No such case has been seen. The registry exists so that if one ever occurred, it would be found rather than missed.

Separately, records about cell-based treatments have to be kept for 30 years by the hospital that gave it. That is a paperwork requirement, not 30 years of appointments.

What monitoring actually looks like

There is no published UK schedule setting out how often you are seen and for what. The registry requires long-term follow-up including blood counts, and beyond that the arrangements come from your own centre. If you want to know what your follow-up will involve, your team is the only reliable source, anyone quoting you a national protocol is describing something that has not been published.

The approval is conditional, and so is the funding

Two things are still provisional, and both say something useful about how certain the evidence is.

• The marketing authorisation is conditional. In the regulator's own words, "further evidence on this medicinal product is awaited", and the manufacturer must keep supplying it.

• NHS funding in England is through a managed access agreement, with evidence collected over five years before the treatment is assessed again.

The five-year figure is not arbitrary. The NICE committee said that if the treatment effect held steady for five years, they would be reassured it was not going to fade.

About the word "cure"

You will see this treatment described as a cure. Within days of each other in early 2025, two parts of the same health system said noticeably different things.

NHS England announced the therapy under the headline that it "offers hope of a cure", and quoted researchers finding a functional cure in 96.6% of trial participants.

NICE's committee, assessing the same evidence, recorded that the absence of pain crises "does not translate directly to a cure", that the assumption of lifetime effectiveness "was based on clinical opinion", and that some people in the trial still had episodes of pain.

Neither is spin. The treatment can transform how someone lives, and it has not been shown to be permanent. Both of those are true, and you are entitled to hear them together.

What does not change

This is the part most often left out. Gene therapy stops new damage; it does not undo damage already done.

Organ damage that happened before treatment, a previous stroke, joint damage, effects on eyes or kidneys, may not improve afterwards. People who have had years of iron loading from transfusions may still need that managed. In the thalassaemia follow-up, around a third of people had not been able to stop iron chelation.

That means your relationship with haematology does not end. Specialists advise staying under your original team as well as the transplant service, because how organ function behaves after gene therapy is not yet known.

Questions you might take to your team

• How often will I be seen, and for how long?

• Which team looks after me long term, the transplant centre or my usual haematologist?

• What is being watched for at those appointments?

• What difference would you expect this to make to damage I already have?

• Would I still need iron chelation, and for how long?

• What would make you think the treatment was wearing off?