Recovery

Recovery starts the moment the cells go in, and it is slower than most people expect. This stage is mostly waiting, for blood counts to come back, for the risk of infection to fall, and for energy to return.

Engraftment

Engraftment is when the treated cells settle into your bone marrow and start making blood again. It is the milestone everything else waits on.

In the trials, neutrophils, the white cells that fight infection, came back first:

• Sickle cell disease: a middle figure of 27 days, ranging from 15 to 40 days.

• Beta thalassaemia: a middle figure of 29 days, ranging from 12 to 56 days.

Platelets, which help blood clot, took longer:

• Sickle cell disease: a middle figure of 35 days, ranging from 23 to 126 days.

• Beta thalassaemia: a middle figure of 44 days, ranging from 20 to 200 days.

For thalassaemia there was a clear difference depending on the spleen: people who had had their spleen removed recovered platelets in about 34 days on average, compared with about 46 days for those who still had one. If that applies to you, it is worth raising, because it changes what a normal recovery looks like in your case.

Every single patient in both trials achieved neutrophil engraftment, and none needed the back-up cells.

The neutropenic period

Between the chemotherapy and engraftment there is a stretch where you have almost no infection defences. This is called neutropenia, and it is the riskiest part of the whole treatment.

Infection during this window is common rather than exceptional: in the thalassaemia trial, 61% of people had at least one episode of fever while neutropenic. It is expected, it is treated urgently, and units are set up for it.

This is why transplant units tell patients to contact them straight away about a temperature or any sign of infection, rather than waiting to see. Your own team will give you their threshold and their number, that instruction comes from them, not from this page.

Things that can go wrong, and how likely they are

• The new cells can fail to take hold. This is why a back-up sample of your own untreated cells is collected and kept before treatment, so it can be given back if needed. It did not happen to anyone in the trials.

• Until platelets recover there is a raised risk of bleeding, and you are monitored for it.

• Because the cells are your own, graft-versus-host disease, a major complication of donor transplants, is not a risk here, and you do not need the immunosuppressant drugs donor recipients take.

That last point matters when you read about transplant generally. Much of what is written describes donor transplants and is more frightening than what applies to you.

Going home

Leaving hospital is not the end of recovery. The following describes transplant recovery generally rather than gene therapy specifically, but the shape holds.

• The immune system carries on rebuilding for up to about 18 months. During that time coughs and colds are more frequent and take longer to shake off.

• Childhood vaccinations usually need repeating, typically starting three to six months afterwards.

• Around day 100 there is normally a full review appointment, and appointments stay frequent for a while before spacing out.

How long until you feel like yourself again is the question everyone asks, and there is no published answer for gene therapy specifically. Anyone who gives you a confident number is guessing. Your own team, who can see your counts and know your history, is the right place to ask.

What the trials showed about life afterwards

For thalassaemia, quality of life was formally measured and improved at two years, by about 14 points on a 164-point scale for adults, and about 12 points on a 100-point scale for children.

For sickle cell, NHS England reported that everyone treated avoided a hospital admission for their sickle cell in the year after treatment, and that almost 98% had still avoided one about three and a half years later.

Follow-up does not stop

You are monitored at least once a year for 15 years, including blood counts, and patients are asked to join a long-term registry. That is not because something is expected to go wrong; it is because these treatments are new and the long-term picture is still being built.

Questions you might take to your team

• What counts as a temperature I should ring about, and what is your number out of hours?

• What would recovery typically look like for someone in my situation?

• When would I be able to go back to work or school?

• When do vaccinations get repeated?

• How often will I be seen in the first year, and after that?

• What would happen if the cells did not take hold?