They started with healthy T-cells from a donor and set about modifying them.
The first base edit disabled the T-cells’ targeting mechanism so they could not attack the patient’s body.
The second removed a chemical marking, called CD7, which is on all T-cells. Removing it is essential for preventing the therapy from self-destructing
The third edit was an “invisibility cloak” that prevented the cells being killed by a chemotherapy drug.
The final stage of genetic modification instructed the T-cells to go hunting for anything with the CD7 marking on it.
Now the modified T-cells would destroy every other T-cell they found whether they were cancerous or healthy, but they would not attack each other.
The therapy is infused into patients and if their cancer cannot be detected after four weeks, then patients have a bone marrow transplant to regrow their immune system.
“A few years ago, this would have been science fiction,” says Prof Waseem Qasim from UCL and Great Ormond Street.
“We have to basically dismantle the entire immune system.
“It’s a deep, intensive treatment, it’s very demanding on the patients, but when it works, it’s worked very well.”
