The therapy - which until recently would have been considered a feat from the realm of science fiction - has stopped an aggressive and incurable blood cancer in some patients, doctors describe.
The treatment involves precisely editing the DNA in white blood cells to transform them into a "living medicine" that fights cancer.
The first girl to undergo this treatment, whose life story we reported on in 2022, remains disease-free and now plans to become a cancer scientist.
Eight children and two adults with acute T-cell lymphoblastic leukemia are currently being treated, and 64 percent of them are in remission.
T-cells are supposed to be the body's guardians, seeking out and destroying threats, but in this particular form of leukemia, they get out of control.
Chemotherapy and bone marrow transplants don't work.
Besides the experimental drug, the only remaining option for those in the trial was to make their death more pleasant.
"I really thought I was going to die and not be able to grow up and do all the things that every child deserves to be able to do," says 16-year-old Alyssa Tepley from Leicester.
She is the first in the world to undergo this therapy at Great Ormond Street Hospital and is now enjoying life.
The revolutionary treatment carried out three years ago involved wiping out her old immune system and building a completely new one.
She spent four months in the hospital and was unable to see her brother in case he brought her an infection.
But now her cancer is completely gone and she only needs annual checkups.
Alice is taking her final exams at high school, is a participant in the Duke of Edinburgh's Award program, is thinking about signing up for driving lessons, and is planning for the future.
“I intend to apply for an internship in biomedicine and, with any luck, one day I will also be involved in blood cancer research,” she said.
The team from University College London (UCL) and Great Ormond Street Hospital used a technology called base editing.
Bases are the language of life.
Four types of bases - adenine (A), cytosine (C), guanine (G) and thymine (T) - are the building blocks of our genetic code.
Just as the letters in our alphabet make up words that carry meaning, the billions of bases in our DNA carry an instruction manual for our body.
Base editing allows scientists to focus on a precise part of the genetic code and then change the molecular structure of just one base, switching it from one type to another, and essentially rewriting the instructions for use.
Researchers wanted to harness the natural power of healthy T-cells to find and destroy threats and turn it against T-cell acute lymphoblastic leukemia.
That's not easy to do.
They had to instruct the good T-cells to hunt down the bad ones without the treatment destroying itself.
They started with healthy donor T-cells and set about modifying them.
Editing the first base disabled the targeting mechanisms of the T-cells so that they could not attack the patient's body.
Another modification removed a chemical tag called CD7, which is found on all T-cells.
Their removal is crucial to preventing the therapy from self-destructing.
The third edit was to put on an “invisibility cloak,” which prevented the cells from being killed by the chemotherapy drug.
The final stage of genetic modification instructed the T-cells to go hunting for anything with the CD7 tag on it.
Now the modified T-cells can destroy any other T-cell they encounter, whether cancerous or healthy, but they will not attack each other.
The therapy is injected into patients and if their cancer cannot be found after four weeks, then patients go for a bone marrow transplant to rebuild their immune system.
"Just a few years ago, this would have been science fiction," says Professor Wassem Kassim, from UCL and Great Ormond Street Hospital.
He adds: "We basically have to dismantle the entire immune system... it's an in-depth, intensive treatment, very demanding on patients, but when it works, it works very well."
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The study, published in the New England Journal of Medicine, reports the results of the first 11 patients treated at Great Ormond Street Hospital and King's College Hospital.
It shows that nine managed to achieve a deep remission that allowed them to undergo bone marrow transplants.
Seven remained disease-free between three months and three years after treatment.
One of the biggest risks of treatment involves infections as the immune system is suppressed.
In two cases, the cancer lost its CD7 markers, allowing it to hide from treatment and return to the body.
"Given how aggressive this particular form of leukemia is, these are quite impressive clinical results and, of course, I'm very happy that we've been able to restore hope to patients who otherwise had lost it," said Dr Robert Chiesa, from the bone marrow transplant department at Great Ormond Street Hospital.
Dr Deborah Yallop, a haematology specialist at the Royal Infirmary, said: “We have seen impressive responses in terms of getting rid of leukaemia that seemed incurable – it is a very powerful approach.”
Commenting on the research, Dr Tanya Dexter, senior medical officer at British stem cell charity Anthony Nolan, said:
"Considering that these patients had a very low chance of survival before the trial, these results give us hope that treatments like this will continue to develop and become available to more patients."
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