The parents of 1-year-old Layla Richards from London gave permission for the experimental treatment when they learned doctors had exhausted all other options.
Experts at Great Ormond Street Hospital, where Layla was treated, say the little girl is "cancer free and doing well.”
Learn more about gene editing with these common questions.
What is the technique, exactly?
Gene editing is an exciting scientific advance that has the potential to treat a wide range of diseases caused by faulty genes.
It involves scientists basically making tiny molecular scissors that can cut and edit genes and reprogram cells.
The technique is officially still in the lab-testing phase. But if it can be perfected, it may have the potential to treat millions of people with genetic diseases.
What gene editing technique was Layla treated with?
Doctors used the "molecular scissors," known as TALEN proteins, to edit genes and create designer immune cells programmed to hunt out and kill drug-resistant leukemia.
Because this treatment is at an early stage, it was sanctioned only because the girl had no other hope of surviving the disease -- called acute lymphoblastic leukemia (ALL) -- and her parents were willing to try it.
Doctors used modified T-cells from donors, known as UCART19 cells, to treat Layla.
"The approach was looking incredibly successful in laboratory studies," says Professor Waseem Qasim, a consultant immunologist at the hospital. "And so when I heard there were no options left for treating this child's disease, I thought, 'Why don’t we use the new UCART19 cells?’"
"The treatment was highly experimental and we had to get special permissions, but she appeared ideally suited for this type of approach."
Layla's parents were also eager to try the treatment. "We didn’t want to accept palliative care, and so we asked the doctors to try anything for our daughter, even if it hadn’t been tried before," says her mother, Lisa.
How was Layla treated?
The treatment consisted of 1 milliliter of UCART19 cells delivered directly into a vein over about 10 minutes.
After that, Layla spent several months in isolation to protect her from infections while her immune system was extremely weak.
Throughout this time, she was generally well.
What was the result?
Great Ormond Street Hospital says there were encouraging signs that the treatment was working after several weeks.
"As this was the first time that the treatment had been used, we didn’t know if or when it would work, and so we were over the moon when it did," says Professor Paul Veys, director of bone marrow transplants at the hospital. "Her leukemia was so aggressive that such a response is almost a miracle."
Once doctors were confident that the leukemia cells had been removed, Layla received a bone marrow transplant to replace her entire blood and immune system, which had been wiped out by the treatment. The child is now said to be recovering well at home.
"I consider ourselves lucky that we were in the right place at the right time to get a vial of these cells," her mother says. "We always said that we had to try new things, as we didn’t want to be saying, 'What if?'"
What's the future for this treatment now?
"We have only used this treatment on one very strong little girl," Qasim says, "and we have to be cautious about claiming that this will be a suitable treatment option for all children. But, this is a landmark in the use of new gene-engineering technology, and the effects for this child have been staggering.
"If replicated, it could represent a huge step forward in treating leukemia and other cancers."
The results are “very promising,” says Dr. Yalda Jamshidi, senior lecturer in human genetics at St George’s University Hospital Foundation Trust. But she says more work is needed to find out how well the treatment works long-term, confirm that the engineered cells aren’t toxic, and show that the treatment would be right for more people.