One-year-old Layla Richards is now cancer-free. IMAGE: Great Ormond Street Hospital

Two infants diagnosed with an aggressive and previously incurable form of leukemia are now in remission, after British doctors say they cured the babies using so-called “designer cells.”

It is the first time in history that cancer has been treated using genetically engineered immune cells from a donor. Details of the two cases were published Wednesday in Science Translational Medicine.

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In each case, scientists engineered a type of immune cell called a T cell to attack cancer cells. Each of the two infants, aged 11 and 16 months, had undergone many previous treatments, and all of them had failed. One of the infants, Layla Richards, attracted press attention in the fall when scientists at Great Ormond Street Hospital announced that Richards, who was diagnosed with cancer at just three months old, was vastly improved just a few months after beginning treatment. But at the time, scientists were hesitant to say that she had been cured. Now, the scientists say that Richards is in remission—and that they have cured a second baby as well, lending more evidence to the therapy’s effectiveness.

The treatment entailed collecting blood from donors, isolating healthy immune T-cells, and then using a genetic engineering tool known as TALENs to deactivate certain T-cell genes that would normally cause them to be rejected once transplanted into a leukemia patient. The T-cells were also engineered to attack cancer cells directly.

Similar treatments using engineered T-cells have been highly successful against blood cancers in other studies. But those studies rely on a patients own blood cells being altered. Using donated cells offers the potential for a cheaper, faster cure.

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Some researchers have expressed skepticism about the therapy, since the infants were also given standard chemotherapy, and the current work does not definitively separate the effects of the two. Still, these early results are promising.

[Science Translational Medicine]