In the latest CRISPR success story, a 13-year-old girl whose leukemia had not responded to other treatments now has no detectable cancer cells.

She received a dose of immune cells that were genetically edited to attack the leukemia, a method that's been used with other cancers.

A form of cancer in the bone marrow tissue, leukemia is caused by mutated immune cells and is normally treated by killing all bone marrow cells in the patient's body before receiving a transplant from a donor. If this falls, the Nobel Prize-winning CAR-T cell therapy can be used instead.

This was the case of Alyssa, a 13-year-old girl from the UK, who received a dose of common immune system weapons called T cells that had been modified to attack cancerous cells in her body. To avoid the extreme costs associated with this, the Great Ormond Street Hospital team at University College London further modified the donor T cells.

"This is quite remarkable, although it is still a preliminary result, which needs to be monitored and confirmed over the next few months," said Robert Chiesa, one of the doctors treating Alyssa, in a statement released by Great Ormond Street Hospital.

While she has no detectable cancer now, it will take several years to determine whether she's truly cancer-free.

This procedure was used before to save the life of a 1-year-old girl, Layla, also in the UK last year, and is now approved by the NHS as a treatment for people with leukemia arising from mutated B cells, another group of immune cells that can lead to the cancer.

New Scientist explains that lead researcher Waseem Qasim at University College London had applied four edits to the cells' DNA, which puts them at risk for dangerous mutations. To circumvent this, he used a different method of the CRISPR gene editing protein that " changes one DNA letter to another," a technique called base-editing.

Alyssa is the first person ever to be treated with base-editing.

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