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A teenage girl's incurable cancer has been cleared from her body in the first use of a revolutionary new type of medicine.

All other treatments for Alyssa's leukaemia had failed.

So doctors at Great Ormond Street Hospital used "base editing" to perform a feat of biological engineering to build her a new living drug.

Six months later the cancer is undetectable, but Alyssa is still being monitored in case it comes back.

Alyssa, who is 13 and from Leicester, was diagnosed with T-cell acute lymphoblastic leukaemia in May last year.

T-cells are supposed to be the body's guardians - seeking out and destroying threats - but for Alyssa they had become the danger and were growing out of control.

Her cancer was aggressive. Chemotherapy, and then a bone-marrow transplant, were unable to rid it from her body.