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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.
Doctors used "base editing" to perform a feat of biological engineering to build a new living drug for leukemia.
Six months later the cancer is undetectable, but Alyssa is still being monitored in case it comes back.
Base editing allows scientists to zoom to a precise part of the genetic code and then alter the molecular structure of just one base, converting it into another and changing the genetic instructions.
Robert Chiesa, from the bone-marrow transplant department, said: "It is extremely exciting. Obviously, this is a new field in medicine and it's fascinating that we can redirect the immune system to fight cancer."
David Liu, one of the inventors of base editing stated, it was "a bit surreal" that people were being treated just six years after the technology was invented.
The treatment was carried out at the Great Ormond Street Hospital.