Policy & Regulation
Gene-editing completed from within a human body for the first time
16 November 2017 -

In a world first, gene-editing has been attempted on cells whilst within a patient. According to the BBC on Thursday, the impressive feat comes courtesy of researchers in California who trialled the experimental treatment on a man with Hunter's syndrome.

Brian Madeux, a 44-year-old man from Arizona, was the patient in the experiment. He hoped the treatment could correct a defect in his DNA that caused Hunter's syndrome. The disease means that he is "in pain every second of the day".

Hunter's syndrome is a rare disease in which people are born without the genetic instructions for an enzyme that breaks down long sugary molecules called mucopolysaccharides. As a consequence, mucopolysaccharides accumulate in the body and damage the brain and other organs. Severe cases are often fatal, with Madeux himself having believed that he "wouldn't live past my early 20s".

Patients with Hunter's syndrome need regular enzyme replacement therapy to break down the mucopolysaccharides. Through the treatment, Madeux hopes that researchers can rewrite his DNA to give him the instructions for making the enzyme.

The treatment

On Monday, the trial treatment was infused into his bloodstream at Oakland's UCSF Benioff Children's Hospital. Two molecular scissors – called zinc finger nucleases – are used to cut the DNA at two precise spots. This generates a new opening.

Coded DNA with the keyed-in instructions is then inserted into the patient's DNA, effectively rewriting their genetic code. The genetic therapy is only activated once inside Madeux's liver cells.

Dr Chester Whitley, one of the doctors working on the trial, told the BBC: "If works as well as it does in mice, this has huge ramifications. I'm very optimistic we have a both safe and efficacious way of providing gene therapy."

'New frontier'

Gene editing has been tested in the past, but cells were taken out of the body, edited and then checked for errors before being put back in. Only certain types of cells can be temporally removed and returned later, such as bone marrow.

The procedure is impossible for some organs, like the liver, heart or brain. This is what pushed doctors to conduct the gene editing from inside the patient's body. The trial is in its early stages; more tests and research must be done to establish safety, but it is promising.

So far, Madeux has suffered no side effects and, should everything continue to go well, researchers hope to complete the procedure on nine other patients.

Dr Sandy Macrae, from Sangamo Therapeutics, which designed the therapy, said: "For the first time, a patient has received a therapy intended to precisely edit the DNA of cells directly inside the body. We are at the start of a new frontier of genomic medicine."

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