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genetic engineeringA new procedure called genome editing has been successfully carried out at Great Ormond Street Hospital.The genome of a batch of donated T cells [immune cells] was altered so that T-cells were modified to seek out and destroy the abnormal leukaemia cells, while also becoming resistant to the chemotherapy drugs.

One-year-old Layla Richards, developed leukaemia when she was five months old. Leukaemia is the commonest cancer in children. Most respond to chemotherapy. If they fail to respond patients go on to have high dose chemotherapy which destroys most of their own blood cells followed by a rescue bone marrow transplant. Layla failed to respond to chemotherapy and a bone marrow transplant so her parents opted to try the experimental technique, previously only used in mice, called genome editing. The DNA inside donated T cells were modified.The T-cells were modified to be accepted by Layla’s immune system and to seek out and destroy the abnormal leukaemia cells, while also becoming resistant to the chemotherapy drugs Layla was taking. Usually chemotherapy destroys the body’s normal cells, such as T cells as well as cancer cells.

DNA editing has been used for a while in the past new DNA was inserted into the cells of patients who had missing or defective instructions in their DNA.

The most famous cases were boys with so-called bubble boy syndrome in the 1990s. They had no immune system and had to live in completely sterile conditions due to a defect in a gene called IL2RG.This was successfully replaced by using a virus to “infect” cells with a healthy copy of the DNA, but trials were abandoned  because these boys developed leukaemia.The problem was the DNA was being inserted almost at random and in such a way that it disrupted the natural functioning of some cells and they became cancerous.

What has happened since then genetic modification is becoming more precise. Viruses being used can place DNA into safer sites in the genome and three key technologies have arrived on the scene.Zinc fingers, Talens and Crispr act as a type of satnav that finds its way to specific sites in our DNA and a pair of molecular scissors that can edit the DNA.

layla richards

In Layla’s case white blood cells were taken from a donor. Talens were used to engineer protection against anti-cancer drugs being given to the patient and to stop them attacking healthy tissue. A virus was used to insert a new gene that would make it attack leukaemia cells. Layla responded well to the treatment and is now back home with her family. She has gone into remission but researchers were keen to stress that it is too soon to say if Layla has been completely cured of the cancer, and there could still be long-term complications. This is exciting experimental work which could lead to treatments for a range of conditions.

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