Alex Lowe, of Wigan, 8 at the time, had slipped into a coma and was on the verge of death when her parents begged doctors for an untested treatment. Brain tumours caused by a virus had left her paralysed and struggling to breathe. Her organs were starting to shut down. Chemotherapy had failed.

She had a transfusion of specially selected white blood cells, called “killer T-cells”. It works by targeting a specific cancer-causing virus.

Robert Wynn, a consultant haematologist at Royal Manchester Children’s Hospital who treated Alex, said: “She was essentially dead. She was in a coma and her body showed signs that she was close to death with the tumour.

“What happened was miraculous. She woke up and returned to being a normal girl. I have seen a lot of things in medicine, but I have never seen anything like this.”

Alex, now 10, was given the treatment two years ago. Her recovery has so amazed doctors that the case is featured in this month’s edition of the medical journal Lancet Oncology. She is back at school and now behaves like any other 10-year-old girl, riding her bicycle and playing outside.

Alex’s mother, Lindsay, 33, said that her recovery had been remarkable. Lindsay said: “I was sat at her bedside waiting for her to die. Doctors told us there was nothing more they could do and she might have only a couple of hours left.

“But a friend in the nursing profession came to tell us about the work of scientists at Edinburgh University. She told us there must be something that could be done.” After Alex was given the infusion, which is administered weekly, doctors began to see clear signs that her condition was improving. By the second or third week she was much better.

Until Alex’s recovery the treatment had been used only in patients who had contracted cancers after organ transplants. The case has raised hopes that it can be modified to fight other cancers. Dorothy Crawford, Professor of Medical Microbiology at Edinburgh University, who runs the T-cell “bank” from which the treatment was taken, described the results as dramatic. “If we show it works with this virus then maybe we can grow another bank for another virus,” she said.

After the cell therapy, Alex was given a bone marrow transplant to build up her immune system, which had been virtually wiped out by the virus. A second brain tumour was also successfully destroyed using the treatment and she will now donate bone marrow to her five-year-old brother, Cory, who suffers from the same condition.

Since Alex’s astonishing recovery a further ten patients have been treated with the cell therapy. Doctors now hope to use the treatment to cure other virus-related tumours such as liver and cervical cancer.

Henry Scowcroft, of Cancer Research UK, which has funded the therapy, said that the treatment had been spectacular. He said: “Therapies like this one, which are highly specific but available ‘off-the-shelf’ so that they can be delivered to the patient quickly, have long been a goal of the cancer research community.”

Alex suffered from an immune deficiency that meant her body could not protect itself against the usually harmless Epstein-Barr virus.

Her father, Simon, 35, said last night: “We seem finally to be getting back to the little girl we had before. She’s now full of beans, like any other 10-year-old.

“We’ve been to hell and back, and even deeper if you can imagine that. There’s absolutely no assurance whatsoever that it [Alex’s illness] won’t come back, but since she’s had a bone- marrow transplant she’s got a new immune system so, fingers crossed, that should be it.”

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