By the time he reached his first birthday, Drew Benson had already undergone a liver transplant and was then fighting a virus which causes a rare type of blood cell cancer. He spent his first two Christmases in hospital.

But now as he approaches his fifth birthday, the lively youngster is completely recovered and looking forward to starting school in a few weeks' time.

The Armagh city boy's mother, Carrie Anne, spoke to the Belfast Telegraph about her relief that he has made a full recovery.

She said her son is doing so well, she and her husband, Tony (39), have " almost forgotten that he was ever ill".

And the 29-year-old also spoke of her family's gratitude that the tot was able to take part in such pioneering research.

Drew was born in November 2002 and was diagnosed with a rare condition known as biliary atresia which is an unknown blockage to the bile duct. He had his gall bladder removed at the age of 10 weeks, but his condition continued to deteriorate.

Doctors ruled that he needed a liver transplant and he underwent one at Birmingham Children's Hospital at the age of nine months. After a few weeks of improvement, Drew started to fail, first with a glandular fever infection, then the Epstein Bar Virus (EBV) and then suspected post-transplant lymphoproliferative disorder (PTLD) which is a type of blood cell cancer.

Up to 10% of patients who undergo an organ transplant can develop PTLD because their immune systems are suppressed due to anti-rejection drugs.

When the future was looking bleak for the tot, who now has two younger brothers and two older half-brothers, he was offered a place on a Cancer Research UK study known as the 'T Cell Trial'.

The programme has involved a team of researchers from the University of Edinburgh injecting patients with blood cells from healthy donors. As Drew was placed on the placebo arm of the trial, he was taken off his anti-rejection drugs, but not injected with blood cells.

"The study wasn't so much our last resort, but we were at the stage where we would have tried anything to help Drew," his relieved mum said.

"When the place was offered, we took it. Drew was suitable to be a placebo so he was taken off his anti-rejection drugs on the understanding that if he did deteriorate, he would be given the new treatment.

"We were amazed when he began to rally. His immune system seemed to kick in and he fought off the virus himself."

Mrs Benson said her son is now in full health and looking forward to starting Armstrong Primary School next month.

"He's fantastic - he never quits, never stops running around. He's just leading a happy, normal healthy life," she said.

"After his transplant he was doing so well and it was such a setback when he started having more problems. But he is now in full health with his new liver. He had chicken pox a while ago, but apart from that he's had no problems.

"There are times he is so well, we nearly forget just how bad he was."

News of Drew's recovery came this week after the researchers announced the results of their trial in the journal Blood.

They found that patients given the treatment showed an " encouraging" response. All the patients in the study had a poor prognosis. The study found that 64% of patients were responding well to the T cell treatment five weeks after being given it. After six months, the response rate was 52%.

Kate Law, director of clinical trials at Cancer Research UK, said: "The results of this study are exciting for transplant patients at risk of PTLD, particularly young children who are more prone to the condition."

If further trials are successful, a single bank of T cells could potentially serve as a global source of immune cells to treat the condition.