Six Billion to 1

A teenager has become the first transplant patient to switch blood groups - at estimated odds of six billion to one. Demi-Lee Brennan had O-negative blood before receiving a replacement liver six years ago. However, she is now O-positive after her body adopted the immune system of the organ's donor.

The switch means the 15-year-old no longer needs immuno-suppressant drugs which are used to stop the body rejecting a new organ.

The drugs are usually taken for life and only a small number of transplant patients have been able to come off them. None is thought to have done so by jumping blood groups.

Experts say that studying what happened to the Australian teenager may open the way to beating organ rejection - the holy grail of transplant medicine.

Richard Thompson, a paediatric hepatology expert at King's College London, said Demi-Lee's case appeared to be unique.

He said: "It's a dramatic, remarkable case and she's been incredibly lucky.

"A small number of people can stop taking anti-rejection drugs altogether after a transplant because they develop a tolerance to the donor organ but this has not been achieved before by a change in blood group. "It can be extremely dangerous to take patients off immunosupressants to see what happens. It can result in rejection and the patient then needs a new organ."

Doctors try to give patients organs from donors of the same blood group.