You have heard about blood groups. And you've been told about blood incompatibility: put A, B or AB blood type into an O type receiver, and you will kill him/her. But this new case published in The New England Journal of Medicine has amazed the scientific world and it is an absolute first.

A 15 years old Australian girl spontaneously changed blood groups and took her donor's blood group following a liver transplant.

"Demi-Lee Brennan was aged nine and seriously ill with liver failure when she received the transplant," doctors at a top Sydney children's hospital told AFP.

9 months after the surgery, the medics found that she had changed blood type and her own immune system to that of the donor after stem cells from the new implanted liver mover into her bone marrow.

"She is now a healthy 15-year-old. I have given several presentations on the case around the world and have heard of none like it. It is extremely unusual -- in fact we don't know of any other instance in which this happened," Michael Stormon, a hepatologist treating her, told AFP.

"In effect she had had a bone marrow transplant. The majority of her immune system had also switched over to that of the donor."

Brennan is now living just like any other outpatient and medics are attempting to get as much information as possible from this case, with further applications in transplant surgery, where rejection of donor organs by the recipient's immune system is a huge impediment.

"It appears that Brennan may be fortunate because a sequence of serendipitous events, including a post-transplantation infection, may have given the stem cells from her donor's liver the chance to proliferate. The task now was to establish whether the same sort of outcome could be replicated in other transplant patients," he said.