CANBERRA: An Australian teenage girl has become the world's first known transplant patient to change blood groups and take on the immune system of her organ donor, doctors said on Friday, calling her a "one-in-six-billion miracle".

Demi-Lee Brennan, now 15, received a donor liver when she was nine and her own liver failed.

"It's like my second chance at life," Brennan told local media, recounting how her body achieved what doctors said was the holy grail of transplant surgery. "It's kind of hard to believe."