Doctors in London say they have cured a baby boy of a life-threatening disease which was destroying his liver.
They implanted cells which acted like a temporary liver, allowing the damaged organ to recover.
The team at King's College Hospital in south London say the technique is a world first.
Eight-month-old Iyaad Syed now looks the picture of health - but six months ago he was close to death. A herpes-simplex virus had damaged his liver causing it to fail.
Instead of going on a waiting list for a transplant, doctors injected donor liver cells into his abdomen.
These processed toxins and produced vital proteins - acting rather like a temporary liver.
The cells were coated with a chemical found in algae which prevented them from being attacked by the immune system.
After two weeks his own liver had begun to recover.
Professor Anil Dhawan, a liver specialist at King's College Hospital, says the whole team at the hospital is delighted:
"This is the first time this treatment has been used to treat a child with acute liver failure. It's only a few months back when I first saw this child who was so sick requiring support on dialysis and a breathing machine.
"We think we have given him another chance of life and seeing him now six months down the road with nearly normal liver function is remarkable."
Dr Ragai Mitry, Head of Liver Processing at King's, who helped in developing the technique, said: "We are very pleased the transplanted liver cells have helped in supporting and delivering the missing metabolic functions of Iyaad's failing liver."
Iyaad's father, Jahangeer, said his son was "a miracle boy".
He added: "Once he had the treatment after 48 hours he started to get better and hope came back. It is brilliant and we are very proud of him."
The question now is whether the technique could be used to benefit other patients with acute liver failure. The team at King's is urging caution - a large clinical trial is needed to test the effectiveness of the technique.
A key benefit over a liver transplant is that Iyaad will not need to take anti-rejection drugs known as immunosuppressants.
Andrew Langford, chief executive of the British Liver Trust, said: "The principle of this new technique is certainly ground-breaking and we would welcome the results of further clinical trials to see if it could become a standard treatment for both adults and children.
"Sadly, we have reached a breaking point with our transplant list in the UK, where approximately 100 people die waiting for a donor liver to become available each year."
King's College Hospital is part of King's Health Partners Academic Health Sciences Centre (AHSC), a collaboration between King's College Hospital; Guy's and St Thomas'; and South London and Maudsley NHS Foundation Trusts, with King's College London university. The partnership aims to accelerate the transition of research from bench to bedside.