A 10-year-old girl has had a major blood vessel in her body replaced with one grown with her own stem cells, Swedish doctors report.
She had poor blood flow between her intestines and liver.
A vein was taken from a dead man, stripped of its own cells and then bathed in stem cells from the girl, according to a study published in the Lancet .
Surgeons said there was a "striking" improvement in her quality of life.
This is the latest in a series of body parts grown, or engineered, to match the tissue of the patient.
Last year, scientists created a synthetic windpipe and then coated it with a patient's stem cells.
A blockage in the major blood vessel linking the intestines and the liver can cause serious health problems including internal bleeding and even death.
In this case, other options such as using artificial grafts to bypass the blockage, had failed.
Doctors at the University of Gothenburg and Shalgrenska University Hospital tried to make a vein out of the patient's own cells.
It used a process known as "decellularisation".
It starts with a donor vein which is then effectively put through a washing machine in which repeated cycles of enzymes and detergents break down and wash away the person's cells.
It leaves behind a scaffold. This is then bathed in stem cells from the 10-year-old's bone marrow. The end product is a vein made from the girl's own cells.
The doctors said: "The new stem-cell derived graft resulted not only in good blood flow rates, but also in strikingly improved quality of life for the patient."
Profs Martin Birchall and George Hamilton, from University College London, said: "The young girl was spared the trauma of having veins harvested from the deep neck or leg with the associated risk of lower limb disorders."
They said this one-off procedure needed "to be converted into full clinical trials... if regenerative medicine solutions are to become widely used".