Japanese scientists have grown a fully functional human liver from stem cells for the first time.
The researchers from Yokohama City University created the organ by transplanting 'liver buds' from human stem cells to restore liver function in mice.
Published in the journal Nature, Takanori Takebe and Hideki Taniguchi showed how they stopped mice with liver failure from dying by transplanting the stem cell-grown structures into them.
At present, there is a huge demand for human livers for transplants. In the US last year, almost 3,000 people died waiting for a liver while 5,800 transplants took place.
Embryonic stem cells were discovered in 1981 but scientists have hitherto been unable to generate a human organ because of the complex interactions between cells and tissues as they develop.
However, the Yokohama City scientists challenged this belief by focusing on the earliest stage of organ creation - the interactions during 'organ bud' development.
There are two main types of stem cells: those that are harvested from embryos, and reprogrammed induced pluripotent stem cells (iPSCs) which are taken from skin and blood.
The researchers used the latter type to make three different cell types that normally combine in the formation of a human liver. They fused them together and found the cells began to grow to form 3D structures called 'liver buds'.
When these were transported into the mice, the liver buds matured and connected with the mouse's blood vessels, and began performing many of the functions of mature human liver cells
The liver is the largest internal and most metabolically complex organ in humans.