The team's liver was grown from human skin cells reprogrammed to an embryo-like state and placed atop growth plates in a specially designed medium. Nine days later, the cells were expressing biomarkers indicative of maturing liver cells known as hepatocytes. With careful timing (informed by hundreds of trials) the team then introduced two more cell types that help recreate organ-like functions, including endothelial cells that line blood vessels.
Two days after that, the cells had assembled themselves into a 3-D, 5-millimeter-long tissue that mimicked early stage liver development. Though lacking bile ducts and not organized in exactly the same neat way natural hepatocytes organize themselves, the tissue did possess functional blood vessels that worked when the tissue was placed under the skin of a mouse. It was also able to metabolize some drugs that mouse livers cannot process but that human livers can.
By this measure, the team calls their tissue the first reported creation of a functioning human organ with working vasculature from pluripotent stem cells.