Two days later, the cell assortment had self-organized to form a three-dimensional "liver bud" — a 5-millimeter-wide chunk of tissue that performed basic liver functions. When they grafted the liver bud into a mouse, the researchers said the tiny organ's blood vessels worked correctly, and it successfully metabolized some drugs that human livers metabolize but which mouse livers normally cannot.
Both feats were presented at the annual meeting of the International Society for Stem Cell Research in Yokohama, Japan, last week. Although further progress is needed before fully functional lab-grown livers and eyes will be ready to implant into a human, outside experts say the new results constitute genuine advances in that direction — and they have other medical uses in the meantime.
Takanori Takebe, a stem-cell biologist at Yokohama City University in Japan, and his team grew a small, rudimentary liver using a recipe of just three types of cells. The trick was figuring out when to introduce each ingredient into the mix of cells: "It took over a year and hundreds of trials," Takebe was quoted as saying in Nature.
First, the researchers placed genetically reprogrammed human skin cells, called "induced pluripotent stem cells," on growth plates in a specially designed chemical bath. After nine days, the cells began developing into hepatocytes, or liver cells. At that point, the researchers added cells taken from an umbilical cord, which would develop into the lining of blood vessels, and cells from bone marrow that can differentiate into bone, cartilage or fat.