Imagine being able to reach into the freezer, take out a cell culture, treat it with growth factors, and produce almost any tissue in the human body. Sounds like science fiction? Today, it is. But the raw material--in the form of a type of universal cell called a "stem" cell--is now growing in the laboratory.
In a long-awaited announcement, biologist James Thomson and his team at the University of Wisconsin, Madison, report in tomorrow's issue of Science that they have isolated stem cells from human embryos and coaxed them to grow in five "immortal" cell lines. In a separate effort, John Gearhart and a team at The Johns Hopkins University School of Medicine are publishing a paper in the 10 November Proceedings of the National Academy of Sciences that describes how they used a different method to derive stem cells from human fetal tissue.
In its early stages, an embryo contains cells that can produce any kind of cell type needed by an adult. These cells have been isolated in monkeys, mice, and a few other animals. But hunting the human stem cell has proven difficult, in part because U.S. law forbids the use of public funds for most research on human embryos.
Thomson secured funding from the Geron Corp. of Menlo Park, California, and derived the cell lines from embryos donated by couples at in vitro fertilization clinics in Wisconsin and Israel. He extracted blastocysts from days-old human embryos and grew them on a layer of mouse "feeder" cells in a lab dish. Other researchers had gone this far, but Thomson went further: He coaxed the balky cells to continue growing without differentiating into specialized tissue cells. To demonstrate that the cells had retained their power, Thomson inserted them into mice and grew embryolike human tumors that contain bone, blood, and gut.
It's an "extremely important" milestone, says Austin Smith, a stem cell researcher at the University of Edinburgh in Scotland. Gearhart describes Thomson's research in an accompanying commentary as "a major technical achievement with great importance for human biology." In a matter of years, some researchers say, it may be possible to grow replacement tissue which could be transplanted into diseased organs. So far, Thomson says, they haven't figured out how to control the development of stem cells. But, he says, "I really believe that within my lifetime I will see diseases treated by these therapies."