The report, by the National Institutes of Health in the American journal Science, raises the remarkable prospect that scientists may be able to grow human organs in the lab that can be transplanted into patients.
Stem cells are powerful cells that give rise to other, more specialised types of cells in the body.
The institute wants to offer its first-ever funding for experiments using stem cells from human embryos, which many scientists say are the most potent and versatile. Anti-abortion groups, however, are lobbying US President George W. Bush to block the money on grounds that destroying human embryos is immoral and unnecessary. They say that somewhat different types of stem cells found in adults are proving to be as versatile as cells from embryos. Until recently, scientists believed that adult bone marrow stem cells could produce various blood cells, but not brain or muscle cells. They thought neural stem cells could produce material for the nervous system, but nothing else.