The Future

Experts warned that significant work remains to be done before the findings can be translated into useful therapies. Scientists know little about how to get stem cells to become one kind of cell or another. They have had some success getting them to become neurons or heart cells by adding specific hormones. But for the most part they must simply watch for the desired kind of cells to erupt out of a mass of maturing stem cells, then tease them away to be grown on their own.

The ability to purify single cell types will be crucial. In one set of experiments done in another lab, batches of cardiac cells grown from mouse stem cells were injected into the hearts of living mice. A few contaminating stem cells must have been present, scientists said, because along with the new cardiac tissue, other tissues began to grow out of the hearts.

Scientists said the first uses for human stem cells will probably be as a source of tissues upon which new pharmaceuticals can be tested and toxins assessed, and to study the earliest stages of embryo development – an endeavor that could lead to treatments for infertility and a reduction in birth defects.