This January, news that South Korean scientist Hwang Woo Suk fabricated research on cloned human stem cells brought more negative attention to an already controversial field. Hwang’s work had been believed to be a breakthrough. His technique for cloning embryonic stem cells genetically matched to patients might have been used by scientists worldwide to cure disease.

1. Cell Loss
Our liver, kidneys and other organs keep a fair number of cells in reserve; still, over time, cell loss may impair their functioning.
De Grey’s fix: Engineer embryonic stem cells to create healthy new versions of every type of body cell. Introduce the stem cells into the body to rejuvenate diseased or flagging tissues. The mechanism to deliver the various cell types to all the right places has yet to be developed.

American stem-cell researchers have been warning for years that their work is being stifled by restrictions while scientists abroad forge ahead. In 2004 that warning hit home when a breakthrough emerged from South Korea.

The national furor over human cloning is certain to continue for years, regardless of whether or not the U.S. Senate heeds President Bush's pleas to ban it. The opportunity to create embryonic stem cells that scientists say could generate every cell type in the body—thereby revolutionizing medicine—gives many people pause for ethical reasons.