Medical and Ethical Issues Cloud Plans to Clone for Therapy

In cloning human embryos and extracting universal stem cells, scientists in South Korea have taken a big step toward a tantalizing goal: growing tailor-made replacement tissues for people who are sick or injured. Imagine new cardiac muscles to restore a heart after a heart attack, insulin-producing cells for diabetics or neurons to stave off Parkinson's disease.

But significant scientific barriers lie between this accomplishment and any actual therapy, experts said. Moreover, ethical objections have put such research off-limits to some scientists - including the many in the United States who rely on federal money - and lack of investment has felled many companies trying to develop cell-replacement therapies.

The South Korean work is a step toward what is called "therapeutic cloning." The work so far is "proof of concept of cloning but it's not therapeutic yet," said Dr. Steven A. Goldman, chief of the division of cell and gene therapy at the University of Rochester Medical Center.

It is likely to be several years before tissues derived this way could even be tested in patients, he and other experts said...