The New York Times
Week in Review
Jan. 5, 2003

The Promise of Therapeutic Cloning

By GINA KOLATA

Scientists wasted little time deploring the announcement by a religious sect that it has created the first human clone. It's not just because Clonaid, the company founded by the leader of the sect, the Raëlians, has so far failed to support its claims with even a shred of evidence. It is also because cloning has two meanings. And scientists worry that the public and Congress don't understand the distinctions.

What many scientists want to do is therapeutic cloning, which would create replacement cells for sick people, cells that their bodies would not reject because they would be genetically identical to their own. They want to cure diseases, not create cloned humans.

What Clonaid said it did is reproductive cloning, which creates humans but has no role in curing disease. Please, scientists plead with the public, don't tar us with the same brush.

"A knee-jerk reaction to Clonaid's claims could set back much important medical research for years," said Dr. Albert H. Teich, head of the Directorate for Science and Policy Programs at the American Association for the Advancement of Science.

For all the handwringing by scientists, you might think that therapeutic cloning is on the verge of curing a disease or two.

But that is not the case.

Therein lies a familiar problem for scientists — that of treading the fine line between touting the promise of the work, at least enough to gain public support and money, and being honest enough about the hurdles that lie ahead.

Despite optimistic statements about curing diseases, almost all researchers, when questioned, confess that such accomplishments are more dream than reality.

Someday, if therapeutic cloning goes well, scientists would take a few cells from a person with a disease, say diabetes, and use them to make an embryo that would have the same genes as the sick person. Implanting that embryo in a woman might enable it to grow into a baby who is a clone of the sick person.

Instead, the embryo would grow in the laboratory for about five days to the blastocyst stage, the point at which the embryo has two distinct cell types. It consists of a hollow ball with another ball of cells inside, known as embryonic stem cells. They, in theory, could develop into any of the body's specialized cells. The other embryo cells would be discarded.

In the case of a diabetic, scientists would prod the stem cells with an as-yet-undefined cocktail of chemicals so they would grow into islet cells of the pancreas. That could replace those lost to the disease. Voilà, a cure.

But no one has yet made a cloned human embryo. In two reported attempts, one by scientists at Advanced Cell Technology and the other by scientists in China, the efforts utterly failed. The eggs died almost immediately and no cloned embryos were produced.

"It's just a big failure," said Dr. Richard Schultz, a developmental and reproductive biologist at the University of Pennsylvania.

As it turns out, cloning is not even the first hurdle. Scientists often find it impossible even to extract and grow stem cells from a normal human blastocyst.

"Forget cloning, just to get human stem cells is not trivial," Dr. Schultz said. "They are difficult to generate and difficult to maintain."

Dr. Robert Lanza, the scientist at Advanced Cell Technology who tried to generate cloned human embryos, agreed that getting stem cells is a challenge in itself. "I know some in the field who have tried with dozens and dozens of embryos, without success," he said.

What about animal research? Can scientists take embryonic stem cells from mouse blastocysts, for example, and use them to cure diseases in mice? Not yet. Questions remain, including how to induce stem cells to grow into the precise type of cell needed, then how to persuade those cells to function properly. For example, what if islet cells, derived from stem cells, are inserted into a diabetic's pancreas and then go into overdrive, churning out too much insulin? Once the cells are in place, they can't be plucked out.

It will take years and much federal money, many predict, before therapeutic cloning has a chance of succeeding. For now, Dr. Schultz said, the promise is all in the distant future. Therapeutic cloning, he said, "is literally in an embryonic stage."