Therapeutic Dreaming: The false promise of experimental cloning.

Polls show that most Americans want to ban all human cloning. President Bush is eager to sign such a measure into law. The House has twice enacted a strong legal prohibition with wide, bipartisan votes. But cloning advocates have so far blocked passage of a ban in the Senate (Brownback/Landrieu) by asserting that "therapeutic cloning" might someday provide stem cell treatments for horrible illnesses such as Parkinson's and multiple sclerosis. (I believe the term "therapeutic cloning," is loaded and misleading. However, I use it here because the term is currently part of the popular lexicon.)

According to the Biotechnology Industry Organization, the biotech industry's lobbying arm, here's how therapeutic cloning would work:

Suppose a middle-aged man suffers a serious heart attack while hiking in a remote part of a National Park. By the time he reaches the hospital, only a third of his heart is still working, and it is unlikely he will be able to return to his formerly active life. He provides scientists a small sample of skin cells. Technicians remove the genetic material from the cells and inject it into donated human eggs from which the chromosomes have been removed. These altered eggs [actually, cloned embryos] will yield stem cells that are able to form heart muscle cells. Since they are a perfect genetic match for the patient, these cells can be transplanted into his heart without causing his immune system to reject them. They grow and replace the cells lost during the heart attack, returning him to health and strength.

This scenario is typical of the hype that has pervaded discussions of therapeutic cloning over the last few years. But now, cold reality is setting in. Biotech researchers and cloning advocates are admitting difficulties in their professional journals, if not yet in the popular press, that make therapeutic cloning look more like a pipe dream than a realistic hope.

Consider a paper by Peter Mombaerts of Rockefeller University, "Therapeutic Cloning in the Mouse," just published by the National Academy of Sciences (NAS). Mombaerts has been investigating therapeutic cloning techniques in mice. It has been tough going. Of these efforts, he sadly reports, "The efficiency, or perhaps better, the lack of efficiency thereof, is remarkably consistent." It takes about 100 tries to obtain one viable cloned mouse embryonic stem cell line.

Mombaerts notes that creating human cloned embryos using "nuclear transfer is unlikely to be much more efficient" than it is in mice, especially given that "the efficiency of nuclear transfer has not increased over the years in any of the mammalian species cloned." Nuclear transfer, more precisely somatic cell nuclear transfer (SCNT), is the same procedure used to create Dolly the sheep. The nucleus from an egg is removed and replaced with the nucleus from a clone donor's somatic cell, such as a skin cell. The modified egg is stimulated with an electric current. If the cloning "works," a cloned embryo is created that then develops just like a naturally created embryo.

Given the significant difficulties researchers have already had, deriving cloned embryonic stem cell lines is likely to be far less efficient in humans than it has been in mice (assuming that it can be accomplished at all).