The False Promise of "Therapeutic" Cloning
Moral considerations aside, human cloning is not going to lead to useful medical treatments.
Mar 11, 2002, Vol. 7, No. 25 • By WESLEY J. SMITH
Contrast that decidedly mixed result with a similar but far more successful experiment involving adult stem cells in rats reported by the Proceedings of the National Academy of Science, December 19, 2000. Researchers at the University of California, Irvine, reported that they were able to stimulate the growth of (adult) neural stem cells in rats suffering from Parkinson's-like symptoms. These cells then migrated to the damaged area of the brain and differentiated into the types of neurons needed to replace the missing/damaged brain cells. An encouraging 80 percent of the rats in the experiment--more than in the experiment using embryonic cells--received therapeutic benefit. Moreover, none developed tumors. The experiment was so successful the scientists reported that their research presented "significant implications with respect to the development of treatments" for both brain injuries and degenerative diseases. They further predicted that their approach could offer "an alternative strategy" to using embryonic cells to treat such ailments.
Tissue rejection presents nearly as high a hurdle to surmount. Unless researchers find a way to prevent the body's immune system from attacking embryonic cells as "foreign," patients receiving embryonic stem cell therapies will require a lifetime regimen of strong drugs to suppress their immune systems. These medications often produce serious side effects such as problems with wound healing, a propensity to suffer opportunistic infections, skin malignancies, and drug-related toxicities.
Researchers have endeavored mightily to solve the problem of tissue rejection, so far without success. One seemingly promising approach--removing from the cells the molecules that stimulate rejection--did not prevent rejection in animal skin graft experiments. So now, back at their drawing boards, researchers contemplate inserting desired genes into the embryonic stem cells to fool the body into thinking that the injected cells are its own. Whether this can be done is not known, but learning how to manipulate embryonic stem cells genetically to thwart rejection is clearly a problem that is also going to take a very long time to overcome--assuming that it can be solved at all.
THE TISSUE rejection conundrum brings us back to human therapeutic cloning. Cloning advocates argue that they must be allowed to legally clone human embryos in order to overcome the rejection problem described above. This is how the process of therapeutic cloning would work: A patient requiring embryonic stem cell therapy would donate his own genetic material, say from a skin biopsy, which would then be used to clone an embryonic identical twin of the patient. The clone embryo would be developed to the blastocyst stage and then destroyed and harvested for the stem cells. The harvested stem cells would then be transformed into the type of tissue required for the patient's treatment. Researchers expect that the clone's virtually identical genetic makeup would fool the patient's immune system into perceiving the injected tissues as "self," thereby overcoming the rejection problem.
That is the theory, and it has been swallowed hook, line, and sinker by many in the media, government, and patient advocacy groups. But a close look at the realities of this scenario shows that it is smoke and mirrors. Even if scientists are ever able to develop a human clone to the blastocyst stage (not a given), and if these clones are not genetically defective (most mammalian clones created to date have had serious genetic anomalies), human cloning will still not be able to help the millions of patients who desperately hope to benefit from clone stem cell therapy.
Here's why: Cloning involves something called nuclear cell transfer. In humans, this is accomplished by removing the nucleus from a human ovum and replacing it with genetic material removed from a cell of the clone donor. The genetically modified egg is then stimulated with an electric current. If it works, a new human organism that is virtually identical to the clone donor comes into being and begins embryonic growth.
There are two absolutely essential ingredients to successful nuclear cell transfer cloning. One is a somatic cell from the clone donor. No problem there. The other is the egg. And here is where therapeutic cloning hits a brick wall: We can only create as many patient clones for therapeutic use as there are eggs available. Thus the entire utility argument over therapeutic cloning boils down to one crucial and unavoidable question: Where are we going to get the eggs we would need to treat the millions of patients who would supposedly benefit from clone embryonic stem cell therapy?