Science & Technology

Twin Freaks

Should Human Cloning be Banned? Maybe.


Human cloning is much in the news in the last few weeks. American and Italian fertility specialists announced that they are going to try to clone a human being sometime in the next 18 months at an unspecified location. The New York Times Magazine publishes "Lab of the Human Clones," detailing the plans of the Raelian UFO sect to clone a baby for a bereaved couple using cells from their 10-month-old baby who died from medical malpractice. Lurid headlines revealed that Australian researchers had used pig eggs to jumpstart human clones.

So, will there be human clones walking among us soon? Actually, of course, there are already plenty of human clones—identical twins. Identical twins have exactly the same genes.

One of the sad points that the New York Times article makes is that a lot people apparently have a deep misconception that cloning can bring back or replace a dead child or other loved one. They have bought into a popular but naïve idea of genetic essentialism—that genes are a recipe for making the same person. However, considering the case of the natural clones called twins helps us think clearly about what clones produced in vitro would be like. Twins are clearly distinct individuals with different points of view because twins have two different bodies and two different brains. Individuality does not reside in our genes, but in our brains and bodies.

A baby born through cloning would simply be a younger twin and would certainly not be the "same" person as the one who donated his genes. Some people oppose human cloning because they worry that clones' lives would be "less open" than people produced in the conventional way. Clones would be born with certain expectations, goes the argument, because people with their exact set of genes would have come before them. The novel genomes produced through sexual reproduction somehow confer more openness to the lives of their carriers.

This is genetic essentialism again. Even twin studies find only a 50 percent to 60 percent correlation in characteristics such as intelligence and temperament. Clones, who will be twins displaced in time, and who will therefore have very different life experiences, will likely share even fewer similarities with their genetic forebears. Anyone seeking to make exact duplicates of themselves or other loved ones through cloning is going to be very surprised.

Once the public understands more completely the limitations of cloning, e.g., one can't bring back the dead, human cloning will likely be used mostly by infertile couples who have no other choice for bearing biologically related children. For the rest of us, producing children the old-fashioned way will remain a lot more fun and a lot cheaper.

One moral objection often heard is that cloned children would be not ends in themselves, but would be means for their parents' self-aggrandizement. And sadly this may be true for some cloned children, but it also true for many children born today in the conventional way. On the other hand, the considerable emotional and financial investment that the parents of cloned children will be making indicates that these children will be very much wanted and treasured by their families.

So what about the Raelian cloning project, known as Clonaid? As described in the New York Times Magazine, it could work. One of the chief problems in cloning mammals so far has been its inefficiency—it takes a lot of failed embryos to produce one healthy cloned animal. Right now, only 2 percent to 4 percent of mammalian clones are long-term survivors, according to Massachusetts Institute of Technology Biology Professor Rudolf Jaenisch. Why such a low survival rate?

Jaenisch points out that many cloned mammal fetuses, e.g., pigs, calves, and sheep develop severe abnormalities. For example, some clones produce larger than normal placentas, others are born twice as big as normal, and some are born with deadly anatomical flaws, like enlarged hearts or defective kidneys.

Jaenisch suspects that the abnormalities result from parental genomic imprinting. Genomic imprinting is seen only in placental mammals (like humans) and is a result of the biological battle between the sexes. Males want their offspring to survive and so favor large progeny, females who need to reserve nutritional resources for themselves tend to favor smaller progeny. Thus imprinted paternal genes tend to promote fetal growth (such as fetal growth factor, Igf2) while maternal genes inhibit fetal growth (a gene known as H19). The size of offspring is determined by the balance of these factors.

To make a long story short, the problem with mammalian cloning may be that the genes from nuclei from mature cells may have lost their proper imprinting due to aging. So when these mature nuclei are inserted into enucleated eggs to produce embryos, their imprinting is wrong. Since there is currently no way to restore it, either paternal or maternal genes affecting fetal growth may end up being dominant creating the developmental imbalances seen in cloned animals. There is no test now available for checking on whether genes are properly imprinted or not, so bringing a healthy clone to term is largely a matter of chance.

In an attempt to overcome this problem and up the chances of successfully bringing a cloned baby to term, the Raelians claim to have lined up 50 female followers to act as surrogate mothers. Once they get started the Raelians say that they will monitor the implanted cloned embryos to make sure that they are developing normally, and will abort any which show signs of being abnormal. However, this primitive procedure could easily miss significant problems and thus risks bringing severely damaged children into the world.

It would be far better for research to continue on cloning other species until scientists understand why the abnormalities occur and can reliably correct them. For example, it might be possible one day to test a whole suite of pre-embryos and then implant only the ones with the proper imprinting. A good benchmark for deciding to proceed with human reproductive cloning would be when researchers are reasonably sure that clones would suffer no more likelihood of birth defects (about 2 percent) than do children produced by sexual reproduction, either in vitro or by conventional means. It's too early now.

One might counter that attempts at human reproductive cloning are little different from the first efforts at in vitro fertilization in which researchers implanted scores of embryos before the first one worked, bringing Louise Joy Brown, the first "test tube" baby, into the world. However, in the case of in vitro fertilization, animal research had identified no problems with increased birth defects resulting from the procedure. That's clearly not the case with mammalian cloning right now.

Should the federal government and other governments outlaw attempts at human reproductive cloning? Attempting to clone a human being now can be thought of as behaving so negligently that one has a high likelihood of maiming a person. It is appropriate to protect people from very negligent behaviors. However, bans unfortunately have a way of becoming permanent. How about a ban limited to five years during which research on cloning other mammals proceeds? One of the worst things that could happen to the hopes of infertile people who look to reproductive cloning as way of having kids, would be for today's hasty cloning efforts to produce defective children. Public revulsion at such an occurrence could set back reproductive cloning for decades.

While we wait for reproductive cloning to mature, there's no reason not to pursue therapeutic human cloning as rapidly as possible. Therapeutic cloning produces immunologically compatible tissues to treat patientes, not babies. Both Britain and Italy recently approved therapeutic cloning to create human embryonic stem cells. The stem cells would be produced using nuclei taken from a patient which would be inserted in enucleated human eggs. The pre-embryos would be allowed to develop to the blastocyst stage (no more than 14 days in Britain) at which point cells would be harvested and hopefully grown into tissues that would match the patient's immune system perfectly. Say, for example, the stem cells might be transformed into brain cells that could be used to treat a patient's Parkinson's disease.

By the way, the production of clones using pig eggs was done by researchers to see if such eggs can be used to create largely human stem cells for therapeutic use. The genes in these stem cells, and thus the tissues created using pig eggs, would be 97 percent human since most genes would be in the inserted human nuclei, while the remaining 3 percent would be pig genes found in the mitochondria which are the energy producing centers found outside a cell's nucleus. Producing human embryonic stem cells is currently limited by the availability of scarce human eggs. It's much easier to obtain pig eggs. Tissues produced this way might be good enough to use as replacement tissues in human patients. One other advantage could be that using pig eggs to produce such tissues might mollify prolife advocates who oppose using human embryonic stem cell research since the cells are not wholly human in origin.

Cloning to make human embryonic stem cells for therapeutic purposes is likely to become an issue sooner rather than later for the Bush Administration. Last year, the National Institutes of Health issued guidelines that would allow federal funding of research using (though not creating) human embryonic stem cells. Bush's anti-abortion allies mistake embryonic stem cells for babies, and thus oppose stem cell research (see " Petri Dish Politics"). However, proponents of stem cell research may have an advocate inside the Bush Administration inasmuch as Secretary of Health and Human Services, Tommy Thompson, although himself prolife, has, in the past, come out in favor of human embryonic stem cell research.

In addition, scores of patient advocate lobbying groups in Washington strongly support human stem research because of the enormous potential health benefits it offers to people suffering from diabetes, heart failure, Parkinson's, spinal cord injuries, Alzheimer's, and many more devastating diseases. So look later this year for a huge battle between the patient advocates and the prolife lobby later this year in Congress.