Dramatic achievements in genetic engineering are rapidly revealing the secrets of how genes work. Some researchers are probing into its social and economic benefits. For example, they are trying to produce more meat and milk from genetically engineered cattle. Moreover, current advances bring medicine closer to curing hereditary illness in humans, instead of merely treating its symptoms, as medical practices are now restricted to doing.
However, many people are worried: what if an evil dictator produces hundreds of copies of himself through cloning in order to take over the world or grieving relatives use cloning to bring their loved ones back to life? The truth is there is no chance that any copy of a human being would be identical either physically or mentally, any more than children are identical to their parents.
Scientists quite reasonably point out that human genetic engineering still faces immense technical obstacles. Getting a new gene into a cell is just the first of many giant steps that are required. Like NASA engineers sending a space probe into another planet, researchers must not only deliver a gene to their target, but then turn it on and get it to work properly.
It was just these problems that thwarted the controversial work of UCLA's Dr. Martin Cline. In July 1980, he tinkered with the bone marrow of two young women suffering from thalassemia, a fatal defect in hemoglobin production. The idea was to give a few of their marrow cells normal genes in hopes that the repaired cells would multiply and cure the inborn defect. It does not appear to have worked. When the experiments were revealed the following autumn, Cline was asked to resign his post as head of his division. The following year, the National Institute of Health stripped him of two federal grants — he had four — worth more than $190,000. The unprecedented punishment was a stern warning to researchers to move slowly in testing gene therapy on people.
Cline's approach is sadly limited as it can apply only to tissues whose cells, like those of bone marrow, continue to divide throughout life so that the genetically engineered cells can eventually replace the natural, defective ones. Many organs produce cells only intermittently or, like the brain, stop altogether once they are fully developed. For defects in these organs, other methods are needed. One hope is to insert the desired gene into a virus that would infect the afflicted tissue and use the virus to get the gene to its target — cells with defective genes.
However, the method, called viral transduction, is problematic. As Thomas Caskey, professor of medicine and biochemistry at Baylor College of Medicine, sees it, "the problem is to engineer a virus so that it will be defective, that is, will not cause a disease, yet will carry the desired gene into a certain
tissue and reproduce it just as disease-causing viruses reproduce their own genes. This is a formidable task, but not insurmountable."
Perhaps riot, but all forms of gene therapy now being explored present problems that will keep them from being widely used. Caskey says "people have gotten the impression that this work is going to lead to miraculous cures, but it is really going to be applicable only to a small category of patients with rare diseases." The trouble is that the gene therapies now under development can work only with inherited diseases limited to a single tissue and there are relatively few of such diseases. Most genetic, disorders have far wider effects. Cystic fibrosis, for example, affects the lungs, intestinal tract, pancreas and sex organs. So far, there is no way to deliver a 'good' gene to all these tissues at once.
Other defects present even more difficult problems. Down's syndrome, the most common cause of severe mental retardation, is genetic, but it is not caused by a single gene. Instead, Down's patients carry an entire extra chromosome, a package of DNA comprising several thousand genes. No one has been able to devise a way to remove that extra chromosome from every cell in a child's body, or to undo the damage it wreaks on the brain. Nor will gene therapy avert such disorders as diabetes, heart disease and high blood pressure. These are all produced in large part by environmental factors, but they develop most often in people genetically predisposed to them. These conditions, too, probably involve more than one gene, medical geneticists believe.
Getting foreign genetic material into a complex organism is no easy task. Most scientists have simply injected the new genes into a fertilized egg through a glass needle finer than a hair. They call this technique microinjection. The process is traumatic and many of the eggs die. However, some survive, and when transferred into the uterus of a host mother, they can live out lives that appear otherwise normal.
The first success of this kind was reported by three Yale scientists, who were able to identify foreign genes in one, or perhaps two, of 150 newborn mice grown from microinjected eggs. Of crucial importance for the future of embryo genetic engineering, those mice passed the gene along to their children and grandchildren. However, it is not enough simply to get the genes into the animal. Once there, they must behave normally and this involves two more problems. The first problem is gene expression: a gene 'expresses' itself by making the protein it is supposed to make. The other problem is gene regulation: a gene must not only make the right protein, but turn it out at the right place and time and in the right amount.
If putting a foreign gene into an embryonic mouse is no easy task, getting the gene to express itself is far more challenging. Since the Yale announcement, a number of research groups have reported
successful gene insertion and even inheritance. However, only three have claimed that the foreign genes in their engineered rodents expressed themselves.
These successes in engineering other species force us to wonder about the genetic manipulation of Homo Sapiens. As we want to heal hereditary illness, we are slipping toward the genetic engineering of human beings almost without realizing it. Nonetheless, genetic engineering will not be forced upon us as a few social forecasters have led us to believe, by a new Hider wishing a mindlessly obedient populace. We will seek out, applaud its humane goals and espouse it greatly.