On the Horizon
BY MICHAEL D. LEMONICK; ALICE PARK; CLARE THOMPSON Gene therapy and gene-based drugs are two ways we could benefit from our growing mastery of genetic science. But there will be others as well, including new kinds of vaccines, new sources of transplant tissue, even techniques doctors may someday use to stave off the aging process. Here are just a few of the remarkable therapies on the cutting edge of genetic research that could make their way into mainstream medicine in the coming years:
Tomorrow's Tissue Factory
While it's true that just about every cell in the body has the instructions to make a complete human, most of those instructions are inactivated, and with good reason: the last thing you want is for your brain cells to start churning out stomach acid or your nose to turn into a kidney. The only time cells truly have the potential to turn into any and all body parts is very early in a pregnancy, when so-called stem cells haven't begun to specialize.Yet this untapped potential could be a terrific boon to medicine. Most diseases involve the death of healthy cells--brain cells in Alzheimer's, cardiac cells in heart disease, pancreatic cells in diabetes, to name a few. If doctors could isolate stem cells, then direct their growth, they might be able to furnish patients with healthy replacement tissue.
It was incredibly difficult, but last fall scientists at the University of Wisconsin managed to isolate stem cells and get them to grow into neural, gut, muscle and bone cells. The process still can't be controlled, and may have unforeseen limitations. But if efforts to understand and master stem-cell development prove successful, doctors will have a therapeutic tool of incredible power.
The same applies to cloning, which is really just the other side of the coin. True cloning, as first shown with Dolly the sheep two years ago, involves taking a developed cell and reactivating the genome within, resetting its developmental instructions to a pristine state. Once that happens, the rejuvenated cell can develop into a full-fledged animal, genetically identical to its parent.
For agriculture, in which purely physical characteristics like milk production in a cow or low fat in a hog have real market value, biological carbon copies could become routine within a few years. This past year scientists have done for mice and cows what Ian Wilmut did for Dolly, and other creatures are bound to join the cloned menagerie in the coming year.
Human cloning, on the other hand, may be technically feasible but legally and emotionally more difficult. Still, one day it will happen. The ability to reset body cells to a pristine, undeveloped state could give doctors exactly the same advantages they would get from stem cells: the potential to make healthy body tissues of all sorts, and thus to cure disease. That could prove to be a true "miracle cure."
--By Michael D. Lemonick
Spiking the Potatoes
We all know that eating fruits and vegetables is good for us, but within the next decade we could be eating broccoli not just to make Mom happy but also as a way to deliver drugs that stave off infectious diseases or that treat various chronic conditions. "The idea of vaccinating people with edible plants is very new," says Dwayne Kirk of the Boyce Thompson Institute for Plant Research in Ithaca, N.Y. "But it's a lot friendlier than injections."Because their cells naturally produce large quantities of protein, potatoes and tomatoes seem for now to be the most efficient vehicles for the new approach. Instead of mixing viral or bacterial DNA in a formula for injection, for example, scientists could insert it into soil bacteria. When the bacteria are taken up by the plant, therapeutic DNA material is stitched into the plant's genome. Another method of getting genes into plants is to coat tiny particles of tungsten or gold with foreign DNA, then shoot the particles directly into plant cells. Either way, the plant's cells start to produce whatever proteins the new genes are designed to make. Immunization begins when the plant or its fruit is eaten, prompting the body to churn out the appropriate antibodies.
Plant-based vaccines are particularly attractive for Third World countries, where storage and distribution of drugs are a problem. Eventually, people in these areas may inoculate themselves against diseases simply by growing a crop of genetically engineered fruits or vegetables and eating a few several times a year.
The technique does not have to be limited to infectious diseases, however. It may even be useful for conditions such as Type I diabetes, in which a patient's own immune system destroys essential insulin-producing cells in the pancreas. For diabetics, eating insulin-bearing tubers could eventually train the body's defenses to stop reacting to insulin as if it were a foreign material, all without the bother--or risk--of a needle.
--By Alice Park
A Shot for Aging Body Parts?
Eight years ago, scientists discovered that the tips of chromosomes in tissue cells shorten each time the cells replicate--until a point is reached where the cells stop dividing altogether. That point, called the Hayflick limit, comes after about 50 replications, and may be at the heart of the process we call aging.Scientists have tried ever since to reactivate the enzyme that lengthens the tips, known as telomeres. Last January they succeeded: Andrea Bodnar and colleagues from the Geron Corp. in Menlo Park, Calif., activated the enzyme telomerase, extended the telomeres and lengthened the life-span of cells in culture by at least 20 divisions past the Hayflick limit. In November, Geron scored another first by reconstituting the telomeres of embryonic stem cells, which are renowned for their ability to turn into any type of cell, making it theoretically possible to rejuvenate parts of any organ with a simple injection.
Not everyone is convinced. Leonard Guarente, a specialist on aging from the Massachusetts Institute of Technology, observes that "telomeres seem to be important in getting cells to divide in vitro, but the onus is to show that short telomeres affect aging in vivo. I don't think we know that yet."
--By Clare Thompson
Beyond Vaccination
Most of us can't remember our first vaccination, but chances are, it was a shot filled with a crippled microbe or perhaps parts of the bug's proteins--just enough to produce a mild infection but not the full-blown disease. Immunizing people against a host of infections in this way has worked reasonably well for more than a century, but geneticists think they can do better.The vaccines of tomorrow are likely to be far more sophisticated concoctions, made up of snippets of raw DNA from the genome of a virus, bacterium or parasite. Using DNA, as opposed to proteins made by a microbe, elicits a more vigorous, aggressive response from the immune system. While most of the current vaccines do a good job of marshaling antibodies against an invading marauder, they often don't reliably coax the body into churning out killer T cells, the smart bombs of the immune system that strike at the offending microbes with great specificity. In early tests, DNA-based vaccines triggered both responses. For example, immunologists reported last fall that patients injected with an experimental DNA-based malaria vaccine showed not just malaria antibodies but also significant levels of killer T cells.
The potential goes beyond bugs. Because gene-based vaccines can easily be manipulated by adding or deleting DNA, doctors are applying the technique to treat various forms of cancer. The work is still limited to animals, but researchers have developed inoculations made up of tumor cells that act as a red flag to rally an animal's immune system against the tumor. "There is a long road ahead" for these cancer vaccines, says Duke University's Dr. Eli Gilboa. "But it's very promising."
--By Alice Park
© 1999 TIME Magazine
Última Atualização: 23/Set/99
