We cannot make a gene, we can only emulate one. In fact, scientists are less interested in reproducing actual genes than they are in copying the stuff genes are made of, clumps of DNA that are the blueprints for manufacturing proteins and chemicals imperative for life.
Formulated in 1985, the polymerase chain reaction (PCR) has enabled scientists to make millions of copies of a single strand of DNA in a matter of hours. The technology both hastens and consolidates the more onerous tasks of genetic mapping and sequencing that once could take several years to complete.
According to an article in U.S. News and World Report, PCR has been used to find genetic defects that cause some types of cancer, to design diagnostic tests for such illnesses as Lyme disease and AIDS, to identify criminals through samples left at crime scenes, and even to recover DNA from frozen mammoths, mummies and other long-dead organisms.
PCR works simply and efficiently. It takes its cue from a process already perfected by every living system: with the aid of an array of enzymes, a cell divides and makes an exact copy of itself, a phenomenon that occurs in the human body millions of times every second.
By heating a strand of DNA inside a test tube, a technician separates the DNA molecule and thus creates two complementary strands of the original double-stranded DNA. Next, short, synthetic DNA molecules known as primers are added to the test tube, at which point the process goes beyond the natural function of a living system. When the test tube is cooled, these primers anneal to one end of the targeted DNA fragment, and with the addition of nucleotides, instruct a DNA-building enzyme where to begin copying.
The result is two new double-stranded pieces of DNA with one end of the target fragment indexed by the primer. Thus there are now four target strands of DNA: the two parentals and the two progenies. The heating and cooling process is repeated and a second primer earmarks the other end of the targeted DNA, yielding an exact duplicate.
Since the process is one of geometric progression, where the number of DNA produced is multiplied exponentially with each repetition, one million copies of the DNA fragment are generated from twenty to thirty such cycles, enabling scientists to implement other tools of genetic engineering to research the specific makeup of the gene.
Transgenic manipulation is another method of producing new DNA. Using a microscope and microsyringe, foreign DNA is injected into animal egg cells so that it can be incorporated with human genes coded to produce either enzymes or proteins and so that its genetic performance can be studied. In what some analysts believe will grow into a $1.5 billion industry, transgenics are expected to help produce leaner livestock and to cultivate animals into “living factories” that manufacture protein-based drugs.
Surely the most ambitious and hopeful sign for the future of genetics is gene therapy, a process that permits “healthy” genes to be injected into the body to combat faulty ones.
According to Dr. Michael Blaese, a researcher at the National Institutes of Health (NIH) who is conducting the first human trials in gene therapy, by the middle of the twenty-first century the technology will “be used for treating everything from cardiovascular disease to senility to cancer as well as for many of the more than four thousand recognized inherited diseases, many of which have no effective treatment at all.”
Gene therapy brings scientists into the nucleus of the cell, where they can manipulate genetic material and explore methods of treating disease at its source. The ultimate goal of gene therapy is to treat inherited metabolic diseases prophylactically, in other words, to treat genetic deficiencies while a child is in utero so that chances of developing ailments such as cancer and heart disease are completely wiped out.
This would be accomplished by repairing a defective gene or adding one which would correct instructions delivered to the cells. Though still in an experimental phase, gene therapy is used to treat such diseases while they are in progress. Some experts believe that in utero gene therapy will be as common as amniocentesis, and instead of just learning about what deformities a child will be born with, or will be predisposed to, the disorders will be corrected before an infant takes its first breath.
As it exists today, gene therapy permits genetically altered DNA to be attached to a disarmed virus which serves as delivery truck to targeted cells. The NIH recently received government approval for what might result in the world’s first cancer vaccine. The vaccine will be made from the patient’s own genetically altered cancerous DNA, which is then reinjected into the body.
This form of gene therapy has been proposed for the treatment of advanced skin cancer, gastrointestinal cancer and kidney cancer.
