GENE THERAPY
Medicine For Your Genes

The Topic In-Depth

Editor's Update
by Sophia Koliopoulos
(October 2001)

Since 1998, when The DNA Files reviewed the state of gene therapy, several patients seem to have benefited from gene therapy. Three young children with a severe immune deficiency were reported to have been helped by gene therapy in 2000. Early-stage studies have also shown promise for using gene therapy to treat patients with hemophilia.

The safety of gene therapy continues to be tested on patients with skin cancer, head and neck cancer, diabetes, Parkinson's disease, certain forms of heart disease, and other life-threatening diseases. The National Institutes of Health, other federal agencies and the pharmaceutical industry currently fund more than 50 gene therapy clinical trials around the world.

And scientists continue to explore a variety of "vectors" for delivering genes specifically to target tissues in the body. So far, most gene therapy approaches have relied on modified viruses to carry genes to target cells. The basis of this approach is that once therapeutic genes are delivered to target cells, the cells' normal biological processes take over, using information encoded within the gene to generate substances to restore health.

In this way, therapeutic viruses carrying "suicide genes" have been used successfully in animal experiments to kill uncontrolled growth like cancer. Conversely, other types of genes have been used safely in animal and human studies, including the trials of patients with severe immunodeficiency or hemophilia, to help immune cells and other cell types proliferate and promote health.

Yet gene therapy is still a along way from becoming widely available, as many people had predicted it would be by 2001: there is still no gene therapy treatment on the market for any disease.

Success in developing vectors that can safely and effectively deliver genes to target tissues and not to other parts of the body has proven to be the biggest challenge to progress in gene therapy. And along with sporadic technical successes, there have been serious medical and social setbacks in the past few years.

The 1998 death of Jesse Gelsinger, which resulted from gene therapy gone awry, has heightened public awareness of the risks of participating in gene therapy clinical studies and, even further, in all types of clinical trials. Federal, institutional and professional groups, including medical journal editors, have since increased their scrutiny of the process of regulating and reporting on results from human research.

Concerns about germ-line gene therapy, a set of strategies which would change genes in not just one patient but his or her offspring as well, resurfaced when researchers in New Jersey announced over half a dozen babies were born following a technique called ooplasmic transfer.

In this technique, some of the contents of a healthy donor cell - including gene-carrying mitochondria - are injected into the egg of a woman with infertility problems. Thus, ooplasmic transfer may be considered to be a form of germline gene therapy because it allows for extra genes (from the donor cell mitochondria) to be incorporated into the germline of the new individual.

The American Association for the Advancement of Science has cited serious ethical concerns in making inheritable genetic modifications in humans. These concerns include the value of genes, impact on the gene pool, and lack of consent by future generations.

Ethical debates over the appropriate use of embryonic stem cells have, at least in the summer of 2001, taken over the headlines in the U.S. The questions at hand, nonetheless, are very similar with those raised by many new medical technologies, including gene therapy. How fast should science be allowed to progress? What risks should we, as a society and as individuals, take? How can we agree on ethical guidelines to safeguard society - and balance them with improving the health of individuals?

Gene Therapy: The Topic In-Depth
by Sally Lehrman
(Originally published in November 1998)

The Promise

Gene therapy, one of the most futuristic applications of gene research, easily captures the imagination. Doctors would repair natural processes at the first point they started to go wrong, using the internal coding of cells instead of surgery, synthetic drugs or radiation. They would fix genes that could lead to trouble, mending the DNA to correct inherited disorders and ward off widespread killers such as cancer and heart disease. But a technology that enables scientists to move around, add or shut down genes - to some degree the essence of our physical being - also awakens dreams and fears of a gene-by-gene re-creation of human beings in the image of science. The prospect of choosing or changing genes to fit a model of ideal health calls into question humanity's understanding of our very identity.

Scientists have tended toward the optimistic extreme when describing the potential capabilities of gene therapy. The media generally have been eager to tag along. Science fiction writers have taken up the vision, creating whole communities reliant on the manipulation of DNA. In Octavia Butler's series Xenogenesis, an alien species of gene traders explore the universe for interesting characteristics and exchange genetic material with humans and other species they encounter. In the Beggars Trilogy by Nancy Kress, a genetically engineered group of humans invent the ultimate gene therapy machine to scour the body of all renegade DNA - thereby ridding people of everything from cancer to the common cold and erasing illness and hunger around the world.

The Progress

Nearly a half century after the idea was born and eight years after the first sanctioned experiment, however, gene therapy remains an infant science. So far no patient has been cured by adding or altering genes, and the technology is a long way from becoming commonly available. More than a thousand patients have participated in gene therapy experiments, but it's still not clear whether any have been helped.

One reason is that only the very sickest people may participate in gene therapy trials, so long-term recovery isn't likely from the start. Since the treatment is still experimental and risky, patients usually must have exhausted all other options. Plus, when possible, they often continue to receive conventional medicines. This makes it hard to tell whether someone has been helped by the gene therapy. Finally, there is still much to be learned about how and when genes act, and exactly how to repair, replace, or interfere with them. Gene therapy is a very complex technology; it has proven quite difficult to deliver functioning genes where they can do the most good in the body. A gene in the wrong place could disrupt the action of other genes and cause harm. And even in the right location, it may not do its job or be able to continue working for long. (Ideally, it would survive a lifetime and pump out health-restoring products at a known or controllable rate.)

Tinkering with Misfiring Genes

In the early days of gene therapy, researchers thought that rare genetic diseases caused by mutations in a single gene would be the best and easiest target for gene therapy. The very first treatment to be tested involved restoring the function of a misfiring gene that caused adenosine deaminase deficiency, a life-threatening immune disorder. Adding a working copy of the problem gene to even a few cells, scientists reasoned, might be enough to cure people or at least extend their lives.

At the same time gene therapy pioneers began to consider ways to study and treat more common diseases, such as cancer. Correcting a single gene error may not be the only way to address disease at the genetic level, they speculated. Rather, making small adjustments in the instructions inside cells might change the course of illness stemming from complex interactions of genes. In 1988, Steven Rosenberg of the National Institutes of Health, in collaboration with his colleagues W. French Anderson and Michael Blaese, won the very first approval to study such a prospect - to use a nontherapeutic "marker" gene to learn about the immune system's natural activity against cancer. This gene tagged cells with a biological marker, highlighting their path as they moved through the body. Rosenberg later would use this information to plan a gene therapy that could boost the immune response to malignancy.

Today, scientists have begun to set aside single gene disorders in favor of addressing such multifaceted diseases, which affect more people. The shift will likely accelerate, since from a commercial point of view, these diseases represent a greater opportunity for profit. As geneticists learn more about the ways diet, environmental factors, and even viruses and bacteria interact with genes to cause disease, they are thinking about using gene therapy to interrupt these processes. They also have begun developing ways to address heart disease through fixing genes.

Gene therapy researchers use knowledge about the role genes play in cancer to try to halt the process of unbridled cell growth and division. Some aim to protect bone marrow cells against harsh chemotherapy drugs, while others attempt to make tumor cells more sensitive to cancer-killing treatments. As companies become more involved in such research, they are focusing on diseases they know represent large market opportunities. Of the 244 gene therapy proposals that had come before the NIH for review by March, 1998, 147 targeted cancer, 33 were for single-gene disorders, and 23 addressed AIDS.

Strategies for Gene Delivery

Before companies or university labs can use gene therapy effectively, they need to figure out how to deliver genes into cells efficiently. This isn't easy, because cells are selective about what they allow inside. Then, once they've entered, the genes must stay active, manufacturing regular amounts of the natural proteins that the body needs to stay healthy. Scientists are studying three methods of gene delivery at the moment - chemical, physical and viral.

Chemical methods trick cells into swallowing DNA by mixing the gene of choice with substances that cells normally ingest, such as calcium phosphate. Or sometimes researchers will package the DNA into liquid spheres called liposomes. These natural messengers fuse with the cell membrane and dump their contents into the cell.

Physical methods may bore holes in the cells in a technique called electroporation, poke through with a microscopic needle, or bombard the cell membrane with tiny gold or tungsten particles shot out of a gene gun. Another method, called naked DNA, doesn't get inside the cell at all. Instead, researchers inject plasmids, circular loops of DNA that multiply on their own, into the bloodstream or the affected tissue. The therapeutic genes inside these plasmid loops operate only for a short time, behaving much like an injected drug.

Viruses may turn out to be the best way to carry genes into cells for long-term activity. These small sequences of DNA or RNA, packaged neatly inside a protein coat, already have developed their own ways to trick their natural hosts into letting them inside. Gene therapy researchers take advantage of a virus' ability to invade cells, but disarm it by slicing out the genes that enable it to reproduce and harm its host.

Retroviruses, a group that includes HIV, were the early favorite in gene therapy. They can integrate themselves randomly into a host cell's genome and quietly replicate along with it. The integrated DNA is then passed on every time the infected cell divides. While retroviruses make attractive delivery vehicles, researchers worry that they might cause trouble by disrupting an important human gene, or even by spontaneously becoming pathogenic once more. Plus they will only enter cells that are dividing, so these invaders aren't helpful in treating cells (like those in muscles) that don't multiply.

Adenoviruses, the viral family that brings you the common cold, show promise as a way to treat genetic diseases (such as cystic fibrosis) that affect tissue in the respiratory tract. Adenoviruses naturally home in on the cells lining the lungs, which they infect fairly easily. Then, instead of integrating into their host's DNA, they inhabit the cell and pump out their own gene products.

At the moment, the most common way of introducing genes into the body is to remove a small amount of the tissue being treated (usually blood cells), use an altered virus to deliver genes into those cells, and then return the transformed material to the patient. This is known as ex vivo gene therapy because it takes place outside the body. In the future, many hope that most gene therapy will be easier, less expensive and conducted in vivo. Researchers would use injections, topical creams or inhalants to insert genes directly into the tissue without removing it from the patient.

The First Attempts

The first federally sanctioned attempt to transfer genes into humans took place in 1988. Steve A. Rosenberg and his colleagues at the National Institutes of Health placed what is known as a marker gene into immune cells taken from the tumors in cancer patients. In this study, the group did not try to introduce any genes that would treat the disease. Instead, they tested their ability to deliver genes that would help them trace the natural activity of tumor-fighting immune cells.

Then in September 1990, W. French Anderson, R. Michael Blaese, and Ken Culver at NIH became the first scientists to test gene therapy in an approved experiment, or clinical trial. They hoped to help children who had adenosine deaminase (ADA) deficiency, an extremely rare condition that often results in death because the immune system fails. Four-year-old Ashanthi DiSilva was the first patient. The study later added another young girl named Cynthia Cutshall.

Both children happened to be born with misfiring copies of the gene that makes ADA. Without this substance, the immune system can barely operate and has trouble coping with the most benign infections. ADA deficiency can be treated with a bone marrow transplant from a matched donor, usually a brother or sister. But this operation is very dangerous and often doesn't work. Plus it's important to get as perfect a match as possible. If a donor cannot be found, patients must take a form of ADA derived from cows called PEG-ADA.

When the girls went into the gene therapy trial, they were both on PEG-ADA but their immune systems were weak. About every month for almost a year Anderson and his colleagues took blood samples, used modified retroviruses to carry the ADA gene into immune system cells (called T-cells) from the blood, then returned the cells to the children's bodies.

After several DNA deliveries, Ashanthi seemed to begin producing at least some of her own ADA, although the effect didn't last. She still returns for occasional treatment. Overall, she is doing well and going to school. Cynthia did not seem to take up the inserted ADA gene as well and produced hardly any of her own ADA. Still, her immune function improved after getting the extra T-cells. Both Ashanthi and Cynthia are still taking PEG-ADA, though less than before, making it difficult to tell which of the two therapies has been more helpful.

Cystic Fibrosis

In the ADA trials, researchers removed cells from the children and then delivered new genes into them. The first attempts to insert genes directly into the body involved cystic fibrosis, the most common hereditary genetic disease among Americans of European descent, a few years later. People with cystic fibrosis have a mutation in a gene called CFTR, which regulates ion balance in the lungs. Their air passages clog up with thick mucus and easily become infected; they also may suffer from digestive problems and damage to their liver, spleen, and pancreas. Those with severe cases of cystic fibrosis have an average life expectancy of about 30 years, although that figure is improving with better treatment and management.

Ronald Crystal (who was working at the National Heart, Lung and Blood Institute at the time) conducted one of the earliest gene therapy trials for cystic fibrosis in 1993. He and his colleagues used a nasal spray to shoot adenoviruses carrying a working version of CFTR into patients' air passages. They hoped the gene could restore lung cells to healthy operation. Some critics worried that delivering genes this way could infect clinicians (or anyone else in the room) as well.

Crystal found that small doses did not result in much absorption of the functioning CFTR gene. But when he increased the dosage, patients suffered an allergic reaction. Five came down with lung infections. On the whole the experiment was a treatment failure, but the researchers said they were able to get useful information out of the study.

Industry

Industry was quick to recognize the commercial potential of gene therapy. Mirroring the trend in other areas of biotechnology, however, much of the initial enthusiasm has waned (and venture capital funding has decreased somewhat) now that the difficulty of developing the technology has become obvious. Still, companies spend more money on gene therapy than the National Institutes of Health and have considerable influence on the direction of research.

About 20 biotech companies specialize in gene therapy programs. Many, such as Genetic Therapy Inc. (GTI) of Gaithersburg, Maryland, were founded on science developed with public funds at universities or the National Institutes of Health. GTI was started through the first-ever transfer of rights for inventions developed at NIH to a single private company -in its case, French Anderson's technology for gene therapy. The deal was quite controversial and the original agreement included a clause requiring that any resulting product be priced "reasonably."

That condition has since been removed. Company executives, pointing out the mission of public research institutions to push their inventions into commercial development, say the change has eliminated a major stumbling block. They add that negotiations for technology transfer can still be arduous.

With licensing royalties in mind, universities and other institutions have begun pursuing ownership rights to federally sponsored research more aggressively. Several fundamental patents now complicate researchers' ability to test their ideas. As a result of the NIH rights transfer to GTI, for example, the Maryland company has the exclusive license to gene therapy performed in cells outside the body. The University of Michigan, which won the patent to any viral vector carrying the CFTR gene, has licensed it exclusively to Genovo Inc., a gene transfer technology company in Philadelphia, Pennsylvania.

GTI was later acquired by Sandoz, the Swiss pharmaceutical company that merged with Ciba Geigy to become Novartis. Other major industry players include Chiron Corp. (Emeryville, California), Vical (San Diego, California), Viagene (San Diego, California, now owned by Chiron), SyStemix (Palo Alto, California, now also a part of Novartis), Targeted Genetics Corp. (Seattle, Washington), Enzo Biochem (Farmingdale, New York), Somatix (Alameda, California, which merged in 1997 with Cell Genesis in Foster City, California), and Megabios Corp. (Burlingame, California), which recently acquired GeneMedicine Inc. of Woodlands, Texas.

Regulatory Safeguards

Before any gene therapy experiment in humans can begin, researchers first need to pass several layers of review. They must first demonstrate their ideas in a test tube, then evaluate the treatment's safety and effectiveness in animals. If the animal data looks good, success in humans isn't anywhere near certain. But positive results do give enough reason to consider the therapy for people.

Once researchers think they're ready for human studies, they must present their proposal to the Institutional Review Board and the Internal Biosafety Committee of the university or company sponsoring the research. These groups typically consider the safety of the research, the balance of risk to benefits for the patients involved, and whether participants will be adequately informed of the risks they're taking.

Following internal review, the protocol may need approval by the National Institutes of Health's Recombinant DNA Advisory Committee (RAC). The NIH created this committee in 1974 to consider ethical, scientific and safety issues related to recombinant genetic experiments that receive federal funds.

At first, the RAC reviewed all federally funded gene therapy trials. But in June 1996, NIH Director Harold Varmus recommended that the RAC be dismantled and that all subsequent proposals be passed directly to the Food and Drug Administration in order to speed research. He planned to give the FDA sole responsibility for scientific scrutiny of planned studies, with the NIH committee taking up gene therapy-related social and policy issues. But complaints by a number of scientists, ethicists and others forced Varmus to reconsider. Instead of eliminating the RAC's oversight responsibilities, he cut the size of the committee from 25 scientists, lawyers, ethicists and consumers to 15. They limit their focus to novel proposals that they agree merit public discussion, and no longer have authority to block experiments. The committee's meetings are open to everyone.

Companies who don't receive public funds don't have to get approval from the RAC. But some ask for it anyway because they want extra scrutiny, which can help win public acceptance for their work.

All gene therapy research proposals, whether government-funded or private, have to be reviewed by the Food and Drug Administration. The FDA is primarily concerned with the safety and efficacy of genetically engineered therapeutics, the safety of the manufacturing process, and the controls that would ultimately insure product quality. Some observers express concern that the agency won't address ethical issues and is too inexperienced with gene therapy to evaluate it effectively. Since the FDA approval process is confidential, meetings and documents are not open to the public. Studies that solely undergo FDA oversight and so don't involve any public review include those not considered novel, and those funded solely by companies.

All new drugs, including genes and vectors used for therapy, must go through three phases of human testing, starting with small safety trials and ending with much larger studies to evaluate how well the treatment works. When the third level of testing is complete, the data can be used to support a request for regulatory approval to begin sales.

At least twice in the history of gene therapy, maverick researchers have tried to sidestep regulators or ignored the precautions urged by their colleagues. In 1971, Stanfield Rogers of Oak Ridge National Laboratory was the first to transfer animal genes into humans. Using a rabbit virus, he tried to restore the ability of two German sisters to make their own arginase, an enzyme that breaks down the amino acid arginine. Too much arginine had caused mental disabilities and epilepsy in the sisters. The experiment didn't work, possibly because Rogers had used a very small dose. The scientific community pounced on Rogers, accusing him of unethical behavior for independently going ahead with a premature and potentially dangerous therapy.

Nearly a decade later, Martin Cline became the first person to attempt gene therapy by putting a normal copy of a human gene into people who lacked it. Cline wanted to treat beta thalessemia, a debilitating genetic blood disease marked by anemia and the buildup of toxic amounts of iron, by inserting into patients the gene that codes for human hemoglobin. But Cline first had to get permission from his employer, the University of California at Los Angeles. After school officials had been deliberating for a year, Cline, frustrated, went ahead and did the experiment in Israel and in Italy. Cline had already treated two patients there when the word came back from Los Angeles: permission denied. When it was discovered that Cline had gone overseas, skipped all of the U.S. processes set up to safeguard genetic experimentation, and even lied about the genes he was using, it set off a furor. Cline resigned from his post as hematology-oncology chief at UCLA and lost most of his funding. No one tried gene therapy again for another decade.

The Germline Debate

There are potentially two types of gene therapy: germ-line and somatic cell. All gene therapy trials now under way and formally under discussion are somatic. They aim to introduce genes into regular body cells but not sperm, eggs or early embryonic cells. Genetic material added to these cells can help patients during their lifetimes, but will not be passed on to their children or future generations.

Germ-line gene therapy involves genetic manipulations of sperm, egg, or early embryonic cells. Because these cells have the capacity to create a whole new person, if their genes are altered, that change will be passed on to future generations. So far, no one has proposed human studies for germ-line genetic manipulation, although some researchers support the concept. They hail the prospect of eliminating disease not only for the life of the patient, but for their offspring. In the long run, advocates say, this approach might be less expensive than somatic gene therapy or the traditional lifelong treatments for chronic genetic conditions. Finally, some argue that scientific freedom - in this case, the ability to pursue germ-line studies - is an important value in our society and must be allowed to express itself within the boundaries of humane research.

Germ-line gene therapy has many opponents, however. There is considerable risk for the developing embryo, in part because scientists lack the technical skills to insure precise insertion of a gene without disrupting other genes. Researchers also don't know much about how genes, even "defective" ones, work together.

The Council for Responsible Genetics in Cambridge, Massachusetts, opposes experimentation in this area mainly on the grounds that it is premature and could eventually lead to eugenics, or reproductive policies intended to promote preferred characteristics: ADA deficiency today, baldness tomorrow. This issue is compounded by the fact that the patients involved - fetuses and future generations yet to be conceived - have no ability to learn about the risks and benefits of the treatment and either reject it or grant their approval. If germ-line gene therapy proves to have disastrous results, opponents ask, who will be accountable to the children of the future?

Although there is an informal, self-imposed moratorium on germ-line gene therapy in humans at the moment, animal scientists frequently use the technology to refine livestock and to create animal models for scientific research. The continuing improvement of germ-line techniques makes it likely society will have to confront the idea of using this treatment in people someday soon. The RAC has decided to start discussing the scientific, safety and ethical implications of germ-line gene therapy, although the group is careful to avoid the appearance of endorsing this goal.

Worries

Many are wary of gene therapy because of its futuristic implications. People raise religious and moral concerns about tinkering with complex natural processes that humans may never fully understand. Even researchers predict that within a couple of years, some of their number will probably be proposing gene therapy to "improve" the human body by, say, restoring lost hair and strengthening muscles. The treatments may at first address only conditions caused by disease, but over time, they'll be more easily applied for enhancement purposes. In September 1997, gene therapy pioneer French Anderson warned government regulators to be alert for experiments that lead in that direction.

The practice of using disarmed viruses and other delivery vehicles to introduce altered genes into humans has raised its own concerns. It's possible that introducing pathogens into people could backfire and trigger the development of dangerous new diseases, even though the organisms have been changed to render them harmless.

Still, work has proceeded in the hope of making important breakthroughs in treating disease. Regulatory agencies have allowed researchers to go ahead very cautiously with clinical trials. In most cases, the experimental studies offer a last-ditch chance to save people who have run out of options.