Giant Step for Gene Therapy

By LEON JAROFF

She weighed around 35 lbs., came down with an occasional cold or ear infection, and appeared to be a healthy four-year-old. But a dark cloud hung . over her future. She suffered from ADA deficiency, the rare, incurable and deadly genetic disease that shuts down the immune system -- a disorder similar to the one that in 1984 finally claimed the life of David, the famous but unfortunate "bubble boy." Only the weekly injection of a newly developed drug seemed to stand between the little girl and the same fate.

Last week, on the 10th floor of the massive Clinical Center of the National Institutes of Health (NIH) in Bethesda, Md., the still unidentified child assumed a historic role. In the first federally approved use of gene therapy, a team of doctors introduced into her bloodstream some 1 billion cells, each containing a copy of a foreign gene. If all goes well, these cells will begin producing ADA, the essential enzyme she requires, and her devastated immune system will slowly begin to recover.

The procedure lacked the drama of an epochal event. For 28 minutes, a grayish liquid in a suspended plastic bag dripped intravenously into the left hand of the child, who sat upright in a bed in the Clinical Center's pediatric intensive-care unit. That was it. But if the technique works as the doctors hope it will, the results could be little short of miraculous. Their patient may eventually begin to lead a normal life, without need for the costly and only partly effective drug now used to extend the lives of young victims of the disease.

The landmark experiment, led by Dr. W. French Anderson, a pioneering advocate of gene therapy, and Drs. R. Michael Blaese and Kenneth Culver, raised the curtain on what some experts believe will be a new era in medicine, when many previously incurable genetic diseases will be contained or even conquered. The long-term impact on society could be enormous. Up to 5% of the infants born in the U.S. are afflicted with often debilitating and sometimes fatal genetic diseases. In most cases, no effective treatment exists for these disorders, which are caused by one or more faulty or missing genes among the estimated 100,000 genes in human DNA.

Each gene consists of a segment of the DNA that is found in the nucleus of every one of the body's 100 trillion cells (with the exception of red blood cells, which have no nuclei). And each gene is responsible for the manufacture of a particular protein that contributes to either the structure or the functioning of the body. If the gene is defective, protein synthesis will be faulty and a deformity or genetic disease will result.

The object of gene therapy, simply put, is to provide the body with healthy replacement genes that can fulfill the intended role of defective ones. "Gene therapy is actually a sophisticated drug-delivery system," Anderson explains. "Anything given now by injection -- growth factor, factor VIII, insulin -- you can just engineer the patient's own cells to pump them out. The advantage is that it's a one-time treatment."

It all sounds rather straightforward, but medical researchers will have to overcome some formidable technological barriers before gene therapy becomes commonplace. Delivering replacement genes to particular cells, inserting them into the correct place in the DNA of those cells and then coaxing the genes to function properly are goals that still often elude scientists.

And there are risks. If a gene is accidentally spliced into a vital segment of a cell's DNA, it could disrupt the functioning of another critical gene. Or it might activate a nearby oncogene, initiating the growth of a tumor. Transplanted without all its accompanying regulatory DNA, the new gene might order the production of too much or too little of a protein, with unforeseen consequences.

These risks and the fears of some critics that the technique could be misused have raised safety and ethical issues that the practitioners of the new art are quick to recognize. "For the first time, we're altering an individual's genes," says W. ("Dusty") Miller, a gene-therapy researcher at the Fred Hutchinson Cancer Research Center in Seattle. "That's a new frontier, and you had better make sure you're doing the right thing. These are really exploratory times for gene therapy, and no one knows where it will lead." Despite his enthusiasm for gene therapy, Anderson too is aware of its implications. "The emotional impact of having somebody manipulate the fundamental blueprint of a human being is very frightening," he acknowledges. "We need to have the public understand it and to have adequate safeguards."

Anderson is painfully familiar with safeguards. He and Blaese first submitted their proposal for treating ADA deficiency in April 1987. Since then, it has been reviewed a dozen times by a variety of NIH regulatory committees and altered again and again to meet their requirements. At long last, early this month, the acting head of the NIH gave final approval, and the way was cleared for the researchers to proceed. Concedes Jay Greenblatt, of the Regulatory Affairs branch of the National Cancer Institute: "The levels of review of this proposal have been incredible."

The gene at the center of all this concern "codes," or provides the blueprint for, adenosine deaminase (ADA), an enzyme that breaks down toxic biological products. In the rare cases of ADA-deficiency children, the gene and, consequently, the enzyme are missing. As a result, the toxins accumulate in the bloodstream, killing essential T cells and B cells and inactivating the immune system. With little or no defense against disease except germ-free environments, like the famous bubble, victims usually died early in childhood; ADA injected directly into their bloodstream could not help; it deteriorated within minutes.

Then, earlier this year, the FDA approved treatment with PEG-ADA, a drug consisting of the enzyme with a chemical sheath that enables it to exist in the bloodstream for days. Weekly injections, at an annual cost of $60,000, have kept some of the dozen or so ADA-deficiency children in the U.S. alive. But a longer-lasting, even permanent treatment that would generate ADA in the bloodstream is obviously preferable.

Anderson and Blaese are confident that gene therapy could fit the bill. Ideally they would prefer to insert ADA genes into bone-marrow stem cells, which would continuously manufacture blood cells containing the gene and ensure a steady supply of the enzyme. But researchers have yet to find a way to isolate marrow stem cells effectively. Instead, the NIH researchers opted for T cells, immune-system cells that can survive in the bloodstream for months and even years.

Extracting viable T cells from their young patient, Anderson and Blaese exposed them to mouse leukemia retro-viruses into which human ADA genes had been spliced. The retroviruses, rendered harmless by genetic engineering, were the vectors, the vehicles that would deliver the genes to their target. They invaded the T cells and, as retroviruses are wont to do, burrowed into the T- cell DNA, carrying the ADA gene with them. Finally, a billion or so T cells, now equipped with ADA genes and floating in the gray solution suspended above the little girl's bed in Bethesda, were dripped into her veins.

Several months may pass before doctors can confirm that the ADA genes are being "expressed" and that the enzyme is being produced. Even so, the child will not be cured. She will have to return monthly for at least two years to ) the NIH, where doctors will infuse her with more engineered T cells and check for possible side effects. But Anderson and Blaese are optimistic. "We're very comfortable with the concept," says Blaese. In the meantime, as a precaution mandated by the FDA, the girl will continue to receive the PEG-ADA drug treatment.

The milestone event should be quickly followed by a second application of human gene therapy, now apparently close to final approval. It has been proposed by NIH's Dr. Steven Rosenberg for treating patients with advanced cases of melanoma, a deadly skin cancer that afflicts 28,000 Americans annually. "We now use radiation, chemotherapy and surgery -- external forces -- on cancer patients," Rosenberg says. "But gene therapy uses the body's own internal mechanism. We're trying to make the body itself reject the disease."

Rosenberg's strategy, devised with the help of Anderson, is to extract immune cells called tumor-infiltrating lymphocytes (TILs) from the tumors of melanoma patients. Rosenberg bathes the TILs in a solution of interleukin-2, a natural substance that invigorates them, and then exposes the TILs to re- engineered mouse leukemia retroviruses.

Like the retrovirus used by Anderson, Rosenberg's delivery system has been made harmless and endowed by recombinant DNA techniques with a human gene. But this gene codes for tumor necrosis factor, a naturally occurring compound that attacks cancer cells. The altered viruses insert themselves and their piggyback gene into the genetic material of the TILs, which are then injected back into the bloodstream of the melanoma patients. If everything goes as planned, the activated TILs will home in on the tumors like guided missiles, attacking the cancerous cells and at the same time releasing the antitumor factor to help finish them off.

Across the U.S., other scientists are preparing their own gene therapy experiments, some using retroviruses, others creating synthetic carriers or experimenting with chemical, electrical and even mechanical techniques to insert genes into cells. At St. Jude Children's Research Hospital in Memphis, Dr. Malcolm Brenner is working with "reporter" genes, which have no therapeutic value and are used merely as markers, in an attempt to learn more about how bone-marrow cells behave in the body and how they could best be used for gene therapy. He is seeking NIH approval to insert reporter genes into the marrow cells of children with cancer in an effort to learn why the disease recurs after remission.

In Ann Arbor, Dr. James Wilson, a University of Michigan geneticist, is polishing a technique for introducing healthy genes into internal organs and blood vessels with genetic defects. Working with rabbits afflicted with familial hypercholesterolemia, a metabolic disorder, Wilson is trying to transfer good genes into defective hepatocytes, cells in the liver that, when functioning properly, help clear LDL cholesterol from the blood. Eschewing a retrovirus vector, he and two University of Connecticut scientists have developed a synthetic protein-DNA complex to deliver the healthy genes. Essentially a gene encapsulated by a protein, the complex zeros in on a receptor on the hepatocyte and is absorbed by the cell, which then incorporates the gene into its own DNA.

After all the controversy that has long surrounded genetic engineering and gene therapy, reaction to last week's pioneering effort has been generally favorable. Abbey Meyers, executive director of the National Organization for Rare Disorders, was ecstatic, noting that people with genetic diseases have been waiting nearly 15 years for the first round of gene therapy experiments. "If we could find a cure for a disease with a genetic component such as diabetes," she says, "that would probably be the most important medical advance of the century, if not of all time."

Arthur Caplan, director of the Center for Biomedical Ethics at the University of Minnesota, who has kept a close eye on genetic advances over the years, is convinced that any ethical concerns "have been adequately met. The risks are similar to those involved when you are trying any innovative, invasive procedure. I don't think there's anything special about it because it's genetic."

Still, the gene therapy currently being practiced affects only the patients. Opposition is bound to swell again if scientists turn toward a goal that is still far off: the genetic engineering of sperm and egg cells. Such Brave New World-style manipulations would affect the genetic endowment of future generations, raise new ethical issues and pose unknown risks.

For now, however, the promise of gene therapy appears to outweigh any potential pitfalls. And the acceptance of the new techniques is particularly sweet for longtime advocates. "Twenty years ago, you couldn't utter the phrase gene therapy without being told you were talking nonsense," says Dr. Theodore Friedmann, a molecular geneticist at the University of California, San Diego. "Now it's taken for granted that it's coming." He sees the day when doctors will be able to treat not only the thousands of diseases caused by a single faulty gene but even complex disorders like Parkinson's and Alzheimer's diseases, which are probably caused by a multitude of genes. Hyperbole? Not at all, says Friedmann. "When it comes to genetics, it's dangerous to be conservative."

Perhaps most gratified by the week's events was Anderson. Ever since his undergraduate days at Harvard, he has been insisting that genetic disease could be cured by genetic alterations. In 1968 his paper suggesting the probability of gene therapy was rejected by the prestigious New England Journal of Medicine on the grounds that it was too speculative. "I was abused for years," says Anderson. "Now, to be taken seriously is so delightful."

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CREDIT: TIME Diagram by Joe Lertola

CAPTION: GENE THERAPY: HOW IT WORKS.

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CREDIT: TIME Diagram by Joe Lertola

CAPTION: FUTURE TARGETS

With reporting by Andrea Dorfman/New York and Dick Thompson/Washington