Researchers Try to Unlock Secrets of Genes to Combat Disorders
High on top of Torrey Pines Mesa, in gleaming laboratories overlooking the blue Pacific, one of the largest concentrations of gene-therapy researchers in the country puzzles over the possibilities of using gene replacement to cure genetic disease.
Here, a soft-spoken pediatrics professor cloned the gene that may hold out hope for victims of the devastating Lesch-Nyhan syndrome. Here, a young scientist from India fashioned the virus that researchers hope some day may deliver new, healthy genes to human bodies.
But the teams at UC San Diego, the Salk Institute and Scripps Clinic admit they are stumped by a common problem: They know how to make and transport genes into bodies; now, how to make them proliferate and function efficiently enough to cure disease?
That question has left them skeptical about the immediate prospects of applying the extraordinary discoveries of gene-therapy research to humans. Some even express doubt about gene therapy’s applicability to the disease on which they have focused.
“Nobody expected these things to be a stumbling block,” said Dr. Inder Verma, the Salk Institute researcher who pioneered the use of retroviruses to transport genes. “ . . . I don’t think we have a shortage of new techniques and ideas. I just think they haven’t been done.
“But there is a conflict between the clinicians and the researchers,” Verma continued, in a recent interview in his sprawling lab on the Torrey Pines bluff. “The clinicians want to cure the patient. . . . But I would be cautious about it. I would like more experimental data.”
“There’s a very high level of expectation,” said UCSD pediatrics Prof. Theodore Friedmann, one of the pioneers of gene therapy nationwide. “It’s not easy for science ever to lay golden eggs on demand. . . . While we sometimes are accused of being coy, it’s true when we say current techniques are not givens, and maybe there will be insurmountable risks and major technical obstacles.”
Though gene-therapy technology has progressed at a stunning clip--most of the advances occurring in the last few years and even recent months--the roots of the work in San Diego stretch back to a time in which the significance of gene defects was barely understood.
Friedmann, now at UCSD, was working in a lab in Washington, D.C., in the late 1960s where researchers discovered the enzyme deficiency involved in Lesch-Nyhan disease. The deficiency is caused by a rare genetic defect, and leads to mental retardation and self-mutilation.
The discovery raised the possibility that “genes might be stuck into viruses,” Friedmann recalled. So in 1971, well before the bioengineering revolution of the late 1970s, he and a colleague authored one of the first major publications anticipating the use of viruses to transport genes throughout the body.
Meanwhile, Verma, now at Salk, was working with tumor viruses at Massachusetts Institute of Technology in the early 1970s. The question arose, if tumor-causing genes can enter a virus and spread throughout a body, “why couldn’t we put other genes in?”
And Ernest Beutler, now at Scripps, was working outside Los Angeles in the early 1960s when a patient came to him with Gaucher’s disease. The genetic defect had left her with a severely enlarged liver, no spleen, and bone fractures. It eventually killed her.
The case had been extraordinarily frustrating. So in the late 1960s, Beutler began exploring ways of trying to treat it. A decade later, when bioengineers began cloning genes, he got the idea of treatment through replacement of the defective gene.
“It became obvious at that time that what until then had been unthinkable was now thinkable,” said Beutler, now chairman of the Department of Basic and Clinical Research at Scripps Clinic and Research Foundation. “You have to realize that until about the mid or late 1970s, the idea of actually being able to isolate a gene and clone it was just a pipe dream.”
Three years ago, Beutler recruited a young researcher to help him clone the gene that is damaged in patients of Gaucher’s disease. The researcher, Dr. Joe Sorge, in turn trained Beutler’s cadre of longtime technical assistants in state-of-the-art biochemistry.
A year ago, Sorge cloned the gene needed for production of an enzyme that enables a body to break down certain substances. In December, he inserted the gene in a special kind of virus and then used this so-called retrovirus to infect cells taken from patients with Gaucher’s disease.
The lab experiment was a success: Enzyme activity in the cells returned to normal.
Meanwhile, nearby at UCSD School of Medicine, Friedmann had cloned the gene that is defective in Lesch-Nyhan patients. Across the street, Verma had been studying the travels of tumor viruses and discovered what he jokingly calls “the glories of retroviruses.”
“We said, ‘Fine. You have the gene, we have the system,’ ” Verma said recently, explaining the beginnings of the crucial collaboration between his lab and Friedmann’s. “ ‘How about if we take your gene to make a virus out of it?’ ”
The idea, as Verma explains it, is to introduce copies of healthy genes into animals or organs. Since viral infections spread rapidly in the body, why not stow the healthy genes in a virus and let it loose?
This is done by removing the protein from the retrovirus--that is, removing the element that enables the virus to create tumors. Verma then substitutes the so-called “gene of interest” in the protein’s place, and supplies other proteins needed for cell replication.
“So, conceptually, you can imagine there’s no difficulty making such a vehicle to transfer genes into organs or into intact animals,” he said. “The question you want to know is where would you like to introduce them to humans?”
One possible answer is the bone marrow stem cells, believed to be constantly producing and replenishing different types of cells for use throughout the body. Verma began mixing mouse bone marrow cells with viruses carrying the genes in question.
“Then you put the bone marrow back into a mouse and let it grow,” said Verma. “Do these animals now make the gene of interest? If they make those (needed) proteins and supply them throughout the entire adult life, that’s what you are looking for.”
As it turns out, the gene has showed up in the spleen cells of the mice, proving the cloned genes can be transported into intact animals. But Verma has encountered an unanticipated problem--one that he says is hanging up researchers nationwide.
“The problem really at the moment that has everybody stymied is that the amount of the protein that is made is very little,” he said. Unless there is sufficient production of protein, “It wouldn’t be enough to do the job,” he said.
Another question is How long will the system work? If a mouse lives two or three years, will the system work over its entire lifetime? Verma, also working with hemophilia and growth disorders, considers answers to those questions crucial before gene therapy is tried on humans.
“But then there are clinicians who have a different viewpoint, who say, ‘I have a patient who will surely die, right away,’ ” he said. “Do you want to wait five years to do it on a mouse before you do it on a human? That’s a very hard question, ethically, for me.”
Beutler and Sorge have encountered similar problems in their work with the genes needed by patients of Gaucher’s disease. So far, it may be infeasible to infect a high enough percentage of bone marrow cells to ensure that the stem cells receive the crucial gene.
In addition, Beutler has concerns about the so-called “wild-type” virus he and Sorge have used in experiments. The virus may be inappropriate for humans since it tends to continue to proliferate and infect other cells, possibly causing tumors.
For that reason, they hope to use a “crippled virus”--a specially engineered and emasculated virus that Sorge was one of the first to design. Unfortunately, the efficiency of infection with a crippled virus is even lower than with a wild-type virus.
“The two problems I mentioned are by no means trivial,” said Beutler. “ . . . But I think they are more technical problems than they are basic problems with the biology of the system. But we are certainly not on the verge of being able to treat a patient.”
“I feel a high degree of confidence that gene therapy will be the treatment of this disease,” Beutler continued. “What I am much less confident about is that in the next five years we will be able to treat it. But I think if we take a longer look--let’s say we look at 25 years or 50 years--I don’t think there’s any question that that’s how it will be done, and maybe with technologies that we don’t dream about today.”
Friedmann may face even greater barriers, since Lesch-Nyhan disease affects the brain. Because the brain is shielded from substances moving through the body by the “blood-brain barrier,” it may be inaccessible through current gene-therapy techniques.
Furthermore, skeptics say that even if researchers could cure a Lesch-Nyhan patient by replacing genes and generating the missing enzyme, it would be impossible to reverse the effects of a lifetime of severe mental retardation.
Friedmann acknowledged that Lesch-Nyhan poses a more complex case than some other diseases likely to be proposed early for treatment in humans. But he said its complexity makes it a good research subject for what it might reveal about the nature of genes.
“There are lots of possible end points to clinical trials,” Friedmann said last week. “ . . . You can certainly ask for a clinical trial to lead to a cure of the disease. . . . You can also ask for a clinical trial to give you information about where genes go and how they go there.”
But he said information-gathering may be an inappropriate goal for clinical trials in the early stages of human gene therapy: “Ideally, you would like to have the initial experiments with humans really produce some major effect on the disease--a cure.”
Sometime in the near future, regulatory officials will approve a proposal for the first clinical trials on humans. Those trials will receive intense publicity, predicted Sorge. Then, the issue may quietly fade away for years.
“Because the diseases that are very common we’re going to have a lot more difficulty doing,” Sorge said, alluding to cystic fibrosis and others. “I think for the really common disease, it’s going to take a whole new generation of technology to even approach curing.”
