Jan. 8, 1999 By Melanie Fridl Ross
GAINESVILLE, Fla.---Using an increasingly promising tool from their gene therapy arsenal, scientists have hit on an innovative way to replace a crucial protein that protects the lungs from the destructive action of an often-fatal lung-liver disease, University of Florida researchers report in the Proceedings of the National Academy of Science.
The approach employs a virus modified to incorporate the protein missing in people with alpha-1-antitrypsin deficiency, which causes early emphysema and severe liver disease. UF scientists injected it into muscle tissue in mice, checking to see whether the protein would be secreted into the bloodstream.
Not only did the method work, but for the first time researchers were able to generate levels of the protein high enough to be therapeutic in humans - a major step ahead. Furthermore, the results were sustained for more than four months with a single injection.
Previous attempts at gene therapy have been hampered by scientists' inability to attain protein levels in the bloodstream high enough to be beneficial and for as long as needed.
"The thing about alpha-1 that makes it a potentially difficult target for gene therapy is that very high serum levels are required to prevent the development of emphysema," said Dr. Terry Flotte, an associate professor of pediatrics, molecular genetics and microbiology and co-director of the Gene Therapy Center at UF's College of Medicine. "The big advance in what we did was that we were able to achieve a circulating level in the blood that would be therapeutic in humans. It's quite promising for therapy -- it's essentially all we needed for proof of the concept."
Considered the second most-common genetic disorder among Caucasians, A1AD affects an estimated 100,000 Americans. One in 50 carries the gene for it. Alpha-1-antitrypsin is produced by the liver and protects the lungs from injury by a common enzyme that normally fights bacteria and cleans up dead lung tissue. A person with A1AD does not generate enough of the protein to adequately protect the lungs, and permanent and irreversible damage results.
Discovered in 1963, A1AD is often mistaken for asthma or chronic obstructive pulmonary disease. Individuals often are not diagnosed until they are in their mid- to late 30s, after extensive lung damage has caused profound disability. The median age of survival is 54.
Current treatment for A1AD includes avoiding exposure to cigarette smoke and weekly injections of alpha-1-antitrypsin. Gene therapy could someday replace the need for weekly shots for individuals battling the disorder.
"Protein replacement patients require weekly IV injections, which are very expensive and painful -- some people just won't do it," Flotte said. "Plus, there's been a limited supply of the protein. If it works at those levels in humans, this has the potential to take the place of protein replacement."
The next step, UF researchers say, is to test the approach in larger animals, and, eventually, in humans, to confirm the doses needed.
"The advantage of working on a disease like alpha-1-antitrypsin deficiency is that we can measure the blood level of the protein and know exactly how close we are to achieving the therapeutic effect. This is in contrast to a disease such as cystic fibrosis, where we don't really know how much is enough, at least not with any certainty," Flotte said.
Results of the research, which was funded by the National Institutes of Health, could be a harbinger for the treatment of other genetic disorders.
"This is also an approach that's generalizable to other diseases where replacement of a protein into the serum is efficacious," Flotte said. "One might imagine any of a number of other disorders, like hemophilia for example, where if you could achieve similar results it would be therapeutic.
"In fact, alpha-1-antitrypsin is required at much higher serum levels than any of the other genetic deficiencies that are treatable by intravenous protein replacement. Therefore, the fact that we can achieve therapeutic levels in this disease bodes well for the general approach of using adeno-associated viral vectors in muscle."
The concept of using the virus in muscle to secrete proteins into the bloodstream was developed by UF pediatric cardiologist Barry Byrne a few years ago. UF is home to a budding A1AD research program that will feature a basic science laboratory focused on the disorder's molecular mechanisms, a clinical research unit directed toward developing new therapies, and a diagnostic laboratory. An added plus: a tissue bank will stock lung and liver tissue samples as well as plasma and serum from individuals with the disease.
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