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Q & A: Gene therapy
Sunday, July 09, 2000
When can we expect gene therapy to become available?
Not as soon as we once thought. "This definitely has not been a banner year for gene therapy," says Dr. Richard Mulligan, director of the Harvard Gene Therapy Initiative. The death of an 18-year-old patient at the University of Pennsylvania in September had a chilling effect, reinforcing the perception that many gene therapists were pushing harder than justified by their technical knowledge. About 4,000 patients have been treated in almost 400 clinical trials of gene therapy, Mulligan notes, with few real successes.
So gene therapy doesn't work?
It's not hopeless. The first gene therapy cures, in fact, have been reported in just the past few months. A team of French scientists cured three boys who were born with severe combined immunodeficiency disease, which usually requires aggressive antibiotic therapy and bone marrow transplants. And Penn scientists in March reported surprising early results from a trial of gene therapy for hemophilia B, the form of the bleeding disease that afflicts a third of U.S. hemophiliacs. As part of a safety test, they injected three boys with small doses not expected to have a noticeable result, but two responded by producing so much clotting factor that they required 80 percent fewer transfusions.
What will be treated with gene therapy?
Cancer, if we are to judge by what's being tested. Three out of every five clinical trials of gene therapy have targeted cancers. It was once thought that rare, single-gene disorders such as the severe immune deficiency cases would be the best gene therapy candidates, but researchers have focused on complex, multiple-gene disorders that are suffered by many people and have more commercial potential.
Will we ever clone people?
No technical barriers are apparent. A better question is: Why would we want to clone people? The idea may seem abhorrent, but researchers say many of us someday may choose to clone ourselves, at least in embryonic form. From a cloned embryo, scientists should be able to extract what may be the most valuable cell known: the embryonic stem cell.
Why are embryonic stem cells such a big deal?
Scientists believe that embryonic stem cells can be used to produce almost any specialized cell in the body. Cells produced from someone's cloned embryonic stem cells could be readily transplanted into that person, without fear of rejection. Liver cells could be produced to repair cirrhosis of the liver, heart cells to repair damage from a heart attack, or pancreatic islet cells to produce insulin in a diabetic.
If stem cells are so effective, why would we need gene therapy?
Many diseases, including diabetes, may well be treated better and sooner with stem cells than by gene therapy. Even if embryonic stem cells can't be used because of technical difficulties in using them or religious objections to sacrificing embryos, researchers are isolating other types of stem cells from the body that may well be used to produce many of these replacement cells.
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