[US] Cancer Risk Exceeds Outlook in Gene Therapy, Studies Find
unclewolf at olypen.com
Fri Jun 13 11:45:36 EDT 2003
New studies suggest that gene therapy might have a greater chance of causing
cancer than previously thought, adding to safety concerns that have troubled
the fledgling field.
Gene therapy often uses partly disabled viruses to carry genes into human
cells to correct gene defects. The new studies, one of which is being
published today, show that these viruses tend to land on or near genes in
the human cells. When that happens, the gene hit by the virus can be
inadvertently switched on or off, contributing to unexpected effects like
"It's sort of potentially rather bad news for gene therapy because you're
hitting just what you'd rather not be hitting," said Dr. Frederic Bushman of
the Salk Institute for Biological Studies, who has done some of the recent
The gene therapy field was jolted several months ago when two children in
France who had been essentially cured of a rare immune disorder by gene
therapy developed leukemia, a blood cancer. Scientists believe the virus
used in the gene therapy inserted its genetic material into or near a
cancer-promoting gene and turned it on.
In the study being published today, in the journal Science, Dr. Shawn M.
Burgess and colleagues at the National Human Genome Research Institute
looked at 903 cases in which murine leukemia viruses, very similar to the
type used in the French gene therapy, infected human cells in culture.
They found the virus hit a gene 34 percent of the time, more than the 22
percent that would have been expected if the process had been random.
Moreover, the virus had a striking preference for the beginning of the
genes, a site that is key to turning genes on or off.
That mean the leukemia cases in the French children were not so surprising
after all, they said.
"This is definitely showing that it can integrate into the most important
regions of gene," said Dr. Xiaolin Wu, a postdoctoral researcher and first
author of the paper. "The risk is definitely much higher than what we
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