"The main potential safety problem in gene therapy comes from the vector rather than from the gene being delivered," said Dr. Terence R. Flotte, an associate professor of pediatrics, director of UF's Genetics Institute and co- director of the Powell Gene Therapy Center. "The strength of our own center has been the focus on this one particular vector that doesn't cause the side effects, such as inflammation, seen with other vectors.
"But you always have to consider the side effects that could occur," Flotte said. "Theoretically, the greatest potential risk is that the DNA from the virus will insert into the DNA of the cell and in doing so change the characteristics of the cell from being a normal cell to a cancer cell. One way this might occur would be if the new DNA was able to effectively switch on a previously silent tumor-causing gene."
In studies in people and animals conducted during the past decade, UF scientists have never seen tumor development associated with AAV-delivered gene therapy, but they wanted to make sure that wasn't an extremely rare side effect they simply hadn't run across.
In its natural state, AAV does incorporate into a host cell's chromosome, but almost always at the same specific site, where it apparently causes no harm. However, in its recombinant form - in which much of its natural DNA is spliced away and what remains is combined with a corrective gene - AAV no longer zeroes in on the same target, Flotte said.
Instead, UF's experiment showed that a protein in the receiving cell helps "tie up" the ends of the recombinant AAV so that it acts as if it were a tiny independent chromosome within the cell's nucleus, Flotte said. The protein - DNA-dependent protein kinase - is abundant in human cells.
"That puts it into a relatively safe form in which the the
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Contact: Victoria White
vjwhite@tampabay.rr.com
352/344-2738
University of Florida
5-Apr-2001