The study showed that the messenger can be as important as the message: Viruses genetically engineered for use as delivery vehicles for transferring therapeutic genes into the body may alone influence gene expression, or which genes are turned on. Moreover, depending on the type of virus, they may do so in potentially harmful ways.
"This basically tells us that the messenger plays an important role in gene expression," said study co-author Dr. Richard J. Samulski, professor of pharmacology and director of UNC's Gene Therapy Center. "At the molecular level, a cascade of cell signaling events occurs irrespective of the therapeutic gene. This is something we didn't anticipate." The report will appear in the March issue of Molecular Therapy, the American Society of Gene Therapy's journal.
The study focused on two viruses: adenovirus and adeno-associated virus, or AAV. These viruses, when genetically engineered, have shown particular promise in laboratory studies as gene transfer vectors and have been used in more than 170 clinical trials.
Samulski and UNC co-author Dr. Jackie L. Stilwell, a postdoctoral researcher, reported there has been significant progress in understanding how viral gene therapy vectors behave in laboratory animals, in terms of acute toxicity effects.
However, they wrote, "systematic comparison of their effects upon cells at the molecular level has not been established." In that regard, the new research offers important new and potentially useful information for predicting the safety of gene delivery in people.
"The field has advanced so rapidly that we can now do toxicity profiles inside an individual cell," Samulski said. "And basically what we're doing here is asking what happens to the genome if a vector or virus comes into the cell."