Gene Therapy Techniques Advance

Pushing the frontiers of gene therapy, Martha Bohn, PhD, and colleagues have found a way to safely deliver and regulate the expression of therapeutic genes in the central nervous system of rats.

Jiang Lixin, PhD, a postdoctoral fellow in Dr. Bohn's lab, created three viral vectors that incorporated human fluorescent green protein to track gene delivery and expression in cells. The vectors delivered genes that were continually expressed but could be turned off with a small dose of doxycycline, a drug approved by the Food and Drug Administration and found to have no side effects. One of the vectors, rAAVS3, showed particularly tight regulation in neurons when gene expression was measured at the protein and molecular RNA levels.

To test the effectiveness of this technique in the brain, researchers injected the vector in the rat striatum, where the neurotransmitter dopamine activates the nerve cells that control coordination. Dr. Bohn and colleagues found that up to 99 percent of the vector-introduced gene was turned off when rats were given doxycycline.

The researchers earlier had found that proteins secreted in the embryonic brain stem promote survival of dopamine neurons. One of these proteins, glial cell line-derived neurotrophic factor (GDNF), promotes growth of not only dopamine neurons but also motor neurons, among others, and may have therapeutic potential for neurodegenerative diseases such as Parkinson's and amyotrophic lateral sclerosis. In rodents with Parkinson's, Dr. Bohn and her research staff found that introducing the GDNF gene halted the progression of the disease.

"GDNF gene therapy has exciting potential to 'cure' Parkinson's disease, but since putting a gene into the brain may lead to expression and increased levels of GDNF protein for years, it will be important to have some way to turn off gene expression to arrest unanticipated side effects," said Dr. Bohn, professor of pediatrics and of molecular pharmacology and biological chemistry.