CONTACT: JENNIFER BROWN
2130 Medical Laboratories
Iowa City IA 52242
(319) 335-9917; fax(319) 335-8034
Release: June 12, 2000
Breakthrough technologies improve prospects for gene therapy at UI center
IOWA CITY, Iowa -- Researchers at the University of Iowa have recently reported
three breakthroughs in the development of gene therapies for cystic fibrosis
(CF) and other genetic diseases.
Gene therapy seeks to cure genetic diseases by replacing defective or disabled
genes with a corrected gene. The correct genes are transported into cells
using certain viruses.
"These gene carrying vectors can be likened to a truck carrying its
genetic cargo (DNA) into cells where it can correct a genetic defect,"
said John Engelhardt, Ph.D., associate professor of anatomy and cell biology,
and internal medicine, and director of the UI Gene Therapy Core Center.
Recent research in Engelhardt's laboratory has focused on improving one
of those vectors, Adeno-associated virus (also called AAV). Over the past
year AAV has attracted great interest from gene therapists and was highlighted
this month at the American Society for Gene Therapy meeting because of its
early success in gene therapy clinical trials for Factor IX deficiency, a
blood clotting disorder. One important benefit of this virus is that it has
never been linked with any human disease. In addition, the genetically engineered
AAV that Engelhardt is using has had all of its viral genes removed.
However, despite the great promise of AAV, a major limitation is that only
relatively small disease genes can be carried. Research conducted in Engelhardt's
lab has resulted in two new strategies to overcome this limitation. Both strategies
proposed to expand the size of the genes that can be delivered with this vector
"In essence, we have created the 'extended cab' version of a pickup
truck except in a miniature version at the virus level," Engelhardt said.
In the first of these strategies developed by Dongsheng Duan, Ph.D., a research
scientist working with Engelhardt, two independent versions of the virus were
delivered to the same cell, one containing the genetic information coding
for a protein and one containing genetic material which enlists the cell's
protein-making machinery and controls when and how much of that protein is
made. After the two viruses simultaneously enter a cell, their genetic material
"joins hands" and allows for high-level production of the therapeutic
protein. This is particularly attractive for the treatment of a disease such
as cystic fibrosis, where the defective gene can barely fit into one virus
and leaves no room for the control elements that are required to get the therapeutic
Engelhardt cautioned that one potential problem is that the control elements
might end up in the host genome and inappropriately control the production
of other proteins, causing problems. He said that further testing would be
needed but at least in muscle, they have not seen this problem occur.
Ziying Yan, Ph.D., another research scientist in Engelhardt's group, reported
a second breakthrough in engineering these viral vectors, described in the
June 6 issue of the Proceedings of the National Academy of Sciences, which
uses a similar strategy to deliver very large genes. In this case the protein-coding
part of the disease gene itself is split between the two virus vectors. This
strategy is unique because it could allow the use of AAV to treat diseases
such as Duchenne Muscular Dystrophy where the defective gene is much too large
to fit into one vector.
"This strategy has greatly enhanced the prospect of gene therapy with
AAV for numerous diseases not previously approachable," Engelhardt said.
"A further advantage of this approach is the potential to deliver all
the genetic information necessary to tell the cell when and how much of the
protein to manufacture (so called promoter regulatory information)."
Often this genetic regulatory information takes up too much space in the current
vector design to be included. The new strategy has found a way to avoid this
In addition to these two related advances, a third discovery has also recently
been reported by Engelhardt's lab. This finding has tremendous implications
for the use of AAV virus in treating CF. UI researchers have figured out why
AAV, even though it enters cells of the lung, is incapable of producing its
For gene therapy to work, the virus must deliver its genetic cargo to the
nucleus of the cell where the therapeutic protein is produced. In the case
of the airway cells, the virus is intercepted and rerouted for disposal. The
cell tags the virus with a molecule called ubiquitin, which marks it for removal.
"In essence, this tag is the equivalent of a curbside trash pick-up
sticker which reroutes the virus to regions of the cell for garbage disposals,"
Engelhardt said. Duan and colleagues discovered that if they interfere with
this "tagging" it greatly increased the ability of the virus to
get to the nucleus and produce its protein, hence allowing for successful
therapy. The chemical compounds used by the researchers to block either the
tagging itself or the disposal process are non-toxic to cells and hence are
of great interest to researchers and companies performing gene therapy for
lung diseases such as CF.
"To date, clinical trials for cystic fibrosis with this virus have
met with only moderate success," Engelhardt said. "Now we feel we
have found a key to let the virus in through the back door so it can express
its therapeutic protein efficiently and treat disease."
Interestingly, this approach also seems to increase gene delivery to organs
other than the lung. These findings appeared in the June issue of the Journal
of Clinical Investigation.
Funding for this research was provided by the National Institute of Health's
National Heart, Lung and Blood Institute, and the Gene Therapy Core Center
is funded by the National Institute of Diabetes and Digestive and Kidney Diseases
and the Cystic Fibrosis Foundation.
University of Iowa Health Care describes the partnership between the
UI College of Medicine and the UI Hospitals and Clinics and the patient care,
medical education and research programs and services they provide.