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In practice, the genetic material is divided between two independent versions of AAV vectors. After the two viruses simultaneously enter a cell, their genetic material "joins hands" and rebuilds a "corrected" gene capable of producing high levels of the therapeutic protein.
"In essence, if one makes the analogy of a viral vector as a pickup truck carrying its genetic cargo into cells, we have created a system that divides the payload onto two trucks and provides the drivers with instructions on how to reassemble the payload once it gets to its destination. Accordingly, our dual vector system is capable of doubling the size of the genes it can deliver into cells," Engelhardt said.
For gene therapy to work effectively, the virus must deliver its genetic cargo to the nucleus of the cell, where the therapeutic protein is produced. However, the cell can circumvent this process, making gene delivery inefficient. In the case of AAV, the virus can be intercepted when it enters the cell and tagged with a molecule called ubiquitin.
"This molecular tagging marks AAV for 'curb side garbage pickup' and subsequent disposal into a cellular 'trash can' called the proteasome," Engelhardt said.
In a second strategy developed in Engelhardt's lab, and also licensed to Targeted Genetics Corporation, this disadvantageous tagging process can be disrupted, greatly increasing the efficiency by which AAV delivers its genes to the nucleus.
The UI Research Foundation, created in 1975, is a free-standing, not-for-profit corporation. Its mission is to enable the use of intellectual property created at the UI. The UI Research Foundation currently has more than 150 active licenses and, since its creation, has helped the UI to obtain more than 300 patents.
"We're delighted by the interest Targeted Genetics has shown in the work of Drs. Engelhardt, Duan and Yan," said Bruce Wheaton, Ph.D., Executive Director of the UI Research Foundation. "We believe that our partnership with Targeted Genetics is a particularly good way of executing our mission since we are hopeful that the firm can help transform the discoveries of the Iowa researchers into beneficial medicines for a range of diseases."
Targeted Genetics Corporation develops gene therapy products for the treatment of acquired and inherited diseases. For more information about Targeted Genetics Corporation visit the company's Web site at http://www.targetedgenetics.com/.
CONTACT: JENNIFER BROWN
5137 Westlawn
Iowa City IA 52242
(319) 335-9917; fax(319) 335-8034
e-mail: brownj@mail.medicine.uiowa.edu
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.
Breakthrough technologies
improve prospects for gene therapy at UI center
Release: June 12, 2000
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., 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 system.
"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 another 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 protein produced.
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 space limitation.
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 therapeutic protein. 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.
CONTACT: JENNIFER BROWN
2130 Medical Laboratories
Iowa City IA 52242
(319) 335-9917; fax(319) 335-8034
e-mail: brownj@mail.medicine.uiowa.edu
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.
UI researchers receive $8 million five-year grant
to study gene therapy
Release October 5, 1998
IOWA CITY, Iowa -- The University of Iowa is one of two institutions nationwide this fiscal year to receive an $8 million grant from the National Institutes of Health and the Cystic Fibrosis Foundation to develop a Gene Therapy Core Center.
The center is intended to facilitate advances in gene therapy research, said John Engelhardt, Ph.D., UI Professor of Anatomy and Cell Biology and Director of the center.
Beverly Davidson, Ph.D., Professor in Internal Medicine is Associate Director of the center.
"A major focus is on cystic fibrosis, but there is also interest in the development of gene therapy for other genetic disorders," Engelhardt said. "The goal of this center is to expand the research base in gene therapy at UI and help new investigators enter the field of gene therapy."
The center will contain four supporting core laboratories essential for the development of gene therapy: the vector core, morphology core, animal models core, and the cell and tissue core. UI researchers studying gene therapy for inherited genetic diseases and outside investigators affiliated with the center will use the cores to help facilitate their research.
The grant will also support more than 26 two-year pilot studies over the five-year period. The studies will include projects proposed by investigators established in the field of gene therapy research, but who have cutting edge, high risk ideas that are not mature enough for funding elsewhere, as well as junior and established investigators in other fields who want to apply their expertise to a specific problem in gene therapy research.
The center is expected to be operational by November. After the five-year funding is up, the center will be eligible for competitive renewal.
CONTACT: L. E. OHMAN
2130 Medical Laboratories
Iowa City IA 52242
(319) 335-6660; fax (319) 335-8034
e-mail: le-ohman@uiowa.edu
UI developing gene therapy
to help reduce problems with organ transplants
Release October 30, 1998
IOWA CITY, Iowa -- Someday doctors may be able to reduce the risk of organ rejection in transplant patients, thanks to a gene therapy that University of Iowa researchers are designing. While the UI research has focused on liver transplantation, the new therapy could also help to decrease the damage caused by heart attack and may even be useful in preventing problems before they occur. "This type of gene therapy for acquired disease is part of an emerging field of therapeutics," said John F. Engelhardt, Ph.D., UI Professor of Anatomy and Cell Biology, and the project's Principal Investigator. "Its application is not limited to the liver."
A team of UI investigators is currently using models to test this gene therapy as the group moves toward the therapy's clinical application for liver transplantation. Different elements of the UI research appeared in the June issue of Nature Medicine and more recently in the October issue of Hepatology.
The UI-designed gene therapy would target ischemia-reperfusion injuries. When organs in the body suffer reduced blood flow, such as during transplants and heart attacks, they lack adequate oxygen to support life. While this condition (called ischemia) is not itself significantly damaging to cells, when blood flow is re-established (called reperfusion) the high levels of oxygen create damaging compounds. "These compounds can signal cells to commit suicide," Engelhardt said. "We have designed a gene therapy that creates a garbage disposal of sorts for clearing these damaging compounds from the body before cell death can occur."
Using an engineered defective common cold virus, the researchers transfer a therapeutic gene, called manganesesuperoxide dismutase (MnSOD), to all liver cells in order to reduce ischemia-reperfusion induced damage.
"The application of this work will hopefully lead to treatments that can increase the success of organ transplantation," Engelhardt said. "The investigators are using similar approaches to reduce the damage caused by heart attacks as well."
By using the gene therapy as soon as possible after the heart attack occurs, physicians can hopefully help the damaged cells to repair themselves, Engelhardt said. This therapy also could help those at high risk of heart attacks by reducing damage from ischemic heart disease.
This type of gene therapy research is part of the UI's newly funded Gene Therapy Core Center, which Engelhardt will direct. The National Institutes of Health and the Cystic Fibrosis Foundation recently awarded the UI an $8 million, five-year grant to develop the center, which is expected to be operational by November. The UI is one of two institutions nationwide that received funding this fiscal year to establish such a center.
CONTACT: JENNIFER CRONIN
2130 Medical Laboratories
Iowa City IA 52242
(319) 335-6660; fax (319) 335-9917
e-mail:jennifer-cronin@uiowa.edu