May 1, 2003 A problem with current efforts in developing a cystic fibrosis gene therapy is that delivering genes into airway cells is inefficient and requires disrupting the integrity of the cell layer. However, a finding by University of Iowa researchers and colleagues may help solve the problem by using a surprising tool -- a modified piece of the Ebola virus. The findings will appear in issue 10 (May) of the Journal of Virology.
The investigators found that taking a small part of the protein coat from the Ebola virus and putting it on another modified virus creates a hybrid vehicle that can attach itself to a receptor on the top surface, or airway side, of lung cells. The genes within the vehicle can then enter the host cell, where they integrate into the host chromosomes. Previously studied gene delivery vehicles can attach only to the bottom surface, which requires breaching the normally closed cell surface layer.
The discovery has implications for treating cystic fibrosis and other lung conditions where the genes needed for healthy lung function are mutated or absent.
"Most people understandably do not think of the Ebola virus in a favorable light, but our approach takes a small part from this bad virus and puts it in a hybrid system to get some good out it," said Paul McCray, M.D., UI professor of pediatrics and lead investigator of the study.
"A large region of the Ebola protein coat, or envelope, is deleted, so it is potentially safer to use," said Patrick Sinn, Ph.D., a UI post-doctoral fellow in pediatrics and the paper's lead author.
The investigation was done in healthy human airway cells that functionally mimic actual human airways. Clinical applications of the finding are only potential at this time.
"We still are multiple steps from knowing whether this Ebola-modified vector can deliver therapeutic genes into the airway cells of people with cystic fibrosis and correct the genetic defect," McCray cautioned. "However, we now have a new tool that allows us to get the virus into the cells without disrupting their integrity by targeting the cells from the air surface side."
People with cystic fibrosis have serious lung and digestive problems because of malfunctioning ion channels. These channels normally regulate salt and water secretions to protect the lungs. The channels are made by a specialized protein, but in people with cystic fibrosis the gene that codes for the protein is mutated. Thus, researchers aim to find ways to insert functional versions of the genes into the airway cells of people with the condition.
In their investigation, the researchers attached the Ebola protein piece to a modified feline immunodeficiency virus, which causes leukemia in cats but no disease in humans. When the hybrid virus is delivered to airway cells, the modified Ebola protein acts like a key that fits into a lock, or receptor, on the top surface of the airway cells. Because the protein piece can "fit" onto the top surface, the integrity of the cell layer is not affected, yet the gene products within the hybrid virus can enter the cell.
In contrast, other gene delivery vectors studied by McCray and others deliver genes by opening "tight junctions" in order to access the bottom surface of cells. Disrupting these junctions is not ideal.
"Normally, cells stick tightly to their neighbors. You can temporarily disrupt the junctions to allow something to pass between the cells; however, there are situations where opening them could be harmful," McCray said. "It may not be a big problem, but it is more desirable not to do it if you don't have to. Using the Ebola virus protein allows us to redirect the delivery virus to the top surface of the cell and avoid the disruption."
The researchers said another advantage of the shortened Ebola protein is that it increases the amount of virus that can be produced. That observation was made by one of the team's collaborators, David Sanders, Ph.D., associate professor of biological sciences at Purdue University.
"Increasing the amount of particles 100-fold becomes really important when you start to consider these viral particles as a drug," McCray said. "The increased production provides enough particles to make additional pre-clinical studies feasible."
The UI investigators eventually want to identify the receptor to which the modified Ebola protein binds. However, their immediate next step is to see how the hybrid virus functions in airway cells taken from people with cystic fibrosis.
The study was supported in part by funding from the National Institutes of Health (NIH) and the Cystic Fibrosis Foundation. In addition, Sinn was supported by a National Research Service Award from the NIH.
The Gene Transfer Vector Core, Cell Culture Core and Cell Morphology Core at the UI provided assistance to the investigators.
For more information about cystic fibrosis research, visit the UI Center for Gene Therapy for Cystic Fibrosis and Other Genetic Diseases at http://genetherapy.genetics.uiowa.edu/.
For more information about cystic fibrosis, visit the Cystic Fibrosis Foundation at http://www.cff.org/.
University of Iowa Health Care describes the partnership between the UI Roy J. and Lucille A. Carver College of Medicine and UI Hospitals and Clinics and the patient care, medical education and research programs and services they provide. Visit UI Health Care online at http://www.uihealthcare.com.
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