Researchers at the University of North Carolina at Chapel Hill report that healthy genes they transferred into human cells one year ago continue to operate normally. The development is an important step along the way to what could develop into more effective methods for treating genetic diseases such as hemophilia and cystic fibrosis.
The scientists attribute their discovery to the successful use of an artificial chromosome to get an entire functioning gene into a human cell. Currently, the state-of-the-art treatment for genetic diseases is to use miniaturized versions of human genes which do not include all of the controlling material which govern how a gene will behave. As a result, the insertion of this portion of genetic material could cause damage including the mutation of cells to bring on illnesses such as cancer.
"By adding an artificial chromosome you don't touch the human genome, you don't modify it, and that's an important safety issue," said Jean Michel Vos, associate professor of biochemistry in the Lineberger Comprehensive Cancer Center at the University of North Carolina-Chapel Hill School of Medicine.
By taking the entire human gene and its regulatory system, researchers have more control over the gene's placement.
To get the gene into the human cell, Vos and his colleagues took round pieces of DNA tissue called plasmids, the artificial chromosomes, and inserted into them healthy genes. Then, they attached the artificial chromosome to a harmless part of the Epstein-Barr virus -- the virus that causes mononucleosis -- to carry the chromosome to the cell.
This use of a harmless part of a virus is a common method scientists use to insert genes into live cells. But the use of Epstein-Barr is remarkable because it is part of what helps the transfer of the entire gene to maintain a stealthy, parallel existence alongside a patient's 46 chromosomes. That's because Epstein-Barr goes undetected by the body's immune system, and this is just the situation Vos desired for the transfer of the gene -- to slip under the radar system.
"[The artificial chromosome] doubles itself alongside the normal chromosomes. It's a simple, elegant system," said Vos.
Epstein-Barr viral cells are also desirable because they are round. Researchers in gene therapy are debating whether using linear or round plasmids -- for the artificial chromosomes -- is desirable. Vos said in using circular plasmids, he avoided having to deal with cell aging, a process that happens when the ends of a chromosome, called telomeres, split off. By having a round plasmid, this splitting doesn't happen. The structure remains stable.
