By Sean Henahan, Access Excellence

The innovative method allows genes to be expressed outside the nucleus of a cell, making it easier for scientists to get disease-fighting genes into tumor cells. Scientists have successfully used the T7T7 gene therapy system, commonly referred to as T7, to express genes in cell cultures and in mouse models, said Thomas E. Wagner, professor of molecular and cellular biology at Ohio University and an inventor of the T7 system.

"We have expressed more than 30 different types of genes using the T7 system, including genes that promote anti-cancer activity," Wagner said.

The T7 vector gene therapy system is unique because it is a nonviral system that works in the cytoplasm of a cell, Wagner said. Other gene therapy techniques work in the nucleus, making them less effective in gene delivery. Another difference between T7 and current gene therapy techniques is that genes expressed using this method are transient and do not become part of the cell's chromosomes. The genes dissipate in a few weeks to a month.

"For treatment of genetic birth defects, permanent gene therapy might be the method of choice," Wagner said. "But to repair or destroy diseased cells, it's not necessary to change the body's genetic makeup permanently. The T7 system is a means to deliver a gene product or drug into a patient without that gene becoming part of the body's genetic machinery."

While the gene therapy system could be used to express any gene, Wagner and other researchers are particularly interested in its cancer-fighting abilities.

Cancer cells divide rapidly, and current gene therapy techniques can be used to inject genes into these cells. But not all cancer cells within a tumor divide at the same time. Current cancer therapies kill dividing cells, but dormant cells can divide after treatment, causing the tumor to come back.

The T7 system would allow scientists to inject a corrective gene into a tumor that would begin working immediately on dividing cells, then lie in wait for other cells that divide later. Such a therapeutic approach would not have the negative side effects of some current cancer treatments because only diseased cells are attacked, he noted:

"This is the benefit of this technique over chemotherapy," he said. "Chemotherapy kills all cells on contact, even healthy cells. The T7 system allows for a more selective treatment that targets only the cancer cells, leaving healthy cells untouched."

The key to T7 lies in its ability to start the genetic process outside the nucleus. The system is loaded with everything it needs for gene expression, including materials similar to those found inside a cell's nucleus. While other gene therapy techniques use only gene DNA, the T7 method uses DNA prebound with T7 RNA polymerase -- a protein that causes the gene to begin producing RNA, an important step in protein synthesis within a cell.

The T7 system is used to inject DNA and T7 RNA polymerase into a region of tissue or muscle containing diseased cells. The DNA is taken up by the cells, and the genes begin to express in the cytoplasm.

The problem with most gene therapy techniques is getting the corrective genes inside the nucleus of diseased cells, said Xandra Breakefield, professor of neurology at Massachusetts General Hospital and Harvard Medical School. By allowing genes to express in the cytoplasm, the T7 system eliminates that problem, said Breakefield, who has experimented with the T7 system.

"The success of gene therapy in cancer treatment depends on gene delivery," she said. "By cutting out some of the steps needed to get the gene to express in a cell, the T7 system will get the gene to the tumor cells more quickly and provide a better therapeutic effect."