U.S scientists have saved two men dying of an aggressive and fatal form of skin cancer by genetically altering the men's own white blood cells to attack their tumours.

The work at the National Cancer Institute in the United States, published Thursday in the September issue of the journal Science, is considered the first major success in battling cancer with gene therapy.

The breakthrough is important because it provides a potential therapy to fight cancer's worst stage, when it has spread throughout the body.

The men had aggressive, incurable melanomas that had not responded to other treatments. They were expected to live only three to six months.

Almost two years after the treatment, they are still melanoma-free.

"It is, I think quite a breakthrough, certainly with the clinical data with responses in two of the 17 patients," Dr. Don Morris of the Tom Baker Cancer Centre in Calgary told CTV Newsnet.

Until now, despite decades of research, success in targeting cancer using the immune system has remained elusive.

"This study gives us real reason for hope and optimism," Morris said, but noted that a great deal of work remains to be done before it can be considered a mainstream treatment for any kind of cancer.

The NCI team genetically manipulated white blood cells called T-lymphocytes. The immune system produces T-cells to kill bacteria and foreign tissues.

But most T-cells don't recognize cancer cells because they look similar to healthy cells.

The NCI team managed to isolate T-cells produced by cancer patients that could recognize cancer. They extracted these special T-cells and enhanced their ability to find cancer cells through genetic manipulation.

Most cancer patients don't produce enough cancer-fighting T-cells to make this viable, however, so the NCI team had to find a way to infect T-cells that don't fight cancer with ones that do.

The treatment is a painstaking process that provides an individualized treatment for every patient using their own T-cells, Morris said, and presents three challenges:

• T-cells have to be collected from individual patients, manipulated in the lab, and then returned to the patient, a process that is very inefficient using today's methodologies.
• A significant number of cancer-fighting T-cells are required if they are to be effective, and they have to be grown in test tubes, which is labour-intensive, time-consuming, and expensive.
• The immune system has to be overcome in order to keep the enhanced T-cells in the body long enough to destroy a tumour.

The latest success is exciting, Morris, said, because one of the biggest challenges has been keeping the enhanced T-cells active in a patient long enough to destroy a tumour.

The NCI team was able to find enhanced T-cells in the two men for months afterward.

Until now, despite decades of research, success in targeting cancer using the immune system has remained elusive.

The treatment did not produce enough cancer-fighting cells in 15 other patients, however, so scientists will have to improve the process.

The experimental treatment is also cancer-specific and has to be produced on a patient-by-patient basis.

Dr. Steven Rosenberg, who led the NCI research, said that work will continue to improve the response rate, and new trials will try to engineer receptors that can recognize and target other cancers, such as lung, breast and colon cancer.

With a report by CTV's Avis Favaro