Two of 17 melanoma patients who participated in a first-ever study that used gene therapy to boost their immune systems achieved total remission and were disease-free 18 months after treatment began.

Lead researcher Steven A. Rosenberg and colleagues National Cancer Institute used gene therapy for the first time to alter the body's immune system, enabling it to combat the disease.

In patients with advanced cancer, T-lymphocytes -- cells that are naturally designed to identify and destroy the type of cells that create tumors -- often do not function properly. The scientists removed T-cells and inserted new genetic material into them, then returned the altered cells to the patients.

The approach succeeded in two patients who remained free of melanoma more than 18 months after starting the therapy.

It remains unclear why the other 15 patients did not respond as favorably to the treatment, but Rosenberg pointed out that the technique still needs refinement. He called the achievement "heartening."

Up to now, the focus in gene therapy has been on developing approaches to cure inherited diseases by replacing entire genes. The latest research suggests a new avenue for battling cancer, which affects a much larger segment of the population.

In the US, about 62,000 people will be diagnosed with melanoma, and it is expected to claim 8,000 lives this year, says the American Cancer Society.