A team of U.S. cancer researchers has genetically engineered normal immune system cells to fight skin cancer.  Cancer specialists caution that this is only a first step that could require years more research and testing.

Researchers at the U.S. National Cancer Institute say they are the first to succeed at using gene therapy to manipulate the body's natural defense system to fight melanoma, the deadliest form of skin cancer. 

Normally, the immune system protects the body from outside invaders, such as bacteria and viruses, and launches only a weak, and, ultimately, futile, response to cancers.

But in work that spans many years, researcher Steven Rosenberg and colleagues at the National Cancer Institute say they have successfully boosted the tumor-fighting ability of lymphocytes or T-cells.

Researchers extract a sample of a patient's lymphocytes and use a harmless retrovirus to attach proteins, called receptors, onto the surface of the T-cells.

Then the reconfigured lymphocytes are reintroduced into the patient, where, Rosenberg says,  the T-cells recognize a target molecule, called an antigen, on the surface of melanoma tumor cells, and destroy it.

"We have several patients who have had widespread melanoma throughout their bodies and not responded to treatment of any other kind," said Mr. Rosenburg.  "And now, a year-and-a-half later, [they] are disease-free by receiving their own genetically engineered lymphocytes that can recognize their cancer."

Fifteen of the patients who tried the therapy did not respond, but two had their tumors wiped out.

The work was published in the journal Science.

Rosenberg reports, the group also has been able to stimulate lymphocytes to recognize other common cancers, but yet have to run tests.

"We haven't treated those patients yet, but the fact that we can now generate those cells in the laboratory that can recognize the cancer at least holds us open to hope that we can use this approach for the treatment of other cancers," he added.

But cancer specialists say that, while the findings of Rosenberg's study are encouraging, people should not expect such a cancer treatment any time soon.

David Berd is a professor of medicine at Thomas Jefferson University in Philadelphia, Pennsylvania, and a cancer vaccine researcher.  Berd thinks Rosenberg's group has a long way to go in developing a successful treatment for cancer. 

He says the tumor antigen targeted by the re-engineered T-cells is found on the surface of many harmless cells in the body, which wants to protect itself from an immune attack. 

So, ultimately, Berd says, the gene therapy might not work in a lot of people.

"Having said that, that doesn't make the paper any less interesting," he said.  "It is just my personal opinion that getting an effective cancer treatment out of this approach is a long shot, but it's still quite an interesting paper."

Meanwhile, researchers at the National Cancer Institute have applied for U.S. regulatory approval to begin conducting human trials of their therapy for cancers other than malignant melanoma.