In what could be a breakthrough in cancer therapy, researchers report in The New England Journal of Medicine today that they succeeded in bolstering a patient's immune system enough to wipe out late-stage malignant tumors on its own. The scientists say the successful experiment could pave the way for new treatments of advanced cancer that spare patients the side effects of chemotherapy, which kills healthy as well as malignant cells.

This is not the first time that researchers attempted to use immunotherapy—or a patient's own infection-fighting cells—to try to destroy tumors. But researchers at the Fred Hutchinson Cancer Research Center in Seattle say this is the first time such a therapy worked on its own, without combining it with drugs or chemotherapy.

Lead study author Cassian Yee, an immunologist, says that he and his team removed so-called CD4+ T cells (a type of infection-fighting white blood cell) from a 52-year-old man with stage IV (the most advanced) melanoma—the deadliest form of skin cancer; it had spread to a lung and a groin lymph node. The researchers grew T cells (that target a specific protein, or antigen, on the tumor cells) in the lab until they had a population they believed was large enough to destroy the cancer.

They infused five billion of the cloned cells into the patient. Two months later, PET (positron emission tomography) and CT (computed tomography) scans did not reveal any tumors—and the patient has remained disease-free for two years, Yee says.

"This is the first example that I can think of where someone actually grew CD4+ T cells outside the body and gave [them] back and got results," says Willem Overwijk, an immunologist at the University of Texas M.D. Anderson Cancer Center in Houston, who was not involved in this study.

Both Yee and Overwijk describe the CD4+ T cells as "helper" T cells, because they are known to trigger other T cells in the body to grow. Among the cells they affect are so-called killer T cells (or CD8+ T cells) that attack tumor cells.

Yee says the injected T cells remained active in the patient's body for at least 80 days—and that the tumors vanished even though only 50 to 75 percent of their own cells released the targeted protein or antigen (known as NY-ESO-1).

"This shows that we were able to broaden the immune response to other tumor [proteins], possibly by harnessing the [T cells] already present in the patient," Yee says.

Although pleased with the results, Yee cautions that the approach thus far has only been tested in one patient. He plans to conduct a larger trial on 10 to 20 patients over the next year or so. If that trial—and subsequent ones are successful—he says the therapy could be a viable treatment option within five years.