April 20, 2009 (Denver) -- Using gene therapy, researchers have re-educated patients' own immune systems to attack prostate tumors in the body.
In the first two patients treated, the experimental treatment reduced PSA levels by 50% to 75%.
PSA levels are a measure of a protein called prostate-specific antigen produced by cells in the prostate. High PSA levels can signal cancer; a reduction in PSA of 50% or more after treatment is a sign that the patient is responding to the treatment.
Both patients had advanced (metastatic) prostate cancer that had spread to other parts of the body. The findings were reported at the annual meeting of the American Association for Cancer Research.
How Designer T Cells Work
In the treatment, gene therapy is used to modify immune-system cells called T cells in such a way as to attack the cancer, says Richard Junghans, MD, associate professor of surgery and medicine at Boston University.
Normally, prostate cancer cells fly under the radar of the immune system, evading the body's surveillance mechanisms. The designer T cells target and attach to a specific protein that is present on many tumor cells.
"We fool the T cells" into thinking the cancer is a foreign invader that needs to be attacked and annihilated, he says. "T cells are the perfect killing machine."
As an extra boost, patients are also given chemotherapy.
To date, neither patient has developed any significant side effects.
Early Results 'Encouraging'
With higher doses of the designer T cells -- which the researchers plan to test soon -- Junghans says he hopes to be able to cure men with metastatic prostate cancer.
"I expect this, or some version of this, to become standard treatment within five years," he says.
Louis Weiner, MD, director of Lombardi Comprehensive Cancer Center in Washington, D.C, says the approach marries two concepts that have been around for about 20 years.
"What [the researchers] have done is to really combine two critical elements" -- redirecting the T cells to attack a cancer and creating more space for them using chemotherapy, he tells WebMD.
While much more study is needed, "the early results are encouraging," Weiner says.