The approach has been tried before, but this research team is the first to activate the body's entire immune system to fight prostate cancer.
"This same concept could be applied to breast cancer or other cancers," said Jonathan Simons, who led the study at the Johns Hopkins Oncology Center.
The researchers used a gene called GM-CSF that activates the immune system, attached it to a common virus and implanted it inside cancerous cells of 11 prostate organs surgically removed from patients.
In eight cases, researchers were able to grow a culture of the modified, cancerous cells in the laboratory. The cells were then irradiated, which kept them alive but stopped them from multiplying further.
After this vaccine was injected, the immune system of all eight patients produced antibodies that identified foreign invaders as well as immune cells that attack and kill infectious cells, Simons said.
The vaccine not only recognized the injected cells as foreign but apparently caused the immune system to recognize cancerous prostate cells remaining in the body as foreign, according to Dr. John Gutheil, clinical research director at the Sidney Kimmel Cancer Center in San Diego.
"It's good stuff, if they've really had immune response," Gutheil said.
"Our immune system doesn't see cancer as being that much different from our normal tissue, a situation we refer to as immune tolerance," he said. "What you're seeing here is people are trying to use GM-CSF to actually override this immune tolerance that we have for our own tissues."
Prostate cancer is the second-leading cause of cancer death among men, behind lung cancer.
Simons said it is also unclear whether the vaccine would cause the immune system to attack normal tissue in prostate cancer patients who have not had the organ removed.
"Chances are the immune system would attack the normal prostate as well, but that's not a big deal because the prostate is not a life-sustaining organ," Gutheil said.
However, he said he believes the vaccine technology can eventually be improved enough so the immune system only targets cancerous cells.
"I've been in the field for decades and people have been skeptical about whether the immune system could ever see prostate cancer," Simons said. "What's truly novel about this paper is not only can the immune system see prostate cancer, but you can activate all the appropriate anti-cancer killing arms."