Experimental Vaccine Seems to Cure Prostate Cancer in Mice

SUNDAY June 19, 2011 -- Preliminary research shows that an experimental vaccine may cure prostate cancer in mice.

Unlike previous cancer vaccine attempts, the new prostate cancer vaccine appears to be smart enough to outfox prostate cancer tumors, but experts caution that the research is still in its infancy and has yet to be tested in humans.

The hunt for effective cancer treatment vaccines has been going on for decades with varying degrees of success early on, but the new prostate cancer vaccine takes a markedly different approach.

Instead of aiming at a few cancer-causing proteins or antigens on the tumor, the new vaccine casts a much a wider net. The goal of a cancer vaccine is to trick the body's immune system into recognizing the tumor as an invader and attacking it. This is typically done using a virus as a host.

The researchers developed a library of genetic material (DNA) from healthy human prostate tissue cells and then inserted them into a virus. The end product was intravenously injected into the mice, which recognized the antigens and launched a potent immune response, according to a report on the findings, published online June 19 in Nature Medicine.

The study reported no side effects, and none of the mice developed autoimmune diseases, which had been reported in previous cancer vaccine trials.

"Many cancer vaccines display one, two or few antigens and, although this is successful in alerting the immune system to the cancer, the tumor eventually outsmarts the vaccine and adapts," explained the study's lead author, Richard Vile, an immunologist and professor at the Mayo Clinic in Rochester, Minn.

Vile said he hopes that the new approach is smarter than the tumor. If the tumor adapts to the antigen, he explained, the vaccine launches a second wave of attacks.

The approach also makes the development easier, he said, as scientists don't have to identify specific antigens or targets. "We clone them all and let the immune system select which is most important," Vile said.

But, this may also prove to be a hurdle in getting U.S. Food and Drug Administration approval to study the vaccine in humans. "The FDA requires that the active proteins be well characterized, and we don't know which the active proteins are," Vile said.

Even so, he said, "we hope to try to put this vaccine into patients within the next three to five years."

Dr. J. Leonard Lichtenfeld, deputy chief medical officer for the American Cancer Society in Atlanta, said that news of the study "certainly holds out hope that this may represent a true advance."

He cautioned, though, that "we have been looking to vaccines for cancer for many decades and have not yet seen a vaccine or immune therapy make the leap from interesting concept to something effective in the clinic."

That said, the approach outlined in the new paper is "very different," Lichtenfeld said, adding that he remains cautiously optimistic about the vaccine.

"We have been excited in the past by some of these reports, and the success has not panned out," he said. "There is still a ways to go before we can get excited and say it will have benefit for patients with prostate cancer."

Willem W. Overwijk, a cancer vaccine researcher at the University of Texas MD Anderson Cancer Center in Houston, agreed. "We have to wait and see if it will work in people," he said. "They are inducing a broad immune response at many targets on the tumor, which makes it harder for the tumor to escape. [If it does], they make a new vaccine targeting the recurring tumor."

But the bottom line remains: "We have to see if this works the same way in people with prostate cancer," Overwijk said. "Stay tuned."

More information

The U.S. National Cancer Institute has more on prostate cancer.

Posted: June 2011


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