Prostate Cancer Vaccine Shows Promise
Method of attack could be used against other tumors, researchers say
FRIDAY, March 4, 2005 (HealthDayNews) -- A new vaccine that dramatically slows the recurrence of prostate cancer by marshaling the patient's own immune system to fight tumor cells looks promising in an early trial, researchers report.
This new vaccine uses the patient's own dendritic cells, white blood cells that activate the immune system, to connect antigens to the body's killer cells, called T-cells. The antigen the researchers targeted is called telomerase, which is secreted by all cancer tumors.
Antigens are protein parts made by viruses or bacteria. These antigens trigger the immune system to attack these invaders. A trick in developing cancer vaccines is training the immune system to recognize tumors as invading antigens.
"This is one of the first steps for the development of a universal cancer vaccine," said lead researcher Dr. Johannes Vieweg, an associate professor of urology and immunology at Duke University. "It may not only be effective in a single tumor system, like prostate cancer, but against many cancers, because telomerase is overexpressed in a variety of cancers."
In their study, Vieweg's team did tests to be sure the patient's immune T-cells were functioning and also monitored the number and types of T-cells during treatment.
Of the 20 patients in the trial, 19 had an increase in anti-telomerase T-cells (CD8 cells). Among nine patients, dendritic cells were genetically modified to increase the type of T-cells called CD4. All nine of these patients had an increased immune response, according to the report in the March 15 issue of the Journal of Immunology.
Moreover, the researchers found that vaccination was linked to a reduction in tumor cells and also to a slowing of increasing PSA levels.
The team found that vaccination allowed the body to distinguish between normal and cancer cells, Vieweg said. "With pinpoint accuracy, we can actually eliminate tumor cells in the patient's body," he said.
Vieweg said this study proved that their vaccine can stop cancer tumor activity without toxic side effects. "Unlike chemotherapy, we have a very specific drug that doesn't cause any side effects, but can stop tumor growth to some extent," he said.
The vaccine is designed to be used with patients who have failed usual treatments. Vieweg is quick to say that a cancer vaccine is not a cure, but rather a way to retard the growth of tumors, making cancer something patients can live with.
"This is a very attainable and worthwhile goal, having something that delays disease for a long time without having any side effects," Vieweg said.
Based on this finding from the Phase 1 trial, the research team is going on to a phase II trial to assess safety and efficacy, Vieweg said.
"Hopefully, this will go all the way and become an important therapy in the future. We are inching toward an effective cancer vaccine. We are not there yet, but we can see the light at the end of the tunnel," he said. "Even if we can't cure cancer yet -- and no drug can do that at this point -- the second-best thing you can provide is hope."
One expert thinks this study is interesting, but whether or not the vaccine can really slow the progression of cancer in a large population is still up in the air.
"This is a potentially interesting antigen, because cancer cells depend on it for survival," said Dr. Howard L. Kaufman, vice chairman of surgical oncology at Columbia University, College of Physicians and Surgeons. "However, it is probably a very weak target."
In addition, Kaufman believes that whether or not the vaccine is really effective has not been proved yet. "It's a little disappointing that the clinical response was not better," Kaufman said. However, the study was too small to really judge the true clinical results of this vaccine, he noted.
Another expert and cancer vaccine researcher echoed Kaufman's remarks. "This is an interesting paper which demonstrates that immune responses can be developed with vaccination strategies in patients with prostate cancer," said Dr. Eric Small, a professor of medicine at the University of California San Francisco.
"However, the study was not designed to evaluate clinical effectiveness," Small said. "The significance of this work is that it adds to the growing body of evidence that prostate cancer is a reasonable target for immunologic manipulations, and provides the basis for further study."
Small should know: In February, his team of researchers reported that another vaccine, called APC8015 (Provenge) extended survival in men with metastatic prostate cancer by 18 percent -- the first time an immune-based therapy has been proven to affect survival in these types of patients.
The American Cancer Society can tell you more about prostate cancer.