Instant Expert: A Vaccine For Cancer
Medicine harnesses the might of the immune system to defeat prostate cancer.
Doctors have been trying to enlist the immune system of patients in the battle against cancer since at least 1893, when physician William Coley of New York Cancer Hospital injected bacteria into a patient’s body in the hopes that it would spur the immune system to fight the bacterial infection and cancer cells alike. The tumor disappeared, and the patient lived for another 26 years. But immunotherapy was eclipsed by radiation and chemotherapy, which showed more-immediate and reproducible results.
Last April, Provenge became the first FDA-approved treatment that retrains the immune system to target cancer. Scientists have tested it only on subjects already near death, in this case men whose tumors had spread beyond their prostate. Those who took Provenge lived an average of 4.1 months longer than those who didn’t. Now researchers at Dendreon, which manufactures Provenge, are looking into whether it can stop the cancer from spreading beyond the prostate. If that can be done, says Paul Schellhammer, a urologist at Eastern Virginia Medical School who studied Provenge in clinical trials, the patient will usually survive.
How To Battle Cancer With a Vaccine
The Principal Characters
For the immune system to target cancer, it first must recognize it, which it can do by using antigenpresenting cells (APCs) to present information about the protein markers antigens—found on cancer cells to the T-cells that will eventually destroy them.
Know Your Enemy
Scientists begin this process by harvesting APCs from patients and incubating them in a flask containing the antigen prostate acid phosphatase (PAP). The APCs swallow up PAP and present the antigen on their surface.
Attack The Tumor
With PAP fragments studding their surface, the primed APCs now serve as the Provenge vaccine. After doctors inject the APCs back into the patient, the APCs circulate in the bloodstream. There, they train the body’s T-cells to attack any cells that display PAP, including prostate-cancer cells.
How Is Provenge Different From Current Immune Therapies For Cancer?
Immune therapies have been around for years. Some provoke a general immune response, like the FDA-approved drug interferon alpha does for leukemia. Others are antibodies— Herceptin binds to breast-cancer cells, hindering their growth. But the effects of those therapies last only as long as they remain in the body. Provenge is the first drug that retrains immune cells to fight cancer after treatment.
What Will Be The Next Cancer Vaccine To Hit The U.S. Market?
Two vaccines effective against non-small- cell lung cancer, the most common type of cancer to affect that organ, are the most likely. In a 2004 study, patients who got Stimuvax, manufactured by Merck KGaA, lived on average 17.3 months longer than unvaccinated patients. A similar vaccine by GlaxoSmithKline is also in clinical trials. “Within five years, I think we’ll see several more vaccines approved,” says James Gulley, a medical oncologist at the National Cancer Institute who is studying a new type of prostate-cancer vaccine called Prostvac. Scientists are currently testing vaccines against ovarian, liver and pancreatic cancers. Several cancer vaccines have already been approved outside the U.S., including ones against skin and colon cancers.
Will Vaccines Eventually Prevent Cancer?
Maybe. But giving a vaccine to the masses, including those who would never otherwise get cancer, makes sense only if the vaccine is extremely safe and cheap, Gulley says. Tests for predicting cancer risk could help doctors decide who to immunize.