More cancers in the eye of the vaccine needle
Our immune systems don't do a great job of protecting us from cancer. The system is designed to attack invaders from the outside, like viruses—things that are not natural parts of us. But cancer isn't an outsider; it grows from our own cells and looks a lot like our own cells. So the immune system is blind to it. The immune-cell armies need to be trained to recognize cancer as an invader, then to attack and destroy it.
That's where so-called therapeutic cancer vaccines can be helpful. Unlike typical vaccines, they don't prevent cancer from starting. Instead, they attack it after it starts. And they do it by teaching the immune system to recognize cancers as the deadly interlopers they are.
A recent compilation of tests lists 21 anticancer vaccines that may have improved patient survival. Lung cancer and melanoma are just a couple. Doctors take great pains to say patients shouldn't get their hopes up based on these early data. But the approaches, as experiments, are intriguing.
Cell Genesys, a biotech firm in South San Francisco, is developing vaccines to treat leukemia, prostate cancer, and pancreatic cancer. For leukemia, the doctors start with "off the shelf" leukemia cells, grown in the lab. They irradiate them to stop them from dividing.
"That's crucial. They're alive but unable to divide," says Peter Working, a cell biologist and senior vice president of the company. "You don't want to give someone a dividing, growing cancer."
The next step is to add a special gene to the cells. This gene makes the leukemia cells secrete a molecular signal that lures immune cells, just as bait attracts fish. Then the juiced-up leukemia cells are injected into the body of a leukemia patient. Lured by the molecular signal, the immune cells smack right into the cancer cells. This forced face-to-face encounter makes the immune cells react to the cancer, which ordinarily they would ignore. The cells then speed off to tell the rest of the immune system about this new invader and how to recognize it. And the immune system goes on the attack.
The company uses the same basic approach for vaccines against prostate and pancreatic cancer. It has seen some patients gain six extra months of life compared with patients who got standard cancer drugs.
But "we're not making claims yet based on this data," says Working. "We need bigger trials, which should be finished in 2008 or 2009."
David Berd tells a similar story about the melanoma vaccine he's developing, M-Vax. Berd is a medical oncologist at Thomas Jefferson University in Philadelphia. His approach is to remove a patient's own melanoma cells, add a chemical called a hapten to every protein found in that melanoma, and put the cells back in the patient. The added hapten—a foreign object—looks suspicious to the immune system.
"This is how you can trick the body into responding to a tumor protein that it won't normally respond to," Berd says.
In preliminary tests in cancer patients, he has seen the vaccine stimulate enough of a reaction that immune cells have gone after melanoma cells. But like Working, Berd cautions this isn't ready for prime time. "We've talked to the U.S. Food and Drug Administration, and they made it very clear that we have to do more and bigger trials under better-controlled conditions," he says.
"It takes a long time to develop an effective anticancer therapy," says John Marshall, an oncologist at Georgetown University who has investigated many of these vaccines. "Remember, it was back in the early 1970s that cancer researcher Judah Folkman said that anti-angiogenesis [starving a tumor of its blood supply] would be a good treatment. But it's only in the last two years that we've gotten drugs like Avastin that put that principle into action. So with cancer vaccines, we're in early trials." He hopes, though, that this time it won't take a quarter century for such trials to bear fruit.
The National Cancer Institute has a fact sheet on cancer vaccines.
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