Therapeutic cancer vaccines show promise

Researchers have been working on the strategy for at least four decades and have suffered many failures, even in vaccines that showed promise in Phase 1 and Phase 2 clinical trials, which test safety and effectiveness of experimental treatments in a small number of patients. "It's been a really frustrating journey for a lot of researchers," Lichtenfeld says. "A lot of hope and a lot of dashed hopes, unfortunately."

Basic research on the immune system in the last 10 to 15 years has led to an explosion of new knowledge about the intricacies of the immune system -- and some clues as to why these early strategies failed. For instance, it's now known that tumors can shut down immune activity in their vicinity. The three new vaccines, as well as many more under development, have incorporated past lessons and new knowledge to improve their odds.

Generally, vaccines are made from a substance that only cancer cells make (or that they make far more of than normal cells do) -- say, a protein that sits on the surface of a tumor cell. Then the vaccine is injected into the body. If the immune system senses that the substance is a foreign invader, then it starts to ramp up a response. The mechanisms vary, but essentially the body makes new immune cells and sends them out on search-and-destroy missions, seeking out anything that contains that same substance, or marker.

In the past, small protein fragments -- called antigens -- that are present in high amounts on cancer cells were used in cancer vaccines. But the ones that were chosen did not stimulate enough of an immune response to attack tumors effectively.

"We know a lot about tumor antigens," says Dr. Leisha Emens, an oncologist at Johns Hopkins University who is researching breast cancer vaccines. "I don't think we've done that great of a job identifying which ones are the most important."

You don't want just any immune response, you want one that will effectively attack the cancer cells, she says.

Dr. Donald Morton, chief of the melanoma program at the John Wayne Cancer Institute in Santa Monica, tells a cautionary tale. He led a different melanoma vaccine all the way through to a Phase 3 clinical trial. With 1,600 patients worldwide, it was much larger than the recent crop of studies. Morton says the rate of survival in the study was the highest he'd ever seen. However, that rate did not differ from the control group, who received only an immune stimulant, and the trial was halted in 2006. "There's no question that some patients responded to the vaccine," he says, based on a review of the data. However, many more patients did not.