The success of two recent cancer vaccine trials has focused attention on a growing area of research, using the body's own immune system to fight cancer. It's an approach that could revolutionize cancer treatment, say experts.

In a study published in the Journal of the National Cancer Institute (Vol. 96, No. 4: 326-331), researchers from Baylor University Medical Center at Dallas reported that their experimental vaccine caused a complete disappearance of advanced non-small cell lung cancer in 3 patients of 43 who were treated. In 7 other patients, the disease did not progress for a period ranging from 5 months to 28 months, while an eighth patient saw his lung tumor shrink by 30%.

The vaccine, called GVAX, was made by altering each patient's own tumor cells to make them stimulate an attack by the immune system against the cancer.

This was the first time immune therapy alone has been shown to be effective against metastatic non-small cell lung cancer, said lead researcher John Nemunaitis, MD. And while it's too soon to call this a cure, the results are certainly "promising," he said, for patients with a disease that is frequently resistant to chemotherapy and often recurs even after a tumor is removed.

The second study, published in the British journal Lancet (Vol. 363, No. 9409: 594-599), described results from a Phase III trial of a vaccine designed to prevent recurrence of kidney cancer. Again, the researchers used patients' own tumor cells to create the vaccine, which was given after surgically removing the diseased kidney. Patients who got the vaccine after surgery did better than those who received no further treatment; moreover, it took longer for their cancer to come back, in those cases where it did recur.

Although these and similar trials are not yet conclusive, cancer vaccine expert Jeffrey Schlom, PhD, of the National Cancer Institute, says they are "suggestive of something that's potentially very important."

"The field is progressing exponentially in terms of knowledge and the types of vaccines that are being used," said Schlom, who heads up NCI's Laboratory of Tumor Immunology and Biology. "This is a very exciting time."

Cancer vaccine research is focused primarily on treating existing cancer, rather than preventing new cases. The idea is to kick-start the immune system so that it attacks tumor cells it would otherwise not recognize as a threat to the body. This is not only a completely different approach to treating cancer, but one that has the potential to be virtually free of deadly side effects, Schlom said.

In the lung cancer vaccine trial, for instance, the most common side effect was relatively mild irritation at the injection site. In the kidney cancer trial, which included 177 vaccinated patients, only 12 vaccine-related side effects were noted, and these also were fairly mild. "So far there have been extremely few toxic side effects" in vaccines that have been tested, Schlom said.

Researchers are pursuing numerous avenues in the search for effective cancer vaccines, including using tumor cells or extracts of tumors from each individual patient. In some vaccines these cells are modified by adding proteins or other substances that stimulate the immune system. Another approach involves placing tumor antigens -- substances that cause an immune system response -- into viruses, which can deliver the antigens into the body very efficiently.

"Some of these vaccines are just entering into clinical trials, some have been in trials for a few years, but it takes years to find out if they work," Schlom explained.

Progress is slow for a number of reasons, not least of which is the complexity and delicacy of the immune system. Doctors must tread carefully.

"Your body in a normal lifespan has to deal with lots of biological insults -- bacteria, viruses, yeast," explained immunologist/microbiologist T.J. Koerner, PhD, scientific program director for the American Cancer Society. "If you disrupted the normal immune system, you might increase susceptibility to other things." Conversely, the immune system might get too revved up and start destroying other cells besides the tumor.

Schlom sees another major obstacle to vaccine therapy: the nature of the clinical trials process itself.

Any new therapy first has to be tested in patients who have failed all conventional treatments. But this type of trial is a poor setting for testing a cancer vaccine, Schlom said. Because many conventional cancer treatments are toxic to cancer cells and normal cells alike, the immune systems of patients in these trials may be too damaged to respond effectively to the vaccine.

Moreover, patients in this situation typically have very large tumors. Not only does a large tumor depress the immune system, it makes any immune response less likely to succeed. Killing 100 tumor cells is far easier than killing 1 billion.

Despite the inherent difficulties involved in the research, both Schlom and Koerner are optimistic.

"There's always the hype and the hope associated with the vaccine being a potential cure-all and that's got to be tempered," said Koerner. "[But] I really think that some subsets of cancer will probably be very beneficially treated."

But continuing clinical trials of promising new therapies is extremely important to success. Patients who are interested in participating in a trial of a cancer vaccine can turn to the NCI's Web site for information, or talk to their doctors. The American Cancer Society also has a great deal of information on clinical trials, including a matching service. Schlom said many cancer centers are conducting vaccine trials, and may be able to point patients to a trial that is right for their particular situation.