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July 14, 2008
Studies Show Cancer Vaccine Progress
Two new studies bring researchers closer to being able to design vaccines to treat cancer.
The U.S. Food and Drug Administration has already licensed 2 cancer vaccines, but these vaccines prevent infections by viruses that can lead to cancer. Researchers hope to develop therapeutic cancer vaccines that can treat cancer by stimulating the immune system to recognize and attack cancer cells without harming normal cells. Finding suitable antigens—targets for vaccines to stimulate the immune system to react against—has proven difficult, as cancer cells produce many of the same products as healthy cells. Two new studies, however, show significant progress toward developing such vaccines.
In one study, which appeared in the Journal of the National Cancer Institute on June 24, 2008, researchers from Thomas Jefferson University designed a vaccine against guanylyl cylase C, a protein found in the lining of the intestine that is also found in all colorectal cancers. Mice were immunized with the vaccine, along with lethal doses of mouse colon cancer cells. The work was funded by NIH’s National Cancer Institute (NCI).
In mice with colon cancer, those immunized with the vaccine had 80% less tumors in the lungs and 90% less in the liver than mice not given the vaccine. The vaccine was also able to prevent the cancer cells from spreading to other organs. Vaccinated mice with colorectal cancer outlived the unvaccinated mice by 50%. The researchers saw no signs that the immune system had attacked healthy cells.
Future studies will use multiple proteins found in colorectal cancer as antigens to make a vaccine that is effective against other types of colorectal cancers and is more potent. The researchers mention several proteins they are already considering for future testing.
In the other study, scientists in NCI’s labs vaccinated mice with a heat-killed yeast that is genetically engineered to make a common tumor protein. The vaccine extended overall survival and reduced tumor size in the animals. The results appeared in the July 1, 2008, issue of Clinical Cancer Research.
The type of yeast used in the study, Saccharomyces cerevisiae, is non-toxic and often used in baking and brewing. It’s also common in cell biology laboratories and can be fairly easily genetically engineered to produce human proteins. The tumor-associated antigen made by the yeast in this study is carcinoembryonic antigen (CEA). CEA is commonly found on cancers of the colon, rectum, stomach, breast and lung.
Mice implanted with metastatic lung cancer cells all died by day 50 if they received no treatment. But by day 70, 35% of mice injected with heat-killed, CEA-producing yeast were still alive. The yeast also proved effective as a vaccine against pancreatic tumor cells.
"These results provide a rationale for evaluating yeast vaccines in cancer immunotherapy studies in humans," said study author Dr. James W. Hodge of NCI’s Center for Cancer Research.
Therapeutic cancer vaccines might be used alone or as co-treatments along with traditional methods. The vaccines could help prevent the spread of cancer while other treatments eradicate the source, increasing treatment success.
—by Vanessa McMains and Harrison Wein, Ph.D.