|
Washington, D.C. — The positive early results of a new cancer vaccine being tested at Georgetown University Medical Center's Lombardi Cancer Center will be presented at the "Molecular Targets and Cancer Therapeutics: Discovery, Biology, and Clinical Applications" Meeting of the American Association for Cancer Research (AACR) October 29 - November 2 in Miami Beach.
It is too early to say definitively whether the vaccine, TRICOM, will prove an effective treatment for many cancer patients. However, this Phase I clinical trial, being conducted by John Marshall, MD, associate professor of medicine at Lombardi, was chosen for presentation because of its positive early results, and because the purpose of this four-day AACR meeting is to showcase new treatments that show promise but that have not been tested widely in humans.
Marshall's presentation is scheduled for October 31 for the news media, and November 1 for other scientists attending the meeting. It will include one patient from his trial—a woman with non-small cell lung cancer, which seems to have disappeared completely after two vaccinations. The woman continues to receive regular vaccinations.
"My presentation includes only one example, but this result, combined with successful results from earlier vaccine trials I've conducted, gives me hope for the future," Marshall said. "I want to keep these findings in perspective, however," he continued. "Cancer vaccines may one day be an effective, less-toxic form of treatment for many people, but they are in the very earliest stages of development at this time and not ready for use in the great number of patients who could one day benefit from them."
The TRICOM clinical trial began in February 2001 and involved up to 42 people with metastatic colorectal cancer or other tumors that express CEA, which stands for carcinoembryonic antigen, a protein found on many tumors. The participants received regular vaccinations with follow-up booster injections to sustain the immune response, combined with standard chemotherapy and radiation appropriate for their type of cancer. The results are still being evaluated.
Standard treatments for cancer, namely chemotherapy and radiation, work by attacking all growing cells whether they are cancerous or healthy. This often results in such debilitating side effects as hair loss, nausea and infection due to a weakened immune system. Cancer vaccines, on the other hand, work by targeting for destruction only the cancer cells, leaving healthy cells untouched.
TRICOM is a "recombinant viral vaccine," meaning that it uses live viruses that have been genetically modified to contain antigens found on the surface of many cancer cells—a technique similar to that used in polio or chicken pox vaccines. These vaccines use a modified form of the virus to help the body recognize the virus as a threat and trigger the immune system to fight it. Cancer vaccines are not used to prevent illness the way chicken pox and polio vaccines are, but rather they activate the body's immune system to recognize and fight cancer.
In the case of TRICOM, the vaccine is attached to a live virus and targets tumors that express CEA. The vaccine is programmed to find CEA everywhere in the body and destroy it, which also destroys the tumor. This is effective not only because of the treatment's non-toxicity, but also because the vaccine is able to find CEA in very small amounts that radiation or chemotherapy likely would miss.
A previous clinical trial at Lombardi tested the vaccinia-CEA and ALVAC-CEA vaccines; in May, Marshall presented results from those investigations at the 2001 meeting of the American Society of Clinical Oncology (ASCO). The findings showed for the first time with this type of vaccine that the vaccine-induced immune responses resulted in increased survival of patients with late-stage metastatic cancer. Studies in mice showed that TRICOM was significantly more effective than the antigen-bearing vaccine alone.
Marshall is collaborating with the vaccine's inventor, Jeffrey Schlom, PhD, of the National Cancer Institute, and Cambridge, Mass.-based Therion Biologics, which manufactures TRICOM. The clinical trial is being funded by a five-year, $1.7 million NCI grant.
|
