Cancer Vaccines: Training the Immune System to Fight Cancer

Article excerpt

Vaccines traditionally have been used to prevent infectious diseases such as measles and the flu. But with cancer vaccines, the emphasis is on treatment, at least for now. The idea is to inject a preparation of inactivated cancer cells or proteins that are unique to cancer cells into a person who has cancer. The goal: to train the person's immune system to recognize the living cancer cells and attack them.

"The best settings are for treating people who have minimal disease or a high risk of recurrence," says Jeffrey Schlom, Ph.D., chief of the Laboratory of Tumor Immunology and Biology at the National Cancer Institute (NCI). "But at this time, most therapeutic cancer vaccines are being studied in people who have failed other therapies."

Cancer vaccines are experimental; none have been licensed by the Food and Drug Administration. But there are about a dozen cancer vaccines in advanced clinical trials, says Steven Hirschfeld, M.D., a medical officer in the FDA's Center for Biologics Evaluation and Research. "Research has shown us that the fundamental approach to cancer vaccines is right; we are moving in the right direction/' he says.

The three standard cancer therapies are surgery to remove tumors; chemotherapy, which modifies or destroys cancer cells with drugs; and radiation, which destroys cancer cells with high-energy X-rays. Immunotherapy, which includes cancer vaccines, is considered a fourth, and still investigational, type of therapy. Cancer vaccines are sometimes used alone, but are often combined with a standard therapy.

While standard treatments alone have proven effective, they also have limitations. Radiation and chemotherapy can wipe out a person's cancer cells, but they also damage normal cells. "We want to find treatment that is more targeted and less toxic," says Hirschfeld. "Cancer vaccines are designed to be specific, targeting only the cancer cells without harming the healthy ones."

The approach has made cancer vaccines generally well tolerated, allowing them to be used in outpatient settings. And they can be added to standard therapy with a low likelihood of causing further serious side effects.

How Cancer Vaccines Work

Cancer is a term for more than too diseases characterized by the uncontrolled, abnormal growth of cells. To the immune system--the body's natural defense system against disease-cancer cells and normal cells look the same. The immune system tends to tolerate the cancer cells, just as it tolerates the normal cells. That's because the immune system doesn't recognize cancer cells as something foreign, Hirschfeld says. Rather, cancer cells are once-normal cells that have gone awry. Cancer vaccines try to get the immune system to overcome its tolerance of cancer cells so that it can recognize them and attack them.

All cells have unique proteins or bits of proteins on their surface called antigens. Many cancer ceils make cancer-specific antigens. The goal of using cancer antigens as a vaccine is to teach the immune system to recognize the cancer-specific antigens and to reject any cells with those antigens. The antigens activate white blood cells called B lymphocytes (B cells) and T lymphocytes (T cells). B cells produce antibodies that recognize a particular antigen and bind to it to help destroy the cancer cells. T cells that recognize a particular antigen can attack and kill cancer cells. In 1991, the first human cancer antigen was found in cells of a person with melanoma, a discovery that encouraged researchers to search for antigens on other types of cancer, according to the NCI.

The two main approaches for cancer vaccines are whole-cell vaccines and antigen vaccines. Whole-cell vaccines may take whole cancer cells from a patient or sometimes several patients, or use human tumor cell lines derived in a laboratory. "Some cell-based vaccines use tumor cells from the patient, some contain something that looks like a tumor cell but was created in a lab, and others are personalized vaccines that use some cells from the patient and some from the lab," Hirschfeld says. …