Jan. 30, 2002 -- Using a patient's own body cells to create a vaccine could be the key to safe and effective cancer treatment that specifically targets each person's unique tumor.
Unlike the vaccines we're all familiar with, cancer vaccines aren't meant to be given to healthy people to prevent cancer. Rather, they are meant to be used in sick patients to rev up their immune system to better fight the cancer.
"Cancer vaccines aim to make the body's own immune system attack [and destroy] cancer cells," says Anne Armstrong, MRCP, a clinical research fellow at the Paterson Institute of Cancer Research in Manchester, England. "Tumor cells, genes, or proteins from tumor cells are [modified and then] given to the patient in a way that kick starts the immune system into attacking the cancer cells," she tells WebMD.
A study reported in the February issue of the Journal of Clinical Investigation suggests that this technique is useful against prostate cancer and may eventually help fight other types of cancer, as well.
"This form of vaccination appears to be non-toxic as opposed to conventional [cancer] therapies, and it can be applied to virtually all cancer types," senior researcher Johannes Vieweg, MD, an associate professor of urology and immunology at Duke University Medical Center tells WebMD. "In most patients, cancers grew at a much slower rate than prior to treatment [with the vaccine]."
Using the Body's Own Defenses
This novel form of cancer treatment involves jump-starting a special type of white blood cell called dendritic cells -- which then activate the immune system and help it attack foreign invaders such as viruses, bacteria, or cancer cells. Dendritic cells do their work by hunting for foreign proteins, or antigens, present on the surface of cancer cells or viruses. They attach to these antigens, and serve them up to killer T cells for destruction.
In prostate cancer, that antigen is a protein called prostate-specific antigen, or PSA. In fact, high levels of PSA in the blood usually indicate the presence of cancer and the level can be monitored to see how well treatment is working.
By placing genetic material from the patient's PSA into these dendritic cells, the Duke researchers produced a "designer" vaccine that specifically targeted each patient's cancer cells.
In the study, 13 men with prostate cancer that had spread beyond the prostate gland received three escalating doses of vaccine. Eight patients had mild side effects -- soreness at the injection site or flu-like symptoms, but these cleared on their own within a few days.
Blood tests in all 13 men showed that the vaccine had successfully boosted the immune system, activating T cells that killed only tumor cells. In comparison, traditional cancer therapy affects many different cells, including those that line the gut and hair follicles, causing the infamous side effects of chemotherapy -- nausea and hair loss.
In the seven men who were not receiving any other form of cancer treatment, six had a significant drop in PSA levels (indicating that their cancers had shrunk ), and three had fewer tumor cells circulating in their blood.
"This study demonstrates the safety and the [effectiveness] of [our] vaccine, [and] also demonstrates that there can be an impact on cancer growth," Vieweg says.
Encouraged by this study, Vieweg's group is now testing "much-improved, second-generation vaccines ... carrying the potential for even more pronounced clinical success" in patients with prostate and kidney cancer.
Problems to Overcome
"Human cancer vaccines have been in development for over 30 years, and none has yet been proven [completely] effective," David Berd, MD, a professor of medical oncology at Thomas Jefferson University in Philadelphia, tells WebMD. Nevertheless, several attempts at creating a cancer vaccine "have been shown to induce anti-tumor immune responses and, occasionally, shrinkage or disappearance of tumors."
In an editorial accompanying the study, Tyler J. Curiel and David T. Curiel from the University of Alabama at Birmingham are also cautiously optimistic about cancer vaccines, but note potential problems. The vaccines might cause the body to generate antibodies that can attack and kill normal tissue (autoimmune disease), a phenomenon similar to what happens in lupus or multiple sclerosis. They also note that the process of cultivating dendritic cells and generating specific vaccines for each patient takes considerable time and money.
"Whether active immunization [with cancer vaccines] will ultimately be useful as an anti-cancer [drugs] is also uncertain," they write.
Research by their group and others has shown that patients given vaccines against ovarian cancer and malignant skin cancer improve initially, but then relapse when their tumor grows tolerant to the vaccine.
What Lies Ahead
While preliminary studies suggest that vaccines produced so far are safe, Armstrong explains that much larger studies will be needed to confirm that they are useful. She anticipates the greatest success will be in cancers that can spontaneously stimulate the immune system, such as melanoma or certain kidney cancers.
Patients interested in ongoing studies of cancer vaccines can visit the National Institutes of Health's clinical trial website at http://www.cancernet.nci.nih.gov.
"Scientists and doctors working in the field of immunotherapy are optimistic that cancer vaccines will, in the future, become part of the treatment options available for patients with cancer," Armstrong says.