By William H. Chambers, PhD
Vaccines are not new. In fact, there is evidence that the ancient Egyptians and Chinese used them many centuries ago. Vaccines work by preparing your own immune system to attack invading pathogens, thus preventing disease. Vaccines have helped us make great inroads against many deadly diseases over the past 60 years, when they became used more widely.
Using vaccines against cancer is relatively new, though. Cancer researchers have been trying to make vaccines for tumors, just like others have made vaccines for measles, mumps, and tetanus.
In the case of diseases like measles, the vaccines are made to be given before the disease ever starts. They prevent the disease. And this is one approach researchers have taken with vaccines to prevent cancer.
We now know that about 20% of cancers are started because of infections, mostly from viruses. One virus that causes cancer is the human papilloma virus (HPV), which causes cervical cancer, as well as anal cancer, some head and neck cancers, and genital cancers.
Because researchers have been able to identify strains of HPV that cause the cancers, they have also now been able to develop vaccines that are highly effective in preventing these HPV infections, and thus prevent many of the cancers they cause.
For cancers that are not caused by an infection, it is more difficult to figure out what to use to prevent the cancer from starting. Viral proteins are an easy target for vaccines, because they are foreign to our immune systems. It's not as simple to target cancer cells, which to the immune system can look very much like normal cells. Still, researchers have tried using vaccines to stimulate the immune system to fight the cancer once it has already started.
It has been difficult to figure out how to get an effective immune response against cancer. Since vaccines stimulate the body's immune system to protect against a disease, obviously they work best when the immune system is functioning properly. With cancer, the immune system is generally not working well. Tumors protect themselves by killing the immune system cells that seek to kill them, or by producing substances that inhibit immune cells. All this makes it very hard to target them with a vaccine.
After many years of trying, scientists have finally had some success in figuring out what to use to get an immune response to prostate cancer, and how to get it to work in people who already have advanced prostate cancer. The vaccine, called Provenge, is showing promise and has been approved by the FDA. This vaccine uses immune cells that are isolated from a particular cancer patient, stimulated in the laboratory to restore their function, loaded with the vaccine, and then re-injected into that patient. However, Provenge is not effective in all cases; the reasons for that are currently being studied.
Studying the use of this vaccine gives us important information on what steps to take to make cancer vaccines more effective. In fact, researchers are also working on vaccines for some of the deadliest cancers, including pancreatic, lung, and melanoma. You'll most certainly be hearing more about cancer vaccines in the future, as we perfect and test their usefulness in preventing and treating these and other cancers. We are closer to realizing the long-held promise of cancer vaccines and expect they will be an increasingly important part of both cancer prevention and cancer therapy.
For more information, see our information on immunotherapy.
Dr. Chambers is director of clinical cancer research and immunology for the American Cancer Society.