In previous articles, I have focused on vaccines as a highly effective public health tool in the battle against infectious disease. What may be less obvious is that vaccines can also be developed that harness the immune system to control cancer. While anti-cancer vaccines are less advanced than traditional vaccines against infectious disease, recent scientific breakthroughs are offering considerable hope for the future.
Cancer vaccines fall into two major categories. The first category acts against cancers that are caused by infectious agents, such as viruses. One such example is the human papilloma virus, which can sometimes cause cervical cancer. A recently developed vaccine against this virus prevents infection and the subsequent incidence of cervical cancer. Another example is the hepatitis B vaccine, which prevents infection by the hepatitis B virus and reduces the incidence of certain liver cancers. Several other infection-related cancers may also succumb to this strategy. Unfortunately, the cancers that can be controlled by this type of vaccine are relatively few.
The second group of cancer vaccines acts against tumors not associated with an infectious agent. The challenge for this type of vaccine is to trick the immune system into distinguishing the tumor cells from healthy cells in the body. This is a significant challenge; since tumor cells are essentially uncontrolled outgrowths of normal cells, they tend to exhibit relatively few distinguishing features for the immune system to latch onto. Nevertheless, most tumor cells do display some components that appear foreign to the immune system and trigger an immune attack. Perhaps the best example is melanoma, a type of skin cancer that expresses a relatively potent antigen that can be targeted by the immune system.
Unfortunately, many clinical trials designed to elicit the immune response to tumor antigens have either failed or had limited success. A key problem is that these vaccines have to be administered after the cancer has already developed rather than preventing the initiation of the cancer (as is the case with cancers associated with infectious agents). The more advanced and bulky the tumor, the more difficult it appears to be for the immune system to attack. In addition, unlike melanoma antigens, many tumor-specific antigens tend to elicit only weak immune responses compared to an infectious agent.
However, recent scientific advances in eliciting tumor immunity have opened up new opportunities and optimism in the cancer vaccine field. The latest successes include vaccines that have shown some efficacy in the treatment of metastatic prostate cancer, metastatic melanoma and follicular lymphoma. These new vaccines are far from perfect, but they are setting the stage for future success. Each is better than the last because of our growing understanding of the initiation of immune responses and the antigens that we need to target. This includes a better understanding of the factors that regulate the nature and strength of immune responses in general. As a result, it is now possible to increase the quality and durability of the immune response. Advances in genetics are also helping researchers search for appropriate tumor antigens that are the Achilles' heel of many cancers. It should be remembered, however, that cancer is really an array of very different diseases, and each will require a unique strategy for its control. Undoubtedly, some will be easier to treat than others.
As with any vaccine, anti-cancer vaccines are essentially boosting our natural ability to eliminate pathogens or undesirable cells from our bodies. In fact, it is likely that the immune system operates on a daily basis to protect us from this disease by eliminating cancer cells that may sporadically appear. The constant immune surveillance for anything foreign, such as the presence of a pathogen or a tumor antigen, is essential for our health. And while the appearance of cancer may be due to the occasional failure of this immune surveillance, our ability to boost immunity offers a tremendous opportunity for the body to heal itself in relatively natural and non-destructive ways.
David L. "Woody" Woodland, Ph.D. is the Chief Scientific Officer of Silverthorne-based Keystone Symposia on Molecular and Cellular Biology, a nonprofit dedicated to accelerating life science discovery by convening internationally renowned research conferences in Summit County and worldwide. Woody can be reached at (970) 262-1230 ext. 131 or firstname.lastname@example.org.