Cancer vaccines

Today, vaccines can prevent some cancers and hold promise as a new way to treat others.

When your immune system has been exposed to a pathogen, or germ, your body toughens its defenses against the specific disease that the pathogen can cause. Vaccines use this principle to boost your immune system’s response to particular microscopic threats. When you receive a vaccine, your doctor introduces a dead or weakened form of a virus, bacteria, or other germ into your body, enhancing your immune system’s ability to respond to and fight off that pathogen.

Using vaccines

In the world of cancer treatment, vaccines have the potential to serve two important functions — preventive and therapeutic.

Preventive vaccines help the body battle germs that are known to cause cancer. For example, one important cancer prevention vaccine helps women build immunity against the human papillomavirus (HPV), which is the most common sexually transmitted infection in the US and can lead to cervical cancer.

Therapeutic vaccines are designed to help your body fight an existing cancer, though as yet no therapeutic cancer vaccine has been able to cure existing cancers. However, researchers believe they are on the verge of discovering a way to treat tumors with vaccines that target the specific proteins on the surface of cancer cells.

The HPV vaccine

The HPV vaccine, which was approved by the Food and Drug Administration (FDA) in June 2006, inhibits infections that can cause genital warts and cervical cancer. Since cervical cancer is the second most common cancer in women throughout the world, the ability to prevent one of its root causes makes the HPV vaccine a revolutionary step forward in women’s health.

However, the vaccine does have some limitations. First of all, there are many varieties of HPV, and the vaccines on the market protect against only some forms of the virus. Fortunately, those include the two HPV types that are responsible for 70% of cervical cancer cases worldwide.

Additionally, sexually active women who have already been exposed to any of the HPV types covered by the vaccine may not receive the full benefit of vaccination.

Finally, while the HPV vaccine is a helpful protective measure, it’s not a failsafe guard against cervical cancer. It’s still important for vaccinated women to receive regular pap tests, which can detect the majority of cervical cancers at an early and treatable stage.

The quest for therapeutic vaccines

While your immune system has a natural ability to fight illnesses, the body typically does not recognize cancer cells as foreign substances, so it does not respond to cancer aggressively. This is partly because tumor cells derive from normal cells, but also because cancer cells have ways of avoiding detection — by shedding the proteins that make them identifiable and reducing the number of molecules the body relies on to activate the immune system.

But there are certain molecules on the surface of cancer cells that are either unique to the cancer or are more abundant in the tumor than they are in healthy tissue. These molecules, typically proteins or carbohydrates, have the potential to act as antigens — substances that activate an immune response because the body recognizes them as foreign. Researchers hope that, by injecting vaccines containing these cancer-specific antigens, they can prompt the immune system to target the cancer cells.

Therapeutic vaccine strategies

Researchers are investigating a variety of approaches for using cancer antigens to stimulate an immune response, including:

Adjuvant vaccines: Doctors vaccinate you with the cancer antigen combined with an adjuvant — a substance known to trigger an immune response. The hope is that, when the immune system targets the adjuvant combined with the antigen, it will also attack the tumor cells.
Dendritic cell vaccines: Doctors remove some of your dendritic cells — special white blood cells that play an important role in the immune system. Using your own cancer antigens, they activate the dendritic cells. When they’re reintroduced to your body, these modified dendritic cells may increase the immune response against cancer.
Viral vectors and DNA vaccines: This approach uses the DNA from the tumor cell that produces the cancer antigen. Doctors combine this antigen-producing DNA sequence with specialized immune cells, which begin to process the gene, produce the cancer antigen, and stimulate immunity against the tumor. Researchers hope to trigger an immune response against the tumor by introducing these antigen-carrying immune cells into the body.