Understanding Cancer Vaccines: What Are They and How Do They Work?

Vaccines that protect against infectious diseases like the flu or pneumonia, are commonly made from a weakened form of the virus that is injected into the body. This causes an immune response that helps to build antibodies and T cells that identify and eliminate the virus.

Cancer vaccines work similarly. An injection in the arm uses the same principle to teach the body to attack cancer cells. Typically, a modified virus or protein with immune stimulation properties is injected to provoke an immune response against specific proteins expressed in cancer cells. This allows for the generation of antibodies and T cells to identify and eliminate cancer cells.

They do both, and there are several types of cancer vaccines.

Some vaccines can prevent cancer by targeting viral infections known to cause cancer. When the virus enters the body, it contains a protein on its surface called an antigen. The vaccine helps the body’s white blood cells identify and destroy the antigens.

The HPV vaccine and the Hepatitis B vaccine are two examples that are approved by the FDA. They work by stimulating immunity against different viruses that can cause or contribute to cancer.

Cancer vaccines are also being developed to target specific genes or mutations, such as the BRCA mutation, and potentially prevent cancer. Another example of a specific mutation is Nous-209, which stimulates immunity against 209 mutated proteins that often occur in people with Lynch Syndrome (a genetic disorder that can lead to some cancers).

Vaccines can also treat cancer by educating and provoking the immune system to target cancer cells in people who already have cancer. The big payoff is in provoking an immune response that stops the cancer cells from returning and spreading. 

Three vaccines are approved to treat cancer: 

• The BCG vaccine has been used to treat bladder cancer since 1990.
• The sipuleucel-t vaccine (PROVENGE) was approved in 2010 to treat metastatic prostate cancer. It is a "personalized vaccine" because it relies on immune cells extracted from a patient’s blood. They are sent to a lab where they are mixed with proteins that target the cancer cells. The blood is injected back into the body to help it fight against the cancer.
• The T-vec vaccine was approved in 2015 to treat advanced metastatic melanoma. It is injected directly into the tumor and works by creating copies of itself, which destroy the cancer cells.

The difficulty stems from the targets that vaccines use. Vaccines train the body’s immune system to target specific proteins. In the case of vaccines against infectious disease there are viral proteins that look very different to the body, so it’s much easier to elicit a targeted immune response. In contrast, cancer cells look very much like normal cells, so there are fewer targets, and it is more difficult to stimulate an immune response against them.

Additionally, advanced tumor-created immune-suppressive microenvironments have evolved to thwart immunity, which makes it harder to achieve potent anti-tumor responses.

They can complement immunotherapy and chemotherapy. 

In the past, doctors avoided using vaccines with chemotherapy because chemotherapy can kill rapidly dividing cancer cells and inhibit the expansion of immune cells. We've since learned that many types of chemotherapy can elicit a type of cell death that can activate immunity. 

Now there are efforts underway to better understand how we can use these therapies with cancer vaccines. In addition, many trials using vaccines employ a type of immunotherapy called "immune checkpoint inhibition." These therapies cut the brakes on immunity and can be used with vaccines to direct and stimulate immunity against tumors.

Side effects like chills, fever, and pain at the injection site occur with cancer vaccines as they do with vaccines to prevent infectious diseases like the flu or pneumonia. These side effects are minimal when compared to the side effects associated with other targeted therapies and chemotherapies. This is a big reason for optimism in the expanded use of cancer vaccines.

Because cancer cells are not foreign--they are the body’s cells--cancer vaccines must initiate the correct immune system response. We want the vaccines to attack the cancer cells and not healthy cells. A misdirected immune response can be another side effect. I

Inflammation and organ damage may also occur, but this depends on the patient’s health as well as other cancer treatments they may be receiving. 

Aside from the cancer vaccines that are already approved, most cancer vaccines are being studied in clinical trials. Some of those trials are occurring at Duke and new ones will start soon. To find a clinical trial for your type of cancer, go to clinicaltrials.gov, enter your cancer plus vaccine. It will list available clinical trials for which you may be eligible. The more patients we enroll in these trials, the faster we can get these therapies approved.

It depends on the type of cancer. Most likely, vaccines will be developed that will be used in combination with other therapies. There may also be vaccines developed that can prevent or reduce the occurrence of some types of cancer.