When you hear the word “vaccine,” you might think of your annual flu shot or COVID booster, but did you know that some vaccines can treat—or even prevent—cancer?
But before we get there, let’s start with the basics—what is a vaccine? How does it protect you from disease?
A vaccine at its core delivers something associated with disease, such as a protein, into your body, which trains your immune system to recognize and react to the disease later on.
Think of it as training a dog on a specific scent.
Flu vaccines, for example, deliver pieces of a protein from the flu virus. Your immune system sees the protein, recognizes that it doesn’t belong in your body, mounts an immune response against it, and stores this information in its “memory.”
Now that your immune system has been trained to respond to this flu protein, it will be ready to attack if you later are infected with the flu, allowing it to rapidly get rid of the virus before it has a chance to make you sick.
Can Vaccines Prevent Cancer?
Yes! Several vaccines protect against human papillomavirus (HPV), the most common cause of cervical cancer and a major cause of anal, oral, throat, and genital cancers. By preventing HPV infection, these vaccines also prevent the cancer-causing changes induced by HPV.
The first HPV vaccine was approved by the U.S. Food and Drug Administration (FDA) in 2006, and since that time, the rate of cervical cancers has dropped significantly among people who were vaccinated as adolescents.
The Center for Disease Control (CDC) recommends HPV vaccines for all adolescents (boys and girls) beginning at age 11 or 12 and up to age 26 for those who didn’t receive them earlier. Some people might be eligible for the vaccine after age 26 as well.
How Do Vaccines Treat Cancer?
The vaccines we’ve discussed so far are preventive vaccines—they help people avoid a particular disease. Other vaccines, known as therapeutic vaccines, are instead used to treat patients already diagnosed.
Therapeutic vaccines for cancer work in the same way as preventive vaccines: biological material is injected into the patient, where it trains the immune system to find and attack disease, cancer in this case.
To date, only one targeted therapeutic cancer vaccine has been approved by the FDA, but researchers have continued to develop and test different types of cancer vaccines, with many of these showing recent promise against hard-to-treat cancers.
Unlike vaccines that target viruses, therapeutic vaccines for cancer train the immune system to attack the patient’s own cells, rather than an invading virus. Researchers, therefore, have to find ways to direct the immune response to cancer cells to avoid damaging healthy tissue.
To minimize effects on normal, noncancerous cells, therapeutic cancer vaccines train the immune system to recognize proteins that are either absent from normal cells or found at significantly lower levels on normal cells. Vaccines expose immune cells to these proteins in various ways, based on the type of vaccine.
Protein-based Vaccines
Sipuleucel-T (Provenge), the sole FDA-approved therapeutic vaccine for cancer, was greenlit in 2010 for prostate cancer. It works by delivering small pieces of a protein found at high levels in prostate cancers. When the patient’s immune cells encounter the delivered protein, they become more likely to attack prostate cancer cells.
Multiple protein-based vaccines delivering other target proteins are under investigation for a variety of cancer types, including head and neck, lung, pancreatic, brain, and colorectal cancers, among others.
While protein-based cancer vaccines can be highly effective and well tolerated, they are expensive, time-consuming, and oftentimes difficult to develop.
RNA-based Vaccines
Another category of cancer vaccines uses messenger RNA (mRNA)—the same design used to develop the first COVID-19 vaccines. Instead of delivering the target protein, these vaccines provide cells with the genetic instructions (in the form of mRNA) to make the protein, which, in turn, stimulates the immune system to seek out and attack cancer.
mRNA-based vaccines can be produced much more rapidly than protein-based vaccines, but delivering the mRNA and preventing bothersome side effects can be a challenge.
mRNA-based vaccines are being tested to treat a myriad of cancer types, with recent success against advanced skin and pancreatic cancers. Many of these vaccines are custom-made for each patient—a level of personalization made possible by the mRNA platform, which allows custom vaccines to be produced quickly and without major delays in treatment.
DNA-based Vaccines
Like RNA-based vaccines, DNA-based vaccines deliver instructions to make the target protein, but they provide the instructions as DNA rather than mRNA.
DNA-based vaccines have many of the same benefits as RNA-based vaccines, including the inexpensive and rapid production. DNA-based vaccines, however, may cause autoimmune reactions or impact the patient’s own DNA. Further, administering DNA-based vaccines requires unconventional methods, and once administered, DNA still has to make its way into a specific compartment of the cell to function.
Despite these challenges, DNA-based vaccines have shown clinical promise against various solid tumors, such as cervical cancer, breast cancer, glioblastoma, and others.
Viral- and Bacterial-based Immune Stimulants
While not quite cancer vaccines, a related category of cancer therapy exploits the innate ability of viruses and bacteria to stimulate the immune response. The bacterial strain Bacillus Calmette-Guérin (BCG), for example, was originally developed as a preventive vaccine for tuberculosis but is now also used to treat bladder cancer. When BCG is administered into a patient’s bladder, it triggers an immune response within the organ that helps kill cancer cells.
Researchers are also using modified viruses that preferentially infect and kill cancer cells to release immune-stimulating molecules from cancer cells, with one such therapy approved to treat certain melanomas.
New Directions in Vaccine Research
Researchers continue to explore innovative strategies to improve therapeutic cancer vaccines, combining them with other immunotherapy drugs, using new technologies to identify and test novel designs, and developing faster ways to produce vaccines.
To learn about anticipated progress in the field of cancer vaccines, check out our interview with cancer vaccine expert Catherine J. Wu, MD, FAACR.
