Cancer vaccines exist, but don’t expect the impossible
Q Since the English physician Edward Jenner developed the first smallpox vaccine in 1796, vaccines have prevented a variety of devastating diseases and saved millions of lives. The World Health Organization lists 26 available vaccines for diseases from cholera to yellow fever, and another 24 are in development for diseases such as malaria and the Zika virus. Not in the list of diseases targeted by current or potential vaccines: cancer. Indeed, despite advances in medicine, and in the treatment of cancer in particular, there is an unfortunate scientific fact that a comprehensive cancer prevention vaccine will likely never be developed. “Biologically impossible,” says Murray Markman, MD, chief of medicine and science at Cancer Treatment Centers of America® (CTCA). “There can be no vaccine for cancer because cancer is not a single entity. There are thousands of different conditions.”
Vaccines play a vital role in preventing some types of cancer and treating others, and are an essential tool to protect cancer patients during treatment that can make them more susceptible to disease.
However, vaccines play a vital role in preventing some types of cancer and treating others, and are an essential tool to protect cancer patients during treatment that can make them more susceptible to disease. Scientists are also studying new cancer vaccines that have shown positive results in clinical trials as a potential treatment for some patients with melanoma, one of the most challenging types of cancer.
Vaccines that specifically target cancer fall into two categories: those designed to prevent some forms of the disease and those designed to treat it.
- Prophylactic or prophylactic vaccines: Currently, only two of these vaccines are used, and neither of them directly prevents cancer. Instead, vaccines work by killing viruses that can cause cancer. The HPV vaccine, for example, targets the strong strains of HPV that cause most cervical, throat, and anal cancers, and many other cancers. The hepatitis B vaccine is designed to help prevent some cases of liver cancer. “These vaccines block inflammatory viruses that can lead to cancer,” says Stephen Lynch, MD, an admissions physician and primary care physician at the hospital near Phoenix. Other viruses, such as HIV, can also cause cancer, but so far no vaccines have been developed to prevent them.
- Therapeutic or therapeutic vaccines: They are designed to stimulate the immune system to attack cancer cells. Two cancer treatment vaccines are currently in use: Sipuleucel-T (Provenge®), which can help treat advanced prostate cancer, and Bacillus Calmette-Guérin (BCG), which was originally developed for tuberculosis and has since been approved for bladder treatment. cancer. “These can be very helpful,” says Dr. Markman. “They are very powerful immunostimulants.”
While some vaccines are used to help prevent and treat some types of cancer, some scientists suspect that these uses could expand significantly, especially since research on new cancer vaccines has not yielded the results that many had hoped. “The history of cancer vaccines is a history of failure,” wrote one author who listed decades of frustration over cancer vaccine research. However, other researchers are not giving up, and a variety of clinical trials are exploring potential new vaccines for a variety of cancers.
However, they remain puzzled by a nagging question: What should a cancer vaccine target? Dozens of cancers are caused by a large number of genetic mutations, making it impossible to develop a vaccine to target all potential mutations. And since cancer cells are the body’s rogue cells, many cancer cells can hide within sight of the immune system. So even when the immune system is boosted by some drugs, it doesn’t always know which targets to attack. “First, you need to identify something that your immune system can attack,” says Dr. Lynch. “The intent of a vaccine is to generate an immune response, and to get soldiers on a mission to attack when presented with an antigen, a bacteria or a virus. Therefore, the pathogen that can attack it must be identified with a vaccine. And that is a great mystery.”
Encouraged by advances in immunotherapy, cancer vaccine research is back in the spotlight. Several research projects are exploring personalized cancer vaccines, such as sipuleucel-T, that use specialized dendritic cells to stimulate an immune response. Dendritic cells are messenger cells that alert T cells to the presence of antigens, which are proteins found in many cancer cells, distinguishing them from normal cells. Researchers take protein fragments from cancer cells, called peptides, from the patient, attach them to the dendritic cells, and then reinject them into the patient. When the vaccine works as designed, dendritic cells detect peptides to T cells, which look for and attack those proteins.
Researchers in Boston are exploring a similar approach, using new antigens specific to cancer cells to create a vaccine for patients with advanced skin cancer. Neoantigens are new antigens that can develop on cancer cells. Researchers identify many new antigens and use computer algorithms to identify potential targets that could be used to develop a therapeutic vaccine. “New antigens are a very attractive target as a vaccine because they are new virus-like antigens that are potentially more visible to the immune system than antigens previously used in cancer vaccines. Mutant antigens are only present in tumor, not in normal cells,” said researcher Patrick A. Ott, MD, MD. , Ph.D., Ascopost.com .
Aside from vaccines designed to treat and prevent cancer, there are those that are used as an essential tool to help cancer patients stay healthy during and after treatment. Some cancer treatments, such as chemotherapy and a stem cell or bone marrow transplant, can seriously compromise a patient’s immune system. This is why it is so important for cancer patients, their caregivers, and their families to receive vaccinations against influenza and other preventable diseases. “Cancer patients who have compromised immune systems need certain vaccines to prevent infection,” says Mashiul Chowdhury, MD, chief of the CTCA Division of Infectious Diseases. ® and an internist at our Philadelphia hospital. “We encourage cancer patients to get certain adult vaccines, because if they develop pneumonia or a viral illness, it is generally more serious in cancer patients and the outcome can be more serious.”
“We encourage cancer patients to get certain adult vaccinations, because if they develop pneumonia or a viral illness, the disease is generally more serious in cancer patients and the outcome may be more serious.”
-Machiul Chowdhury, MD, chief, Division of Infectious Diseases, CTCA®
Dr. Choudary recommends that doctors and patients follow the adult vaccination protocol established by the Centers for Disease Control and Prevention (CDC). Includes annual flu shot. Cancer patients may also need to avoid live vaccines or those who use live viruses to vaccinate against the disease. “If you give a live virus vaccine to an immunocompromised patient, the virus can replicate itself and the patient can get that infection instead of preventing the infection,” Dr. Chaudhry says. Patients should also avoid contact with people who have received live vaccines for the same reason. Also, patients who have had stem cell or bone marrow transplants may require new boosters or vaccines post-treatment, because these transplants often reverse the immunization effect of previous vaccines.
However, one of the biggest challenges in keeping patients healthy during treatment is getting them to vaccinate. “A large number of people are afraid of vaccines,” says Dr. Choudary. Conspiracy theories linking vaccines to autism or other conditions have led some parents to refuse to vaccinate their children. But the risks of avoiding vaccines are high. In 2017, a measles outbreak in Minnesota infected 79 people, many of them unvaccinated children. More than 125 infected people in California have been linked to trips to Disneyland. The CDC survey showed that 28 of these patients were intentionally not vaccinated due to personal beliefs. “There is absolutely no scientific evidence that vaccines cause autism,” says Dr. Choudary. “It’s very frustrating.”
Despite overwhelming evidence that HPV can prevent cancer, the number of girls and young women who are vaccinated against HPV is still very low. And even fewer boys and young men are vaccinated: Fewer than 11 percent of male candidates for the HPV vaccine get it. As a result, the incidence of HPV-related head and neck cancer has exceeded the incidence of cervical cancer in women. “It’s a serious problem, when we have vaccines that have been shown to reduce cancer rates and people aren’t using them,” says Dr. Markman.
Learn more about the immune system’s complex relationship to cancer.