31 January 2024
Check Up #22 - Cancer vaccines
Cancer vaccines: preventative or therapeutic?
We are used to hearing about vaccines that prevent diseases, protecting us from them before we ever catch them. They train the immune system to recognise and fight common bacteria and viruses. One or several shots suffice to ensure that, when we are actually confronted with the danger, our body’s immune system will produce the right cells and antibodies to protect us: the disease will be prevented before it ever affects our body. Sometimes the vaccine’s effects are lifelong, in other cases you need a periodical boost to maintain a strong level of immunity.
Common examples of these preventative vaccines are those against measles and many other childhood illnesses; against tuberculosis, against tetanus, against poliomyelitis, against the flu or covid-19 – to give a few examples. They have saved – and continue to save – millions of lives.
Even though some of them protect us better than others, most of these vaccines (think about the yearly flu or covid-19 shots) are efficacious enough at preventing the most lethal forms of the diseases they target. And in some cases, against measles or smallpox for instance, vaccines have offered such levels of protection that massive vaccination campaigns have managed to eradicate those once-lethal diseases.
As for cancer vaccines, they can be of two types: those that prevent cancer and those that treat cancer.
There are actually two well-known vaccines that are cancer-preventing. One is the hepatitis B vaccine, which prevents infection by the hepatitis B virus, a cause of liver cancer – and can therefore be said to prevent this cancer. The other is the human papillomavirus (HPV) vaccine, which prevents infection by several strains of HPV, a virus that can lead to cancer of the cervix. Vaccines preventing other cancers are being researched, but we have a long way to go and such “magic bullets” are not expected to be available anytime soon.
In fact, most vaccines currently being researched and tested against cancer attack the disease after it appears: they are so-called therapeutic vaccines or treatment vaccines. There is one singular instance worth mentioning here as a mere curiosity: in a kind of off-label use, the BCG vaccine, a preventative vaccine against tuberculosis, is being administered as a therapeutic vaccine to treat early-stage bladder cancer.
Researchers are testing therapeutic vaccines for many types of cancer, including: bladder cancer, brain tumours, breast cancer, different stages of cervical cancer, colorectal cancer, kidney cancer, leukaemia, lung cancer, melanoma, myeloma, pancreatic cancer, and prostate cancer.
Therapeutic vaccines are a type of cancer treatment called immunotherapy. They work to boost the immune system of cancer patients to fight their existing tumours (rather than to prevent them from occurring). Simply put, doctors give these vaccines to people who already have cancer. Treatment vaccines are currently not a first line of treatment: they are used, for instance, to destroy any cancer cells still left in the body after other, more conventional, treatments have been performed.
Therapeutic vaccines are made of antigens, which are molecules that cause the immune system to produce antibodies against them. Taking advantage of the fact that certain antigens are only present on the surface of cancer cells, these antigen vaccines boost the immune system's ability to detect those cancer cells and destroy them – ideally sparing healthy cells. But because things are never as simple as they seem, more often than not the difficulty in developing these vaccines lies in identifying antigens that are truly cancer-specific.
In some cases, therapeutic cancer vaccines can be personalised, that is, made from samples of one person's particular tumour – and thus target that person’s particular cancer antigens. On the other hand, they can also contain more “universal” antigens, which are not specific to any individual person.
Sources:
https://www.cancer.net/
https://www.cancerresearch.org/
https://www.mskcc.org/
