Anti-cancer vaccines

Immunotherapy is a developing form of treatment for cancer and is becoming more effective as more clinical trials are undertaken. However, there are some drawbacks to these vaccines that need to be resolved in order to make immunotherapy an accepted treatment. 

Photo Credit: Forbes

There are two types of anti-cancer vaccines: preventative and therapeutic. 

Preventative vaccines target oncoviruses, which are viruses that trigger the development of a cancer. If scientists can limit the transmission of the virus, they can limit the development of the cancer in the population.  The human papilloma virus is known to cause cervical cancer, so a HPV vaccine was created and administered to teenage girls (the demographic at risk of contracting HPV). Another vaccine that you may not know is preventative for cancer is the Hepatitis B vaccine. This vaccine protects the patient against liver cancer. However, these preventative vaccines are not applicable to all cancers because not all are linked to viruses. Thus, therapeutic vaccines were developed.

Therapeutic vaccines are known as immunotherapy and they help a patient who is already diagnosed with cancer. Rather than prohibit the development of an initial tumour, it prevents a relapse and aids the immune system in fighting the cancer cells. As a result, the cancer will stop spreading. The vaccines can target Tumor Specific Antigens (TSA’s) or Tumour Associated Antigens (TAA’s). TSA’s are more personalised to a particular cancer that a patient may have and thus more effective. Personalised vaccines are created from the specific tumour inside a patient that has been removed during surgery. Unfortunately, they can be costly and labour intensive to administer. TAA’s are less effective and their lack of selectivity can cause an autoimmune response. An autoimmune response would damage the healthy cells in the body as well as the cancer cells because the immune system can not differentiate between the two. The TSA’s are favoured because they can detect the mutations that a cancer cell has undergone in a patient and target neoantigens (‘new antigens’), making the likelihood of healthy cells being damaged in the process less likely. 

Photo Credit: Historyofvaccines,org

However, there are some challenged that the existing vaccines need to overcome, mostly due to the effects cancer tumours can have on the body. Cancer cells suppress the immune system which is why they are able to divide and spread without being detected by the white blood cells. A vaccine could supply the information to a immune system but the immune system may be so weakened that it will not be effective. Furthermore, ill or old patients will have damaged immune systems, making the vaccine a less effective treatment for them. Scientists have found a way around this in two ways. Firstly, scientists can add a adjuvant to the vaccine. Adjuvants are immunological agents that improve the immune response by stimulating the production of more antibiotics or providing longer lasting immunity. Secondly, doctors can administer the vaccine alongside other forms of therapy which will mean the treatments will work concordant to each other. This approach is often taken when a tumour is too large because a vaccine has a slower effect than chemotherapy or radiotherapy. 

Another important set back is that cancer cells originate from the host’s own healthy cells. As a result, they are good at hiding from the immune system. Cancer cells have a thick coating of sialic acid on the outside which indicate to the immune system that it is not a harmful or foreign cell. Therefore, even if a vaccine boosts immune response, it may not be able to recognise a cancer cell among healthy cells. Some technologies are being developed which can strip the sialic acid off of the cancer cell so that the immune system can detect and deactivate the tumour. 

The prospect of having anti-cancer vaccines seemed to be science fiction a few years ago but now clinical trails are being run and a few vaccines have even been approved by the FDA. For example, the Sipuleucel-T vaccine has been approved for prostate cancer. Preventative vaccines are not much of a shock, but therapeutic vaccines could help treat a multitude of different cancers that differ from patient to patient. 

Photo Credit: YourGenome

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