Can a Vaccine Treat or Prevent Colorectal Cancer?
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Colorectal cancer is one of the most heterogeneous cancers, with various risk factors often working in tandem and increasing the rate of cancerous growth in the colon. As such, much of colorectal cancer prevention and risk reduction has been focused on tackling these risk factors, like switching to a healthier diet or avoiding tobacco and alcohol. For higher risk individuals or those who are genetically predisposed to colorectal cancer, cancer surveillance is often undertaken to monitor each individual’s condition to ensure that any cancerous growth is detected as early as possible.
However, there may be yet other ways to prevent cancerous development, albeit specific to different stages, and this could be done through cancer vaccines.
What is a cancer vaccine?
We typically understand vaccines to be a means to acquire immunity against diseases. These are often administered through injections, following which the immune system of vaccinated individuals are able to deal with the threat of disease.
While cancer vaccines similarly target the disease, a key difference lies in what is recognized as a threat. In other diseases, viruses or bacteria are the foreign entities targeted by immune cells. Conversely, cancer cells — bearing in mind that these originate from the body — are the key targets, and as such, the mechanisms leading to an immune response are also different.
How is a cancer vaccine used?
For colorectal cancer, a lot of research has been done to explore the possibility of a vaccine as part of treatment. Given that there are no approved colorectal cancer vaccines as of yet, we are still a ways away from a vaccine that can prevent colorectal cancer. Nonetheless, while the key area of application lies in treatment, there is more evidence that the immune system is more robust during the early phases of cancer development. Hence, there is a possibility that a vaccine could prevent cancer progression, or prevent it from starting in those that are at high risk of developing cancer, such as individuals with hereditary cancer syndromes (Lynch syndrome or familial adenomatous polyposis (FAP).
As such, a vaccine that can be used to treat a subset of colorectal cancer patients could improve the overall survival rate, particularly if the chances of cancer progression are also greatly reduced.
What types of cancer vaccines are there?
Given that every individual’s immune system is unique, cancer vaccines have to be tailored according to each individual patient. The vaccines are designed so that immune cells will be able to locate cancer cells — which are typically well hidden — and destroy them.
What must first be done is determining the correct type of tumor antigen. Antigens are markers that help the body’s immune system recognize a threat. While it usually indicates a foreign entity, tumor antigens are proteins that are not produced by non-cancerous cells, or are newly formed proteins (neoantigens) due to higher mutation rates in cancer cells. Immune cells must then recognize these tumor antigens and attack cancer cells, thereby removing them from the body.
There are two types of tumor antigens: tumor-associated antigens (TAAs) and tumor-specific antigens (TSAs). While TAAs are usually expressed on both tumor and normal cells, but in higher quantities on tumor cells, TSAs are expressed only by cancer cells. Depending on the antigen type, different types of cancer vaccines can be formulated to act on different cell types.
The different types of possible cancer vaccines are summarized in the table below.
Type of vaccine | Description |
|---|---|
Molecular-based vaccine | Molecular-based vaccines include those that utilize peptide or full-length proteins, DNA and mRNA. Peptides or proteins may contain direct antigens, while DNA or mRNA vaccines encode tumor antigens that are expressed after immunization. |
Cancer cell vaccine | This cell-based vaccine is a direct approach to tumor immunotherapy and uses the patient’s whole tumor cell to create the vaccine. This method includes all the features unique to the patient’s cancer cells, allowing the immune system to correctly identify malignant tumor cells (as opposed to healthy cells, which is then referred to as autoimmune response). |
Dendritic cell vaccine | This is another cell-based vaccine. Dendritic cells are antigen-presenting cells and are crucial for immune activation, particularly the activation of T lymphocytes. Dendritic cells produce antigen material of tumor cells and present it on the cell surface in order to activate T cells. |
Vector-based vaccine | Vector-based vaccines use foreign entities such as viruses, bacteria and yeast that have been modified to express cancer antigens to initiate an immune response. |
How the immune system “learns” to recognize cancer cells.
Source: Journal of Hematology and Oncology
While there are many different types of cancer vaccines that can be used, all of them ultimately serve the same purpose of rendering the immune system functional against malignant cancer cells where they would originally not be recognized as a threat. With many different vaccines for colorectal cancer now in clinical trials, we may soon have a way to rely on our immune system to combat cancerous growth. If this cancer research reaches a breakthrough, it could change the approach to cancer treatment and prevention, offering a hopeful future for the fight against colorectal cancer.
