Immunotherapy is novel approach that uses the body’s own immune system to fight cancer, a ‘demon’ that clearly remains one of the most dreaded diseases. Our immune system – with its army of specialized cells, chemical substances, tissues and organs – fights and protects our body from a range of disease-causing pathogens. And it CAN even destroy cancer cells.
The immune system employs special cells and complex mechanisms to target and fight cancer cells. As the understanding of these mechanisms are evolving, it is opening new, exciting avenues to manage cancer with better outcomes in terms of improved quality of life, increased lifespan and reduced recurrence rate.
How our immune system works
Our immune system is remarkable in its ability to identify and selectively target foreign invaders such as bacteria, viruses, parasites and fungi, while leaving healthy cells and tissues alone. We have already discussed how our immune system is smart enough to distinguish between healthy and unhealthy cells in one of our previous articles, “Immune System and Pathogens .”
Summing it up, foreign invaders or germs contain certain proteins called antigens. Our immune system doesn’t recognize these proteins as a part of the body and launches an attack to get rid of them.
Why immune system has limitations in fighting cancer?
Our immune system has a tough time dealing with cancer cells as they have developed various mechanisms to escape the attack. But most importantly, the immune system doesn’t always see cancer cells as something foreign. It is because these cells emerge from our own cells. Cancer happens when our normal cells undergo a series of mutations and start growing out of control – becoming less and less like healthy cells.
In addition, cancer cells find several ways to fool the immune system – easily slipping through its defences. Thus, they continue to grow and spread in the body without any restraint while successfully preventing the immune system from attacking them.
Scientists have recognized this pattern and have found ways to either:
- Boost the immune system response to fight cancer cells more effectively, or
- Empower the immune system to identify and target the cancer cells
Types of cancer immunotherapy
Monoclonal antibodies typically work by exposing the cancer cells to the immune system, making them more susceptible to the attack. How does it work?
- Immune system attacks invading pathogens by recognizing specific proteins or markers (antigens) on these foreign substances.
- Immune system makes antibodies. These specialized proteins bind to antigens to neutralize the pathogens.
- Researchers can create antibodies in the lab that can target a specific antigen found on the cancer cells. These are known as monoclonal antibodies (mAbs).
More information on monoclinical antibodies can be found here
These are the drugs specially designed to block the ability of cancer cells to evade the immune system attack. How does it work?
- Every time the immune system is in an alert mode, the body creates certain checkpoints in the immune response. It makes sure that immune cells do not mistakenly target healthy cells.
- Cancer cells have learned to recognize these checkpoints and take advantage of this property to stop the immune cells from further attacking them.
- Checkpoint inhibitors disable the cancer cells to use these checkpoints; and reactivates the immune system army of T cells and B cells to fight cancer.
For example, drugs like Pembrolizumab (Keytruda) and Nivolumab (Opdivo) are used to target PD-1 – a specific checkpoint protein on T cells. According to American Cancer Society, these drugs have been found to be helpful in treating many types of cancer, “including melanoma of the skin, non-small cell lung cancer, kidney cancer, head and neck cancers, and Hodgkin lymphoma”.
More information on checkpoint inhibitors can be found here.
Adoptive T-cell therapy
The purpose here is to boost the numbers and functions of T cells – helping them to launch a much more fierce attack against cancer. How does it work?
- Doctor collects T cells from a patient’s tumour.
- Extracted T cells are re-engineered in the lab – to boost their numbers and natural ability to detect and destroy cancer cells.
This therapy has thus far shown tremendous potential in fighting leukaemia and lymphoma in both children and adults .
Our immune cells release certain chemicals, called cytokines, that help in regulating the growth and functions of other immune cells. These chemicals also play a crucial role in how the immune system responds to cancer. In this therapy, cytokines, more specifically interferons and interleukins, are injected into the patients. How does it work?
- Interleukin-2 (IL-2) are chemicals that help immune cells to grow and replicate much faster. A lab version of IL-2 has been approved to treat melanoma and advanced kidney cancer .
- Interferons are chemicals that help the body to develop resistance against cancers and infections. Out of three type of interferons (IFN-alfa, IFN-beta and IFN-gamma), only IFN alfa is used in immunotherapy. IFN alfa is believed to work through various mechanisms; for example, by increasing the efficiency of immune system to target cancer cells or by directly slowing down the growth of cancer cells. IFN alfa also possibly works by limiting the growth of new blood vessels that supply additional nutrients to the tumor.
More information about how cytokines can help treat different types of cancers can be found here.
These vaccines work like normal vaccines that use weakened or killed viruses or bacteria to kick start an immune response. How does it work?
- These vaccines are made up of cancer cells or antigens. Sometimes these vaccines are created in the laboratory by extracting a patient’s own immune cells and exposing these cells to cancer cells.
- When injected, these vaccines help the immune system to launch a better response to destroy cancer cells.
- Some vaccines help treat cancer and even keep cancer from recurring following conventional treatments. Some vaccines are also believed to prevent certain kind of cancers.
This therapy has shown potential but is still in nascent stages. Several studies and clinical trials are underway to determine the efficacy and side-effects of this treatment. Provenge® is the only vaccine approved in the US to treat cancer so far. It’s used to treat advanced prostate cancer when hormone therapy fails to achieve the desired result . There is currently a class action suit underway in Japan regarding a cervical cancer vaccine which highlights much more research must be down in this area.
There is a lot of excitement about how immunotherapy might be helpful in treating different kinds of cancers. But it is still used in clinical trials and given to either patients with advanced stage cancers or those whose cancer has come back or has spread with the conventional treatment.
Yes, there are risks involved. This is because activating or boosting the immune system functions might backfire. There is a probability that the immune system starts to attack the patient’s healthy cells and tissues.