Immunotherapy uses a person’s own immune system to attack and destroy cancer cells. Cells in the human body grow and age every day and when the immune system detects senescent and atypical cells, it removes them. Cancer cells are, however, particularly difficult to identify; they can deceive the immune system and evade its attacks, then grow and spread in the human body.
Immunotherapy uses the patient’s immune system to identify cancer cells and attack them by adjusting how the immune system reacts or by studying how cancer cells hide from immune cells.
There are mainly five types of immunotherapy:
1. Immune checkpoint inhibitors
Immune checkpoint inhibitors are the most common type of immunotherapy. When certain proteins on the surface of immune cells (T cells, for example) bind to the proteins on cancer cells, an “off” signal is triggered, thus blocking the attack of T cells. This on/off switch is called “immune checkpoint”.
Commonly used immune checkpoint inhibitors can target proteins like CTLA-4 or PD-1 on immune cells or PD-L1 on the surface of cancer cells, avoiding the binding of the proteins on immune and cancer cells. This avoids an “off” signal from being sent, thus allowing the T cells to attack cancer cells.
2. CAR-T cell therapy
CAR-T cell therapy is currently mainly used for curing blood cancer. It involves collecting immune cells from the patient’s blood. The immune cells are then genetically altered in a lab so that they can recognize cancer cells. Finally, the modified cells are infused back into the patient’s body.
3. Oncolytic virus therapy
In recent years, research has been conducted to treat cancer, for example melanoma, with oncolytic viruses. Also known as virotherapy, oncolytic virus therapy involves modifying viruses with biotechnology to attack cancer cells. When cancer cells are infected with these lab-modified oncolytic viruses, the cancer cells burst and die, releasing cancer antigens that stimulate the immune system to attack other cancer cells.
4. BCG treatment
This is a type of immunotherapy commonly used for treating early-stage bladder cancer. After a patient undergoes endoscopic surgery, the doctor infuses a solution containing the BCG bacteria into the bladder through a catheter. The treatment typically lasts for one year and is aimed at reducing the risk of cancer recurrence.
5. Cancer vaccines
Similar to other viral vaccines, cancer vaccines, which are made up of proteins found on the surface of cancer cells (also known as "cancer antigens"), are injected into the patient’s body. This trains the immune system to recognize and attack the cancer cells associated with such antigens.
After over a decade of research, checkpoint inhibitors have been used to treat many cancers, both early- and late-stage.
Examples of early-stage cancers:
Immunotherapy is frequently used in treating late-stage cancer. Immunotherapy can be used alone or in combination of two immunotherapies, or with chemotherapy or targeted therapy. For example:
Although immunotherapy has been widely adopted in treating different types of cancer, it does not necessarily apply to all cancer types. Research data, pathology reports and biomarkers (for example PD-L1, tumor mutation burden (TMB), microsatellite instability (MSI) and mismatch repair deficiency (MMR)) should be taken into consideration before use. Pancreatic cancer is just an example where no evidence showing immunotherapy is effective.
The primary goal of immunotherapy for late-stage cancer patients is to control the tumor growth. However, some data has shown that immunotherapy can destroy all cancer cells, i.e. completion remission. However, such good outcomes are not commonly seen. While immunotherapy may have a high efficacy in several cancer types, it does not work equally well for every patient. Moreover, some patients may develop drug resistance over time.
Immunotherapy uses a person’s own immune system to attack cancer cells, but healthy cells can also be inadvertently targeted in the process. Since the immune system can potentially affect all the cells in one’s body, immunotherapy may lead to a wide range of side effects.
Side effects may occur in different body parts, including skin rashes, diarrhea, endocrine disorders (such as low thyroid or cortisol levels), impaired liver or kidney function. Fortunately, most side effects tend to be mild, with severe side effects occurring in less than 5% of cases. Doctors will closely monitor patients for symptoms and react promptly when necessary.
Unlike targeted therapy and chemotherapy, the side effects of immunotherapy can appear anytime during treatment or even after discontinuation of the immunotherapy. Therefore, follow-up care is crucial even after the completion of immunotherapy.
Cancer treatment is rapidly evolving, and it is believed that the development of additional anti-cancer drugs targeting the immune system will bring new breakthroughs in fighting against cancer while reducing side effects.
Special thanks to Dr. Wendy Wing-Lok Chan, Department of Clinical Oncology, the University of Hong Kong for authoring and editing this article.
