Our bodies naturally heal after our skin gets cut, and they can defend against the common cold. So, why not cancer?
The relationship between our body’s natural defense system – known as the immune system – and cancer is complex. Sometimes the immune system recognizes and destroys cancer. But cancer often finds a way to avoid immune destruction. Other times, immune cells have a flaw that leads to cancer, such as with B-cell lymphoma. But a type of cutting-edge cancer therapies known as immunotherapy use immune cells to effectively treat some cancers.
To understand the basics of the immune system and its role in cancer, we spoke with immunologist Matthew Gubin, Ph.D.
What is the immune system?
The immune system is a collection of organs and cells that helps keep us healthy. It does this by distinguishing between what we refer to as self (our own normal cells and tissue) and things that make us sick, such as bacteria, viruses and fungi. We call those pathogens. The immune system can also sometimes recognize and destroy cancer.
Most cells that make up the immune system can be found within our bloodstream. Known as white blood cells, they travel to different areas of the body, depending on where they’re needed. They develop from hematopoietic stem cells, which are produced in our bone marrow.
What are the functions of lymphocytes?
Lymphocytes are a type of white blood cells. They play a critical role in keeping us healthy. Without them, we can’t survive.
T cells protect us from infection. In our daily lives, we’re constantly exposed to pathogens, such as bacteria, viruses and fungi. Without T lymphocytes, also called T cells, every exposure could be life-threatening. T cells can wipe out infected or cancerous cells. They also direct the immune response by helping B lymphocytes to eliminate invading pathogens.
B cells create antibodies. B lymphocytes, also called B cells, create a type of protein called an antibody. These antibodies bind to pathogens or to foreign substances, such as toxins, to neutralize them. For example, an antibody can bind to a virus, which prevents it from entering a normal cell and causing infection. B cells can also recruit other cells to help destroy an infected cell.
How does cancer treatment affect T cells and B cells?
Traditional cancer treatments like chemotherapy and radiation therapy can impact the immune system in a couple of ways. First, they can cause a drop in the number of white blood cells in the body, which increases the risk of infection. Chemotherapy treats cancer by going after any cell that multiplies quickly. But by nature, T cells and B cells rapidly divide to replenish themselves. So, patients on these drugs may see their cell counts drop. Radiation therapy can lead to a lower number of white blood cells in the body, too. But after treatment stops, the immune system recovers, and thanks to bone marrow, most patients’ bodies replenish those immune cells.
Also, while chemotherapy and radiation directly destroy some tumor cells, a large amount of them may go untouched. These cancer treatments cause the dying tumor to release products that can act as an alarm for the immune system and that T cells, B cells and other elements of the immune system can recognize.
These traditional treatments work in two ways:
directly destroy tumor cells and
help the immune system recognize and eliminate the tumor
What are the innate immune system and the adaptive immune system?
Our immune system has two arms: the innate immune system and the adaptive immune system. Although they’re often considered two separate entities, they work together.
The innate immune system is the first line of defense. It sends out the alarm that something is wrong. It generally recognizes patterns in cells that help sort self from pathogens. For example, when an innate immune cell comes into contact with a bacteria cell, it identifies it as not self because bacteria have a cell wall structure that’s not found in human cells.
The adaptive immune system includes the T cells and B cells. Unlike the cells of the innate immune system, T cells and B cells can identify specific features of pathogens – or cancer. DNA provides the instructions for a cell’s growth, survival and reproduction. When there’s a change in the DNA, it can cause a cell to divide more quickly and, in some cases, lead to cancer. It also slightly changes the protein the cell produces, but T cells and B cells can recognize this subtle difference and identify the cell as harmful.
How do vaccines work with our immune system?
The immune system has memory. It can respond more rapidly and effectively to pathogens it’s previously come across. Before we had a vaccine for the chickenpox, if you were exposed to the virus as a kid, you were largely protected from getting it again. That’s because your memory B cells and T cells recognized and neutralized the virus before it caused issues.
Thanks to the memory of T cells and B cells, vaccines can keep us from getting sick, or they make the infection much less severe. For example, the COVID-19 mRNA vaccines work by giving instructions to your cells to create a harmless portion of the coronavirus that T cells and B cells recognize and store in their memory. That way, if you’re exposed to the virus, your memory B and T cells will rapidly respond and destroy the virus.
Our immune system is very powerful, but it’s also very regulated. It’s designed to prevent from attacking normal tissue. Without these features, the immune system malfunctions, can damage normal tissue and lead to autoimmune diseases. But, unfortunately, these safety mechanisms sometimes allow cancer to avoid destruction by the immune system.
And sometimes cells of the immune system can become the cancer itself, such as with leukemias and lymphomas. With these diseases, certain white blood cells change as a result of genetic and environmental factors and begin to multiply in an uncontrolled manner. They often lose their real function, use up nutrients and result in cancer.
But another approach, known as cellular therapies, manipulate immune cells outside of the body to help treat cancer. With therapies like CAR T cell therapy, CAR NK cell therapy and TIL therapy, cells are removed from a patient and manipulated in a lab to be better at recognizing cancer cells or more equipped to destroy them and then put back into the patient.
We have more to learn about how the immune system can be used to treat cancer, but it’s an exciting time for scientists, physicians and patients alike.