Introduction to Immunotherapy
What is the immune system?
Our immune system is one of our body’s most important defense mechanisms. Most
commonly we think about it protecting us from infections – things like bacteria and
viruses – which is a really important job of our immune system! But our immune system
also helps protect us from cancer and can even be used to treat certain cancers.
In our bodies, our immune system is made up of immune cells called white blood cells.
Different types of white blood cells are responsible for different parts of the defense.
Some white blood cells kill bacteria, viruses, or other cells directly. Some white blood
cells create a memory of an invader so that the body can respond faster next time – this
is what happens when you have “immunity” to something. One way the immune system
creates immunity is by producing antibodies. Antibodies are proteins that circulate in
the blood and are specially designed to identify specific invaders. For example, if you
get strep throat, your immune system creates antibodies against the streptococcal
bacteria. Those antibodies identify and latch on to the streptococcal bacteria and alert
white blood cells to come kill it. Finally, there are also white blood cells that help control
the immune system and tell it when it’s time to calm down. This helps stop the process
when a threat is resolved and keeps the immune system from attacking cells that are
supposed to be there (normal cells). When this process is broken, you can get
diseases called autoimmune diseases where the immune system is attacking your own
body.
How does the immune system protect us from cancer?
As our bodies are growing and developing our cells are always dividing to form new
cells. This requires the cell to copy its genetic material so that the two new cells are
exact replicas of one another. This is a complicated process that sometimes goes
wrong. Most of the time, your immune system recognizes this “bad” copy, and the cell
is destroyed.
How to cancer cells escape the immune system?
Incredibly rarely, the immune system may not detect a mistake. When those “bad” cells
remain in the body and divide and grow, they can form a tumor or cancer. Cancer cells
are tricky and develop ways to avoid being destroyed by the immune system. Normally,
the immune system will make antibodies that recognize the surface of abnormal cells.
Cancer cells can actually decrease the markers on their surface so that they can “hide”
from the immune system. Cancer cells can also secrete substances that signal the
immune system to be quiet or turn off the immune system and recruit the white blood
cells that calm down the immune response. They can also create physical barriers that
protect them from the immune system or make the environment around them
inhospitable for white blood cells.
It is very hard for the immune system to overcome these cancer defense mechanisms.
Although there are ways to boost your immune system with dietary changes like taking
vitamins, cancer cells are usually too smart and powerful for even the healthiest of
immune systems to conquer on their own.
How can we help the immune system kill cancer cells?
Luckily, scientists are developing more and more ways to help the immune system
attack cancer cells. Using the immune system to treat cancer is called immunotherapy.
Immunotherapy comes in many different forms. Many types of immunotherapy are
designed for very specific types of cancer and not all cancers are susceptible to known
immunotherapy options – although we’re working on it!
Antibodies
One option is to give extra antibodies that are created in a lab that can attach to a
marker on the cancer cell surface. These antibodies will latch on to the cancer cells and
promote the body’s own white blood cells to kill the cells. Antibodies can also be given
with other medicines that help boost the immune response or together with
chemotherapy. For an antibody to work, you have to have a marker that is expressed
on most of the cancer cells. Sometimes, we have to test tumor cells to prove they have
the specific marker before we will give the antibodies. The most common tumor we
treat with an antibody is neuroblastoma.
Cellular therapy
Another option is to give a patient extra white blood cells. This can be the patient’s own
white blood cells that have been modified and are given back to the patient or white
blood cells that are collected from a donor and given to the patient.
Sometimes, a patient is just given extra white blood cells either alone or with
chemotherapy. Sometimes, the cells are modified or changed to make them more
effective against a patient’s specific cancer cells.
One specific type of cellular therapy is “tumor infiltrating lymphocytes” or TILs. TILs are
white blood cells that are naturally within or near the patient’s tumor. To be used as a
treatment, they are extracted from the patient’s tumor, expanded in a laboratory, and
given back to the patient.
Another type of modified cellular therapy is “chimeric antigen receptor T-cells” or “CAR
T-cells.” White blood cells called T-cells can directly kill invaders like bacteria or cancer
cells. They recognize what to kill through a receptor on their surface that identifies a
specific marker on the surface of their target. In a CAR T-cell, a receptor that is
attracted to a patient’s cancer cells is added to T-cells in the laboratory. Those T-cells
are expanded and then given back to the patient. These T-cells can then target the
cancer cells and kill them.
Cancer vaccines
Just like vaccines to prevent infection, scientists have developed vaccines against
cancer. When a patient receives the cancer vaccine, their immune system creates its
own antibodies to attack the cancer.
Checkpoint Inhibitors
One way that the immune system is prevented from attacking normal cells and causing
autoimmune diseases is through “off switches” called check points. Cancer cells can
also activate these “off switches” in an effort to evade the immune system. Check point
inhibitors are medicines that can block the “off switch” and keep the immune cells
turned on so they can attack the tumor cells.
Side effects
Most side effects of immunotherapies are related to over activation of the immune
system. You can see fevers and vital sign (respiratory rate, heart rate, blood pressure)
changes just like when the immune system is fighting an infection. You can also see
side effects that look like autoimmune disease – immune cells attacking normal cells.
For example, you can see inflammation of the lungs or GI tract.
Is immunotherapy for everyone?
Many immunotherapies are designed to treat specific cancers, and some cancers aren’t
as susceptible to attack by the immune system. More immunotherapy treatments are being
developed all the time. Talk to your child’s physician about what options exist for your child’s cancer.
– Dr. Sutton, Kathryn
