In 2020 the world stopped due to an outbreak of COVID19. Around the world, journalists and scientists tried to break scientific expressions, such as virus, vaccines, and immune system, into simple ideas that everyone could grasp. People worldwide may now recognize the immune system as our body’s police force, that exists to fight invaders, as a virus. However, this immune-police force can help to fight not only outside invaders but also inside intruders, such as cancer.
But how?
In a very similar way by which the immune system identifies a virus, through antigens. These are proteins that are usually not present in our body so are seen as external invaders. Do you remember listening about the spike proteins in the news during COVID19? That’s it, a protein that was present in COVID19 virus and we used it as a base to produce vaccines, because it is seen by our immune system as an antigen, activating our police forces to fight COVID19.
Now the tricky part is, cancer cells, despite coming from healthy cells that we have in our bodies can also have proteins that we usually do not have, for instance, cancer cells can modify the proteins they produce (we have a really cool post explaining how cells produce proteins- What If a Cell Was a city? – The Industry of Protein Production). Thus, cancer cells have antigens that can activate the immune system against cancer, like traces that our police forces can follow to find the invader.
So why do we have cancer?
Although our immune defenses can kill cancer cells in the beginning of their conversion to the criminal side, often cancer cells act like true crime experts and learn ways to widen their antigen traces, becoming invisible to our immune-police forces and growing their gang. Here it’s where scientists come with their police academy to train more and better police agents.
In this academy, immune cells get better at recognizing and killing cancer cells, therefore, they can be used as treatment. To this we call: Cancer Immunotherapy. Despite just being in clinical use since the 2000s, immunotherapy is already considered the 4th pillar of cancer treatment along with surgery, chemo- and radiotherapy.
To accomplish this, in the past years, keen scientists have created multiple police tools and trained several police agents. This is the example of the most famous agent of our immune system- T cells.
These are police agents that kill cancer cells once they recognize them by their antigens. Although efficient, for T cells to see cancer cells, the antigens need to be shown by specific molecules called- Major Histocompatibility complex (MHC). These MHC molecules are often decreased in cancer cells, making cancer invisible to T cells. To overcome this, T cells can be changed in the laboratory to identify cancer antigens that are not shown in these MHC molecules. To this we call CAR-T cells.
Additionally, cancer cells can also armor themselves with weapons that impede T cells to kill them. For this, scientists create an antidote- proteins that cover those weapons, protecting the T cell agents and letting them do their work. This antidote has the name of immune checkpoints inhibitors (ICI), created by James P. Allison and Tasuku Honjo, which were awarded the Nobel Prize of Medicine 2018.
Figure 1. Cancer Immunotherapy Strategies. T cells see cancer cells by antigens shown at MHC molecules. Since cancer cells can decrease their MHC molecules, one strategy is to use CAR-T cells, which are T cell changed in laboratory to see antigens not in MHC molecules. Cancer cells can also increase molecules (immune checkpoints) that decrease T cell killing activity.To protect T cell activity, immune checkpoint inhibitors (ICI) were created.
Many other agents are being trained in this police academy, including forensic agents (dendritic cells) whose expertise is to look for antigens and show them to T cells. Improving this police academy training is a key mission, as cancer cells can change their modus operandi. Despite the challenges, scientists around the world work every day in this mission with the belief that justice will prevail.