Immunogenetics: The future of Cancer Treatment
As long as you are alive you are being exposed to pathogens. There are million of different kinds of bacteria, virus and parisites around us. It might feel very gross and you may feel the urge to carry hand sanitizer around you but don’t worry. Your body will keep you safe!
You should thank your immune system! Your immune system is a complex defense system your body has against foreign substances. You can think of it as your own personal army. Like the barbed wires on a fence, your skin acts as the first layer of defense.This first layer of defense is called your innate immune system.
Innate Immune System
Ok so, what is this first layer of defense our body has against these pathogens. We as stated before, has skin as our first layer of defense. This is the physical part of our innate immune system. This also includes, mucus, tears, stomach acid, oils, and even your saliva. But thats just the beginning. There are more chemical and even cellular defenses as part of our innate immune system.
One main chemical defense is inflamation. This is basically where white blood cells water leave the blood vessels and enter the tissue. This then allows them to fight the disease. The next type of chemical defense is anti-microbials. This could be short-chain fatty acids or short peptides. These are important because they distrupt cellular integrity in cells. They are usually produced by epithelial cells or even the white blood cells.
Next we have complement. This is basically a group of peptides that are usually produced by the liver and form a Membrane Attack Complex. The cell forms holes in the cell membranes of the pathogens, which in the end causes them to die because of the rush of water entering them. But another role they play is to increase inflammation and promote phagocytosis.
Now finally to our cellular defense mechanisms. All cellular innate immune cells come from the common myeloid progenitor cell. But I’ll intro those later. Let’s take a look at some of those cells. So our innate immune system is made up of natural killer cells, macrophages, neutrophils, dendritic cells, mast cells, basophils, eosinophils.
At first we have out dendritic cells and out macrophages. These are also called Anti-gen presenting cells because they are responsible for presenting antigens to our T-cells and B-Cells, which are part of our adaptive immune and that we will get too later.
Next we have basophils and mast cells which are responsible for producing histamines. Histamine is responsible for causing innflamation. These cells usually are right under your mucus membrane. They are also part of the reason for allergies.
Natural Killer Cells. This cell is considered innate because they dont have to be activated the same way our T or B cells do. They usually target virus infected cells but are also responsible for targeting tumor cells.
Next is Neutrophils. We have more of these circulating in our blood than any other WBC. They are phagocytic and can release bleach or peroxide.
Finally Eosinophils. These are crucial when fighting off parasites.
The cells make up the innate part of our beloved immune system. But after this first layer, we get into the adaptive immune system. It gets really crazy and cool from here!
Adaptive Immunity?
So, as its name suggests, this part of our immune system that has the ability to adapt and learn. It is made up of two main cells, T-Cells and B-Cells. But let’s start from the beginning.
We start out journey in our bones, specifically bone marrow. Our body marrow contains multi-potential hematopoietic stem and progenitor cells. Now just becuse these are stem cells does not mean they can turn into every-type of cell in our body. Those are pluripotent stem cells, which are only present during the development of the fetus.
But these multi-potential hematopoietic stem cells have the power to turn into two different types of cells, common myeloid progenitor or common lymphoid progenitor cell. Myeloid progenitor cells have the ability to turn into any cell in our innate immune system and lymphoid progenitor cell can turn into T-cells or B-cells , or our adaptive immune system.
The differentiation of the lymphoid progenitor cell takes place in our thymus. The cell can turn into either a naive (CD4+ or CD8+) T-cell or a naive B-cell. If during this process, a T-cell has receptors to regonize self-antigens, it will be destroyed. We don’t want the T-cell attacking our own cells.
When the naive T-cell is developed from the lymphoid progenitor cell, they all have CD4 and CD8 co-receptors. However, when they mature, proliferate and differentiate they will become either a Naive CD8 T-cell or a Naive CD4 T-cell. The only difference between the two is that the Naive CD8 T-cell has the CD8 co-receptor and Naive CD4 T-cell has the CD4 co-receptor.
The naive CD8 T-cell will become activated when an infected antigen presenting cell such as a phagocyte presents an antigen on the MHC (major histocompatibility complex) class I. This will activate the the naive CD8 cell to become a cytotoxic T-cell also commonly known as CD8 cytotoxic T-cell. Cytotoxic T-cells destroy infected cells with the same specific antigen that was presented by the infected phagocyte. This is their goal, to kill infected cells.
But what about the naive CD4 T-cell? The naive CD4 cell will become activated when a non-infected antigen presenting cell such as a phagocyte presents the foreign antigen on an MHC (major histocompatibility complex) class II. Once the CD4 cell becomes activated it can become a T-helper cell. The main job of these T-helper cells is to enhance the immune response. This can be done by activating B-cell, natural killer cells or other macrophages and phagocytes.
Now lets move to the member of our adaptive immune system, the B-Cell! The naive B-cell that came from the lymphoid progenitor cell has anti-bodies. These anti-bodies can recognize specific anti-gens of a pathogen. The B-cell will engulf a pathogen and process it. It will then present an anti-gen on a MHC class II receptor to T-helper cell. The helper T-Cell will then tell the B-cell to proliferate into either a plasma cell or a memory B-cell.
Plasma cells will secrete specific anti-bodies towards that anti-gen. But memory B-Cells will keep record of that same anti-gen so that in a future infection with the same anti-gen will get resolved quickly.
Antibodies can do three main things, Neutralize, opsonize or active complement.
- Neutralization-when anti-bodies prevent adhesion and also neutralize the pathogen.
- Opsonization- anti-bodies will coat a pathogen making it easier for pathogens to engulf.
- Active Complement- anti-bodies will again help for phagocytosis but also help to lyse the pathogen.
Ok, now we we have a general idea about our immune system, both innate and active. But lets quickly hop on to another topic. GENE EDITING!!!
What is Gene Editing?
First, try to imagine building your dream house, but you have limited intructions. It’s not going to be easy and it will take you quite a long time.
Now imagine not having the instructions for something complex, like you and me, humans! Designing drugs and curing diseases is much harder. We also simply don’t know as much as we could.
We guess what…as of 2003, we have the entire human genome mapped out.
The human genome project was a massive worldwide project where the whole world came together to determine all the base pairs of the human genome. A genome is the genetic blueprint of any organism. They provide instructions for every single protein that is produced in any organism ever alive. The project took 13 years, from 1990–2003. It’s been over 17 years since we mapped the human genome. But what if we could edit our genes…
Introducing…CRISPR!
CRISPR (clustered regularly interspaced short palindromic repeats) is a family of DNA sequences found within the genomes of prokaryotic organisms such as bacteria and archaea. These sequences are derived from DNA fragments from viruses that have previously infected the prokaryote and are used to detect and destroy DNA from similar viruses during subsequent infections. Hence these sequences play a key role in the antiviral defense system of prokaryotes.
Bacteria use a Cas-9 enzyme as part of their immune system. When a virus inserts its DNA into the bacteria, the bacteria will use this enzyme to make a cut, therefore disabling the DNA. What if we could use this technequie to edit certain DNA to our advantage? This is exactly what gene editing is.
In short, they act like an eraser. You can remove genes you dont want and add genes you want. This could result in new proteins not getting produced or getting produced to your advantage.
This technology is being tested in a wide area of subjects. Proposals and ideologies have been brought up but legal and ethical issues have limited its use.
There are also other methods to edit our genes such as ZFN’s (Zinc Finger Nucleases) or TALEN’s.
Immunology X Gene Editing
The ability to edit our genes has given us lots of power over the function of our cells.
Our immune system is responsible for important reactions in our body such as regulation of pathogens, or even regulating cancer growth. Like all cells, immune cells have DNA and genes. What if we could edit these genes of these immune cells to help our body fight diseases like cancer.
Cancer is one of the leading causes of death in the world. Over half a million people die from these diseases each year. But what exactly is cancer ?
Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body.
In 2020, there will be an estimated 1.8 million new cancer cases diagnosed and 606,520 cancer deaths in the United States
How can we use our own immune system to battle cancer?
CAR T cell Therapy
The problem with cancer cells is that they are not recognized by the body, allowing them to proliferate and cause harm. This is because they disguise themselves, similar to a thief wearing a mask and can not be recognized by the immune system. This is where CAR T cells come in!
CAR (Chimeric antigen receptor) T cells are T cells that have been genetically engineered to produce an artificial T cell receptor for the use in immunotherapy. They are considered to be “chimeric” because they combine both anti-gen binding and T cell activating functions into a single receptor. The idea behind using CAR T immunotherapy is to modify T cells to recognize cancer cells and effectively target and eliminate them.
How are CAR T cells produced?
The first step in the production of CAR T cells is to isolate the T cells from the human blood. If the blood is from the patient’s own blood then it is called autologous treatment but if the blood is from another healthy donor, it is called allogeneic treatment. But the idea is the same, to isolate the T cells. A machine used to purify and seperate the T cells is a leukocyte apheresis. T cells fall under the category of PBMC (Peripheral Blood Mononuclear Cells). These PBMC’s are separated and purified.
After being removed and separated the T cells are sent to a cell processing center where they proliferate and grow in numbers. To help the T cells expand, it is common to use interleukin 2 (IL-2) or even anti-CD3 antibodies. Once they have grown in number they are purified again.
After being purified the T cells are genetically modified to have the constructed CAR receptor. In the past retroviral vectors have been used, usually through gammaretrovirus (RV) or a lentivirus (LV) vector. However, the new CRISPR/Cas9 system is becoming more popular instead of the retrovirus due to the precision of where exactly the CAR gene could inserted into the genome.
Before the insertion of the CAR T cell, the patient must go through chemotherapy. This is in order to reduce the amount of leukocytes in the body to reduce competition and and allow for the expansion of the engineered CAR T cells.
The CAR receptor
CAR receptors combine many factors of normal T cell activation into a single receptor. The receptor is made up of four main regions, an antigen recognition domain, an extracellular hinge region, a transmembrane domain, and an intracellular T-cell signaling domain.
Antigen Recognition Domain is the part of the receptor that is exposed outside the cell. It is responsible for interacting with the target molecules and targeting the CAR T cell to any cell with the matching molecule. This part of the receptor is obtained from monoclonal antibodies and linked together as a scFV (single-chain variable fragment). The scFv is a chimeric protein made from both heavy and light chains of immunoglobins that are connected with a shorter linker peptide. These light and heavy immunoglobins regions are pre-selected due to their binding ability to the target antigens.
Hinge Region consists of a hydrophobic alpha helix that is between the antigen recognition region and the cell’s outer membrane. It promotes antigen binding and also synapse formation between the target cells and the modified CAR T cell.
Transmembrane Domain is basically responsible for keeping the CAR receptor stable on the cell membrane.
Intracellular T-cell signaling domain lies in inside the cell. Just like normal T cells, CAR T cells rely on the phosphorylation of immunoreceptor tyrosine-based activation motifs (ITAMs). There also needs to be co-stimulatory molecules. Some successful co-stimulatory molecules are CD28, CD27, CD134 (OX40), and CD137 (4‐1BB).
Development of CAR T cells
As the CAR T cell developed more small molecules were added in order to enhance performance.
- Second Generation CAR’s added co‐stimulatory domain, like CD28 or 4‐1BB.
- Third Generation CAR’s combined multiple co-stimulatory domains, such as CD28–41BB or CD28-OX40 in order to augment the T -cell activity.
- Fourth Generations CAR’s added more factors to help optimize performance such as the addition of IL-2, IL-5, IL-12 and co-stimulatory ligands.
So what?
What have CAR’s been able to do? What can they do? What are its limits?
As you know, these cells have been genetically modified in order to help target specific receptors on the cancer cells in hopes of eliminating the cancer.
Much of the early CAR T cell research has focused on blood cancers, especially the ones that target the CD19 receptor, like acute lymphoblastic leukemia (ALL) and diffuse large B-cell lymphoma(DLBCL).
However, solid tumor have been more difficult to target. The problem is we need better understanding and knowledge about the specific receptors that are on there solid tumors. We DON’T want the CAR T cell attacking our own somatic cells.
CAR T cells are also really expensive! They can not be afforded as a treatment for everyone. In the future we need to work on making them cheaper and more available to a larger population.
TL;DR
- Our immune system is a complex system in our body containing different techniques and methods to protect us from harmful pathogens.
- Gene Editing gives us the ability to edit the genome in order to produced desired effects.
- Using gene editing technologies we can arm our immune system to fight disease.
- CAR T cells have the potential to kill cancer cell but have limitations such as, of target effects and availability to the greater population.
Thanks for reading! Feel free to check out my other articles on Medium.
If you’d like to discuss any of the topics above, I’d love to get in touch with you! — Send me an email at sbmohammed03@gmail.com or message me on Linkedin!
