StemCell Therapy for Inflammatory and Immunologic Disease
Stem Cell Therapy for Immune Mediated Disease Made Easy
Stem cell therapy is new and challenging as are the new developments in our understanding of how the immune system works. I am a practitioner who is 35 years past my graduation date and have used analogies through my practice life to render complex concepts more accessible. As I have studied stem cell therapy and the newest concepts of immunology, I find myself building analogies which I use to teach my staff and my clients about these concepts. Analogies can however only go so far and technical details have their place as well in anything this complex. I have chosen to keep the analogies in blue ink and the technical details in red ink. Reading the black text will give you all the information but will not be as fun.
Our immune system protects us from infection and disease in the same way that the armed forces and police protect the country from foreign invasion and terrorists. Our immune system evolved over millions of years to prevent the number one cause of death – acute infection from trauma. However, in our modern world infection as a cause of death is no longer common. Death is more likely to be the result of chronic diseases such as heart disease, COPD, stroke, cancer and diabetes. Where does this leave the immune system? Is the reason immune mediated diseases are frequent as simple as our large military force (our immune system) overreacting? And how does stem cell therapy fit into this picture? To answer this, we must understand some of the details of how the immune system works
Immune System Basics
We can think of the immune system as working in four phases:
The first phase is identification of the threat and activation of the T-lymphocytes. (Analogy) A terrorist with a bomb is reported to the local police who refer it to the bomb squad and the military is called in. (Details) Antigen presenting cells or APCs, (dendritic cells/macrophages) spot the foreign invader/antigen and send chemical signals to the T-cells.
The second phase is to recruit more cells to come and fight the invaders. The perp is jailed and processed and specialized troops are called in because a larger plot is suspected. Several different types of lymphocytes are activated; Cytotoxic T-cells (Killer T-Cells), Helper-T cells, B-cells, Natural Killer Cells and Memory cells are all activated.
The third phase is destruction of the bacteria, virus or foreign material. The battle begins and the troops destroy the enemy or terrorist cell with bullets, bombs, the SWAT team or hand to hand combat. The T lymphocytes, Natural Killer Cells, Macrophages attack using cytokines like Tumor Necrosis Factor, and Killer T Cells attack using cell to cell contact and B cells attack by creating antibodies.
The fourth phase is to stop the attack and start cleaning up the debris and determining self vs non-self. The attack is called off, the enemy bodies are identified and studied to be ready for future attacks and the battlefield is cleaned up. T-regulatory cells act when they don’t see any foreign invaders left. They instruct Suppressor T-cells to go in and call off the fight and remember with Memory T cells for future reference what the invaders look like.
The fourth phase has a major role in preventing autoimmune disease. After trauma or infection, the body must clean up damaged cells as well as the foreign invaders. The T-regulatory and T-suppressor cells must be able to recognize “self” versus “non-self” in the future and make sure only “non-self” are attacked. If there are not enough T-regulatory and T-suppressor cells autoimmune disease (where our own tissues are attacked by the immune system) can result. We have an immune system that was designed to work in a much tougher environment than we have today. It has kept us alive for millions of years. How does it go wrong and start attacking our own cells? In other words, why would our military suddenly start attacking our own civilians? It all comes down to the Major Histocompatibility Complex.
WHITELISTING, BLACKLISTING and PROFILING
Whitelisting is the practice of only allowing known or preapproved entities to access services or products. (MHC I is an example of a whitelist of cells that are allowed in the body). It is the reverse of Blacklisting. In computing, a blacklist is a control system that denies entry to users, programs, or network addresses that are on the blacklist. (Antibodies and Activated T- Cells are examples of a blacklist of infections that are to be kept out of the body).
Offender profiling, also known as criminal profiling, is an investigative tool used by law enforcement agencies to identify likely suspects. (Toll Like Receptors (TLRs) recognize patterns of molecules that are likely to be an infection and inform the cellular defenses.)
Understanding the Major Histocompatibility Complex and what it does.
A large section of our DNA contains the coding for the Major Histocompatibility Complex One (MHC I). The purpose of the MCH I is to determine the difference between “self” and “non-self” so that we can defend against foreign invaders. Think of it as a whitelist of all your allies with pictures of them their uniforms and equipment. Anything not on the list – “shoot first, ask questions later”. Over millennia, the body has been attacked by many different invaders and
infections, so our DNA has adapted different methods for determining “self” and “non-self”. The MHC I is a unique group of “sticky” proteins on the surface of the cell; like a fingerprint which is identical for every cell in the body. Potential invaders are checked for this fingerprint and if it does not match then it is considered foreign and the immune defenses kick in.
How does the immune system get it wrong?
Over the years the MCH I has used many different methods of identifying “self” and “non-self” all of which have been preserved and saved through time. This reduplication of effort, however, can lead to errors. Like using a copy machine to make copies of copies until they get smeared or difficult to read. In the past our immune system got lots of practice dealing with invaders and was good at correctly identifying intruders. Imagine having a large army trained to fight the enemy but they don’t know what the enemy looks like. Everyone is on full alert, on constant watch for the enemy. One day somebody points to their neighbor and says, “she is a witch”. The local authorities pass the information up the chain and the military officer checks her picture against his list of allies. Unfortunately, his list has been copied a dozen times and it is hard to tell if it is the same woman. The officer says you could be right; “She is a witch”, and before you know it, the Salem Witch Trails are in full swing all over again, with witches being burned everywhere
When the immune system gets it wrong a normal cell with the correct fingerprint is somehow deemed to be foreign. This can happen when the body is stressed by other factors such as environmental stress. When ”self” is incorrectly identified as “non-self” T-regulatory (TReg cell) and T-suppressor cells should stop the reaction and restore calm. In the Salem witch analogy, a person in authority (T-regulatory cell) should have said “she is not a witch, she is your neighbor, put that fire out and lets all get back to work. Without T-regulatory and T-suppressor cells to keep the immune system in check autoimmune diseases like rheumatoid arthritis, inflammatory bowel disease, psoriasis, Crohn’s Disease, asthma and many others can develop
A healthy immune system will have an ample supply of T-regulatory and T-suppressor cells available to prevent autoimmunity from developing. These cells are only created during and
after a “war”/serious infection. But when the immune system is not being used for its intended purpose of preventing death from serious infection it can get out of balance and turn on itself.
What do lymphocytes do?
Lymphocytes are divided into two main groups based on where they develop. B -cells come from bone marrow and T-cells from the thymus gland. B-cells are cloned in lymph nodes and are responsible for making antiBodies. T-cells are thought of as having cell-to-cell combat
How does an animal know it is infected?
Toll-like receptors (TLRs) are now counted among the key molecules that alert the immune system to the presence of microbial infections. TLRs are a type of pattern recognition receptor (PRR) and recognize molecules that are broadly shared by pathogens but distinguishable from host molecules, collectively referred to as pathogenassociated molecular patterns (PAMPs). TLRs are a class of proteins that play a key role in the innate immune system. They are single, membranespanning, noncatalytic receptors usually expressed on sentinel cells such as macrophages and dendritic cells, that recognize structurally conserved molecules derived from microbes. Once these microbes have reached physical barriers such as the skin or intestinal tract mucosa, they are recognized by TLRs, which activate immune cell responses.
techniques. Modern microscopy and immunofluorescent staining techniques have led to greater understanding of the complexity of the immune system.
An abnormal cell (one infected by a virus or bacteria or even a cancer cell) will have abnormal proteins or antigens attached to the fingerprint (MHC I – Major Histocompatibity Complex) on the surface of the cell. There are sentry type cells in the tissues called dendritic cells (DC). Using Toll-Like Receptors (TLRs) these sentries will take hold of some of the antigen (it is now known as an Antigen Presenting Cell) and present it to the T-cell. The T-cell becomes activated and either becomes a cytotoxic or killer T-cell (Tc) or a Helper T-Cell (Th). The killer T-cells (Tc) (we can see a characteristic surface protein called CD8 on the surface now) will destroy the cells displaying the antigens, make clones of itself to continue the attack and make memory cells who will be ready for the next attack. Production of helper T-cells (they have CD4 proteins on their surface) enables specific immunities to develop against infections like intracellular bacteria or protozoa, viruses, fungi or helminth parasites. Th cells also activate B-cells which produce antibodies
In our analogy, the sentry either spots a terrorist cell/enemy force or uses profiling to tell there is an enemy about. They grab a piece of the uniform or take a photo or piece of the enemy and show it to the other troops. The troops grab their weapons and attack everything wearing the enemy colors or looking exactly like the terrorist. At the same time, they send someone for reinforcements (the clones), send intel to headquarters (the memory cells) and request more support for the battlefield (helper T-cells).
The helper T-cells produce cell chemicals called cytokines which trigger a cascade of cell stimulation and production of more cytokines. The result is inflammation which is characterized by Heat, Pain, Swelling, Redness and loss of function. Table 1. lists some of the cytokines and their effects. Helper T-cells attract white cells to the affected area and direct the white cells in the production of cytokines. Helper T-cells are like a mobile command unit; they direct different types of troops and weapons in the fight against the enemy. Helper T-cells stimulate B-cells to produce antibodies. Helper-T cells attract Macrophages and Neutrophils and Natural Killer (NK) Cells which kill any cell with antibody attached to it. Memory cells are T-cells that will convert to killer cells the next time they see the same invader.
The battle continues until Regulatory T-cells (TReg cells) start to turn off the immune response and resolve the inflammation. Regulatory T-cells come in two forms Natural or Induced. Natural Regulatory T-cells come from the thymus. Induced T-regulatory cells also known as Suppressor cells are T-cells that adapt to the invasion. The Suppressor-T cells play an important role in identifying “self” versus “non-self”. Cells that are damaged by the inflammatory response need to be removed but after the infection has been cleared, we don’t want them to be attacked by the immune system. After the battle has been won, the attack troops will be sent back to base (by the Regulatory T cells) and a cleanup crew will tidy up the battlefield. Enemy and allied causalities are separated and counted. Damaged buildings will be demolished, and the ground cleared. Some specialized officers (Suppressor-T cells) will have the job of updating the records of what the enemy look like and maintaining troops and supplies ready to attack if they come back
Cytokines and What they Do
Cytokines are proteins produced by cells that trigger the next part of the inflammatory cascade process. Think of them as chemical signals or chemical warfare that affect other cells to make them do their stuff. Cytokines have names like Tumor Necrosis Factor, Interferon or Interleukin. The names don’t tell us much about what they do. Table 1 lists the more important cytokines and their effects. There are over 50 cytokines known today with more being discovered all the time. Most of these chemicals are inflammatory, a few are anti-inflammatory and some switch between the two depending on the conditions.
Why do we need to know about cytokines? autoimmune diseases like rheumatoid arthritis, IBS, psoriasis, dry eye, ulcerative colitis or asthma to name just a few are common. All these diseases have the same final common pathway in the inflammation cascade. These diseases represent the burning of the witch, innocent cells who get mistakenly attacked by our immune system. There is a new group of drugs which work by blocking Tumor Necrosis Factor and Interleukins. Like stopping the messages getting to the troops to tell them to burn the witches. Blocking the action of cytokines is one way of treating autoimmune diseases. Table 3. lists some of the biological drugs used for human autoimmune disease and describes how they work.
These drugs work but they are expensive, must be administered for life and can have some lethal side effects. They are like using the fire brigade to put out the fire in order to save the witch. They don’t prevent the fire or stop the next innocent from being burned. Wouldn’t it be better to prevent the autoimmune reaction instead of trying to stop it after it happens?
In veterinary medicine we encounter many autoimmune diseases including atopy, immune mediated hemolytic anemia (IMHA), keratoconjunctivitis sicca (KCS), a.k.a. dry eye, diabetes, inflammatory bowel disease (IBS), asthma, glomerulonephritis, feline miliary dermatitis, feline odontoclastic resorptive lesions (FORL), sudden acquired retinal degeneration syndrome (SARDS) and many others. In the veterinary field we often rely on corticosteroids for lack of a better solution to these debilitating diseases. Is there another solution? Can’t we stop the fires from starting? Yes, we can, with Stem Cell Therapy!
Stem Cells are “SuperCells”
Stem cell therapy is a relatively new branch of medicine and it is often poorly understood by the lay person and medical professional alike. At first it was thought that embryos were the only source of stem cells. Now we know that stem cells live in every tissue of the body. Their purpose is to heal and restore function when tissues are attacked or damaged. They exist in a form of suspended animation. When the cells are activated, they divide and change (differentiate) to meet the needs of the repair job at hand. Stem cells are like a superhero who lives among the normal people hidden – like the mild mannered reporter Clark Kent. Once the alarm is sounded, he finds a phone booth and out comes Superman. They produce their own chemical messengers (cytokines) that influence the surrounding environment to promote regeneration, reduce inflammation and to modulate (control) the immune system. Stem cell therapy uses our own stem cells or donor cells to repair tissue or to stop autoimmune diseases from happening.
If stem cells are in all the tissues, why have we not used them before now?
Mesenchymal stem cells, from bone marrow or fatty tissue, are the most commonly used cells in veterinary medicine. When we look at them under a normal or even an electron microscope, they look just like fibroblasts, the cells that form scar tissue. It was only recently that new microscopy techniques allowed us to differentiate between fibroblasts and stem cells. Stem cells may look like a fibroblast, but their DNA is more active, a stem cell can change into a different cell type when the need arises. A fibroblast can only ever become a fibrocyte. The difference in the stem cell DNA is reflected in different surface proteins on the stem cell. By using fluorescent stains that bind to the proteins we can show that tissue contains stem cells. The surface proteins are called Characteristics of Differentiation (CD) since they help us differentiate the cells based on their function. There are about 500 of these CD surface proteins. They can tell us if a cell is a white blood cell, a fibroblast, a stem cell, a nerve cell a liver cell and so on. Staining for specific CDs allows us to prove that the cells we are using for therapy are stem cells. CD are also used to determine the type of lymphocyte. A CD3+ lymphocyte is naive and has not been activated yet but a CD4+ lymphocyte is a Helper T Cell and a CD8+ lymphocyte is a Killer T Cell.
How do we know we have stem cells?
The International Society for Cellular Therapy has suggested 3 minimum physical criteria to define Mesenchymal Stem Cells. (1) They stick to plastic. We can take some fatty tissue, break it up with enzymes and put it in a plastic culture flask and incubate the cells with special nutrients. After 48 hours, we pour off all the liquid and the cells that stick to the plastic are stem cells. (2) Stem Cells must contain certain surface molecules called CDs which can be determined by fluorescent microscopy. (3) Stem cells can differentiate in the laboratory to bone, fat and cartilage by changing the constituents of the media they are fed.
Because stem cells look like fibroblasts it is very difficult to determine the exact characterization of the cells we are growing. Imaging Stations (computerized microscopes) enable close monitoring of our live cultures of cells as well as enabling fluorescent characterization of cellular function. When we are coaxing cells to differentiate into different tissue types, we need to be able to tell when the cells are ready to use for therapy. This system along with careful application of immunocytochemistry staining enables us to design cell cultures for successful therapy.
It is essential that these cells be observed in a sterile disease free environment. This means having a microscope that you do not have to place your eyes on to use.
The phase contrast microscope lives in our biological safety cabinet. The screen is behind a protective glass shield with a laminar flow of sterile air washing over it to prevent bacteria from dropping into the cultures while they are being observed. This is the only way to check the cells daily without risking infection.
The following are actual screen captures from our microscope station showing how we can use a combination of immunocytochemistry and equipment to see stem cell types. The relatively recent advent of fluorescent stains that select for stem cell specific proteins has allowed us to tell the difference between stem cells and fibroblasts. In Figure 4 you can see the outline of a cell and its nucleus, but you cannot tell if this cell is a stem cell or a fibroblast. Figure 5 has the cell and the nucleus outlined. The images in figures 6 through
11 are from our fluorescent microscope using regular light and phase contrast showing stem cells.
In figure 6 we see the cell nucleus using a fluorescent stain called DAPI. The cellular detail that we could see in the brightfield view is gone. To see the rest of the cell we will use a stain for the cytoplasm. Stem Cells manufacture alkaline phosphatase in their cytoplasm.
The “Texas Red” stain shows alkaline phosphatase which helps us understand the cellular function not just the cellular structure. Figure 7 shows the red channel of light indicating these are indeed stem cells.
Multiple stains can be used at the same time which is called counterstaining. The microscope will allow us to merge light frequencies so we can see both the red and the blue spectrum superimposed.
In Figure 8 the fluorescent stain brings out structural proteins that cannot be seen with the brightfield light and the redlight channel and the bluelight channel are merged to show the complete cell.
Figure 9 shows the same cells stained with CD44. CD44 is a cell surface glycoprotein involved in cell interactions, cell adhesion and cell migration. This stain is visible with green fluorescence. So, only the green channel is shown in this image.
Once these images are captured for each fluorescent channel, they can be combined so that different parts of the cells can be seen at once. Or individual channels can be viewed or mixed to highlight different aspects of the cell structure. See Figures 10 and 11.
The utilization of this imaging system requires the knowledge of stem cell structure, function and the application of special stains, blocking agents, counterstains and antibody combinations, in addition to the microscopic equipment necessary to enable this technology but the results are brilliant in more ways than one.
What types of tissues can stem cells treat?
The stem cells that we find in fat and bone marrow are from the mesoderm and are called mesenchymal stem cells. Mesenchymal stem cells can change (differentiate) into any cell type from the mesoderm layer. All cells of the body share identical DNA. Embryonic stem cells have access to all regions of the DNA and can theoretically create any cell of any tissue. We know that all the body tissues develop from one of three layers in the embryo. These layers are called the endoderm, mesoderm and ectoderm. The endoderm germ layer gives rise to the gut, respiratory tract, glands and inner ear; the mesoderm gives rise to connective tissue such as cartilage, collagen, bone, fat, and muscle and blood cells; ectoderm gives rise to the skin and nervous system. Mesoderm as we mentioned earlier is responsible for the development of the blood cells. White blood cells control our immune system. Mesenchymal stem cell DNA therefore has access to the elements that create the events that manage the defense and inflammatory systems of the body. Table 2 lists the three embryonic germ layers and which cell types they become.
How Stem Cells Are Able to Make Different Cell Types
Think of the cell’s DNA as the “cookbook” of the body within which resides all the “recipes” of life. This cookbook has three volumes, volume one is the endoderm, volume two is the mesoderm and volume three is the ectoderm. Within each volume are the chapters. Each chapter represents the cell type. There is a chapter that contains the recipes for the cartilage cells, another chapter for bone cells another chapter for connective tissue like fibrocytes and so on.
The cells have access only to the volume and chapter of the DNA cookbook which they originated from. So, fibroblasts cannot cook the recipes of the cartilage cells and so on. Yet mesenchymal stem cells have access to the whole volume of the book representing all the cells of mesodermal origin.
DNA Methylation is the Key to the Cookbook
The process by which the access to certain “volumes” and “chapters” of the DNA is regulated is called methylation. Methyl groups (CH3) can be added to two of the DNA’s four bases; cytosine and adenine, turning off up to 80% of the “recipes” of the DNA of any adult cell. Embryonic stem cells on the other hand are 100% demethylated (methyl groups are removed shortly after fertilization). As the embryo develops, adult cells and tissues are formed. The stability of the tissues is then “locked” by methylation of the DNA of the completed cells. Stem cells have more of the DNA available “unlocked” or demethylated for transcription allowing them to cook up more cells within the volume of the DNA that they contain.
Stem cells for arthritis
We can see from the table that mesenchymal stem cells can be used to repair collagen, bone and cartilage. Stem cells are very useful for the treatment of musculoskeletal disorders such as arthritis and tendon damage.
When we add stem cells to a joint with arthritis it is like dropping special troops into a war zone. They stop the war (inflammation) and send out signals (cytokines and growth factors) to recruit specialists to rebuild the city (cells to regenerate the tissues).
Drug therapies for arthritis can reduce the pain and slow the progression of the disease but stem cells can help to restore healthy tissues.
Stem cells for autoimmune disease
White blood cells also form from the mesoderm layer. Therefore, mesenchymal stem cells should be able to influence lymphocytes and autoimmune diseases. We know that mesenchymal stem cells are immunoprivileged and/or immunoevasive. This means that they can safely be used as donor cells with the same species without risk of rejection, much the same as blood donation. This type of stem cell would be classed as allogenic stem cells. When we use a person or animals’ own cells to treat them, we call this autologous stem cells. Stem cells can influence the proliferation, recruitment, function and fate of immune cells including T cells, B cells, Dendritic cells and Natural killer cells through both cytokines and cell-to-cell contact. Stem cells retard the activation of T-cells, inhibit cytokine release from helper T-cells, produce anti inflammatory cytokines which inhibit Tumor Necrosis Factor and Interleukins and stimulate the production of Regulatory T-cells and Suppressor T-cells.
In other words, the stem cells get to the war zone and put out the fire. They tell everyone to go home. They replace the wornout copies of the list of friends versus foes and tell everyone they better be 100% sure they have a real witch before they start lighting any fires. Stem cells don’t just put out the fire, they fix the underlying problem. Stem cells have the potential to cure many conditions where we have only been able to manage the symptoms until now.
How Do We Know Stem Cells Work?
Stem cells reside within normal tissues and are held in “suspended animation” or hibernation until activated. Activation is largely the result of chemical signals that are present when tissues are damaged, or the immune system is engaged. These chemicals are Interferon Gamma (INF-γ) Tumor Necrosis Factor Alpha (TNF-α), Interleukin One (IL-1), and Interleukin Seventeen (IL-17).
These chemicals signals (cytokines/chemokines) are very powerful and can be remembered using the analogy of the “Four Horsemen of the Apocalypse” as they foretell death and destruction.
Figure 13. The Four Horsemen of the Apocalypse. The White Horse represents Pestilence or Infection, The Second Red Horse represents War. The Third Black Horse represents Famine. The Fourth Pale Horse represents death. The initiation of infection is heralded by release of Interferon (White Horse), War is chemically induced by IL-1 release (Red Horse), the Th17 cells decide (scales) about self-vs. non-self (Black Horse), and Death ensues with Tumor Necrosis Factor release (Pale Horse).
White Horse – The first horse or White Rider represents Pestilence or Infection. Interferon alpha (IFN- α) raises the alarm of infected cells to prevent future infection.
Red Horse – The second horse was Red, and the rider carries a sword representing War. Interleukin 1 (IL-1) initiates the war called inflammation.
Black Horse – The third horse was Black, and the rider held the Scales of Justice determining who starved from Famine or lived with grain given. Interleukin 17 (IL-17) produced by Th17 cells which are instrumental in (falsely) deciding which tissues are “self” vs. ones that are “not-self”. Self are saved non-self are killed through autoimmunity.
Pale Horse – The Fourth Horse was the Pale Horse representing Death. Tumor Necrosis Factor (TNF- α) causes cells to die when activated.
Interferon Gamma the White Horse – Pestilence
Is known as the immune interferon and is the product of leukocytes that are stimulated by foreign antigens such as viral infection. INF-γ activates macrophages and induces the major histocompatibility complex type two (MCH II) to express immune molecules. It directly inhibits viral replication. IFN-γ can cause autoimmunity when excessively released. IFN-γ is produced by Natural Killer (NK) Cells and Natural Killer T (NKT) Cells.
Interleukin One the Red Horse – War
The IL-1 family is a group of 11 cytokines (chemical cell to cell messengers) that initiates and regulates the immune and inflammatory responses in the presence as well as the absence of infection. For example, damaged tissue in ischemia or lack of blood flow as in a stroke stimulates the release of IL-1. Inflammation as a result of the attack of normal tissues is mediated by IL-1 such as rheumatoid arthritis. Many new drugs have been developed for autoimmune disease such as rheumatoid arthritis that blocks IL-1 activity. IL-1 also has a major role in neuroinflammation. Both TNF- α and IL-1 are implicated in the cause of the breakdown of the blood brain barrier.
Interleukin Seventeen the Black Horse – Famine
Th17 cells can decide who lives and who dies depending on their fate decision to become a harmful Th17 cell or helpful TReg17 cell. Interleukin 17 is a pro inflammatory cytokine. This cytokine is produced by a group of T helper cells known as T helper 17 cells (Th17 cells). IL-17 activates the induction of chemokines. These chemokines recruit the immune cells, such as monocytes and neutrophils to the site of inflammation following an invasion of the body by pathogens. IL-17 acts in concert with TNF-α and IL-1. IL-17 signaling is often observed in the pathogenesis of various autoimmune disorders, such as psoriasis and inflammatory bowel disease (IBD). However, Th17 cells can alter their differentiation program ultimately giving rise to protective or anti inflammatory cells. These protective and non pathogenic Th17 cells induced by IL-6 and TGF-β are termed as TReg17 Cells.
Tumor Necrosis Factor the Pale Horse – Death
– Tumor necrosis factor alpha is a cytokine involved in inflammation. TNF- α is responsible for the cardinal signs of inflammation (heat, swelling, pain, redness and loss of function). It is primarily produced by activated macrophages, although it can be produced by many other cell types such as T Helper lymphocytes (Th) cells, Natural Killer (NK) cells, neutrophils, mast cells, eosinophils, and neurons. The primary role of TNF-α is in the regulation of immune cells. TNF-α can induce fever, cause cell death, cause muscle wasting, initiate inflammation and inhibit tumor formation and virus replication. TNF-α excess has been implicated in a variety of human diseases including Alzheimer’s disease, cancer, major depression, psoriasis and inflammatory bowel disease (IBD).
Role of Stem Cells in Inflammation and Autoimmunity
The Four Horseman analogy described how cytokines activate local hibernating stem cells by chemically communicating to the stem cell “there is a war zone about”. Part of the normal job of the stem cells is to regulate war, to stop war once the enemy is defeated, and to regulate who is a friend vs. who is foe. The war must be stopped before healing and rebuilding can occur, therefore, the stem cell is able to chemically stop the soldiers from fighting and inactivate the toxins of chemical warfare while regulating self vs. non-self. Part of the normal role of stem cells is to prevent autoimmunity from developing.
Big Pharma and Immune-mediated Disease
Before we discuss how stem cells accomplish this dampening of the war zone, we should mention the current arsenal of chemicals that have been developed by our modern pharmaceutical companies to battle this issue. Autoimmune disease is mediated through the activation of the same Four Horsemen of the Apocalypse mentioned above and most of the immune modulating drugs are against these cytokines or their production. The newest chemicals are called JAK inhibitors. JAK is Janus Kinase and it is a protein cluster that receives cytokine messages at the cell surface and relays them to the DNA for processing. Blocking JAK is therefore blocking cytokines. One such JAK inhibitor drug commonly seen in advertisements is Xeljanz (tofacitinib) produced by Pfizer. This drug is licensed for Rheumatoid Arthritis (RA) and Psoriatic Arthritis. It is used along with methotrexate. When compared to its closest competitor for treatment of RA, Humira, (TNF-α inhibitor) Humira proved better than Xeljanz as Humira does not need to be combined with methotrexate to be effective. Nevertheless, in the third quarter of 2016 Xeljanz made Pfizer $278 million. Xeljanz is a billion dollar a year drug that costs the patient $25,000 per year to take and it does not work as well as other drugs in the market. The following table details some of the other similar drugs and their modes of action. Notice how many block the “Four Horsemen” TNF-α, IFN-γ, IL-1 and IL-17.
The Big Problem with Drugs
Many of these names you will recognize, hopefully you do not have to take any of these drugs. The issue is that these drugs have a very specific target that acts to turn off the immune system’s attack on tissues. These drugs also turn off the immune system in general, opening the body to other infections and cancer and even death as side effects. The good thing is they are FDA approved, which means their mode of action has been proven effective. In other words, if you inhibit TNF-α you can treat autoimmune disease, if you inhibit IL-1 you can stop much of the activation and recruitment of the immune system, if you can stop IL-17 you can shut down a cascade of damaging cytokines. If you can inhibit the Janus Kinase signaling pathway to the DNA you can stop many of the harmful cytokines from being produced. Drugs that do these things have FDA approval. These drug companies have spent millions of dollars developing and testing and proving these effects are real. This is the good news. The bad news is that anything that competes with these products will have serious problems if they threaten this multi billion dollar market.
Why Stem Cells are Better than Drugs
The following diagram shows the interactions between stem cells and T Lymphocytes. The stem cells are activated by the Four Horsemen and then they start producing chemicals that stop the war, send the soldiers home, halt the production of chemical warfare, and mitigate the damage.
The stem cells promote regulatory T-cells (TR cells) which reset the major histocompatibility complex (MCH I and II) in determining what is “lf” vs. “Non-self”
Stem cells reduce the production, proliferation of harmful cytokines by reducing the number of and activation of T-Cells.
Stem cell products affect monocytes to reduce the formation of dendritic cells and create anergic T- Cells.
Stem Cells regulate the response to antigens and decrease the activation of all T-cells especially the Th-17 cells and killer T Cells and natural killer cells.
All these effects are moderated by the local tissue conditions. There are positive and negative feedback loops that regulate the degree of immune suppression, tolerance or activation. The effectiveness of stem cells at modulating inflammation eclipses any of the drugs we just mentioned.
Figure 14. Stem Cell Actions on T-Lymphocytes. Stem Cells Are Activated by Interleukin 17 (IL-17), Interleukin 1 (IL-1), Tumor Necrosis Factor alpha (TNF-α), and Interferon gamma (IFN-γ). This activation causes the stem cell to secrete Interleukin 10 (IL-10), Transforming Growth Factor β1 (TGF-β1), Prostaglandin E2(PGE2), Indoleamine 2,3 dioxygenase (IDO), Mesenchymal Stem Cell cytokines (MSC cytokines), Human Lymphocyte Antigen G5 (HLA-G5) and Cytotoxic T-Lymphocyte associated pro-tein (CTLA-4). All act to affect T-Cells. Helper T Cells (CD4 T cells), T regulatory cells (TR1, Th1, TR2, Th2), Cytotoxic T Cells (CD8, or Killer T-cells), Natural Killer Cells (NK), Dendritic Cells (DC). The result is reduced immune response, increased immune tolerance, and resetting of the Major Histocompability Complex or Human Lymphocyte Antigen (HLA).
When challenged, the immune system initiates defense mechanisms in four phases: identification of the invader, activation of T-lymphocytes, recruitment of clones and destruction of the invader and clean up. This is like a war zone where offending invaders are vanquished, infected cells are killed, and normal tissues are damaged in the process. In the fourth phase, the immune system initiates a cleanup and learning mode where memory cells are programmed for future attacks, self vs. non-self is distinguished, and the cellular response is stopped. The successful halt of attack depends on the actions and numbers of the regulatory T lymphocytes (TReg) and Suppressor-T cells. If there is an imbalance in these cells or in the cytokines that create these cells, the attack may not in fact be halted and may continue against normal tissues long after the inciting insult is gone. This results in type IV hypersensitivity or in auto immunity. The harmful byproducts of this immune mediated attack are the Four Horsemen of the Apocalypse A.K.A. Interferon gamma (IFN-γ), Interleukin-1 (IL-1), Interleukin -17 (IL-17), and Tumor necrosis factor alpha (TNF-α). These cytokines wake mesenchymal stem cells from their suspended animation state. The graphic in Figure 14 and Table 4 detail the results of this activation. Activated stem cells release the cytokine Interleukin -10 which negates the effects of three of the four horsemen; it blocks IL-1 and stops the production of IFN-γ and TNF-α. These activated stem cells also release transforming growth factor (TGF) which inhibits the actions of all T-cells including T-helper 17 cells the producers of IL-17; the last horseman to fall. Using additional chemokines and cytokines, stem cells stop the fighting at the front line, stop the recruitment and enlistment of new cells to the battle and halt the production of the war machinery through restriction of the supply line of tryptophan (necessary for T cell function) and inflammatory lipopolysaccharides. If this were not enough, the actions of these stem cells is also to increase the creation of and the number of TReg cells and Suppressor T- cells to enlist them in stopping the battle. This scenario does happen naturally but not at the intensity necessary to prevent auto immunity. Adequate numbers of live activated stem cells applied therapeutically to the affected site is necessary to change the fate of the auto immune disease state from active to quiescent. Therapeutic application of stem cells also resets the Major Histocompatibility Complex so that recurrence of the auto immune disease state is unlikely to recur soon.
We have explained the function of adipose derived stem cells compared to embryonic stem cells. We have described how stem cells modulate the immune system to control inflammation and start the repair process. We have shown how stem cells work to treat auto immune disease. We have shown how stem cells compare to drugs. With stem cell therapy, the effects are safe and natural and self limiting. The effects are proven, use natural pathways and pose no long term danger to the animal.
The US Government tracks all research both publicly and privately funded at https://clinicaltrials.gov/ and I suggest you go there, use their search engine to see the work that has been done with stem cells therapy. You will find over 7,000 different stem cell research studies.