NR: Switching from politics to science, one of the more compelling sets of slides in your talks is in the injury response cascade (see page 48). I was wondering if you could talk about how MSCs can affect the injury response and how that relates to chronic injuries and chronic inflammation?
AC: It turns out that MSCs exist in the body on every single blood vessel. When a blood vessel is broken, inflamed, or involved in a chronic wound, those perivascular (surrounding a blood vessel) cells come off and differentiate into what I call MSCs. An MSC in this context is a cell that makes drugs or molecules that are specific to the site where the injury has occurred. For example, the MSCs in brains of patients with stroke, or in hearts of patients with heart attack, though they’re similar, will make different cascades of molecules. These cells naturally function to protect sites of injury from an over-aggressive immune system that is always trying to survey and interrogate injured tissues, looking for invasive components. And so, your natural immune response brings these very aggressive immune cells into the injury field. The MSCs slow them down and tell them to go away because they are not needed. They let the body know that the injury can take care of itself, and that it’s not a huge infection.
These MSCs are sentinels for injury. Not only do they put up a local curtain on their front side, which stops these aggressive immune cells, but from the backside, these MSCs also produce molecules that allow the injured tissue to slowly heal without scarring. This is real tissue regeneration—not simply plugging the hole with a scar, but with more tissue, which takes time. The MSCs set up an environment in which real regeneration can take place.
The problem is that, as adults age, we lose blood vessels, and therefore we lose these very important regenerative cells. Very often, we need a booster shot of more MSCs. There are two ways to do that: You can isolate the MSCs from your own body and get them back to the injury site; or you can use cells from someone else. Because of the curtain of molecules produced by the MSCs, which is directed against immune cells, the MSC is sort of hidden from the immune system. Your MSCs in my body would temporarily not be seen by my immune system. Some people call this immune-privileged, but that’s not the case—the immune system eventually catches up with them. But for the short term, MSCs pour out molecules so the immune system can’t see them. In essence, they are camouflaged. We call this immuno-evasion: MSCs evade the immune system.
In older people who don’t have enough local MSCs, in particular for heart attack, you can inject MSCs from somebody else into the blood stream. The allogeneic MSCs will dock at the injury site and supplement the local MSCs, producing therapeutic effects. There’s a gigantic number of clinical trials now in play using MSCs both from the patient and from an u elated donor. So umbilical MSCs, which come from discarded tissue, are just as good as your own MSCs. In fact, when they are put in culture and caused to divide, they are actually more plentiful than your own MSCs as an adult.
There are a variety of ways in which you can propagate MSCs and get them to expand, and a variety of ways to get them to sites of injury. Direct to the injury site (e.g. into the knee cavity) is one way; and systemic delivery into the blood stream is another way to introduce MSCs from outside the body. MSCs put up this curtain of molecules, which protects the injured tissue from immune surveillance. In people who have a defective curtain, destruction of tissue by the immune system occurs. We call this autoimmune disease. Multiple sclerosis (MS) is an autoimmune disease in which the immune system attacks nerve coverings, destroying myelin. Therefore, the myelin insulation gets attacked by the immune system, short-circuiting those nerves. That’s the basic clinical cause of MS. So even if you give somebody bk their own MSCs, they may be defective. In people with autoimmune disease, it is probably better to deliver someone else’s MSCs from normal, healthy donors who don’t have autoimmune diseases. The choice between autologous (from yourself) versus allogeneic (someone else’s) is a medical decision that needs to be made depending on the disease that these cells are introduced for treatment. This is subtlety. There is no question in my mind that some individuals will have MSCs with defects, and that’s going to be the reason for certain autoimmune diseases.
NR: In the last couple years, Dr. Sun in Nanjing, China has done a bunch of work on lupus. He has identified the actual defect in the MSCs of people with lupus, and it’s led to a lot of clinical trials, one very recently published.
AC: We are going to sponsor an investigator-initiated trial for rheumatoid arthritis (RA), which is quite similar to lupus in lots of ways. But the important aspect of the trial we’re going to conduct here in Cleveland is that we are going to use newly diagnosed rheumatoid patients. The FDA has allowed some companies to conduct clinical trials using MSCs in patients with refractory RA—patients who have tried every standard treatment but still continue to worsen. From our standpoint, a newly diagnosed patient would be perfect because all the downstream horrible effects of RA haven’t happened yet. These patients’ immune systems are overreacting to certain tissues at joints. We are going to take those allogeneic MSC preparations and optimize the cells for their response to these kinds of inflammatory situations at joints. We’ve developed an assay for picking a donor who will provide us with MSCs with the maximum response to inflammation, therefore having a better chance of curing the patients of their RA.
NR: That’s a great idea. Like a surrogate assay?
AC: It’s very simple. We have eight or nine donors from whom we’ve gotten bone marrow. We’ve isolated their MSCs and then exposed them to, for example IL-1. We pick a donor who gives us the best muting of that IL-1 response.
NR: We’re doing similar things. We take an immortalized monocyte line, expose it to lipopolysaccharide, co-culture it with the MSCs, and look at their secretions. We look for the maximum suppression of TNF-alpha and IL-6.
AC: Yeah, that’s similar to what we are looking at. We’ve developed another potency assay for the ability of MSCs to make antibiotic proteins, and to optimize the immune system for taking care of massive infections. So for kids with cystic fibrosis, because of the secretion problems they have, they get massive lung infections. We will take kids 18 or older with cystic fibrosis, who have been through every antibiotic known to man to quell their lung infections, and we give them allogeneic MSCs, donor MSCs that have been put in culture with Pseudomonas or Staphylococcus bacteria. We’ve identified a donor spectacular in his killing activity. We look at the immune response and the bacterial carcasses, which cause an endotoxin effect. We want a special macrophage to come in and clean them up. We have a donor who is particularly gifted at producing cells that carry away the carcasses. We want to specifically tune the cells to the disease state we’re using them for.
NR: Wow, that’s very interesting. It is mind blowing that these cells produce drugs that kill microbes. When was that discovered?
AC: We were partially responsible for discovering that. These molecules are called defensins, and they’ve been studied by dentists for twenty to thirty years. Defensins are naturally secreted in your mouth—it’s how you control the bacteria loads that go to your gastrointestinal tract. These molecules have not only been studied as proteins, but their genes have been cloned. It turns out the MSCs have these same sequences in their genome, and if they bump into a bacterium, they produce defensins. If there are no bacteria around, these molecules have no adverse effects on any other cells. As a matter of fact, young women who have monthly bleeds never get sepsis. They have broken blood vessels, and when a pericyte comes off and differentiates into an MSC, if a bacterium is present and bumps into it, goodbye bacterium.
NR: Can we visit the safety issue of using cells from another person—allogeneic MSCs? You mentioned that there are a lot of trials using allogeneic cells. Many people fear the use of stem cells for the treatment of cancer, because they are afraid of getting non-malignant tumors from MSCs. The fact that allogeneic umbilical cord MSCs have temporary immune privilege worries some people. Can you explain the mechanism by which allogeneic MSCs are allowed to be used clinically? And what is the mechanism in the body from the cells that makes them safe?
AC: These cells have been introduced into 30,000 to 50,000 people worldwide, and we don’t know of any adverse events. The fear that these cells will cause cancer is a misnomer, and it’s my fault because I named them mesenchymal stem cells. Everything I’ve just said about their abilities has nothing to do with a stem cell. If you have a heart attack, MSCs trigger the body’s production of new cells, not new heart muscles. Calling them mesenchymal stem cells is inappropriate for what they do in the body, which is diff erent than what they do in a petri dish. It’s correct in that I can make MSCs “dance” on a petri dish, but back in the body they don’t do that dance. They make drugs, naturally. I’ve written a paper to rename them to medicinal signaling cells—still MSCs. They make medicines that signal the tissue to regenerate itself. In a simplistic sense, they manage the patient’s own capacity to regenerate tissues. We are always regenerating tissues, which is one of the most important aspects of life in general. In all of your tissues—every single tissue in your body—cells drop dead and are perfectly replaced. For example, every single second, 15 million blood cells drop dead and are perfectly replaced. They are perfectly replaced because in your bone marrow is a stem cell that gives its own stem cells. Your liver, heart, kidney, and skin also have their own stem cells. Every single day millions of cells are dropping dead and being replaced. That replacement is how we stay alive. If you can’t regenerate that tissue, you won’t be around very long.
That, indeed, is what the MSC manages. It manages your innate capacity to regenerate every single tissue of your body where the MSC resides—your liver, your fat, your skin, etc. The important aspect of MSCs put back in the body is to understand that they don’t form tissues and so won’t form cancers. One of the problems right from the beginning of MSC therapies is that cancers with a solid tumor in your body have what we call leaky blood vessels. If you put an MSC into your body and you already have a tumor growing, it will go to that tumor, see it as injured tissue, and pervert it to get larger. So there are experiments that are now being done where people are putting powerful suicide genes in MSCs and giving them to patients with tumors to trigger the tumor to commit suicide. But by themselves the MSCs will not form tumors. Again, 30,000 to 50,000 patients with no adverse events. When we have given MSCs to a couple million patients, we’ll fi nd complications, and we’ll deal with them.
An important aspect missing from our regulatory process is transparency. We need a public website to register the clinical conditions of people who are getting MSCs. When they come for regular checkups, their conditions and outcome results can be monitored and put on the website. Those of us who are interested will see any problems immediately and be able to deal with them. To put this into modern context, consider the drug Vioxx, a non-steroidal anti-inflammatory drug that has since been taken off the market because it led to death in people with cardiac problems. If information from those patients had been on a publicly accessible, real-time website, those deaths could have been prevented. We would have ranted and raved to stop the medication from being used in cardiac patients. [The manufacturer] Merck allowed a hundred people to die. Then to save their name, they withdrew the drug from the market, which is itself a crime because it’s a useful drug. Transparency in reporting is one of the most important aspects of using new technologies.
MSCs produce these curtains of molecules that mute the response of the immune system, allowing the MSCs to evade the immune surveillance. Therefore, allogeneic MSCs can be used. In the end, this is one of the cheapest ways to provide suitable therapies for a large variety of diseases.
NR: I want to talk to you about vascular density with age. Do you have a reference for vascular density from skeletal maturity to old age? Is there a reference for that?
AC: They’re not published, and no one’s done a systematic study. It’s hugely labor intensive to standardize the histological preparations for you to get quantitative information. But the best data available has to do with skin. If you take a skin biopsy from younger patients, you see variegations at the junction of the dermis and epidermis—they’re called rete ridges. Underneath the dermis are huge loops of capillaries, which are what make baby skin the softest and most wonderful skin to touch—it’s so highly vascularized because of these deep ridges. You can tell the age of somebody by these ridges. If you look at my skin biopsy, I don’t have any ridges anymore.
NR: So if you’re just looking at the skin, if you start with a baby at 100 in vascular density, at your age it would be what?
AC: I would say I’m at a two.
NR: Essentially, the homes for the MSCs—capillaries—disappear with age, so the MSCs also disappear with age because they die when the blood vessels diminish, is that correct?
AC: Yeah. With these skin biopsies, I can also tell whether a patient has diabetes or not because diabetics have half the blood vessel density of an age-matched control. That’s why you see diabetic foot ulcers as such a difficult malady to treat, because their standard blood vessel density is so low.
NR: So they have fewer resources to repair.
AC: Right, so when they get a bleed, the number of MSCs that come in from the surrounding area is likewise diminished.
NR: Could you talk about the vascular density of liver tissue versus other tissues? And why the regenerative capacity of the liver is so good?
AC: The liver is organized like this: Arteries come in, then you have a bunch of liver cells, and then you have drain veins. Around every single arterial capillary in the liver, there are liver stem cells. Those stem cells divide, and their progeny begin differentiating into liver cells. The most differentiated liver cells, the hepatocytes, are sitting next to the vein. If you cut through a piece of liver in the just the right way, you can see the whole differentiation pattern from the stem cell to the most differentiated cell next to the vein. So blood comes in through the artery and gets detoxified as it goes to the vein. All of those cells, from the most primitive, newly differentiated hepatocyte all the way to the most highly differentiated hepatocyte has a certain capacity to detoxify the blood. What’s interesting is that, when you cut off a hunk of liver, if you’re going to survive, that liver needs lots of arteries and blood vessels. Sitting next to every one of those surviving arteries is a liver stem cell. They divide like wildfire, and they produce in rapid time the newly regenerated liver.
Sitting next to every single liver stem cell is an MSC pericyte, and that pericyte is obligatory for the expansion and differentiation of those liver stem cells. Those cells—the MSC pericytes that are sitting next to those stem cells—have a special name (hepatic stellate cells), have been studied extensively, and are highly unusual perivascular cells.
Every tissue in your body regenerates to some extent. You have a neural stem cell, a cardiac stem cell, a liver stem cell, etc. In all those stem cells there is a universal site that you could describe for every single stem cell, and the way to picture it in your mind is: that stem cell is sitting on top of a blood vessel’s vascular endothelial cell. Sitting right next to it is an MSC pericyte. So both the stem cell and the pericyte are in contact with the endothelial cell. That’s the universal stem cell niche, whether it’s in your brain, your liver, or your heart, there is an MSC pericyte. Therefore, every time one of your tissues gets injured, the MSC pericyte is activated, which then activates the tissue-specific stem cell.
NR: I know there are not complete data on this, but if you look at the spinal cord—the vasculature of the spinal cord itself and the vascular density—there are data showing that the white matter, which is the majority of the cord, has one-fifth the vascular density of the gray matter. What would you think overall is the differential? The cord does have innate regenerative capacity but relative to the liver it is lacking. What would be the percentage?
AC: There’s no way of doing that, but I would state the following: If you cut somebody’s spinal cord and squirted in some MSCs from the outside, one of the things all MSCs do— all of them—is they inhibit scar formation. We know that, even in cut spinal cords, those nerves can regenerate, but they can’t regenerate if scar tissue moves across the cut site. So therefore, in animals it’s shown that if you cut the spinal cord in half and squirt in MSCs and no scars form, eventually the nerves will regenerate down the tracks that are already there.
It’s the same with stroke. The important thing with strokes is you get this big blood clot, and that kills some of the axons, the nerves that are carrying information. If you make sure that no scar forms, those nerves can regenerate down the tracks that are there. That is how you can get coordinate function back—the tracks are still there. That has been shown in animal models and is one of the reasons why MSCs have a chance of being really useful for stroke patients. We normally teach stroke patients how to make new routings for their nerves. If you inhibit scar formation, the normal axons regenerate.
NR: One more question. What do you think of our facilities in Panama?
AC: As I tell people, I’ve gloved and gowned and gone into the GMP facility, which is as good as any GMP facility that I know in the United States. The fact that you have a way of selecting efficacious cells makes this an unusual facility. My mantra every time I talk to you is the same: publish, publish, publish. Because we need outcome data. That goes for every clinic in the United States and elsewhere.
NR: Our MS study data are complete, and I would love for you to look at it.
AC: Happy to do it.