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Host – Dan Keller
Hello, and welcome to Episode Thirty-Seven of Multiple Sclerosis Discovery, the podcast of the MS Discovery Forum. I’m your host, Dan Keller.
This week’s podcast features an interview with Jeanne Loring, who works with human induced pluripotent stem cells in a mouse model of MS. But to begin, we’d like to tell you about one of the most useful features of the MS Discovery Forum.
Each week somewhere between 30 and 110 papers related to multiple sclerosis are published in the scientific literature. At MSDF, we endeavor to list them all, publishing links to a curated set of each week’s new papers every Friday at msdiscovery.org/papers.
The first step in curating this list is an automated PubMed query that pulls all papers containing the terms multiple sclerosis, myelin, optic neuritis, acute disseminated encephalomyelitis, neuromyelitis optica, transverse myelitis, experimental autoimmune encephalomyelitis, cuprizone, neurodegeneration, microglia, and several related terms. This query returns many false positives. MSDF editors read all the titles and most of the abstracts and make judgments about which papers are directly relevant to MS or related disorders. Last week, for example, the query returned 139 papers and, in our judgment, only 58 of them – 42% – were truly MS-related. Some weeks the proportion is even lower than that.
The query terms neurodegeneration, myelin, and microglia are responsible for most of the false positives. Neurodegeneration, in particular, returns many references related to other neurodegenerative disorders, such as Alzheimer’s disease, Parkinson’s disease, amyotrophic lateral sclerosis, stroke, and hypoxia, to name a few. Editorial judgments on which articles are relevant are often subjective, and we frequently struggle with those decisions. It’s easy to decide relevance when an article actually mentions multiple sclerosis. It’s harder when it mentions only myelin or only Th17 cells. If you think we’ve missed an important MS-related article—or if you think we’ve included an irrelevant article—I hope you’ll let us know by emailing us at editor@msdiscovery.org. And we’re open to suggestions on how to adjust our PubMed query to decrease false positives and false negatives.
Once we’ve chosen which of the articles to include in the week’s list, we select between two and four of them as Editors’ Picks. Those are the week’s articles that seem to us to be the most important or interesting or intriguing. Once again, we invite readers to take issue with our choices. We’d love to hear about important articles that we have not designated Editors’ Picks or, on the contrary, Editors’ Picks that don’t deserve the honor.
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Now to the interview. Dr. Jeanne Loring is Professor of Developmental Neurobiology and Director of the Center for Regenerative Medicine at the Scripps Research Institute in San Diego. She and her collaborators have been testing human neural precursor cells derived from embryonic stem cells in a mouse model of MS. The cells are injected into the spinal cords of immunocompetent mice with a model of MS induced by a neurotropic hepatitis virus. The cells are rejected within a week, but in that time they suppress the immune system and induce remyelination.
Interviewer – Dan Keller
In terms of how you came upon your most recent finding about human pluripotent stem cells in the mouse model of MS, could you give me a little bit of the back story?
Interviewee – Jeanne Loring
Oh yeah, sure. It was really interesting. So Tom Lane and I set out to try to develop a stem cell therapy for MS using human cells. So as a control experiment, we took human pluripotent stem cells, in this case embryonic stem cells, and turned them into neural precursors; differentiated them just a little bit. And then we transplanted them into Tom’s mouse model of MS. These mice were not immunosuppressed, and so we expected the cells to be rejected. And this was just our first experiment. But the results were not what we expected. After the cells were rejected, the mice started getting better, and their clinical scores improved. And then after several months, these mice were almost indistinguishable from normal mice.
The first thing we thought was that we’d gotten the cages mixed up, and we were looking at something different. But we’ve repeated the experiment now more than a hundred times, and about 75% of the time we get the same result. So what this tells us is that these cells that we put into the animals are having some effect during the seven days that they exist in the animals that leads to both immunosuppression and remyelination and a clinical improvement which is quite remarkable.
MSDF
When you say 75% of the time, does that mean you get almost no effect 25 % of the time? Or does it mean that 75% or the mice? Because that would say whether you’re making your stem cells right or not.
Dr. Loring
It’s 75% of the mice.
MSDF
How do you explain it at this point, or where do you go from here to find a way to explain it?
Dr. Loring
So once we’d realized that we had a phenomenon that was repeatable, we realized that there was something special about these cells. And we tested other cell types, like the pluripotent stem cells that they were derived from, and human fibroblasts, and discovered that neither one of those was effective. And since then we’ve also tried other ways of making neural precursor cells, and those cells aren’t effective either. So it’s something extremely special about the cells that we used in these experiments, which is very lucky when you think about it.
So we’ve now, both Tom and I – even though we’re not in the same place – we’ve set out to try to find out what it is about these cells that gives them these properties. Our first sort of cut on this – our hypothesis – is that the cells are secreting something that has a lasting effect. Our sort of big picture idea is that there are probably more than one protein or glycoprotein being secreted. And together they suppress the immune system so they act on the inflammatory response so that they increase the number of regulatory T cells that are produced and decrease the other T cell types. And they induce remyelination.
So Tom is now working on trying to identify what factors these cells make that are inducing the T regulatory cells. And on my side, we’re trying to identify what it is that makes them remyelinate.
MSDF
When you make these cells, how do you know you got a good batch? Can you characterize them? Are there biomarkers, and you can say, “We did it right this time?”
Dr. Loring
Yes. In fact, that turns out to be really important because we did it wrong a few times. And we have a gene expression signature. It’s essentially diagnostic assay for this particular cell type. We’ve boiled it down to a set of qRT-PCR markers. And, because we have collaborators in Australia, we had to be able to transfer this quality control assay to them. So far it seems like those markers, I think it’s a group of 10 or 12 markers, seem to be predictive of the cells’ working in the animals.
MSDF
And just to clarify, that’s real time quantitative polymerase chain reaction? How are you going about characterizing what they’re doing? I mean, are you doing cytokine measurements or you’re looking at cells that get produced in the mice?
Dr. Loring
Tom is really handling the cells that get produced in the mouse. He’s doing the T cell analysis. What we’re doing, we developed an in vitro cell culture method to look for the effect of these cells on maturing oligodendroglia in culture. And we found that something secreted by these cells which shows up in their culture medium actually induces maturation of oligos – of OPCs – in vitro. I guess that’s another result that we didn’t expect to be quite so clear. So that shows that there’s something that is secreted by the cells. I mean, that’s the most likely idea. And on Tom’s side, he’s shown that the conditioned medium from the cells induces T-reg generation. And on our side, we’ve shown that conditioned medium from the cells induces oligo maturation.
So now we’re trying to figure out what it is in that conditioned medium because now we think we can do a cell-free therapy for MS if we can identify what the factors are. It would be much simpler for us to do even a protein therapy for MS than it is to do a cell therapy. So both sides are taking sort of a candidate gene approach in which we’re identifying the proteins that are most highly specifically expressed in the cells that work in the mice. We have a list of those proteins, and we’ve sort of snatched a few candidates out of that group, and we’re testing to see whether each one of those proteins in purified form has the same effect as the conditioned medium.
The other approach, which is more tedious but more likely to actually tell us what’s going on is for us to fractionate the medium into different sized proteins and then test each one of those fractions. We’re in the process of doing that right now.
MSDF
But it sounds like these cells are pluripotent. Not pluripotent in the normal sense of a stem cell leading to different lineages, but they have a couple of effects. One is the immunomodulatory, the other is regenerating oligodendrocytes. Do you think it really requires the gamish of proteins? If you fractionate them, will you possibly lose the signal? And that’s a big matrix to put back together again.
Dr. Loring
Yes, it is. And obviously, if we get no signal from our fractions, we’ll put our fractions back together again and try to find out whether – there are only three fractions, really, right now. So we’ll try different combinations of these fractions to try to find out if we can reproduce the effect. The effect is quite robust. We essentially get no maturation in medium conditioned by other cell types, but we get very strong maturation when we use conditioned medium from this particular neural precursor cell.
MSDF
If you only have three fractions now, is it because you just have chosen not to fractionate it even more until you know what’s going on?
Dr. Loring
Yes, we’re trying to hone in on it. So we don’t want too many different things to look at right away. I’m hoping that we find that only one of those fractions works, and that we can discover everything is within that fraction, but I really can’t predict what’s going to happen.
MSDF
It sounds like the approach would be to put everything in except one each time as opposed to keep adding back. You’ve got to find the one critical one missing that makes the thing not work.
Dr. Loring
Yes, and eventually we will do that with specific antibodies, but right now that is, since we don’t really have our candidates narrowed down enough, that isn’t a viable approach. But you’re absolutely right. We want to find out if that’s missing, whatever the things that are that are missing. And I’m hoping it’s not so complex that it’s five or six or seven proteins, because that’ll make it much harder for us.
MSDF
How do characterize the condition of the mice?
Dr. Loring
So that’s Tom’s area of expertise. It’s essentially an observation of the mice over time. We have a movie which I can show you, but I can’t actually do it in a recording. It’s quite obvious when the mice – they’re blind scored so the person who looks at the mice and sees how well they’re walking around doesn’t know whether they’re controls or experimentals. If you just see the movies that are selected at particular times after the cells have been transplanted, it’s quite dramatic. They have a much better clinical score. Essentially, they’re almost normal after six months.
MSDF
And how are you sure that the cells you injected into the spinal cord are gone, that they’ve been rejected completely?
Dr. Loring
That’s a good question. We used a method for live imaging of cells in which we use luciferase to label the cells. And then we used an instrument which allows us to image the cells in mice – in living mice – over time. So we did this in individual mice and saw that they disappeared over time. And after eight days we couldn’t detect them anymore. That doesn’t mean there isn’t one or two left because the resolution isn’t that high. We will go back eventually and look through sections of the spinal cords and see whether we can detect any. The other thing we can do is (skip 13:37) a human-specific markers. So we can just take a section of the spinal cord and find out if there’s any human cells in it at all, or any human genes in it at all. But we haven’t done that yet.
MSDF
Do the cells have to be gone? Have you tried injecting a second time?
Dr. Loring
No, we haven’t. We don’t know. We really don’t know. It would be very interesting if it reversed the effects. Then we’d really have a problem to solve.
MSDF
What else is there important to add or that we’ve missed that’s important to this kind of research?
Dr. Loring
So our dream is that we will identify a group of proteins and the concentration of those proteins necessary to have these two effects in this mouse model. And then we will do some biological engineering. We’ll be putting the cells into these little spheres and matrix that allows slow release of these proteins or controlled release of these proteins. And then, instead of putting cells in, we’ll put these beads in. And I don’t know whether that would end up being the final product or not, but there are lots of ways to deliver proteins, and this one I find rather attractive because it doesn’t require pumps or syringes. And I think that’s certainly the direction we’re going to try to go in. And so Tom Lane and I have just gotten an NIH grant for five years of funding, which seems like a very long time to me. So in five years we will have discovered the best way to deliver these things. We’ll discover what they are and the best way to deliver them. Tom has put conditioned medium into the mice, and it also works.
MSDF
Because I was going to ask, had you encapsulated the cells just to see that the supernatant does it without cell contact?
Dr. Loring
It turns out that the conditioned medium itself, you inject that into spinal cord, it’s not as dramatic an effect, but you have a clear clinical improvement.
MSDF
Have you tried injecting it either IV or intraperitoneally?
Dr. Loring
Yes. Well, we didn’t inject the conditioned medium. We did try injecting the cells, and they pretty much stayed where we injected them. These cells, unlike mesenchymal stem cells, they aren’t very migratory. So they don’t really have the receptors that cause them to move to areas of inflammation like CXCR4, for example; they don’t express that on their surfaces. So that does not seem to be a good delivery method for these cells. They don’t go anywhere.
MSDF
I was also thinking that if something they secrete is important, whether it circulates. Maybe they’re not making enough concentration if you inject them outside of the central nervous system, but it seems like you’re going to be faced with a little cumbersome problem in a clinical situation years and years ahead from now if you have to keep injecting proteins into the spinal cord as opposed to more peripheral.
Dr. Loring
I agree. And the solution to that is generally to look for peripheral effects and then try to suppress those when you do a therapy like this. That’s a long time, and we could certainly imagine how we would do it. But we need to know what those proteins are before we can decide on whether we expect them to have effects peripherally or not. But I agree with you; delivering them intravenously would be far easier.
MSDF
I know you have a lot of work ahead of you now with this, but is there another animal model of MS – or even another mouse model of MS – where you can see if it works even in a mouse model different from this one?
Dr. Loring
Yes, we’re actively pursuing that with our collaborators in Australia. And it’s interesting because they’ve gotten some positive preliminary results using the EAE model, but the approach to the EAE model I’ve realized is quite different. Generally, what people do is they provide the therapy at the time that the pathology is developing, and they try to prevent it, which is a really different idea than what we had using the mice that are already paralyzed. So they have found that if you can deliver the cells at least close to the spinal cord, then you can see some effects. The problem is that in Australia, and this is one of those technical things we had not anticipated, they don’t have permission to inject cells into the spinal cord. So they have to go through their animal rights people or their animal protection groups and try to get permission to do so. So with Craig Walsh at UC Irvine we have started doing parallel experiments with the EAE model. I’m not necessarily sure that it’s going to have similar effects. I mean, I really don’t know.
MSDF
Can you describe how these mice in your experiments were made to have MS?
Dr. Loring
Yes, they were given a virus, a neurotropic virus, which kills off the oligodendroglia. They become demyelinated, and there is a secondary inflammatory response. So the mice are actually paralyzed in their hind quarters at least by the time we put the cells in. They have to be fed by hand. So this is not a trivial thing to do. But we’re trying to reproduce the effects during the progressive form of MS, for example, or during an attack of MS. So we’re trying to repair the mice or cure the mice that are in a condition which would be similar to the worst case scenario for people with MS.
MSDF
Do you think this may also have effects not only on the myelin, but also on damaged neurons?
Dr. Loring
We don’t know, because the mice haven’t really had enough time to get a lot of neuronal damage, but that’s a very good question. We don’t know yet.
MSDF
I appreciate it. Thank you.
Dr. Loring
You’re welcome. It was a pleasure.
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Thank you for listening to Episode Thirty-Seven of Multiple Sclerosis Discovery. This podcast was produced by the MS Discovery Forum, MSDF, the premier source of independent news and information on MS research. MSDF’s executive editor is Robert Finn. Msdiscovery.org is part of the non-profit Accelerated Cure Project for Multiple Sclerosis. Robert McBurney is our President and CEO, and Hollie Schmidt is vice president of scientific operations.
Msdiscovery.org aims to focus attention on what is known and not yet known about the causes of MS and related conditions, their pathological mechanisms, and potential ways to intervene. By communicating this information in a way that builds bridges among different disciplines, we hope to open new routes toward significant clinical advances.
We’re interested in your opinions. Please join the discussion on one of our online forums or send comments, criticisms, and suggestions to editor@msdiscovery.org.
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