Hello, and welcome to Episode Forty-Six of Multiple Sclerosis Discovery, the podcast of the MS Discovery Forum. I’m your host, Dan Keller.
This week’s podcast features the first part of a two-part interview with Dr. Hans Lassmann, who discusses biomarkers in multiple sclerosis. But first, here are some of the new items in the MS Discovery Forum.
According to our curated list of the latest scientific articles related to MS, 61 such articles were published last week. To see the list, go to msdiscovery.org and click on Papers. We selected two of those papers as Editors’ Picks. One, on the prevalence of pain in MS, found that around two-thirds of MS patients experience pain, and this symptom is associated with disability, depression, and especially anxiety. The other editor’s pick is a study of a toxin produced by Clostridium perfringens, a common bacterium often found in the gut that produces an MS-like disease in sheep. This epsilon toxin selectively kills oligodendrocytes while preserving all other neural elements.
Our Drug-Development Pipeline includes continually updated information on 44 investigational agents for MS. During the past week we added 2 new trials and 5 other pieces of information. The drugs with important additions are dalfampridine, dimethyl fumarate, and fingolimod. To find information on all 44 compounds, visit msdiscovery.org and click first on Research Resources and then on Drug-Development Pipeline
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Now to the interview. Dr. Hans Lassmann of the Medical University of Vienna in Austria, is one of the most prolific and highly respected MS researchers in the world. In this first part of a two part interview, Dr. Lassmann discusses biomarkers in MS and related conditions such as neuromyelitis optica and how the two conditions may differ important for therapy.
Interviewer – Dan Keller
Let’s talk about new markers in MS or differentiating conditions from MS. What’s coming along, and what do we know now?
Interviewee – Hans Lassmann
Well, there has been a very important development during the last years. And this was the technical development of assays which can really identify pathogenic autoantibodies which can modify the inflammatory process in the central nervous system. The major trick behind was that these assays are, in essence, based on cells which are transfected with the respective antigen, and so they express the respective antigen on the surface of the cell. And one can now identify those autoantibodies which really bind to the surface of the cell and are pathogenic, in comparison to those antibodies which recognize epitopes, for instance, within the cells, which cannot be reached by the antibodies in the in vivo situation, and which, therefore, are not pathogenic.
MSDF
Can you give me some examples of these kinds of antibodies?
Dr. Lassmann
So the first antibody which was the antibody against aquaporin 4, which has been shown to be associated with neuromyelitis optica, at least with a large fraction of patients with neuromyelitis optica. And this antibody then was very well characterized, and it turned out that it is directed against aquaporin 4, which is a water channel in astrocytes. And when patients have these antibodies on the background of an inflammatory disease in the central nervous system, these antibodies can reach their astrocytic targets and destroy the astrocytes, which then leads to secondary demyelination and neurodegeneration.
Having these antibodies, it was then possible to define the clinical spectrum of the disease, and it turned out that it is very strictly associated with neuromyelitis optica, but that the spectrum of the disease is broader than only affecting the spinal cord and the optic nerve. So these patients actually have also lesions in other regions of the brain. But they are still different from those lesions which you see multiple sclerosis.
It was then also possible to define the clinical spectrum of the disease. And, again, differences to multiple sclerosis became very clear. And, finally, it was also possible to then look in these patients with these aquaporin 4 antibodies how they respond to the current treatment strategies which have been established for multiple sclerosis. And it turned out that several of the key therapies for multiple sclerosis, including interferons but also natalizumab or fingolimod, can actually make the disease worse in patients with neuromyelitis optica.
So that was the first example that a disease which has originally been defined as a disease in the spectrum of multiple sclerosis has emerged as a separate and distinguishable disease which requires also different treatment in the patients.
MSDF
It seems like neuromyelitis optica has components of autoimmune disease. So why do these compounds that work in MS potentially make the condition worse in NMO?
Dr. Lassmann
This is currently not yet clear. One possibility is that the action of pathogenic antibodies makes the difference. The immune mechanisms are certainly different in a purely T-cell mediated disease, in comparison to disease which is mediated by a combination of T-cells and antibodies. And that could possibly explain why differences are seen.
There is another possibility is that some of these drugs actually stimulate the B-cell response or increase the B-cell response in the peripheral blood, and with that possibly also the antibody response. So, in that case, the T-cell mediated inflammation would be suppressed, but the antibody-mediated effects would be enhanced. And that could certainly also play a role. But these are, at the present moment, not proven.
MSDF
But even in MS there’s evidence for B-cell trafficking and B-cell participation, but it seems to be less important or am I off base?
Dr. Lassmann
No, this is a very interesting question. There is clearly a B-cell component in multiple sclerosis, and it has also been shown that depleting B-cells, for instance, with an antibody against CD20 can actually have a very good therapeutic effect in multiple sclerosis. However, we have to keep in mind that B-cells not only produce antibodies, but they have also other immunological functions. So one function, for instance, is that they help the T-cells, for instance, by very efficient antigen presentation. So by eliminating B-cells, you get also a decrease of the T-cell response. But this is not only one possibility. There are other possibilities that B-lymphocytes actually can also produce cytokines – proinflammatory cytokines – which may directly act on the tissue and damage the tissue independent from antibodies.
MSDF
Getting back to NMO, if someone tests negative for antibody, but has clinical signs, does that rule out NMO or are you just not detecting antibodies or is it always required or not?
Dr. Lassmann
So it rules out an aquaporin 4 antibody associated form of NMO, but a fraction of NMO patients – it’s around between 10 and 20% – which have a clinical presentation of NMO, but have no antibodies against aquaporin 4. There is currently very much effort to define what is the mechanism in these patients. And it turned out that a fraction of these aquaporin 4 antibody-negative NMO patients actually have antibodies against myelin oligodendrocyte glycoprotein.
And this leads, actually now, to a second type of disease which can be separated from multiple sclerosis. These are patients with high titers of pathogenic antibodies against myelin oligodendrocyte glycoprotein. Now, again, these patients, when you look at them at pathology, you would clearly define the disease as multiple sclerosis because they have inflammation, and they have very selective primary demyelination. And this is different from what you see in NMO where the astrocyte pathology is the earliest event. But in those patients with the MOG antibodies, its demyelination sort of hallmark, actually, of multiple sclerosis…of the disease process in multiple sclerosis.
However, when you now analyze these patients with mock antibodies, clinically you see that the clinical presentation is different from the classical presentation of multiple sclerosis patients. These antibodies are, for instance, frequent in children with inflammatory demyelinating disease of a spectrum of acute disseminated encephalomyelitis or relapsing disseminated encephalomyelitis or even patients with a disease similar to relapsing, remitting multiple sclerosis. This is in children.
In adults, you find these antibodies in a fraction of NMO patients. But there are also other patients who have a disease which is more similar to what is seen in multiple sclerosis, with the exception that they have relatively large and aggressive lesions, and also that they have, relatively frequently, lesions in the brain stem such as, for instance, the pons or the medulla oblongata. And, again, it seems to be that here a new disease entity appears which can be separated from multiple sclerosis.
Regarding therapy of these patients, we don’t have yet the data which we need to have. It can be speculated that the therapeutic response may possibly be more similar to those patients with NMO in comparison to the classical MS patients, but to know that we would have to have much larger cohorts of patients who have been treated with the different regimes.
MSDF
Do some of these do worse on the typical MS treatments such as natalizumab or fingolimod?
Dr. Lassmann
These data currently are not yet existing. It’s also because, due to these possible problems related to NMO, generally now, patients with mock-antibody-associated diseases are more likely to be treated with global immunosuppression or with rituximab, so the anti-CD20 antibody. And clinicians are very reluctant to use these therapies which have been shown to make disease worse in NMO in these mock patients. So we don’t have the data, currently.
MSDF
Are there separate etiologies, does it look like here, the MOG versus classical MS?
Dr. Lassmann
This comes to the important question about the etiology of MS in general. We have to admit that we don’t know what is the real etiology of multiple sclerosis. It is thought to be an autoimmune disease, but this is not finally proven. It may also be associated with infections – Epstein-Barr virus infection is, for instance, one possible example. And there are certainly other theories also, which discuss completely different mechanisms of disease pathogenesis in multiple sclerosis. It is clearly that all these diseases, including NMO, mock antibody associated disease, and MS are chronic inflammatory diseases. But what drives the inflammation is currently not yet known.
MSDF
Is it possible there’s an initial insult to oligodendrocytes which then sort of precipitate a chain reaction cascade?
Dr. Lassmann
This is also one of the theories which is put forward, but one has to say that with a bit caution, because there are experimental models where you can actually destroy oligodendrocytes in the central nervous system which do not lead to an autoimmune disease which is somehow related or similar to multiple sclerosis.
MSDF
Anything interesting or important to add on the subject, in this context?
Dr. Lassmann
I think what is now of interesting new research line is to search for additional autoantibodies in the population of multiple sclerosis patients. There are indications from pathology that there are certainly more patients who may have pathogenic autoantibodies, in comparison to those patients which now can be identified as NMO or mock-autoantibody-associated disease. There is a relatively recent study suggesting that another channel, a potassium channel on oligodendrocytes and astrocytes, the KIR4.1 channel, may also be a target for pathogenic autoantibodies in multiple sclerosis. Here, however, we are still in the very early stage because the test systems are not yet fully reproducible. And we will see in the future whether this antibody association with the KIR4.1 antibody really holds true in MS patients. And if that’s the case, what patients are they and whether they differ in any way in their clinical presentation or also response to therapy.
MSDF
Is there a way to survey patients and essentially see what commonalities they have in antibody reactivity, and zero in on it that way, looking at a wide array of antibodies in various patients and seeing if they have reactivities in common?
Dr. Lassmann
I think this is valid as a second step. But there is another alternative strategy which is now very well established also for other diseases, including paraneoplastic diseases or other autoimmune diseases. In that case, one can actually take the sera of the patients, and there are now new technologies developed where you can put these sera, for instance, on brain sections – normal brain sections – of either humans or animals and test whether they bind to specific structures.
This has been tried for nearly 30 years now, but only recently, new technologies became available which make that in a much more specific way. And this has been very successful in identifying new diseases which are associated with antibodies against a variety of neurotransmitter receptors or ion channels. So they certainly, in general, have not the spectrum of multiple sclerosis. They may have epilepsy. They may have psychosis. They may have motor neuron diseases, other things. But, on the other hand, the same technique can also be used to identify in multiple sclerosis patients whether some of them have actually antibodies which bind to brain tissue. And when that is established, one can actually then isolate the specific protein with the antibodies out of the brain tissue, and then, with modern molecular biology technology, can identify the antigen.
This is a strategy which has very nicely and very successfully shown for other diseases. And this was also, in principle, the strategy how people found evidence for these, for instance, KIR4.1 antibodies and also for the NMO antibodies.
MSDF
Finally, do you envision being able to develop specific treatments if you find out specific autoantibodies or causes of some of these conditions?
Dr. Lassmann
It may very well be. I think there are two dimensions on that. The one dimension is that such patients have pathogenic autoantibodies, and that certainly will have implications for therapy. That means that you will try to block the pathogenic action of the antibodies in general. In that case, it doesn’t make a difference whether the antibody is now directed against a neuron or against an astrocyte or against an oligodendrocyte. And this is a strategy which is actually now already approached in many different conditions, and neuromyelitis optica certainly is a disease where this is relatively advanced in this respect.
Now, the other possibility would be to try to find therapies which are then counteracting specifically the destruction of the particular cells which contain the antigen. So it can very well be that, for instance, an antibody against a neurotransmitter receptor will have a different implication on neuronal function, in comparison to an antibody against an astrocyte or an oligodendrocyte. Here, if these are just blocking antibodies and not antibodies which destroy the tissue, one can actually then try also symptomatic therapies with interfering with these channels directly.
MSDF
Is there any thought towards trying to induce tolerance or clonal deletion of the pathogenic clones?
Dr. Lassmann
This is obviously the dream of immunologists, and it would be extremely attractive. And it works extremely well in inbred mouse models with a very well-defined disease induction process. The strategy is very dangerous in a genetically heterogeneous population and also in a disease process which may be induced by different mechanisms. So, in that case, the big danger is that this tolerizing strategy in certain patients, for instance, with a certain histocompatibility genetics, actually is counterproductive and increases the immune response. And this is actually a problem which is very, very difficult to solve, in the aim of translating this mouse data into humans.
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Thank you for listening to Episode Forty-six 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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Host – Dan Keller
Hello, and welcome to Episode Forty-Five 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 Dr. Simon Hametner, who discusses the role of iron in multiple sclerosis. But first, here are some of the new items on the MS Discovery Forum.
According to our curated list of the latest scientific articles related to MS, 59 such articles were published last week. To see the list, go to msdiscovery.org and click on Papers. We selected two of those papers as Editors’ Picks. One, published in Nature Reviews Neurology proposes a definition of aggressive multiple sclerosis as well as a treatment algorithm. The other editor’s pick, published in the journal Neurology, reports on a randomized, placebo-controlled study on patients switching from natalizumab to fingolimod, concluding that shorter washout periods may be better.
Our Drug-Development Pipeline includes continually updated information on 44 investigational agents for MS. During the past week we added 3 new trials, we updated information on 2 other trials, and we added 9 other pieces of information. The drugs with important additions and changes are daclizumab, dimethyl fumarate, fingolimod, interferon beta-1a, laquinimod, and natalizumab. To find information on all 44 compounds, visit msdiscovery.org and click first on Research Resources and then on Drug-Development Pipeline
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Now to the interview. Dr. Simon Hametner works with Hans Lassmann at the Medical University of Vienna in Austria. We spoke about iron accumulation in MS in cells of the central nervous system and what iron may be doing.
Interviewer – Dan Keller
Let's talk about iron and neurodegeneration. What specifically are you looking at?
Interviewee – Simon Hametner
We are looking at the formalin-fixed, paraffin-embedded brain tissue from multiple sclerosis patients and controls, and we're looking, for example, at iron in these tissues. We're also looking now at proteins which are engaged in the management of iron in these tissues, for example, now.
MSDF
What are you finding different in MS patients that you don't see in healthy people?
Dr. Hametner
So we see iron accumulation, for example, in microglia and macrophages in MS, which are related to MS lesions. There are, for example, some MS lesions which have macrophages around those lesions, and we don't see much of iron in macrophages and microglia in healthy control tissue. We also see iron loss in multiple sclerosis because the iron is normally stored in oligodendrocytes in the controls. And this is also the case for MS, but in MS we also see a loss of this iron in the oligodendrocytes, especially at the oligodendrocytes which are closed to MS lesions.
MSDF
Do you know the mechanism of why you're seeing these differences in iron?
Dr. Hametner
We are now performing the research to find about these mechanisms. We have some prior indications, for example, hephaestin upregulation on oligodendrocytes in the vicinity of the lesions, but these data were not so straightforward. We are now also looking for ferroportin; ferroportin is an iron exporter of glial cells, it's actually ubiquitously expressed in mammalian cells. And all the glial cells also can express ferroportin, and we found it also in the oligodendrocytes; we now undertake this research. We think that oligodendrocytes really upregulate ferroportin and hephaestin in order to export iron.
MSDF
Is the iron detrimental?
Dr. Hametner
It depends. We don't think that it is, per se, detrimental; we see loads of iron in the deep grey matter nuclei and it seems that the brain can handle that quite well. But if there is even a minor amount of iron in the extracellular space even in the ferrous form – because iron normally is stored in the ferric and the trivalent form in ferritin – but if we see even minor amounts in the ferrous form, then it might be detrimental at very low amounts actually.
MSDF
Is this a result or a marker of what's going on, or does it really contribute somehow to the disease?
Dr. Hametner
This is a very interesting question. We think that iron really colocalizes or is found and accumulated at sites where things are going on with these lesions which accumulate iron in the microglia and macrophages around them. On the other hand, you can detect it very nicely with magnetic resonance imaging today. So we think that on the one hand it does play a role in the disease pathogenesis, and on the other hand we think that we can detect really these sites of iron accumulation, for example, around MS lesions.
MSDF
Are you doing this only on fixed patient tissue, or do you have animal models of this; how are you exploring it?
Dr. Hametner
We have this fixed material on the MS, and I think it's really important to also characterize the human material in very detail to perform all the necessary analysis to characterize what's going on in the human tissue. But, of course, as you mentioned animal models, it's very important to look at the EAE models. And collaboration partners have done that from McGill University in Montreal, Juan Zarruk and Sam David, and we are collaborating with them. And actually now they have been looking at some iron transporters and we are looking at exactly the same iron transporters now in the MS tissue. And they have found it in the same cell types, these iron transporters, in the EAE model being upregulated in the course of EAE as we see now in the MS tissues actually. So we really look for confirmation also from animal models from our collaboration partners.
MSDF
And does this work with various kinds of animal models, or is it restricted to the EAE?
Dr. Hametner
This survey has now been performed on the EAE, so it is a mock EAE actually and that they have performed a relapsing-remitting mock EAE in the chronic EAE model, and they have characterized those proteins, but they also do spinal cord injury models and they have performed a very interesting experiment on iron-loading in macrophages in the course of spinal cord injury where the iron gets into the macrophages possibly from a hemoglobin source from erythrocytes in the traumatic lesional tissue. And we think that regardless of the source of iron, it has these detrimental effects in the macrophages and triggers them to have a pre-inflammatory – or so to speak, M1 state – and are detrimental to the surrounding tissue.
MSDF
This is macrophages or also microglia?
Dr. Hametner
So in the spinal cord injury model, it was mainly macrophages. In the acute phases of the EAE at the peak of the disease, it was also mainly macrophages, but later they also found iron in the animal model within microglia, as we do also in MS. We have these early lesions where there are a bunch of macrophages in these classical active lesions, and these are mainly macrophages, and if they are iron-loaded, it is in the macrophages. But for the later lesions for these chronic active lesions which have this iron ring around the lesion, we find it also within macrophages but also microglia.
MSDF
So does this change the oxidative environment inside the macrophage?
Dr. Hametner
That's a good question. We think that it does change something with the macrophages because they seem to die. So we have these dying macrophages in the EAE model, as they have observed it, but in the MS we saw this dystrophic microglia at the lesion edge. So these are microglia which are highly iron-loaded probably for some time, and they have these nice processes. And if these processes get those beads and the process fragmentation and these process budding and blips in the processes, we call them senescent or that dystrophic microglia. And we have indications that this is really related to the iron load of this microglia. And then they get diminished towards the inactive centers of the lesion. So we think that at the edge of chronic active or slowly expanding MS lesions, these get iron-loaded in microglia and they don't handle it quite well, and then they die and get diminished towards the inactive centers.
MSDF
So when they die, do they release this and is it affecting other cells?
Dr. Hametner
We believe so. We think more or less that it is necessarily released into the extracellular space if an iron-loaded cells just dies by necrosis, or apoptosis, or something in between. So it is just released into the extracellular space. It has to be taken up by other cells; for example, other microglia, or other macrophages, or even astrocytes; it seems that it is really liberated. But, of course, it is hard to say whether iron within a specific microglia has been acquired by some other microglia which has died, or by some oligodendrocyte which has died, or even another source. But the fact is although we are sure that they have really accumulated lots of iron, and given actually the concentration of iron in these microglia and the surrounding tissue, we do think that there must be other sources than only oligodendrocytes by which iron gets into these microglia.
MSDF
Where do you go from here? What do you see the steps in the research?
Dr. Hametner
I think it is necessary to characterize these rings around lesions which have these iron-loaded microglia and macrophages, to characterize at which disease phases these rings occur, and, of course, this is very interesting because you can use it in vivo. Because one of the things we are really sure is that we can image iron within microglia at the lesion edge of those lesions very nicely at 7 Tesla of magnetic resonance imaging; we are very sure that this is iron then within microglia and macrophages. And if we can relate pathologically the disease mechanisms or the degenerative actions going on in these lesions to the presence of iron, we then can also relate our in vivo findings from MRI with the things which are going on there, like neural degeneration and demyelination, for example.
MSDF
Do you find that the iron-sensitive MRI imaging correlates with duration of the disease or stage or clinical condition?
Dr. Hametner
Yes, we think so from our pathological material. So we think that in the progressive stage of MS, there are these lesions which are the slowly-expanding lesions, and they have these chronic activity, chronic demyelinating activity at the lesion edge. And we think it's a typical feature of progressive MS. It remains to be determined whether this also holds true in vivo. If you make an MRI, an iron-sensitive MRI, and you look for iron rings around MS lesions, for example, by susceptibility-weighted imaging or by quantitative susceptibility mapping or even Ultrastar imaging, if you look at these iron rings around lesions, it remains to be determined at which disease phase is, because in the pathological material we have more of the chronic cases and we have very few relapsing-remitting. So we cannot say what's really going on in the relapsing-remitting disease because we don't have this material pathologically.
MSDF
Right, you would have to find people in various stages who probably died from something else; they're not going to be advanced MS patients at that point. Is there some relationship of your findings to the idea of oxidative stress?
Dr. Hametner
Yes, we have these overactivity for malondialdehyde or E06, which is this antibody against oxidized phospholipids, and we have found actually by working performed partly in this lab that there is a higher activity for oxidative stress of various glial cells in the lesions. But as for the microglial degeneration, we did not see so many microglia being positive for these markers. So the microglia, they seem to die, but we only have these morphological features of dystrophic or senescent microglia actually from the pathological side. On adjacent side, if you stain for iron and you stain for oxidized phospholipids, you see partly that there is a 1:1 colocalization. But we don’t see these always actually.
I think what's really clear is that there is lots of oxidative stress in MS lesions, but even in early MS lesions which on iron stainings don't have so much iron, because on these early lesions we actually see predominant iron loss. If you have a very highly active MS lesion in the early stages, you see iron loss, and you will see also oxidative damage there. So there is also other factors leading to oxidative stress, like NADPH oxidase, for example, the p22phox, the functional subunit of NADPH oxidase, which we have shown in this lab that it is upregulated on macrophages and microglia, but also in the absence of iron.
MSDF
What tips the balance between loss and iron accumulation?
Dr. Hametner
That's an interesting question, actually a complicated one. You're right, we see on the one hand iron loss, and we see iron accumulation. So in the early stages, we see iron loss around MS lesions, in the MS lesions, because oligodendrocytes try to get rid of their intracellular iron possibly to prevent the iron efflux or iron liberation, which is uncontrolled if there is demyelination and oligodendrocyte degeneration actually. So we think that inflammation in the early phases of the disease leads to this efflux, which we think also involves not only oligodendrocytes, but also astrocytes. So we now think actually that oligodendrocytes probably efflux the iron towards astrocytes, and those astrocytes then might efflux it towards the periphery even. So I think inflammation is an obvious candidate to trigger this upregulation of iron efflux mechanisms.
I think what drives the iron accumulation within the microglia at the lesion edges is a different story. We think that these are two unrelated processes. On the one hand you have these iron loss mechanisms, the iron efflux mechanisms from the oligos leading to iron loss in early MS lesions, and this seems to be a protective phenomenon; this is, so to speak, a protective reaction of the glial cells against oxidative stress. But in later lesions, in chronic active lesions with this iron accumulation within microglia and macrophages, and we don't think that they are really correlated. So we think these are two distinct processes going on in MS, probably even in two distinct phases of the disease.
MSDF
Is there anything interesting to add?
Dr. Hametner
I think the really crucial question is now to find out about the source of iron for microglia and macrophages, and even to find out about the source of iron for the oligodendrocytes. We are not so sure whether this is really transferrin-bound iron entering the brain and being loaded in oligodendrocytes, as you find it in control tissue, control brains. And we don't think that this is only this iron from the oligodendrocytes which is then loaded into the microglia and macrophages; we think there are additional sources possibly from the vasculature.
MSDF
Very good, thank you.
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Thank you for listening to Episode Forty-five 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.
[outro music]
[intro music]
Host – Dan Keller
Hello, and welcome to Episode Forty-Four 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 Dr. Monika Bradl, who discusses animal models of neuromyelitis optica, NMO. But first, here are some of the new items on the MS Discovery Forum.
According to our curated list of the latest scientific articles related to MS, 69 such articles were published last week. To see the list, go to msdiscovery.org and click on Papers. We selected two of those papers as Editors’ Picks. One – on the use of MRI in NMO –included no fewer than 48 co-authors, a veritable Who’s Who of prominent MS researchers. The other editor’s pick, which had “only” 36 co-authors, was a large study providing strong evidence that disease-modifying treatment reduces disability worsening events in clinically isolated syndrome and early MS.
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Now to the interview. Dr. Monika Bradl is an associate professor in the center for brain research at the Medical University of Vienna, Austria. I talked to her in her office about her work with animal models of neuromyelitis optica to probe what occurs in the early stages of the disease. She first describes why animal models are important.
Interviewee – Monika Bradl
NMO is a very rare disease, and so you have the problem that you get only very little pathological material, and so when you want to know what's going on at the very beginning of the disease you have to use animal models. And so our pioneer work there in the NMO field was to find out whether the antibody that characterizes about 80% of NMO patients, that's an antibody directed against aquaporin-4, water channel astrocytes, is pathogenic or not. And so what we did is that we injected this antibody then in experimental animals. When we had the animals without any additional CNS inflammation going on, they remained completely fine, and that was at that time a bit of a debate because people thought that the antibodies could enter the central nervous system anyhow.
But then it turned out that this failure of the antibody to reach the uninflamed brain had also predecessor in humans. There they had an NMO patient in Japan who was diagnosed with NMO, and when they found that he has pathogenic antibodies, they were first afraid because this patient was blood donor with the Japanese Red Cross, and so at that time then they stored serum samples of all the blood donors for quite some time, and they found out that this person had pathogenic antibodies already for more than 10 years without showing any signs of disease.
And so this was then the human patient correlated to what we found in our NMO animals, and what we then also saw is immediately when we make our CNS inflammation with CNS-specific T cells which break open the blood-brain barrier, then the antibody gets access to the central nervous system, binds to the astrocytes, and then induces two different type of killing procedures. So the astrocytes are then killed with either the help of complement or with the help of a mechanism that's called antibody-dependent cytotoxicity; so both of these mechanisms are then responsible for tissue destruction.
Interviewer – Dan Keller
Getting back to the Japan patient, did they also follow the recipients of that person's blood? It seems like this patient did not have that second hit which would allow the antibody to cause problems, but giving it passively to someone who already had the first hit might cause a problem. Did they look at the recipients?
Dr. Bradl
I'm sure they did, but there are no records about it to my knowledge. They might have been published in Japanese in some of these Japanese journals, but not in the international journals. But I'm quite sure that there was no immediate transfer of the disease with these antibodies because that would have made headlines. So one can conclude from that that this must have been harmless.
MSDF
And what animal models are you using?
Dr. Bradl
We are using rat models, but there are other groups that are working in mice. We use Lewis rats and we think they are great because the rat complement works with the human antibodies, so it provides the help. And we have an NMs strain the Lewis rat which is extremely susceptible to all different types of autoimmune diseases, and so therefore we like rats and their CNS is larger and nicer. But people who work with mice, they also have advantages because they can use the entire transgenic zoo of knockouts or gene-mutated animals, and with this they can learn more about the contribution of individual molecules to the disease process.
MSDF
Now that you bring up the mice, are some mice more susceptible based on MHC than others; are some resistant?
Dr. Bradl
There you have to consider one peculiarity of the mouse system. If you use mice, then you have the wrong complement system. So no matter what kind of inbred strain you use, you have to transfer human complement along with the human antibodies to get an effect, plus people who use the mouse model directly inject complement and antibodies into that brain to circumvent the blood-brain barrier. And when they do that, the MHC type of the particular mouse strain doesn't play a role.
MSDF
Is this using only passively transferred antibody, or do you try to raise antibodies by injecting antigen or modifying antigen?
Dr. Bradl
Yup. We desperately try to do so, but I have to say that this was not a real success story. So we first tried, as many other people did, to use just convention and normal aquaporin-4 as it is normally produced, or longer fragments of this, but obviously this does not work. And we now know that the antibody recognizes its target only if the aquaporin-4 is correctly folded within the same membrane. And only if this is the case, then there are three extra cellular loops which are available for antibody binding, and these three loops must be properly oriented and strictly optimally aligned in order for the antibody to bind. And this can only be hardly mimicked in the animal model just by immunization.
We then tried also to immunize with membranes of aquaporin-4 transfected cells, and there we got a little of antibody titer, but when we used these antibodies to stain tissue in order to find out whether they are good one, we saw much more staining than we would have liked, and so that means that the membranes are probably contain some antigens which were then, after immunization, targets of antibody responses. So this was so far in our hands a failure. And as far as I know, we are not the only ones that suffer from that. So there is currently, unfortunately, no model which works after immunization with aquaporin-4.
MSDF
Where do you go from here?
Dr. Bradl
Well, we are currently modifying our animal models to the extent that we study much more the T cell responses, and we also try to modify the B cell site, but this is a bit of a, let's call it easy way modification. Because we learned along the way that when we have a very, very, very good NMO IgG from a patient, we can work with very low antibody titers, and so that gives us a very nice animal model. And we also know that there are some NMO IgGs which make high titers in the patients but which are relatively lousy in animal models. So we learned from this that we just select and search for the best animal IgG for the model to transfer this; that's the B cell side. And on the T cell side, you'll find T cells in NMO lesions, but people had a hard time to get aquaporin-4 specific T cells.
So it was not quite clear whether one needs aquaporin-4 specific T cells at all for the formation of lesions, or whether any other activated T cell that recognizes different proteins in the CNS could do the job as well. So over the last few months, we now were really able to produce really highly pathogenic aquaporin-4 specific T cells which do the job and which guide lesions to sites where they are also seen in NMO patients. And so with this we were now able to really advance our model much, much more than we had done before.
MSDF
So these T cells you've generated, and these are directly cytotoxic?
Dr. Bradl
We are not dealing with CD8-positive or cytotoxic T cells, we are dealing with helper T cells. And these helper T cells, we know that they exist because the pathogenic antibodies of the patients have a phenotype that needs T cell help in their formation. But it was all the time unclear whether the T cells only help in antibody formation, or whether they also help in localizing lesions to the correct places. And now we have really for the first time the impression that we have a cell line that does exactly this.
MSDF
How do you translate what you're finding out in the animal models to the clinical situation? Is it developed enough now that you can make correlates?
Dr. Bradl
Well, that's a good point. I mean, when you look, for example, at our T cell work, then we observed in our animals that there are a large number of epitopes available for antigen recognition by T cells in the rat. And then it turned out that people observed the same thing in mice, and now we know it's also the same thing in humans. And then when you have so many different epitopes or so many different parts of a protein that can be recognized by the immune system, then you have to figure out whether all of them could give rise to pathogenic T cells or not.
And in the Lewis rat, for example, one knows that on myelin basic protein, there are two adjacent peptides which can induce very nice T cell responses, but only one T cell response is pathogenic and the other harmless. And so we initially were facing the same problem with our Lewis rats and the many different epitopes on aquaporin-4, and there we found out that in principle we can also rise T cell responses against many of these epitopes, but we have to use an enormous amount of T cells to get lesions in the CNS.
But with our new T cell line, now we know that we only have to use very few cells to get the lesion, so they are the dominant pathogenic T cells. And it's quite nice that in NMO patients with a very peculiar MHC phenotype – that's an MHC phenotype that's mostly seen Brazilian NMO patients – they recognize dominantly an epitope that's very close to ours, and they termed this also immunodominant epitope. And it could be that it's pathogenic as well, but there is not yet any proof for that in humans.
MSDF
Looking at aquaporin-4 as a target in NMO, do these cells just use it as a target to destroy the cell that it's on, or does it result in a pathologic process by inhibiting the action of the channel?
Dr. Bradl
There are reports about knockout animals where there is no aquaporin-4 available, also on astrocytes in the CNS. And these animals are apparently healthy under normal conditions, but they show a disease phenotype under conditions where there is tissue swelling going on; for example, under ischemia, and so they cannot cope with that properly. So that means the complete absence of this channel is also bad. Then there are currently two different groups of thinking in the scientific community. There are reports that antibodies can bind to aquaporin-4 and inhibit water flow through this channel, but there are other groups that could not reproduce it. And at the moment it could just be a matter of different antibody preparations or different test systems or different species, so this issue is not 100% solved yet.
MSDF
Anything we've missed or interesting to add on the topic?
Dr. Bradl
I think the only thing one can say is that since NMO is such an extremely rare disease and since this makes it necessary that people all over the world cooperate with each other, that leads to an enormously research-friendly atmosphere and an enormous willingness of the people to cooperate with each other, and so on all different types of subjects.
MSDF
How many patients are there?
Dr. Bradl
Well, when you look here in Austria, we have about 8 million inhabitants; there are 8,000 MS patients and approximately 80 NMO patients. And this frequency is more or less encountered throughout the world; it's a very rare disease.
MSDF
Very good, thank you.
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Thank you for listening to Episode Forty-four 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.
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