Host – Dan Keller
Hello, and welcome to Episode Seventy-nine of Multiple Sclerosis Discovery, the podcast of the MS Discovery Forum. I’m Dan Keller.
Wouldn't it be great to be able to predict who will develop MS? Then those people could be followed prospectively, possibly medication could eventually avert the disease, and at least some medical planning could be done early. Immunologist Dr. Nancy Monson, an associate professor in the department of neurology and neurotherapeutics at the University of Texas Southwestern Medical Center in Dallas, has developed a promising diagnostic test for relapsing-remitting MS that looks at unique antibody gene mutation signatures in B cells in cerebrospinal fluid.
Interviewee – Nancy Monson
We can identify with 86-92% accuracy patients who either have MS or will develop MS in the future.
Interviewer – Dan Keller
How long is the future?
So the longest patient we've tracked so far is 17 months out.
And how quickly might this turn into MS?
As soon as immediate. It kind of depends on, you know, what the patient's history has been really in that respect.
This is tested so far on a pretty small cohort, is that right?
No, we tested it on three different smaller cohorts here at UT Southwestern. And then when DioGenix licensed the IP on MS PreCISe, they actually took it to clinical trials, and we're writing that workup now. And that was 300 patients in that trial.
It looks like there's very good sensitivity, but what's the specificity in terms of other kinds of neurological diseases, inflammatory diseases, anything else?
Right. So we're just starting to figure that out. So the accuracy is based on comparing true patients who convert or evolve to MS versus patients who do not. That's where the accuracy mathematics comes from. But in that respect, the control patients that we've looked at so far, the majority of them have very low scores to no score detectable at all in those patients. But some of them do have higher scores. And we don't understand that yet, because we don't really understand any CNS disease for that matter and how the immune system is operating in there. But we're working on trying to expand the control cohorts that we can really kind of nail down, you know, which ones they'll be different from and which ones they won't be different from.
Is it worth doing healthy controls also?
Not really. Healthy controls are always really low, and so I don't think that's a very fair comparer because it's just not very stringent, right? It's not very hard to be able to figure out who are the healthy donors with MS PreCISe. But when you start looking at people that mimic MS, like people with sarcoidosis and people with neuromyelitis optica, you know, then, you start to really have a rigorous ability to test MS PreCISe. And it's quite possible, when we start expanding those kind of control cohorts, the mimics of MS, that the MS PreCISe scoring mechanism will have to be adjusted to kind of push those different control groups away from the MS group and distinguish the two better.
When we talk about these gene mutation signatures, what are you really looking at? Or for?
So if you think about B cells in the blood, they produce antibodies, which are designed to survey the entire body for infection. Okay? So the way that they do that is to have a really great ability to bind to infectious agents or foreign agents in your body. So the mechanism that a B cell uses to do that is called somatic hypermutation or affinity maturation. And what that means is just fancy immunology speak for saying that they incorporate mutations into their antibody genes in order to bind to their targets better, okay? So it makes them more effective in being able to find them and to stick to them.
So we've done an initial look at the different antibody genes that were being used by MS patients versus our control cohorts, and didn't really see that the genes themselves were that different that they were using. So then we thought, well, maybe it's the somatic hypermutations that they're putting into those genes that are really different from what we see in the controls, and that's what turned out to be true. So it turns out that there is a family of antibody genes that incorporate these somatic hypermutations allowing them to bind to their target better that we don't see in healthy people or people with other neurological diseases. In fact, in some cases some of these codons will accumulate mutations up to seven times more than what we see in control cohorts. And that's what MS PreCISe is based on, is the accumulation of those mutations into those six codons. So the more mutations there are in those six codons, the higher the MS PreCISe score you get, and the more likely it is that you actually have MS.
Are you essentially losing tolerance here, because of the hypermutation there's more chance that you're going to start to recognize self-antigens?
So we have actually taken the antibodies that have these somatic hypermutations in those six codons and looked to see if they bind to human brain tissue. And it turns out that they absolutely do, hands down. We've tested 38 of those so far, and 90% of them bind to neurons in the brain. So we know they bind to self-antigens, right? But that doesn't necessarily mean that they've lost tolerance or that they're proinflammatory, for example. It's possible that the B cells that are making these antibodies are actually somehow able to quiet the immune system. We don't know yet because we haven't been able to do those experiments to see. But obviously, when you see a lot of B cells that are reactive to the brain, right, that they're antibodies are reacted to the brain, that is an alarm to us that they have probably overstepped their boundaries, have not gone to school correctly and done what they're supposed to do. But we still have some experiments to do to make sure that that's what's going on with it.
I suppose that leads to a question of, are they pathogenic in themselves? Or are they bystanders or regulatory somehow else?
Right. That's a really good question, and we don't know the answer to that. There're some experiments we can do to start testing that, but it's very tricky to do those experiments, particularly in the mouse models we have right now. We're not going to give these antibodies to people and see if they get MS, right? So you have to do all that testing in animals or in vitro. And because no one prior to this time has ever actually been able to demonstrate that antibodies from B cells of any type in MS patients actually bind to brain tissue, I mean, this is completely undiscovered country. We're kind of out there on our own trying to figure out how to best ask those questions, and it's a little bit tricky. But I'm fortunate to have a lot of really brilliant people that work with me, and so we'll work on trying to figure out how we can test that in the best way.
It seems that people have been looking for years for the antigen or antigens that are being reacted against in MS. Can you isolate anything and try to stimulate these B cells to nail down what the antigen might be? Or because they're so hypermutable, they might react to anything and then expand on their own anyway?
Well, we know that they don't recognize all targets, right? So we just published a paper in November of this past year, actually it was October when it came out online. But what that shows is that these MS PreCISe-based antibodies bind to neurons and astrocytes in the gray matter of the human brain. And they don't bind to other tissues. They don't bind to other cell type. They are really fairly specific to neurons and glia in the brain. So we know that part of it already. But the question is, you know, what are they doing there? And is it just an epiphenomenon (is what they call it, right)? Is it just a bystander effect that we're even able to find them? So we just don't know the answers to those questions yet. But all those are good possibilities.
Does this depend on the natural propensity of the immune system to create a lot of diversity, generate diversity, because it seems like what you're talking about are all replacement or substitution mutations within these codon hot spots? If you had a deletion or frame shift or something else, you wouldn't see it, because they're not even functional, I assume?
Right. That's exactly right. You got that right.
Is there any value in combining MRI with the antibody gene signatures for a higher predictive power?
So let me be very clear. This test is not meant to replace MRI. MRI is a gold standard in the field. It is essential for physicians to be able to understand the disease and to come up with a plan for how to treat those patients. This is just meant to be a very powerful, supportive, preclinical diagnostic tool to help them base their decisions appropriately. So that's what we're mostly excited about. So, yeah, absolutely. Combined with MRI, I think it'll do an even better job. We actually in the clinical trial we just finished, it's not published yet, what we showed was that when you combine MS PreCISe with oligoclonal banding, the OCB test, that actually you can boost the accuracy of MS PreCISe up to 96% when you combine it with OCB. So that tells us, also, at a scientific level that not only are the genetics of the antibodies important to drive disease, but also that the antibodies probably plays a role in their conversion to MS as well.
Based on the efficacy of rituximab that's been shown, and what you've been finding, is there any thought to doing something more permanent, like using CAR T cells to eliminate B cells almost permanently?
So as a B cell biologist, it's really somewhat offensive to think that we are going to get rid of B cells in all these people, and they're going to be able to be okay with that. We rely a lot on B cells differentiating into plasma cells and living in the bone marrow and making antibodies against things that we see all the time. But when we start depleting B cells from people long-term, it's possible that their humoral immunity, which is composed partly of the B cells and their antibody products, will not be able to fight newer infections because, you know, there's no new B cells to learn about those new infections.
So no, I don't think it's a wise decision that we continue to use rituximab and ocrelizumab. I think that they are the next step. They're a transitional stage that we need before we can get to the true gold standard, which would be a way to deplete just the B cells that are involved in pathogenesis of the disease. My stump on that would be that we should be making B cell depleting antibodies that only recognize those B cells that carry the MS PreCISe antibodies, and those are the B cells we should be getting rid of. But we have a lot of work to do to be able to show that they really are the ones that drive evolution to MS.
What is MS PreCISe? Is this a commercial test now?
So MS PreCISe is its commercial name, but it has not been rolled out yet. It's just beginning into a CLIA lab right now. So hopefully within the next year, it will be an orderable test.
One thing I noticed in one of your papers was you said it wasn't feasible at the time the paper was written to be doing this en masse because it was a very tedious procedure. So does this test essentially make it more feasible?
Yeah. The way we discovered MS PreCISe was actually looking at the antibody genetics of single B cells, which we sequenced using Sanger sequencing. Sanger sequencing is a very elegant immunogenetics-type method. So we spent about a year and a half re-tooling that technology to use next-generation sequencing. So now all we need to do is get a spinal fluid from a patient, and then we extract the DNA directly from that, and we sequence from the entire pool instead. And actually, what's nice about it is we also get a much deeper database from each single patient because we see all of the DNA from that sample now instead of just the few B cells we were able to sort before. It's really nice in that respect because we get a much broader idea of the repertoire. So that is what MS PreCISe is based on is being able to use next-generation sequencing now to really pull those antibody genetics out of individual patients.
What are the unanswered questions at this point?
Well, there are a lot. But I think the one that strikes me the most is whether or not we can pull the antibody gene signature out of the blood. If we can do that, it would get rid of all these spinal fluid taps that our patients have to undergo right now. And so we're working really hard to see if we can find a way to pull them out of the blood so we don't have to do these spinal fluid samplings any more. That's probably our biggest one.
The other thing that we're really interested in, once we can find the signature in the blood, it shouldn't be too hard for us, then, to start asking questions about whether or not family members have a higher risk of getting MS. Which is probably one of the primary questions I get from patients all the time: Can you test my daughter? You know, I'm worried about her maybe getting MS someday. And so that motivates us to think, yeah, we got to get this test ready in the blood so we can start asking those kind of questions. I also think MS PreCISe will be a good monitoring tool. I mean, maybe we do keep treating patients with rituximab, but we don't re-treat them unless they're MS PreCISe score starts to creep back up again. So we're hoping that it's a way to also monitor efficacy of different drugs for that matter. So those are the things we're really working on pretty hard right now.
Great. I appreciate it. Thanks.
Sure. Thank you.
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For Multiple Sclerosis Discovery, I'm Dan Keller.