Autoimmune disorders — where the immune system mistakes something harmless in the body for a pathogen or threat — are not much fun for the people who are stuck with them. And these disorders have been gradually increasing in prevalence over the last couple of decades. I’ve got one myself. Lucky me! Actually, I am lucky in a way, because with treatment, mine is currently under control. But treating autoimmune disorders generally means dampening the immune system as a whole, and that increases risk for infections, cancers, and other things that a healthy immune system can help stop.
So the more specific we can get with these treatments, the better. The best thing of all would be to somehow let the immune system know that whatever it keeps mistakenly attacking (usually a protein) is actually OK, and so it should leave that particular thing alone but otherwise keep on keepin’ on. But how could we do that? We do know very well how to prime the immune system to go after something specific, for example by giving a vaccine. But how do we get it to leave a specific thing alone, especially if it’s already started attacking that thing?
Well, thanks to efforts centered at the University of Chicago, we’ve got the basics down for how to do this. The body has ways to designate proteins as “safe” — if it didn’t, our immune system would just go crazy and attack everything — and we’ve recently learned a lot more about how that works. In a September 7 article in Nature Biomedical Engineering, D. Scott Wilson, Jeffrey A. Hubbell, and their colleagues describe how they took advantage of this emerging knowledge to design “inverse vaccines”.
Their first successes? Reducing pathology to zero in mice with encephalomyelitis (the mouse analog of multiple sclerosis) and reversing the established immune response to a simian immunodeficiency virus (SIV) vaccine in macaques. What’s really important here is that an already-established immune response to something very specific can be knocked down, because that is what we will need to do to treat autoimmune disorders in humans without compromising the immune system:
“In the past, we showed that we could use this approach to prevent autoimmunity,” said Jeffrey Hubbell, a professor of Tissue Engineering and lead author of the new research. “But what is so exciting about this work is that we have shown that we can treat diseases like multiple sclerosis after there is already ongoing inflammation, which is more useful in a real-world context.”
The great thing about the inverse-vaccine approach is that it’s actually pretty simple to implement. People have tried nanoparticles and gene therapy and so forth to try and address the autoimmune problem, but those kinds of things are still fraught with complications. In the study we’re talking about today, all these researchers had to do was take the protein being mistakenly attacked, put the right kind of tag on it, and inject it. Difficulty level very similar to that of a conventional vaccine.
But how do you just stick a tag on a protein and thereby get the immune system to chill out and stop attacking it? Well, tip your hat to the Hubbell lab, because learning that was the hard part!
It’s long been known that the liver is a bit of a safe haven from the immune system, and with good reason. The liver is the first to encounter blood from the intestines, and it is also where old platelets and erythrocytes and other types of cells that undergo programmed cell death go to get broken down. So the liver has to deal with a lot of stuff that is foreign and/or usually not exposed to the immune system and yet is not a threat. That includes proteins from food, intestinal bacteria, and all those broken-down cells.
The interesting thing is that T cells interact with the liver a lot, much more routinely than with other internal organs. You’d think that would mean Immune Armageddon, because wouldn’t these T cells see all kinds of strange stuff in the liver and just start attacking it all? But the liver has a special relationship with T cells. Hepatocytes, which make up 80% of the cells in the liver, chop up proteins and show them to T cells in such a way that the T cells learn that these things are not harmful, and so the immune response to these things is blunted. That usually works out well for the body, with the exception of a few things like hepatitis C, a virus that attacks the liver and often finagles a free pass from the immune system for this reason.
So let’s say the body is mistakenly attacking the neural protein myelin, as it does in multiple sclerosis. Maybe we could curb that by delivering myelin protein to the hepatocytes. They’d chew it up, show it to T cells, and convince them that it’s OK. Then myelin-attacking T cells would change their tune, lose their anger, leave neurons alone, have a couple brews, and join us on Friday Night Beer Blog.
In multiple sclerosis, the immune system attacks the myelin sheath, impairing neural function
But how do you deliver a specific protein like myelin only to liver cells in such a way that they’ll take the myelin up, digest it, and display it the right way on their surfaces so that T cells get the message? You can now see why people have tried nanoparticle delivery (make a little vehicle that ships myelin protein specifically to hepatocytes) or gene therapy (try to get hepatocytes to make myelin protein themselves by sticking a myelin gene into them). But you can imagine that these things aren’t easy to do in practice.
This is where the Hubbell lab found an elegant solution. They were able to do it because they solved a little liver puzzle in 2021. It had been appreciated for a while that one way old dilapidated cells find their way to the liver to get broken down is by losing a certain type of sugar molecule (sialic acid) from their surfaces as part of programmed cell death. A lot of cell-surface proteins are “glycosylated”, or coated with chains of sugar molecules, for many reasons. Usually sialic acid is at the end of those sugar chains as a kind of protective cap. When that sialic acid is lost, the underlying sugar molecules (often galactose, in the form of N-acetylgalactosamine) are exposed, and apparently that’s the signal for a one-way ticket to oblivion in the liver.
Hubbell’s team showed that they could mimic this response by tagging a protein like myelin with exposed galactose molecules, to make it pose as an aging cell. Not only would such tagged proteins find their way into the liver, but they would be processed by hepatocytes and shown to T cells. And therefore T cells would learn not to attack them anymore. Bam!
Structure of the tagged antigen. The protein we want to designate as “safe” (the antigen) is tagged with a polymer that contains many repeats of the N-acetylgalactosamine pendant hanging off the main chain. The “self-immolative linkage” will break when the antigen gets to a hepatocyte, and the long tag will fall off of the antigen
So what this means is, let’s say you have a patient with multiple sclerosis. You tag some myelin with a string of N-acetylgalactosamine molecules in such a way that it poses as a dilapidated cell. This myelin is escorted to the liver and gets into hepatocytes, which then present it to T cells to convince them that myelin is “safe” and they shouldn’t attack it anymore.
This worked so well in mice I literally recoiled from the graph below when I first saw it. Mice were first intentionally made to have simulated multiple sclerosis, so that they were prone to myelin attack by their own immune systems. This was done by injecting them with T cells generated in other mice that had been vaccinated with a big chunk of the myelin protein (called MOG) and also with Complete Freund’s Adjuvant (CFA), which is basically dried bacteria to spook the immune system into action. So these donated T cells were ready to hit the ground running and attack myelin in the recipient mice.
This transfer of activated T cells from mouse to mouse is called “adoptive transfer”, so when you see it in the figure below, you’ll know what that is. That happened at “Day 0”. Then the recipient mice were also treated with inverse vaccine (“pGal-MOG”) on Days 0, 3, and 6 to see if the multiple sclerosis effect could be countered.
Inverse vaccine stops simulated multiple sclerosis cold
This graph — yes, the one I recoiled from — shows what happens if you treat such mice with saline solution as a control (they get the disease), if you treat them with plain old untagged MOG (they get the disease), if you treat them with an antibody called α-VLA-4 that should delay onset of disease by blocking T cells from accessing the brain (they get the disease after a few days’ delay), and finally if you treat them with inverse vaccine, or galactose-tagged MOG (green circles). In the last case, the green circles form a flat line at zero. The disease is absolutely stopped cold.
They saw the same thing in a different mouse multiple sclerosis model where the disease comes on, then diminishes, then relapses again. Relapse happened in all the controls, but when the mice were treated with pGal-MOG (the galactose-tagged myelin), there was no relapse. This is especially important because it means that the treatment can subdue an immune response that is already underway, such as in humans with autoimmune disorders.
Before we go pumping this inverse vaccine into human beings, it would be nice to see some effectiveness in other primates. Autoimmune “disease model” primates are not really widely available, so we need to test this out in a different way. We can do that by vaccinating primates against something so that they develop a strong immune response to it, then seeing if we can quell that immune response with our inverse vaccine.
That was done with macaques and simian immunodeficiency virus (SIV) here. Two sets of macaques were injected with an SIV vaccine three times (at weeks 0, 6, and 12), and they all generated a vigorous immune response. Then at weeks 18, 22, and 26, they got either the inverse vaccine or saline solution as a control.
In this case the inverse vaccine is a tagged version of one of the proteins made by SIV called Nef. So we want to see if the inverse vaccine can tamp down the strong T-cell response to Nef in these macaques. In other words, can the inverse vaccine put the brakes on a strong immune response that is already underway, as happens in an autoimmune disease, in a primate?
Right after the first inverse-vaccine treatment at 18 weeks, the T-cell response to Nef is indeed cut dramatically (-40% for inverse vaccine vs. +100% for the control), and then it gradually diminishes in both sets of macaques, as expected.
Inverse vaccine counters the immune response of the SIV vaccine
All of this together means that we now have an elegant way to designate specific proteins as “safe”, and thus convince the immune system to stop attacking them. Keep in mind that this is only version 1.0 with short treatments. We’ll absolutely get better at this over time.
Phase I clinical trials are underway, and so far celiac patients (for whom the immune system flips out over gluten) have had the inverse vaccine administered safely. That’s what you like to see in Phase I. No complications developing. Next up is Phase II, where we begin to look at efficacy in humans.
If you’ve been following immune-system research over the last few years, you probably agree with me that we are in a golden age of understanding, where we are starting to have a real shot at subduing diseases that have plagued us since before we even started walking upright. Multiple sclerosis, Crohn’s disease, rheumatoid arthritis, lupus, celiac disease, Type I diabetes, myasthenia gravis, ulcerative colitis, psoriasis, …. the list goes on. We’re on an irreversible path to defeating each and every one of these. All of their days are numbered. It is only a matter of time.
