This episode summarizes a PNAS study reporting CD163‑targeted lipid nanoparticles that deliver FAP‑specific CAR mRNA to liver macrophages in situ, producing CAR‑macrophages that clear activated hepatic stellate cells and promote fibrosis resolution in mouse models.
0:00Welcome to Base by Base, the papercast that brings Gen Owings to you wherever you are. Thanks for listening, and don't forget to follow and rate us in your podcast app. So today we are taking a deep dive into a, well, a major global health challenge.
0:14Liver scarring, right? Or fibrosis. Yeah, it really is a massive driver of global disease. And the scary part is it often just sits quietly in the background for years or, you know, even decades. Right.
0:26Until it has caused irreversible damage to a vital organ. It's one of those conditions that has long been viewed as just a one-way street, but I want you to imagine something for a second. What if we could program your body's own cellular cleanup crew to specifically hunt down and eat the exact cells causing the scarring without touching healthy tissue?
0:45It's a profound question, honestly, because you know, for the longest time in hepatology. The study of the liver, the idea of reversing permanent organ damage like advanced liver fibrosis, was considered practically impossible.
0:56Right. Right. The conventional wisdom was just that once the scar tissue was laid down in those thick bands, that was it. The tissue was ruined. Exactly. But the research we're looking at in this deep dive, it represents a real potential paradigm shift.
1:09It is fundamentally changing how we might actively reverse that damage rather than, um, just trying to slow it down. Yeah, and today we celebrate the work of the researchers at Shengjing Hospital of China Medical University and the affiliated hospital of Guangdong Medical University, who have advanced our understanding of macrophage-based immunotherapy for chronic liver disease.
1:32They really have. It's just a brilliant demonstration of using advanced molecular tools to solve, well, pretty devastating biological problem. It really is. And, you know, to grasp the elegance of what this team achieved.
1:44We 1st have to talk about the liver's natural state of balance because it's such a resilient organ, right? Absolutely. Arguably the most resilient in the human body. Under normal conditions, your main liver cells that paticites.
1:55They maintain this perfect equilibrium. They are constantly synthesizing and degrading collagen and other structural proteins to keep the organ flexible. It's a finely tuned system. But when the liver gets chronically injured, that balance completely breaks down, and by chronic injury, we mean things like excessive alcohol intake or viral hepatitis, like hep B or C.
2:18Yeah, or even metabolic and autoimmune issues, that chronic injury creates a constant state of inflammation. And that brings us to the main culprits of fibrosis, which are the hepatic stell itself, or HSCs.
2:31I love the way we can visualize these. Think of a paddic stell itself as like microscopic construction workers living in your liver. Normally, they are completely quiet. Right, they just sit around. Exactly.
2:41They store vitamin A, take their lunch break, mind their own business, but when the liver gets chronically injured, they get this massive chemical distress signal. They become activated, and they essentially go rope.
2:53They put on their hard hats and start pouring way too much concrete. Yeah, which, in the body, is the extracellular matrix or ECM. And that excess extracellular matrix is the actual scar tissue. Right.
3:03And because they just keep pouring and pouring, that concrete eventually physically chokes the healthy litter cells, it prevents them from filtering toxins from your blood. It's a great analogy, and here is the crucial biological detail.
3:14When these hepatic stellic cells go rogue and overproduce that concrete, they express a very specific marker on their surface. Like a molecular flag. Exactly. It's a protein called fiberblast activation protein or FAP.
3:28Now, FAP is barely detectable in a healthy adult liver, but in a fibratic liver. It lights up like a neon sign, specifically on the surface of these hyperactive construction workers. Okay, so we have a very clear, very specific target.
3:43If you find FAP, you find the rogue cells. Now, knowing what we know about modern medicine, my mind immediately goes to car car T cell therapy. Which makes sense. Right. Because we already use engineered T cells and oncology to hunt down specific cancer cells.
3:57So why wouldn't we just program ParkRT cells to hunt down anything expressing this FAP marker? It's the logical next step, and you aren't the 1st to think of it. Researchers have actually tried using car RT cells to target activated fibroblasts in other contexts, like um, healing damage after heart failure.
4:15Okay, so it has been tried. It has. But there's a massive fundamental problem with using P cells for this specific job. When you engineer a T cell, its biological imperative is to survive indefinitely in the body as a memory cell.
4:31Which is fantastic. If you're fighting a blood cancer that might try to sneak back 5 years later, you want that permanent patrol. Exactly. But fibroblast activation. Those construction workers pouring concrete is a critical part of normal, healthy wound healing.
4:44Oh, man, I see where this is going. Let me guess, if I have a permanent army of engineered anti-fiberblast T cells patrolling my bloodstream forever. What happens if I get a paper cut a year from now? Or if you need surgery?
4:58You'd be in serious trouble. You need those fibroblasts to heal that paper cut or close that surgical incision. Having a lifelong suppression of these cells is highly hazardous. Wow, it could literally prevent your body from healing everyday injuries.
5:10Exactly. So the clinical need here naturally points to a temporary, highly targeted solution rather than a permanent cellular alteration. We need the cleanup crew to come in, do their job and then, you know, clock out for good.
5:23Okay, let's unpack this because this is where the researchers introduced a completely novel approach that avoids the permanent T-Cell trap. Right. They took a totally different route. Yeah. Instead of taking cells out of the patient's body, engineering them in some multimillion dollar lab and putting them back in, they used MRNA lipid nanoparticles, LNPs, to engineer macrophages in situ, meaning right there inside the living liver.
5:49And the in situ aspect is the true breakthrough here. Macrophages are basically the body's natural scavengers, but delivering instructions to them inside a living creature is a major hurdle. Because they're hard to target.
6:01Yeah. Think of unmodified LMPs, like the ones used in some MRNA vaccines, is delivery trucks without a specific address. They tend to go everywhere and get taken up systemically by various cells. Right.
6:12if you want to specifically engineer liver macrophages, you need a targeting mechanism. So to fix this, the researchers chemically attached specific antibodies to the outside of these microscopic fat bubbles, the LNPs.
6:24Exactly. And these antibodies were designed to hunt for and bind to a receptor called CD 163. Let me theorize for a second. If they're looking for CD 163, I am guessing that receptor is something uniquely worn by our target macrophages, like a specific uniform.
6:38You are spot on. CD 163 is a receptor heavily restricted to macrophages, specifically a subtype known as m2 polarized macrophages. And it just so happens that these M2 macrophages are highly prevalent in the fibrotic liver.
6:53Oh, that's convenient. It is. So by putting these CD 163 antibodies on the surface of the nanoparticle, the delivery truck actively docks onto the macrophage. This triggers a biological process called receptor mediated endocytosis.
7:06Which basically means the macrophage swallows the LNP hole, right? Precisely. It engulfs it, brings the nanoparticle inside, and safely drops off its MRNA cargo right inside the target cells cytoplasm.
7:19Then the macrophage reads at MRNA and builds the FAP hunting receptor. Wait, I have to push back here for a second. Let's say the delivery works perfectly. The macrophage builds the radar. It finds the rogue construction worker pouring the concrete.
7:32How do we know the macrophage actually has the biological engine to digest these tough scar producing cells? It's one thing to hand a security guard a wanted poster. It's another thing entirely to ask them to dismantle a bulldozer.
7:45That's really good analogy. Right. I mean, macrophasias eat dead cellular debris all the time, but eating a tough activated fiber blast seems like a tall order. It is an excellent and it's precisely why the design of the chimeric antigen receptor, or CAR, is so elegant here.
8:01They didn't just give the macrophage a targeting system to find FAP. They fundamentally upgraded its engine. Okay, how did they do that? The FAP car architecture. They coded into the MRNA, uses 2 key internal signaling domains.
8:15The 1st is called CD3 Zeta. This is the primary signal. Got it. When the macrophage grabs the FAP cell, CD3 Zita activates a pathway called NF kappa B, which essentially tells the macrophage, attack and consume.
8:28Okay, so that is the primary attack order. What's the 2nd domain? The 2nd is CD 28. This is a costimulatory domain. Its job is to ramp up a completely different pathway. The PI3K pathway. So if CD3 Zeta is hitting the gas pedal to attack.
8:42CD 28 is like, I don't know, disabling the engine's speed limiter at the exact same time to give it maximum torque. Yes, exactly. This specific dual engine combination of CD3, Zeta, and CD28 boost the macrophase's fagacidic power.
8:57Its physical ability to engulf and literally eat other cells by more than 10 times compared to a normal macrophase. 10 times. Wow. Yeah, it turns a regular scavenger into an absolute powerhouse. That is wild.
9:08But, you know, having a perfectly designed molecular delivery truck and a supercharged engine is great in theory. We need to see what happens when it hits the biological highway. Do these supermacrophages actually cure the disease?
9:19Well, the researcher started in a controlled environment. The initial in vitralab results, testing this in a Petri dish, were incredibly promising. Right, because in the lab, when they put these modified macrophages, which they called a P car M in a dish with the rogue FAP positive cells, they specifically honed in and ate the targets.
9:40They did, but they also shifted their overall personality. They moved from a somewhat passive state into a pro-inflammatory M1 state. So they went from being pacifists to being in active combat mode. Essentially, yes.
9:54They started producing inflammatory combat signals like aisle one beta and IL 6 while actively dropping markers associated with a previous passive state. Here's where it gets really interesting. Because a Petri dish is one thing, but a living breathing organism is incredibly complex.
10:10Absolutely. They then tested this in living mice with severe liver fibrosis, and they were thorough. They didn't just use one type of liver damage. They used various models of severe chemically induced liver damage, as well as damage induced by specialized toxic diets.
10:24Yeah, the robust testing across different models is what makes this paper stand out. They wanted to ensure that therapy worked regardless of how the liver got scarred in the 1st place. That makes sense.
10:35And what happened when they injected them? But when they injected these CD 163 targeted LNPs into the mice, they saw something remarkable regarding biodistribution. The modified LNPs bypassed the general systemic circulation almost entirely.
10:49Oh, wow. So they didn't end up in the lungs or the brain. No, they went straight to the liver and the spleen. And what about that persistence problem we talked about earlier with T cells? The whole, I need to be able to heal a paper cut next year issue.
11:02This is the beauty of targeting macrophages with MRNA instead of T cells with DNA. Macrophages are terminally differentiated. They do not divide rapidly like T cells do. Oh, right. Because they aren't dividing.
11:14The MRNA inside them doesn't get diluted out or passed on forever. It persists and produces the supercharged FAP hunting proteins for up to 14 days, and that it simply degrades naturally. So it's a completely self-limiting therapy.
11:28The cleanup crew does the job for 2 weeks and then goes back to normal. Exactly. I love that. And the results on the liver itself were just staggering. The mice showed massive drops in hydroxy proline, which is a major building block of collagen.
11:44Right, the concrete was disappearing. Yeah, and their blood levels of enzymes that indicate liver damage absolutely plummeted. And when the researchers actually looked at the tissue under a microscope.
11:55Those rogue construction workers, the activated stell cells were almost entirely cleared out. But the clearance of the scar tissue is really only half the story. The other half is hepatocite rejuvenation.
12:07We discussed how the excess concrete physically chokes the healthy liver cells. Well, once the macrophage is ate, the rogue cells and stopped the concrete production, the healthy liver cells actually started proliferating again.
12:18The data on that was so satisfying to read. They tracked a specific protein that basically acts as a neon sign for active cell division, and it went way up. At the same time, the biological signals that tell a cell to die dropped dramatically.
12:31Yeah, the healthy liver wasn't just surviving. It was literally waking back up and rebuilding itself. What's fascinating here is how this happened on a tissue wide level. To really understand this, the researchers used a technique called single cell RNA sequencing.
12:46Which lets them look at it cell by cell. Exactly. It allows them to analyze the genetic behavior of every individual actor in the organ. And they found that the LMP treatment didn't just add CR macrofiches to the mix.
12:58It completely reprogrammed the entire local immune neighborhood. Let me see if I have this right. It's like sending in a specialized task force that doesn't just eliminate the bad guys, but their very presence rallies the local community to start rebuilding the town square.
13:13Precisely. The single cell sequencing showed that the treatment massively expanded a highly specific reparative subset of naturally occurring macrophages known as Sam's. Scar associated macrophages, right?
13:25Yes. Specifically, it boosted the populations expressing an enzyme called MMP 12. Okay, MMP 12. I remember reading about this If the rogue cells are pouring concrete, MMP 12 is essentially the biological solvent for that excess concrete, right?
13:41It's the enzyme that physically breaks down the existing scar tissue. Exactly. MMP 12 is crucial for clearing out the extracellular matrix that is already there. So you have the engineered macrophages, stopping new concrete from being poured, and rallying the local Sams to dissolve the old concrete.
13:59That's incredible. It is, but this actually raises a really important biological question about how macrophages deal with dying cells in the 1st place. I'm really glad you brought that up, actually, because I was struggling with a piece of this puzzle.
14:10I've read that dying or rogue cells in the body often put up a molecular don't eat me flag. Right. CD 47. Yeah. It's basically a fake VIP badge that sells hold up to fool the immune system. They flash the CD 47 badge and the macrophage says, oh, you're on the list.
14:26I'll leave you alone. So how did these engineered macrophages bypass that security system? This is where that dual engine SRR design we discussed earlier comes back into play, specifically the CD 28 part.
14:38We know the Don't Eat Me Flags, ED 47, usually binds to the macrophage and sends an inhibitory signal to stop it from eating. But that CD 28 costingulatory domain inside the engineered FAP car essentially overrides this resistance. By powerfully activating the PI3K pathway, the CD 28 signal acts like a sharp eyed bouncer who recognizes the fake VIP badge.
15:01Oh, that makes sense. The pathway forcefully overrides the don't eat me signal. It drives the macrophages into an MMP 12 high, super eating repetitive state, forcing them to clear the cellular debris that would otherwise just sustain the inflammatory fibrotic cycle.
15:16So they are actively hunting the rogue cells, dissolving the existing concrete and completely ignoring the false security alarms. It's an incredible multi-pronged attack on the fibrosis. If we connect this to the bigger picture.
15:29The potential for clinical application in humans is substantial. The researchers were very forward thinking here. They didn't just stop at mouse model. Great, they tested human cells. Yeah. They successfully created humid derived FA Car MRNA.
15:42They proved that it worked efficiently in human macrophages in the lab. Furthermore, they demonstrated that the FAP target is highly expressed in human fibrotic livers across various real world conditions.
15:56Whether the scarring is from alcohol, viruses, or metabolic disease. Exactly. The target is absolutely present in humans, and the human cells can be engineered to hunt it. But as with all groundbreaking science on this deep dive, We have to maintain a healthy skepticism and look at the real world hurdles for getting this out of a lab and into clinical practice.
16:15We are dealing with incredibly complex biological systems here. Absolutely. We must be entirely impartial about the limitations of the current study. One of the primary clinical concerns is the potential immunogenicity of the antibody fragments attached to the outside of the LNPs.
16:31Because anytime you introduce lab made, exogenous antibodies into a human, There's a risk that the patient's immune system will recognize them as foreign invaders, right? Precisely. Like, the body recognizing the delivery truck itself as an intruder.
16:44And that causes the immune system to create anti-dug antibodies. And those anti-drug antibodies could either neutralize the treatment completely before it even reaches the liver, so it stops working, or potentially trigger a severe adverse immune reaction.
16:58Yes. That's a significant hurdle. What about where the LNPs end up? You mentioned they mostly go to the liver and spleen. That mostly is the key word. While the targeted LNPs went predominantly to the target organs, deeper long-term safety evaluations are strictly necessary, we have to be absolutely certain about the off target distribution.
17:18Because if they go somewhere else. Right. Even low-level expression of the FAP target, or the CD 163 docking receptor, on other cell types in the body. Could theoretically lead to healthy cells being mistakenly targeted and eaten by these supercharged microphases?
17:33So what does this all mean? If we step back and look at the entirety of this research, we're looking at a fundamentally new way to treat severe organ damage. By delivering FEP car MRNA directly to liver macrophages via CD 163 targeted lipid nanoparticles, we can successfully program the body's own immune system to selectively hunt and eat scar causing cells right there inside the living organ.
17:56And crucially, it's not just about cellular destruction. This approach not only halts the progression of liver fibrosis, but it actively restores the entire immune microenvironment. Yeah, it shifts the cellular landscape from a toxic state of chronic scarring to one that actively promotes tissue healing, concrete dissolving, and hepatocite regeneration.
18:15It is a brilliant example of using the body's own systems to outsmart a disease, which leaves us with this final thought for you to ponder. What does this mean for the future of treating other fibrotic diseases?
18:27Could we one day program our immune system to reverse scarring in the heart or lungs just as effectively? This episode was based on an open access article under the CCBY 4.0 license. You can find a direct link to the paper and the license in our episode description.
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