(Guest Lecture) Why Stem Cells Matter - William Matsui, MD | RT Austin, TX Mar 25, 2023

Okay, so I, you know, as Greg was saying, you wanted to, you wanted me to talk about topic about stem cells. And this is something that, you know, I've studied for a long time in the lab. It's something that we study in more multiple cancers besides myeloma. And so we just wanted to sort of provide some conceptual thoughts and then maybe think about, you know, how we would use this to create new therapies. And one thing I will say is, is that just like every, I don't know about good science problem, most science problems, you can't really answer it with just one experiment. So it's something you sort of go through over and over again to try to come up with sort of refining the answer, refining your thoughts over time. So question is, you know, what are stem cells? And I think the easiest place to think about it is there are two very easy places. So one is in the blood system. So we all have, you know, if we're doing, let's say, a autologous stem cell transplant, the thing we do first, we collect stem cells and then we put them in the freezer. Right. And the reason why we do that is, is that once we get our melphalan, if we just gave melphalan, we would harm the stem cells that were there. And since they make all the blood in our circulation, it would take a long time for them to come back. Right. But if we give autologous stem cells right after the chemotherapy, then that's supposed to go into the bone marrow and then you repopulate it. And then you form blood much faster. Right. So one thing to think about is in an autologous transplant, really the cancer fighting part is the melphalan and the stem cell part is like the antidote to the melphalan. Right. It brings your blood counts back faster. So how do we, how is blood set up? And so this has been work that's been done over like about 60 years, trying to figure out, well, what are different ways that we could think about blood being made and what is the actual thing? So there are two sort of general models of how blood is made. So one is, it's a stem cell model where you have a cell way up at the top. And that's one that probably lives a very long time. And what it does is it will divide and it will produce cells and those cells will ultimately become the blood cells that are running around in your circulation. So early on, one of the thoughts was that all of these different cell types down here, red cells, platelets, infection fighting white cells, that each one of these cells had a stem cell. So there was like a stem cell for red blood cells, a stem cell for platelets, a stem cell for neutrophils. But in fact, they all come from one place. All right. So some aspects about this that I think are notable. So one is that we have estimated that we have about a hundred thousand of these stem cells in us, but every day we need to make 90 billion blood cells to replace the ones that we've lost. So we have a hundred thousand that we get at the beginning of our life. And then they have to last for however long we last. People say, well, how long do stem cells live? And I say, they just kind of live longer than you live, right? Because they need to produce blood the entire time. So the normal output is about 90 billion cells. So if you think about it, this is a super fine tuned system, right? Because if you increase it just by a little bit, you're going to have leukemia. If you decrease it by just a little bit, you're going to have anemia and all these other problems. So it's super fine tuned. So that's one of the things about stem cells. The other is, is that B cells are sort of around for your entire lifetime. And so one of the thoughts is, is that to get, make a cancer, and this is a very old thought, is that you need at least two mutations in a cancer. One is not enough in most cases. So if you mutate a cell, right, then, and it's not become a cancer cell, there are two things that can happen. One is, is that it lives a normal lifespan and then it dies. So it never gets a second hit and never becomes cancer. The second is, is that it's cooking along and it gets another one and now it turns into cancer. All right? So it's thought that these cells, stem cells, are really the place where cancer forms primarily because they're the ones that hang around the longest, right? And they're in the mode of producing these things. So you can go up or down in the production. So stem cells are matter of point, stem cells are super important just for blood formation. And the two properties they have, they last a long, long time and they continually produce cells you need. They themselves, it's interesting because all of the cells at the bottom are the cells we need to live, right? We need red blood cells. If we don't have red blood cells, we can't carry oxygen around. That's compatible with life. If we have no neutrophils for a long, long time, we'll get infections. That's not compatible with life. So the cells at the bottom do stuff. They do the stuff that we need them to do. The cell at the top is completely, if you have an infection, we give you a bunch of stem cells. That's not useful, right? Because they can't find infections. They can't carry oxygen. Their job is to make all of these other cells and then the bottom cell do the actual action that we need. So in that cell at the top lasts forever, makes all these cells, but has no real good functional property to prevent because the ones at the bottom do all the heavy lifting, the stuff we need on the data they base, but they can't make themselves. So what they are is something called terminally differentiated. So if you think about neutrophils, you make neutrophils through this whole system and neutrophils last about six hours and then they're gone. Red blood cells, you make red blood cells, they last about 180 days. Playlists last probably about two weeks. So they all have a life span, a finite life span, so you need to keep feeding them from the top. So how do we apply this concept to something like myeloma? So myeloma is a disease that happens down at the bottom. So if you look at the bottom, those are plasma cells. And so the way where plasma cells come from, they come from actually these hematopoietic stem cells, the stem cells I was talking about earlier, but then they go through this very specific maturation pathway where they become B cells and then they go out into the circulation and then they look for things to interact with. And because they're part of the immune system, when they see something that they think they should protect us against, they go ahead and make plasma blasts, plasma cells, and the job of plasma cells is to make the antibodies that protect us. So, and it's part of that, you make memory B cells. So if you get vaccinated once, the next time that thing comes around, you'll recognize it sooner because you don't have to go through this whole process, right? And you'll get a mobile testing. So plasma cells down at the bottom, their job is to make antibodies, right? Their job is not to make more plasma cells, right? So just like in hematopoiesis, what we think is that, you have hematopoietic stem cells here, but memory B cells are the cells that you have, you carry around for your entire life, right? So there are things, so there's this great study that was done way back when there's a fear about smallpox as a biological weapon. So there are many people who have been vaccinated against smallpox, and then they stopped doing it because they said smallpox has been eradicated. So there's no smallpox anywhere in the world, right? But if you go back to those individuals, even though they've never seen smallpox, there's no chance that they've seen smallpox in the last 40, 50 years, you look for evidence of immunity against smallpox, you can find it easily because those cells are going to remember and they stick around. So that aspect of sticking around forever is very similar to stem cells. The other thing is that the aspect of they are the factory and they make these things that actually produce the antibodies we need, that's very similar and parallel. So question is, is that where does myeloma come from? Does it come from the plasma cells, or does it come from somewhere earlier on? Right, so that was one of the first questions that we decided to ask. So as I said, you can have really two different types of cells, tumor cells in just about every patient you look at. So the first one are these plasma cells, and they are the majority of tumor cells. Like when we do a bone marrow to diagnose myeloma, what are we looking for? We're looking for plasma cells, right? So that tells us what it is. They are the things that are responsible for why people run into problems. So they're in the bones, so they weaken the bone and people get a fracture, right? They are in the bone marrow and so you can't make as many red blood cells, so you get anemia. The immunoglobulin that's produced, the M protein or the light chain goes into the kidneys and that's what causes kidney failure. So plasma cells are the things that are making antibodies. Those are why people get sick. The normal plasma cells, as I said earlier, their job is to make antibodies. Their job is not to make themselves. Take plasma cells, put them in a dish, they're going to sit there and they'll make antibodies, but they're not going to ever die. So then B cells are that cell that's earlier. So one question is, is it how do we know that B cells are related to the myeloma plasma cells? So the way that it was done, and this has been done by about 10 labs, this was all worked on early 90s, was that if you think about a myeloma cell, it is making an antibody and that antibody is very, very, very specific. And most people, we have no idea what that antibody is against. It's against smallpox, against flus, against whatever. We have no idea, but you're making one specific kind. All the cells are making the exact same kind of antibody and that's why you get an M protein because it all is the same. So if we look at the gene, at the DNA level, at the gene that encodes that antibody, if we take that sequence, it's unique to this cell, and we go through and we look at all other cells in the body and we say, look, is this gene there? Because it's a marker now for the tumor, we can find that in B cells of every single patient. The problem is that the plasma cells, the ratio of B cells to plasma cells is probably something like one in 10,000 to one in a thousand. So they are a little, little tiny part of your team. But since B cells normally make plasma cells, could it be that in this scenario, B cells, myeloma B cells are now making myeloma plasma cells? That's where the fact is coming. So we did this one experiment many, many years ago where we just took plasma cells from patients and we put them into these mice that have no immune system so you can grow human cells in them. Or we took B cells and then we put those in another set of mice. So if you pick the actual plasma cells, the actual myeloma cells, put them into an animal, the animal does fine. It doesn't get injured. If you put B cells in, you wait a while and then you actually develop myeloma in those animals. So the B cells, which is transferring the ability of this myeloma to grow, and then you take the B cells out again, put them in another mice, and those mice get myeloma as well. So in this system, it seems like B cells are the things that give rise to all the plasma cells. So those are what we think of as being sort of the stem cell compartment in the disease. So one question is, is that, well, why does this matter? And so we did this one experiment. So we sort of hammered home and this is not fair to do to patients and say, look, myeloma isn't curable. Myeloma isn't curable. We're trying to control it, but it's not curable. So the question is, why is it, why might it be curable? So if we think about the drugs we use to treat myeloma, dexamethasone, Revlimid, Belkaid, those things are really good at getting rid of plasma cells. And we know that because we do that every single day. But the question is, is that, well, what about the other cells, the B cells? So if we do this experiment where we treat plasma cells and B cells and we sort of see what their functional properties are, the drugs that we normally give to myeloma patients, dexamethasone, RVD, those work against the plasma cells, but the B cells, they don't work. They don't work against those cells because they're just different types of cells. If we use at the very end an antibody called rituximab that we give to lymphoma patients, and lymphoma cells are B cells. If we do that, then antibody just has no efficacy against the plasma cells because the antigen is CD20 is out there, but it now starts to work against the B cells just like it does on lymphoma. So if you think about this and you think about, okay, well, how do we develop drugs in general? How does someone make a drug in the lab and then it suddenly gets into a person? So the way we do it is we take a drug, we show that it's effective, let's say in the lab or whatever, and then now I do my first clinical trial. My first clinical trial is going to be something called a phase one trial, which is primarily looking at safety. We're going to give it to someone and make sure that it's safe because that's the most important thing. If it's effective, that's icing on the cake, but the first thing is to just show it's safe. So that's the first step. The second step is a phase two study, which is does it actually do anything to the myelo? So in that study, we take a group of myelo patients, we give them this drug that we know is safe because they went through the first round, and we say, look, does it make the myeloma go away? Does it make it go down? And if you think about it, if it goes down, it makes it goes away, then you say, aha, this is a really good drug for myeloma. If it doesn't make it go down, but it's safe, you say, this is a dud. It doesn't work. It doesn't work for myeloma. But if you look at this chart, maybe what we're doing is we're selecting drugs that kill the plasma cells, but we're not selecting drugs that kill the other cells. So those are always stuck left remaining. And if you don't get rid of those things, you're always going to go back. So that's one of the concepts. So one question is, is that can we actually prove that this is reasonable on people? And one of the ways that this was done was with a colleague of ours named Al Garfell, who's at the University of Pennsylvania. So this is what a standard auto transplant is. We collect the stem cells, we give the myeloma, we give the stem cells back, and they hang on for the ride, and then it's going to go down and come back up. So that's how a myeloma transplant is done. So Al did this experiment, along with his colleagues at UPenn, where they took 11 patients. These are all patients who relapsed within one year of their first transplant. So as Hans was talking about earlier, there's this functional high risk, so if you relapse very quickly after your treatment, that's probably a more aggressive case of myeloma. So these are people who already had an autologous transplant. They had cells, their stem cells banked. So the question was that, well, now can we use a CAR T cell against B cells? So it's not against BCMA, it's against CD19, which is against the cells. So they collected T cells, they made the CAR T cells, and they were making these anyway for lymphomas and different leukemias. You give the high dose myeloma, you don't give this high dose because it's the second transplant. You give the stem cells back, you wait about two weeks when their counts are coming back, and then that's when you give them the CAR T cell. This was an experiment that they did. So what did they see? So this is a little bit of a weird sign, but so if you look at the blue bar, that's how long people went before they relapsed for the first transplant, and then the red bar is the second. Okay, so what you can see in most people is that the blue bar is longer than the red bar. So if you have a transplant, you relapse, then you have a second transplant, almost universally the second transplant is not going to work as well, you're going to go less amount of time before you relapse. Okay, and it makes sense because you already had a transplant in that. So when he looked, when they looked, they looked at 324 people with two of these transplants, and in all of them, the red bar was shorter than the blue bar, which makes sense. So when they did this thing with CAR T cells, they actually had a couple of people, so the first one, zero one, the second one went longer, right, before compared to the first transplant, number five did the same thing, and eventually number 12. So you had three patients here where they got these CAR T cells against the B cells. There's none of this CD19 on the myeloma cells, which is not talking targeting the plasma cell. So you see this issue where it looks like maybe you're extending time because you're attacking now those. So this was like a really great experiment. So one of the things that we did with Penn was that we wanted to say, look, if we have BCMA CAR T cells, we know they attack the plasma cells. We have CD19 CAR T cells, we know they attack the B cells, so it's that universally work. So in this experiment, we took clinical samples and we used CAR T cells against CD19 against B cells or against BCMA, which is plasma cells. We mix them up, let things kill one another, and then put them into this acid. So if you're near the top, like where the red squares and green triangles are, those are just cells that don't do anything. If you look at B cells, now in some of the patients, you're getting this really great effect where you're able to like kill everything off and it doesn't come back. With BCMA, you sort of see this mattering, but it's sort of a span of things. If you use both things that target B cells and BCMA, so CD19 and BCMA, you really get great results in this acid. So one of the thoughts is, well, maybe you shouldn't just use a BCMA CAR T cell, maybe you couple that with like CD19 CAR T cells. So that's a study that's been ongoing at Penn. The other way that people have done it, there are a couple of products where people are doing CAR T cells that target BCMA and target B cells, CD19 at the same time. So those would be interesting things for a school kid. All right. So two other things. So one is, is that like, if we can't know whether or not to target BCMA, well, maybe we target the things that the pathways we know give them the properties of living for a long time than making a lot of cells. So there are a bunch of different things up here, developmental signaling pathways. And so the idea behind that is, so when you make a cancer, you're making a new organ. Right? So all the things that you use to make an organ, those things are maybe turned on when you make cancer. But there are other things here that we've studied and looked at. The one other thing about this is that, is that if you think about what I said in the beginning about the system has to be precisely regulated. Right? And so if you look at all, if you look at folks, they have a certain amount of immunoglobulin in them. It's not sky high. It's not really low. It's like a certain much. So there's some ability for the system to control itself. Otherwise you'd have too much antibody or not enough. Too much plus and cells are not enough. So one idea is, is that there's an interplay between B cells and plasma cells. Some out, tell B cells, hey, you can stop making the cell or they have an ability to say, look, we need more now. So will you make one up? So one of the things we're studying in the lab is this relationship between B cells and plasma cells. And the idea is, can you fool the B cells into thinking there are plenty of plasma cells around and that like, the other thing to think about here is what Abbas was talking about is that MGUS is, you got cells, too many of them, but they're sort of just sitting there. Right? So let's say you have a myeloma that actually growing, causing bone damage, all of it. So what if we did something like replace your myeloma with MGUS? Right? So if you had MGUS, if you're able to get rid of that myeloma, you replace it with M.B. It's there, you see it, but maybe it's not hurting you because it's M.B. Right? So that's one of the other things we're trying to think about is to replace themselves with other things. And so that's a big part of what the lab is trying to do. So in conclusion, you know, stem cells are important with these properties. They can be really different from person to person because of the mutations, where you are, like if you're early in your disease, which is late, if you're MGUS versus small brain versus myeloma. And then we're trying to think about these ways to target the cells. One thing is, is that their stem cells have many different cancers, right? Obviously. So if we find something that targets stem cell properties, maybe it's effective for like a lot of different cancers, but if we attack stem cell properties, what happens to your normal stem cells? We have stem cells in our brain, right? That help us survive. We have stem cells in our bone marrow that produce, but we got to be careful about thinking about like hitting those cells that we're just going after to like it at stem cell. Probably. So that was a lot and much of it was probably confusing, but that's my talk.