How Long Is CAR T-Cell Therapy Effective in Myeloma? An Expert Explains
Is CAR T-cell therapy a cure for myeloma? Dr. Rahul Banerjee, a myeloma specialist and researcher, discusses the reasons that CAR T-cell therapy may lose effectiveness and the potential impact of undergoing another round CAR T-cell therapy.
Dr. Rahul Banerjee is a physician and researcher specializing in multiple myeloma and an assistant professor in the Clinical Research Division at the University of Washington Fred Hutchinson Cancer Center in Seattle, WA. Learn more about Dr. Banerjee.
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Transcript:
Katherine Banwell:
This one is from Jennifer. Why do CAR T-cell transplants not last longer? Is it possible to do a second transplant if the first CAR T transplant stops working?
Dr. Rahul Banerjee:
It’s a great question. So, it’s an excellent question. So, the only thing I would say semantically is, right, in my head, CAR T cells are not transplants per se, because I’m not changing the bone marrow. So, I would transplant a stem cell transplantation, separate from CAR T.
Why do CAR T cells stop working? So, the short answer is we can speculate. We don’t know for sure for any individual patient. Three different buckets are involved. Three different things can happen. One, the T cells can stop working or disappear from circulation. So, that’s possible. CAR T cells don’t last forever. That’s actually okay, right? People often wonder like, “Man, I wish the CAR
T cells could last forever.” I don’t know that I’d want that because as I alluded to, for as long as the CAR T cells are there, patients are immunocompromised, and so that can certainly interfere with the quality of life.
So, it’s not necessarily true that the CAR T cells need to be there forever, but if they’re not there, or if they’re exhausted, which is actually a true scientific word for them not being able to activate and kill that cell when they recognized a protein, the BCMA, that’s one problem.
The second problem is the myeloma cells can mutate. I alluded to this briefly earlier, where the cells can learn to shut off the protein, BCMA, or they can mutate the protein in just a way that the
CAR T is no longer able to bind.
And the third is something called the tumor microenvironment. And this is a little bit more complicated, kind of a grab bag of different things here. The idea is that myeloma cells have a lot of tricks, and they can use all of the cells around them to make it hard for the CAR T cells to get in, to get into the bone marrow and kill them all. And the T cells can be shut off before they even get there.
So, it’s one of those three things in general. Which one is it for an individual patient? Hard to say. And so hopefully in the future, we’ll have better diagnostic tests to be able to identify who is a patient where another BCMA targeted therapy would work well versus, “Oh no, these myeloma cells are no longer expressing BCMA, let’s move on to a different target like GPRC5D.” We’re not there yet. We’ll get there hopefully in a couple of years, is my goal.
Then, you know, Jennifer, that’s a good question. Well, can we do a second CAR T? And that’s very practical. What I would say is if the first CAR T therapy did what we expected it to do, if it lasted for as many years as I would expect for Abecma, that’s typically 12 to 18 months. For Carvykti, that’s typically over 24 months.
If it worked and then it stopped working, and then probably the T cells are long gone, it’s reasonable to try CAR T therapy again. In general, I would recommend, I strongly recommend a different CAR T-cell therapy, even if it’s targeting the same class, like BCMA, it’s going from ide-cel (Abecma) to cilta-cel (Carvykti) or vice versa.
The risk with giving the same CAR T-cell product again is that even though the T cells are a patient’s own T cells, the protein is slightly foreign. Abecma was derived from decades of mouse research. Carvykti was made from decades of llama research, believe it or not. Again, there’s no mouse or llama involved with the actual products nowadays, but in making the sequence years ago that came to them, they are foreign. There are foreign sequences on them, and so everyone’s host immune system eventually recognizes these cells as foreign.
And so if you were to give the exact same product again, immediately the body would reject it the second time around, because it recognizes them and has learned to recognize it as foreign. But changing to a different CAR T cell is very reasonable.
And again, for these newer GPRC5D targeted CAR T cells that, again, don’t target BCMA the way that Abecma, ide-cel or cilta-cel, Carvykti do, but target a different protein entirely, for those patients generally there’s no restriction on whether they’d received a prior CAR T cells. Ideally, it should be at least several months away, at least like a year or so, but if that’s happened and they stopped working, very reasonable. In fact, some of the trials actually require that patients going on to the study of a GPRC5D product have had a prior BCMA therapy of some sort before, and so they’re kind of built into the architecture of things. So, I think it’s very reasonable.
Obviously, there are some unknown unknowns, right? What do you do if the T cells are being manipulated twice, so to speak. Patients ask me about that. I will say just to put that fear to rest, in general, by the time that someone’s had myeloma come back after the first CAR T cells, I alluded to this, the CAR T cells are long gone. So, there’s nothing left.
But again, every case is different, and future research will help us kind of figure out how best to do this.
