Triple-Target CAR T Cells: Benefits and Challenges

In part 1 of our interview with Leland Metheny, MD, lead investigator for the phase 1 BAFF CAR T clinical trial, hematologist-oncologist at University Hospitals Seidman Cancer Center, and assistant professor of medicine at Case Western Reserve University School of Medicine in Cleveland, Ohio, he explained how a new triple-target chimeric antigen receptor (CAR) T-cell therapy works in multiple myeloma and what are the primary and secondary outcomes of the trial investigating this potential therapeutic approach. Here he continues the discussion by telling us of the benefits and challenges this treatment poses and how electroporation, its method of delivery, may be superior to lentiviral vectors, which are most commonly used to deliver CAR Ts to patient cells.

This transcript has been lightly edited for clarity.

Transcript

What are the potential benefits and challenges of targeting 3 receptors vs conventional CAR T therapies?

So with conventional CAR Ts, there's often 1 type of receptor that's recognized, CD19, in certain lymphomas, and BCMA [B-cell maturation antigen] in myeloma. What we have found, as a community of practitioners, is that one of the ways that cancer escapes or relapses after CAR T is that the cancer cells themselves downregulate or eliminate that target from their surface. So, for certain types of lymphomas after CD19 CAR T-cell therapy, when they relapse, the lymphoma cells lack CD19. And for a certain percentage of patients with multiple myeloma, when their myeloma relapses after BCMA CAR T-cell therapy, BCMA is not on the surface or very highly downregulated, as we say. So that's a mechanism of relapse that's well characterized for CAR T-cell [therapy]. So when you have 3 targets on a cell surface, it's a lot harder genetically for cancer cells to downregulate all 3 receptors at once, and so therefore there's less chance of that immune escape, or target escape, from cancer cells with these types of therapies.

How does electroporation improve on lentiviral vector delivery for CAR T therapy?

For many years, the way to integrate DNA into a cell was lentiviral transfection—using a virus itself as a kind of Trojan horse to get DNA into the cell. Over the years, it's become more refined and more safe and more effective. One of the things is that when foreign DNA is integrated into the DNA of a cell with viral transfection, oftentimes it's integrated in places in the DNA that are important and transcribed. Meaning that sometimes the DNA is inserted into a necessary gene, and so there's a higher chance that when you're using viral transfection, that that DNA that you're trying to insert into the DNA of a healthy cell might actually get into a place that causes problems. So that's number one. Number 2, it can be fairly expensive in that regard. The manufacturing of these viruses is highly regulated, as you might understand when you're dealing with viruses being transcribed into living human cells. So those are the 2 issues that kind of have been identified with viral transfection

This electroporation uses nonviral techniques. And so what in general happens is these cells are put in kind of a bath with the DNA, that's kind of protected in that bath, and then electricity is kind of flowed through that bath. What happens is the cells, the T cells that you want to transfect, develop little pores due to that electromagnetic charge, and just by the fact that the DNA is negatively charged and the interior of the cells is positively charged, that DNA is then brought into the cell—and so you don't need a virus to kind of get the DNA into the cell. Then, you use certain types of enzymes to integrate that DNA into the healthy human T cell, and that integration is random. So that integration occurs in places that are transcribed and nontranscribed, and so the potential is that there's less of a chance for integration of that DNA into important parts or necessary parts of the DNA.

Those are some of the benefits of electroporation vs viral transcription into human DNA.

As you might think, viruses are really, really good at integrating DNA into the human cell, and so the efficiency of viral transfection is really, really good. We kind of use nature's natural strengths to integrate DNA into the human cells. The electroporation doesn't have kind of that Trojan horse, and so the efficiency of integrating DNA into the cell is less than—or at least has been in the past—viral transduction. So you get less efficiency of inserting the DNA into those cells. That's okay. We can still generate the appropriate number of cells, but the efficiency is a little less there.