Michel Sadelain, MD, PhD
Chimeric antigen receptors (CARs) are now being targeted with CRISPR/Cas9, the latest in a series of genome editing tools. In trials done on mice, CRISPR has been effective in creating more potent CAR T cells that enhance tumor rejection.
Senior author Michel Sadelain, MD, PhD, and fellow researchers at his lab at Memorial Sloan Kettering Cancer Center, have recently published evidence to show that this CRISPR technology can deliver the synthetic receptor CAR to the TRAC locus in the genome of the T cell.
Although CRISPR is not yet used in humans, the technology is developing swiftly and showing potential, says Sadelain.
“It is really quite mind-boggling what we can do now with efficiency and precision. It is a completely new way of thinking about a medicine that starts with a human cell, which is modified to acquire not one, but multiple features that increase its therapeutic potency.”
In an interview with OncLive,
Sadelain, director of the Center for Cell Engineering and the Gene Transfer and Gene Expression Laboratory at Memorial Sloan Kettering Cancer Center, discussed CRISPR and its effect on CAR T cells.
OncLive: Could you provide some background on CRISPR?
: CRISPR is a very hot topic—it is a revolutionary technology that has gone through a number of improvements over the years. Genome editing is based on enzymes and nucleases that are targeted to a specific DNA sequence, and when the nuclease is introduced into a cell and targeted, it will cut just the gene that is chosen. There have been nucleases before this—and this one is just as effective—but is easier to manipulate. And so more people have started to use it, which includes us, for the purpose of this particular study.
Another hot topic is CAR. You can then introduce CARs to T cells, and we at Sloan Kettering and a few others have shown that if you engineer T cells with CARs, you can turn T cells into pretty effective antitumor agents. By the time it got to clinical trials, 2 other groups who had read our papers tried it as well, NCI and UPENN. So, our center, and these 2 others, provided clinical proof of activity in different forms of lymphoma and leukemia, showing that T cells engineered with CARs can be very effective in some pretty nasty cancers.
Now, the way that T cells are engineered to do that makes use of what is called retroviral vectors. That is what is used in research all the time, and that is also how these clinical applications were developed. Once you have designed the CAR and the gene for the CAR, you use a retroviral vector to carry the gene inside the T cell and the gene then inserts itself on a chromosome and it becomes permanent property of that T cell. That T cell now makes the CAR protein, so that is why it recognizes and kills those tumor cells. There are also a few people who use another technique, which is called a transposon, to again, shuttle the gene coding for the CAR inside the T cell.
How does your study add to the development of CRISPR in the cancer space?
CAR T cells that are engineered with these vectors work, there are these clinical results that I just mentioned. But, what we sought to do in this study was answer the following question: could we make the CRISPR work in human T cells? And once we have that, can we pinpoint a location on the chromosome where the CAR gene will go and insert itself?
So, instead of being integrated at all of these possible locations, resulting in variegated expression, now every T cell that you make in the lab would have the gene always at that same chosen location and predictably, they would all express the CAR in the same way. We did that and we picked the location, and the location is a gene called TRAC, and we are going to put the CAR gene in that TRAC locus. We succeeded in that and it was highly efficient. And indeed—as you would expect now—all T cells express the CAR at the exact same level. That is clearly in contrast to what you get with the retroviral vectors, which, as expected, their expression is much more variable because the gene is not inserted in the same place in every T cell. Then the surprises came, one of which was when we evaluated these cells in animal models of leukemia in vivo, we found that the cells that had the CAR gene inserted into the TRAC locus worked far better than the T cells that had the randomly integrated CARs. Again, those cells can work in the clinic, there are clinical results to prove that, but TRAC CAR T cells work far, far better.