The next evolution of gene therapies may involve pitting T cells with different modifications against one another in a “race” inside a human to determine which edits produce the best results against a tumor, an expert panel predicted.
Researchers across the globe have discovered dozens of genes that could be targeted to make T cells more durable and effective in tumor microenvironments, but testing them one at a time could cost millions of dollars and take a century, according to a presentation hosted by Friends of Cancer Research and Parker Institute for Cancer Immunotherapy.
“We’d like to not limit it to just one guess. We’d like to make many guesses,” Alex Marson, MD, PhD, director of Gladstone-UCSF Institute of Genomic Immunology and Parker Institute for Cancer Immunotherapy at Gladstone Institutes, said.
“There’s technology that now makes this possible,” he added. “[CRISPR-Cas9] is not only efficient at editing sites in the genome, it’s incredibly flexible, and we are increasingly expert as a field at being able to direct CRISPR at any site in the genome.”
There is potential for development of new modified cellular therapies that contain “a library or a pool” of unique CRISPR molecules that can be inserted into CARs or T-cell receptors, Marson added.
“That means you could end up with a population where each CAR T cell has a different gene knocked out,” he said. “We’d like to be able to then infuse that into a patient and see which ones continue to grow in blood or, ideally, even in a tumor microenvironment.”
Rewriting the human genome
About 1,100 CAR-T trials are currently being conducted globally, and more than 34,000 individuals have been treated with a CAR-T products since the creation of the therapy, Carl H. June, MD, Richard W. Vague professor in immunotherapy and director of the Center for Cellular Immunotherapies at Perelman School of Medicine at University of Pennsylvania, said during his presentation.
The durability of CAR T cells has been demonstrated in numerous studies, with some still detectable 17 years after infusion, June said.
“CAR T cells can be living drugs, which his why we’ve been attracted to them — the fact that they can potentially be lifelong both to eradicate a tumor and stay active for immunosurveillance,” he explained.
However, “Not all T cells are created equal,” June said. “You can insert the CAR, but it depends on the CAR signaling domain and then issues of where the lentiviral vector or retrovirus inserts — and you can gain a function or loss of function, depending on where these insertions are.”
June supported this with yet-unpublished results from labs at University of Pennsylvania and Stanford University that showed “intentional dual-knock into TRAC and TET2 leads to enhanced proliferation, decreased checkpoint expression and improved antitumor effects.”
Researchers can use gene editing such as zinc finger nucleases, transcription activator-like effector nucleases (TALEN), meganucleases and CRISPR-Cas9 to take advantage of this information.
“We can literally rewrite the human genome now,” June said. “It’s fair to say when we started CAR T cells none of us thought this would be possible.”
The ‘race’
Marson described the success of CAR-T as “miraculous” in a range of patients, which now includes those affected by autoimmune diseases.
“We still haven’t really seen the home run that we all want” in solid tumors, Marson said.
Numerous reasons factor into why solid tumors present more difficulties than hematologic malignancies, he explained.
T cells can become “exhausted” or “dysfunctional” from attacking. Solid tumors can secrete metabolites and cytokines that can turn T cells off. They can have checkpoints that “silence” T cells. Other immune cells can suppress the T cells as well, Marson said.
“If we want to design successful T cell therapies for the future, we have to think about a target profile of what these cells will look like,” he added. “Cells need to survive the tumor’s defenses and be able to proliferate and clear out the tumor. Researchers could accomplish that through various edits.
“We still don’t know what the gene modification is that’s going to be the ultimate winner for what’s going to make the most effective CAR T cells,” he said.
The idea of a “race” to see which edits are most effective could be possible because of technological advances, according to Marson.
Those developing novel therapies could determine “winners” based on DNA sequencing techniques, seeing which edited genes accumulate the most in the tumor microenvironment.
“We can, in a population of T cells, disrupt or knock out every gene in the genome,” Marson said. “There are 20,000 genes. We can get rid of a different one in each cell and then race them against each other.”
Marson’s team tested every gene in the genome in a tumor microenvironment and found various genes that could potentially resist suppression, including one that had not been studied, RASA2.
“RASA2 is not alone,” he said, adding that it represents just one of a number of “really promising candidates” that have emerged from unbiased genetic studies done directly in human T cells.
“It’ll take millions and millions and millions of dollars and a century if we did these sequentially,” he said. “There’s an opportunity to take advantage of the technology, not only to identify the candidates for which genes we want to modify, but to actually take advantage of this flexible technology to test things in pools and measure the effects of individual gene modifications within a pool inside of a patient.”
Addressing safety concerns
Marcela V. Maus , MD, PhD, director of the cellular immunotherapy program at Mass General Cancer Center and Healio | HemOnc Today Associate Medical Editor, expressed optimism about the potential of a race.
“Introducing specific, trackable, biologic changes into autologous T cell products would allow the field to make stronger associations between underlying biology and clinical effects,” she said.
However, Maus also understood safety concerns the strategy could elicit.
The FDA issued a safety warning in November about possible secondary malignancies following CAR-T; however, studies in the past several months have indicated those events are “very rare,” as Healio previously reported.
June affirmed those numbers in his presentation. In separate retrospective studies at University of Pennsylvania and Stanford University, more than 1,500 patients had received CAR-T and only 43 developed secondary malignancies, none of which could be attributed to the CAR-T itself.
CAR-T does have two predominant treatment-related toxicities, but clinicians have become more adept at treating cytokine release syndrome and immune effector cell-associated neurotoxicity, Maus said.
Could those, or secondary malignancies, become worse if patients are infused with a pool of edited cells?
Maus did not believe so, referencing previous research about “competitive repopulation” with two CAR T products that contained multiple gene knockouts.
The two known cases of CAR-T lymphoma involved patients receiving cells with 50 edits in them, she said.
“The number of gene edits per cell may increase the safety risk, but not necessarily the overall number of gene edits in the product — because it’s not about the heterogeneity or the amount of heterogeneity in the product, it’s about how many gene edits or gene fusions or translocations could occur in any individual cell,” Maus added.
Safety measures could be implemented to reduce the risk for significant adverse events.
Maus highlighted multiple aspects of product design, characterization of the product, protocol design and release testing criteria that could be used to increase safety.
“An intentionally heterogenous pool of autologous T cells appears complex, but safety concerns are largely limited to on-target effects and T-cell editing,” she said. “Intentional heterogeneity offers the same or higher potential benefit to individual subjects participating in a first-in-human clinical trial as typical CAR T-cell trials.”
