CRISPR gene editing may put universal T-cell therapy within reach
Few scientific advances have generated the optimism and enthusiasm that surround CRISPR.
CRISPR — which stands for clustered regularly interspaced short palindromic repeats — is half of the CRISPR/Cas9 system for genetic engineering that earned Emmanuelle Charpentier, PhD, and Jennifer A. Doudna, PhD, the 2020 Nobel Prize in chemistry.
Its ability to disrupt or correct and insert genetic material has been heralded as a potentially transformative scientific advance that may lead to breakthrough therapeutics for cancer, rare genetic diseases, infectious diseases and other conditions.
“The CRISPR system will revolutionize all of medicine — every corner of it,” Joseph McGuirk, DO, professor of medicine and director of the blood and marrow transplant program at University of Kansas Medical Center, told Cell Therapy Next.
The field of cancer cell therapy is no stranger to genetic manipulation.
Chimeric antigen receptor T-cell therapy was the first gene-edited therapy approved in the United States, although the process differs from CRISPR in that it uses transduction via viral vectors that allow for the insertion of an antigen-binding receptor on the surface of a patient’s T cells.
Extensive clinical research is underway to assess CRISPR gene editing in combination with CAR T cells. McGuirk is involved with several such trials at his institution.
“It’s a hot ticket right now,” said McGuirk, adding the Nobel Prize recognized the technology’s “game changer” status. “It’s an exciting, extremely promising new world coming down the line. CRISPR is going to drive toward that world.”
Cell Therapy Next spoke with experts about how oncologists, geneticists and researchers are collaborating to determine how CRISPR gene editing can produce more effective CAR T cells that have the potential to be more durable, less costly and available on demand.
Beyond Personalized Medicine
CRISPR — one of many gene-editing techniques available to researchers — has been celebrated as a dramatic leap forward because it is relatively cost-effective and easy to use, putting it within reach of nearly every biology lab.
“CRISPR technology has transformed the landscape of genome editing with its simplicity and versatility,” Samantha M. Fix, PhD, postdoctoral fellow at The University of Texas MD Anderson Cancer Center, and colleagues wrote in a review published in March in Cancer Discovery.
CRISPR provides considerable advantages compared with older gene-editing techniques, according to Fix and colleagues.
“The CRISPR system can be designed to target virtually any genomic sequence simply by altering the [guide] RNA sequence,” they wrote. “This enables rapid design and implementation of new CRISPR gene knockout/knock-in strategies.”
Eric B. Kmiec, PhD, geneticist and director of the Gene Editing Institute at Helen F. Graham Cancer Center and Research Institute at ChristianaCare, noted the CRISPR-Cas9 system is based on previous knowledge of how a naturally occurring bacteria behaves.
By comparison, other gene-editing systems — such as TALEN or zinc finger nucleases — are man-made and must be reengineered each time to target the specific site where the DNA sequence is cleaved.
“If you were to isolate the fundamental units — the CRISPR RNA part and the Cas protein, the two parts of the CRISPR-Cas9 system — they can be used with very little reengineering quite broadly in mammalian cells,” Kmiec told Cell Therapy Next. “CRISPR is easier to use because we understand a lot more about how it works naturally, and that allows us to implement it with [far] fewer questions.”
The primary goal of using CRISPR gene editing on CAR T cells is to make more effective therapies faster, not necessarily to create more CAR-Ts that treat a wider array of cancers, Kmiec said.
“Gene editing has been a primary part of the T-cell world and CAR-T therapy from the beginning,” Kmiec said. “If gene editing is going to go into the T cell even further and knock out genes in the T-cell genome, then it will allow it to be more benign and won’t cause an immune response.”
Such a process could produce “the universal T cell,” Kmiec said. This could create on-demand therapies derived well ahead of time from T cells of healthy donors.
“This is the off-the-shelf T cell that people talk about, and CRISPR and gene editing are going to be heavily involved in creating a T cell that will work ... in anyone’s body,” he added.
CRISPR will move CAR-T beyond the realm of personalized medicine that requires weeks of off-site engineering, Kmiec said.
“Gene editing is going to play a major role in CAR T-cell therapy and immunotherapy simply by being able to engineer a cell or a T-cell that will have much broader application and not cause such a negative reaction,” he said. “It isn’t really going to increase the use in all [people with cancer] because [CAR-T] targets very specific antigens.”
Edward A. Stadtmauer, MD, section chief of hematologic malignancies in the Perelman School of Medicine at the University of Pennsylvania, and colleagues conducted the first phase 1 clinical trial of CRISPR-edited CAR T cells in humans. They published their results last year in Science.
“I’m the country doctor in this whole process, not the engineer in the lab,” Stadtmauer told Cell Therapy Next.
Since the trial began in 2016, the efficiency of CRISPR gene editing has nearly doubled, Stadtmauer said.
“The technology really has improved substantially,” he added.
Three patients — one with sarcoma and two with multiple myeloma — underwent treatment during the study. Two had stable disease after CAR-T infusion, but all three experienced disease progression and required subsequent alternative therapies.
The CAR T cells used four separate gene-editing maneuvers, including the insertion of a receptor that recognizes the NY-ESO-1 antigen on the surface of cancer cells, in addition to other edits that help prevent T-cell fratricide and removal of a gene encoding PD-1 to improve antitumor immunity.
“The most important findings we had was that it was safe, we did not see significant cytokine syndrome or neurotoxicity, and the cells persisted,” Stadtmauer said. “We’ve demonstrated that this can be safe and feasible, but the time has come to use 2021 technology — and maybe even 2022 technology — to do this process in an even more effective way.”
Stadtmauer highlighted another key observation: High-risk patients treated with CAR T cells often experience a substantial increase in disease burden while waiting for their therapy to be manufactured.
“It’s a real limitation sometimes to having the optimal outcome,” he said.
The primary aim of using CRISPR gene editing for CAR T cells is to create a more effective therapy in less time, Stadtmauer said.
Currently, the only way to feasibly create such a therapy faster would be via allogenic — or donor — T cells.
“They could potentially be destroyed by the host before they have the chance to do anything because they are identified as foreign,” Stadtmauer said.
CRISPR technology provides a potential solution given its capability to remove the inherent T-cell receptor and major histocompatibility type markers on the cells, he said. It also removes PD-1 to make CAR T cells more active and effective.
“This is the direction that current research is really focusing on,” Stadtmauer said. “[We are] trying to engineer allogeneic CAR T cells available via an off-the-shelf product.”
‘Ready to Roll’ Cell Therapy
Developing effective CAR T-cell therapies requires cooperation and cutting-edge technology, according to Theresa LaVallee, PhD, vice president of translational medicine and regulatory affairs with Parker Institute for Cancer Immunotherapy.
LaVallee, who has experience on the clinical development and manufacturing sides of CAR T cells, said CRISPR is the type of “transformative technology for gene editing” that will allow teams to develop more effective, more readily available therapies.
“Collaboration, technology and science-driven approaches ... are the key parameters for making a CAR-T,” she told Cell Therapy Next. “[The process requires] not just technology and information, but real depth of understanding of T-cell biology and the ability to manufacture its targets.”
The phase 1 CARBON trial is one such collaboration designed to combine cutting-edge gene editing with CAR T-cell therapy to create off-the-shelf products that are more effective than autologous products.
The open-label, multicenter trial evaluated the safety and efficacy of CTX110 (CRISPR Therapeutics) for adults with relapsed or refractory non-Hodgkin lymphoma who received at least two prior lines of therapy.
CTX110 — an allogeneic, CD19-targeted, CRISPR/Cas9 gene-edited CAR T-cell therapy designed to treat CD19-positive B-cell malignancies — uses three gene edits to create an allogeneic CAR-T. The edits include knocking out the class I major histocompatibility complex to enhance T-cell persistence, knocking out the T-cell receptor that recognizes foreign antigens to prevent graft-versus-host disease and precise location of the CAR to create a more consistent product.
Eleven patients in the CARBON trial completed a 1-month follow-up assessment by the data date of Sept. 28, 2020.
Researchers reported no dose-limiting toxicities or GVHD cases among the 10 patients who received the three lowest doses evaluated in the study. Three (30%) of those patients achieved complete response. The two patients who achieved complete response remained in complete response at the time of analysis.
Autologous CAR T-cell therapies employ the patient’s own cells. CRISPR gene editing can knock out certain genes, allowing researchers to develop off-the-shelf therapies from healthy donor cells.
“Patients who are donating their own cells have gotten beaten up with chemotherapy, and chemotherapy affects the lymphocytes,” said McGuirk, an investigator on the CARBON trial.
The result is a therapy that comprises cells “that weren’t doing their job in the first place,” he added.
“That’s the T cell that you’re collecting and genetically manipulating to attack a cancer cell,” McGuirk said. “Maybe that’s not the best cell to use.”
CRISPR technology may help develop donor-based therapies ahead of time, alleviating much of the concern about patients with high-risk advanced disease who may progress or die while waiting for their CAR T-cell therapy to be manufactured.
“Now you have a real drug,” McGuirk said. “You could take it off the shelf and ship it overnight ... to a center that needs it and not have weeks of manufacturing. It’s already ready to roll.”
‘Gee Whiz Science’
Researchers studying how to apply CRISPR to CAR T cells all seem to agree one modality will have an impact on the other. The question is the extent of that impact.
“Gene-editing tools will help construct the universal T cell, which can then be used in a more broad-spectrum sense to treat more patients,” Kmiec said.
CRISPR is the right gene-editing tool to accomplish this goal, he added.
“Frankly, it is the only tool we have to do it,” Kmiec said. “For the number of receptors and changes that need to be made on the cell so it doesn’t illicit an immune response, CRISPR is the most efficient tool. [It is the] easiest to use and easiest to apply.”
Kmiec called the development of a universal T cell the “brass ring” of CAR-T development but acknowledged that such a therapy would be effective for a limited population whose cancer has targetable antigens, much like CD19 for lymphoma or leukemia.
“But you have to do your best and, in most cases, I think there will be [positive] effects,” he said. “There is definitely a need for this universal T cell and the best engineering tool is CRISPR, so it’s a natural fit.”
CRISPR gene editing will transform CAR-T, LaVallee said. Future research on its utility will focus on how to improve T-cell fitness, deliver more effective anti-tumor payloads and successfully identify new target antigens, she added.
“The ability to ask more questions — and to answer these questions — relies on collaboration,” LaVallee said. “Using [CRISPR] technology for the efficiency and precision of delivering gene edits is really making a big difference.”
CRISPR has the potential to transform CAR T-cell therapy if the technology can produce therapies faster and with enough volume to meet current demand, Stadtmauer said.
Nevertheless, even some small improvements would be enough to have a profound effect on clinical care, he said.
“Creating off-the-shelf cells that are effective would be transformative for day-to-day care,” Stadtmauer said.
From a clinician’s perspective, the hardest part of CAR T-cell therapy is the need to “strategize for a number of months” until the patient receives the therapy, Stadtmauer said.
“The real transformation would be having them available in real time, even if there is no change in the effectiveness of the cells,” he said. “I see CAR T cells as revolutionary. I see a CRISPR manipulation of those cells as incremental and something that will incrementally make this treatment and technology better.”
McGuirk expressed an even greater sense of optimism about CRISPR’s potential impact on CAR T-cell therapy and cancer treatment.
“It’s an extremely foundational part of the future of cancer therapeutics — I can say that with confidence,” McGuirk said. “My wife says never to say this because people will think [I’m] old-fashioned and corny, but it’s ‘gee whiz science.’”
- CRISPR Therapeutics. CRISPR Therapeutics reports positive top-line results from its phase 1 CARBON trial of CTX110 in relapsed or refractory CD19+ B-cell malignancies. Available at: www.crisprtx.com/about-us/press-releases-and-presentations/crispr-therapeutics-reports-positive-top-line-results-from-its-phase-1-carbon-trial-of-ctx110-in-relapsed-or-refractory-cd19-b-cell-malignancies. Accessed July 30, 2021.
- Fix SA, et al. Cancer Discov. 2021;doi:10.1158/2159-8290.CD-20-1083.
- Stadtmauer EA, et al. Science. 2020;doi:10.1126/science.aba7365.
- For more information:
- Theresa LaVallee, PhD, can be reached at firstname.lastname@example.org.
- Joseph McGuirk, DO, can be reached at email@example.com.
- Eric B. Kmiec, PhD, can be reached at firstname.lastname@example.org.
- Edward A. Stadtmauer, MD, can be reached at email@example.com.