Novel techniques may provide ‘incredible’ benefits to enhance CAR T-cell therapy
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Multiple studies published since this summer suggest chimeric antigen receptor T-cell therapies are comparably effective in real-world settings as they have been in pivotal clinical trials.
The findings — investigators contend — support broader use of the modality for approved indications, which include relapsed or refractory leukemia, lymphoma and multiple myeloma.
They also place renewed emphasis on efforts to identify ways to improve the effectiveness of CAR-T while minimizing toxicities.
Healio | HemOnc Today spoke with CAR-T investigators about how a novel therapeutic approach may improve the persistence and functionality of CAR T cells, and how deleting a gene from CAR T cells may increase tumor-killing capabilities.
‘Beyond our expectations’
A novel therapeutic approach may improve the persistence and functionality of CAR T-cell therapy, helping to prevent relapse.
The CAR-Enhancer (CAR-E) technique also could help CAR T cells retain memory of cancer cells, allowing them to attack again if cancer does recur.
Researchers plan to conduct a phase 1 trial to evaluate CAR-E for patients with multiple myeloma, with the goal of building off the promise demonstrated so far in laboratory cultures and extensive animal models.
“The results were beyond our expectations,” Mohammad Rashidian, PhD, researcher at Dana-Farber Cancer Institute and assistant professor of radiology at Harvard Medical School, told Healio. “I’m very hopeful that this will save people’s lives.”
Two of the six FDA-approved CAR-T therapies target B-cell maturation antigen (BCMA) in multiple myeloma. About 80% of patients respond to these treatments, but response rarely persists.
For example, half of individuals who receive idecabtagene vicleucel (Abecma; Bristol Myers Squibb, 2seventy bio) relapse within a year, and “almost everyone” relapses within 2 to 3 years, Rashidian said.
“These CAR T cells lose their functionality and don’t form proper memory,” Rashidian said. “They kill 99.9% of cancer cells, they don’t see anything else, and they don’t get any more stimulation because they get their stimulation from killing cancer cells. They start going away.”
Several research teams have attempted to engineer CAR T cells to address this challenge.
Rashidian and colleagues explored a different approach that they hope can work regardless of cancer type.
The platform delivers a fused molecule with two components — a weakened form of interleukin-2 plus the antigen to which the CAR is designed to bind.
Researchers tested the approach on BCMA CAR T cells used to treat multiple myeloma. They attached the BCMA protein to a low-affinity “almost dead” IL-2, Rashidian said.
The BCMA antigen will bind to CAR T cells, and then the low-affinity IL-2 “taps on the CAR T cell’s IL-2 receptor” due to proximity to keep signaling it, he added.
Investigators saw “robust” proliferation of CAR T cells, Rashidian said.
“We were thinking it would result in a modest enhancement,” Rashidian said. “Sometimes you get a 50% better response, but what we saw was night and day.”
This may allow patients to be treated with far fewer CAR T cells than they receive under current protocols.
“In most cases, patients get hundreds of millions of CAR T cells. We think we can lower that and inject maybe a couple million,” Rashidian said. “Patients can get CAR T cells much faster with much lower infrastructure. You can just expand CAR T cells in vivo in patients. We can adjust the level of proliferation that we want with the dosing of CAR-E and the schedule.”
The CAR-E product — which would be off the shelf, similar to other protein therapeutics — delivered “incredible enhancements” in memory formation, Rashidian added.
“Those memory CAR T cells can re-expand and not allow the tumor relapse to take over,” Rashidian said.
If patients do relapse, additional doses of CAR-E — even months after initial CAR-T infusion — can restimulate CAR T cells, findings in mouse models showed.
“The tumor antigen that is growing in some distant organ — let’s say in the liver — may not be enough to provide sufficient stimulation for memory CAR T cells residing in the spleen to expand,” Rashidian said. “The CAR-Enhancer will go everywhere. It will find those good-quality memory T cells residing somewhere tumors are not, and help them re-expand and come back into circulation.”
Rashidian and colleagues formulated two hypotheses as to the technique’s effectiveness.
“One is that this BCMA binds to CAR T cells and anchors this low-affinity IL-2, which then taps on the receptor and signals,” he said. “The second hypothesis is that this causes both the CAR and IL-2 to signal — it’s signaling from both sides. Some synergistic effect is causing this substantial transcriptomic change and this very long-lasting impact.”
Impact could be ‘very strong’
Once they secure funding, researchers plan to conduct a phase 1 trial for patients with multiple myeloma who have received BCMA-directed CAR T-cell therapy.
The dose escalation trial would evaluate and determine safety and efficacy.
The protein itself should not cause adverse events, Rashidian said.
“Patients with this type of multiple myeloma already have high levels of circulating BCMA and, though the IL-2 is toxic, its low affinity is expected to limit most IL-2-related toxicities,” he said.
The protein also has a short half-life, decreasing 50% in a few hours and clearing almost entirely within a day, Rashidian said.
Adverse events likely would stem from the enhancer’s impact on CAR T cells, and proliferation could lead to cytokine release syndrome and neurotoxicity.
“If we can do a good clinical trial, show that it’s safe and we can adjust the dose and schedule, the impact could be very strong,” Rashidian said. “I would expect that this will result in full tumor clearance. That’s what I hope.”
If the trial proves successful, the approach could be used with other CAR-T products, Rashidian said.
“As long as we can target the CAR, then we think it will work,” he said.
Deleting the CD5 gene
Deleting the CD5 gene from CAR T cells improved their expansion, durability and tumor-killing capabilities, according to study findings.
Researchers plan to evaluate this approach in a phase 1 trial of patients with CD5-bearing T-cell lymphomas.
If the trial replicates the findings observed in early models, investigators believe CD5 “knockout” eventually could be used to improve existing CAR-T products and guide development of others, including those that target solid tumors.
“I have six [or] seven models that show CD5 knockout improves CAR T-cell function,” Marco Ruella, MD, assistant professor of hematology-oncology at University of Pennsylvania’s Perelman School of Medicine and scientific director of Penn Medicine’s lymphoma program, told Healio. “I have no doubts about it.”
‘Pretty striking’ improvement
Ruella and colleagues did not start their research investigating CD5 knockout.
In fact, Ruella compared the discovery to his experience at Penn.
He grew up in Turin, Italy, and arrived at Penn for postdoctoral work. He planned to stay a couple years but after Carl H. June, MD — director of the Center for Cellular Immunotherapies at Perelman School of Medicine — helped pioneer tisagenlecleucel (Kymriah, Novartis), the first FDA-approved CAR-T product, Ruella could not bring himself to leave.
“The story completely changed,” Ruella said.
Ruella and colleagues initially investigated CD5 as a target to treat T-cell lymphoma.
CAR-Ts have produced significant results in non-Hodgkin’s lymphoma, multiple myeloma and other hematologic cancers; however, they have not been as effective in T-cell lymphoma, Ruella said.
“Less than 20% of patients with T-cell lymphoma survive at least 5 years,” Ruella said.
Researchers developed a CAR-T to target CD5 but, because normal T cells also express CD5, the cells began killing each other.
Ruella and colleagues decided to use CRISPR-Cas9 technology to knock out CD5.
Not only did the cells not kill each other, the CD5 knockout approach yielded “pretty striking” antitumor improvement over the original CAR T cells, Ruella said.
Researchers knocked out CD5 in multiple models — first with CD19 CAR, then to another blood cancer model using CD30. They observed improvement in both.
This approach also is relevant for solid tumors, Ruella said.
“We use a clinical-grade mesothelin CAR-T that was used in the clinic at Penn for pancreatic cancer,” he said. “We developed the CAR-T, removed CD5 and, again, we had a several logs less disease in the mice that were treated with the CD5 knockout CAR-T.”
Researchers also have data with HER2 CAR and prostate cancer, as well as with T cell receptor-redirected T cells.
Researchers believe deleting CD5 removes multiple inhibitors.
“CD5 serves like an anchor, which a lot of factors bind to, and most of them are inhibitory factors,” said Ruella, citing CBL-B and SHP-1 proteins as examples. “If you remove CD5, those factors are not able to get to the immune synapse and are not able to inhibit CAR signaling, and, as a result, the CAR T cell without CD5 has a much stronger activation in all our models.”
Hoping for ‘huge success’
The phase 1 dose-escalation trial is open for individuals with relapsed or refractory CD5-positive T-cell lymphoma without peripheral blood disease.
Researchers will investigate safety and feasibility as primary endpoints. They also will evaluate response.
Approximately 10% to 15% of patients treated with FDA-approved CAR-T products achieve complete response, Ruella said.
“Anything that goes beyond that would be a huge success,” he added.
The study can accommodate up to 30 patients, but researchers expect to have a good idea of the safety and feasibility after 12 are treated.
Ruella and colleagues hope to enroll at least three patients by the end of the year, and they hope to have a sense of early results in the first quarter of 2025.
Ruella is particularly excited about the 5-day manufacturing period for the CAR product. Current FDA-approved products take between 7 to 10 days to make, he said.
“During this manufacturing, the T cells get sort of exhausted — they differentiate,” he said. “Every day in manufacturing, you get a lesser quality of the product. We decided to have 5-day manufacturing to get a much stronger product that is way more active.”
The CD5 knockout product may produce more cytokine release syndrome and neurotoxicity because of the proliferation and persistence of the CAR T cells, Ruella said.
It also is possible the CAR-T will attack healthy T cells that have a CD5 gene, which could lead to infections. However, researchers believe that can be managed in one of three ways.
The CAR-T product has a “mirroring, binding domain,” Ruella said. “It binds to the antigen through an antibody called single chain variable fragment, which we think over time is going to be immunogenic.”
Each trial participant also will have a plan for stem cell transplantation, if necessary.
Lastly, the CAR-T product will be given with CD5-negative T cells.
“We show that they can recognize viruses like Epstein-Barr virus, cytomegalovirus and so on,” Ruella said. “While we are infusing a product that can be toxic to the T cells, we [also] are infusing T cells that don’t have CD5, so they’re not going to be killed but [they will] have the ability to protect the patient from infection.”
T-cell lymphoma is an orphan disease, so treatments can be fast-tracked if successful, Ruella said.
In 5 years, he hopes CD5 knockout can be a curative option for patients with T-cell lymphoma, and that the safety and efficacy support testing it for other types of hematologic and solid cancers.
“That would be the dream,” he said. – by Josh Friedman
For more information:
Mohammad Rashidian, PhD, can be reached at mohammad_rashidian@dfci.harvard.edu.
Marco Ruella, MD, can be reached at mruella@upenn.edu.
References:
Patel RP, et al. Sci Immunol. 2024;doi:10.1126/sciimmunol.adn6509.
Rakhshandehroo T, et al. Nat Biotechnol. 2024;doi:10.1038/s41587-024-02339-4.
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