The rapid rise of chimeric antigen receptor T (CAR T-cell) therapy has allowed hematologists to make great strides in treating aggressive cases of multiple myeloma and several types of lymphoma and leukemia. But patients with chronic lymphocytic leukemia (CLL), the most common leukemia in adults, have been left out.
“These are the two immunotherapies that have the most potential right now,” said Ohio State University, Columbus, hematologist Kerry A. Rogers, MD, in an interview. She went on to say that these treatments could be a boon for patients with CLL who don’t respond well to targeted therapy drugs or are so young that those medications may not retain effectiveness throughout the patients’ lifespans.
As the American Cancer Society explains, CAR T therapy is a way to get T cells “to fight cancer by changing them in the lab so they can find and destroy cancer cells.” The cells are then returned to the patient.
As the National Cancer Institute says, “If all goes as planned, the CAR T cells will continue to multiply in the patient’s body and, with guidance from their engineered receptor, recognize and kill any cancer cells that harbor the target antigen on their surfaces.”
According to Dr. Rogers, CAR T therapy is less toxic than stem cell transplantation, a related treatment. That means older people can better tolerate it, including many CLL patients in their late 60s and beyond, she said. (Side effects of CAR T therapy include cytokine release syndrome, nervous system impairment, and weakening of the immune system.)
Thus far, CAR T therapy has been approved by the U.S. Food and Drug Administration to treat lymphomas, some forms of leukemia, and multiple myeloma. “Despite the excitement around these therapies, they lead to long-term survival in fewer than half of the patients treated,” cautions the National Cancer Institute, which also notes their high cost: more than $450,000 in one case.
CAR T therapy is not FDA-approved for CLL. “There are many reasons why CAR T is less effective in patients with CLL versus other lymphomas,” said Lee Greenberger, PhD, chief scientific officer of the Leukemia & Lymphoma Society, in an interview. “For one, many patients with heavily pretreated CLL – prior to any use of CAR T – have mutations that are known to be difficult to treat. Dysfunctional T cells are also common in patients with CLL, and there’s often a lower number of available T-cells to manufacture.”
The results of a phase 1/2 trial released in August 2023 offered new insight about CAR T for CLL. In the open-label trial reported in The Lancet, 117 U.S. patients with CLL or small lymphocytic lymphoma underwent a form of CAR T therapy called lisocabtagene maraleucel after failing treatment with two lines of therapy, including a Bruton´s tyrosine kinase inhibitor. Among 49 patients at a specific dose, “the rate of complete response or remission (including with incomplete marrow recovery) was statistically significant at 18%,” the researchers reported. A total of 51 patients in the entire study died.
The rate of undetectable minimal residual disease blood was 64%. That rate is impressive, said University of Texas MD Anderson Cancer Center leukemia specialist Nitin Jain, MD, in an interview. It’s not nearly as high as researchers have seen in other disease settings, but it’s “a good, good thing for these patients. We’ll have to see in the longer follow-up how these patients fare 2, 3, or 4 years down the line.”
Dr. Rogers, the Ohio physician, said doctors had hoped durable benefit in the Lancet study would be more impressive. An important factor limiting its value may be the aggressiveness of the disease in patients who have already failed several treatments, she said. “The efficacy of CAR T might be improved by giving it as an earlier line of therapy before the CLL has become this aggressive. But it’s difficult to propose that you should use this before a Bruton´s tyrosine kinase inhibitor or venetoclax because it’s expensive and difficult.”
What’s next for CART T research in CLL? Understanding the best timing for treatment will be key, Dr. Rogers said.
The Leukemia & Lymphoma Society’s Dr. Greenberger predicted that “we will begin to see CAR T explored in CLL patients whose disease has a high risk of failing approved agents, such as Bruton´s tyrosine kinase and B cell lymphoma 2 inhibitors. However, CLL patients may still receive prior therapy with more effective Bruton’s tyrosine kinase or B cell lymphoma 2 inhibitors in the future before using CAR T. This will likely be heightened as more Bruton´s tyrosine kinase inhibitors become generic in the next 5 to 10 years and, hopefully, less expensive than CAR T therapy.”
In the big picture, he said, “treatment of CLL with CAR T is possible, but still needs significant improvements if it is to become a mainline therapy in the future.”
CAR T therapy remains available via clinical trials, and Dr. Rogers said it is “currently an important option for patients whose CLL has become resistant to standard targeted agents. We can certainly expect to extend someone’s expected survival by years if they have a favorable response.” She acknowledged that the cost is quite high, but noted that targeted therapies are also expensive, especially over the long term. They can run to $10,000-$20,000 a month. Bispecific antibodies are also being explored as potential therapy for CLL. “They’re really exciting,” Dr. Rogers said, with the potential to spur responses similar to those from CAR T therapy.
A 2022 review described these drugs as “molecules that combine antibody-directed therapies with cellular mediated immunotherapy.” The FDA explains that “by targeting two antigens or epitopes, they can cause multiple physiological or antitumor responses, which may be independent or connected.”
According to Dr. Greenberger, many bispecifics are in clinical trials now. However, “in the context of CLL, actually, the data is actually very, very limited. The development is just starting, and there are phase 1 and phase 2 trials ongoing.”
But data from lymphoma trials are encouraging, he said, and bispecifics “are actually looking as good as CAR T in some settings.”
Regimens can be a challenge for patients taking bispecifics, Dr. Greenberger said. “Repeat dosing with a step-up dosing approach to start is typically required when treating lymphoma.”
On the other hand, Dr. Rogers noted that antibody treatment can be easier for hematologists to arrange than CAR T therapy and stem cell transplants. “From an administrative side, there’s not as many things you need to have set up. So it’s able to be administered in a wider variety of settings,” she said,
Bispecific side effects include cytokine release syndrome and neurotoxicity as well as infusion reactions, Dr. Greenberger said, adding that “I would not exclude cost as a challenge.”
According to Formulary Watch, the bispecific Columvi (glofitamab-gxbm), which recently gained FDA approval to treat diffuse large B-cell lymphoma, is estimated to cost $350,000 for an 8.5-month round of treatment. Reuters reported that the bispecific Talvey (talquetamab-tgvs), which just received FDA approval to treat multiple myeloma, is estimated to cost $270,000-$360,000 for 6-8 months of treatment.
For now, bispecific trials “are mostly now reserved for patients with CLL who become resistant to our current standard targeted agents,” Dr. Rogers said. “It’s a little unclear if you can do CAR T therapy first and then bispecifics, or bispecifics and then CAR T therapy.”
What’s coming next for bispecifics? “On the horizon is better ease of administration, which is already being addressed by subcutaneous dosing for some bispecifics in lymphomas,” Dr. Greenberger said. “There’s also the possibility of combining bispecifics with conventional therapy.”
Dr. Rogers discloses ties with Genentech, AbbVie, Novartis, AstraZeneca, Janssen, Pharmacyclics, Beigene, and LOXO@Lilly. Dr. Greenberger discloses employment with the Leukemia & Lymphoma Society, which supports academic grants and a venture philanthropy via the Therapy Acceleration Program.
Dr. Jain reports ties with Pharmacyclics, AbbVie, Genentech, AstraZeneca, Pfizer, and numerous other disclosures.