NEW YORK—Two chimeric antigen receptor (CAR) T-cell therapies—axicabtagene ciloleucel (Yescarta ®) and tisagenlecleucel (Kymriah™)—are already approved in B-cell lymphoma by the U.S. Food and Drug Administration.
A third, lisocabtagene maraleucel, will most likely be approved before too long.
Despite differences in their costimulatory molecules, persistence, efficacy, and toxicity profiles, they all have high overall response rates and a fall-out of response during the first 3 to 6 months.
Longer-term follow-up is necessary to determine whether CAR T-cell therapy is actually curative.
“But based on the way things are looking,” said Reem Karmali, MD, of Robert H. Lurie Comprehensive Cancer Center of Northwestern University, “it seems this might be a realistic expectation.”
“CAR T-cell therapy is clearly effective and has been a ground-breaking form of therapy,” she said, “but there seems to be two sides to the coin. There are a number of challenges that we face with CAR T-cell therapy.”
Dr. Karmali outlined those challenges in a presentation at the NCCN 13th Annual Congress: Hematologic Malignancies.
One of the biggest challenges, according to Dr. Karmali, is patient selection.
First, patients must have an adequate hematopoietic reserve to ensure successful CAR T-cell manufacture.
Dr. Karmali referred to the JULIET study, in which 7% of patients failed the manufacturing process due to insufficient apheresis.
Second, the patient’s disease must be stable enough to make it through the time it takes to manufacturing the CAR product, which is typically 2 to 4 weeks.
Third, the patient’s overall health must be good enough to tolerate CAR T toxicities. “The patient needs good major organ function as well as preserved neurologic function,” she explained, “to withstand the unique toxicities that come with CAR T-cell therapy, specifically CRS [cytokine release syndrome] and neurotoxicity.”
The major toxicities are CRS and CAR‑T‑cell‑related encephalopathy syndrome (CRES).
Dr. Karmali pointed out there is also a theoretical risk of insertional oncogenesis from viral transduction used in manufacturing the T cells, and an off-tumor on target-effect that can result in B-cell aplasia and hypogammaglobulinemia.
The profiles of inflammatory cytokines and inflammation markers differ for each CAR construct and are driven in different ways. However, IL-6 is an important mediator for CRS and IL-6 receptor blockade is effective in managing the toxicity.
The drug of choice is tocilizumab, Dr. Karmali said, and for patients who are refractory to tocilizumab, siltuximab can be used.
“Steroids are extremely useful for CRS,” she added, “because they hold down inflammation and prevent immune activation.”
Steroids are also the mainstay for managing the neurotoxicity of CAR T-cell therapy because they help stabilize the blood-brain barrier.
“It’s important to make a note,” she said, “that there actually have been a number of analyses that have looked at the impact of using IL-6 receptor blockade and steroids on CAR T-cell expansion and persistence and there really doesn’t seem to be an impact.”
“So we really ought to use these quite liberally for grade 2 or higher toxicity without worrying about dampening the effect of CAR T-cell therapy,” she emphasized.
Dr. Karmali outlined a few new directions to address the challenges with CAR T-cell therapy, such as switchable CARs that can be turned on or off and potentially improve safety; development of new constructs that may improve homing; improvement in persistence; use of combination and sequencing strategies; and improved antigen selection that may be effective with other lymphoproliferative diseases.
“A provocative question is whether CAR T-cell therapy can actually replace autologous stem cell transplant as second-line therapy,” she said. “This is actually being actively evaluated in a number of clinical trials including ZUMA-7 (NCT03391466).”
“I think another provocative question is whether CAR T-cell therapy can be used as consolidation in CR1 [first complete remission],” she added.
The rationale for using CAR Ts as either a replacement for autologous stem cell transplant or in CR1 is that there may be minimal residual disease present that would be enough to elicit a CAR T-cell effect, she explained.
“Ultimately, one envisions the following paradigm for the treatment of lymphomas across the board,” Dr. Karmali concluded.
“Specifically, chemotherapy with a targeted agent for rapid cytoreduction, followed by CAR T-cell consolidation in combination with either other cellular therapies or immunotherapy as a means of eradicating the minimal residual disease and ensuring a pathway to cure.”