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Researchers say they have conducted the first trial of CD19-directed chimeric antigen receptor (CAR) T-cell therapy in which CD4+ and CD8+ cells were administered in equal proportions.
And the assurance that each patient received the same mixture of cells allowed the team to draw clear conclusions about the effects of administering CAR T-cell therapy at different doses.
The researchers detailed these conclusions in The Journal of Clinical Investigation.
This phase 1/2 trial (NCT01865617) was funded, in part, by Juno Therapeutics, the company developing the CAR T-cell therapy as JCAR014.
The work was also funded by the National Cancer Institute, private philanthropists, and the Life Sciences Discovery Fund.
Patients and treatment
The researchers reported data on 32 patients who had relapsed or refractory, CD19+ B-cell acute lymphoblastic leukemia and a median age of 40 (range, 20–73). Two of these patients were excluded due to complications prior to receiving treatment.
The 30 patients who were treated in this study had received a median of 3 prior intensive chemotherapy regimens (range, 1–11). Eleven patients had failed a hematopoietic stem cell transplant (HSCT). And all patients had detectable disease in the bone marrow, extramedullary sites, or cerebrospinal fluid at baseline.
To create the CAR T-cell therapy, the researchers modified CD8+ and CD4+ T-cell subsets separately to express a CD19-targeted CAR incorporating 4-1BB and CD3ζ signaling domains. The cells were then formulated in a defined ratio of CD4+:CD8+ CAR T cells.
Patients underwent lymphodepletion with a cyclophosphamide-based regimen (alone or with fludarabine or etoposide) and then received CAR T cells 48 to 96 hours later. The CAR T cells were given at 3 dose levels—2 × 105/kg (DL1), 2 × 106/kg (DL2), and 2 × 107/kg (DL3).
Toxicity
The first 2 patients who received CAR T-cell therapy at DL3 developed severe toxicities, including 1 patient who died. So DL3 was not given to any subsequent patients.
Two patients died after CAR T-cell infusion. One patient had severe cytokine release syndrome (CRS) and multiorgan failure and died on day 3. The other patient had transient severe CRS with irreversible neurologic toxicity and died on day 122.
The most common adverse event observed in the first 14 days after CAR T-cell infusion was CRS, which occurred in 25 patients. Seven patients had severe CRS that put them in the intensive care unit.
However, for the patients treated at DL1 and DL2, dexamethasone alone or with tocilizumab resolved CRS.
Fifteen patients developed severe neurotoxicity (grade 3 or higher), either with CRS or after it resolved. For all but 1 patient (the aforementioned patient who died), neurologic symptoms and signs resolved.
Response
One patient died before response assessment, so 29 patients were evaluable. Twenty-seven of these patients (93%) achieved bone marrow remission by flow cytometry.
Of the 2 patients who did not achieve a complete response (CR), 1 underwent an allogeneic HSCT after receiving CAR T cells. After HSCT, she relapsed, was re-enrolled on the trial, and achieved a CR after receiving a higher dose of CAR T cells (DL2).
Twenty-five patients (86%) achieved a CR without evidence of minimal residual disease by flow cytometry and conventional karyotyping, FISH, or QPCR.
“Patients who come onto the trial have really limited options for treatment,” said study author Cameron Turtle, MBBS, PhD, of the Fred Hutchinson Cancer Research Center in Seattle, Washington.
“They have refractory acute leukemia. So the fact that we’re getting so many into remission is giving these people a way forward.”
Unfortunately, not all patients stayed in CR. Some relapsed and were treated again with CAR T cells, and 2 patients relapsed with leukemias that were immune to the CAR T cells. The researchers said it is still too early to know the long-term outcomes of the therapy.
“This is just the beginning,” Dr Turtle said. “It sounds fantastic to say that we get over 90% remissions, but there’s so much more work to do make sure they’re durable remissions, to work out who’s going to benefit the most, and extend this work to other diseases.”
Lessons learned
The researchers said that, because these CAR T cells had a defined CD4+:CD8+ composition, this study provides the first clear evidence of the relationships between the CAR T-cell dose patients receive and their outcomes after infusion.
The team found that high doses of CAR T cells and high tumor burden increase the risks of severe CRS and neurotoxicity. However, certain biomarkers can identify patients at the highest risk of toxicity.
Levels of IL-6, IFN-γ, and TNF-α on the first day after CAR T-cell infusion were significantly higher in patients who later developed severe neurotoxicity. Levels of these biomarkers were also higher in patients who were later sent to the intensive care unit.
Furthermore, risk-stratified CAR T-cell dosing based on bone marrow disease burden decreased toxicity.
The researchers also said they observed CD8+ T-cell-mediated anti-CAR transgene product immune responses in some patients, which limited CAR T-cell persistence and increased the risk of relapse.
And including fludarabine in the lymphodepletion regimen resulted in better CAR T-cell persistence and disease-free survival than when cyclophosphamide was given alone or with etoposide.
