Though CD19-directed chimeric antigen receptor (CAR) T-cell therapies have shown great promise for the treatment of hematologic malignancies, the possibility of routinely bringing these therapies into practice is hampered by difficulties in manufacturing CAR T-cell products, the heterogeneity of anti-tumor responses, and the potential for severe treatment-related toxicities.
According to results of a phase I/II trial published in Blood, young patients treated with CD19 CAR T-cell therapy at a maximum tolerated dose (MTD) of 1×106 cell/kg achieved high rates of minimal residual disease (MRD)-negative complete remission (CR). The products were engineered with a defined CD4/CD8 T cell ratio, a uniform level of CAR expression, and a less differentiated phenotype – a process associated with a high manufacturing success rate.
“This study reinforces that a high rate of remission can be obtained with CD19-directed CAR therapy,” lead author Rebecca A. Gardner, MD, from the Ben Towne Center for Childhood Cancer Research at the Seattle Children’s Research Institute, told ASH Clinical News. “Additionally, this manufacturing platform has a very high feasibility rate in deriving CAR T-cell products in heavily treated patients.”
The study included 45 children and young adults (median age = 12.3 years; range = 1.3-25.4 years) with relapsed/refractory CD19-positive B-lineage acute lymphocytic leukemia (ALL). The researchers included patients who were between the ages of 1 and 27 years, weighed ≥10 kg, had a life expectancy of ≥8 weeks, had adequate organ function, and had an absolute lymphocyte count of ≥100 cells/µL.
Most patients (62%; n=28) had previously undergone hematopoietic cell transplantation (HCT), and had confirmed CD19-positive leukemia recurrence (defined as ≥0.01% disease), no active graft-versus-host disease, and no immunosuppressive therapy for ≥4 weeks prior to the study. Patients who had not undergone HCT were required to have second or later marrow relapse, with or without extramedullary disease. Patients with significant neurologic deterioration.
Seven patients had previously received CD19-directed therapy, including blinatumomab (n=6) and second-generation CD19-specific CAR T cells (n=1).
All patients had successful manufacturing of a clinical CAR T-cell product; 33 products were manufactured from fresh apheresis material, and 12 from cryopreserved CD4 and CD8 T-cell subsets. However, two patients were not infused with CAR T cells because their products did not meet the study’s manufacturing specifications.
Detectable engraftment and expansion of CAR T cells was observed in 98 percent of treated patients (n=42/43), and B-cell aplasia (BCA; a marker of T-cell persistence) occurred in 93 percent of patients (n=40).
All patients pretreated with fludarabine and cyclophosphamide to achieve lymphodepletion (n=14) achieved uniform engraftment of functional CAR T cells (defined as CAR T cells in the blood and subsequent development of BCA and MRD-negative remission). The median time to peak engraftment in peripheral blood was 10 days (range = 7-18 days).
After a median follow-up of 9.6 months (range = 2-28 months), the estimated 12-month event-free survival was 50.8 percent (95% CI 36.9-69.9) and the overall survival was 69.5 percent (95% CI 55.8-86.5). All remissions occurred by day 21.
Disease burden, relapsed/refractory status, prior HCT, and cytogenetic status did not affect MRD-negative CR, according to the authors.
Eighteen of the 40 patients who achieved MRD-negative CR relapsed. Seven of those patients also had loss of cell surface detection of CD19; among the other 11 patients, median time from T-cell infusion to relapse was 5.98 months (range = 1.25-14 months), with a median time from loss of BCA to relapse of 3.7 months (range = 0-11 months).
Twenty-nine patients who achieved MRD-negative CR did not go on to receive consolidative HCT and 13 were still in continuous CR after a median follow-up of 12.2 months (range = 1.9-27.5 months). “A longer duration of post-remission functional persistence of CAR T cells, as inferred by ongoing BCA, correlated significantly with the durability of remission,” the authors noted.
Among the 40 complete responders, loss of functional CAR T cells was associated with a greater risk of CD19-positive leukemic relapse (hazard ratio [HR] = 34; 95% CI 2.1-552; p=0.01), whereas the HR for all relapses, including CD19-positive and -negative, was 3.5 (95% CI 1.01-11.88; p=0.04).
The most common adverse events were cytokine release syndrome (CRS; 93%; n=40/43) and neurotoxicity (49%; n=21/43). “A correlation between disease burden at the time of CAR T-cell infusion and severity of CRS was not observed (p=0.56), nor with CD19 antigen load (p=0.13),” the authors reported. Notably, there were no cases of cerebral edema, a safety concern that has emerged in trials of other CAR T-cell therapies.
“These data establish the feasibility of this advanced manufacturing platform and support further study of this highly defined CD19 CAR T-cell product,” the authors concluded.
The study is limited by its short follow-up period, small patient numbers, and non-comparative design. Furthermore, “since this is a phase I study, additional data will be informative from the phase II study to better delineate potential risk factors of toxicity and relapse,” Dr. Gardner told ASH Clinical News. The researchers are conducting a phase II study treating patients at the MTD of 1×106 cell/kg following fludarabine and cytarabine lymphodepletion.
Gardner RA, Finney O, Colleen Annesley C, et al. Intent to treat leukemia remission by CD19CAR T cells of defined formulation and dose in children and young adults. Blood. 2017 April 13. [Epub ahead of print]