The findings, if validated in a prospective study, could help cut the rate of relapses after initial response to CAR T-cell therapy, which currently approaches 50%, the investigators noted.
In 152 pediatric and young adult patients with relapsed or refractory B-cell acute lymphoblastic leukemia (B-ALL) who underwent CD-19-directed CAR T-cell therapy after cyclophosphamide/fludarabine lymphodepleting chemotherapy, estimated fludarabine exposure was associated with cumulative incidence of relapse (CIR) and a composite endpoint that included loss of B-cell aplasia (BCA) or relapse, Vanessa Fabrizio, MD, and colleagues found.
Dr. Fabrizio, a pediatric hematologist and oncologist at Children’s Hospital Colorado and the University of Colorado Cancer Center in Aurora, was a fellow at Memorial Sloan Kettering (MSK) Cancer Center during the study.
Optimal fludarabine exposure was identified by the investigators as an area under the curve (AUC) of at least 13.8 mg*hr/L. The fludarabine exposure AUC was calculated for each patient by using a validated pharmacokinetics population model.
Multivariable analyses controlling for baseline patient factors and fludarabine exposure showed that patients without optimal exposure had a 2.5-fold higher CIR (hazard ratio, 2.45), and a twofold higher risk of relapse or loss of BCA (HR, 1.96), compared with those who had optimal fludarabine exposure, they reported.
High pre-infusion disease burden was associated with an increased risk of relapse and death (HRs, 2.66 and 4.77, respectively), they said.
The study was published online Nov. 17 in Blood Advances.
“We know that [with] fludarabine ... everyone’s body clears it differently,” principal investigator Kevin J. Curran, MD, said in an interview.
MSKCC
Dr. Kevin J. Curran
Factors affecting clearance include kidney function and weight, and it is simple to determine the optimal dose based on these factors and apply that in practice, said Dr. Curran, a pediatric oncologist and assistant attending physician specializing in cellular therapy at MSK Kids.
In fact, in prior studies, optimal fludarabine exposure in patients undergoing allogeneic hematopoietic cell transplantation has been shown to “decrease nonrelapse mortality due to improved immune reconstitution and subsequently improve survival,” he and his colleagues wrote, explaining the rationale for the study.
The participants, who were part of the Pediatric Real-World CAR Consortium (PRWCC), had a median age of 12.5 years, and 131 of 152 (86%) responded to CAR T-cell therapy. The 12-month OS was 75.1%, the 12-month CIR was 36.4%, and 67% of patients had optimal fludarabine exposure, the authors said.
The findings indeed suggest that one way to improve outcomes without changing the actual cell therapy is to tailor the lymphodepleting therapy prior to CAR T-cell therapy, said Dr. Curran.
“That’s what this does. It’s exciting because cell therapy is very effective [in terms of] initial response, but what we don’t like is the durability of the response,” he said “The next step is to prove it in a prospective study.”
A phase 2 study looking at personalized dosing, as opposed to the standard 30 mg/m2 that most patients receive, is planned for 2022, he noted.
The study was supported by a St Baldrick’s/Stand Up 2 Cancer Pediatric Dream Team Translational Cancer Research Grant, the Virginia and D.K. Ludwig Fund for Cancer Research, and a National Cancer Institute Cancer Center Support Grant. Dr. Curran has served as a consultant for Novartis and Mesoblast, and received research funding from Novartis and Celgene. Dr. Fabrizio reported having no disclosures.