HESTER: A Phase II Study Evaluating Efficacy and Safety of Tisagenlecleucel Reinfusion in Pediatric and Young Adult Patients with Acute Lymphoblastic Leukemia Experiencing Loss of B-Cell Aplasia

Background: Tisagenlecleucel is an anti-CD19 chimeric antigen receptor (CAR)-T cell therapy approved for pediatric and young adult patients with relapsed/refractory (r/r) B-cell acute lymphoblastic leukemia (B-ALL) and adult patients with r/r diffuse large B-cell lymphoma. The ELIANA trial showed efficacy (81% overall remission rate [ORR]; 60% complete remission [CR]) and safety of tisagenlecleucel in r/r B-ALL (Maude et al. N Engl J Med. 2018). In the ELIANA trial, sustained remissions were associated with B-cell aplasia, an expected on-target effect of tisagenlecleucel and a pharmacodynamic marker for tisagenlecleucel persistence. In some patients who demonstrated short CAR-T cell persistence, reinfusion with 1 or more additional doses of tisagenlecleucel has restored B-cell aplasia and produced a 60% CR rate in patients who were reinfused with humanized CD19-targeted CAR-T cell therapy (Maude et al. J Clin Oncol. 2016). This prolongs the period of tisagenlecleucel activity and immunosurveillance and may therefore prolong durable remission. We introduce a trial in progress investigating the efficacy and safety of tisagenlecleucel reinfusion in pediatric and young adult patients with B-ALL experiencing a loss of B-cell aplasia.

Study Design and Methods: HESTER (NCT04225676) is a phase II, open-label, multicenter trial to determine the efficacy and safety of tisagenlecleucel reinfusion in pediatric and young adult patients with B-ALL experiencing loss of B-cell aplasia. Eligible patients must be ≤25 years of age with a confirmed diagnosis of CD19(+) leukemia. Patients must have been previously infused with commercial tisagenlecleucel and have at least 1 additional dose of commercial tisagenlecleucel prescribed to them in the course of medical practice. Commercial tisagenlecleucel must be given for reinfusion within 9 months of the initial manufacturing date. Patients must have loss of B-cell aplasia defined as peripheral blood (PB) absolute B lymphocyte count ≥50/μL or PB B lymphocyte ≥10% of the total lymphocytes; patients are not required to be minimal residual disease negative (MRD)(-). Karnofsky (age ≥16 years) or Lansky (age <16 years) performance status must be ≥50 at screening. Patients treated with prior gene/adoptive T-cell therapy other than tisagenlecleucel and patients with active central nervous system involvement by malignancy are excluded.

The primary efficacy endpoint is the proportion of patients who reestablish B-cell aplasia within 12 months of reinfusion as measured by circulating B lymphocytes (<50/μL) and presence of tisagenlecleucel cells by quantitative polymerase chain reaction (qPCR) in the PB. Secondary outcomes include the ORR (CR + CR with incomplete blood count recovery) during the 12 months post reinfusion, event-free survival, overall survival, MRD status, and safety; immunogenicity and tisagenlecleucel persistence (by qPCR) are exploratory endpoints. Subgroup analysis of efficacy outcomes will include patients with a loss of B-cell aplasia within 9 months of first infusion who are MRD(+) at time of enrollment, as well as patients with very early (<3 mo), early (≤3 to <6 mo), and later (≥6 mo) loss of B-cell aplasia following first infusion. Safety will be assessed throughout the trial.

For the primary analysis, a minimum of 10% of patients reestablishing B-cell aplasia within 12 months after reinfusion is expected with an estimated true rate of 25%. All secondary and exploratory variables will be summarized descriptively. Estimated enrollment is about 54 patients in the United States.

Clinical Trial Information: NCT04225676