Real-World Outcomes for Pediatric and Young Adult Patients with Relapsed or Refractory (R/R) B-Cell Acute Lymphoblastic Leukemia (ALL) Treated with Tisagenlecleucel: Update from the Center for International Blood and Marrow Transplant Research (CIBMTR) Registry

Background: Tisagenlecleucel is an autologous CD19-directed T-cell immunotherapy indicated in the USA for treatment of patients up to 25 years (y) of age with B-cell ALL that is refractory or in second or later relapse. Overall response rate was 82% with 24 months' (mo) follow-up in the registrational ELIANA trial [Grupp et al. Blood 2018]; pooled data from ELIANA and ENSIGN revealed similar outcomes upon stratification by age (<18y and ≥18y) [Rives et al. HemaSphere 2018]. Early real-world data for tisagenlecleucel from the CIBMTR registry reported similar efficacy to ELIANA with no new safety signals [Pasquini et al. Blood Adv 2020]. Outcomes are reported here for patients who received tisagenlecleucel in the real-world setting, stratified by age (<18y and ≥18y).

Methods: This noninterventional prospective study used data from the CIBMTR registry and included patients aged ≤25y with R/R ALL. Eligible patients received commercial tisagenlecleucel after August 30, 2017, in the USA or Canada. Age-specific analyses were conducted in patients aged <18y and ≥18y at the time of infusion. Efficacy was assessed in patients with ≥12mo follow-up at each reporting center and included best overall response (BOR) of complete remission (CR), duration of response (DOR), event-free survival (EFS), relapse-free survival (RFS) and overall survival (OS). Safety was evaluated in all patients who completed the first (100-day) assessment. Adverse events (AEs) of interest - including cytokine release syndrome (CRS) and neurotoxicity - were monitored throughout the reporting period. CRS and neurotoxicity were graded using the ASTCT criteria.

Results: As of October 30, 2020, data from 451 patients were collected, all of whom received tisagenlecleucel. The median time from receipt of leukapheresis product at the manufacturing site to shipment was 27 days (interquartile range: 25-34). Patients aged ≥18y appeared to have greater disease burden at baseline than those aged <18y, indicated by lower rates of morphologic CR and minimal residual disease (MRD) negativity prior to infusion. Older patients were also more heavily pre-treated before infusion. All other patient characteristics at baseline were comparable between the two groups (Table 1).

In the efficacy set (median follow-up 21.5mo; range 11.9-37.2; N=322), BOR of CR was 87.3% (95% CI 83.1-90.7); MRD status was available for 150 patients, of whom 98.7% were MRD negative. Median DOR was 23.9mo (95% CI 12.3-not estimable [NE]), median EFS was 14.0mo (9.8-24.8) and median RFS was 23.9mo (13.0-NE); 12mo EFS and RFS were 54.3% and 62.3%, respectively. For OS, the median was not reached. Efficacy outcomes were generally similar across age groups (Table 1).

In the safety set (median follow-up 20.0mo; range 2.6-37.2; N=400), most AEs of interest occurred within 100 days of infusion. Any-grade CRS was observed in 58.0% of patients; Grade ≥3 in 17.8%. Treatment for CRS included tocilizumab (n=113; 28.3% of all patients) and corticosteroids (n=31; 7.8%). Neurotoxicity was observed in 27.3% of patients; Grade ≥3 in 10.0%. Treatment for neurotoxicity included tocilizumab (n=17; 4.3% of all patients) and corticosteroids (n=28; 7.0%). During the reporting period, 82 (20.5%) patients died; the most common cause of death was recurrence/persistence/progression of primary disease. CRS and chimeric antigen receptor (CAR)-T cell-related encephalopathy syndrome were the primary cause of death in 2 patients and 1 patient, respectively. Overall, safety data were similar across age groups, although more patients aged ≥18y experienced any-grade CRS or neurotoxicity and were subsequently treated (Table 1).

Conclusions: Updated registry data for pediatric and young adult patients with R/R ALL treated with tisagenlecleucel revealed that patients aged ≥18y had a greater disease burden and were more heavily pre-treated at baseline than patients aged <18y. The overall efficacy and safety profiles of commercial tisagenlecleucel reflected those observed in the clinical trial setting [Grupp et al. Blood 2018; Rives et al. HemaSphere 2018] and were broadly consistent across age groups. Some important differences between the <18y and ≥18y groups were identified, which may point to challenges in timely identification and/or referral of older patients for CAR-T cell therapy.

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