Tisagenlecleucel Leukapheresis and Manufacturing Outcomes in Patients Less Than 3 Years of Age with Relapsed/Refractory Acute Lymphoblastic Leukemia

Background: Tisagenlecleucel is an anti-CD19 chimeric antigen receptor (CAR)-T cell therapy approved for patients (pts) ≤25 years of age with B-cell acute lymphoblastic leukemia (B-ALL) that is refractory or in second or later relapse. Pts <3 years of age were excluded from tisagenlecleucel clinical trials in relapsed/refractory (r/r) ALL (NCT02435849 [ELIANA]; NCT02228096 [ENSIGN]). We present leukapheresis and tisagenlecleucel manufacturing outcomes in pts <3 years old with r/r B-ALL in the US commercial setting since regulatory approval.

Methods: Qualified pts were <3 years of age at time of request for commercial tisagenlecleucel, with manufacturing data after August 30, 2017 (date of first FDA approval of tisagenlecleucel). Only pts whose tisagenlecleucel was manufactured and administered in the US were included; tisagenlecleucel was manufactured at Morris Plains, NJ, USA. Pt leukapheresis and manufacturing outcome data are presented for all pts and stratified by weight (<10 kg and ≥10 kg) and age (<1 year old and 1-3 years old). These data provide an extended analysis (cut-off March 31, 2021) from the previous report (Eldjerou, 2019).

Results: Among 65 pts, the median age was 15.6 months (range, 3.6-36); median body weight was 10.4 kg (range, 6-20) at leukapheresis; 105 leukaphereses were performed in 65 pts (49 <10 kg and 56 ≥10 kg). A median of 1 leukapheresis day was required to meet adequate cell counts (range, 1-4 <10 kg and 1-6 ≥10 kg). The median total blood volume reported in 53/65 pts was 3.5 L (range, 1.3-14.3). The acceptance criteria for tisagenlecleucel manufacture (total nucleated cells: ≥2.0 × 10 ⁹, CD3+ count: ≥1.0 × 10 ⁹, CD3%: ≥3%) were met in 59/66 (26 <10 kg and 33 ≥10 kg) leukapheresis materials; 7/66 did not meet acceptance criteria but proceeded to manufacturing. Following leukapheresis, median percent cell populations were: T cells 55.1% (58% <10 kg and 54.8% ≥10 kg), B-cells 16.9% (20.3% <10 kg and 14.6% ≥10 kg), natural killer cells 4% (3.8% <10 kg and 4.7% ≥10 kg), and monocytes 3.9% (2.6% <10 kg and 4.9% ≥10 kg).

Manufacturing success is the formulation of a final product within approved specifications. Out of 66 manufacturing batches (23 batches <1 year old and 43 batches 1-3 years old; 29 batches <10 kg and 37 batches ≥10 kg), 55 (83.3%) were successful. Of the 59 manufacturing batches that met acceptance criteria, 50 were within specification, 2 were terminated, and 7 were out-of-specification due to cell viability (n=4), CAR+% expression (n=2), or another reason (n=1). One pt who experienced manufacturing failure was remanufactured successfully with a second attempt. Of the 7 batches that did not meet the acceptance criteria, 5 were within specifications and 2 were terminated. The median manufactured cell dose was 2.3x10 ⁶ CAR+ viable T cells/kg [range, 0.23-4.6x10 ⁶ (2.5x10 ⁶ <10 kg and 2.1x10 ⁶ ≥10 kg)], median percent cell viability was 90.6% [range, 66.7%-98.3% (91.9% <10 kg and 90% ≥10 kg)], median CAR+ percent expression was 12.0% [range, 2.1%-37.2% (12.2% <10 kg and 11.8% ≥10 kg)]. From 2017 to 2021, the frequency of CD3+ cells present in the leukapheresis material was greatest in 2021 (Figure, left panel). The percentage of in-specification products was 69%-83% in 2017 to 2019 and increased to 89% and 100% in 2020 and 2021, respectively. Additionally, the number of terminations decreased over time (Figure, right panel).

Measures for successful leukapheresis in low-weight infant/toddler pts include verification of absolute lymphocyte and/or CD3+ counts on the day prior to the leukapheresis procedure, maintenance of hematocrit levels at 40%, adequate venous access, blood prime of the leukapheresis instrument, prevention of hypocalcemia, and consideration for allowing for >1 day of leukapheresis for the pt to meet the acceptance criteria when medically feasible/safe. During leukapheresis, hypothermia must be prevented, and the pt must be monitored for hypocalcemia, hypomagnesemia, and alkalosis.

Conclusions: Leukapheresis and tisagenlecleucel manufacturability in pediatric pts with r/r B-ALL <3 years old and low weight (lowest 6 kg, youngest 3.6 months) continues to be feasible and leukapheresis and manufacturing outcomes show an improvement over time. Communication among cross-functional teams within and between the institution and manufacturer have been key for achieving these advancements. Clinical outcome data for these pts are currently being explored.

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