Cost-Effective Manufacture and Promising Initial Efficacy of huCART19 Cells Manufactured Using the Clinimacs Prodigy Platform

Introduction: The manufacturing process for CD19-directed CAR T cells, a life-saving therapy for B-ALL, remains first generation: non-automated, labor-intensive, and requiring expensive clean room facilities for GMP cell manufacture. This approach impacts both patient (pt) safety and access, producing constraints on availability of therapy and manufacturing turnaround. Use of the CliniMACS Prodigy platform allows for GMP, rapid, semi-automated, clinical-scale processing of humanized (hu)CART19 cell products in a point-of-care system and addresses many of these constraints. Based on preclinical data that demonstrated superior efficacy of huCART19 T cells manufactured on the Prodigy platform, we launched a Phase 1/2 study (NCT 05480449) of huCART19 for pediatric B-ALL, with complete Phase 1 and interim Phase 2 results presented here.

Methods: Phase 1 included only children and young adults previously treated with CAR T cells. Phase 2 included both CAR-naïve and CAR-exposed patients (pts). After fludarabine/cyclophosphamide lymphodepletion, pts were infused with Prodigy-manufactured huCART19 cells.

Results: From 11/2022-05/2024, 17 pts were enrolled. Of 16 pts infused (median age 12 years, range 3-26), 11 were CAR-exposed and 5 were CAR-naïve. Among CAR-exposed pts, 6 had relapsed after CAR therapy, and 5 had developed early B cell recovery. Of CAR-naïve pts, 2 had primary refractory and 3 had multiply-relapsed (all post hematopoietic stem cell transplant, HSCT) disease. Ten pts had evidence of disease at infusion: morphologic (n=6), non-CNS extramedullary (n=1), measurable residual disease by flow cytometry (flow-MRD, n=1), or by high-throughput sequencing (NGS-MRD, n=2).

100% of pts had cells successfully manufactured at the protocol dose in 7-9 days. The median infused cell dose was 4.6x10⁶ huCART19 cells/kg (range, 2-5x10⁶). For all but one patient, 3 surplus doses were also manufactured. Marginal manufacturing cost per patient was $28,427. Dose optimization occurred without a dose limiting toxicity (DLT), and the recommended phase 2 dose (RP2D) was achieved at 5x10⁶ huCART19 cells/kg. Cytokine release syndrome (CRS) was observed in 11 pts (grade 1=8, grade 2=2, grade 3=1) and immune effector cell-associated neurotoxicity syndrome (ICANS) in 2 pts (grade 3=1, grade 4=1). In the Phase 2 retreatment setting, 1 pt with a prior history of seizure disorder and severe neurotoxicity after prior CAR therapy developed fatal cerebral edema in the setting of grade 4 ICANS on day 7.

Among the 15 pts evaluable for response at day 28, the overall response rate was 100% (complete morphologic remission, n=14; partial response, n=1 [patient with non-CNS extramedullary disease]), 14 of whom (93%) were flow-MRD negative. There were 13 pts evaluable for NGS (Clonoseq)-MRD at day 28, of which 10 (77%) had undetectable NGS-MRD. One additional pt cleared NGS-MRD at month 3 without intervention. In CAR-naïve pts, 5/5 pts (100%) achieved flow MRD-negative CR; although, 1 patient remained with detectable NGS-MRD. In CAR-exposed pts evaluated at day 28, flow MRD-negative CR was achieved in 8/10 (80%) with one pt with detectable NGS-MRD at day 28 that cleared by month 3 without intervention.

With a median follow-up of 4.7 months, event-free survival at 6 months was 94% (95% CI 83%-100%) and at 12 months was 78% (95% CI 53%-100%); pts were censored at alternate treatment or HSCT (n=2) and study withdrawal (n=1). There have been no additional patient deaths from disease or toxicity.

Conclusion: Prodigy-manufactured huCART19 T cells yielded a 100% overall response rate in evaluable pts, with a 100% MRD-negative CR rate in CAR-naïve patients, and an 80% flow MRD-negative CR rate in patients with a poor response to prior CAR. This trial shows feasibility of manufacturing 4-1BB cells on the Prodigy cost-effectively, with successful manufacture for each pt and all products meeting release criteria. Investigation will continue into the significance of NGS-MRD positivity following Prodigy-manufactured huCART19 therapy, durability of remission, and potentially faster automated GMP manufacturing.